In this paper a study on the thermal behaviour of C4A3S̄ (in an open system and up to 1500 °C) is presented as well as the kinetics of decomposition of this compound. At temperatures higher than 1300 °C, the thermal decomposition of C4A3S̄ starts. Such a process is linked to a loss of SO2 simultaneously with a production of CA and CaO. After that CA and CaO reacts giving C12A7. If the temperature is lower than 1400 °C or even being higher than 1400 °C (between 1400 and 1500 °C) although only during the first moments, the decomposition process of C4A3S̄ occurs through a solid-gas reaction. This reaction is controlled by a first order kinetic and can be represented by the following equation: F1 (α) = Ln (1 − α) = − kT having a energy of activation Ea = 538 Kj mol. When the temperature surpasses 1400 °C then a melting of at least C12A7 and CA phases takes place. It occurs in such a way that when α > 0,5, the C4A3S̄ decomposition is produced in the presence of a quantity of liquid enough for considerably modifying its kinetic.

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