US4221776A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Manufacture of acicular ferrimagnetic iron oxides
Assignee: Emtec Magnetics GmbH
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Filing: 1979-01-25
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Granted: 1980-09-09
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Expires: 1999-01-25
Abstract
Abstract A process for the manufacture of acicular ferrimagnetic iron oxide by reducing heat-treated acicular iron(III) oxide hydroxide with an organic compound which decomposes in the presence of iron oxide at from 450° to 650° C., followed by at least partial oxidation with an oxygen-containing gas at from 200° to 500° C., wherein the iron(III) oxide hydroxide employed is heat-treated at from 450° to 700° C. and has a surface area, measured by the BET method, of from 10 to 23 m 2 /g.
Inventors
- 👤 Horst Autzen
- 👤 Helmut Jakusch
- 👤 Eberhard Koester
- 👤 Werner Loeser
- 👤 Peter Rudolf
- 👤 Wilhelm Sarnecki
- 👤 Werner Steck
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-27 11:19
CPC Classifications
C; C01; C01G; C01G49/00; C01G49/02; C01G49/06; G; G11; G11B; G11B5/00; G11B5/62; G11B5/68; G11B5/70; G11B5/706; G11B5/70626; G11B5/70642; G11B5/70647; G11B5/70652; G11B5/70678; G11B5/70684; G11B5/70694; C01P; C01P2004/00; C01P2004/10; C01P2006/00; C01P2006/12; C01P2006/42
Claims Analysis
Total Claims: 4
Claim 1
Independent Claim
185 words
A process for the manufacture of acicular ferrimagnetic iron oxide which comprises: (a) Heating acicular particles of synthetic lepidocrocite or a mixture of lepidocrocite and goethite containing at least 60% lepidocrocite in air or in an inert gas atmosphere and at a temperature in the range of 450° to 600° C. for a time sufficient to produce acicular particles having a surface area, measured by the BET method, of from 10 to 20 m 2 /g; (b) Reducing the resulting acicular particles to acicular magnetite particles by heating the same at a temperature in the range of 450° to 650° C. under an inert gas and in contact with an organic reducing compound which decomposes at said reducing temperature in the presence of iron oxide; and (c) oxidizing the resulting magnetite particles at a temperature in the range of 200° to 500° C. and in the presence of air to convert said magnetite particles into acicular ferrimagnetic gamma-ferric oxide particles having a coercive force greater than 28.0 kiloamps/m, measured at a field strength of 100 kiloamps/m and a tap density of 1.2 g/cm 3 .
Claim 2
Dependent Claim
185 words
A process for the manufacture of acicular ferrimagnetic iron oxide which comprises: (a) Heating acicular particles of synthetic lepidocrocite or a mixture of lepidocrocite and goethite containing at least 60% lepidocrocite in air or in an inert gas atmosphere and at a temperature in the range of 450° to 600° C. for a time sufficient to produce acicular particles having a surface area, measured by the BET method, of from 10 to 20 m 2 /g; (b) Reducing the resulting acicular particles to acicular magnetite particles by heating the same at a temperature in the range of 450° to 650° C. under an inert gas and in contact with an organic reducing compound which decomposes at said reducing temperature in the presence of iron oxide; and (c) oxidizing the resulting magnetite particles at a temperature in the range of 200° to 500° C. and in the presence of air to convert said magnetite particles into acicular ferrimagnetic gamma-ferric oxide particles having a coercive force greater than 28.0 kiloamps/m, measured at a field strength of 100 kiloamps/m and a tap density of 1.2 g/cm 3 .
Claim 3
Dependent Claim
139 words
A process for the manufacture of acicular ferrimagnetic iron oxide which comprises: (a) Heating acicular particles of synthetic lepidocrocite or a mixture of lepidocrocite and goethite containing at least 60% lepidocrocite in air or in an inert gas atmosphere and at a temperature in the range of 450° to 600° C. for a time sufficient to produce acicular particles having a surface area, measured by the BET method, of from 10 to 20 m 2 /g; and (b) converting the resulting particles to acicular ferrimagnetic gamma-ferric oxide particles having a coercive force greater than 28.0 kiloamps/m, measured at a field strength of 100 kiloamps/m and a tap density of 1.2 g/cm 3 , by heating said particles in air, at a temperature below about 500° C. and in contact with an organic reducing compound which decomposes at said temperature.
Claim 4
Dependent Claim
139 words
A process for the manufacture of acicular ferrimagnetic iron oxide which comprises: (a) Heating acicular particles of synthetic lepidocrocite or a mixture of lepidocrocite and goethite containing at least 60% lepidocrocite in air or in an inert gas atmosphere and at a temperature in the range of 450° to 600° C. for a time sufficient to produce acicular particles having a surface area, measured by the BET method, of from 10 to 20 m 2 /g; and (b) converting the resulting particles to acicular ferrimagnetic gamma-ferric oxide particles having a coercive force greater than 28.0 kiloamps/m, measured at a field strength of 100 kiloamps/m and a tap density of 1.2 g/cm 3 , by heating said particles in air, at a temperature below about 500° C. and in contact with an organic reducing compound which decomposes at said temperature.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1983-09-09 | 1984-03-10 | 1984-09-09 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1987-09-09 | 1988-03-10 | 1988-09-09 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1991-09-09 | 1992-03-10 | 1992-09-09 | $7700.00 | Window Closed / Lapsed |