US 3925114 A
Description (OCR text may contain errors)
United States Patent 1191 Takahashi et a1.
[ PROCESS FOR PREPARATION OF MAGNETIC ALLOY POWDER  Inventors: Noboru Takahashi; Mutsuaki Nakamura; Sadao Ozaki; Hiromasa lsono; Iwao F ukushima, all of Yokohama, Japan  Assignee: Victor Company of Japan, Limited,
Japan  Filed: Apr. 29, 1974  Appl. No.: 465,300
 Field of Search 75/.5 A, .5 AA, .5 R;'
 References Cited UNITED STATES PATENTS 2,497,268 2/1950 Neel 75/ 5 AA 1 Dec. 9, 1975 2,651,105 9/1953 Neel 75/.5 AA 2,660,522 11/1953 La Tronche 75/.5 AA 2,853,374 9/1958 Schaufelberger 75/.5 AA
OTHER PUBLICATIONS Bozorth, R; Ferro Magnetism, New York, 1951. pp. 184-185.
Primary Examiner-Walter R. Satterfield Attorney, Agent, or Firm-Robert E. Burns; Emmanuel J. Lobato; Bruce L. Adams  ABSTRACT 10 Claims, 17 Drawing Figures US. Patent Dec. 9, 1975 Sheet 1 of2 3,925,114
20 Al (mole '1.)
PRIOR ART 300 A00 TEMPERATURE ("c m 63,; mzbjmmv women 5280 FIG. 6
10 Al (mole'h) FIG. 7
Al (molc'h) FIG. 3
PRIOR ART TEMPERATURE c) FIG. 8
10 Al (moleh) FIG. 4
PRIOR ART TEMPERATURE W2) U.S. Patent Dec. 9, 1975 Sheet 2 of 2 3,925,114
300 300 TEMPERATURE c) F I G 9 300 400 TEMPERATURE (c) A w3 M2255 womom M2058 FIG I4 300 400 TEMPERATURE c) FIG. I O
300 400 TEMPERATURE c) FIG. I6
300 400 TEMPERATURE c) A mAm MESH: 5:35.22: 2398 FIG. I I
300 A00 TEMPERATURE (c) F I G I7 300 400 TEMPERATURE ("c PROCESS FOR PREPARATION OF MAGNETIC ALLOY POWDER The present invention relates generally to a process for the preparation of magnetic powder materials composed of Fe, Co and/or Ni, and more particularly to an improvement of a process of preparing such magnetic alloy powders by reduction of oxalates at elevated temperatures.
A magnetic material for use in recording media such as magnetic tapes is required to have a high residual magnetization and a large coercive force. In recent years, the familiar iron oxide powder has been gradually replaced by superior magnetic metal or alloy powders to meet growing requirements for magnetic tapes of higher recording densities. Typical examples of such magnetic powder materials are ferromagnetic metals such as Fe, Co and Ni, and their alloys.
These magnetic metal and alloy powders are usually prepared by a reduction process, in which a crystalline powder of a single, binary or ternary oxalate (or formate) is reduced through heating in a reducing atmosphere. As is known, chemical and physical properties such as composition, mean particle size and particle size distribution of a magnetic powder material produced by such a process are dependent on reaction conditions used for the preparation of the oxalate or formate. It is also known that the magnetic properties of the obtain ed powder materials are greatly dependent of the reduction reaction conditions besides the above reaction conditions. In general, easiness of reduction of these oxalates and extent of sintering of unit particles are varied as the reduction reaction conditions are varied. Until now, therefore, various reduction temperatures and heating times have been tried to obtain an alloy powder of excellent and balanced magnetic properties.
However, a problem in the art is that such reduction conditions have not similar but rather diverse influences on the various magnetic properties of a magnetic alloy powder. For example, a set of conditions suitable for increasing the saturation magnetization causes the unit particles to grow excessively large. This is due to progress of sintering, and results in a decreased coercive force. Under another set of conditions, which gives a large coercive force, saturation magnetization is greatly reduced because of insufficient progress of the reduction reaction and/or a partial oxidation of the reduced powder due to its relatively strong chemical activity. Consequently, it has been next to impossible to obtain a magnetic powder material having both a high residual magnetization value and a large coercive force, no matter what set of reduction conditions might have be chosen.
It is an object of this invention to provide such powders.
It is therefore a general object of the present invention to provide a process of preparing a magnetic alloy powder having a high residual magnetization and a large coercive force with an extremely little sacrifice in satu ration magnetization.
It is a more particular object of the invention to pro' vide a process of preparing an intermediate oxalate which gives such a magnetic powder material upon reduction.
It is another object of the invention to provide an appropriate temperature range for reduction of such an oxalate.
According to the present invention, these objects are accomplished essentially by allowing Fe, Co and/or Ni ions to react with oxalic acid, in the presence of Al ion, to precipitate a crystalline oxalate powder containing Al and at least one of the above three ferromagnetic metals. The amount of Al is preferably from I to 20 mole% of the total metal moles. The obtained crystalline oxalate powder is then reduced into a magnetic alloy powder in the usual way preferably at a temperature range between about 300to about 400C.
The invention will be more clearly understood from the following detailed description with reference to the accompanying drawings, in which:
FIGS. 1-4 are graphs showing variations of magnetic properties of a magnetic alloy powder prepared by a conventional process as function of reduction temperatures;
FIGS. 5-8 are graphs showing variations of similar properties of a magnetic alloy powder prepared by the process of the invention, as function of Al content;
FIGS. 9-12 are graphs similar to FIGS. 1-4 for a magnetic alloy powder prepared by the process of the invention with 4 mole% Al; and
FIGS. 13-17 are similar graphs to FIGS. 9-12 in the case of 7 mole% Al.
As summarized above, the improvement according to the invention, by the introduction of Al into a starting solution is adaptable for the preparation of either any individual metal powder of Fe, Co and Ni with aluminum or any of their mixed alloys. Hereinafter, however, the description will concern only the preparation of Fe- Co-Ni series ternary magnetic alloys with aluminum as a typical example to facilitate comparison of experimental data.
In a process according to the invention, water-soluble salts such as chlorides of Fe, Co and Ni are dissolved in water together with a similar salt of Al. The aqueous solution is adjusted to a suitable acidity, preferably to about pI-I L5, and is then mixed and stirred with a solution of oxalic acid C I-I O, 2H O in a water miscible solvent, preferably in acetone containing a small amount of toluene. The stirring is continued usually for about 10 min at room temperature or at a slightly elevated temperature to precipitate crystalline multicomponent Fe, Co, Ni and Al oxalates. The precipitate is considered not a simple mixture of four kinds of oxalates, but a crystalline four-component oxalate. A crystalline powder of this oxalate obtained through filtration, washing and drying of the precipitate is heated for several hours in a reducing atmosphere, usually in a stream of hydrogen, at a temperature ranging from about 300 to 400C to give a novel magnetic alloy powder. To accomplish the objects of the invention, it is necessary to establish a substantial co-existence of Al ion with the other three metal ions; in other words, the amount of Al in the aqueous solution should be at least about 1 mole% ofthe total metals. Existence of only a trace of Al, for example, up to 0.] mole% has little effect on the magnetic properties of a resulting alloy powder.
The introduction of Al into the intermediate oxalate crystal system contributes to remarkably augment both,
EXAMPLE l An oxalic acid solution was prepared by dissolving 252g of C l-l O .2H O in 200 ml of acetone followed by the addition of 5 ml of toluene. The temperature of the solution was kept at 35C in a constant temperature bath. This kind of oxalic acid solutions were used throughout the succeeding examples.
Meanwhile, 8.8g of FeCl .nH O, 8.6g of CoCl .6H O, 0.4g of NiCl .6l-l O and 0.2g of AlCl .6l-l O were dis solved in 75 ml of water. The aqueous solution was adjusted to pH L5 and was heated to 35C.
Then, the aqueous solution was poured into the oxalic acid solution all at once with vigorous stirring, and stirring was continued for min, keeping the liquid temperature at 35C, to allow the metal ions in the solution to completely react with the acid. The resulting precipitate was filtered, washed and dried to give a crystalline powder of mixed Fe, Co, Ni and Al oxalates. This procedure for preparation of the oxalates was unchanged throughout the succeeding examples.
The obtained oxalate powder was reduced into an alloy powder under the following conditions, which where common to all examples except for temperature.
80 mg of the oxalate powder was put in a platinum boat and was heated in a 0.5 I/min stream of hydrogen at 310C for 6 hr.
The resulting alloy powder showed the following magnetic properties:
Coercive force 880 Oe Saturation magnetization l9] emy/g Residual magnetization 64 emu/g These values and those which were obtained in the following examples and references are shown together in a Table at the end of the Reference example 2.
EXAMPLE 3 Example 2 was repeated except that the reduction was carried out at 330C.
EXAMPLE 4 Example 3 was repeated except that the reduction temperature was 370C.
EXAMPLE 5 The chloride solution was prepared by dissolving 8.2g of FeCl .nH O, 8.0g of CoCl .6H O, 0.3g of NiCl- -6H2O and 1.3g of AlCl '6H O in 75 ml of water. The reduction temperature was 330C.
EXAMPLE 6 Example 5 was repeated except that the reduction was carried out at 370C.
EXAMPLE 7 The chloride solution was composed of 7.9g of FeCl .nl-l O, 7.9g of CoCl hH O, 0.4g of NiCl .6l-I O, l.6g of AlCl .6l-l O and 75 ml of water. The reduction temperature was 300C.
EXAMPLE 8 Example 7 was repeated except that the reduction temperature was 330C.
EXAMPLE 9 7.0g of FeCl .nl-l O, 6.9g of CoCl .6H O, 0.3g of NiCl bl-l o and 3.6g of AlCl .6H O were dissolved in 75 ml of water, and the reduction was carried out at 330C.
For comparison, two reference examples will be presented, in which no Al and only about 0.1 mole% of Al were used, respectively. The reduction was carried out at 330C, and the remaining conditions were similar to those in the above examples.
REFERENCE EXAMPLE 1 8.8g of FeCl .nl-l O, 8.7g of CoCl .6H O and 0.4g of NiCl .6H O were dissolved in 75 ml of water.
REFERENCE EXAMPLE 2 The chloride solution was similar to that in Example 1 except that AlCl .6l-l O was decreased to 0.02g.
Table of the experimental data Reduction Coercive Saturation Residual Al Tern peraturc Force Magnetization Magnetization (m l PC) i /g! mu/g1 EX. l about 1 3H] 880 I9] 64 EX. 2 4 3l0 980 I80 67 EX. 3 4 330 )ll) I90 66 EX 4 4 370 750 l 90 54 EX 5 7 330 900 190 63 EX. 6 7 370 800 190 S7 EX. 7 8 300 I020 [45 54 EX. 8 8 330 930 I94 70 EX. 9 I8 330 960 I73 64 REF. l 0 330 700 200 REF 2 about 0.l 330 700 203 EXAMPLE 2 It will be apparent from the above Table that an Al- Example 1 was repeated except that the chloride socontaining Fe-Co-Ni alloy powder prepared by a prolution was prepared by dissolving 8.5g of FeCl .nl-I O, 8.2g of CoCl .6H O, 0.3g of NiCl .6H O and 0.7g of AlCl .6l-l O in 75 ml of water.
cess of the invention shows a remarkable increase both in coercive force and residual magnetization accompanied with only a slight decrease in saturation magneti- 4.5 zation as compared with analogous alloys containing no or only a trace of Al.
Such advantages of the inventiori are illustrated in the graphs of the accompanying drawings to'gether with influences of the Al content in the mixed crystal and the reduction temperature on the magnetic properties of the resulting alloy powders.
The graphs of FIGS. 1, 2, 3 and 4 show the effect of the reduction temperature in a conventional process on the coercive force, saturation magnetization, residual magnetization and the rectangular ratio (residual magnetization/saturation magnetization), respectively, of a Fe-Co-Ni alloy powder. The abscissas represent the reduction temperature, and the ordinates the relative values of the above properties, in which 1.0 represents the value obtained through reduction at 330C.
Referring to FIG. 1, the coercive force increases as the reduction temperature is decreased. If a coercive force about 1.2 times as large as that attained through the reduction at 330C (which is commonly employed in conventional methods) is desired, the reduction tem perature must be lowered to about 280C. Such a low temperature, however, causes the reduction reaction to proceed very slowly or not at all, and hence requires an extremely long reaction time and/or the use of a catalyst. Besides, even if the desired increase in the coercive force is attained by reduction at a temperature below 300C, both the saturation and residual magnetization values decrease sharply at such a temperature as seen from FIGS. 2 and 3. FIG. 4 also indicates that a significant increase in the coercive force is impossible when reduction is carried out at about 300C.
FIGS. 5-8 show the effect of the Al introduction into a Fe-Co-Ni alloy having a composition substantially equal to that obtained by reduction of the oxalates of Example 2 at 330C. The abscissas represent the amount of the introduced Al in mole% of the total metals, and the ordinates represent the relative values of the magnetic properties being scaled by the same standard as in FIGS. 1-4.
As seen from FIG. 5, the coercive force increases re markably as the Al content is increased up to about 5 mole% and continues to slightly increase thereafter. Augmentation in the residual magnetization is also attained in a wide range of Al content, but a peak exists in FIG. 7 at about 4 mole% Al content. Although the saturation magnetization in FIG. 6 decreases gradually as Al is increased, the rate of drop is very low, and FIG. 8 shows that the rectangular ratio is increased in a manner similar to the coercive force in FIG. 5. To put these data together, it is apparent that the introduction of Al into a Fe-Co-Ni alloy powder in an amount from about 1 to about mole% of the total metals brings about a surprising improvement in the coercive force and residual magnetization of the alloy with only an insignificant reduction of the saturation magnetization. Even when only 1 mole% of Al was added as illustrated in Example 1, the coercive force and residual magnetization increased by about 40 percent and about 30 percent, respectively, and the rectangular ratio was increased by about 50 percent compared with a corresponding conventional alloy containing no Al, while decrease in the saturation magnetization was limited to about 5 percent. When a great importance is attached to the saturation magnetization, the Al content is preferably limited to about l0 mole% at the most.
FIGS. 9-16 show the effect of the reduction temperature in the process according to the invention, in which 6 the ordinates are scaled by. the same standard as in FIGS. 1-4. FIGS. 9-12 and 13-17 stand for 4 mole% A] content and 7 mole%, respectively.
As seen from these Figures, the augmentation in the coercive force and residual magnetization by the introduction of Al can be attained when the reduction of the crystalline oxalate is carried out at a temperature from about 300to about 400C. When a maximum augmentation is wanted, the reduction temperature is preferably kept within a range between about 3 l0and about 350C.
In addition to the above described merits of a process of the invention, the simplicity and ease of practical application should be noted as important advantages of the process.
What is claimed is:
1. A process for the preparation of an aluminum-containing magnetic alloy powder, comprising iron and at least one of cobalt and nickel, the process comprising the steps of:
preparing an aqueous solution of water-soluble salts of the respective alloy component metals and a water-soluble salt of aluminum, the amount of said salt of aluminum being such that the amount of aluminum ion in said solution is between I and 20 mole of the total metal ions;
regulating pH of said solution to about 1.5;
preparing a solution of oxalic acid in a mixture of a major amount of acetone and a minor amount of toluene;
mixing said aqueous solution and said solution of oxalic acid with stirring to precipitate a crystalline powder consisting of the oxalates of said alloy component metals and aluminum; and
heating said crystalline powder in a hydrogen atmosphere at a temperature between 300 and 400C until said powder is reduced to powdered metal magnetic alloy. 2. A process according to claim 1, wherein said mixture consists of about 200 parts by volume of acetone and about 5 parts by volume of toluene.
3. A process according to claim 2, wherein said solution of oxalic acid is prepared by dissolving about 25 parts by weight of oxalic acid as C d- 0 211 0 in about parts by weight of said mixture.
4. A process according to claim 1, wherein said water-soluble salts of the respective alloy component metals and said water-soluble salt of aluminum are chlorides.
5. A process according to claim 1, wherein said heating step is continued for about 6 hr.
6. A process according to claim 1 for the preparation of a magnetic alloy powder of Fe, Co, Ni and Al, comprising the steps of:
preparing an aqueous solution of FeCl CoCl NiCl and AlCl the amount of AlCl being such that the amount of aluminum ion in said solution is between 1 and 20 mole of the total metal ions;
regulating pH of said solution to about 1.5;
preparing a solution of oxalic acid in a mixture of about 200 parts by volume of acetone and about 5 parts by volume of toluene by dissolving about 25 parts by weight of oxalic acid as C H O .2I-I O in about 165 parts by weight of said mixture;
mixing said aqueous solution with said solution of oxalic acid with stirring to precipitate a crystalline powder of the oxalates of Fe, Co, Ni and Al; and
7 8 heating said crystalline powder in a stream of hydro- 8. A process according to claim 6, wherein said temgen gas at a temperature between 300and 400C p r mr i between 3lOand 350C. for about 6 hr to form said magnetic alloy powder. 9- A magnetic metal alloy powder prepared accord- 7. A process according to claim 6, wherein said ing to the Proms5 of claim amount of aluminum ion is between I and 10 mole of A magnet: metal powder prepared accord' mg to the process of claim 8. the total metal IOIIS. 4r t UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO. 1 3,925,11 r DATED December 9, 1975 INVENTOR(S) Nobor'u TAKAHASHI et al It is certified that error appears in the above-rdentified patent and that said Letters Patent are hereby corrected as shown below:
In the Heading of the patent, please insert as Item  the following:
--Foreign Application Priority Data l May 1973 Japan HEB- 49125 23 August 1973 Japan 48-93883 Signed and Scaled this sixth D3) Of April 1976 :UTHC. MASON C. MARSHALL DANN Heslmg ()jju'er (mmm'ssr'rmer uj'latenrs and Trademarks