EFFECT OF THE PROPORTIONS OF WATER AND DIMETHYFORMAMIDE IN SULFURIC-ACID-SOLUTIONS ON THE PASSIVATION OF IRON, NICKEL, AND CHROMIUM

The potentiostatically determined potential region corresponding to th e passive state in certain metals becomes smaller with an increase in the amount of DMFA in the solvent The potential at which chromium corr odes freely increases sharply in solutions with a predominance of DMFA , and the so-called cathodic current loop disappears. on its anodic I, E-curve. Data on the effect of potential and the composition of the s olvent on the kinetics of the passivation of iron and disturbance of t he passive state in the presence of Cl- ions is compared with data for berate buffer solutions in identical mixtures of H2O-DMFA. The compar ison shows that the nature of the electrolyte plays an important role. A discussion is presented of the possibility of the participation of undissociated H2SO4 molecules, having oxidative properties, in the for mation of the oxide layer on a passive Fe electrode.