CA2119934C

CA2119934C - Moldable crystalline magnetic material for high-frequency applications

Info

Publication number: CA2119934C
Application number: CA002119934A
Authority: CA
Inventors: Wilhelm Muller; Gerald Peter Diel
Original assignee: Individual
Current assignee: MILLER CARMEN INGE
Priority date: 1994-03-24
Filing date: 1994-03-24
Publication date: 2003-04-22
Anticipated expiration: 2014-03-24
Also published as: CA2119934A1

Abstract

A mouldable crystalline magnetically permeable material for high frequency electrical applications having naturally occurring crystalline iron oxide black sand with at least 50% by weight iron oxide calculated as Fe-Fe2O4, the crystalline iron oxide black sand uniformly distributed in a mouldable matrix.

Description

''- MOLDABLE CRYSTALLINE MAGNETIC MATERIAL
FOR HIGH-FREOOENCY APPLICATIONS
Field of the Invention This invention relates to the f field of highly permeable electro-magnetic materials and in particular to the application of such materials to power cores and electro-magnetic interfer-ence shielding.
Background of the Invention As described in United States Patent No. 5,198,138, which issued March 30, 1993 to Yamamoto et al., for "Spherical Ferrite Particles and Ferrite Resin Composite for Bonded Magnetic Core" ferrite particles and a ferrite resin composite may be used as a magnetic core material of a transformer, electro-magnetic wave absorption or shielding. Yamamoto et al. teach that a bonded magnetic core is generally produced by kneading a magnetic material with a resin such as nylon or phenol resin, and molding the resulting mixture by compression molding or injection molding. Further taught is that an oxide material such as Mn-Zn ferrite and Ni-Zn ferrite may be used as the magnetic material and that such material is generally obtained by mixing a main raw material such as Fe203, Zn0 and Mn0 or Ni0 in advance by wet or dry blending so as to have a desired composition, granulating the resulting mixture into particles having a diameter of several milimetres to several tens of milimetres, calcining the obtained particles and pulverizing the calcined particles into particles having an average particle diameter of several micro-meters to several hundred micro-meters.
Yamamoto et al. recognize that a bonded magnetic core is required to have a magnetic permeability as large as possible and that in order to obtain a bonded magnetic core having a large 2~~ 9~,~~
magnetic permeability, it is advantageous to use ferrite particles having a large magnetic permeability as the magnetic material. Yamamoto et al. point out that following the conven tional method, as set out above, the crystal grains grow as large as several hundred micro-meters and become non-uniform.
Yamamoto et al. also point out that for the mass production of cores having a complicated shape, in addition to large magnetic permeability, fluidity of the ferrite resin composite for producing the bonded magnetic core is important and may be dependent on the properties of the ferrite particles which are mixed with the base materials of the resin composite. They state that the magnetic permeability of the ferrite resin composite has a tendency to be enlarged with the increase in the magnetic permeability of the ferrite particles mixed. They state that the fluidity of the ferrite resin composite improves as the average particle diameter of the ferrite particles mixed becomes smaller and the surface of the particles become smoother.
Further it is stated that the magnetic permeability of the ferrite particles has a close relation to the average particle diameter and, hence, a magnetic permeability of the ferrite resin composite is enlarged with the increase in the average particle diameter. On the other hand, when the average particle size of the ferrite particles increases, the fluidity of the ferrite resin composite is deteriorated.
Consequently, Yamamoto et al. propose that it is important to use spherical granules for ferrite particles and that these spherical granules be formed by spray-drying a slurry containing iron oxide or iron oxide hydroxide powder so as to obtain granules having an average particle diameter of 25 to 180 micro-meters.
Applicant is also aware of United States Patent No.
5,186,854 which issued February 16, 1993 to Edelstein for ~~~9~3~
'"~'°"Composites Having High Magnetic Permeability and Method of Making". Edelstein discloses a ceramic composite material which in its preferred embodiment comprises crystalline ferrous ferrite, Fe304, as a matrix with small particles of metallic iron embedded in it, or alternatively, that the ferrous ferrite matrix be amorphous. An example is given where Fe-Fe304 composites were produced by reactive sputtering of Fe in an argon-oxygen mixture which was then thermally treated after deposition to obtain the desired oxide phase.
Applicant is aware of United States Patent No.
4,543,208 which issued September 4, 1985 to Hoie et al. for "Magnetic Core and Method of Producing Same". Hoie et al. teach a magnetic core as a moulded product comprising a magnetic powder, a binder resin and an inorganic compound powder. More specifically what is taught is a magnetic core comprising a moulded product of either one or both of an iron powder and an iron alloy magnetic powder having a mean particle size of 10 to 100 micro-meters and 1.5 to 40 percent as a total amount in terms of volume ratio of insulating binder resin and insulating inorganic compound powder. Thus disclosed is a magnetic core to be used for a reactor or a transformer connected to a semi-conductor element in high-frequency current applications so as to provide good magnetic permeability and magnetic flux density.
It is disclosed that the inorganic compounds may include calcium carbonate, silica, magnesia, alumina, hematite, mica, various glasses, or a suitable combination thereof. It is taught that a magnetic core containing the Hoie et al. material may be made by mixing pre-determined amounts of iron powder, iron alloy magnetic powder or a mixture thereof with a binder resin and inorganic compound powder and then compressing the resulting mixture in a mould.
Applicant is further aware of United States Patent No.
5, 206, 459 which issued April 27, 1993 to Aldissi for "Conductive ~~~9~3~
"polymeric Shielding Materials and Articles Fabricated Therefrom"
in which it is disclosed that shield material may contain shaped ferrite particles dispersed within a polymeric binder, such as a fluorocarbon polymer and that the shaped particles are generally spherical.
Also taught in United States Patent No. 4, 906, 522 which issued March 6, 1990 to Miller for "Compounds of Nickel, Iron and Phosphorous" is preparing compositions of Nickel, Iron and Phosphorous by fusing Nickel and Ferro Phosphorous and grinding or atomizing the fused composition to form a conductive pigment having a particle size from 0.1 to 15 microns which can be incorporated into a suitable resin binder for use in EMI
shielding coatings or the like.
Thus in the prior art attempts have been made to produce magnetically permeable magnetic material, referred to by Yamamoto et al. as "highly" permeable material, which may be formed into various shapes for use as magnetic cores, shielding or the like. Consequently, it is an object of the present invention to provide for the use of material until now considered to be naturally occurring waste material, which material also otherwise naturally occurs, such material being found in crystal-line form and having relatively "high" magnetic permeability, low hysteresis in the manner of amorphous materials, and convenient particle size so as to be virtually ready in an unprocessed state for mixing into a resin binder for moulding into any desired shape for use as a core, EMI shielding or the like.
Summary of the Invention A mouldable crystalline magnetically permeable magnetic material for high frequency electrical applications comprises naturally occurring crystalline iron oxide black sand having at least 50~ by weight iron oxide calculated as Fe-Fe204, the ''crystalline iron oxide black sand uniformly distributed in a mouldable matrix.
The crystalline iron oxide black sand of the present invention for use in high frequency electrical applications may also be used in its crystalline powdered form, that is, without necessarily being held in a resin matrix or the like, so long as it can be formed into the desired shape for a specific electrical application and the crystalline iron oxide uniformly distributed.
Further, the percentage by weight of iron oxide calculated as Fe-Fe204 may be higher than 50 0 .
Filtering or screening of the crystalline iron oxide black sand may be employed to restrict the range of particle sizes from that occuring in natural black sand for example by screening black sand ffirst magnetically and then through a ffirst 150 mesh screen and through a second 100 mesh screen. The material thus caught by the 100 mesh screen may then be used where relatively uniforn particle size is desired in a high frequency electrical application or where particle size is not of importance then the black sand material left over after removing the material caught in the 100 mesh screen may be used.
Brief Description of the Drawings Figure 1 is a plot of sample A EMI attenuation.
Figure 2 is a plot of sample B EMI attenuation.
Figure 3 is a plot of sample C EMI attenuation.
Figure 4 is a plot of EMI attentuation by prior art shielding.
Figure 5 is a plot showing the elements of sample A.

2~:~~93~
'' Figure 6 is an enlarged view of representative particles of material of the present invention.
Detailed Description of the Preferred Embodiment An evaluation was conducted of a sample of so-called black sand removed from a beach on the West Coast of the Queen Charlotte Islands in the Province of British Columbia, Canada.
As an initial step the entire black sand raw material was magnetically screened to remove non-magnetic material prior to being filtered by a standard mining sieve. This sample was broken down into three sub-samples referred to hereinafter for simplicity as Sample A, Sample B and Sample C. Sample A was merely the magnetically screened black sand raw material. Sample B was culled from the magnetically screened black sand raw material by screening the raw material through a standard mining sieve and removing the screened magnetically screened black sand from between the 100 and 150 mesh screens. Sample C was merely the left-over material after removing sample B from the screened magnetically screened black sand raw material.
Samples A, B and C were then tested for suitability in two particular applications, namely, power cores and electro magnetic interference ("EMI") shielding.
In the EMI shielding application the samples were tested and compared to identical tests performed on commercially available EMI suppression materials, namely, so-called split ferrites manufactured by StewardTM Inc., P.O. Box 510, Chatta-nooga, Tennessee, 37401 U.S.A. In particular StewardTM EMI
suppression materials No. 27 and 28 were tested. Tests were conducted to determine EMI suppression characteristics for samples A, B and C and for the StewardTM reference samples for frequencies up to approximately 3.75 GHz. See for example Figure 2~~~93~
i for the EMI suppression characteristics of Sample A as compared to those of the baseline data which represented the unshielded EMI. Figures 2 and 3 illustrate the same test conducted on samples B and C, respectively. Figure 4 is, for comparison, the EMI suppression characteristics of the StewardTM No. 27 and 28 materials.
The EMI characteristics of each of samples A, B and C
and that of the StewardTM reference materials No. 27 and 28 were measured from the plots illustrated in Figures 1 through 4 and the results are tabulated in Table 1.
The results in Table 1 are broken down into four frequencies, namely, 100 MHz, 200 MHz, 2 GHz and 3.75 GHz. For each of these four frequencies, Table 1 illustrates 3 variables, namely, distance in centimetres as measured off the plots illustrated in Figures 1 through 4, dB attenuation converted from the measurements, and an attenuation factor such that an attenuation factor of, for example, 3 means that only 1/3 of the signal passed through. Also provided is the weight for each of samples A, B and C and the weights of the StewardTM materials so that a specific attenuation can be calculated.
From the test results it was determined that at 2 GHz sample A was more than 25% superior to the best of the StewardT"' materials and at 3.75 GHz all of samples A, B and C were superior to the StewardTM materials, and notably that sample C attenuated more than 3 times more effectively than the best StewardTM
material.
It was determined that sample A, that is, black sand raw material, was primarily iron oxide calculated as Fe-Fez04 as found in its natural crystalline form. It is also known that such black sand is available as the waste by-product from gold mining operations. Black sand is magnetic and, apart from Fe-_ 7 _ 21~9~3~
Fe204 contains various other elements such as aluminum, silicon, calcium, titanium, vanadium and manganese (see Figure 5 for spectral analysis showing relative component quantities).
However, black sand is primarily Fe-Fez04, being approximately 8 6 o Fe-Fe204 by weight .
For use in a power core magnetically separated iron oxide may be screened to produce iron oxide material correspon-ding to sample B. It has been determined that the particle sizes for this material ranged from 126 to 282 microns, approximately, using the Waddel diameter approximation for an equivalent area circle. The Waddel diameter approximation was considered appropriate in that, as illustrated in Figure 6 which is an electron microscope image at 100 times magnification of sample B, the particles shape could be approximated as spherical.
Full particulars of a breakdown of the elements contained in both sample A and sample B are contained in Tables 2 and 3 respectively. Tables 4 and 5 are a detailed breakdown of the particle sizes contained in samples A and B, respectively.
A form was prepared in the desired shape for the power core, for example toroidal, rectangular, "E"-shaped, "H"-shaped, or "C"-shaped. An epoxy was then prepared. EpoxyliteTM type stator impregnating resin was used as the binder. Iron oxide crystalline powder corresponding to sample B was then mixed with the prepared resin until a consistent distribution of the iron oxide in the resin binder was achieved. Of course, other binders could be utilized to provide the iron oxide binding matrix.
The iron oxide and resin mix was then poured into the prepared form and agitated or stirred to eliminate air bubbles to thereby maximize density and permeability of the core to magnetic field lines. Alternatively, a vacuum injection process could be employed to minimize air bubbles in the core.
_ g -_ ~.~.~9~3~
The iron oxide resin mix was then cured, either at room temperature or at low temperatures, for example 150 degrees if accelerated curing was desired. Once cured, the core was removed from the form and edges de-burred.
As the design objectives of the present invention were high relatiive permeability so as to readily accept magnetic lines, and low hysteresis to minimize heating, other elements having a relatively high permeability may be added to the iron oxide resin mix. Such elements may make the core application more advantageously suited for low frequency applications, for example by using spinel ferrites such as manganese zinc ferrite which has very high low frequency permeability. Cores manufac tured using material of the present invention may thus be tailored or tuned to specific frequencies.
The process to produce an EMI shield using material of the present invention is identical to that of producing a power core as set out above, with the exception that the forms are shaped to provide the desired encasing shielding.
As will be apparent to those skilled in the art in the light of the foregoing disclosure, many alterations and modifica-tions are possible in the practice of this invention without departing from the spirit or scope thereof. Accordingly, the scope of the invention is to be construed in accordance with the substance defined by the following claims.

Table 1 sample mass (gm) 98 105 86 130 135 »»~~r»ri»
freauency Sample" Steward # scale MHz A B C 27 28 100 cm on plot 0.00 0.30 0.00 4.05 3.85 12 cml 16 dB
100 dB 0.00 0.40 0.00 5.40 5.13 100 factor 1.00 1.10 1.00 3.47 3.26 200 cm on plot 0.05 1.05 0.05 7.45 7.95 12 cm/ 16 dB
200 dB 0.07 1.40 0.07 9.93 10.6 200 factor 1.02 1.38 1.02 9.85 11.5 2000 cm on plot 2.40 1.35 1.60 1.70 2.25 12 cm/ 80 dB
2000 dB 16.0 9.00 10.7 11.3 15.0 2000 factor 39.8 7.94 11.7 13.6 31.6 3750 cm on 1.551.50 2.20 1.40 1.20 12 cm/ 80 plot dB

3750 dB 10.310.0 14.7 9.33 8.00 3750 factor 10.810.0 29.3 8.58 6.31 9q Table 2 2119934 24-Sep-199.:. ~9: ~4:E0 SHMF~LE A, OVERALL
Gccelerating voltaa_e E'~1~ ~ f.e!J
Eleam - sample incidence angle 9V7.V7 degrees Xray emergence angle '0.~.'~ decrees Xr-av - window incidence angle ~. ~c'~ degr~ees Window this!<ness 7. ~ mic;~ons STANZARLLESS EDS Ri'dAL'ISiS
( ZAF CLRRECTIOhlS 'J I;=,, MAV IC V ) ELEMEi~IT l)E I i=;-f GM !_~ F~EC
GHT I C I S I ON

it L INE F~ERCENT~ ~: SIuMA
PERCENT f.-RA T
IO#'.~
ITER

a 1 KA ~. 03 9 . 34 ~ . 12 4~. ~c~ 151 S l KA ~.=.r. l ~. c5 ~ . 1 ~ V'~. ~b~:~7 Ca f,A V7. 4;:.V7, ~~ ~~. 03 w~. k'~~c~4~

Ti KA 1. i9 1. 25 ~. 04 O. 0131 V N.A V:~. ~c~. 24 ~7J. 0c 41. ~~V76:8 Mn KR fit. ~. 61 ~. ~4 ~ . ~~73 Fe KA 96. 69 77. 76 0. ~8 v7. 9.:38 S

TOTAL 1~~.
~t0 NOTE: ATOMICF~ERCENTis normal red to l~c~ki l DENOTE:K-RAT i0 =
K-RRTIO
x R

where R = reference(standard)/reference(sample>

NORMALIZATION FACTOR: 0.910 ZAF Correction Factors Elament Z factor A factor F factor A1 0. G51 5. 638 0. 999 Si 4~. 669 4. X06 ~. 999 Ca ~ . 817 1. 340 ~. 969 Ti x.919 1. 191 0.91 V t~.948 1. 145 v7.867 Mn a. 964 1. X91 a. 964 Fe 47. 95:s 1 . X71 1. ~~t~

Table 3 2119934 E7-Sep-199.:' ~8: ~~+: G,~ SRMF~LE B, OVERALL
Accelerating voltage L~.v.'~ KeV
Beam - sample incidence angle 9~t.v~ degrees :ray emercance angle Lit. v~ degr~ees Xrav _- window incidence angle ~.~ decrees llindGw ~:I"IlC:ine55 7...°~ ttilnr'Cns STANDf: =;DLESS EDS ~=sNFiLYS 18 ~;~AF Cfli~-,~:EnTT._G('lj V_A MAGIC V) ELEME>rIT ~~i~~IGH ;~TOMI1:,F~RECISION
T

LThIE ~ERCEVT F~ECGENT'~;~ SIGMA
K-RATIflk~
I TER

AI KA 6. v'~4 11. Sid v~, 1E v:~. v~181 S l Y.A 4. 71 8. 4~ ~. >~8 ~. ~ 191 Crc i'.ct ~Zt. ,~8 V5. 47 ~. kc t~. V~~c'~39 Ti KtA 1. ~c 1. 59 4a. 04 ~ ~1~7 Fe KA r37..a5 78.,:.~ v7. E5 v7.94L1 TOTAL 1 ~t~. k~~

~hIOTE: ATOMIC fERCEi~ITis normalised to l~tV~

~~IVOTE: K-RATIO =
K-RATIO x R

w~era R = reference(standard)lr2ferencetsamplei f~ORMALIZATI01~ FF~CTOR: ~.9~d9 ZAF Corsect l on Fact ors Element Z factor A factor F factor-A1 ~.65~ 5.641 v7.999 5i Qt.6b9 4.056 r~.999 Ca ~. $17 1. G~9 ~7. 969 Ti ~. 918 1. 191 0. 91~

Fe Q. 95.~ 1. ~7~ 1. ~v7~

G

Table 4 X119934 KEVEX Feat~_~re Analysis 27-Sep-1993 11:~~:16 54 Feat~_tres 54 Rccepted Featv_vres Units = microns urea Including Holes ..
Min. - ~. i4iE+~4 Max. - ~. 57~E+05 Mean = ~. 199E+0~ Std. Dev. - k' . 1 ~t3F_+~5 Waddel Diameter Min. - 42. 3 Max. - L7~. Mean = 1~4. Std. Dev. - 4~. 1 Longest Dimension Min. - 73. 4 Max. - 361. Mean = 193. Std. Dev. - ~~~ 6 ~~lean Dimension Per~endic~_~lar Min. - 19. 1 Max. - 174. Mean = 97. 4 Std. Dev. - ~8.
c~ d Table 'rJ 211994 KEVEX Feature Rnalysis ~7-Sep-199.: ltd:4~:~c~4 49 Feat~_~res 49 Rccepted Feat~_~res Units = microns 4rea Inel~_iding Holes Min. - ~. 311E+~4 Max. - 0. 4c7E+~5 Mean k. 195E+~~ Std. Dev. -= r . 3~4E+v74 Waddel Diameter = equivalent circle Min. - 6c. 7 Max. - ~3I. Mearc 1~~. Std. Dev. 3~. 9 = -Longest Dimension Min. - i~t4. Max. - L89. hlean 198. Std. Dev. 4L. S
= -Mean Di..rnension F~erpendi~=~llar, Min. - c9. S Max. - lo~c~. Mean 9,~. Std. Dev. L~. 1 = 1 -c~ a

Claims

1. A mouldable crystalline magnetically permeable material for high frequency electrical applications comprises naturally occurring crystalline iron oxide black sand having at least 50% by weight Fe-Fe2O4, said crystalline iron oxide black sand uniformly distributed in a mouldable matrix, wherein the percentage volume by weight of said crystalline iron oxide black sand is 100%

2. A mouldable crystalline highly permeable magnetic material for high frequency electrical applications comprises crystalline iron oxide black sand having at least 50% by weight Fe-Fe2O4, said crystalline iron oxide black sand uniformly distributed in a mouldable matrix, wherein the percentage volume by weight of said crystalline iron oxide black sand is 100%.

3. A mouldable crystalline highly permeable magnetic material for high frequency electrical applications comprises crystalline iron oxide black sand having at least 50% by weight Fe-Fe2O4, said crystalline iron oxide black sand uniformly distributed, wherein the percentage volume by weight of said crystalline iron oxide black sand is 100%.

4. A mouldable crystalline magnetically permeable material for high frequency electrical applications comprises naturally occurring crystalline iron oxide black sand having at least 50% by weight Fe-Fe2O4, said crystalline iron oxide black sand uniformly distributed in a mouldable matrix, wherein said iron oxide comprises particle sizes ranging between 73 microns and 361 microns.

5. A mouldable crystalline magnetically permeable material for high frequency electrical applications comprises naturally occurring crystalline iron oxide black sand having at least 50% by weight Fe-Fe2O4, said crystalline iron oxide black sand uniformly distributed in a mouldable matrix, wherein said iron oxide comprises particle sizes ranging between 126 microns and 282 microns.

6. A mouldable crystalline highly permeable magnetic material for high frequency electrical applications comprises crystalline iron oxide black sand having at least 50% by weight Fe-Fe2O4, said crystalline iron oxide black sand uniformly distributed in a mouldable matrix, wherein said iron oxide comprises particle sizes ranging between 73 microns and 361 microns.

7. A mouldable crystalline highly permeable magnetic material for high frequency electrical applications comprises crystalline iron oxide black sand having at least 50% by weight Fe-Fe2O4, said crystalline iron oxide black sand uniformly distributed in a mouldable matrix, wherein said iron oxide comprises particle sizes ranging between 126 microns and 282 microns.

8. A mouldable crystalline highly permeable magnetic material for high frequency electrical applications comprises crystalline iron oxide black sand having at least 50% by weight Fe-Fe2O4, said crystalline iron oxide black sand uniformly distributed, wherein said iron oxide comprises particle sizes ranging between microns and 361 microns.

9. A mouldable crystalline highly permeable magnetic material for high frequency electrical applications comprises crystalline iron oxide black sand having at least 50% by weight Fe-Fe2O4, said crystalline iron oxide black sand uniformly distributed, wherein said iron oxide comprises particle sizes ranging between microns and 282 microns.

10. A method for producing mouldable crystalline iron oxide magnetic material comprises the steps of:
(a) mixing crystalline iron oxide powder having at least 50% by weight Fe-Fe2O4 with a matrix material so as to uniformly distribute said iron oxide within said matrix material; and (b) forming said iron oxide and matrix material mix into a desired shape, wherein said method includes the initial steps of screening said iron oxide powder first through a screen of 150 mesh and, second, through a screen of 100 mesh and discarding all but that material caught by said 100 mesh screen.

11. A method for producing mouldable crystalline iron oxide magnetic material comprises the steps of:

(a) mixing crystalline iron oxide powder having at least 50% by weight Fe-Fe2O4 with a matrix material so as to uniformly distribute said iron oxide within said matrix material; and (b) forming said iron oxide and matrix material mix into a desired shape wherein said method includes the initial steps of screening said iron oxide powder first through a screen of 150 mesh and, second, through a screen of 100 mesh and discarding said iron oxide powder caught in said 100 mesh screen.

12