PRODUCTION OF MAGNETIC PARTICLE POWDER OF NEEDLE CRYSTAL ALLOY

摘要

PURPOSE:To obtain magnetic particle powder of a needle crystal alloy having large specific surface areas and desired coercive force by coating the needle crystal alpha- FeOOH particles of a high axial ratio obtd. by adding a water soluble Mg salt to mixed suspensions of prescribed raw materials and subjecting the same to an oxidation treatment with an Ni and/or Al compd. then reducing the same by heating. CONSTITUTION:Suspensions contg. Fe(OH)2 of >=11pH are prepd. from an aq. soln. of ferrous sulfate added with a water soluble Mg salt (e.g.; MgSO4) so as to contain 0.1-20.0atom% in terms of Mg with respect to Fe and an aq. NaOH soln. Air is supplied to such suspensions to effect oxidation reaction, thereby allowing the Mg- contg. needle crystal alpha-FeOOH particles of 0.3-20mum long axis and >=20:1 axial ratio in average value to grow. An Ni and/or Al compd. of 0.5-10.0atom% in terms of Ni and/or Al is added and mixed to and with the suspensions contg. the above-described needle crystal particles. The resultant Mg-contg. needle crystal alpha-FeOOH particles coated with the Ni and/or Al compd. are reduced by heating in a reducing gas, whereby the magnetic particles of the needle crystal Fe-Mg alloy coated with the Ni and/or Al compd. are obtained.