Environmental study of Cr2O3–Al2O3 green ceramic pigment synthesis

A green pigment was synthesised based on a Cr2−xAlxO3 solid solution, using a standard ceramic industry composition with and without different mineralisers and using raw materials industrial grade reagents. The resulting products were compared with a pigment made using chemically pure (CP grade) to establish the most appropriate reagents for achieving minimum Cr(VI) segregation during the pigment washing stage, and comparable chromatic qualities to those of a standard industrial pigment. Chromium sesquioxide was used as Cr(III) precursor instead of a Cr(VI) compound, and the chromium content was also optimised. The X-ray photoelectron spectroscopy (XPS) results indicated that a solid solution only forms when CP grade reagents are used. This is consistent with the scanning electron microscopy (SEM) and X-ray diffraction (XRD) data obtained in the study. Smaller Cr(VI) and B contents were found in the washing liquids when CP grade reagents were used, but the resulting chromatic quality was slightly lower than that of a standard pigment made and used in the ceramic industry.