The influence of stirring and γ-Al2O3 or Na2O additives on the gyrolite formation in the CaO-quartz-H2O system

The influence of stirring and gamma-Al2O3 or Na2O additives on the gyrolite (Ca16Si24O60(OH)(8)center dot 14H(2)O) 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. Waterlsolid 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 degrees 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 degrees C 1.13 nm tobermorite (Ca5Si6O15(OH)(2)center dot 5H(2)O) dominates in the products. In the stirred Cao-quartz-Na2O-H2O system gyrolite formed more quickly - 24 hours of isothermal curing at 200 degrees C than in the unstirred suspension - 32 h. The results show that the addition of gamma-Al2O3 in the CaO-quartz-Na2O-H2O suspension stabilizes gyrolite and prevents its transformation to pectolite (NaCa2Si3O8(OH)).