Metals and Alloys

Question 1

characteristics of metals?

Answer 1

hard
lustrous 
closely packed crystalline structures
opaque
conductors of heat and electricity

Question 2

define alloy?

Answer 2

mixture of 2 of more metals

Question 3

2 metal alloy?

Answer 3

binary alloy

Question 4

3 metal alloy?

Answer 4

ternary alloy

Question 5

what do the metals in an alloy display in the molten state?

Answer 5

mutual solubility

Question 6

Define nucleation

Answer 6

nucleation is the formation of crystals in a metal during cooling from molten to solid

Question 7

define homogenous nucleation

Answer 7

single site of nucleation as the metal is pure and has no foreign particles

Question 8

what does homogenous nucleation require during manufacturing?

Answer 8

specialised equipment

Question 9

define heterogenous nucleation

Answer 9

multiple site nucleation as there are foreign particles present on which the crystals can form

Question 10

what type of nucleation are the majority of dental materials manufactured by?

Answer 10

heterogeneous nucleation

Question 11

What are crystals termed as?

Answer 11

grains

Question 12

When do grains/crystals stop growing?

Answer 12

when all the molten metal is used up

Question 13

what is the term for the interface between 2 grains in a polycrystalline material?

Answer 13

grain boundary

Question 14

what does grain size influence and how is it controlled?

Answer 14

the physical properties of the mould; controlled by manufacturer

Question 15

give 2 factors influencing grain size

Answer 15

temperature and shape of the mould

Question 16

what are grain boundaries under?

Answer 16

high local stress

Question 17

how are grain boundaries visualised?

Answer 17

light reflecting microscope, polished metal surface, ETCHING

Question 18

give 3 ways of shaping readily deformable, malleable and ductile metals and alloys

Answer 18

hammering, rolling, pressing

Question 19

give 2 others ways to shape metals and alloys

Answer 19

casting, amalgamation

Question 20

define amalgamation

Answer 20

mixing with Hg

Question 21

define ductility

Answer 21

maximum degree of EXPANSION in response to an applied TENSILE force

Question 22

define malleability

Answer 22

maximum degree of COMPRESSION in response to an applied COMPRESSIVE force

Question 23

upon cooling from molten what are the possible levels of solubility the metals in an alloy might display?

Answer 23

• remain soluble in each other to form a solid solution
• be completely insoluble in each other
• be partially soluble in each other
• form intermettalic compounds if the metals have a high affinity for one another

Question 24

what are the 3 types of solid solution in an alloy?

Answer 24

• ordered solid solution
• random solid solution
• interstitial solid solution

Question 25

define 'ordered solid solution'

Answer 25

component metal atoms have specific sites in a common lattice

Question 26

define 'random solid solution'

Answer 26

component metal atoms have random sites in a common crystal lattice

Question 27

define what is meant by 'interstitial solid solution'

Answer 27

atoms of one metal lie within the primary lattice of the other

Question 28

define the hardening effect of solid solutions in alloys

Answer 28

as atoms of differing radii form mechanical resistance to dislocations, the solution hardens

Question 29

give 3 risks of insolubility of metals in an alloy

Answer 29

electrolytic corrosion areas of pure metal A areas of pure metal B (no mixing in some areas)

Question 30

give 2 risks of partial solubility of metals in an alloy

Answer 30

solid solution of metal B in metal A | solid solution of metal A in metal B

Question 31

Give the value of Tm in cooling curves graphs

Answer 31

melting point (time melted)

Question 32

what is formed when metals have a high affinity for each other?

Answer 32

intrmettalic compounds are formed with precise chemical formulation

Question 33

what does the plateau (Tm) indicate in a cooling curve graph?

Answer 33

indicates the temperature constant during crystallisation

Question 34

When metals in an alloy have different melting points, what does this mean for crystallisation?

Answer 34

crystallisation occurs over a range of temperatures

Question 35

what results from heating an alloy too fast?

Answer 35

cored structure

Question 36

describe cored structure

Answer 36

metal on outside is cooled and solid; metal on inside is hot and molten

Question 37

what are phase diagrams useful for?

Answer 37

to make predictions on structure and coring

Question 38

what do phase diagrams show?

Answer 38

the phases of states (liquid/solid) in the metals of an alloy