THERMODYNAMIC ANALYSIS OF THE BN-NH3 SYSTEM AT HIGH-PRESSURES

The temperature dependence of the equilibrium solubility of hBN and cB N in the supercritical ammonia up to 4.2 GPa have been calculated usin g phenomenological thermodynamic models. Experimental data on hBN solu bility in ammonia in the termperature range of 850 to 1500 K have been used For the determination of the interaction parameters of the regul ar solutions' model for the liquid phase. It was shown that the experi mental data on cBN solubility in ammonia in the whole experimental p, T-region can be best expressed by using the value of Delta H-tr = -162 00 J/mol for the hBN --> cBN transformation enthalpy, that was found e arlier by fluorine combustion calorimetry. The results obtained are in good agreement with the equilibrium p, T-phase diagram of boron nitri de.