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3. Dental Materials > Metals and Alloys > Flashcards

Metals and Alloys Flashcards

1
Q

what is an alloy?

A

mixture of 2 or more metals

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2
Q

in molten state metals display ? solubility

A

mutual

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3
Q

what are the two classifications of metals?

A

noble metals - highly resistant to oxidation and corrosion e.g. gold, platinum

base metals e.g. cobalt, copper, nickel

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4
Q

describe the structure of metals when solid?

A

regular crystalline structure

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5
Q

as metal cools solidification starts at specific sites called ?. ? in metal molten mass enable metal atoms to deposit on them.

A

nuclei
impurities

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6
Q

what happens during crystal growth when metal cools?

A

nuclei grow in 3 dimensional directions forming branched structures called dendrites

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7
Q

when metals cool, when does crystal growth stop?

A

when crystals touch each other

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8
Q

what is a grain boundary?

A

when crystals touch each other

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9
Q

what affect does decreasing the grain size have on the concentration of grain boundaries?

A

smaller grain size
higher concentration of grain boundaries

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10
Q

mechanical properties of metals are enhanced by what grain size?

A

smaller

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11
Q

how can manufacturer control the grain size? 3

A

rapid cooling - smaller grains
slow cooling - larger grains
temperature and shape of mould

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12
Q

what is amalgamation?

A

metal mixed with mercury (Hg)

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12
Q

define ductility

A

the maximum degree of extension in response to an applied tensile force

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13
Q

define malleability

A

the maximum degree of compression in response to an applied compressive force

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14
Q

on cooling from molten components metals may remain soluble in each other - solid solutions
what are the 3 types of solid solution?

A

ordered solid solution
random solid solution
interstitial solid solution

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15
Q

what is an ordered solid solution

A

component metal atoms have specific sites in the lattice

16
Q

what is a random solid solution?

A

metal atoms occupy random sites in common crystal lattice

17
Q

what is a interstitial solid solution?

A

atoms of one lie within the primary lattice sites of another

18
Q

name 3 properties of pure metals

A

harder
stronger
higher elastic limits

19
Q

on cooling molten component metals may be insoluble in each other (this is rare). this means they are susceptible to what?

A

electrolytic corrosion

20
Q

on cooling molten component of metals may be partially soluble in each other. the metals have two different phases, what are they?

A

phase 1: solid solution of metal B in metal A
phase 2: solid solution of metal A in metal B

21
Q

on cooling molten component of metals may be partially soluble in each other. solubility is ? dependant. when temperature decreases from melting point to room temperature solubility ?

A

temperature
decreases

22
Q

on cooling molten component of metals may form intermettalic compounds if the metals have affinity for each other. what are the properties of this type of alloy? 4

A

less potential for slip plane movement as few crystal imperfections
hard
brittle
low ductility

23
Q

is this temperature time graph for pure metals or alloys?

A

pure metals

24
Q

what does the plateau region indicate?

A

temperature constant during crystallisation

25
Q

Metal A has the highest melting point. at T1 crystallisation is rich in A or B?

A

A

26
Q

metal A has the highest melting point. at T2 crystallisation is rich in A or B?

A

B

27
Q

what happens between T1 and T2?

A

crystallisation over a range of temperatures. crystallisation starts at T1 and is complete at T2

28
Q

what is coring?

A

alloy is cooled too fast. the exterior portion solidifies whilst the inner portion remains hot and soft. the exterior has a different composition to the interior reducing the alloys quality and performance.

29
Q

coring affects what?

A

corrosion resistance

30
Q

what is the upper line called?

A

liquidus line

31
Q

what is the lower line called?

A

solidus line

32
Q

understand this

A

nice one

33
Q

when alloy components are insoluble in each other crystallisation occurs when?

A

at a specific temperature

34
Q

what is a eutectic alloy?

A

melting point lower than component metals

35
Q

in this region what states are A and B?

A

A is solid
B is solid

36
Q

in this region what states are A and B?

A

A is solid
B is liquid

37
Q

in this region what states are A and B?

A

A is liquid B is solid

38
Q

where is the eutectic point (eutectic alloy)

A

3. Dental Materials (7 decks)

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