The influence of iron content on the promotion of the zircon structure and the optical properties of pink coral pigments

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 starting amount of the ferric salt in the sol-gel reacting mixture was varied in order to obtain Fe2O3/Zr molar ratios in the range 0.7-10%. The products of the sol-gel reaction were calcined in the range 800-1300 °C. X-ray diffractograms, EDX analyses and diffuse reflectance spectra were obtained and analysed for all the calcined powders; the colour of the pigments was characterised on the grounds of the CIE (Commission Internationale de l'Eclairage) standard procedure (CIE L∗a∗b∗ measurements). Results from the structural and spectral characterisations are examined and cross-compared to produce a consistent picture of the role played by iron on the promotion of the zircon lattice and on the optical properties of the reaction products.