Ceramic pigments with sphene structure obtained by both spray- and freeze-drying techniques

The present study is focused on the procedure of spray- and freeze-drying techniques for the preparation of Cr-doped sphene pigments (CaSn0.98Cr0.02SiO5, CaTi0.98Cr0.02SiO5) from an aqueous solution of precursor salts, followed by calcinations of the resulting powders in absence of additives. The evolution of the present crystalline phases with applied thermal treatments was studied by X-ray powder diffraction and thermal analysis. The powder morphology was analysed by scanning electronic microscopy. The behaviour of the chromium ion was clarified by ultraviolet and visible spectroscopy. The colour efficiency of pigments was evaluated by colourimetric analysis (CIE L⁎a⁎b⁎ system).

Cr-doped sphene pigments were synthesised by the spray- and freeze-drying procedures, followed by calcinations of the resulting powders. The obtained materials possess a grain-size distribution mainly between 1 and 5 µm, which is significantly small and hence facilitates its direct application in ceramic glazes, avoiding additional grinding. The mechanism of the colour appearance showed that Cr-doped CaSnSiO5 pigments developed peculiar pink hues, whereas the Cr-doped CaTiSiO5 exhibited brown colourations, due to the combination of Cr(III) and Cr(IV) cations dissolved in the sphene matrix.Figure optionsDownload as PowerPoint slide