Process for preparing ferrimagnetic acicular ferric oxide

Details Process for preparing ferrimagnetic acicular ferric oxide Process for preparing ferrimagnetic acicular ferric oxide

1976-09-14

1978-06-20

Vertiz, O. R.

Coating processes

Magnetic base or coating

252 6256, 423140, 423634, 427213, 427215, B05D 512

Patent

active

040962920

ABSTRACT:
A process is disclosed for preparing .alpha.-Fe.sub.2 O.sub.3 in the form of acicular particles substantially free from occluded boils or cavities, and containing from 0.2 to 2% by weight of SiO.sub.2, and having a mean axial ratio between 6 and 8, and an intrinsic coercive force of 320 - 370 Oe. An aqueous solution of FeSO.sub.4. 7H.sub.2 O is treated with alkali, in the presence of air, thus forming acicular .alpha.-FeOOH, which is then dehydrated, reduced at Fe.sub.3 O.sub.4 under fluidizing conditions, and oxidized to .gamma.-Fe.sub.2 O.sub.3 at 200.degree.-350.degree. C under fluidizing conditions. The formation of the acicular .alpha.-FeOOH is carried out at a yield of 0.5-2.5 kg of ferric Fe per hour per m.sup.3 of reactor; the reaction product is filtered and washed and the .alpha.-FeOOH particles are coated with 0.2-2% by weight of SiO.sub.2, from an aqueous suspension of .alpha.-FeOOH brought to a temperature ranging from 50.degree. to 90.degree. C, adding Na.sub.2 SiO.sub.3, and adjusting the final pH to 5.5-6.5; the .alpha.-FeOOH treated with SiO.sub.2 is dehydrated and simultaneously reduced to Fe.sub.3 O.sub.4 at a temperature between 480.degree. and 550.degree. C with a gaseous mixture selected from the class consisting of H.sub.2 + H.sub.2 O, CO + CO.sub.2, and H.sub.2 + CO + H.sub.2 O + CO.sub.2.

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