HDDR of Sm-Co alloys using high hydrogen pressures

The hydrogen absorption behaviours of SmCo5 and Sm2O17 alloys were investig ated by differential scanning calorimetry (DSC) at hydrogen pressures up to 70 bar. X-ray diffraction studies and microstructural observations showed that the exothermic signal at about 100 degrees C can be attributed to the respective interstitial absorption reactions, whereas the second exothermic signals at about 600 degrees C for hydrogen pressures above 5 bar correspo nd to the respective disproportionation reactions of the Sm-Co phases into Sm hydride and Co or Go-rich phases. The favourable effect of high hydrogen pressures can be explained in terms of a decrease of the free enthalpy of the samarium hydride for increasing hydrogen pressures. The disproportionat ed material could be recombined successfully by removing the hydrogen in a second heat treatment in vacuum. Investigations of the magnetic properties showed coercivities mu(0J)H(C) of up to 2.1 and 0.6 T for high-pressure dis proportionated and subsequently recombined SmCo5 and Sm-2(Co, Fe, Cu, Zr)(1 7) powders, respectively. demonstrating clearly the positive effect of the hydrogen treatment on the coercivity. (C) 1999 Published by Elsevier Scienc e B.V. All rights reserved.