Structure of Solids

Question 1

Define Co-ordination number

Answer 1

number of nearest neighbour atoms for the BCC/FCC unit cell

Question 2

Example BCC metals

Answer 2

Fe, Mo, Cr

Question 3

Formula for Atomic Packing Factor (APF)

Answer 3

APF = Volume of Atoms/Volume of unit cell

Question 4

Example FFC metals

Answer 4

Cu, Al, Au

Question 5

Polymorphism

Answer 5

Polymorphism describes materials that can exist in more than one crystal structure.
E.g., iron at room temperature has a BCC structure, but at 912 degrees celsius, it has an FCC structure.

Question 6

Ceramics

Answer 6

Consisting of metals and non-metals joined by ionic and covalent bonds. Arranged in a crystalline manner. E.g., Rock Salt Structure, Silicate Structure.

Must be balanced in charges (electrically neutral), and structure is determined by relative sizes of ions.

Question 7

Silicate Structure

Answer 7

Type of Ceramic. Most common: rock, soil, clay, sand, all made up by silicate tetrahedra.

Question 8

Chill crystals

Answer 8

Small equiaxed grains that forms due to heterogeneous nucleation (When molten metal is poured into a mould)

Question 9

Grain Boundary

Answer 9

Imperfection. Mismatch in lattice orientation. High-energy regions due to free electrons.

Question 10

Anisotropic

Question 11

Crystallographically equivalent

Question 12

Slip

Question 13

Vacancy

Question 13

Substitutional atom

Question 14

Interstitial atoms

Question 14

Edge & screw dislocation

Question 15

Porosity

Question 16

Homogeneous vs heterogeneous nucleations

Question 16

Grain

Question 16

Polycrystalline

Question 17

Equiaxed grains

Question 18

Columnar Grains

Question 19

What makes material anisotropic?

Answer 19

In the middle of grain structure development: Equiaxed grains, columns meet in middle, dendrite formation, or hole/pore in the middle.

Question 20

Grain refiners

Question 21

Hall-Path effect

Answer 21

Grain boundaries inhibit dislocation movement, making mechanical property of metal less ductile (strong). Yield Stress = Constant + kd^-0.5

Question 22

Work Hardening

Answer 22

During plastic deformation of metals, the grains are individually deformed. This makes more dislocations. Increase in dislocation density means they will inhibit dislocation movements causing "traffic jam", material is stronger.

Question 23

Cold-worked

Answer 23

Metal plastically deformed at temperature below recrystallisation temperature

Question 24

Hardness

Answer 24

Material's resistance to localised plastic deformation (indentation test)

Question 25

Recrystallisation

Answer 25

New grains (low dislocation density and equiaxed) nucleate at pre-existing grain boundaries - thermodynamic driving force is stored strain energy, going from high energy state (lots of dislocations) to lower energy state (less dislocations)