Lecture 7 - Crystal Strcuture 3 Flashcards
What happens to the density of metals when the temperature decreases
Density decreases as they aren’t as closely packed
What type of structure has random packing and why
Amorphous - less densely packed
What type of structure has organised regions and why
Crystalline - more densely packed
How do solids form
Generally solidify from melt
What are the 3 phases of matter
Liquid
Gas
Solid
A gas is a set of matter with what
No definite shape of volume
A liquid is a state of matter with
With definite volume but without definite shape
A solid is a state of matter of
Definite shape and volume
What is a missing atom called
A vacancy
What is an extra atom called
Interstitial
What are a plane of atoms in the wrong place called
Dislocations
What happens to the number of vacancies when temperature increases
Vacancies increase
Therefore number of atoms per unit volume decreases thus density decreases
What does a vacancy depend on
Temperature
What is a self interstitial
Same atoms but would severely distort the lattice structure
What is substitutional
Different but similar sized atom
What is an interstitial impurity atom
Can be another smaller atom
What are two effects of interstitial
Normally not the same size therefore distort the lattice structure
Distorsión of the lattice structure leads to stress within the lattice
What are the 3 major types of lattice imperfection’s (dislocations)
Edge dislocation
Screw dislocation
Mixed dislocation
What is edge dislocation
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
What is the movement of edge dislocations like
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
What is the application of edge dislocation and what does sit produce
Application of shear stress which produces motion
(Bonds are broken and new ones are formed)
(Can move one atomic spacing at a time)
What occurs when you get multiple motions of edge dislocations
Can get motion across a grain
