OPTIMIZATION OF THE ALTERNATING VOLTAGE PASSIVATION PROCESS FOR STAINLESS-STEEL

In the alternating voltage passivation process (AVPP), a potential square wave is applied for a certain time at a constant direct current (DC) bias potential. Effects of the process parameters DC bias potential (E(o)), pulse length (P), pulse amplitude (A), and ratio (R(o)) of the duration of the anodic to the cathodic portion of the pulse on the passive properties of type 304 (UNS S30400) stainless steel (SS) were determined using factorial design experiments. The passive properties were evaluated by recording anodic polarization curves in 0.1 M sulfuric acid (H2SO4), from which the critical current density (i(crit)) and the passive current density (i(p)) were determined These polarization curves were measured after open-circuit potential (OCP) decay experiments from which the time (t(p)) for OCP decay was determined. For E(o) = 300 mV(SCE), P = 90 ms, A = 1,050 mV, and R(o) = 4:1, an increase of t(p) by a factor of 130 with respect to the untreated sample was observed, while i(crit) decreased by a factor of 100. A significant decrease in i(p) also was noted.