Chromate-free pigments for anti-corrosion protection of D16 aluminum alloy

• Yu.A. Kuzenkov, N.P. Andreeva, Yu.I. Kuznetsov and S.V. Oleynik

A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Leninsky pr. 31, 119071 Moscow, Russian Federation

Abstract: Painting systems for the protection of aluminum alloys often contain pigments that can perform various functions, including an anti-corrosion function. Chromate pigments are widely used for this purpose, but their use is now limited for environmental reasons. Although inorganic phosphate pigments have been well studied and used as replacements for chromate pigments, organic alkyl phosphates may also be promising. It is known that alkyl phosphates can serve as effective inhibitors against the formation of pits on aluminum and other metals in chloride-containing media, and in turn, phosphorus-containing molybdenum heteropoly compounds can suppress local corrosion of aluminum alloys. In this work, the protective properties of two new types of chromate-free pigments based on adducts of phosphorus-molybdic acid with amines of various structures and salts of dioctylphosphoric acid in chloride-containing media have been studied. It has been shown that the protective properties of the dioctylphosphate anion are due to its high adsorption capacity on the surface of D16 alloy. Moreover, the protective ability of extracts of aqueous pigments synthesized by the reaction of phosphomolybdic acid with amines depends on the chemical structure of the amine and increases in the series primary – secondary – tertiary amine. It has been shown that all new pigments inhibit pitting corrosion of D16 aluminum alloy in chloride-containing media more effectively than zinc chromate.

Keywords: aluminum alloys, anti-corrosion pigments, corrosion inhibitors, adsorption, ellipsometry, alkyl phosphates

Int. J. Corros. Scale Inhib., 2023, 12, no. 3, 984-994
doi: 10.17675/2305-6894-2023-12-3-11

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