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M3 Dental Materials > Metals and Alloys > Flashcards

Metals and Alloys Flashcards

1
Q

characteristics of metals?

A 
hard
lustrous 
closely packed crystalline structures
opaque
conductors of heat and electricity
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2
Q

define alloy?

A

mixture of 2 of more metals

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3
Q

2 metal alloy?

A

binary alloy

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4
Q

3 metal alloy?

A

ternary alloy

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5
Q

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

A

mutual solubility

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6
Q

Define nucleation

A

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

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7
Q

define homogenous nucleation

A

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

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8
Q

what does homogenous nucleation require during manufacturing?

A

specialised equipment

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9
Q

define heterogenous nucleation

A

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

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10
Q

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

A

heterogeneous nucleation

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11
Q

What are crystals termed as?

A

grains

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12
Q

When do grains/crystals stop growing?

A

when all the molten metal is used up

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13
Q

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

A

grain boundary

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14
Q

what does grain size influence and how is it controlled?

A

the physical properties of the mould; controlled by manufacturer

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15
Q

give 2 factors influencing grain size

A

temperature and shape of the mould

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16
Q

what are grain boundaries under?

A

high local stress

17
Q

how are grain boundaries visualised?

A

light reflecting microscope, polished metal surface, ETCHING

18
Q

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

A

hammering, rolling, pressing

19
Q

give 2 others ways to shape metals and alloys

A

casting, amalgamation

20
Q

define amalgamation

A

mixing with Hg

21
Q

define ductility

A

maximum degree of EXPANSION in response to an applied TENSILE force

22
Q

define malleability

A

maximum degree of COMPRESSION in response to an applied COMPRESSIVE force

23
Q

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

A
  • 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
24
Q

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

A
  • ordered solid solution
  • random solid solution
  • interstitial solid solution
25
Q

define ‘ordered solid solution’

A

component metal atoms have specific sites in a common lattice

26
Q

define ‘random solid solution’

A

component metal atoms have random sites in a common crystal lattice

27
Q

define what is meant by ‘interstitial solid solution’

A

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

28
Q

define the hardening effect of solid solutions in alloys

A

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

29
Q

give 3 risks of insolubility of metals in an alloy

A

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

30
Q

give 2 risks of partial solubility of metals in an alloy

A

solid solution of metal B in metal A

solid solution of metal A in metal B

31
Q

Give the value of Tm in cooling curves graphs

A

melting point (time melted)

32
Q

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

A

intrmettalic compounds are formed with precise chemical formulation

33
Q

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

A

indicates the temperature constant during crystallisation

34
Q

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

A

crystallisation occurs over a range of temperatures

35
Q

what results from heating an alloy too fast?

A

cored structure

36
Q

describe cored structure

A

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

37
Q

what are phase diagrams useful for?

A

to make predictions on structure and coring

38
Q

what do phase diagrams show?

A

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

M3 Dental Materials (7 decks)

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