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 f orms isostructural (P4(2)/mnm tetragonal) Nd2Fe14BHx, x less than or e qual to 5, hydrides. Heating to higher temperatures, under the same cl osed volume, results in a partial release of interstitial H between 25 0 and 450 degrees C. Above 450 degrees C, the resultant alloy undergoe s a phase transformation in a nanocrystalline mixture of NdH2+delta, w ith 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 na nometer to micrometer range, depending on the way of annealing at fina l temperature. The results are discussed in terms of the correlation o f magnetic and microstructural properties.