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robbypowell's version from 2016-12-12 01:56

Corrosion

Question Answer
What is the Second Law of Thermodynamicsin a closed system, no processes will tend to occur that increase the net organization (or decrease the net entropy) of the system (or more simply put... things fall apart... entropy increases unless energy is applied to counteract it)
Define: the degradation of a material due to a reaction with its environmentthrough a chemical or electrochemical processCorrosion
_______ corrosion is the electrochemical action of two dissimilar metals in the presence of an electrolyte and an electron conductive path; it -occurs when dissimilar metals are in contact and the less noble metal will corrodeGalvanic corrosion
galvanic interaction between cast gold and amalgam is increased considerably when the amalgam contains _____Zinc
T/F: many of the corrosive reactions that occur, occur regardless of material typeTrue
T/F: most forms of corrosion only happen with materials that are very susceptibleFalse ("many of the corrosive reactions that occur, occur regardless of material type" most reaction types occur with all materials, its just a matter of the extent)
T/F: the level of degradation products generated for a material will depend on the esterase make-up of an individual's saliva in combination with the specific formulation of monomer components usedTrue
T/F: the level of degradation products generated for a material will is unrelated to salivary compositionFalse (affected by the esterase make-up of an individual's saliva in combination with the specific formulation of monomer components used)
What type of corrosion is produced by most direct chemical attacks (e.g., as by an acid)Uniform/General Corrosion
In Galvanic Corrosion... will the more or less noble metal corrode more?Less noble metal corrodes more
T/F: Galvanic interactions between dental restorative materials can be detected by patients and result in painTrue (called oral electrogalvanic pain or galvanic shock)
T/F: Galvanic interactions between dental restorative materials are too small to detected by patientsFalse (pain from this is called oral electrogalvanic pain or galvanic shock, and commonly results form interactions between gold and amalgam, especially amalgams containing zinc)
what type of corrosion is produced at the region of contact of metals with metals or metals with nonmetals, creating a reduction in pH and Cl- ions in the micro-environmentPitting Corrosion (aka Crevice Corrosion)
What are the "two essential factors" in the initiation and propagation of the crevice corrosion phenomenon?reduction in pH and increase in the concentration of chloride ions
T/F: Intergranular corrosion can be decreased by increasing grain sizeTrue (less area between grains)
T/F: Intergranular corrosion can be decreased by decreasing grain sizeFalse (increasing grain size, though, decreases this type of corrosion because less area between grains)
_______ is rapid corrosion that occurs at the interface between contacting, highly loaded metal surfaces when subjected to slight vibratory motionsFretting
Some believe that ______ corrosion is responsible for most of Ti release into tissuesFretting
_______ corrosion is the result of a combination of an aggressive chemical environment and high fluid-surface velocitieserosion corrosion
_________ is -rare form of corrosion found in copper alloys, gray cast iron, and some other alloys where the alloy loses the active component of the metal and retains the more corrosion resistant component in a porous "sponge" on the metal surfaceDealloying (also generalized form of preferential corrosion you use in resin bonding to Ni-Cr-Be)
__________ corrosion can take many forms and can be controlled by biocides or by conventional corrosion control methods, but is caused by microbes and their biofilm micro-environmentMicrobial Corrosion
_____ ______ corrosion occurs when two or more areas of a metal surface are in contact with different concentrations of the same solutionConcentration cell corrosion (accumulation of food debris can alter the microenvironment electrolyte altering corrosion)
Corrosion can be delayed by coating the surface with a ________ metalNoble (but if the coating is breached you will have a great galvanic cell)
A highly ________ restoration decreases surface defects and pits and makes a restoration more resistant to corrosionPolished
Passivating surface by treating with an electrochemical process is called ________Electroplating
what are the two types of stress that can contribute to Stress Corrosion (either independently or in combination)Applied Loads & Residual stress (from manufacturing)
____________ corrosion or corrosion fatigue is relevant for RPD's due to repeated removal and insertion and the pattern in grain boundaries from this repeated insertion and removalStress Corrosion
T/F: Zirconia can be affected by Intergranular corrosion, despite its not being an alloyTrue
T/F: Zirconia does not manifest inter granular corrosion because it is not an alloyFalse (its structure is granular and water can attack grain boundaries causing micro cracks)
In the typical galvanic reaction (the common example) Gold acts as a/an ______ (cathode/anode) and _______ (gives up/accepts) electrons; amalgam acts as a/an ______ (cathode/anode) and _______ (gives up/accepts) electronsGold: Cathode; Accepts electrons; Amalgam: Anode; Gives Up electrons
Galvanic interactions comes from current generated when two metals interact because of the difference in their ______ _____Electrode Potential
_______ (chemical cleavage with the addition of water to chemical structure) occurs to restorative materials due to many salivary enzymesHydrolysis
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