Inorganic Pigments Based on Complex Oxides for Protective-Decorative Aluminophosphate-Bonded Coatings

Abstract

Spinel pigments ranging from moderate blue to dark blue were synthesized by the method of self-propagating high-temperature synthesis. Oxides of cobalt Co3O4, magnesium MgO, zinc ZnO, and aluminum hydroxide Al(OH)3were used as initial components. Magnesium nitrate Mg(NO3)2·6H2O served as an oxidizing agent, and aluminum powder (ASD-4) was used as a reducing metal. The phase composition of pigments was studied by X-ray diffraction (Dron-UM-1, filtered CuK $\alpha$ radiation). The surface morphology of the samples was investigated by scanning electron microscopy (Philips SEM 515). The dispersed composition of the powders was determined with a Delsa Max PRO analyzer. To understand the processes occurring during the synthesis of pigments, the thermal behavior of substances was studied on a STD Q-600 thermal analyzer in the temperature range of $25\div 1400$ °C at a heating rate of 10 deg/min. The released gases were studied with a Pglab VG mass spectrometer combined with a thermal analyzer. The studies have shown that fast SHS reactions and high synthesis temperatures rapidly destroy the structure of Al(OH)3, which is the initial reagent, with the release of gaseous reaction products, which prevents spinel sintering. The formed active aluminum oxide reacts with the oxides of cobalt, magnesium, and zinc with the formation of spinel pigments with a particle size of ∼ $1-2 \mu_{\mathrm{m}}$ . Aluminate spinels based on the oxides of zinc, magnesium, and cobalt easily form solid substitution solutions. Obtaining spinel SHS-pigments of micron size directly in the combustion simplifies their flow chart, eliminating the grinding stage.