The formation of monosulphate from tetracalcium aluminoferrite and magnesium sulphate

The formation of monosulphate, by hydration of a tetracalcium aluminoferrit e powder, was investigated by isothermal calorimetry and X-ray diffraction (XRD) analyses. Hydration reactions were carried out isothermally at temper atures ranging from 25 to 80 degrees C in 0.25M, 0.5M, 1.0M, 2.0M, and 3.0M magnesium sulphate solutions. Gypsum was the initial hydration product in all magnesium sulphate concentrations and was the only crystalline hydratio n product in 2.0 M and 3.0 M magnesium sulphate solutions. Monosulphate was the dominant crystalline phase produced over the entire temperature range when hydration was carried out in magnesium sulphate concentrations between 0.25 M and 1.0 M. XRD and calorimetry also demonstrated that small amounts of calcium aluminium hydroxide, calcium aluminate carbonate hydrate and ma gnesium aluminate hydrate phases formed at the lower temperatures and in lo w (0.25M and 0.5M) magnesium sulphate concentrations. No crystalline phases incorporating iron were observed regardless of magnesium sulphate concentr ation or temperature.