Inhibiting properties of precipitated and co-precipitated manganese-containing compounds
Protecting metals from corrosion is one of the most important scientific, engineering, and economical problems. Its efficient solutions comprise painting with application of anticorrosive primers. These generally contain inhibiting pigments that suppress corrosion processes. The most efficient, though very toxic ones are chromates. Constantly increasing environmental requirements to components of paint coatings make it imperative to develop low-toxicity anticorrosive pigments. A productive trend in search for a solution to this problem is the use of complex metal oxides, in particular, manganites, as pigments. The proximity of the properties of chromium and manganese favors their use as anticorrosive pigments: the latter is also characterized by complexing ability and high oxidative potential. The corresponding manganites were obtained by precipitation from aqueous solutions by reducing permanganates in an alkaline medium in the presence of calcium and barium ions. The study of their properties showed that, despite the high inhibitory ability of aqueous extracts, an obstacle to their widespread use as anticorrosion pigments is the high content of water-soluble substances, which can lead to formation of bubbles as a result of osmotic phenomena when the paintwork is exposed to moisture or water. Codeposition of calcium manganite and phosphate eliminated this disadvantage, offering new opportunities for expansion of the range of low-toxicity anticorrosive pigments.