Process for producing acicular magnetic metallic particle powder

A process for producing acicular magnetic metallic particles comprising the steps of:

• preparing an aqueous suspension of at least one acicular metal oxide particles as starting material selected from the group consisting of acicular ferric oxide particles, acicular iron (III) oxide hydroxide particles and each of these ones containing Co and/or Ni while adjusting the pH of the suspension at a value higher than 8;
• adding an amorphous water-soluble silicate into the suspension as fully agitated under non-oxidizing atmosphere so as to prevent the hydrolytic and oxidative decomposition of the amorphous silicate in the suspension into crystalline silica through this step while the pH of the suspension is in the range of 8-12, thereby providing homogeneous and dense coats of amorphous silicate on the acicular metal oxide particles;
• converting the resultant amorphous silicate coats on the particles into the crystalline silica coats by water-washing or neutralization with acid;
• and
• thereafter heating the particles in a stream of reducing gas at a temperature between 400.degree.-800.degree. C. and to thereby obtain acicular magnetic metallic particles.