CRYSTAL DEFECT

                                      CRYSTAL DEFECT

                                                 https://ese-generalstudies.blogspot.com



A perfect crystal refers to crystals with every atom of the same type in the correct position, does not exist. All crystals have some defects. Defects contribute to the mechanical properties of metals. In fact, “defect” is sort of a misnomer since these features are commonly intentionally used to manipulate the mechanical properties of a material. Adding alloying elements to a metal is one way of introducing a crystal defect. Nevertheless, the term “defect” will be used,crystalline defects are not always bad.

 There are basic classes of crystal defects:

1)point defects:-It is due to lattice vacancies, self-interstitial atoms, substitution impurity atoms, and interstitial impurity atoms


2)linear defects:-IT forms due to dislocations.

3)planar defects :- Planar defects include grain boundaries, stacking faults and external surfaces.

Frenkel defect:-type of 'point defect' in a crystal structure where an atom or ion is displaced from its normal position to an interstitial one.

.                        

Schottky defect:-A Schottky defect consists of a pair of anion and cation vacancies→ this maintains charge neutrality.

                 

                                                                                                                                          

BRAVAIS LATTICE

                                     BRAVAIS  LATTICE

Seven crystal system are as follows:-

Crystal System	Lengths	Angles
cubic	a=b=c$a=b=c$	α=β=γ=90∘$\alpha =\beta =\gamma ={90}^{\circ }$
trigonal	a=b=c$a=b=c$	α=β=γ<120∘$\alpha =\beta =\gamma <{120}^{\circ }$, ≠90∘$\ne {90}^{\circ }$
hexagonal	a=b≠c$a=b\ne c$	α=β=90∘$\alpha =\beta ={90}^{\circ }$, γ=120∘$\gamma ={120}^{\circ }$
tetragonal	a=b≠c$a=b\ne c$	α=β=γ=90∘$\alpha =\beta =\gamma ={90}^{\circ }$
orthorhombic	a≠b≠c$a\ne b\ne c$	α=β=γ=90∘$\alpha =\beta =\gamma ={90}^{\circ }$
monoclinic	a≠b≠c$a\ne b\ne c$	α=β=90∘≠γ$\alpha =\beta ={90}^{\circ }\ne \gamma$
triclinic	a≠b≠c$a\ne b\ne c$	α≠β≠γ

Chemical Bonding

                                                 Chemical Bonding 

There are two types of chemical bonds:-

1)Primary bonds:- it is interatomic bond.

2)Secondary bonds:-It is intermolecular bonds,it is also known as Vander waals bond.It acts between nucleus of one atom and electrons of other atom.

                                                                PRIMARY BONDS

Primary bonds are further subdevided into following categories:-

IONIC BONDS:-It is unidirectional in nature.

COVALENT BONDS:-it's nature is directional

METALLIC BONDS:-It acts between electron cloud and positive ions.

                                                         SECONDARY BONDS

Secondary bonds are classified in these categories:-

DISPERSION BONDS:-It is formed due to polarization,polarization is due to displacement between centres of positive and negative charge,electron distribution is not symmetrical.

DIPOLE BONDS:-it is formed due to unequal sharing of electrons between two atom,permanent dipoles are created from this bondings.

HYDROGEN BONDS:-This is special type of dipole bonds formed between atoms of hydrogen and oxygen.

                                          FREE ESE/IES GENERAL STUDIES GS STUDY MATERIAL

MATERIAL SCIENCE CONTENTS

MATERIAL SCIENCE CONTENTS


Chemical Bonding 

Crystal Solids 

Imperfection in Solids 

Phase Diagram.

Processing of Metals 

Mechanical Properties

Electrical Properties

Magnetic Properties

Optical Properties 

Ferrous Metals 

Non-Ferrous Metals 

Polymers 

Ceramics

Composites 

Corrosion and Degradation