THE FORMATION AND GROWTH OF HYDROUS OXIDE FILM ON STAINLESS-STEEL IN ALKALINE-SOLUTION BY POTENTIAL CYCLING

By repetitive potentiodynamic cycling in 1 mol dm(-3), NaOH solution a hydrous oxide him was formed on a stainless steel AlSl type 302. For the oxide growth, the optimal sweep rate of 50 mV s(-1) between -1.7 a nd 0.5 V(SCE) was found. The voltammetric data of stainless steel acco mpanied by those of the 64Fe-36Ni and 80Ni-20Cr binary alloys were use d in the elucidation of stainless steel surface oxidation/reduction pr ocesses. The two main pairs of hydrous oxide peaks in the cyclic volta mmogram of SS 302 belong to the Fe(OH)(2)/FeOOH and Ni(OH)(2)/NiOOH tr ansitions. By recording the open-circuit potential in 0.1 mol dm(-3) s ulphuric acid the stability test was carried out. The uncycled electro de reached the active potential of -0.45 V almost immediately. Only on e cycle in NaOH solution improved its stability. When the hydrous oxid e was grown up to the charge storage capacity of 18 mC cm(-2) (express ed by the means of voltammetric charge of anodic Fe(OH)(2)/FeOOH trans ition), the open-circuit potential was still on the positive side afte r 6 days.