An experimental investigation of the formation enthalpies of intermetallic phases in the TM(Co,Fe)-REM(Tb,Ho,Er) systems

While the phase diagrams data for the Co-REM (Tb,Ho,Er) and Fe-Ho systems have been recently evaluated, the data on the enthalpy of formation data for the intermetallic compounds is still quite scarce. The enthalpies of formation of the intermetallic compounds Co17Tb2, Co17.12Ho1.88, Co17.25Er1.75, Co7Tb2 and Fe3Ho were determined using the drop-solution calorimetry. The following values for the formation enthalpies have been obtained in the current work: Delta H degrees f (Tb2Co17)= -6.3 +/- 2.0 kJ/mol/atom, Delta H degrees f(Ho1.88Co17.12)=-7.2 +/- 1.7 kJ/mol/atom, Delta H degrees f(Er1.75Co17.25)=-10.8 +/- 1.8 kJ/mol/atom, Delta H degrees f(Tb2Co7)=-20.7 +/- 2.1 kJ/mol/atom, Delta H degrees f(HoFe3)=-12.0 +/- 1.9 kJ/mol/atom. The dependencies of the formation enthalpies and melting temperatures from the atomic number of REM have been analysed for Co-REM compounds.