Determination of the melting parameters of boron nitride

The melting parameters of pyrolytic boron nitride under nitrogen pressure up to $50$ MPa were investigated. The region of parameters where condensed boron nitride exists in thermodynamic equilibrium was determined first with the help of a thermodynamic calculation. Then, based on experiments performed in this region, the brightness temperature of melting of boron nitride was measured at a wavelength of $0.633\,\mu$m: $2720 \pm 45$ K. The true melting temperatures of boron nitride were calculated using the values obtained for the emissivity by the two methods: $3370 \pm 75$ and $3230 \pm 90$ K.