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48 Cards in this Set
- Front
- Back
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What is metallic bonding?
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Metallic bonding is the electromagnetic interaction between delocalized electrons, called conduction electrons, and the metallic nuclei within metals. Understood as the sharing of "free" electrons among a lattice of positively-charged ions (cations),
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Dr. Brantley should us a picture of a Microstructure of Cast Gold Ingot Showing Equiaxed Grains - what are these?
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Equiaxed crystals are crystals that have axes of approximately the same length. Crystals of equal axial length have more planes on which to slip and thus have higher strength and ductility.
ductility is tensile strength related |
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What structure is gold like?
1. schematic face-centered cubic structure 2. schematic body-centered cubic structure 3. simple cubic |
1. face centered cubic is like the structure of gold
(side note: simple cubic is not used except for teaching) |
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What is mvt of edge dislocation?
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Dislocations move in response to an external stress
As soon as a critical shear stress is reached, the dislocation starts moving and deformation is no longer elastic but plastic, because the dislocation will not move back when the stress is removed. The example shows the movement of an idealized edge dislocation in a cubic primitive lattice (which does not exist in nature). The grey lines show the projection of the lattice planes, the dislocation line (red symbols) is perpendicular to the screen and bounds the extra lattice plane. The dislocation line moves on its glide plane and produces, upon leaving the crystal (and thus disappearing), an elementary step on the crystal surface. Note that after the dislocation disappeared, the crystal is completely stressfree. For macroscopic deformation in three dimensions, many dislocations have to move through the crystal. |
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T/F Distributions of dislocation is relatively uniform at small strains
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true
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T/F Cell walls of high dislocation density form at large strains
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true
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Stainless steel, becuse of its low stacking-fault energy, shows a more uniform distribution of dislcations at large strains.
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true
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What are these properties of? What metal?
- most noble and corrosion-resistant metal - most ductile and malleable metal - too weak for dental restorations unless other alloying elements are used - Melts at 1063 degrees C - Not tarnished by air or water, and does not dissolve in HCl, H2SO4, and HNO3 - Can be etched by aqua regia |
GOLD
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T/F Gold is noble AND precious
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treu
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_____ metals do not form stable oxides at room temp.
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noble
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noble metals have the _______ (lowest/highest) tenedency to lose electrons and become positive ions
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lowest
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There are 7 noble metals in oral environment. name them.
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gold, platinum, palladium, iridium, ruthenium, rhodium, and osmium
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What is the noble metal conent of dental alloys on manufacturer pakaging?
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Au + Pt + Pd
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______ is NOT a noble metal in oral environment. (what is an example of this?)
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Silver eg; black AgS formation
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How are precious metals classified?
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based upon unit metal price and not electrochemistry
(how rare is it?) relatively common and inexpensive metals become precious when very high purity is required |
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What is a Carat (K)?
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parts in 24 with pure gold = 24K
Sometimes used to describe dental alloys, but provides no information about other elements |
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What is Fineness and houw is it measured?
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parts in 1000 with pure gold = 1000 [Also express as a decimal - pure gold = 1.000]
Fineness used for specification of dental solders |
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When speaking of Avoirdupois and Tory Weight Systems.
1 lb Avoirdupois = ? [common US system] 1 lb Troy = ? [used for noble metals] 1 lb Troy = ? Avoridupois 1 Troy oz. = ? dwt penny weights 1 dwt = ? grams [Noble alloys are typically packaged in 1 dwt or 2 dwt pieces] |
When speaking of Avoirdupois and Tory Weight Systems.
1 lb Avoirdupois = ? [common US system] 1 lb Troy = 16 oz [used for noble metals] 1 lb Troy = .823 lb Avoridupois 1 Troy oz. = 20 dwt penny weights 1 dwt = 1.555 grams |
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What do you include in your 'triad cost' for making a metal crown?
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Metal (cheapest)
Lab fees Office Fees |
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With the Current approximate Unit metal prices - what is the most expensive -> least?
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Platinum - $930/oz
Gold - $850/oz Palladium - $180/oz Silver - $11/oz |
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What are the properties of Pure, 22K, and Coin Gold?
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Pure - Tensile Strength: 105 - breaks easily
22K - TS: 240 - middle Coin - TS: 395 - substantially stronger |
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What alloy is used for dental gold casting?
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Coin Gold and 22K gold formerly used for dental restorations...
Types I-IV high -gold casting alloys date from 1930's, but lower-gold composistions now used ANSI/ADA Specification No. 5 formerly had minimum (Au + Pt + Pd) but now deleted now expanded to include all casting alloys for all-metal restorations |
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The hardness of the alloys will never be as hard as the enamel (350), but can be as hard as dentin (180)
what are the strengths of the types? |
Type I - 59-90 - weakest
Type 2 - 90-120 3 - 120-150 4 150 min (quenched) nd 220 min. (hardened) - strongest |
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What is the elastic modulus?
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An elastic modulus, or modulus of elasticity, is the mathematical description of an object or substance's tendency to be deformed elastically (i.e., non-permanently) when a force is applied to it. The elastic modulus of an object is defined as the slope of its stress-strain curve in the elastic deformation region
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The ANSI/ADA now has specification no.5 that manufacturer's have to place certain items on the products which are?
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must specify weight percentages of 3 major elements, any noble metals not one of three major elements and any hazardous elements
Mechanical propert requirements: .1% yield strength, % elongation, and modulus of elasticity |
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What are these factors of?
Cost of metal per dwt burnishability solderability experience of the dental lab |
alloy selection factors
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What are the two major types used in an inlary or onlay?
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Type II - inlays and onlays subject to moderate stress
Type III - 3/4 crowns, full cast crowns, and short-span fixed partial dentures |
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What type is used becuase of it's highest stress items:
thin veneer crowns, long-span FPD's, and removable partial denture (RPD), framworks (obsolete) |
Type IV
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What are the roles of major element in Gold Casting Alloys
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Gold - provides ductility, tarnish and corrosion resistance
Copper - rincipal elemnt for ardening and strengthening Silver - counteracts effct of copper on color and substitutes economically for gold without degrading mechanical properties Platinum and Palladium - also provide tarnish and corrosion rsistance, as well as strengthening (limited amounts because small percentages substantially raise alloy melting temperature) Zinc oxygen scavenger during meltig to minimize oxidation of other elements, and considered to improve castability or fluidity of molten alloy. |
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How do solid solutions in metals work? (substitutional vs. interstitial)/
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substitutional solid solution - when full solute atoms completely replace solvent or matrix atoms
interstitial solid solution - no solvent matrix atoms are replaced solute atoms are found inbetween the atoms |
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T/F at high temperature - more random organization occurs.
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true
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What do the unit cells look like for ordered AuCu Phase[tetragonal structure] vs. disordered AuCu3 [fcc structure]
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ordered: copper is found at the 4 points of the cube and 2 inthe center of the top and bottom faces, gold is found in the center of the 4 side faces
Disordered: gold is found in the four corners and copper is centered at each face |
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Why would small amounts of indium and gallium be present in gold casting alloys?
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hardening and strengthening
- very small amounts (less than 100 ppm) of iridium or ruthenium are generally incorp. by manufacturers to provide grain refinement. |
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From Type I -> Type IV does the amount of gold in the alloy inc. or dec?
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decreases, strength inc. hardness inc.
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Does ductility inc./dec from Type I -> Type IV
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decreases occur in ductiltiy (eas of adjustment and burnishabiltiy for casting), melting temperature, and amount of gold
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The product "midas" contains what percentage of gold in it's composition? it's a type III
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not quite 50% -
Hardness: quenched - 160 hardness - 240 |
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Types II and IV alloys termed "heat-hardenable" becuase that have sufficient ____ for ordering reaction.
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copper
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Types I and II contain insufficient copper and cannot be ________ by heat treatment
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hardenend
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Hardening isa historic term - that means what?
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remembe that strength is increased along with hardness -
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In normal dental lab practice, gold casting alloys are not subject to ______ procedure.
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hardening
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When you quench an alloy do you harden or soften it?
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soften
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Solid solution hardening provided by ? (what elements)
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copper, platinum, palladium, silver and zinc
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Order hardening proivded by
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copper
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Grain size refinement (typically 100 ppm iridium) also improves compositional homogeneity and tarnsih and corrosion resistance - the smaller the grain the (harder/softer) material
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harder
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What are the 2 procedures done to harden alloy:
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bench - cool casting or furnace heat-treat casting after adjustments made
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ordered phase is AuCu for ____(high/low) gold alloys and AuCu3 is for ____ gold alloys.
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high
low |
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what is the effect of multiple castings on mechanical properties of Midas?
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the more you cast the lower the yield strength
tensile strength decreases percent elongation decreases as well |
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For the ordering transformation in gold casting alloys you need slow cooling through ordering temperature range - what does this represent on the gol-copper phase diagram
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"domes"
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