Thermodynamic analysis of the bn-nh, system at high pressures

Abstract

The temperature dependence of the equilibrium solubility of hBN and cBN in the supercritical ammonia up to 4.2 GPa have been calculated using phenomenological thermodynamic models. Experimental data on hBN solubility in ammonia in the temperature range of 850 to 1500 K have been used for the determination of the interaction parameters of the regular solutions' model for the liquid phase. It was shown that the experimental data on cBN solubility in ammonia in the whole experimental p, Region can be best expressed by using the value of ΔH_tr= −16200 J/mol for the hBN → cBN transformation enthalpy, that was found earlier by fluorine combusfiion calorimetry. The results obtained are in good agreement with the equilibrium p, T-phase diagram of boron nitride.

Key Words:

• Boron nitride
• ammonia
• solubility
• thermodynamic analysis
• high pressure