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

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 SmCo5 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 SmCo5 phase completely disproportionates into Sm hydride (SmH2±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 SmCo7 phase with a TbCu7 structure. The coercivity of SmCo7 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 SmCoC2 and cubic Co phases.