Enthalpy and Gibbs energy of formation of neodymium dicarbide

CO partial pressures over the univariant three-phase region containing NdO _1.5(s), C(s) and NdC ₂(s) were measured by using a quadrupole mass spectrometer (QMS) between 1403 and 1588 K. The NdC ₂(s) phase was generated in situ starting from a mixture of NdO _1.5(s) and C(s). The second-law and third-law enthalpies of the reaction NdO 1.5 ( s )+3.5 C ( s )= NdC 2 ( s )+1.5 CO ( g ) at 298 K were calculated. The enthalpy of formation of NdC ₂(s) was derived from the enthalpy of reaction and the enthalpies of formation of NdO _1.5(s) and CO(g) taken from the literature. The Gibbs energy of formation of NdC ₂(s) was derived from the Gibbs energy of formation of NdO _1.5(s) and CO(g) from the literature. The third-law enthalpy of the reaction is (648.1±1.0) and (647.6±1.0) kJ mol −1 based on thermal functions of NdC ₂(s) derived from those of UC _1.94 and ThC _1.94, respectively. The recommended enthalpy and Gibbs energy of formation of NdC ₂(s) at 298 K are −(90.8±6.0) and −(122.2±6.0) kJ mol −1 , respectively.