Hydrated ferric oxide needle crystals - obtd. by air oxidn. of soln. contg. ferrous and ammonium salts.

摘要

prepd. by addn. to an Fe(II) salt soln. of an NH4 salt so that the NH4+ concn. in the mixed soln. is at least 30 g/litre. The mixt. is then partially neutralised with NH3 and oxidised with air so that a liq. contg. crystalline nuclei is obtd. An Fe(II) salt soln. is then added continuously to the seeded liq. which is simultaneously kept at pH 4.0-6.5 by addn. of NH3 and air oxidised. Prod. is useful as yellow pigment or as raw material for magnetic prods. alpha-Hydrated Fe2O3 for the above uses must be in the form of needle crystals of suitable and uniform dimensions. Previous processes did not give the required particle size of uniformity and suitable crystals had to be prepd., sepd. and used for seeding which involved complex processes. The invention enables all these problems to be avoided and provides a simple, continuous process.