Chromium(IV) Stabilisation in New Ceramic Matrices by Coprecipitation Method: Application as Ceramic Pigments

In this paper the stabilization of Cr⁴⁺ in new ceramic matrices as willemite Zn₂SiO₄ and galium‐gadolinium garnet GGG (Gd₃Ga₅O₁₂) is studied and compared with the chromium‐sphene ceramic pigment using the traditional solid reaction and an unconventional coprecipitation method.The chromate amount etched from the powders using Cr^III and Cr^VI precursors on ceramic and coprecipitation routes are analysed in order to evaluate the environmental impact on the waste water. Cr‐willemite and codoped Ca, Cr‐GGG produces solid solutions of Cr⁴⁺ ion occupying tetrahedral and dodecahedral sites, respectively, while Cr⁴⁺ into sphene lattice occupies octahedral sites. Cr‐willemite are stable when used as ceramic pigment in habitual tile glazes but Cr‐GGG unstabilses and produces green colour associated to Cr³⁺ solved in the glaze. Coprecipitate powders are more reactive than ceramic powders but in Cr‐GGG stabilizes the metastable Ca₃Cr₂O₈ oxide. Chromate amount in washing hot water are not dependent of the chromium precursor but depends of the allowed reactivity level and the reaction media.