Phase transformation of FeCr ₂ O ₄ to (Fe,Cr) ₂ O ₃ solid solution pigment powders: Effect of post‐heating temperature

Abstract Iron chromite powders were synthesized via solution combustion route using iron(III) nitrate nonahydrate and chromium(III) nitrate nonahydrate as starting materials, as well as glycine–urea, glycine–citric acid, and glycine–ethylene glycol mixtures as fuels. The effect of postheating at different temperatures on the structure, molecular, microstructure, and chromatic properties of powders and tiles colored by in‐glaze powders was studied. The X‐ray diffraction patterns showed that as‐synthesized powders were obtained in crystalline FeCr ₂ O ₄ phases moreover, postheating of the powders led to d ‐space shift and oxidation and formation of (Fe,Cr) ₂ O ₃ solid solution phase regardless of fuel type. Phase transformation of FeCr ₂ O ₄ to (Fe,Cr) ₂ O ₃ solid solution was observed at 500/750°C depending on the dominant phase of as‐synthesized particles. Fourier transform infrared analysis illustrated that the band positions of octahedral M–O and tetrahedral M–O bonds were shifted due to Fe cations movement from their position and lattice shrinkage by increasing of post‐heating temperature. Moreover, scanning electron micrographs showed that Fe _0.7 Cr _1.3 O ₃ semispherical fine particles were formed from porous spongy FeCr ₂ O ₄ particles due to oxidation and phase transformation during the postheating. Furthermore, chromatic properties of the samples were represented. The color properties of the pigments showed that the formation of brown pigments is provided with the phase transformation from FeCr ₂ O ₄ to (Fe,Cr) ₂ O ₃ at a temperature of up to 750°C. Moreover, increasing the color purity to this temperature is related to the removal of residual carbonaceous matters. The chromatic properties of the glazed tiles colored using the pigments showed that postheating between 250 and 500°C led to more brown appearance.