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Biomaterials Exam 1 > Metals > Flashcards

Metals Flashcards

1
Q

Metal definition

A

Any of a class of chemical elements generally characterized by ductility, luster, conductivity of heat and electricity

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2
Q

Alloy definition

A

a mixture of metals

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3
Q

8 properties of metals

A 
Usually strong/hard and stuff
tough - not brittle
lustrous
dense
good conductors of electricity
good conductors of heat
opaque
ductile, malleable
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4
Q

casting metal

A

pouring liquid metal into mold

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5
Q

machining metal

A

cutting - drilling, turning…

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6
Q

cold working metal

A

deforming metal in solid state - forging, extruding…

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7
Q

powder metallurgy

A

pouring metal powder into mold and sintering

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8
Q

Metallic bonding

A

Primary/strong bonding in metals
+ ions surrounded by a cloud of electrons
Electrons can move

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9
Q

What are the consequences of metallic bonding?

A
  1. High conductivity (thermal and electrical) due to the movement of e-
  2. Opacity - electrons absorb electromagnetic and photon energy
  3. easy to form alloys
  4. High plasticity
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10
Q

All metals have a ______ structure

A

crystalline

technically polycristalline

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11
Q

Crystalline material definition

A

Shows a long-range regular arangement of atoms
eg. metals
In conrast to amorphous/glassy materials

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12
Q

unit cell

A

Smallest repeating unit in a crystal

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13
Q

What are the 3 common unit cells of the metals used in dentistry?

A

body centered cubic
face centered cubic
hexagonal close packed

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14
Q

Many of the properties of metals can be explained in relation to _____ in their crystalline structures

A

imperfections

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15
Q

What are the 3 types of crystal imperfections in metals

A

point defects
line defects
plane defects

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16
Q

What are the types of point defects a metal can have

A

impurities - substitutional, interstitial

vacancies

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17
Q

substitutional impurity point defect

A

One of the points in the crystal lattice is replaced by a different thing

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18
Q

interstitial impurity point defect

A

impurity lies between points of crystal lattice

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19
Q

vacancy point defect

A

a piece of the crystal lattice is missing

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20
Q

The easiness of having impurities (atoms of another nature in positions of the crystal lattice of metals, point defects) justifies that metals can be ______

A

easily alloyed (mixed)

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21
Q

Line defects

A

Dislocation in structure of metal
Formation of an extra semiplane of atoms in the metal structure
Below extra semiplane there is a line defect where the semiplane does not continue

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22
Q

Plane defect

A

When a metal cools after being liquid - solidifies as a multicrystalline/multigranular structure
Crystals with different crystal orientation join togethr forming grain boundaries = plane defects

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23
Q

metals are an agglomerate of small ______

A

crystals/grains

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24
Q

metals have a _____ structure

A

polycrystalline

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25
Q

grain size/shape influences the ______ of metals

A

mechanical properties

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26
Q

A metal with _______ grains/crystals is stronger. why?

A

smaller
finer - less coarse
More grain boundaries/plane defects per volume

27
Q

fibrous grain strucure of metals in obtained via ____

A

cold working

28
Q

Elastic strain of metals

A

recoverable
stretching of inter-atomic bonds
on removal of force atoms return to their equilibrium position
metallic bond acts as A SPRING

29
Q

metallic bonds act as…

A

a spring

30
Q

elasticity of metals depends mainy on…

A

the resistance of the metallic bond to be stretched

31
Q

Sum of elastic deformation of metallic bonds accounts for…

A

the overall elastic deformation of the metallic material

32
Q

Modulus of elasticity of a metal mainly depends on

A

the chemical nature of each metal

hardly depends on other structural features of the metal

33
Q

Mechanism of plastic strain in metals

A

permanent

movement/slip of dislocations

34
Q

The easier it is to create dislocations in a metal, the _____ it is

A

softer

35
Q

How could you strengthen a metal?

A

treat/process metal to make dislocations difficult

36
Q

How does cold working a metal change it?

A

Introduces more dislocations, more interaction between dislocations = harder to move them
STRENGTHENS
too much = brittle
Lead to fibrous structure

37
Q

Casting of a metal results in

A

equiaxed structure

38
Q

Effects of recrystallization after cold working a metal

A

Further heating = reformation of equiaxed structure, elimination of dislocations, erases deformation/cold working history of metal
SOFTER

39
Q

Effect of grain growth during metal processing

A

even more heating
larger grains formed in same volume of metal
less grain/crystal boundaries, less impediment of dislocation
SOFTER

40
Q

What are the steps in mechanical/thermal history (processing) of a metal

A

casting
cold working
recrystallization
grain growth

41
Q

metals are very tough because they can develop significant ____

A

plasticity - form/move dislocations

42
Q

if dislocations are difficult to move, the metal will be more ____, less ____

A

brittle
tough
Like ceramics

43
Q

Polymers have permanent deformation because they are _____

A

viscoelastic

viscous component - disentanglement of molecules

44
Q

Metals are not viscoelastic, their plasticity does not depend on the time you apply a load, but ____

A

the magnitude of the load

45
Q

Pure metals are often not used in dentistry because

A

they are often too soft and ductile

46
Q

Why are alloys stronger than pure metals?

A

The movement of dislocations is more difficult when introducing a new metal in the pure metal structure

47
Q

What are the 4 types of solid alloys

A

solid solution
complete solid insolubility
partial solid insolubility
intermetallic compound

48
Q

solid solution alloy

A

perfect solubility

1 phase present - no separation

49
Q

What are the 2 types of solid solution alloy

A

substitutional

interstitial

50
Q

substitutional solid solution alloy

A

2 metals in alloy have same crystal lattice (unit cell) and similar atomic size
Similar chemical valency (same # electrons to share)
no rxn to form intermetallic compounds

51
Q

Which metals are used to alloy in dentistry? which kind of alloy do they form? why?

A

gold, copper, silver, platinum, palladium
substitutional solid solution alloy
All have fcc crystal structures and similar atom size

52
Q

interstitial solid solution alloy

A

atoms of one metal between crystal lattice of other metal

53
Q

Example of interstitial solid solution (dental)

A

Stainless steel - instruments, ortho wires

carbon atoms inside of iron crystal structure

54
Q

complete solid insolubility alloy

A

total incompatibility of 2 metals
like oil and water
rare

55
Q

partial solid insolubility alloy

A

Once initial solid solution is formed, on further cooling (specific conditions) - precipitation of a second phase occurs
= Same metals mixed in different quantities with different unit cells
Resulting alloy is STRONGER (harder, more brittle) because the 2nd phase pins the movement of the dislocations

56
Q

intermetallic compounds

A

compounds with specific and well defined stoichiometry/composition
MERCURY AMALGAMS

57
Q

You cannot really change the rigidity of a metal, but you can change the

A

strength

58
Q

We use metals in dentistry because metals can be both very ____ and ____

A

strong

tough

59
Q

metals used inthe mouth must be biocompatible, aka…

A

resistant to corrorsion in aggressive environment of mouth
NO release of metallic ions
Limits range of metals that can be used

60
Q

Which metallic alloys are used in dentistry?

A

Noble alloys - nonreactive
Stainless/passivated alloys - initially reactive then stop
mercury

61
Q

What are dental examples of noble alloys?

A

alloys based in:
gold
platinum
palladium

62
Q

Dental examples of stainless/passivated alloys

A

stainless steel
chromium based
titanium based

63
Q

List the applications of alloys in dentistry

A 
amalgam
inlays, crowns, bridges, dentures
bonding to porcelain
wires, brackets, bands
implants
instruments

Biomaterials Exam 1 (7 decks)

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