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Dental Materials > Metals and Alloys > Flashcards

Metals and Alloys Flashcards

1
Q

structure of materials at room temperature?

A

hard and lustrous, closely packed crystal structure, radiopaque, conduct heat/electricity

excpetion = Hg liquid at room temp

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2
Q

what is an alloy?

A

2 metals = binary

3 metals = ternary

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3
Q

crystal structure in metals?

A

crystaline, many small particles, form from molten

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4
Q

what is an alloy system?

A

all possible combinations of an alloy

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5
Q

what do alloys display in the molten state?

A

mutual solubility - alloys dissolve in each other

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6
Q

what happens when metals cool?

A

impurities allow metal atoms to deposit upon them = nucleate crystal growth

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7
Q

how to grains grow?

A

grains grown until all of the melt is a metal.

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8
Q

what is a grain boundary?

A

where grains abut their neighbours

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9
Q

heterogenous nucleation?

A

many sites of nucleation

majority

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10
Q

homogenous nucleation?

A

one site
pure metal = 4 atoms
specialised equipment

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11
Q

how does grain size affect physical properties?

A

rapid solidification

extra nucleation sites - e,g addition of iridium to gold

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12
Q

if the temperature of the mould is similar to the melt whathappens?
diff to melt?

A

slow cooling = large grain

rapid cooling = small grain

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13
Q

if the temp of the mould is sim shape of mould?

A

initiate growth and influence direction of crystal growth

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14
Q

how to visualise grain boundaries?

A

light reflecting microscope
polished metal surfaces - irregularities scatter light
application of acid - attack areas under stress - grain boundaries

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15
Q

how to shape metals and alloys?

A

cam be readily deformable, malleable, ductile =
hammering, rolling, pressing, drawn into a wire
can be wrought/cold working

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16
Q

what is ductility?

A

max degree of extension in response to applied tensile force

17
Q

what is malleability?

A

max degree of compression in response to applied compressive force

18
Q

on cooling from molten components alloys may?

A
  • remain soluble in each other - solid solution
  • be completely insoluble in each other
  • be p/soluble in each other
  • form intermettalic compounds if metals have affinity for each other
19
Q

what is an ordered solid solution?

A

metals atoms have specific states in a common lattice
one shown substantial - similar atomic radii
radii differ - distortions of lattice

20
Q

what is a random solid solution?

A

random sites in a common crystal lattice

21
Q

interstitial solid solution?

A

atoms of one lie within the primary lattice sites of the other, atomic radii dependent

22
Q

properties of pure metals?

A

harder, stronger, higher elastic limits

23
Q

what is the hardening effect?

A

atoms of diff radii form mechanical resistance to dislocations

24
Q

what happens to grains when drawn into a wire?

A

elongated in direction of drawing into a laminer structure

limit to how much remodelling can take place

25
Q

what is casting?

A

molten into an investment mould

26
Q

what is amalgamation?

A

mix with Hg, plastic mass, hardening, chem reaction, crystallisation

27
Q

insolubility of metals?

A

rare
areas of each pure metal
risks electrolytic corrosion

28
Q

partial solubility of metals?

A

alloy has diff phases
solid solition of metal b in a
solid solution of metal a in b

29
Q

what is metal affinity?

A

form intermetallic compounds
precise chem formaulation
specific valence requirements satisfied - few crystal imperfections = less potential for skip plane movement
hard brittle, low ductility

30
Q

cooling curves?

A

melt metal/alloy

record and plot temp versus time

31
Q

what is tm?

A

melting point

where plateau’s = crystallisation

32
Q

what is a phase diagram?

A

series of cooling curves for alloys of diff compositions

make structural/coring predictions

33
Q

for each metal composition calculate?

A

T1, T2, = temp of crystalisation of metal A, temp of crystalisation of metal B
plot against % of compositions

34
Q

what can you predict between liquidus and solidus?

A

predict solid and liquid compositions

35
Q

the larger the seperation between liquidis and solidus the greater the what?

A

greater the coring

36
Q

the point where alloy components are insoluble in each other mean what?

A

the sepcific part where crystallisation occurs at specific temperatures

37
Q

what is a eutectic alloy?

A

behaves like a pure metal
narrow melting range
narrow melting point lower then component metals
application as solders

Dental Materials (13 decks)

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