The corrosion reaction of iron in acid solutions have been studied by means of chemical kinetics. The cathodes of local cells in iron are oxygen electrodes at higher pH than 4 and hydrogen electrodes at lower pH than 4. The corrosion ersistivity of metals
K is related to the standard electrode potential
EM0 and the specific reaction rate constant of hydrogen electrode
K1 by the expression
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oindentwhere
n is the valency of metal ions. 1>α>0,
T the absolute temperature and
R and
F are universal constants. There seems to be some relation between
K and the work function of metals. The general Eq. of corrosion rate are as follows:
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\
oindentwhere β is a constant of the anode film, β≥1,
C is the concentration of adsorbed water molecule on metals,
DM is the diffusion constant of metal ions and δ
m the thickness of diffusion layer.
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