Effect of Nickel and Tungsten on Repassivation Rate of Stainless Steels in Chloride Solution by Potential Step Chronoamperometry

Abstract

This chapter presents a study to determine the effect of nickel (Ni) and Tungsten (Wi) on the repassivation rate by a scratch test and a potential step chronoamperometry (PSC) test. For this, three experimental alloys with the basic composition of 30% Cr and 4% Mo, and nickel with purity of 99.9%, were used. For the polarization test, the specimen was potentiodynamically polarized from the potential more active to the open circuit potential by 50mV at the scan rate of 20mV/min, after the corrosion potentials had been stabilized. For the rapid scratch test, the repassivation currents were measured every one millisecond during and after the passive film was removed by a rapid scratch method. The scratch test and the potential step PSC test found that nickel and tungsten affected repassivation rate by blocking the passivation by metal that did not participate in the formation of passive film, and by stabilizing the film formed by molybdenate (MoO42-) after accelerating the dissolution rate of iron by tungsten. © 2006 Elsevier B.V. All rights reserved.