Dr. Brantley (Metal Structures and Gold Alloys) Flashcards
type of unit cell used by gold and most other alloy materials
face-centered
what is responsible for permanent deformation?
schematic movement of edge location
- dislocations move along slip planes under stress
- blocked at grain boundaries
what should be done to strengthen materials?
- dec grain size
- incorporate other materials to form alloys
- work hardening (deform at room temp)
- form precipitates
- regions of ordered structure
when a strategy is put in place to strengthen a metal it generally increases ____ and decreases _____
- hardness
- ductility
what are some notable properties of gold?
- not tarnished by air or water (most corrosive resistant)
- most malleable and ductile
what metal is NOT a noble metal in the oral environment?
silver
what are precious metals?
based on unit metal price not electrochemistry
common metals can become precious in high purities
part in 24 with pure gold
carat(k)
part in 1000 with pure gold
fineness
*used for specification of dental solders
1 lb Troy = ___ oz (used for gold)
1 lb Avoirdupois = ____ oz
1 oz Troy = ____ dwt = 31.1 grams
- 12 (used for gold)
- 16
- 20 dwt
while coin gold and 22k gold were formerly used for dental restorations, what is the current standard for dental casting alloy?
ISO 22674 from types 0-5
- 0.2% offset yeild strength minimum
- minimum % elongation after fracture
what are the 4 main alloy selection factors?
- cost
- burnishability
- solderability
- experience of the dental lab
ISO classification that is very low stress-bearing restoration for small veneered one-surface inlays
type 0
ISO classification that is low stress-bearing single tooth restoration for veneered or unveneered one-surface inlays
type 1
ISO classification that is single tooth fixed restoration (crowns)
type 2
ISO classification that is multiple fixed restorations (bridges)
type 3
ISO classification that is composed of thin sections subjected to very high forces (RPDs, thin veneered crowns)
type 4
ISO classification that is appliances requiring combination of high stiffness and strength (thin RPDs)
type 5
element that provides ductility, tarnish (discolor), and corrosion resistance
gold
element that is the PRINCIPLE ELEMENT FOR HARDENING AND STRENGTHENING
copper
element that counteracts effects of copper on color and substitutes economically for gold w/o degrading mechanical properties
silver
element that is an oxygen scavenger during melting to minimize oxidation of other elements, and considered to improve cast ability or fluidity of molten alloy
zinc
type of unit cell for ordered AuCu3
simple cubic
type of unit cells for disordered AuCu3
face-centered
very small amounts of ____ give grain refinements of gold
iridium
what are the three trends going from ISO type 1 - 5
- inc in yield strength and dec in percentage elongation after fracture (inc hardness)
- increase in total other element besides gold
- dec ease of adjustment and burnish ability (makes sense bc less gold)
what is needed for proper ordering transformation to occur
slow cooling through temperature range
if it happens to fast (quenching) it will be too soft
