Effect of ball milling time on microstructure and magnetic properties of Fe-W nanocrystalline composite synthesised by hydrogen reduction and sintering

摘要

Sintered nanocrystalline Fe–W composites were synthesised by isothermal reduction of a Fe2O3–nWO3 powder mixture in pure hydrogen at 900uC. Before reduction, a 1:1 mixture of the powdersnwas ball milled thoroughly for 3, 9 or 15 h, then compacted and dried at 90uC for 24 h. Thenreduced powders were re-compacted and sintered at 1000uC for 2 h in hydrogen. The reductionnbehaviour was studied by thermogravimetric analysis. The microstructure, phase composition,npore distribution and magnetic properties of the initial oxide mixtures and of the reduced andnsintered products were characterised. Complete reduction was achieved in all cases, to give annanocrystalline homogenous composite with Fe of 13 nm crystallite size and W of 38 nm. A densencrystalline structure was observed within sintered samples having a total porosity of 52–54%. Thenmagnetic coercivity (Hc) of the sintered Fe–W specimens increased with increasing milling time,nwhereas magnetisation (Ms) decreased.