Synthesis and color performance of CaCoSi2O6 pyroxene, a new ceramic colorant

•Different compositions of Ca1-xCo1+xSi2O6 (0 ≤ x ≤ 1) powders were prepared by using the solid state method.•Among the different composition a monophasic pink pyroxene (CaCoSi2O6) was obtained.•The pink pyroxene (CaCoSi2O6) was subjected to technological tests and color analysis.•We found that it behaves like a dye, completely dissolving in the melted glaze.

The pyroxene structure was successfully used as a crystalline host for a new Co-based pink pigment. Different compositions of Ca1−xCo1+xSi2O6 (0 ≤ x ≤ 1) powders were prepared by using the solid state method with different temperatures and times of annealing. The characterization of the fired samples was performed by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), colorimetry and technological tests simulating the ceramic applications. A monophasic pink clinopyroxene was obtained for compositions close to the CaCoSi2O6 end-member. For increasing cobalt content, an assemblage of Co-olivine, Co-åkermanite and Ca,Co-pyroxene was found. Samples containing Co-åkermanite have a deep blue color stemming from Co2+ in tetrahedral coordination, while those with Co-olivine are violet due to Co2+ in octahedral coordination. The best conditions for the synthesis of a CaCoSi2O6 single phase were then investigated, finding that a proper annealing cycle at 1150 °C prevents the formation of metastable Co-åkermanite. The CaCoSi2O6 pyroxene was tested as a ceramic pigment into glazes and glassy coatings. In most cases, it behaves like a dye, completely dissolving in the melted glaze, analogously to Co-olivine.

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