EP0672294B1 - Materiaux magnetorheologiques utilisant des particules a surface modifiee - Google Patents

Materiaux magnetorheologiques utilisant des particules a surface modifiee Download PDF

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EP0672294B1
EP0672294B1 EP94900405A EP94900405A EP0672294B1 EP 0672294 B1 EP0672294 B1 EP 0672294B1 EP 94900405 A EP94900405 A EP 94900405A EP 94900405 A EP94900405 A EP 94900405A EP 0672294 B1 EP0672294 B1 EP 0672294B1
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particle
magnetorheological
particles
magnetorheological material
iron
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EP0672294A1 (fr
EP0672294A4 (fr
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Keith D. Weiss
J. David Carlson
Donald A. Nixon
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Lord Corp
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Lord Corp
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
    • H01F1/44—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of magnetic liquids, e.g. ferrofluids
    • H01F1/447—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of magnetic liquids, e.g. ferrofluids characterised by magnetoviscosity, e.g. magnetorheological, magnetothixotropic, magnetodilatant liquids

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  • the present invention relates to a method of preparing certain fluid materials which exhibit substantial increases in flow resistance when exposed to magnetic fields. More specifically, the present invention relates to magnetorheological materials that utilize a surface-modified particle component in order to enhance yield strength.
  • Bingham magnetic fluids or magnetorheological materials Fluid compositions which undergo a change in apparent viscosity in the presence of a magnetic field are commonly referred to as Bingham magnetic fluids or magnetorheological materials.
  • Magnetorheological materials normally are comprised of ferromagnetic or paramagnetic particles, typically greater than 0.1 micrometers in diameter, dispersed within a carrier fluid and in the presence of a magnetic field, the particles become polarized and are thereby organized into chains of particles within the fluid.
  • the chains of particles act to increase the apparent viscosity or flow resistance of the overall material and in the absence of a magnetic field, the particles return to an unorganized or free state and the apparent viscosity or flow resistance of the overall material is correspondingly reduced.
  • These Bingham magnetic fluid compositions exhibit controllable behavior similar to that commonly observed for electrorheological materials, which are responsive to an electric field instead of a magnetic field.
  • Both electrorheological and magnetorheological materials are useful in providing varying damping forces within devices, such as dampers, shock absorbers and elastomeric mounts, as well as in controlling torque and or pressure levels in various clutch, brake and valve devices.
  • Magnetorheological materials inherently offer several advantages over electrorheological materials in these applications. Magnetorheo-logical fluids exhibit higher yield strengths than electrorheological materials and are, therefore, capable of generating greater damping forces.
  • magnetorheological materials are activated by magnetic fields which are easily produced by simple, low voltage electromagnetic coils as compared to the expensive high voltage power supplies required to effectively operate electrorheological materials.
  • Magnetorheological or Bingham magnetic fluids are distinguishable from colloidal magnetic fluids or ferrofluids.
  • colloidal magnetic fluids the particles are typically 5 to 10 nanometers in diameter.
  • a colloidal ferrofluid does not exhibit particle structuring or the development of a resistance to flow. Instead, colloidal magnetic fluids experience a body force on the entire material that is proportional to the magnetic field gradient. This force causes the entire colloidal ferrofluid to be attracted to regions of high magnetic field strength.
  • Magnetorheological fluids and corresponding devices have been discussed in various patents and publications.
  • U.S. Pat. No. 2,575,360 provides a description of an electromechanically controllable torque-applying device that uses a magnetorheological material to provide a drive connection between two independently rotating components, such as those found in clutches and brakes.
  • a fluid composition satisfactory for this application is stated to consist of 50% by volume of a soft iron dust, commonly referred to as "carbonyl iron powder", dispersed in a suitable liquid medium such as a light lubricating oil.
  • U.S. Pat. No. 2,886,151 describes force transmitting devices, such as clutches and brakes, that utilize a fluid film coupling responsive to either electric or magnetic fields.
  • An example of a magnetic field responsive fluid is disclosed to contain reduced iron oxide powder and a lubricant grade oil having a viscosity of from 2 to 20 mPa.s (2 to 20 centipoises) at 25°C.
  • valves useful for controlling the flow of magnetorheological fluids is described in U.S. Pat. Nos. 2,670,749 and 3,010,471.
  • the magnetic fluids applicable for utilization in the disclosed valve designs include ferromagnetic, paramagnetic and diamagnetic materials.
  • a specific magnetic fluid composition specified in U.S. Pat. No. 3,010,471 consists of a suspension of carbonyl iron in a light weight hydrocarbon oil.
  • Magnetic fluid mixtures useful in U.S. Pat. No. 2,670,749 are described to consist of a carbonyl iron powder dispersed in either a silicone oil or a chlorinated or fluorinated suspension fluid.
  • magnetorheological material mixtures are disclosed in U.S. Patent No. 2,667,237.
  • the mixture is defined as a dispersion of small paramagnetic or ferromagnetic particles in either a liquid, coolant, antioxidant gas or a semi-solid grease.
  • a preferred composition for a magnetorheological material consists of iron powder and light machine oil.
  • a specifically preferred magnetic powder is stated to be carbonyl iron powder with an average particle size of 8 micrometers.
  • Other possible carrier components include kerosene, grease, and silicone oil.
  • U.S. Pat. No. 4,992,190 discloses a rheological material that is responsive to a magnetic field.
  • the composition of this material is disclosed to be magnetizable particles and silica gel dispersed in a liquid carrier vehicle.
  • the magnetizable particles can be powdered magnetite or carbonyl iron powders with insulated reduced carbonyl iron powder, such as that manufactured by GAF Corporation, being specifically preferred.
  • the liquid carrier vehicle is described as having a viscosity in the range of 1 to 1000 mPa.s (1 to 1000 centipoises) at 38°C (100°F).
  • suitable vehicles include Conoco LVT oil, kerosene, light paraffin oil, mineral oil, and silicone oil.
  • a preferred carrier vehicle is silicone oil having a viscosity in the range of about 10 to 1000 mPa.s (10 to 1000 centipoises) at 38°C (100°F).
  • US-A-39117538 describes a method of preparing a ferrofluid including grinding coarse magnetic materials and disperisng the particles into a carrier fluid.
  • AU-A162371 describes a magnetic fluid composition including magnetic particles having dimensions of 2 to 100 microns dispersed in a liquid carrier.
  • JP-A-3219602 describes a method of preparing a magnetic particle fluid wherein a soft magnetic substance powder is coated with a resin fluid and is dispersed in a carrier fluid.
  • magnetorheological material In many demanding applications for magnetorheological materials, such as dampers or brakes for automobiles or trucks, it is desirable for the magnetorheological material to exhibit a high yield stress so as to be capable of tolerating the large forces experienced in these types of applications. It has been found that only a nominal increase in yield stress of a given magnetorheological material can be obtained by selecting among the different iron particles traditionally utilized in magnetorheological materials. In order to increase the yield stress of a given magneto-rheological material, it is typically necessary to increase the volume fraction of magnetorheological particles or to increase the strength of the applied magnetic field.
  • a high volume fraction of the particle component can add significant weight to a magnetorheological device, as well as increase the overall off-state viscosity of the material, thereby restricting the size and geometry of a magnetorheological device capable of utilizing that material, and high magnetic fields significantly increase the power requirements of a magnetorheological device.
  • the present invention is a method of preparing a magnetorheological fulid material comprising:
  • Corrosion products on the surface of a magnetically active particle results from both chemical and electrochemical reactions of the particle's surface with water and atmospheric gases, as well as with electrolytes and particulates or contaminants that are either present in the atmosphere or left as a residue during particle preparation or processing.
  • Corrosion products can either be compact and strongly adherent to the surface of the metal or loosely bound to the surface of the metal and can be in the form of a powder, film, flake or scale.
  • the most common types of corrosion products include various forms of a metallic oxide layer, which are sometimes referred to as rust, scale or mill scale.
  • Abrader processing involves the physical or mechanical removal of the contamination products by impacting the surface of the magnetically active particles at a high velocity with an abrasive media.
  • This abrasive media can either be an abrasive additive to the magnetorheological material or a form of grinding media used as a processing aid.
  • Chemical treatment methods or techniques applicable to the removal of contamination products during the preparation of the magnetorheological material include acid etching, cleaning or pickling and alkaline cleaning and combinations thereof. These may also be used in combination with electrolytic and/or ultrasonic cleaning. Additional chemical treatment methods may include metal reduction or reactive gas processes, plasma cleaning, ion etching, sputter cleaning and combinations thereof.
  • barrier coatings that are effective in protecting the surface of the particles can be comprised of nonmagnetic metals, ceramics, high performance thermoplastics, thermosetting polymers and combinations thereof. In order to effectively protect the surface of the particle from recontamination by a contamination product, it is necessary that this coating or layer substantially encase or encapsulate the particle.
  • Figure 1 is a plot of magnetorheological effect at 25°C as a function of magnetic field strength for magnetorheological materials prepared in accordance with Example 12 and comparative Example 13.
  • the present invention relates to a method of making a magnetorheological material comprising :
  • the contamination products can essentially be any foreign material present on the surface of the particle and the contamination products are typically corrosion products.
  • the formation of corrosion products on the surface of a magnetically active particle results from both chemical and electrochemical reactions of the particle's surface with water and atmospheric gases, as well as with electrolytes and particulates or contaminants that are either present in the atmosphere or left as a residue during particle preparation or processing.
  • Examples of atmospheric gases commonly involved in this surface degradation process include O 2 , SO 2 , H 2 S, NH 3 , NO 2 , NO, CS 2 , CH 3 SCH 3 , and COS.
  • a metal may resist attack by one or more of these atmospheric gases, the surface of a metal is typically reactive towards several of these gases.
  • Examples of chemical elements contaminating the surface of metal particles resulting from known powder processing techniques and methods include carbon, sulfur, oxygen, phosphorous, silicon and manganese.
  • Examples of atmospheric particulates or contaminants involved in the formation of corrosion products on various metals include dust, water or moisture, dirt, carbon and carbon compounds or soot, metal oxides, (NH 4 )SO 4 , various salts (i.e., NaCl, etc.) and corrosive acids, such as hydrochloric acid, sulfuric acid, nitric acid and chromic acid. It is normal that metallic corrosion takes place in the presence of a combination of several of these atmospheric gases and contaminants.
  • Corrosion products can either be compact and strongly adherent to the surface of the metal or loosely bound to the surface of the metal as a powder, film, flake or scale.
  • the most common types of corrosion products include various forms of a metallic oxide layer, which are sometimes referred to as rust, scale or mill scale.
  • the present invention is based on the discovery that the removal of contamination products from the surface of a magnetically polarizable particle causes the particle to be particularly effective in creating a magnetorheological material which is capable of exhibiting high yield stresses. Contamination products can be efficiently removed from the surface of metallic particles through abrader processing, chemical treat-ment or a combination thereof. In order to be effective, these techniques must be employed during the preparation of the magnetorheological material ( in situ ) or immediately prior to either the preparation of the magnetorheological material or the application of a particle barrier layer or coating.
  • Abrader processing involves the physical or mechanical removal of the contamination products resulting from impacting the surface of the magnetically active particles at a high velocity with an abrasive media.
  • This abrasive media can either be an abrasive additive to the magnetorheological material or a form of grinding media used only as a processing aid.
  • the abrasive additive of the invention must be a material capable of sufficiently abrading a magnetorheological particle so as to substantially remove the contamination products from the surface of the particle.
  • the abrasive additive must, therefore, possess a substantial degree of hardness or roughness so as to effectively abrade the surface of the magnetorheological particle.
  • Various types of abrasive materials capable of removing contamination products from the surface of a metal are well known to those skilled in the art of tribology or superabrasives and can be utilized as abrasive additives in the invention.
  • the abrasive additives of the invention are typically in the form of a powder and can be comprised of various materials such as the oxides of aluminum, chromium, zirconium, hafnium, titanium, silicon, and magnesium; the carbides, nitrides and borides of aluminum, silicon and boron; and cermets, such as WC-Co and Ni-Cr-Al 2 O 3 , as well as combinations thereof.
  • abrasive additives include diamond dust, garnet, corundum, alumina, black mineral slag, Cr 2 O 3 , HfO 2 , TiO 2 , MgO, glass, sand, silica, aluminum silicates, pumice, rouge, emery, feldspar, SiC, B 4 C, BN, Si 3 N 4 , AlN, cerium oxide, and fused alumina, as well as other refractory or ceramic abrasives.
  • Iron oxides have also been found to be effective as abrasive additives for purposes of the present invention. Specifically, it has been found that the relatively hard iron oxides can be utilized in combination with relatively soft iron powders such that the contamination products are removed from the surface of the iron by the iron oxides. It should be noted that although used in relatively minor amounts in the overall magnetorheological material, the iron oxides are magnetically active and also function as an additional magnetorheological particle in combination with the iron.
  • the iron oxide includes all known pure iron oxides, such as Fe 2 O 3 and Fe 3 O 4 , as well as those containing small amounts of other elements, such as manganese, zinc or barium. Specific examples of iron oxide include ferrites and magnetites with ferrites being preferred.
  • the silica useful as an abrasive additive in the invention must be hydrophobic.
  • the surface of the silica must be treated so as to contain a minimal amount of hydroxyl funtionality and the silica must be relatively free of adsorbed moisture. It is important that the surface of the silica be chemically treated to be hydrophobic since it has been found that conventional drying of otherwise hydrophilic silica (e.g., silica gel such as that supplied by PPG Industries under the trade name HI-SIL 233) is not sufficient to render the silica hydrophobic for purposes of the invention. Although not completely understood, it is believed that an excess of adsorbed moisture and/or hydroxyl functionality prevents the hydrophilic silica from sufficiently abrading the surface of the particle component.
  • the hydrophobic silica of the invention can be prepared by reacting the hydroxyl groups on the surface of the silica with various organofunctional monomeric silanes or silane coupling agents, such as hydroxysilanes, acyloxysilanes, epoxysilanes, oximesilanes, alkoxysilanes, chlorosilanes and aminosilanes as is known in the art.
  • the hydroxyl groups on the surface of the silica may also be reacted with polymeric compounds such as silicone oils, mineral oils and paraffin oils.
  • the modification of the surface of silica with various materials to render the silica hydrophobic is described by W.
  • hydrophobic silicas include those commercially obtainable under the trade names AEROSIL and CABOSIL from Degussa Corporation and Cabot Corporation, respectively.
  • the preferred abrasive additives of the present invention include hydrophobic silica, iron oxides, and alumina because of their potential to contribute to the formation of a thixotropic network as described hereinafter. Iron oxides are specifically preferred due to their magnetorheological activity and relatively high specific gravity.
  • the diameter of the abrasive additives utilized herein can range from about 0.001 to 50.0 ⁇ m, preferably from about 0.001 to 20.0 ⁇ m with about 0.001 to 5.0 ⁇ m being specifically preferred.
  • These abrasive additives are typically utilized in an amount ranging from about 0.05 to about 10.0, preferably from about 0.1 to about 5.0, with about 0.2 to about 3.0 percent by volume of the total magnetorheological material being especially preferred.
  • the abrasive additive In order to be effective, the abrasive additive must be caused to impact the surface of a magnetorheological particle with a kinetic energy high enough to efficiently remove contamination products from the surface of the particle. This can be carried out during the preparation of the magnetorheological material ( in situ ), immediately prior to the preparation of the magnetorheological material or immediately prior to the application of a protective coating to the particle.
  • the abrasive additive is combined with the magnetorheological particle component, carrier fluid and any optional ingredients, and the resulting combination of ingredients is initially mixed by hand with a spatula or the like and then more thoroughly mixed with a homogenizer, mechanical mixer, mechanical shaker, or an appropriate milling device such as a ball mill, sand mill, attritor mill, colloid mill, paint mill, pebble mill, shot mill, vibration mill, roll mill, horizontal small media mill, or the like (all hereinafter collectively referred to as "mixing devices").
  • the mass of the abrasive additive, as well as the velocity achieved by this additive during the mixing or dispersing process determines the magnitude of kinetic energy available for the removal of contamination products from the magnetorheological particles.
  • the velocity of the abrasive additive is dependent upon the viscosity of the magnetorheological material and the speed at which the mixing device is operated. For a typical magnetorheological material with a viscosity less than about 1000mPa•s (1000 centipoise) at 25°C, sufficient velocity is achieved by the abrasive additive to effectively remove contamination products from the magnetorheological particles when the mixing device is operated with a minimum tip speed of about 50 ft/min.
  • the ingredients must be mixed together or dispersed for a sufficient length of time to substantially remove contamination products from the surface of the magnetorheological particle.
  • An increase in the velocity of the abrasive additive will usually result in a decrease in the required mixing or dispersion time.
  • the ingredients should be mixed for a period of time typically ranging from about 1 minute to 24 hours, preferably ranging from about 5 minutes to 18 hours. A certain amount of experimentation may be required to determine the optimum parameters that will allow for efficient removal of contamination products from a particular magnetorheological particle.
  • Confirmation of the substantial removal of contamination products from the surface of a magnetorheological particle may be obtained by utilizing various material characterization techniques known to those skilled in the art of analytical chemistry and surface analysis.
  • Examples of several known techniques for the quantitative/qualitative detection of atomic and/or molecular species include neutron activation analysis; scanning ion mass spectrometry (SIMS); x-ray methods, such as x-ray powder diffraction, x-ray fluorescence spectroscopy (XRF), x-ray photoelectron spectroscopy (XPS) and electron spectroscopy for chemical analysis (ESCA); and microscopy methods, such as scanning tunneling microscopy (STM), scanning electron microscopy (SEM), scanning auger microanalysis (SAM), and electron probe microanalysis (EPMA).
  • Microscopy of powder samples are typically performed using an ultramicrotomy procedure well known to those skilled in the art.
  • the above mixing procedure is followed except that only the magnetorheological particle and abrasive additive are utilized.
  • the abraded particle may be immediately combined with the other ingredients to prepare a magnetorheological material or immediately coated with a protective coating to prevent the reformation of corrosion products.
  • the abraded particle is combined with the other ingredients of the magnetorheological material or coated with a protective coating within no more than about 60 minutes, preferably within no more than about 30 minutes, after completion of the mixing procedure, unless the particles are stored for a longer time period under a contaminant-free atmosphere.
  • Contamination products can also be removed from the particle component through abrader processing using various grinding media as a processing aid.
  • This form of abrader processing can also be performed during the preparation of the magnetorheological material or immediately prior to either preparing the magnetorheological material or applying a protective coating to the particles.
  • the type of grinding media and the nature of the corresponding equipment needed to perform this abrading process are described as those capable of reducing or changing the diameter or size of the particle component. Specific types of appropriate media and equipment are well known to those skilled in the art of manufacturing paints and coatings.
  • Devices such as homogenizers, mechanical mixers and shakers that do not utilize a milling-type process, and are therefore not capable of reducing particle size, provide inadequate removal of contamination products from the surface of magnetorheological particles for purposes of the present invention, unless an abrasive additive as previously described is utilized in combination with the device.
  • Examples of common grinding media appropriate for use as a processing aid include balls, beads, pellets, pebbles, grit or shot comprised of various materials including stainless steel, ceramic, porcelain, flint, high carbon steel, high manganese steel, cast nickel alloy, low carbon forged steel, tungsten carbide, glass, zirconium silicate, zirconium oxide, and aluminum oxide.
  • Examples of common media milling devices or mills that utilize these types of grinding media include sand mills, ball mills, attritor mills, pebble mills, shot mills, vibration mills and horizontal small media mills.
  • the grinding media may be in the form of a wheel, disc or blade, such as that typically used in roll mills. A more complete description of media mills is provided by G.
  • the grinding media must be caused to impact the surface of a magnetorheological particle with a kinetic energy high enough to sufficiently remove contamination products from the surface of the particle. It is the mass of the grinding media, as well as the velocity achieved by this media during the milling process that determines the magnitude of kinetic energy available for the removal of contamination products from the magnetorheological particles.
  • the velocity of the grinding media is dependent upon the viscosity of the magnetorheological material and the speed at which the milling device is operated.
  • the grinding media For a typical magnetorheological material with a viscosity less than about 1000 mPa•s (1000 centipoise) at 25°C, sufficient velocity is achieved by the grinding media to effectively remove contamination products from the magnetorheological particles when the milling device is operated with a minimum tip speed of about 1.5 m -1 (300 ft/min).
  • the ingredients must be mixed together or dispersed for a sufficient length of time to substantially remove contamination products from the surface of the magentorheological particle. An increase in the velocity of the grinding media will usually result in a decrease in the required milling time.
  • the ingredients should be mixed for a period of time typically ranging from about 1 hour to 48 hours, preferably ranging from about 2 hours to 24 hours. A certain amount of experimentation may be required to determine the optimum parameters that will allow for efficient removal of contamination products from a particular magnetorheological particle.
  • abrasive additives can be utilized in combination with grinding media and, in this case, the efficiency of the corresponding milling device may be increased resulting in a lesser amount of both time and speed of the milling device needed to remove the contamination products from the surface of the magnetorheological particle.
  • Removal of contamination products from the surface of the magnetorheological particle can also be accomplished through acid or alkaline cleaning techniques.
  • the cleaning can be carried out during the preparation of the magnetorheological material ( in situ ), immediately prior to the preparation of the magnetorheological material or immediately prior to the application of a protective coating to the particle.
  • the cleaning methods or techniques applicable to the removal of contamination products during the preparation of the magnetorheological material include combination with electrolytic cleaning or ultrasonic cleaning such as the combination of electrolytic cleaning and alkaline cleaning commonly utilized in the electroplating industry.
  • alkaline cleaners useful in the invention include alkali metal orthophosphates, condensed phosphates, hydroxides, carbonates, bicarbonates, silicates and borates.
  • Alkaline cleaners are typically utilized in combination with a surfactant as is known in the art.
  • Examples of common acid cleaners useful in the invention include organic acids, such as citric, tartaric, acetic, oxalic and gluconic acid, acid salts, such as sodium phosphate, ammonium persulfate, sodium acid sulfate and bifluoride salts, and inorganic acids, such as sulfuric acid, phosphoric acid and hydrochloric acid.
  • organic acids such as citric, tartaric, acetic, oxalic and gluconic acid
  • acid salts such as sodium phosphate, ammonium persulfate, sodium acid sulfate and bifluoride salts
  • inorganic acids such as sulfuric acid, phosphoric acid and hydrochloric acid.
  • Acid and alkaline cleaning during the preparation of the magnetorheological material can be carried out by adding an acid or alkaline cleaner to the ingredients utilized to prepare the magneto-rheological material and then thoroughly mixing the ingredients first by hand with a spatula or the like and then with a mechanical mixing device.
  • the acid or alkaline cleaner is typically utilized in an amount ranging from about 0.1 to 5.0, preferably from about 0.5 to 3.0, percent by weight of the particle component.
  • Ultrasonic cleaning during the preparation of the magnetorheological material is typically carried out by passing sound waves at high frequencies through the material. These ultrasonic waves create tiny gas bubbles throughout the carrier component, which vigorously cleans the surface of the particles. This technique is often used in conjunction with acid or alkaline cleaning as previously described.
  • the acid or alkaline methods are applicable to the removal of contamination products immediately prior to either preparing the magnetorheological material or applying a protective coating
  • a protective coating can be applied to the surface of the particle.
  • the protective coating substantially, preferably entirely, encase or encapsulate the particle.
  • Protective coatings that substantially encapsulate the particle are to be distinguished from insulation coatings, such as those presently found on carbonyl iron powder such as the insulated reduced carbonyl iron powder supplied by GAF Corporation under the designations "GQ-4" and "GS-6.”
  • the insulation coatings found on insulated reduced carbonyl iron are intended to prevent particle-to-particle contact and are simply formed by dusting the particles with silica gel particulates. Insulation coatings therefore do not substantially encapsulate the particle so as to prevent the formation of contamination products.
  • the sporadic coverage of a particle's surface by an insulation coating can be seen in the scanning electron micrographs presented in the article by J. Japka entitled "Iron Powder for Metal Injection Molding" ( International Journal of Powder Metallurgy , 27 (2), 107-114). Incomplete coverage of the particle's surface by a coating typically will result in the accelerated formation of contamination products through the process described above for solid atmospheric particles, such as dust and soot.
  • Iron oxide previously described in the literature as being useful as an insulation coating, cannot be used as a protective coating for purposes of the present invention because iron oxide itself is a corrosion product.
  • the protective coatings of the invention that are effective in preventing the formation of contamination products on the surface of magnetorheological particles can be composed of a variety of materials including nonmagnetic metals, ceramics, high performance thermoplastics, thermosetting polymers and combinations thereof.
  • thermosetting polymers useful for forming a protective coating include polyesters, polyimides, phenolics, epoxies, urethanes, rubbers and silicones, while thermoplastic polymeric materials include acrylics, cellulosics, polyphenylene sulfides, polyquinoxilines, polyetherimides and polybenzimidazoles.
  • Typical nonferrous metals useful for forming a protective coating include refractory transition metals, such as titanium, zirconium, hafnium, vanadium, niobium, tantulum, chromium, molybdenum, tungsten, copper, silver, gold, and lead, tin, zinc, cadmium, cobalt-based intermetallic alloys, such as Co-Cr-W-C and Co-Cr-Mo-Si, and nickel-based intermetallic alloys, such as Ni-Cu, Ni-Al, Ni-Cr, Ni-Mo-C, Ni-Cr-Mo-C, Ni-Cr-B-Si-C, and Ni-Mo-Cr-Si.
  • transition metals such as titanium, zirconium, hafnium, vanadium, niobium, tantulum, chromium, molybdenum, tungsten, copper, silver, gold, and lead, tin, zinc, cadmium
  • Ceramic materials useful for forming a protective coating include the carbides, nitrides, borides, and silicides of the refractory transition metals described above; nonmetallic oxides, such as Al 2 O 3 , Cr 2 O 3 , ZrO 3 , HfO 2 , TiO 2 , SiO 2 , BeO, MgO, and ThO 2 ; nonmetallic nonoxides, such as B 4 C, SiC, BN, Si 3 N 4 , AlN, and diamond; and various cermets.
  • nonmetallic oxides such as Al 2 O 3 , Cr 2 O 3 , ZrO 3 , HfO 2 , TiO 2 , SiO 2 , BeO, MgO, and ThO 2
  • nonmetallic nonoxides such as B 4 C, SiC, BN, Si 3 N 4 , AlN, and diamond
  • various cermets such as B 4 C, SiC, BN, Si 3 N 4 , AlN, and diamond.
  • the protective coatings of the invention can be applied by techniques or methods well known to those skilled in the art of tribology. Examples of common coating techniques include both physical deposition and chemical vapor deposition methods. Physical deposition techniques include both physical vapor deposition and liquid or wetting methods. Physical vapor deposition methodology includes direct, reactive, activated reactive and ion-beam assisted evaporation; DC/RF diode, alternating, triode, hollow cathode discharge, sputter ion, and cathodic arc glow discharge ion plating; direct, cluster ion and ion beam plating; DC/RF diode, triode and magnetron glow discharge sputtering; and single and dual ion beam sputtering.
  • Common physical liquid or wetting methodology includes air/airless spray, dip, spin-on, electrostatic spray, spray pyrolysis, spray fusion, fluidized bed, electrochemical deposition, chemical deposition such as chemical conversion (e.g., phosphating, chromating, metalliding, etc.), electroless deposition and chemical reduction; intermetallic compounding, and colloidal dispersion or sol-gel coating application techniques.
  • Chemical vapor deposition methodology includes conventional, low pressure, laser-induced, electron-assisted, plasma-enhanced and reactive-pulsed chemical vapor deposition, as well as chemical vapor polymerization. A thorough discussion of these various coating processes is provided in Bhushan .
  • the preferred abrader processing and chemical treatment methods of the invention include those performed during the preparation of the magnetorheological material.
  • abrader processing is generally preferable over chemical treatment.
  • the magnetically active particle component to be modified according to the present invention can be comprised of essentially any solid which is known to exhibit magnetorheological activity and which can inherently form a contamination product on its surface.
  • Typical particle components useful in the present invention are comprised of, for example, paramagnetic, superparamagnetic, or ferromagnetic compounds.
  • Specific examples of particle components useful in the present invention include particles comprised of materials such as iron, iron nitride, iron carbide, carbonyl iron, chromium dioxide, low carbon steel, silicon steel, nickel, cobalt, and mixtures thereof.
  • the particle component can be comprised of any of the known alloys of iron, such as those containing aluminum, silicon, cobalt, nickel, vanadium, molybdenum, chromium, tungsten, manganese and/or copper.
  • the particle component can also be comprised of the specific iron-cobalt and iron-nickel alloys described in the U.S. patent number 5,382,373.
  • the particle component is typically in the form of a metal powder which can be prepared by processes well known to those skilled in the art. Typical methods for the preparation of metal powders include the reduction of metal oxides, grinding or attrition, electrolytic deposition, metal carbonyl decomposition, rapid solidification, or smelt processing. Various metal powders that are commercially available include straight iron powders, reduced iron powders, insulated reduced iron powders, and cobalt powders.
  • the diameter of the particles utilized herein can range from about 0.1 to 500 ⁇ m and preferably range from about 1.0 to 50 ⁇ m.
  • the preferred particles of the present invention are straight iron powders, reduced iron powders, iron-cobalt alloy powders and iron-nickel alloy powders.
  • the particle component typically comprises from about 5 to 50, preferably about 15 to 40, percent by volume of the total composition depending on the desired magnetic activity and viscosity of the overall material.
  • the carrier fluid of the magnetorheological material of the present invention can be any carrier fluid or vehicle previously disclosed for use in magnetorheological materials, such as the mineral oils, silicone oils and paraffin oils described in the patents set forth above.
  • Additional carrier fluids appropriate to the invention include silicone copolymers white oils, hydraulic oils, chlorinated hydrocarbons, transformer oils, halogenated aromatic liquids, halogenated paraffins, diesters, polyoxyalkylenes, perfluorinated polyethers, fluorinated hydrocarbons, fluorinated silicones, and mixtures thereof.
  • transformer oils refer to those liquids having characteristic properties of both electrical and thermal insulation.
  • Naturally occurring transformer oils include refined mineral oils that have low viscosity and high chemical stability. Synthetic transformer oils generally comprise chlorinated aromatics (chlorinated biphenyls and trichlorobenzene), which are known collectively as "askarels", silicone oils, and esteric liquids such as dibutyl sebacates.
  • the carrier fluid of the invention may also be a modified carrier fluid which has been modified by extensive purification or by the formation of a miscible solution with a low conductivity carrier fluid so as to cause the modified carrier fluid to have a conductivity less than about 1 x 10-7 S/m.
  • modified carrier fluids can be found in WO 94/09097.
  • Polysiloxanes and perfluorinated polyethers having a viscosity between about 3 and 200 mPa•s ( 3 and 200 centipoise) at 25°C are also appropriate for utilization in the magnetorheological material of the present invention.
  • the preferred carrier fluids of the present invention include mineral oils, paraffin oils, silicone oils, silicone copolymers and perfluorinated polyethers, with silicone oils and mineral oils being especially preferred.
  • the carrier fluid of the magnetorheological material of the present invention should have a viscosity at 25°C that is between about 2 and 1000 mPa•s (2 and 1000 centipoise), preferably between about 3 and 200 mPa•s (3 and 200 centipoise), with a viscosity between about 5 and 100 mPa•s (5 and 100 centipoise) being especially preferred.
  • the carrier fluid of the present invention is typically utilized in an amount ranging from about 50 to 95, preferably from about 60 to 85, percent by volume of the total magnetorheological material.
  • a thixotropic network is defined as a suspension of particles that, at low shear rates, form a loose network or structure sometimes referred to as clusters or flocculates.
  • the presence of this three-dimensional structure imparts a small degree of rigidity to the magnetorheological material, thereby reducing particle settling.
  • this structure is easily disrupted or dispersed. When the shearing force is removed, this loose network is reformed over a period of time.
  • a thixotropic network or structure is formed through the utilization a hydrogen-bonding thixotropic agent and/or a polymer-modified metal oxide. Colloidal additives may also be utilized to assist in the formation of the thixotropic network.
  • the formation of a thixotropic network utilizing hydrogen-bonding thixotropic agents, polymer-modified metal oxides and colloidal additives is further described in WO 94/10693.
  • a thixotropic network in the invention can be assisted by the addition of low molecular weight hydrogen-bonding molecules, such as water and other molecules containing hydroxyl, carboxyl or amine functionality.
  • low molecular weight hydrogen-bonding molecules such as water and other molecules containing hydroxyl, carboxyl or amine functionality.
  • Typical low molecular weight hydrogen-bonding molecules other than water include methyl, ethyl, propyl, isopropyl, butyl and hexyl alcohols; ethylene glycol; diethylene glycol; propylene glycol; glycerol; aliphatic, aromatic and heterocyclic amines, including primary, secondary and tertiary amino alcohols and amino esters that have from 1-16 atoms of carbon in the molecule; methyl, butyl, octyl, dodecyl, hexadecyl, diethyl, diisopropyl and dibutyl amines; ethanolamine; propanolamine; ethoxyethylamine; dioctylamine; triethylami8ne; trimethylamine; tributylamine; ethylenediamine; propylene-diamine; triethanolamine, triethylenetetramine; pyridine; moropholine; imidazole; and mixture
  • An additional surfactant to more adequately disperse the particle component may be optionally utilized in the present invention.
  • Such surfactants include known surfactants or dispersing agents such as ferrous oleate and naphthenate, sulfonates, phosphate esters, glycerol monooleate, sorbitan sesquioleate, stearates, laurates, fatty acids, fatty alcohols, and the other surface active agents discussed in U.S. Pat. No. 3,047,507.
  • Alkaline soaps, such as lithium stearate and sodium stearate, and metallic soaps, such as aluminum tristearate and aluminum distearate can also be presently utilized as a surfactant.
  • the optional surfactants may be comprised of steric stabilizing molecules, including fluoroaliphatic polymeric esters, such as FC-430 (3M Corporation), and titanate, aluminate or zirconate coupling agents, such as KEN-REACT® (Kenrich Petrochemicals, Inc.) coupling agents.
  • a precipitated silica gel such as that disclosed in U.S. Patent No. 4,992,190, can be used to disperse the particle component. In order to reduce the presence of moisture in the magnetorheological material, it is preferred that the precipitated silica gel, if utilized, be dried in a convection oven at a temperature of from about 110°C to 150°C for a period of time from about 3 to 24 hours.
  • the surfactant if utilized, is preferably a "dried" precipitated silica gel, a fluoroaliphatic polymeric ester, a phosphate ester, or a coupling agent.
  • the optional surfactant may be employed in an amount ranging from about 0.1 to 20 percent by weight relative to the weight of the particle component.
  • magnetorheological materials according to the invention where contamination products are removed from the surface of the magnetorheological particle in situ has previously been described. If contamination products are removed from the particle immediately prior to either the preparation of the magnetorheological material or the application of a protective coating, the magnetorheological materials of the present invention can be prepared by simply mixing together the carrier fluid, the pre-treated particle component, and any optional ingredients.
  • the ingredients of the magnetorheological materials may be initially mixed together by hand with a spatula or the like and then subsequently more thoroughly mixed with a homogenizer, mechanical mixer, mechanical shaker, or an appropriate milling device such as a ball mill, sand mill, attritor mill, colloid mill, paint mill, pebble mill, shot mill, vibration mill, roll mill, horizontal small media mill or the like, in order to create a more stable suspension.
  • a homogenizer such as a ball mill, sand mill, attritor mill, colloid mill, paint mill, pebble mill, shot mill, vibration mill, roll mill, horizontal small media mill or the like.
  • the mixing conditions for the preparation of a magnetorheological material utilizing a magnetorheological particle that has had contamination products previously removed can be somewhat less rigorous than the conditions required for the preparation and in situ removal of contamination products.
  • the dynamic yield stress for the magnetorheological material corresponds to the zero-rate intercept of a linear regression curve fit to the measured data.
  • the magnetorheological effect at a particular magnetic field can be further defined as the difference between the dynamic yield stress measured at that magnetic field and the dynamic yield stress measured when no magnetic field is present.
  • the viscosity for the magnetorheological material corresponds to the slope of a linear regression curve fit to the measured data.
  • the magnetorheological material is placed in the annular gap formed between an inner cylinder of radius R 1 and an outer cylinder of radius R 2 , while in a simple parallel plate configuration the material is placed in the planar gap formed between upper and lower plates both with a radius, R 3 .
  • either one of the plates or cylinders is then rotated with an angular velocity ⁇ while the other plate or cylinder is held motionless.
  • a magnetic field can be applied to these cell configurations across the fluid-filled gap, either radially for the concentric cylinder configuration, or axially for the parallel plate configuration.
  • the relationship between the shear stress and the shear strain rate is then derived from this angular velocity and the torque, T, applied to maintain or resist it.
  • Example 1 a magnetorheological material is prepared by slowly adding a total of 117.9 g of carbonyl iron powder (Sigma Chemical Company) to a mixture of 3.54 g of an 11 N phosphoric acid solution, which is prepared using phosphoric acid (99%, Aldrich Chemical Company) and distilled water, and 28.29 g of 20 cstk mineral oil (DRAKEOL 10, Pennzoil Products Company). The temperature of the magnetorheological material is maintained during this initial mixing procedure within the temperature range of about 30 to 45°C.
  • the fluid is initially mixed by hand with a spatula (low shear) and then more thoroughly dispersed into a homogeneous mixture through the use of a high speed disperserator (high shear) equipped with a 16-tooth rotary head.
  • the weight amount of the chemically treated iron particles in the magnetorheological material is equivalent to a volume fraction of about 0.30.
  • the magnetorheological material is stored in a polyethylene container.
  • Example 2 a magnetorheological material is prepared according to the procedure described in Example 1. However, in this example the phosphoric acid solution is replaced with 3.54 g of an 11 N sulfuric acid solution, which is prepared using sulfuric acid (95-98%, Aldrich Chemical Company) and distilled water. The amount of mineral oil is adjusted to maintain the particle volume fraction in the magnetorheological material at 0.30. The magnetorheological material is stored in a polyethylene container.
  • Example 3 a magnetorheological material is prepared according to the procedure described in Example 1. However, in this example a total of 117.9 g of carbonyl iron powder (Sigma Chemical Company), 2.35 g of stearic acid (Aldrich Chemical Company) as a dispersant and 28.67 g of 20 cstk mineral oil (DRAKEOL 10, Pennzoil Products Company) are mixed together. The weight amount of untreated iron particles in the magnetorheological material is equivalent to a volume fraction of about 0.30. The conventional magnetorheological material is stored in a polyethylene container.
  • the magnetorheological materials prepared in Examples 1, 2 and 3 are evaluated through the use of parallel plate rheometry. A summary of the magnetorheological effect observed for these magnetorheological materials at various magnetic field strengths and 25°C is provided in Table 1. A significantly higher magnetorheological effect is observed for the magnetorheological materials utilizing particles wherein contamination products have been removed by chemical treatment (Examples 1 and 2) as compared to a magnetorheological material containing conventional untreated particles (Example 3). At a magnetic field strength of 40 x 10 4 A•m -1 (5000 Oersted) the magnetorheological effect exhibited by the magnetorheological materials containing the chemically treated particles is about 71% greater than that exhibited by a conventional magnetorheological material.
  • a magnetorheological material is prepared by mixing together a total of 123.2 g of carbonyl iron powder (Sigma Chemical Company), 2.46 g of stearic acid (Aldrich Chemical Company) as a dispersant and 34.20 g of 200 cstk silicone oil (Dow Corning Corporation). This weight amount of iron particles is equivalent to a volume fraction in the magnetorheological material of about 0.30.
  • the fluid is made into a homogeneous mixture using an Union Process 01HD attritor mill equipped with a 110 cm 3 tank.
  • the grinding media used in this attritor mill is in the form of stainless steel balls. This mill has the capability to reduce the mean size and distribution of the particle component when the impacting grinding media has high kinetic energy.
  • This grinding media imparts sufficient kinetic energy to remove the contamination products from the particle component when the agitator shaft and arms of this mill are rotated at tip speed of about 1.5m•s -1 (300 ft./min).
  • the maximum tip speed of this mill is measured to be about 3.0 m•s -1 (600 ft./min).
  • the magnetorheological material is aggressively milled in this abrader process over a 48-hour period with a tip speed of about 2.3m.s -1 (445 ft./min).
  • the magnetorheological material is separated from the grinding media and stored in a polyethylene container.
  • a magnetorheological material is prepared according to the procedure described in Example 4. However, in this example the mill is operated with a tip speed of about 1.3m•s -1 (250 ft./min). over a 96-hour period. The rotation of the agitator shaft and arms at this angular speed does not impart sufficient kinetic energy to the stainless steel grinding media to remove the contamination products from the surface of particle component.
  • the conventional magnetorheological material is separated from the grinding media and stored in a polyethylene container.
  • the magnetorheological materials prepared in Examples 4 and 5 are evaluated through the use of parallel plate rheometry. A summary of the magnetorheological effect for these magnetorheological materials at various magnetic field strengths and 25°C is provided in Table 2. A significantly higher magnetorheological effect is observed for the magnetorheological material utilizing particles wherein contamination products have been removed by stainless steel grinding media in an abrader process (Example 4) as compared to a magnetorheological material containing conventional particles (Example 5). At a magnetic field strength of 2.4 x 10 4 A.m -1 (3000 Oersted) the magnetorheological effect exhibited by the magnetorheological material containing the abrader process modified particles is about 69% greater than that exhibited by a conventional magnetorheological material.
  • a magnetorheological material is prepared by adding together a total of 117.9 g of reduced iron powder (ATOMET 95G, Quebec Metal Powders Limited), 8.75 g of Mn/Zn ferrite powder (#73302-0, D. M. Steward Manufacturing Company) as an abrasive additive, 2.53 g polyoxy-ethylene/silicone graft copolymer (SILWET L7500, Union Carbide Chemicals and Plastics Company, Inc.) as a thixotropic agent and 29.13 g of 10 cstk silicone oil (L-45, Union Carbide Chemicals and Plastics Company, Inc.).
  • the fluid is initially mixed by hand with a spatula (low shear) and then more thoroughly dispersed into a homogeneous mixture through the use of a high speed disperserator (high shear) equipped with a 16-tooth rotary head and operated at a tip speed of about 2.0m•s -1 (400 ft./min). for about 5 minutes.
  • the weight amount of the iron particles in the magnetorheological material is equivalent to a volume fraction of about 0.30.
  • the presence of the abrasive ferrite powder in this magnetorheo-logical material efficiently removes the contamination products from the surface of the iron particles.
  • the magnetorheological material whose particle component has been modified by abrader processing is stored in a polyethylene container.
  • a magnetorheological material is prepared according to the procedure described in Example 6 with the exception that the abrasive ferrite powder is excluded.
  • the weight amount of the oil component is modified to maintain an iron particle volume fraction in the magnetorheological material of 0.30.
  • This conventional magnetorheo-logical material is stored in a polyethylene container.
  • the magnetorheological materials prepared in Examples 6 and 7 are evaluated through the use of parallel plate rheometry. A summary of the magnetorheological effect observed for these magnetorheological materials at various magnetic field strengths and 25°C is provided in Table 3. A significantly higher magnetorheological effect is observed for the magnetorheological material utilizing particles wherein contamination products have been removed by the presence of an abrasive additive in an abrader process (Example 6) as compared to a magnetorheological material containing conventional particles (Example 7).
  • the magnetorheological effect exhibited by the magnetorheological material containing the abrader process modified particles is about 147% greater than that exhibited by a conventional magnetorheological material.
  • Example 8 a magnetorheological material is prepared by adding together a total of 117.9 g of straight carbonyl iron powder (MICROPOWDER S-1640, GAF Chemicals Corporation), 1.18 g of Boron Carbide (99%, Johnson Matthey Company) as an abrasive additive, 2.36 g organomodifed polydimethylsiloxane copolymer (SILWET L7500, Union Carbide Chemicals and Plastics, Company, Inc.) as a hydrogen-bonding thixotropic agent and 27.55 g of 10 cstk silicone oil (L-45, Union Carbide Chemicals and Plastics Company, Inc.).
  • MICROPOWDER S-1640 straight carbonyl iron powder
  • Boron Carbide 99%, Johnson Matthey Company
  • SILWET L7500 organomodifed polydimethylsiloxane copolymer
  • SILWET L7500 organomodifed polydimethylsiloxane copolymer
  • the fluid is initially mixed by hand with a spatula (low shear) and then more thoroughly dispersed into a homogeneous mixture through the use of a high speed disperserator (high shear) equipped with a 16-tooth rotary head and operated at a tip speed of about 20 M•s -1 (400 ft./min.) for about 5 minutes.
  • the weight amount of the iron particles in the magnetorheological material is equivalent to a volume fraction of about 0.32.
  • the presence of the abrasive additive in this magnetorheological material efficiently removes the contamination products from the surface of the iron particles.
  • the magnetorheological material whose particle component has been modified by abrader processing is stored in a polyethylene container.
  • Magnetorheological materials are prepared in Examples 9 and 10 according to the procedure described for Example 8. However, in Example 9 the boron carbide powder is replaced with 1.51 g silicon carbide powder (alpha, 99.8%, Johnson Matthey Company) as an abrasive additive. In Example 10, the abrasive additive is replaced with 2.43 g iron (II, III) oxide powder (97%, Johnson Matthey Company). The weight amount of the iron particles in each of the magnetorheological materials is equivalent to a volume fraction of about 0.32. The magnetorheological materials whose particle component has been modified by abrader processing is stored in a polyethylene container.
  • a magnetorheological material is prepared according to the procedure described in Example 8. However, in this case no abrasive additive is incorporated into the magnetorheological material. The amount of the carrier oil component is appropriately increased to insure that the volume fraction of iron particles in the magnetorheological material is about 0.32.
  • the conventional magnetorheological material is stored in a polyethylene container.
  • the magnetorheological materials prepared in Examples 8, 9, 10 and 11 are evaluated through the use of parallel plate rheometry.
  • a summary of the magnetorheological effect observed for these magnetorheological materials at various magnetic field strengths and 25°C is provided in Table 4.
  • a significantly higher magnetorheological effect is observed for the magnetorheological materials utilizing particles wherein contamination products have been removed by the presence of an abrasive additive or iron oxide particles in an abrader process (Examples 8-10) as compared to a magnetorheological material containing conventional particles (Example 11).
  • the magnetorheological effect exhibited by the magnetorheological material containing the abrader process modified particles is about 74% greater than that exhibited by a conventional magnetorheological material.
  • a magnetorheological material is prepared by adding together a total of 117.9 g of reduced carbonyl iron powder (MICROPOWDER R-1430, GAF Chemicals Corporation), 1.90 g of hydrophobic fumed silica (CABOSIL TS-720, Cabot Corporation) and 29.95 g of 10 cstk silicone oil (L-45, Union Carbide Chemicals and Plastics Company, Inc.).
  • the fluid is initially mixed by hand with a spatula (low shear) and then more thoroughly dispersed into a homogeneous mixture through the use of a high speed disperserator (high shear) equipped with a 16-tooth rotary head and operated at a tip speed of about 20 m•s -1 (400 ft./min.) for about 5 minutes.
  • the weight amount of the iron particles in the magnetorheological material is equivalent to a volume fraction of about 0.32.
  • the presence of the abrasive hydrophobic silica powder in this magnetorheological material efficiently removes the contamination products from the surface of the iron particles.
  • the magnetorheological material whose particle component has been modified by abrader processing is stored in a polyethylene container.
  • a magnetorheological material is prepared according to the procedure described in Example 12 with the exception that the hydrophobic silica powder is replaced with an identical amount of a hydrophilic silica gel dispersant (HI-SIL 233, PPG Industries).
  • This silica gel dispersant which has previously been disclosed as a dispersant in U.S. Patent No. 4,992,190, is dried in a convection oven at 130°C for 24 hours prior to use.
  • This magnetorheological material contains a particle volume fraction of 0.32.
  • This conventional magnetorheological material is stored in a polyethylene container.
  • the magnetorheological materials prepared in Examples 12 and 13 are evaluated through the use of parallel plate rheometry. A summary of the magnetorheological effect observed for these magnetorheological materials at various magnetic field strengths and 25°C is provided in Figure 1. A significantly higher magnetorheological effect is obtained for the magnetorheological material utilizing particles wherein contamination products have been removed by the presence of an abrasive hyrophobic silica additive in an abrader process (Example 12) as compared to a magnetorheological material containing conventional particles (Example 13).
  • the magnetorheological effect exhibited by the magnetorheological material containing the abrader process modified particles is about 167% greater than that exhibited by a conventional magnetorheological material.
  • magnetorheological materials that contain a particle component that has been modifed by the removal of inherent contamination products through chemical treatment or abrader processing exhibit a significantly higher magnetorheological effect than conventional magnetorheological materials.

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Claims (8)

  1. Procédé de préparation d'un matériau magnétorhéologique, comprenant l'étape qui consiste à :
       se procurer un fluide porteur et une particule à activité magnétique, ayant un diamètre d'environ 1 à 500 µm ;
       caractérisé en ce qu'il comprend en outre les étapes qui consistent à :
       modifier la particule en éliminant les produits de contamination de la surface de la particule par traitement à l'abrasif, nettoyage acide, nettoyage alcalin ou bien utilisation d'une combinaison de ces traitements ; et combiner la particule avec le fluide porteur avant ou immédiatement après la modification de la particule pour créer un matériau magnétorhéologique.
  2. Procédé selon la revendication 1, dans lequel l'étape consistant à modifier la particule comprend l'opération qui consiste à frapper la surface de la particule à grande vitesse à l'aide d'un agent abrasif.
  3. Procédé selon la revendication 2, comprenant en outre l'étape qui consiste à appliquer un revêtement de protection sur la surface de la particule, les produits de contamination étant éliminés immédiatement avant l'application du revêtement de protection sur la surface de la particule.
  4. Matériau magnétorhéologique comprenant un fluide porteur et une particule à activité magnétique, caractérisé en ce qu'il contient en outre un additif d'élimination de contaminants, choisi dans le groupe constitué par un agent de nettoyage acide, choisi dans le groupe comprenant les acides organiques, les sels d'acides et les acides inorganiques ; un agent de nettoyage alcalin choisi dans le groupe comprenant les orthophosphates de métaux alcalins, les phosphates condensés, les hydroxydes, les carbonates, les bicarbonates, les silicates et les borates, seuls ou en combinaison avec un tensioactif, et un additif abrasif choisi dans le groupe constitué par l'égrisée, le grenat, le corindon, l'alumine, les scories minérales noires, le Cr2O3, l'HfO2, le TiO2, le MgO, le verre, le sable, la silice hydrophobe, les silicates d'aluminium, la pierre ponce, le rouge à polir, l'émeri, le feldspath, le SiC, le B4C, le BN, le Si3N4, l'AlN, l'oxyde de cérium, la magnétite et l'alumine fondue ; la particule ayant un diamètre d'environ 1 à 500 µm.
  5. Matériau magnétorhéologique selon la revendication 4, dans lequel la particule à activité magnétique est essentiellement encapsulée par un revêtement de protection composé d'un matériau choisi dans le groupe constitué par les polymères thermodurcissables, les métaux non magnétiques, les céramiques et des combinaisons de ceux-ci, et a un diamètre situé dans la plage allant de 1 à 500 µm.
  6. Matériau magnétique selon la revendication 5, dans lequel le polymère thermodurcissable comprend un polyester, un polyimide, un polymère phénolique, un polymère époxy, un uréthanne, un caoutchouc ou un silicone.
  7. Matériau magnétique selon la revendication 5, dans lequel le métal non magnétique comprend le titane, le zirconium, l'hafnium, le vanadium, le niobium, le tantale, le chrome, le molybdène, le tungstène, le cuivre, l'argent, l'or, le plomb, l'étain, de zinc, le cadmium, un alliage intermétallique à base de cobalt ou un alliage intermétallique à base de nickel.
  8. Matériau magnétique selon la revendication 5, dans lequel la céramique comprend un carbure, un nitrure, un borure ou un siliciure d'un métal de transition réfractaire, Al2O3, Cr2O3, ZrO3, HfO2, TiO2, SiO2, BeO, MgO, ThO2, B4C, SiC, BN, Si3N4, AlN, le diamant ou un cermet.
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WO2012004236A1 (fr) 2010-07-09 2012-01-12 Eckart Gmbh Pigments de fer en forme de feuillets, fluide magnéto-rhéologique, et dispositif correspondant
WO2015038355A1 (fr) 2013-09-11 2015-03-19 Astronautics Corporation Of America Lits particulaires à porosité élevée stabilisés de manière structurelle par de l'époxy

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EP0672294A1 (fr) 1995-09-20
RU2115967C1 (ru) 1998-07-20
JP3226925B2 (ja) 2001-11-12
DE69329975T2 (de) 2001-07-19
JPH08503009A (ja) 1996-04-02
WO1994010694A1 (fr) 1994-05-11
CN1088021A (zh) 1994-06-15
RU95110047A (ru) 1997-01-27
EP0672294A4 (fr) 1995-06-14
DE69329975D1 (de) 2001-04-05
CA2148001A1 (fr) 1994-05-11

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