Lecture 4 week four Imperfections in Solids

Question 1

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what are the types of Crystalline imperfections ?

Answer 1

0D, point defects:
atoms missing or in irregular places in the lattice (vacancies,
interstitials, impurities,
- 1D, linear defects:
groups of atoms in irregular positions
- 2D, planar/area/surface defects:
interfaces between homogeneous regions of the material
- 3D, volume defects:
extended defects

Question 2

Point Defects

Answer 2

Vacancies
Self-interstitials

Question 3

Vacancies

Answer 3

it is when a lattice position that is vacant because of an atom missing

Question 4

Self-Interstitials

Answer 4

an atom that occupies a place outside the normal lattice postion

Question 5

Equlibrium Vacancy Concentration:Point defects

Answer 5

This means the equilibrium number of vacancies (they exponentially increase with temperature

Question 6

impurities in solids

Answer 6

ALL real solids are impure
impurity atoms have been added intentionally to impart specific characteristics to materials

Question 7

solid solutions

Answer 7

solvent=Elements that is present in the greatest amount
Solute ;componetn that is present in minor amount
SOLID SOLUTION;A homogenous structure that maintains the crystal structure of host atom with randomly dispersed impuritiies

Question 8

Import exam stufff

what are the conditions for complete substitutional solid solutions(Hume -Rothery rule)

Answer 8

1. Atomic size: need to “fit” - the difference in atomic radii (r) between the solute
   and solvent atom types should be less than about 15%.
2. Crystal structure: crystal structures for metals of both atom types must be
   the same.
3. Electronegativities: should be comparable (otherwise new intermetallic phases
   favors to form)
   * Proximity in periodic table
4. Valency (close or similar)
   * All are being equal; a metal will have a greater tendency to dissolve a metal of higher valency
   than one of lower valency.

Question 9

what are dislocations

Answer 9

A dislocation is a linear or one-dimensional defect around which some atoms are misaligned.
* The interatomic bonds are significantly distorted only in the immediate vicinity of the dislocation
line. This area is called the dislocation core.
* Dislocations slip between crystal planes as a result of dislocation motion.
* they usually produce permanent (plastic) deformation

Question 9

Specification of composition

Answer 9

it is often necessary to express the composition (or concentration) of an alloy in
terms of its constituent elements

Question 9

Linear defects :Dislocation

Answer 9

A dislocation is a linear or one-dimensional defect around which some atomes are misaligned
The interatomic bonds are significantly distorted only in the immediate vicinity of the dislocation
line. This area is called the dislocation core.
* Dislocations slip between crystal planes as a result of dislocation motion.
* Dislocations usually produce permanent (plastic) deformation.