Synthesis of coloured ceramic pigments by using chromite and manganese ores mixtures (Síntese de pigmentos cerâmicos coloridos usando misturas de cromita e de minérios de manganês)

The aim of this work is not only the synthesis of black ceramic pigment with spinel structure using local and inexpensive minerals (chromite and manganese ores) but also throw some light on the relations between the structure and the colour of obtained pigment. Ultimate utilization spinel solid solution in ceramic materials is mostly due to their structure characteristics, their thermal and chemical stability. In this study colour pigments were ned by calcinations at 1250 oC starting from a mixture of chromite and manganese oxide. Different compositions were tested containing 30, 40 and 50 wt.% of manganese oxide (low and high content respectively). The phase composition and microstructure characterization of both raw material and obtained pigments were evaluated by X-ray diffraction, X-ray fluorescence, polarizing microscope and scanning electron microscope. Furthermore, the colour measurements of the obtained pigments and tiles were evaluated. Composition of all pigments reveal the spinel structure with Cr2FeO4; hematite was also recorded in the mixture of low manganese. The degree of lightness is relatively same in the pigments mixtures of both manganese types. However, tiles could be considered lightness compared with its pigments, especially of the high manganese type. The solid state calcinations reactions are indeed able to form intense brown pigments that can be used as a stain for industrial ceramic applications. The production of less expensive black ceramic pigments from low cost and less pure raw materials that can be utilized in Egypt to substitute for the imported pure oxides or salts is proved superior performance for producing painted pigments.