Iron doped zirconium silicate prepared by a sol-gel procedure. The effect of the reaction conditions on the structure, morphology and optical properties of the powders

A sol-gel reaction starting from Si and Zr alkoxides, in water-ethanol mixtures, was employed to obtain iron doped zirconium silicate powders (zircon). The speciation of the ferric salt to be added to the starting mixture was varied, the anion matching, in each case, the anionic partner of the acid catalysing the gel polycondensation reaction. The effects of varying the time of the two separate hydrolysis steps leading to the gel formation were investigated. The products of the sol-gel reaction were calcined in the range 800-1300degreesC. The specific surface areas of all the samples were measured by the BET method; X-ray diffractograms and diffuse reflectance spectra were obtained and analysed for all the calcined powders. Results from the structural, morphological and spectral characterisations were examined and compared to produce a consistent picture of the key factors leading to the formation, growth, aggregation and optical properties of the reaction products.