Abstract: A magnetic powder is disclosed which is characterized by possessing a powder compression characteristic such that the magnetic powder, after being packed in a closed container, pressed at a load of 400 kgf/cm.sup.3, and relieved of the load, exhibits a packing density in the range of 2.5 to 3.5 g/cm.sup.3 and a geometric standard deviation of not more than 1.5 in the particle diameter distribution. A magnetic recording medium using the magnetic powder mentioned above has high packing and, consequently, secures high output, and has ample diminution of noise.

Abstract: A magnetic recording medium is disclosed, which has a magnetic layer containing a hexagonal ferrite powder dispersed in a resin binder, the magnetic layer being formed on a nonmagnetic supporting substrate, wherein the hexagonal ferrite powder is a compound represented by the following chemical formulaAO.2 (M.sup.1 0).Fe.sub.16-x M.sup.2.sub.x 0.sub.24where A is at least one element selected from the group consisting of Ba, Sr, Ca, and Pb; M.sup.1 is at least one element selected from the group consisting of Zn, Ni and Co; M.sup.2 is one combination selected from the group consisting of a combination of two elements of Co and Ti, a combination of two elements of Ti and Zn, and a combination of three elements of Co, Ti and Zn; and x designates a number in the range from 0.6 to 3.0, the hexagonal ferrite powder having an average diameter/thickness ratio in the range from 2.0 to 5.

Abstract: An object of the present invention is to provide a magnetic powder for magnetic recording and a magnetic recording medium wherein stability of a coercive force of each of the magnetic powder and the magnetic recording medium is improved.The magnetic powder for magnetic recording and the magnetic recording medium having the magnetic powder used therfor are characterized in that the magnetic powder is composed mainly of a plate-shaped ferrite having a crystalline anisotropy and containing an element effective for reducing a temperature coefficient of coercive force of the magnetic powder, and that a difference between a coercive force (Hc) of the magnetic powder at a room temperature and a coercive force (Hc(s)) of the magnetic powder in such a state that the magnetic powder is dispersively deposited on the surface of silica (SiO.sub.2) powder particles is 100 (Oe) or less.

Abstract: A magnetic powder is disclosed which is characterized by possessing a powder compression characteristic such that the magnetic powder, after being packed in a closed container, pressed at a load of 400 kgf/cm.sup.3 and relieved of the load, exhibits a packing density in the range of 2.5 to 3.5 g/cm.sup.3 and a geometric standard deviation of not more than 1.5 in the particle diameter distribution. A magnetic recording medium using the magnetic powder mentioned above has high packing and, consequently, secures high output, and has ample diminution of noise.

Abstract: A magnetic powder for magnetic recording is disclosed which comprises composite magnetic particles (A), each of which contains hexagonal ferrite and spinel structure ferrite, and single phase magnetic particles of hexagonal ferrite (B). When the mixing ratio [(A):(B)] of (A) and (B) in the range from 5:95 to 95:5, remarkable effect can be obtained. Especially, when the mixing ratio of (A) and (B) is in the range from 5:95 to 30:70, the dispersion property is improved due to disturbance of magnetic stacking. Thus, the magnetic powder in this mixing ratio is particularly suitable for magnetic recording in a short wavelength range. When the mixing ratio of (A) and (B) is in the range from 70:30 to 95:5, the reproduction output is improved due to activation of (A). Thus, the magnetic powder in this mixing ratio is specifically suitable for magnetic recording in a long wavelength range.

Abstract: A magnetic powder for magnetic recording is disclosed which comprises composite type magnetic particles (A), each of which contains hexagonal ferrite and spinel structure ferrite, and single phase type magnetic particles of hexagonal ferrite (B). When the mixing ratio of (A) and (B) in the range from 5:95 to 95:5, remarkable effect can be obtained. Especially, when the mixing ratio of (A) and (B) is in the range from 5:95 to 30:70, the dispersion property is improved due to disturbance of magnetic stacking. Thus, the magnetic powder in this mixing ratio is particularly suitable for magnetic recording in a short wavelength range. When the mixing ratio of (A) and (B) is in the range 70: 30 to 95:5, the reproduction output is improved due to activation of (A) . Thus, the magnetic powder in this mixing ratio is specifically suitable for magnetic recording in a long wavelength range.

Abstract: Disclosed is a silicon nitride sintered body comprising 85 to 99 mole % of .beta.-Si.sub.3 N.sub.4, 1 to 5 mole % as the oxide (M.sub.2 O.sub.3) of at least one compound of an element (M) selected from the group consisting of Sc, Vb, Er, Ho and Dy and less than 10 mole % of excessive oxygen (O.sub.2) based on the three components, wherein the excessive oxygen/M.sub.2 O.sub.3 molar ratio is lower than 2.

Abstract: A molding method of ceramic body comprising the following steps of:preparing a ceramic slurry by adding, to ceramic raw material powders, a solvent, organic dispersant and caking agent and mixing them altogether; casting said ceramic slurry into a mold; cooling it to a temperature lower than the melting point of said caking agent; and taking it out of the mold.This molding method is capable of dissolving cracking generation during releasing the ceramic body from a mold, facilitating machining, decreasing the binder amount of organic compounds, diminishing a firing shrinkage and obtaining a higher dimension accuracy.

Abstract: Disclosed is a silicon nitride sintered body comprising 85 to 99 mol % of .beta.-Si.sub.3 N.sub.4, 1 to 5 mol % as the oxide (M.sub.2 O.sub.3) of at least one compound of an element (M) selected from the group consisting of Sc, Vb, Er, Ho and Dy and less than 10 mol % of excessive oxygen (O.sub.2) based on the three components, wherein the excessive oxygen/M.sub.2 O.sub.3 molar ratio is lower than 2.

Abstract: A magnetic recording powder comprising a hexagonal barium ferrite substituted with a coercive force control element. This magnetic powder is preliminarily treated with sulfate ion-containing water so as to convert any free barium ions in the magnetic powder to a water insoluble compound such as BaSO.sub.4 or BaS.sub.2 O.sub.7. There is also proposed a magnetic recording medium having a magnetic layer containing such a magnetic powder as mentioned above.

Abstract: A magnetic recording medium in which a hexagonal crystalline system ferromagnetic powder having a specific surface area of 25 to 50 m.sup.2 /g is dispersed in a resinous binder is suitable for high-density recording which is low in noise and is excellent in orientation properties.

Abstract: A matnetic recording powder comprising a hexagonal barium ferrite substituted with a coercive force control element. This magnetic powder is preliminarily treated with sulfate ion-containing water so as to convert any free barium ions in the magnetic powder to a water insoluble compound such as BaSO.sub.4 or BaS.sub.2 O.sub.7. There is also proposed a magnetic recording medium having a magnetic layer containing such a magnetic powder as mentioned above.

Abstract: Disclosed is a magnetic recording medium comprised of a substrate and a layer of magnetic powder coated on a surface of the substrate, characterized in that the magnetic powder is hexagonal crystals having single domain crystalline magnetic anisotropy, particle sizes of 0.01 to 0.3 .mu.m, particle size/thickness ratios of 2.3 to 15 and the tapping packing rate of said magnetic powder is 15% or more.

Abstract: A powder for a magnetic recording medium comprising a plurality of magnetic particles and a coating covering the surfaces of the magnetic particles. The coating is a residue resulting from the thermal decomposition of an organic material. The powder is manufactured by applying one or more organic materials to the surfaces of a plurality of magnetic particles by dispersing the magnetic particles in a solution containing the organic material. The magnetic particles, having the organic material as a coating, are separated from the solution, and the magnetic particles are heated to a temperature at which the organic material decomposes.

Abstract: A hexagonal ferrite magnetic powder for high density magnetic recording, having an improved dispersibility in a binder or paint is obtained by melting a mixture of hexagonal ferrite-forming components and a glass-forming component, and rapidly cooling the resultant molten mixture to obtain an amorphous material. The amorphous material is thermally treated to precipitate fine particles of the hexagonal ferrite therein. The amorphous material containing the precipitated fine particles is dissolved such that the glass-forming component remains on each of said fine particles in an amount of 0.01 to 0.3% by weight based on the weight of the particles.