Discoid hematite particles were prepared by a catalytic phase transformation method using co-precipitates of Fe(III) and Al(III) as a precursor. The effect of various factors such as the concentration of Al(III) ions, reaction temperature, the level of Fe(II) on the formation of these hematite particles was investigated. The product was characterized by XRD, SEM, TEM, ED, XPS. The magnetism and thermal stability of the product were also studied. The result shows that these discoid hematite particles can be prepared at initial pH 9, molar ratio nFe(II)/nFe(III)≤0.04 and nAl/nFe(III)＝0.14 in 100～140 ℃. The substitution of Fe(III) with Al(III) in the structure may cause a change in unit cell edges and magnetic performance due to their different ionic radii, although Fe and Al ions have the same valence and their oxides are isostructural equivalents belonging to the corundum system. The discoid α-Fe2O3 particles have been confirmed to be single crystal particles by ED pattern and they have good thermal stability.

Key words: Al-doping, discoid α-Fe2O3, single crystal particle, catalytic phase transformation