Well-dispersed α-FeOOH prismatic particles with short axis length of 0.1 μm and axial ratio of 3 were obtained by a hydrothermal treatment of Fe
2O
3·2 H
2O which had been precipitated by the reaction between FeCl
3 and NaOH in water at 10°C. These seed particles were air-oxidized to hrow in an FeSO
4 aqueous solution with immersed Fe metal, in which the short axis length grew preferably compared with long axis length, retaining crystal morphology. After the crystal growth of 100 hours, uniform crystalline α-FeOOH particles with short axis length of 0.3 μm and axial ratio of 2 were obtained by a hydrothermal treatment at 200°C for 1 hour in a 1 mol/l of NaOH aqueous solution. Hiding power and brightness of the particles were improved by twice compared with those of the seed particles.
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