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
