Process for inhibiting corrosion of metal and corrosion-inhibiting layer

Abstract

Corrosion of ferrous metal and aluminum surfaces, in particular, is inhibited by a layer of an organic-metallic complex of a polyamine with a (i) metal oxide, or (ii) metallate ion, or (iii) water-soluble metallate salt, in aqueous systems having a pH greater than about 7. The polyamine contains at least four (4) amine groups, two of which are secondary amine groups. The effect of the N atoms stretched over the length of the polyamine produces a 'caging effect'0 which immobilizes the oxide, or metallate ions, thus forming the protective layer. The organic-metallic complex deposited on the metal's surface forms the 'amine-metallic' layer which may be either an 'amine-metal oxide complex' which is a coordination complex, or, an 'amine-metallate complex'. The amine-metallate complex may be either an ionic complex of 'amine.metallate ions', or, a mixture of the polyamine and metallate salt which mixture is not a complex, but in solution, behaves like one, and is therefore referred to as an admixture complex of an 'amine+metallate salt'. The organic-metallic complex may be present in a concentration from about 10 ppm to about 5% by wt in neutral or basic aqueous solution. In the lower range of this conc. up to about 2000 ppm, the complex is useful in aqueous process streams; in the higher range, from 2000 ppm to 5%, for a rinse for phosphated metal parts, in lieu of a conventional chromate rinse.