US3575862A - Ferrite core composition and method of preparation - Google Patents

Abstract

FERRITE CORES, USEFUL OVER A WIDE TEMPERATURE RANGE, CONSISTING OF ABOUT 0.14 TO ABOUT 1.65 MOLE PERCENT TUNGSTIC TRIOXIDE, ABOUT 1 TO ABOUT 8 MOLE PERCENT MANGANESE OXIDE, ABOUT 11.35 TO ABOUT 17.86 MOLE PRECENT LITHIUM OXIDE AND ABOUT 75 TO ABOUT 86 MOLE PERCENT FERRIC OXIDE. THESE FERRITE CORES ARE MAGNETIC MATERIAL HAVEING A HIGH SQUARENESS RATIO THEREFORE HAVING A A BI-STABLE MAGNETIC PROPERTY USEFUL FOR STORING INFORMATION. A METHOD OF PREPARATION IS DESCRIBED WHEREIN THE CORE IS SINTERED FOR A PERIOD WHICH CAN BE AS SHORT AS ABOUT 10 TO 25 MINUTES.

Description

United States Patent 3,575,862 FERRITE CORE COMPOSITION AND METHOD OF PREPARATION Earl J. Hoopes, Philadelphia, Pa., assignor to Fabri-Tek Incorporated, Minnneapolis, Minn. No Drawing. Filed Mar. 18, 1969, Ser. No. 808,295

Int. Cl. C04b 35/26 US. Cl. 25262.61 16 Claims ABSTRACT OF THE DISCLOSURE Ferrite cores, useful over a wide temperature range, consisting of about 0.14 to about 1.65 mole percent tungstic trioxide, about 1 to about 8 mole percent manganese oxide, about 11.35 to about 17.86 mole percent lithium oxide and about 75 to about 84 mole percent ferric oxide. These ferrite cores are magnetic material having a high squareness ratio therefore having a a bi-stable magnetic property useful for storing information. A method of preparation is described wherein the core is sintered for a period which can be as short as about 10 to 25 minutes.

SUMMARY OF THE INVENTION This invention relates to bi-stable ferrite cores many types of which are generally well known in the art. More specifically, this invention relates to cores comprising a novel composition consisting essentially of tungstic trioxide (W0 manganese oxide (MnO), lithium oxide (Li O) and ferric oxide (Fe O Those skilled in the art will recognize that many known ferrite cores have the disadvantage of too narrow a temperature range over which they will exhibit stable operating characteristics. Also, those skilled in the art will recognize the importance to production costs of the ability to prepare cores with a significantly decreased sintering time.

Cores prepared according to the novel composition and method described herein are operable over a wide range of temperatures extending from 55 C. to 125 C. Furthermore, and more important, these core exhibit stable operating characteristics over any 75 C.l00 C. temperature range within the broad temperature range mentioned above without requiring compensation.

Also, this invention is concerned with a method of preparing these cores wherein the sintering step can be accomplished in about 10 to 25 minutes or can extend over a period as long as about 8 hours.

DEFINITIONS The term squareness ratio commonly denoted R is defined herein as:

where B signifies the flux density in gauss, and H denotes the maximum field strength (in oersteds) at the point of magnetic saturation.

Other terms used herein are defined as follows:

3,575,862 Patented Apr. 20, 1971 Symbol Name Definition Response voltage obtained at a ful read-current pulse, when preceded by a full write-current pulse.

Response voltage obtained at a full read-current pulse preceded by a specific number of partial read-current pulses.

Response voltage obtained at a full read-current pulse, when preceded by a full read-current pulse followed by a specified nuisnber of partial write-current pu es.

o Core peaking time Time between the 10% levelofreadcurrent pulse and the peak of the V1 signal.

s Core switching time Time between 10% level of the readcurrent pulse and 10% level on the trailing edge of the uV1 signal.

Hu Coercive force The magnetomotive force per unit area necessary to demagnetize a core whic had previously been in the opposite state of magnetic saturation.

S.v Switching coetficienL... S..=t(H-H r 1 Read-disturbed 1 response voltage.

V: Disturbed zero response voltage.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The relative proportions of the constituents which produce the improved wide temperature cores in accordance with this invention lie within the following ranges, expressed in approximate mole percentages.

W0 0.14-1.65 MnO 1-8 Li O 11.35-17.86 Fe O 84 A preferred range of mole percentages for the constituents is:

wo 0.22 0.7s MnO 1-s Li O 11.35-17.86 Fe O 75-84 The specific examples illustrate the desirable properties of cores prepared in accordance with this invention and having the following dimensions: outside diameter-about 0.0230 inch, inside diameter-about 0.0150 inch, thicknessabout 0.0055 inch.

EXAMPLE Mole percent W0 0.7 MnO 2.6 Li O 16.4 Fe O 80.3

The components or initial constituents have ben listed herein as oxides. However, other compounds may be used initially in preparing the mixture prior to the sintering or firing step. For example, hydroxides or more preferably carbonates are generally used in preparing ferrite cores because they are easier to handle, are commercially available in high purity form, and tend to increase the intimacy of the body upon burn off. The following mixture uses carbonates as certain constituents:

EXAMPLE Mole percent 0.7

TABLE I Sintering time 8 hours 8 hours 8 hours. sintering temp 1,065 1,065 O 1,074 Oxygen fiow 0.15 cu./ft./h1: 0.15 on. ft;./hr 0.15 on. ftJhr.

Core density (as 2.56 grn./ce 3.08 gm./cc 3.08 gin/cc. pressed).

Response and timing characteristics Other cores, prepared as indicated in Table II below were found to possess similar desirable properties:

TABLE 11 Core density Response and Timing Characteristics Oxygen (as sintering Sintering flow, pressed), Vt r dVz T s time temp., 0. cu. it.[hr gun/cc. (mv.) (mm) (mv.) (nsj (21s.)

1, 086 2. 68 32 28 9 123 275 1, 087 0. 5 2. 68 37 32 11 116 235 1, 089 0. 5 2. 68 37 32 8 116 261 1, 088 0. 5 2. 68 36 32 8 129 271 088 0. 5 2. 68 36 32 7 128 270 1, 099 0. 5 2. 68 32 25 11 121 268 1, 090 0. 5 2. 68 43 31 11 123 251 1, 100 0. 5 2. 66 27 24 7 142 333 1, 087 0. 5 2. 56 32 28 111 231 1, 085 0.5 3. 08 37 33 5 139 283 1, 086 0. 5 3. 08 43 37 6 141 294 30 minutes- 1, 140 2. 5 3. O8 31 28 9 147 286 13 36 minutes- 1, 110 3. 08 28 26 8 132 270 14 46 minutes 1, 120 20 3. 08 28 24 9 161 303 15--- 8 hours 1, 080 0. 5 3. 08 32 28 9 123 260 16 o 1, 080 0. 6 3. 08 33 7 138 283 -mesh screen. The mixture was then heated at a reaction temperature of between about 650 C. and 950 C. for about 4 hours and then milled in alcohol again for 24 hours with 50% additional milling media, after which it was pan dried and sieved once more.

After an additional period of drying, the batch was mixed with a resin binder, for example about 3.8% by weight of Flexalyn 80M dissolved in methyl ethyl ketone. This mixture was then sieved and dried again.

The screened reacted powder was then pressed into toroidal cores having the dimensions described above. The pressed cores were then sintered, preferably between about 1000" C. and 1300 C., in an oxidizing atmosphere, such as air, but preferably oxygen, and then removed from the sintering furnace after cooling to about 200 C., and finally were air-quenched.

If the cores are sintered in air, an annealing or postsintering is necessary at a reduced temperature. The annealing may be carried out in an inert atmosphere, such as nitrogen, argon, neon or helium containing a small amount of oxygen, i.e., about 1-3 volume percent, or in the alternative it may be carried out in a pure oxygen atmosphere. Sintering in an oxygen atmosphere does not usually require the annealing step.

During sintering, the oxidizing atmosphere gas should be passed through a drying apparatus before passing into the sintering or firing furnace and over the cores that are being fired. This step is necessary to prevent volatilization of the lithium component.

The data included in Table I is illustrative of the typical properties of cores prepared according to the invention under the conditions indicated and which are similar in composition to the examples described above.

The values for the characteristics listed above in Table I were obtained from a test set-up in which the testing conditions were as follows:

between points).

The same testing conditions produced the characteristics listed in Table 11, except the drive current for Examples 6, 8 and 14 was 710 ma., and for Example 12 was 755 ma.

For similar core properties but improved productthroughput per furnace-hour, it has been discovered that the sintering step can be drastically shortened contrary to the usual practice in this art. Examples 12, 13 and 14 above are illustrative of this discovery of a short cycle hot insertion sintering method.

In the short cycle hot insertion sintering method the cores are loaded on platinum firing vehicles. These platinum firing vehicles are then placed end-to-end on a quartz firing carrier. The carrier and platinum trays are mounted on a loading fixture positioned at the end of a muffie furnace. The loading fixture may also be used to quench the platinum trays and may therefore be equipped with a water-cooled cop er heat sink. The carrier is loaded into a pre-heated muflie to a predetermined position and allowed to remain at sintering temperature for about at least 10 minutes. After about 10 minutes, the carrier is withdrawn to What was originally the loading position. The platinum trays may then be quenched on the Watercooled heat sink. A change in firing time will require an inversely proportional change in firing temperature; that is, if all other conditions are constant, a decrease in sintering time will necessitate a proportional increase in sintering temperature. Therefore, in the short sintering method, the sintering temperatures are generally higher as illustrated by Examples 12, 13 and 14. Further test examples of short time hot insertion sintering are shown in the following Table III.

6 ing in amount from about 0.14 to about 1.65 mole percent for a tungsten constituent about 1 to about 8 mole percent for a manganese constituent about 11.35 to about 17.86 for a lithium constituent, balance iron constituent comprising the steps of: mixing the initial tungsten, manganese, lithium and iron constituents together in predetermined relative proportions; processing to standard ferromagnetic ceramic techniques; pressing at least a portion of the mixture into the shape of a core; and sintering the TABLE III Response and timing characteristics Oxygen sintering Sintering flow, cu. V1 V1 a Ts time temp, C. it./hr. (n1v.) (mv.) (mv.) (ns.) (ns.)

1, 100 1 43. 37. 0 9. 6 128 277 l, 100 1 48. 0 40. 9. 9 125 275 1, 100 1 41. 5 36. 2 9. 5 127 286 1, 100 1 39. 9 35. 8 9. 7 135 290 1, 100 1 45. 2 34. 7 11. 6 121 259 l, 100 1 37. 3 33. 5 9. 4 130 284 1, 100 1 40. 2 36. 0 8. 2 140 300 1, 100 1 38. 9 35. 3 8. 0 145 310 1, 100 1 36. 0 32. 4 9. 5 131 285 do 1, 100 1 44. 2 35. 5 11.8 119 258 12 minutes 1, 150 1 47. 7 36. 4 14. 3 125 260 16 minutes 1, 130 1 40. 4 37. 5 9. 4 135 270 do 1, 130 1 46. 7 42. 0 11. 3 125 255 22. 5 1, 120 1 34. 9 30. 6 9. 9 125 265 minutes minutes 1, 120 1 33. 2 31. 3 9. 5 135 260 12 minutes 1, 130 1 31. 7 29. 5 10. 8 130 250 Note-The values for the characteristitm listed above in Table III were obtained from a test set-up in which the testing conditions were as follows, with all drive current at a 0.61

The advantage of short sintering is that it reduces the furnace time per load from over a period of many hours to about 10 to minutes, thereby improving manufacturing speed and efficiency. It is believed that such short sintering times have not been possible in the prior art as far as square hysteresis loop, high speed lithium ferrites are concerned.

The features and embodiments described above will suggest many modifications of the invention to those familiar with this art. It is accordingly desired that this invention be limited only by the following claims.

What is claimed is:

1. A ferrite core consisting of about 0.14 to about 1.65 mole percent tungstic trioxide, about 1 to about 8 mole percent manganese oxide, about 11.35 to about 17.86 mole percent lithium oxide, balance ferric oxide.

2. The core of claim 1 wherein the ferric oxide is present in an amount ranging from about 75 to about 84 mole percent.

3. The core of claim 2 wherein the tungstic trioxide is present in an amount ranging from about 0.22 to about 0.78 mole percent.

4. The core of claim 1 wherein the tungstic tiroxide is present in an amount of about 0.7 mole percent, the manganese oxide about 2.6 mole percent, the lithium oxide about 16.4 mole percent, balance ferric oxide.

5. The core of claim 4 wherein the ferric oxide is present in an amount of about 80.3 mole percent.

6. A method of preparing ferrite cores wherein the initial constituents consist of oxides or carbonates rangpressed core in an oxidizing atmosphere at a temperature of at least 1000 C. for a period of at least about 10 minutes.

7. The method of claim 6 wherein the mixture is pressed to a density of about 2.56 to about 3.08 gm./cc. prior to sintering.

8. The method of claim 6 wherein the sintering step is accomplished in dry air at a temperature of between about 1000 C. and about 1300 C. for a period of about 8 hours, and sintering is followed by an annealing step which is accomplished at a reduced temperature in an inert atmosphere containing a small amount of oxygen.

9. The method of claim 8 wherein the sintering temperature is between about 1000 C. and about 1100 C.

10. The method of claim 8 wherein the cores are allowed to cool to' about 200 C. before removal from the sintering apparatus and then are air-quenched.

11. The method of claim 6 wherein the sintering step is accomplished in dry oxygen at a temperature of between about 1000 C. and about 1300 C. for a period of about 8 hours.

12. The method of claim 11 wherein the cores are allowed to cool to about 200 C. before removal from the sintering apparatus and then are air-quenched.

13. The method of claim 6 wherein the pressed cores are sintered for about 10 to about 46 minutes at a temperature of at least about 1050 C.

14. The method of claim 13 wherein sintering is accomplished in dry oxygen.

8 15. The method of claim 13 wherein the pressed cores References Cited are placed in a pre-heated furnace and reach sintering UNITED STATES PATENTS temperature within about 2.5 minutes.

2,980,619 4/1961 Wetzel 25262.56 16. The method of claim 15 wherein the coresare re- 3,223,641 12/1965 Lessofi et a1. 252 62 61 moved from the furnace to a water cooled heat $111k and 5 3 372 123 3/1968 E SV 81 dt et a1 25Z 62 61 cooled in room atmosphere to room temperature within about 2 minutes. ROBERT D. EDMONDS, Primary Examiner