US3226327A - Ferrite compositions and method of manufacture - Google Patents

Description

Dec. 28, 1965 FERRITE Filed July 31, 1962 F. R. MONFORTE ET AL COMPOSITIONS AND METHOD OF MANUFACTURE 2 Sheets-Sheet 2 IN GAUSS MAGNET/C INDUCTION l I l l l l MAGNET/C INDUCTION IN GAUSS -o.5o o.25 0 +0.25 +0.50 +|.o F/ELD STRENGTH (H) M/ 05/25 7503 -O.50 -O.25 0 +0.25 +0.50 FIELD STRENGTH (H) /N OERSTEDS VENTORS F. R. MONFORTE 8V F. J. SCH/VETTLEIQ ATTORNEY United States Patent ()fiice 3,226,327 Patented Dec. 28, 1965 3,226,327 FERRITE COMPOSITIONS AND METHOD OF MANUFACTURE Frank R. Monforte, Passaic Township, Morris County, and Frank J. Schnettler, Morristown, N.J., assignors to Bell Telephone Laboratories, Incorporated, New York, N.Y., a corporation of New York Filed July 31, 1962, Ser. No. 213,639 7 Claims. (Cl. 252-625) This invention relates to a method for making ferrite materials having a substantially rectangular hysteresis loop characteristic and low coercive force, and further to the materials so produced.

Ferrite materials having substantially rectangular hysteresis loops and low coercive forces are well known in the art and advantageously utilized in magnetic memory devices such as that described in an article by J. A. Rajchman in the October 1953 Proceedings of the Institute of Radio Engineers, Volume 41 No. 10, pages 1407- 1421, entitled A Myriabit Magnetic Core Matrix Memory Element.

United States Patent 2,715,109 issued August 9, 1955, to Albers-Schoenberg, describes a MnO-MgOFe O ferrite system exhibiting particularly desirable hysteresis loop and coercive force characteristics. This system encompasses the compositional range of 5 to 60 mol percent MnO, 8 to 50 mol percent MgO, and 25 to 50 mol percent Fe O A lowering in the coercive force exhibited by these compositions, particularly over the compositional range 4-67 mol percent MnO, 8-55 mol percent MgO, and 25-475 mol percent Fe O is realized with zinc oxide additions of up to 8 percent by weight of composition, in accordance with United States Patent 2,981,689, issued April 25, 1961 to Albers-Schoenberg. Additions above 8 percent are strictly avoided due to the adverse effect of the zinc oxide additions on the hysteresis loop characteristic of the ferrite system.

As discussed in these patents, calcium oxide additions to these compositions over the restricted range of 0.5 to 5.0 percent by weight of composition act to further lower coercive force without significantly detracting from the rectangularity of the hysteresis loop. Additions of at least 0.5 percent are required to noticeably lower coercive force, while additions above 5.0 percent sufficiently detract from the rectangular hysteresis loop characteristic so as to preclude their use.

In accordance with the instant invention, it has been determined that calcium inclusions in the above-identified magnesium-manganese ferrite compositions in amounts smaller than heretofore utilized by the art result in significantly lower coercive force values when the calcium is added by the method of the invention.

More particularly, it has been found that the introduction of calcium during the ferrite-forming process in the form of a soluble salt having a solubility with respect to calcium of at least one gram of calcium per 100 cc. of water permits the attaining or minimum coercive force values while maintaining rectangularity of the hysteresis loop. A low coercive force, rectangular hysteresis loop composition result from calcium additions made by this method over the calcium inclusion range of 0.075 to 0.30 percent by weight of the composition.

A more complete understanding of the invention may be gained from the following description in conjunction with the accompanying drawing, in which:

FIG. 1 is a graph on coordinates of coercive force in oersteds against weight percent calcium showing the coercive force of two identical ferrite compositions containing varying amounts of calcium, the calcium being added as a carbonate to the composition depicted by curve 1 and as a soluble salt to the composition depicted by curve 2;

FIGS. 2 through 4 are graphs on coordinates of magnetic induction B in gauss against field strength H in oersteds, showing reproductions of the actual pictures of hysteresis loops as traced on the screen of an oscilloscope of three identical ferrite compositions containing varying amounts of calcium added to the compositions during processing as a soluble salt, the ferrites being fired at a temperature of 1300 C. for 7 /2 hours; and

FIG. 5 is a graph on coordinates of magnetic induction B in gauss against field strength H in oersteds, showing a reproduction of an actual picture of a hysteresis loop as traced on the screen of an oscilloscope of a MgO-MnO-ZnOFe O ferrite composition containing 0.2 percent by weight calcium added to the ferrite as a soluble salt, the ferrite being fired at a temperature of 1250 C. for 10 hours.

Referring more particularly to FIG. 1, depicted curve 1 shows the relationship between coercive force and calcium content of MnO-MgO-Fe O ferrite composition in which the calcium was added as calcium carbonate. This curve is substantially identical to the one resulting when calcium is added as calcium oxide. Commensurate with the art, for example United States Patent 2,715,109, calcium heretofore has been utilized in the ferrite-forming process as either the oxide or carbonate.

Curve 2 of FIG. 1 depicts the relationship between coercive force and calcium content of the same composition as curve 1. However, in accordance with the invention, calcium was added as a soluble salt, in this instance calcium acetate. This curve is exemplary of other soluble calcium salts, such as calcium benzoate, having a solubility with respect to calcium of at least one gram of calcium per cc. of water.

The significant decrease in coercive force realized by calcium additions in the form of soluble salts is illustrated by a comparison of curves 1 and 2. As shown by curve 2, calcium additions in the form of soluble salts result, for 0.1 percent calcium, in a decrease in coercive force from 1.04 to 0.67 oersteds. Increasingly larger additions result in a correspondingly sharp decrease in coercive force until, for example, a coercive force of 0.22 5 oersted is achieved for calcium additions of 0.25 percent by Weight. Although not plotted, further decreases in coercive force result from even larger additions.

In contrast, as shown by curve 1, calcium additions in the form of oxides or carbonates result, for 0.1 percent calcium, in a decrease in coercive force from 1.04 oersteds to 0.775 oersted. Thereafter, further calcium additions cause the coercive force to increase to an essentially stable value of 1.0 to 1.04 oersteds over the calcium inclusive range of 0.25 to 0.72 percent by weight of composition. A decrease to 0.71 oersted is then experienced over the calcium inclusion range of 0.8 to 1.0 percent. Although not plotted, further calcium additions up to 1.6 percent decrease the coercive force to 0.65 oersted.

Both ferrite compositions depicted by curves 1 and 2 of FIG. 1 have the same basic ferrite composition: 32.1 mol percent magnesium oxide, 25 mol percent manganese oxide, and 42.9 mol percent ferric oxide. Both compositions Were processed under identical conditions including a final firing at 1300 C. for 12.5 hours. The data exemplified by curves 1 and 2 of FIG. 1 is exemplary of all magnesium-manganese ferrite compositions disclosed in United States Patents 2,715,109 and 2,981,689.

FIGS. 2 through 4 show the hysteresis loops associated with a 32.1 mol percent magnesium oxide, 25 mol per cent manganese oxide, and 42.9 mol percent ferric oxide ferrite composition containing 0, 0.1, and 0.25 percent by weight calcium, respectively, the calcium being added to the composition during processing as calcium acetate. The 0.1 percent calcium-containing composition, in common with the calcium-free compositions, exhibits good rectangul-arity and sharp corners. The 0.25 percent calcium-containing composition, while also exhibiting good rectangul-arity, has somewhat rounded corners. Although not shown in the figures, it has been found that the corners of the hysteresis loops of compositions containing an amount of calcium in excess of 0.30 percent are too rounded to satisfy the requirements of a rectangular loop ferrite.

Commensurate with the dual objectives of forming a low coercive force, rectangular hysteresis loop ferrite composition, the data discussed in conjuction with the figures dictates a calcium content for the previously described ferrite compositions of 0.075 to 0.30 percent calcium by weight of the composition. Calcium inclusions greater than 0.30 percent adversely affect the rectangularity of the hysteresis loop, with inclusions less than 0.075 percent being too small to sufficiently minimize coercive force. Based on these considerations, a preferred calcium content range is 0.13 to 0.30 percent by weight, with an optimum range being 0.20 to 0.25 percent.

FIG. 5 shows the hysteresis loop associated with a 20 mol percent magnesium oxide, 23.1 mol percent manganese oxide, 39.5 mol percent ferric oxide, and 17.4 mol percent zinc oxide ferrite composition containing 0.2 percent by weight calcium. As shown, the zinc-containing composition exhibits good rectangularity and the corners of the curve, while being somewhat rounded, are sufficiently sharp to satisfy the requirements of a rectangular hysteresis loop ferrite. Zinc oxide additions in excess of 18 mol percent sufficiently detract from the rectangularity of the loop as to preclude their inclusion in the magnesium-manganese ferrite compositions disclosed in United States Patents 2,715,109 and 2,981,689.

As evidenced by FIG. 5, therefore, the calcium-containing compositions of the invention permit the beneficial inclusion of zinc oxide in amounts up to 18 mol percent (14 percent by weight of composition). In contrast, United States Patent 2,981,689 precludes such additions in amounts greater than 8 percent by weight due to their adverse effect on the rectangularity of the loop.

With the exception that calcium is initially present as a soluble salt, the ferrite-forming process of the invention is otherwise conventional and, as such understood by the art. Commensurate with the art, such processing includes forming a slurry of the desired components, the components being present as the oxides or other compounds which, with firing, will yield the oxides. The slurry also contains calcium present as a soluble salt having a solubility with respect to calcium of at least one gram of calcium per 100 cc. of water. Since the amount of water necessary to form the slurry is sufficient to dissolve the salt, the salt may be introduced to the slurry mixture as either the salt per se or a solution of the salt in water.

After mixing the components, the slurry is dried, resulting in a fine dispersion of the calcium salt throughout the mixture. The mixture is then calcined, which causes the salt to decompose, leaving calcium oxide finely dispersed throughout the calcined mixture. In accordance with accepted practice, an illustrative calcining example would comprise heating the mixture over an appropriate temperature range of 800 C. to 1100 C. for 2 to 16 hours.

The agglomerations formed during calcining are broken up by ball milling, generally for a period of 5 to hours, in a carrier such as water, acetone, ethanol, or carbon tetrachloride. Typically, a binder is added during ball milling to aid in properly binding the composition together. Although not so limited, conventional binders include polyvinyl alcohol or Opal Wax (hydrogenated castor oil) for a water carrier and parafiin or Hal-owax (chlorinated naphthalene) for organic carriers.

The ball-milled slurry is then dried and the resulting solids granulated into particles of nearly uniform size. Generally, a 10 or #20 United States standard mesh is used for this purpose. The particles are then formed into the desired configuration under pressures in the order of 5,000 to 50,000 pounds per square inch. Final firing of the shaped body completes formation of the ferrite com-position. Such firing involves heating at temperatures preferably in the order of 1200 C. to 1350 C. for several hours, for example 7 to 15 hours. The firing is generally carried out in an oxygen-containing atmosphere, the fired product being then cooled to room temperature in an inert atmosphere such as nitrogen.

It is understood that the preceding outline of one method for preparing ferrite articles is to be construed as illustrative only, other methods being readily apparent to those skilled in the art. The only critical processing step differing from that conventionally utilized by the art is the addition of calcium as the previously discussed soluble salt to the mixture of desired components before the calcining step.

The following specific examples are given by way of illustration, and are not to be construed as limiting in any way the scope and spirit of the invention.

Example 1 54.7 grams magnesium carbonate, 58.0 grams manganese carbonate, 138.1 grams ferric oxide, and 0.79 gram calcium acetate were dry mixed. The mixed ingredients were funneled into an Eppenbach Homo-Mixer and enough distilled water was added thereto to form a slurry. The slurry was then dried in a heated planetary mixer. The dry filter cake thus obtained was then calcined in air at a temperature of 900 C. for 16 hours. After calcining, the mixture was ball-milled in carbon tetrachloride for 16 hours. A ten percent by weight addition of Halowax to serve as a binder was introduced during ball milling. After ball milling, the solvent was substantially removed by drying the mixture in a heated planetary mixer. The material was then granulated by passing it through a #20 United States standard screen mesh and then further dried for six hours in a vacuum at a temperature of 45 C. to remove the last traces of the solvent. The material was then shaped into a ring having the dimensions 0.50 inch OD. and 0.35 inch I.D. under a pressure of 50,000 pounds per square inch. After shaping, the ring was dewaxed by bringing it to a temperature of 400 C. over a period of six hours and maintaining the 400 C. temperature for another six hours. The final firing of the ring was carried out in an oxygen atmosphere at a temperature of 1300 C. for 7.5 hours. The ring was then allowed to cool to room temperature in a nitrogen atmosphere.

The formed ring had the composition of 32.1 mol percent magnesium oxide, 25 mol percent manganese oxide, 42.9 mol percent ferric oxide, and 0.1 percent calcium by weight of the composition. The ring had the hysteresis loop depicted by FIG. 3 of the drawing and a coercive force of 0.67 oersted.

Example 2 54.7 grams magnesium carbonate, 58.0 grams manganese carbonate, and 138.1 grams ferric oxide were dry mixed. The mixed ingredients were funneled into an Eppenbach Homo-Mixer and enough distilled Water was added thereto to form a slurry. milliliters of calcium acetate solution containing 1.97 grams of calcium acetate was then added to the slurry, which then underwent the same processing steps described in conjunction with Example 1.

The formed ring had the composition: 32.1 mol percent magnesium oxide, 25 mol percent manganese oxide, 42.9 mol percent ferric oxide, and 0.25 percent by weight calcium. The ring had the hysteresis loop depicted by Example 3 33.2 grams magnesium carbonate, 52.2 grams manganese carbonate, 124.1 grams ferric oxide, 27.9 grams zinc oxide, and 1.58 grams calcium acetate were dry mixed. The mixture then underwent the same processing steps described in conjunction with Example 1.

The formed ring had the composition: mol percent magnesium oxide, 23.1 mol percent manganese oxide, 39.5 mol percent ferric oxide, 17.4 mol percent zinc oxide, and 0.2 percent by Weight calcium. The ring had the hysteresis loop depicted by FIG. 5 of the drawing and a coercive force of 0.13 oersted.

What is claimed is:

1. A method of making a rectangular hysteresis loop ferrite composition comprising the steps of slurrying with water, drying, and calcining a mixture comprising components equivalent to 5 to 60 mol percent manganese oxide, 8 to 50 mol perecnt magnesium oxide, to mol percent ferric oxide, and containing from 0.075 to 0.30 percent calcium by Weight of the mixture added as a soluble salt having a solubility with respect to calcium of at least one gram of calcium per 100 cc. of Water, shaping the resultant material under pressure into the desired configuration, and firing the shaped material at a temperature of from 1200 C. to 1350 C., the said soluble salt being of such nature as to yield calcium oxide during the said method.

2. The method in accordance with claim 1 wherein said mixture contains from 0.13 to 0.30 percent calcium added as calcium acetate.

3. The method in accordance with claim 2 wherein said mixture contains from 0.20 to 0.25 percent calcium.

4. A method of making a rectangular hysteresis loop MnO 4 to 67 MgO 8 to Fe O 25 to 47.5 ZnO 0 to 18 and from 0.075 to 0.30 percent calcium by weight of the mixture added as a soluble salt having a solubility with respect to calcium of at least one gram of calcium per cc. of Water, shaping the resultant material into the desired configuration under a pressure of 5,000 to 50,000 pounds per square inch, and firing the shaped material at a temperature of from 1200 C. to 1350 C., the said soluble salt being of such nature as to yield calcium oxide during the said method.

5. The method in accordance with claim 4 wherein said mixture contains from 0.13 to 0.30 percent calcium added as calcium acetate.

6. The method in accordance with claim 5 wherein said mixture contains from 0.20 to 0.25 percent calcium.

7. Product produced by the method of claim 1.

References Cited by the Examiner UNITED STATES PATENTS 2,903,429 9/1959 Guillaud 25262.5 2,981,689 4/1961 Albers-Schoenberg 25262.5

FOREIGN PATENTS 1,174,680 11/1958 France.

TOBIAS E. LEVOW, Primary Examiner.

MAURICE A. BRINDISI, Examiner.

Claims (2)

1. A METHOD OF MAKING A RECTANGULAR HYSTERESIS LOOP FERRITE COMPOSITION COMPRISING THE STEPS OF SLURRYING WITH WATER, DRYING, AND CALCINING A MIXTURE COMPRISING COMPONENTS EQUIVALENT TO 5 TO 60 MOL PERCENT MANGANESE OXIDE, 8 TO 50 MOL PERCENT MAGNESIUM OXIDE, 25 TO 50 MOL PERCENT FERRIC OXIDE, AND CONTAINING FROM 0.075 TO 0.30 PERCENT CALCIUM BY WEIGHT OF THE MIXTURE ADDED AS A SOLUBLE SALT HAVING A SOLUBILITY WITH RESPECT TO CALCIUM OF AT LEAST ONE GRAM OF CALCIUM PER 100 CC. OF WATER, SHAPING THE RESULTANT MATERIAL UNDER PRESSURE INTO THE DESIRED CONFIGURATION, AND FIRING THE SHAPED MATERIAL AT A TEMPERATURE OF FROM 1200*C. TO 1350*C., THE SAID SOLUBLE SALT BEING OF SUCH NATURE AS TO YIELD CALCIUM OXIDE DURING THE SAID METHOD.

7. PRODUCT PRODUCED BY THE METHOD OF CLAIM 1.

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