US4280918A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Magnetic particle dispersions
Assignee: International Business Machines Corp
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Filing: 1980-03-10
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Granted: 1981-07-28
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Expires: 2000-03-10
Abstract
Abstract A magnetic dispersion is prepared by adjusting the pH of a mixture containing magnetic particles to a value which results in a positive electrostatic charge on the particles, while a mixture containing colloidal silica particles at the same pH results in negative electrostatic charges on the silica particles. Combining these mixtures causes the silica particles to coat and irreversibly bond to the magnetic particles resulting in better dispersion and less aggregation of the magnetic particles.
Inventors
- 👤 Andrew M. Homola
- 👤 Sondra L. Rice
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-23 22:55
CPC Classifications
H; H01; H01F; H01F1/00; H01F1/44; H01F1/445; Y; Y10; Y10S; Y10S516/00; Y10S516/924; Y10S516/928
Claims Analysis
Total Claims: 8
Claim 1
Independent Claim
101 words
A method of manufacturing a magnetic dispersion containing magnetic particles, comprising the steps of: leaching the dry magnetic particles in an acid to form a slurry; adjusting the pH of the said slurry to between 3 and 6 to produce a positive electrostatic charge on said magnetic particles; adding to said slurry a dispersion of colloidal particles having a pH between 3 and 6, the colloidal particles having a negative electrostatic charge thereon; and mixing said slurry with said dispersion, the opposite charges on said particles causing the colloidal particles to be attracted to and irreversibly bond to the magnetic particles.
Claim 2
Independent Claim
101 words
A method of manufacturing a magnetic dispersion containing magnetic particles, comprising the steps of: leaching the dry magnetic particles in an acid to form a slurry; adjusting the pH of the said slurry to between 3 and 6 to produce a positive electrostatic charge on said magnetic particles; adding to said slurry a dispersion of colloidal particles having a pH between 3 and 6, the colloidal particles having a negative electrostatic charge thereon; and mixing said slurry with said dispersion, the opposite charges on said particles causing the colloidal particles to be attracted to and irreversibly bond to the magnetic particles.
Claim 3
Dependent Claim
16 words
A method in accordance with claim 1, in which said colloidal particles are colloidal silica particles.
Claim 4
Dependent Claim
24 words
A method in accordance with claim 1, in which said colloidal particles have a uniform size distribution and size relation to said magnetic particles.
Claim 5
Dependent Claim
24 words
A method in accordance with claim 1, in which the pH of said slurry and of said colloidal dispersion is between 3.0 and 3.7.
Claim 6
Dependent Claim
31 words
A method in accordance with claim 1, including the step of raising the pH of said resulting mixture to approximately 9.5 to increase the electrostatic repulsion forces between said silica particles.
Claim 7
Dependent Claim
24 words
A method in accordance with claim 5, in which said colloidal particles have a uniform size distribution and size relationship to said magnetic particles.
Claim 8
Dependent Claim
24 words
A method in accordance with claim 1, including the step of removing water from the mixture by solvent exchange to produce a non-aqueous mixture.
References Cited (Backward Citations)
US2733160A
Cited
US2085129A
Cited
US2731326A
Cited
US2885366A
Cited
US3042616A
Cited
FR1294982A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1984-07-27 | 1985-01-26 | 1985-07-28 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1988-07-27 | 1989-01-26 | 1989-07-28 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1992-07-27 | 1993-01-26 | 1993-07-28 | $7700.00 | Window Closed / Lapsed |