material science-crystallography (atomic radius,apf,bonding energy)
DESCRIPTION
GIVES IDEA ABOUT CRYSTAL STRUCTURES AND OTHER RELATED TOPICSTRANSCRIPT
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
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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
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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
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CLASSIFICATION OF
MATERIALS Classification based on chemical
make –up
Classification based on arrangement
of atoms
Classification based on application
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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
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Composites- composites are
combination of other above three
categories to produce best , high
quality engineering materials.
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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
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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
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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
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Where ‘E0’ is the minimum energy required separate two atoms in an infinite position.
CRYSTAL STRUCTURE
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HCP
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. 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
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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
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TOTAL NO.OF ATOMS IN A
UNIT CELL
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FOR SIMPLE CUBIC STRUCTURE-
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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
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BCC
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FCC
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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.
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