| 摘要 |
Pigmentary, anhydrous, red iron oxide is prepared by calcining at preferably 400-600 DEG C. a yellow iron oxide or magnetite to form anhydrous red oxide seed which is suspended in an aqueous ferrous sulphate solution in the presence of metallic iron and an oxidizing agent. When formation of the iron oxide is complete it may be filtered off, washed and dried at 100-110 DEG C., 5-30 g. of oxide seed may be added per litre of the bath. The ferrous sulphate solution is preferably maintained at 50-100 DEG C., and may contain 10 g. of ferrous ion per litre. The oxidizing agent when in the form of a gas, e.g. oxygen or air, is bubbled through the ferrous sulphate solution. The colour of the resulting pigment may be varied from a light red to a purplish-blue-red by described variations in the reaction conditions. Specification 153,792 is referred to. |
