Cr-doped perovskite and rutile pigments derived from industrial by-products

In order to enhance the use of environment-friendly materials and to stimulate waste recycling, this work has developed brown-maroon inorganic pigments belonging to rutile (TiO2) and perovskite (CaTiO3) structures. They were obtained by solid state reaction of industrial residues mixtures: tionite (i.e. insoluble residue of titania slag processing), Cr/Ni plating sludge and marble cutting/sawing sludge, for sake of comparison, analogous formulations were prepared by using reagent-grade precursors. Chromiumdoped (0.04 mole of Cr2O3) perovskite and rutile pigments were obtained at 1200°C and their phase composition, microstructure, optical properties and technological behaviour were characterized by XRD, SEM, DRS and application in glazes, respectively. The presence of impurities (e.g. Fe, Ni, Al, Si) in the wastes induced the crystallization of secondary phases, like wollastonite (CaSiO3) and titanite (CaTiSiO5), whose occurrence slightly shaded off the final colouration of the waste-based pigments; a further addition of chromium is required to improve their colouring power in transparent glazes. The diffuse reflectance spectroscopy shows that the colour development, in both structures, is due to the partial substitution of titanium by chromium in octahedral coordination