Pres Res: Metals

Question 1

What are characteristics of metal?

Answer 1

• Luster
• Good thermal and electrical conductors
• High fracture toughness
• Stronger, more ductile, and denser than nonmetals

Question 2

What is the general bonding and structure of metals?

Answer 2

Metallic bonding

Crystalline structure

Question 3

What are the noble metals in dentistry?

Answer 3

PROGRIP
Palladium
Ruthenium
Osmium
Gold
Rhodium
Iridium
Platinum

Question 4

What are the 3 major noble metal used in dentistry?

Answer 4

Gold (Au), Palladium (Pd), and Platinum (Pt).

Question 5

What has a greater tendency to corrode in the mouth, noble metals, or base metals?

Answer 5

Base metals

Question 6

High noble alloys composition:

Answer 6

Gold > 40% weight

Noble metal content > 60% weight

Question 7

Titanium and Titanium alloys composition:

Answer 7

Titanium is > 85% weight

Question 8

Noble alloys composition:

Answer 8

Noble metal content is > 25 % weight

Question 9

Predominantly Base Alloys composition:

Answer 9

Noble metal content < 25% weight

Question 10

Type I alloy:

Answer 10

Soft
Sustainable stress is low
No occlusion
Ex: Inlays

Question 11

Type II alloy:

Answer 11

Medium
Sustainable stress is moderate
Light occlusion
Ex: onlays and inlays

Question 12

Type III alloy:

Answer 12

Hard
Sustainable stress is high
Full occlusion
Ex: Crowns, Short-span fixed partial dentures

Question 13

Type IV alloy:

Answer 13

Extra-Hard
Sustainable stress is very high
Ex: thin veneer crowns, long-span fixed partial dentures, removable partial dentures.

Question 14

Type of nucleation for a pure metal: Solid forms from the liquid, sometimes requires “supercooling” (line dips below MP/Solidification temp)

Answer 14

Homogeneous Nucleation

Question 15

Type of nucleation for a pure metal: Walls of container or impurity particles catalyze nucleation

Answer 15

Heterogeneous nucleation

Question 16

Do alloys have a melting point or melting range?

Answer 16

Melting range
(Some very specific alloy comps. have a mp)

Question 17

Rapid cooling produces more or less nuclei, smaller or larger grains?

Answer 17

More Nuclei

Smaller grains

Question 18

Slow cooling produces more or less nuclei, smaller or larger grains?

Answer 18

Fewer Nuclei

Larger grains

Question 19

Finer grain size vs. larger grain: yield strength, composition, and is it corrosive

Answer 19

Increase yield strength
Composition uniformity
Corrosion Resistance

Question 20

What are the types of microstructures?

Answer 20

Equiaxed- common for casting alloys

Dendritic

Question 21

Solid Solutions of Metals: amount “in solution” depends on:

Answer 21

1. Size (similar sizes= substitution solubility)
2. Crystal structure (greater if same)
3. Valence (greater if same charge)
4. Chemical reactivity (Nobles with nobles, base metals with base metals).

Question 22

Eutetic point:

Answer 22

Liquid solidifies into two solid phases.

Question 23

What are the 4 strengthening mechanisms of metals?

Answer 23

1. Solid Solution Strengthening
2. Strain or Work Hardening (or Cold Working)
3. Precipitation Hardening
4. Transformation Strengthening

Question 24

Solid Solution Strengthening:

Answer 24

Higher strength and hardness
Less ductile than either pure metal
Melting range, melt below highest melting point
Higher corrosion resistance than multi-phase alloys

Question 25

Strain Hardening (cold working)

Answer 25

Strength and hardness increase
Ductility decreases
Increasingly becomes more difficult to shape
Heat treatment to regain workability

Question 26

Precipitation Hardening of Metals

Answer 26

Solute atoms are not dissolved but form separate 2nd phase particles dispersed in the matrix.

Question 27

Transformation Strengthening Of Metals:

Answer 27

Change in morphology of the lattice structure which occurs upon heating and cooling (FCC to BCC).