JPS63260827A - Production of magnetic powder - Google Patents

Abstract

PURPOSE:To enable production of magnetic powder having an uniform and fine particle diameter and excellent magnetic characteristics, by adding a flux to coprecipitates in the presence of an alkaline substance to evaporate moisture and firing the resultant substance in producing a ferrite, such as Ba, by a coprecipitating method. CONSTITUTION:An aqueous solution containing Fe ions and one or more metallic ions of Ba, Sr, Ca and Pb at a molar ratio so as to provide 8-16mol. Fe ions and 0.8-3mol. one or more metallic ions is mixed with an aqueous solution of an alkali so as to afford pH >=5. The resultant coprecipitates, which are then heated in the presence of an alkaline substance in an amount of >=0.2mmol. based on 1mol. Fe atom therein and a flux at >=700 deg.C to afford <=70wt.% moisture content. The resultant substance is subsequently fired at 600-1,200 deg.C. The aimed magnetic powder having an equally uniform average particle diameter as small as <=0.15mu and improved magnetic characteristics without aggregating or sintering of particles is obtained by this method.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a method for producing magnetic powder, and more specifically, a method for easily producing hexagonal ferrite magnetic powder consisting of fine particles particularly suitable for high-density magnetic recording media. Relating to a method of manufacturing.

(Prior Art) In recent years, with the demand for higher density magnetic recording, perpendicular magnetic recording methods that record a magnetic field in the thickness direction of a magnetic recording medium have been attracting attention.

By the way, ferrite having hexagonal uniaxial magnetization anisotropy, such as paricum ferrite, is known to be a magnetic powder suitable for the above-mentioned perpendicular magnetic recording method.
Ha) is an appropriate value (200 to 20,000・), the saturation magnetization (σI) is as high as possible, and the particles are small (generally 0
．． 3 particles or less) and is uniform, free of particle agglomeration, sintering, etc., and has good dispersibility.

Conventionally, various methods are known for producing barium ferrite, such as coprecipitation method, flux method, hydrothermal synthesis method, glass crystallization method, and others. This method has been proposed in JP-A No. 60002, JP-A-58-2223, and JP-A-60-115204. Further, as a method of adding a fluxing agent to the coprecipitate, for example, Japanese Patent Application Laid-Open No. 61-55901 and Japanese Patent Application Laid-Open No. 61-1741
No. 18 is known.

(Problems to be Solved by the Invention) The production of barium ferrite by the coprecipitation method allows for very good mixing with various metals added in small amounts for coercive force control and other purposes, resulting in uniform ferrite. Since the coprecipitate is a microcrystalline powder, it has many advantages such as being able to be turned into ferrite at a relatively low temperature.

By the way, the average particle size of the magnetic powder particles used for perpendicular magnetic recording is not superparamagnetic because it directly affects the surface properties, playback output, etc. when made into recording media such as tapes and disks. It is important that they be small and uniform in degree (0.01 mm or less).

However, the particle size of magnetic powder obtained by the coprecipitation method is generally relatively large, at least 0.151 m (Japanese Patent Laid-Open No. 61-1
(See Japanese Patent Laid-Open Publication No. 74118) In addition, agglomerated powder is likely to be produced, and particles with a particle size of about 0.541 are included, resulting in poor uniformity in shape (see Japanese Patent Application Laid-Open No. 58-2223). I can't say enough about the excellent manufacturing method. In the method of adding a flux to the coprecipitate, the average particle size is 0.15 to 0.25.
Large as #L (see Japanese Patent Application Laid-Open No. 174118/1983)
In addition, the particle size distribution is large, and it is still not sufficient as a magnetic powder for perpendicular magnetic recording.

Generally, in the coprecipitation method, the voice is at least 10 or higher, usually -12
A coprecipitate is obtained under the above conditions with a large excess of alkali, which is filtered and then washed with a large excess of water until substantially no alkaline substances are present in the coprecipitate (Japanese Patent Laid-Open No. 58-56302
(see publication). This is done to avoid the presence of sintered powder during firing if alkaline substances remain in the coprecipitate.

The present inventors aimed to produce hexagonal ferrite magnetic powder with uniform and small particle size, no particle agglomeration or sintering, good dispersibility, and excellent magnetic properties.
As a result of intensive research, we were surprised to find that, contrary to the conventional wisdom as mentioned above, we included an alkaline substance in the coprecipitate, added a flux to it, heated the water to evaporate, and fired it, then added the flux, etc. The inventors have discovered that the above object can be achieved by washing away with water, and have completed the present invention.

(Means for solving the problem) According to the present invention, Fe ions are 8 to 16 moles,
An aqueous solution containing ions of one metal or 29 or more metals selected from the group consisting of Ba, Sr, Ca, and Pb in a molar ratio of 0.8 to 3 moles and an alkaline aqueous solution in which - is 5 or more. Mix to obtain a coprecipitate, and heat the coprecipitate at a temperature of 70°C or higher in the presence of an alkaline substance and a flux of 0.2 mmol or more per mol of Fe atoms in the coprecipitate. to reduce the moisture content to 70% by weight or less, then to 600% by weight.
Provided is a method for producing magnetic powder characterized by firing at a temperature of ~1200°C.

According to the present invention, the average particle size of the obtained magnetic powder is 0.15
It is possible to obtain magnetic particles that are as small as 300 yen or less, are uniformly arranged, have no agglomeration or sintering, have good dispersibility, and have excellent magnetic properties.

Fe ions, Ba ions used in the present invention,
Sr ions, Ca ions, PB ions, and various metal ions (for example, Mg e So + Yt vrTa,
Mo+W, Re, Ru t Os e Rh,
Ir + Pd*Pt.

Ag g Hg g Ga + Go # Amp
To I Co HN1 # Mn H2n , Ti
, In, Nb, am, Nd, Zr
, Cr z La.

Cu, Cct, AtpTt, Ss,
SneP, Sb, Bt.

Ss, D@, Pr + Tb, Gd,
To prepare an aqueous solution containing one or more metal ions selected from Yb, Th, U, etc., water-soluble metal salts of each metal, such as nitrates, sulfates, and
Oxide compounds, ammonium salts, carbonates, acid anhydrides, condensed acids, etc. can be used. In particular, if the Fe ion raw material is chloride, nitrate or sulfate, and Ba ion, Sr
It is preferable that the raw materials for the ions, C1 ions and pb ions are chlorides or nitrates. Even in this case, there are no particular restrictions on the raw materials for each of the free metal ions that are added in small amounts to control magnetic properties or the like.

In order to obtain the desired magnetic powder in the present invention, at least 8 to 16 moles of Fe ions, Ba, 8r*Ca, and P
An aqueous solution containing ions of one or more metals selected from the group consisting of b in a molar ratio of 0.8 to 3 moles must be used. In addition, when adding a small amount of the various metal ions mentioned above for the purpose of controlling magnetic properties, etc., the total amount of these added metal ions is desirably 4 moles or less with respect to the above molar ratio. This is because only when the molar ratio of each metal ion is in such a range, the magnetic powder for magnetic recording can exhibit excellent magnetic properties (coercive force of 200 to 20,000 e and saturation magnetization of 40 emu AI or more).

Further, the concentration of the metal ions in the aqueous solution is preferably such that the total amount of metal ions is 10 mol/l or less, more preferably 2 mol/l or less.

On the other hand, the alkaline component used in the alkaline aqueous solution is not particularly limited as long as it is water-soluble, and examples thereof include alkali metal hydroxides, carbonates, ammonia, ammonium carbonate, and the like. For example, NaOH.

KOH, Na2CO,, NaHCOs, K2CO2
, KHCO3°NH4OH, (NH4)2Co3, etc., and the combination of hydroxide and carbonate is particularly preferred.

The concentration of the alkaline aqueous solution is such that the total amount of alkali metal ions and/or ammonium ions is preferably 25 mol.
/j' or less, more preferably 10 mol/J or less.

In the method of the present invention, the metal ion aqueous solution and the alkaline aqueous solution are mixed to obtain an aqueous solution containing a coprecipitate. In this case, the aqueous alkali solution may be added to the aqueous metal ion solution, or conversely, the aqueous metal ion solution may be added to the aqueous alkaline solution, or they may be mixed all at once.

In the present invention, - of the aqueous solution containing the coprecipitate must be 5 or more, and preferably has a pH of 8 or more at a liquid temperature of 25° C. from the viewpoint of the magnetic properties and powder properties of the magnetic powder.

Further, in the present invention, the temperature during coprecipitation can be arbitrarily selected within the range of 0 to 100°C.

In the present invention, the solution containing the coprecipitate obtained in this way is filtered and washed with water according to a conventional method, and the water-soluble substances contained in the solution containing the coprecipitate, such as excess alkaline substances, are removed.
The nine NaCl generated during coprecipitation and various metal ions that did not co-precipitate may be washed away, or in the present invention, such washing is not performed sufficiently, and an appropriate amount of the solution containing the coprecipitate is washed. - It is also possible to simply filtrate and concentrate.

Solution K containing the water-washed coprecipitate or unwashed coprecipitate thus obtained, an alkaline substance, and a flux are added.

The alkaline substance to be added may be any substance that exhibits -8 or more when made into a 1 mol/l aqueous solution, but in addition to the alkali component used to generate the coprecipitate mentioned above, alkaline earth Metal hydroxides, carbonates, and amines and other water-soluble organic alkaline compounds are commonly used.

The amount of the alkaline substance added is 0.2 mmol or more, preferably 0.5 mmol or more per mole of Fe contained in the coprecipitate.
It is sufficient if the amount is more than 5 moles, but if the amount added is more than 5 moles, no further effect will be observed.

On the other hand, the flux added at the same time is usually one or more compounds selected from the group consisting of sodium chloride, potassium chloride, barium chloride, stronticum chloride, sodium 9m sulfate, potassium sulfate, and lithium sulfate. is used, and usually 0.0
It is added in an amount of 1 to 1011 times by weight, preferably 0.05 to 3 times by weight.

In the present invention, when using a solution containing a coprecipitate that has not been sufficiently washed as a substitute for the solution of the coprecipitate washed with water, it is necessary to appropriately select the amount of the solution containing the coprecipitate. Substances such as sodium chloride can be used effectively.

Furthermore, it is also possible to control the amount of alkaline substances, sodium chloride, etc. by adding hydrochloric acid, nitric acid, acetic acid, sulfuric acid, etc. to the washed coprecipitate.

It is preferable to add the alkaline substance and flux in the presence of water, but the coprecipitate is usually in the form of a cake or slurry containing sufficient moisture.

The coprecipitate to which the alkaline substance and flux are added is heated to 70° C. or higher to evaporate and dry the moisture. Specific methods for evaporative drying include drum dryers, spray dryers,
Examples include paddle dryers and groove dryers. In the present invention, the temperature at which water is evaporated is always 70°C.
It must be more than that. If this temperature is below 70°C, the average particle size of the magnetic powder obtained will be 0.15 μm or more.

It is better to evaporate the moisture sufficiently, but if the moisture content is 70
If it is less than or equal to 1, there is no problem. After most of the moisture has been evaporated in this manner, the material is dried at an appropriate temperature, usually 100 to SOO DEG C., to evaporate the remaining moisture.

This dried product may be fired as it is, but for the purpose of uniform firing, it should be pulverized, tableted, or extruded at a temperature of 600 to 1200°C, preferably 650 to 950°C. Bake at ℃. Baking time is 0.
A suitable firing time is 5 to 50 hours, and the firing atmosphere may be either a nitrogen atmosphere or an oxygen atmosphere, but it is usually preferable to carry out the firing in an air atmosphere. Further, preliminary firing may be performed in advance of the firing.

The fired product fired at 600 to 1200°C is then washed and dried. Cleaning may be carried out by any method as long as it can sufficiently remove impurities such as metal chlorides, metal sulfates, metal nitrates, other alkali metal ions, and excess barium hydroxide contained in the fired product. . As the cleaning liquid, water or an aqueous solution such as acetic acid, nitric acid, or hydrochloric acid can be used.

The baked product that has been sufficiently washed is then dried, but the drying method is not particularly limited.

(Effect of the invention) The hexagonal ferrite magnetic powder obtained by the present invention is
It is made up of uniform particles with an average particle diameter of 0.115 particles or less, each of which is individually dispersed. In addition, this magnetic powder does not cause particle aggregation or sintering, has good dispersibility, and has a particle size of 200 to 2000.
It exhibits a coercive force of 0e and a saturation magnetization of 40 emu/iP or more. Regarding coercive force, various elements (e.g. Co,
It can be freely controlled by adding T1, etc.).

Further, according to the present invention, the coercive force can be increased to 20,000e or more, and it can be used as a permanent magnet such as a rubber magnet or a plastic magnet.

In this case as well, the average particle size of the resulting magnetic powder can be reduced to 0.15 mm or less, resulting in a much higher coercive force than conventionally used magnetic powder for rubber magnets and glass magnets. be able to.

(Example) The present invention will be described in more detail with reference to Examples below. In addition, the coercive force and saturation magnetization in the examples were measured using a VSM (vibrating magnetism measurement device), and the maximum applied magnetic field m 10 KO・
, Measured at a measurement temperature of 28°C. The average particle diameter was calculated by measuring the maximum diameter of 400 particles from a photograph taken with a transmission electron microscope and calculating the arithmetic mean.

-Also, the compositional formula of the magnetic powder shown in the examples uses the atomic ratio of each element at the time of raw material preparation. The display of oxygen in the magnetic powder components has been omitted for the sake of brevity.

Example I B Hatake ct2・2H200, 55 mol, Tic/, 40.
375 moles of CoCl2'6H200, 375 moles of CoCl2'6H200, and 5,25 moles of FeCA3'6H20 were dissolved in 101 distilled water in this order, and this was used as liquid A. NaOH17,
5 mol of Na2Co and 4.72 mol of Na2Co were dissolved in 15 ml of distilled water at room temperature, and this was used as Solution B. After gradually adding Solution A to Solution B heated to 50°C, the mixture was stirred at 50°C for 1 hour. The voice after stirring was 10.9. The aqueous solution containing the coprecipitate thus obtained was filtered and washed with water, and added with NaOH4,
2? After adding NaCL400iP (equivalent to 20 mmol per atomic mole of Fel), the mixture was boiled to about 100° C. using an electric heater, and the water was evaporated while stirring and mixing well until the water content reached 50 cm. The cake-like coprecipitate thus obtained was further dried completely at 300°C, and then fired in an electric furnace at a firing temperature of 850°C for 2 hours. This fired product was washed with water until all soluble materials were removed, filtered and dried to obtain a "1.1" 10.5 CoO,75"0.7
A barium ferrite magnetic powder represented by No. 5 was obtained. The fine powder thus obtained had an average particle size of 0.061 tsn.
The particles were in the form of a plate with a thickness of 0.019 #L, and each particle was disjointed, but all together, and had a beautiful shape.

When we measured the magnetic properties, Ha was 7200e and σ Hata was 5.
It was 6 emu/f.

Example 2 Solution A and Solution B were produced in the same manner as in Example 1, and after gradually adding Solution B and Solution KA heated to 50°C, the mixture was stirred at 50°C for 1 hour. A panoramic view of the aqueous solution containing the coprecipitate thus obtained is shown in IA.
After filtration, add NaOH to the solution containing the coprecipitate.
,5iP (equivalent to 1 lulu and 12 ml of Fe raw atom)
After adding NaCL 2.59, heat to about 100℃ using an electric heating machine.
The water content was reduced to below 50 cm. Example 1 below
Barium ferrite was produced in the same manner. The barium ferrite fine particle powder thus obtained has an average particle size of 0.
．． It was a plate-like material with a thickness of 0.062 μm and a thickness of 0.015 μm, and each particle was perfectly aligned and had a nice shape. The magnetic properties were 7450e for He and 57 emu for C8.

Comparative Example 1 Barium ferrite was produced in the same manner as in Example 1 except that NaOH and NaC2 were not added to the filtered and washed coprecipitate. The obtained barium ferrite fine particles had an average particle size of 0.39 and a thickness of 0.0.
Although the particles were in the form of a #9 #L plate, many particles were seen to be strongly aggregated, and the particle size was widely distributed from large particles of 0.71 sn or more to particles of about 0.15 prIL. Shi, it was uneven and the shape was ugly. As for the magnetic properties, Hc was 8310@, and σS was 31 emuAI-.

Comparative Example 2 I4lium ferrite was produced in the same manner as in Example 1, except that NaCt was not added to the coprecipitate that had been flushed with water. The obtained parylum ferrite fine particle powder had a plate shape with an average particle size of 0.95 mm and a thickness of 0.22 prn, but many particles were observed to be strongly agglomerated, and the particle size was The particles were widely distributed, ranging from large particles of 3.0 particles or more to particles of about 0.3 particles, and were irregular and in poor shape.

The magnetic properties are He: 11200e, σS: 46 emu
/iP.

° Comparative Example 3 Instead of evaporative drying at 100°C using an electric heating machine, -
Barium ferrite was produced in the same manner as in Example 1, except that it was freeze-dried at 5° C. until moisture was removed. The obtained barium ferrite fine particle powder has an average particle size of 0.25
twn, and was in the form of a plate with a thickness of about 0.05 cotton. Also H
e was 6360·, and C3 was 41 emu.

Examples 3 to 13 Same as Example 1 except that the voice during coprecipitation, the type and amount of added alkaline substance, and the type and amount of flux shown in Table 1 were changed to those shown in Table 1. Barium ferrite was produced in a similar manner. The amount of the alkaline substance added in Table 1 is the amount per atomic mole of iron.

Examples 14-24 In Example 1, F@Ct3・6H20 of liquid A was 5.1
5 mol, and further 0.1 mol for each of thallium nitrate, stannic chloride, zirconyl nitrate, neodymium nitrate, nickel nitrate, steel nitrate, zinc nitrate, and indicum nitrate as component raw materials shown in Table 2. For liquid A, sodium silicate, ammonium tungstate, and ammonium metavanadate each have a concentration of 0.1
Ba was added in the same manner as in Example 1, except that mol of Ba
1.1", o, 3"0.75"0.75 MO,2
(M is Ttr Sn + Zr, Nd, Nj
, Cu.

Barium ferrite magnetic powder represented by Zn, In, St, W or V) was manufactured.

Table 2 shows the average particle size, thickness, coercive force, and saturation magnetization of these magnetic powders. All of these magnetic powders had individual particles that were uniform and had a neat shape.

Table 2

Claims (1)

[Claims] An aqueous solution containing 8 to 16 moles of Fe ions and 0.8 to 3 moles of ions of one or more metals selected from the group consisting of Ba, Br, Ca, and Pb; A coprecipitate is obtained by mixing with an alkaline aqueous solution so that the pH becomes 5 or more, and the coprecipitate is mixed with an alkaline substance of 0.2 mmol or more per mol of Fe atoms in the coprecipitate and a fluxing agent of 70 mmol or more in the presence of an alkaline substance and a flux. Heat to a temperature of ℃ or higher to reduce moisture content to 70% by weight
A method for producing magnetic powder, which is characterized in that: