EP0208391A2
Expired / Lapsed
EP
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Electrically conductive ferrofluid compositions and method of preparing and using same
Assignee: Ferrofluidics Corp
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Filing: 1986-03-19
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Granted: —
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Expires: 2006-03-19
Abstract
Abstract An electrically conductive ferrofluid composition and a method of preparing and of using the electrically conductive ferrofluid composition in a ferrofluid seal apparatus are all provided according to the invention. The 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 are stabilized in the ferrofluid composition by a surface active dispersing agent. The electrically conductive ferrofluid composition(24) is usefully employed in a ferrofluid exclusion seal apparatus (seen in the Fig.) to provide an electrically conductive seal apparatus for a computer disk drive (12, 14, 16). Ferrofluid exclusion seal apparatus is also useful in sputtering apparatus in the semi-conductive industry.
Inventors
- 👤 Kuldip Raj
- 👤 Lucian Borduz
- 👤 Hanumaiah L. Gowda
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-03 15:06
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: 53
Claim 1
Independent Claim
68 words
An electrically conductive ferrofluid composition, which composition comprises: a) a liquid carrier; b) magnetic particles in an amount sufficient to provide magnetic properties to the ferrofluid composition; c) 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 magnetic and electrically conductive particles in the liquid carrier.
Claim 2
Dependent Claim
68 words
An electrically conductive ferrofluid composition, which composition comprises: a) a liquid carrier; b) magnetic particles in an amount sufficient to provide magnetic properties to the ferrofluid composition; c) 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 magnetic and electrically conductive particles in the liquid carrier.
Claim 3
Dependent Claim
126 words
The electrically conductive ferrofluid composition, which composition comprises: a) a liquid carrier; b) finely divided single domain ferromagnetic 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 an average 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; e) the composition characterized by thixotropic behaviour and having an electrical resistivity of about 10³ ohm-cm or less.
Claim 4
Dependent Claim
126 words
The electrically conductive ferrofluid composition, which composition comprises: a) a liquid carrier; b) finely divided single domain ferromagnetic 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 an average 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; e) the composition characterized by thixotropic behaviour and having an electrical resistivity of about 10³ ohm-cm or less.
Claim 5
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 6
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 7
Independent Claim
44 words
A method of providing a ferrofluid seal about a rotating member subject to the accumulation of static charges which method comprises: sealing the rotary member with an electrically conductive ferrofluid composition to provide an electrically conductive path to ground for the electrically conductive ferrofluid.
Claim 8
Independent Claim
44 words
A method of providing a ferrofluid seal about a rotating member subject to the accumulation of static charges which method comprises: sealing the rotary member with an electrically conductive ferrofluid composition to provide an electrically conductive path to ground for the electrically conductive ferrofluid.
Claim 9
Dependent Claim
83 words
An electrically conductive ferrofluid seal apparatus which apparatus comprises: a) a ferrofluid seal apparatus means to provide one or more radial gaps between the apparatus means and a member to be sealed; and b) electrically conductive ferrofluid compositions retained in one or more of the radial gaps to form a seal with the member by the magnetic flux of the seal apparatus; and c) conductive means to form an electrically conductive path to ground for static charges from the electrically conductive ferrofluid composition.
Claim 10
Dependent Claim
83 words
An electrically conductive ferrofluid seal apparatus which apparatus comprises: a) a ferrofluid seal apparatus means to provide one or more radial gaps between the apparatus means and a member to be sealed; and b) electrically conductive ferrofluid compositions retained in one or more of the radial gaps to form a seal with the member by the magnetic flux of the seal apparatus; and c) conductive means to form an electrically conductive path to ground for static charges from the electrically conductive ferrofluid composition.
Claim 11
Dependent Claim
123 words
An electrically conductive ferrofluid seal apparatus which comprises: a) an annular permanent magnet to surround a rotary shaft to be sealed; b) a first and second pole piece to surround the rotary shaft, the pole pieces in a magnetic flux relationship with the permanent magnet and one end of each pole piece extending into a close, non-contacting relationship with the surface of the rotary shaft to form a first and a second radial gap about the rotary shaft; and c) an electrically conductive ferrofluid dispersed in the first and second radial gap to form a first and second ferrofluid seal about the rotary shaft; and d) conductive means to conduct electrical charges from the electrically conductive ferrofluid in the radial gap to ground.
Claim 12
Dependent Claim
123 words
An electrically conductive ferrofluid seal apparatus which comprises: a) an annular permanent magnet to surround a rotary shaft to be sealed; b) a first and second pole piece to surround the rotary shaft, the pole pieces in a magnetic flux relationship with the permanent magnet and one end of each pole piece extending into a close, non-contacting relationship with the surface of the rotary shaft to form a first and a second radial gap about the rotary shaft; and c) an electrically conductive ferrofluid dispersed in the first and second radial gap to form a first and second ferrofluid seal about the rotary shaft; and d) conductive means to conduct electrical charges from the electrically conductive ferrofluid in the radial gap to ground.
Claim 13
Dependent Claim
18 words
The composition of claim 1 wherein the liquid carrier is a hydrocarbon oil or ester base liquid carrier.
Claim 14
Dependent Claim
25 words
The composition of claim 1 or 7 wherein the magnetic particles comprise single domain ferromagnetic particles having a diameter of less than about 1000 Å.
Claim 15
Dependent Claim
25 words
The composition of claim 1, 7 or 8 wherein the ratio of dispersing agent to magnetic particles ranges from about 0.5/1 to 20/1 by weight.
Claim 16
Dependent Claim
26 words
The composition of claim 1, 7, 8 or 9 wherein the ratio of dispersing agent to carbon particles ranges from about 0.01/1 to 20/1 by weight.
Claim 17
Dependent Claim
25 words
The composition of claim 1, 7, 8, 9 or 10 wherein the composition has an electrical resistivity of about 10³ ohm-cm or less at 27°C.
Claim 18
Dependent Claim
27 words
The composition of claim 1, 7, 8, 9, 10 or 11 wherein the carbon particles or agglomerates range in size from about 20 Å to 1 millimeter.
Claim 19
Dependent Claim
31 words
The composition of claim 1 or any one of claims 7 to 12 wherein the individual carbon particles and the magnetic particles range in size from about 20 to 300 Å.
Claim 20
Dependent Claim
34 words
The composition of claim 1 or any one of claims 7 to 13 wherein the carbon particles are present in an amount of from about 1 to 25 percent by weight of the composition.
Claim 21
Dependent Claim
28 words
The composition of claim 1 or any one of claims 7 to 14 wherein the carbon particles have a surface area of about 100-3000 metres square per gram.
Claim 22
Dependent Claim
39 words
The composition of claim 1 or any one of claims 7 to 15 wherein the carbon particles comprise carbon black particles produced by a furnace process and which have a dry electrical resistivity of about 10² to 10⁻² ohm-cm.
Claim 23
Dependent Claim
27 words
The composition of claim 1 or any one of claims 7 to 16 characterized in that electrical resistivity of the composition decreases with an increase in temperature.
Claim 24
Dependent Claim
21 words
The composition of claim 1 or any one of claims 7 to 17 wherein the dispersing agent is an anionic surfactant.
Claim 25
Dependent Claim
31 words
The composition of claim 1 or any one of claims 7 to 18 wherein the dispersing agent is selected from the group consisting of fatty acids, petroleum sulfonates and phosphate esters.
Claim 26
Dependent Claim
20 words
The composition of claim 1 or any one of claims 7 to 19 wherein the magnetic particles are magnetite particles.
Claim 27
Dependent Claim
24 words
The composition of claim 1 or any one of claims 7 to 20 wherein the liquid carrier comprises an ester oil or a polyalphaolefin.
Claim 28
Dependent Claim
111 words
An electrically conductive ferrofluid composition having an electrical resistivity of about 10³ ohm-cm or less, which composition consists essentially of: a) a non-volatile 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 29
Dependent Claim
111 words
An electrically conductive ferrofluid composition having an electrical resistivity of about 10³ ohm-cm or less, which composition consists essentially of: a) a non-volatile 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 30
Dependent Claim
32 words
The composition of claim 2 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 31
Dependent Claim
20 words
The composition of claim 2 or 23 wherein the carbon particles are carbon black particles produced by a furnace process.
Claim 32
Independent Claim
52 words
A method of preparing an electrically conductive ferrofluid composition which method comprises: dispersing in ferrofluid composition comprising a carrier liquid and dispersed magnetic particles an effective electrical conductive amount of electrically conductive carbon particles to provide an electrically conductive ferrofluid composition characterized by an electrical resistivity of less than about 10³ ohm-cm.
Claim 33
Independent Claim
52 words
A method of preparing an electrically conductive ferrofluid composition which method comprises: dispersing in ferrofluid composition comprising a carrier liquid and dispersed magnetic particles an effective electrical conductive amount of electrically conductive carbon particles to provide an electrically conductive ferrofluid composition characterized by an electrical resistivity of less than about 10³ ohm-cm.
Claim 34
Dependent Claim
28 words
The method of claim 25 which includes: adding a dispersing agent to the ferrofluid composition in an amount effective to disperse and stabilize the electrically conductive carbon particles.
Claim 35
Dependent Claim
26 words
The method of claim 25 or 26 which includes adding from about 1 to 25 percent by weight of the carbon particles to the ferrofluid composition.
Claim 36
Dependent Claim
59 words
The method of claim 25, 26 or 27 which includes: a) separately adding a dispersing agent and the carbon particles to a liquid carrier which is compatible with the liquid carrier of the ferrofluid composition; b) dispersing the carbon particles in the liquid carrier; and c) adding the liquid carrier with the dispersed carbon particles to the ferrofluid composition.
Claim 37
Dependent Claim
42 words
The method of claim 2 or any one of claims 23 to 28 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 38
Dependent Claim
32 words
The method of claim 2 or any one of claims 23 to 29 wherein the ratio of the dispersing agent to the carbon particles ranges from about 0.01/1 to 20/1 by weight.
Claim 39
Dependent Claim
24 words
The method of claim 3 which includes dispersing the carbon particles to provide individual carbon particles of about 20 to 300 Å particle size.
Claim 40
Dependent Claim
30 words
The method of claim 3 or 31 wherein the carbon particles comprise furnace process carbon black particles having a surface area of about 100 to 3000 meters square per gram.
Claim 41
Dependent Claim
69 words
The method of claim 3, 31 or 32 wherein the carbon particles are present in an amount of from about 1 to 25 percent by weight of the electrically conductive ferrofluid composition and the ratio of the total dispersing agent to the carbon black particles ranges from about 0.01/1 to 20/1, and the electrically conductive ferrofluid composition is characterised by an electrical resistivity of about 10³ ohm-cm or less.
Claim 42
Dependent Claim
19 words
The method of claim 4 wherein the ferrofluid composition contains an electrically conductive amount of dispersed carbon particles therein.
Claim 43
Dependent Claim
18 words
The method of claim 4 or 34 wherein the rotating member comprises a rotating computer disk drive shaft.
Claim 44
Dependent Claim
26 words
The method of claim 4, 34 or 35 wherein the electrically conductive ferrofluid composition is characterised by an electrical resistivity of about 10³ ohm-cm or less.
Claim 45
Dependent Claim
22 words
The seal apparatus of claim 5 wherein the ferrofluid composition is characterized by an electrical resistivity of about 10³ ohm-cm or less.
Claim 46
Dependent Claim
22 words
The seal apparatus of claim 5 or 37 wherein the ferrofluid composition contains an electrically conductive amount of carbon particles dispersed therein.
Claim 47
Dependent Claim
41 words
The seal apparatus of claim 5, 37 or 38 which includes at least one electrically conductive pole piece which forms at least one radial gap at the one end thereof and which forms a part of the conductive means to ground.
Claim 48
Dependent Claim
20 words
The seal apparatus of claim 5, 37, 38 or 39 wherein the conductive means comprises an electrically conductive coating path.
Claim 49
Dependent Claim
39 words
The seal apparatus of claim 5 or any one of claims 37 to 40 which includes a rotary shaft member and at least one pole piece which at one end forms a radial gap with the rotary shaft member.
Claim 50
Dependent Claim
38 words
The seal apparatus of claim 5 or any one of claims 37 to 41 wherein the ferrofluid seal apparatus comprises a plurality of radial gaps and electrically conductive ferrofluid is employed in a plurality of the radial gaps.
Claim 51
Dependent Claim
23 words
The seal apparatus of claim 5 or any one of claims 37 to 42 wherein the member comprises a rotary computer disk shaft.
Claim 52
Dependent Claim
20 words
The seal apparatus of claim 6 wherein the electrically conductive ferrofluid contains an electrically conductive amount of dispersed carbon particles.
Claim 53
Dependent Claim
19 words
The seal apparatus of claim 6 or 44 which includes a rotary shaft of a computer disk drive apparatus.
References Cited (Backward Citations)
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