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Standard molar enthalpies of formation for the two mixed alkali/alkaline earth metal borates of LiBaB9O15 and NaBaB9O15

Ning Li,Rui-Bin Zhang,Zhi-Hong Liu

Two pure mixed alkali/alkaline earth metal borates with three-dimensional framework, LiBaB 9 O 15 and NaBaB 9 O 15 , have been synthesized by high-temperature solid state reaction, and characterized by XRD, FT-IR, DTA–TG techniques and chemical analysis. The molar enthalpies of solution of LiBaB 9 O 15 and NaBaB 9 O 15 in 1   mol   L −1 HCl(aq), and of LiCl·H 2 O(s)/NaCl(s) in [1   mol   L −1 HCl   +   H 3 BO 3   +   Ba(OH) 2 ·8H 2 O](aq) have been determined by microcalorimeter at 298.15   K, respectively. From these data and with the incorporation of the previously determined enthalpy of solution of H 3 BO 3 (s) in 1   mol   L −1 HCl (aq), together with the use of the standard molar enthalpies of formation for Ba(OH) 2 ·8H 2 O(s), LiCl·H 2 O(s)/NaCl(s), H 3 BO 3 (s), HCl(aq) and H 2 O(l), the standard molar enthalpies of formation of −(6796.8   ±   7.3)   kJ   mol −1 for LiBaB 9 O 15 and −(6829.9   ±   7.3)   kJ   mol −1 for NaBaB 9 O 15 were obtained on the basis of the appropriate thermochemical cycles.