Chapter 17 Flashcards
dissolution
material loss due to corrosion and scaling of the material
oxidation
formation of oxides on the material that normally results in weight gain
corrosion/oxidation is driven by _________
transfer of electrons
metals readily ______ electrons
give up
oxidation reaction
M -> M^+n+ +ne
reduction reactoin
M^n+ + ne -> M
what reaction happens at an anode
oxidation
what reaction happens at a cathode
reduction
what is the standard condition to test potential
platinum electrode with 1M H+ ions electrolyte
noble metals
inert metals
active metals
highly reactive
the metal _______ on the galvanic series table corrodes (gets oxidized)
lower
net voltage of circuit
V = V2 - V1
V2 = reduction
V1 = oxidation
when does a redox reaction take place as expected
when change in V is positive
what happens if molarities of electrolytes are not 1M
must adjust using equation
passivity
some metals react with oxygen in the air and form a very stable oxide on a metal’s surface which protects it from corrosion
sacrificial anodes
attach a sacrificial anode to a metal that is more likely to corrode to stop corrosion of important material (cathode)
sacrificial anode materials
zinc, magnesium, aluminum
impressed current cathodic protection
pipeline connected to an external electric circuit that drives electrons in the opposite way they would normally flow
galvanizing
applying a protective coating of zinc onto steel since zinc is more reactive
uniform surface corrosion
-protected against by generic corrosion prevention
-occurs all over the material
galvanic corrosion
two metals with different EMF are put together in an electrolyte, less noble metal corrodes while more noble metal is protected
galvanic corrosion, rate of corrosion is proportional to ______
surface area in contact
crevice corrosion
when there is a concentration gradient in the electrolyte, typically occurs in tight corners where proper mixing is difficult
intergranular corrosion
forms on microstructure level - related to formation of phases on grain boundaries
selective leaching
intentional dissolution of an element from a material that leaves behind a porous material with poor mechanical performance
erosion - corrosion
especially prevalent in pipes where a fluid is causing corrosion and the movement of the fluid causes erosion
stress corrosion
combination of loading and corrosive environment, stress from the load lowers activation energy required for corrosion
