Powders Synthesized from Water Solutions of Sodium Silicate and Calcium and/or Magnesium Chlorides

Powders with phase composition including quasi-amorphous phases and calcium carbonate CaCO3 in the form of calcite or aragonite and sodium halite NaCl as a reaction by-product were synthesized from 0.5M aqua solutions of sodium silicate and 0.5M aqua solutions of calcium and/or magnesium chlorides. Starting solutions were taken in quantities which could provide precipitation of hydrated calcium and/or magnesium silicates with molar ratios Ca/Si = 1 (CaSi), Mg/Si = 1 (MgSi) or (Ca+Mg)/Si = 1 (CaMgSi). Hydrated calcium and/or magnesium silicates, hydrated silica, magnesium carbonate, hydrated magnesium carbonate or hydrated magnesium silicate containing carbonate ions are suspected as components of quasi-amorphous phases presented in synthesized powders. Heat treatment of synthesized powders at 400, 600, 800 °C and pressed preceramic samples at 900, 1000, 1100 and 1200 °C were used for investigation of thermal evolution of the phase composition and microstructure of powders and ceramic samples. Mass loss of powder samples under investigation during heat treatment was provided due to evacuation of H2O (m/z = 18), CO2 (m/z = 44) and NaCl at temperatures above its melting point. After sintering at 1100 °C, the phase composition of ceramic samples included wollastonite CaSiO3 (CaSi_1100); enstatite MgSiO3, clinoenstatite MgSiO3 and forsterite Mg2SiO4 (MgSi_1100); and diopside CaMgSi2O6 (CaMgSi_1100). After sintering at 1200 °C, the phase composition of ceramics CaSi_1200 included pseudo-wollastonite CaSiO3. After heat treatment at 1300 °C, the phase composition of MgSi_1300 powder included preferably protoenstatite MgSiO3. The phase composition of all samples after heat treatment belongs to the oxide system CaO–MgO–SiO2. Ceramic materials in this system are of interest for use in different areas, including refractories, construction materials and biomaterials. Powders prepared in the present investigation, both via precipitation and via heat treatment, can be used for the creation of materials with specific properties and in model experiments as lunar regolith simulants.