Week 3

Question 1

Chemical Imperfection/Defect

Answer 1

Impurity of foreign atoms is always present

Solid solution = Solvent (host atoms) + Solute

Question 2

What are the types of chemical imperfection/defects

Answer 2

Substitutional: solute atoms replace/substitute host atoms
Interstitial: solute atoms fill voids among host atoms

Question 3

Hume-Rothery Rules

Answer 3

1. Atomic size factor - less than 15% difference in atomic radii
2. Crystal structure
3. Electronegativity
4. Valence - greater the difference in valence, lower solubility

Question 4

Coordination number

Answer 4

number of host atoms touching

Question 5

Weight percent (wt%)

Answer 5

c1 = m1/(m1+m2) x 100

Question 6

Atom percent (at%)

Answer 6

c1’ = n1/(n1+n2) x 100

Question 7

wt% to at%

Answer 7

c1' = (c1a2)/(c1a2 +c2a1) x 100
c2' = (c2a1)/(c1a2 +c2a1) x 100

Question 8

at% to wt%

Answer 8

c1 = (c1'a1)/(c1'a1+c2'a2) x 100
c2 = (c2'a2)/(c1'a1+c2'a2) x 100

Question 9

Point Defects

Answer 9

1. Vacancy - simplest point defect, increases entropy

2. Self-interstitial - an atom from the crystal that is crowded into interstitial site

Question 10

Linear Defects

Answer 10

One dimensional defect around which some of the atoms are misaligned

Question 11

Interfacial defects

Answer 11

Boundaries that have two dimensions and normally separate region of materials that have different crystal structure and/or crystallographic orientations

1. External surfaces
2. Grain boundary
3. Phase boundary
4. Twin boundaries
5. Miscellaneous