Hydrogenation and disproportionation of SmCo5 compound by high energy ball milling in heptane

Abstract A traditional hydrogenation disproportionation desorption recombination (HDDR) technique succeeds in fabricating bonded Nd–Fe–B magnet while encounters difficulty in the fabrication of Sm–Co magnet, due to the higher thermodynamic stability of the Sm–Co compounds against the disproportionation by hydrogen. To induce the disproporationation of Sm–Co compounds, high pressure hydrogen under high temperature has to be employed. This paper reports a hydrogenation and disproporationation reactions of SmCo 5 compound that does not involve gaseous hydrogen: high energy ball milling in heptane. The H atom comes from heptane. Being milled for more than 600 min, the SmCo 5 phase completely disproportionates into Sm hydride (SmH 2 ± δ ) and cubic Co. Heating the disproportionated powder in vacuum from room temperature to 800 °C, two desorption processes, one between 200 and 400 °C and the other around about 600 °C, were observed. The desorbed gas is proved to be hydrogen by gas chromatography. The Heated product consists of mainly hexagonal SmCo 7 phase with a TbCu 7 structure. The coercivity of SmCo 7 phase is larger than 1 T, being able to meet the demand of permanent magnetic application. Excess high energy ball milling results in the appearance of minor SmCoC 2 and cubic Co phases.