Study of hydrogen interaction with intermetallics R2Fe17 (R = Nd, Sm, Ho) by Calvet calorimetry

For the first time, the interaction of magnetic materials R2Fe17 (R = Nd, Sm, Ho) with hydrogen at 200 and 250 degrees C and a hydrogen pressure of up to 50 atm was studied by Calvet calorimetry. The dependences P = f(C), Delta Habs.(des.) = f(C) and Delta Sabs. = f(C) were obtained (P is the equilibrium pressure of hydrogen, Delta H is the enthalpy of the reaction, Delta S is the entropy of the reaction, C = H/IMC). It was found that the values of the enthalpy of the reaction of hydrogen with IMC (intermetallic compound) change with changes in the temperature of the process, the concentration of hydrogen in the metal matrix, as well as during the transition from one compound to another. On the plots of the dependence Delta Habs. (des.) = f (C) two sections can be distinguished where the enthalpy values are constant. It is suggested that the observed changes in the thermodynamic parameters of the process are related to the order of filling the interstitial sites 9e and 18g. The process of filling 9e interstitial sites occurs in two stages with different enthalpy (entropy) of the reactions. (C) 2021 Published by Elsevier B.V.