Rs. Mottram et al., Application of hydrogen vibration milling in the processing of NdFeB and (Nd,Pr)FeB permanent magnets, INT J HYD E, 24(2-3), 1999, pp. 257-261
A Hydrogen Vibration Mill (HVM) was designed, constructed and then used to
produce Nd-Fe-B powders. The powders were processed to give fully; dense, s
intered magnets. When exposed to hydrogen, Nd-Fe-B material undergoes decre
pitation, splitting bulk material into highly friable particles, suitable f
or milling. The supply of hydrogen to the mill was from a LaNi5 store.
The mill construction allowed in situ hydrogenation and milling at 0.5-5 ba
r H-2. This occurred in a stainless steel chamber of 1000 cm(3) capacity wi
th carbon chrome milling balls. The amplitude of vibration was 2-4 mm at 45
Hz. The in situ decrepitation and dry milling facilitated a low oxygen con
tamination, which is beneficial to sintering and magnetic properties. A mil
ling time of 3 h yielded powders of 7 mu m mean diameter, suitable for prod
ucing magnets. The best properties obtained were an energy product of 305 k
Jm(-3), with coercivity of 704 kAm(-1). (C) 1999 International Association
for Hydrogen Energy. Published by Elsevier Science Ltd. All rights reserved
.