Synthesis of (Fe,Cr)2O3 solid solution pigment powders for ink application

Iron chromite pigment was synthesized via solution combustion using iron(III) nitrate nonahydrate and chromium(III) nitrate nonahydrate as starting materials, and glycine, urea, citric acid, and ethylene glycol as fuels. The effect of postheating temperature on the structure, microstructure, and chromatic properties of the synthesized powders was also studied. X-ray diffraction patterns showed that the as-synthesized powders were amorphous to crystalline FeCr₂O₄ phases, depending on fuel type. Moreover, regardless of the fuel type, postheating led to the d-space shift and oxidation and formation of (Fe,Cr)₂O₃ solid solution. Phase transformation of FeCr₂O₄ to (Fe,Cr)₂O₃ solid solution was observed at 500/750°C depending on the dominant phase present in the as-synthesized particles. Fourier transform infrared analysis illustrated a shift in the band position of octahedral M–O and tetrahedral M–O bonds due to the movement of Fe cations and the lattice shrinkage by increasing the postheating temperature. Moreover, scanning electron micrographs showed that Fe_0.7Cr_1.3O₃ semispherical fine particles consisted mainly of porous and spongy FeCr₂O₄ particles due to the oxidation and phase transformation during postheating. According to chromatic measurements, the ink prepared by using the powders synthesized in the presence of glycine and post-heated at 500°C showed reddish-brown color which could be considered a promising candidate for tile decoration application. Furthermore, rheology studies revealed that the prepared ink showed non-Newtonian shear thinning behavior.