Thermodynamics of Silicon Nitride. I. Standard Molar Enthalpy of Formation Δ}fHmo at the Temperature 298.15K of α-Si3N4 and β-Si3N4

Published

January 1, 1999

Author(s)

P A. O'Hare, I. Tomaszkiewicz, C M. Beck, H. J. Seifert

Abstract

Fluorine bomb calorimetric measurements of the massic energy of the reaction: Si₃N₄ (cr, α- or β-) + 6F₂(g) = 3SiF₄(g) + 2N₂(g) have shown that, within the combined uncertainties of the experiments, there is a negligible enthalpy difference between the α- and β- forms of Si₃N₄ at the temperature T= 298.15 K. The standard molar enthalpies of formation at T = 298.15 K have been determined: Δ}_fH_m^o(α-Si₃N₄) = -(828.9 ± 3.4) kJ.mol^-1, Δ}_fH_m^o(β-Si₃N₄) = -(827.8 ± 2.5) kJ.mol^-1. These results are approximately 40 kJ.mol^-1 more negative than the recommended value given in the most recent authoritative compilation of chemical thermodynamic information for inorganic substances. The enthalpy difference between α and β forms, (1 ± 4) kJ.mol^-1 at T = 298.15 K, is too small to be measured reliably by combustion calorimetry. It supports an earlier estimate of 1.25 kJ.mol^-1 from a modelling study, and unpublished results from recent low-temperature calorimetric measurements.

Citation

Journal of Chemical Thermodynamics

Volume

31

Pub Type

Journals

Keywords

calorimetry, enthalpy of formation, enthalpy of transition, silicon nitride

Citation

O'Hare, P. , Tomaszkiewicz, I. , Beck, C. and Seifert, H. (1999), Thermodynamics of Silicon Nitride. I. Standard Molar Enthalpy of Formation {Δ}_fH_m^o at the Temperature 298.15K of α-Si₃N₄ and β-Si₃N₄, Journal of Chemical Thermodynamics (Accessed November 8, 2024)