Ceramics-Silikáty 49 (2) 104-108 (2005)

HEAT EVOLUTION AND MECHANISM OF HYDRATION IN CaO-Al₂O₃-SO₃ SYSTEM

M. Dováľ, M. Palou, V. Kovár

The hydration behavior of CaO-Al₂O₃-SO₃ system has been investigated over the temperature range of 25 to 80°C and at three different water/solid ratios 0.5, 0.7 and 1.0 using isothermal conduction calorimeter. In the defined system, C₄A₃S known as Klein compound was supposed to be the main mineral phase. An increase in the temperature of hydration brought about initial acceleration of all samples treated under different water/solid ratios, as indicated by the increased hydration rate. Also, there was a clear evidence of increasing intensity of the main peaks with increasing water/solid ratio at hydration temperature of 25°C and 40°C. Contrarily, at higher temperatures (60°C and 80°C) the magnitude of hydration decreased with increasing water/solid ratio. Kinetics of hydration C₄A₃S can be described by Avrami model. The value of kinetic exponent n = 3 implies that the hydration was controlled by nucleation and three-dimensional crystal growth. Calculated values of activation energy for water/solid ratio 0.5, 0.7 and 1.0 were 21.0, 17.2 and 16.4 kJ/mol.

Keywords: Hydration, Calcium sulfoaluminate, Calorimetry, Kinetics, Mechanism