The use of mechanochemical activation for the synthesis of garnet-based pigments

Green pigments based on uvarovite Ca₃Cr₂[SiO4]₃ were obtained from cheap silica-containing materials of the Siberian region by high-temperature solid-phase synthesis with the use of mechanical activation of an initial mixture. The chemical composition of quartz sand and marshallit, the main initial components of pigments, is determined using an optical emission spectrometer with inductively coupled plasma (iCAP 6300 Duo, Thermo Scienfitic). The structure and phase composition of initial materials and reaction products were analyzed by X-ray diffraction (DRON-UM1 diffractometer, filtered CuKa-radiation), IR spectroscopy (Nicolet 5700 FTIR spectrometer), and scanning electron microscopy (Philips SEM 515). Calcium carbonate is shown to decompose during mechanochemical activation. The reactions occurring during the synthesis of pigments were studied using a thermal analyzer (SDT Q600) in the temperature range of 25-1200°C at a heating rate of 20 deg/min. Mechanical activation of initial components in a planetary mill M3 with an acceleration of 45 g for 300 s leads to a decrease in the synthesis temperature by 200°C and increases the degree of conversion of the final products.