Abstract: Black magnetic iron oxide particles of the present invention having an average particle diameter of 0.1 to 0.3 &mgr;m, comprise: black spinel iron oxide particles as core particles; and a surface coat formed on the surface of each core particle, comprising fine spinel iron oxide particles, the content of FeO in a surface layer having a thickness of from a surface of each black magnetic iron oxide particle to about 3.5% per a radius of each black magnetic iron oxide particle, being 8 to 14% by weight based on the weight of Fe contained in said surface layer. Such black magnetic iron oxide particles not only have a sufficient blackness and excellent electrical properties, flowability and electrification property (charging property), but also exhibit a good compatibility with binder resins such as aromatic vinyl-based resins, acrylic-based resins and copolymer resins thereof, and a good dispersibility in these resins for a magnetic toner.

Abstract: Magnetite particles of the present invention have an average particle diameter of 0.05 to 0.50 .mu.m, each of the magnetite particles having a plurality of mountain-shaped protrusions with unsharpened crests on a surface of each magnetite particle, and the number of the mountain-shaped protrusions formed on the surface of each magnetite particle being in the range of 2 to 30 when viewed in projected plan; magnetic iron oxide particles for magnetic toner comprising not less than 60%, in particle number, of the said magnetite particles; and a magnetic toner comprising the said magnetic iron oxide particles and a binder resin. The magnetite particles of the present invention are free from the falling-off from toner particles. The toner particles of the present invention shows a good fluidity and produces visual images having a higher definition upon development of electrostatic latent images.

Abstract: Magnetic particles for a magnetic toner comprise:Fe.sup.2+ -containing iron oxide particles having an average particle size of 0.05 to 0.30 .mu.m,containing not less than 0.9 atm % and less than 1.7 atm % of silicon, calculated as Si, based on Fe,having a substantially cubic shape each ridge of which has a curved surface, andhaving a ratio .phi. represented by the following formula of more than 1.0 and less than 1.4:.phi.=l/wwherein l represents an average maximum length of said Fe.sup.2+ -containing particles and w represents an average minimum length of said Fe.sup.2+ -containing particles.

Abstract: Magnetite particles of the present invention have an average particle diameter of 0.05 to 0.50 .mu.m, each of the magnetite particles having a plurality of mountain-shaped protrusions with unsharpened crests on a surface of each magnetite particle, and the number of the mountain-shaped protrusions formed on the surface of each magnetite particle being in the range of 2 to 30 when viewed in projected plan; magnetic iron oxide particles for magnetic toner comprising not less than 60%, in number, of the said magnetite particles; and a magnetic toner comprising the said magnetic iron oxide particles and a binder resin. The magnetite particles of the present invention are free from the falling-off from toner particles. The toner particles of the present invention shows a good fluidity and produces visual images having a higher definition upon development of electrostatic latent images.

Abstract: A magnetic toner containing 100 parts by weight of magnetic Fe.sup.2+ -containing iron oxide particles having an average particle size of 0.05 to 0.30 .mu.m, containing not less than 0.9 atm % and less than 1.7 atm % of silicon, calculated as Si, based on Fe, having a substantially cubic shape each ridge of which has a curved surface, and having a ratio .phi. represented by the following formula of more than 1.0 and less than 1.4:.phi.=l/wwherein l represents an average maximum length of said Fe.sup.2+ -containing particles and w represents an average minimum length of said Fe.sup.2+ -containing particles, and 10 to 900 parts by weight of a toner resin.

Abstract: Disclosed herein is iron oxide particles comprising:100 parts by weight of material iron oxide particles having a specific surface area represented by the following formula (1):6/(.rho..multidot.d.sub.3).times..phi..sub.S (1)wherein .rho. represents a specific gravity of said iron oxide particles, d.sub.3 represents an area-average particle diameter (0.1 .mu.m.ltoreq.d.sub.3 .ltoreq.1.0 .mu.m) and .phi..sub.S represents an area shape factor) (1.0.ltoreq..phi..sub.S .ltoreq.2.0); and0.25 to 10 parts by weight (calculated as an oxide) of the fine particles of the oxygen compound, the fine particles of the hydrate or mixed fine particles thereof of one element selected from the group consisting of Al, Si, Zr and Ti, which are adhered to the surfaces of said iron oxide particles;the increment of said specific surface area of said iron oxide particles being 1 to 6 m.sup.2 /g, and the increment of said specific surface area with respect to the amount of said fine particles being not less than 0.35.

Abstract: Spherical magnetic iron oxide particles for a magnetic toner comprise:Fe.sup.2+ -containing iron oxide particles having an average particle diameter of 0.05 to 0.30 .mu.m,containing 1.7 to 4.5 atm % of silicon, calculated as Si, based on Fe and not more than 0.35 wt % of sulfur based on the total weight of said Fe.sup.2+ -containing iron oxide particles, andhaving a sphericity .phi. (.phi.=l/w) of 0.8 to 1.0, and a coercive force (Hc) and the average particle diameter (d .mu.m) which satisfy the following relationship:147-322.7.times.d.ltoreq.Hc.sub.(10 kOe) .ltoreq.207-322.7.times.d.

Abstract: The disclosure describes coated granular magnetite particles comprising:granular magnetite particle as a core, andM.sub.x Fe.sub.2+y O.sub.z as a surface layer, wherein M is Zn or Co, 0.4.ltoreq.x.ltoreq.1, x+y=1, and 4.0.ltoreq.z.ltoreq.4.3,the amount of M in said M.sub.x Fe.sub.2+y O.sub.z being 0.5 to 6 mol % based on the total Fe content in said granular magnetite particle as a core; anda process for producing the coated granular magnetite particles.

Abstract: Magnetic toner particles composed of magnetite core particles containing 0.10 to 1.00 wt % silicon and a hydrous coprecipiate of silica and alumina deposited or adhered on the surfaces of the magnetite core particles. The magnetic toner particles have an area-average diameter of 0.05 to 1.0 .mu.m.

Abstract: Granular magnetite particles useful as coloring pigments assuming a black color and containing elemental aluminum, 3 to 6 wt %, in the magnetite crystal lattice. The magnetite has a spinel structure with a lattice constant of 8.340 to 8.375 .ANG..

Abstract: Disclosed herein is iron oxide particles comprising:100 parts by weight of material iron oxide particles having a specific surface area represented by the following formula (1):6/(.rho..multidot.d.sub.3).times..phi..sub.s ( 1)wherein .rho. represents a specific gravity of said iron oxide particles, d.sub.3 represents an area-average particle diameter (0.1 .mu.m.ltoreq.d.sub.3 .ltoreq.1.0 .mu.m) and .phi..sub.s represents an area shape factor) (1.0.ltoreq..phi..sub.s .ltoreq.2.0); and0.25 to 10 parts by weight (calculated as an oxide) of the fine particles of the oxygen compound, the fine particles of the hydrate or mixed fine particles thereof of one element selected from the group consisting of Al, Si, Zr and Ti, which are adhered to the surfaces of said iron oxide particles;the increment of said specific surface area of said iron oxide particles being 1 to 6 m.sup.2 /g, and the increment of said specific surface area with respect to the amount of said fine particles being not less than 0.35.

Abstract: Disclosed herein is iron oxide particles comprising:100 parts by weight of material iron oxide particles having a specific surface area represented by the following formula (1):6/(.rho..multidot.d.sub.3).times..phi..sub.s (1)wherein .rho. represents a specific gravity of said iron oxide particles, d.sub.3 represents an area-average particle diameter (0.1 .mu.m.ltoreq.d.sub.3 .ltoreq.1.0 .mu.m) and .phi..sub.s represents an area shape factor) (1.0.ltoreq..phi..sub.s .ltoreq.2.0); and0.25 to 10 parts by weight (calculated as an oxide) of the fine particles of the oxygen compound, the fine particles of the hydrate or mixed fine particles thereof of one element selected from the group consisting of Al, Si, Zr and Ti, which are adhered to the surfaces of said iron oxide particles;the increment of said specific surface area of said iron oxide particles being 1 to 6 m.sup.2 /g, and the increment of said specific surface area with respect to the amount of said fine particles being not less than 0.35.