Inversion degree, morphology and colorimetric parameters of cobalt aluminate nanopigments depending on reductant type in solution combustion synthesis

Abstract Blue-colored ceramic nanopigments with the composition of CoAl2O4 were synthesized by solution combustion method using glycine (CoAl2O4-Gly), poly(vinyl alcohol) (CoAl2O4-PVA) and urea (CoAl2O4-Urea) as reductants and fuels. The morphology and chemical composition of the nanopigments were studied using SEM and EDS, respectively. The composition of the crystalline phase was examined using XRD. The crystallite sizes were calculated using the modified Scherrer method, Williamson-Hall method and size-strain plot method. Particles of the CoAl2O4-PVA sample have smaller crystallite sizes, whereas particles of the CoAl2O4-Urea sample have larger crystallite sizes. Thermal gravimetric analysis showed that thermal decomposition of cobalt(II) and aluminum nitrates is accompanied by the release of gases. As a result of material loosening, finely dispersed powders with high porosity were formed. FTIR-spectra of all the nanopigments contain absorption bands related to stretching vibrations of the Me-О bonds (400-700 cm−1). Stretching and deformation vibrations of water molecules are present as well. Color characteristics of the obtained nanopigments depend on the fuel used for the combustion synthesis. The pigment CoAl2O4-PVA has saturated blue-green color. The obtained spinel-type nanomaterials possess high suspension stability and can be used as pigments in ceramic technology.