Ceramics-Silikáty 51, (2) 106 - 111 (2007)

The influence of stirring and γ-Al₂O₃ or Na₂O additives on the gyrolite (Ca₁₆Si₂₄O₆0(OH)₈ ·14H₂O) formation process in the CaO–quartz–H₂O mixture has been examined. The molar ratios of primary mixtures were CaO/(SiO₂ + Al₂O₃) = 0.66 and Al₂O₃/(SiO₂ + Al₂O₃) = 0 or 0.025. Water/solid ratio of the suspension was equal to 10.0. Hydrothermal synthesis has been carried out in rotating autoclave (10 rpm) under the saturated steam pressure at 200°C; the duration of isothermal curing was 2, 4, 6, 8, 16, 24, 32, 48, or 72 hours. It has been found that in the pure mixture the presence of stirring has not positive influence on the gyrolite formation. Even after 72 h hydrothermal treatment at 200°C 1.13 nm tobermorite (Ca₅Si₆O₁₅(OH)₂ ·5H₂O) dominates in the products. In the stirred CaO–quartz–Na₂O–H₂O system gyrolite formed more quickly - 24 hours of isothermal curing at 200°C than in the unstirred suspension - 32 h. The results show that the addition of γ-Al₂O₃ in the CaO–quartz–Na₂O–H₂O suspension stabilizes gyrolite and prevents its transformation to pectolite (NaCa₂Si₃O₈(OH)).