MEtals and Alloys Flashcards
what metals make up the “royal family”?
Rhodium, paladium, silver (not in mouth), osmium, iridium, platinum, and gold
are the “royal” faily as they do not corrode
what make up the new rich elements?
titanium, chromium, cobalt and nickel – not royal bc they corrode, but corrode only once and are stable
what make up the elements that work for the ryoal family?
copper and zinc– clean and strengthen
define alloy
a substance made by combining two or more metallic elements, esp to give greater strength or resistance to corrosion;
an alloy is produced by fusion of elements above their melting point
define precious metal
containing metals of high economic value;
define noble metal
precious metal that is resistant to tarnish
define high gold alloys
greater than 75% gold or other noble metals (type I-IV)
define medium gold alloys
25-75% gold or other noble metals; which means gold represent less than every other atom
define low gold alloys
less than 25% gold or any other noble metal
define gold substitute alloys
precious metal alloys that don’t contain gold
define base metal alloys
alloys not containing any precious metals for corrosion resistance, but generate a protective oxide film on their surface which prevents continuing corrosion
define carat
part of pure gold in the alloy out of 24; e.g. if gold is 24 caraat gold it is pure gold; if 18 carat, it is 75% pure gold
define fineness
parts per 1000 of gold; pure gold is 1000 fine, 75% gold is 750
define pennyweight
weight measuring 24 g; 1 pennyweight -= 1.555 g = 24 grains
why would gold be put in an alloy?
to offer corrosion resistance and increase ductility and malleability
why would copper be added to an alloy?
to increase hardness
why would silver be added to an alloy?
to counteract the orang ecolour of copper and also to reduce the melting temp; as well, it increases ductility and malleability
why would palladium be added into an alloy?
increase melting point, hardness, absorb H2 gas that can cause porosity in casting, reduce corrosion, as whitens gold
why would platinum be added to an alloy?
increase melting point, hardness, tensile strength, decrease coeff. of thermal expansion, and reduce corrosion
why would zinc be added to an alloy?
prevents oxidation by forming ZnO film during melting, increases fluidity; decreases surface tension (improves castability)
what are some high noble alloys?
noble metal not less than 60% wt an gold not less than 40%
- Au-Pt-Pd
- Au-Pd-Ag
- Au-Pd
what are some noble alloys?
min 25% noble metal
- Pd-Ag
- Pd-Cu-Gallium
- Pd-Ga
whata are some predominantly base ?
noble metal less than 25% wt
- Ni-Cr
what are some properites of high gold casting alloys?
from type I-IV: hardness, strength, ductility, and corrosion resistance
what influences the relewase of toxic element s from alloys?
- corrosion resistant ability
- alloy microstructure
what are some required characteristics of dental laloys?
- physical properties must meet a moinimum standard for the type of resto it’s being used for
- must have resisliency
- should be tarnish resistant
- should be tough
- should have good fatigue resistance
what are the typical properites of alloys?
- crystalline structures
- increased hardness (but not Hg)
- increase ultimate tensile strength
- increased ductility
- increased burnishability
- a melting RANGE
- good conduction (heat, electricity)
what is a unit cell?
the basic component of the crystalline structure of metals; attoms are arranged in either a simple cubic structure (unstable), FCC, BCC, or hexagonal close packed in PURE metals
FCC has HIGHER DUCTILITY whereas HCP has LOWER ductility
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which metals have an FCC config?
Au, Pd, Ag, Cu, Ni, Al
which metals have a BCC config?
Cr, Fe
which metals ahve anHCP config?
Ti, Co,Zn
what are the three possible outcomes when an alloy cools?
- solid sol’n –> metal are soluble with each other and cool to a homogenous structure; can have two types: substitutional (atoms replace one another in lattice) or interstital where one atom is smaller and fills the gaps between the larger atoms)
- compound (intermetallic) : when metals are sol as liquid but not as solids; heterogenous
- eutectic : unique atomic percentage ratio between the components– as each pure has its own distinct bilk lattice arrangement
elements of similar diameter mix well with each other as they can replace each other in their lattice structures; form a solid so;’n and exhibit solid solubility
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what is a multiphase alloy?
alloy formed of two or more elements which are present in amounts which exeed their solubility limit in one another; one or more phase will ppt out
what is a slip plane?
the plane along which the dislocation moves – move through lattice to form a new shape
what is elastic limit?
the stress required to initiate the movement of atoms within the lattice to new positions
define plastic defomation
application streess is greater than the elastic limit and causes material to be deformed permanently as a result of the dislocation movement
what are extra half planes?
dislocations – defects responsible for deformation
somehow connected to ductility idk
the amount of energy relquired to move dislocations through the crystal structure is related to the strength of the material
force required depends on:
- type of space lattice: cubic type is easiest to move
- grain size: small fine particles slip more easily)
- pure metals have fairly low strength hardness and proportional limit–easier to move
- alloys have high strength so dislocation is more difficult
what are CoCr alloys used for?
partial dentures and frameworks
what are NiCr alloys used for?
inlays, crowns, and bridges
what are Ag alloyds used for?
surgical splint
what are Ti and Ti alloys used for?
partial denture frameworks, crowns and bridges, inlays
the solid solution of an alloy depends on the alloy size, crystal structure, etc – e.g. metaals with a similar atomic diameter can replace each other in the lattice structure
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what are the different forms an alloy may take?
- pure metal phase
- solid solution
- intermetallic compound
the resistance to elastric strain is indicated by the high elastic modulus of metals
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define elastric strain in terms of lattice structure
elastic stretching of lattice–ALL atoms are shifted from their equilibrium positon by a FRACTION of their atomic spacing
study slide 21 and 22
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