Magnetic iron oxide particles and method of producing the 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.
Claims4
Magnetic iron oxide particles comprising spindle-shaped magnetite particles having the formula FeO.sub.x .multidot.Fe.sub.2 O.sub.3, 0<X.ltoreq.1 with the surface coated with 0.5 to 15.0 atomic % of Co based on Fe and Co, said magnetic iron oxide 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, a coercive force of 480 to 1,000 Oe and a corrected print-through characteristic Q.sub.3 at a coercive force of 700 Oe and a major axial diameter of 0.2 .mu.m of not less than 52 dB and showing a substantially uniform particle size, said particles produced by a process comprising the steps of:
- (a) aging an aqueous suspension 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;
- optionally heating said spindle-shaped goethite particles to form spindle-shaped hematite particles;
- (c) reducing said spindle-shaped goethite particles or spindle-shaped hematite particles in a reducing gas to produce spindle-shaped magnetite particles;
- (d) mixing an aqueous dispersion of said spindle-shaped magnetite particles with at least an aqueous Co salt solution and an aqueous alkaline solution so that the mixed dispersion has a pH of not less than 11;
- and
- (e) heating said mixed dispersion to a temperature of 50.degree. to 100.degree. C., thereby producing Co-coated spindle-shaped magnetite particles
- wherein said corrected print-through characteristic Q.sub.3 at a coercive force of 700 Oe and a major axial diameter of 0.2 .mu.m calculated from the following equation:
- Q.sub.3 =40.times.(0.2-A)+Q.sub.2
- wherein A is a major axial diameter (.mu.m) and Q.sub.2 is calculated from the following equation:
- Q.sub.2 =(700-C).times.0.02+B
- wherein B is a measured value of print-through characteristic (dB) and C is a measured value of a coercive force (Oe).
Magnetic iron oxide particles comprising spindle-shaped magnetite particles having the formula FeO.sub.x .multidot.Fe.sub.2 O.sub.3, 0<X.ltoreq.1 and containing zinc with the surface coated with 0.5 to 15.0 atomic % of Co based on Fe and Co, said magnetic iron oxide 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 8, a coercive force of 480 to 1,000 Oe and a corrected print-through characteristic Q.sub.3 at a coercive force of 700 Oe and a major axial diameter of 0.2 .mu.m of not less than 52 dB and showing a substantially uniform particle size, said particles produced by a process comprising the steps of:
- (a) aging an aqueous suspension 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;
- (b) blowing an oxygen-containing gas into the suspension containing said FeCO.sub.3 to oxidize it and produce spindle-shaped goethite particles;
- optionally heating said spindle-shaped goethite particles to form spindle-shaped hematite particles;
- (c) reducing said spindle-shaped goethite particles or spindle-shaped hematite particles in a reducing gas to produce spindle-shaped magnetite particles containing zinc;
- (d) mixing an aqueous dispersion of said spindle-shaped magnetite particles containing zinc with at least an aqueous Co salt solution and an aqueous alkaline solution so that the mixed dispersion has a pH of not less than 11;
- and
- (e) heating said mixed dispersion to a temperature of 50.degree. to 100.degree. C., thereby producing Co-coated spindle-shaped magnetite particles containing zinc wherein said corrected print-through characteristic Q.sub.3 at a coercive force of 700 Oe and a major axial diameter of 0.2 .mu.m is calculated from the following equation:
- Q.sub.3 =40.times.(0.2-A)+Q.sub.2
- wherein A is a major axial diameter (.mu.m) and Q.sub.2 is calculated from the following equation:
- Q.sub.2 =(700-C).times.0.02+B
- wherein B is a measured value of print-through characteristic (dB) and C is a measured value of a coercive force (Oe).
Magnetic iron oxide particles comprising spindle-shaped maghemite particles with the surface coated with 0.5 to 15.0 atomic % of Co based on Fe and Co, said magnetic iron oxide 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, a coercive force of 480 to 1,000 Oe and a corrected print-through characteristic Q.sub.3 at a coercive force of 700 Oe and a major axial diameter of 0.2 .mu.m of not less than 57.0 dB and showing a substantially uniform particle size, said particles produced by a process comprising the steps of:
- (a) aging an aqueous suspension 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;
- optionally heating said spindle-shaped goethite particles to form spindle-shaped hematite particles;
- (c) reducing said spindle-shaped goethite particles or spindle-shaped hematite particles in a reducing gas to produce spindle-shaped magnetite particles, and oxidizing the thus obtained spindle-shaped magnetite particles to produce spindle-shaped maghemite particles:
- (d) mixing an aqueous dispersion of said spindle-shaped maghemite particles with at least an aqueous Co salt solution and an aqueous alkaline solution so that the mixed dispersion has a pH of not less than 11;
- and
- (e) heating said mixed dispersion to a temperature of 50.degree. to 100.degree. C., thereby producing Co-coated spindle-shaped maghemite particles
- wherein said corrected print-through characteristic Q.sub.3 at a coercive force of 700 Oe and a major axial diameter of 0.2 .mu.m is calculated from the following equation:
- Q.sub.3 =40.times.(0.2-A)+Q.sub.2
- wherein A is a major axial diameter (.mu.m) and Q.sub.2 is calculated from the following equation:
- Q.sub.2 =(700-C).times.0.02+B
- wherein B is a measured value of print-through characteristic (dB) and C is a measured value of a coercive force (Oe).
Magnetic iron oxide particles comprising spindle-shaped maghemite particles containing zinc with the surface coated with 0.5 to 15.0 atomic % of Co based on Fe and Co, said magnetic iron oxide 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 8, a coercive force of 480 to 1,000 Oe and a corrected print-through characteristic Q.sub.3 at a coercive force of 700 Oe and a major axial diameter of 0.2 .mu.m of not less than 57.0 dB and showing a substantially uniform particle size, said particles produced by a process comprising the steps of
- (a) aging an aqueous suspension 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;
- (b) blowing an oxygen-containing gas into the suspension containing said FeCO.sub.3 to oxidize it and produce spindle-shaped goethite particles;
- optionally heating said spindle-shaped goethite particles to form spindle-shaped hematite particles;
- (c) reducing said spindle-shaped goethite particles or spindle-shaped hematite particles in a reducing gas to produce spindle-shaped magnetite particles containing zinc, and oxidizing the thus-obtained spindle-shaped magnetite particles containing zinc to produce spindle-shaped maghemite particles containing zinc;
- (d) mixing an aqueous dispersion of said spindle-shaped maghemite particles containing zinc with at least an aqueous Co salt solution and an aqueous alkaline solution so that the mixed dispersion has a pH of not less than 11;
- and
- (e) heating said mixed dispersion to a temperature of 50.degree. to 100.degree. C., thereby producing Co-coated spindle-shaped maghemite particles containing zinc wherein said corrected print-through characteristic Q.sub.3 at a coercive force of 700 Oe and a major axial diameter of 0.2 .mu.m is calculated from the following equation:
- Q.sub.3 =40.times.(0.2-A)+Q.sub.2
- wherein A is a major axial diameter (.mu.m) and Q.sub.2 is calculated frown the following equation:
- Q.sub.2 =(700-C).times.0.02+B
- wherein B is a measured value of print-through characteristic (dB) and C is a measured value of a coercive force (Oe).
Dependencies are inferred from the claim text.