Gaseous Metal Nitrides. II. The Dissociation Energy, Heat of Sublimation, and Heat of Formation of Zirconium Mononitride

Abstract

The ZrN molecule has been identified in the vapor phase over a ZrN–BN mixture at temperatures above 2400°K using a combination of effusion and mass spectrometric techniques. Its apprearance potential was measured as 7.9 ± 0.4 eV. From the experimentally determined partial pressures the equilibrium constants and the enthalpy for the gaseous reaction ZrN = Zr + 0.5 N2 have been calculated. The reaction enthalpy was obtained as ΔH°298 = 22.0 ± 5.0 kcal/mole. Combined with published thermodynamic data this reaction enthalpy yields the following thermodynamic properties for gaseous ZrN: ZrN(g) = Zr(g) + N(g) D°298 = 135.0 ± 6.0 kcal ZrN(s) = ZrN(g) ΔH°s, 289 = 211.4 ± 9.0 kcal Zr(s) + 0.5N2(g) = ZrN(g) ΔH°f, 298 = 123.5 ± 7.0 kcal.