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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 solu - tion for4CaO·5B 2 O 3 ·7H 2 O in approximately1mol·L -1 HCl was determined.The standard molar enthalpy of for - mation-(11658.74 ± 8.93)kJ·mol -1 for4CaO·5B 2 O 3 ·7H 2 O was obtained from this result,measured enthalpies of solution of H 3 BO 3 in1mol·L -1 HCl(aq.),of CaO in(HCl+H 3 BO 3 )aqueous solution,and the standard molar en- thalpies of formation of CaO(s),H 3 BO 3 (s)and H 2 O(l).
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 solu- tion for 4CaO · 5B 2 O 3 · 7H 2 O in approximately1mol·L -1 HCl was determined. The standard molar enthalpy of for-mation- (11658.74 ± 8.93) kJ · mol -1 for4CaO · 5B 2 O 3 · 7H 2 O was obtained from this result, measured enthalpies of solution of H 3 BO 3 in 1 mol·L -1 HCl (aq.), of CaO in (HCl + H 3 BO 3) aqueous solution, and the standard molar enamel formation of CaO (s), H 3 BO 3 (s) and H 2 O (l).