Hydrogen absorption and desorption in Nd2Fe14B

Absorption and desorption of hydrogen by the permanent magnet material Nd2Fe14B have been studied using a microcomputer-controlled, thermomanometric analyzer with an initial hydrogen pressure of approximately 1 bar. Primary absorption occurs in the range 200–300 °C and results in the formation of a stable hydride with increased lattice parameters and Curie temperature. Subsequent hydrogen desorption, which is virtually complete by 650 °C, leaves the sample in an intermediate state. A second absorption step at about 720 °C corresponds to disproportionation of the Nd2Fe14B phase into α-Fe, Fe2B, and NdH2. Desorption of hydrogen from a hydrogenated sample heated in vacuum is maximum at 300 °C.