OPTIMIZATION OF THE ALTERNATING VOLTAGE PASSIVATION PROCESS FOR STAINLESS-STEEL

In the alternating voltage passivation process (AVPP), a potential squ are wave is applied for a certain time at a constant direct current (D C) bias potential. Effects of the process parameters DC bias potential (E(o)), pulse length (P), pulse amplitude (A), and ratio (R(o)) of th e duration of the anodic to the cathodic portion of the pulse on the p assive properties of type 304 (UNS S30400) stainless steel (SS) were d etermined using factorial design experiments. The passive properties w ere evaluated by recording anodic polarization curves in 0.1 M sulfuri c 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 experime nts 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 obse rved, while i(crit) decreased by a factor of 100. A significant decrea se in i(p) also was noted.