Quantitative Control of C2S Crystal Transformation
Crystal transformation of dicalcium silicate (2CaO•SiO2, C2S) has influences on the microstructure, hydraulicity, and grindability of cement clinker. The transformation of β-C2S to γ-C2S can destroy the clinker nodule integrity by volume expansion due to the low density of the γ-phase. It can be used to pulverize cement clinkers for saving grinding energy, but the hydraulicity of γ-C2S is lower than β-C2S. Quantitative control of C2S crystal transformation could balance the energy saving and hydraulicity. The influences of sintering temperatures, cooling methods and chemical impurities on the transformation were investigated. The results show that the appropriate sintering temperature of γ-C2S was 1250～1500 °C, and the rate of cooling should not be higher than 500 °C/min to guarantee β-C2S transform to γ-C2S. Chemical impurities (Na2O, P2O5, B2O3, Cr2O3 and K2O) were stabilizers of β-C2S, which could prevent β-C2S transforming to γ-C2S. The stability effect was related to their concentrations. The characteristic concentrations of Na2O, P2O5, B2O3, Cr2O3 and K2O were approximately 1.2%, 0.3%, 0.3%, 1.0% and 1.5%, respectively. Above these concentrations, most of β-C2S could be stabilized rather than transforming to γ-C2S. In “transition zone”, C2S crystal transformation could be controlled quantitatively by adjusting the stabilizer concentration.
Dongye Sun, Wen-Pei Sung and Ran Chen
M. Zhao "Quantitative Control of C2S Crystal Transformation", Applied Mechanics and Materials, Vols. 121-126, pp. 311-315, 2012