| Abstract: A pure calcium borate mineral, 4CaO·5B2O3·7H2O , was synthesized by phase transformation of double salt under hydrothermal condition and characterized by XRD, IR and chemical analysis. The molar enthalpy of solution for 4CaO·5B2O3·7H2O in approximately 1 mol·L-1 HCl was determined. The standard molar enthalpy of formation -(11 658.74±8.93) kJ·mol-1 for 4CaO·5B2O3·7H2O was obtained from this result, measured enthalpies of solution of H3BO3in 1 mol·L-1 HCl (aq.), of CaO in (HCl+H3BO3) aqueous solution, and the standard molar enthalpies of formation of CaO(s), H3BO3(s) and H2O(l). |
