Abstract
The effect of halide ions on the anodic passivation of zirconium in acid, neutral and alkaline solutions was studied. In the presence of fluorine ion, dissolution of zirconium was observed in acid solution and pitting corrrosion in neutral solution, but in alkaline solution zirconium was not attacked. In the presence of chlorine or bromine ion, pitting corrosion of zirconium was observed in solutions of any pH value, but pitting by chlorine ion and that by bromine ion was prevented comparatively by presence of nitrate or nitrite ion and hydroxyl ion, respectively. Neutral iodide solution, without any oxyanions, can pit zirconium, but the solution containing some oxyanion caused no pitting. Oxidizing agents promote the start of pitting, but general anions (e.g. SO42−, SO32−, NO3−, NO2−, OH−) prevent corrosive action of halide ions. The pitting corrosion potential, 0.20-0.23 V (vs. S.C.E) for chlorine ion 0.1 mol/L, 0.45-0.50 V for bromine ion, and 0.82-0.86 V for iodine ion, did not vary with current density. A linear relation exists between the pitting corrosion potential and the logarithm of the halide ion concentration. Halide ions cause a greater number of smaller pits in the order of Cl−<Br−<I−.
