Brantley: Metals and Alloys

Question 1

The crystalline structure of metals refers to the atomic arrangement that forms ______ repeating pattern during _______.

Answer 1

3D

Solidification

Question 2

Metals have ____ electrical and thermal conductivity due to the presence of loosely bound or free valence electrons.

Answer 2

high

Question 3

Metals have the ability to undergo permanent deformation from movement of dislocations at the atomic level. The two important types of deformation are:

Answer 3

1. Ductility

2. Malleability

Question 4

What are the two major characteristics of metallic bonding?

Answer 4

1. Loosely bound or free valence electrons form a gas

2. Crystalline arrangement of ionic cores

Question 5

During solidification of metals, the ____ ________ are the last regions to solidify, have greater atomic disorder, and contain higher concentrations of impure atoms.

Answer 5

Grain Boundaries

Question 6

A _____ _____ is the smallest repeating portion of the 3D crystal structure.

Answer 6

Unit Cell

Question 7

Unit cells are defined by the axial lengths and angles. What are the three important unit cell arrangements?

Answer 7

1. Simple Cubic
2. Body-Centered Cubic
3. Face-Centered Cubic

Question 8

Nobel metals take on which cubic structure (unit cell arrangement)?

Answer 8

Face Centered Cubic

Question 9

At high temperatures, which cubic structure do iron atoms hold?

Answer 9

Face Centered Cubic

Question 10

At low temperatures, which cubic structure do iron atoms hold?

Answer 10

Body Centered Cubic

Question 11

Which kind of movement provides a mechanism for permanent deformation of metals?

Answer 11

Movement of dislocations

Question 12

Dislocations move along ____ ______ under action of shear stress.

Answer 12

Slip Planes

Question 13

True or False: Dislocation movement is blocked at grain boundaries.

Answer 13

True: Slip planes do not extend into adjacent grains, and therefore dislocation is blocked at grain boundaries

Question 14

______ is calculate as a quotient of length change and original gauge length.

Answer 14

Strain

Question 15

_______ is calculated as applied force divided by original cross-section area in center of gauge section.

Answer 15

Stress

Question 16

Mechanisms for strengthening metals are based on impeding the movement of ________.

Answer 16

Dislocations

Question 17

What are some strategies for strengthening metals?

Answer 17

1. Decrease grain size (more grain boundaries)
2. Form alloys with other elements
3. Work Hardening
4. Formation of precipitates in microstructure (need heat*)
5. Regions of ordered structure within disorder (need heat*)

Question 18

When some strategy is applied to strengthen a metal, generally there is an increase in hardness and a decrease in __________.

Answer 18

Ductility

Question 19

True or False: Recrystallization of a cast dental alloy is possible without sufficient permanent deformation.

Answer 19

FALSE. permanent deformation comes with recrystallization

Question 20

What are two important properties of Gold?

Answer 20

1. Not tarnished by air or water, and does not dissolve in HCl, H2SO4, or HNO3
2. Can be etched by aqua regia

Question 21

____ is too weak for dental restorations unless other alloying elements are used.

Answer 21

Gold

Question 22

What are the three most important noble metals in dentistry?

Answer 22

Gold
Platinum
Palladium

Question 23

Which metal cannot be classified as a noble metal in the oral environment?

Answer 23

Silver

forms black AgS

Question 24

Classification of precious metals is based upon ____ _____ and not electrochemistry.

Answer 24

Unit Price

Question 25

True or False: Common and inexpensive metals can become "precious" when very high purity is acquired.

Answer 25

True

Question 26

What is the difference between carats and fineness when concerned with Gold purity?

Answer 26

Carat (k) = parts in 24 with pure gold -Used to describe metal alloys Fineness = parts in 1000 with pure gold -Used for specification of dental solders

Question 27

What is the issue with using "carat" to describe dental alloys containing gold?

Answer 27

The carat describes parts of gold (out of 24) but it does NOT provide any information regarding other elements within the alloy

Question 28

How many ounces are in 1 lb Avoirdupois?

Answer 28

16 ounces (this is the common US system)

Question 29

How many ounces are in 1 lb Troy?

Answer 29

12 ounces (this is used for Nobel Metals)

Question 30

How many ounces are in 1 lb Troy?

Answer 30

12 ounces (this is used for Nobel Metals)

Question 31

One Troy ounce is equal to how many penny weights?

Answer 31

1 Troy Ounce = 20 dwt (penny weight)

Question 32

Nobel metals are typically packaged in ___ dwt or ____dwt pieces. What does "dwt" stand for?

Answer 32

1 2 Penny weight

Question 33

True or False: Instability of the economy causes the price of gold to rise.

Answer 33

True in 2012: Gold was $1710 per oz in 2014: Gold was $1197 per oz

Question 34

True or False: Instability of the economy causes the price of gold to rise.

Answer 34

True in 2012: Gold was $1710 per oz in 2014: Gold was $1197 per oz

Question 35

What is coin gold? How does its hardness compare to that of pure/cast gold?

Answer 35

Coin Gold is a combination of Silver, Gold, and Copper | Coin is much HARDER than pure gold

Question 36

How does elongation of coin gold compare to that of pure/cast gold?

Answer 36

Elongation is the same for both pure and coin gold

Question 37

True or False: Type I-IV high gold casting alloys were used in dental castings, but the compositions used now are much higher gold.

Answer 37

False. | Lower-Gold compositions are now used

Question 38

True or False: The ADA specification for No.5 dental casting alloys has been withdrawn and the current standard is ISO 22674.

Answer 38

True

Question 39

What are four of the alloy selection factors?

Answer 39

Cost of the metal per pennyweight Burnishability Solderability Experience of the dental Lab

Question 40

Within ISO classification of Casting Alloys, there are types ____ to ______. Which types are used only for very low and low stress bearing restorations?

Answer 40

Types 0-5 Very Low Stress: Type 0 Low Stress: Type 1

Question 41

Which types of Casting Alloys are most commonly used?

Answer 41

Type 2 and Type 3

Question 42

In casting alloys, which metal(s) provides ductility and tarnish/corrosion resistance?

Answer 42

Gold

Question 43

In casting alloys, which metal(s) is the principal element for hardening and strengthening but could reduce corrosion-resistance if exceeding 12%?

Answer 43

Copper - Want for hardness - Too much = corrosion/tarnish

Question 44

In casting alloys, which metal(s) counteracts the color effect of copper and is an economical substitute for gold?

Answer 44

Silver

Question 45

In casting alloys, which metal(s) acts as an oxygen scavenger during melting to minimize oxidation of other elements and improves castability?

Answer 45

Zinc

Question 46

In cast alloys, which metal(s) provide tarnish resistance and strength but can substantially increase alloy melting temperature?

Answer 46

Platinum | Palladium

Question 47

Unit cells for disordered AuCu3 are _______ and unit cells for ordered AuCu3 are _______.

Answer 47

disordered: fcc (face centered cubic) ordered: simple cubic

Question 48

Board question: In Gold Casting Alloys, Small amounts of _____ and ______ may be present to provide hardening and strengthening.

Answer 48

Indium | Gallium

Question 49

Very small amounts of ______ are generally incorporated to provide grain refinement.

Answer 49

iridium

Question 50

What does "grain refinement" mean for gold casting alloys?

Answer 50

Improves mechanical properties Improves compositional uniformity in microstructure Improves corrosion resistance

Question 51

Going from ISO Type 1 to Type 5, yield strength _____ and percent elongation after fracture (ductility) _______.

Answer 51

Strength Increases | Ductility Decreases

Question 52

Going from ISO Type 1 to Type 5, for Gold Alloys the amount of other elements will ____ and the amount of gold will _______.

Answer 52

Increase other elements | Decrease gold

Question 53

Going from ISO Type 1 to Type 5, the ease of adjustment and burnishability will _______.

Answer 53

Decrease

Question 54

True or False: Type 5 casting alloy is harder than Type 1 casting alloy.

Answer 54

True

Question 55

True or False: Type 5 casting alloy is easier to burnish than Type 1 casting alloy.

Answer 55

False

Question 56

"________ hardening" in Gold casting alloy is provided by copper, platinum, palladium, silver, and zinc.

Answer 56

Solid-Solution

Question 57

"________ hardening" in Gold casting alloy is provided by copper (sufficient amount must be present for transformation to occur).

Answer 57

Order

Question 58

_____ cooling through an appropriate temperature range enables ordering to occur (gold-copper phase).

Answer 58

Slow

Question 59

The "softened condition" from cooling rate that is too rapid for ordering transformation is referred to as _____ of casting.

Answer 59

Quenching

Question 60

A hardened condition that results from ________ transformation can be achieved through Bench-Cool or Furnace Heat-Treat casting.

Answer 60

ordering

Question 61

Boards: Ordered phase for traditional high-gold alloys (>70%) is _______ and for lower-gold (~50%) is ______.

Answer 61

AuCu | AuCu3

Question 62

Traditional high-gold alloy composition were approximately ____ Au (ISO Types 2/3/4). Whereas, reduced-gold alloys commonly used in dental clinics are _____ Au (ISO Type 3/4).

Answer 62

High Gold: 77% 74.5% 68.8% Reduced Gold: 46%

Question 63

The new economical Pd-Ag Alloy for widespread clinical use has a similar yellow shade as gold alloys but contains ____% gold.

Answer 63

2%