Preparation of praeseodymium-doped ZrSiO4 by a sol-gel route

Praseodymium-doped ZrSiO4 pigments were prepared using alkoxides of zirconium and silicon. The preparation of the gels and their characterisation by TGA and infra-red spectroscopy are described. XRD patterns of samples calcined at different temperatures in the range 1000-1400 C are shown. Peaks relating to the formation of ZrSiO4 and monoclinic or tetragonal ZrO2 are noted. Use of NaF and NaCl as mineralisers produced mainly ZrSiO4 with only trace amounts of monoclinic and virtually no tetragonal ZrO2. Formation of ZrSiO4 was even more complete if MgCl2 was added. Complete transformation to ZrSiO4 at moderate temperatures can only be achieved by adding mineralisers, even when using sol-gel powders. The colour of the pigments obtained was determined by the CIE system and characterised by L*-, a*- and b*- values. Chromatic values of sol-gel powder prepared with only 2% Pr6O11 were nearly the same as those of a commercial product containing 3.84% Pr6O11. Reflectance spectra of the commercial and sol-gel powders gave fairly similar curves. Despite the fact that the alkoxide starting materials are more expensive than oxides, this sol-gel route may be economically advantageous because smaller amounts of the most expensive material, Pr6O11, are needed. 9 refs.