Metal Structures (Brantley) Flashcards
What atomic structure does gold, silver, copper nickel etc form?
Face centered cubic
What are some properties of metal?
- atoms form 3d repeating pattern during solidification
- high electrical/heat conductivity
- ability to undergo permanent deformation
- form positive ions in solution
- opaque
- non esthetic
What is a unit cell?
The smallest repeating portion of the 3d crystal structure
What are the types of unit cell?
- simple cubic
- body centered cubic
- face centered cubic
- hexagonal close packed
What metals have hexagonal close packed structure?
Titanium at low temp and zinc
T or F metals can be permanently deformed
T- they sure can
What curve is used to assess metal strength?
Stress strain curve
What are some properties of gold?
- most noble and corrosion resistant metal
- most ductile and malleable metal
- too weak for dental use unless mixed w alloy
- very high melting temp 1063 degrees C
- not tarnished by air
- can be etched by Aqua Regina
T or F: silver is a noble metal in oral environment
False: silver is NOT a noble metal in oral environment
What metal is added into an alloy to increase hardness?
Copper
What is the ISO standard mechanical property requirements?
- offset yield strength minimum
- minimum percentage elongation after fracture
What are some alloy selection factors?
- cost of metal per pennyweight
- burnish ability
- solderability
- experience of dental lab
What percentage of dental restoration is gold?
50
What are two other important elements in gold casting alloys?
- Indium and gallium: hardening
- iridium: grain refinement
What is the gold trend from type 1 to type 5 alloys?
Type 1 to 5 means less gold and more hard but lower melting point
What process on casting makes the allow more soft?
Quenching!
What alloy is currently being used in the clinic that replaced Midas to to its better properties?
Argen
