ISSN 0862-5468 (Print), ISSN 1804-5847 (online) 

Ceramics-Silikáty 36, (2) 105 - 108 (1992)


HYDROTHERMAL REACTIONS IN THE SYSTEM 3CaO.SiO₂ - CaSO₄.2H₂O - H₂O
 
Šatava Vladimír
 
Institute of the Chemistry of Glass and Ceramic Materials, Czechoslovak Academy of Sciences, Sokolská 38, 120 00 Prague 2, Czechoslovakia

The DHA method was used to investigate the sequence of reactions taking place in aqueous suspensions of mixtures of tricalcium silicate and gypsum, at heating rates of 1 to 10 °C/min. The first product to form is crystalline hydroxylellestadite Ca₁₀(SiO₄)₃.(SO₄)₃(OH)₂, and after the calcium sulphate has been spent, calcium hydrosilicate C₃SH1.5 is produced. Extrapolation to zero heating rate shows that hydroxylellestadite can already form at a temperature of 95 °C, and C₃SH1.5 at temperatures higher than 160 °C. The size of hydroxylellestadite crystals is larger by an order of quantity than that of C₃H1.5 crystals, and this is probably the cause of decreasing mechanical strength with increasing proportion of hydroxylellestadite in the reaction product.


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