Iron-based oxide magnetic powder and method for producing same

Patent metadata

Field	Value
Publication number	US-12428310-B2
Application number	US-202017764229-A
Country	US
Kind code	B2
Filing date	Sep 29, 2020
Priority date	Sep 30, 2019
Publication date	Sep 30, 2025
Grant date	Sep 30, 2025

Abstract

A 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 are added to a reaction system to adjust the pH of the reaction system from 1.0 to 3.0 or lower. Hydroxycarboxylic acid is added to the obtained reaction solution and the pH of the reaction system is then neutralized from 7.0 to 10.0 or lower. The obtained precipitate of a substituent metal element-containing iron oxyhydroxide is coated with silicon oxide, followed by heating so as to form particles of ε-iron oxide in which Fe sites are partially substituted by other metal elements, and then, a slurry containing the particles is classified. The iron-based oxide magnetic powder has a particle shape close to a perfect sphere and is suitable for use in a magnetic recording medium.

First claim

The invention claimed is:

1. An iron-based oxide magnetic powder, comprising particles of ε-iron oxide or ε-iron oxide in which Fe sites are partially substituted by other metal elements, wherein an average particle diameter measured with a transmission electron microscope is 10 nm or more and 20 nm or less, the number ratio of particles with a particle diameter of 8 nm or less is 3% or less, the number ratio of particles with a particle diameter of 20 nm or more is 25% or less, the average circularity of particles measured with a transmission electron microscope is 0.955 or more, and the coefficient of variation of the particle diameter measured with a transmission electron microscope is 19% or less.

2. The iron-based oxide magnetic powder according to claim 1 , wherein the metal element that partially substitutes the Fe sites is one or more types of Ga, Co, and Ti.

3. The iron-based oxide magnetic powder according to claim 1 , wherein the metal element that partially substitutes the Fe sites is one or more types of Ga, Co, Ti, Ni, Mn, Cr, Nd, Dy, and Gd.

4. A method for producing an iron-based oxide magnetic powder composed of particles of ε-iron oxide or ε-iron oxide in which Fe sites are partially substituted by other metal elements, comprising:
a raw material solution preparation step of preparing a raw material solution containing trivalent iron ions, or trivalent iron ions and ions of a metal element that partially substitutes the Fe sites, and an alkaline aqueous solution for neutralizing the raw material solution;
a first neutralization step of continuously or intermittently adding each of the raw material solution and the alkaline aqueous solution to a reaction system and mixing so as to adjust the pH of the reaction system to 1.0 or higher and 3.0 or lower;
a step of adding a hydroxycarboxylic acid to the aqueous solution after the first neutralization step;
a second neutralization step of neutralizing the pH to 7.0 or higher and 10.0 or lower by adding an alkali to the aqueous solution to which the hydroxycarboxylic acid is added, thereby obtaining a slurry containing a precipitate of an iron oxyhydroxide or a substituent metal element-containing iron oxyhydroxide;
a step of adding a silicon compound having a hydrolyzable group to the slurry containing the iron oxyhydroxide or the substituent metal element-containing iron oxyhydroxide, thereby coating the iron oxyhydroxide or the substituent metal element-containing iron oxyhydroxide with a hydrolysate of the silicon compound;
a step of heating the substituent metal element-containing iron oxyhydroxide coated with the hydrolysate of the silicon compound, thereby forming ε-iron oxide or ε-iron oxide, in which Fe sites are partially substituted by other metal elements, coated with silicon oxide;
a step of removing the silicon oxide on the ε-iron oxide or the ε-iron oxide, in which Fe sites are partially substituted by other metal elements, coated with the silicon oxide, thereby obtaining a slurry containing the ε-iron oxide or the ε-iron oxide, in which Fe sites are partially substituted by other metal elements;
a step of adding a quaternary ammonium salt at a concentration of 0.009 mol/kg or more and 1.0 mol/kg or less as a surface modifier to the slurry containing the ε-iron oxide or the ε-iron oxide, in which Fe sites are partially substituted by other metal elements, and also adjusting the pH to 11.0 or higher and 14.0 or lower;
a step of subjecting the surface modifier-containing slurry to a dispersion treatment, thereby obtaining a dispersion slurry of particles of the ε-iron oxide or the ε-iron oxide, in which Fe sites are partially substituted by other metal elements; and
a step of classifying the dispersion slurry of the particles of the ε-iron oxide or the ε-iron oxide, in which Fe sites are partially substituted by other metal elements.

5. The method for producing an iron-based oxide magnetic powder according to claim 4 , wherein the first neutralization step is a step of continuously or intermittently adding each of the raw material solution and the alkaline aqueous solution containing an alkali in an amount of 0.4 equivalents or more and 0.9 equivalents or less with respect to the total amount of an acid group contained in the raw material solution to the reaction system which does not contain trivalent iron ions or ions of a metal element that partially substitutes the Fe sites and mixing so as to adjust the pH of the reaction system to 1.0 or higher and 3.0 or lower.

6. The method for producing an iron-based oxide magnetic powder according to claim 5 , wherein in the first neutralization step, the addition rate of each of the raw material solution and the alkaline aqueous solution is adjusted so as to maintain the cumulative addition amount of the alkali with respect to the total cumulative addition amount of the acid group contained in the raw material solution within a range of 0.4 equivalents or more and 0.9 equivalents or less through the step.

7. The method for producing an iron-based oxide magnetic powder according to claim 5 , wherein the cumulative addition amount of the alkali with respect to the total cumulative addition amount of the acid group contained in the raw material solution is set to 0.6 equivalents or more and 0.9 equivalents or less through the first neutralization step.

8. The method for producing an iron-based oxide magnetic powder according to claim 4 , wherein the first neutralization step is a step in which when each of the raw material solution and the alkaline aqueous solution is continuously or intermittently added to the reaction system which previously contains trivalent iron ions, or trivalent iron ions and ions of a metal element that partially substitutes the Fe sites, the amount of the trivalent iron ions and the ions of the metal element that partially substitutes the Fe sites previously contained in the reaction system is set to 50 mol % or less of the sum of the amount of the trivalent iron ions and the ions of the metal element that partially substitutes the Fe sites and the amount of the trivalent iron ions and the ions of the metal element that partially substitutes the Fe sites contained in the raw material solution added to the reaction system, and each of the raw material solution and the alkaline aqueous solution containing an alkali in an amount of 0.4 equivalents or more and 1.8 equivalents or less with respect to the total amount of an acid group contained in the raw material solution is continuously or intermittently added to the reaction system and mixed so as to adjust the pH of the reaction system to 1.0 or higher and 3.0 or lower.

9. The method for producing an iron-based oxide magnetic powder according to claim 8 , wherein the cumulative addition amount of the alkali with respect to the total cumulative addition amount of the acid group contained in the raw material solution is set to 0.4 equivalents or more and 1.8 equivalents or less through the first neutralization step.

10. The method for producing an iron-based oxide magnetic powder according to claim 4 , wherein in the first neutralization step, the raw material solution and the alkaline aqueous solution are added over 10 minutes or more.

11. The method for producing an iron-based oxide magnetic powder according to claim 4 , wherein the average diameter measured with a dynamic light scattering particle size distribution analyzer of the slurry containing the iron oxyhydroxide or the substituent metal element-containing iron oxyhydroxide obtained in the second neutralization step is 300 nm or less.

12. The method for producing an iron-based oxide magnetic powder according to claim 4 , wherein iron (III) ch

Assignees

• Univ Tokyo
• Dowa Holdings Co Ltd

Inventors

• Ohkoshi Shin-Ichi
• Namai Asuka
• Tokoro Hiroko
• YOSHIKIYO Marie
• YAMAGA Kazuhiro
• Miyamoto Yasuto
• Mineyama Yuki
• Sakane Kenji
• Kawahito Tetsuya

Classifications

• C01P2004/64

  Nanometer sized, i.e. from 1-100 nanometer · CPC title

• C01P2004/04

  obtained by TEM, STEM, STM or AFM · CPC title

• B82Y40/00

  Manufacture or treatment of nanostructures · CPC title

• B82Y30/00

  Nanotechnology for materials or surface science, e.g. nanocomposites · CPC title

• B82Y25/00

  Nanomagnetism, e.g. magnetoimpedance, anisotropic magnetoresistance, giant magnetoresistance or tunneling magnetoresistance · CPC title