New synthetic method and thermochemistry of 4CaO• 5B2O3•7H2O

A pure calcium borate mineral, 4CaO(.)5B(2)O(3)(.)7H(2)O, 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(.)5B(2)O(3)(.)7H(2)O 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(.)5B(2)O(3)(.)7H(2)O was obtained from this result, measured enthalpies of solution of H3O3 in 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).