material science-crystallography (atomic radius,apf,bonding energy)

MATERIAL SCIENCE

-CRYSTALLOGRAPHY

(ME010 304)

BY

Asst.Prof. ABHILASH KK

MATERIAL SCIENCE

Study of materials is basically a study

of structure and properties of

engineering materials and on

investigation of structure-property

relationship

Structure-the arrangement of internal

components of matter in a material

Property- response of material when

exposed to an external stimulus

asst.prof. ABHILASH KK 2

LEVEL OF STRUCTURE

MACRO SCOPIC: Substance visible to naked eye

MICROSCOPIC: Structure obtained under optical microscope.magnification upto 1500 times linear

Sub structure: refers to the structure as obtained using a microscope

Crystal structure: showing arrangement of atoms with in the materials. The main technique employed for determining the crystal structure is X-ray diffraction


Electronic structure: it refers to arrangement of electrons in outer orbital of individual atoms in a solid material. spectroscopic technique are used in determining electron structure

Nuclear structure: provides the details regarding constituents with in the nucleus of atoms in the material. nuclear magnetic response and mossbaur studies are the usual technique used


CLASSIFICATION OF

MATERIALS Classification based on chemical

make –up

Classification based on arrangement

of atoms

Classification based on application


Classification based on chemical

make up Metals-metals are the elements with 1,2,3

valance electrons in outer shells. engineering materials are either metals or its alloys

Ferrous & non-ferrous

Ceramics-ceramics are in organic components between metallic and non –metallic elements.these includes oxides ,carbides,nitrides,borides,cilicates etc.ofvarious metals. Example- glasses, clay..etc

Polymers-organic compounds based on carbon ,hydrogen and other non-metalicelements .They are either natural material or synthetically processed materials like plastics,phenol ..etc


Composites- composites are

combination of other above three

categories to produce best , high

quality engineering materials.


Classification based on

arrangement of atoms in a

material Crystalline material-in which atoms are

arranged in regular, repetitive manner having long range order. Example-materials and some ceramics

Amorphous materials: in which atomic arrangement does not have any order of atoms

Example-ceramics and a few polymers Molecular materials: grouping of atoms

in short range order exists. Example- most of the polymers


Based on application

Structural materials-no moving

parts(eg.-dams,buildings)

Materials for machines-moving

parts(automobile)

Materials for devices-materials for

small parts of devices like measuring

instruments


Bonding force

Consider two atoms which are separated by a small distance ,then we can see that force between atoms is very high

force can be classified in to two-attractive force (fa),repulsive force(fr)

Net force fn= fa+fr At the point where net force equal to

zero is known as point of equilibrium where fa and fr balance each other

Here the distance between centers of two atoms(equilibrium state) is known as bond length ,denoted as r0



Where ‘E0’ is the minimum energy required separate two atoms in an infinite position.

CRYSTAL STRUCTURE


HCP


. SPACE LATTICE:-space lattice is defined as an array of points in three dimensions in which every point has identical to that every other points in the array

UNIT CELL:-The tiny block formed by arrangement of small group of atoms is called a unit cell. The unit cell is the smallest component of the space lattice

LATTICE POINT:-if Each atoms in lattice is replaced by a point, then each point is called lattice point


Co-ordination number:-it is defined as

the number of nearest atoms which

are directly surrounding a given atoms

SIMPLE CUBIC STRUCTURE:-6

BODY CENTERED CUBIC-8

FACE CENTERED CUBIC-12


TOTAL NO.OF ATOMS IN A

UNIT CELL


FOR SIMPLE CUBIC STRUCTURE-


ATOMIC RADIUS

ATOMIC RADIUS:-defined as the distance between nearest neighbours in a crystal of a pure element

Simple Cubic Structure:-In this structure, atoms touch each other along the lattice, as shown in Fig.

a = 2r or r = a/2

SC


BCC


FCC


ATOMIC PACKING

FACTOR(APF) Atomic packing factor(APF)-defined as

the fraction of volume occupied by the

atoms in a unit cell, compared to the

total available volume of the unit cell.


material science-crystallography (atomic radius,apf,bonding energy)

Engineering