Silicate bonding of inorganic materials

Abstract

The high-temperature behaviour of compacts pressed from granular minerals bonded with sodium silicate and treated with CO₂, SO₂ or H₂S to produce good green (unfired) strength was studied. Samples gassed with CO₂ contain bicarbonate and carbonate species which decompose on heating in at least four stages up to 1000°C. I R spectroscopy suggests that the more thermally stable species may be silicate carbonates. The temperatures of the decomposition reactions depend on the nature of the mineral matter and the composition of the sodium silicate. On heating, the sulphite species formed during SO₂-gassing are oxidized to sulphate which thermally decomposes with evolution of SO₂ in several stages, suggesting the presence of silicate-sulphate complexes, by analogy with the carbonated system. Heated H₂S-gassed specimens form oxy-sulphur species which behave differently to those of the SO₂-treated system. The fired strength of CO₂, SO₂ and H₂S-gassed specimens is generally greater than for ungassed materials. With CO₂ gassing, the greatest improvement in strength is obtained with sodium silicates of lower pH (higher SiO₂:Na₂O ratio).