Ceramics

A wide-ranging group of materials whose ingredients are clays, sand and felspar.

Clays

Contain some of the following:• Silicon & Aluminium as silicates• Potassium compounds• Magnesium compounds• Calcium compounds

Sand contains Silica and Feldspar or Aluminium Potassium Silicate.

Types of Ceramics

• Whitewares• Refractories• Glasses• Abrasives• Cements

Comparison metals v ceramics

CeramicsMetals

Bonded Clay Ceramics

Made from natural clays and mixtures of clays and added crystalline ceramics.

These include:• Whitewares • Structural Clay Products • Refractory Ceramics

Whitewares

• Crockery• Floor and wall tiles• Sanitary-ware• Electrical porcelain• Decorative ceramics

Whiteware: Bathrooms

Slip Casting

Sinter and Serve

Whitewares

Refractories

Firebricks for furnaces and ovens. Have high Silicon or Aluminium oxide content.Brick products are used in the manufacturing plant for iron and steel, non-ferrous metals, glass, cements, ceramics, energy conversion, petroleum, and chemical industries.

Refractories

• Used to provide thermal protection of other materials in very high temperature applications, such as steel making (Tm=1500°C), metal foundry operations, etc.

• They are usually composed of alumina (Tm=2050°C) and silica along with other oxides: MgO (Tm=2850°C), Fe2O3, TiO2, etc., and have intrinsic porosity typically greater than 10% by volume.

• Specialized refractories, (those already mentioned) and BeO, ZrO2, mullite, SiC, and graphite with low porosity are also used.

Refractory Brick

Amorphous Ceramics (Glasses)

• Main ingredient is Silica (SiO2) • If cooled very slowly will form crystalline structure. • If cooled more quickly will form amorphous structure

consisting of disordered and linked chains of Silicon and Oxygen atoms.

• This accounts for its transparency as it is the crystal boundaries that scatter the light, causing reflection.

• Glass can be tempered to increase its toughness and resistance to cracking.

Glass Types

Three common types of glass:• Soda-lime glass - 95% of all glass, windows

containers etc.• Lead glass - contains lead oxide to improve

refractive index• Borosilicate - contains Boron oxide, known as

Pyrex.

Glasses

• Flat glass (windows)• Container glass (bottles)• Pressed and blown glass (dinnerware)• Glass fibres (home insulation)• Advanced/specialty glass (optical fibres)

Glass Containers

Pressed Glass Processing

SoftenedGob

Blow Molding

Softened glass

Glass in Buildings

Plate Glass Drawing Processes

Tempered Glass

The strength of glass can be enhanced by inducing compressive residual stresses at the surface.

The surface stays in compression - closing small scratches and cracks.

Small Scratches

Hardening Processes

• Tempering:– Glass heated above Tg but below the softening point

– Cooled to room temp in air or oil– Surface cools to below Tg before interior

– when interior cools and contracts it draws the exterior into compression.

• Chemical Hardening:– Cations with large ionic radius are diffused into the surface– This strains the “lattice” inducing compressive strains and

stresses.

Armoured Glass

• Many have tried to gain access with golf clubs and baseball bats but obviously the glass remains intact ! From time to time a local TV station intends to show videos of those trying to get at the cash!!

Leaded Glass

Crystalline Ceramics

Good electrical insulators and refractories.• Magnesium Oxide is used as insulation material in

heating elements and cables.• Aluminium Oxide• Beryllium Oxides• Boron Carbide• Tungsten Carbide. • Used as abrasives and cutting tool tips.

Abrasives

• Natural (garnet, diamond, etc.)• Synthetic abrasives (silicon carbide, diamond,

fused alumina, etc.) are used for grinding, cutting, polishing, lapping, or pressure blasting of materials

Cements

• Used to produce concrete roads, bridges, buildings, dams.

Advanced Ceramics

• Advanced ceramic materials have been developed over the past half century

• Applied as thermal barrier coatings to protect metal structures, wearing surfaces, or as integral components by themselves.

• Engine applications are very common for this class of material which includes silicon nitride (Si3N4), silicon carbide (SiC), Zirconia (ZrO2) and Alumina (Al2O3)

• Heat resistance and other desirable properties have lead to the development of methods to toughen the material by reinforcement with fibers and whiskers opening up more applications for ceramics

Advanced Ceramics

• Structural: Wear parts, bioceramics, cutting tools, engine components, armour.

• Electrical: Capacitors, insulators, integrated circuit packages, piezoelectrics, magnets and superconductors

• Coatings: Engine components, cutting tools, and industrial wear parts

• Chemical and environmental: Filters, membranes, catalysts, and catalyst supports

CERAMICS MATERIALSApplications of ceramics- refractories- sensors- capacitors- the magnetic strip on a credit card- space shuttle protection from high temperature- addition to paints- found in bone and teeth- spark plugs

Ceramics exhibit good strength under compression and virtually no ductility under tension. Ceramics are inorganic and non-metallic materials that are commonly electrical and thermal insulators, brittle and composed of more thanone element (e.g., two in Al2O3)

Ceramics make up one of three large classes of solid materials. The other material classes include metals and polymers. The combinationof two or more of these materials together to produce a new materialwhose properties would not be attainable by conventional means is called a composite. Examples of composites include steel reinforced concrete, steel belted tyres, glass or carbon fibre - reinforced plastics(so called fibre-glass resins) used for boats, tennis rackets, skis, and racing bikes.

The word ceramic, derives its name from the Greek keramos, meaning "pottery", which in turn is derived from an older Sanskrit root, meaning "to burn". The Greeks used the term to mean "burnt stuff" or "burned earth". Thus the word was used to refer to a product obtained through the action of fire upon earthy materials

DEFINITIONS

GLASSES

CERAMIC MATERIALS

CLAY REFRACTORIES ABRASIVES CEMENTSGLASSESADVANCED CERAMICS

GLASS CERAMICS

STRUCTURALCLAY

PRODUCTS

WHITEWARES

FIRECLAY

SILICA

BASIC

SPECIAL

CERAMIC GROUPING

Ceramics can be classified based on chemical composition – oxides, carbides, nitrides, sulfides and fluorides. Or they can be grouped according to their major functions. Ceramics found in coatings – glazes, are ceramic coatings applied to glass objects and enamels are ceramic coatings applied to metallic objects.

Alumina (Al2O3):

Diamond (C):

Silica (SiO2):

Silicon carbide:

Silicon nitride (Si3N4):

Titanium oxide (TiO2):

Zirconia (ZrO2):

FunctionFunction ApplicationApplication ExamplesExamples

Electrical Electrical Capacitor dielectricsCapacitor dielectrics

Microwave dielectricsMicrowave dielectrics

Conductive oxidesConductive oxides

SuperconductorsSuperconductors

Electronic packagingElectronic packaging

InsulatorsInsulators

Solid-oxide fuel cellsSolid-oxide fuel cells

PiezoelectronicPiezoelectronic

Electro-opticalElectro-optical

BaTiOBaTiO33, SrTiO, SrTiO33, Ta, Ta22OO55,,

BaBa22TiTi99OO2020, Al, Al22OO33 Ba(Mg Ba(Mg1/31/3TaTa2/32/3)O)O33, , Ba(ZnBa(Zn1/31/3TaTa2/32/3)O)O33, BaTi, BaTi44OO99, ,

In-doped SnOIn-doped SnO2 2 (ITO)(ITO)

YBaYBa22CuCu33OO7-x7-x (YBCO) (YBCO)

AlAl22OO33

PorcelainPorcelain

ZrOZrO22, LaCrO, LaCrO33

Pb(ZrPb(ZrxxTiTi1-x1-x)O)O33 (PZT) (PZT)

PLZT, LiNbOPLZT, LiNbO33

Magnetic Magnetic Recording mediaRecording media

Ferrofluids, credit cards,Ferrofluids, credit cards,

Circulators, isolators,Circulators, isolators,

Inductors, magnets Inductors, magnets

γγ-Fe-Fe22OO33, CrO, CrO22(chrome cassettes)(chrome cassettes)

FeFe33OO44

Nickel zinc ferrite Nickel zinc ferrite

Manganese zinc ferriteManganese zinc ferrite

OpticalOptical Fibre opticsFibre optics

GlassesGlasses

LasersLasers

LightingLighting

Doped SiODoped SiO22

SiOSiO22 based based

AlAl22OO33, yttrium aluminium garnate, yttrium aluminium garnate

AlAl22OO33, glasses, glasses

AutomotiveAutomotive Oxygen sensors, fuel cellsOxygen sensors, fuel cells

Catalyst supportCatalyst support

Spark plugsSpark plugs

TiresTires

Windshields/windowsWindshields/windows

ZrOZrO2 2

CordieriteCordierite

AlAl22OO33

SiOSiO22

SiOSiO22 based glasses based glasses

Mechanical/Mechanical/structuralstructural

Cutting toolsCutting tools

CompositesComposites

AbrasivesAbrasives

WC-Co cermetsWC-Co cermets

Silicon-aluminium-oxynitride Silicon-aluminium-oxynitride (Sialon), Al(Sialon), Al22OO33

SiC, AlSiC, Al22OO33, silica glass fibres, silica glass fibres

SiC,AlSiC,Al22OO33, diamond,BN, ZrSiO, diamond,BN, ZrSiO44

BiomedicalBiomedical ImplantsImplants

DentistryDentistry

Ultrasound imagingUltrasound imaging

HydroxyapatiteHydroxyapatite

Porcelain, AlPorcelain, Al22OO33

PZTPZT

ConstructionConstruction BuildingsBuildings ConcreteConcrete

GlassGlass

SanitarywareSanitaryware

OthersOthers Defense Defense

Armor materialsArmor materials

SensorsSensors

NuclearNuclear

Metal processingMetal processing

PZT, BPZT, B44CC

SnOSnO22

UOUO22

AlAl22OO33, SiO, SiO22-based refractories-based refractories

OO22 sensors, casting molds sensors, casting molds

ChemicalChemical CatalysisCatalysis

Air, liquid filtrationAir, liquid filtration

SensorsSensors

Paints, rubberPaints, rubber

Oxides (AlOxides (Al22OO33,ZrO,ZrO22,ZnO,TiO,ZnO,TiO22))

DomesticDomestic Tiles, sanitarywareTiles, sanitaryware

Whiteware, kitchenware,Whiteware, kitchenware,

Pottery, art, jewelryPottery, art, jewelry

Clay, AlClay, Al22OO33, SiO, SiO22-based and -based and glass ceramics, diamond, ruby, glass ceramics, diamond, ruby, cubic, zirconiacubic, zirconia

Properties of Ceramics

MaterialMaterial Melting Melting point point (°C)(°C)

Thermal Thermal expansion expansion

coefficient (x10coefficient (x10--

66 cm/cm)/°C cm/cm)/°C

Knoop Hardness Knoop Hardness (HK) (100 g)(HK) (100 g)

AlAl22OO33 20002000 6.86.8 21002100

BNBN 27322732 0.57, -0.460.57, -0.46 50005000

SiCSiC 27002700 3.73.7 25002500

DiamondDiamond 1.021.02 70007000

MulliteMullite 18101810 4.54.5 __

TiOTiO22 18401840 8.88.8 __

Cubic Cubic ZrOZrO22

27002700 10.510.5 __

MaterialMaterial D(g/D(g/cmcm33))

T T (psi)(psi)

F (psi)F (psi) C (psi)C (psi) Y (psi)Y (psi) Ft Ft (psi√in)(psi√in)

AlAl22OO33 3.983.98 30,00030,000 80,00080,000 400,000400,000 56 x 1056 x 1066 5,0005,000

SiC (sintered)SiC (sintered) 3.13.1 25,00025,000 80,00080,000 560,000560,000 60 x 1060 x 1066 4,0004,000

SiSi33NN44 (rxn (rxn

bonded)bonded)2.52.5 20,00020,000 35,00035,000 150,000150,000 30 x 1030 x 1066 3,0003,000

SiSi33NN44 (hot (hot

pressed)pressed)3.23.2 80,00080,000 130,000130,000 500,000500,000 45 x 1045 x 1066 5,0005,000

SialonSialon 3.243.24 60,00060,000 140,000140,000 500,000500,000 45 x 1045 x 1066 9,0009,000

ZrOZrO22 (partially (partially

stabilized)stabilized)5.85.8 65,00065,000 100,000100,000 270,000270,000 30 x 1030 x 1066 10,00010,000

ZrOZrO22

(transformation (transformation toughened)toughened)

5.85.8 50,00050,000 115,000115,000 250,000250,000 29 x 1029 x 1066 11,00011,000

Tensile strength = T; Flexural strength = F; Young’s modulus = Y;Compressive strength = C; Fracture toughness = Ft; Density = D.

Synthesis and processing of ceramic powders

Consolidation into a dense, monoclinic object using

sintering or firing

Synthesis of ceramic powders

Ball milling, blending, spray drying of powders using processing additives

Shaping of powders into useful shapes (green ceramics) using pressing,

slip casting, tape casting

Final sintered ceramic product

Secondary processing (e.g. grinding, cutting, polishing, electroding,

coating etc.)

DIFFERENT TECHNIQUES FOR PROCESSING OF ADVANCED CERAMICS

These techniques are used to convert properly processed powders into desirable shape to form the green ceramic (is a ceramic that has not yet been sintered.

Slip casting;

Compaction (uniaxial or isostatic);

Tape casting;

Extrusion;

Injection molding;

See Figure 15-2 on page 539 of Askeland and Phule

Characteristics of sintered ceramics

Important in sintered ceramics – grain size, grain size distribution, and the level and type of porosity.

Grains and grain boundaries: Ceramics with small grain size are stronger than coarse – grained ceramics. Finer grain size reduces stresses that develops at grain boundaries due to anisotropic expansion and contraction. Average grain size properly controlled produces magnetic, dielectric and optical properties.

Porosity: Pores represent defects in polycrystalline ceramics and are usually detrimental to the mechanical properties of bulk ceramics. Pores may be either interconnected or closed. The apparent porosity measures the interconnected pores and determine permeability or ease with which gases or fluids seep through ceramic components.

Apparent porosity = Ww – Wd / Ww – Ws x 100 (W = weight either after removal from water (s), dry (d) or suspended in water (s).

True porosity = ρ - B / ρ x 100 (B = bulk density, ρ = true density or specific gravity of the ceramic material.

Inorganic Glasses

Non-crystalline materials especially based on silica (others are based on fluorides, sulfides and alloys). Define glass: a metastable material that has hardened and become rigid without crystallizing. Below the glass temperature the rate of volume contraction on cooling is reduced and material considered glass not undercooled liquid.

Undercooledliquid

liquid

Glass

Crystalline

Tg Tm

Den

sity

When silica crystallizes on cooling, abrupt change in the density is observed

Silicate glasses are most widely used, fused silica made from pure silica has high melting point and the dimensional changes during heating and cooling are small. Oxides can be classified as glass formers (silica), intermediates (aluminium oxide) and modifiers (magnesium oxide) – cause glass to devitrify or crystallize as they break up the network structure.

Modified silicate glasses; Modifiers break up the network of the silica. When Na2O is added Na+ ions enters the holes in the network while O2- ions becomes part of the network structure. The O:Si ratio becomes large and when it reaches 2.5 glass is difficult to form. Modifiers reduces melting points and viscosity of the silica making it possible to produce glass at lower temperatures.

Glass formers – B2O3, SiO2, GeO2, P2O5, V2O3

Intermediates – TiO2, ZnO, PbO2, Al2O3, BeO

Modifiers – Y2O3, MgO, CaO, PbO, Na2O

Glass manufacturing

At high temperatures and with viscosity controlled so that glass can be shaped without breaking. Liquid range – sheet and plate glass produced when glass is in a molten state. Liquid tin used to form smooth surface on glass.

Working range – shapes for containers or light bulbs can be formed by pressing, drawing or blowing glass into molds. Glass is heated in the working range so that is formable but not runny.

Annealing range – annealed to reduce residual stresses during forming. Large glass castings are often annealed and slowly cooled to prevent cracking.

Tempered glass – quenching the surface of plate glass with air causing the surface layers to cool and contract. Used in car and home windows shelving for refrigerators, ovens, furnitures. Laminated glass – consist of two annealed glass pieces with a polymer (polyvinylbutyral, PVB) in between used to make car wind shields.

GlassGlass SiOSiO22 AlAl22OO33 CaOCaO NaNa22OO BB22OO33 MgOMgO PbOPbO

Fused silicaFused silica 9999

vycorvycorTMTM 9696 44

PyrexPyrexTMTM 8181 22 44 1212

Glass jarsGlass jars 7474 11 55 1515 44

Window glassWindow glass 7272 11 1010 1414 22

Plate glassPlate glass 7373 11 1313 1313

Light bulbsLight bulbs 7474 11 55 1616 44

FibersFibers 5454 1414 1616 1010 44

ThermometerThermometer 7373 66 1010 1010

Lead glassLead glass 6767 66 1717

Optical flintOptical flint 5050 11 1919

Optical crownOptical crown 7070 88 1010

E-glass fibersE-glass fibers 5555 1515 2020 1010

S-glass fibersS-glass fibers 6565 2525 1010

Glass Composition – most glass are based on silica, modifiers such as Na2O (soda), CaO. Common commercial glass contains approximately 75% SiO2, 15%Na2O and 10% CaO = soda line glass. Borosilicate glass – contains 15% B2O3, used in lab glassware, glass ceramics and containers for high level radioactive waste.

Calcium aluminosilicate glass or E-glass (20% Al2O3, 12%MgO and 3%B2O3) – used for general purpose fiber for composite materials such as fiber glass.

Fused silica – gives best resistance to high temperature, thermal shock and chemical attack. Photochromic glass – darkened by the UV portion of sunlight used for sunglasses. Polychromatic glasses – sensitive to all light not just UV light.

Glass ceramics – are crystalline materials derived from amorphous glasses. Glass-ceramics have a substantial level of crystallinity (>70 – 99%). Formability and density of glass becomes important. Glass is crystallized using heterogeneous nucleation by such oxides such as TiO2 and ZrO2. In making glass ceramics – first step is to assure that no crystallization during cooling from the forming temperature.

Forming

Nucleation

Growth

Melting

Time

Tem

pera

ture

(°C

) 1600

900

800

650

1250liquidus

Softening point

Annealingpoint

-4 x 104

-107.6

-1013.4 Vis

cosi

ty µ

(poi

se)

Cooling must be rapid to avoid the start of crystallization. Isothermal and continuous cooling values for lunar glass. The rate of nucleation of precipitates is high at low temperatures, whereas rate of growth is high at higher temperatures

Heat treatment profile for glass-ceramic fabrication.

Nucleation of the crystalline phase is controlled in two ways; first the glass contains agents such as TiO2, that react with other oxides and form phases that provides the nucleation sites. Second heat treatment is designed to provide number of nuclei, the temperature should be relatively low in order to maximize the rate of nucleation.

Processing and Applications of clay products:

Clay products are traditional ceramics used for producing pipe, brick, cooking ware. Clay – kaolinite and water serve as the initial binder for the ceramic powders, which are typically silica. Feldspar, [(K,Na)2O.Al2O3.6SiO2 , is used as a flux (glass forming) agent during later heat treatment.

Forming techniques for clay products;The powders, clay, flux and water are mixed and formed into shape. Dry or semi-dry mixtures are mechanically pressed into green shapes, isostatic pressing may be done, the powders are placed into a rubber mold and subjected to high pressures

Clay

Glassy bondLiquid phaseformed

Firing time

Drying and Firing of Clay products; During drying, excess moisture is removed and large dimensional changes occur. Temperature and humidity are controlled to provide uniform drying – minimizing stresses, distortion and cracking. Firing – produces rigidity and strength of the ceramic materials. During heating the clay dehydrates an vitrification or melting begins. Impurities and fluxing agent reacts with ceramic materials and clay producing low-melting point liquid phase at the grain surfaces.

The liquid helps eliminate porosity and after cooling changes to a rigid glass. The glassy phase provides ceramic bond and shrinkage

Refractories – components of equipments used in production, refining and handling of metals and glasses, for constructing heat treating furnaces. They must survive high temperatures without being corroded or weakened. Refractory bricks contain 20 to 25% apparent porosity to provide improved thermal insulation.

Acid refractories -

Base refractories -

Neutral refractories -

RefractoryRefractory SiOSiO22 AlAl22OO33 MgOMgO FeFe22OO33 CrCr22OO33

AcidicAcidic

SilicaSilica 95-9795-97

Superduty firebrickSuperduty firebrick 51-5351-53 43-4443-44

High-alumina firebrickHigh-alumina firebrick 10-4510-45 50-8050-80

BasicBasic

MagnesiteMagnesite 83-9383-93 2-72-7

OlivineOlivine 4343 5757

NeutralNeutral

ChromiteChromite 3-133-13 12-3012-30 10-2010-20 12-2512-25 30-5030-50

Chromite-magnesiteChromite-magnesite 2-82-8 20-2420-24 30-3930-39 9-129-12 30-5030-50

Compositions of typical refractories (weight percentage)

Other ceramic materialsCements: A chemical reaction converts a liquid resin to a solid that joins the particles. CO2 gas acts as a catalyst to dehydrate sodium silicate to produce glassy material.

xNa2O.ySiO2.H2O + CO2 = glass

Coatings:

Thin films and Single crystals:

Fibers:

GLASS

• Glass is an amorphuos,inorganic,homogeneous,transparent or translucent material.

TYPES OF GLASS• Soda lime glass• Potash lime glass• Potash lead glass

PROPERTIES OF GLASS

• It can not deform.• It is hard.• It has resistance to scratches.• It is brittle.• It is affected by alkalies.• It is transparent or translucent.• It is no effect of air & water.

PLASTIC

• The plastic is an organic substance and it consists of natural or synthetic binders or resins with or eithout moulding components.

TYPES OF PLASTIC<1>THERMO PLASTIC<2>THERMOSETTING PLASTIC

PROPERTIES OF PLASTIC• It is light in weight.• Specific gravity of plastic is 1.40.• They are low electrical conductivity.• They are low thermal conductivity• They can absorb shocks.• USES• To make waterproof doors,bags.• To make furniture .• To make optical lenses, frameas.

Composite Materials

• Composites are combinations of two more separate materials on a microscopic level, in a controlled manner to give desired properties. The properties of a composite will be different from those of the constituents in isolation.

• When two materials are combined together to form a composite, one of the materials will be in “Reinforcing phase” and the other material will be in “Matrix phase”. Typically, reinforcing material in the form of fibres, sheets or particles are strong with low densities while the matrix is usually a ductile or tough material.

• Glass » Reinforcing material• Polyester » Matrix material• Glass + Polyester » GRP (Glass fibre reinforced

plastic)

Classification

• Natural composites• Man-made composites

• Several natural materials can be grouped under natural composites.Eg.: Bone, Wood etc.,

• Man-made composites are produced by combining two or more materials in definite proportions under controlled conditions. Eg:

• Mud mixed straw to produce stronger mud mortar and bricks.• Ferro-cement• Concrete and RCC• Plywood, Chipboards, Decorative laminates• Asbestos Cement Sheets• Reinforced Glass• Fibre Reinforced Plastic (FRP)• Carbon Composites

Properties of Composites

• Composites posses excellent strength and stiffness

• They are very light materials• They possess high resistance to corrosion,

chemicals and other weathering agents.• They can be moulded to any shape and size

with required mechanical properties in different directions

Disadvantages of composites

• High production cost• Difficult to repair• Susceptible to damage

Uses of composite materials

• Extensively used in space technology and production of commercial air-planes.

• Used in the production of sport goods.• Used for general industrial and engineering

structures• Used in high speed and fuel efficient transport

vehicles