Self-Activation of Passivated 316 Stainless Steel in Sulfuric acid

초록

The self-activation of passivated 316 stainless steel was examined in a sulfuric acid solution. The stability of the anodically formed film on a 316 stainless steel surface was measured under several values of applied cathodic current densities. The self-activation time, τo represents the period from the passive-active state to the active state. The results showed that τo increased with increasing pH, the passivation time and the passivation potential. Under various conditions, the equation, ie=qo/τo - io, could be obtained. Compared with 304 stainless steel, the passive film on 316 stainless steel seemed to be more stable because the results showed the longer self-activation time and the smaller value of io. By analysis of these parameters, the thickness of passive film on 316 stainless steel was quantitatively calculated. The passive film formed on 316 stainless steel was thicker than that of 304 stainless steel. The passive films formed above 0.6V(vs. SCE) showed two step self-activation behavior. The first step self-activation represented the reduction of outer layer of passive film, and the second step self-activation represented the reduction of inner layer. It was suggested from these results that the formed passive film at this range of potential is composed of a two-layer structure with the thicker outer layer and the more stable inner layer.