α-Fe2O3 nano-platelets prepared by mechanochemical/thermal processing

A new method to prepare plate-shaped Fe 2 O 3 nanoparticles was investigated and their magnetic properties were characterised. First, Fe 2 O 3 nanoparticles of ~ 6 nm in diameter were synthesised by mechanochemical processing, involving the solid-state exchange reaction Fe 2 (SO 4 ) 3  + 3 Na 2 CO 3  → Fe 2 (CO 3 ) 3  + 3 Na 2 SO 4  → Fe 2 O 3  + 3 Na 2 SO 4  +  3 CO 2 (g) effected by high-energy ball milling and subsequent heat treatment at 400 °C. Next, nano-platelets were grown from the nanoparticles by further heat treatment in a salt matrix at 700 °C. Removal of the salt and by-product phases after heat treatment led to well-dispersed platy haematite particles of 20–200 nm in diameter with aspect ratio of 4–10. The hematite nano-platelets were weakly ferromagnetic with coercivity of ~ 160 Oe and remanent magnetisation of 0.2 emu/g.