Development of blue ceramic dyes from cobalt phosphates

In this study the development of blue ceramic dyes from compositions based on phosphate structures have been investigated. The replacement of cobalt by copper or iron to minimize the Co content have been considered. MFeO(PO₄) (M = Co, Cu) solid solutions have been obtained with Co_1−xCu_xFeOPO₄ (0 ≤ x ≤ 1) compositions prepared from gels and fired at 1000 °C/2 h. Co_1−xCu_xFeOPO₄ compositions are not indicated to minimize the Co content in ceramic dyes because they decompose in glazed samples and pinhole defect is obtained. From FeCoOPO₄–2FePO₄ compositions, Co₃Fe₄(PO₄)₆ structure introduces the Co²⁺ ions into glassy matrix and suitable blue materials are obtained. In the conditions of this study, optimal cobalt amount is about 10 wt% Co from Co_1−xFe_1+xO_1−x(PO₄)_1+x (x ≈ 0.6) compositions.