Iron-based soft magnetic powder for dust core, method for production thereof, and dust core
An iron-based magnetic powder for dust cores has layers of phosphoric acid-based film and silicone resin film sequentially formed on the surface thereof. The phosphoric acid-based film contains at least one element selected from the group consisting of Co, Na, S, Si, and W. The iron-based powder effectively keeps insulation among iron powder particles, excels in mechanical strength even though the amount of insulating material is reduced due to achieve high-density forming, and exhibits good thermal stability necessary for electrical insulating properties even after high-temperature heat treatment.
1. An iron-based magnetic powder for dust cores which comprises an iron-based magnetic powder and layers of phosphoric acid-based film and silicone resin film sequentially formed on the surface thereof, wherein said phosphoric acid-based film at least contains Co.
2. The iron-based magnetic powder for dust cores as defined in claim 1 , wherein the silicone resin film is one which has been precured by heat treatment at 100-200° C. for 5 to 100 minutes.
3. The iron-based magnetic powder for dust cores as defined in claim 1 , wherein the silicone resin to form the silicone resin film is a trifunctional methyl silicone resin.
4. An iron-based magnetic powder for dust cores which comprises an iron-based magnetic powder and layers of phosphoric acid-based film and silicone resin film sequentially formed on the surface thereof, wherein said phosphoric acid-based film contains Co and at least one other element selected from the group consisting of Na, S, Si, and W.
5. The iron-based magnetic powder of claim 1 , wherein Co is contained in the phosphoric acid-based film by mixing a compound selected from the group consisting of Co 3 (PO 4 ) 2 and Co 3 (PO 4 ) 2 .8H 2 O in the phosphoric acid-based film.
6. The iron-based magnetic powder of claim 4 , wherein at least one other element selected from the group consisting of Na, S, Si, and W is contained in the phosphoric acid-based film by mixing a compound selected from the group consisting of Na 3 [PO 4 .12WO 3 ].nH 2 O, Na 4 [SiW 12 O 40 ].nH 2 O, Na 2 WO 4 .2H 2 O, SiO 2 .12WO 3 26H 2 O, and H 2 SO 4 in the phosphoric acid-based film.
7. The iron-based magnetic powder of claim, wherein at least one element selected from Mg and B is additionally contained in the phosphoric acid-based film.
8. The iron-based magnetic powder of claim 4 , wherein at least one element selected from Mg and B is additionally contained in the phosphoric acid-based film.
9. The iron-based magnetic powder of claim 7 , wherein at least one element selected from Mg and B is contained in the phosphoric acid-based film by mixing a compound selected from the group consisting of MgO and H 3 BO 3 in the phosphoric acid-based film.
10. The iron-based magnetic powder of claim 8 , wherein at least one element selected from Mg and B is contained in the phosphoric acid-based film by mixing a compound selected from the group consisting of MgO and H 3 BO 3 in the phosphoric acid-based film.
11. The iron-based magnetic powder of claim 1 , wherein Co is contained in the phosphoric acid-based film in the following amount based on 100 mass % of iron powder coated with the phosphoric acid-based film:
Co: 0.005-0.1 mass %.
12. The iron-based magnetic powder of claim 4 , wherein the elements, when they are contained in the phosphoric acid-based film, are contained in the following amounts based on 100 mass % of iron powder coated with the phosphoric acid-based film:
Co: 0.005-0.1 mass %,
Na: 0.002-0.6 mass %,
S: 0.001-0.2 mass %,
Si: 0.001-0.2 mass %, and
W: 0.001-0.5 mass %.
13. The iron-based magnetic powder of claim 1 , wherein the phosphoric acid-based film is 1-250 nm thick and the amount of the film is 0.01-0.8 mass %.
14. The iron-based magnetic powder of claim 4 , wherein the phosphoric acid-based film is 1-250 nm thick and the amount of the film is 0.01-0.8 mass %.
15. The iron-based magnetic powder of claim 1 , wherein the silicone resin film is 1-200 nm thick, the amount of the silicone resin film is 0.05-0.3 mass %, and the total thickness of the phosphoric acid-based film and the silicone resin film is less than 250 nm.
16. The iron-based magnetic powder of claim 4 , wherein the silicone resin film is 1-200 nm thick, the amount of the silicone resin film is 0.05-0.3 mass %, and the total thickness of the phosphoric acid-based film and the silicone resin film is less than 250 nm.
17. The iron-based magnetic powder for dust cores as defined in claim 4 , wherein the silicone resin film is one which has been precured by heat treatment at 100-200° C. for 5 to 100 minutes.
18. The iron-based magnetic powder for dust cores as defined in claim 4 , wherein the silicone resin to form the silicone resin film is a trifunctional methyl silicone resin.