Application of hydrogen vibration milling in theprocessing of NdFeB and (Nd, Pr)FeB permanent magnets

• Published in: International journal of hydrogen energy Vol. 24; no. 2; pp. 257 - 261
• Main Authors: Mottram, R.S, Yartys, V, Guegan, P.W, Harris, I.r
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01-03-1999
• ISSN: 0360-3199; 1879-3487
• DOI: 10.1016/S0360-3199(98)00072-X

A Hydrogen Vibration Mill (HVM) was designed, constructed and thenused to produce Nd-Fe-B powders. The powders were processed to give fully, dense, sinteredmagnets. When exposed to hydrogen, Nd-Fe-B material undergoes decrepitation, splitting bulkmaterial into highly friable particles, suitable for milling. The supply of hydrogen to the mill wasfrom a LaNi
5 store.
The mill construction allowed in situ hydrogenation and milling at 0.5–5 bar H
2. This occurred in a stainless steel chamber of 1000 cm
3 capacity with carbon chromemilling balls. The amplitude of vibration was 2–4 mm at 45 Hz. The in situ decrepitation and drymilling facilitated a low oxygen contamination, which is beneficial to sintering and magneticproperties. A milling time of 3 h yielded powders of 7
μm mean diameter, suitable forproducing magnets. The best properties obtained were an energy product of 305 kJm
−3, with coercivity of 704 kAm
−1.