US3917538A - Ferrofluid compositions and process of making same - Google Patents

Ferrofluid compositions and process of making same Download PDF

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US3917538A
US3917538A US324414A US32441473A US3917538A US 3917538 A US3917538 A US 3917538A US 324414 A US324414 A US 324414A US 32441473 A US32441473 A US 32441473A US 3917538 A US3917538 A US 3917538A
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dispersant
particles
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magnetic particles
ferrofluid
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Ronald E Rosensweig
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Ferrofluidics 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

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  • Ferrofluid is a ferromagnetic fluid displaying superparamagnetism, having a magnetic polarizability that is substantially uniform and having the property such that when a gradientmagnetic field is applied to it, a body force is developed within it which can exceed by orders of magnitude the ordinary force of gravity on a unit volume of the material.
  • ferrofluid comprises a colloidal dispersion of finely divided magnetic particles of subdomain size whose liquid condition is remarkably unaffected by the presence of an applied magnetic field, and which particles resist settling under the influence of gravitational, centrifugal, magnetic or other force fields.
  • Ferrofluid particles typically ranging in size up to about 300 A remain uniformly dispersed throughout the liquid carrier due to thermal agitation.
  • Ferrofluids are described in my publication Magnetic Fluids, International Science and Technology, July 1966, pp 48-56; U.S. Pat. No. 3,215,572; in the publication of R. Kaiser and G. Miskolczy, Magnetic Properties of Stable Dispersions of Subdomain Magnetite Particles, J. Applied Physics, Vol. 41, No. 3, Mar. 1, 1970, pp 1064-1072; in A Catalog of Magnetic Fluids, Ferrofluidics Corporation, Burlington, Massachusetts 1972 and elsewhere.
  • a magnetic powder is reduced in size to the colloidal range as by ball-mill grinding in the presence of a liquid carrier and a grinding aid which serves also as a dispersing agent.
  • the dispersing agent is typically a surfactant comprising a polar long-chain molecule whose polar group adsorbs onto the surface of the particle to produce a monomolecular protective coating that prevents particles from attaching to each other.
  • My invention relates to an improved process for the preparation of ferrofluids and to the ferrofluids so produced, and in particular, concerns a process for the flocculation of magnetic particles from a ferrofluid in an irreversible manner, and the treatment of such irreversibly flocked particles to prepare improved ferrofluid compositions.
  • ferrofluids may be flocculated by the addition of foreign agents or solvents in an irreversible manner such that the dispersant employed; that is, the surfactant that originally stabilized the magnetic particles in the ground ferrofluid, is removed and separated from the ground particles.
  • the irreversibly flocked magnetic particles from which the first dispersant agent has been removed may be treated with another dispersant agent so that the dispersant agent is attached to said particles, and that such particles may be employed to prepare alternate ferrofluid compositions.
  • Such alternate ferrofluid compositions prepared by my process and the particles of my process exhibit improved properties over prior art ferrofluid compositions.
  • ferrofluid compositions of my invention are well suited for application in magnetic fluid seals, bearings and related devices.
  • My alternate ferrofluid compositions exhibit better; that is, lower, viscosity properties, while the high packing of the volume fractions of the irreversibly flocked particles in the ferrofluid composition permits saturation magnetization of over 300 gauss.
  • My ferrofluid composition provides for the advantages of a wide temperature range of operation, high magnetic intensity, low viscosity, oxidation resistance and colloidal stability in the presence of intense magnetic field gradients.
  • My process comprises preparing a ferrofluid composition by preparing a dispersion of colloidal-size magnetic particles, and a dispersant in a liquid carrier, such as by grinding through a ball-milling operation coarse magnetic solids in the presence of a long-chain polar molecule as a surfactant and dispersant, with a water carrier.
  • My process then includes removing the dispersant from the ground magnetic particles of the ferrofluid composition, such as by adding a foreign agent or solvent to flocculate the particles, and the wet dispersant-stripped particles removed from the supernatant liquid.
  • the wet dispersant-stripped particles are then washed free of any solvent and any remaining dispersant agents,'and heated to drive off moisture and to ob tain dried dispersant-stripped irreversibly flocked particles.
  • Such irreversibly flocked particles are then treated with a dispersant, and redispersed in another and different carrier liquid to provide an alternate ferrofluid composition having improved properties.
  • the treatment of the irreversibly flocked, dried magnetic particles with a dispersant attaches the dispersant to the magnetic particles.
  • the second dispersant may be attached to the magnetic particles by grinding the particles in a ball mill, together with the dispersant and the alternate carrier liquid to obtain the alternate ferrofluid composition.
  • My process permits the preparation of ferrofluids wherein the ratio of magnetic solid-core particle volume relative to the total volume of the dispersantcoated particle is greater than found in ferrofluids prepared by direct grinding processes. This greater volume permits much better packing of the magnetic solid particles in the liquid carrier. For example, a comparison of a 120 Angstrom versus a Angstrom spherical particle, with both having a 20 Angstrom dispersant coating, provides for a 16 percent increase in solid packing density; however, I have found that such increase in solid packing by my process provides for unexpected increases in saturation mgnetization over that expected for the improved packing density.
  • FIGS. 1 a, b and c are schematic presentations of the stability of magnetic particles in ferrofluid compositions.
  • FIG. 2 is a schematic process-flow sheet illustrating the process of preparing the improved alternate ferrofluid compositions of my invention.
  • FIGS. 1 a, b and c schematically illustrate various states of stability of colloidal magnetic particles of a ferrofluid composition, with FIGS. 1 a and b directed to stability states of the particles of the prior art, while FIG. 1 c is directed to the stability state of the magnetic particles of my invention, which particles have been irreversibly flocculated.
  • the magnetic particles 12 are suspended in a liquid carrier 10, the carrier containing the dispersing agent for dispersant, typically, a long-chain surfactant molecule having a polar group 14, with the polar group illustrated by a circular configuration, with the long-chain portion of the molecule schematically illustrated by a jagged line attached to the polar circular head.
  • the dispersing agent for dispersant typically, a long-chain surfactant molecule having a polar group 14
  • the polar group illustrated by a circular configuration
  • the long-chain portion of the molecule schematically illustrated by a jagged line attached to the polar circular head.
  • FIG. 1 illustrates the stabilized magnetic particles of the prior art, the particles showing a stabilized condition, with the surfactant molecules adsorbed on the particle surface.
  • the long-chain-like tails of the surfactant molecules are extended and well solvated with the surrounding liquid carrier 10.
  • the adsorbed monomolecular surfactant layers on the adjacent particles furnish a steric hindrance, preventing the particles surfaces from approaching close enough to agglomerate the particles under the influence of van der Waals or magnetic forces of attraction.
  • the stabilized condition of the magnetic particles as illustrated in FIG. 1 a are those prepared in a typical process for preparing ferrofluid compositions.
  • FIG. 1 b illustrates a reversibly flocculated group of particles wherein the surfactant, while still adsorbed on the surface of the particles, is recoiled to a smaller effective radius by such reversible flocculation.
  • the shielding is incomplete with the particles loosely bound together under the forces of mutual attraction.
  • Ferrofluid compositions containing reversibly flocculated particles as illustrated in FIG. 1 b are typically prepared in a manner set forth in my US. Pat. No. 3,531,413.
  • FIG. 1 0 schematically illustrates the irreversibly flocculated particles condition in a ferrofluid composition of the present invention and process, wherein the surfactant molecules 14 are no longer secured to the particles surface, but instead, by my process, have been removed and are held in solution by a surrounding liquid carrier.
  • the surfactant-stripped magnetic particles illustrated in FIG. 1 c and prepared by my process are more or less firmly attached to each other as illustrated, and will not redisperse in the flocculant-free carrier liquid, whereas the particles of the prior art in a reversible flocculation as depicted in FIG. 1 b would redisperse.
  • An important feature of my invention is my discovery and recognition of two different types of flocculations in ferrofluid compositions containing magnetic particles, and the incorporation of such recognition into a process which provides particular advantages for the preparation of ferrofluids and for the ferrofluid composition so prepared.
  • the materials which may be employed in the practice of my process and the preparation of my improved ferrofluid compositions are those materials, such as magnetic particles, dispersants and the carriers which are presently employed for ferrofluid compositions.
  • the finely divided magnetizable particles include the materials usually recognized as being magnetic, such as magnetite, gamma iron oxide, chromium dioxide, ferrites, such as manganese-zinc ferrite, manganese ferrite, nickel ferrite and many similar materials.
  • Such materials include also elements and metallic alloys, such as cobalt, iron, nickel, gadolinium, and Samarium-cobalt.
  • the preferred materials for practice of the present invention are magnetite and gamma iron oxide.
  • such magnetic particles are present in a ferrofluid composition in particle size ranging from about 20 A to 300 A, with the average in particle size being from about A to A.
  • the magnetic particles are usually present up to about 20% by volume of the ferrofluid composition, and more typically, from about 2 to 15% by volume.
  • the liquid carrier employed in ferrofluid compositions in the practice of my invention initially should be a liquid which is relatively inexpensive, easily evaporated, of low viscosity and noncombustible, with the preferred liquid carrier for the initial stages or the preparation of the initial ferrofluid composition being water.
  • the second carrier liquid employed in the preparation of the alternate ferrofluid composition by my process is typically characterized by being of a relatively low viscosity, having a wide temperature range for stability which would include a low pour point and a high flash point, and have a low volatility such that the resulting ferrofluid composition may be usefully employed and sealed in a vacuum condition on rotary bearings or similar applications.
  • liquid materials may be employed as the liquid carrier in either the first or second stage of my invention, but more typically, the second stage of the invention to prepare the alternate ferrofluid compositions, which materials would include hydrocarbons, both aromatic and aliphatic; for example, toluene, xylene, cyclohexane, heptane, kerosene, mineral oils and the like; halocarbons, such as fluorocarbons which would include the fluorinated and chlorinated ethers, esters and the derivatives of C C materials, such as perfluorinated polyethers; esters to include polyesters, di and triesters, such as azealates, phthalates, sebaccates, such as, for example, dioctyl phthalates, di-2 ethylhexyl azealates, silicate esters and the like.
  • hydrocarbons both aromatic and aliphatic
  • halocarbons such as fluorocarbons which would include the fluorinated and
  • a dispersant or dispersing agent which is typically a surfactant which may be employed in my ferrofluid process and composition includes a wide variety of materials which would aid in the dispersion of the magnetic particles.
  • Such dispersants are characterized as surfactants or surface-active agents, and would include, for example, succinates, sulfonates, phosphated alcohols, amine long-chain acid reaction products, phosphate esters, polyether alcohols to include alkylphenoxypolyethoxyethanols, polyether acids and similar materials which are characterized by suppressing the surface tension of water, and which include a polar group and a long-chain tail; for example, C -C
  • the surfactant is typically present in my ferrofluid compositions in a ratio of surfactant to magnetic particles of about 1:2 to 10:1 by volume; for example, 5:2 by volume, of the solid magnetic particles.
  • FIG. 2 illustrates a process-flow block diagram in my process for preparing irreversibly flocked particles and alternate ferrofluid compositions.
  • coarse magnetic solids typically having a size of l to 2 microns (10,000 to 20,000 Angstroms in size)
  • a surfactant-water solution to produce a stable, colloidal, magnetizable ferrofluid, as presently known in the prior art and as illustrated in FIG. 1 a.
  • the nature and behavior of ferrofluids are quantitatively described in the in sertion Ferrohydrodynamics in the Encyclopedia Dictionary of Physics, Supplement 4, Pergamon Press.
  • the surfactant employed is chosen to produce a ferrofluid composition which may be irreversibly flocculated.
  • the ferrofluid composition so prepared is then irreversibly fiocculated by the addition of a solvent-flocculating agent, typically a polar solvent, such as a ketone, ester or alcohol; for example, acetone or methylethyl ketone.
  • a solvent-flocculating agent typically a polar solvent, such as a ketone, ester or alcohol; for example, acetone or methylethyl ketone.
  • the colloidal magnetic particles of the ferrofluid composition are then precipitated free of the liquidwater carrier, and also free of the initial surfactant employed.
  • the initial liquid carrier that is, water, and the surfactant are removed in the supernatant liquid after precipitation of the particles, and the wet dispersantstripped particles so precipitated recovered.
  • the wet dispersant-stripped particles are then waterwashed several times to remove any traces of residual solvent or surfactant.
  • the washed magnetic particles are then carefully heated to drive off the moisture so as to provide dry, dispersant-stripped magnetic particles.
  • the dry, dispersant-stripped particles are then treated with another and typically a different surfactant, such as by coating, or as shown, grinding in a ball mill, in the presence of an alternate carrier liquid to form an alternate ferrofluid composition of my invention, and having enhanced characteristics and properties.
  • the alternate ferrofluid composition so prepared may be of the reversible or irreversible type.
  • the alternate ferrofluid composition is prepared by again grinding in a ball mill the dry, dispersant-stripped particles in the presence of the alternate dispersant, and the alternate carrier liquid.
  • the initial carrier liquid is water
  • the alternate carrier liquid to prepare the alternate ferrofluid composition may be water, but is preferably an organic material.
  • the original surfactant employed for the preparation of the first ferrofluid compositions may be employed as the' alternate dispersant, the use of such surfactant has not been found as effective as a new and different surfactant as the alternate dispersant in preparing the alternate ferrofluid compositions.
  • the alternate ferrofluid compositions prepared by my process exhibit improved properties over the first ferrofluid compositions using such liquid carrier.
  • the term irreversibly flocked refers to that condition in which the magnetic particles will not disperse in any liquid carrier in that condition.
  • the flocculating agent originally employed must be removed, and a new surfactant. employed. I have found, for example, that prior art ferrofluid compositions of magnetic particles and oil typically have an average size of Angstroms, while my alternate ferrofluid compositions prepared by my process using the same materials have an average size of Angstroms, and because of their condition of larger particle size, better packing is accomplished, and, therefore, better magnetic susceptibility and lower viscosity is obtained.
  • the original liquid carrier employed is water
  • the alternate dispersant employed should be different from the dispersant originally employed.
  • DuPont Co Sodium alkylnapthalene sulfonate
  • DuPont Co Sodium hydrocarbon sulfonate Petroleum sulfonate Phosphorated higher alcohol P 'yUs' s 3 10):
  • Alkylaryl sodium sulfonate (M.W. 460 Avg) Free acid of a complex organic phosphate ester Bryton HY Bryton Chemical Co. Synthetic sodium petroleum sulfonate Bryton Calcium 45 Bryton Chemical Co. Synthetic calcium petroleum sulfonate Teric N8 I.C.I.A.N.Z. Ltd. Nonylphenol 8 moles ethylene oxide Surfactant 157 DuPont Co. Perfluoropolyether carboxylic acid EXAMPLE 1 Saturation magnetixation Carrier liquid Magnetic particle Dispersing Agent 200 gauss Distilled water (83% vol.) Magnetite (Fe O (4% vol.) Aerosol C6l (13% vol.) American Cyanamid Co.
  • the powder comprised magnetic particles of the desired colloidal size which were free from any dispersant. These particles were loosely bonded together, but were well suited to be redispersed in an alternate carrier liquid by my process.
  • the dried dispersant-free powder was then combined with a surfactant and carrier liquid, and redispersed in a ball mill in an alternate ferrofluid composition as follows:
  • Ball milling was carried out for a period of one to three weeks. I found that virtually all the magnetic solid became colloidally dispersed in the new liquid carrier.
  • Table III compares a ferrofluid of the prior art with the alternate ferrofluid of my invention.
  • the direct grind ferrofluid was prepared with a dibasic acid ester (see Table I), while the alternate ferrofluid employed water as the direct grind carrier with the same dibasic acid ester employed as the carrier after irreversible flocculation as described.
  • a system of coated large particles by irreversible flocculation takes up less bulk than a system of small particles flocculated reversibly having the same thickness of coating, and, accordingly, the viscosity is lower.
  • EXAMPLE 2 Stripped dispersant-free magnetite particles obtained as described in Example 1 may be coated with many other dispersing agents.
  • a useful screening test is to add a small quantity of the stripped particles that have been pulverized to a small quantity; e.g., 5 c.c., of carrier liquid/surfactant solution and stir. Suitable combinations of materials produce an instantaneous peptization of at least a portion of the magnetic particles.
  • My process and the above testing technique are very valuable in eliminating the time and expense associated with the filling, running and clean-up of balls and ball mills associated with experimental searching for successful ferrofluid grind combinations in the past.
  • My screening test requires but a few minutes and provides information that previously required one to several weeks to obtain.
  • Table IV identifies a series of surfactant/solvent combinations that have been identified and successfully produced in this fashion. Details of the surfactants and solvents are provided in Tables I and II.
  • This ferrofluid composition combines the properties of immiscibility with white mineral oil, colloidal stability against freeze/thaw, permits polystyrenesurfaces to be preferentially wetted by white mineral oil, and freedom from phase separation by emulsification of the ferrofluid into an adjacent liquid phase of white mineral oil.
  • the original direct persant is effective only in the role of steric protection.
  • a further general advantage provided by the process of my invention is the time saving in producing lots of specialty ferrofluid compositions.
  • a master batch of C6l/water base ferrofluids may be processed in a series of operations that require from three to six or more months time to complete to provide a dry, stripped powder of the particles.
  • the powder may then be relatively rapidly converted to the desired specialty ferrofluid in typically 1 to 3 weeks.
  • a process for preparing an improved ferrofluid composition which process comprises in combination:
  • a. preparing a first ferrofluid composition comprising a dispersion of colloidal-size magnetic particles in a dispersant in a polar liquid carrier;
  • first carrier liquid of the first ferrofluid composition comprises water
  • second carrier liquid of the second ferrofluid composition comprises a nonaqueous liquid
  • step of coating the flocked particles and redispersing such particles in the second carrier liquid is accomplished by grinding the recovered flocked particles in a ball mill in the presence of the second dispersant and the second carrier liquid.
  • the second disperimpuls comprises, in a ratio of dispersant-to-magnetic particles, from about 1:2 to :1 by volume.
  • the second ferrofluid composition comprises from about 2 to by volume of magnetic particles.
  • a ferrofluid composition which comprises a solution of a low-volatility liquid diester carrier and a dispersant, and colloidal-size magnetic particles dispersed in said solution, the composition having a saturation magnetization of between about 300 to 800 gauss, and having a viscosity of from about 100 to 2000 cps, the magnetic particles comprising magnetite or gamma iron oxide, the dispersant comprising, in a ratio of dispersant-to-magnetic particles, from about 1:2 to 10:1 by volume, and the composition comprising from about 2 to 15% by volume of magnetic particles, the magnetic particles having a particle size of about 120 Angstroms.
  • the flocked dispersant-free magnetic particles having a particle size of from about 20 to 300 Angstroms produced by the process of claim 1, the particles essentially free of adsorbed surfactant and incapable of being redispersed in the first carrier liquid without the addition of a dispersant.
  • a process of preparing an improved ferrofluid composition of low viscosity and high magnetization saturation which process comprises in combination:
  • a ferrofluid composition which comprises a solution of a diester liquid carrier, a dispersant, and colloidal-size magnetic particles dispersed in said solution, the composition having a saturation magnetization of over 300 gauss, and having a viscosity of from about to 2000 cps.
  • composition of claim 25 wherein the dispersant is a polyisobutene succinic acid derivative.
  • composition of claim 25 wherein the composition comprises a ratio of dispersant-to-magnetic particles of about 1:2 to 10:1 by volume.
  • composition of claim 25 wherein the magnetic particles comprise magnetite or gamma iron oxide.
  • composition of claim 25 wherein the magnetic particles of the ferrofluid composition have an average particle size of from about 20 to 300 Angstroms.
  • composition of claim 25 wherein the ferrofluid composition comprises from about 2 to 15% by volume of magnetic particles.
  • composition of claim 25 wherein the composition has a magnetic saturation of between about 300 to 800 gauss.

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Abstract

A process for preparing irreversibly flocked magnetic particles, which process increases the versatility of the size-reduction process for the preparation of ferrofluids. The process comprises producing a ferrofluid in an aqueous carrier liquid with a dispersing agent by grinding coarse magnetic materials, removing the dispersing agent and attaching a different dispersing agent to the ground magnetic particles, and redispersing the particles in another carrier liquid. The process provides for the preparation of irreversibly flocked magnetic particles, and the preparation of alternate ferrofluids containing such particles.

Description

' United States atent [1 1 osensweig Nov. 4, 1975 FERROFLUID COMPOSITIONS AND PROCESS OF MAKING SAME [75] Inventor:
[73] Assignee:
Ronald E. Rosensweig, Summit, NJ.
Ferrofluidics Corporation, Burlington, Mass.
22 Filed: Jan. 17, 1973 21 Appl. N0; 324,414
[52] US. Cl 252/6251; 252/6252 [51] Int. C13... HOlF 1/25; l-lOlF 1/00; C10M 3/00; CO9D 11/00 [58] Field of Search 252/6256, 62.5], 62.52, 252/6254, 62.62
[56] References Cited UNITED STATES PATENTS 3,531,413 9/1970 Rosensweig 252/6262 OTHER PUBLICATIONS R. Kaiser et al., Magnetic Properties of Stable Dispersions of Subdomain Magnetite Particles, J. Applied Physics, Vol. 41, No. 3 Mar. 1, 1970, pp. 1064-1072.
Primary ExaminerF. C. Edmundso Attorney, Agent, or Firm-Richard P. Crowley [57] ABSTRACT 32 Claims, 4 Drawing Figures COARSE MAGNETIC SOLIDS DISPERSANT GRIND WATER FERROFLUID SOLVENT FLOCCULATING FLOCCU E SUPERNATANT AGENT WET DISPERSANT STRIPPED PARTICLES WATER-. WA
WATER AND I SOLVENT HEAT MOISTURE DRY DISPERSANT STRI PPED PARTICLES R ALTERNATE $514211? GRND CARRIER LIQUID ALTERNATE FERROFLUID FERROFLUID COMPOSITIONS AND PROCESS OF MAKING SAME BACKGROUND OF THE INVENTION Ferrofluid is a ferromagnetic fluid displaying superparamagnetism, having a magnetic polarizability that is substantially uniform and having the property such that when a gradientmagnetic field is applied to it, a body force is developed within it which can exceed by orders of magnitude the ordinary force of gravity on a unit volume of the material. Typically, ferrofluid comprises a colloidal dispersion of finely divided magnetic particles of subdomain size whose liquid condition is remarkably unaffected by the presence of an applied magnetic field, and which particles resist settling under the influence of gravitational, centrifugal, magnetic or other force fields. Ferrofluid particles typically ranging in size up to about 300 A remain uniformly dispersed throughout the liquid carrier due to thermal agitation.
Ferrofluids are described in my publication Magnetic Fluids, International Science and Technology, July 1966, pp 48-56; U.S. Pat. No. 3,215,572; in the publication of R. Kaiser and G. Miskolczy, Magnetic Properties of Stable Dispersions of Subdomain Magnetite Particles, J. Applied Physics, Vol. 41, No. 3, Mar. 1, 1970, pp 1064-1072; in A Catalog of Magnetic Fluids, Ferrofluidics Corporation, Burlington, Massachusetts 1972 and elsewhere.
In the prior art, a magnetic powder is reduced in size to the colloidal range as by ball-mill grinding in the presence of a liquid carrier and a grinding aid which serves also as a dispersing agent. The dispersing agent is typically a surfactant comprising a polar long-chain molecule whose polar group adsorbs onto the surface of the particle to produce a monomolecular protective coating that prevents particles from attaching to each other.
US. Pat. No. 3,531,413, hereby incorporated by reference, describes a method for transferring magneticcoated particles of a ferrofluid from one carrier liquid to another by a process of flocculation using a foreign solvent, separation of flocculated particles from supernatant liquid, and transfer of the particles into an alternate solvent in which the coated particles are dispersible. The carrier liquids that are employed must be similar in their physical chemical properties. The flocculation process is here termed reversible with the coating of a dispersing agent on the particles as in the prior art remaining attached and unchanged. As a result, the coated, flocked particles are redispersable into the 7 pure original solvent.
SUMMARY OF THE INVENTION My invention relates to an improved process for the preparation of ferrofluids and to the ferrofluids so produced, and in particular, concerns a process for the flocculation of magnetic particles from a ferrofluid in an irreversible manner, and the treatment of such irreversibly flocked particles to prepare improved ferrofluid compositions.
I have discovered that ferrofluids may be flocculated by the addition of foreign agents or solvents in an irreversible manner such that the dispersant employed; that is, the surfactant that originally stabilized the magnetic particles in the ground ferrofluid, is removed and separated from the ground particles. I have further found that the irreversibly flocked magnetic particles from which the first dispersant agent has been removed may be treated with another dispersant agent so that the dispersant agent is attached to said particles, and that such particles may be employed to prepare alternate ferrofluid compositions. Such alternate ferrofluid compositions prepared by my process and the particles of my process exhibit improved properties over prior art ferrofluid compositions. In particular, the ferrofluid compositions of my invention are well suited for application in magnetic fluid seals, bearings and related devices. My alternate ferrofluid compositions exhibit better; that is, lower, viscosity properties, while the high packing of the volume fractions of the irreversibly flocked particles in the ferrofluid composition permits saturation magnetization of over 300 gauss. My ferrofluid composition provides for the advantages of a wide temperature range of operation, high magnetic intensity, low viscosity, oxidation resistance and colloidal stability in the presence of intense magnetic field gradients.
My process comprises preparing a ferrofluid composition by preparing a dispersion of colloidal-size magnetic particles, and a dispersant in a liquid carrier, such as by grinding through a ball-milling operation coarse magnetic solids in the presence of a long-chain polar molecule as a surfactant and dispersant, with a water carrier. My process then includes removing the dispersant from the ground magnetic particles of the ferrofluid composition, such as by adding a foreign agent or solvent to flocculate the particles, and the wet dispersant-stripped particles removed from the supernatant liquid. The wet dispersant-stripped particles are then washed free of any solvent and any remaining dispersant agents,'and heated to drive off moisture and to ob tain dried dispersant-stripped irreversibly flocked particles. Such irreversibly flocked particles are then treated with a dispersant, and redispersed in another and different carrier liquid to provide an alternate ferrofluid composition having improved properties. The treatment of the irreversibly flocked, dried magnetic particles with a dispersant attaches the dispersant to the magnetic particles. The second dispersant may be attached to the magnetic particles by grinding the particles in a ball mill, together with the dispersant and the alternate carrier liquid to obtain the alternate ferrofluid composition.
My process permits the preparation of ferrofluids wherein the ratio of magnetic solid-core particle volume relative to the total volume of the dispersantcoated particle is greater than found in ferrofluids prepared by direct grinding processes. This greater volume permits much better packing of the magnetic solid particles in the liquid carrier. For example, a comparison of a 120 Angstrom versus a Angstrom spherical particle, with both having a 20 Angstrom dispersant coating, provides for a 16 percent increase in solid packing density; however, I have found that such increase in solid packing by my process provides for unexpected increases in saturation mgnetization over that expected for the improved packing density.
BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 a, b and c are schematic presentations of the stability of magnetic particles in ferrofluid compositions.
FIG. 2 is a schematic process-flow sheet illustrating the process of preparing the improved alternate ferrofluid compositions of my invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1 a, b and c schematically illustrate various states of stability of colloidal magnetic particles of a ferrofluid composition, with FIGS. 1 a and b directed to stability states of the particles of the prior art, while FIG. 1 c is directed to the stability state of the magnetic particles of my invention, which particles have been irreversibly flocculated. As illustrated, the magnetic particles 12 are suspended in a liquid carrier 10, the carrier containing the dispersing agent for dispersant, typically, a long-chain surfactant molecule having a polar group 14, with the polar group illustrated by a circular configuration, with the long-chain portion of the molecule schematically illustrated by a jagged line attached to the polar circular head.
FIG. 1 illustrates the stabilized magnetic particles of the prior art, the particles showing a stabilized condition, with the surfactant molecules adsorbed on the particle surface. The long-chain-like tails of the surfactant molecules are extended and well solvated with the surrounding liquid carrier 10. The adsorbed monomolecular surfactant layers on the adjacent particles furnish a steric hindrance, preventing the particles surfaces from approaching close enough to agglomerate the particles under the influence of van der Waals or magnetic forces of attraction. The stabilized condition of the magnetic particles as illustrated in FIG. 1 a are those prepared in a typical process for preparing ferrofluid compositions.
FIG. 1 b illustrates a reversibly flocculated group of particles wherein the surfactant, while still adsorbed on the surface of the particles, is recoiled to a smaller effective radius by such reversible flocculation. The shielding is incomplete with the particles loosely bound together under the forces of mutual attraction. Ferrofluid compositions containing reversibly flocculated particles as illustrated in FIG. 1 b are typically prepared in a manner set forth in my US. Pat. No. 3,531,413.
FIG. 1 0 schematically illustrates the irreversibly flocculated particles condition in a ferrofluid composition of the present invention and process, wherein the surfactant molecules 14 are no longer secured to the particles surface, but instead, by my process, have been removed and are held in solution by a surrounding liquid carrier. The surfactant-stripped magnetic particles illustrated in FIG. 1 c and prepared by my process are more or less firmly attached to each other as illustrated, and will not redisperse in the flocculant-free carrier liquid, whereas the particles of the prior art in a reversible flocculation as depicted in FIG. 1 b would redisperse. An important feature of my invention is my discovery and recognition of two different types of flocculations in ferrofluid compositions containing magnetic particles, and the incorporation of such recognition into a process which provides particular advantages for the preparation of ferrofluids and for the ferrofluid composition so prepared.
The materials which may be employed in the practice of my process and the preparation of my improved ferrofluid compositions are those materials, such as magnetic particles, dispersants and the carriers which are presently employed for ferrofluid compositions. For example, the finely divided magnetizable particles include the materials usually recognized as being magnetic, such as magnetite, gamma iron oxide, chromium dioxide, ferrites, such as manganese-zinc ferrite, manganese ferrite, nickel ferrite and many similar materials. Such materials include also elements and metallic alloys, such as cobalt, iron, nickel, gadolinium, and Samarium-cobalt. The preferred materials for practice of the present invention are magnetite and gamma iron oxide. Typically, such magnetic particles are present in a ferrofluid composition in particle size ranging from about 20 A to 300 A, with the average in particle size being from about A to A. The magnetic particles are usually present up to about 20% by volume of the ferrofluid composition, and more typically, from about 2 to 15% by volume.
The liquid carrier employed in ferrofluid compositions in the practice of my invention initially should be a liquid which is relatively inexpensive, easily evaporated, of low viscosity and noncombustible, with the preferred liquid carrier for the initial stages or the preparation of the initial ferrofluid composition being water. As more fully described hereinafter, the second carrier liquid employed in the preparation of the alternate ferrofluid composition by my process is typically characterized by being of a relatively low viscosity, having a wide temperature range for stability which would include a low pour point and a high flash point, and have a low volatility such that the resulting ferrofluid composition may be usefully employed and sealed in a vacuum condition on rotary bearings or similar applications. A wide variety of liquid materials may be employed as the liquid carrier in either the first or second stage of my invention, but more typically, the second stage of the invention to prepare the alternate ferrofluid compositions, which materials would include hydrocarbons, both aromatic and aliphatic; for example, toluene, xylene, cyclohexane, heptane, kerosene, mineral oils and the like; halocarbons, such as fluorocarbons which would include the fluorinated and chlorinated ethers, esters and the derivatives of C C materials, such as perfluorinated polyethers; esters to include polyesters, di and triesters, such as azealates, phthalates, sebaccates, such as, for example, dioctyl phthalates, di-2 ethylhexyl azealates, silicate esters and the like.
A dispersant or dispersing agent which is typically a surfactant which may be employed in my ferrofluid process and composition includes a wide variety of materials which would aid in the dispersion of the magnetic particles. Such dispersants are characterized as surfactants or surface-active agents, and would include, for example, succinates, sulfonates, phosphated alcohols, amine long-chain acid reaction products, phosphate esters, polyether alcohols to include alkylphenoxypolyethoxyethanols, polyether acids and similar materials which are characterized by suppressing the surface tension of water, and which include a polar group and a long-chain tail; for example, C -C The surfactant is typically present in my ferrofluid compositions in a ratio of surfactant to magnetic particles of about 1:2 to 10:1 by volume; for example, 5:2 by volume, of the solid magnetic particles.
FIG. 2 illustrates a process-flow block diagram in my process for preparing irreversibly flocked particles and alternate ferrofluid compositions. In my process, coarse magnetic solids, typically having a size of l to 2 microns (10,000 to 20,000 Angstroms in size), were reduced by grinding a ball mill in the presence of a surfactant-water solution to produce a stable, colloidal, magnetizable ferrofluid, as presently known in the prior art and as illustrated in FIG. 1 a. The nature and behavior of ferrofluids are quantitatively described in the in sertion Ferrohydrodynamics in the Encyclopedia Dictionary of Physics, Supplement 4, Pergamon Press. The surfactant employed is chosen to produce a ferrofluid composition which may be irreversibly flocculated.
The ferrofluid composition so prepared is then irreversibly fiocculated by the addition of a solvent-flocculating agent, typically a polar solvent, such as a ketone, ester or alcohol; for example, acetone or methylethyl ketone. On the addition of the solvent-flocculated agent, the colloidal magnetic particles of the ferrofluid composition are then precipitated free of the liquidwater carrier, and also free of the initial surfactant employed. The initial liquid carrier; that is, water, and the surfactant are removed in the supernatant liquid after precipitation of the particles, and the wet dispersantstripped particles so precipitated recovered.
The wet dispersant-stripped particles are then waterwashed several times to remove any traces of residual solvent or surfactant. The washed magnetic particles are then carefully heated to drive off the moisture so as to provide dry, dispersant-stripped magnetic particles. The dry, dispersant-stripped particles are then treated with another and typically a different surfactant, such as by coating, or as shown, grinding in a ball mill, in the presence of an alternate carrier liquid to form an alternate ferrofluid composition of my invention, and having enhanced characteristics and properties. The alternate ferrofluid composition so prepared may be of the reversible or irreversible type. As illustrated, the alternate ferrofluid composition is prepared by again grinding in a ball mill the dry, dispersant-stripped particles in the presence of the alternate dispersant, and the alternate carrier liquid. By my process, alternate ferrofluid compositions having improved magnetic and viscous properties have been produced, lengthy processing time eliminated, and more versatile ferrofluid composi- 6 tions produced which have alternate and improved chemical compositions.
In the preferred embodiment of my invention, the initial carrier liquid is water, while the alternate carrier liquid to prepare the alternate ferrofluid composition may be water, but is preferably an organic material. Further, while my tests indicate that the original surfactant employed for the preparation of the first ferrofluid compositions may be employed as the' alternate dispersant, the use of such surfactant has not been found as effective as a new and different surfactant as the alternate dispersant in preparing the alternate ferrofluid compositions. Where the same or similar carrier liquid is employed, as employed in the first ferrofluid composition, the alternate ferrofluid compositions prepared by my process exhibit improved properties over the first ferrofluid compositions using such liquid carrier.
In the process of my invention, the term irreversibly flocked refers to that condition in which the magnetic particles will not disperse in any liquid carrier in that condition. To obtain the benefits of my process, the flocculating agent originally employed must be removed, and a new surfactant. employed. I have found, for example, that prior art ferrofluid compositions of magnetic particles and oil typically have an average size of Angstroms, while my alternate ferrofluid compositions prepared by my process using the same materials have an average size of Angstroms, and because of their condition of larger particle size, better packing is accomplished, and, therefore, better magnetic susceptibility and lower viscosity is obtained. Thus, in my process, in its preferred embodiment, the original liquid carrier employed is water, while the alternate dispersant employed should be different from the dispersant originally employed. The advantages and techniques of my process and] alternate ferrofluid compositions will be illustrated by the following examples wherein Tables I and ll provide details of the materials employed in the examples.
TABLE I CARRIER LlQUlDS Stabilizing Agent Aerosol 22 Alkanol BG Alkanol I895 Pyronate 5O Victawet 58B Polyisobutene succinic acid derivative (PIBSA) Di-Z-ethyl hexyl phosphate STABlLlZlNG AGENTS USED TO REDISPERSE COLLOIDAL MAGNETITE PARTICLES Source Description Tetrasodium N-( 1,2 dicarboxyethyl )N-octadecylsulfosuccinamate American Cyanamid Co.
DuPont Co. Sodium alkylnapthalene sulfonate DuPont Co. Sodium hydrocarbon sulfonate Petroleum sulfonate Phosphorated higher alcohol P 'yUs' s 3 10):
M.W. lOOO (approx.) Reaction product with polyethylene amine Witco Chemical Corp.
Stauffer Chemical Co.
Enjay Chemical Co.
Pfaltz and Bauer lnC.
TABLE II-continued Stabilizing Agent Description Acto 500 Humble Oil & Refining Antar LM4OO GAF Corp. Chem. Div.
Alkylaryl sodium sulfonate (M.W. 460 Avg) Free acid of a complex organic phosphate ester Bryton HY Bryton Chemical Co. Synthetic sodium petroleum sulfonate Bryton Calcium 45 Bryton Chemical Co. Synthetic calcium petroleum sulfonate Teric N8 I.C.I.A.N.Z. Ltd. Nonylphenol 8 moles ethylene oxide Surfactant 157 DuPont Co. Perfluoropolyether carboxylic acid EXAMPLE 1 Saturation magnetixation Carrier liquid Magnetic particle Dispersing Agent 200 gauss Distilled water (83% vol.) Magnetite (Fe O (4% vol.) Aerosol C6l (13% vol.) American Cyanamid Co.
An ethanolated alkylguani dine amine complex To the ferrofluid so prepared was added an equal volume of acetone as a flocculating agent, and the solution stirred. The colloidal particles immediately flocculated and began to settle under gravity. A source of magnetic field or other means may be used to accelerate the settling process. The supernatant liquid was decanted and discarded.
Water was added to the precipitated particles with stirring, and it was found that the particles did not stably redisperse; i.e., the flocculation was irreversible. This water was discarded as a supernatant and served to remove excess acetone and any dispersant that may be present. The wash was repeated three times, then the solids were dried. Drying was carried out under infrared lamps or in an oven at 200F until a dry black granular solid powder was obtained. Care should be taken not to heat excessively, since overheating leads to formulation of a dry brownish solid that is not suited for further processing.
The powder comprised magnetic particles of the desired colloidal size which were free from any dispersant. These particles were loosely bonded together, but were well suited to be redispersed in an alternate carrier liquid by my process.
The dried dispersant-free powder was then combined with a surfactant and carrier liquid, and redispersed in a ball mill in an alternate ferrofluid composition as follows:
Alternate Carrier Liquid Toluene (90% vol.) Magnetic solids Fe o (4% vol.) Alternate Stabilizing Agent PIBSA (see Table II) (6% vol.)
Ball milling was carried out for a period of one to three weeks. I found that virtually all the magnetic solid became colloidally dispersed in the new liquid carrier.
Of course, it is possible to ball mill directly the magnetite with toluene as the liquid carrier and PIBSA as the dispersant to produce a colloidal ferrofluid. However, the produce is greatly inferior in its ability to be concentrated due to its higher viscosity at a given level of magnetic saturation.
The data of Table III compares a ferrofluid of the prior art with the alternate ferrofluid of my invention. The direct grind ferrofluid was prepared with a dibasic acid ester (see Table I), while the alternate ferrofluid employed water as the direct grind carrier with the same dibasic acid ester employed as the carrier after irreversible flocculation as described.
The comparative viscosities and ability to concentrate are typified in Table III below.
TABLE III COMPARISON OF VISCOSITY vs MAGNETIZATION MAGNETIZATION (gauss) VISCOSITY (1 cp at 30C) Ferrofluid employing PIBSA as produced in the prior art by direct grind techniques cannot be concentrated beyond about 300 gauss, while my invention permits concentration of over 300 gauss and beyond 500 gauss. My improved ferrofluids may have viscosities of to 2000 cps at gauss levels of 300 to 800. In fact, ferrofluid compositions with saturation magnetization up to and in excess of 800 gauss have been prepared by my process.
Although not wishing to be bound by any particular theory, it is believed that the improved properties of lower viscosity at a given level of gauss for my alternate ferrofluids are based on the better concentrating ability; i.e., ability of particles to pack as in FIG. 1 0, due to the larger particle size present in preparations carried out according to my process. Electron micrograph study shows that the average particle size in Water/C61 dispersant ferrofluid is larger Angstroms) than for particles prepared by direct grinding in the system Toluene/PIBSA dispersant lOO Angstroms). Thus, at a given level of saturation gauss, a system of coated large particles by irreversible flocculation takes up less bulk than a system of small particles flocculated reversibly having the same thickness of coating, and, accordingly, the viscosity is lower.
EXAMPLE 2 Stripped dispersant-free magnetite particles obtained as described in Example 1 may be coated with many other dispersing agents. A useful screening test is to add a small quantity of the stripped particles that have been pulverized to a small quantity; e.g., 5 c.c., of carrier liquid/surfactant solution and stir. Suitable combinations of materials produce an instantaneous peptization of at least a portion of the magnetic particles.
My process and the above testing technique are very valuable in eliminating the time and expense associated with the filling, running and clean-up of balls and ball mills associated with experimental searching for successful ferrofluid grind combinations in the past. My screening test requires but a few minutes and provides information that previously required one to several weeks to obtain.
Table IV identifies a series of surfactant/solvent combinations that have been identified and successfully produced in this fashion. Details of the surfactants and solvents are provided in Tables I and II.
TABLE IV EXAMPLE 3 For the purposes of illustration only of the range and nature of my invention, redispersion of stripped dispersant-free magnetic particles from the initial aqueous ferrofluid composition of Example 1 back into a water carrier using an alternate and different dispersing agent has been demonstrated, employing the following dispersants: Aerosol 22, Alkanol BG, Alkanol I89S, Pyronate 50 and Victawet 58B.
TABLE IV ALTERNATE FERROFLUIDS OF NONAQUEOUS BASE PRODUCED BY CONVERSION OF THE WATER BASE FERROFLUID Surfactant Solvent l. Acto 500 Chevron M2V 2. Antara LM400 Chevron M2V 3. Bryton HY Chevron M2V 4. Bryton Calcium 45 Chevron M2V 5. Teric N8 Chevron MZV 6. Di-2 Ethyl hexyl White Mineral Oil Phosphate 7. Surfactant I57 DuPont E-3 The aqueous alternate ferrofluid employing as a dispersant Aerosol 22 is particularly useful in display devvices, such as those described in my US. Pat. No. 3,648,269. This ferrofluid composition combines the properties of immiscibility with white mineral oil, colloidal stability against freeze/thaw, permits polystyrenesurfaces to be preferentially wetted by white mineral oil, and freedom from phase separation by emulsification of the ferrofluid into an adjacent liquid phase of white mineral oil. By comparison, the original direct persant is effective only in the role of steric protection.
A further general advantage provided by the process of my invention is the time saving in producing lots of specialty ferrofluid compositions. Thus by my process, a master batch of C6l/water base ferrofluids may be processed in a series of operations that require from three to six or more months time to complete to provide a dry, stripped powder of the particles. The powder may then be relatively rapidly converted to the desired specialty ferrofluid in typically 1 to 3 weeks. In
fact, if complete conversion is not desired, a useful product can be often obtained on an overnight basis in many instances. Thus, as little .as one-day processing produces a ferrofluid that previously typically required several months, or was not producible at all.
What I claim is:
1. A process for preparing an improved ferrofluid composition, which process comprises in combination:
a. preparing a first ferrofluid composition comprising a dispersion of colloidal-size magnetic particles in a dispersant in a polar liquid carrier;
b. adding a flocculating agent to the first ferrofluid composition to precipitate the magnetic particles from the first composition separating the precipitate from the supernatant liquid to obtain flocked precipitated magnetic particles which are characterized in that such flocked particles will not redisperse in the polar liquid carrier without the addition of a dispersant;
c. recovering essentially dispersant-free magnetic precipitated particles;
d. coating the surface of the flocculated precipitated magnetic particles with a second dispersant; and
e. redispersing said coated particles in a second carrier liquid to provide a second ferrofluid composition of improved properties and characteristics.
2. The process of claim 1 which includes drying the recovered magnetic precipitated particles.
3. The process of claim 1 wherein the second dispersant employed to obtain the second ferrofluid composition is different from the dispersant in the first ferrofluid composition.
4. The process of claim 1 wherein the second liquid carrier in the second ferrofluid composition is different from the liquid carrier in the first ferrofluid composition.
5. The process of claim 1 wherein both the second dispersant and the second carrier liquid are different from the first dispersant and the first carrier liquid of the first ferrofluid composition.
6. The process of claim 1 wherein the first and second carrier liquids comprise water.
7. The process of claim 1 wherein the first carrier liquid of the first ferrofluid composition comprises water, and the second carrier liquid of the second ferrofluid composition comprises a nonaqueous liquid.
8. The process of claim 1 wherein the step of coating the flocked particles and redispersing such particles in the second carrier liquid is accomplished by grinding the recovered flocked particles in a ball mill in the presence of the second dispersant and the second carrier liquid.
9. The process of claim 1 which includes the step of washing the dispersant-free particles to remove residual traces of the dispersant from the surface of the particles, and, thereafter, drying the magnetic particles.
'10. The process of claim 1 wherein the first carrier liquid is water, and wherein the flocculating agent added to the first ferrofluid composition comprises a polar solvent.
11. The process of claim 1 wherein the second carrier liquid comprises a liquid fluorocarbon.
12. The process of claim 11 wherein the fluorocarbon comprises a perfluorinated polyether liquid.
13. The process of claim 1 wherein the second carrier liquid comprises a diester liquid.
14. The process of claim 1 wherein the magnetic particles of the first ferrofluid composition have an average particle size of from about 20 to 300 Angstroms.
15. The process of claim 1 wherein the magnetic particles comprise magnetite or gamma iron oxide.
16. The process of claim 1 wherein the second disperssant comprises, in a ratio of dispersant-to-magnetic particles, from about 1:2 to :1 by volume.
17. The process of claim 1 wherein the second ferrofluid composition comprises from about 2 to by volume of magnetic particles.
18. The process of claim 1 wherein the first liquid carrier is water, and the second flocculating agent is a ketone, ester or alcohol.
19. The process of claim 1 wherein the magnetic particles of the second ferrofluid composition have an average particle size of about 120 Angstroms.
20. The process of claim 1 which includes:
a. drying the essentially dispersant-free magnetic precipitated particles; and
b. ball milling the dry magnetic particles with the second carrier liquid and second dispersant to provide the second ferrofluid composition.
21. The process of claim 1 wherein the first carrier liquid is water, and the second carrier liquid is a mineral oil.
22. A ferrofluid composition which comprises a solution of a low-volatility liquid diester carrier and a dispersant, and colloidal-size magnetic particles dispersed in said solution, the composition having a saturation magnetization of between about 300 to 800 gauss, and having a viscosity of from about 100 to 2000 cps, the magnetic particles comprising magnetite or gamma iron oxide, the dispersant comprising, in a ratio of dispersant-to-magnetic particles, from about 1:2 to 10:1 by volume, and the composition comprising from about 2 to 15% by volume of magnetic particles, the magnetic particles having a particle size of about 120 Angstroms.
23. The flocked dispersant-free magnetic particles having a particle size of from about 20 to 300 Angstroms produced by the process of claim 1, the particles essentially free of adsorbed surfactant and incapable of being redispersed in the first carrier liquid without the addition of a dispersant.
24. A process of preparing an improved ferrofluid composition of low viscosity and high magnetization saturation, which process comprises in combination:
a. grinding in a ball mill coarse magnetic solids, a water-soluble dispersant, and a water carrierliquid to provide a first ferrofluid composition of colloidal-size stable magnetic particles;
b. adding a polar solvent as a flocculating agent to the first ferrofluid composition to precipitate the magnetic particles from the first ferrofluid composition separating the precipitate from the supernatant liquid to obtain flocked, dispersant-free magnetic particles which are characterized in that such flocked particles will not redisperse in the polar liquid carrier without the addition of a dispersant;
c. washing the dispersant-free precipitated particles with water to remove the flocculating polar solvent and any residual traces of the dispersant;
. heating the washed precipitated particles to a temperature not in excess of about 200F to remove moisture, and to produce dry, flocculated dispersant-free, magnetic particles; and
e. grinding in a ball mill the dry flocked particles in the presence of an alternate and different dispersing agent and a second carrier liquid to provide a second ferrofluid composition.
25. A ferrofluid composition which comprises a solution of a diester liquid carrier, a dispersant, and colloidal-size magnetic particles dispersed in said solution, the composition having a saturation magnetization of over 300 gauss, and having a viscosity of from about to 2000 cps.
26. The composition of claim 25 wherein the liquid carrier comprises a nonaqueous carrier, and the average particle size is about Angstroms.
27. The composition of claim 25 wherein the dispersant is a polyisobutene succinic acid derivative.
28. The composition of claim 25 wherein the composition comprises a ratio of dispersant-to-magnetic particles of about 1:2 to 10:1 by volume.
29. The composition of claim 25 wherein the magnetic particles comprise magnetite or gamma iron oxide.
30. The composition of claim 25 wherein the magnetic particles of the ferrofluid composition have an average particle size of from about 20 to 300 Angstroms.
31. The composition of claim 25 wherein the ferrofluid composition comprises from about 2 to 15% by volume of magnetic particles.
32. The composition of claim 25 wherein the composition has a magnetic saturation of between about 300 to 800 gauss.

Claims (32)

1. A PROCESS FOR PREPARING AN IMPROVED FERROFLUID COMPOSITION WHICH PROCESS COMPRISES IN COMBINATION: A. PREPARING FIRST FERROFLUID COMPOSITION COMPRISING A DISPERSION OF COLLOIDAL-SIZE MAGNETIC PARTICLES IN A DISPERSANT IN A POLAR LIQUID CARRIER, B. ADDING A FLOCCULATING AGENT TO THE FIRST FERROFLUID COMPOSI-, TION TO PRECIPITATE THE MAGNETIC PARTICLES FROM THE FIRST COMPOSITION SEPARATING THE PRECIPATE FROM THE SUPERNATANT LIQUID TO OBTAIN FLOCKED PRECIPITATED MAGNETIC PARTICLES WHICH ARE CHARACTERIZED IN THAT SUCH FLOCKED PARTICLES WILL NOT REDISPERSE IN THE POLAR LIQUID CARRIER WITHOUT THE ADDITION OF A DISPERSANT, C. RECOVERING ESSENTIALLY DISPERSANT-FREE MAGNETIC PRECIPITATED PARTICLES, D. COATING THE SURFACE OF THE FLOCCULATED PRECIPITATED MAGNETIC PARTICLES WITH SECOND DISPERSANT, AND E. REDISPERSING SAID COATED PARRTICLES IN A SECOND CARRIER LIQUID TO PROVIDE A SECOND FERROFLUID COMPOSITION OF IMPROVED PROPERTIES AND CHARACTERISTICS.
2. The process of claim 1 which includes drying the recovered magnetic precipitated particles.
3. The process of claim 1 wherein the second dispersant employed to obtain the second ferrofluid composition is different from the dispersant in the first ferrofluid composition.
4. The process of claim 1 wherein the second liquid carrier in the second ferrofluid composition is different from the liquid carrier in the first ferrofluid composition.
5. The process of claim 1 wherein both the second dispersant and the second carrier liquid are different from the first dispersant and the first carrier liquid of the first ferrofluid composition.
6. The process of claim 1 wherein the first and second carrier liquids comprise water.
7. The process of claim 1 wherein the first carrier liquid of the first ferrofluid composition comprises water, and the second carrier liquid of the second ferrofluid composition comprises a nonaqueous liquid.
8. The process of claim 1 wherein the step of coating the flocked particles and redispersing such particles in the second carrier liquid is accomplished by grinding the recovered flocked particles in a ball mill in the presence of the second dispersant and the second carrier liquid.
9. The process of claim 1 which includes the step of washing the dispersant-free particles to remove residual traces of the dispersant from the surface of the particles, and, thereafter, drying the magnetic particles.
10. The process of claim 1 wherein the first carrier liquid is water, and wherein the flocculating agent added to the first ferrofluid composition comprises a polar solvent.
11. The process of claim 1 wherein the second carrier liquid comprises a liquid fluorocarbon.
12. The process of claim 11 wherein the fluorocarbon comprises a perfluorinated polyether liquid.
13. The process of claim 1 wherein the second carrier liquid comprises a diester liquid.
14. The process of claim 1 wherein the magnetic particles of the first ferrofluid composition have an average particle size of from about 20 to 300 Angstroms.
15. The process of claim 1 wherein the magnetic particles comprise magnetite or gamma iron oxide.
16. The process of claim 1 wherein the second disperssant comprises, in a ratio of dispersant-to-magnetic particles, from about 1:2 to 10:1 by volume.
17. The process of claim 1 wherein the second ferrofluid composition comprises from about 2 to 15% by volume of magnetic particles.
18. The process of claim 1 wherein the first liquid carrier is water, and the second flocculating agent is a ketone, ester or alcohol.
19. The process of claim 1 wherein the magnetic particles of the second ferrofluid composition have an average particle size of about 120 Angstroms.
20. The process of claim 1 which includes: a. drying the essentially dispersant-free magnetic precipitated particles; and b. ball milling the dry magnetic particles with the second carrier liquid and second dispersant to provide the second ferrofluid composition.
21. The process of claim 1 wherein the first carrier liquid is water, and the second carrier liquid is a mineral oil.
22. A ferrofluid composition which comprises a solution of a low-volatility liquid diester carrier and a dispersant, and colloidal-size magnetic particles dispersed in said solution, the composition having a saturation magnetization of between about 300 to 800 gauss, and having a viscosity of from about 100 to 2000 cps, the magnetic particles comprising magnetite or gamma iron oxide, the dispersant comprising, in a ratio of dispersant-to-magnetic particles, from about 1:2 to 10:1 by volume, and the composition comprising from abOut 2 to 15% by volume of magnetic particles, the magnetic particles having a particle size of about 120 Angstroms.
23. The flocked dispersant-free magnetic particles having a particle size of from about 20 to 300 Angstroms produced by the process of claim 1, the particles essentially free of adsorbed surfactant and incapable of being redispersed in the first carrier liquid without the addition of a dispersant.
24. A process of preparing an improved ferrofluid composition of low viscosity and high magnetization saturation, which process comprises in combination: a. grinding in a ball mill coarse magnetic solids, a water-soluble dispersant, and a water carrier liquid to provide a first ferrofluid composition of colloidal-size stable magnetic particles; b. adding a polar solvent as a flocculating agent to the first ferrofluid composition to precipitate the magnetic particles from the first ferrofluid composition separating the precipitate from the supernatant liquid to obtain flocked, dispersant-free magnetic particles which are characterized in that such flocked particles will not redisperse in the polar liquid carrier without the addition of a dispersant; c. washing the dispersant-free precipitated particles with water to remove the flocculating polar solvent and any residual traces of the dispersant; d. heating the washed precipitated particles to a temperature not in excess of about 200*F to remove moisture, and to produce dry, flocculated dispersant-free, magnetic particles; and e. grinding in a ball mill the dry flocked particles in the presence of an alternate and different dispersing agent and a second carrier liquid to provide a second ferrofluid composition.
25. A ferrofluid composition which comprises a solution of a diester liquid carrier, a dispersant, and colloidal-size magnetic particles dispersed in said solution, the composition having a saturation magnetization of over 300 gauss, and having a viscosity of from about 100 to 2000 cps.
26. The composition of claim 25 wherein the liquid carrier comprises a nonaqueous carrier, and the average particle size is about 120 Angstroms.
27. The composition of claim 25 wherein the dispersant is a polyisobutene succinic acid derivative.
28. The composition of claim 25 wherein the composition comprises a ratio of dispersant-to-magnetic particles of about 1: 2 to 10:1 by volume.
29. The composition of claim 25 wherein the magnetic particles comprise magnetite or gamma iron oxide.
30. The composition of claim 25 wherein the magnetic particles of the ferrofluid composition have an average particle size of from about 20 to 300 Angstroms.
31. The composition of claim 25 wherein the ferrofluid composition comprises from about 2 to 15% by volume of magnetic particles.
32. The composition of claim 25 wherein the composition has a magnetic saturation of between about 300 to 800 gauss.
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Cited By (101)

* Cited by examiner, † Cited by third party
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US4025448A (en) * 1975-12-29 1977-05-24 Union Carbide Corporation Superparamagnetic wax compositions useful in magnetic levitation separations
US4094804A (en) * 1974-08-19 1978-06-13 Junzo Shimoiizaka Method for preparing a water base magnetic fluid and product
US4108767A (en) * 1975-09-02 1978-08-22 Georgia-Pacific Corporation Separation of an aqueous or water-miscible liquid from a fluid mixture
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US4292615A (en) * 1977-06-07 1981-09-29 Shigeo Ohashi Switching element
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US4315827A (en) * 1979-11-08 1982-02-16 Ferrofluidics Corporation Low-vapor-pressure ferrofluids and method of making same
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US4576725A (en) * 1983-07-13 1986-03-18 Toyota Jidosha Kabushiki Kaisha Magnetic fluid incorporating fine magnetic powder and method for making the same
US4579173A (en) * 1983-09-30 1986-04-01 Exxon Research And Engineering Co. Magnetized drive fluids
US4604222A (en) * 1985-05-21 1986-08-05 Ferrofluidics Corporation Stable ferrofluid composition and method of making and using same
US4608186A (en) * 1984-07-30 1986-08-26 Tdk Corporation Magnetic fluid
US4624797A (en) * 1984-09-17 1986-11-25 Tdk Corporation Magnetic fluid and process for preparing the same
US4626370A (en) * 1984-09-17 1986-12-02 Tdk Corporation Magnetic fluid
US4701276A (en) * 1986-10-31 1987-10-20 Hitachi Metals, Ltd. Super paramagnetic fluids and methods of making super paramagnetic fluids
EP0250236A1 (en) * 1986-06-19 1987-12-23 Ferrofluidics Corporation Low viscosity, electrically conductive ferrofluid composition
US4717266A (en) * 1986-06-12 1988-01-05 Spectra-Physics, Inc. Low friction ferrofluid bearing arrangement
US4731239A (en) * 1983-01-10 1988-03-15 Gordon Robert T Method for enhancing NMR imaging; and diagnostic use
US4741850A (en) * 1986-10-31 1988-05-03 Hitachi Metals, Ltd. Super paramagnetic fluids and methods of making super paramagnetic fluids
US4849120A (en) * 1986-05-13 1989-07-18 Price John T Magnetically controllable couplings containing ferrafluids
US4855079A (en) * 1986-10-31 1989-08-08 Hitachi Metals, Ltd. Super paramagnetic fluids and methods of making super paramagnetic fluids
EP0328497A1 (en) * 1988-02-08 1989-08-16 SKF Nova AB Superparamagnetic liquid
EP0249229A3 (en) * 1986-06-12 1990-04-11 Basf Aktiengesellschaft Superparamagnetic solid particles
EP0365498A1 (en) * 1988-10-18 1990-04-25 SKF Nova AB Electrically conductive fluids
US4956113A (en) * 1988-02-16 1990-09-11 Nok Corporation Process for preparing a magnetic fluid
US4957644A (en) * 1986-05-13 1990-09-18 Price John T Magnetically controllable couplings containing ferrofluids
US5007513A (en) * 1990-04-03 1991-04-16 Lord Corporation Electroactive fluid torque transmission apparatus with ferrofluid seal
US5069216A (en) * 1986-07-03 1991-12-03 Advanced Magnetics Inc. Silanized biodegradable super paramagnetic metal oxides as contrast agents for imaging the gastrointestinal tract
US5124060A (en) * 1989-10-25 1992-06-23 Nippon Seiko Kabushiki Kaisha Magnetic fluid composition
US5143637A (en) * 1990-02-20 1992-09-01 Nippon Seiko Kabushiki Kaisha Magnetic fluid composition
US5147573A (en) * 1990-11-26 1992-09-15 Omni Quest Corporation Superparamagnetic liquid colloids
US5171424A (en) * 1990-10-22 1992-12-15 Ashland Oil, Inc. Magnetic separation of old from new cracking catalyst by means of heavy rare earth "magnetic hooks"
US5190635A (en) * 1989-04-03 1993-03-02 Ashland Oil, Inc. Superparamagnetic formation of FCC catalyst provides means of separation of old equilibrium fluid cracking catalyst
US5198098A (en) * 1990-10-19 1993-03-30 Ashland Oil, Inc. Magnetic separation of old from new equilibrium particles by means of manganese addition
US5219554A (en) * 1986-07-03 1993-06-15 Advanced Magnetics, Inc. Hydrated biodegradable superparamagnetic metal oxides
WO1994010694A1 (en) * 1992-10-30 1994-05-11 Lord Corporation Magnetorheological materials utilizing surface-modified particles
WO1994010691A1 (en) * 1992-10-30 1994-05-11 Lord Corporation Magnetorheological materials based on alloy particles
WO1994010693A1 (en) * 1992-10-30 1994-05-11 Lord Corporation Thixotropic magnetorheological materials
WO1994010692A1 (en) * 1992-10-30 1994-05-11 Lord Corporation Low viscosity magnetorheological materials
US5320906A (en) * 1986-12-15 1994-06-14 Vestar, Inc. Delivery vehicles with amphiphile-associated active ingredient
DE4309333A1 (en) * 1993-03-17 1994-09-22 Silica Gel Gmbh Superparamagnetic particles, process for their production and use thereof
US5578238A (en) * 1992-10-30 1996-11-26 Lord Corporation Magnetorheological materials utilizing surface-modified particles
US5577948A (en) * 1992-04-14 1996-11-26 Byelocorp Scientific, Inc. Magnetorheological polishing devices and methods
US5598908A (en) * 1995-06-05 1997-02-04 Gse, Inc. Magnetorheological fluid coupling device and torque load simulator system
US5670077A (en) * 1995-10-18 1997-09-23 Lord Corporation Aqueous magnetorheological materials
US5676877A (en) * 1996-03-26 1997-10-14 Ferrotec Corporation Process for producing a magnetic fluid and composition therefor
US5769996A (en) * 1994-01-27 1998-06-23 Loctite (Ireland) Limited Compositions and methods for providing anisotropic conductive pathways and bonds between two sets of conductors
US5795212A (en) * 1995-10-16 1998-08-18 Byelocorp Scientific, Inc. Deterministic magnetorheological finishing
EP0859379A1 (en) * 1997-02-12 1998-08-19 Ferrofluidics Corporation Stable polysiloxane ferrofluid compositions and method of making same
US5826885A (en) * 1996-10-02 1998-10-27 Rigaku/Usa, Inc. Magnetic fluid sealing device
US5834197A (en) * 1994-05-11 1998-11-10 Genera Technologies Limited Methods of capturing species from liquids and assay procedures
US5851644A (en) * 1995-08-01 1998-12-22 Loctite (Ireland) Limited Films and coatings having anisotropic conductive pathways therein
US5863455A (en) * 1997-07-14 1999-01-26 Abb Power T&D Company Inc. Colloidal insulating and cooling fluid
DE19758350C1 (en) * 1997-12-22 1999-03-11 Mediport Kardiotechnik Gmbh Magnetic fluid comprising magnetic nano-particles dispersed in a polar carrier fluid
DE19758335C1 (en) * 1997-12-22 1999-03-11 Mediport Kardiotechnik Gmbh Magnetic fluid comprising ferro- or ferrimagnetic nanoparticles dispersed in a non-polar carrier fluid
US5916539A (en) * 1993-03-02 1999-06-29 Silica Gel Ges. M.B.H. Superparamagnetic particles, process for producing the same and their use
US5916641A (en) * 1996-08-01 1999-06-29 Loctite (Ireland) Limited Method of forming a monolayer of particles
US5948321A (en) * 1997-04-04 1999-09-07 Hong; Chin-Yih Rex Magnetic fluid thin film displays, monochromatic light switch and tunable wavelength filter
US5954991A (en) * 1997-04-04 1999-09-21 Hong; Chin-Yih Rex Ordered structures in homogeneous magnetic fluid thin films and method of preparation
US5958282A (en) * 1997-02-21 1999-09-28 Ferrofluidic Corporation Low cost method for manufacturing ferrofluid
US5968316A (en) * 1995-06-07 1999-10-19 Mclauglin; John R. Method of making paper using microparticles
US5975536A (en) * 1997-09-30 1999-11-02 Rigaku/Usa, Inc. Rotary motion feedthrough with rotating magnet system
US6180226B1 (en) 1996-08-01 2001-01-30 Loctite (R&D) Limited Method of forming a monolayer of particles, and products formed thereby
US6190561B1 (en) 1997-05-19 2001-02-20 Sortwell & Co., Part Interest Method of water treatment using zeolite crystalloid coagulants
US6193844B1 (en) 1995-06-07 2001-02-27 Mclaughlin John R. Method for making paper using microparticles
US6199867B1 (en) 1997-09-30 2001-03-13 Rigaku/Usa, Inc. Rotary motion feedthrough device
US6402876B1 (en) 1997-08-01 2002-06-11 Loctite (R&D) Ireland Method of forming a monolayer of particles, and products formed thereby
US6423172B1 (en) * 1998-01-30 2002-07-23 Loctite (R&D) Limited Method of forming a coating onto a non-random monolayer of particles, and products formed thereby
US20020136693A1 (en) * 1984-11-23 2002-09-26 Heinz Gries Magnetic particles for diagnostic purposes
US6503414B1 (en) 1992-04-14 2003-01-07 Byelocorp Scientific, Inc. Magnetorheological polishing devices and methods
US20030154923A1 (en) * 2002-02-19 2003-08-21 Innovative Technology Licensing, Llc Mechanical translator with ultra low friction ferrofluid bearings
DE10205332A1 (en) * 2002-02-06 2003-08-28 Berlin Heart Ag Production of magnetic core nanoparticles or dispersion, used e.g. for magnetic fluid seal, acoustic or oscillation damping, biological or clinical purpose comprises coprecipitation of a solution of an iron(III) and a metal(II) salt
US6613721B1 (en) * 1993-12-29 2003-09-02 The Timken Company Colloidal suspensions for use as a lubricant or additive
US20030180508A1 (en) * 1996-08-01 2003-09-25 Mcardle Ciaran Bernard Method of forming a monolayer of particles having at least two different sizes, and products formed thereby
US20050175702A1 (en) * 2002-06-01 2005-08-11 Muller-Schulte Detlef P. Thermosensitive polymer carriers having a modifiable physical structure for biochemical analysis, diagnosis and therapy
US6962685B2 (en) 2002-04-17 2005-11-08 International Business Machines Corporation Synthesis of magnetite nanoparticles and the process of forming Fe-based nanomaterials
US20070087385A1 (en) * 2003-11-25 2007-04-19 Magnamedics Gmbh Spherical and magnetical silicagel carriers having an increase surface for purifying nucleic acids
US20070135655A1 (en) * 2002-02-01 2007-06-14 Mario Visca Use of fluorinated additives in the etching or polishing of integrated circuits
US20070148437A1 (en) * 2003-10-28 2007-06-28 Magnamedics Gmbh Thermosensitive, biocompatible polymer carriers with changeable physical structure for therapy, diagnostics and analytics
US7341757B2 (en) 2001-08-08 2008-03-11 Nanoproducts Corporation Polymer nanotechnology
US7387673B2 (en) 1996-09-03 2008-06-17 Ppg Industries Ohio, Inc. Color pigment nanotechnology
RU2356630C1 (en) * 2007-12-18 2009-05-27 Открытое акционерное общество "Научно-исследовательский и проектный институт по переработке газа" ОАО "НИПИгазпереработка" Method for magnetic fluid regeneration
US20100054981A1 (en) * 2007-12-21 2010-03-04 Board Of Regents, The University Of Texas System Magnetic nanoparticles, bulk nanocomposite magnets, and production thereof
RU2387482C1 (en) * 2008-12-11 2010-04-27 Открытое акционерное общество "Научно-исследовательский и проектный институт по переработке газа" (ОАО "НИПИгазпереработка") Installation for regenerating magnetic liquid
US7708974B2 (en) 2002-12-10 2010-05-04 Ppg Industries Ohio, Inc. Tungsten comprising nanomaterials and related nanotechnology
DE102008060708A1 (en) 2008-12-05 2010-06-17 Dianogen Gmbh Improving contrast properties of medical polymer substrates in framework of imaging processes using magnetic nanoparticles, noble metal colloids or paramagnetic salts, by introducing magnetic nanoparticles or noble metals on the substrate
US20120056121A1 (en) * 2010-07-02 2012-03-08 Sri Lanka Institute of Nanotechnology (Pvt) Ltd. Process for preparation of nanoparticles from magnetite ore
WO2012095369A1 (en) 2011-01-13 2012-07-19 Matrix Microscience Limited Methods of capturing bindable targets from liquids
CN103736457A (en) * 2013-12-19 2014-04-23 中南大学 Preparation method and magnetic activated carbon prepared by same
US8721896B2 (en) 2012-01-25 2014-05-13 Sortwell & Co. Method for dispersing and aggregating components of mineral slurries and low molecular weight multivalent polymers for mineral aggregation
WO2014123672A1 (en) * 2013-02-05 2014-08-14 Board Of Regents, The University Of Texas System Hydrophobic paramagnetic nanoparticles as intelligent crude oil tracers
US9150442B2 (en) 2010-07-26 2015-10-06 Sortwell & Co. Method for dispersing and aggregating components of mineral slurries and high-molecular weight multivalent polymers for clay aggregation
US9242295B2 (en) 2007-12-21 2016-01-26 The Univeristy Of Texas At Arlington Bulk nanocomposite magnets and methods of making bulk nanocomposite magnets
US9804153B2 (en) 2012-08-29 2017-10-31 Inguran, Llc Magnetic removal or identification of damaged or compromised cells or cellular structures
US10553342B2 (en) 2016-07-13 2020-02-04 The United States Of America As Represented By The Secretary Of The Army Deformable inductor having a liquid magnetic core
US20220145158A1 (en) * 2019-04-18 2022-05-12 King Abdullah University Of Science And Technology Stable magnetic drilling mud and method
US11630108B2 (en) 2012-08-29 2023-04-18 Inguran, Llc Cell processing using magnetic particles

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3531413A (en) * 1967-09-22 1970-09-29 Avco Corp Method of substituting one ferrofluid solvent for another

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3531413A (en) * 1967-09-22 1970-09-29 Avco Corp Method of substituting one ferrofluid solvent for another

Cited By (134)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4094804A (en) * 1974-08-19 1978-06-13 Junzo Shimoiizaka Method for preparing a water base magnetic fluid and product
US4108767A (en) * 1975-09-02 1978-08-22 Georgia-Pacific Corporation Separation of an aqueous or water-miscible liquid from a fluid mixture
US4025448A (en) * 1975-12-29 1977-05-24 Union Carbide Corporation Superparamagnetic wax compositions useful in magnetic levitation separations
FR2382486A1 (en) * 1977-03-02 1978-09-29 Ibm MAGNETIC INK AND OBTAINED INK MANUFACTURING PROCESS
US4292615A (en) * 1977-06-07 1981-09-29 Shigeo Ohashi Switching element
US4315827A (en) * 1979-11-08 1982-02-16 Ferrofluidics Corporation Low-vapor-pressure ferrofluids and method of making same
US4308603A (en) * 1979-11-16 1981-12-29 The United States Of America As Represented By The Secretary Of The Navy Ferrofluid transducer
US4295971A (en) * 1980-08-14 1981-10-20 The United States Of America As Represented By The Secretary Of The Interior Method for clarifying slimes
US4430239A (en) 1981-10-21 1984-02-07 Ferrofluidics Corporation Ferrofluid composition and method of making and using same
US4485024A (en) * 1982-04-07 1984-11-27 Nippon Seiko Kabushiki Kaisha Process for producing a ferrofluid, and a composition thereof
DE3312565A1 (en) * 1982-04-07 1983-10-20 Nippon Seiko K.K., Tokyo METHOD FOR PRODUCING A FERROFLUID AND FERROFLUID COMPOSITION
USRE32573E (en) * 1982-04-07 1988-01-05 Nippon Seiko Kabushiki Kaisha Process for producing a ferrofluid, and a composition thereof
US4435302A (en) 1982-05-28 1984-03-06 The United States Of America As Represented By The Secretary Of The Interior Concentrating and reclaiming magnetic fluids
US4445940A (en) * 1982-11-30 1984-05-01 Georgia-Pacific Corporation Process to remove corrosion deposits using aqueous-base ferromagnetic fluids
US4731239A (en) * 1983-01-10 1988-03-15 Gordon Robert T Method for enhancing NMR imaging; and diagnostic use
US4576725A (en) * 1983-07-13 1986-03-18 Toyota Jidosha Kabushiki Kaisha Magnetic fluid incorporating fine magnetic powder and method for making the same
US4579173A (en) * 1983-09-30 1986-04-01 Exxon Research And Engineering Co. Magnetized drive fluids
US4608186A (en) * 1984-07-30 1986-08-26 Tdk Corporation Magnetic fluid
US4624797A (en) * 1984-09-17 1986-11-25 Tdk Corporation Magnetic fluid and process for preparing the same
US4626370A (en) * 1984-09-17 1986-12-02 Tdk Corporation Magnetic fluid
US20020136693A1 (en) * 1984-11-23 2002-09-26 Heinz Gries Magnetic particles for diagnostic purposes
US4604222A (en) * 1985-05-21 1986-08-05 Ferrofluidics Corporation Stable ferrofluid composition and method of making and using same
US4957644A (en) * 1986-05-13 1990-09-18 Price John T Magnetically controllable couplings containing ferrofluids
US4849120A (en) * 1986-05-13 1989-07-18 Price John T Magnetically controllable couplings containing ferrafluids
US4717266A (en) * 1986-06-12 1988-01-05 Spectra-Physics, Inc. Low friction ferrofluid bearing arrangement
EP0249229A3 (en) * 1986-06-12 1990-04-11 Basf Aktiengesellschaft Superparamagnetic solid particles
EP0250236A1 (en) * 1986-06-19 1987-12-23 Ferrofluidics Corporation Low viscosity, electrically conductive ferrofluid composition
US5069216A (en) * 1986-07-03 1991-12-03 Advanced Magnetics Inc. Silanized biodegradable super paramagnetic metal oxides as contrast agents for imaging the gastrointestinal tract
US5219554A (en) * 1986-07-03 1993-06-15 Advanced Magnetics, Inc. Hydrated biodegradable superparamagnetic metal oxides
US4701276A (en) * 1986-10-31 1987-10-20 Hitachi Metals, Ltd. Super paramagnetic fluids and methods of making super paramagnetic fluids
US4741850A (en) * 1986-10-31 1988-05-03 Hitachi Metals, Ltd. Super paramagnetic fluids and methods of making super paramagnetic fluids
US4855079A (en) * 1986-10-31 1989-08-08 Hitachi Metals, Ltd. Super paramagnetic fluids and methods of making super paramagnetic fluids
US5320906A (en) * 1986-12-15 1994-06-14 Vestar, Inc. Delivery vehicles with amphiphile-associated active ingredient
EP0328497A1 (en) * 1988-02-08 1989-08-16 SKF Nova AB Superparamagnetic liquid
US4938886A (en) * 1988-02-08 1990-07-03 Skf Nova Ab Superparamagnetic liquids and methods of making superparamagnetic liquids
US4956113A (en) * 1988-02-16 1990-09-11 Nok Corporation Process for preparing a magnetic fluid
EP0365498A1 (en) * 1988-10-18 1990-04-25 SKF Nova AB Electrically conductive fluids
US5190635A (en) * 1989-04-03 1993-03-02 Ashland Oil, Inc. Superparamagnetic formation of FCC catalyst provides means of separation of old equilibrium fluid cracking catalyst
US5124060A (en) * 1989-10-25 1992-06-23 Nippon Seiko Kabushiki Kaisha Magnetic fluid composition
US5143637A (en) * 1990-02-20 1992-09-01 Nippon Seiko Kabushiki Kaisha Magnetic fluid composition
US5007513A (en) * 1990-04-03 1991-04-16 Lord Corporation Electroactive fluid torque transmission apparatus with ferrofluid seal
US5198098A (en) * 1990-10-19 1993-03-30 Ashland Oil, Inc. Magnetic separation of old from new equilibrium particles by means of manganese addition
US5171424A (en) * 1990-10-22 1992-12-15 Ashland Oil, Inc. Magnetic separation of old from new cracking catalyst by means of heavy rare earth "magnetic hooks"
US5147573A (en) * 1990-11-26 1992-09-15 Omni Quest Corporation Superparamagnetic liquid colloids
US7261616B2 (en) 1992-04-14 2007-08-28 Qed Technologies International, Inc. Magnetorheological polishing devices and methods
US6503414B1 (en) 1992-04-14 2003-01-07 Byelocorp Scientific, Inc. Magnetorheological polishing devices and methods
US5577948A (en) * 1992-04-14 1996-11-26 Byelocorp Scientific, Inc. Magnetorheological polishing devices and methods
WO1994010693A1 (en) * 1992-10-30 1994-05-11 Lord Corporation Thixotropic magnetorheological materials
WO1994010692A1 (en) * 1992-10-30 1994-05-11 Lord Corporation Low viscosity magnetorheological materials
US5578238A (en) * 1992-10-30 1996-11-26 Lord Corporation Magnetorheological materials utilizing surface-modified particles
US5599474A (en) * 1992-10-30 1997-02-04 Lord Corporation Temperature independent magnetorheological materials
WO1994010691A1 (en) * 1992-10-30 1994-05-11 Lord Corporation Magnetorheological materials based on alloy particles
US5645752A (en) * 1992-10-30 1997-07-08 Lord Corporation Thixotropic magnetorheological materials
US5382373A (en) * 1992-10-30 1995-01-17 Lord Corporation Magnetorheological materials based on alloy particles
WO1994010694A1 (en) * 1992-10-30 1994-05-11 Lord Corporation Magnetorheological materials utilizing surface-modified particles
US5916539A (en) * 1993-03-02 1999-06-29 Silica Gel Ges. M.B.H. Superparamagnetic particles, process for producing the same and their use
DE4309333A1 (en) * 1993-03-17 1994-09-22 Silica Gel Gmbh Superparamagnetic particles, process for their production and use thereof
US6613721B1 (en) * 1993-12-29 2003-09-02 The Timken Company Colloidal suspensions for use as a lubricant or additive
US6110399A (en) * 1994-01-27 2000-08-29 Loctite (Ireland) Limited Compositions and method for providing anisotropic conductive pathways and bonds between two sets of conductors
US5769996A (en) * 1994-01-27 1998-06-23 Loctite (Ireland) Limited Compositions and methods for providing anisotropic conductive pathways and bonds between two sets of conductors
US5834197A (en) * 1994-05-11 1998-11-10 Genera Technologies Limited Methods of capturing species from liquids and assay procedures
US5598908A (en) * 1995-06-05 1997-02-04 Gse, Inc. Magnetorheological fluid coupling device and torque load simulator system
US5968316A (en) * 1995-06-07 1999-10-19 Mclauglin; John R. Method of making paper using microparticles
US6193844B1 (en) 1995-06-07 2001-02-27 Mclaughlin John R. Method for making paper using microparticles
US6149857A (en) * 1995-08-01 2000-11-21 Loctite (R&D) Limited Method of making films and coatings having anisotropic conductive pathways therein
US5851644A (en) * 1995-08-01 1998-12-22 Loctite (Ireland) Limited Films and coatings having anisotropic conductive pathways therein
US5839944A (en) * 1995-10-16 1998-11-24 Byelocorp, Inc. Apparatus deterministic magnetorheological finishing of workpieces
US5795212A (en) * 1995-10-16 1998-08-18 Byelocorp Scientific, Inc. Deterministic magnetorheological finishing
US6106380A (en) * 1995-10-16 2000-08-22 Byelocorp Scientific, Inc. Deterministic magnetorheological finishing
US5670077A (en) * 1995-10-18 1997-09-23 Lord Corporation Aqueous magnetorheological materials
US5676877A (en) * 1996-03-26 1997-10-14 Ferrotec Corporation Process for producing a magnetic fluid and composition therefor
US6056889A (en) * 1996-03-26 2000-05-02 Ferrotec Corporation Process for producing a magnetic fluid and composition therefor
US5916641A (en) * 1996-08-01 1999-06-29 Loctite (Ireland) Limited Method of forming a monolayer of particles
US20030180508A1 (en) * 1996-08-01 2003-09-25 Mcardle Ciaran Bernard Method of forming a monolayer of particles having at least two different sizes, and products formed thereby
US6180226B1 (en) 1996-08-01 2001-01-30 Loctite (R&D) Limited Method of forming a monolayer of particles, and products formed thereby
US6977025B2 (en) 1996-08-01 2005-12-20 Loctite (R&D) Limited Method of forming a monolayer of particles having at least two different sizes, and products formed thereby
US8058337B2 (en) 1996-09-03 2011-11-15 Ppg Industries Ohio, Inc. Conductive nanocomposite films
US8389603B2 (en) 1996-09-03 2013-03-05 Ppg Industries Ohio, Inc. Thermal nanocomposites
US7387673B2 (en) 1996-09-03 2008-06-17 Ppg Industries Ohio, Inc. Color pigment nanotechnology
US5826885A (en) * 1996-10-02 1998-10-27 Rigaku/Usa, Inc. Magnetic fluid sealing device
EP0859379A1 (en) * 1997-02-12 1998-08-19 Ferrofluidics Corporation Stable polysiloxane ferrofluid compositions and method of making same
US5851416A (en) * 1997-02-12 1998-12-22 Ferrofluidics Corporation Stable polysiloxane ferrofluid compositions and method of making same
US5958282A (en) * 1997-02-21 1999-09-28 Ferrofluidic Corporation Low cost method for manufacturing ferrofluid
US5948321A (en) * 1997-04-04 1999-09-07 Hong; Chin-Yih Rex Magnetic fluid thin film displays, monochromatic light switch and tunable wavelength filter
US5954991A (en) * 1997-04-04 1999-09-21 Hong; Chin-Yih Rex Ordered structures in homogeneous magnetic fluid thin films and method of preparation
US6086780A (en) * 1997-04-04 2000-07-11 Hong; Chin-Yih Rex Ordered structures in homogeneous magnetic fluid thin films and method of preparation
US6190561B1 (en) 1997-05-19 2001-02-20 Sortwell & Co., Part Interest Method of water treatment using zeolite crystalloid coagulants
US5863455A (en) * 1997-07-14 1999-01-26 Abb Power T&D Company Inc. Colloidal insulating and cooling fluid
US6402876B1 (en) 1997-08-01 2002-06-11 Loctite (R&D) Ireland Method of forming a monolayer of particles, and products formed thereby
US6199867B1 (en) 1997-09-30 2001-03-13 Rigaku/Usa, Inc. Rotary motion feedthrough device
US5975536A (en) * 1997-09-30 1999-11-02 Rigaku/Usa, Inc. Rotary motion feedthrough with rotating magnet system
DE19758350C1 (en) * 1997-12-22 1999-03-11 Mediport Kardiotechnik Gmbh Magnetic fluid comprising magnetic nano-particles dispersed in a polar carrier fluid
DE19758335C1 (en) * 1997-12-22 1999-03-11 Mediport Kardiotechnik Gmbh Magnetic fluid comprising ferro- or ferrimagnetic nanoparticles dispersed in a non-polar carrier fluid
US6423172B1 (en) * 1998-01-30 2002-07-23 Loctite (R&D) Limited Method of forming a coating onto a non-random monolayer of particles, and products formed thereby
US7341757B2 (en) 2001-08-08 2008-03-11 Nanoproducts Corporation Polymer nanotechnology
US20070135655A1 (en) * 2002-02-01 2007-06-14 Mario Visca Use of fluorinated additives in the etching or polishing of integrated circuits
DE10205332A1 (en) * 2002-02-06 2003-08-28 Berlin Heart Ag Production of magnetic core nanoparticles or dispersion, used e.g. for magnetic fluid seal, acoustic or oscillation damping, biological or clinical purpose comprises coprecipitation of a solution of an iron(III) and a metal(II) salt
DE10205332B4 (en) * 2002-02-06 2004-02-12 Berlin Heart Ag Process for the production of magnetic nanoparticles
US20030154923A1 (en) * 2002-02-19 2003-08-21 Innovative Technology Licensing, Llc Mechanical translator with ultra low friction ferrofluid bearings
US6962685B2 (en) 2002-04-17 2005-11-08 International Business Machines Corporation Synthesis of magnetite nanoparticles and the process of forming Fe-based nanomaterials
US20060239901A1 (en) * 2002-04-17 2006-10-26 Shouheng Sun Process of making metal containing iron oxide and iron sulfide based nanoparticle materials
US7410625B2 (en) 2002-04-17 2008-08-12 International Business Machines Corporation Process of making metal containing iron oxide and iron sulfide based nanoparticle materials
US7128891B1 (en) 2002-04-17 2006-10-31 International Business Machines Corporation Process of making metal containing iron oxide and iron sulfide based nanoparticle materials
US20050175702A1 (en) * 2002-06-01 2005-08-11 Muller-Schulte Detlef P. Thermosensitive polymer carriers having a modifiable physical structure for biochemical analysis, diagnosis and therapy
US7708974B2 (en) 2002-12-10 2010-05-04 Ppg Industries Ohio, Inc. Tungsten comprising nanomaterials and related nanotechnology
US20070148437A1 (en) * 2003-10-28 2007-06-28 Magnamedics Gmbh Thermosensitive, biocompatible polymer carriers with changeable physical structure for therapy, diagnostics and analytics
US7919333B2 (en) 2003-11-25 2011-04-05 Magnamedics Gmbh Spherical and magnetical silicagel carriers having an increase surface for purifying nucleic acids
US20070087385A1 (en) * 2003-11-25 2007-04-19 Magnamedics Gmbh Spherical and magnetical silicagel carriers having an increase surface for purifying nucleic acids
RU2356630C1 (en) * 2007-12-18 2009-05-27 Открытое акционерное общество "Научно-исследовательский и проектный институт по переработке газа" ОАО "НИПИгазпереработка" Method for magnetic fluid regeneration
US20100054981A1 (en) * 2007-12-21 2010-03-04 Board Of Regents, The University Of Texas System Magnetic nanoparticles, bulk nanocomposite magnets, and production thereof
US9704625B2 (en) 2007-12-21 2017-07-11 Board Of Regents, The University Of Texas System Magnetic nanoparticles, bulk nanocomposite magnets, and production thereof
US10726979B2 (en) 2007-12-21 2020-07-28 Board Of Regents, The University Of Texas System Bulk nanocomposite magnets and methods of making bulk nanocomposite magnets
US9242295B2 (en) 2007-12-21 2016-01-26 The Univeristy Of Texas At Arlington Bulk nanocomposite magnets and methods of making bulk nanocomposite magnets
DE102008060708A1 (en) 2008-12-05 2010-06-17 Dianogen Gmbh Improving contrast properties of medical polymer substrates in framework of imaging processes using magnetic nanoparticles, noble metal colloids or paramagnetic salts, by introducing magnetic nanoparticles or noble metals on the substrate
RU2387482C1 (en) * 2008-12-11 2010-04-27 Открытое акционерное общество "Научно-исследовательский и проектный институт по переработке газа" (ОАО "НИПИгазпереработка") Installation for regenerating magnetic liquid
US10192660B2 (en) * 2010-07-02 2019-01-29 Sri Lanka Institute of Nanotechnology (Pvt) Ltd. Process for preparation of nanoparticles from magnetite ore
US20120056121A1 (en) * 2010-07-02 2012-03-08 Sri Lanka Institute of Nanotechnology (Pvt) Ltd. Process for preparation of nanoparticles from magnetite ore
US9540469B2 (en) 2010-07-26 2017-01-10 Basf Se Multivalent polymers for clay aggregation
US9150442B2 (en) 2010-07-26 2015-10-06 Sortwell & Co. Method for dispersing and aggregating components of mineral slurries and high-molecular weight multivalent polymers for clay aggregation
WO2012095369A1 (en) 2011-01-13 2012-07-19 Matrix Microscience Limited Methods of capturing bindable targets from liquids
US8721896B2 (en) 2012-01-25 2014-05-13 Sortwell & Co. Method for dispersing and aggregating components of mineral slurries and low molecular weight multivalent polymers for mineral aggregation
US9090726B2 (en) 2012-01-25 2015-07-28 Sortwell & Co. Low molecular weight multivalent cation-containing acrylate polymers
US9487610B2 (en) 2012-01-25 2016-11-08 Basf Se Low molecular weight multivalent cation-containing acrylate polymers
US11531026B2 (en) 2012-08-29 2022-12-20 Inguran, Llc Magnetic removal or identification of damaged or compromised cells or cellular structures
US9804153B2 (en) 2012-08-29 2017-10-31 Inguran, Llc Magnetic removal or identification of damaged or compromised cells or cellular structures
US10324086B2 (en) 2012-08-29 2019-06-18 Inguran, Llc Magnetic removal or identification of damaged or compromised cells or cellular structures
US11630108B2 (en) 2012-08-29 2023-04-18 Inguran, Llc Cell processing using magnetic particles
US11662344B2 (en) 2012-08-29 2023-05-30 Inguran, Llc Magnetic removal or identification of damaged or compromised cells or cellular structures
US12332239B2 (en) 2012-08-29 2025-06-17 Inguran, Llc Magnetic removal or identification of damaged or compromised cells or cellular structures
WO2014123672A1 (en) * 2013-02-05 2014-08-14 Board Of Regents, The University Of Texas System Hydrophobic paramagnetic nanoparticles as intelligent crude oil tracers
CN103736457A (en) * 2013-12-19 2014-04-23 中南大学 Preparation method and magnetic activated carbon prepared by same
CN103736457B (en) * 2013-12-19 2016-07-06 中南大学 The preparation method of a kind of magnetic active carbon and the magnetic active carbon prepared by the method
US10553342B2 (en) 2016-07-13 2020-02-04 The United States Of America As Represented By The Secretary Of The Army Deformable inductor having a liquid magnetic core
US20220145158A1 (en) * 2019-04-18 2022-05-12 King Abdullah University Of Science And Technology Stable magnetic drilling mud and method

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