Gold materials (5)

Question 1

Metallic Bonding major characteristics

Answer 1

Loosely bound or free valence electrons that form a “gas” and crystalline arrangements of ionic cores

Question 2

Elements with similar valence electron configurations…

Answer 2

Have similar properties

Question 3

Schematic solidification of metallic materials

Answer 3

Grains are microscopic single crystals

Grain boundaries are the last regions to solidify and contain higher concentrations of impurity atoms

Question 4

Microstructure of cast gold

Answer 4

Polishing scratches and casting porosity are visible

Question 5

Iron atoms at ______ temperatures have cubic crystalline structure

Answer 5

low

Question 6

Titanium atoms at ______ temperatures have cubic crystaline structure

Answer 6

high

Question 7

Simple Cubic Structure

Answer 7

Unit cell on corners

Question 8

Body-centered cubic structure

Answer 8

Unit cell on corners and in center

Question 9

Face-centered cubic structure

Answer 9

Unit cell on corners and in the center of each face

Question 10

Unit cell

Answer 10

Smallest repeating potion of a 3D crystal cells

Defined by the axial lengths and angles

Question 11

Dislocations move along slip planes under what action?

Answer 11

Shear stress

Question 12

Dislocation movement is blocked where?

Answer 12

Grain boundaries, since slip plane does not extend into adjacent grain

Question 13

Elastic modulus

Answer 13

The change in stress with an applied strain

Question 14

Proportional limit

Answer 14

Up to this point, stress and strain are proportional

Question 15

Yield strength

Answer 15

The stress point at which a material begins to form plastically

Question 16

Ultimate tensile strength

Answer 16

The maximum stress a material can take before breaking

Question 17

Ductility

Answer 17

A materials ability to deform under tensile stress

Question 18

Properties of gold

Answer 18

Most noble and corrosion-resistnt metal
Not tarnished by air or water, and does not dissolve in HCl, H2SO4, and HNO3
Can be etched by aqua regia
Too weak for dental restorations unless other allowing elements are used
Melts at 1063

Question 19

Properties of noble metals

Answer 19

Do not form stable oxides at room temp

Lowest tendency to lose electrons and become positive ions

Question 20

What are the noble metals?

Answer 20

Gold
Platinum
Palladium
Iridium
Ruthenium
Rhodium
Osmium

Question 21

Precious metal classification

Answer 21

Based on metal price, not electrochemistry

Question 22

T/F - Relatively common and inexpensive metals become precious when very high purity is required?

Answer 22

True

Question 23

Carat (k)

Answer 23

Parts in 24, with pure gold being 24k

Sometimes used to describe dental alloys, but provides no information about other elements

Question 24

Fineness

Answer 24

Parts in 1000 with pure gold being 1000

Used for specification of dental solders

Question 25

1 lb Avoirdupois = (in oz)

Answer 25

16 oz

Question 26

1 lb Troy = (in oz)

Answer 26

12 oz

used for noble metals

Question 27

1 lb Troy = (in Avoirdupois)

Answer 27

0.823 lb Avoirdupois

Question 28

1 Troy oz = (in dwt)

Answer 28

20 dwt

Question 29

1 dwt = (in g)

Answer 29

1.555 g

Question 30

What is the minimum offset yield strength?

Answer 30

0.2%

Question 31

What does gold do in an alloy?

Answer 31

Provides ductility, tarnish, and corrosion resistance

Question 32

What does Copper do in a gold alloy?

Answer 32

Principal element for hardening and strengthening gold alloys

Question 33

What does Silver do in a gold alloy?

Answer 33

Counteracts the effect of copper on color and substitutes economically for gold without degrading mechanical properties

Question 34

What does platinum and palladium do in a gold alloy?

Answer 34

Also provide tarnish and corrosion resistance, as well as strengthening

Question 35

What does Zinc do in a gold alloy?

Answer 35

Oxygen scavenger during melting to minimize oxidation of other elements, and consider to improve cast ability or fluidity of molten alloy

Question 36

What happens to yield strength going from ISO Type 1 - Type 5?

Answer 36

Yield strength increases

Question 37

What happens to ductility going from ISO Type 1 to Type 5?

Answer 37

Ductility decreases