INFLUENCE OF MgO/SiO₂ RATIO AND ADDITIVES ON BIONANOFORSTERITE POWDERS CHARACTERISTICS

Abstract

Forsterite (Mg₂SiO₄) powders were synthesized by solid state reaction from basic magnesium carbonate and silicon dioxide. The MgO/SiO₂ molar ratio was established at 2:1, 2:1.05 and 2:1.10. In order to realize a complete reaction between compounds and avoiding the MgO (periclase) presence in the final product, an excess of SiO₂ was added. Boric acid in small quantity was used as a mineralizer. The six mixtures were designed and prepared in the laboratory. After a good homogenization and mechanical activation, the raw mixtures were thermally treated at 800 °C, 900 °C, 1000 °C, 1200 °C, 1300 °C and 1350 °C with a heating rate of 2 °C/min and one hour plateau at maximum temperature. The grain size distribution of the powders obtained at 800 °C, 900 °C and 1000 °C, according to the particle analyzes, are in the nanometer range. Increasing the temperature the size of grains is increased at micrometer dimensions indicating the presence of agglomerates. The mineralogical compositions evidenced by X-ray powder diffraction (XRPD) showed as the main crystalline compound the forsterite beginning of 1200 °C temperature. The crystallinity index of forsterite depends on the thermal treatment conditions, being highest at 1350 °C. A small quantity of MgO at the maximum temperature in compositions without boric acid was identified. The shape and morphology of forsterite crystals were evidenced by TEM analyses.