Thermodynamic data of belite polymorphs

Abstract

One major component of Portland cement clinker is Ca2SiO4 (C2S, belite). Synthetic samples of three polymorphs, β-C2S (larnite), γ-C2S (calcio olivine), and x-C2S were investigated by high-temperature oxide melt solution calorimetry at 700 °C to obtain their enthalpies of formation. A natural sample of wollastonite (CaSiO3) was measured for comparison. Low-temperature heat capacity data of the C2S phases were recorded by relaxation calorimetry using a PPMS. Supplementary DSC data of β- and γ-C2S were obtained to verify their heat capacity evolution to 400 °C.The recommended values for β-C2S and γ-C2S are:ΔfH0298γ−C2S = −2316.0 ± 4.5 kJ mol−1, S0298γ−C2S = 119.7 ± 0.9 J mol−1 K−1,CP(γ-C2S) = (249.098 − 1949.5 T–0.5 – 1.60822 ∙ 106 T−2 + 2.77532 ∙ 108 T−3) J K−1 mol−1, [T] = K,ΔfH0298β−C2S = −2307.6 ± 4.5 kJ mol−1, S0298β−C2S = 122.2 ± 0.9 J mol−1 K−1, andCP(β-C2S) = (259.721 − 2466.09 T–0.5 + 2.62687 ∙ 106 T−2 – 4.77891 ∙ 108 T−3) J K−1 mol−1, [T] = K.