Dental Alloys Flashcards
pure gold is – for use in the mouth
too soft
– form natural barrier to the movement of dislocations
grain boundaries
solute atom – directly for the solvent atom at the normal lattice site of the crystal
substitutes
alloys are liquid – liquidous line
above
– can crystalize at a constant temp (have a melting point) but not over a range of temp
partial solid solution
defect known as – weakens the crystalline structure
dislocation
dislocations are frequent in – such as gold
face centered cubic (FCC)
FCCs:
Ag, Au, Cu, Pt, Pd,
why is a fine grain desirable in a dental metal
high strength
but
high corrosion
low ductility
rate of cooling controls –
grain size
few nuclei, larger grains –
slow cooling
more nuclei, smaller grains from –
rapid cooling and add grain refiners
restricting dislocation motion makes material –
stronger
3 ways to restrict dislocation
control grain size, alloying, strain hardening
gold crown alloy: parent atom = gold (95%), common substitute atom
Cu
substitute atoms have same –
crystal structure
atomic size of parent and substitute atoms are within – of each other
15%
parent and substitute atoms must have same –
valency
alloys are solid – the solidus line
below
alloys are – between the liquids and solidus lines
mixture of solid and liquid
wide melting ranges make – difficult to cast
alloys
examples of wide melting ranges
Au-Ag-Pt
Ag-Pd
partial solid solution: liquids and solidus lines meet at –
eutectic composition
partial solid solution behaviors like a – at eutectic composition
pure metal
alloy at eutectic composition
eutectic alloy
eutectic alloy has a melting temp –
lower than either pure components
eutectic alloy’s – can be utilized to form low melting temp materials such as solders to join other metals
low melting pt
