Does K_2CaSiO_4 Exist? A Phase-Analytical Study in the System K_2O-CaO-SiO_2 with Implications for the Characterization of Residual Materials

摘要

K_2CaSiO_4 or K_2O x CaO x SiO_2 has been reported to be a major constituent of residual materials that are of interest for the field of applied mineralogy, including ashes from biomass combustion as well as fertilizers produced from the residues of oil-shale industry or from steehnaking slags. Unfortunately, contradictory results concerning basic crystallographic and physicochemical data of this compound have been described in the literature. In a series of solid-state reactions we tried to prepare this material for a more detailed investigation. The temperature regime for the subsolidus synthesis experiments was selected according to previous studies where the occurrence of this so-called "1:1:1" phase had been reported. The samples were characterized by thermal and X-ray fluorescence analysis as well as X-ray powder diffraction. Our results indicate that "K_2CaSiO_4 does not exist as a crystalline phase in the ternary system K_2O-CaO-SiO_2 and that the 1:1:1 compound, mentioned in earlier studies is actually misinterpreted K_2Ca_2Si_2O_7. Furthermore, the start of melt formation of an oxide mixture with composition K_2O x CaO x SiO_2 has been determined to be 1170℃, which is dramatically lower than the value of 1630℃ mentioned in the only available comprehensive but more than 80 years old phase analytical study on potassium calcium silicates.