The HD and HDDR processes in the production of Nd-Fe-B permanent magnets

Abstract

This paper describes work done on an EC-funded project to develop and scale up the hydrogenation, disproportionation, desorption and recombination (HDDR) process. The hydrogen decrepitation (HD) and HDDR processes are summarized together with earlier work showing that the HD process has considerable economic advantages and the recombination stage of the HDDR process is critical, but that it may be separated from the disproportionation stage. Holding the material for extended times in the disproportionated state increases the coercivity of the HDDR material and this improvement tails off exponentially with time. It is also shown that raising the temperature during disproportionation improves the loop shape and remanence of the HDDR material whilst reducing the hydrogen pressure during disproportionation reduces the time dependence of the reaction, allowing much shorter processing times.