metal alloys Flashcards
Where are some metals and alloys in dentistry?
Amalgams- Ag/Sn/Cu alloy, Hg
Inlays/onlays- Au alloys, Pd alloys
Crowns- stainless steel, Au alloys, Pd alloys, Ni/Cr alloys
Bridges- Au alloys, Pd alloys, Ni/Cr alloys
Dentures- Co/Cr alloys, stainless steel
Dental implants- Ti
Stainless steel- iron, carbon, chromium, nickel
What is a metal?
Crystalline material held together by metallic bonds
Cations in lattice with a sea of electrons
What are different crystal structures?
FCC- face centred cubic (packing factor 0.74) eg. Ni, Cu, Au
BCC- body centred cubic (packing factor 0.60) eg. Cr, Mo, Ta
What does metal microstructure like?
Polycrystalline structure of grains and grain boundaries
Liquid freezes to solid-
Liquid has nuclei of crystallisation, which grow into crystals and grow until they hit other crystals forming grain boundaries
How do you look at metals under the microscope?
Etch in acid
The boundaries are high energy areas which are revealed w etch
Creates grain contrast depending on crystallographic orientation
What is an alloy?
Metals used in combination w other metals
Eg. Amalgams, stainless steel
What are the three types of alloys?
Substitutional solid solutions
Interstitial solid solutions
Intermetallic combounds
What is a substitutional solid solution?
Different atoms have SAME valency and crystal structure
Their atomic size is within 15%
Eg. Au and Cu
Require similar atomic radius and structure
What is an interstitial solid solution?
Solute atom is SMALLER than solvent atom
Solute occupies space between solvent
Distortion of lattice- accommodating extra atoms
Eg. Fe and C
What is an intermetallic compound?
Formed when two or more metals combine with a discrete composition/stoichiometric ratio
Eg. Amalgam
Ag3Sn and Cu6Sn5 compound
What is a phase?
Different crystal structures
A homogeneous physically distinct part of a system that’s separated from other parts by a definite physical boundary
What does an alloy have to do w phases?
Alloy can have a single or multiple phases
Can have distinctly different composition and different crystalline structures
What is a phase diagram?
Phases in alloy depend on composition and temperature
Phase diagram represents this
There’s a phase in between solid and liquid that is solid+liquid (range of temperatures for this)
This is divided by the liquidus and solidus lines
