DIFFERENTIAL SCANNING CALORIMETRIC STUDY OF HYDROGEN INDUCED AMORPHIZATION IN C15 LAVES PHASE GDCO2

Differential scanning calorimetry and x-ray diffractometry have been used to monitor reactions of the C15 Laves phase GdCo2 during constant-rate heating in a hydrogen atmosphere and to determine the enthalpy change of each reaction. The values of the enthalpy change DELTAH of hydrogen absorption, hydrogen-induced amorphization and crystallization are evaluated to be -67.2, -10.2, and -9.8 kJ/mol Gd, respectively. On the other hand, DELTAH of hydrogen desorption is +31.4 kJ/mol Gd. The amorphous a-GdCo2Hx alloy crystallizes to GdH2 and Co. Therefore, the total value of DELTAH of the above reactions along with the formation of GdCo2, -103 kJ/mol Gd, becomes nearly equal to that of formation of GdH2, -101 kJ/mol Gd.