Preparation of acicular gamma-iron(III) oxide of high coercive force

A process for the preparation of highly coercive acicular gamma-iron(III) oxide from acicular iron(III) oxide hydroxide at a temperature of from 190.degree. to 700.degree. C. comprising:

• continuously passing the iron(III) oxide hydroxide into a first zone of a furnace having two or more heating zones, the temperature of the first zone being maintained at from 190.degree. to below 250.degree. C., said iron(III) oxide hydroxide being dehydrated to acicular .alpha.-iron(III) oxide;
• conveying the .alpha.-iron(III) oxide into the remaining heating zone or zones which zone or zones are at a temperature of from 300.degree. to 700.degree. C. and reducing the .alpha.-iron(III) oxide to magnetite in said remaining zone or zones by means of a gaseous mixture of an inert gas and an organic substance that is decomposable at a temperature above 250.degree. C. in the presence of iron oxide and which has a boiling point above 250.degree. C.;
• and thereafter oxidizing the magnetite to acicular gamma-iron(III) oxide with an oxygen containing gas at from 150.degree. to 400.degree. C., wherein the gaseous mixture acting as the reducing agent is produced by passing a stream of inert gas heated to above 250.degree. C. through said organic substance which is also heated to above 250.degree. C., said inert gas being heated to a temperature not less than the temperature to which the organic substance is heated, and the gaseous mixture on introduction into the furnace is first brought into contact with the .alpha.-iron(III) oxide entering said remaining heating zone or zones.