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

A new method to prepare plate-shaped Fe₂O₃ nanoparticles was investigated and their magnetic properties were characterised. First, Fe₂O₃ nanoparticles of ~6nm in diameter were synthesised by mechanochemical processing, involving the solid-state exchange reaction Fe₂(SO₄)₃+3 Na₂CO₃→Fe₂(CO₃)₃+3 Na₂SO₄→Fe₂O₃+3 Na₂SO₄+ 3 CO₂ (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 20–200nm in diameter with aspect ratio of 4–10. The hematite nano-platelets were weakly ferromagnetic with coercivity of ~160Oe and remanent magnetisation of 0.2emu/g.