Effect of post heating on the phase transformation of FeCr۲O۴ to (Fe,Cr)۲O۳ solid solution pigment powders

Iron chromite was 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 post heating at different temperatures on the structure, molecular, microstructure and chromatic properties of powders was studied. The X-ray diffraction (XRD) patterns showed that as synthesized powders were obtained in crystalline FeCr۲O۴ phases Moreover, post heating of the powders led to d-space shift and oxidation and formation of (Fe,Cr)۲O۳ solid solution phase regardless of fuel type. Phase transformation of FeCr۲O۴ to (Fe,Cr)۲O۳ solid solution was observed at ۵۰۰/۷۵۰œC depending of dominant phase of as synthesized particles. Fourier transform infrared (FTIR)analysis illustrated that band position of octahedral M-O and tetrahedral M-O bonds were shifted due to Fecations movement from their position and lattice shrinkage by increasing of post heating temperature.Moreover, scanning electron micrographs showed that Fe۰.۷Cr۱.۳O۳ semi spherical fine particles wereformed from porous spongy FeCr۲O۴ particles due to oxidation and phase transformation during the postheating. Furthermore, chromatic properties of the samples were represented. The color properties of thepigments showed that the formation of brown pigments is provided with the phase transformation fromFeCr۲O۴ to (Fe,Cr)۲O۳ in the temperature range of ۷۵۰ °C. Also, increasing the color purity to thistemperature is related to the removal of residual carbonaceous matters. The best sample prepared at thistemperature has the following specifications: a*= ۸.۸۱, b*= ۸.۹۴ & L* = ۲۳.۷, which can be considered as asuitable candidate for brown ceramic pigment.

کلیدواژه ها:

Iron chromite ، post heating ، Chromatic properties ، phase transformation.