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Crystaline Imperfections & Polymer Structures
Demonstrate an understanding of the several types of crystalline defects and etc
14
Mechanical Engineering
Undergraduate 3
05/07/2014

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Term
Crystalline Defect examples
Definition
point defects (thermal vibration)
Linear defects (dislocations)
Planar defects
Complete lacking in crystalline order (amorphous)
Term
Solid solution(chemical imperfection)
Definition
Commercial metal alloys : solid solution
A. Substitutional & B. interstitial solid solution
Term
Substitutional solid solution
Definition
Hume-Rothery rules (for substitutional solid solution)
1.Less than about 15% difference in atomic radii
2.The same crystal structure
3.Similar electronegativities (ability of the atom to attract electron)
4.The same valence
Term
Interstitial solid solution
Definition
Smaller atom simply to fit into spaces
Occur when atom sizes differ greatly
Energetically unstable structure
Produces considerable local strain (C in alpha-Fe)
Term
Point defects
Definition
zero-dimensional imperfection
structural defects (independently of chemical impurities)
Defects with the crystalline point lattice
Two types:
1.Vacancy
2.interstitial
Term
Burgers Vector
Definition
Quantitative designation
Displacement vector (a vector to close the loop)
Magnitude of the structural defect
Term
Edge dislocation
Definition
burgers vector is perpendicular to the dislocation line
Term
Screw dislocation
Definition
Spiral stacking of crystal planes around the dislocation line
Burgers vector is parallel to the dislocation line
Term
Mixed dislocation
Definition
Most linear defects in actual material
Both edge and screw dislocation
Term
Numerous forms of planner defects
Definition
1.Twin boundary
-Structurally mirror images
-Deformation (hcp), annealing (fcc)
2.Surface defect
-Surface atoms are different from bulk atoms
3.Grain boundary
-Region between two crystals or grains
Term
Noncrystalline solids 3 Dimensional imperfections)
Definition
1.Oxide glass
2.Amorphous semiconductor
3.Amorphous metal
Term
Oxide glass:
Definition
-Rapid cooling silicate
-Random stacking
-Zachariasen model
Term
Amorphous semiconductor
Definition
-Economic advantage
-Complex electronic property
Term
Amorphous metal
Definition
-Metallic glasses, Bernal model
-Rapid cooling of liquid metal to prevent crystallization (1°C/s)
-Uniformity of the noncrystalline structure eliminates the grain boundary (High strengths and excellent corrosion resistance)
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