Physicochemical Study of the Self-Disintegration of Calcium Orthosilicate (β→γ) in the Presence of the C₁₂A₇ Aluminate Phase

The β-γ polymorphic transition of calcium orthosilicate (C₂S) is a key phenomenon in cement chemistry. During this transition, the compound expands due to structural changes and a significant reduction in its density is observed, leading to its disintegration into a powder with a very high specific surface area. Owing to this tendency of the C₂S material to "self-disintegrate", its production is energy-efficient and thus environmentally friendly. A physicochemical study of the self-disintegration process was conducted with the aim of determining how the amount of dodecacalcium hepta-aluminate (C₁₂A₇) in calcium orthosilicate (C₂S) affects the temperature at which the polymorphic transi-tions from α'L-C₂S to β-C₂S and from β-C₂S to γ-C₂S undergo stabilization. The applied techniques included differential thermal analysis (DTA), calorimetry and X-ray diffraction (XRD), and they made it possible to determine what C₂S/C₁₂A₇ phase ratio in the samples and what cooling rate constitute the optimal conditions of the self-disintegration process. The optimal cooling rate for C₂S materials with a C₁₂A₇ content of up to 60 wt% was determined to be 5 K·min^-1. The optimal mass ratio of C₂S/C₁₂A₇ was found to be 70/30, which ensures both efficient self-disintegration and desirable grain size distribution.