Brantley: Metals and Alloys Flashcards
The crystalline structure of metals refers to the atomic arrangement that forms ______ repeating pattern during _______.
3D
Solidification
Metals have ____ electrical and thermal conductivity due to the presence of loosely bound or free valence electrons.
high
Metals have the ability to undergo permanent deformation from movement of dislocations at the atomic level. The two important types of deformation are:
- Ductility
2. Malleability
What are the two major characteristics of metallic bonding?
- Loosely bound or free valence electrons form a gas
2. Crystalline arrangement of ionic cores
During solidification of metals, the ____ ________ are the last regions to solidify, have greater atomic disorder, and contain higher concentrations of impure atoms.
Grain Boundaries
A _____ _____ is the smallest repeating portion of the 3D crystal structure.
Unit Cell
Unit cells are defined by the axial lengths and angles. What are the three important unit cell arrangements?
- Simple Cubic
- Body-Centered Cubic
- Face-Centered Cubic
Nobel metals take on which cubic structure (unit cell arrangement)?
Face Centered Cubic
At high temperatures, which cubic structure do iron atoms hold?
Face Centered Cubic
At low temperatures, which cubic structure do iron atoms hold?
Body Centered Cubic
Which kind of movement provides a mechanism for permanent deformation of metals?
Movement of dislocations
Dislocations move along ____ ______ under action of shear stress.
Slip Planes
True or False: Dislocation movement is blocked at grain boundaries.
True: Slip planes do not extend into adjacent grains, and therefore dislocation is blocked at grain boundaries
______ is calculate as a quotient of length change and original gauge length.
Strain
_______ is calculated as applied force divided by original cross-section area in center of gauge section.
Stress
Mechanisms for strengthening metals are based on impeding the movement of ________.
Dislocations
What are some strategies for strengthening metals?
- Decrease grain size (more grain boundaries)
- Form alloys with other elements
- Work Hardening
- Formation of precipitates in microstructure (need heat*)
- Regions of ordered structure within disorder (need heat*)
When some strategy is applied to strengthen a metal, generally there is an increase in hardness and a decrease in __________.
Ductility
True or False: Recrystallization of a cast dental alloy is possible without sufficient permanent deformation.
FALSE. permanent deformation comes with recrystallization
What are two important properties of Gold?
- Not tarnished by air or water, and does not dissolve in HCl, H2SO4, or HNO3
- Can be etched by aqua regia
____ is too weak for dental restorations unless other alloying elements are used.
Gold
What are the three most important noble metals in dentistry?
Gold
Platinum
Palladium
Which metal cannot be classified as a noble metal in the oral environment?
Silver
forms black AgS
Classification of precious metals is based upon ____ _____ and not electrochemistry.
Unit Price
True or False: Common and inexpensive metals can become “precious” when very high purity is acquired.
True
What is the difference between carats and fineness when concerned with Gold purity?
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
What is the issue with using “carat” to describe dental alloys containing gold?
The carat describes parts of gold (out of 24) but it does NOT provide any information regarding other elements within the alloy
How many ounces are in 1 lb Avoirdupois?
16 ounces (this is the common US system)
How many ounces are in 1 lb Troy?
12 ounces (this is used for Nobel Metals)
How many ounces are in 1 lb Troy?
12 ounces (this is used for Nobel Metals)
One Troy ounce is equal to how many penny weights?
1 Troy Ounce = 20 dwt (penny weight)
Nobel metals are typically packaged in ___ dwt or ____dwt pieces. What does “dwt” stand for?
1
2
Penny weight
True or False: Instability of the economy causes the price of gold to rise.
True
in 2012: Gold was $1710 per oz
in 2014: Gold was $1197 per oz
True or False: Instability of the economy causes the price of gold to rise.
True
in 2012: Gold was $1710 per oz
in 2014: Gold was $1197 per oz
What is coin gold? How does its hardness compare to that of pure/cast gold?
Coin Gold is a combination of Silver, Gold, and Copper
Coin is much HARDER than pure gold
How does elongation of coin gold compare to that of pure/cast gold?
Elongation is the same for both pure and coin gold
True or False: Type I-IV high gold casting alloys were used in dental castings, but the compositions used now are much higher gold.
False.
Lower-Gold compositions are now used
True or False: The ADA specification for No.5 dental casting alloys has been withdrawn and the current standard is ISO 22674.
True
What are four of the alloy selection factors?
Cost of the metal per pennyweight
Burnishability
Solderability
Experience of the dental Lab
Within ISO classification of Casting Alloys, there are types ____ to ______. Which types are used only for very low and low stress bearing restorations?
Types 0-5
Very Low Stress: Type 0
Low Stress: Type 1
Which types of Casting Alloys are most commonly used?
Type 2 and Type 3
In casting alloys, which metal(s) provides ductility and tarnish/corrosion resistance?
Gold
In casting alloys, which metal(s) is the principal element for hardening and strengthening but could reduce corrosion-resistance if exceeding 12%?
Copper
- Want for hardness
- Too much = corrosion/tarnish
In casting alloys, which metal(s) counteracts the color effect of copper and is an economical substitute for gold?
Silver
In casting alloys, which metal(s) acts as an oxygen scavenger during melting to minimize oxidation of other elements and improves castability?
Zinc
In cast alloys, which metal(s) provide tarnish resistance and strength but can substantially increase alloy melting temperature?
Platinum
Palladium
Unit cells for disordered AuCu3 are _______ and unit cells for ordered AuCu3 are _______.
disordered: fcc (face centered cubic)
ordered: simple cubic
Board question: In Gold Casting Alloys, Small amounts of _____ and ______ may be present to provide hardening and strengthening.
Indium
Gallium
Very small amounts of ______ are generally incorporated to provide grain refinement.
iridium
What does “grain refinement” mean for gold casting alloys?
Improves mechanical properties
Improves compositional uniformity in microstructure
Improves corrosion resistance
Going from ISO Type 1 to Type 5, yield strength _____ and percent elongation after fracture (ductility) _______.
Strength Increases
Ductility Decreases
Going from ISO Type 1 to Type 5, for Gold Alloys the amount of other elements will ____ and the amount of gold will _______.
Increase other elements
Decrease gold
Going from ISO Type 1 to Type 5, the ease of adjustment and burnishability will _______.
Decrease
True or False: Type 5 casting alloy is harder than Type 1 casting alloy.
True
True or False: Type 5 casting alloy is easier to burnish than Type 1 casting alloy.
False
“________ hardening” in Gold casting alloy is provided by copper, platinum, palladium, silver, and zinc.
Solid-Solution
“________ hardening” in Gold casting alloy is provided by copper (sufficient amount must be present for transformation to occur).
Order
_____ cooling through an appropriate temperature range enables ordering to occur (gold-copper phase).
Slow
The “softened condition” from cooling rate that is too rapid for ordering transformation is referred to as _____ of casting.
Quenching
A hardened condition that results from ________ transformation can be achieved through Bench-Cool or Furnace Heat-Treat casting.
ordering
Boards: Ordered phase for traditional high-gold alloys (>70%) is _______ and for lower-gold (~50%) is ______.
AuCu
AuCu3
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).
High Gold:
77% 74.5% 68.8%
Reduced Gold:
46%
The new economical Pd-Ag Alloy for widespread clinical use has a similar yellow shade as gold alloys but contains ____% gold.
2%
