US3533949A - Heat treating method for obtaining a ferrite with a high muq product - Google Patents

Heat treating method for obtaining a ferrite with a high muq product Download PDF

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Publication number
US3533949A
US3533949A US684628A US3533949DA US3533949A US 3533949 A US3533949 A US 3533949A US 684628 A US684628 A US 684628A US 3533949D A US3533949D A US 3533949DA US 3533949 A US3533949 A US 3533949A
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product
temperature
ferrite
cooling
oxygen
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US684628A
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Paul I Slick
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AT&T Corp
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Bell Telephone Laboratories Inc
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    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/01—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics
    • C04B35/26—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on ferrites
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/01—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics
    • C04B35/26—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on ferrites
    • C04B35/265—Compositions containing one or more ferrites of the group comprising manganese or zinc and one or more ferrites of the group comprising nickel, copper or cobalt

Definitions

  • precooling comprising either rapid cooling or cooling in an oxygen-poor atmosphere to a temperature above the Curie point and thereafter slowly cooling to room temperautre in an oxygen-rich atmosphere.
  • the resulting product is useful as a core material in inductors at high frequency.
  • This invention relates to a method for heat treatment of a ferrite which results in a high pQ value and for inductors containing the ferrite as a core material, to the resulting material.
  • L is the series inductance of the coil with its intended magnetic core
  • 7 is the frequency of the exciting magnetic field
  • R is the effective series resistance arising from core loss in the material.
  • the value of the permeability ,u. is also important in core materials since it determines the magnitude of inductance. Thus, a high uQ product is generally recognized as a desirable property of core material.
  • Certain nickel zinc cobalt ferrites have been found to have acceptable permeability and high quality factors at frequences up to 1.5 megahertz. Due to these high quality factors, nickel zinc cobalt ferrites are likely candidates for use as core materials in inductors at higher frequencies, that is, within the range of 1.5 to 20 megahertz. It is generally recogv hour is described in Pat. 3,242,089, issued to Bartow and Head on Mar. 22, 1966. This was done in order to be able to vary ,u and Q after the inductors cores had already been fired and ground to size.
  • the present invention significantly improves the ,uQ products over the prior art for certain nickel zinc cobalt ferrites, by means of a novel heat treatment method, enabling their use at frequencies within the range of 1.5 to 20 megahertz.
  • the method is a heat treatment following firing consisting of the following steps: Precooling, comprising either rapid cooling in any atmosphere or cooling in an oxygen-poor atmosphere containing from .7 to 10% oxygen, remainder nitrogen or any substantially inert nonreactive gas, down to a temperature above the Curie point, and within the range of from 475 C. to 700 C.; followed immediately by the optional step of quenching to a temperature below 300 C.; followed by annealing in air or other oxygen-bearing atmosphere containing at least 18% oxygen, from a temperature of from 475 C. to 700 C. at a cooling rate of up to C. per hour.
  • This mixing is usually carried out by forming a slurry with water in a ball mill. This step can also serve to reduce the powdered materials to the desired grain size.
  • the material is then dried, and calcined at a temperature of from 800 C. to 1100 C. for from 2 to 16 hours.
  • Ball milling is again carried out after the calcining step in order to break up the agglomerations formed during calcining and in order to further insure a completely homogeneous mixture. This is usually done for a period of from 5 to hours, in a carrier such as water, acetone, ethanol, or carbon tetrachloride.
  • a binder is added during ball milling.
  • conventional binders include polyvinyl alcohol or hydrogenated castor oil for a water carrier and paraffin (chlorinated naphthalene) for organic carriers. If polyvinyl alcohol is used as a binder, it is preferred to add it to the slurry after ball milling is completed, however, because of its tendency to cause foaming of the slurry during ball milling. A deflocculating agent such as gum arabic will tend to counteract such foaming of the slurry, but will not prevent it entirely. Pressing aids such as zinc stearate emulsion and zinc stearate powder may also be added after calcining, the emulsion being added to the slurry, and the powder being added to the subsequently dried material.
  • a zinc stearate emulsion is added in the amount of from .5 to by weight of the calcined powder and zinc stearate powder is added in the amount of from .1 to .5 by Weight of the calcined powder.
  • a deflocculant such as gum arabic, is desirable, and is usually present in the amount of from .5 to 2.0% by weight of the calcined powder.
  • Both the emulsion and the powder are desired additions, since they are generally known to perform different functions as pressing aids due to their different physical forms.
  • Drying the slurry to powder is the next step. Spray drying is preferred because it is thought to improve flowability of powder being pressed into green bodies.
  • the material is next shaped into the desired configuration under a pressure of from 3 to tons per square inch, to a size which allows for subsequent shrinkage during firing.
  • the material in this state is ready for firing. It is fired at a temperature between 1100 C. and 1250 C., above which temperature range the volatilization of zinc becomes appreciable, and below which the time required for densification becomes excessive.
  • the final [LQ product is substantially independent of firing atmosphere and firing time within the range of 3 to 12 hours. Each of the remaining steps is critical to obtaining a high 3 product.
  • the first of these steps has as its object a minimization of oxygen contact with the surface of the ferrite, and may be carried out either by rapid cooling or cooling in an oxygen-poor atmosphere.
  • Precooling is carried out from the firing temperature to a temperature above the Curie point, within the range of 475 C. to 700 C.
  • the Curie temperature is defined as the temperature above which the spontaneous magnetization M vanishes fairly suddenly. While the Curie temperature will never fall below 450 C. for the range of compositions specified, it may become higher than 450 C. For example, as the amounts of iron and nickel are increased, the Curie temperature will increase to as high as 585 C. However, as the amount of zinc is increased, the Curie temperature Will decrease, but not below 450 C. for the zinc contents given above. Cobalt additions, being small, have a negligible effect on the Curie temperature.
  • Cooling to a temperature above 700 C. necessitates the introduction of the next step above this temperature, which results in a detrimental effect on the final ,uQ product.
  • Rapid cooling may be at a rate of from 400 C. per hour to 2000 C. per hour, below which the minimization of oxygen contact with the surface of the ferrite is insufiicient for obtaining an optimum ,uQ product and above which cracking of the fired ferrite body becomes a problem.
  • the rate of cooling may vary from 30 C. per hour to 400 C. per hour and the oxygen content from .7 to 10% oxygen in an atmosphere whose remainder is nitrogen or other substantially inert nonoxidizing atmosphere. The smaller amount of oxygen corresponds to the slower cooling rate and the larger amount of oxygen corresponds to the faster cooling rate.
  • the second step which is critical to the obtaining of an optimum ,uQ product is low cooling or annealing in an atmosphere containing at least 18% oxygen from a tem perature above the Curie point within the range of 475 C. to 700 C.
  • the cooling rate has no lower limit.
  • the uQ product increases exponentially as the cooling rate decreases.
  • the cooling rates above 30 C. per hour produce [.LQ products below 20,000 at a frequency of 15 megahertz and cooling rates above C. per hour produce a negligible improvement in ,uQ product over rapid cooling.
  • the parts are extracted from the furnace at any temperature below 250 C.
  • EXAMPLE 1 Powdered zinc oxide, ZnO, cobalt carbonate, CoCO nickel carbonate, NiCO and iron oxide, Fe O were combined so that the atom percent of the metals in the final fired material, including an allowance for about 1% The materials were combined with an equivalent weight of distilled water, and the mixture transferred to a steel ball mill and milled for one hour. A piece of hardened filter paper was wetter and placed in a funnel. It was filtered to a solid cake. The cake was dried at 120 C. for 12 hours, pulverized, and calcined at 900 C. for 16 hours in air. To this material was then added 056% by weight of starting materials of calcium oxide, 1.0% of gum arabic and 60.0% of distilled water.
  • the resultant mixture was ball-milled for 7 /2 hours.
  • a zinc stearate emulsion was added in the amount of 1.5%, and the mixture was milled for an additional one-half hour.
  • To the resulting slurry was added 1% by weight of polyvinyl alcohol (20% solution) and the combination was rn'nred for 15 minutes.
  • the material was then spray-dried and blended by means of granulation with .25% by weight of zinc stearate powder so that the resulting mixture passed an 80-mesh screen but was held by a 325-mesh screen.
  • the powder was pressed at about 15 tons per square inch to a green density of about 2.8 grams per cubic centimeter. It was then fired according to the following schedule.
  • EXAMPLE 2 The same procedure as in Example 1 was carried out except that the annealing rate was 30 C. per hour.
  • a method for obtaining a nickel zinc cobalt ferrite having a high ,uQ product comprising the steps of: (1) slurrying with water, drying and calcining a mixture comprising components having a cation content equivalent to 72 to 82 atom per-cent iron, 10 to 27 atom percent nickel, 1 to 13 atom percent zinc and .4 to 1.2 atom percent cobalt; (2) shaping the resultant material under pressure into the desired configuration; and (3) firing the shaped material at a temperature of from 1100 C. to 0 C.; characterized in that firing is followed immediately by; (4) precooling to a temperature of from 475 C. to 700 C., said precooling consisting of rapid cooling in any atmosphere at a rate of from 400 C.
  • annealing which consists of slowly cooling the material from a temperature of from 475 C. to 700 C. at a rate of up to 100 C. per hour in an atmosphere containing at least 18% oxygen, remainder substantially gases which are nonreactive with respect to the surface of the ferrite.
  • precooling is followed immediately by quenching to a temperature below 400 C. at a cooling rate of from 400 C. per hour to 2000 C. per hour, followed by machining of the ferrite material, followed by annealing.

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Ceramic Engineering (AREA)
  • Manufacturing & Machinery (AREA)
  • Materials Engineering (AREA)
  • Structural Engineering (AREA)
  • Organic Chemistry (AREA)
  • Soft Magnetic Materials (AREA)
  • Magnetic Ceramics (AREA)
US684628A 1967-11-21 1967-11-21 Heat treating method for obtaining a ferrite with a high muq product Expired - Lifetime US3533949A (en)

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US68462867A 1967-11-21 1967-11-21

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US (1) US3533949A (enrdf_load_stackoverflow)
BE (1) BE722747A (enrdf_load_stackoverflow)
DE (1) DE1809811B2 (enrdf_load_stackoverflow)
FR (1) FR1603507A (enrdf_load_stackoverflow)
GB (1) GB1251988A (enrdf_load_stackoverflow)
NL (1) NL148580B (enrdf_load_stackoverflow)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2260539A (en) * 1991-09-11 1993-04-21 American Res Corp Virginia Ferrimagnetic core materials for megahertz frequency high flux density transformers and inductors

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2989472A (en) * 1955-10-20 1961-06-20 Steatit Magnesia Ag Ferrite with constricted magnetic hysteresis loop
US3242089A (en) * 1962-08-20 1966-03-22 Western Electric Co Heat-treating method for modifying permeability and quality factor of nickel-zinc-cobalt ferrite

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2989472A (en) * 1955-10-20 1961-06-20 Steatit Magnesia Ag Ferrite with constricted magnetic hysteresis loop
US3242089A (en) * 1962-08-20 1966-03-22 Western Electric Co Heat-treating method for modifying permeability and quality factor of nickel-zinc-cobalt ferrite

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2260539A (en) * 1991-09-11 1993-04-21 American Res Corp Virginia Ferrimagnetic core materials for megahertz frequency high flux density transformers and inductors
US5626789A (en) * 1991-09-11 1997-05-06 American Research Corp. Of Virginia Ferrimagnetic core materials for megahertz frequency high flux density transformers and inductors
US6433299B1 (en) 1991-09-11 2002-08-13 American Research Corporation Of Virginia Monolithic magnetic modules for integrated planar magnetic circuitry and process for manufacturing same

Also Published As

Publication number Publication date
DE1809811A1 (de) 1969-10-09
NL6816316A (enrdf_load_stackoverflow) 1969-05-23
DE1809811B2 (de) 1971-04-29
FR1603507A (enrdf_load_stackoverflow) 1971-05-03
BE722747A (enrdf_load_stackoverflow) 1969-04-01
GB1251988A (enrdf_load_stackoverflow) 1971-11-03
NL148580B (nl) 1976-02-16

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