Material property correlations for uranium mononitride: IV. Thermodynamic properties

Abstract

The experimental data for the specific heat ( C P ), enthalpy ( H), entropy ( S), Gibbs free energy ( G) and the free energy function (FEF), nitrogen and uranium vapor pressures ( P N 2, U ), and melting point ( T m ) of uranium mononitride (UN) have been collected and reviewed. Empirical correlations for these properties as functions of temperature ( T, in K) or nitrogen pressure ( P n 2 , in atm) were developed and are given as: C p( J/mol K)=51.14(Θ/T) exp(Θ/T) [ exp(Θ/T)−1] 2 +9.491×10 −3(T)+ 2.642×10 11 T 2 exp{−18081/T} , H(T)−H(298 K)( J/mol)= 51.14Θ exp(Θ/T)−1 +4.746×10 −3(T) 2−8148.34+1.461×10 7 exp{−18081/T} , S( J/mol K)= 51.14(Θ/T) exp(Θ/T)−1 −51.14 ln{1− exp(−Theta;/T)}+9.491×10 −3(T)+16.31, G( J/mol) = 51.14(T) ln{1− exp( −Θ T )} −4.746×10 −3(T) 2−16.31 + 1.461 × 10 7 exp{ −18081 T } , FEF(J/mol K) = −51.14 ln{1− exp(−Θ/T)}+4.746×10 −3(T)+ 8148.34 T +16.31− 1.461×10 7 T exp{−18081/T} , log 10(P N 2 , atm) = 1.822 + 1.882×10 −3(T)−23543.4/T , log 10(P U, atm) = 6.965 − 5.137×10 −4(T)−26616.1/T T m(K) = 3035.0(P N 2 ) 0.02832 , where Θ is the empirically determined Einstein temperature of UN, 365.7 K. The specific heat correlation was constructed from experimental data in the range of 298 ≤ T ≤ 2628 K. The enthalpy, entropy, Gibbs free energy and free energy function correlations were derived from the specific heat correlation and are therefore only strictly applicable over the same temperature range. The nitrogen and uranium vapor pressure correlations are valid for 1400 ≤ T ≤ 3107 K and 1400 ≤ T ≤ 2400 K, respectively, and the melting point correlation is valid for 10 −13 ≤ P N 2 ≤ 7.5 atm. However, all of the correlation forms employed are very stable; thus, application of these correlations to temperatures above the experimental limits should yield reasonable estimates for these properties.