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Biomaterials Exam 1 > Metals > Flashcards

Metals Flashcards

(63 cards)

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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
grain size/shape influences the ______ of metals
mechanical properties
26
A metal with _______ grains/crystals is stronger. why?
smaller finer - less coarse More grain boundaries/plane defects per volume
27
fibrous grain strucure of metals in obtained via ____
cold working
28
Elastic strain of metals
recoverable stretching of inter-atomic bonds on removal of force atoms return to their equilibrium position metallic bond acts as A SPRING
29
metallic bonds act as...
a spring
30
elasticity of metals depends mainy on...
the resistance of the metallic bond to be stretched
31
Sum of elastic deformation of metallic bonds accounts for...
the overall elastic deformation of the metallic material
32
Modulus of elasticity of a metal mainly depends on
the chemical nature of each metal | hardly depends on other structural features of the metal
33
Mechanism of plastic strain in metals
permanent | movement/slip of dislocations
34
The easier it is to create dislocations in a metal, the _____ it is
softer
35
How could you strengthen a metal?
treat/process metal to make dislocations difficult
36
How does cold working a metal change it?
Introduces more dislocations, more interaction between dislocations = harder to move them STRENGTHENS too much = brittle Lead to fibrous structure
37
Casting of a metal results in
equiaxed structure
38
Effects of recrystallization after cold working a metal
Further heating = reformation of equiaxed structure, elimination of dislocations, erases deformation/cold working history of metal SOFTER
39
Effect of grain growth during metal processing
even more heating larger grains formed in same volume of metal less grain/crystal boundaries, less impediment of dislocation SOFTER
40
What are the steps in mechanical/thermal history (processing) of a metal
casting cold working recrystallization grain growth
41
metals are very tough because they can develop significant ____
plasticity - form/move dislocations
42
if dislocations are difficult to move, the metal will be more ____, less ____
brittle tough Like ceramics
43
Polymers have permanent deformation because they are _____
viscoelastic | viscous component - disentanglement of molecules
44
Metals are not viscoelastic, their plasticity does not depend on the time you apply a load, but ____
the magnitude of the load
45
Pure metals are often not used in dentistry because
they are often too soft and ductile
46
Why are alloys stronger than pure metals?
The movement of dislocations is more difficult when introducing a new metal in the pure metal structure
47
What are the 4 types of solid alloys
solid solution complete solid insolubility partial solid insolubility intermetallic compound
48
solid solution alloy
perfect solubility | 1 phase present - no separation
49
What are the 2 types of solid solution alloy
substitutional | interstitial
50
substitutional solid solution alloy
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
Which metals are used to alloy in dentistry? which kind of alloy do they form? why?
gold, copper, silver, platinum, palladium substitutional solid solution alloy All have fcc crystal structures and similar atom size
52
interstitial solid solution alloy
atoms of one metal between crystal lattice of other metal
53
Example of interstitial solid solution (dental)
Stainless steel - instruments, ortho wires | carbon atoms inside of iron crystal structure
54
complete solid insolubility alloy
total incompatibility of 2 metals like oil and water rare
55
partial solid insolubility alloy
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
intermetallic compounds
compounds with specific and well defined stoichiometry/composition MERCURY AMALGAMS
57
You cannot really change the rigidity of a metal, but you can change the
strength
58
We use metals in dentistry because metals can be both very ____ and ____
strong | tough
59
metals used inthe mouth must be biocompatible, aka...
resistant to corrorsion in aggressive environment of mouth NO release of metallic ions Limits range of metals that can be used
60
Which metallic alloys are used in dentistry?
Noble alloys - nonreactive Stainless/passivated alloys - initially reactive then stop mercury
61
What are dental examples of noble alloys?
alloys based in: gold platinum palladium
62
Dental examples of stainless/passivated alloys
stainless steel chromium based titanium based
63
List the applications of alloys in dentistry
``` amalgam inlays, crowns, bridges, dentures bonding to porcelain wires, brackets, bands implants instruments ```

Biomaterials Exam 1 (7 decks)

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