Magnetic iron oxide particles and method of producing same
AssigneeToda Kogyo Corporation
InventorsAtsushi Takedoi, Mamoru Tanihara, Tosiharu Harada, Masaru Isoai, Kazuhiro Fujita
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Abstract
Disclosed herein are magnetic iron oxide particles which have a spindle shape and a substantially uniform particle size and shape, and are substantially free of dendrites and have a large axial ratio (major axial diameter/minor axial diameter) and an excellent print-through characteristic, and a method of producing the same.
Claims8
Magnetic iron oxide particles comprising spindle-shaped magnetite (FeO.sub.x.Fe.sub.2 O.sub.3, 0<x.ltoreq.1) particles having a major axial diameter of 0.1 to 0.3 .mu.m, an axial ratio (major axial diameter/minor axial diameter) of not less than 7, and a print-through characteristic of not less than 45 dB and showing a substantially uniform particle size, said particles produced by a process comprising:
- (a) aging an aqueous solution containing FeCO.sub.3 obtained by reacting an aqueous alkali carbonate with an aqueous ferrous salt solution in a non-oxidizing atmosphere at a temperature of 40.degree. to 60.degree. C. for 50 to 100 minutes, the amount of aqueous alkali carbonate being 1.5 to 3.5 times equivalent based on Fe.sup.2+ in said aqueous ferrous salt solution;
- (b) blowing an oxygen-containing gas into the suspension containing said FeCo.sub.3 to oxidize it and produce spindle-shaped goethite particles;
- (c) providing spindle-shaped goethite particles coated with a sintering preventing material;
- and
- (d) reducing either said spindle-shaped goethite particles coated with the sintering preventing material, or spindle-shaped hematite particles obtained by heating said spindle-shaped goethite particles coated with the sintering preventing material in a reducing gas.
Magnetic iron oxide particles comprising spindle-shaped magnetite (FeO.sub.x.Fe.sub.2 O.sub.3, 0<x.ltoreq.1) particles containing zinc and having a major axial diameter of 0.1 to 0.3 .mu.m, an axial ratio (major axial diameter/minor axial diameter) of not less than 8, and a print-through characteristic of not less than 45 dB and showing a substantially uniform particle size, said particles produced by a process comprising:
- (a) aging an aqueous solution containing FeCO.sub.3 obtained by reacting an aqueous alkali carbonate with an aqueous ferrous salt solution in a non-oxidizing atmosphere at a temperature of 40.degree. to 60.degree. C. for 50 to 100 minutes, the amount of aqueous alkali carbonate being 1.5 to 3.5 times equivalent based on Fe.sup.2+ in said aqueous ferrous salt solution,
- wherein a zinc compound is added to a solution of said aqueous alkali carbonate, said aqueous ferrous salt solution, or said suspension containing FeCO.sub.3 in the course of aging prior to oxidation;
- (b) blowing an oxygen-containing gas into the suspension containing said FeCO.sub.3 to oxidize it and produce spindle-shaped goethite particles;
- (c) providing spindle-shaped goethite particles coated with a sintering preventing material;
- and
- (d) reducing either said spindle-shaped goethite particles coated with the sintering preventing material, or spindle-shaped hematite particles obtained by heating said spindle-shaped goethite particles coated with the sintering preventing material in a reducing gas.
Magnetic iron oxide particles comprising spindle-shaped maghemite particles having a major axial diameter of 0.1 to 0.3 .mu.m, an axial ratio (major axial diameter/minor axial diameter) of not less than 7, and a print-through characteristic of not less than 53 dB and showing a substantially uniform particle size, said particles produced by a process comprising:
- (a) aging an aqueous solution containing FeCO.sub.3 obtained by reacting an aqueous alkali carbonate with an aqueous ferrous salt solution in a non-oxidizing atmosphere at a temperature of 40.degree. to 60.degree. C. for 50 to 100 minutes, the amount of aqueous alkali carbonate being 1.5 to 3.5 times equivalent based on Fe.sup.2+ in said aqueous ferrous salt solution;
- (b) blowing an oxygen-containing gas into the suspension containing said FeCO.sub.3 to oxidize it and produce spindle-shaped goethite particles;
- (c) providing spindle-shaped goethite particles coated with a sintering preventing material;
- (d) reducing either said spindle-shaped goethite particles coated with the sintering preventing material, or spindle-shaped hematite particles obtained by heating said spindle-shaped goethite particles coated with the sintering preventing material in a reducing gas;
- and
- (e) oxidizing the thus obtained spindle-shaped magnetite particles to produce maghemite particles.
Magnetic iron oxide particles comprising spindle-shaped maghemite particles containing zinc and having a major axial diameter of 0.1 to 0.3 .mu.m, an axial ratio (major axial diameter/minor axial diameter) of not less than 8, and a print-through characteristic of not less than 53 dB and showing a substantially uniform particle size, said particles produced by a process comprising:
- (a) aging an aqueous solution containing FeCO.sub.3 obtained by reacting an aqueous alkali carbonate with an aqueous ferrous salt solution in a non-oxidizing atmosphere at a temperature of 40.degree. to 60.degree. C. for 50 to 100 minutes, the amount of aqueous alkali carbonate being 1.5 to 3.5 times equivalent based on Fe.sup.2+ in said aqueous ferrous salt solution,
- wherein a zinc compound is added to a solution of said aqueous alkali carbonate, said aqueous ferrous salt solution, or said suspension containing FeCO.sub.3 in the course of aging prior to oxidation;
- (b) blowing an oxygen-containing gas into the suspension containing said FeCO.sub.3 to oxidize it and produce spindle-shaped goethite particles;
- (c) providing spindle-shaped goethite particles coated with a sintering preventing material;
- (d) reducing either said spindle-shaped goethite particles coated with the sintering preventing material, or spindle-shaped hematite particles obtained by heating said spindle-shaped goethite particles coated with the sintering preventing material in a reducing gas;
- and
- (e) oxidizing the thus obtained spindle-shaped magnetite particles containing zinc to produce maghemite particles containing zinc.
Dependencies are inferred from the claim text.