Abstract
Composition dependence of chemical activation energy was considered by separating apparent activation energy（ΔQa）of pure Fe, Cr and Fe-Cr alloys 1N-H2SO4 solution into two factors, chemical and electric one.
Corrosion reaction of Fe-Cr alloys was found to be determined by anodic dissolution of metals and cathodic reaction of H＋ reduction had less effect on the reaction. Thus, relationship between chemical activation energy and Cr content was investigated in terms of metal dissolution. We assume that the standard electrode potential of Fe-Cr alloy decreased linearly with increasing Cr content based on the fact that the standard electrode potential of pure Fe is more noble than that of pure Cr and also on the results indicating that corrosion potential of Fe-Cr alloys decreased linearly with Cr content. From the assumption, chemical activation energy（Q0）was estimated by subtracting electric factor from ΔQa. It was found that Q0 decreased lineally by the increase of Cr content in the range of no more than 40％ Cr, but it increased with Cr content in the range higher that 40％ Cr.
We estimated chemical activation energy of Fe and Cr（partially mole activation energy）in Fe-Cr alloys for obtained Q0 by applying the concept of the additive of thermodynamic partial molar quantity. And it was revealed that Q0 of Cr was remarkably decreased in Fe-Cr alloys compared with one in pure Cr. It was considered that increase of corrosion rate with Cr content of Fe-Cr alloys was attributable to decrease of Q0 of Cr in pure Cr comparing to one of Cr in Fe-Cr alloys.
