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DEFECTS IN SOLIDS
12
Defects in solids
NURUL AFFIRA BINTI MAZAR (S43552)
NUR AMIRAH BINTI YUSOF (S43068)
DEFINITION
Definition
The term imperfection or defect is generally used to describe any deviation of the ideally perfect crystal from the periodic arrangement of its constituents.
Line defect
Line defect
- A line defect is a line along which whole rows of atoms in a solid are arranged anomalously.
- The resulting irregularity in spacing is most severe along a line called the line of dislocation.
- There are 2 types of dislocation :
- Edge dislocation
- Screw dislocation
Types of dislocation
Point defect
Point defect
- Point defects are where an atom is missing or is in an irregular place in the lattice structure.
- Point defects include self interstitial atoms, interstitial impurity atoms, substitutional atoms and vacancies.
- There are 4 types of point defects :
- Vacancy
- Ion-pair vacancy
- Interstitialcy
- Displaced ion
Types
Planar defect
Planar defect
- A Planar Defect is a discontinuity of the perfect crystal structure across a plane.
- There are 3 types of planar defect :
- Grain boundaries
- Tilt boundaries
- Twin boundaries
Types
b) Tilt Boundaries
A Tilt Boundary, between two slightly mis-aligned grains appears as an array of edge dislocations.
c) Twin Boundaries
A Twin Boundary happens when the crystals on either side of a plane are mirror images of each other.
a) Grain Boundaries
a general planar defect that
separates regions of
different crystalline
orientation (i.e. grains)
within a polycrystalline solid.
Volume Defects
Volume defect
- Volume defects are Voids, i.e. the absence of a number of atoms to form internal surfaces in the crystal.
- They have similar properties to microcracks because of the broken bonds at the surface.
- Examples include
- Pores
- Void
- Cracks
- Foreign inclusions
Figure
b) Void on a piece of metal
a) Cluster of microcracks in a melanine granule irradiated by short laser pulse