WO1999007502A1 - Encapsulated nanometer magnetic particles - Google Patents
Encapsulated nanometer magnetic particles Download PDFInfo
- Publication number
- WO1999007502A1 WO1999007502A1 PCT/US1998/016233 US9816233W WO9907502A1 WO 1999007502 A1 WO1999007502 A1 WO 1999007502A1 US 9816233 W US9816233 W US 9816233W WO 9907502 A1 WO9907502 A1 WO 9907502A1
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- WIPO (PCT)
- Prior art keywords
- metal
- core
- shell material
- composite
- particles
- Prior art date
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F9/00—Making metallic powder or suspensions thereof
- B22F9/02—Making metallic powder or suspensions thereof using physical processes
- B22F9/12—Making metallic powder or suspensions thereof using physical processes starting from gaseous material
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
- B22F1/08—Metallic powder characterised by particles having an amorphous microstructure
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
- B22F1/16—Metallic particles coated with a non-metal
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
- B22F1/17—Metallic particles coated with metal
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- B82Y25/00—Nanomagnetism, e.g. magnetoimpedance, anisotropic magnetoresistance, giant magnetoresistance or tunneling magnetoresistance
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
- C08K9/00—Use of pretreated ingredients
- C08K9/02—Ingredients treated with inorganic substances
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
- G11B5/62—Record carriers characterised by the selection of the material
- G11B5/68—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent
- G11B5/70—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent on a base layer
- G11B5/712—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent on a base layer characterised by the surface treatment or coating of magnetic particles
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
- G11B5/84—Processes or apparatus specially adapted for manufacturing record carriers
- G11B5/855—Coating only part of a support with a magnetic layer
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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
- H01F1/0036—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties showing low dimensional magnetism, i.e. spin rearrangements due to a restriction of dimensions, e.g. showing giant magnetoresistivity
- H01F1/0045—Zero dimensional, e.g. nanoparticles, soft nanoparticles for medical/biological use
- H01F1/0063—Zero dimensional, e.g. nanoparticles, soft nanoparticles for medical/biological use in a non-magnetic matrix, e.g. granular solids
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- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F2998/00—Supplementary information concerning processes or compositions relating to powder metallurgy
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Definitions
- the present invention is broadly concerned with novel nanoscale polymetallic composite particles, as well as magnetic recording media (e.g., flexible tapes and rigid disks) and integrated circuits using polymetallic nanoscale particles. More particularly, the invention pertains to such composite particles and end products wherein, in preferred forms, the nanoscale composite particles have an average diameter of from about 5-500 nm with an elemental metal core surrounded by a metal-containing shell material.
- U.S. Patents Nos. 4,588, 708 and 4,877,647 describe catalyst and metallic coatings made by the Solvated Metal Atom Dispersion (SMAD) process.
- SAD Solvated Metal Atom Dispersion
- This method utilizes metal vapors (i.e., atoms) that are produced by heating pieces of elemental metal in a high temperature crucible up to the vaporization point of the metal while under vacuum.
- the metal vapor is condensed on the inside walls of the vacuum vessel which is cooled to a very low temperature.
- the vapors of an organic solvent are codeposited with the metal vapor on the low temperature vessel wall, forming a frozen matrix.
- the frozen matrix contains metal atoms, atomic oligomers such as dimers, trimers and small metal clusters.
- the atoms and oligomers Upon warming, the atoms and oligomers begin to migrate and bond to each other to form metal particles of various sizes, dependent upon the concentration of the metal atoms in the solvent, the chemical structure of the solvent, warm-up rate, and other parameters.
- Two important facets of this process are: (1) as the clusters grow they become heavier and less mobile, and (2) as the clusters grow solvent binds to the cluster surface and tends to slow further growth.
- the SMAD process yields metal clusters/particles in a solvent medium free of extraneous reagents.
- the SMAD process forces atoms of the immiscible elements to combine at low temperatures, so that metastable alloy composite particles form. Upon heating of these particles, controlled phase segregation can be accomplished since there is a natural tendency for the two elements to separate. Although it cannot be predicted which metal will nucleate and form the core, and which will form the shell, experience has shown that the metal possessing the stronger metal-metal bonds will generally form the core material.
- the ferromagnetic particles should be a single domain unit that possess two stable opposite magnetic poles along a preferred axis.
- the switching field is the minimum magnetic field needed to switch the magnetic poles in the single domain particles.
- the size of the switch units is important in the performance of the recording medium. They should be small enough to allow recording of the intended magnetization pattern and to provide a high signal-to- noise ratio, which requires the use of small switch units that are partially independent, so that one unit is not strongly affected by the magnetization of the other units. Additionally, a magnetic recording medium must be chemically stable under the conditions of use.
- metallic Fe, Co, or Ni being extremely oxophilic in ultrafine particle form, are generally not useful. Instead, iron oxide, chromium oxide, barium ferrite and cobalt-enhanced iron oxide are most commonly employed. However, such metal oxides have relatively low magnetization intensities and are therefore not optimum for recording materials.
- elemental iron has a magnetization intensity of 1700 emu/cm 3 , which is several times that of the oxides. Accordingly, elemental iron would be admirably suited for use in recording media if the oxophilic properties thereof could be appropriately controlled.
- the present invention overcomes the problems outlined above and provides novel polymetallic (especially bimetallic) composite particles having an average diameter of from about 5-500 nm (more preferably from about 10-100 nm and most preferably from about 15-60 nm) with an elemental metal core surrounded by a metal- containing shell material; the core and shell material are thermodynamically immiscible and each is evaporable at a temperature of up to about 2000 °C under a vacuum.
- the shell material is preferably non-magnetic and selected from the group consisting of In, Nd and metal salts; in many instances, the metal moiety of such salts is different than the core metals.
- Preferred metal salts are the metal oxides and halides, particularly the fluorides.
- the core fraction of the composite particles is present at a level of at least about 30% by weight, more preferably from about 30-90% by weight, most preferably from about 50-70% by weight.
- the shell material is present at a level of up to about 70% by weight, more preferably from about 10-70% by weight, and most preferably from about 30-50% by weight.
- Core metals are normally selected from the group consisting of the transition metals, and especially Fe, Al, Mg, Cr, Co, Ni, Pd, Au, Cu, and Ag.
- the shell material may be an elemental metal such as an alkaline earth metal, or a metal salt; the metal salts are normally selected from the group consisting of the metal oxides, sulfides and halides, especially the metal fluorides.
- the composites are preferably formed by co-condensation of vapors of the core elemental metal and the metallic shell material, followed by heating of the condensate.
- a conventional SMAD reactor can be used for this purpose.
- the core metal and metallic shell material are heated to their respective vaporization temperatures in individual crucibles within the SMAD reactor under a vacuum of at least about 10 ⁇ 3 Torr.
- the exterior walls of the SMAD reactor are typically cooled to a temperature of about -100°C and lower.
- the magnetic recording media of the invention are generally flexible tape or rigid disk media.
- the tapes comprise an elongated web of synthetic resin substrate material having a magnetic coating applied to at least one face thereof.
- the magnetic coating includes a synthetic resin binder with magnetizable particles dispersed therein, the particles being of the type described above with an elemental core surrounded by a metal-containing shell material.
- the core and shell material are thermodynamically immiscible and each is evaporable at a temperature of up to about 2000 °C under a vacuum.
- the magnetizable particles have two stable opposite magnetic poles switchable under the influence of an externally applied magnetic field.
- the core metal is preferably selected from the group consisting of Ni, Fe, Cr, and Co
- the metallic shell material is selected from the group consisting of non-magnetic elemental metals and metal salts (e.g., elemental lithium, magnesium and gold, and magnesium fluoride).
- the shell material should be more oxophilic than the elemental core metal so that any trace oxygen is scavenged.
- the shell material should be inert and essentially impermeable to oxygen and other environmental gases. This enables the core metal to remain purely metallic in use and inhibits formation of deleterious oxides.
- the substrates can be selected from a wide variety of materials such as polyethylene terephthalates, polyethylene napthalates, aramids and polyimids. These substrates would typically have a thickness of from about 1-10 thousandths of an inch.
- the magnetic coatings applied to the substrates are fabricated by mixing the magnetic particles in synthetic resin binders such as those selected from the group consisting of the polystyrenes, vinyl chloride copolymers, vinylidene chloride copolymers, poly vinyl acetate resins, acrylate and methacrylate resins, polyurethane elastomers, modified cellulose derivatives, epoxy and phenoxy resins, polyamids and combinations of poly ethers with -OH groups with polyesters and polyisocyanates.
- synthetic resin binders such as those selected from the group consisting of the polystyrenes, vinyl chloride copolymers, vinylidene chloride copolymers, poly vinyl acetate resins, acrylate and methacrylate resins, polyurethane elastomers, modified cellulose derivatives, epoxy and phenoxy resins, polyamids and combinations of poly ethers with -OH groups with polyesters and polyisocyanates.
- Such magnetic coatings can have from about 1-80%
- Rigid magnetic disks may be prepared by applying a coating made up of a synthetic resin (for example, phenol-formaldehyde, urea-formaldehyde, epoxy, polyvinyl acetate and silicone resins) with the above described magnetic particles to a rigid disk (e.g., made of aluminum or other suitable material); the particle loading in such coatings are the same as used in the fabrication of flexible web media.
- a synthetic resin for example, phenol-formaldehyde, urea-formaldehyde, epoxy, polyvinyl acetate and silicone resins
- Fig. 5 is a powder X-ray diffraction pattern of heat treated and passivated Fe-Nd SMAD particles heat treated at (A) 450°C, (B) 325 °C, and (C) 225 °C;
- Fig. 6 is a graph of saturation magnetization values versus temperature for non- heat treated fresh and exposed Fe-Nd SMAD particles
- Fig. 7 is a graph of coercivity versus temperature for non-heat treated fresh and exposed Fe-Nd SMAD particles
- Fig. 8 is a graph of saturation magnetization versus Fe crystallite size for passivated Fe-Nd SMAD particles
- Fig. 10 is a powder X-ray diffraction pattern of different Fe crystallite sizes in Fe-Mg F 2 SMAD particles heat treated at different particles;
- Fig. 11 is a TEM photo (150 nm) of Fe-Mg F 2 SMAD particles heat treated at
- Fig. 12 is a TEM photo (600 nm) of Fe-Mg F 2 SMAD particles heat treated at 500°C for 2 hrs.;
- Fig. 13 is a graph of saturation magnetization values versus Fe crystallite size for passivated Fe-Mg F 2 SMAD particles (percentage of Fe bulk value, 220 emu/g of
- Fig. 14 is a schematic representation illustrating the encapsulation of Fe core metal within Mg F 2 shell material
- Fig. 15 is a powder X-ray diffraction pattern of fresh and passivated CO-Mg F 2 SMAD particles: (A) fresh, as prepared; (B) heat treated at 200 °C and passivated; (C) heat treated at 400 °C and passivated; and (D) heat treated at 700 °C and passivated;
- Fig. 16 is a TEM photo (200 nm) of Co-Mg F 2 SMAD particles heat treated at 400°C for 2 hrs.;
- Fig. 17 is a TEM photo (300 nm) of Co-Mg F 2 SMAD particles heat treated at 600°C for 2 hrs.;
- Fig. 18 is a graph of Co crystallite size versus heat treatment temperature for Co-Mg F 2 SMAD particles heat treated at different temperatures;
- Fig. 19 is a graph of saturation magnetization values versus Co crystallize size for passivated Co-Mg F 2 SMAD particles
- Fig.20 is a graph of magnetic coercivity versus Co crystallite size for passivated Co-Mg F 2 SMAD particles
- Fig. 21 is a schematic representation illustrating the encapsulation of Co core metal within Mg F 2 shell material
- Fig. 22 is a powder X-ray diffraction pattern of fresh and passivated Ni-Mg F 2
- SMAD particles (A) fresh, as prepared; (B) (B) heat treated at 200°C and passivated;
- Fig. 23 is a TEM photo (300 nm) of Ni-Mg F 2 SMAD particles heat treated at 500°C for 2 hrs.;
- Fig. 24 is a graph of saturation magnetization values versus Ni crystallize size for passivated Ni-Mg F 2 SMAD particles;
- Fig.25 is a graph of magnetic coercivity versus Ni crystallite size for passivated Ni-Mg F 2 SMAD particles.
- X-ray powder diffraction SCINTAG 3000 XRD diffractometer X-ray powder diffraction (XRD) was used to study the chemical compositions and structures of the powders. For samples with a fresh surface, degassed mineral oil was applied to coat the sample for temporary protection from oxidation by forming a powder/oil paste in an argon-filled dry-box. XRD analysis (which lasts for about one hour) was carried out immediately after the coating because the protection from mineral oil was effective for only a few hours. For samples with passivated surfaces, no such precaution was taken. X-ray powder diffraction was also used to estimate the crystallite sizes of the core metal particles.
- t 0.91 ⁇ /B ⁇ o ⁇ B
- ⁇ the X-ray wavelength
- t the crystallite diameter in A
- B the width of the peak at half height
- ⁇ B the half value of the peak position in degrees.
- the direct information from BET measurement is the surface area of the particles.
- the average size of the particles were calculated from the specific surface area data, as follows : Given a group of spherical particles N with the total mass of M, the average specific area of these particles is:
- the Mossbauer spectra were obtained on a Ranger Scientific Inc. MS- 1200 Mossbauer spectrometer. Mossbauer spectroscopy was used to study the oxidation states and the fine structures (e.g., core metal crystallite size, surface/interface effect on the M ⁇ ssbauer parameters of the core metal) of core metal species in the samples.
- Magnetic properties of the samples were taken from a MPMS2 (Magnetic Property Measurement System) SQUID (Superconducting Quantum Interference Device) magnetometer designed by Quantum Design.
- the field range of the equipment was ⁇ 55,000 Oe, with a sensitivity of 10" 8 emu.
- Fresh samples were protected in mineral oil in a gel capsule during the measurement. Magnetization curves of these samples were taken at different temperatures between 10K and 300K in fields up to 55,000 Oe.
- This method involved the codeposition of a metallic shell material (e.g., In or MgF 2 ) with a core metal (such as Fe) as well as the simultaneous deposition at 77K of an excess of a hydrocarbon diluent (solvent) as described by Klabunde et al., J. Am. Chem. Soc. , 98 (1979), Eree Atoms, Clusters, and Nanoscale Particles, Academic Press (1994), Active Metals — Preparation, Characterization, Applications, VCH Publ., 237
- the SMAD apparatus comprises a vacuum flask provided with a jacket for liquid nitrogen cooling.
- the center of the flask is equipped with electric crucibles independently controlled for vaporizing the core metal and the metallic shell material, and with an inlet for the solvent.
- the solvent vaporizes on entry, and then condenses on the inner walls of the flask together with the vaporized core metal and metallic shell material atoms. This condensation and cooling generates a frozen matrix of core metal, metallic shell material atoms and solvent which collects on the walls of the flask.
- the liquid nitrogen cooling is discontinued.
- the flask can then be warmed to spur kinetic growth of the bimetallic particles.
- the metastable particles are then isolated and heat treated to cause phase segregation into core/shell composite particles.
- the metallic shell material In order to be successful, the metallic shell material must be inert toward the core metal atoms and growing clusters, and be capable of protecting the encapsulate core metal clusters from air oxidation.
- pentane Prior to the evaporation of a core metal and a metallic shell material, pentane was pre-dried by refluxing over Na/K with benzophenone. Before being deposited on the SMAD reactor, the dried pentane (held in a Schlenk tube) was degassed on a vacuum line with liquid nitrogen. The crucibles used were tungsten baskets obtained from R.
- the tungsten baskets were coated with a water based alumina cement (Zircar Alumina Cement) obtained from Zircar Products, Inc.
- the Zircar Alumina Cement consisted of 70% alumina in a combination of milled fibers and sub-micro particles.
- Alumina cement is mildly acidic (pH 5) and forms a strong bond on removal of the water solvent.
- the coated crucibles Prior to use, the coated crucibles were heated at about
- the crucibles that contained the core metal (such as Fe) and the metallic shell material (such as In or MgF 2 ) were warmed up at increments of about 100 ° C for about two hours at each increment to a temperature about 100-200 ° C below the boiling points of the starting materials. This slow heating process effectively outgassed the starting materials, and minimized sudden vaporization surges during deposition.
- the crucibles were heated approximately 40-50 ml of pentane was deposited on the walls of the reactor.
- the evaporation of the core metal was initiated after a steady evaporation of the metallic shell material was achieved.
- the heating of the core metal was carefully controlled by slowly increasing the voltage to the crucible to prevent pressure surges in the reactor.
- the reactor was closed off from the vacuum line.
- the liquid nitrogen dewar was removed to allow the reactor to warm to room temperature.
- the vacuum was re-applied to transfer the pentane to a cold trap and a black powder was obtained.
- the reactor was closed off from the vacuum line again and filled with argon to normal pressure.
- the lower part of the reactor containing the final product was quickly removed, covered with an aluminum foil, and carefully transferred into an argon-filled dry-box. Heat treatments at various temperatures were applied to the collected SMAD particles to increase the sizes of the core metal crystallites within these particles.
- a certain amount of the sample usually 70-100 mg, was transferred into a Pyrex glass tube in the argon-filled dry-box.
- the glass tube filled with argon was then sealed on a hydrogen/oxygen flame. After the sample was heated at the desired temperature over the desired time period, the sample tube was cut open in the dry-box and stored in a sample vial.
- EXAMPLE 1 In this example, using the preferred method described above, a sample was prepared using iron as the core metal and indium as the metallic shell material. The properties of Fe and In are shown in Table 1 as follows:
- the sample After being heated at 300°C, the sample showed signals for Fe, In, ⁇ -Fe O 3 , and In O 3 .
- the 350°C sample a similar pattern was evident.
- the In signals and the signals of indium oxide were about the same strength.
- the evaporation of iron and neodymium was carried out using the preferred method described above.
- Fe was evaporated out of an alumina-coated tungsten crucible and Nd from a boron nitride crucible placed in a tungsten basket with alumina coating on the outside in the presence of pentane at 77K and 10 "3 torr.
- Several reactions were carried out using a Fe:Nd 1:1 molar ratio system. In a typical reaction in which about 0.56 g of Fe (10.0 mmole) and 1.50g of Nd (10.4 mmole) were used, 1.6g of black pyrophoric powder was collected. Elemental analysis of the powder gave
- the pyrophoric fresh Fe-Nd powders were then heat-treated under argon at different temperatures ranging from 250°C to 750°C for two hours. After the heat treatments, these powders were slowly passivated in air allowing a layer of metal oxides to form on the surfaces of these powders. No evident physical changes were observed on the stabilized powders after they had been stored in sample vials for six months.
- a X-ray powder diffraction pattern of the fresh Fe-Nd SMAD powder showed only one broad peak due to metallic iron.
- the XRD patterns of heat-treated and passivated powders showed that the iron began to crystallize at very low temperature (Fig. 5), but clear signals for Nd 2 O 3 were not observed until the heat treatment temperature reached 500°C. In addition, no clear signals for iron oxides or metallic Nd could be seen after any of the heat treatments.
- a weak signal for the Fe-Nd inter- metallic compound Fe 2 Nd was observed for samples heated at 500°C and above.
- the average XRD ⁇ -Fe crystallite sizes, estimated with the Scherrer formula, are listed in Table 5 along with the BET surface area data and the estimated sample densities.
- the BET overall particle sizes listed in this table were estimated from the BET surface area data and the sample densities under the assumption that all the particles had a spherical shape. For comparison, the estimated TEM sizes of these particles are also listed in Table 5.
- the M ⁇ ssbauer data indicated the presence of pure ⁇ -Fe, while the rest of the signal was assigned to ⁇ -Fe 2 O 3 and Fe Nd. Since the signals of ⁇ -Fe 2 O 3 and Fe 2 Nd (each as a doublet) overlap with each other, their relative abundance could not be assessed.
- the hyperfme field of the fresh, unexposed Fe-Nd powder (324 KOe) was slightly lower than the standard value (333 KOe). This indicated a close-range electronic interaction between iron (electronegativity 1.8) andNd (electronegativity 1.1) atoms that enabled Fe atoms to withdraw some electron density from the surrounding Nd atoms.
- the Mossbauer data showed that when the samples were heat-treated at temperatures higher than 450°C, at least 70% by mass of the iron atoms were protected from further oxidation (as ⁇ -Fe) after the powders were stabilized by oxidative passivation of the surfaces.
- a Mossbauer spectrum of the sample heat-treated at 750°C showed a slightly lower content of the ⁇ -Fe phase because more Fe atoms formed Fe 2 Nd at this high temperature.
- the extensive sintering of the surface layer led to shrinking of the protecting shell resulting in the exposure of the Fe crystallite core to oxygen.
- the passivated Fe-Nd particles demonstrated very low coercivities of 12.6-105 Oe at 300K.
- room-temperature coercivity values can be as high as 1 ,050 Oe.
- These Fe-Nd powders must therefore be considered soft magnetic materials and consist of Fe° clusters protected by Fe 2 Nd and Nd 2 O 3 coatings.
- EXAMPLE 3 The Fe-MgF 2 system studied in this example using the preferred method described above had a Fe to MgF 2 molar ratio of 1 :2 where 0.80 g of Fe (14.3 mmole) and 1.78 g MgF 2 (28.6 mmole) were co-evaporated and deposited at 77K with pentane vapor. The evaporation temperature of MgF 2 under the normal SMAD reactor pressure (about 10 "3 torr) was 1100°C. About 2 g of the product was collected. Fig. 9 gives the XRD patterns of the as-prepared samples as well as the heat-treated and passivated Fe-MgF 2 (molar ratio 1 :2) powders.
- the TEM photos show that, after being heated at lower temperatures, the Fe-MgF 2 particles still had a near single-phase structure with the Fe crystallites embedded in a matrix of MgF 2 demonstrating that the Fe crystallites grew very little.
- the temperature reached 500°C, severe phase separation occurred. Most of the Fe clusters aggregated into very large Fe particles (50 to 100 nm), and only a small number of the smaller Fe crystallites remained.
- there were actually two groups of Fe crystallites One group included the large Fe particles with a size range of around 100 nm, and the other group contained the smaller 10-15 nm Fe crystallites.
- the large Fe particles accounted for more than 90% of the total mass of the Fe in these materials whereas the small Fe crystallites represented less than 10% of the total Fe mass.
- the MgF 2 crystals After heat-treatments at the temperatures of 500°C and 600 °C, the MgF 2 crystals also grew into large pieces with a size range of a few hundred nanometers.
- the magnetization data in Table 9 and the information provided in Fig. 13 show that after being heated at temperatures of 400°C and above, more than 85% of the Fe atoms were protected when these particles were exposed to air.
- a schematic illustration for the formation of encapsulated Fe clusters in a MgF 2 matrix using the SMAD method is shown in Fig. 14.
- EXAMPLE 4 In this example, the evaporation of Co and MgF 2 followed the preferred method as described above.
- the Co-MgF 2 system had a molar ratio of 1 :2 in which 0.80 g of cobalt (13.6 mmole) and 1.69g of MgF 2 (27.2 mmole) were co-evaporated in the presence of pentane at 77K.
- Fig. 15 gives the XRD patterns of the fresh, as-prepared Co-MgF 2 powders as well as the heat-treated and passivated samples.
- the average size of the Co crystallites of the fresh, as-prepared sample was estimated at about 4.5 nm by using the Scherrer formula for XRD broadening. All the XRD patterns showed metallic cobalt and MgF 2 , and no clear signals of cobalt oxides could be observed.
- the estimated XRD sizes and the estimated TEM sizes of cobalt crystallites in these samples are listed in Table 11. TEM photos of these particles are given in Figs. 16 and 17.
- Cobalt had a bulk magnetization value of 162.5 emu/g of Co and, thus, at least 80% of the cobalt atoms were protected so long as these particles were heated at temperatures higher than 500°C before they were exposed to air as illustrated in Table 12 and Fig. 19.
- the Co-MgF 2 system had a much narrower Co size distribution, therefore, a simplified schematic illustration of the encapsulation of Co particles in the MgF 2 matrix is given in Fig. 21.
- EXAMPLE 5 The evaporation of Ni and MgF 2 also followed the preferred method as described above. Ni vaporized at about 1400 oC under the SMAD reactor pressure of about 10 "3 torr.
- the Ni-MgF 2 system had a molar ratio of 1 :2 in which 0.80g of Ni (13.6 mmole) and 1.69g of MgF 2 (27.2 mmole) were co-evaporated in the presence of pentane at 77K.
- Fig. 22 gives the XRD patterns of the fresh, as-prepared and the heat-treated and passivated Ni-MgF 2 particles. The average size of the Ni crystallites was estimated at 5.8 nm in the fresh, as-prepared sample.
- the magnetized tape was studied using a Hall probe. A 400-1000 milliGauss signal was detected. The magnetization direction was reversed, and again a 400-1000 milliGauss signal was detected. For a comparison, a normal commercial magnetic tape was measured for remnant magnetization, which showed a signal of about 500 milliGauss.
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WO2000018591A1 (en) * | 1998-09-29 | 2000-04-06 | Securency Pty Ltd. | Security document including a nanoparticle-based authentication device |
EP1447712A4 (en) * | 2001-11-01 | 2008-04-02 | Toray Industries | Methods of producing photosensitive ceramic composition and multi-layer substrate using it |
EP1447712A1 (en) * | 2001-11-01 | 2004-08-18 | Toray Industries, Inc. | METHODS OF PRODUCING PHOTOSENSITIVE CERAMIC COMPOSITION AND MULTI−LAYER SUBSTRATE USING IT |
KR100861857B1 (en) * | 2001-11-01 | 2008-10-07 | 도레이 가부시끼가이샤 | Methods of producing photosensitive ceramic composition and multi-layer substrate using it |
WO2003086660A1 (en) * | 2002-04-09 | 2003-10-23 | The Government Of The United States Of America As Represented By The Secretary Of The Navy | Magnetic nanoparticles having passivated metallic cores |
JP2010501344A (en) * | 2006-08-30 | 2010-01-21 | ユミコア・アクチエンゲゼルシャフト・ウント・コムパニー・コマンディットゲゼルシャフト | Core / shell type catalyst particles and method for producing them |
WO2008025750A1 (en) * | 2006-08-30 | 2008-03-06 | Umicore Ag & Co. Kg | Core/shell-type catalyst particles and methods for their preparation |
CN101522345A (en) * | 2006-08-30 | 2009-09-02 | 尤米科尔股份公司及两合公司 | Core/shell-type catalyst particles comprising metal or ceramic core materials and methods for their preparation |
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US8227372B2 (en) | 2006-08-30 | 2012-07-24 | Umicore Ag & Co. Kg | Core / shell-type catalyst particles comprising metal or ceramic core materials and methods for their preparation |
US8288308B2 (en) | 2006-08-30 | 2012-10-16 | Umicore Ag & Co. Kg | Core/shell-type catalyst particles and methods for their preparation |
US8304362B2 (en) | 2006-08-30 | 2012-11-06 | Umicore Ag & Co. Kg | Core/shell-type catalyst particles and methods for their preparation |
US8691717B2 (en) | 2006-08-30 | 2014-04-08 | Umicore Ag & Co. Kg | Core/shell-type catalyst particles and methods for their preparation |
KR101436410B1 (en) * | 2006-08-30 | 2014-09-01 | 우미코레 아게 운트 코 카게 | Core/shell-type catalyst particles comprising metal or ceramic core materials and methods for their preparation |
US8058204B2 (en) | 2008-10-24 | 2011-11-15 | GM Global Technology Operations LLC | Method for generating a shell of noble metal overlaid on a core of non-noble metal, and catalysts made thereby |
EP2399756A1 (en) * | 2010-06-23 | 2011-12-28 | Fábrica Nacional De Moneda Y Timbre | Security element |
Also Published As
Publication number | Publication date |
---|---|
US6045925A (en) | 2000-04-04 |
EP1007252A1 (en) | 2000-06-14 |
CA2301536A1 (en) | 1999-02-18 |
EP1007252A4 (en) | 2009-05-27 |
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