Test One: Properties Of Metals And Alloys Flashcards
What atomic reasons are there for metallic properties?
Lattice structure and cloud of valence electrons
Definition of a metal
an element that forms positive ions in solutions/they lose electrons in solutions
What are some properties of metals?
Luster from electrons, high density, strength, and ductility, and excellent conductivity
Why are gold and platinum used as pure metals in dentistry?
do not tend to ionize readily, have high melting temperatures and are malleable
What are noble metals?
Noble metals have low corrosion in the mouth. Examples: gold, platinum, paladium, ruthenium, rhodium, iridium, and osmium
What are base metals?
Metals that have higher corrosion in the mouth. Examples: silver, copper, zinc, indium, gallium, nickel, cobalt and chromium
What is the difference between corrosion and tarnish?
Corrosion is the irreversible loss of electrons and metal mass which leads to loss of properties. Tarnish is a buildup of a chemical film on the surface of a metal which dulls the luster or brightness of the surface.
What are the types of corrosion?
General corrosion- uniform loss of metal from the surface
Pitting corrosion- the localized loss of metal, common in base metal alloys which are naturally protected by a thin film oxide. The film locally breaks down causing the release of electrons from the metal surface. Galvanic corrosion- occurs when two or more metals with different electrode potential connected by an electrolyte. The metal that is less noble will corrode more than if it was in the solution by itself
Crevice corrosion- corrosion in a narrow space or joint
What is an alloy?
Mixture of two or more metals
What are the three types of alloys?
Solid Solutions-metals soluble in each other at room temp like Au, Ag, Cu for crowns
Eutectics- metals dissolve as liquids but not at room temp like AgCu phase of amalgam or plumbers solder (PbSn)
Intermetallic Compounds- compound with specific stoichiometry can ratio like Ag2Sn in amalgam
How do grains affect the material properties?
Grains form when the material is solidifying. Smaller grains have higher tensile strength and more uniform properties
How does phase affect alloys?
Single phase is when all areas have the same composition where there is generally a lower corrosion rate
Multiple phase alloys have many areas of diff compositions that have higher corrosion rate
How are alloys hardened?
Solid solution- second element added in a random position, increases hardness and tensile strength
Ordered solution- second element occupies a specific position which further increases strength and hardness
Dispersed phase- Fine second phase dispersed throughout first phase which increases strength and corrosion
Atomic vs weight composition of alloys
Weight composition is based on mass
Atomic composition is based on number of atoms
What is a wrought alloy and why is it important for dentistry?
Metal is cast then formed into another shape by rolling it into wrought form. These are used for ortho wire, Endo files, and rpd clasps
