Claims
- 1. Cobalt-coated magnetic iron oxide particles satisfying the following equations (1), (2) and (3):
- 20.ltoreq.SSA.ltoreq.50 (1)
- -16.70.ltoreq.log [V].ltoreq.-3.05 log [SSA]-11.35 (2)
- 0.10.ltoreq.Fe.sup.2+ /total Fe.ltoreq.0.30 (3)
- where SSA is a BET specific surface area (m.sup.2 /g), and V is a magnetic switching unit (cm.sup.3) .
- 2. The cobalt-coated magnetic iron oxide particles according to claim 1, wherein the equation (2) is -16.70.ltoreq.log [V].ltoreq.-3.05 log [SSA]-11.50.
- 3. The cobalt-coated magnetic iron oxide particles according to claim 1, wherein the equation (3) is 0.20.ltoreq.Fe.sup.2+ /total Fe.ltoreq.0.30.
- 4. A process for producing cobalt-coated magnetic iron oxide particles according to claim 1, comprising the steps of:
- producing iron oxide particles having a concentration of Fe.sup.2+ of 0.10 to 0.36 as expressed by Fe.sup.2+ /total Fe by directly reducing lepidocrocite particles, or thermally dehydrating lepidocrocite particles at a lower temperature than that causing transformation to hematite particles and then reducing the dehydrate in the range of 250.degree. to 500.degree. C.; and
- then conducting oxidation at a temperature of 200.degree. C. or lower; and
- coating a cobalt compound or combination of a cobalt compound and at least one compound of metals other than cobalt which improve the ferromagnetic and noise characteristics of the resulting coated particles, on the surfaces of the iron oxide particles in an oxidizing or inert atmosphere.
- 5. The process for producing cobalt-coated magnetic iron oxide particles according to claim 4, wherein the iron oxide particles have a concentration of Fe.sup.2+ of 0.20 to 0.36 as expressed by Fe.sup.2+ /total Fe.
- 6. The process for producing cobalt-coated magnetic iron oxide particles according to claim 4, wherein the iron oxide particles have a concentration of Fe.sup.2+ of 0.28 to 0.36 as expressed by Fe.sup.2+ /total Fe.
- 7. The process for producing cobalt-coated magnetic iron oxide particles according to claim 4, wherein the lepidocrocite particles have an aluminum compound deposited on the surfaces of its particles.
- 8. The process for producing cobalt-coated magnetic iron oxide particles according to claim 7, wherein the amount of the aluminum compound deposited is 0.05 to 3.0% by weight Al based on the weight of the lepidocrocite.
- 9. The process for producing cobalt-coated magnetic iron oxide particles according to claim 4, wherein said step of coating a cobalt compound or combination of a cobalt compound and at least one compound of metals other than cobalt, said at least one compound of metals is selected from the group consisting of Fe, Mn, Zn, Ni and Cr.
Priority Claims (2)
Number |
Date |
Country |
Kind |
4-362114 |
Dec 1992 |
JPX |
|
5-052843 |
Feb 1993 |
JPX |
|
Parent Case Info
This is a continuation of application Ser. No. 08/174,469, filed on Dec. 28, 1993, which was abandoned upon the filling hereof.
US Referenced Citations (8)
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Continuations (1)
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Number |
Date |
Country |
Parent |
174469 |
Dec 1993 |
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