Processing and characterisation of various mixed oxide and perovskite-based pigments for high temperature ceramic colouring application

The potential of using new mixed oxides based on perovskite and cerium oxide-based pigments, for high temperature (above 1000 °C) ceramic colouring applications is presented in this paper. The solid-state synthesis method was used to manufacture the various pigment precursor powders used in this study. In the case of Er6MoO12, orange–yellow colours were observed at calcination temperatures of 1200 °C and 1300 °C with different soaking times. Examination of the X-ray diffraction pattern generated after heat treatment at 1200 °C for 2 h revealed the single-phase nature of the compound. However, when applied to unleaded commercial transparent glaze, the pigment powder changed to a light pink colour indicating instability of the pigment in the glaze. Similarly mixed oxides such as Ba0.5La0.5 Na0.5 Cu0.5Si4O10 and Ba0.5La0.5 Na0.5 Cu0.5Si2O6 produced vivid blue and violet–blue colour powders, respectively when calcined between 950 °C and 1050 °C for different soaking times. X-ray diffraction patterns for Ba0.5La0.5 Na0.5 Cu0.5Si4O10 showed the presence of the phases which included (a) BaCuSi4O10 (b) La2Si2O7 (c) SiO2 and La2O3 (trace) whereas Ba0.5La0.5 Na0.5 Cu0.5Si2O6 confirmed the presence of the phases such as (a) BaCuSi4O10 and (b) BaCuSi2O6. These pigment powders were also not stable and light-green colours were observed when they were immersed in the unleaded commercial transparent glaze. Finally, AxB(2−x−y)CryO3 (A = rare earth and B = Al) perovskite-type compounds produced a variety of shades of red and yellow colour depending on the rare earth, the value of x and y, and the calcination temperature. An intense brownish-red colour was obtained when the rare earth Erbium was used with x = 1, y = 0.06. From the X-ray diffraction trace, Er (Al Cr)O3 was found to be the only phase present. SEM micrographs indicated the presence of agglomerates as well as two different types of crystals in terms of morphology. EDX spectra confirmed that both types of crystals had the same composition. When applied in an unleaded transparent glaze, the brownish-red colour pigment powders turned into very pale yellow in the glaze, again indicating instability of the pigment powder in the commercial transparent glaze.