Sintered ferrite magnet and its production method

Patent metadata

Field	Value
Publication number	US-9601247-B2
Application number	US-201314417678-A
Country	US
Kind code	B2
Filing date	Jul 24, 2013
Priority date	Jul 31, 2012
Publication date	Mar 21, 2017
Grant date	Mar 21, 2017

Abstract

A sintered ferrite magnet comprising main phases of ferrite having a hexagonal M-type magnetoplumbite structure, first grain boundary phases existing between two main phases, and second grain boundary phases existing among three or more main phases, the second grain boundary phases being dispersed in its arbitrary cross section, and the second grain boundary phases having an average area of less than 0.2 μm 2 , are produced by calcining, pulverizing, molding and sintering raw material powders having the general formula of Ca 1-x-y La x A y Fe 2n-z Co z , wherein 1−x−y, x, y and z and n representing a molar ratio are in desired ranges; 1.8% or less by mass of SiO 2 and 2% or less by mass (as CaO) of CaCO 3 being added to a calcined body after calcining and before molding; and the sintering step being conducted with a temperature-elevating speed of 1-4° C./minute in a range from 1100° C. to a sintering temperature, and a temperature-lowering speed of 6° C./minute or more in a range from the sintering temperature to 1100° C.

First claim

What is claimed is:

1. A method for producing a sintered ferrite magnet comprising main phases of ferrite having a hexagonal M-type magnetoplumbite structure, first grain boundary phases existing between two main phases, and second grain boundary phases existing among three or more main phases; said second grain boundary phases being dispersed in an arbitrary cross section of said sintered ferrite magnet; and said second grain boundary phases having an average area of less than 0.2 μm 2 ; said method comprising the steps of
preparing raw material powders comprising metal elements of Ca, La, an element A which is Ba and/or Sr, Fe and Co, which are represented by the general formula of Ca 1-x-y La x A y Fe 2n-z Co z , wherein 1−x−y, x, y and z representing the atomic ratios of said metal elements, and n representing a molar ratio meet:
0.3≦1−x−y≦0.65,
0.3≦x≦0.65,
0≦y≦0.2,
0.25≦z≦0.65, and
4.5≦n≦7;
calcining said raw material powders to obtain a calcined body;
pulverizing said calcined body to powder;
molding said powder to obtain a green body; and
sintering said green body to obtain a sintered body;
0-1.8% by mass of SiO 2 and 0-2% by mass (as CaO) of CaCO 3 being added to 100% by mass of said calcined body after calcining and before molding; and
said sintering step being conducted with a temperature-elevating speed of 1-4° C./minute in a temperature range from 1100° C. to a sintering temperature, and a temperature-lowering speed of 6° C./minute or more in a temperature range from the sintering temperature to 1100° C.

2. The method for producing a sintered ferrite magnet according to claim 1 , wherein the amount of SiO 2 added is 1-1.8% by mass, and the amount (as CaO) of CaCO 3 added is 1-2% by mass.

3. The method for producing a sintered ferrite magnet according to claim 2 , wherein the amount of SiO 2 added is 1.1-1.6% by mass, and the amount (as CaO) of CaCO 3 added is 1.2-2% by mass.

4. The method for producing a sintered ferrite magnet according to claim 1 , wherein 900 or more second grain boundary phases exist in a region of 53×53 μm 2 in an arbitrary cross section of the sintered ferrite magnet.

5. A sintered ferrite magnet comprising main phases of ferrite having a hexagonal M-type magnetoplumbite structure, first grain boundary phases existing between two main phases, and second grain boundary phases existing among three or more main phases; said second grain boundary phases being dispersed in its arbitrary cross section; and said second grain boundary phases having an average area of less than 0.2 μm 2 ;
wherein the sintered ferrite magnet comprises metal elements of Ca, La, an element A which is Ba and/or Sr, Fe and Co, and 0-1.8% by mass of SiO 2 ; said metal elements having the general formula of Ca 1-x-y La x A y Fe 2n-z Co z , wherein 1−x−y, x, y and z representing the atomic ratios of said metal elements, and n representing a molar ratio meet:
0.3≦1−x−y≦0.75,
0.2≦x≦0.65,
0≦y≦0.2,
0.25≦z≦0.65, and
3≦n≦6.

6. The sintered ferrite magnet according to claim 5 , wherein 900 or more second grain boundary phases exist in a region of 53×53 μm 2 in an arbitrary cross section of the sintered ferrite magnet.

Assignees

• Hitachi Metals Ltd

Inventors

• Kobayashi Yoshinori
• Hosokawa Seiichi
• Oda Etsushi

Classifications

• C04B2235/3227

  Lanthanum oxide or oxide-forming salts thereof · CPC title

• C04B2235/85

  Intergranular or grain boundary phases · CPC title

• C04B2235/3418

  Silicon oxide, silicic acids or oxide forming salts thereof, e.g. silica sol, fused silica, silica fume, cristobalite, quartz or flint · CPC title

• C04B2235/786

  Micrometer sized grains, i.e. from 1 to 100 micron · CPC title

• C04B2235/3275

  Cobalt oxides, cobaltates or cobaltites or oxide forming salts thereof, e.g. bismuth cobaltate, zinc cobaltite · CPC title