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公开(公告)号：US20220344087A1
公开(公告)日：2022-10-27
申请号：US17762423
申请日：2020-09-29
Applicant: DOWA ELECTRONICS MATERIALS CO., LTD.
Inventor： Yasuto MIYAMOTO , Kazuhiro YAMAGA , Yuki MINEYAMA
Abstract: A method for making an iron-based oxide magnetic powder includes adding raw material solution containing trivalent iron ions, or trivalent iron ions and ions of a metal element that partially substitutes Fe sites, and an alkaline aqueous solution for neutralizing the raw material solution to a reaction system to adjust the pH of the reaction system to 1.0 or higher and 3.0 or lower. Hydroxycarboxylic acid is added to the obtained reaction solution and thereafter the pH of the reaction system is neutralized to 7.0 or higher and 10.0 or lower. The obtained precipitate of a substituent metal element-containing iron oxyhydroxide is coated with silicon oxide and then heated, whereby an iron-based oxide magnetic powder is obtained with a reduced content of fine and coarse particles, a particle shape close to a perfect sphere, and particles of ε-iron oxide in which Fe sites are partially substituted by other metal elements.
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公开(公告)号：US20230192508A1
公开(公告)日：2023-06-22
申请号：US17924163
申请日：2021-08-24
Applicant: DOWA ELECTRONICS MATERIALS CO., LTD.
Inventor： Yasuto MIYAMOTO
CPC classification number: C01G51/40 , G11B5/714 , H01F1/11 , C01P2002/50 , C01P2004/64 , C01P2006/42 , C01P2004/04
Abstract: A dispersed iron oxide magnetic powder slurry, in which the average secondary particle diameter of ε-type iron oxide measured with a dynamic light scattering particle size distribution analyzer is 65 nm or less, and which has good dispersibility, is obtained by adding a quaternary ammonium salt serving as a first dispersant and an alkali to a slurry containing ε-type iron oxide particles to bring the pH at 25° C. to 11 or higher, and thereafter adding an organic compound, which is an organic acid serving as a second dispersant and having two or more carboxy groups in the molecule, and in which one type or two types of a hydroxy group and an amino group are bound to carbon that does not constitute a carboxy group other than the carboxy groups to bring the pH at 25° C. of the slurry to 4 or higher and lower than 11.
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公开(公告)号：US20230352224A1
公开(公告)日：2023-11-02
申请号：US18127707
申请日：2023-03-29
Applicant: DOWA ELECTRONICS MATERIALS CO., LTD. , FUJIFILM CORPORATION
Inventor： Akifumi ONODERA , Yasuto MIYAMOTO , Masaki KOSHIKO , Toshio TADA , Takashi FUJIMOTO
IPC: H01F1/34
CPC classification number: H01F1/348
Abstract: A magnetic powder for a magnetic recording medium includes magnetic particles in which Ba in hexagonal barium ferrite is partially substituted with Sr, wherein a Dx volume represented by Dx volume (nm3) = Dxc × π × (Dxa/2)2 is 2,200 nm3 or less, and an Sr/(Ba+Sr) molar ratio is 0.01 to 0.15. One that satisfies Ku ≥ 0.1 × [Sr/(Ba+Sr) molar ratio] + 0.13 is more preferred. For the formulas, Dxc is a crystallite diameter (nm) in a c-axis direction of a hexagonal ferrite crystal lattice, Dxa is a crystallite diameter (nm) in an a-axis direction of the same crystal lattice, π is a circular constant, and Ku is a magnetocrystalline anisotropy constant (MJ/m3). By providing the hexagonal ferrite magnetic powder formed of fine particles, an effect of improving the perpendicular squareness ratio SQ of a magnetic recording medium is large.
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