Preparation of monodisperse peanut-type α-Fe₂O₃ particles from condensed ferric hydroxide gel

Recently, it has been found that monodisperse pseudocubic hematite particles 1.65 μm in mean edge length can be obtained in large quantities of the order of the molality with a yield close to 100%, by adding 100 ml of 5.4 N NaOH to 100 ml of well-stirred 2.0 M FeCl₃ and aging the resulting condensed gel of Fe(OH)₃ for 8 days at 100°C. The method was provisionally referred to as the gel-sol method. As an application of this technique, when 90 ml of 6.0 N NaOH and 10 ml of sulfate or phosphate solution were added instead of 100 ml of 5.4 N NaOH, the pseudocubic particles turned into peanut-type particles via an ellipsoidal shape with increasing concentration of the additives.