Thermodynamic properties of gallium hydroxide oxide (alpha -GaOOH) at temperatures to 700 K

The standard molal thermodynamic properties of alpha -GaOOH at T were retrieved from low-T heat capacity measurements, solubility measurements of alpha -GaOOH and beta -Ga (sub 2) O (sub 3) , and data available from the alpha -GaOOH-beta -Ga (sub 2) O (sub 3) transformation in the presence of aqueous solutions. The heat capacity of alpha -GaOOH as a function of T was found to be consistent with C degrees (sub p) = 54.38 + 0.06418 T-11.3 X 10 (super 5) /T (super 2) (J/mol/K) in the range 298-700 K. The estimated standard molal entropy is 51.61 + or - 0.26 J/mol.K, and the estimated standard Gibbs free energy of formation from the elements is -627.9 + or - 2.0 kJ/mol. These data allowed the prediction that alpha -GaOOH and beta -Ga (sub 2) O (sub 3) are the stable phases in the Ga-O-H system at saturated water vapour P below and above 573 K, respectively.