US4604229A
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Electrically conductive ferrofluid compositions and method of preparing and using same
Assignee: Ferrofluidics Corp
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Filing: 1985-03-20
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Granted: 1986-08-05
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Expires: 2005-03-20
Abstract
Abstract An electrically conductive ferrofluid composition and a method of preparing and using the ferrofluid composition in a ferrofluid seal apparatus, and which ferrofluid composition comprises a liquid carrier having a colloidal dispersion of ferromagnetic particles in an amount sufficient to provide magnetic properties to the ferrofluid composition and carbon particles in an amount sufficient to provide electrical conductive properties to the ferrofluid composition, the ferromagnetic and carbon particles stabilized in the ferrofluid composition by a surface active dispersing agent. The electrically conductive ferrofluid composition is usefully employed in a ferrofluid exclusion seal apparatus to provide an electrically conductive seal apparatus particularly useful for computer disk drives and sputtering apparatus in the semiconductive industry.
Inventors
- 👤 Kuldip Raj
- 👤 Lucian Borduz
- 👤 Hanumaiah L. Gowda
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-01 08:47
CPC Classifications
F; F16; F16C; F16C33/00; F16C33/02; F16C33/04; F16C33/06; F16C33/10; F16C33/1025; F16C33/103; F16C33/1035; F16C41/00; F16C41/002; F16J; F16J15/00; F16J15/16; F16J15/40; F16J15/43; G; G11; G11B; G11B19/00; G11B19/20; G11B19/2009; G11B33/00; G11B33/14; G11B33/1446; G11B33/1473; H; H01; H01B; H01B1/00; H01B1/20; H01B1/24; H01F; H01F1/00; H01F1/44; H01F1/442; F16C2370/00; F16C2370/12; Y; Y10; Y10S; Y10S277/00; Y10S277/919
Claims Analysis
Total Claims: 28
Claim 1
Independent Claim
77 words
An electrically conductive ferrofluid composition, which composition consists essentially of: (a) a nonvolatile liquid carrier; (b) colloidal-size single domain magnetic particles in an amount sufficient to provide magnetic properties to the ferrofluid composition; (c) colloidal-size electrically conductive carbon particles in an amount sufficient to provide electrical conductive properties to the ferrofluid composition; and (d) a dispersing agent in an amount sufficient to disperse and stabilize the colloidal magnetic and electrically conductive carbon particles in the liquid carrier.
Claim 2
Dependent Claim
77 words
An electrically conductive ferrofluid composition, which composition consists essentially of: (a) a nonvolatile liquid carrier; (b) colloidal-size single domain magnetic particles in an amount sufficient to provide magnetic properties to the ferrofluid composition; (c) colloidal-size electrically conductive carbon particles in an amount sufficient to provide electrical conductive properties to the ferrofluid composition; and (d) a dispersing agent in an amount sufficient to disperse and stabilize the colloidal magnetic and electrically conductive carbon particles in the liquid carrier.
Claim 3
Dependent Claim
18 words
The composition of claim 1 wherein the liquid carrier is a hydrocarbon oil or ester base liquid carrier.
Claim 4
Dependent Claim
23 words
The composition of claim 1 wherein the magnetic particles comprise single domain ferromagnetic particles having a diameter of less than about 1000 Å.
Claim 5
Dependent Claim
22 words
The composition of claim 1 wherein the ratio of dispersing agent to magnetic particles ranges from about 0.5/1 to 20/1 by weight.
Claim 6
Dependent Claim
22 words
The composition of claim 1 wherein the ratio of dispersing agent to carbon particles ranges from about 0.01/1 to 20/1 by weight.
Claim 7
Dependent Claim
22 words
The composition of claim 1 wherein the composition has an electrical resistivity of about 10 3 ohm-cm or less at 27° C.
Claim 8
Dependent Claim
21 words
The composition of claim 1 wherein the carbon particles or agglomerates range in size from about 20 Å to 1 millimeter.
Claim 9
Dependent Claim
23 words
The composition of claim 1 wherein the individual carbon particles and the magnetic particles range in size from about 20 to 300 Å.
Claim 10
Dependent Claim
26 words
The composition of claim 1 wherein the carbon particles are present in an amount of from about 1 to 25 percent by weight of the composition.
Claim 11
Dependent Claim
20 words
The composition of claim 1 wherein the carbon particles have a surface area of about 100-3000 meters square per gram.
Claim 12
Dependent Claim
33 words
The composition of claim 1 wherein the carbon particles comprise carbon black particles produced by a furnace process and which have a dry electrical resistivity of about 10 2 to 10 -2 ohm-cm.
Claim 13
Dependent Claim
19 words
The composition of claim 1 characterized in that electrical resistivity of the composition decreases with an increase in temperature.
Claim 14
Dependent Claim
15 words
The composition of claim 1 wherein the dispersing agent is an anionic or cationic surfactant.
Claim 15
Dependent Claim
130 words
The electrically conductive ferrofluid composition, which composition consists essentially of: (a) a nonvolatile liquid carrier; (b) finely divided single domain ferromgnetic particles having an average particle size of from about 20 to 300 Å; (c) electrically conductive carbon particles in an amount of from about 1 to 25 percent by weight of the composition, the undivided carbon particles having a particle size of 20 to 300 Å and an aggregate particle size of up to 1 millimeter; (d) a surface active dispersing agent to disperse and stabilize the magnetic and carbon particles, the ratio of the dispersing agent to the carbon particles ranges from about 0.01/1 to 20/1 by weight; and (e) the composition characterized by thixotropic behavior and having an electrical resistivity of about 10 3 ohm-cm or less.
Claim 16
Dependent Claim
130 words
The electrically conductive ferrofluid composition, which composition consists essentially of: (a) a nonvolatile liquid carrier; (b) finely divided single domain ferromgnetic particles having an average particle size of from about 20 to 300 Å; (c) electrically conductive carbon particles in an amount of from about 1 to 25 percent by weight of the composition, the undivided carbon particles having a particle size of 20 to 300 Å and an aggregate particle size of up to 1 millimeter; (d) a surface active dispersing agent to disperse and stabilize the magnetic and carbon particles, the ratio of the dispersing agent to the carbon particles ranges from about 0.01/1 to 20/1 by weight; and (e) the composition characterized by thixotropic behavior and having an electrical resistivity of about 10 3 ohm-cm or less.
Claim 17
Dependent Claim
34 words
The composition of claim 14 wherein the carbon particles have a surface area of about 100-3000 meter square per gram and have a dry electrical resistivity of about 10 +2 to 10 -2 ohm-cm.
Claim 18
Dependent Claim
18 words
The composition of claim 14 wherein the carbon particles are carbon black particles produced by a furnace process.
Claim 19
Independent Claim
89 words
A method of preparing an electrically conductive ferrofluid composition, which method comprises: (a) dispersing an electrically conductive amount of electrically conductive carbon black particles having an undivided particle size of less than about 5000 Å and aggregates of less than about 1 millimeter with a surface active dispersing agent in a liquid carrier to obtain a carbon black-containing liquid carrier; and (b) mixing the carbon black particles containing the liquid carrier with a ferrofluid composition comprising a compatible liquid carrier, a compatible dispersing agent and finely divided ferromagnetic particles.
Claim 20
Independent Claim
89 words
A method of preparing an electrically conductive ferrofluid composition, which method comprises: (a) dispersing an electrically conductive amount of electrically conductive carbon black particles having an undivided particle size of less than about 5000 Å and aggregates of less than about 1 millimeter with a surface active dispersing agent in a liquid carrier to obtain a carbon black-containing liquid carrier; and (b) mixing the carbon black particles containing the liquid carrier with a ferrofluid composition comprising a compatible liquid carrier, a compatible dispersing agent and finely divided ferromagnetic particles.
Claim 21
Dependent Claim
24 words
The method of claim 17 which includes dispersing the carbon particles to provide individual carbon particles of about 20 to 300 Å particle size.
Claim 22
Dependent Claim
28 words
The method of claim 17 wherein the carbon particles comprise furnace process carbon black particles having a surface area of about 100 to 3000 meters square per gram.
Claim 23
Dependent Claim
34 words
The method of claim 17 which includes employing a compatible, but different dispersing agent to disperse the carbon black particles than the dispersing agent used to disperse the magnetic particles in the ferrofluid composition.
Claim 24
Dependent Claim
23 words
The composition of claim 1 wherein the dispersing agent is selected from the group consisting of fatty acids, petroleum sulfonates and phosphate esters.
Claim 25
Dependent Claim
12 words
The composition of claim 1 wherein the magnetic particles are magnetite particles.
Claim 26
Dependent Claim
16 words
The composition of claim 1 wherein the liquid carrier comprises an ester oil or a polyalphaolefin.
Claim 27
Dependent Claim
112 words
An electrically conductive ferrofluid composition having an electrical resistivity of about 10 3 ohm-cm or less, which composition consists essentially of: (a) a nonvolatile liquid carrier; (b) single domain magnetite particles in an amount of from about 5 to 20 weight percent of the composition and having a particle size of about 20 to 300 Å; (c) carbon black particles derived from a furnace process in an amount of from about 5 to 18 weight percent of the composition and having a particle size of about 20 to 300 Å; and (d) a cationic or nonionic surface active dispersing agent in an amount to disperse and stabilize the magnetite and carbon particles.
Claim 28
Dependent Claim
112 words
An electrically conductive ferrofluid composition having an electrical resistivity of about 10 3 ohm-cm or less, which composition consists essentially of: (a) a nonvolatile liquid carrier; (b) single domain magnetite particles in an amount of from about 5 to 20 weight percent of the composition and having a particle size of about 20 to 300 Å; (c) carbon black particles derived from a furnace process in an amount of from about 5 to 18 weight percent of the composition and having a particle size of about 20 to 300 Å; and (d) a cationic or nonionic surface active dispersing agent in an amount to disperse and stabilize the magnetite and carbon particles.
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) | 1989-08-04 | 1990-02-03 | 1990-08-05 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1993-08-04 | 1994-02-03 | 1994-08-05 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1997-08-04 | 1998-02-03 | 1998-08-05 | $7700.00 | Window Closed / Lapsed |