Praseodymium-zircon pigment powders were successfully prepared at different calcination temperatures with sodium fluoride NaF as mineraliser, using the solid state synthesis method. The powders were characterised using techniques such as XRD, SEM and TEM. Qualitative investigation of the phases using XRD showed the presence of large amounts of unreacted zirconia after calcination at 900 and 950uC, whereas from 1000 to 1200uC zircon was found to be the major phase, together with a small amount of zirconia. Quantitative investigation of phases was carried out using an external standard method. The weight fraction of unreacted zirconia at 1000uC was found to be 0 . 056. SEM observation of powders exposed at various calcination temperatures indicated the presence of tetrahedral crystals, and this was enhanced by the addition of the NaF mineraliser. TEM observations showed lattice defects and elastic strains in the samples at various calcination temperatures.

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The influence of cerium oxide on the colour hue of the praseodymium-zircon yellow pigment is presented in the present paper. A variety of pigment compositions were prepared by systematically altering the cerium to praseodymium oxide ratio. After milling of the raw materials the prepared powders were calcined at various temperatures for 2 h soaking times. Orangeyellow colour products were observed in each case. Colour and reflectance measurements were carried out using a spectrophotometer in order to optimise the pigment powders in terms of composition and calcination temperature. Structural characterisations on the optimised powder sample were carried out using X-ray diffraction (XRD) and scanning electron microscopy (SEM). X-ray diffraction analysis indicated that zircon was the major phase with traces of unreacted zirconia. From SEM, growth of the tetrahedral zircon crystals and the presence of small amount of unreacted zirconia were observed, which were in a good agreement with the results obtained from XRD. The average particle size of the sample after grinding for 1 h was found to be 12 mm. Finally, as a demonstration of the stability of the pigment, an orange-yellow glaze tile was manufactured when the pigment powder was applied in the commercial unleaded transparent glaze.