Fabrication and densification of magnetic alpha-Fe/Al2O3 nanocomposite by mechanical alloying

Fabrication of nanocomposite material for the Fe2O3-Al system by mechanical alloying (MA) has been investigated at room temperature. It is found that a-Fe/Al2O3 nanocomposite powders in which Al2O3 is dispersed in a-Fe matrix are obtained by mechanical alloying of Fe2O3 with Al for 5 hours. The change in magnetization and coercivity also reflects the details of the solid state reduction process of hematite by pure metal of Al during mechanical alloying. Densification of the MA powders was performed in a spark plasma sintering (SPS) machine using graphite dies at 1000 o C and 1100 degrees C under 60 MPa. Shrinkage change after SPS of MA'ed sample for 5 hrs was significant above 700 degrees C and gradually increased with increasing temperature up to 1100 degrees C. X-ray diffraction result shows that the average grain size of alpha-Fe in alpha-Fe/Al2O3 nanocomposite sintered at 1100 degrees C is in the range of 180 nm. It can be also seen that the coercivity (Hc) of SPS sample sintered at 1000 degrees C is still high value of 88 Oe, suggesting that the grain growth of magnetic alpha-Fe phase during SPS process tend to be suppressed.