WO1990015423A1 - Colloides liquides superparamagnetiques - Google Patents

Colloides liquides superparamagnetiques Download PDF

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Publication number
WO1990015423A1
WO1990015423A1 PCT/US1990/003177 US9003177W WO9015423A1 WO 1990015423 A1 WO1990015423 A1 WO 1990015423A1 US 9003177 W US9003177 W US 9003177W WO 9015423 A1 WO9015423 A1 WO 9015423A1
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WIPO (PCT)
Prior art keywords
magnetic
particles
colloid
fluid
titanium
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Application number
PCT/US1990/003177
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English (en)
Inventor
Mark S. Chagnon
Original Assignee
Omni Quest Corporation
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Omni Quest Corporation filed Critical Omni Quest Corporation
Publication of WO1990015423A1 publication Critical patent/WO1990015423A1/fr

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
    • H01F1/44—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of magnetic liquids, e.g. ferrofluids
    • H01F1/442—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of magnetic liquids, e.g. ferrofluids the magnetic component being a metal or alloy, e.g. Fe
    • 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

Definitions

  • Magnetic colloids are liquids havingM magnetic properties in which ferromagnetic materials are collodially suspended. Such ferrofluids or magnetic liquids must show a high degree of stability (e.g., to gravitational and magnetic fields) in order to perform well in various commercial devices and be responsive to external magnetic fields.
  • a stable magnetic colloid or ferrofluid in a high magnetic field gradient requires small ferromagnetic particles of generally less than 200 angstroms in diameter.
  • the ferromagnetic particles are usually coated with one of several layers of surfactants to prevent agglomeration.
  • Typical ferrofluid compositions are described, for example, in U.S. Patent No. 3,700,595, (1972), wherein anionic surfactants, such as fatty acids, alcohols, amines or amides and other organic acids are employed as dispersing surface active agents; U.S. Patent No.
  • a properly stabilized ferrofluid composition typically undergoes practically no aging or separation, remains liquid in a magnetic field and after removing of the magnetic field shows no hysteresis.
  • a stabilized ferrofluid exhibits stability by overcoming generally three principal attractive forces; van der Waals, inter- particle-magnetics and gravitational forces.
  • carbon black to a typ ical ferrofluid composition provides a composition which tends to be pseudoplas tic when amounts greater than about five (5%) percent of carbon black are used, while a low concentration of carbon black (e.g., less than 5%) provides a Newtonian, non-conductive composition.
  • a stable, low viscosity, highly electrically conductive ferrofluid composition is needed, with or without carbon black, particularly for use in computer seals, as well as for other devices where a stable, low viscosity, highly electrically conductive ferrofluid composition is
  • the present invention relates to low viscosity, electrically conductive magnetic fluid compositions and methods of preparing and using such compositions.
  • the present composition contains magnetic particles, an electrically conductive surfactant, a dispersing agent and a carrier fluid.
  • the compositions are made by coating the magnetic particles with the electrically conductive surfactant, adding a dispersing agent and dispersing the coated particles in the carrier fluid, thereby forming a gravitationally and magnetically stable colloidal dispersion.
  • the present compositions are superparamagnetic, that is, they do not retain magnetic properties once the magnetic field has been removed.
  • the present magnetic fluids provide stable, low viscosity highly conductive compositions which are useful as liquid seals for computer disk drives and other applications.
  • the colloidal dispersions of the present invention are superparamagnetic, that is, they experience force in a magnetic field gradient but do not become permanently magnetized.
  • Superparamagnetic particles rapidly lose their magnetic properties in the absence of an applied magnetic field, yet they also possess high susceptibility to magnetic fields.
  • superparamagnetic particles are easy to handle since they are sensitive to magnetic field gradients, and resist aggregating after removal of an external magnetic field.
  • compositions are stable colloidal dispersions of superparamagnetic particles.
  • colloidal dispersion or “colloid” as used herein refers to a gravitationally and magnetically stable dispersion of finely divided magnetic particles of submicron size in a carrier fluid, which particles remain substantially uniformly dispersed throughout the liquid carrier even in the presence of a magnetic field, and which resist gravitational settling.
  • compositions which are the subject of the present invention contain magnetic particles which are coated with an electrically conductive surfactant, and dispersed in a carrier fluid with a dispersing or suspending agent, which agent helps to maintain the stability of the colloid.
  • Magnetic particles which are useful in the present composition are metal, metal alloy or metal oxide particles comprised of clusters of superparamagnetic crystals.
  • Metals and oxides of metals which appear in the Periodic Table in Groups 4a and b, 5a and b, 6a and 7a (the transition metals) can be used to make the magnetic particles.
  • Compounds which are particularly useful include those selected from the group consisting of magnetite (Fe 3 O 4 ), hematite (Fe 2 O 3 ), iron, iron alloys, nickel, cobalt, cobalt ferrite, samarium cobalt, barium ferrite, chromium dioxide, aluminum-nickel-cobalt alloys and gadolinium.
  • the average particle size depends on the selection of the ferromagnetic materials, and generally ranges from about 20 angstroms (A) to about 500 angstroms (A). For use in a very high magnetic field gradient, particle sizes of from bout 95 A to 105 A are particularly preferred for use in the present
  • the ferromagnetic particles are generally present in the composition in an amount ranging from about 5 to about 80% percent by weight of the carrier fluid.
  • surfactant is adsorbed as a conductive shell around the magnetic particle.
  • surfactant should have a conductivity of less than about
  • surfactant include alkyl or alkoxide organometallic compounds. Particularly useful surfactants are those selected from the group consisting of tetraethoxy
  • triethylaminohexyl titanium tetraethyl titanium, triethylcarboxyhexyl titanium, trie thylcarboxyhexyl hafnium, tetraethyl antimony, tetraethyl antimony tin, triethylcarboxyhexyl zirconium, tetraethyl hafnium, tetraethyl tin, titanium tetraisopropoxide, antimony titanium tetraisopropoxide, Mitsubishi T1 powder
  • a dispersing or suspending agent is employed to disperse the particles in the carrier fluid and to add stability to the colloid.
  • Surfactants can be used as dispersing or suspending agents. Any surfactant may be employed which forms a stable colloid, including
  • nonionic, cationic or anionic surfactants The amount and nature of the surfactant varies depending on the particular liquid carriers used, the type and size of the ferromagnetic particles and the type and stability of the dispersion desired.
  • the ratio of the dispersing agent to the magnetic particles may vary, but a ratio of from about 0.5:1 to 20:1 by weight is generally used.
  • dispersing agents include surfactants which are ionic organic materials having the general structure:
  • YH is an adsorptive head region
  • R is an organic spacer arm region
  • R' is an electron-rich organic function
  • R" is a solubilizing tail; wherein : YH is a polar functional group that bonds by means of covalent linkage, chemisorption, adsorption, or ionic interaction to the surface of the magnetic particle.
  • YH can be, for example, a functional group selected from the group consisting of: carboxylate (COO-), amide (NH 2 ), sulfate phosphate metal chloride salts
  • the carboxylate group can be mono-, di- or trisubs tituted on the terminal carbon atom, such as:
  • YH is a cation or anion
  • R is an aliphatic chain (C 4 to C 20 ), aromatic ring or a cyclic aliphatic group. Addition of polar
  • R is aliphatic, the length of the R chain is useful in changing the magnitude of the charge on YH .
  • R' is a linking group that causes a change in electron density, separating the polar R-YH portion of the molecule from the nonpolar tail.
  • R" is a hydrophobic tail that has a similar
  • R is generally, but not
  • colloidal dispersions in perfluorinated liquids can be formed by utilizing as a dispersing agent a fluorocarbon sufactant having the following formula: where n is an integer from 3 to 50 preferably 5 to 25; and where R is -OOH, -OH -OONH 4 , -ONH 2 -NH 2 , with OOH being preferred.
  • Dispersing agents which are useful in the present composition include, for example, oleic acid and
  • the relative proportions of the dispersing agent to the suspended solids can vary widely so long as there is a sufficient concentration of the surfactant component to provide at least a mono-molecular covering of the
  • the proportions of dispersing agent to the particles can be, for example, a useful range for forming stable suspension of particles is a ratio of dispersing agent to the particles of from about 0.5:1 to about 20:1 by weight.
  • the amount of surfactant present in the composition is generally from about 5% to about 10% by weight, of the total
  • the present composition is formed by dispersing the particles, which have been coated with the organometallic surfactant and the dispersing agent, in a carrier fluid that forms the continuous phase of the colloid
  • Carrier fluids which provide properties that are useful for the end applications, and exhibit a similar solubility parameter to the R" surfactant tail, can be used in the present invention.
  • Materials that are useful as carrier liquids are compounds selected from the group consisting of: water, hydrocarbon solvents having from about 4 to about 40 carbon atoms, fluoroethers, ester or diester oils and ⁇ -olefins.
  • fluoroethers which can be used as carrier fluids include Freon E-3, Freon E-5 and Freon E-9, Krytox AA, AB, AC, AD, and Krytox 143, all available from
  • Particularly preferred carrier fluids include toluene, and low vapor-pressure oils such as ⁇ -olefin oils, di-2-ethylhexyl azylate, dioctyl azylate, dioctyl sebacate and dioctyl adipate.
  • the present colloids can be made according to the following general procedure: the metallic magnetic particles are made and contacted with the organometallic surfactant under conditions sufficient to cause the surfactant to adsorb or bond to the surface of the particle. The coated particles are then contacted with the dispersing agent under conditions sufficient to coat the particles with the dispersing agent, and then
  • Magnetic particles used in the present compositions can be produced according to the following general procedure: an aqueous slurry is formed of the magnetic particles by contacting a metallic salt (e.g., FeCl 2 ) with water, and adding a strong base, such as ammonium hydroxide (NH 4 OH) causing the metal to precipitate forming a slurry. The mixture is agitated, at a
  • An alternate method for preparing superparamagnetic particles is based on precipitation of iron metal from an aqueous iron chloride, nitrate or sulfate solution.
  • about 10g of sodium borohydride podder is added to about 100 ml of 95% (by weight) aqueous solution of ferrous chloride (FeCl 2 ) under constant agitation, the mixture is kept at a temperature of about 25-90°C during the addition of the sodium borohydride.
  • the particles are removed from the reaction mixture by addition of an external magnetic field. The particles are washed with 5 100 ml portions of distilled water and then used as the magnetite in the preparation of the fluid.
  • Another embodiment of the method of preparing superparamagnetic particles is to grind commercial magnetite (Pfizer) for 30 days as an aqueous or
  • the electrically conductive compound is added to the aqueous slurry, and the mixture is stirred to allow the metal particles to be coated with the compound.
  • the dispersing or suspending agent e.g., oleic acid
  • the carrier fluid e.g., toluene
  • the ferrofluid compositions of the present invention have varying saturation magnetization values, which may range from about 10 to about 800 gauss. Values of about 100 to about 500 gauss are particularly useful.
  • the viscosity of the compositions is generally from about 1 to 10,000 centipoises (cps) at 25°C; viscosities at 25°C of about 25 to about 5000 cps are preferred.
  • the conductivity of the present compositions is generally less than 1x10 -7 ohms/cm 2 .
  • Preferred magnetic liquid compositions having improved electrical conductivity contain:
  • Ferromagnetic particles such as iron (Fe)
  • compositions are useful as a liquid crystal display.
  • the present compositions are useful as a liquid crystal display.
  • compositions can be used in a wide variety of commercial applications such as for magnetic seals, as dampening liquids in inertia dampers, as heat transfer liquids in the voice coil loudspeakers, as bearing liquids, as ferrolubricants for domain detection, for oil prospecting and other applications.
  • the present electrically conductive ferrofluid compositions are particularly useful in computer disk drive applications.
  • the present composition is placed around the shaft in the disk drive mechanism, where it forms a hermetically sealed, liquid sealing ring, which also conducts electrical charges away from the shaft so as to prevent charge build up on the disk.
  • Example 2 Conductivity Agent and Surfactant Addition
  • Example 3 40 grams of the conductive organometallic compound carboxyhexyltriethyl antimony tin were added to the aqueous slurry prepared as described in Example 1. The mixture was stirred for a period of 5 minutes to insure complete adsorption of the conductive organometallic compound to the surface of the particles. 40 grams of oleic acid (VWR Scientific) were then added to the mixture and the mixture was stirred for 30 minutes and heated to a temperature of 70°C during that period. At the conclusion of the 30 minute reaction period, 100 ml of toluene were added to the mixture and the resulting toluene-based ferrofluid was extracted from the reaction vessel. The product had a magnetization of 350 gauss and a conductivity of 3 x 10 -5 ohms/cm 2 . Example 3
  • a magnetic fluid was prepared as described in
  • a magnetic fluid was prepared as described in
  • resulting magnetic fluid colloid had a viscosity at 25°C of 100 cps, a magnetization of 300 gauss and a vapor pressure at 25°C of 3 x 10 - 6 torr.
  • a magnetic fluid was prepared as in Examples 1 and 2, except that toluene was substituted as a carrier fluid by olefin oil (Mobil-1, Mobil Oil Co.).
  • the resulting magnetic fluid colloid had a viscosity of 200 cps, a vapor pressure at 25°C of 3 x 10 5 torr and a conductivity of 3 x 10 -5 ohms/cm 2 .
  • a magnetic fluid was prepared as described in
  • the resulting magnetic fluid colloid had a magnetization of 350 gauss and a conductivity of 2.5 x 10 -5 ohms/cm 2 .

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Soft Magnetic Materials (AREA)
  • Lubricants (AREA)

Abstract

Colloïdes liquides superparamagnétiques électro-conducteurs, leurs procédés de production et d'utilisation. Les colloïdes liquides magnétiques contiennent des particules magnétiques enrobées d'un composé organo-métallique conducteur qui transmet les caractéristiques magnétiques et conductrices au fluide. Les particules magnétiques enrobées sont dispersées dans un fluide porteur qui transmet au fluide ses propriétés de viscosité, d'écoulement et de pression de vapeur.
PCT/US1990/003177 1989-06-05 1990-06-05 Colloides liquides superparamagnetiques WO1990015423A1 (fr)

Applications Claiming Priority (2)

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US36123089A 1989-06-05 1989-06-05
US361,230 1989-06-05

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WO1990015423A1 true WO1990015423A1 (fr) 1990-12-13

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JP (1) JPH05500732A (fr)
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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1997048109A1 (fr) * 1996-06-13 1997-12-18 Lord Corporation Fluide magnetorheologique contenant de l'organomolybdene
WO1999041758A1 (fr) * 1998-02-14 1999-08-19 Studiengesellschaft Kohle Mbh Nanocolloides magnetiques anticorrosion proteges par des metaux precieux
DE102007028663A1 (de) * 2007-06-21 2008-12-24 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. Magnetorheologische Kompositmaterialien mit hartmagnetischen Partikeln, Verfahren zu deren Herstellung sowie deren Verwendung
US7758660B2 (en) * 2006-02-09 2010-07-20 Headwaters Technology Innovation, Llc Crystalline nanocatalysts for improving combustion properties of fuels and fuel compositions incorporating such catalysts

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
SU947052A1 (ru) * 1975-04-28 1982-07-30 Всесоюзный Научно-Исследовательский И Проектный Институт По Переработке Газа Ферромагнитна жидкость и способ ее получени
EP0208391A2 (fr) * 1985-03-19 1987-01-14 Ferrofluidics Corporation Composition d'un fluide magnétique électriquement conducteur et procédé pour sa fabrication et son utilisation
DE3737909A1 (de) * 1986-11-11 1988-05-26 Nippon Seiko Kk Elektrisch leitende ferrofluid-zusammensetzung
DE3709852A1 (de) * 1987-03-24 1988-10-06 Silica Gel Gmbh Adsorptions Te Stabile magnetische fluessigkeitszusammensetzungen und verfahren zu ihrer herstellung und ihre verwendung

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
SU947052A1 (ru) * 1975-04-28 1982-07-30 Всесоюзный Научно-Исследовательский И Проектный Институт По Переработке Газа Ферромагнитна жидкость и способ ее получени
EP0208391A2 (fr) * 1985-03-19 1987-01-14 Ferrofluidics Corporation Composition d'un fluide magnétique électriquement conducteur et procédé pour sa fabrication et son utilisation
DE3737909A1 (de) * 1986-11-11 1988-05-26 Nippon Seiko Kk Elektrisch leitende ferrofluid-zusammensetzung
DE3709852A1 (de) * 1987-03-24 1988-10-06 Silica Gel Gmbh Adsorptions Te Stabile magnetische fluessigkeitszusammensetzungen und verfahren zu ihrer herstellung und ihre verwendung

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
CHEMICAL ABSTRACTS, Vol. 97 No. 20, November 1982, (Columbus, Ohio, US), see page 754* Abstract 173809b, & SU, A, 947052 (All-Union Scientific-Research Institute for Gas-Processing) 30 July 1982* *

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1997048109A1 (fr) * 1996-06-13 1997-12-18 Lord Corporation Fluide magnetorheologique contenant de l'organomolybdene
WO1999041758A1 (fr) * 1998-02-14 1999-08-19 Studiengesellschaft Kohle Mbh Nanocolloides magnetiques anticorrosion proteges par des metaux precieux
US6491842B1 (en) * 1998-02-14 2002-12-10 Studiengesellschaft Kohle Mbh Anticorrosive magnetic nanocolloids protected by precious metals
US7758660B2 (en) * 2006-02-09 2010-07-20 Headwaters Technology Innovation, Llc Crystalline nanocatalysts for improving combustion properties of fuels and fuel compositions incorporating such catalysts
DE102007028663A1 (de) * 2007-06-21 2008-12-24 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. Magnetorheologische Kompositmaterialien mit hartmagnetischen Partikeln, Verfahren zu deren Herstellung sowie deren Verwendung

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Publication number Publication date
EP0520988A1 (fr) 1993-01-07
JPH05500732A (ja) 1993-02-12

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