Cathodic Behavior of Iron Single Crystals and the Oxides Fe[sub 3]O[sub 4], Gamma-Fe[sub 2]O[sub 3], and Alpha-Fe[sub 2]O[sub 3]

The cathodic behavior of iron, , and have been investigated in the borate/ buffer solution of . The hydrogen overpotential on iron is found to vary on surfaces of different crystallographic orientation and with changes in the surface microstructure. The immersion potentials and cathodic reduction behavior with regard to reduction potential and current efficiency of the three oxides are sufficiently different to allow unambiguous distinction to be made between the oxides. Of the two cubic oxides, is reduced with an apparent current efficiency of less than 17%, whereas the apparent current efficiency for is greater than 60% at a reduction potential some 300 mv more positive than that for . Air exposure of causes the transformation of up to 25Aå of the surface layer to . This technique of cathodic reduction is suitable for both qualitative and quantitative measurements of thin oxide films on iron.