[0001] The present invention relates to a rheological fluid which is responsive to a magnetic
field.
[0002] Rheological fluids responsive to magnetic fields are known. Rheological fluids responsive
to electric fields are also known. Such fluids are used in clutches, shock absorbers,
and other devices. A characteristic of these rheological fluids is that, when they
are exposed to the appropriate energy field, solid particles in the fluid move into
alignment and the ability of the fluid to flow is substantially decreased.
[0003] Electric field responsive fluids and magnetic field responsive fluids include a vehicle,
for instance a dielectric medium, such as mineral oil or silicone oil, and solid particles.
In the case of a magnetic field responsive fluid, the solid particles are magnetizable.
Examples, of solid particles which have been heretofore proposed for use in a magnetic
field responsive fluid are magnetite and carbonyl iron. The fluid also may contain
a surfactant to keep the solid particles in suspension in the vehicle.
[0004] A brochure published by GAF Corporation of Wayne, New Jersey, containing the code
lM-785, captioned "Carbonyl Iron Powders", contains a discussion of carbonyl iron
powders marketed by GAF Corporation. The iron particles are classified as "straight
powders", "alloys", "reduced powders", and "insulated reduced powders". An example
of a "straight powder" which is listed is a powder known as carbonyl "E".
[0005] A brief discussion is contained in the brochure concerning magnetic field responsive
fluids. It is stated: "The spherically shaped particles of carbonyl iron presumably
act like ball bearings in magnetic fluid coupling applications. The smallness of the
iron particles gives larger surface area and more contacts than other powders and,
hence, better transmission when locked. A lubricant and dispersant are generally required
for best results." The discussion contains no disclosure concerning the type of carbonyl
iron or dispersant to be employed in a magnetic field responsive fluid.
[0006] A publication entitled "Some Properties of Magnetic Fluids", J. D. Coolidge, Jr.
and R. W. Halberg, AIEE Transactions, Paper 55-170 (Feb. 1955), pages 149-152, discloses
the use of different carbonyl irons in a fluid responsive to a magnetic field. The
carbonyl irons disclosed include carbonyl "E" and carbonyl "SF", so-called straight
powders, and carbonyl "L", carbonyl "HP", and carbonyl "C", all reduced powders. The
article contains no conclusions concerning the preference of one carbonyl iron over
another in a magnetic field responsive fluid.
[0007] A publication entitled "The Magnetic Fluid Clutch" by Jacob Rabinow, NBS Tech. Rep.
No. 1213 (1948) [also, Trans. Amer. Inst. Elec. Eng. Preprint 48-238 (1948)] discloses
the use of hydrogen reduced iron and carbonyl iron "SF", a "straight" powder as indicated
above.
[0008] In US-A-2,597,276, a method for insulating the particles of ferromagnetic metal powders,
especially those obtained by thermal decomposition of metal carbonyls, particularly
iron carbonyl, is disclosed. The resulting insulated powders are used to produce magnetic
cores and other molded articles.
[0009] The above-referenced documents contain no conclusion concerning the preference of
one carbonyl over another in a magnetic field responsive fluid.
[0010] A publication entitled "The Magnetic Fluid Clutch" by S. F. Blunden, The Engineer,
191, 244 (1951) discloses the use of two grades of carbonyl iron, grade "ME" and grade
"MC". Grade "ME" is said to be mechanically "hard" and grade "MC" is said to be mechanically
"soft". Here also, no preference is given for one carbonyl iron over another.
[0011] A publication entitled "Further Development of the NBS Magnetic Fluid Clutch", NBS
Tech. News Bull., 34, 168 (1950) discloses the use of carbonyl "E" powder in a magnetic
fluid. Other compositional information concerning the fluid is also given.
[0012] US-A-4,604,229 discloses the combination of a hydrocarbon carrier with 4%-10% magnetite,
8%-12% electrically conductive carbon black, and a dispersing agent. Powder magnetite
(Fe₃O₄) is the fully oxidized magnetic oxide of iron, carbonyl iron, or iron-nickel.
A similar disclosure is contained in US-A-4,673,997.
[0013] US-A-3,006,656 discloses a magnetic particle shock absorber using a composition which
can contain carbonyl iron, a vehicle such as oil, and graphite. Carbonyl iron and
magnetite are described as equivalant materials in the composition. It is not indicated
in the patent which carbonyl iron was used.
[0014] US-A-2,519,449 discloses the combination of carbonyl E and solid, powdered graphite
in a 50/50 blend. The continuous phase or dielectric medium in the composition is
air. The graphite functions as a lubricant.
[0015] US-A-2,661,596 discloses a magnetically-responsive fluid which comprises 100 parts
of iron carbonyl powder, 10 parts dielectric oil, and 2 parts dispersant, such as
ferrous oleate. The form of carbonyl iron used is not disclosed. US-A-2,663,809 and
US-A-2,886,151 disclose the use of carbonyl iron in a fluid coupling. The form of
carbonyl iron used is not disclosed.
[0016] US-A-2,772,761 discloses an electromagnetic clutch using a magnetically-responsive
fluid comprising an iron powder which is an 80/20 blend of plast-iron and carbonyl
"E", and a dispersant comprising 39% graphite, 46% naptha, and 15% alkyl resin, by
way of example.
[0017] In US-A-4,737,886, an electroviscous fluid is disclosed. The fluid is responsive
to an electric field. Fluids responsive to magnetic fields are also discussed. It
is stated in the patent that such magnetic fields require "relatively large electric
currents and substantial electrical circuits (for example, large coil windings) to
cause the proper response in the fluid".
[0018] A publication entitled "Quest, Summer, 1986, pages 53-63, by Jack L. Blumenthal,
published by TRW Corporation, discloses the composition and properties of a carbonaceous
material comprising fibrous carbon particles manufactured in a carbon disproportion
reaction. The carbon fibers of the individual particles are intertwined forming a
porous structure. The particles are capable of incorporating and suspending other
finely divided powders in fluids.
[0019] It is an object of the present invention to provide an improved rheological magnetic
field responsive fluid which has a high speed of responsiveness to a magnetic field
and which magnetic field may be created by a relatively low current flow through a
small number of coil windings.
[0020] The fluid composition of the present invention comprises a vehicle and solid magnetizable
particles suspended in the vehicle. Preferably, the fluid composition also contains
a dispersant. In accordance with the present invention, the magnetizable particles
are insulated, reduced carbonyl iron particles.
[0021] The present invention also resides in the discovery of a novel dispersant for a magnetic
field responsive fluid, which dispersant is fibrous carbon particles, each particle
of which comprises intertwined carbon fibers having a length-to-diameter ratio in
the range of about 10:1 to about 1,000:1. Preferably, the fibers have a surface area
of about 300 square meters per gram.
Brief Description of the Drawings
[0022] Further features of the present invention will become apparent to those skilled in
the art to which the present invention relates from reading the following specification
with reference to the accompanying drawings, in which:
Fig. 1 is a view of an apparatus which uses a rheological fluid in accordance with
the present invention;
Fig. 2 is a sectional view taken along line 2-2 of Fig. 1;
Fig. 3 is a plan view of a blade used in the apparatus of Fig. 1;
Fig. 4 is a perspective view of an electromagnet used in the apparatus of Fig. 1;
Fig. 5 is an enlarged sectional view taken along line 5-5 of Fig. 4;
Fig. 6 is a plan view of the electromagnet of Fig. 4; and
Fig. 7 is a graph illustrating operational characteristics of the apparatus of Fig.
1.
Description of a Preferred Embodiment
[0023] The fluid composition of the present invention comprises a vehicle, such as mineral
oil, silicone oil, or CONOCO LVT oil; an insulated reduced carbonyl iron; and preferably
a dispersant of intertwined carbon fiber particles.
[0024] Carbonyl iron is manufactured by the decomposition of iron pentacarbonyl Fe(CO)₅.
This process produces a spherical unreduced particle which has what is referred to
as an onion-skin structure due to minute carbon deposits in alternating layers. The
carbon content is about 1%. Reduction or de-carburization of the unreduced powder
is carried out by exposing the powder to a hydrogen atmosphere, followed by compaction.
This destroys the onion-skin structure and produces a composite of randomly arranged
minute iron particles. The carbon content of the powder is about 0.075%.
[0025] In accordance with the present invention, the reduced powders have an insulation
coating to prevent particle-to-particle contact. The particles are physically soft
and compressible. Their shape is spherical. Reduced particles which are also insulated
are marketed by GAF Corporation under the designations "GQ-4" and "GS-6". The following
Table 1 gives physical and chemical properties for the insulated, reduced powders:

The data of Table 1 can be found on page 4 of the GAF brochure mentioned above, bearing
the identifying code IM-785. The disclosure of the GAF brochure is incorporated herein
by reference.
[0026] The insulation coating can be any particle-coating agent capable of insulating the
carbonyl iron particles and preventing interparticle eddy currents or dielectric leakage.
The insulation coating on the "GQ-4" and "GS-6" powders is a discontinuous layer of
silicon oxide, primarily silicon dioxide. Silicon comprises about 6.9 atomic percent
of the surface composition of the carbonyl iron particles. Silicon dioxide is very
dielectric, and provides electrical resistivity.
[0027] It is believed that the reduced powders have a more random arrangement of minute
iron particles than the so-called "straight" powders, and that this results in a lower
hysteresis effect than with the "straight" powders. The insulation on the powders
enhances the efficiency of the magnetic fluid in reducing parasitic eddy currents
around the particles, which eddy currents could adversely affect the magnetic field
strength in the fluid.
[0028] When the magnetic fluid composition of the present invention is used in certain coupling
applications, such as in a clutch, the moving parts of the clutch stir the composition
effectively and no dispersant is required. This is particularly the case where permanent
magnets are used, and thus the clutch is never demagnetized. In such an instance,
settling of the iron particles presents no problems.
[0029] In those applications where a dispersant is required, the composition of the present
invention can employ any dispersant or surfactant conventionally employed with a fluid
responsive to a magnetic field. Examples of surfactants employed in the prior art
are: dispersants, such as ferrous oleate or ferrous naphthenate; aluminum soaps such
as aluminum tristearate or aluminum distearate; alkaline soaps, such as lithium stearate
or sodium stearate, employed to impart thixotropic properties; surfactants such as
fatty acids, e.g., oleic acids; sulfonates, e.g., petroleum sulfonate; phosphate esters,
e.g., alcohol esters of ethoxylated phosphate esters; and combinations of the above.
[0030] A preferred dispersant material is fibrous carbon. Fibrous carbon is a carbon particulate
in which each carbon particle is composed of a large number of intertwined small carbon
fibers. One such fibrous carbon is "TRW Carbon", trademark, TRW corporation. The "TRW
Carbon" is disclosed in the publication "Quest", mentioned above. The disclosure of
this publication is incorporated herein by reference.
[0031] The "TRW Carbon" is made in a catalytic carbon disproportion reaction in which a
low heating value fuel gas or other source of carbon is used as the reaction feed.
The individual fibers in the fibrous carbon are from 0.05 to 0.5 microns in diameter
and up to several thousand times as long as they are thick. A preferred average length
to diameter ratio is in the range of about 10:1 to about 1,000:1. Most of the fibers
contain a single crystallite of a ferrous metal (such as iron, nickel, cobalt, or
their alloys) or ferrous metal carbide. The carbon fibers grow during the disproportion
reaction from opposite faces of the single crystallites. The crystallite usually represents
1 to 10 percent by weight of the material, but can be reduced to as low as 0.1 percent
by acid leaching. Except for the crystallite, the fibers are almost pure carbon plus
a small amount of hydrogen such as 0.5 to 1 percent. The fibers may be either hollow
or porous.
[0032] Intertwining of the fibers into aggregated particles occurs during the disproportion
reaction. The intertwining and formation of small interstices in the carbon particles
allows the fibrous carbon to incorporate the micron-sized carbonyl iron paticles and
mechanically suspend the carbonyl iron particles dispersed in a fluid carrier. The
fibrous carbon particles have a large surface area of about 300 square meters per
gram and a low bulk density of about 0.02 to about 0.7 grams per milliliter. Pore
volume of the fibrous carbon particles typically is about 0.5 to about 0.9 milliliters
per gram.
[0033] The fibrous carbon particles have fluid-like characteristics and flow like a liquid
similar to graphite. When placed in a liquid vehicle, in a dispersing amount, they
thicken or gell the vehicle preventing settling of the carbonyl iron particles. They
form a thixotropic mixture with the vehicle which has good flow properties when exposed
to shear. The viscosity of the thixotropic mixture is relatively independent of temperature.
[0034] The vehicle of the composition of the present invention can be any vehicle conventionally
employed in a fluid responsive to a magnetic field. Examples of suitable vehicles
are set forth in the prior art referenced above. Preferably, the vehicle employed
is an oil having a viscosity at about 37,78°C (100°F) between one and 1,000 centipoises.
Specific examples of suitable vehicles and their viscosities are set forth in the
following Table 2:
TABLE 2
Vehicle |
Viscosity |
Conoco LVT oil |
1.5 centipoises at 37,78°C (100°F) |
Kerosene |
1.9 centipoises at 27,22°C (81°F) |
Light paraffin oil |
20 centipoises at 37,78°C (100°F) |
Mineral oil (Kodak) |
40 centipoises at 37,78°C (100°F) |
Silicone oil |
700 centipoises at 37,78°C (100°F) |
[0035] The proportions of ingredients employed in the composition of the present invention
can vary over wide ranges. In those compositions requiring the use of a dispersant,
the dispersant is employed in an amount effective to disperse the carbonyl iron particles
and to maintain such particles in suspension in the vehicle. The amount of vehicle
used is that amount necessary for the vehicle to function as the continuous phase
of the composition. Air pockets in the composition should be avoided. The remainder
of the composition is essentially the carbonyl iron powder. Preferably, the carbonyl
iron to dispersant weight ratio is about 90:10 to about 99.5:0.5. The weight of the
vehicle is about 15% to about 50% of the combined weight of the carbonyl iron and
dispersant.
[0036] Particular ratios selected depend upon the application for the composition of the
present invention. Preferably, the proportions are such that the composition of the
present invention has thixotropic properties and is mechanically stable in the sense
that the compositions remain homogeneous for prolonged periods of time.
[0037] In those compositions consisting essentially of insulated, reduced carbonyl iron
and vehicle, the vehicle is employed in an amount effective so that it is the continuous
phase in the composition. The specific amount used is dependent upon the properties
of the vehicle, such as viscosity. A preferred weight ratio of vehicle to carbonyl
iron is in the range of about 15%-55% vehicle to about 85%-45% carbonyl iron.
Example
[0038] In this Example, 99% by weight carbonyl iron and 1% by weight TRW carbon were mixed
together. A mixture of 20% by weight of Conoco LVT oil and 80% by weight of the carbonyl
iron and TRW carbon mixture was then homogenized in a homogenizer for 12-24 hours
under vacuum. Intensive mixing in the homogenizer functioned to thoroughly mix the
TRW carbon and carbonyl iron with entrapment of the carbonyl iron in the fibrous structure
of the TRW carbon. It also effected thorough wetting of all surfaces of the TRW carbon
and carbonyl iron with LVT oil. The particular carbonyl iron employed was carbonyl
"GS-6", trademark GAF Corporation.
[0039] A test apparatus was constructed to determine the coupling load characteristics of
the composition under various conditions. The test apparatus is similar in construction
to the shock absorber disclosed in co-pending Application Serial No. 339,126, filed
April 14, 1989, assigned to the assignee of the present application. The test apparatus
is illustrated in the drawings of this application.
[0040] Referring specifically to Figs. 1 and 2, the test apparatus 12 comprises a non-magnetic
aluminum housing 14. The housing 14 comprises first and second housing sections 16
and 18 (Fig. 2) which are fastened together by bolts 20. The housing sections 16,
18 define a fluid chamber 22 (Fig. 2) in the right end portion 24, as viewed in the
drawings, of the housing. A shaft 26 extends through the left end portion 28, as viewed
in the drawings, of the housing 14. The shaft 26 has shaft end sections 30 and 32
(Fig. 2) and a shaft center section 34. The shaft 26 rotates in bearing assemblies
36 and 38. Seals 40, 42 prevent fluid leakage along the shaft 26.
[0041] The center section 34 of the shaft 26 has a square configuration. A rotor blade 44
is fixed to the center section 34 so as to rotate with the shaft. The rotor blade
44 has a configuration as shown in Fig. 3. It extends radially from the shaft center
section 34 into the fluid chamber 22.
[0042] The right-end portion 24 of the housing 14 has an opening 45 in which holder 46 for
an electromagnet 54 is located and an opening 47 in which a holder 48 is located for
an electromagnet 56. The holders 46, 48 have chambers 50, 52, respectively, in which
the electromagnets 54, 56 are located.
[0043] The holders 46, 48 are secured to the housing sections 16 and 18 by means of brackets
58, 60, respectively. Screws 62, 64 hold the coil holders 46, 48 to the brackets 58,
60, respectively. Screws 66 (Fig. 1) hold the brackets 58, 60 to the housing sections
16, 18. The electromagnets 54, 56 can be chemically bonded to the holders 46, 48 or
alternatively fastened to the holders by screws not shown. The non-magnetic material
of the housing 12 and holders 46, 48 minimizes leakage of magnetic flux from the electromagnets
54, 56.
[0044] Figs. 4, 5 and 6 show details of the electromagnets 54, 56. Each electromagnet 54,
56 comprises a soft iron core 70 around which an electrical coil 72 is wound. The
electrical coil 72 is covered with an encapsulating material such as an epoxy. Each
of the electromagnets 54, 56 has a pair of wire ends 74. An outer soft iron pole 76
extends around the coil 72.
[0045] The electromagnets 54, 56 are mounted so that the poles of the electromagnets 54
face the poles of the electromagnet 56. The rotor blade 44, and the fluid chamber
22, are positioned between the electromagnets 54, 56. The spacing between one electromagnet
and the blade is about 0.25 millimeters. The blade thickness is about two millimeters.
In the present Example, the center core 70 of each electromagnet has a diameter of
38,10 mm (1.50 inches). The outside diameter of each electromagnet is 76,20 mm (three
inches). The outer pole 76 has a radial thickness of 4,76 mm (0.1875 inches). Each
electromagnet coil 72 has 894 wire turns.
[0046] When the coils 54, 56 are energized, each electromagnet generates its own magnetic
field. Lines of magnetic flux are established between the two electromagnets. The
lines of magnetic flux pass through the fluid in the fluid chamber 22 and through
the rotor blade 44. These lines of magnetic flux act on the fluid in the fluid chamber
22 to vary the resistance to movement of the rotor blade 44 in the fluid.
[0047] To test the coupling strength of the magnetic fluid of the present invention, when
exposed to a magnetic field, the shaft 26 was connected by means of arms 78 (Fig.
2) to a torque motor (not shown). The torque motor was associated with a means for
measuring torque. Different currents were applied to the electromagnets 54, 56. The
torque required to turn the blade in the magnetic fluid in chamber 22, under the influence
of the magnetic field, was measured. The results of the test are shown in Fig. 7.
[0048] Referring to Fig. 7, the current flow in amp-turns is plotted along the X axis. The
current employed varied from zero to about three and one-half amps (3129 amp turns).
The resistance to turning of the blade 44 in terms of Pa [pounds per square inch]
is given along the Y axis and varied from about zero to about 344,74·10³ Pa (50 psi).
This measurement was obtained by dividing the pounds of torque required to turn the
blade by the blade surface area exposed to the magnetic responsive fluid in chamber
22. Also measurements were taken at different frequencies of oscillation varying from
0.5 Hertz to 5 Hertz.
[0049] As shown, the resistance to turning at zero current was nearly zero indicating excellent
lubricating properties of the composition of the present invention. The resistance
to turning increased rapidly with increase in current flow up to about 262·10³- 330,95·10³
Pa (38-48 pounds per square inch) at 3129 amp-turns (about 3 1/2 amps). The measurements
were taken at different frequencies and all measurements followed quite similar curves
indicating that the composition of the present invention is relatively frequency insensitive.
[0050] In contrast, a conventional magnetic field responsive fluid would require currents
of substantially greater magnitude to achieve equivalent coupling strength. That is,
a conventional magnetic field responsive rheological fluid might provide a coupling
strength of less than 6,89476 10³ Pa (one pound per square inch) with a magnetic field
generated with a current flow of about 3129 amp-turns. Thus, the rheological fluid
of the present invention permits the construction of very compact, magnetic field
responsive fluid devices having a relatively high coupling strength.
[0051] From the above description of a preferred embodiment of the invention, those skilled
in the art will perceive improvements, changes and modifications. Such improvements,
changes and modifications within the skill of the art are intended to be covered by
the appended claims.
1. A rheological fluid composition which is responsive to a magnetic field, said fluid
composition comprising an oil vehicle, and a solid magnetizable particulate suspended
in said vehicle, characterized in that said magnetizable particulate is an electrically
insulated reduced carbonyl iron present in said composition in an amount effective
to provide said composition with magnetic properties.
2. The fluid composition of claim 1 wherein said carbonyl iron has a particle size in
the range of 3 to 6 microns.
3. The fluid composition of claim 1 wherein the oil vehicle is 15 to 55 weight percent
of the mixture of oil vehicle and the carbonyl iron is 85 to 45 weight percent of
the mixture of oil vehicle and carbonyl iron.
4. The fluid composition of claim 1 wherein the insulation on said carbonyl iron is a
layer of silicon oxide and the carbon content of said iron is less than 0.1% by weight.
5. The fluid composition of claim 1 wherein said composition comprises a dispersant for
dispersing the magnetizable particulate throughout the oil vehicle, the oil vehicle
being the continuous phase of the composition, and wherein said dispersant comprises
fibrous carbon particles, the fibers of which have a length-to-diameter ratio in the
range of about 10:1 to about 1,000:1, and wherein said oil vehicle has a viscosity
in the range of about one to 1,000 centipoises at 37,78°C (100°F).
6. The fluid composition of claim 5 wherein said composition comprises:
said electrically insulated reduced carbonyl iron and said dispersant in the ratio
of about 0.5 to 10 weight parts of said dispersant to about 90 to 99.5 weight parts
of said carbonyl iron; and
said oil vehicle comprises about 15 to 50 weight percent of the combined weight
of the carbonyl iron and the dispersant.
7. The fluid composition of claim 1 wherein said insulated, reduced carbonyl iron comprises
reduced carbonyl iron insulated with a silicon oxide.
8. The fluid composition of claim 1 wherein said fluid composition further comprises
a dispersant, said dispersant comprising fibrous carbon particles the fibers of which
have a length-to-diameter ratio in the range of about 10:1 to about 1,000:1 and a
surface area of about 300 square meters per gram.
9. The fluid composition of claim 8 wherein said insulated, reduced carbonyl iron comprises
reduced carbonyl iron insulated with a silicon oxide.
10. The fluid composition of claim 8 wherein said fluid composition further comprises
said carbonyl iron and dispersant in the ratio of about 90 to 99.5 weight parts of
said carbonyl iron to about 10 to 0.5 weight parts of said dispersant, and said oil
vehicle in the proportion of about 15 to 50 weight percent based on the combined weight
of the carbonyl iron and the dispersant.
1. Eine rheologische Fluidzusammensetzung, die auf ein magnetisches Feld anspricht, wobei
die Fluidzusammensetzung ein auf Öl basierendes Trägermedium enthält sowie einen festen,
magnetisierbaren, aus Partikeln bestehenden Stoff, der in dem Trägermedium suspendiert
ist, dadurch gekennzeichnet, daß der magnetisierbare, aus Partikeln bestehende Stoff
ein elektrisch isoliertes, reduziertes Carbonyleisen ist, das in der Zusammensetzung
in einer Menge vorliegt, die der Zusammensetzung magnetische Eigenschaften verleiht.
2. Fluidzusammensetzung nach Anspruch 1, bei der das Carbonyleisen eine Partikelgröße
im Bereich von 3 bis 6 µm besitzt.
3. Fluidzusammensetzung nach Anspruch 1, bei der das auf Öl basierende Trägermedium 15
bis 55 Gew.-% des auf Öl basierenden Trägermediumgemischs ausmacht und das Carbonyleisen
85 bis 45 Gew.-% der Mischung aus auf Öl basierendem Trägermedium und Carbonyleisen
ausmacht.
4. Fluidzusammensetzung nach Anspruch 1, bei der die Isolierung auf dem Carbonyleisen
eine Schicht aus Siliziumoxid ist und der Kohlenstoffgehalt des Eisens weniger als
0,1 Gew.-% beträgt.
5. Fluidzusammensetzung nach Anspruch 1, bei der die Zusammensetzung ein Dispergiermittel
zum durchgehenden Dispergieren des magnetisierbaren, aus Partikein bestehenden Stoffs
im auf Öl basierenden Trägermedium enthält, wobei das auf Öl basierende Trägermedium
die zusammenhängende Phase der Zusammensetzung ist, und bei der das Dispergiermittel
faserige Kohlenstoffpartikel enthält, deren Fasern ein Verhältnis von Länge zu Durchmesser
im Bereich von ungefähr 10:1 bis ungefähr 1000:1 besitzen, und bei der das auf Öl
basierende Trägermedium eine Viskosität im Bereich von ungefähr 1 bis 1000 Zentipoise
bei 37,78°C (100°F) besitzt.
6. Fluidzusammensetzung nach Anspruch 5, bei der die Zusammensetzung enthält:
das elektrisch isolierte, reduzierte Carbonyleisen und das Dispergiermittel im Verhältnis
von ungefähr 0,5 bis 10 Gewichtsteilen des Dispergiermittels zu ungefähr 90 bis 99,5
Gewichtsteilen des Carbonyleisens; und
das auf Öl basierende Trägermedium mit ungefähr 15 bis 50 Gew.-% des zusammengenommenen
Gewichts des Carbonyleisens und des Dispergiermittels.
7. Fluidzusammensetzung nach Anspruch 1, bei der das isolierte, reduzierte Carbonyleisen
reduziertes, durch ein Siliziumoxid isoliertes Carbonyleisen enthält.
8. Fluidzusammensetzung nach Anspruch 1, bei der die Fluidzusammensetzung zusätzlich
ein Dispergiermittel enthält, wobei das Dispergiermittel faserige Kohlenstoffpartikel
enthält, deren Fasern ein Verhältnis von Länge zu Durchmesser im Bereich von ungefähr
10:1 bis ungefähr 1000:1 und eine Oberfläche von ungefähr 300 m² je Gramm besitzen.
9. Fluidzusammensetzung nach Anspruch 8, bei der das isolierte, reduzierte Carbonyleisen
reduziertes, durch ein Siliziumoxid isoliertes Carbonyleisen enthält.
10. Fluidzusammensetzung nach Anspruch 8, bei der die Fluidzusammensetzung ferner das
Carbonyleisen und das Dispergiermittel im Verhältnis von ungefähr 90 bis 99,5 Gewichtsteilen
des Carbonyleisens zu ungefähr 10 bis 0,5 Gewichtsteilen des Dispergiermittels enthält
und das auf Öl basierende Trägermedium im Anteil von ungefähr 15 bis 50 Gew.-%, basierend
auf dem zusammengenommenen Gewicht des Carbonyleisens und des Dispergiermittels.
1. Composition rhéologique de fluide sensible à un champ magnétique, ladite composition
de fluide comprenant un porteur à base d'huile et une matière solide particulaire
suspendue dans ledit porteur, caractérisée en ce que ladite matière particulaire est
un fer-carbonyle réduit électriquement isolant, présent dans ladite composition en
quantité suffisante pour donner à ladite composition des propriétés magnétiques.
2. Composition de fluide suivant la revendication 1, dans laquelle ledit fer-carbonyle
possède une taille de particule dans une gamme de 3 à 6 microns.
3. Composition de fluide suivant la revendication 1, dans laquelle le porteur à base
d'huile constitue 15 à 55 pour cent en poids du mélange de porteur à base d'huile
et le fer carbonyle constitue 85 à 45 peur cent en poids du mélange de porteur à base
d'huile et du fer-carbonyle.
4. Composition de fluide suivant la revendication 1, dans laquelle l'isolement du fer-carbonyle
est constitué par une couche de silice et le contenu en carbone dudit fer est de moins
de 0,1 pour cent en poids.
5. Composition de fluide suivant la revendication 1, dans laquelle ladite composition
comporte un dispersant pour disperser la matière particulaire magnétisable partout
dans le porteur à base d'huile, ledit porteur à base d'huile étant la phase continue
de la composition, et dans laquelle ledit dispersant comporte des particules fibreuses
de carbone dont les fibres ont une relation longueur-à-diamètre dans la gamme d'environ
10:1 à 1000:1, et dans laquelle ledit porteur à base d'huile possède une viscosité
dans la gamme d'environ 1 à 1000 centipoises à 37,78°C (100°F).
6. Composition de fluide suivant la revendication 5, dans laquelle ladite composition
comporte:
ledit fer-carbonyle réduit électriquement isolant et ledit dispersant dans une relation
d'environ 0,5 à 10 pour cent en poids dudit dispersant à environ 90 à 99,5 pour cent
en poids dudit fer-carbonyle; et
ledit porteur à base d'huile comporte environ 15 à 25 pour cent en poids du poids
combiné de fer-carbonyle et de dispersant.
7. Composition de fluide suivant la revendication 1, dans laquelle ledit fer-carbonyle
réduit et isolant comporte du fer-carbonyle réduit isolé par un silice.
8. Composition de fluide suivant la revendication 1, dans laquelle ladite composition
de fluide comporte en outre un dispersant, ledit dispersant comportant des particules
fibreuses de carbone dont les fibres possèdent une relation longueur-à-diamètre dans
la gamme d'environ 10:1 à environ 1000:1 ainsi qu'une aire de surface d'environ 300
mètres carrés par gramme.
9. Composition de fluide suivant la revendication 8, dans laquelle ledit fer-carbonyle
réduit et isolant comporte du fer-carbonyle réduit isolé par un silice.
10. Composition de fluide suivant la revendication 8, dans laquelle ladite composition
de fluide comporte en outre ledit fer-carbonyle et dispersant dans une relation d'environ
90 à 99,5 pour cent en poids dudit fer-carbonyle à environ 10 à 0,5 pour cent en poids
dudit dispersant, et ledit porteur à base d'huile dans la proportion d'environ 15
à 50 pour cent en poids basée sur le poids combiné du fer-carbonyle et du dispersant.