Lecture 7 - Crystal Strcuture 3

Question 1

What happens to the density of metals when the temperature decreases

Answer 1

Density decreases as they aren’t as closely packed

Question 2

What type of structure has random packing and why

Answer 2

Amorphous - less densely packed

Question 3

What type of structure has organised regions and why

Answer 3

Crystalline - more densely packed

Question 4

How do solids form

Answer 4

Generally solidify from melt

Question 5

What are the 3 phases of matter

Answer 5

Liquid
Gas
Solid

Question 6

A gas is a set of matter with what

Answer 6

No definite shape of volume

Question 7

A liquid is a state of matter with

Answer 7

With definite volume but without definite shape

Question 8

A solid is a state of matter of

Answer 8

Definite shape and volume

Question 9

What is a missing atom called

Answer 9

A vacancy

Question 10

What is an extra atom called

Answer 10

Interstitial

Question 11

What are a plane of atoms in the wrong place called

Answer 11

Dislocations

Question 12

What happens to the number of vacancies when temperature increases

Answer 12

Vacancies increase
Therefore number of atoms per unit volume decreases thus density decreases

Question 13

What does a vacancy depend on

Answer 13

Temperature

Question 14

What is a self interstitial

Answer 14

Same atoms but would severely distort the lattice structure

Question 15

What is substitutional

Answer 15

Different but similar sized atom

Question 16

What is an interstitial impurity atom

Answer 16

Can be another smaller atom

Question 17

What are two effects of interstitial

Answer 17

Normally not the same size therefore distort the lattice structure
Distorsión of the lattice structure leads to stress within the lattice

Question 18

What are the 3 major types of lattice imperfection’s (dislocations)

Answer 18

Edge dislocation
Screw dislocation
Mixed dislocation

Question 19

What is edge dislocation

Answer 19

It is when there is an extra plane of atoms in the lattice structure and atoms beside the plane are squashed, while atoms below the plane are stretched

Question 20

What is the movement of edge dislocations like

Answer 20

Difficult to break atomic bonds in a perfect crystal
Effect of defects is to allow relative movement of atoms
Stressed atomic bonds can be broken and then reformed with other atoms

Question 21

What is the application of edge dislocation and what does sit produce

Answer 21

Application of shear stress which produces motion
(Bonds are broken and new ones are formed)
(Can move one atomic spacing at a time)

Question 22

What occurs when you get multiple motions of edge dislocations

Answer 22

Can get motion across a grain