Abstract
The hydrogen absorption behaviours of SmCo 5 and Sm 2Co 17 alloys were investigated 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°C can be attributed to the respective interstitial absorption reactions, whereas the second exothermic signals at about 600°C for hydrogen pressures above 5 bar correspond to the respective disproportionation reactions of the Sm–Co phases into Sm hydride and Co or Co-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 disproportionated material could be recombined successfully by removing the hydrogen in a second heat treatment in vacuum. Investigations of the magnetic properties showed coercivities μ 0J H C of up to 2.1 and 0.6 T for high-pressure disproportionated and subsequently recombined SmCo 5 and Sm 2(Co,Fe,Cu,Zr) 17 powders, respectively, demonstrating clearly the positive effect of the hydrogen treatment on the coercivity.
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