Effect of phosphorus-doping on ternesite: Structure, thermal stability and hydration

Abstract

The successful synthesis of the solid solution Ca5(Si1-x/2O4)2S1-x/2PxO4 (C5S2S̅Px, x = 0.05, 0.10, 0.15, 0.20) was confirmed through analysis of X-ray diffraction and energy dispersive spectrometer data. Rietveld refinement revealed that the purity of ternesite can reach up to 99.42 % at a doping concentration of 5 %. Furthermore, changes in X-ray diffraction peaks and morphology suggest a shift in the preferred growth direction of crystallites as a result of the introduction of impurity element. The incorporation of P elements in C5S2S̅Px not only effectively reduces weight loss under high-temperature conditions but also elevates the temperature at which decomposition occurs. Isothermal calorimetry data indicates that C5S2S̅Px-CSA samples display higher cumulative heat release compared to C5S2S̅–CSA. Furthermore, the presence of C5S2S̅P0.20 accelerates the hydration kinetics of CSA cement by hindering ettringite formation. Moreover, varying levels of phosphorus doping in C5S2S̅Px have resulted in enhanced compressive strength at various ages of CSA cement maturation.