Passive-Active Transition Behavior of 304 Stainless Steel

Abstract

The passive-active transition behavior of a 304 stainless steel was investigated by observing the self-activation behavior and nano-scale galvanostatic cathodic reduction experiment. The self-activation time, τ0 was dependent remarkably on concentration of sulfuric acid. It was appeared that applied nano-scale cathodic current density dissolved the passive film on a 304 stainless steel surface and shortened the activation time in galvanostatic cathodic reduction experiments. The applied cathodic current density was proportional to the reciprocal of activation time. From this linear relationship, the rate of the self-activation process, i0 was obtained. The i0 increased with increasing H2SO4 concentration. And i0 also increased with increasing passivation potential and passivation time. The stability of passive film increased in accordance with increasing τ0 and decreasing i0. Therefore, it was concluded that the stability of passive film on austenitic stainless steel is evaluated by the kinetic parameters of the self-activation rate i0 and the self-activation time, τ0.

A Direct Measurement of the Activation Potential of Stainless Steels in Nitric Acid

“…Many studies of the "activation potential" have been made on various materials including pure iron, 11,12 iron-chromium alloys 12,14 and more complex alloys involving nickel and other elements. 16,17 They lead to an establishment of a linear dependence between the activation potential and the logarithm of the proton activity. These measurements have mostly been performed in sulfuric acid using linear * Electrochemical Society Member.…”

“…16,17 They lead to an establishment of a linear dependence between the activation potential and the logarithm of the proton activity. These measurements have mostly been performed in sulfuric acid using linear sweep voltammetry.…”

“…Measurements of E a can also be based on the spontaneous activation behavior of stainless steels in sulfuric acid. 15,17 After a passivation polarization of the sample in sulfuric acid, the potential at which passivity decays spontaneously to an active potential on shutting off this anodic polarization has been also called the "Flade potential". 16,19 Once again, this method cannot be applied to nitric acid because the sample is spontaneously passive.…”