US2989473A - Ferrite with constricted magnetic hysteresis loop - Google Patents

Ferrite with constricted magnetic hysteresis loop Download PDF

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US2989473A
US2989473A US616817A US61681756A US2989473A US 2989473 A US2989473 A US 2989473A US 616817 A US616817 A US 616817A US 61681756 A US61681756 A US 61681756A US 2989473 A US2989473 A US 2989473A
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oxide
ferrite
hysteresis loop
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constricted
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Eckert Oskar
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Steatit Magnesia AG
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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
    • 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

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  • Ferromagnetic metals with constricted hysteresis loops have, as is well known, at small field strength within the constriction area, constant permeability, i.e., permeability independent of the field strength equal to the initial permeability, very low hysteresis losses and, in general, small residual losses.
  • constant permeability i.e., permeability independent of the field strength equal to the initial permeability
  • very low hysteresis losses very low hysteresis losses and, in general, small residual losses.
  • such materials may be subjected to thermo-magnetic treatment.
  • thermomagnetic treatment in this connection, is meant the passing thru a thermic cycle during the simultaneous presence of a magnetic longitudinal or transverse field.
  • the concept of longitudinal or transverse field is, in this connection, to be understood as relative to the later measuring field; a longitudinal or transverse field, respectively, means that such field, during the thermomagnetic treatment, is parallel, respectively vertical, to the later measuring field.
  • these ferromagnetic materials display a substantial alteration of the form of the hysteresis loop, and hence a change of the magnetic properties.
  • This invention is based on the discovery that it is possible to make specific ferrites showing a constricted magnetic hysteresis loop which are, consequently, capable of thermomagnetic treatment similarly as for metals.
  • the invention teaches the production of such ferrites of the nickel-cadmium and manganese-cadmium ferritesystems which can be subjected to thermomag-netic treatment of the above type, and are distinguished from hitherto familiar ferrites by the fact that, under the same manufacturing conditions, they have constricted hysteresis loops.
  • ferrites with this characteristic in the nickel-cadmium and manganesecadmium ferrite systems must have a composition of at least 50 mol percent Fe 0 and a small addition of cobalt oxide.
  • the addition of cobalt oxide is suitably determined between 0.1 and 5% by weight, calculated on the total basic batch of the nickel-cadmium and manganese-cadmium ferrites expressed in metallic oxides.
  • the invention has shown that it is particularly advantageous to choose the cobalt oxide content between 0.35 and 1.5% by weight, calculated on the basic batch.
  • the nickel-cadmium and manganese-cadmium ferrites in question which react strongly to the addition of cobalt oxide with a constricted loop, cover, in the three-component system Fe O -NiO-CdO or Fe O Mn 0 --CdO, the area defined in FIGS. 3 and 4 of the drawing by the pentagonal points A, B, C, D, E, or the four points A, B, C, D, respectively.
  • the compositions at the corners in percent by weight are: pentagonal points A, B, C, D, E, or the four points A, B, C, D, respectively.
  • the compositions at the corners in percent by weight are:
  • the above ferrites may be prepared in the usual way, either by joint or partial precipitation, from corresponding metal salt solutions, or, as is customary in ceramic arts, they may be prepared for further processing by wet milling and mixing of the respective metal oxides.
  • the powdered mixtures thus obtained may, after drying, be given the desired form either immediately by dry pressing, extruding, or similar methods, or it may be desirable, before ceramic forming, to proceed with a calcining firing of the entire mass or only a part thereof, preferably between 750 and 1150" C. for the system Fe O -NiO CdO or 750 to 1200 C. for the system Fe2O -Mn O CdO.
  • the formed parts of both of these systems are sintered, depending on the compositions, at temperatures between 1250 C. and 1380 C.
  • the cooling speed is dependent upon the volume of the fired body. As a criterion, it may be stated that for a ring of about 46mm. outside diameter, 34 mm. inside diameter, and 1 0 mm.
  • the cooling time from 700 C. to room temperature should take not less than 12 hours. If the rings are cooled rapidly, the eifeot of loop constriction does not occur. However, the constriction may be regained even for rings cooled too rapidly, by re-heating them to a temperature of about 700 C., and cooling them slowly, as above described.
  • the further ceramic procedure is the same for both systems and in both processes consists in that after 6 hours of grinding, the slip is poured through a 4900 mesh screen (4900.meshes per square cm.) into a porcelain dish, and :dried.
  • the powder thus obtained is pressed, according to ceramic pressing techniques, into rings having dimensions of 59 mm. outside diameter, 35.8 mm. inside diameter, and 12 mm. height, the amount of pressure applied being about 500 to 1000 kg./cm.
  • the NiCd or MnCd ferrite pieces, thus obtained, are sintered in a kiln at 1320 C. for one hour, whereupon the heat is shut 0E.
  • the rings are cooled to room temperature in the kiln during a period of approximately 24 hours.
  • the ferrite rings thus obtained are provided with 0.4 mm. copper enameled wire with windings as primary winding, and, as secondary winding, further 200 windings with 0.2 mm. copper enameled wire are applied.
  • FIGS. 1a and 1b oscillographic photograph of this ferrite, produced in accordance with the invention, is shown in FIGS. 1a and 1b; one can distinctly recognize the loop constriction of the hysteresis loop.
  • the ferrite toroid as prepared in either of the examples, with 100 windings as a primary winding, is placed in a kiln. While heating to 600 C., and slow cooling for 12 hours to room temperature, a longitudinal magnetic field is maintained by means of the ring winding by 1 a. direct current, corresponding to a magnetic field strength of about 15 a.-windings/cm. If the hysteresis loop of the ferrite after this thermomagnetic treatment is recorded in the same manner as described above, the result is analogous to that of metal when they are subjected to heat treatment in the longitudinal magnetic field; a complete change of the form of the hysteresis loop takes place, as may be seen in FIGS. 2a and 2b respectively.
  • heat treatment in the transverse magnetic field may be carried out with corresponding effect (see the above cited book by Bozorth).
  • ferrites with distinctly rectangular hysteresis loop may be produced which are of importance to the entire fields of electronics and for magnetic amplification for telephone and high-frequency fields;
  • ferrites with thermic cross magnetization ferrites of high quality and a permeability independent of field strength may be produced, which are particularly suitable for the field of telecommunication.
  • a fired ferrite body as claimed in claim 1 characterized in that the cobalt oxide content is between 0.35 and 1.5% by weight of said composition.
  • a fired ferrite body as claimed in claim 2 in which the ferrite is of the iron oxide, nickel oxide, cadmium oxide system and in which the proportions of said components come within area ABC 'D-E of FIG. 3 of the drawing, the corners of this area defining the following compositions:
  • a process of making a ferrite body with a constricted hysteresis loop comprising providing a milled powder mixture consisting essentially of cadmium oxide, iron oxide, 0.1 to 5% by weight of cobalt oxide and an additional metal oxide selected from the group consisting of nickel oxide and manganese oxide, the iron oxide content being from about 72.5% to 89% by weight and over 50 mol percent of the metal oxides of the system, forming the powder mixture to the shape desired, sintering the shaped product at about 1250 C. to about 1380 C. and thereafter slowly cooling the sintered product from about 700 C. down to room temperature over a period of at least about 12 hours.

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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)
  • Magnetic Ceramics (AREA)
  • Soft Magnetic Materials (AREA)
  • Compounds Of Iron (AREA)

Description

June 20, 1961 o. E-CKERT FERRITE WITH CONSTRICTED MAGNETIC HYSTERESIS LOOP Filed Oct. 18, 1956 2 Sheets-Sheet 1 @E v Ami AAWA/VV 20 V A VWy NVV AAA/M 3w vw INVENTO June 20, 1961 o. ECKERT 2,989,473
FERRITE WITH CONSTRICTED MAGNETIC HYSTERESIS LOOP Filed Oct. 18, 1956 2 sheets-sheet 2 JTzEd; v E5=Eb Fe? 03 INVENTOR.
g (Jg E $165137 Q Wi United States Patent 2,989,473 WITH CONSTRICTED MAGNETIC HYSTERESIS LOOP Oskar Eckert, Lauf (Pegnitz), Germany, assignor to 'Steatit-Magnesia Aktiengesellschaft, Lauf (Pegmtz),
Germany, a corporation of Germany Filed Oct. 18, 1956, Ser. No. 616,817 Claims priority, application Germany Oct. 24, 1955 Claims. (Cl. 252-625) Ferromagnetic metals with constricted hysteresis loops (see, for example, Bozorth, Ferromagnetism, by Nostrand Co., Inc., 1951, pages 498 to 499), have, as is well known, at small field strength within the constriction area, constant permeability, i.e., permeability independent of the field strength equal to the initial permeability, very low hysteresis losses and, in general, small residual losses. As indicated in the above-cited literature, such materials may be subjected to thermo-magnetic treatment. By thermomagnetic treatment, in this connection, is meant the passing thru a thermic cycle during the simultaneous presence of a magnetic longitudinal or transverse field. The concept of longitudinal or transverse field is, in this connection, to be understood as relative to the later measuring field; a longitudinal or transverse field, respectively, means that such field, during the thermomagnetic treatment, is parallel, respectively vertical, to the later measuring field. Thru this type of treatment, these ferromagnetic materials display a substantial alteration of the form of the hysteresis loop, and hence a change of the magnetic properties. This invention is based on the discovery that it is possible to make specific ferrites showing a constricted magnetic hysteresis loop which are, consequently, capable of thermomagnetic treatment similarly as for metals.
The invention teaches the production of such ferrites of the nickel-cadmium and manganese-cadmium ferritesystems which can be subjected to thermomag-netic treatment of the above type, and are distinguished from hitherto familiar ferrites by the fact that, under the same manufacturing conditions, they have constricted hysteresis loops.
'In accordance with the invention, ferrites with this characteristic in the nickel-cadmium and manganesecadmium ferrite systems must have a composition of at least 50 mol percent Fe 0 and a small addition of cobalt oxide. The addition of cobalt oxide is suitably determined between 0.1 and 5% by weight, calculated on the total basic batch of the nickel-cadmium and manganese-cadmium ferrites expressed in metallic oxides. The invention has shown that it is particularly advantageous to choose the cobalt oxide content between 0.35 and 1.5% by weight, calculated on the basic batch. The nickel-cadmium and manganese-cadmium ferrites in question, which react strongly to the addition of cobalt oxide with a constricted loop, cover, in the three-component system Fe O -NiO-CdO or Fe O Mn 0 --CdO, the area defined in FIGS. 3 and 4 of the drawing by the pentagonal points A, B, C, D, E, or the four points A, B, C, D, respectively. The compositions at the corners in percent by weight (see FIG. 3) are: pentagonal points A, B, C, D, E, or the four points A, B, C, D, respectively. The compositions at the corners in percent by weight (see FIG. 3) are:
m0, NiO C(lO Patented June 20, 1961 The corner points for the system Fe O Mn O -CdO (see FIG. 4) are: I
ice
F8203 M11203 Odo The above ferrites may be prepared in the usual way, either by joint or partial precipitation, from corresponding metal salt solutions, or, as is customary in ceramic arts, they may be prepared for further processing by wet milling and mixing of the respective metal oxides. The powdered mixtures thus obtained may, after drying, be given the desired form either immediately by dry pressing, extruding, or similar methods, or it may be desirable, before ceramic forming, to proceed with a calcining firing of the entire mass or only a part thereof, preferably between 750 and 1150" C. for the system Fe O -NiO CdO or 750 to 1200 C. for the system Fe2O -Mn O CdO. The formed parts of both of these systems are sintered, depending on the compositions, at temperatures between 1250 C. and 1380 C. To produce the constricted hysteresis loop in ferrites, in accordance with the invention, it is necessary that the cooling take place slowly, particularly in the temperature range between 700 C. and room temperature. The cooling speed is dependent upon the volume of the fired body. As a criterion, it may be stated that for a ring of about 46mm. outside diameter, 34 mm. inside diameter, and 1 0 mm.
height, the cooling time from 700 C. to room temperature should take not less than 12 hours. If the rings are cooled rapidly, the eifeot of loop constriction does not occur. However, the constriction may be regained even for rings cooled too rapidly, by re-heating them to a temperature of about 700 C., and cooling them slowly, as above described.
Examples of the invention follow hereafter.
The further ceramic procedure is the same for both systems and in both processes consists in that after 6 hours of grinding, the slip is poured through a 4900 mesh screen (4900.meshes per square cm.) into a porcelain dish, and :dried. The powder thus obtained is pressed, according to ceramic pressing techniques, into rings having dimensions of 59 mm. outside diameter, 35.8 mm. inside diameter, and 12 mm. height, the amount of pressure applied being about 500 to 1000 kg./cm. The NiCd or MnCd ferrite pieces, thus obtained, are sintered in a kiln at 1320 C. for one hour, whereupon the heat is shut 0E. The rings are cooled to room temperature in the kiln during a period of approximately 24 hours. The ferrite rings thus obtained are provided with 0.4 mm. copper enameled wire with windings as primary winding, and, as secondary winding, further 200 windings with 0.2 mm. copper enameled wire are applied. The
oscillographic photograph of this ferrite, produced in accordance with the invention, is shown in FIGS. 1a and 1b; one can distinctly recognize the loop constriction of the hysteresis loop.
The following experiment proves that ferrites produced in accordance with the invention are susceptible to thermomagnetic treatment:
The ferrite toroid, as prepared in either of the examples, with 100 windings as a primary winding, is placed in a kiln. While heating to 600 C., and slow cooling for 12 hours to room temperature, a longitudinal magnetic field is maintained by means of the ring winding by 1 a. direct current, corresponding to a magnetic field strength of about 15 a.-windings/cm. If the hysteresis loop of the ferrite after this thermomagnetic treatment is recorded in the same manner as described above, the result is analogous to that of metal when they are subjected to heat treatment in the longitudinal magnetic field; a complete change of the form of the hysteresis loop takes place, as may be seen in FIGS. 2a and 2b respectively.
In analogous manner, heat treatment in the transverse magnetic field may be carried out with corresponding effect (see the above cited book by Bozorth).
The technical progress obtained with such ferrites in accordance with the invention, may be seen in the following: with thermic longitudinal magnetization, for example, ferrites with distinctly rectangular hysteresis loop may be produced which are of importance to the entire fields of electronics and for magnetic amplification for telephone and high-frequency fields; with thermic cross magnetization, ferrites of high quality and a permeability independent of field strength may be produced, which are particularly suitable for the field of telecommunication.
I claim:
1. A fired ferrite body having a constricted magnetic hysteresis loop which ferrite is susceptible to thermomagnetic treatment to alter the hysteresis loop characteristics and consisting essentially of the components cadmium oxide, iron oxide, 0.1-5% by weight of cobalt oxide and an additional metal oxide selected from the group consisting of nickel oxide and manganese oxide, the iron oxide content of said body being from 72.5 to 89% by weight and over 50 mol percent calculated on the total amount of metal oxides in the body, said constricted magnetic loop characteristic being obtained by gradually cooling the fired body from 700 C. down to room temperature over a period of at least twelve hours.
2. A fired ferrite body as claimed in claim 1 characterized in that the cobalt oxide content is between 0.35 and 1.5% by weight of said composition.
3. A fired ferrite body as claimed in claim 2 in which the ferrite is of the iron oxide, nickel oxide, cadmium oxide system and in which the proportions of said components come within area ABC 'D-E of FIG. 3 of the drawing, the corners of this area defining the following compositions:
A=72.5% F6 0 27.5% N10, 0% CdO, by Weight B=72.5% Fe O 7.5% NiO, 20% CdO, by weight C=79.0% Fe O 1.0% NiO, 20% CdO, by Weight D=87.5% Fe O 1.0% NiO, 11.5% CdO, by weight E=87.5% Fe O 12.5% NiO, 0% CdO, by Weight 4. A process of making a ferrite body with a constricted hysteresis loop comprising providing a milled powder mixture consisting essentially of cadmium oxide, iron oxide, 0.1 to 5% by weight of cobalt oxide and an additional metal oxide selected from the group consisting of nickel oxide and manganese oxide, the iron oxide content being from about 72.5% to 89% by weight and over 50 mol percent of the metal oxides of the system, forming the powder mixture to the shape desired, sintering the shaped product at about 1250 C. to about 1380 C. and thereafter slowly cooling the sintered product from about 700 C. down to room temperature over a period of at least about 12 hours.
5. A fired ferrite body having a constricted magnetic hysteresis loop of the iron oxide, manganese oxide, cadmium oxide system containing in addition between about 0.1 and 5% of cobalt oxide, the proportions of iron oxide, manganese oxide and cadmium oxide in said ferrite coming within area A--B-CD of FIG. 4 of the drawing, the corners of this area defining the following compositions:
A=76% F6203, 24.0% Mn O 0% CdO, b weight B=76% Fe O 2.5% Mn O 21.5% CdO, by weight c=s9% R 0 2.5% 11411 0,, 8.5% CdO, by weight D=89% Fe,o,, 11.0% Mn O 0% CdO, by weight the proportion of iron oxide in said ferrite being over 50 mol percent calculated on the metal oxides in said system, said constricted magnetic loop characteristic being obtained by gradually cooling the fired body from 700 C. down to room temperature over a period of at least twelve hours.
References Cited in the file of this patent UNITED STATES PATENTS 2,549,089 Hegyi Apr. 17, 1951 2,565,861 Leverenz et al Aug. 28, 1951 2,723,239 Harvey Nov. 8, 1955 2,736,708 Crowley Feb. 28, 1956 FOREIGN PATENTS 669,571 Great Britain Apr. 2, 1952 1,117,385 France Feb. 20, 1956 201,673 Australia May 2, 1956 1,127,577 France July 16, 1956 756,374 Great Britain Sept. 3, 1956 OTHER REFERENCES Sailpeter: Philips Tech. Communication, March 1948, pp. 3-8.
R.C.A. Review, September 1950, vol. 11, No. 3, pages 321-363.
Weil: Comptes Rendus, vol. 234, pp. 1351, 1352, Mar. 24, 1952.
Wijn et al.: Philips Tech. Rev., August 1954, pages 52, 56.
Economos: J. Amer. Ceramic Soc., July 1955, pp. 241- 242.
Bozoroth et al.: Physical Review, vol. 99, pp. 1788- 1798, Sept. 15, 1955.

Claims (1)

1. A FIRED FERRITE BODY HAVING A CONSTRICTED MAGNETIC HYSTERESIS LOOP WHICH FERRITE IS SUSCEPTIBLE TO THERMOMAGNETIC TREATMENT TO ALTER THE HYSTERESIS LOOP CHARACTERISTICS AND CONSISTING ESSENTIALLY OF THE COMPONENTS CADMIUM OXIDE, IRON OXIDE, 0.1-5% BY WEIGHT OF COBALT OXIDE AND AN ADDITIONAL METAL OXIDE SELECTED FROM THE GROUP CONSISTING OF NICKEL OXIDE AND MANGANESE OXIDE, THE IRON OXIDE CONTENT OF SAID BODY BEING FROM 72.5 TO 89% BY WEIGHT AND OVER 50 MOL PERCENT CALCULATED ON THE TOTAL AMOUNT OF METAL OXIDES IN THE BODY, SAID CONSTRICTED MAGNETIC LOOP CHARACTERISTIC BEING OBTAINED BY GRADUALLY COOLING THE FIRED BODY FROM 700*C. DOWN TO ROOM TEMPERATURE OVER A PERIOD OF AT LEAST TWELVE HOURS.
US616817A 1955-10-20 1956-10-18 Ferrite with constricted magnetic hysteresis loop Expired - Lifetime US2989473A (en)

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DEST10447A DE1057254B (en) 1955-10-20 1955-10-20 Process for the production of ferromagnetic ferrite bodies with a constricted hysteresis loop
DEST10460A DE1057255B (en) 1955-10-20 1955-10-24 Process for the production of ferromagnetic ferrite bodies with a constricted hysteresis loop

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US3081264A (en) * 1958-04-09 1963-03-12 Matake Kurokawa Method of preparing a magnetic recorder powder
US3072576A (en) * 1958-05-27 1963-01-08 Aladdin Ind Inc Ferrites having rectangular hysteresis loops and method for manufacture of same
DE1182129B (en) * 1958-06-04 1964-11-19 Licentia Gmbh Process for the production of a magnetic core material with an almost rectangular hysteresis loop
US3055832A (en) * 1960-06-10 1962-09-25 Ampex Magnetically annealed ferrite material
DE1696456B1 (en) * 1965-03-24 1970-11-12 Telefunken Patent Process for the production of a substoechiometric ferrite with an almost rectangular, temperature-stable hysteresis loop for switching ring cores
DE1646997B1 (en) * 1965-08-10 1972-06-29 Siemens Ag PROCESS FOR MANUFACTURING A FERROMAGNETIC SWITCH CORE FROM FERRITE WITH A RECTANGULAR HYSTERESIS LOOP
JPS5227358B1 (en) * 1967-05-25 1977-07-20
JPS5231555B1 (en) * 1967-07-25 1977-08-16
US3533949A (en) * 1967-11-21 1970-10-13 Bell Telephone Labor Inc Heat treating method for obtaining a ferrite with a high muq product
US3609083A (en) * 1970-03-17 1971-09-28 Bell Telephone Labor Inc Heat treatment of nickel zinc cobalt ferrite

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US2549089A (en) * 1948-12-15 1951-04-17 Rca Corp Mixed ferrite compositions, including lithium ferrite
US2565861A (en) * 1947-09-26 1951-08-28 Rca Corp Magnetic materials
GB669571A (en) * 1948-03-27 1952-04-02 Philips Electrical Ind Ltd Improvements in or relating to magnet cores for electromagnetic devices
US2723239A (en) * 1952-09-29 1955-11-08 Rca Corp Ferrospinel compositions
US2736708A (en) * 1951-06-08 1956-02-28 Henry L Crowley & Company Inc Magnetic compositions
FR1117385A (en) * 1954-01-12 1956-05-22 Philips Nv Method of manufacturing a substantially rectangular hysteresis cycle magnetic core
GB756374A (en) * 1952-11-08 1956-09-05 Licentia Gmbh A method for the manufacture of ferrite cores
FR1127577A (en) * 1955-06-07 1956-12-19 Schlumberger Prospection Improvements to shaped charge devices used for perforation

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US2452530A (en) * 1943-05-15 1948-10-26 Hartford Nat Bank & Trust Co Magnetic core
BE456575A (en) * 1943-07-01
US2636860A (en) * 1944-07-06 1953-04-28 Hartford Nat Bank & Trust Co Magnetic core
US2640813A (en) * 1948-06-26 1953-06-02 Aladdin Ind Inc Reaction product of a mixed ferrite and lead titanate
DE1017521B (en) * 1953-11-27 1957-10-10 Steatit Magnesia Ag Process for the production of ferromagnetic, ceramic bodies with high quality at high frequency
FR1110334A (en) * 1954-07-13 1956-02-10 Improvements to such ferromagnetic materials
FR1125577A (en) * 1955-05-03 1956-11-02 Lignes Telegraph Telephon Ferromagnetic materials with rectangular hysteresis cycle

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US2565861A (en) * 1947-09-26 1951-08-28 Rca Corp Magnetic materials
GB669571A (en) * 1948-03-27 1952-04-02 Philips Electrical Ind Ltd Improvements in or relating to magnet cores for electromagnetic devices
US2549089A (en) * 1948-12-15 1951-04-17 Rca Corp Mixed ferrite compositions, including lithium ferrite
US2736708A (en) * 1951-06-08 1956-02-28 Henry L Crowley & Company Inc Magnetic compositions
US2723239A (en) * 1952-09-29 1955-11-08 Rca Corp Ferrospinel compositions
GB756374A (en) * 1952-11-08 1956-09-05 Licentia Gmbh A method for the manufacture of ferrite cores
FR1117385A (en) * 1954-01-12 1956-05-22 Philips Nv Method of manufacturing a substantially rectangular hysteresis cycle magnetic core
FR1127577A (en) * 1955-06-07 1956-12-19 Schlumberger Prospection Improvements to shaped charge devices used for perforation

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US2929787A (en) 1960-03-22

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