Production of iron triad-based colored spinels by the self-propagating high-temperature synthesis

Abstract

Blue, green, and khaki spinels were produced by self-propagating high-temperature synthesis (SHS) using Co3O4–ZnO–Mg(NO3)2·6H2O–Al(OH)3–Al, Ni2O3–ZnO–Cr2O3–Al(OH)3–Al, and Co2O3–Fe2O3–Al(OH)3–Al mixtures. The composition of the synthesis products was characterized by X-ray diffraction and IR spectroscopy. The oxides Co3O4, Co2O3, ZnO, Ni2O3, Cr2O3, Fe2O3, and aluminum hydroxide Al(OH)3 were used for the synthesis. Fuel was provided by aluminum powder (ASD-4). The spinel-type ceramic pigments were synthesized using layer-by-layer combustion, which involves two parallel exothermic reactions: aluminum oxidation and aluminothermic reactions. The fast self-propagating reactions and high synthesis temperatures rapidly destroy the structure of Al(OH)3 hydroxide in the starting mixture, producing gaseous reaction products that prevent the sintering of the spinels. The surface morphology of pigment powders and their composition was studied using a Quanta 3D 200i, FEI Co. scanning electron microscope and a Philips SEM 515 scanning electron microscope equipped with a local energy dispersive X-ray analysis (EDAX). The particle size of the synthesized spinels was approximately 1–5 μm. Colored spinels powders obtained by the SHS process can be used as ceramic pigments.