Synthesis of MgO–SiO 2 and CaO–SiO 2 amorphous powder by sol–gel process and ion exchange

Abstract

The processing of binary or ternary metal–oxide spherical powders often provides ideal starting materials for the preparation of ceramics or glasses, and the use of these powders can lead to excellent properties. Amorphous spherical powders composed of SiO 2 and MgO or CaO were synthesized by using Na 2O–SiO 2 spherical powder as a starting material and then conducting ion-exchange between the magnesium or calcium ions and the sodium ions in the Na 2O–SiO 2 powder. The maximum amount of magnesium or calcium in the powder was Mg/Si=0.5 or Ca/Si=0.8. The ratios of Mg/Si and Ca/Si were then determined by controlling the alkaline-earth concentration of the suspension used for the ion exchange. The ratio of Mg 2+ or Ca 2+ to consumed Na + as a result of the ion exchange was estimated to be 1.0, and it was found that OH − around Si–ONa also participates in the ion exchange. The ratio of water to ethanol in the reaction mixture also influenced the ion exchange.