Properties of CaCl2 hydrate with an inorganic powder. Part 2.—Melting behaviour and thermodynamic properties of CaCl2·nH2O (n= 6.00–7.35) with α-Al2O3 or α-SiC powder

Abstract

The melting behaviour of CaCl₂·nH₂O (n= 6.00 and 7.35) coexisting with two powders, α-Al₂O₃ and α-SiC, has been investigated by differential scanning calorimetry (DSC). With α-Al₂O₃ powder and CaCl₂· 6.00H₂O, the melting point of the hydrate and the molar enthalpy of melting decreased as the water content decreased and the specific surface area of the powder increased. The observed melting point corresponded to the transition point shown by the electrical conductivity. With α-SiC powder and CaCl₂· 6.00H₂O, the melting point and molar enthalpy of fusion for the hydrate were constant over the range 17.2–48.0 vol.% hydrate content. These observations led to the conclusion that the phase transition of the hydrate near the surface of the solid phase was significantly influenced by the hydrophilicity of the surface of the powder.