Dowa Mining Co., Ltd.

Dowa Engineering Co., Ltd.

Seiichi Hisano

Kazushi Sano

Kazuhisa Saito

Yoshichika Horikawa

Yuichi Sato

Toshio Ueda

Seiji Isoyama

Yasuhiko Aihara

Shinichi Konno

Kazuyuki Matsumoto

Kenji Murata

Masayasu Senda

Satoshi Aizawa

Kenichi Inoue

Kazumasa Tezuka

Akito Inoue

Hyoichi Sasaki

Ikuo Watanabe

Akio Sawabe

A ferromagnetic powder containing iron as the principal component and containing more than 5 to 50 at. % Co, 0.1 to 30 at. % Al, 0.1 to 10 at. % of a rare earth element inclusive of Y, 0.05% by weight or less of an element belonging to Group 1 of the Periodic Table, and 0.1% by weight or less (inclusive of 0% by weight) of an element belonging to Group 2 of the Periodic Table, the powder comprising flat acicular particles having a mean major axis length of 0.01 to 0.40 &mgr;m and a crystallite diameter as determined by X-ray diffraction (Dx) of 50 to 250 angstrom, provided that the cross section diameter in the minor axis direction cut perpendicular to the major axis has a larger width and a smaller width, and that this cross section ratio in the minor axis direction, which is a larger width to smaller width ratio, uniformly yields a value of greater than 1, preferably 1.5 or higher, and the powder yielding a &sgr; /Dx ratio of 0.7 or higher, wherein, &sgr; represents the saturation magnetization and Dx represents the crystallite size determined by X-ray diffraction.

Ferromagnetic powder

A powder for use in the lower layer of a coating magnetic recording medium, comprising acicular particles with a mean major axis length in a range of from 0.01 to 0.5 &mgr;m and a mean minor axis length in a range of from 0.01 to 0.05 &mgr;m, provided that the acicular particles are flat acicular particles which, when cut in a direction perpendicular to the major axis, uniformly exhibit a cross section having a larger width to smaller width ratio of greater than 1, and that the quantity of discharged H O at 100&deg; C. is in a range of from 0.1 to 2.0% by weight.

Powder for use in lower layer of coating type magnetic recording medium

Iron oxyhydroxide particles that are composed of acicular particles having an average major axis of 0.01 to 0.5 &mgr;m and containing not less than 0.1 wt. % and not more than 30 wt. % of Al in the iron oxyhydroxide and that release not less than 0.1 wt. % and not more than 2 wt. % of H,O at 100&deg; C. are used as particles of a lower layer of a coating type magnetic recording medium having a multi-layer structure. The acicular particles include ones having two or more branches whose branching direction is skewed toward a two-dimensional orientation.

Particle for lower layer of coating type magnetic recording medium

Particles for lower layer of coating type magnetic recording medium

A coating type magnetic recording medium having a multilayer structure exhibits excellent strength, surface smoothness, and weather resistance is formed on a substrate, and comprises a magnetic layer of magnetic particles dispersed in a resinous binder, and a non-magnetic layer of non-magnetic particles dispersed in a resinous binder. The magnetic particles are composed of acicular ferromagnetic metal particles of Fe containing Co, Al, rare earth elements, periodic table group 1a and 2a elements. The non-magnetic particles are composed of acicular particles of .alpha.-FeOOH.

Coating type magnetic recording medium having a multilayer structure

There is provided an accicular ferromagnetic metal powder with which one can produce magnetic media for high-density recording that are improved in storage stability and magnetic characteristics. The improved ferromagnetic metal powder essentially consists of iron and 50 atm % based on the amount of iron of cobalt and at least one of aluminum and yttrium or any other rare earth element and contains no more than 0.05 wt % of an element of Group Ia of the periodic table (Li, Na, K). The amount of aluminum is in the range of 0.1-30 atm %, the amount of yttrium or any other rare earth element is in the range of and 0.1-10 atm %, each being based on the total quantity of the metal elements present. In either of these cases, the residue of an element of Group IIa of the periodic table (Mg, Ca, Sr, Ba) is preferably 0.1 wt % or less.

Ferromagnetic metal powder

There is provided a metallic magnetic powder with which one can produce magnetic media for high-density recording that are improved in storage stability and magnetic characteristics. The improved ferromagnetic metal powder contains no more than 0.05 wt % of an element of Group Ia of the periodic table. The powder may optionally contain 0.1-30 atm % of aluminum and/or 0.1-10 atm % of Y or any other rare earth element based on the total quantity of the metal elements present. In either of these cases, the residue of an element of Group IIa of the periodic table is preferably 0.1 wt % or less.

A permanent magnet made of an R--Fe--B--C or R--Fe--Co--B--C based alloy, where R is at least one rare-earth element, comprising individual magnetic crystal grains that are covered with an oxidation-resistant protective film. The protective film surrounding the individual magnetic crystal grains having a thickness of 0.001-30 .mu.m and 0.05-16 wt. % of the protective film comprising C.

Permanent magnet alloy having improved resistance

A process for producing a permanent magnet alloy based on a R--Fe--B--C system wherein R is at least one of the rare earth elements including Y, comprising the steps of preparing a molten crude alloy, producing a powder directly therefrom or after casting it into an alloy ingot and then grinding it into the powder, compacting the thus obtained powder and sintering the compacted product, the ingot or powder of the alloy before being sent to the compacting step being subjected to a heat treatment which is carried out at a temperature of 500.degree.-1,100.degree. C. for a period of 0.5 hour or more so as to produce a permanent magnet alloy based on an a R--Fe--B--C system whose individual magnetic crystal grains are covered with an oxidation-resistant protective film which has a C content higher than that of the individual crystal grains.

Process for production of permanent magnet alloy having improved

A permanent magnet made of an R-Fe-B-C or R-Fe-Co-B-C based alloy (where R is at least one rare-earth element) consisting of its individual magnetic crystal grains that are covered with an oxidation-resistant protective film is promising as a practicable next-generation magnet because of its having not only excellent magnetic properties inclusive of magnetic force that surpasses Sm-Co based magnets but also such highly improved oxidation resistance that may withstand use in practical applications for a prolonged time period without being coated on its outermost exposed surface with an oxidation-resistant protective film. Said protective film surrounding the individual magnetic crystal grains contains at least one, preferably substantially all, of the alloying elements of which said magnetic crystal grains are made, with 0.05-16 wt. %, preferably 0.1-16 wt. % of said protective film being composed of C.

Permanent magnet alloy having improved resistance to oxidation and

Reaction heat values of basic aluminum sulfate solution with acid such as sulfuric acid are correlative with an amount of base contained in said solution. The difference of temperatures of said solution before and after its reaction with said acid is utilized as an indication for the calibration of the basic amount in the solution. This calibration is effectively utilized for the control of the basic amount of said solution which is employed in the removal of SO.sub.2 gas from a waste gas.

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Chiba, Japan

Seiichi Hisano