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BCS > Metals and alloys > Flashcards

Metals and alloys Flashcards

1
Q

Examples of metals and alloys in dentistry

A 
Amalgam - restorations
Cobalt chromium - dentures
Stainless steel - braces
Gold - restorations
Titanium -  implants
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2
Q

Metals in amalgams

A

Ag/Sn/Cu alloy and Hg

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3
Q

Metals in inlays/ onlays

A

Au alloys, Pd alloys

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4
Q

Metals in crowns

A

Stainless steel, Au alloys, Pd alloys, Ni/Cr alloys

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5
Q

Metals in bridges

A

Au allots, Pd alloys, Ni/Cr alloys

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6
Q

Metals in dentures

A

Co/Cr alloys, stainless steel

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7
Q

Metals in dental impants

A

Titanium

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8
Q

What is a metal?

A

A crystalline material held together by metallic bonds (free electrons and cation)

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9
Q

Compare crystal structures

A

Face centred cubic (packing factor 0.74)

Body centred cubic (packing factor 0.6)

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10
Q

Metal microstructure

A

(Usually) polycrystalline structure consisting of grains and grain boundaries

  • Must polish and etch to see this, creates contrast
  • Liquid: nuclei of crystallisation
  • Solid: grain and grain boundaries (frozen)
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11
Q

Which metal are used in their pure form in dentistry

A

Gold, platinum and titanium

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12
Q

Types of alloys

A
  • Substitutional solid solutions
  • Interstitial solid solutions
  • Intermetallic compounds
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13
Q

Subsitutional solid solutions

A
  • diff atoms have same valency with same crystal structure
  • atomic size within 15%
    e. g. Au and Cu
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14
Q

Interstitial solid solutions

A
  • solute atom ≤ solvent atom
  • solute atoms occupy space between solvent atoms
  • distortion of lattice occurs to accomodate extra atoms
  • e.g. Fe and C
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15
Q

Intermetallic compounds

A
  • Formed when 2 or more metals combine with discrete composition/ stochiometric ratio
  • e.g. amalgam: contains silver/tin compound (Ag3Sn) and copper/ tin compound (Cu6Sn5)
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16
Q

What is a phase?

A

A homogenous physically distinct part of a system that is separated from other parts by definite physical boundary
-alloys can be single or multiple phase

17
Q

Bonds in metals

A

Metallic bonds can be weak (e.g. Hg) or strong (e.g. Ni)

18
Q

What is a phase diagram?

A

Means of presenting phases in an allot graphically, depending on composition and T

19
Q

Difference in cooling curve for pure metal and alloy

A

Alloy has phase of liquid + solid

Pure metal goes from liquid straight to solid

20
Q

Creation of phase diagram

A

100% metal A + melting T (Tm)
Metal A and B + liquid and solid zone
100% metal B + Tm
Join up dots

21
Q

What is the eutectic point?

A

The one T where the alloy acts like a pure metal (changes from solid to liquid)

22
Q

Learn phase diagrams in word doc

A

LEARN PHASE DIAGRAMS IN WORD DOC

BCS (35 decks)

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