Hydrogenation and disproportionation of Sm2Fe17-xGax at high hydrogen pressures

In order to apply the hydrogenation-disproportionation-desorption-recombination process for the preparation of highly coercive Sm2Fe15Ga2Cy, which exhibits excellent magnetic properties together with a high thermal stability, the disproportionation of Sm2Fe17-xGax was investigated, A systematic study of the hydrogen absorption behavior of Sm2Fe17-xGax (x = 0, 0.5, 1, and 2) at hydrogen pressures between 0.5 and 8 bar by means of hydrogen differential thermal analysis (HDTA) showed that increased hydrogen pressures promote the disproportionation of the stabilized 2:17 phase. X-ray diffraction investigations of the HDTA samples showed a decreasing content of the 2:17 phase for increasing hydrogen pressures. It was possible to achieve a nearly full disproportionation even for the most stable compound Sm2Fe15Ga2 by applying a pressure of 8 bar. Microstructural changes within the disproportionated mixture as a result of the applied pressure have been documented in detail by high resolution scanning electron microscopy. (C) 1998 American Institute of Physics. [S0021-8979(98)22611-9].