Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C1/00—Making non-ferrous alloys
  • C22C1/04—Making non-ferrous alloys by powder metallurgy
  • C22C1/0433—Nickel- or cobalt-based alloys
• • 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
• • 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
• • 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
  • G11B5/706—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 composition of the magnetic material
  • G11B5/70605—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 composition of the magnetic material metals or alloys
• • 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
  • G11B5/706—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 composition of the magnetic material
  • G11B5/70605—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 composition of the magnetic material metals or alloys
  • G11B5/70621—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 composition of the magnetic material metals or alloys containing Co metal or alloys
• • 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
  • G11B5/714—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 dimension of the magnetic particles
• • 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
  • H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
  • H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
  • H01F1/032—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials
  • H01F1/04—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys
  • H01F1/06—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys in the form of particles, e.g. powder
  • H01F1/061—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys in the form of particles, e.g. powder with a protective layer
• • 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
  • H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
  • H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
  • H01F1/032—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials
  • H01F1/04—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys
  • H01F1/06—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys in the form of particles, e.g. powder
  • H01F1/065—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys in the form of particles, e.g. powder obtained by a reduction
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/29—Coated or structually defined flake, particle, cell, strand, strand portion, rod, filament, macroscopic fiber or mass thereof
  • Y10T428/2982—Particulate matter [e.g., sphere, flake, etc.]
  • Y10T428/2991—Coated
  • Y10T428/2998—Coated including synthetic resin or polymer

Definitions

• This invention relates to magnetic powders and their preparation. It relates more particularly to very small ferromagnetic particles of cobalt and its alloys and to a method of making same, and to a magnetic recording member having these particles as its magnetic pigment.
• Ferromagnetic particles are employed in a variety of applications. For example, in the form of coatings on tapes, cards, drums and disks, they serve as the recording medium for information recorded in magnetic form. They are used also to form magnets. They have further application in connection with microwave circuitry and various electronic equipment.
• Ferromagnetic particles of cobalt and cobalt-iron have been known as useful as recording pigments, the particles being produced by a number of old processes. These processes include both the direct chemical reduction of cobalt from an oxide and electrolytic deposition of the metal. Cobalt particles have also been prepared by thermal decomposition of cobalt-containing compounds such as cobalt carbonyl and cobalt oxalate.
• the particles produced with these prior techniques do not form a recording pigment having optimum recording characteristics.
• the sigma value (the intensity of magnetization (M) divided by the density of the material), is too small, i.e., generally less than 60 e.m.u./g.
• the prior particles oxidize to an appreciable extent and often carry an excessively thick surface coating of a polymer to protect them from further oxidation, the sigma values drop below the 60 e.m- .u./g. figure.
• Squareness is defined as the ratio of the remanent magnetization (M,-) to the saturation magnetization (M,).
• M,- remanent magnetization
• M, saturation magnetization
• the prior cobalt powders generally have relatively low squareness figures for the bulk material, i.e., less than 0.25.
• Cobalt powder has also been prepared by direct reduction from cobalt hydroxide.
• the cobalt particles are coated with a polymer and in this form they exhibit a high coercive force.
• the pressence of excessive polymer on the particles lowers the sigma value. Also sometimes it reacts adversely with the binder on the substrate.
• this invention aims to provide magnetic cobalt-containing particles having superior magnetic characteristics which enable them to be used as a highquality magnetic recording pigment.
• Another object of the invention is to provide single domain cobalt and cobalt-containing particles.
• a further object of the invention is to provide cobalt and cobalt-containing particles which are characterized by minimum resistance to dispersion in organic matrices such as would be caused by excessive interparticle agglomeration.
• Still another object of the invention is to provide a powder-like recording pigment composed of essentially single-domain ferromagnetic cobalt or cobaltcontaining particles of relatively uniform shape.
• Another object of the invention is to provide a method of making cobalt and cobalt-containing particles having one or more of the above characteristics.
• a further object of the invention is to provide superior magnetic recording members having the above improved ferromagnetic cobalt and cobalt-containing particles as the recording pigment.
• Another object of the invention is to provide cobalt particles having sufficient alloying metal therein to markedly increase the oxidation resistance thereof, especially in the presence of moisture.
• the invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others, and the particle possessing the feature, properties, and the relation of elements, which are exemplified in the following disclosure, and the scope of the invention will be indicated in the claims.
• the objects of this invention are accomplished by providing small, ferromagnetic cobalt and cobalt-containing particles of uniform shape which do not tend to agglomerate during their fabrication. These particles have a typical diameter of 0.02 to 0.5 micron and a typical length of 0.02 to 2.0 microns.
• the actual particles which must ultimately be dispersed in a binder will be up to about 1 micron in length and will often be chain-like segments, i.e. acicular, consisting of more spherical elemental particles from about 0.01 micron to 0.2 micron in size, most advantageously from 0.02 to 0.07 micron.
• Measurements on a bulk sample of unoriented cobaltbearing particles of this invention give coercivities greater than 400 oersteds' with typical values ranging from 600 to 1000 oersted and more.
• the samples also have high saturation magnetization, in excess of 60 e.m.u./g.
• the bulk material is characterized by a high degree of squareness, e.g. ratios on the order of 0.25 to 0.6.
• the cobalt and cobaltcontaining particles of this invention have magnetic and physical properties which make them especially suitable as the magnetic pigment in magnetic recording members.
• the advantages of the recording members are not only due to the magnetic characteristics of the particles noted above, but also they are due to the fact that particles can be oriented in essentially the same direction and can be distributed in a very thin layer with a close relationship to one another in a binder on a substrate. This, in turn, results in more uniform magnetic characteristics in a recording member incorporating these particles as the recording pigment.
• Our process for producing magnetic particles may be divided into two basic parts. First, we create a multiplicity of very small, decomposable, acicular cobalt salt particles. Then, we coat the salt particles with, or immerse them in, an organic material such as silicone oil, polyacrylic ester resin, polyamide or the like, and heat the coated particles in a reducing atmosphere. The material minimizes inter-particle agglomeration or sintering so that each particle is reduced to a metal while still maintaining its individual acicular shape.
• an organic material such as silicone oil, polyacrylic ester resin, polyamide or the like
• the coating is substantially eliminated either by later washing in a suitable solvent or by thermal decomposition during the firing step, or by evaporation or sublimation or the like so that it does not materially degrade the magnetic and physical characteristics of a recording member incorporating the resulting metal particles.
• Cobalt or cobalt-containing particles made in this way tend to be quite pyrophoric initially. Therefore, care must be taken at the outset to maintain them in a substantially oxygen-free atmosphere and to bring them into contact with oxygen relatively slowly. When this is done, a very thin oxide surface coating forms on the particles, retarding their further oxidation and thus rendering them stable. lt should be understood that this oxide coating forms only a minor portion of each particle. Consequently, the particle is composed largely of pure cobalt or cobalt alloy.
• the cobalt-containing crystals from which the cobalt particles are reduced are small and acicular.
• they are produced by a two-step, or successive, precipitation process. Specifically, we use a double precipitation process in which we first precipitate a compound having the requisite particle size but not the desired acicular shape. This first precipitate is then reacted to precipitate an acicular crystalline salt that can subsequently be treated to provide small metal particles.
• the first precipitate is preferably highly insoluble and therefore it has a very low concentration insolution.
• the second precipitate is also highly insoluble. Consequently, there is little material in solution to support crystal growth of the second precipitate. As discussed below, this permits controlled acicular crystal growth and, specifically, it permits size control within desirable limits, e.g. about 0.01 to 2 microns in diameter.
• a finely-divided, cobalt-containing suspension such as the hydroxide or the carbonate is prepared by mixing an aqueous solution of sodium hydroxide or sodium carbonate with an aqueous solution of a cobalt salt, such as cobalt chloride. Then, oxalic acid is reacted with the suspension to form cobalt oxa- 4 late.
• relatively low precipitation temperatures e.g. 20C
• each mixture is vigorously agitated to minimize agglomeration of the precipitated oxalate particles.
• the parent hydroxide (or carbonate) particles serve not only as sources of the cobalt ions, but also as nucleating sites for the oxalate crystals.
• crystal growth is probably limited by a boundary layer around each crystal and, especially in a vigorously agitated suspension, the boundary layer'is thinner at the ends than the sides of these particles, thereby promoting acicular growth.
• the parent particles serve as reservoirs to replace the cobalt ions that are taken up by the oxalate crystals.
• the process provides the desired low concentration without requiring an unduly large volume of solution to provide a reasonably large yield of the organic cobalt salt. Also important is the fact that the hydroxide particles are used up in the process. These disappearing sites thus leave no impurities in the final material. Y
• the oxalate has a relatively low molecular weight; that is, the organic radical does not take up as much of the volume as would high molecular weight materials. ln the ensuing reduction of the cobalt, this aids in providing compact particles with minimum shrinkage.
• the precipitation is often carried out in a wateralcohol mixture or another such solubility-depressing medium to reduce the solubility of the precipitate to a level which discourages excessive growth of the oxalate crystals and facilitates particle shape and size control by means of the water-alcohol ratio. It also appears to facilitate control of the acicularity of the oxalate. Excellent results have been obtained with a 50 percent 50 percent water-alcohol mixture and mixtures containing up to percent alcohol have been tried with good results. In many circumstances, water alone is useful. Also, acetone and other water soluble solvents may be used in lieu of alcohol. Apparently for reasons not clearly understood some water is needed in order to produce reasonably good oxalate crystals.
• cobalt oxalate length-to-diameter ratios of the order of IO-to-l have been obtained.
• length-to-diameter ratios are of the order of 3-to-l.
• These particles are further characterized by being very small, e.g. as low as 0.05 micron in diameter and by being relatively uniform in size.
• Cobalt content is preferably 43 percent of metal content in these cobalt salts.
• inter-particle agglomeration is preferably limited to maintain the particles below about 0.1 micron average diameter.
• the average diameter is maintaine below about 0.05 micron.
• the salt advantageously comprises a quantity of cobalt such that, on reduction of said salt to metal, the metal contains at least 43 percent cobalt.
• Polymers and other organic chemicals that have been used as the coating material include silicone oil, silicone polymer, silanes, epoxy resin, polyacrylic aster, and polyurethane.
• the organic material is applied in a suitable solvent to ensure complete coverage of the oxalate crystals.
• the particles can be immersed in the organic medium if it is a liquid such as, for example, a liquid hydrocarbon.
• the range of organic material to be decomposed is conveniently from 1 to percent by weight of the oxalate being reduced.
• a very sig' nificant part of the polymer preferably about 8 percent or more be left as residue.
• the major part of the residue be removed before use.
• the decomposition residue should be less than 5 percent of the metal content of the oxalate.
• the coated oxalate particles are heated to a temperature of approximately 325410C in a reducing atmosphere such as hydrogen or hydrogen-nitrogen to reduce the cobalt (or cobalt alloy) and, at the same time, internally sinter the cobalt in each particle.
• a reducing atmosphere such as hydrogen or hydrogen-nitrogen to reduce the cobalt (or cobalt alloy) and, at the same time, internally sinter the cobalt in each particle.
• the reducing temperature falls much below 330C, the oxalate crystals do not decompose readily.
• the reducing temperature exceeds 400C, excessive inter-particle sintering starts to occur and the resulting agglomerates degrade the magnetic characteristics of the material.
• a temperature of about 370C produces optimum results.
• Bulk samples of unoriented cobalt particles and cobalt-alloy particles of this invention exhibit particularly high coercivity and sigma values and are characterized by a high degree of squareness.
• masses of unbound particles exhibit coercivities ranging from 400 up to over 1,000 oersteds.
• the saturation magnetization values of our acicular cobalt powders range from 60 to 120 e.m.u./g. which is significantly greater than the corresponding values exhibited by conventional materials.
• our materials may have a squareness figure as high as 0.6.
• novel material produced by the present inven tion and in particularly that material having squareness values over 0.35 and coercivities over 500, has a flat coercivity-to-temperature relationship compared to pre-existing ferromagnetic materials.
• Coercivity values generally remain above 500 at 100C and decrease only about 20 percent in magnetic coercivity between 0C and 100C.
• the resultant products show a surprisingly higher signal (unbiased sine-wave recording) output over a wider frequency than products heretofore known.
• Nickel is a particularly useful metal for use in forming cobalt alloys according to the process of the invention. It has been discovered that use of nickel allows one to more accurately pre-select the magnetic properties of the alloy. This may be because the nickel fits so well into a cobalt lattice system. In any event, the resultant nickel-cobalt alloys are predictably formed. Moreover, such alloys have outstanding resistance to degradation with time. That is, they have improved resistance to oxidation even under conditions of heat or hu' midity. Nickel alloys containing at least 43 percent, but preferably from 60 percent to percent cobalt, are the most advantageous materials for use in many magnetic recording applications.
• EXAMPLE I A quantity of 238 g. of CoCl is dissolved in a container to form a 1 liter aqueous solution. Then g. of sodium hydroxide is dissolved in a second container to form a second 1 liter aqueous solution. The cobalt chloride and sodium hydroxide solutions are mixed together, using a magnetic agitator bar, in a 4 liter beaker for three minutes to form a cobalt hydroxide precipitate. Then g. of oxalic acid are dissolved in a separate container to form a l /2 liters aqueous solution.
• the oxalic acid solution is mixed thoroughly into the cobalt hydroxide precipitate for 5 minutes to form a cobalt oxalate precipitate.
• the resultant mixture is filtered in a Buchner funnel and washed several times with water. Then it is rinsed several times with acetone and air dried.
• the resulting cobalt oxalate particles are acicular, (that is needle-shaped).
• 0.05 g. of silicone polymer oil (sold under the trade designation, G.E. RTV91O Diluent) is mixed with 0.95 g. of the acicular cobalt oxalate particles using sufficient tetrahydrofuran to insure uniform coating of the silicone oil on the particles.
• the coated particles are air dried.
• the coated particles are charged into a 1 inch diameter glass tube in a tube furnace, heated to 360C in a hydrogen atmosphere, and held at this temperature for 1 hour, thereby reducing the metal salt to cobalt.
• the material is then cooled to room temperature while still in a hydrogen atmosphere, and subjected to a 2 minute argon purge.
• the product is washed several times with acetone.
• a magnet is used to effect separation from the wash, and the separated material is air dried.
• the resulting product is a strongly magnetic powder having a coercivity of 705 oersteds, a sigma value of 82 e.m.u./g., and a squareness figure 0.40.
• the particles are composed mainly of cobalt, and have little or no silicone oil on their surfaces. Also the cobalt particles are acicular with an average particle size of 0.3 microns in diameter by 1 micron in length.
• Cobalt particles are prepared as described in Example 1, except that the cobalt oxalate crystals are not coated with silicone oil during their reduction step. Now the resultant cobalt particles have a coercivity of 313 oersteds, a sigma value of 101 e.m.u./g., and a squareness characteristic of only 0.21.
• EXAMPLE 3 Cobalt oxalate crystals are prepared in accordance with Example I. Then 0.05 g. of silane, (sold under the trade designation Dow-Corning Z6020), is mixed with 0.95 g. of oxalate crystals prepared in accordance with Example 1 using a small quantity of tetrahydrofuran as a solvent for the silane to insure coating of the silane on the particles. Then the coated particles are air dried. Following this, the coated metal salt is charged into a glass tube in a tube furnace. The material is heated to 360C under an argon atmosphere for /2 hour. It is held at 360C under a hydrogen atmosphere for a period of 1 hour.
• silane sold under the trade designation Dow-Corning Z6020
• the product obtained had a coercivity of 810 oersteds, a sigma value of 72.5 e.m.u./g. and a squareness characteristic of 0.43.
• the powder was composed of acicular cobalt particles.
• EXAMPLE 4 A quantity of 2.0 grams of 2 l/2% epoxy-solution (5 g. of epoxy sold by Resyn Corporation under the name Resypox 1628, 0.75 g. of tetraethylenepentamine) in tetrahydrofuran is mixed with 0.95 g. of cobalt oxalate prepared in accordance with Example 1, and an additional quantity of 2.05 g. of tetrahydrofuran is added to insure complete coating of the oxalate particles. Then the coated material is air dried. The coated material is charged into a glass tube in a tube furnace, heated to 360C in an argon atmosphere for V; hour, and held at 360C in a hydrogen atmosphere for 1 hour.
• the dry product has a coercivity of 825 oersteds
• the powder is composed of essentially pure cobalt particles bearing little residual organic coating.
• EXAMPLE 5 A quantity of 2.0 g. of 2 /2 percent G.E. SE-33 silicone gumstock dissolved in tetrahydrofuran is mixed with 0.95 g. of cobalt oxalate salt prepared in accordance with Example 1 and with 2.0 grams of tetrahy drofuran to insure complete coating of the salt particles. The coated material is then air dried (mixed). Following this the coated salt particles are charged into a glass tube, placed in a tube furnace, and heated to 360C in an argon atmosphere for /2 hour. Then the material is held at this same temperature for 1 hour before being cooled to room temperature while still in the hydrogen atmosphere.
• the material is washed with acetone using a magnet to effect separation from each wash liquid, and air dried.
• the product obtained is a ferromagnetic metallic powder having a coercivity of 750 oersteds, a sigma value of 77 e.m.u./g. and squareness characteristic of 0.42.
• the powder is composed of acicular cobalt particles.
• EXAMPLE 6 A quantity of 238 g. of CoCl .6H O is dissolved in a container in 500 ml. of denatured alcohol and 500 ml. of water. Also 80 g. of sodium hydroxide is dissolved in a separate container in 500 ml. of water and 500 ml. of denatured alcohol. Then the solution is cooled to room temperature. Following this, the cobalt chloride and sodium hydroxide solutions are mixed together in a 4 liter beaker in a magnetic mixer for 5 minutes. During this period, a cobalt hydroxide precipitate forms in the beaker. In a separate beaker, g. of oxalic acid are dissolved in 750 ml.
• the oxalic acid solution is mixed into the cobalt hydroxide precipitate for 5 minutes to form a cobalt 0xalate precipitate.
• the precipitate is filtered in a Buchner funnel and the oxalate cake is washed with 2 liters of acetone. Then the oxalate is redispersed in 1 liter of acetone and then filtered.
• the acetone-wet cake is mixed with 75 grams of 10 percent solution of Estane 5702, a polyurethane-type rubber, manufactured by B. F. Goodrich & Co. in tetrohydrofuran. This mix is spread on a polyethylene sheet to air dry.
• Coated oxalate salt is then charged into an aluminum boat which is approximately 16 inches long and 2 /2 inches wide and 1.9 inches high.
• the interior of this boat is separated into four elongate compartments by three equally spaced and centered fins.
• the filled boat is placed in a sealed 2 /8 inch diameter stainless steel tube.
• the tube in turn is placed in a 3-inch diameter 24 inches long, tube furnace so that the filled aluminum boat is equally distant from each end of the furnace.
• Argon is fed through the stainless steel tube at a rate of 800 cc. per minute.
• heat is applied to the stainless steel tube and in 1 hour the contents of the boat reaches 360C. After 30 minutes, the atmosphere is changed to hydrogen, which is passed through the tube at a flow rate of 800 cc.
• the resulting product obtained is ferromagnetic metallic powder having a coercivity of 813 oersteds, a sigma value of 86 e.m.u./g. and a squareness characteristic of 0.46.
• the powder is non-pyrophoric and is composed of acicular cobalt particles having cobalt oxide coatings and exhibiting minimal interparticle sintering.
• EXAMPLE 7 A quantity of 100 g. of coated cobalt oxalate is prepared in accordance with Example 6 and charged into an aluminum boat.
• the boat is 16 inches long and 1.72 inches wide and 1.3 inches high and has two equally spaced lengthwise fins which divide the boat into three elongated compartments.
• the filled boat is charged into a sealed 2-inch diameter stainless steel tube.
• the tube is then placed in an aluminum muffle in a 3-inch diameter by 24-inch long tube furnace such that the filled aluminum boat is equally distant from each end of the furnace.
• Argon is then fed through the stainless steel tube at a rate of 400 cc. per minute. At the same time, heat is applied and the stainless steel tube is brought up to 380C.
• the gas is changed to hydrogen at a rate of 400 cc. per minute and temperature is maintained at 380C for 120 minutes.
• the stainless steel tube containing the filled aluminum boat is taken out of the furnace and cooled externally with ice and the contents allowed to reach room temperature in a hydrogen atmosphere.
• the reactor is purged with argon for 10 minutes at a rate of 400 cc. per minute.
• the contents in the boat are then transferred to a polyethylene bag with an argon atmosphere without allowing air to come into contact with the contents. After 4 days two holes are pierced in the bag so that the contents of the bag are exposed to oxygen only very gradually. After four more days the contents are removed from the bag.
• the product obtained is a ferromagnetic powder with a coercivity of 940 oersteds, a sigma value of 98 e.m.u./g. and a squareness characteristic of 0.45.
• the powder is composed of substantially acicular cobalt particles which carry oxide coatings so that they are stable.
• EXAMPLE 8 Coated oxalate crystals are prepared in accordance with Example 6 except that the acetone wet cake is mixed with 75 g. of epoxy solution (10 grams of epoxy sold by Resyn Corporation under the name Resypox 1628, 1.4 grams of tetraethylenepentamine, 90 grams of acetone). The mix is spread on a sheet of polyethylene and air dried and allowed to cure at room temperature. Following this, a quantity of 100 g. of pre-coated cobalt oxalate is charged into an aluminum boat and reduced in accordance with the procedure described in Example 7.
• the material obtained is a black ferromagnetic powder having a coercivity of 938 oersteds, a sigma value of l 13 e.m.u./g. and a squareness characteristic of 0.50.
• the powder is comprised of very small acicular cobalt particles with oxide coatings which render them stable.
• Cobalt oxalate crystals are prepared in accordance with Example 6 except that the acetone wet cobalt oxalate cake is divided into 22 forty-gram batches each batch containing 6.68 grams of cobalt oxalate. Each batch is then sealed in a 2-ounce bottle and is stored for use in subsequent work. Following this, 3.5 g. of an acetone solution containing l0 percent polyurethane sold under the trade designation Estane 5702 by B. F. Goodrich, is mixed with the contents of one bottle. The contents is then emptied from the bottle onto a poly ethylene sheet, spread out and air dried.
• the mix is then charged into a l-inch diameter glass tube in a tube furnace and heated to 360C in an argon atmosphere for 20 minutes.
• the material is held at this temperature in argon for 25 minutes and held for a further min utes at the same temperature in a hydrogen atmosphere.
• the mix is then cooled in the hydrogen atmosphere at room temperature and subjected to a 2- minute argon purge.
• the contents of the tube are then poured into an argon filled polyethylene bag and sealed. After 4 days, two holes are punched in the bag so that the oxygen gradually contacts the contents of the bag.
• the material removed from the bag is a ferromagnetic powder having a coercivity of 875 oersteds, a sigma value of 84 e.m.u./g. and a squareness characteristic of 0.415.
• the powder is composed of ferromagnetic acicular cobalt particles having oxide coatings which render them stable.
• EXAMPLE 10 A quantity of 1.75 grams of an acetone solution containing 10 percent polyurethane sold under the trade designation Estane 5702 by B. F. Goodrich Co., are mixed with the contents of another bottle of the oxalate in Example 9 and the resulting mix is spread out on a sheet of polyethylene and air dried. This dried mix is charged into a tube and heated as described in Example 9.
• the resultant product is a ferromagnetic powder having a coercivity of 625 oersteds, a sigma value of 92 e.m.u./g. and a squareness characteristic of 0.31. Again the powder is composed of very small stable acicular cobalt particles.
• EXAMPLE 1 l A quantity of 7 grams of the polyurethane solution described in Examples 9 and 10 is mixed with the contents of a third bottle of oxalate stored for use in Example 9. The mix is then spread on a sheet of polyethylene and air dried. Following this the material is reduced as described in Example 9. The product obtained is a ferromagnetic powder having a coercivity of 937 oersteds, a sigma value of 79 e.m.u./g. and a squareness characteristic of 0.46.
• EXAMPLE 12 The coated cobalt oxalate crystals are prepared in accordance with Example 9 except that the bottle contents are mixed with 3.5 grams of a 10 percent solution of Resypox 1574 solid epoxy sold by Resyn Corporation in acetone. The epoxy contains no curing agent. The resultant mix is spread on a sheet of polyethylene and air dried and reduced to produce a ferromagnetic powder as described in Example 9.
• the ferromagnetic powder obtained has a coercivity of 875 oersteds, a sigma value of 92 e.m.u./g. and a squareness characteristic of 0.40.
• EXAMPLE 13 A quantity of 3.5 grams of a solution containing percent Estane 5702 polyurethane and 0.5 percent of a silica sold under the trade designation HiSil 233 in acetone is mixed with the contents of another bottle of the material in Example 9. The mix is then spread on a sheet of polyethylene and air dried. Following this it is reduced as described in Example 9. The powder obtained has a coercivity of 500 oersteds, a sigma value of 97 e.m.u./g. and a squareness characteristic of 0.30.
• EXAMPLE 14 The material in another bottle of Example 9 is air dried and treated in accordance with that Example except that the cobalt oxalate salt particles are left uncoated.
• the product obtained is a powder composed of cobalt particles which are substantially sintered to gether.
• the material has a coercivity of 313 oersteds, a sigma value of 97 e.m.u./g. and a squareness charac teristic of 0.22.
• EXAMPLE 15 A quantity of 12.08 CoCl .6l-l O and 10.0 g. FeCl .4- H O is dissolved in 50 ml, denatured alcohol and 50 ml. of water in a container.
• sodium hydroxide is dissolved in 50 ml. alcohol and 50 ml. water in a second container.
• the two solutions are mixed together in a magnetic stirrer for 2 minutes at room temperature to form an ironcobalt hydroxide precipitate.
• a quantity of 13.5 g. of oxalic acid dissolved in 75 ml. denatured alcohol and 75 ml. water is mixed with the precipitate for 2 minutes.
• the resultant mixture is filtered in a Buchner funnel and washed several times with acetone and air dried. Following this, 1.0 g.
• Example 10 a 5 percent Estane 5702 polyurethane described in Example 10 and charged into a 1 inch diameter glass tube in a tube furnace and heated for 30 minutes at 360C in argon then it is held at 360C in hydrogen for g 90 minutes. Following this it is cooled to room temperature in hydrogen and then subjected to a 2 minutes argon purge.
• the resulting powder was composed of stable iron cobalt particles and had a coercivity of 750 oersteds, a sigma value of 90 e.m.u./g. and a squareness of 0.43.
• EXAMPLE 16 A quantity of 10 g. of sodium hydroxide is dissolved in water to form a 100 ml. of solution. Also 23.8 grams of cobalt chloride CoCl .6H O is dissolved separately in water to form a 100 ml. solution. The two aqueous solutions are then mixed together in a beaker in a magnetic mixer for 3 minutes forming a cobalt hydroxide precipitate. The precipitate is at room temperature. Then 150 ml. of l M oxalic acid is mixed into the cobalt hydroxide precipitate for 5 minutes at room temperature. The resultant product is a precipitate of cobalt oxalate salt which is then filtered in a Buchner funnel.
• the resultant product is composed of cobalt oxalate crystals with an average particle size of 3.0 micron in length and 1.0 micron in diameter. Following this the cobalt oxalate crystals are coated with 5percent epoxyhardener and reduced as described in Example 4.
• the resultant product is a ferromagnetic powder having a coercivity of 825 oersteds, a sigma value of 75.5 e.m- .u/g. and a squareness characteristic of 0.45.
• the powder is composed of substantially unsintered acicular stable particles composed of cobalt. The particles have an average particle size of 0.3 micron in diameter and 1.0 micron in length.
• EXAMPLE 17 A quantity of 238 g, sodium hydroxide is dissolved in a solution of 90 ml. denatured alcohol and 10 ml. water. Also 23.8 g. of cobalt chloride (CoCl .6H O) is dissolved in a second container with 90 ml. denatured alcohol and 10 ml. water. The contents of the two containers are mixed together in a magnetic mixer at room temperature for 5 minutes to form a cobalt hydroxide precipitate. Then 13.5 g. oxalic acid are dissolved in 135 ml. denatured alcohol and 15 ml. water are mixed with the cobalt hydroxide precipitate for 5 minutes at room temperature.
• the resultant mix is then filtered through a Buchner funnel, washed with acetone and air dried.
• the product obtained is a cobalt oxalate precipitate with the oxalate crystals having an average particle size of 0.1 micron in diameter and 1.0 micron in length.
• the cobalt oxalate crystals are then coated with a 10 percent epoxy solution-hardener and reduced as described in Example 8.
• the resultant product is a stable ferromagnetic powder composed of substantially unsintered cobalt metal particles having an average particle size of 0.035 micron in diameter and 0.35 micron in length.
• the powder has a coercivity of 750 oersteds, a sigma value of 29 e.m.u./g. and a squareness of 0.43.
• Solution B is then added slowly while mixing in the Waring Blender, and the resulting mixture is poured into a one quart steel jar containing 125 grams of A inch diameter steel balls. The jar is capped and then shaken for 1.5 hours on a Red Devil Paint Conditioner, Model No. 51 10. Then the mixture is separated from the steel balls by straining and weighing. For each 1.0 gram mix obtained, 0.47 gram of solution C was added under the action of the Waring Blender.
• the resulting mix is then coated onto 1.42 mil poly-. ethylene terephthalate film with a Bird Film Applicator and then passed over a 1,200 gauss bar magnet to achieve particle orientation.
• the film is dried for 5 minutes at room temperature and then 5 minutes at C.
• the coated film is then subjected to measurements in a Research Engineering and Development, Inc. B-H meter at 5,000 oersted applied field.
• the tape has a coercivity of l,000 oersteds, a squareness characteristic of 0.6, and a saturation magnetization (Ms) of 2300 gauss.
• the volume fraction of cobalt in the coating in 21 percent.
• Conventional iron oxide tape prepared in the same way and with the same volume fraction of HR-280 iron oxide has a coercivity of 250 oersted, a squareness of 0.66 and an Ms value of 1,025 gauss.
• a nickel-cobalt particle is formed using the procedure described below and the following quantities of reactants and solvents:
• NaOH solution lbs., 13 oz. in 72 lbs, 1002. of water.
• NiCl 6H O and CoCl solution 4 lbs., 8.502. of former salt and 10 lbs., 8.802. of latter salt in 66 lbs of water.
• Oxalic acid solution 10 lbs., 12 oz. of acid in 123 lbs.
• Resymide llsolution 100 grams Alcohol added to Resymide solution: 600 grams.
• An aqueous solution of COCI- is prepared.
• An aqueous solution of sodium hydroxide is poured into the cobalt chloride solution to form a precipitate of cobaltous hydroxide.
• a color change (to purple) is usually noted after the first 25 percent of the hydroxide solution has been added.
• an aqueous solution of oxalic acid is added to the cobaltous hydroxide slurry. This addition is carried out over about 90 seconds during which time the resulting slurry mixture of metal oxalate acquires a tannish-pink hue. After the addition, the slurry is mixed for about 8.5 more minutes before being filtered. The filtration is conveniently carried out in a pressure-filter having paper filter elements on four 18 inch diameter filter plates. The effective pore size of the paper is less than 1 micron.
• the acicular metal oxalate subjected to filtration does not require the use of a filter aid; that is, the metal oxalate has what would be termed in the paper industry a high freeness. It does not plug the filter and is sufficiently porous to facilitate a fast and effective separation of oxalate particles from the filtrate. It is thought that this characteristic is assignable to the acicular nature of the oxalate particles and a kind of bridging action which prevents a toodense packing of the filter cake.
• the resultant precipitate is washed twice with a mixture of 25 percent acetone in water. Thereupon, the precipitate is subjected to three more washings, each using acetone, and dried at about C, i.e., at about ambient temperature.
• the dried metal oxalate filter cake is placed in a 7 /2- gallon bowl of a food-type mixer. To this bowl is also charged an ethanol-based solution typically containing 100 grams of a commercially-available polyamide resin solution sold under the trade designation Resymid 14 l 125 by Resyn Corp. After a mixing period of about 4 minutes, the resulting slurry is spread out on stainless steel pans and dried with circulating air at about 30C. The dried material is passed with a Number 40 screen and loaded into seven aluminum reactor trays which are 2 /2 feet by 1 foot by /2 inch deep.
• the trays are placed in a reactor so the oxalate contents do not contact the atmosphere within the oven.
• the reactor is closed and fitted with connections to accommodate the flow of purge gas, and purged with nitrogen for two hours.
• the purge gas is changed from nitrogen to a mixture of 10 percent hydrogen and 90 percent nitrogen and the heators of the reactor are set at 722F.
• the temperature rises to the 720F 725F range over a period of about 3 hours. After this initial three-hour period, the material is heated within the 700 725F for an additional 3 hours.
• a considerable amount of CO continues to be evolved from decomposing oxalate.
• the oven door is opened and room temperature air is allowed to cool the reactor.
• the contents of the trays are still enclosed in the reactor and are under purge with the nitrogen/hydrogen mixture.
• the reactor is taken out of the oven and cooled by being packed in ice for about 30 minutes, then equilibrated in ambient air for another 30 minutes.
• the purge gas is now changed to a mixture of 3 percent oxygen and 97 percent nitrogen and this gas is used to slowly oxidize the surface of metal particles within the reactor for about 14 hours.
• the reactor After the 14 hour period of controlled surface oxidation, the reactor is opened to the atmosphere, but the material is usually given another 3 to 5 hours to equilibrate with the atmosphere before being packaged and sealed in polyethylene bags.
• the resultant material has the following magnetic properties:
• Cobalt powders produced by the process of Example 19 have oil absorption values of from about 0.50 cc. of linseed oil per gram of powder to 2.00 cc per gram of powder. The variation is primarily caused by the nature and quantity of polymer residue thereon. Such materials also have a surprisingly low apparent bulk density of about 0.15 grams per cubic centimeter.
• EXAMPLE 20 Although the most advantageous particles of the invention are prepared according to the use of oxalate particles formed according to the preferred double precipitation process, particles formed by other processes are also favorably influenced by use of a reduction procedure as used by this invention.
• EXAMPLE 2 This example is presented to show the utility of resin coating during the high temperature reduction of cobalt powders manufactured by other than theoptimum process.
• a cobalt material was prepared according to the procedure of Example 20.
• a sample of the resultant powder was mixed with a polyamide resin solution. This solution was prepared from 40 grams of a material sold under the trade designation Resymide l 125 by Resyn Corporation and 320 grams of the denatured alcohol. The 0.5 gram of solution was diluted with another gram of alcohol before the cobalt powder was mixed therein. After mixing, the wetted powder was spread out at air dry at about 30C.
• a dry powder-like composition consisting essentially of l acicular particles of metal oxalate crystals of at least an average 1.5:1 length-to-diameter ratio and (2) from 1 to 15v percent by weight of a polymeric resin intimately associated therewith, and forming a coating over said oxalate crystals.
• composition as defined in claim 1 wherein said organic material is solid thermally decomposable, polymeric resin which, on being heated to about 370C in a non-oxidizing atmosphere will decompose, forming a liquid in the course of its decomposition.
• composition as defined in claim 1 wherein said organic material is a polyamide polymer.
• composition as'defined in claim 1 wherein said oxalate contains nickel and iron as metal components thereof.
• a dry powder-like composition formed of a mass (1) acicular particles of a metal-containing thermally decomposable organic salt crystals, and (2) a polymeric coating over said crystals.
• composition as defined in claim 5 wherein said metal comprises at least about 60 percent of cobalt and at least about 15 percent nickel.

Landscapes

• Engineering & Computer Science (AREA)
• Metallurgy (AREA)
• Chemical & Material Sciences (AREA)
• Power Engineering (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Organic Chemistry (AREA)
• Paints Or Removers (AREA)
• Compositions Of Macromolecular Compounds (AREA)
• Hard Magnetic Materials (AREA)
• Magnetic Record Carriers (AREA)
• Manufacture Of Metal Powder And Suspensions Thereof (AREA)

Priority Applications (16)

Applications Claiming Priority (2)

Publications (1)

Family

ID=26825704

Family Applications (1)

Country Status (15)

Cited By (6)

Citations (6)

• 1972
  • 1972-02-22 US US228387A patent/US3892673A/en not_active Expired - Lifetime
  • 1972-03-17 IL IL39014A patent/IL39014A/en unknown
  • 1972-03-17 DE DE19722213131 patent/DE2213131A1/de not_active Withdrawn
  • 1972-03-22 IT IT67909/72A patent/IT954521B/it active
  • 1972-03-22 AT AT243672A patent/AT331052B/de not_active IP Right Cessation
  • 1972-03-23 FR FR7210228A patent/FR2130609B1/fr not_active Expired
  • 1972-03-23 CH CH434372A patent/CH566396A5/xx not_active IP Right Cessation
  • 1972-03-23 ES ES401098A patent/ES401098A1/es not_active Expired
  • 1972-03-23 CA CA137,973A patent/CA972190A/en not_active Expired
  • 1972-03-23 BE BE781111A patent/BE781111A/xx not_active IP Right Cessation
  • 1972-03-23 SE SE7203791A patent/SE388962B/xx unknown
  • 1972-03-24 JP JP47029693A patent/JPS5245660B1/ja active Pending
  • 1972-03-24 GB GB1407672A patent/GB1382724A/en not_active Expired
  • 1972-03-24 NL NL7203970A patent/NL7203970A/xx not_active Application Discontinuation
  • 1972-03-24 IE IE386/72A patent/IE36220B1/xx unknown

Patent Citations (6)

Also Published As

Similar Documents

Legal Events