Studies on synthesis, characterization and thermochemistry of Mg2[B2O4(OH)2]•H2O

A new magnesium borate Mg-2[B2O4(OH)(2)] . H2O has been synthesized by the method of phase transformation of double salt at hydrothermal condition and characterized by XRD, IR, TG and DSC. The enthalpy of solution of Mg-2[B2O4(OH)(2)] . H2O in 0.9764 mol L-1 HCl was determined. With the incorporation of the enthalpies of solution of H3BO3 in HCl (aq), of MgO in (HCl+H3BO3) (aq), and the standard molar enthalpies of formation of MgO(s), H3BO3(s), and H2O(l), the standard molar enthalpy of formation of -(3185.78 +/- 1.91) kJ mol(-1) of Mg-2[B2O4(OH)(2)] . H2O was obtained.