Ferromagnetic particles and process for producing the same, and anisotropic magnet, bonded magnet and compacted magnet

Patent metadata

Field	Value
Publication number	US-9378876-B2
Application number	US-201213980703-A
Country	US
Kind code	B2
Filing date	Jan 19, 2012
Priority date	Jan 21, 2011
Publication date	Jun 28, 2016
Grant date	Jun 28, 2016

Abstract

Ferromagnetic particles including an Fe 16 N 2 compound phase in an amount of not less than 80% as measured by Mössbauer spectrum and each having an outer shell in which FeO is present in the form of a film having a thickness of not more than 5 nm. Ferromagnetic particles may be made by subjecting iron oxide or iron oxyhydroxide having an average major axis diameter of 40 to 5000 nm and an aspect ratio (major axis diameter/minor axis diameter) of 1 to 200 as a starting material to dispersing treatment to prepare aggregated particles; subjecting the iron compound particles passed through a mesh to hydrogen reducing treatment at a temperature of 160 to 420° C.; and then subjecting the resulting particles to nitridation treatment at a temperature of 130 to 170° C.

First claim

The invention claimed is:

1. A process for producing ferromagnetic particles comprising an Fe 16 N 2 compound phase in an amount of not less than 80% as measured by Mössbauer spectrum, and each having an outer shell in which FeO is present in the form of a film having a thickness of not more than 5 nm, the process comprising the steps of:
subjecting iron oxide or iron oxyhydroxide having an average major axis diameter of 40 to 5000 nm and an aspect ratio (major axis diameter/minor axis diameter) of 1 to 200 as a starting material to dispersing treatment to prepare aggregated particles having D50 of not more than 40 μm and D90 of not more than 150 μm;
allowing the obtained aggregated particles to pass through a mesh having a size of not more than 250 μm;
subjecting the iron compound particles passed through the mesh to hydrogen reducing treatment at a temperature of 160 to 420° C.; and
then subjecting the resulting particles to nitridation treatment at a temperature of 130 to 170° C.

2. The process for producing ferromagnetic particles according to claim 1 , wherein a saturation magnetization value as of the ferromagnetic particles as measured at 5 K is not less than 150 emu/g.

3. The process for producing ferromagnetic particles according to claim 1 , wherein a volume fraction of the FeO in the ferromagnetic particles is controlled such that a ratio of a volume of the FeO to a whole volume of the particles is not more than 25%.

4. The process for producing ferromagnetic particles according to claim 1 , wherein a coercive force He of the ferromagnetic particles is not less than 1.5 kOe.

5. The process for producing ferromagnetic particles according to claim 1 , wherein a nitridation rate of the ferromagnetic particles is 8.0 to 13 mol %, wherein the nitridation rate is determined from a lattice constant of the ferromagnetic particles.

6. The process for producing ferromagnetic particles according to claim 1 , wherein a BET specific surface area of the ferromagnetic particles is 5.0 to 40 m 2 /g.

Assignees

• Takahashi Migaku
• Ogawa Tomoyuki
• Ogata Yasunobu
• Kobayashi Naoya
• Polwatta Gallage Chammika Ruwan
• Kohara Kaori
• Toda Kogyo Corp
• Univ Tohoku

Inventors

• Takahashi Migaku
• Ogawa Tomoyuki
• Ogata Yasunobu
• Kobayashi Naoya
• Polwatta Gallage Chammika Ruwan
• Kohara Kaori

Classifications

• B22F1/00

  Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties · CPC title

• C01P2006/42

  Magnetic properties · CPC title

• C22C29/16

  based on nitrides {(containing cubic BN or wurtzitic BN and diamond C22C26/00)} · CPC title

• C01B21/0622

  with iron, cobalt or nickel · CPC title

• C01P2004/54

  Particles characterised by their aspect ratio, i.e. the ratio of sizes in the longest to the shortest dimension · CPC title