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CHAPTER 1Part 1
MATERIAL STRUCTURE ANDBINARY ALLOY
SYSTEM
Atomic Structure
nucleus
Electron : charge magnitude : -1.60x10-19 C
Proton : + 1.60x10-19 C
Neutron : neutral, no charge
• Is the basic unit of matter.
• 3 basic particles of atoms are : ELECTRON, PROTON AND NEUTRON
Remember an atom will contain equal number of P and E !!
Element structure• Is the substance that is made up from one type of atom. • Cannot be broken down into any simpler substances by
chemical method.
• Has its own atomic mass.
• Has equal number of protons and number of electrons.
Example : Hydrogen is made up of one type of atom containing 1 proton and 1 electron.
MOLECULE AND COMPOUND
MOLECULE : 2 OR more atoms that are chemically joined together.Example : H2, O2 , H20
COMPOUND : contains more than 1 type element. ( at least 2 different elements)Example : H20 , CO2, NH3
Remember : All compounds are molecules but not all molecules are compounds!!
H2 O2 H20Molecules but not compound because each is composed of a single element
Molecule and compound
The Periodic Table• Is a tabular arrangement of chemical elements.
• Is organized on the basis of their atomic number,
electron configuration and recurring chemical
property.
• Elements are presented in order of increasing
atomic number ( number or proton)>> row
• Elements arrayed in similar electron structure
as well as chemical and physical properties >>
column
HOW TO FIND NUMBER OF PROTON ,
ELECTRON AND NEUTRON OF AN
ELEMENT ?
6
CCARBON12.011
Try this
CRYSTALLINE STRUCTURES• Atoms in crystalline solids : positioned in an order and repeated
pattern.
• The repetitive entities in such structure is called the unit cells.
• Most common metals exists in at least one of three relatively
simple crystal structures; which is
a) BCC – body centered cubic b) FCC – face-centered cubic
b)HCP – hexagonal close-packed
Example : Atomic Radii and Crystal
Structure for few metals
BCC Structure• Has cubic unit cell with atoms located at all 8 corners and a single atom at
the cube center
• Has two atoms per unit cell, one in the center and 1/8 of each of the 8 corner atoms.
• Lattice parameter @ length of unit cell can be calculated by using the following formula.
cellt2atoms/uni1)(18)8
1(atomsofNumber
a
a
R 3
4Ra
Where,
R = atomic radius
a = unit cell length
FCC Structure• Has atoms located at each of the corners and centers of all the cube
faces.
• Has 4 atoms per unit cell, one-half at each of six faces and 1/8 of
each of the 8 corner atoms.
• Lattice parameter @ length of unit cell can be calculated by using
the following formula , where, a=unit cell length and
R= atomic radius.
cellt4atoms/uni)2
1(68)
8
1(atomsofNumber
a
a
4R
R
22Ra
HCP Structure• Has a unit cell that is hexagonal.
• The top and bottom faces consists 6 atoms that form a regular
hexagons and surround a single atom in the center.
• Another plane consists 3 additional atoms which is situated in
the middle.
• Has 6 atoms per unit cell, 1/6 of each of the 12 top and bottom
face corner atoms, ½ of each of the center face atoms and 3
midplane interior atoms.
Where a and c represents the short and long unit cell dimensions respectively
Terms in Recrystallization Process
• Is the formation of a new set of strain-free grains
within a previously cold-worked material usually by an
annealing heat treatment.
• Crystal structure – the manner in which atoms/ions are
arrayed in space.
• Space lattice – the regular geometrical arrangement of
atoms
Lattice Not Lattice
Space Lattice and Crystal
Terms in Recrystallization Process
2 different orientations of grains
Grain Boundary
•Grain – an individual crystal in a polycrystalline metal or ceramic.
•Grain Boundary – the interface separating two adjoining grains
having different crystallographic orientations.
Atomic Bonding in Solids• Atomic bonding is the interatomic forces that bind the
atoms together.• There are primary and secondary bonds found in solids:
Primary / Chemical Bonding > stronger bonds 3 types of primary bond:-
Ionic Covalent Metallic
Secondary / Physical Bonding > weaker bonds 2 types of secondary bond:-
Van der Waals Hydrogen
Ionic Bonding• Electrically charged ions are formed by the transfer of
electron from one atom to another.
• Found in compounds composed of both metallic and
nonmetallic elements.
• Example : NaCl , MgO
• Characteristics :
stable, hard, brittle,
electrically and
thermally insulative.
Tendency to lose outermost electrons( donor > +ve ion)
Tendency to gain electrons
(acceptor > -ve ion)
Covalent Bonding• Involving sharing of electrons between adjacent atoms.
• 2 atoms that are covalently bonded will each contribute at least 1e
to the bond.
• Nonmetallic elemental molecules ( H2, Cl2, F2) and molecules
containing dissimilar atoms ( CH4, H2O, HNO3, HF) are covalently
bonded.
• Characteristics : Varies
Diamond ( strong, hard, high melting temperature)
Bismuth ( very weak, low melting temperature)
(Methane)
• Valence electrons form a “sea of electrons” that is uniformly dispersed
around the metal ion cores and act as a form of glue for them.
• Found in metals and their alloys. Ex: Fe (iron), W (tungsten)
• Characteristics:
Good electrical and thermal conductors due to their free valence electrons
Opaque neither transparent (allowing all light to pass through) nor
translucent (allowing some light to pass through)
Ductile (material's ability to deform under tensile stress(stretched into a
wire)
Metallic Bonding
Metal ions / Ion cores
Sea of electrons / Electron cloud
• Van der Waals resulted from attractive forces between electric dipoles. Weakest bond Exists between all atoms or molecules, inert gas (which has
stable e structure, and between covalently bonded molecules.
Ex : Ar, Cl2
• Hydrogen bonding Most common in covalent bonded molecules. Found to exist between some molecules that have hydrogen
as one of the constituents. Ex : NH3, H2O
Secondary Bonding
+ - + -
Atomic or molecular dipoles
Van der Waals bonding
between two dipoles
THE END