Gold materials (5) Flashcards
Metallic Bonding major characteristics
Loosely bound or free valence electrons that form a “gas” and crystalline arrangements of ionic cores
Elements with similar valence electron configurations…
Have similar properties
Schematic solidification of metallic materials
Grains are microscopic single crystals
Grain boundaries are the last regions to solidify and contain higher concentrations of impurity atoms
Microstructure of cast gold
Polishing scratches and casting porosity are visible
Iron atoms at ______ temperatures have cubic crystalline structure
low
Titanium atoms at ______ temperatures have cubic crystaline structure
high
Simple Cubic Structure
Unit cell on corners
Body-centered cubic structure
Unit cell on corners and in center
Face-centered cubic structure
Unit cell on corners and in the center of each face
Unit cell
Smallest repeating potion of a 3D crystal cells
Defined by the axial lengths and angles
Dislocations move along slip planes under what action?
Shear stress
Dislocation movement is blocked where?
Grain boundaries, since slip plane does not extend into adjacent grain
Elastic modulus
The change in stress with an applied strain
Proportional limit
Up to this point, stress and strain are proportional
Yield strength
The stress point at which a material begins to form plastically
Ultimate tensile strength
The maximum stress a material can take before breaking
Ductility
A materials ability to deform under tensile stress
Properties of gold
Most noble and corrosion-resistnt metal
Not tarnished by air or water, and does not dissolve in HCl, H2SO4, and HNO3
Can be etched by aqua regia
Too weak for dental restorations unless other allowing elements are used
Melts at 1063
Properties of noble metals
Do not form stable oxides at room temp
Lowest tendency to lose electrons and become positive ions
What are the noble metals?
Gold Platinum Palladium Iridium Ruthenium Rhodium Osmium
Precious metal classification
Based on metal price, not electrochemistry
T/F - Relatively common and inexpensive metals become precious when very high purity is required?
True
Carat (k)
Parts in 24, with pure gold being 24k
Sometimes used to describe dental alloys, but provides no information about other elements
Fineness
Parts in 1000 with pure gold being 1000
Used for specification of dental solders
