Phase transformation of FeCr₂O₄ to (Fe,Cr)₂O₃ 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 FeCr2O4 phases moreover, postheating of the powders led to d‐space shift and oxidation and formation of (Fe,Cr)2O3 solid solution phase regardless of fuel type. Phase transformation of FeCr2O4 to (Fe,Cr)2O3 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 Fe0.7Cr1.3O3 semispherical fine particles were formed from porous spongy FeCr2O4 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 FeCr2O4 to (Fe,Cr)2O3 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.

Solution combustion synthesis of FeCr2O4:Zn,Al pigment powders

“…Zinc, iron, nickel, chromium, and aluminum are more adequate for brown spinels; Cr 3+ in octahedral and Zn 2+ , Fe 2+ , and Al 3+ in tetrahedral sites due to the charge and ionic compatibility. 29 In our previous works, FeCr 2 O 4 powders as a brown pigment were synthesized by a solution combustion method, and the effect of fuel type, mixing of fuel, postheating process and temperature on the structure, microstructure, molecular bonds, and optical properties of powders were studied for pigment 30,31 and ink applications. 32 The topic of synthesis of beige/brown pigment in the Fe, Zn, Cr, and Al spinel system has been reported, but the subject of changing the brown color of iron chromite due to doping with zinc and aluminum has received less attention yet.…”

“…In our previous works, FeCr 2 O 4 powders as a brown pigment were synthesized by a solution combustion method, and the effect of fuel type, mixing of fuel, postheating process and temperature on the structure, microstructure, molecular bonds, and optical properties of powders were studied for pigment 30,31 and ink applications 32 …”