Enthalpy and Gibbs energy of formation of neodymium dicarbide

Abstract

CO partial pressures over the univariant three-phase region containing NdO1:5 (s), C(s) and NdC2 (s) were measured by using a quadrupole mass spectrometer (QMS) between 1403 and 1588 K. The NdC2 (s) phase was generated in situ starting from a mixture of NdO1:5 …s† and C(s). The second-law and third-law enthalpies of the reaction NdO1:5 (s) ‡ 3:5 C…s† ˆ NdC2 …s† ‡ 1:5 CO…g† at 298 K were calculated. The enthalpy of formation of NdC2 …s† was derived from the enthalpy of reaction and the enthalpies of formation of NdO1:5 (s) and CO(g) taken from the literature. The Gibbs energy of formation of NdC2 (s) was derived from the Gibbs energy of formation of NdO1:5 (s) and CO(g) from the literature. The third-law enthalpy of the reaction is (648:1) and (647:6)kJ/mol based on thermal functions of NdC2 (s) derived from those of UC1:94 and ThC1:94 , respectively. The recommended enthalpy and Gibbs energy of formation of NdC2 (s) at 298 K are -90:8 and -122:2kJ/mol,respectively.