Sodium molybdate has been gaining widespread acceptance as a corrosion inhibitor. Although it is an inorganic material, molybdate's low toxicity to fish and other aquatic life has made it very attractive from an environmental point of view.

Sodium molybdate is an anodic inhibitor, which forms a complex with iron as the basis of its film. When iron corrodes, molybdate anions, in competition with other anions, adsorb to form a nonprotective complex with ferrous iron. Due to dissolved oxygen, the ferrous iron is oxidized to the ferric form and the ferrous molybdate complex transforms to ferric molybdate, which is both insoluble and protective in neutral and basic waters. This protective film may be more complex than simple ferric molybdate in that it probably also contains ferric oxides. The eventual accumulation of a double layer increases the protection afforded by the film.

Since sodium molybdate forms its film by adsorption, other easily adsorbed anions, such as chloride and sulfate, are competitive and can interfere with passivation. Therefore, increased concentrations of molybdate are required when high concentrations of these ions are present.

The nature of sodium molybdate passivation is such that, when used alone, relatively high concentrations of inhibitor must be maintained to achieve acceptable results. For this reason, inhibitors like phosphonate, zinc and phosphate are incorporated into a synergistic blend with molybdate to form an effective treatment program. This allows the molybdate concentration to be reduced to cost-effective concentrations that provide acceptable results.