Blue-violet ceramic pigments based on Co and Mg Co 2− xMg xP 2O 7 diphosphates

Abstract

Solid solutions of Co and Mg diphosphates with compositions Co 2− x Mg x P 2O 7 ( x = 0, 0.1, 0.2, 0.3, 0.5, 0.7, 1.0, 1.5 and 1.8) have been prepared and characterized for the first time as alternative low-toxicity blue ceramic pigments. The compositions were prepared through the conventional coprecipitation route and calcined up to 1000 °C/2 h. Samples were characterized by thermal analysis, XRD, SEM/EDX, UV–vis-NIR spectroscopy and colour measurements (CIE- L * a * b *). Isostructural Co 2− x Mg x P 2O 7 diphosphate solid solutions (monoclinic system and P21/ c spatial group) formed successfully within the studied range of compositions, accompanied only by a minor quantity of residual Co or Mg orthophosphates (M 3(PO 4) 2). Interestingly, the obtained solid solutions developed nice blue-violet colourations even with high Mg doping after enamelling within double-firing ( x = 1.5–1.8) and single-firing ( x = 1.0–1.5) ceramic glasses. These optimal compositions containing a minimized Co amount (measured values around 7–16 wt%) could be therefore less toxic alternatives to the conventional Co 3(PO 4) 2 blue ceramic pigment.