Production of finely divided acicular magnetic iron oxides
AssigneeBayer Aktiengesellschaft
InventorsLutz Leitner, Franz Hund
Life of this patent
Estimating the term…
Abstract
In the production of acicular, ferromagnetic iron oxide of high coercive force by oxidizing an iron (II)-hydroxide suspension with an oxygen-containing gas to form acicular iron (III) oxide hydroxide and dehydrating the iron (III) oxide hydroxide, optionally tempering, reducing and/or reoxidizing this into magnetic iron oxide, the improvement which comprises effecting the oxidation of the iron (II)-hydroxide suspension at a pH of at least about 13, the suspension including SiO.sub.2 in the form of a sol or soluble salt, the resulting iron (III) oxide hydroxide having SiO.sub.2 deposited thereon.
Claims6
In the production of acicular, ferromagnetic iron oxide of high coercive force by oxidizing an iron (II)-hydroxide suspension with an oxygen-containing gas to form acicular iron (III) oxide hydroxide and dehydrating the iron (III) oxide hydroxide, optionally tempering, reducing and re-oxidizing this into magnetic iron oxide, the improvement which comprises effecting the oxidation of the iron (II)-hydroxide suspension at a pH of at least 13, before the oxidation is more than 95% complete but after the oxidation is more than 50% complete SiO.sub.2 being present in the suspension in the form of a sol or soluble salt, the resulting iron (III) oxide hydroxide having SiO.sub.2 deposited thereon.
Dependencies are inferred from the claim text.