FURTHER-STUDIES OF HYDROGENATION, DISPROPORTIONATION, DESORPTION AND RECOMBINATION PROCESSES IN A ND5FE2B6 BORIDE

The hydrogen absorption and desorption characteristics of, Nd5Fe2B6 we re studied in this work, particularly at high temperatures where the h ydrogenation, disproportionation, desorption and recombination (HDDR) process takes place. Two events of hydrogen absorption were observed f or the p-Nd5Fe2B6 compound when heated in hydrogen (p(H-2)=1 bar). In the lower temperature region (from 335 to 745 degrees C) the formation of an insertion type rhombohedral hydride Nd5Fe2B6Hx was observed, le ading to a rather small anisotropic lattice expansion (up to 2.63 vol% ) in the [001] direction. At temperatures higher than 745 degrees C, a disproportionation of this hydride occurs resulting in the formation of NdH3-x, NdB4 and eta-Nd1.1Fe4B4. The recombination of the three pha se mixture proceeds readily on heating in vacuum, employing conditions similar to those applied in the HDDR route for phi-Nd2Fe14B.