ENGR 220 Final Exam Questions with Verified Solutions Rated A+ (Already Passed)
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Course
ENGR 220
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ENGR 220
ENGR 220 Final Exam Questions with Verified Solutions Rated A+ (Already Passed)
deterioration mechanism - metals - Answers loss of material via dissolution (corrosion), formation of oxide scales/films which may flake off (oxidation)
deterioration mechanism - ceramics - Answers relatively deterior...
ENGR 220 Final Exam Questions with Verified Solutions Rated A+ (Already Passed)
deterioration mechanism - metals - Answers loss of material via dissolution (corrosion), formation of
oxide scales/films which may flake off (oxidation)
deterioration mechanism - ceramics - Answers relatively deterioration resistant bc already oxidized,
issues mainly at high temps and very extreme environments
deterioration mechanism - polymers - Answers degradation (dissolve in some solvents...absorb and
swell, UV and other radiation, heat, etc. can break covalent bonds
what is corrosion? - Answers destructive, electrochemical attack of a material
what is corrosion mechanism? - Answers actual atomic molecular or ionic transport process occurring at
the interface between material and its environment
what is metallic corrosion? - Answers electrochemical process - reaction involving transfer of electron
from one material to another
what is oxidation? - Answers metals lose or give up one or more valence electrons
what is reduction? - Answers metals give up or gain one or more valance electrons
why are ceramics immune to environmental degradation? - Answers many common ceramics are stable
oxides
delta v must be _______ for reaction to proceed spontaneously in direction assumed - Answers positive
if delta v is negative..... - Answers negative arrow must be reversed
what is the galvanic series? - Answers ranks relative reactivity of various metals/alloys in seawater ---
practical series developed to rank relative nobility of coupled metals in specific environments at specific
temps
what happens when material passivates? - Answers formulation of highly adherent, very thin, protective
oxide film on metal surface
examples of inert metals - Answers Cr, Fe, Ni, Al, and many of their alloys
pilling-bedford ratio - Answers determines level of protection
pilling-bedford ratio (PBR) if less than 1 - Answers film = porous, less than 100% coverage, unprotective
pilling-bedford ratio (PBR) if greater than 1 - Answers compressive internal stresses; 2-3 may crack and
spall
pilling-bedford ratio (PBR) if equal to 1 - Answers ideal for file being productive
, generalized attack/uniform corrosion assumptions - Answers - electrochemical corrosion is the only
deterioration mechanism
- anodic + cathodic reactions take place all over electrode surface with location of reactions changing
places on the surface
- no significant macroscopic differences in electrolyte concentration over the metal surface
- metal fairly homogenous
uniform attack corrosion - Answers oxidation and reduction reactions occur uniformly over surfaces
(general "rusting")
galvanic corrosion - Answers dissimilar metals physically joined, in the couple (Galvanic couple) more
anodic one corrodes
- ex. Zn, Mg very anodic
crevice corrosion - Answers by geometry develops different concentration of dissolved species between
2 pieces of material (rivet hole, gasket)
pitting corrosion - Answers gravity driven, downward propagation of small pits and holes
selective leaching corrosion - Answers preferential corrosion of solid solutions - 1 element or constituent
- depending on nature/environment exposed to 1 or more elements can be dissolved)
process zinc goes through to be dissolved - Answers dezincification
erosion corrosion - Answers mechanical abrasion of passivating layer and chemical attack (at pipe
elbows/bends)
stress corrosion - Answers corrosion at crack tips when a tensile stress is present
intergranular corrosion - Answers corrosion along grain boundaries, often where special phases exist
general attack/uniform corrosion - Answers - uniform over a surface, leading to relatively even thickness
reduction
- results in greater material mass loss bc occurs over entire surface
- easily distinguishable as long as component is visible
- effects can be predicted by taking observations overtime
- internal corrosion makes observation more challenging
for metallic corrosion to occur, which conditions must be satisfied? - Answers - at least one oxidation
half reaction
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