US3198716A - Magnetic material and method of preparing the same - Google Patents

Magnetic material and method of preparing the same Download PDF

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Publication number
US3198716A
US3198716A US161033A US16103361A US3198716A US 3198716 A US3198716 A US 3198716A US 161033 A US161033 A US 161033A US 16103361 A US16103361 A US 16103361A US 3198716 A US3198716 A US 3198716A
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particles
electrolyte
iron
current density
ions
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US161033A
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Fred E Luborsky
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General Electric Co
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General Electric Co
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Priority to US161033A priority Critical patent/US3198716A/en
Priority to GB44992/62A priority patent/GB955058A/en
Priority to CH1449862A priority patent/CH417786A/de
Priority to DEG36677A priority patent/DE1181927B/de
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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
    • H01F1/01—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
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
    • C25C5/00—Electrolytic production, recovery or refining of metal powders or porous metal masses
    • C25C5/02—Electrolytic production, recovery or refining of metal powders or porous metal masses from solutions

Definitions

  • US. Patent 2,974,104 Paine et al., assigned to the same assignee as the present invention, discloses magnetic materials composed of elongated, single domain particles, exhibitin very hi h energy products. These magnetic materials are prepared by electrolytically depositing, at a constant optimum current density, particles of iron or iron-cobalt alloys into a liquid metal cathode, such as mercury, under quiescent interface conditions between the liquid cathode and the electrolyte.
  • a liquid metal cathode such as mercury
  • Such magnetic materials have been found to have a wide distribution of particle structures, a characteristic which results in a decrease in the magnetic quality of the assembly of particles.
  • To produce magnetic material of the greatest possible total magnetic energy it would be desirable to produce particles of the optimum shape and, consequently, particles whose structures or shapes are as nearly uniform as possible.
  • the present invention involves the disco ery that particles of substantially uniform structure may be produced it, during at least a portion of the electrodeposition cycle of the fine particles, the cathode current density is progressively lowered to maintain a substitially constant maximum coercive force in the electrodeposited particles.
  • the current c sity By so lowering the current c sity, it has been found that particles of nearly cont structure and of significantly improved magnetic properties are obtained.
  • a purified electrolyte is used in the foregoing electrodeposition procedure.
  • a purified electrolyte is meant an electrolyte specially treated to remove organic impuritie in a manner more fully set out hereinafter.
  • FEGURE 1 shows the intrinsic coercive force values of particles electrodeposited at constant current as a functioncn of current density and time
  • FEGURE 3 illustrates graphically two schedules for progressively lowering the current density to maintain Bdhdfllfi Patented Aug. 3, 1965 ICC a nearly constant coercive force and packing fraction in the eiectrodeposited particles.
  • the invention is based upon the following considerations.
  • the iron atoms condense into particles in a closely packed ordered array at the interface between the liquid cathode and the electrolyte.
  • a gradual change in the particle shape takes place as deposition proceeds.
  • This variation in particle shape is believed to be due to gradual changes in the environment of the growing particle or fiber as the electrodeposition proceeds. This results in part from an increase in the thickness of the mass of particles formed by the elongated iron fibers.
  • the increasing mass of particles near the surface of the mercury reduces the rate of flow of mercury to the surface where the fibers are growin Concurrently, the greater mass of iron particles tends to push upward toward the interface because of its greater buoyancy as compared with mercury.
  • the rate of iron deposition is dependent on the current density, and if this current density is kept constant in the face of the changing environment at the point of electrodeposition, the fiber structures will not grow uniformly.
  • the present invention compensates for this changing environment by progressively lowering the current density and hence the rate of iron deposition.
  • the gel contains only elongated fibers while under the gel in the r'luid mercury phase some essentially spherical particles are normally present.
  • the better quality elongated particles in gel form may then be relatively easily separated and removed from the poorer quality spherical particles.
  • a further advantage of the progressive decrease of the current density is a resulting increase of two to three-fold in the production rate of the fine particles.
  • to make a magnet having a total energy product of 6.0 million gauss-oersted from deposition at constant current requires deposition at 0.005 amp/cm. for 500 minutes or 0.0025 amp/cm. for 1000 minutes, or equivalent combinations, resulting in 0.05 gram of iron per cm. of mercur surface in 1000 minutes.
  • the same or better quality material has been made by starting deposition at 0.01 amp/cm. for 120 minutes and then progressively dropping the current density of 0.005 amp/cm. for 360 minutes. This produced about 0.065 gram of iron per cm. of mercury in only 480 minutes. This corresponds to a three-fold increase in yield per unit time.
  • FIGURE 1 plots the contour lines of constant intrinsic coercive force (H in oersteds of iron particles deposited at constant current with a charcoal-treated electrolyte.
  • the intrinsic coercive force values of the iron particles were measured at -196 C. in their dilute state after optimum aging and tin treatment. It'can be seen from FIGURE 1 that at a given constant current the coercive force of the deposited particles progressively changes during the electrodeposition procedure.
  • FIGURE 2 corresponds to FIGURE 1 except that the contour lines are those of constant packing fraction (P.F.) in percent rather than coercive force.
  • the contour lines of FIGURE 2 represent the packing fraction of iron particles in the gel phase deposited from a charcoaltreated electrolyte. It can be seen that as deposition continues at constant current, the packing fraction increases. It can also be seen from FIGURES l and 2 that the slope of the contour lines of constant coercive force and the slopes of the contour lines of constant packing fraction are approximately the same.
  • the rate at which the cathode current density should be progressively lowered to achieve optimum structural uniformity and magnetic properties can be determined by following along the slope of the best magnetic properties,
  • the slope for intrinsic coercive force will be about the same as that of total magnetic energy but the former is more conveniently measured and hence is used herein to determine the schedule for lowering the current density. This slope will correspond to the constant coercive force contour line (see FIGURE 1) having the highest value.
  • the density or packing fraction of the solid gel formed with the use of a purified electrolyte is maintained constant during electrodeposition, it has been found that structurally uniform particles are obtained.
  • the packing fraction is a measure of the volume density of the particles and specifically, the volume of electrodeposited particles per total volume of a given sample.
  • a proper schedule for lowering of the current density may be relatively easily determined by following that contour line of constant packing frac tion (FIGURE 2) corresponding to the best magnetic properties.
  • FIGURE 3 illustrates a program or schedule for progressively lowering the current density by following a constant maximum coercive force contour line (FIGURE 1) during electrodeposition of iron and iron cobalt, respectively.
  • FIGURE 1 illustrates a program or schedule for progressively lowering the current density by following a constant maximum coercive force contour line (FIGURE 1) during electrodeposition of iron and iron cobalt, respectively.
  • FIGURE 3 illustrates a program or schedule for progressively lowering the current density by following a constant maximum coercive force contour line (FIGURE 1) during electrodeposition of iron and iron cobalt, respectively.
  • the electrodeposition procedure of the present invention may be carried out in the same manner set fourth in the above Paine et al. Patent 2,974,104 except that the current density is progressively lowered during electrodeposition to maintain a constant particle structure.
  • the process comprises electrolytically depositing ferromagnetic particles into a liquid metal cathode, preferably mercury, from an acidic electrolyte comprising ions of the ferromagnetic material while maintaining a quiescent interface between the cathode and the electrolyte.
  • the electrolyte or plating solution consists of the soluble salts of the ferromagnetic metals in the form of, for example, sulfates or chlorides.
  • the pH of the electrolyte is made acidic with, for example, sulfuric or hydrochloric acid, a preferred pH being about two.
  • a consumable anode is used of either the pure ferromagnetic metal or alloys of several ferromagnetic metals.
  • a non-consumable anode of an inert material such as platinum or graphite, may also be used.
  • a current density between 0.001 amp/cm. and 0.1 amp/cm. may be used although values around 0.01 amp/cm. are preferred.
  • the electrolyte will be at room temperature of 20-30 C. during the electrodeposition although other electrolyte temperatures may be used if suitable adjustments are made in current density and time of deposition.
  • the electrodeposited particles are removed as a mercury slurry. If the electrolyte has been treated so as to inhibit hydrogen evolution, the electrodeposited particles in the gel only are removed to obtain the best and most uniform particles.
  • the particles are then heat-treated, to optimize their physical shape and produce maximum coercive force, for from 5-20 minutes at temperatures up to 300 C. and preferably at about 150-200 C. and then cooled.
  • the fine particles may be coated with, for example, tin or antimony, the latter in accordance with US. Patent 2,999,778, assigned to the same assignee as the present invention.
  • Lead, as a matrix is then added in elemental form as chunks or pellets of lead as set forth in US.
  • Patent 2,999,777 assigned to the same as signee as the present invention.
  • the particles are then aligned and compressed and the remaining mercury removed as, for example, by vacuum distillation at an elevated temperature.
  • the mercury-free mixture of aligned particles and matrix is then ground into a powder and may be either hot or cold pressed and realigned into their final magnet structure.
  • the particles, subsequent to the coating step with tin or antimony, may be aligned in a mold by a magnetic field and compressed to any desired packing fraction.
  • the resulting magnets are suitable for evaluation of their magnetic properties but contain from 20 to percent mercury.
  • EXAMPLE 1 Iron particles were deposited using an electrolyte of approximately 2 molal FeSO in distilled water. The electrolyte was treated with roughly an equal volume of activated cocoanut charcoal (614 mesh) overnight, filtered into a circulating system containing a pump, a cotton filter cylinder, additional activated cocoanut charcoal, a temperature controller and the deposition cell. The pH was adjusted to 2.13. The cell was assembled on a shock mounted platform using an iron anode and a stainless steel screen, with Aa" openings, beneath the mercury pool. After some preliminary deposition to remove depositable impurities, deposition into fresh mercury was then performed fol-lowing the current density-time schedule depicted in FIGURE 3.
  • the particular current density variation with time was chosen so as to approximate the deposition of the best particles at all times as indicated by the property contour lines shown in FIGURE 1 and corresponding to uniform packing density lines as shown in FIGURE 2.
  • the electrolyte was slowly circulated at the rate of 0.15 liter/min. and maintained at 25 C. +-2 C.
  • the gel structure was then removed as a single unit by lifting it out on the screen.
  • a suitable portion was then aged for 20 minutes at 170 0, treated with excess saturated tin-mercury amalgam, placed into a mold, aligned and compressed to 50,000 pounds per square inch.
  • Table I compares the room temperature properties (collumn 3) of magnets prepared as set forth in Example 1 with the corresponding properties (columns 1 and 2) of the best iron particle magnets prepared by elec-trodeposition at 25 C. at constant current with untreated and charcoal-treated electrolyte.
  • 4 BJB is the ratio of residual to saturation induction.
  • EXAMPLE 2 Iron-cobalt alloy particles were deposited using the procedures set forth in Example 1 for pure iron particles, except that the electrolyte had a pH of 1.8 and contained 15.45 percent Co++ by weight as determined by chemical analysis.
  • the anode was an alloy of 37.5 percent Co62.5 percent Fe and the particles deposited contained 37.7 percent Ctr-62.3 percent Fe by weight.
  • the sample was aged at 200 C. for 40 minutes, tin-treated as before and then further aged at 180 C. for 20 minutes.
  • the sample was aged at 200 C. for 40 minutes, tin-treated as before and then further aged at 180 C. for 20 minutes. The
  • Table ll below summaries the room temperature properties (column 3) of magnets prepa ed in accordance with Example 2 and compares these properties with the properties (columns 1 and 2) of the best iron-cobalt particles prepared at constant current with untreated and with charcoal-treated electrolyte.
  • This invention is particularly useful in the electrodeposition of particles of iron or iron-cobalt alloys.
  • other known ferromagnetic materials including iron, cobalt, nickel and alloys of iron, cobalt and nickel with each other or with other ferromagnetic alloying constituents or with minor amounts of non-ferromagnetic constituents such as manganese or platinum.
  • Magnetic material comprising elongated, single domain particles selected from the class consisting of iron, cobalt, nickel and alloys of iron, cobalt and nickel, produced in accordance with the process of claim 1.
  • a process of preparing fine particle magnetic material comprising electrolytically depositing fine particles in the form of a gel into a liquid metal cathode during an electrodeposition cycle sutliciently long to produce elongated single-dornain magnetic particles from a purified electrolyte comprising ions selected from the class consisting of iron ions, cobalt ions, nickel ions and combinations thereof, while maintaining a quiescent interface between said cathode and said electrolyte,
  • the cathode current density during a major portion of said electrodeposition cycle being progressively lowered within the range from a maximum of 5 amps./ cm.2 to a minimum of 0.001 amp/cm. to maintain a substantially constant maximum coercive force in the electrodeposited particles.
  • a process of preparing fine particle magnetic material comprising electrolytically depositing fine particles in the form of a gel into a liquid metal cathode during an electrodeposition cycle surliciently long to produce elongated single-dornain magnetic particles from a purified electrolyte comprising ions selected from the class consisting of iron ions, cobalt ions, nickel ions and combinations thereof, while maintaining a quiescent interface between said cathode and said electrolyte,
  • the cathode current density during a major portion of said electrolytic deposition being progressively lowered within the range from a maximum of 5 amps./ cm? to a minimum of 0.001 amp/cm. to maintain a substantially constant packing fraction in the gel of fine particles, said packing fraction corresponding to that producing the highest magnetic propertiles.
  • a process of pre aring tine particle magnetic material comprising electrolytically depositing fine particles into a liquid metal cathode during an electrodeposition cycle sufficiently long to produce elongated single-domain magnetic particles from a purified electrolyte comprising ions selected from the class consisting of iron ions, cobalt ions, nickel ions, and combinations thereof, while maintaining 21 quiescent interface between said cathode and said electrolyte, to form a gel phase of electrodeposited elongated particles and a fluid phase comprising electrodeposited essentially spherical particles,
  • the cathode current density during a major portion of said electrolytic deposition being progressively low- 7 8 el'ed within the range from a maximum of 5 amps./ FOREIGN PATENTS cm. to a minimum of 0.001 arnpjcm. to maintain 803 844 11/53 Gmat Germany a substantially constant maximum coercive force in l the electrodeposited paflicles and recovering the gel OTHER REFERENCES Phase y o e trodeposited elongated pariicles. 5 Thompson, Electrochemistry, MacMillan Co., 1925,

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Power Engineering (AREA)
  • Electroplating And Plating Baths Therefor (AREA)
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US161033A 1961-12-21 1961-12-21 Magnetic material and method of preparing the same Expired - Lifetime US3198716A (en)

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Application Number Priority Date Filing Date Title
US161033A US3198716A (en) 1961-12-21 1961-12-21 Magnetic material and method of preparing the same
GB44992/62A GB955058A (en) 1961-12-21 1962-11-28 Improvements in magnetic material
CH1449862A CH417786A (de) 1961-12-21 1962-12-11 Verfahren zur Herstellung von feinen Teilchen aus magnetischem Material
DEG36677A DE1181927B (de) 1961-12-21 1962-12-19 Verfahren zur Herstellung von magnetischen Einbereichsteilchen

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CH (1) CH417786A (de)
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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3525677A (en) * 1969-03-24 1970-08-25 Ncr Co Electrodeposition of constant-composition thin films

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB803844A (en) * 1956-02-08 1958-11-05 Electro Chimie Metal Improvements in or relating to the electrolytic production of iron powder
US2974104A (en) * 1955-04-08 1961-03-07 Gen Electric High-energy magnetic material
US3100167A (en) * 1960-10-19 1963-08-06 Gen Electric Magnetic material

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2974104A (en) * 1955-04-08 1961-03-07 Gen Electric High-energy magnetic material
GB803844A (en) * 1956-02-08 1958-11-05 Electro Chimie Metal Improvements in or relating to the electrolytic production of iron powder
US3100167A (en) * 1960-10-19 1963-08-06 Gen Electric Magnetic material

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3525677A (en) * 1969-03-24 1970-08-25 Ncr Co Electrodeposition of constant-composition thin films

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CH417786A (de) 1966-07-31
DE1181927B (de) 1964-11-19
GB955058A (en) 1964-04-08

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