STIMULATION OF THE PASSIVATION OF IRON BY TUNGSTATE, MOLYBDATE AND CHROMATE IONS

The effects of tungstate, molybdate and chromate ions on the passivation of iron were investigated, and these oxyanions stimulated the passivation especially at lower pH. The results were rationalized by the dissolution-precipitation mechanism of iron passivation. In order to bring about the passivity of iron, it was required that iron first dissolves into solution, and then a ferric hydroxide or a ferric complex with oxyanion should be produced on the metal surface, which was followed by the dyhydration or the condensation reaction of these compounds to form ferric oxide. © 1979.