Non-conventional synthesis of Cr-doped SnO2 pigments

It is shown that Cr–SnO2 violet pigments can be synthesised by heating at 1300 °C precursors obtained by pyrolysis at 600 °C of aerosols generated from aqueous solutions of tin (IV) chloride and chromium (III) nitrate. This method is simpler than the conventional one and permits to control the particle size distribution not requiring grinding. In addition, it is a continuous technique which makes it suitable for industry. The effects of the chromophore (Cr) concentration on the colour properties of the pigments were evaluated. The optimum pigment obtained by this procedure corresponds to a Cr/Sn molar ratio in the 0.04–0.05 range. The colour changes originated as a consequence of the heat treatment of the precursors obtained by pyrolysis of aerosols up to the development of the desired pigments were interpreted in terms of the variations of the oxidation state of the Cr species during calcination.