Synthesis of Nd2Fe14B nanocrystals using interstitial hydrides

Nd2Fe14B absorbs interstitial hydrogen on heating at 150-220 degrees C in H-2 gas, at about 1 bar initial pressure, in a closed volume and forms isostructural (P4(2)/mnm tetragonal) Nd2Fe14BHx, x less than or equal to 5, hydrides. Heating to higher temperatures, under the same closed volume, results in a partial release of interstitial H between 250 and 450 degrees C. Above 450 degrees C, the resultant alloy undergoes a phase transformation in a nanocrystalline mixture of NdH2+delta, with delta less than or equal to 1, and Fe(B). Subject to subsequently heating under a a dynamic vacuum at 800-900 degrees C, the NdH2+delta releases H and yields Nd atoms, which react with highly reactive Fe(B) particles and finally yield Nd2Fe14B particles of various sizes of nanometer to micrometer range, depending on the way of annealing at final temperature. The results are discussed in terms of the correlation of magnetic and microstructural properties.