Thermodynamic properties of RE2Co17 intermetallics at high temperatures (RE = Pr, Nd, Gd, Tb, Dy, Ho, Er, Tm, Lu)

A set of thermodynamic properties of the Co rich part of the Co/rare earth (RE) systems is presented for almost all the elements in the rare earth series. This set of data comes entirely from the emf vs. T experimental measurements obtained by galvanic cells with CaF2 single crystal as electrolyte. The standard enthalpy and entropy of formation of RE2Co17 intermetallics have been obtained and compared with previous results found for the RE2Ni17 and RE2Fe17 intermetallics. The values of the enthalpy of formation of RE2Co17 intermetallics are intermediate between the two series above. The RE2Co17 entropy of formation is positive from Pr to Dy and negative from Ho to Tm. The value of Lu2Co17 is notably positive. The RE solubility in Co has been evaluated by the shift of the fcc Co (200) lattice parameter with respect to the pure Co as shown by the corresponding XRD feature. Along the RE examined, the activity at 1000 K of RE in the Co solid solution changes from (7.1 ± 0.1) · 10−6 for Dy to (3.8 ± 0.2) · 10−4 for Pr.

► Thermodynamics of the Co rich part of the Co/rare earth (RE) systems is presented.
► Data comes from the emf vs T measurements by cells with CaF2 as solid electrolyte.
► Δf  HT¯⦵ and Δf  ST¯⦵ of RE2Co17 were compared with RE2Ni17 and RE2Fe17.
► Δf  HT¯⦵ values of RE2Co17 intermetallics are intermediate between the two series above.
► For RE2Co17, Δf  ST¯⦵ > 0 from Pr to Dy and <0 from Ho to Tm.