The Energetics of High Temperature Oxidation and Formation Mechanisms in Binary Lanthanide Nitrides (LnN)

Authors:
  • PUPascal Uhlemann
    Pascal Uhlemann
  • WVWilliam Vance
    William Vance
  • MHMathew Heaney
    Mathew Heaney
  • NYNatalie Yaw
    Natalie Yaw
  • CSChristian Schreinemachers
    Christian Schreinemachers
  • PHPeter Höhn
    Peter Höhn
  • GMGiuseppe Modolo
    Giuseppe Modolo
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Abstract
Nitride-based materials present exceptional thermal properties for advanced material applications, however accurate determination of their thermodynamic properties is critical for deployment. Herein, the standard enthalpies of formation, Δ H f ° , for all Ln N compounds ( Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Lu; excluding Pm) are determined via high temperature oxide melt calorimetry. These measurements are supported by high temperature oxidation studies of La, Ce, Sm, Eu, Er, Yb bearing Ln N compounds using a combination of X-ray diffraction and thermogravimetric analysis, and compared against similar measurements on other Ln N compounds. 1 The Δ H f ° were found to systematically correlate with the ionic radius of Ln + 3 cations, with smaller Ln bearing nitrides having more negative values. A discontinuity in Δ H f ° was further observed between larger and smaller Ln bearing Ln N compounds, consistent with the lanthanide tetrad effect. Using determined Δ H f ° with literature references, Gibbs energies of formation (Δ G f ° ), oxidation (Δ G ox ° ) and hydrolysis (Δ G hyd ° ) are calculated and compared against uranium nitride (UN) in the context of UN based nuclear fuel and spent nuclear fuel (SNF) management. The calculations indicate that the occurrence of Ln N phases within UN based SNF should lead to stabilisation of the structure and inhibit its oxidation.

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