US3951784A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Fine powder classification by ferrofluid density separation
Assignee: Avco Corp
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Filing: 1975-01-29
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Granted: 1976-04-20
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Expires: 1995-01-29
Abstract
Abstract A method of separating small diameter non-magnetic particles of different densities by using a low magnetic saturation ferrofluid and a high magnetic gradient to produce levitation by overcoming the magnetic attraction of the particles. Application of a constant gradient field of a level below the magnetic saturation level of the ferrofluid forms the ferrofluid into a density gradient column. Each non-magnetic particle levitates to the level inside the ferrofluid having the same apparent density as the particle. The ferrofluid contains magnetic particles with a mean effective core diameter less than about 50 angstroms and a stabilizing agent layer on the particle exceeding about 50 angstroms. Perfluorinated carriers and surfactants are preferred for their relatively high intrinsic density.
Inventors
- 👤 Robert Kaiser
- 👤 Leon Mir
- 👤 Richard A. Curtis
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-05 16:14
CPC Classifications
B; B03; B03C; B03C1/00; B03C1/32
Claims Analysis
Total Claims: 8
Claim 1
Independent Claim
54 words
A method of constructing a density gradient column in a ferrofluid comprising the step of: supplying a column of ferrofluid having a magnetization magnetic field intensity curve which includes a saturation region; and passing a constant gradient magnetic field through the ferrofluid, the maximum level of said magnetic field being below said saturation region.
Claim 2
Independent Claim
54 words
A method of constructing a density gradient column in a ferrofluid comprising the step of: supplying a column of ferrofluid having a magnetization magnetic field intensity curve which includes a saturation region; and passing a constant gradient magnetic field through the ferrofluid, the maximum level of said magnetic field being below said saturation region.
Claim 3
Independent Claim
115 words
A method of separating small diameter substantially non-magnetic particles having a diameter of 1 mm or less of different densities comprising: immersing said particles in a ferrofluid having a magnetic saturation of 100 gauss or less; applying a magnetic field of sufficient magnitude to produce a magnetic gradient capable of overcoming the forces produced by gravity to levitate the particles in said ferrofluid; and said magnetic field being a constant gradient field of a level lower than the magnetic saturation level of said ferrofluid whereby the ferrofluid is formed into a density gradient column and each non-magnetic particle therein levitates to a level in said ferrofluid having substantially the same apparent density as said particle.
Claim 4
Independent Claim
115 words
A method of separating small diameter substantially non-magnetic particles having a diameter of 1 mm or less of different densities comprising: immersing said particles in a ferrofluid having a magnetic saturation of 100 gauss or less; applying a magnetic field of sufficient magnitude to produce a magnetic gradient capable of overcoming the forces produced by gravity to levitate the particles in said ferrofluid; and said magnetic field being a constant gradient field of a level lower than the magnetic saturation level of said ferrofluid whereby the ferrofluid is formed into a density gradient column and each non-magnetic particle therein levitates to a level in said ferrofluid having substantially the same apparent density as said particle.
Claim 5
Dependent Claim
36 words
A method as in claim 1 wherein the magnetic particles of the ferrofluid have a mean effective magnetic core diameter of less than about 50A angstroms and a stabilizing agent layer thereon exceeding about 30A angstroms.
Claim 6
Dependent Claim
15 words
A method as in claim 1 wherein said magnetic gradient is greater than 1,000 oersted/centimeter.
Claim 7
Dependent Claim
90 words
A method as in claim 1 wherein the non-magnetic particles in said ferrofluid exhibit a ratio of particle attraction forces (F ss ) to particle separation forces (F 1 ) applied by said magnetized ferrofluid of less than 10, based on a computation ##EQU15## where: a = center to center spacing between particles D = diameter of the particles M = magnetic dipole moment per unit volume of ferrofluid ρ2 = density of the more dense particles ρ1 = density of the less dense particles g = acceleration of gravity.
Claim 8
Dependent Claim
20 words
A method as in claim 1 wherein the ferrofluid is temperature controlled to an essentially constant temperature during the separation.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1979-04-20 | 1979-10-20 | 1980-04-20 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1983-04-20 | 1983-10-20 | 1984-04-20 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1987-04-20 | 1987-10-20 | 1988-04-20 | $7700.00 | Window Closed / Lapsed |