engleski

Cobalt doped willemite synthesis

Cobalt blue alongside prussian blue is one of the world’s most famous blue pigments. While the latter has no significant consequences for human health, cobalt blue is toxic when inhaled or ingested. A safer and environmentally preferable way of obtaining cobalt blue like pigments is doping of different nontoxic and natural minerals with small amounts of cobalt. In this work doping of zinc silicate mineral, willemite Zn2SiO4, with 5, 10 and 15 mol.% of Co with the aim of obtaining Zn2-xCoxSiO4 was carried out. Thermal properties of sol-gel derived samples were examined with simultaneous differential thermal and thermogravimetric analysis (DTA/TGA), which showed standard effects and mass loss for this type of synthesis, and crystallization effect at 800 °C for willemite. X- ray powder diffraction analysis (XRD) showed amorphous and crystalline nature of raw samples, as well as the formation of willemite phase at 800 °C with accompanying ZnO phase and change of willemite crystallinity with increase of annealing temperature from 800 to 1000 °C, while samples doped with 15 mol.% Co show the presence of ZnCoO2 phase. Fourier transform infrared spectroscopy (FTIR) shows characteristic bands for present oxides and their bonds with adsorbed water and carbon dioxide. Coloration of prepared samples changes with annealing temperature whereas higher Co concentrations and temperatures accentuate the intense blue colour. Diffuse reflectance spectroscopy (DRS) shows higher absorbance with annealing temperature and specific bands as a result of different Co coordination present in the samples.

Willemite, doping, cobalt blue

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