Prodn. of ferromagnetic needle-like gamma iron (III) oxide - having high coercive field strength and used in prodn. of magnetic recording supports

摘要

Prodn. is claimed of needle-like gamma-Fe(III) oxide modified with Sn-dioxide from Fe(III) oxide hydroxide contg. Lepidocrokite obtd. by adding alkalis to an aq. Fe(II) salt soln. under simultaneous oxidn. by introducing air into the aq. suspension, reducing the Fe(III) oxide hydroxide with H2 at 280-550 deg.C to magnetite and subsequently oxidising the magnetite with O2-contg. gases at 200-380 deg.C to form needle-like gamma-Fe(III) oxide. The prodn. of the Fe(III) oxide hydroxide contg. 5-40 wt.% residual Fe(III) the Sn-dioxide in an amt. of 0.1-1.0 wt.% is pptd. to aq. suspension by adding a hydrolisable Sn-cpd. and then the residual Fe(II) converted to Fe(III) oxide hydroxide. The Sn-dioxide-contg. Fe(III) oxide hydroxide is pref. tempered before being reduced to magnetite at 280-550 deg.C. USE/ADVANTAGE - The ferromagnetic Fe(III) oxide can be used in the prodn. of magnetic recording supports. It has a high coercive field strength and consists of stable individual particles which are not destroyed in the dispersing process necessary for the mfr. of magnetic supports.