SKP Engineering Collegeskpec.edu.in/wp-content/uploads/2017/11/Engineering... · 2018-04-05 · (i) Scales and sludges (ii) Boiler corrosion. [CO1-L2-June 2005, Dec 2006, Jan 2010]

S.K.P. Engineering College, Tiruvannamalai II SEM

Chemistry Department 1 Engineering Chemistry - II

SKP Engineering College

Tiruvannamalai – 606 611

A Course Material

on

Engineering Chemistry - II

By

Dr.R.Rajmohan,

Mr.S. Prabu,

Assistant Professor

Chemistry Department



Quality Certificate

This is to Certify that the Electronic Study Material

Subject Code: CY 6251

Subject Name: Engineering Chemistry - II

Year/Sem: I/II

Being prepared by me and it meets the knowledge requirement of the University

curriculum.

Signature of the Authors

Name : Dr.R.Rajmohan

Designation : Professor

Name:S. Prabu

Designation: Assistant Professor

This is to certify that the course material being prepared by Dr.R.Rajmohan and

Mr.S.Prabu is of the adequate quality. He has referred more than five books and one

among them is from abroad author.

Signature of HD Signature of the Principal

Name: C.S. Nivetha Name: Dr.V.Subramania Bharathi

Seal: Seal:



CY6251 ENGINEERING CHEMISTRY - II L T P C 3 0 0 3

UNIT I WATER TECHNOLOGY 9

Introduction to boiler feed water-requirements-formation of deposits in steam boilers

and heat exchangers- disadvantages (wastage of fuels, decrease in efficiency, boiler

explosion) prevention of scale formation -softening of hard water -external treatment

zeolite and demineralization - internal treatment- boiler compounds (phosphate, calgon,

carbonate, colloidal) - caustic embrittlement-boiler corrosion-priming and foaming-

desalination of brackish water –reverse osmosis.

UNIT II ELECTROCHEMISTRY AND CORROSION 9

Electrochemical cell - redox reaction, electrode potential- origin of electrode potential-

oxidation potential- reduction potential, measurement and applications - electrochemical

series and its significance - Nernst equation (derivation and problems). Corrosion-

causes- factors- typeschemical, electrochemical corrosion (galvanic, differential

aeration), corrosion control - material selection and design aspects - electrochemical

protection – sacrificial anode method and impressed current cathodic method. Paints-

constituents and function. Electroplating of Copper and electroless plating of nickel.

UNIT III ENERGY SOURCES 9

Introduction- nuclear energy- nuclear fission- controlled nuclear fission- nuclear fusion-

differences between nuclear fission and fusion- nuclear chain reactions- nuclear reactor

power generatorclassification of nuclear reactor- light water reactor- breeder reactor-

solar energy conversion- solar cells- wind energy. Batteries and fuel cells:Types of

batteries- alkaline battery- lead storage batterynickel-cadmium battery- lithium battery-

fuel cell H2 -O2 fuel cell- applications.

UNIT IV ENGINEERING MATERIALS 9

Abrasives: definition, classification or types, grinding wheel, abrasive paper and cloth.

Refractories: definition, characteristics, classification, properties – refractoriness and

RUL, dimensional stability, thermal spalling, thermal expansion, porosity; Manufacture

of alumina, magnesite and silicon carbide, Portland cement- manufacture and

properties - setting and hardening of cement, special cement- waterproof and white

cement–properties and uses. Glass - manufacture, types, properties and uses.



UNIT V FUELS AND COMBUSTION 9

Fuel: Introduction- classification of fuels- calorific value- higher and lower calorific

values- coalanalysis of coal (proximate and ultimate)- carbonization- manufacture of

metallurgical coke (Otto Hoffmann method) - petroleum- manufacture of synthetic petrol

(Bergius process)- knocking- octane number - diesel oil- cetane number - natural gas-

compressed natural gas(CNG)- liquefied petroleum gases(LPG)- producer gas- water

gas. Power alcohol and bio diesel. Combustion of fuels: introduction- theoretical

calculation of calorific value- calculation of stoichiometry of fuel and air ratioignition

temperature- explosive range - flue gas analysis (ORSAT Method).

TOTAL: 45 PERIODS

TEXT BOOKS

1. Vairam S, Kalyani P and SubaRamesh.,“Engineering Chemistry”., Wiley India

PvtLtd.,New

Delhi., 2011

2. DaraS.S,UmareS.S.“Engineering Chemistry”, S. Chand & Company Ltd., New Delhi ,

2010

REFERENCES

1 Kannan P. and Ravikrishnan A., “Engineering Chemistry”, Sri Krishna Hi-tech

Publishing

Company Pvt. Ltd. Chennai, 2009

2. AshimaSrivastava and Janhavi N N., “Concepts of Engineering Chemistry”, ACME

Learning

Private Limited., New Delhi., 2010.

3. RenuBapna and Renu Gupta., “Engineering Chemistry”, Macmillan India Publisher

Ltd., 2010.

4 Pahari A and Chauhan B., “Engineering Chemistry”., Firewall Media., New Delhi.,

2010



CONTENTS

S.No Particulars Page

1 Unit – I 6

2 Unit – II 13

3 Unit – III 48

4 Unit – IV 61

5 Unit – V 78



Unit – I

Water Treatment

Part – A Prerequisite

1. Understand and solve the various boiler troubles and water treatment methods.

2. Water treatment techniques will facilitate the importance of water purities in various

industrial applications.

3. Types of water and conditions for being portable water.

1 Define. Hardness of water. [CO1-L1-Apr 96, Apr 97] Hardness is the property of water which does not produce lather with soap. It can be detected by treating soap with water, C17 H35 COONa + CaCl2 → (C17 H35 COO) 2Ca + 2NaCl

2 List the salts responsible for permanent and temporary hardness? [CO1-L1-Jan 2008, May 2003]

Permanent hardness is due to sulphates & chlorides of Ca 2+& Mg 2+ Temporary hardness is due to carbonates and bi-carbonates of Ca 2+& Mg 2+. 3 Name the hardness of water is expressed? [CO1-L1] The concentrations of hardness producing salts are usually expressed in terms of CaCO3 equivalents. 4 What are scales & sludge? [CO1-L1-May 2009] Scales the hard adherent coating on the inner walls of the boiler .it is called scales. Ex.Ca (HCO3)2, CaSO4, Mgcl2, etc., Sludge is loose and slimy precipitate which is called as sludge. Ex.MgCl2, MgCO3, MgSO4, CaCl2.,

5. What are priming & foaming. [CO1-L1-Jan 2011] Priming is the process of production of wet steam. Foaming is the formation of stable bubbles.



6. What is caustic embrittlement? How it is prevented? [CO1-L1-June 2007, Dec

2009, Jan 2010] Caustic embrittlement means intercrystalline cracking of boiler metal. It is prevented by

adding sodium phosphate instead of sodium aluminates. By adding tannin, lignin to the

boiler water, which blocks the hair cracks.

Cracking or breaking of boiler parts is due to the attack of NaOH on boiler. This is other wise called as intercrystalline cracking. The mechanism of caustic embrittlement is as follows.

Na2CO3 + H2O 2NaOH + CO2 This NaOH reacts with iron and forms sodium ferroate and causes brittlement of boiler parts.

Fe + 2NaOH Na2FeO2 + H2↑ Remedial measures:

Sodium phosphate can be used as softening agent instead of Na2CO3

Tannin and lignin can be added to boiler to block hair line crack 7. Why CaCO3 is used as a standard material for representing hardness? [CO1-L2-June 2010] The concentration of hardness producing salts are usually expressed interms of an equivalent amount of CaCO3.The molecular weight of CaCO3 is whole number and it is the most insoluble salt

8. What is calgon conditioning? Why is calgon better compared to other methods?

[CO1-L2-July 2008, June 2005, Jan 2010] Calgon is Sodium hexa meta phosphate. When hard water is treated with calgon, it forms a highly soluble complex and prevents formation of scales and reduces the problem of sludge disposal. So, calgon conditioning is better compared to other internal conditioning methods 9. Traces of MgCl2 results corrosion in cyclic way. How? [CO1-L2-May 2001] Dissolved MgCl2, CaCl2 undergoes hydrolysis in water at high temperature as follows: MgCl2 + 2H2O Mg(OH)2 + 2HCl Fe + 2HCl FeCl2 + H2↑ FeCl2 + 2H2O Fe(OH)2 + 2HCl The acid formed in the above reactions leads to cyclic reaction causing continuous corrosion on boiler walls



10. During purification why is it necessary to pass water first through the cation exchanger and then through the anion exchanger? [CO1-L2-Feb 2010] Cation exchangers are easily attacked by alkalis, whereas all type if ion exchangers are not attacked by acids. When water is first passed through a cation exchanger, salts present in water are converted into corresponding acids. Which on passing into an anion exchanger do not harm it and finally get converted into pure water. If reverse sequence is used, alkalis produced on passing water through anion exchanger harms the cation exchanger in subsequent steps.

Part - B 1. Explain the following troubles in boiler feed water. (i) Scales and sludges (ii) Boiler corrosion. [CO1-L2-June 2005, Dec 2006, Jan 2010] (i) Scale and sludge formation When water is heated continuously in boiler, the concentration of dissolved salts in water increases progressively. After reaching a saturation limit, the dissolved salts are thrown out of water in the form of precipitates. If the precipitate is loose, slimy and non-adherent, it is called as sludge. On the other hand, if the precipitate is hard and adherent crust or coating on the inner wall of boiler, it is called as scale. Sludge: Sludge are formed due to the presence of MgCl2, MgCO3, MgSO4 and CaCl2. They have greater solubilities in hot water than cold water. Disadvantages:

Sludges are poor conductor of heat

Excessive formation of sludge decrease the efficiency of boiler Removal & Preventive measure: Sludge formation can be prevented by using soft water and it can be removed by ‘Blow down’ operation Scales: Formation of Scales Scales are formed due to the following reasons

Decomposition of CaHCO3 which leads to the formation of CaCO3 scale (In low pressure boiler, but in high pressure boiler CaCO3 is soluble)

Due to decrease in solubility of CaSO4 at high temperature

Trace of MgCl2 which produce Mg(OH)2 scale

Presence of SiO2 in water which produces calcium or magnesium silicate scales Disadvantages:

Scales are poor conductor of heat

It decreases the efficiency of boiler

It causes danger of explosion of boiler



Removal & Preventive measure: Scales can be avoided by using soft water. It can be removed by thermal shock, acid and other chemical treatments (ii) Boiler corrosion Corrosion in boilers is caused due to the presence of dissolved oxygen, dissolved carbon dioxide and dissolved salts. (a) Boiler corrosion due to dissolved oxygen Dissolved oxygen in boiler attacks the boiler material at high temperature to form rust. 4Fe + 6H2O + 3O2 4Fe(OH)3 Removal methods

Dissolved Oxygen can be removed by addition of hydrazine or sodium sulphite. Hydrazine addition is efficient method among all, because of due to the formation of N2 and H2O

N2H4 + O2 N2 (g) + 2H2O 2 Na2SO3 + O2 2 Na2SO4

It can also be removed by mechanical de-aeration (b) Boiler corrosion due to dissolved CO2 Dissolved CO2 reacts with water to produce carbonic acid which turns the water acidic and it causes corrosion of boilers. CO2 + H2O H2CO3 Removal methods

Dissolved CO2 removed by addition of ammonium hydroxide 2NH4OH + CO2 (NH4)2CO3 + H2O

It can also be removed by mechanical de-aeration (c) Dissolved MgCl2 Dissolved MgCl2, CaCl2 undergoes hydrolysis in water at high temperature as follows:

MgCl2 + 2H2O Mg(OH)2 + 2HCl Fe + 2HCl FeCl2 + H2↑ FeCl2 + 2H2O Fe(OH)2 + 2HCl

The acid formed in the above reactions leads to cyclic reaction causing continuous corrosion on boiler walls. Removal methods Corrosion by acid can be removed by addition of alkali to boiler water. 2. Explain demineralization of water by ion-exchange method with its advantages and disadvantages. [CO1-L2-Dec 2002, May 2007, May 2008, Jan 2009, Jan 2010] Demineralization process is the process of removal of all type of ions (both cation & anion) present in the water by passing the water through ion-exchange resin.



Ion-exchange resins are organic polymer which is insoluble, long chain, high molecular weight, cross linked with micro porous structure. The functional groups attached to the chains are responsible for the ion-exchanging properties. Cation exchange resin: They are resins containing acidic functional groups (-COOH, -SO3H) which are capable of exchanging their H+ ion with other cations in hard water. Eg. Sulphonated coal, sulphonated polystyrene R-SO3

-H+, R-COOH = R-H+ Anion exchange resin: They are resins containing basic functional groups (-NH2, -OH) which are capable of exchanging their anions with other anions in hard water Eg. Cross linked quaternary ammonium salt, urea-formaldehyde resin R-NH2, R-NR3OH- = R’-OH- Process: The hard water is first passed through a cation exchanger. Here all the cations such as Ca2+

, Mg2+, Na+, K+ etc., in the water sample gets adsorbed in the resin and

replaces equivalence number of H+ ions. Reaction:

At cation exchanger:

2R-H+ + Ca2+ R2-Ca2+ + 2H+ R-H+ + Na+ R-Na+ + H+ At anion exchanger: The cation free water is then passed through the anion exchanger which adsorbs all anions such as Cl-, SO4

2-, HCO3- etc., present in the water and replaces equivalence

number of OH-. 2R’-OH- + SO4

2- R2-SO42- + 2OH-



R’-OH- + Cl- R-Cl- + OH- The water coming out of the anion exchanger is completely free from cations and anions. This water is known as demineralised water or deionised water. After a certain period, the exchanging capacity of resin gets exhausted. Regeneration: Exhausted resin can be regenerated using HCl and NaOH with cation exchanger and anion exchanger respectively. R2-Ca2+ + 2HCl 2R-H+ + CaCl2 R2-SO4

2- + 2NaOH 2R’-OH- + Na2 SO4 Advantages:

Simple method, anyone can operate

The treated water has very little hardness (~2ppm)

Highly acidic and alkaline water can also be treated Disadvantages:

Water containing Fe, Mn and turbid water can not be treated

It is expensive.

3. Explain the various internal conditioning methods of boiler feed water.[CO1-L2-Dec 2005, June 2006, Dec 2006, Jan 2009, Jan 2010, Jan 2013] Internal conditioning is addition of suitable chemicals into the boiler to remove hardness producing substances in water. The added chemicals are otherwise called boiler compounds. Some internal conditioning methods are given below. (i) Carbonate conditioning In low pressure boilers, scale formation can be avoided by adding sodium carbonate to boiler water. The scale forming salts like CaSO4 is converted into CaCO3 which can be removed by blow down operation.

Na2CO3 + CaSO4 CaCO3 + Na2SO4 (ii) Phosphate conditioning In high pressure boiler, scale can be avoided by adding suitable sodium phosphate depending upon the pH of water. Calcium phosphate gets precipitated which can be removed by blow down operation.

2Na3PO4 + 3CaSO4 Ca3(PO4)2 + 3Na2SO4 Generally three types of phosphates are employed

Name of the phosphate Formula Nature of

phosphate Nature of water

Trisodium phosphate Na3PO4 Highly alkaline Used for highly acidic water

Disodium hydrogen phosphate Na2HPO4 Weakly alkaline Used for weakly acidic water



Monosodium hydrogen phosphate NaH2PO4 Acidic Used for alkaline water

(iii) Calgon conditioning Calgon is Sodium hexa meta phosphate Na2[Na4(PO3)6], Calgon reacts with Ca or Mg ions in water to form soluble complex and this prevents scale formation in boiler. This is a superior method among all internal conditioning methods because of no need of secondary operation such as blow down operation. 2CaSO4 + Na2[Na4(PO3)6] Na2[Ca2(PO3)6 + 2 Na2SO4 Soluble complex 4. Explain desalination of brackish water by reverse osmosis method with its advantages. [CO1-L2-May 2008, Jan 2009, Jan 2010, Jan 2013]

Water containing dissolved salts with a salty taste is called brackish water. It cannot be used for drinking purpose. The process of removing extra common salt from saline water is known as desalination. Principle: When two solutions of different concentration are separated by a semi-permeable membrane, flow of solvent (water) takes place from a region of lower concentration to higher concentration. This process is called osmosis. The driving force in this phenomenon is called osmotic pressure. If a excess of pressure higher than osmotic pressure is applied to the higher concentration side, the flow of solvent is reversed ie. Solvent molecule is forced to move from higher concentration side to lower concentration side across the membrane. This process is called reverse osmosis. Thus, in reverse osmosis method, pure water (solvent) is separated from its contaminants rather than removing contaminants from water. This membrane filtration is also called ’Super filtration’ or ‘Hyper filtration The membranes used are cellulose acetate, Polyamide, Sulphone etc.

Method: In this method, pressure of order 15-40 K/cm2 is applied to the impure water to force its pure water out through the semi-permeable membrane, leaving behind the dissolved solids (both ionic and as well as non-ionic). The membrane consists of very thin film of cellulose acetate, affixed to either side of a perforated tube. Now a day, membranes made of polymethacrylate and polyamide polymers are used. If a hydrostatic pressure



in excess of osmotic pressure is applied on concentrated side, pure solvent (water) is separated from its contaminants. Advantages:

It removes all types of impurities ie. ionic, non-ionic and colloidal particles

It removes colloidal silica which cannot be removed by demineralization method.

The life time of the membrane is high (2 years)

Maintenance cost is low

Membrane can be replaced within short time

Unit II

Electrochemistry And Corrosion

Part – A

Prerequisite

1. To get the knowledge about the construction and the working principle of

electrochemistry.

2. To know about electrochemical cells, emf and applications of emf measurements.

3. To understand the principles of corrosion and types of corrosion in metal & alloys and

their protection and solve the corrosion problem

1. Define electrochemical cell. [CO2-L1- Apr/May-2009] Electrochemical cells are the cells in which chemical energy is converted into electrical energy. Electrochemical cell otherwise termed as galvanic cells or voltaic cells. Here the anode caries negative charge and cathode carries a positive charge. The emf produced in the cell is measured by potentiometer. Example: Daniel cell. 2. Compare metallic and electrolytic conduction. [CO2-L2]

S.No Metallic conduction Electrolytic conduction

1. It involves the flow of electrons in a

conductor.

It involves the movement of ions in

a solution.

2. It does not involve any transfer of

matter.

It involves transfer of electrolyte in

the form of ions.

3. Conduction decreases with increase

in temperature.

Conduction increases with

increase in temperature.



3. What is salt bridge? List the functions of salt bridge. [CO1-L2-May/June-2009]

It consists of a U-tube containing saturated solution of KCl or NH4NO3 in agar-agar gel. It connects the two half cells of the galvanic cells. Functions of salt bridge:

It eliminates liquid junction potential. It provides the electrical continuity between the two half cells.

4. Identify the conditions for an electrochemical cell to act as a standard cell?

[CO2-L2-May/June-2009] Electrochemical cells are the cells in which chemical energy is converted into

electrical energy. The conditions of an electrochemical cell to act as a standard cell are

The e.m.f of the cell is reproductive. The temperature co-efficient of e.m.f (change in e.m.f with temperature)

should be very low.

5. What is electrode potential? How is it developed? [CO2-L2-Apr/May-2009] Electrode potential: It is the measure of the tendency of a metallic electrode to

lose or gain electrons, when it is in contact with a solution of its own salt. Electrode potential development: It is developed when a metal is placed in a

solution of its own salt. Example: Electrode potential is developed when zinc electrode dipped in 1 M ZnSO4 solution and a copper electrode dipped in 1 M CuSO4 solution. 6. Define the following terms: (i) Single electrode potential (ii) Standard

electrode potential. [CO2-L1-May/Jun 2014,Apr/May-2010] (i) Single electrode potential: It is the measure of the tendency of a metallic electrode to lose or gain electrons, when it is in contact with a solution of its own salt. (ii) Standard electrode potential: It is the measure of the tendency of a metallic electrode to lose or gain electrons, when it is in contact with a solution of its own salt of 1 molar concentration at 250 C. 7. Write about oxidation and reduction potential. [CO2-L2-June/July-2009] Oxidation potential: The tendency of an electrode to lose electrons is called the oxidation potential.

Zn Zn2++2e-

4. No change in chemical properties of

the conductor.

Chemical reactions occur at the

two electrodes.



Reduction potential: The tendency of an electrode to gain electrons is called the oxidation potential. Cu2++2e- Cu

8. What is called Helmholtz electrical double layer? [CO2-L1-Apr/May-2009] Helmholtz electrical double layer: It is a sort of layer, (positive and negative ions) formed all around the metal, which prevents further passing of the positive ions from or to the metal. A difference of potential is consequently set up between the metal and the solution. At equilibrium, the potential difference becomes a constant value, which is known as the electrode potential of a metal.

9. What is a Standard Hydrogen Electrode? [CO2-L1-June 2013, June 2011] Standard Hydrogen Electrode: Hydrogen electrode consists of platinum foil, that is connected to a platinum wire and sealed in a glass tube. Hydrogen gas is passed through the side arm of the glass tube. This electrode, when dipped in a 1N HCl and hydrogen gas at 1 atmospheric pressure is passed forms a standard hydrogen electrode. The electrode potential of SHE is zero at all temperatures. Cell representation:

10. What is a calomel electrode? [CO2-L1-Jun2013, Dec 2010]

Calomel electrode: Calomel electrode is a secondary reference electrode. It

consists of a glass tube containing mercury at the bottom over which mercurous

chloride is placed. The remaining portion of the tube is filled with a saturated solution of

KCl. The bottom of the tube is sealed with a platinum wire. The side tube is used for

making electrical contact with a salt bridge. The electrode potential of the calomel

electrode is + 0.2422 V.

Cell representation: Hg(l), Hg2Cl2(s), KCl (sat); E° = 0.2422 V

11. Interpret the Nernst equation for reduction potential and oxidation potential. [CO2-L2-May 2003]

Nernst equation: o n2.303RTE E log M

nF

When, R=8.314 J/K/mole; F=96500 coulombs; T=298k

For reduction potential red

o n+0.0591E = E + log M

n

For oxidation potential o n+

oxi

0.0591E = E - log M

n

12. List out the applications of Nernst equation. [CO2-L1- Dec 2008]

Pt , H2(1 atm)/H

+

(1 M); E° = 0 V



Nernst equation is used to calculate the electrode potential of unknown

metal. The corrosion tendency of metals can be predicted. Used to calculate EMF of a cell. pH of a solution can be calculated by measuring the EMF. Concentration of the solution in galvanic cell can be determined. Concentration of the solution in galvanic cell can be determined.

13. Find the cell reactions of the following cells. [CO2-H1-May/Jun-2014]

(a) Zn(s)/Zn2+ (0.01M)//Ni2+

(0.5M)/ Ni(s) At Anode: Zn(s) Zn2++2e-(oxidation) At Cathode: Ni2++2e- Ni(s) (reduction) Zn(s) + Ni2+ Zn2++ Ni(s) (b) Ag (s) /Ag+

(aq) //pt,H2(g)/H2(g) At Anode: 2Ag (s) 2Ag++ 2e- (oxidation) At Cathode: 2H++ 2e- H2 (g) (reduction) Cell reaction: 2Ag (s) +2H+ 2Ag+ + H2(g)

14. Find the cell reactions of the following cells. [CO2-H1-May/Jun-2014]

(a) Zn(s)/Zn2+ (aq) // Ag+ (aq) / Ag (s) At Anode: Zn Zn2+

(aq) +2e-(oxidation) At Cathode 2Ag +

(aq) +2e- 2 Ag(s)(reduction) Cell reaction: Zn + 2Ag+

(aq) Zn2+ (aq) +2Ag(s)

(b) Ni (s) /Ni 2+

(1M) // Pb 2+(s) /Pb (1M)

At Anode: Ni(s) Ni2++2 e- (oxidation) At Cathode: Pb2++2 e- Pb(s) (reduction) Cell reaction: Ni(s) + Pb2+ Ni2++ Pb(s)

15. Find the emf of the following cell Zn/Zn2+(0.1M)//Ag+

(10.0M)/Ag. [CO2-H1] Given that, E0

Zn2+

/Zn = -0.76V and E0Ag+/Ag = +0.80V.

Solution: The chemical reaction involved is

Zn Zn 2+ + 2e- (anode reaction)



2Ag+ + 2e- 2Ag (cathode reaction)

Zn+2Ag+ Zn2+ + 2 Ag (cell reaction)

E0cell=E right-Eleft

= E Ag-EZn

o + o 2+

Ag Zn

0.0591 0.0591E = [E + log(Ag )]-[E + log(Zn )]

n n

o o

Ag Zn

0.0591 0.0591E = [E + log(10)]-[E + log(0.1)]

1 2

o o

Ag Zn

0.0591 0.0591E = [E - E ]+ ×(1) - ×(-1)

1 2

0.80- -0.76 0.0591 + 0.0E = [ ]+ 2955

.56+0.08865 = 1.6487 V. E =1

16. Find the single electrode potential for copper metal in contact with 0.15M Cu2+ solution. E0 for copper = +0.34V. [CO2-H1-Apr/May-2011]

Solution: Concentration of Cu2+ = 0.15M,E0 = 0.34V

The Nernst equation for reduction potential of Cu2+ is

o 2+

cu

0.0591E = [E + log(Cu )]

n

0.0591E = [0.34 + log(0.15)]

2

0.34 + 0.02955 -0.8E = [ 239 ]

0.34 + (= -0.0243

Electrode potential of Cu = 0.3157 V.

17. Define an electrochemical series. [CO2-L1-May/Jun 2013,Nov/Dec-2012]

When various electrodes are arranged in the order of their increasing values of standard reduction potential on the hydrogen scale, then the arrangement is called electrochemical series. The standard electrode potential of a number of electrodes are given in the electrochemical series. Thse values are determined potentiometrically by combining the electrode with another standard electrode, whose electrode potential is zero.

18. List out the applications of EMF series. [CO2-L1-Nov/Dec-2011] Applications of EMF series:



Calculation of standard emf of the cell. Relative ease of oxidation (or) reduction. Displacement of one element by the other. Determination of standard free energy change (ΔG) and equilibrium

constant for the reaction. Hydrogen displacement behavior. Predicating Spontaneity (or) feasibility of Redox reactions.

19. Zn reacts with dil. Sulphuric acid but Ag does not. Find the reason. [CO2-

L2-May/Jun-2013] Metals with negative reduction potential will displace the Hydrogen from an acid solution. For example Zn reacts with dil. H2SO4 to displace H2 gas from it whereas Ag does not. Because, metals with negative reduction potential, which displaces the H2 gas. Zn+ H2SO4 ZnSO4 + H2 E

oZn = - 0.76V

Ag+ H2SO4 No reaction EoAg = +0.80V

20. Check the feasibility of redox reaction in terms of EMF and free energy?

[CO2-H2] Feasibility of redox reaction: Spontaneity of redox reaction can be predicted from the emf value of the complete cell reaction.

If the Eo of the cell is positive, the reaction is spontaneous. If the Eo of the cell is negative, the reaction is not feasible.

An element having lower reduction potential can displace another metal having higher reduction potential from its salt solution spontaneously.

21. Define corrosion. Mention its causes. [CO2-L1-May/Jun-2011] Corrosion: Corrosion is defined as the gradual destruction or deterioration of metals or alloys by the chemical or electrochemical reaction with its environment.

Causes of corrosion:Metals occur in nature in two different forms. Native state: The metals occur in native (or) free (or) uncombined state are non-reactive with the environment. Example: Au, Pt, Ag Combined state: Except noble metals, all other metals are reactive and react with environment and form stable compounds, as their oxides, sulphides, chlorides and carbonates. Example: Fe2O3, ZnO, PbS, CaCO3etc,

22. How does the overvoltage affect the rate of corrosion? [CO2-L2-Nov/Dec -2008]

Over voltage: The over voltage of a metal in the corrosive environment is inversely proportional to corrosion rate. Example: The normal hydrogen voltage of Zinc metal, when it is dipped in 1 M H2SO4 is 0.7 volt. Here the rate of corrosion is low. By adding small amount of impurity like



CuSO4 to H2SO4, the hydrogen over voltage is reduced to 0.33V.This results in increased rate of corrosion of Zinc metal.

23. Outline a note on the stable and unstable oxide layer with example. [CO2-H1]

Stable Oxide Layer: A stable oxide layer is a fine-grained in structure, and gets adsorbed tightly to the metal surface. Such a layer is impervious in nature and stops further oxygen attack through diffusion. Such a film behaves as a protective coating and no further corrosion can develop. Example: Oxides of Al, Sn, Pb, Cu, etc., are stable oxide layers. Unstable Oxide Layer: Unstable oxide layer is mainly produced on the surface of noble metals, which decomposes back into the metal and oxygen. Metal Oxide Metal + Oxygen Example: Oxides of Pt, Ag, etc., are unstable oxide layers.

24. State Pilling bed-worth’s ratio. [CO2-L1-May 2011,Nov/Dec-2010] Pilling bed-worth’s ratio: The ratio of the volume of the oxide formed to the volume of the metal consumed is called “Pilling-Bed worth ratio” PB ratio = Volume of metal oxide Volume of metal consumed

25. What is hydrogen embrittlement? [CO2-L1] Hydrogen embrittlement: Hydrogen embrittlement (at ordinary temperature) When metals contact to H2S at ordinary temperature causes evolution of atomic hydrogen. Fe + H2S −−−−−> FeS + 2H This atomic hydrogen diffuses readily into the metal and collects in the voids, where it recombines to form molecular hydrogen H + H −−−−−> H2↑ Collection of these hydrogen gases in the voids develops very high pressure, which causes cracks and blisters on metal. Thus, the process of formation of cracks and blisters on the metal surface, due to high pressure of hydrogen gas is called hydrogen embrittlement.

26. Write a note on decarburization with equations. [CO2-L1] Decarburization: At higher temperature atomic hydrogen is formed by the thermal dissociation of molecular hydrogen. Heat H2 2H When steel is exposed to this environment, the atomic hydrogen readily combines with carbon of steel and produces methane gas.



C + 4H CH4↑ Collections of these gases in the voids develop very high pressure, which causes cracking. Thus the process of decrease in carbon content in steel is termed as “decarburisation” of steel.

27. Under what conditions electro chemical corrosion occurs? [CO2-L2-June/July-2010]

Wet corrosion occurs under the following conditions. When two dissimilar metals or alloys are in contact with each other in the

presence of an aqueous solution or moisture. Example: Galvanic corrosion of Zinc-Iron bimetallic couple.

When a metal is exposed to varying concentration of oxygen or any electrolyte.

Example: Metals partially immersed in water.

28. What happens when iron metal contacts with a neutral solution? [CO2-L2-May/June-2010]

At Anode Iron dissolves as Fe2+ with the liberation of electrons. Fe −−−−−> Fe2+ + 2e− (oxidation) At Cathode The liberated electrons flow from anodic to cathodic part through metal, where the electrons are taken up by the dissolved oxygen to form OH− ions. ½ O2 + H2O + 2e− −−−−−> 2OH− Thus, the net corrosion reaction is Fe2+ + 2OH− −−−−−> Fe(OH)2↓ If enough O2 is present Fe(OH)2 is easily oxidised to Fe(OH)3, a rust (Fe2O3H2O) 4Fe(OH)2 + O2 + 2H2O −−−−−> 4Fe(OH)3 Brown rust

29. List out the difference between chemical and electro chemical corrosion. [CO2-L2-Nov/Dec2012]

S.No Chemical corrosion Electrochemical corrosion

1. Occurs in dry condition Occurs in wet condition

2.

Due to the direct chemical attack Due to the large number of cathodic and anodic areas



3. Even homogeneous metal surface gets

corroded

Only heterogeneous metal surface gets corroded

4. Self-controlled Continuous process

5.

It follows adsorption mechanism. Ex: formation of mild scale on iron surface

It follows electrochemical reaction. Example: Rusting of iron in moist atmosphere.

30. What is galvanic corrosion? [CO2-L1-Nov/Dec-2010, Nov/Dec-2009] Galvanic corrosion is the one type of electrochemical corrosion. When two different

metals are in contact with each other in presence of an aqueous solution or moisture, galvanic corrosion occurs. Here, the more active metal (with more negative electrode potential) acts as anode and the less active metal (with less negative electrode potential) acts as cathode. Example: Zn-Fe couple and Cu-Fe couple.

31. How is galvanic corrosion prevented? [CO2-L2-May/Jun 2013] Galvanic corrosion can be minimised by the following two ways.

By providing an insulating material between the two metals. Example: Galvanic corrosion of zinc-iron couple.

By selecting two metals as close as possible on the emf series. Example: Steel screw in a brass marine hardware corrodes.

Providing smaller area for cathode and larger area for anode.

32. What is meant by concentration cell corrosion? Give some examples. [CO2-L1-May/Jun 2009]

Concentration cell type of corrosion occurs when a metal is exposed to varying concentration of oxygen or any electrolyte on the surface of the base metal.Metals partially immersed in water (or) conducting solution (called water line corrosion).If a metal is partially immersed in a conducting solution the metal part above the solution is more aerated and hence become cathodic. On the other hand, the metal part inside the solution is less aerated and thus, become anodic and suffers corrosion.

33. Give the mechanism of pitting corrosion. [CO2-L2-Nov/Dec-2010] Mechanism of pitting corrosion: Pitting is a localised attack, resulting in the formation of a hole around which the metal is relatively unattached.



Metal area covered by a drop of water, sand, dust, scale, etc. Let us consider a drop of water or aqueous NaCl resting on a metal surface. The area covered by the drop of water acts as an anode due to less oxygen concentration and suffers corrosion. The uncovered area (freely exposed to air) acts as a cathode due to high oxygen concentration.

34. How to avoid the galvanic corrosion in corrosion control? [CO2-L2] If two different metals are joined, galvanic corrosion will occur. In such a case galvanic corrosion is prevented by

Selecting the metals as close as possible in the electrochemical series. Providing smaller area for cathode and larger area for anode. Inserting an insulating material between the two metals.

35. What is a sacrificial anode? [CO2-L1] Sacrificial anode: Sacrificial anodic protection method is used for the protection of ships and boats. Sheets of Mg or Zn are hung around the hull of the ship. Zn or Mg will act as anode compared to iron (ship or boat is made of iron), so corrosion concentrates on Zn or Mg. Since they are sacrificed in the process of saving iron, they are called sacrificial anodes.

36. Compare the differences between sacrificial anodic method and impressed current cathodic method. [CO2-L2]

S.No Sacrificial anodic method Impressed current method



1

No external power supply is necessary

External power supply must be present

2

Requires replacement of Sacrificial anode

Anodes are stable

3 Low investment High investment

4

This is most economical method especially when short term protection is required.

This method is well suited for large structures and long term operations.

37. Define paints. Mention its characteristics. [CO2-L2-Dec 2009]

Paint is a mechanical dispersion of one or more finely divided pigments in a medium (thinner + vehicle). When a paint is applied to a metal surface, the thinner evaporates, while the vehicle undergoes slow oxidation forming a pigmented film. Characteristics of a good paint:

It should spread easily on the metal surface. It should have high hiding (covering) power. It should not crack on drying. It should adhere well to the surface. The colour of the paint should be stable. It should be a corrosion and water resistant. It should give a glossy film.

` 38. Summarize the constituents of good paints. [CO2-L2]

Constituents of good paints: Pigments:Pigments are solid and colour producing substances in the

paint. Vehicle (or) drying oil:This is a non-volatile portion of a medium and

film forming constituent of the paint. These are high molecularweight fatty acids present in vegetable and animal oils.

Thinners (or) solvents:This is a volatile portion of a medium. It easily evaporates after application of the paint.

Extenders (or) fillers:These are white (or) colourless pigments. Driers:These are the substances, used to accelerate the process of

drying.



Plasticisers :These are chemicals added to the paint to provide elasticity to the film and to prevent cracking of the film.

Anti-skinning agents:These are chemicals added to the paint to prevent gelling and skinning of the paint.

39. Explain pigments? Mention the functions of pigments in paint. [CO2-L2-Apr 1996, Apr 1994]

Pigment: Pigments are solid and colour producing substances in the paint. Functions:

It gives colour and opacity to the film. It also provides strength to the film. It protects the film by reflecting the destructiveuv rays. It increases weather resistance of the film.

40. Write about pigment volume concentration. [CO2-L1]

Pigment volume concentration is an important property of paint. The following equation is used to calculate the P.V.C. P.V.C . = Volume of pigment in the paint Volume of (pigment+vehicle) in the paint Higher the volume of P.V.C, lower will be the durability, adhesion, consistency of the paint.

41. What is metallic coating? [CO2-L1-Nov/Dec-2010] Metallic coating: Surface coatings made up of noble metals are known as metallic coatings. Metallic coatings are mostly applied on steel and iron surfaces, because they are cheap and commonly used construction materials. The following are two important metallic coatings.

Electroplating Electroless plating.

42. Explain the principle of electroplating. [CO2-L2]

Electroplating is the process in which the coating metal is deposited on the base metal by passing a direct current through an electrolytic solution containing the soluble salt of the coating metal.The base metal to be plated is made cathode of an electrolytic cell, whereas the anode is either made of the coating metal itself or an inert material of good electrical conductivity.

43. Summarize the objective of electroplating on metals. [CO2-L2]

To increase the resistance to corrosion of the coated metal. To improve the hardness and physical appearance of the article. To increase the decorative and commercial values of the article.



To increase resistance to chemical attack. To improve the properties of the surface of the article.

44. Summarize the principles of electro less plating? [CO2-L2-May/Jun 2013]

Electro less plating is a technique of depositing a noble metal (from its salt solution) on a catalytically active surface of the metal, to be protected, by using a suitable reducing agent without using electrical energy. The reducing agent reduces the metallic ions to metal, which gets plated over the catalytically activated surface giving a uniform thin coating. Metal ions + Reducing agent −−−−−> Meta + Oxidised product(s) (Deposited)

45. List out the advantages of electroless plating over electroplating. [CO2-L1-July 2009, May 2011]

No electricity is required. Electroless plating on insulators (like plastics, glass) and

semiconductors can be easily carried out. Complicated parts can also be plated uniformly. Electroless coatingspossess good mechanical, chemical and magnetic

properties.

46. Compare electroplating with electroless plating. [CO2-L2]

S.No Electroplating Electrolessplating

1 It is carried out by passing current It is carried out by auto catalytic redox reaction

2 Separate anode is employed Catalytic surface acts as an anode

3 Anodic reaction:M Mn++ ne

- Anodic reaction:R O + ne

-

4 Cathodic reaction is

Mn+ + ne

- M

Cathodic reaction is

Mn+ + ne

- M

PART-B 1. Describe the construction and working of an electrochemical cell and explain

the redox reactions occurring in it. [CO2-L2-May/June-2011, Nov/Dec-2010,

May/June-2009]



Galvanic cells are electrochemical cells in which the electrons, transferred due to redox

reaction, are converted to electrical energy.

Example: Daniel cell

Cell device (Construction): Daniel cell consists of a zinc electrode dipped in 1 M ZnSO4 solution and a copper electrode dipped in 1 M CuSO4 solution. Each electrode is known as a half cell.The two solutions are inter connected by a salt bridge and the two electrodes are connected by a wire through the voltmeter.

Reactions occurring in the cell At anode: Oxidation takes place in the zinc electrode by the liberation of electrons, so this electrode is called negative electrode or anode. At cathode: Reduction takes place in the copper electrode by the acceptance of electrons, so this electrode is called the positive electrode or cathode. Zn Zn2+ + 2e− (at anode)

Cu2+ + 2e− Cu (at cathode)

Cu2+ + Zn Zn2+ + Cu (net cell reaction)

The electrons liberated by the oxidation reaction flow through the external wire and are consumed by the copper ions at the cathode. Salt bridge

It consists of a U-tube containing saturated solution of KCl or NaNO3 in agar-agar

gel.

It connects the two half cells of the galvanic cells.

Functions of salt bridge

(i) It eliminates liquid junction potential.

(ii) It provides the electrical continuity between the two half cells.

Conditions for a cell to act as standard cell

The conditions for an electrochemical cell to act as a standard cell are



(i)The e.m.f of the cell is reproductive.

(ii)The temperature-coefficient of e.m.f(change in e.m.f with temperature)

should be very low.

2. Explain the origin of electrode potential and formation of Helmholtz electrical

double layer. [CO2-L2-June/July-2010, May-2009, July-2009]

A metal (M) consists of metal ions (Mn+) with valence electrons. When the metal (M) is placed in a solution of its own salt, any one of the following reactions will occur. (i)Positive metal ions may pass into the solution.

M −−−−−>Mn+ + ne− (oxidation)

(ii)Positive metal ions from the solution may deposit over the metal.

Mn+ + ne− −−−−−> M (reduction)

Example 1: Zn electrode dipped in ZnSO4 solution

When Zn electrode is dipped in ZnSO4 solution, Zn goes into the solution as Zn2+

ions. Now, the Zn electrode attains a negative charge, due to the accumulation of valence

electrons on the metal. The negative charges developed on the electrode attract the

positive ions from solution. Due to this attraction the positive ions remain close to the

metal.

Example 2: When Cu electrode is dipped in CuSO4 solution, Cu2+ ions from the

solution deposit over the metal. Now, the Cu electrode attains a positive charge, due to

the accumulation of Cu2+ ions on the metal. The positive charges developed on the

electrode attract the negative ions from solution. Due to this attraction, the negative

ions remain close to the metal.

Zn electrode in Cu electrode in ZnSO4 solution CuSO4 solution Thus, a sort of layer (positive (or) negative ions) is formed all around the metal.

This layer is called Helmholtz electrical double layer. This layer prevents further passing of

the positive ions from or to the metal. A difference of potential is consequently set up



between the metal and the solution. At equilibrium, the potential difference becomes a

constant value, which is known as the electrode potential of a metal.

Thus, the tendency of an electrode to lose electrons is called the oxidation

potential, and the tendency of an electrode to gain electrons is called the reduction

potential.

3. Outline the single electrode potential of Zn measured using calomel electrode?

[CO2-H1-Nov/Dec-2009, June-2006]

To measure the electrode potential of Zn, a cell is made by combining the

saturated calomel electrode with Zn electrode, the potential of which is to be

determined. Since the reduction potential of the coupled Zn electrode is less than E° of

calomel electrode (+ 0.2422 V), the calomel electrode will act as cathode and Zinc

electrode will act as anode.

The following cell reaction will occur in the above cell

At Anode: Zn Zn2+ (aq) +2e- (oxidation)

At Cathode: Hg2Cl2(s) +2e- 2Hg(l) (reduction) Cell reaction: Zn + Hg2Cl2(s) ZnCl2+2Hg(l) The emf of the above cell is measured and the electrode potential is calculated from the emf as follows Ecell = E°right − E°left

Ecell = E°cal − E°Zn

E°Zn = E°cal − Ecell

= + 0.2422 − 1.0025

E°Zn = − 0.7603 volt.



4. Find the Nernst equation for electrode potential and mention its application. [CO2-H1-June-2014, 2009, Dec-2010, May-2011]

Consider the following redox reaction Mn++ne- M

For such a redox reversible reaction, the free energy change (G) and its equilibrium constant (K) are interrelated as

[Pr oduct]G RTln K RTln

[Reac tant]

o [Pr oduct]G G RTln

[Reac tant] (1)

Go= Standard free energy change. The above equation is known as Van’t Hoff isotherm.

In Van’t Hoff isotherm equation, the decrease in free energy (-G) will produce electrical energy. In the cell, if the reaction involves transfer of ‘n’ number of electrons, then ‘n’ faraday of electricity will flow. If E is the emf of the cell, then the total electrical energy (nEF) produced in the cell is

G nFE o oG nFE (2)

Vant Hoff isotherm: o [Pr oduct]G G RTln

[Reac tant]

Comparing equation 1 and 2, it becomes

o

n

[M]nEF nE F RTln

[M ] (3)

Divide the above equation (3) by –nF, the activity of solid metal [M]=1

o

n

RT [1]E E ln

nF [M ]

o nRTE E ln M

nF

o n2.303RTE E log M

nF

(4)

When, R=8.314 J/K/mole; F=96500 coulombs; T=298k



For reduction potential red

o n+0.0591E = E + log M

n (5)

For oxidation potential o n+

oxi

0.0591E = E - log M

n (6)

The above equation 5 & 6 are known as “Nernst equation for electrode potential”. Applications of Nernst equation:

Nernst equation is used to calculate electrode potential of unknown metal. Corrosion tendency of metals can be predicted. Used to calculate EMF of a cell. pH of a solution can be calculated by measuring the EMF. Concentration of the solution in galvanic cell can be determined. Concentration of the solution in galvanic cell can be determined.

5. Explain briefly about electrochemical (or) EMF series? List its applications with suitable examples. [CO2-L2-Dec-2005, June-2006, Dec-2010, June -2012]

Definition When the various electrodes (metals) are arranged in the order of their increasing values of standard reduction potential on the hydrogen scale, then the arrangement is called electrochemical series.

Significance of emf series: 1. Calculation of standard emf of the cell



The standard emf of a cell (E°) can be calculated if the standard electrode potential valuesare known using the following relation. E°cell = E°R.H.E − E°L.H.E 2. Relative ease of oxidation (or) reduction

Higher the value of standard reduction potential (+ve value) greater is the

tendency to get reduced. (i.e. Metals on the top (–ve value) are more easily ionised)

(oxidised).

The fluorine has higher positive value of standard reduction potential (+ 2.87 V),

and shows higher tendency towards reduction. The lithium has highest negative value (− 3.01 V) and shows higher

tendency towards oxidation.

3. Displacement of one element by the other Metals which lie higher in the emf series can displace those elements which lie below them in the series. For example, we may know whether Cu will displace Zn from the solution or vice-versa. We know that standard reduction potential of Cu & Zn. i.e., E°Cu2+/Cu = + 0.34 V and E°Zn2+/Zn = − 0.76 V. So, Cu2+ has a great tendency to acquire Cu form, than Zn2+ has for acquiring Zn form. So, Cu2+ has a great tendency to acquire Cu form, than Zn2+ has for acquiring Zn form. 4. Determination of equilibrium constant for the reaction Standard electrode potential can also be used to determine the equilibrium constant (K) for the reaction. We know that From the value of E°, the equilibrium constant for the cell reaction can be calculated. 5. Hydrogen Displacement Behavior Metals with negative reduction potential (i.e., the metals placed above H2 in the emf series) will displace the hydrogen from an acid solution. Example:Zinc reacts with dil H2SO4 to give H2 but Ag does not, why? Zn + H2SO4 ZnSO4 + H2 ↑ E°Zn = − 0.76 volt The metal with positive reduction potential (ie., the metals placed below H2 in the emf series) will not displace the hydrogen from an acid solution. Ag + H2SO4 No reaction Eo

Ag = + 0.80 volt

o

o

o

O O

ΔG RTlnK 2.303RTlogK

- Δ G log K

2.303 RT

nFE 2.303 RT

ΔG nFE



6. Predicting Spontaneity of Redox Reactions

Spontaneity of redox reaction can be predicted from the emf (E°) value of the complete cell reaction. (i) If the E° of the cell is positive, the reaction is spontaneous. (ii) If the E° of the cell is negative, the reaction is not feasible. In general, an element having lower reduction potential can displace another. Metal having higher reduction potential from its salt solution, the reaction is spontaneous. 6. Explain in detail about the causes of corrosion and factors connected with

metal which influence the rate of corrosion of metal. [CO2-L2-Dec-2011, Dec-2010, June 2008]

Corrosion: If the metal or alloy structures are not properly maintained, they deteriorate slowly by the action of atmospheric gases, moisture and other chemicals. This phenomenon of deterioration or destruction of metals and alloys is known as corrosion. Causes of corrosion: Metals occur in nature in two different forms.

Native state. Combined state.

Native state: The metals occur in native (or) free (or) uncombined state are non-reactive with the environment. They are noble metals exist as such in the earth crust. They have very good corrosion resistance. Example: Au, Pt, Ag Combined state: Except noble metals, all other metals are reactive and react with environment and form stable compounds, as their oxides, sulphides, chlorides and carbonates. They exist in their form of stable compounds called ores and minerals. Example: Fe2O3, ZnO, PbS, CaCO3etc, Factors influencing the rate of Corrosion: The rate and extent of corrosion mainly depends on (i) Nature of the metal. (ii) Nature of the environment. Nature of the Metal: 1. Position in EMF Series: The extent of corrosion depends on the position of the metal in the emf series. Metals above the hydrogen in emf series get corroded vigorously. Lower the reduction potential, greater is the rate of corrosion. When two metals are in electrical contact, the more active metal (or the metal having high negative reduction potential) undergoes corrosion. 2. Relative Areas of the Anode and Cathode: The rate of corrosion will be more, when the cathodic area is larger. When the cathodic area is larger, the demand for electrons will be more and this results in an increased rate of corrosion (dissolution) of metals at anodic area. 3. Purity of the Metal: The 100% pure metal will not undergo any type of corrosion. But, the presence of impurities in a metal creates heterogeneity and thus



galvanic cells are set up with distinct anodic and cathodic area in the metal. Higher the percentage of impurity, faster is the rate of corrosion of the anodic metal. 4. Over Voltage or Over Potential:The over voltage of a metal in the corrosive environment is inversely proportional to corrosion rate. Nature of the surface film:The nature of the oxide film formed on the metal surface decides the extent of corrosion which can be decided by Pilling-Bed worth rule. Nature of the Corrosion Product:If the corrosion product is soluble in the corroding medium; the corrosion rate will be faster. Similarly, if the corrosion product is volatile (like MoO3 on Mo surface), the corrosion rate will be faster.

7. Explain about the factors connected with environment which influence the rate of corrosion. [CO2-L2-Dec-2011, Dec-2010, June 2008]

Nature of the Environment: 1. Temperature:The rate of corrosion is directly proportional to temperature. This is because, the rate of chemical reaction and the rate of diffusion of the ions increases with rise in temperature. Hence the rate of corrosion increases with temperature. 2. Humidity:The rate of corrosion will be more, when the humidity in the environment is high. The moisture acts as a solvent for the oxygen in the air to produce the electrolyte, which is essential for setting up a corrosion cell. 3. Presence of Corrosive Gases:The acidic gases like, CO2, SO2, H2S and fumes of HCl, H2SO4, etc., produce electrolytes, which are acidic and increases the electrochemical corrosion. Presence of Suspended Particles: Particles like, NaCl, (NH4)2SO4 along with moisture act as powerful electrolytes and thus accelerate the electrochemical corrosion. 4.Effect of pH:The possibility of corrosion with respect to pH of the electrolytic solution and the electrode potential of the metal is correlated with the help of a pourbaix diagram. From the diagram it is clear that the rate of corrosion can be altered by shifting the point ‘Z’ into immunity or passivity regions. The iron will be immune to corrosion, if the potential is changed to about − 0.8 V by applying external current. On the other hand, the rate of corrosion of iron can also be reduced by moving into the passivity region by applying positive potential.



The diagram clearly indicates that the rate of corrosion can also be reduced by increasing the pH of the solution by adding alkali. Thus the rate of corrosion will be maximum when the corrosive environment is acidic. i.e. pH is less than 7.

8. Describe a note on chemical corrosion with suitable mechanism. [CO2-L1-May 2005, Dec 2008]

Dry corrosion is due to the attack of metal surfaces by the atmospheric gases such as oxygen, hydrogen sulphide, sulphur dioxide, nitrogen, etc. There are 3 main types of dry corrosion. 1. Oxidation corrosion (or) corrosion by oxygen. 2. Corrosion by hydrogen. 3. Liquid-metal corrosion. Oxidation Corrosion (or) Corrosion by Oxygen: Oxidation corrosion is brought about by the direct attack of oxygen at low or high temperatures on metal surface in the absence of moisture. Alkali metals (Li,Na, K, etc.) Alkaline-earth metals (Mg, Ca, Sn, etc.) are rapidly oxidised at low temperature. At high temperature, almost all metals (except, Ag, Au and Pt) are oxidised. Mechanism: Oxidation occurs first at the surface of the metal resulting in the formation of metal ions (M2+), which occurs at the metal / oxide interface. M −−−−−> M2+ + 2e−

Oxygen changes to ionic form (O2−) due to the transfer of electron from metal, which occurs at the oxides film / environment interface. ½ O2 + 2e− −−−−−> O2−



Oxide ions react with the metal ion to form the metal-oxide film. M + ½ O2 −−−−−> M2+ + O2− ≡ MO(Metal-oxide film)

Pilling-Bed worth Ratio:The ratio of the volume of the oxide formed to the volume of the metal consumed is called “Pilling-Bed worth ratio”. Corrosion by Hydrogen: Hydrogen embrittlement (at ordinary temperature) When metals contact to H2S at ordinary temperature causes evolution of atomic hydrogen. Fe + H2S −−−−−> FeS + 2H This atomic hydrogen diffuses readily into the metal and collects in the voids, where it recombines to form molecular hydrogen. H + H −−−−−> H2↑ Collection of these hydrogen gases in the voids develop very high pressure, which causes cracks and blisters on metal. Thus, the process of formation of cracks and blisters on the metal surface, due to high pressure of hydrogen gas is called hydrogen embrittlement. Decarburisation (at Higher Temperature): At higher temperature atomic hydrogen is formed by the thermal dissociation of molecular hydrogen. when steel is exposed to this environment, the atomic hydrogen readily combines with carbon of Steel and produces methane gas. C + 4H −−−−−> CH4↑ Collections of these gases in the voids develop very high pressure, which causes cracking. Thus the process of decrease in carbon content in steel is termed as “decarburization” of steel. Liquid - Metal Corrosion:

Heat

2H 2H



This is due to the chemical action of flowing liquid metal at high temperature. The corrosion reaction involves (i) Either dissolution of a solid metal by a liquid metal. (or) (ii) Liquid metal may penetrate into the solid metal.

9. Outline the mechanism of electrochemical corrosion by hydrogen evolution and oxygen absorption. [CO2-H1-Nov/Dec-2010, May/June-2010]

Wet (Or) Electrochemical corrosion: Wet corrosion occurs under the following conditions.

When two dissimilar metals or alloys are in contact with each other in the presence of an aqueous solution or moisture.

When a metal is exposed to varying concentration of oxygen or any electrolyte.

Mechanism of wet corrosion: At anode: In anodic part, oxidation (or) dissolution of metal occurs. M M2+ + 2e- At cathode: In cathodic part, reduction reaction occurs, which depends on nature of the corrosive environment (a) Acidic environment: If the corrosive environment is acidic, hydrogen evolution occurs at cathodic part. 2H+ + 2e- H2 (b) Neutral environment: If the corrosive environment is neutral, hydroxide ion forms at cathodic part 1/2O2 + 2e- + H2O 2OH- Thus,the metal ions(from anodic part0 and non-metallic ions 9from cathodic part) diffuse towards eachother through conducting medium and form a corrosion product between anode and cathode. (a) Hydrogen Evolution Type Corrosion: “All metals above hydrogen in the electrochemical series have a tendency to get dissolved in acidic solution with simultaneous evolution of hydrogen gas”

All metals above hydrogen in the electrochemical series have a tendency to get dissolved in acidic solution with simultaneous evolution of hydrogen gas. When iron metal contacts with non-oxidizing acid like HCl, H2 evolution occurs. At Anode



Iron undergoes dissolution to give Fe2+ ions with the liberation of electrons Fe −−−−−> Fe2+ + 2e− (Oxidation) At Cathode The liberated electrons flow from anodic to cathodic part, where H+ ions get reduced to H2. 2H+ + 2e− −−−−−> H2↑ (Reduction) (b) Absorption of oxygen (Or) Formation of hydroxide ion type corrosion: The surface of iron is usually, coated with a thin film of iron oxide. However, if the oxide film develops, some crack will come and anodic areas are created on the surface while the remaining part acts as cathode.When iron metal contacts with a neutral solution of an electrolyte in presence of oxygen, OH−ions are formed. Eg: When iron metal contacts with a neutral solution of an electrolyte in presence of oxygen, OH− ions are formed.

At Anode Iron dissolves as Fe2+ with the liberation of electrons. Fe −−−−−> Fe2+ + 2e− (oxidation) At Cathode The liberated electrons flow from anodic to cathodic part through metal, where the electrons are taken up by the dissolved oxygen to form OH− ions. ½ O2 + H2O + 2e− −−−−−> 2OH− Thus, the net corrosion reaction is Fe2+ + 2OH− −−−−−> Fe(OH)2↓ If enough O2 is present Fe(OH)2 is easily oxidised to Fe(OH)3, a rust (Fe2O3H2O) 4Fe(OH)2 + O2 + 2H2O −−−−−> 4Fe(OH)3 Brown rust

10. Carry out the corrosion control by material selection and design aspects. [CO2-L3-June-2014, 2010, 2009, May-2012] 1. By Selection of the Metal: Selection of right type of metal is the main factor for corrosion control. Thus, noble metals are used in ornaments and in surgical instruments, as they are most immune to corrosion.



2. By using Pure Metal: Pure metals have higher corrosion resistance. Even a small amount of impurity may lead to severe corrosion. 3. By alloying: Corrosion resistance of many metals can be improved by alloying. For example, stainless steel containing chromium produces a coherent oxide film, which protects the steel from further attack. 4. By proper design: The corrosion is prevented by proper designing .Some of the important rules for designing, which must be observed are given below.

Avoid galvanic corrosion: Selecting the metals as close as possible in the electrochemical series.

Drainage affects corrosion: Tanks and other containers must be designed in such a way that, the whole of the liquid should be drained off completely

Avoid sharp corners and bends: Sharp corners or edges should always be avoided, and hence erosion corrosion can be avoided by smooth corners or curved pipe bends

Avoid crevices:Crevices allow moisture and dirt, which results in increased electrochemical corrosion. This can be prevented by filling the crevices with filler.

11. Discribe about Galvanic corrosion and Differential aeration corrosion. [CO2-L1-May/June-2009, Nov/Dec-2009] Galvanic corrosion is the one type of electrochemical corrosion. When two

different metals are in contact with each other in presence of an aqueous solution or moisture, galvanic corrosion occurs. Here, the more active metal (with more negative electrode potential) acts as anode and the less active metal (with less negative electrode potential) acts as cathode. Zn – Fe Couple: In which zinc (more active or higher in emf series) dissolves in preference to iron (less active metal) i.e., Zn acts as anode and undergoes corrosion and Fe acts as cathode. Cu – Fe Couple: In which iron (more active, when compared to Cu) dissolves in preference to copper (less active) i.e., Fe acts as anode and undergoes corrosion and Cu acts as cathode. Examples for galvanic corrosion: Steel screw in a brass marine hardware corrodes:This is due to galvanic corrosion. Iron (higer position in electrochemical series) becomes anodic and is attacked and corroded, while brass (lower in electrochemical series) acts as cathodic and is not attacked. Bold and Nut made of the same metal is preferred:



It is preferred in practice, because galvanic corrosion is avoided due to homogeneous metals (no anodic and cathodic part). Prevention:Galvanic corrosion can be minimised by the following two ways.

By providing an insulating material between the two metals. By selecting two metals as close as possible on the emf series.

Differential aeration (or) concentration cell corrosion: Concentration cell type of corrosion occurs when a metal is exposed to varying concentration of oxygen or any electrolyte on the surface of the base metal. Eg:Metals partially immersed in water (or) conducting solution (called water line corrosion).If a metal is partially immersed in a conducting solution the metal part above the solution is more aerated and hence become cathodic. On the other hand, the metal part inside the solution is less aerated and thus, become anodic and suffers corrosion.

At anode (less aerated): Corrosion occurs M −−−−−> M2+ + 2e− At cathode (more aerated part): OH− ions are produced ½ O2 + H2O + 2e− −−−−−> 2OH− Examples for Differential Aeration Corrosion Pitting or localised corrosion: Pitting is a localised attack, resulting in the formation of a hole around which the metal is relatively unattached. Crevice corrosion: If a crevice between different metallic objects or between metal and non-metallic material is in contact with liquids, the crevice becomes the anodic region and suffers corrosion. This is due to less oxygen in crevice area. The exposed areas act as the cathode. Pipeline corrosion: Differential aeration corrosion may also occur in different parts of pipeline.Buried pipelines or cables passing from one type of soil to another say, from clay (less aerated) to sand (more aerated) may get corroded due to differential aeration. Corrosion on wire fence: Wire fence in which the areas where the wires cross are less aerated than the rest of the fence and hence corrosion occurs at the wire crossings, which are anodic. According to differential aeration corosion,the wire corrosing corroded fastly.



Other Examples for Differential Aeration Corrosion:

Corrosion occurring under metal washers, where oxygen cannot diffuse easily.

Lead pipeline passing through clay to hinder undergo corrosion. Since the pipeline under cinders is more aerated, it gets corroded easily.

12. Describe the sacrificial anode methods of corrosion control. [CO2-L1-May-2012, June-2010, June-2009, Dec-2006]

Sacrificial anodic protection method: Sacrificial anodic protection method is used for the protection of ships and boats. Sheets of Mg or Zn are hung around the hull of the ship. Zn or Mg will act as anode compared to iron (ship or boat is made of iron), so corrosion concentrates on Zn or Mg. Since they are sacrificed in the process of saving iron, they are called sacrificial anodes. Al, Zn, Mg are used as sacrificial anodes.

Applications of sacrificial anodic protection:

Sacrificial anodic protection method is used for the protection of ships and boats.

Protection of underground pipelines, cables from soil corrosion. Insertion of Mg sheets into the domestic water boilers to prevent the

formation of rust Calcium metal is employed to minimize engine corrosion.

13. Explain the control of corrosion by the use of impressed current cathodic

protection. [CO2-L2-Dec-2009, May-2009, 2008] Impressed current cathodic method, an impressed current is applied in the opposite direction of the corrosion current to nullify it, and the corroding metal is converted from anode to cathode.This can be done by connecting negative terminal of the battery to the metallic structure, to be protected, and positive terminal of the battery is connected to an inert anode. Inert anodes used for this purpose are graphite, platinised titanium. The anode is buried in a “back fill” (containing mixture of gypsum,



coke, breeze, sodium sulphate). The “back fill” provides good electrical contact to anode .

Applications of impressed current cathodic protection:

Structures like tanks, pipelines can be protected by impressed current cathodic protection method.

The line towers like transmission line towers, underground water pipe lines, oil pipe lines can be protected by impressed current cathodic protection method.

Ships, boat can be protected by impressed current cathodic protection method.

14. Explain the following (i) Electroplating of copper. (ii) Electroless plating of nickel. [CO2-L2-Dec-2009, 2008] (i) Electroplating of copper: Principle: Electroplating is the process in which the coating metal is deposited on the base metal by passing a direct current through an electrolytic solution containing the soluble salt of the coating metal.The base metal to be plated is made cathode of an electrolytic cell, whereas the anode is either made of the coating metal itself or an inert material of good electrical conductivity. Objective of electroplating on metals:

To increase the resistance to corrosion of the coated metal. To improve the hardness and physical appearance of the article. To increase the decorative and commercial values of the article. To increase resistance to chemical attack. To improve the properties of the surface of the article.

Objectives for electroplating on non-metals: To increase strength. To preserve and decorate the surfaces of non-metals like plastics, wood,

glass, etc. For making the surface conductivity by utilization of light weight, non-

metallic materials. Theory:



If the anode is made of coating metal itself in the electrolytic cell, during electrolysis, the concentration of electrolytic bath remains unaltered, since the metal ions deposited from the bathon cathode are replenished continuously by the reaction of free anions with the anode.

If the anode is made of an inert material like graphite, electrolyte should be added continuously to maintain the concentration of the coating metal ions in the bath.

Process: Object is treated with dil.HCl or dil. H2SO4. Object acts as cathode.Copper foil as

the anode. Copper sulphate is electrolyte.Copper dissolves in the electrolyte and deposits uniformly on the copper object by passing current.

Various chemical reactions: CuSO4 ionizes as CuSO4 Cu2+ +SO4

2- At Cathode: On passing current, Cu2+ ions move to the cathode and get deposited there as Cu metal. Cu2+ + 2e- Cu At Anode: The free sulphate. The ions migrate to the copper anode and dissolve an equivalent amount of Cu to form CuSO4. Cu2+ +SO4

2- CuSO4 In order to get strong, adherent and smooth deposit certain additives (glue, gelatin, etc.,) are added to the electrolytic bath. To improve the brightness of deposit, brightening agents are added in the electrolytic bath. The favourable conditions for a good electrodeposite are optimum temperature (40-45oC), optimum current density (30-40mA/cm2) and low metal ion concentrations. Characteristics of copper plating:

The deposits of copper are used for electrical and electronic applications.

It is used as a protective coating for steel articles. It is coated at the bottom of stainless steel cooking utensils to affect

better heat transfer.



It is an under coat for Ni-Cr electrodeposit for smoothening out the irregularities.

It is used for high quality decorations and high oxidation resistant coatings.

(ii) Electroless plating: Principle: Electro less plating is a technique of depositing a noble metal (from its salt solution) on a catalytically active surface of the metal, to be protected, by using a suitable reducing agent without using electrical energy. The reducing agent reduces the metallic ions to metal, which gets plated over the catalytically activated surface giving a uniform thin coating. Metal ions + Reducing agent −−−−−> Metal + Oxidised product(s) (Deposited) Example : Electroless plating of nickel: Step I: Pretreatment and activation of the surface

The surface to be plated is first degreased by using organic solvents or alkali, followed

by acid treatment. Activation depends on the type of metal (or) alloy (or) non-metal

used.

Example:

The surface of the stainless steel is activated by dipping in hot solution of

50% dil H2SO4.

The surface of Mg alloy is activated by thin coating of Zn and Cu over it.

Metals and alloys like Al, Cu, Fe, brass, etc., can be directly Ni − plated without

activation.

Non-metallic articles (like plastics, glass, etc.,) are activated by dipping

them in the solution containing SnCl2 + HCl, followed by dipping in palladium

chloride solution. On drying a thin layer of Pd is formed on the surface.

Step II. Preparation of plating path

Nature of the

compound

Name of the

compound

Quantity (g/l) Function

Coating solution Nickel chloride 20 Coating metal

Reducing agent Sodiumhypophosphite 20 Metal ions reduced

Complexing agent

cum exaltant

Sodium succinate 15 Improves the

quality

Buffer Sodium acetate 10 Control the pH

Optimum pH 4.5 - -

Optimum 93oC - -



temperature

Step III Procedure for plating:

The pretreated object is immersed in the plating bath for the required time. During which

the following reduction reaction will occur and the Ni gets coated over the object.

Various Reactions

At Cathode:Ni2+ + 2e− −−−−−> Ni

At Anode: H2PO2− + H2O −−−−−> H2PO3

− + 2H+ + 2e-

Net reaction:Ni2+ + H2PO2−+H2O −−−−−> Ni + H2PO3

−+ 2H+

Application of electroless plating:

Electroless Ni–plating is extensively used in electronic appliances. Electroless Ni–plating is used in domestic as well as automotive fields (e.g.,

jewellery, tops of perfume bottles.) Electroless Ni–coated polymers are used in decorative and functional works. Electroless Cu & Ni coated plastic cabinets are used in digital as well as

electronic instruments. 15. Explain about the constituents and functions of paints? [CO2-L2-June-2014] Paint: Paint is a mechanical dispersion of one or more finely divided pigments in a medium (thinner + vehicle). When a paint is applied to a metal surface, the thinner evaporates, while the vehicle undergoes slow oxidation forming a pigmented film. Characteristics of a good paint:

It should spread easily on the metal surface. It should have high hiding (covering) power. It should not crack on drying. It should adhere well to the surface. The colour of the paint should be stable. It should be a corrosion and water resistant. It should give a glossy film. `

Constituents of paints: Pigments:Pigments are solid and colour producing substances in the paint. Example::Linseed oil,dehydrated castor oil. Functions:

It gives colour and opacity to the film. It also provides strength to the film. It protects the film by reflecting the destructiveUV rays. It increases weather resistance of the film.

Vehicle (or) drying oil:This is a non-volatile portion of a medium and film forming constituent of the paint. These are high molecular weight fatty acids present in vegetable and animal oils.



Functions: They form a protective film by the oxidation and polymerisation of the oil. They hold the pigment particles together on the metal surface. They impart water repellency, toughness and durability to the film.

Thinners (or) solvents:This is a volatile portion of a medium. It easily evaporates after application of the paint. Functions:

It reduces the viscosity of the paint, so that it can be easily applied on the surface.

It dissolves the oil, pigments, etc. and produces a homogeneous mixture.

It increases the elasticity of the film. It increases the penetrating power of the vehicle.

Extenders (or) fillers:These are white (or) colorless pigments.Eg: Talc, gypsum, china clay. Functions:

It reduces the cost of the paint. It retards the settling of the pigment in all paints. It modifies the shades of the pigments. It prevents shrinkage and cracking.

Driers:These are the substances, used to accelerate the process of drying.Eg: Metallic soaps,linoleates and resonates of Co,Mn and Pb. Functions:

They act as oxygen-carriers (or) catalysts. They provide oxygen, which is essential for oxidation, polymerisation of

drying oil. Plasticisers :These are chemicals added to the paint to provide elasticity to the film

and to prevent cracking of the film. Eg:Triphenyl phosphate, tricresyl phosphate, etc.

Anti-skinning agents:These are chemicals added to the paint to prevent gelling and

skinning of the paint. Eg:Polyhydroxy phenol.

Pigment volume concentration:Pigment volume concentration is an important

property of paint. The following equation is used to calculate the P.V.C.

P.V.C . = Volume of pigment in the paint Volume of (pigment+vehicle) in the paint Higher the volume of P.V.C, lower will be the durability, adhesion, consistency of the paint.



16. (a) Detect the single electrode potential of zinc in 0.05 M ZnSO4 solution at 250C (E0

Zn/Zn2+= 0.76) [CO2-H2] Given- Concentration of ZnSO4=0.05M Eo

Zn/Zn2+

=-0.763(std.oxidation potential of Zn)

n=2

Nernst equation for oxidation potential of Zn is

o 2+0.0591E = E log

nZn

0.0591

E = 0.763 log 0.052

= 0.763-0.02955(-1.301)

= 0.763+0.0384

Oxidation potential of Zn =0.8014 V (b) Detect the reduction potential of Cu2+/Cu = 0.5 M at 250C. (E0

Cu2+/Cu= +0.337V). [CO2-H2-Nov/Dec-2009] Solution: concentration of Cu2+= 0.5M, E0 = 0.337V

The Nernst equation for reduction potential of Cu2+ is

o 2+0.0591E = E log Cu

n

0.0591

E = 0.337 log 0.52

E = 0.337 + 0.02955(-0.3010)

= 0.337-0.0089

Reduction potential of Cu = 0.328 V.

(c) Detect the standard electrode potential of zinc electrode dipped in 0.1 M ZnSO4

solution at 250C. (E0Zn/Zn2+= 0.76) [CO2-H2]

Solution: Given-

Concentration of ZnSO4=0.1M E0

Zn2+/Zn=0.763(std.oxidation potential of Zn)

n=2

Electrode reaction is Zn Zn2+ (aq) +2e-

Nernst equation for oxidation potential of Zn is

o 2+0.0591E = E log Zn

n



0.0591E = 0.763 log 0.1

2

=0.763-0.02955(-1) =0.763+0.02955 Oxidation potential of Zn =0.7896 V (d) Find the potential of the lead electrode that is in contact with a solution of 0.015 molar Pb2+ ions .Standard electrode potential E0 for Pb Pb2+ + 2e- is +0.13V. [CO2-H1] Std.oxidation potential is given as Pb Pb2+ + 2e- ; Eo= +0.13V. Solution: Concentration of Pb2+= 0.015M,E0 = 0.13V

The Nernst equation for oxidation potential of Pb2+is

o 2+0.0591E = E log Pb

n

o 0.0591E = E log 0.015

2

= 0.13-0.02955(-1.824)

=0.13+0.0539

Oxidation potential of Pb = 0.184 V.

Unit – III

Energy Resources

Part – A

Prerequisite 1. To study about the nuclear reaction and power generation from nuclear reactors.

2. To understand the principles and generation of energy from batteries, solar cells, wind

mills and fuel cells.

1. What is photogalvanic cell (or) solar cells? [CO3-L1-Jan 2008, Jan 2013]

Photo galvanic cell is the cell one, which converts solar energy directly into electrical energy. It consists of a p-type and n-type semiconductors. They are in close



contact in each other. As the solar energy is available freely and also it is pollution free, in future its utility is very important. 2. What are the general components of nuclear reactor? [CO3-L1-Jan 2008] i) Fuel rods ii) Control rods iii) Coolants iv) Moderators v) Pressure vessel vi) Protective shield vii) Turbine 3. Define. Nuclear fission. [CO3-L1-July 2008, May 2009] It is the process of splitting of heavier nucleus into two (or) more smaller nuclei with simultaneous liberation of large amount of energy. 4. Define Fuel Cell. [CO3-L1] Fuel cell is a voltaic cell, which converts the chemical energy of the fuels directly into electricity without combustion. In these cells, the reactants, products and electrolytes pass through the cell. Fuel + Oxygen Oxidation products + Electricity. 5. Define Nuclear fusion. Give one example. [CO3-L1] The process of combination of lighter nuclei into heavier nuclei, with simultaneous liberation of large amount of energy. Nuclear fusion occurs in sun. Example: 1H2 + 1H2

2He4 + Energy 6. What is breeder reactor? [CO3-L1-Jan 2009, Jan 2013] Breeder reactor is the one which converts non-fissionable material (U238, Th232 ) into fissionable material(U235, Pu239 ). 7. What is wind energy? [CO3-L1] Moving air is called wind. Energy recovered from the force of the wind is called wind energy. 8. What are the applications of lithium batteries? [CO3-L1-June 2009] Button sized Li batteries are used in calculators, watches, cameras, mobile phones, laptop computers, etc. 9. What are non-conventional energy sources? [CO3-L1] The energy which comes from natural resources such as sunlight, wind, tides, rain, etc., are nonconventional energy sources (or) renewable energy sources. 10. What is a battery? How does it differ from a cell? [CO3-L2-June 2006]

A battery is an arrangement of several electrochemical cells connected in series that can be used as a source of direct electric current. Thus, a cell contains only one anode and cathode.



A battery contains several anodes and cathodes.

11. What are the important requirements of a battery? [CO3-L2] A useful battery should fulfill the following requirements

It should be light and compact for easy transport.

It should have long life both when it is being used and when it is not used.

The voltage of the battery should not vary appreciably during its use.

12. What is primary battery or primary cells? Give an example. [CO3-L1-June 2006]

Primary cells are cells in which the electrode and the electrode reactions cannot be reversed by passing an external electrical energy. The reactions occur only once and after use they become dead. Therefore they are not chargeable.

13. What are secondary cells? [CO3-L1-Jan 2013] Secondary cells are cells in which the electrode reactions can be reversed by passing an external electrical energy. Therefore they can be recharged by passing electric current and used again and again. These are also called storage cells or accumulators.

14. What are the advantages of alkaline battery over dry cell? [CO3-L2-Feb 2010]

Zinc does not dissolve readily in a basic medium.

The life of alkaline battery is longer than the dry battery because there is no corrosion on Zn.

PART B

1. Construct a nuclear reactor with components and explain with neat diagram. [CO3-H1-June 2009, June 2005, Jan 2010, Jan 2013]

It is a device in which fission reaction of radioactive materials can be carried out at controlled rate. The energy released during this reaction is utilized for generation of electricity. The nuclear reactor consists of the following parts



1. Reactor Core: The reactor core comprises

Fuel rods

Moderator

Control Rods

Coolant (i) Fuel Rods It is the material used to produce heat energythat starts the chain reaction. Functions:

Natural or enriched uranium or any other fissionable material is used as fuel in the form of rods or strips. eg.- U235, Pu239

Fuel rods are clad with Al or Stainless Steel or Mg alloy or Zr to provide corrosion Resistance.

(ii) Control rods It is the material which control the nuclear reaction by absorbing neutrons Functions:

It absorbs the neutrons which avoid violent conditions.

To make a reaction fast or slow or shut down, control rods are operated by exit the reactor or inserting it into middle of the core or lowering to the bottom of reactor.

Ex. Cadmium (Cd), Boron (Br)

43Cd113 + 0n1

43Cd114 + γ ray

5B10 + 0n

1 5B

11 + γ ray (iii) Moderator It is the material used to reduce fast moving neutron to slow moving neutron. Functions:



The role of moderator is to reduce kinetic energy fast moving neutrons into slow moving neutrons in a small fraction of a second.

The kinetic energy of fast moving neutrons is 1 meV it is reduced to 0.25 eV. Ex. Materials like graphite, beryllium, heavy water, ordinary water are used as moderators.

moderator

Fast neutrons slow neutrons Properties of good moderator A good moderator should possess

High slowing power, good resistance for corrosion, high melting point, Must be chemically stable and inert, should be available in pure form, should possess high thermal conductivity and must be cheap.

(iv) Coolants: It is the material used to reduce the heat produced in the reactor core. Functions:

It is used to remove the intense heat produced during chain reactions Ex. Liquid metal such as sodium and potassium, heavy water, organic liquids, ordinary water are used for high temperature in fast reactor, air, CO2, H2 etc. are used for low power reactor.

A reactor in which ordinary water is used as both moderator and coolant is called light water nuclear power plant.

Note: CO2 is generally not used as coolant when graphite is used as moderator. Because, at high temperature graphite reacts with CO2 to form CO. This causes the thinning of graphite rod and this is called as eating of graphite. 2. Reflector

A reflector reflects back the neutrons that break out from the surface of the core

Usually graphite is used as reflector. 3. Pressure Vessel

Its role is to maintain the pressure as high as 200 kg/cm2 and aid the circulation of coolant

It encloses the reactor core and reflector. 4. Shielding This is used to protect the emission of radiation from the reactor. There are two shields.

U

235



Thermal shield and Biological shield A thermal shield is a 50-60 cm thick iron or steel covers nearer to the reactor which absorbs most γ radiation. A biological shield is a few decimeter thickness of concrete layer which protect any emission of γ radiation and neutron.

Functions:

The environment and operating personals are protected from destruction in case of leakage of radiation.

5. Heat exchanger To transfer the heat energy from core and utilize it to convert water to steam. 6. Turbine The steam produced in the above process rotates a turbine to finally convert mechanical energy to electrical energy. 2. Explain the conversion of non-fissionable material into fissionable material in breeder reactor? [CO3-L2-Jan 2010, June 2014]

The non fissionable material will be converted to fissionable material (U 238 is converted to Pu239,Th232 )

The process of obtaining a fissile nucleides (fissionable material or secondary fuel) from a fertile nucleides (non-fissionable material or primary fuel) is called fuel breeding and the reactor is called a breeder reactor

Breeder reactors makes the nuclear fuel economic and reduces the solid waste

Due to the above reasons the breeder reactors are more popular than other type of reactors

Illustration:

92U238 + 0n

1 94Pu239 + 2e-

94Pu239 + 0n1 Fission products + 3 0n

1 In breeder reactor, out of the three neutrons emitted in the fission of U 235, only one is used for propagating the chain reaction. The other two are allowed to react with U238. Thus fissionable atoms of Pu 239 are produced for each atom of U 235 consumed. Therefore, the breeder reactor produces more fissionable material than it uses. Hence Pu 239 is a man made nuclear fuel and is known as secondary nuclear fuel.

3. Explain solar energy and their utilization. [CO3-L2-May 2008, Jan 2009, Jan 2010] The process of direct conversion of solar radiation into useful energy is called solar energy conversion. It can be done by two methods.

Thermal conversion

Photo conversion Thermal conversion:



It involves the absorption of thermal energy in the form of IR radiation directly Eg. (i) Solar cooker: It uses the solar heat by reflecting the solar radiation using a mirror directly onto a glass sheet which covers the black insulated box. The box contains raw food materials. The food cooked in a solar cooker is more nutritious due to slow heating moreover the direction of the cooker has to be adjusted according to the direction of the sun rays. Eg. (ii) Solar water heater: It consists of an insulated box inside of which is painted with black paint. It also contain glass lid which is used to receive and store the solar heat. The black painted copper coil is present inside the box is allowed to flow in the cold water which gets heated up and flows out into storage tank. From the storage tank, hot water is supplied through pipes. Photo conversion: It involves conversion of light energy into electrical energy.

Eg. Photo galvanic cells (or) voltaic cell (or) solar cells: Solar cell is a device, which converts the solar energy into electrical energy. When a large number of solar cells are connected in series, we get solar battery. Principle: Solar cells are working on the principle of photovoltaic effect. When the solar rays fall on the two layers (p and n) of semi conductor, a potential difference between the two layers is produced, this causes flow of electron from one layer to another layer through external circuit. Construction: Solar cells consist of a p-type semiconductor (such as Silicon doped with Boron) and n-type semiconductor (such as Silicon doped with Phosphorous). They are close contact with each other. Working: When the solar rays fall on the top layer of p-type semiconductor, the electron from the valence bond get promoted to the conduction band and cross the p-n junction into n-type semiconductor. Thereby potential difference between two layers is created, which causes flow of electron (ie., an electric current). The potential difference and hence current increases as more solar rays fall on the surface of the top layer. Thus, when this p and n layers are connected to an external circuit, electrons flow from n layer to p layer, and hence current is generated. Applications of solar cells:

Solar cells can be used for lighting purpose, solar pumps.

It is also used in calculators, electrical watches, radios and Tv’s.

Solar energy can be stored in Ni-Cd batteries and lead acid batteries.

It is used to drive vehicles.

Solar cells made up of Si are used as a source of electricity in space crafts and satellites.

Advantages:



Solar cell can be used in remote isolated areas, forest and hilly regions

Maintenance cost is low.

Solar cells are non-polluting.

Their life time is long. Disadvantages:

1.Capital cost is higher. 2.Storage of energy is not possible.

4. Describe the working of primary alkaline battery. [CO3-L2] Alkaline battery is an improved form of the dry cell, in which the electrolyte NH4Cl is replaced with KOH or NaOH. This makes cell last longer mainly because the zinc anode corrodes less rapidly under basic conditions than under acidic conditions. Alkaline battery consists of a zinc cylinder (anode) filled with an electrolyte consisting of powdered Zn, KOH and MnO2 and is made into paste with starch and water. A graphite rod (cathode) is immersed in the electrolyte in the center of the cell.

Cell Reactions: Anode: Zinc Cathode: Graphite rod + MnO2 paste Electrolyte: Aqueous KOH containing ZnCl2 Anode reaction: Zn(s) + 2OH-

(aq) Zn(OH)2(s) + 2e- Cathode reaction: MnO2(s) + H2O(l) +2e- Mn2O3(s) +OH-

(aq) Overall Cell reaction: Zn(s) + 2MnO2(s) + H2O(l) Zn(OH)2(s) + Mn2O3 (s) EMF of the cell is 1.5 V per cell Applications: Used in calculators, watches, camera, flash lights etc. Advantages:

Zinc does not dissolve in basic medium.

It has longer life time because there is no corrosion on Zn in alkaline medium.

No voltage drop



5. Describe the working of the Nickel cadmium battery. [CO3-L2-June 2006, May 2008, Jan 2009, Jan 2010] Anode: Cd Cathode: NiO2 Electrolyte: 20 -25 % aqueous KOH Nickel-Cadmium battery consists of cadmium anode and a metal grid containing paste of NiO2 acting as cathode. The electrolyte in this cell is KOH. Cell representation Cd | Cd (OH)2 || KOH (aq) | NiO2 | Ni Working (discharging): During discharging, at anode Cd is oxidized to Cd2+ ions and insoluble Cd(OH)2 is formed. At anode:

Cd Cd2+ + 2e- Cd2+ + 2OH- Cd(OH)2

Cd+ 2OH- Cd(OH)2 + 2e-

At cathode: NiO2 is reduced to Ni2+ ions which further combines with OH- to form Ni(OH)2

NiO2 + 2H2O + 2e- Ni (OH)2 + 2OH- Net Cell reaction

Cd + NiO2 + 2H2O Cd (OH)2 + Ni(OH)2 + Energy Recharging: The cell can be charged by passing electric current in the opposite direction. The electrode reaction gets reversed. As a result, Cd is deposited on anode and NiO2 on cathode. Cd(OH)2 + Ni(OH)2 + energy Cd + NiO2 + 2H2O Capacity: 1.2 – 1.4 V per cell Advantages:

It is smaller and lighter.

It has long life time than lead acid battery.

Like dry cell, it can be packed in a sealed container. Disadvantages: It is more expensive than lead acid battery. Applications: It is used in calculators, digital cameras, cordless appliances, pagers, tape recorders, flash lights, medical devices, electric vehicles, space appliances etc 6. Explain the construction and working of Lead acid battery. [CO3-L2-June 2006, Jan 2008, Jan 2013, Dec 2008, June 2009, Jan 2010]



It is a secondary battery which can operate both as a voltaic cell and an electrolytic cell. When it acts as voltaic cell it supplies electrical energy and becomes run-down. When it is recharged, the cell operates as an electrolytic cell. Description: Anode: Pb Cathode: PbO2 Electrolyte: Dil. H2SO4 (1.2 -1.3 g/ml) In Lead acid battery, Anode is made up of Pb and Cathode is PbO2. A number of lead plates (anode) are connected in parallel and a number of PbO2 plates (cathode) are also connected in parallel. Various plates are separated from each other by insulator like rubber or glass fiber. The entire combination is immersed in dil. H2SO4 having a density of 1.30 g/ml. Cell representation: Pb | PbSO4 || H2SO4(aq) | PbO2 | Pb

Working: Discharging: At Anode Lead is oxidized to Pb2+ ions which further combines with SO4

2- ions to form insoluble PbSO4. Pb + SO4 PbSO4 + 2e-

At Cathode: PbO2 is reduced to Pb2+ ions which further combines with SO4

2- ions to form insoluble PbSO4. PbO2 + 4H+ + SO4

2- + 2e- PbSO4 + 2H2O Net Cell reaction: Pb + PbO2 + 4H+ + 2SO4

2- 2PbSO4 + 2H2O From the above reaction is clear that PbSO4 is precipitated in both the electrodes and H2SO4 is used up. Therefore, the concentration of H2SO4 decreases and hence the density of H2SO4 falls below 1.2 g/ml. So battery needs recharging. Recharging The cell can be charged by passing electric current in the opposite direction. The electrode reaction gets reversed. As a result, Pb is deposited on anode and PbO2 on cathode. The density of H2SO4 also increases. At negative terminal (cathode)



PbSO4 + 2e- Pb + SO42-

At positive terminal (Anode) PbSO4 + 2H2O PbO2 + H2SO4 + 2H+ + 2e- Net reaction 2PbSO4 +2H2O + energy Pb + PbO2 + 2H2SO4 Capacity: 2V per cell Advantages:

It is made easily.

It produces very high current.

The self-discharging rate is low when compared to other rechargeable batteries.

It also acts effectively at low temperatures. Disadvantages:

Recycling of this battery causes environmental hazards.

Mechanical strain and normal bumping reduces battery capacity. Applications:

Used mainly in automobiles like cars, electrical vehicles, trains.

Also used in mines, laboratories, hospitals, broad casting stations telephone exchanges, etc.

7. Explain the construction and working of Hydrogen-Oxygen fuel cell. [CO3-L2-Jan 2010, Jan 2013, June 2014]

Fuel cell is a voltaic cell, which converts the chemical energy of the fuel directly into electricity without combustion. Fuel + Oxygen Oxidation products + Electricity Hydrogen – Oxygen fuel cell: It is a simplest and most successful fuel cell in which the fuel hydrogen and the oxidizer oxygen and the liquid electrolyte are continuously passed through the cell. Description: It consists of a two porous electrodes anode and cathode. The porous electrodes are made of compressed carbon containing a small amount of catalyst (Pt, Pd, Ag). In between the two electrodes, an electrolytic solution such as 25% KOH or NaOH is filled. The two electrodes are connected through the voltmeter. Working: Hydrogen (fuel) is bubbled through the anode compartment, where it is oxidized. The oxygen (oxidiser) is bubbled through cathode compartment, where it is reduced.



Cell reactions: At Anode: Hydrogen gas passed through the anode is oxidized with the liberation of electron which then combines with hydroxide ion to form water. 2H2 + 4OH- 4H2O + 4e- At Cathode: The electrons, produced at the anode, pass through the external wire to the cathode where it is absorbed by oxygen and water to produce hydroxide ions. O2 + 2H2O + 4 e- 4 OH- Overall cell reaction: At anode: 2H2 + 4OH- 4H2O + 4e- At cathode: O2 + 2H2O + 4 e- 4 OH- Net reaction: 2H2 + O2 2H2O Emf of the cell = 0.8 to 1.0 V. Fuel battery: When large number of fuel cells is connected in series, it forms fuel battery. Advantages:

Fuel cells are efficient (75%) and take less time for operation.

It is pollution free technique.

It produces electric current directly from the reaction of a fuel and oxidizer.

It produces drinking water. Disadvantages:

Fuel cell cannot store electric energy as other cells do.

Electrodes are expensive and short lived.

Storage and handling of Hydrogen gas is dangerous. Applications:

H2-O2 fuel cells are used as auxiliary energy source in space vehicles, submarines or other military vehicles.



In case of H2-O2 fuel cells, the product water is proved to be a valuable source of fresh water by the astronauts.

8. Discuss the working of secondary Lithium Batteries. [CO3-L2-Jan 2010]

Lithium cells consists of “Li” anode (E0= -3.05V).

It is the lightest metal and selection of cathode depends on the required capacity.

Lithium reacts violently with water and with atmospheric nitrogen; hence organic solvents are used as electrolyte in “Li” cells (ex. THF/ ether).

To improve the conductivity, salt of Li is added as a solute. (ex: Lithium per chlorate / lithium tetra fluorophosphates).

Lithium battery is a solid state battery. Anode is lithium and cathode can be any of TiS2, MnO2, V2O5, MoO2, Cr3O8, CoO2 etc. The electrolyte is a solid electrolyte. The solid electrolyte permits the passage of ions through lattice voids.

Lithium Titanium disulphide battery: Anode: Lithium Cathode: TiS2 Electrolyte: Conducting Polymer (permeable only to cation & not electrons) Construction: Lithium battery consists of a Lithium anode and TiS2 cathode. A solid electrolyte, generally a polymer is packed between the electrodes. The electrolyte permits the passage of only the ions but not that of electrons.

Cell representation Li | Polymer | TiS2

Working (discharging): When the anode is connected to cathode, Li+ ions move from anode to cathode. The anode is elemental Li which is the source of Li+ ions and electrons. The cathode is a material capable of receiving the Li+ ions and electrons. Anode reaction: Li Li+ + e- Cathode reaction: TiS2 + e - TiS2

- Net Cell reaction Li + TiS2 Li+ + TiS2

- LiTiS2 Recharging: Lithium battery can be recharged by supplying an external current, which drives the Li+ ions back to the anode. LiTiS2 Li + TiS2



Capacity: 3 V per cell Advantages Lithium battery is considered to be the cell of the future because

It is light weight so easily portable.

It produces high energy. ( 1kg of Li stores 150 Watt ,1kg Ni-Cd stores 70 Watts,6 kg Pb acid stores 150 Watt)

It has solid electrolyte, hence no leakage.

It lasts hundreds of charging cycles.

It can be made into convenient shapes and sizes. Limitations

Explosive due to reactivity with water and nitrogen

Lasts only 2-3 years from date of manufacture irrespective of usage

Sensitive to high temperature Applications: Used in calculators, transistors, headphones, cordless appliances, laptops etc. 9. Write a note on primary Lithium batteries. [CO3-L2] (i) Lithium sulphur battery: Anode: Lithium in molten state (electron donor) Cathode: Sulphur in molten state (electron acceptor) Electrolyte: Solid β-Alumina (NaAl11O17) Anode is made of Li. Sulphur is electron acceptor, The electron from Lithium is conducted to Sulphur by graphite. Solid β-Alumina (NaAl11O17) is used as solid electrolyte which separates anode and liquid sulphur. The solid electrolyte allows the Li+ ions to migrate to equalize the charge, but will not allow the big polysulphide product ions. The battery is operated at high temperatures as Li and S should be in molten states.

Anode reaction: 2 Li 2 Li+ + 2 e- Cathode reaction: S + 2 e- S2- The S2- formed reacts with elemental Sulphur to form polysulphide ion

S2- + nS [S n+1]2-

Poly sulphide Net Cell reaction: 2 Li + S 2 Li+ + S2-



The direct reaction between Li and S is prevented by β-alumina present in the cell. Capacity: 3.7 V per cell Advantages:

Li-S battery is light weight.

It possesses high energy density. Applications It is used in power tools and electric vehicles. (ii) Li-MnO2 battery: The Lithium- Manganese dioxide battery is the most widely used lithium primary battery. The electrolytic MnO2 should be heated to more than 300 0C to effectively remove water before incorporating it in the cathode. This is very important to get good performance of the cell. The anodic and cathodic reactions are Anode reaction: Li Li+ + e- Cathodic reaction: Step I: X Li + + x e- + MnO2 Lix MnO2 This first step is homogeneous reaction in which a partially lithiated material is formed. This step is further followed by a heterogeneous process to a new phase, The structure of which is yet to be conclusively determined. Step II: (1-x) Li+ + (1-x) e- + Lix MnO2 LiMnO2 The energy density of the system depends on the type of the cell and the current drain. Applications:

Cylindrical shape cells are used in fully automatic cameras.

Coin cells are used in electronic devices like calculators, watches etc.,

Unit – IV

Engineering Materials



Part – A

Prerequisite

1. To learn about the preparation, properties and uses of abrasives,

2. To know about the refractory for engineering applications.

3. To gain the knowledge about the method of manufacture of portland cement.

4. To know the glass materials for the future industrial development.

1. Define refractories. How can they be classified? [CO4-L2-June 2005, Jan 2013] Refractories :Refractories are materials that can withstand high temperatures without softening or deformation in shape.They are used for the construction of lining in furnaces,Kilns. Refractories are classified into 3 types (1)Acidic refractories : Alumina,Fireclay. (2)Basic refractories : Magnesite, Dolomite. (3)Neutral refractories: Graphite, Carborundum. 2. What is refractorinesss? How it is measured? [CO4-L2-Jan 2010] Refractoriness:It is the ability of the material to withstand very high temperature without softening or deformation under particular service condition. The refractoriness of a refractory is generally measured as the softening temperature and is expressed interms of Pyrometric Cone Equivalent (PCE). 3. What is RUL Test? [CO4-L1-Dec 2005] RUL test is conducted by applying a constant load of 3.5 or 1.75 kg/cm2 to the test refractory specimen of size base 5cm2 and height 75 cm and heating in the furnace at a standard rate of 10oc per minute the temperature at which the refractory deforms by 10% is called refractoriness under load (RUL). A good refractory should have high RUL value 4. What is Porosity of a refractory? [CO4-L1] It is defined as the ratio of its pore volume to the bulk volume. Porosity (P)=(W-D)/(W-A)*100 5. Name two refractories which should not be kept in direct contact with fireclay refractory. Why? [CO4-L2-Dec 2006] Magnesite and Dolomite refractories cannot be placed in direct contact with fire clay refractory, because they are basic and react with acidic fire clay refractory. 6. What is abrasive? How it is measured? [CO4-L2-Dec 2008]



Abrasives are hard substances used for polishing, shaping, grinding operations. They are characterized by high melting point, high hardness and chemically inactive. Types: Natural abrasives-Diamond and quartz. Artificial abrasices-Silicon carbidVicker’s scale. 7.How is Carborundum prepared? [CO4-L2] It is prepared by heating a mixture of sand (SiO2) and Coke (carbon) with small amount of saw dust in an electric furnace to about 2200oc.

2200oc SiO2 + 3C SiC + 2CO↓ 8. Give the applications of Garnet and Emery. [CO4-L1] Garnet : It is used in making abrasive paper and abrasive cloth, and also in glass grinding and polishing metals. Emery: It is used in the tip of cutting and drilling tools, and also it is used in making abrasive paper and cloth. 9. What is Portland cement? Give its properties. [CO4-L1-Apr 1996] Cement is named as Portland cement because during setting and hardening of a paste of cement, the colour and hardness resembles of Portland stone(a type of lime stone). Portland cement is obtained by heating an intimate mixture of argillaceous(clay- containing)and calcareous (lime –containing)materials to about 1500oC. It is then mixed with gypsum. Property: This cement possess quick setting and hardening property. 10. Write a note on hydrophobic cement? [CO4-L1] Hydrophobic cement: Water-Proof cement (or) Hydrophobic cement is a cement obtained by adding water-proofing substances like calcium stearate, aluminium stearate and gypsum with tannic acid to ordinary Portland cement during grinding. 11. What is thermal spalling? How will it be controlled? [CO4-L2-May 2011] Thermal spalling is the property of breaking, cracking or peeling off refractory materials under high temperature. It can be controlled by

i)Using high porosity, low co-efficient of expansion and good thermal conductivity refractory. ii)Avoiding sudden temperature changes. iii)By modifying the furnace design.

12. What is white cement? Give its properties. [CO4-L2]



It is white in colour due to the absence of iron compounds. It is obtained by calcining the raw materials of Portland cement which are free from iron oxide. Properties:

1.It is more expensive than ordinary Portland cement. 2.It acts as pore-blocking and water repelling agents.

13. What is Glass? Mention few types of it. [CO4-L2] Glass is an amorphous, hard, brittle, transparent or translucent, super-cooled liquid, obtained by fusing a mixture of a number of metallic silicates.

Types: 1.Soda-lime or Soft glass 2.Potash-lime or hard glass 3.Borosilicate glass

14. Mention objectives of PCE test. [CO4-L2]

1.To determine the softening temperature of a test refractory material. 2.To classify the refractories. 3.To determine purity of refractory. 4.To find servicing temperature.

15. Define hardening and setting of cement. [CO4-L1-Oct 1995] Setting: It is defined as the stiffening of the original plastic mass, due to formation of tobermonite gel. Hardening: It is defined as the development of strength due to formation of crystals. 16. Write a note on norbide. [CO4-L1-June 2006] It is prepared by heating a mixture of boron oxide [B2O3] and coke [carbon] in an electric furnace to about 27000C. 2B2O3 + 7C B4C + 6 CO↑ It is hardness is nine on mhos scale, light weight and black coloured compound, highly resistance to chemical attack and erosion. 17. How is alundum prepared? [CO4-L2-Dec 2006] It is prepared by heating a mixture of calcined bauxite, Coke and iron in an electric furnace to about 40000C.

Bauxite [Al] + 3O2 2Al2O3 18. Write the composition of flint glass and borosilicate glass. [CO4-L2-March 2001] Flint glass: K2O.PbO. 8SiO2 Borosilicate glass: SiO2 [80.5%], B2O3 [13%], Al2O3 [3%], K2O[3%] and Na2O[0.5%]



19. What are the raw materials used in manufacturing of a cement. [CO4-L2-May 2003] 1. Calcareous materials. CaO [eg: Limestone] 2. Argillaceous materials, Al2O3 and SiO2 [eg: clay] 3. Powdered coal or fuel oil.

Part – B 1. Explain in detail on refractoriness and RUL of a refractory. [CO4-L2-Jan 2009,

May 2004] Refractoriness: It is the ability of a material to withstand very high temperature without softening or deformation under particular service conditions. How to measure refractoriness: Since most of the refractories are mixture of several metallic oxides, they do not

have a sharp melting points. So the refractoriness of a refractory is generally measured as the softening

temperature and is expressed interms of Pyrometric Cone Equivalent (PCE). Pyrometric Cone Equivalent: Pyrometric Cone equivalent is the number , which represents the softening temperature of a refractory specimen of standard dimension(38mm height and 19 mm triangular base) and composition.

Refractory PCE number Softening temperature

(I) silica bricks 32 17100C

(II) Alumina bricks 36-38 1800-18500C

(III) Magnesite bricks 38 18500C

Objectives of PCE Test: To determine the softening temperature of a test refractory material. To classify the refractories. To determine the purity of refractories. To check whether the refractory can be used at the particular servicing

temperature. Measurement:



Refractoriness is determined by comparing the softening temperature of a test cone with that of a series of segar cones.

Segar cones (also called Pyrometric cones) are Pyramid shaped standard refractory of definite composition and dimensions and hence it has a definite softening temperature.

A test cone is prepared from a refractory, for which the softening temperature to be determined, as the same dimensions of segar cones. Then the test cone is placed in an electric furnace along with segar cones.

The furnace is heated at a standard rate of 10oC per minute,during which softening of segar cones occur along with test cone. The temperature at which the apex of the cone touches the base is taken as its softening temperature.

PCE numbers are given, based on the softening temperature of the standard segar cones.

PCE number Softening temperature(0C)

1 1010

2 1025

If the softening temperature lies between the softening temperature of two consecutive segar cones, the PCE number of the test refractory is approximately taken as the average of two values. A good refractory should have high refractoriness.

RUL: Refractoriness under load The temperature at which the refractory deforms by 10% is called refractoriness

under load(RUL). Refractories, used in industries and in metallurgical operations, should bear

varying loads.



Hence refractories should have high mechanical strength under operating temperatures.

Generally softening temperature decreases with increases of load. The load bearing capacity of a refractory can be measured by RUL test.

RUL Test: RUL test is conducted by applying a constant load of 3.5 or 1.75 kg/cm2 to the

test refractory specimen of size base 5cm2 and height 75 cm and heating in the furnace at a standard rate of 10oc per minute the temperature at which the refractory deforms by 10% is called refractoriness under load(RUL).

A good refractory should have high RUL value

2. Explain in detail on Dimensional stability, Thermal spalling and Porosity. [CO4-L2-June 2006] (i) Dimensional stability:

It is the resistance of a refractory material to any volume changes when exposed to high temperature over a prolonged time.. Dimensional changes are of two types.

(i) Reversible (ii) Irreversible

Reversible dimensional changes: This results due to the uniform expansion or contraction of a refractory material.

So the dimensional changes of a good refractory material must be reversible. Irreversible or permanent changes:

This may be due to contraction or expansion of refractory material. Phase transformations may also occur during heating and cooling. Irreversible changes occur in the following cases Example: (i) Magnesite bricks shrink in service.

Magnesite is an amorphous material (specific gravity is 3.05). On heating it is gradually converted into more dense crystalline form of periclase (specific gravity is 3.54). Magnesite Periclase (amorphous) (crystalline) (ii) Silica bricks expand in service.

Silica bricks expand on heating due to the transformation of one form to another form. This is accompanied by a considerable increase in volume. 870 0 C 1475 0 C Quartz Tridymite Crystallite Crystalline α-form β-form A good refractory material should have high dimensional stability (ii) Thermal spalling:



Thermal spalling is the property of breaking, cracking or peeling off a refractory material under high temperature. Thermal spalling is caused due to

Uneven expansion and contraction of refractory material due to rapid change in temperature.

Slag penetration Thermal spalling can be decreased by avoiding sudden temperature changes, using high porosity bricks, using good thermal conductivity bricks, over firing refractory bricks at high temperature, by modifying furnace design. A good refractory material should have low thermal spalling. (iii) Porosity All refractory contain pores. Pores may be open or closed. It is the ratio of the volume of the pores to the bulk volume W-D P = *100 W-A 3. Explain in detail on alumina, magnesite bricks and silicon carbide. [CO4-L2-

May 2007, Jan 2009, Jan 2013, June 2009, Jan 2010, June 2014]

ALUMINA BRICKS or FIRE CLAY BRICKS. Alumina bricks contain 50 % or more of Al2O3. They are generally manufactured by mixing calcined bauxite with clay binder. Grinding and mixing: The raw materials (calcined bauxite and SiO2) are ground to fine powder and mixed with required amount of water to convert it into pasty material. Moulding: The slurry is poured into moulds to get required shape and size by either hand moulding or mechanical moulding. Drying: The moisture and volatile matter are removed by heating the moulded brick in tunnel driers heated by steam. Firing: The dried bricks are fired at 1200 – 14000C for 6-8 days in tunnels or shaft or rotary kiln. Properties:

Alumina bricks are acidic and non-conducting (high porosity)

They possess low coefficient of expansion hence high resistance to thermal spalling.

They have appreciable RUL and abrasion resistance.

They are inert to action of gases like CO2, H2 and natural gas.

They are very stable to both oxidizing and reducing conditions. Applications:

Medium duty bricks containing 50 – 60 % Al2O3 are used in lining of cement rotary kilns, soaking pits, hearth furnace etc.,



High duty alumina bricks containing 75 % Al2O3 are used in Aluminium and Brass melting furnaces, lower parts of soaking pits.

It is also used in steel industries. MAGNESITE BRICKS Basic refractory: contains MgO manufactured by mixing powdered calcined magnesite (MgO) with magnesia or sulphite or iron oxide as binding material. Manufacture: Grinding & Mixing: magnesite + binding material = made into fine powder + water to convert into pasty material. Moulding: done by machine pressing or hand moulding Drying: carried out at ordinary temperature to remove moisture Firing: done in Kiln to about 1500’C for 8 hours PROPERTIES

• Basic refractory • Used upto 2000’C without load • Used upto 1500’C with load of 3.5kg/cm2 • Relative density is 3.53 • Low resistance to acidic slags • Chemically inert to basic slags • Poor abrasion resistance • High thermal conductivity

USES • When using this refractory high temperature is required to be maintained • Used in steel industry for lining of basic converters and open hearth furnaces • Hot mixer linings, copper converters and reverberatory furnaces

SILICON CARBIDE(SiC) BRICKS • Neutral refractories • Carborundum • Manufacture:

sand 54% coke 34% saw dust 10% common salt 2% SiO2 + 3C SiC + 2CO + Heat Mixture is heated in an electric furnace at 2000oC for 36Hrs.

• Common salt (NaCl)-remove iron impurities. Saw dust

• increases the porosity of the charge. • Facilitates the escape of CO & other volatile matter from the reaction. • Carborundum removed from furnace &mixed with bonding agent like

graphite,clay,silicon nitride. • Sic shaped, dried and fired at 1500ᵒc.

Propertries:



• High thermal conductivity. • Low thermal expansion. • High refractoriness. • Withstand high temperature. • High resistance to spalling and abrasion. • Stable upto 900ᵒ C

USES: Sic used in

• Muffle furnace for good thermal conductivity. • Heating elements in furnaces-globars. • To make high conducting crucibles.

4. Give a detailed account of siliceous and non- siliceous abrasives. [CO4-L2-Jan 2009, Dec 2005, Jan 2010] i] Quartz It is pure crystalline silica [SiO2]. Its hardness is 7 on mhos scale. Uses: It is used for grinding pigment in the paint industry and also as granules in grinding machine. ii] Garnet It is mixture of trisilicates of alumina, magnesia and ferrous oxide. Its hardness range from 6-7.5 on mhos scale. The main garnet used as an abrasive is a complex calcium- aluminium iron silicate. Uses:It is used in making abrasive paper and abrasive cloth and also in glass grinding and polishing metals. (i)Diamond: It is a pure crystalline carbon. It is the hardest known substance. Its hardness is 10 on Moh’s scale. It is chemically inert and not affected by acids or alkalis. The off- colour diamond is called borts and black colour diamond is called carbonado. Use: It is used in drill points, cutting rocks, stones and grinding wheels. (ii) Corundum: It is a pure crystalline alumina (Al2O3). Its hardness on Moh’s scale is 9. Uses: It is used for grinding glasses, gems, lenses, metals. (iii) Emery: It is a fine-grained, opaque, black coloured mineral. It consists of 55-75% crystalline alumina. 20-40% magnesite. 12% other minerals. Its hardness is 8 on Moh’s scale. Uses: it is used in the tip of cutting and drilling tools, and also it is used in making abrasive paper and cloth.



5. Write short notes on the synthetic abrasives. [CO4-L1-Jan 2013, Jan 2010, Dec 2005, May 2009] (1) Silicon carbide Manufacture 60% sand SiO2 40% coke saw dust (evolve gases & it increases porosity) Salt (reacts with impurities & removed as volatile chlorides) 20000C for 36 hours.

SiO2 + 3C SiC +2CO Moh’s scale = 9.3 SiC + bonding material = required shape then dried and fired

Properties: Possess high thermal conductivity Low expansion & low density Resistant to abrasion and thermal spalling Strong and withstand loads up to 16500C Heat conductivity is intermediate between metal and ceramic Electrically intermediate between conductors and insulators

Uses Hard materials for making grinding dies, Cutting and sharpening tools. To prepare scartch,wear resistant Coatings. Used in refractory industry. Neutron absorber. Radiation protection, shielding. Welding electrodes, boriding agent.

(2) NORBIDE

MANUFACTURE: 27000C B2O3 +7C B4C +6CO

Moh’s scale = 9

Properties: Moh’s scale- 9, light weight, black coloured compound, chemically inert, corrosion resistant, Uses: Cutting steel, tungsten carbide, in grinding dies, and for cutting and sharpening hard tools (3) ALUNDUM

Manufacture Heating a mixture of bauxite, coke and iron in an electric furnace to about

4000 o It is artificial corundum. It is less brittle and tougher



4Al + 3O2 2Al2O3 Al2O3 + 2C + iron heated to about 40000C

Uses: grinding of hard steels and other materials of high tensile strength 6. Explain about i] abrasive paper ii] abrasive cloth iii] grinding wheel. [CO4-L2-June 2000] Abrasive paper [or] cloth Manufacture:The roll of paper or cloth is made to pass through a series of rollers, and a thin coating of glue is applied on its upper side. It is then passed under hopper [Fig] from which the grit of abrasive is allowed to fall and spread evenly on the glued paper or cloth then it is dried in warm drying room. Finally, it is allowed to age for few days, so that the glue sets firmly.

Uses: It is used to prepare smooth wood, metal and plastic surfaces. Examples: Alumina and Silicone Carbide iii] As grinding wheels: Manufacture: Grinding wheel is manufactured by mixing abrasive grains with binder. The mixture is moulded in to desired shape and heated and cured. Uses: It is used for the removal of scales from iron surfaces, Cutting tool sharpening. 7. What is Portland cement? Discuss its manufacturing process by wet process. [CO4-L2-Nov 2003] Cement is named as Portland cement because during setting and hardening of a paste cement, the colour and hardness resembles to a Portland stone [a type of lime stone]. Manufacturing: 4- Steps

Mixing of raw materials 2.Burning 3. Grinding 4.Storage and Packing 1. Mixing of raw materials.



Wet process: The calcareous material [lime stone] is crushed, powdered and stored in a storage tank [called siols]. The argillaceous material [clay] is thoroughly is washed with water to remove any adhering organic matter and stored in a basin. Then the powdered lime stone [from soils] and wet clay [from basin] are led to grinding mills, where they are mixed to from a paste called Slurry. The slurry is led to a correcting basin where its chemical composition may be adjusted. Thus the slurry containing about 38 to 40% of water stored in storage tank. 2.BURNING: Burning of “dry raw mix” or “slurry” is carried out in rotary kiln. The rotary kiln is a long horizontal steel cylinder (2.5-3.0 m dia and 90 to 120 m length) lined inside with refractory bricks, which rotates at a speed of 1 r.p.m. The kiln is set in slightly inclined position of about 5-60 to allow the material to travel slowly from one end to the another end. PROCESS: The “dry raw-mix” or “corrected-slurry” is fed into the kiln from the upper end, while the hot flame is forced into the kiln from the lower end. Due to slope and slow rotation, the materials gradually descends in the kiln into different zones of increasing temperatures.

(i)Drying Zone: The upper part of the kiln is known as drying zone, where the temperature is about 4000C. In this zone, most of the water in the slurry gets evaporated. (ii)Calcination Zone:



The central part of the kiln is known as calcinations zone where the temperature is about 10000C. In this zone, limestone gets decomposed into CaO and CO2.

CaCO3 CaO + CO2↑ Lime stone Quick lime (iii)Clinkerng Zone: The lowest part of the kiln in known as clinkering zone, where the temperature is about 1350- 15000C. In this zone lime reacts with clay (containing Al2O3, SiO2, Fe2O3) to form various Bogue compounds( C2S,C3S,C3A,C4AF)

2 CaO + SiO2 2 CaO . SiO2 ( C2S) 3 CaO + SiO2 3 CaO . SiO2 ( C3S)

3 CaO + Al2O3 3 CaO . Al2O3 ( C3A) 4 CaO+ Al2O3 + Fe2O3 4 CaO . Al2O3 . Fe2O3 (C4AF) These bogue compounds fuse together to form small, hard, grayish coloured stone like mass called cement clinkers. 3.GRINDING : The hot clinkers are cooled with atmospheric air and then pulverized together with 2-3% gypsum in ball mills. Gypsum act as a retarding agent for quick setting of cement. 4.STORAGE AND PACKING: The cement coming out of the grinding mill is stored in a concrete storage silos. Then the cement is packed in jute bags by automatic machine. 8. Explain setting and hardening of cements with the reaction involved. [CO4-L2-May 2003, June 2014]

• Due to hydration & hydrolysis of Bogue compounds of cement with water. • Anhydrous compound converted into soluble gels & crystals • Ability to surround the inert materials like sand, crushed stone,bricks. • Setting-changing plastic state of cement to stiff solid state. • Gel formation, low compressive strength.

Hardening • Rate of gain of strength. • Compressive strength of concrete increases with the passage of time. • Stable gels,crystals.

CHEMISTRY INVOLVED IN SETTING AND HARDENING OF CEMENT 1. When water mixed with cement powder, tricalcium aluminate starts hydration &

responsible for initial setting of flash setting of cement. C3A responsible for setting action of cement. 3CaO.Al2O3+6H2O 3CaO.Al2O3.6H20+880 kJ/kg

2. After hydration of C3A, hydration of C3S starts. C3S hydration responsible for initial strength of cement. 2(3CaO.SiO2)+6H2O CaO.2SiO2.3H2O+3Ca(OH)2+500kJ/kg

Tobermonite gel crystalline



3. Dicalcium silicate (C2S) reacts with water . Strength of concrete after 7 days of its placement, C2S starts contributing strength & continues for one year. 2(2CaO.SiO2)+4H2O 3CaO.2SiO2.3H2O+Ca(OH)2+250 KJ/Kg

• Final setting & hardening of cement are due to the formation of tobermonite gel & crstalline Ca (OH)2

• Tetra calcium alumino ferrate (C4AF) is more or less inactive compound. • It does not contribute strength to cement. • Function of Gypsum in cement • C3A+6H2O C3A.6H2O+Heat • C3A+ x.CaSO4.2H2O C3A.xCaSO4.2H2O

Gypsum calcium sulpho aluminate • The above reaction prevents high concentration of alumina in cement. • Retard the initial setting of cement.

Heat of hydration • Water mixed with Portland cement, heat is liberated. • These reactions lead to setting & hardening of cement.

Average heat liberated-500 KJ/Kg.

Constituents C3A C3S C4AF C2S

Heat of hydration(KJ/Kg) 880 500 420 250

Thus the final setting and hardening of cement is due to the formation of tobermonite

gel plus crystallization of Ca(OH)2 and hydrated tricalcium aluminate.Development of

compressive strength of the cement , due to hydration and hydrolysis of Bogue

compounds, are shown in the graph.



9. Discuss about the properties and uses of various types of cement. [CO4-L2] I] White cement or white Portland cement Properties: It is more expensive than ordinary Portland cement. It acts as pore –blocking and water repelling agent.

Uses: It is used to make concrete which is impervious to water under pressure. It is used in the construction, where absorption of water needs to be avoided. It is used in the construction of bridges and structures under water.

II] Water- proof cement or Hydrophobic cement Properties: It is more expensive than ordinary Portland cement. It acts as pore –blocking

and water repelling agent. Uses: It is used to make concrete which is impervious to water under pressure. It is used in the construction, where absorption of water needs to be avoided. It is used in the construction of bridges and structures under water.

10. Write a note on manufacturing of glass. [CO4-L1-May 2003, Nov 2003, June 2014] GLASS: Glass is an amorphous, hard, brittle, transparent or translucent, supercooled liquid, obtained by fusing a mixture of a number of metallic silicates. It possesses no sharp melting point, crystalline structure and definite formula. Glass may be represented as → xR2O.yMO.6SiO2



Manufacturing of glass involves the following 4 steps STEP-1: MELTING: The raw materials in proper proportions,(e.g., sand, soda ash and lime stone for

common glass)are mixed and finely powdered.The homogeneous mixture (known as Batch)is fused with some broken glass,called “Cullet”in the pot(or) tank of the tank furnace,in which heating is done by burning producer gas and airmixture over the charge.

The Cullet melts at a comparatively low temperature and assist in melting the rest of the charge.During melting of ordinary soda-glass,the following series of reactions occur.The reaction is an acid-base reaction leading to the formation of various silicates. CaCO3 + SiO2 → CaSiO3 + CO2↑ Na2CO3 + SiO2 → Na2 SiO3 + CO2↑

STEP-2 WORKING OF MOLTEN GLASS: The molten glass is then worked into articles of desired shapes by either blowing

or moulding or pressing between rollers. STEP-3 ANNEALING: Glass articles are then allowed to cool gradually to room temperature (sudden

cooling must be avoided, because cracking occurs). The longer the annealing period, the better is the quality of the glass.

STEP-4 FINISHING: The glass articles, after annealing period, are subjected to finishing process such

as cleaning, polishing, cutting, sand – blasting. 11. Explain elaborately on the composition and uses of any four glasses. [CO4-L2-Apr 2002, May 2003] SODA-LIME (OR) SOFT GLASS: Raw materials: Silica(sand), Calcium carbonate and soda ash. Composition: Na2O.CaO.6SiO2 Uses: They are used as window glasses, electric bulbs, bottles, plate-glasses, jars, cheaper table wares, where high temperature – resistance and chemical stability are not required. LEAD GLASS OR FLINT GLASS: Raw materials: Lead oxide (instead of calcium oxide) and Silica are fused. For dense optical glasses, as much as 80% of PbO is in corporated. In addition, K2O is used, instead of sodium oxide. Composition: K2O.PbO.6SiO2 Uses:Lead glasses are used for high-quality table wares, neon sign turbings, optical purposes (like lenses, etc), electrical insulators.



High lead content glasses are used for extra-dense optical glasses for widows and shields to protect personal from X-rays and gamma –rays in medical and atomic energy fields respectively. POTASH LIME OR HARD GLASS: Raw materials: Silica (sand), Calcium carbonate and Potassium carbonate. Composition: K2O.CaO.6SiO2 Uses: These glasses are used for manufacturing combustion tubes,chemical apparatus. BORO SILICA GLASS (OR) PYREX GLASS OR JENA GLASS: Raw materials: Silica, boron with a small amount of alumina and some oxides. Composition: SiO2(80.5%),B2O3(13%), Al2O3(3%), K2O(3%) and Na2O(0.5%) Uses: It is used in industry for pipelines for corrosive liquids, gange glasses, superior laboratory apparatus, kitchenwares, television tubes, chemical plants, electrical insulators.

Unit –V

Fuels And Combution

Part – A

1. To learn about the manufacturing methods of fuels and combustion and its

chemical properties.

2. To know the type of fuels with examples

3. To get the knowledge about the theory of combustion, calorific value.

1. Why gaseous fuels are superior to all the other fuels? [CO5-L2-Dec 2009, June 2011]

They don’t produce any ash or smoke. The have high C.V. and high thermal efficiency. Even they can be generated from poorest quality of solid fuel.

2. List the importance of proximate analysis. [CO5-L2-Nov 1994, Apr 1997, July 2009] Higher the percentage of moisture in the coal indicates will reduce C.V,

consumes more heat and increases the transport cost. Higher the percentage of volatile matter indicates large amount of fuel is

required to vaporize the volatile matter as well as produces long flame with high smoke.

Higher the percentage of ash results in decrease in C.V along with hindrance in transfer of heat.



Higher the percentage of carbon will not only increases the C.V but also gives an idea to design the furnace.

3. Mention the importance of ultimate analysis. [CO5-L2] Higher the percentage of C and H in coal l indicates the good quality of

coal as well as increasing the C.V. Nitrogen is inert in nature hence, its presence should be low. Though Sulphur will increases the C.V. of the fuel, but it will leads to

corrosion of the furnace by forming SO2 and SO3 during combustion reaction, which upon mixed with steam forming corrosive vapors.

Higher the percentage of Oxygen indicates the higher amount of moisture, there by decreasing the C.V.

4. Define carbonization. [CO5-L1] When coal is heated in the absence of air, it is converted in to dense, porous, and coherent mass called as coke. This process is called as carbonization 5. List the important characteristics of Metallurgical coke. [CO5-L1]

It should have very low moisture, ash, sulphur and phosphorous contents. It should possess high porosity and high C.V. along with high mechanical

strength to withstand the weight of ore, fuel and flux. It should be cheap and shouldn’t be too reactive.

6. What is Knocking? Explain the Mechanism of Knocking. [CO5-L2-June 2006, Dec 2009, June 2013] The explosive combustion of petrol and air mixture produces shock waves in I.C. engine, which hit the walls of the cylinder and piston producing a rattling sound is known as knocking. Mechanism of Knocking Beyond a particular compression ratio, the petrol mixture suddenly burns into flame.

The rate of flame propagation increases from 25m/s to 2500m/s, which propagates very fast, producing a rattling sound. The activated peroxide molecules decompose to give number of gases products which produces thermal shock waves which hit the walls of the cylinder and piston causing a rattling sound which is known as knocking.

7. Define octane number. [CO5-L1-May 2008, May 2010, May 2011] Octane number is defined as the percentage of isooctane present in a standard mixture of isooctane and n-heptane, which knocks at the same compression ratio as the petrol being tested. Isooctane is the branched chain hydrocarbon has least knocking rate, hence its octane number is arbitrarily fixed as 100. N-heptane a straight chain hydrocarbon has highest tendency to knock hence its octane number is fixed as zero. Octane number of petrol is 80 means it contains 80% by volume isooctane and 20% by volume n- heptane.



8. Define Cetane number. [CO5-L1-June 2010, July 2009, June 2011] It is defined as the percentage of cetane present in standard mixture of a cetane and 1- methylnaphthalene, which knocks at the same compression ratio as the diesel fuel being tested. 9. What are Antiknocking agents? [CO5-L1-Dec 2006] These are the substances added to petrol in order to prevent knocking in I.C. Engines. TEL : Tetra Ethyl led. TML: Tetra Methyl led. MTBE : Methyl Tertiary Butyl Ether and diethyl telluride. 10. Write the composition of CNG and LPG. [CO5-L1-May 2011] CNG: CH4 = 88.5%, C2H6 = 5.5%, C3H8 = 3.7% and C4H8 = 1.8% LPG: Propane = 24.7%, Butane = 38.5%, Isobutane = 36.7% 11. List the advantages of LPG and CNG. [CO5-L2-June 2011, June 2000] CNG: It produces comparatively less pollution than petrol and diesel. Octane number of CNG is 130, higher than most of the fuel. It produces lesser noise as well as lesser emission of carbon particles. It is highly safety since it ignites only at higher temperature.

LPG: It’s C.V 3 times higher than natural gas and 7 times higher than coal gas. Easy to storage, handling and use. Portability in steel cylinder/container makes its use possible in remote isolated

places. 12. Define GCV and LCV. [CO5-L1-Dec 2005, June 2006] Gross calorific value (G.C.V) is defined as the total amount of heat produced, when a unit quantity of the fuel is completely burnt and the products of combustion are cooled to room temperature. Net calorific value (N.C.V) is defined as the net heat produced, when a unit quantity of the fuel is completely burnt and the products of combustion are allowed to escape. 13. How is water gas superior to producer gas? [CO5-L2-Dec 2009, June 2011] a) Its calorific value is higher (2800 kcal/m3) b) It possesses less amount of N2 content c) It is used for the production of H2, power alcohol and carburetted water gas (water gas + oil gas)



14. Arrange the following fuels in increasing order of octane number. [CO5-L3] n-Heptane, 1-methyl naphthalene n-Heptane and Hexadecane Ans: Hexadecane, n-Heptane, n-Heptane and 1-methyl naphthalene. 15. What is the disadvantage of TEL? [CO5-L1-June 2010] When leaded petrol is used as fuel in the IC engine it will be deposited as Pb and PbO2 after the combustion reaction. As a result the walls of the engine are coated with lead which will decrease the efficiency of the engine. To avoid this ethylene dibromoide is added, which removes the deposit as volatile lead bromide as follows.

Pb + (CH2)2Br2 PbBr2 + C2H4 But these will lead air pollution as lead can create neurological disorder in brain if inhaled by human beings. Hence, TEL should be avoided. Nowadays, aromatic phosphates are used to avoid this problem. 16. In what way coking coal and caking of coal are differ from each other. [CO5-L2-Dec 2012] When coal undergoes carbonization, if the product is soft, plastic and coherent mass then it is called as caking of coal. On the other hand if the product is dense, porous and strong mass of coke is formed it is called as coking of coal. 17. What is the drawback of presence of sulphur in the coal? [CO5-L2] The combustion products of sulphurie., SO2 and SO3 are harmful and have

corrosion effects on equipments. The coal containing sulphur is not suitable for the preparation of metallurgical

coke as it affects the properties of the metal. Number of phases = 2

Part-B 1. Explain the proximate analysis of coal. [CO5-L2-TCY A.U. July 2009, June 05, Dec 05, Dec 06] (1)Proximate Analysis It involves the determination of percentage of (i) Moisture content. (ii) Volatile matter. (iii) Ash content. (iv) Fixed carbon in coal. 1. Moisture content About 1 gm of powdered air-dried coal sample is taken in a crusible, and is heated at 100 -105C in an electric hot-air oven for 1 hour. The loss in weight of the sample is found out and the % of moisture is calculated as % of moisture in coal = loss in weight of the coal / weight of air−dried coal x 100



2. Volatile matter After the analysis of moisture content the crusible with residual coal sample is covered with a lid, and is heated at 950 -20 C for 7 minutes in a muffle furnace. The loss in weight of the sample is found out and the % of volatile matter is calculated as % of volatile matter in coal = loss in weight of the coal / weight of air−dried coal x 100 3. Ash content After the analysis of volatile matter, the crusible with residual coal sample is heated without lid at 700 – 50 C for 1⁄2 an hour in a muffle furnace. The loss in weight of the sample is found out and the % of ash content is calculated as % of ash content in coal = weight of ash formed /weight of air−dried coal x100 4. Fixed carbon It is determined by subtracting the sum total of moisture, volatile and ash contents from 100. % of fixed carbon in coal = 100 − % of moisture content +volatile matter +ash content SIGNIFICANCE (i) Moisture content High percentage of moisture is undesirable because (i) it reduces the calorific value of coal, (ii) moisture in coal consumes more heat in the form of latent heat of evaporation and hence more heat is to be supplied to the coal, (iii) it increases the transport cost. (ii) Volatile matter High percentage of volatile matter is undesirable because (i) it reduces the calorific value of coal, (ii) large proportion of fuel on heating will distill over as vapour, which escapes out unburnt, (iii) coal with high percentage of volatile matter burns with a long flame with high smoke, (iv) the coal containing high percentage of volatile matter do not coke well. (iii) Ash content High percentage of ash content is undesirable because (i) it reduces the calorific value of coal, (ii) ash causes hindrance to heat flow as well as produces clinkers, which blocks the air supply through the fuel, (iii) it increases the transporting, handling and storage costs, (iv) it involves additional cost in ash disposal. (iv) Fixed carbon (i) High percentage of fixed carbon is desirable because higher the percentage of fixed carbon in a coal, greater is its calorific value,



(ii) the percentage of fixed carbon helps in designing the furnace and the shape of the fire-box. 2. How will you carryout ultimate analysis of coal? [CO5-H1-TCY A.U. Dec 2009] Ultimate analysis: It is the analysis used to know the percentage of elements such as Carbon, Hydrogen, Nitrogen and Sulphur present in the coal. Estimation of Carbon and Hydrogen: A known quantity of sample of coal is heated in the current of oxygen in a combustion apparatus. As a result, Hydrogen and Carbon present in the coal is converted in to H2O and CO2 respectively as follows.

H2 +1/2 O2 H2O 2 18

C + O2 CO2

12 44 These vapors are then adsorbed by allowing to pass through anhydrous CaCl2 and KOH tubes of known weights. From the increase in weights of these tubes, the percentage of Carbon and hydrogen can be calculated as follows. % of Carbon in coal = Increase in weight of KOH tube X 12 X 100 Weight of coal taken 44 Significance: Higher the amount of Carbon and Hydrogen indicates higher C.V, and quality of

coal. ii) Estimation of Nitrogen (Kjeldahl’s method) A known quantity of pure and powdered coal is heated with con.H2SO4 in the presence of K2SO4 as catalyst in the Kjeldahl’s flask. As a result, Ammonium sulphate is formed as a clear solution as follows.

N2+3H2+H2SO4 (NH4)2SO4 The clear solution is then treated with excess of KOH and liberated Ammonia is adsorbed in a known volume of Std.0.1N HCl. The amount of unused acid present can be found by titrating the solution with NaOH using Methyl Orange as indicator. From the above values the percentage of Nitrogen can be found as follows.

% of Hydrogen in coal = Increase in weight of anhydrous CaCl2 tube X 2 X 100

Weight of coal taken 18

% of Nitrogen in coal=Volume of acid consumed X N X 1.4

Weight of coal taken



Significance: Nitrogen does not contribute any thing to C.V and hence its presence is not

much needed. iii) Estimation of Sulphur (Eschka method): A known amount of coal is heated in bomb-calorimeter along with 1:2 Sodium carbonate and Magnesium carbonate. The extract is treated with BaCl2. The precipitated sulphate is filtered, dried and weighed. From the weight of Sulphate, the Sulphur present in the coal can be calculated as follows.

S + 2O2 SO42- BaCl2BaSO4

Significance:

Though sulphur’s presence increases C.V, it is highly undesirable. Because, it

will form SO2 and SO3 as combustion products which causes air pollution as

well as corrosion with moisture.

iv)Estimation of Oxygen:

% of Oxygen = 100-(% of C + % of H2 + % of N2 + % of S) Significance: Higher amount of Oxygen indicates higher moisture and hence it is undesirable. Lesser amount of Oxygen indicates higher Calorific value.

3. Explain the manufacturing of metallurgical coke by Otto Hoffman’s recovery of bi-products method.[CO5-L2-June 2006, July 2009, Dec 2009, May 2008, Dec 2012] Metallurgical Coke: When coal is heated in the absence of air, the volatile matter escapes and produces hard, strong, porous and coherent mass. It is called as metallurgical coke. Otto Hoffman’s Method: He developed this method so as to increase the thermal efficiency of carbonization process and recovery of valuable by-products. Description:

% of Sulphur in coal = 32 X Weight of BaSO4 formed X 100

233 X Weight of coal taken



Otto-Hoffman’s chamber

1—Tar,2-Ammonia,3-Napthalene , 4-Benzene and 5-H2S Recovery chambers. It consists of silica chambers having dimension about 10 to 12m long and 3 to

4m height along with 0.4 to 0.5m wide. Each chamber is provided with a charging hole(for introducing coke) at the top and iron door at the bottom for discharging coke.

Coal is introduced in to the chambers. It is then tightly closed to avoid the entry of air. Then, the chambers are heated to 1200oC using preheated air and producer gas.

Initially the gases are preheated by passing them through 2nd and 3rd hot regenerators. At the same time, the hot flue gases formed during carbonization process are allowed to pass through between 1st and 4th chamber up to 1000oC.

For economical heating, direction of inlet gases and the flue gases are frequently changed. The recycling of flue gases to produce heat energy is known as regenerative heat economy. Time required to complete the carbonization process is 12 to 20 hours and the yield is 70%.

Recovery of bi-products: The coal gas comes out from the chamber is allowed to pass through different recovery chambers to collect useful bi-products. i) Recovery of tar: When coal gas is allowed to pass through the 1st chamber, where ammonia is sprayed. As a result tar gets deposits at the bottom and can be used for the other purpose. ii) Recovery of Ammonia: It is then allowed to pass through the 2nd chamber, where water is sprayed. As a result, ammonia (used in the 1st step) get deposit as NH4OH .

1

2 3 4 5



iii) Recovery of Naphthalene: The gases then allowed to pass through the next chamber, where cold water is sprayed. As a result naphthalene gets condensed. iv)Recovery of Benzene: The gases then allowed to pass through the next chamber, where petroleum is sprayed. As a result benzene gets condensed in to liquid. v)Recovery of H2S: The remaining gases is allowed to pass through the purifier packed with moist Fe2O3 where, H2S is retained. Advantages: 1. It requires lesser time for carbonization along with recovery of valuable by-products. 2. Heating is done externally by producer gas.

4. Give a brief account of refining of petroleum and the products obtained and

their uses. [CO5-L2-Nov 2003, Dec 2009, June 2013]

REFINING OF PETROLEUM

Thus, the process of removing impurities and separating the crude oil into various fractions having different boilingpoints is called Refining of Petroleum. The process of



Fig 5.2 Fractional distillation of crudepetroleum refining involves the following steps Step 1: Separation of water (Cottrell’s process) The crude oil from oil well is an extremely stable emulsion of oil and salt water. The crude oil is allowed to flow between two highly charged electrodes, where colloidal water droplets combine to form large drops, which is then separated out from the oil. Step 2: Removal of harmful sulphur compounds Sulphur compounds are removed by treating the crude oil with copper oxide. The copper sulphide formed is separated out by filtration. Step 3: Fractional distillation

vapourised. The hot vapours are then passed into the bottom of a “fractionating column” (Fig 4.2). The fractionating column is a tall cylindrical tower containing a number of horizontal stainless steel trays at short distances. Each tray is provided with small chimney covered with a loose cap. When the vapours of the oil go up in the fractionating column, they become cooler and get condensed at different trays. The fractions having higher boiling points condense at lower trays whereas the fractions having lower boiling points condense at higher trays. The gasoline obtained by this fractional distillation is called straight-run gasoline. Various fractions obtained at different trays are given in



Table 5.1. Various fractions, compositions and their uses

5. What is synthetic petrol? How is it manufactured by Bergius process? [CO5-L2-TCY A.U. Dec 2009, Chen A.U. May 2009, Dec 2005] 1. BERGIOUS PROCESS In this process, (fig. 5.2) the finely powdered coal is made into a paste with heavy oil and a catalyst powder (tin or nickel oleate) is mixed with it. The paste is pumped along with hydrogen gas into the converter, where the paste is heated to 400 −4500C under a pressure of 200 −250 atm.



During this process hydrogen combines with coal to form saturated higher hydrocarbons, which undergo further decomposition at higher temperature to yield mixture of lower hydrocarbons. The mixture is led to a condenser, where the crude oil is obtained. The crude oil is then fractionated to yield (i) Gasoline (ii) Middle oil (iii) Heavy oil. The middle oil is further hydrogenated in vapour phase to yield more gasoline. The heavy oil is recycled for making paste with fresh coal dust. The yield of gasoline is about 60% of the coal used. 6. Explain the causes, mechanism and prevention of knocking of Petrol in I.C. engines. [CO5-L2-M.U Apr, 94, Dec 2006] KNOCKING Definition Knocking is a kind of explosion due to rapid pressure rise occurring in an IC engine. Causes of knocking in S.I (Spark Ignition) Engine [Petrol engines] In a petrol engine, a mixture of gasoline vapour and air at 1:17 ratio is used as fuel. This mixture is compressed and ignited by an electric spark. The products of oxidation reaction (combustion) increases the pressure and pushes the piston down the cylinder. If the combustion proceeds in a regular way, there is no problem in knocking. But in some cases, the rate of combustion (oxidation) will not be uniform due to unwanted chemical constituents of



gasoline. The rate of ignition of the fuel gradually increases and the final portion of the fuel-air mixture gets ignited instantaneously producing an explosive sound known as “Knocking”. Knocking property of the fuel reduces the efficiency of engine. So a good gasoline should resist knocking. Chemical structure and knocking The knocking tendency of fuel hydrocarbons mainly depends on their chemical structures. The knocking tendency decreases in the following order. Straight chain paraffins -Branched chain paraffins -Cycloparaffins -Olefins =Aromatics. Thus olefins of the same carbon-chain length possess better anti-knock properties than the corresponding paraffins. Improvement of antiknock characteristics The octane number of fuel can be improved by (i) blending petrol of high octane number with petrol of low octane number, so that the octane number of the latter can be improved, (ii) the addition of anti-knock agents like Tetra-Ethyl Lead (TEL), (iii) now a days aromatic phosphates are used as antiknock agent because it avoids lead pollution. Octane number Octane number is introduced to express the knocking characteristics of petrol.. Definition Thus octane number is defined as ‘the percentage of iso-octane present in a mixture of iso-octane and n-heptane.’

CH3 −CH2 −CH2 −CH2 −CH2 −CH2 −CH3 LEADED PETROL (ANTI KNOCK AGENT) The anti-knock properties of a gasoline can be improved by the addition of suitable additives. Tetra ethyl lead (TEL) (C2H5)4 Pb is an important additive added to petrol. Thus the petrol containing tetra ethyl lead is called leaded petrol.TEL dissociated to give C2H5 free radicals.This converts straight chain compound into branched chain compound .This increases the anti knocking property.During combustion lead is oxidized to lead oxide and this gets deposited inside the engine.To avoid this ethylmbromide is added to TEL.This convert Pb0 to lead bromide,which escapes through the exhaust.



But this creates atmospheric pollution. So now a days aromatic phosphates are used instead of TEL. 7. What are LPG and CNG? Discuss the advantages of LPG over gaseous fuel and CNG over LPG. [CO5-L2-Nov 2009] COMPRESSED NATURAL GAS When the natural gas is compressed, it is called Compressed Natural Gas (CNG). The primary component present in CNG is methane. It is mainly derived from natural gas. The natural gas can either be stored in a tank of a vehicle as compressed natural gas (CNG) at 3,000 or 3,600 psi or asliquified natural gas (LNG) at typically 20-150 psi. The average composition of CNG is as follows Constituents Percentage (%) Methane 88.5 Ethane 5.5 Propane 3.7 Butane 1.8 Pentane 0.5 Properties 1. CNG is the cheapest, cleanest and least environmentally impacting alternative fuel. 2. Vehicles powered by CNG produce less carbonmonoxide and hydrocarbon (HC) emission. 3. It is less expensive than petrol and diesel.

5. CNG requires more air for ignition. Uses CNG is used to run an automobile vehicle just like LPG. ADVANTAGE OF CNG OVER LPG 1. CNG produces less pollutants than LPG. 2. CNG is cheaper and cleaner than LPG. 3. The octane rating of CNG is high, hence the thermal efficiency is more. 4. It does not evolve sulphur and nitrogen gases. 5. It mixes very easily with air than the other gaseous fuels. LIQUEFIED PETROLEUM GAS (LPG) It is obtained as a by-product during fractional distillation of crude petroleum oil or by cracking of heavy oil. It consists of propane and butane. It can be readilyliquefied under



pressure, so it can be economically stored and transported in cylinders. The average composition of LPG is as follows. Constituents Percentage (%) n-Butane 38.5 Iso butane 37 Propane 24.5 Its calorific value is about 25,000 kcal/m3 Uses 1. It is used as a domestic and industrial fuel 2. It is also used as a motor fuel. Advantages 1. LPG consists of hydrocarbons, so it burns cleanly without leaving any residue. 2. The LPG (hydrocarbons) has higher calorific value than the other gaseous fuels containing H2 or CO. The calorific value is 7 times higher than coal gas and 3 times higher than natural gas. 3. LPG is characterized by high thermal efficiency and heating rate. 4. It is easy to manipulate. 5. Comparatively it is less of health hazard, even in case of leakage. 6. Needs little care for maintenance. 7. It is free from CO, so it is less hazardous. Disadvantages 1. Due to its faint odour, leakage cannot be easily detected. 2. Its octane value is low. 3. Handling must be done under high pressure. 4. LPG is suitable only for the engines working under high compression ratio. 8. Explain the various reactions involving in the manufacturing of Producer gas. [CO5-L2-Dec 2009] Producer gas is essentially a mixture of Carbon Monoxide, Hydrogen and Nitrogen. It is clean, cheap and easily preparable gas. It is insoluble in water poisonous in nature. Its C.V. is 900-1300Kcal/m3 . Its composition is as follows: CO:22-30%, H2:8-12%, N2:50-55% and CO2:3%



Description: It consists of a tall steel vessel, 3m in diameter and 4m in height inside of which is lined with refractory bricks. It is provided with an inlet for introduction of coke at the top and a side door for waste gas exit. A mixture of air and steam 0.35kg/kg of coal is supplied from the inlet in the left side. The following reactions are taking place in the various zones as follows. i) Ash Zone: It is the lowest zone where ash is present for about 0.8m thickness. The grate of producer plant is protected from the intense heat of combustion by ash. ii) Combustion or Oxidation zone: In this zone, coal is oxidized by air to CO and CO2. As the reactions are exothermic, the temperature may exceed 1100oC .

C + O2 CO2 C + ½ O2 CO

iii) Reduction Zone: It is the middle zone of the reactor, where CO2 formed in the oxidation zone further reacts with red hot coal present in this zone forming free H2and CO . As the reactions are endothermic in nature the temperature of this zone drops to 1000oC.

C + 2CO2 2CO C + H2O CO + H2

C +2 H2O CO2 + H2

iv) Distillation Zone: It is the top most layer of the bed(400-800oC)where the incoming coal is preheated by outgoing gases.



Uses: It is cheap, clean and can be easily prepared. It is used as reducing agent in much metallurgical process.

9. Explain the manufacturing of water gas. [CO5-L2-Dec 2009] It is also known as blue gas having following composition. H2 = 51%, CO = 41%, N2 = 4%, (CH4+CO2) = 4% Its calorific value is 2, 800 kcal/m3. It is higher than that of producer gas due to the higher percentage of Hydrogen in water gas than in producer gas. Preparation: It is prepared by passing the steam over red hot coal or coke along with air. It consists of a steel vessel about 3m wide and 4m height, lined inside with refractory bricks. It has a cup and cone feeder at the top and side opening for water gas exit. At the bottom it has two inlets for the introduction of air and steam.

When steam and water is passed alternatively over a red hot coke at 900-1000oC the following reaction will takes place.

1. When steam is supplied over coke at 900-1100oC, it will form Carbon monoxide and hydrogen. The reaction is endothermic and hence the temperature will decrease.

C + H2O CO + H2

2. In order to raise the temperature of coke bed to 1100oC, the steam is cut-off and air is supplied. As a result following exothermic reaction will occur.

C + O2 CO2



2C + O2 2CO Hence, the temperature of the bed will be over 1100oC. The above processes are repeated alternatively to maintain proper temperature for the reaction to occur. Uses: It is used as an illuminating gas, as a fuel gas and for the production of power alcohol. 10. How will you carry out flue gas analysis using Orsat apparatus? [CO5-L2-July 2009, Dec 2009, Dec 2012, June 2014] Flue gas: Mixture of gases like CO2, CO, O2 etc coming out from the chamber is called as flue gases. With the help of Orsat apparatus their analysis can be easily done. Description:

It consists of an horizontal glass tube, to which a graduated burette (100 cc) is connected with one end. It is covered by a water jacket so as to maintain the constant temperature during the experiment.

The lower end of the burette is connected with a water reservoir (mixed with little NaCl to avoid solubility of gases) to adjust the volume of the gas in the burette by lowering or raising the reservoir.

The free end of the glass tube is connected with a ‘U’ tube through a 3 way stopcock. The tube packed with fused CaCl2 and glass wool to avoid the entry of moisture and dirt (smoke).

The horizontal tube is connected with 3 different absorption bulbs packed with different chemicals as follows



BULB REAGENTS ABSORPTION

OF GASES

A Potassium hydroxide(250g/500ml distilled water) CO2

B Alkaline Pyrogallol( pyrogallic acid + KOH in

distilled water)

CO2 and O2

C Ammoniacal Cuprous Chloride(Cuorous chloride

+ Ammonia in distilled water)

CO2 O2 and

CO

Absorption of CO2 The stopper of the absorption bulb-A containing KOH is opened and the flue

gas is allowed to enter into the bulb – A, where CO2 present in the flue gas is absorbed by KOH. It is again sent in to the burette by lowering the water reservoir(separating funnel) for several times to ensure the complete absorption of CO2.

Decrease in volume of flue gas in the burette indicates the volume of CO2 . Absorption of O2

The stopper of the bulb-A is closed and the the gas is allowed to enter into the bulb – B where O2 present in the flue gas is completely absorbed by alkaline Pyrogallol, decrease in volume of flue gas in the burette indicates the volume of O2 .

Absorption of CO Finally, the gas enters into the bulb – C where CO present in the flue gas is

absorbed by Ammoniacal Cuprous chloride. Decrease in volume of flue gas in the burette indicates the volume of CO.

Remaining gas in the burette after the absorption of the CO2 , CO & O2 is Nitrogen. Advantages:

It gives an idea about complete or incomplete combustion of fuel. Presence of CO in fuel indicates the incomplete combustion indicating short

supply of O2 . Presence of O2 in the fuel indicates the complete combustion and excess of O2

11. Calculate minimum quantity of air Require for complete combustion of fuels. [CO5-H2] For efficient combustion, it is essential that the fuel must be brought into intimate contact with sufficient quantity of air.The combustible constituents usually present in a fuel enter into the process of combustion are C, H, S and O. But non-combustible constituents N, CO2 and ash present in the fuel do not take any O2 during combustion.



The amount of oxygen and air required for the completecombustion of a givenquantity of fuel can be calculated by taking the following points into consideration. 1. Substances always combine in definite proportions, which are determined by the molecular weights of the substances. Examples (a) Combustion of carbon

12 parts by weight of C require 32 parts by weight of O2.(or) 1 part by volume of C requires 1 part by volume of O2 for complete combustion There foreC parts by weight of carbon require

(b) Combustion of hydrogen

4 parts by weight of H2 require 32 parts by weight of O2 (or) 2 parts by volume of H2 require 1 part by volume of O2 H parts by weight of hydrogen require parts by weight of O2. Some of the hydrogen is present in the combined form with oxygen (ie., as H2O). This combined hydrogen does not take part in combustion reaction. Therefore, the quantity of combined hydrogen must be deduced from the total hydrogen in the fuel.

Now 1 part by weight of H2 combines with 8 parts by weight of O2



Volume (or) weight of oxygen required for complete combustion of some combustible matters.

2. Amount of O2 required by the fuel will be given by subtracting the amount of O2 already present in the fuel from the total or theoritical amount of O2 required by the fuel. Net amount of O2 required Total amount of O2 required −O2 present in the fuel. 3. Air contains 21% of O2 by volume and 23% of O2 by weight. Hence from the amount of O2 required by the fuel, the amount of air required can be calculated.

4. Molecular mass of air is taken as 28.94 g/mol 5. Density of air at NTP 1.29 kg/m3 6. 22.4 litres (or 22,400 ml) of any gas at NTP (ie 0C and 760 mm of Hg) has a mass equal to its 1 mol (gram molecular weight). Thus 22.4 litres of CO2 at NTP will have a mass of 44 g (44 is the molecular weight of CO2) 7. Excess air for combustion It is necessary to supply excess air for complete combustion of the fuel. It is found out from the theoretical amount of air as follows. The amount of air required if excess air is supplied

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SKP Engineering Collegeskpec.edu.in/wp-content/uploads/2017/11/Engineering... · 2018-04-05 · (i) Scales and sludges (ii) Boiler corrosion. [CO1-L2-June 2005, Dec 2006, Jan 2010]