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Sp 15- Fixed Restorative Final > Brantley: Metals and Alloys > Flashcards

Brantley: Metals and Alloys Flashcards

1
Q

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

A

3D

Solidification

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2
Q

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

A

high

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3
Q

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

A
  1. Ductility

2. Malleability

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4
Q

What are the two major characteristics of metallic bonding?

A
  1. Loosely bound or free valence electrons form a gas

2. Crystalline arrangement of ionic cores

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5
Q

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

A

Grain Boundaries

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6
Q

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

A

Unit Cell

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7
Q

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

A
  1. Simple Cubic
  2. Body-Centered Cubic
  3. Face-Centered Cubic
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8
Q

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

A

Face Centered Cubic

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9
Q

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

A

Face Centered Cubic

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10
Q

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

A

Body Centered Cubic

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11
Q

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

A

Movement of dislocations

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12
Q

Dislocations move along ____ ______ under action of shear stress.

A

Slip Planes

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13
Q

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

A

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

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14
Q

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

A

Strain

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15
Q

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

A

Stress

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16
Q

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

A

Dislocations

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17
Q

What are some strategies for strengthening metals?

A
  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*)
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18
Q

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

A

Ductility

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19
Q

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

A

FALSE. permanent deformation comes with recrystallization

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20
Q

What are two important properties of Gold?

A
  1. Not tarnished by air or water, and does not dissolve in HCl, H2SO4, or HNO3
  2. Can be etched by aqua regia
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21
Q

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

A

Gold

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22
Q

What are the three most important noble metals in dentistry?

A

Gold
Platinum
Palladium

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23
Q

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

A

Silver

forms black AgS

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24
Q

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

A

Unit Price

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25
Q

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

A

True

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26
Q

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

A

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

27
Q

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

A

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

28
Q

How many ounces are in 1 lb Avoirdupois?

A

16 ounces (this is the common US system)

29
Q

How many ounces are in 1 lb Troy?

A

12 ounces (this is used for Nobel Metals)

30
Q

How many ounces are in 1 lb Troy?

A

12 ounces (this is used for Nobel Metals)

31
Q

One Troy ounce is equal to how many penny weights?

A

1 Troy Ounce = 20 dwt (penny weight)

32
Q

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

A

1
2
Penny weight

33
Q

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

A

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

34
Q

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

A

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

35
Q

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

A

Coin Gold is a combination of Silver, Gold, and Copper

Coin is much HARDER than pure gold

36
Q

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

A

Elongation is the same for both pure and coin gold

37
Q

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

A

False.

Lower-Gold compositions are now used

38
Q

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

A

True

39
Q

What are four of the alloy selection factors?

A

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

40
Q

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

A

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

41
Q

Which types of Casting Alloys are most commonly used?

A

Type 2 and Type 3

42
Q

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

A

Gold

43
Q

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

A

Copper

  • Want for hardness
  • Too much = corrosion/tarnish
44
Q

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

A

Silver

45
Q

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

A

Zinc

46
Q

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

A

Platinum

Palladium

47
Q

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

A

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

48
Q

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

A

Indium

Gallium

49
Q

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

A

iridium

50
Q

What does “grain refinement” mean for gold casting alloys?

A

Improves mechanical properties
Improves compositional uniformity in microstructure
Improves corrosion resistance

51
Q

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

A

Strength Increases

Ductility Decreases

52
Q

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

A

Increase other elements

Decrease gold

53
Q

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

A

Decrease

54
Q

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

A

True

55
Q

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

A

False

56
Q

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

A

Solid-Solution

57
Q

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

A

Order

58
Q

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

A

Slow

59
Q

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

A

Quenching

60
Q

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

A

ordering

61
Q

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

A

AuCu

AuCu3

62
Q

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).

A

High Gold:
77% 74.5% 68.8%

Reduced Gold:
46%

63
Q

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

A

2%

Sp 15- Fixed Restorative Final (10 decks)

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