The effects of oxidizing agents on the formation of chemical conversion coatings on mild steels in an Na 2MoO 4H 3PO 4 type aqueous solution

Abstract

The effects of oxidizing agents were investigated in the chemical conversion treatment of mild steels in a 0.1 M Na 2MoO 4H 3PO 4 type aqueous solution. Oxidizing agents that were appropriate for accelerating the formation of chemical conversion coatings were NaClO 3 or NaNO 2 at pH 2 and NaNO 2 or H 2O 2 at pH 5. The chemical conversion coatings formed when polished steels in the treatment solution had an electrode potential in the corrosion region, but not when the potential was in the passive region. The electrode potential of rusted steels was probably a more noble value than that of polished steel in the solution at pH 1–6 because the rust was dissolved away. The weight of the resulting coatings increased with increasing time and temperature of treatment.