Corrosion inhibition of stainless steel 347 in the mixture of phosphoric and acetic acid using phosphorus ylide compound

Abstract

Cathodic and anodic polarization behaviour of SS₃₄₇ in mixture of highly concentrated phosphoric and acetic acid in the presence of various amounts of dimethyl 2-(2-hydroxyphenyl amino)-3-(tri phenylPhosphoranylidene) butanedioate (L-OH) at different temperatures (20, 30, 40, 50±1ºC) have been investigated potentiodynamically. The cathodic and anodic Tafel slopes values calculated from the polarization curves indicate that the corrosion rate decreases with increasing L-OH concentration. The corrosion potential (Ecorr) and passive potential (Ep) increased (shifted slightly toward positive potential) while corrosion current density (Icorr) and passivation current (Ip) decreased with increasing L-OH amount. Critical potential for passivity (Ecr) did not show any remarkable change but critical current density (Icr) often decreased with increasing L-OH concentration. Maximum inhibition efficiency (95%) is obtained for the alloy in acid solution containing 60 ppm of L-OH. The open circuit potential after polarization attained positive value indicating formation of passive film on the surface of experimental sample. Activation energy (Ea) and Gibbs free energy (∆Gads) for adsorption of L-OH are calculated. The values of ∆Gads decreased (attained more negative values) with increasing temperatures.