Protective and water-repellent properties of alkylcarboxylic and alkylphosphonic acid films on technically pure magnesium

Abstract

The formation of superhydrophobic coatings using low‑toxicity corrosion inhibitors is a promising method for corrosion protection of metals and alloys. In this study, the effects of surface roughness and the of the adsorbed substance structure on wettability and corrosion resistance of commercially pure magnesium were investigated. Surface roughness was created by three different methods: paper grinding, etching in nitric acid solution and laser treatment. Oleic, stearic and octadecylphosphonic acids were investigated as potential surface modifiers for the formation of corrosion resistant superhydrophobic coatings. It has been shown that the protective and hydrophobic properties of acid films on magnesium, as well as their stability, are determined by both the initial surface morphology and the nature of the inhibitors. Experimentally, the laser treatment was found to be preferable to mechanical and chemical surface preparation and the best hydrophobic agent among the studied acids is phosphonic acid. The most stable films with excellent superhydrophobic and protective properties in atmospheres of high humidity and salt spray clamber are formed in a solution of 0.001 M octadecylphosphonic acid on the surface of magnesium with high roughness. In addition, the effect of vinyltrimethoxysilane on the protective and hydrophobic properties of stearic acid and octadecylphosphonic acid films was investigated. The results of direct corrosion tests and wetting contact angle degradation kinetics studies showed that the protective and hydrophobic properties of stearic acid can be enhanced by its layer-by-layer adsorption with silane. They practically reach the parameters of octadecylphosphonic acid.