JPS63184309A - Stabilization of ferromagnetic metal powder - Google Patents

Abstract

PURPOSE:To obtain highly stable ferromagnetic metal powder by immersing ferromagnetic metal powder in organic solvent dissolving organic metal compound, forming metal hydrate by hydrolysis of such organic metal compound, depositing metal hydrate on the ferromagnetic metal particle surface and thereafter conducting heat treatment. CONSTITUTION:An organic metal compound, which dissolves to an ordinary organic solvent not easily binding with ferromagnetic metal powder such as toluene, heptane, easily subjected to hydrolysis and generates very stable hydrate with such hydrolysis, can be used. As a metal generating such hydrate explained above, an organic metal compound of the metal such as Al, Si, B, Ti, Zn and Zr may be used. As the material, which shows solubility and is easily subjected to hydrolysis and allows hydrate obtained to change to an oxide with the heat processing, for example, metal alkoxide compound, metal alkyl compound are preferable. the heat treatment must be conducted in an inactive gas atmosphere, in hydrogen gas, or in a reducing gas atmosphere mainly composed of hydrogen.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing fine ferromagnetic metal powder particles as a magnetic material in a magnetic recording medium suitable for high-density recording.

Conventional magnetic materials for magnetic recording are made of finely shaped particles with high uniformity, have a high coercive force (Hc), and have a saturation magnetization (σS) in order to achieve high output and low noise in a wide recording wavelength range.・Both residual and remanent magnetization (σr) are large, and the squareness ratio (Rs・σr
/σS) is also basically required to have as large a magnetic property as possible. Among these, regarding magnetic powder as a magnetic material, ferromagnetic metal powder was first put to practical use as a material for audio magnetic tapes due to its excellent magnetic properties, and was also put into practical use as a material for 8 mm videos. In the case of acicular metal powder particles containing iron as the main component, excellent magnetic potency based on sufficiently high Hc and σS values is utilized, but usually 1 μw. Since it is a fine particle, it has extremely strong oxidizing activity against air.
Stability is considered to be an important physical property in order to ensure applicability as a magnetic recording medium and provide authenticity.

Conventionally, methods for ensuring this kind of stability include (1) a method of providing an oxidized layer on the surface of the fine particles, (2) a method of forming a special N-retaining layer on the surface of the fine particles, and (3) a method of forming a special N-retaining layer on the surface of the fine particles. A method has been proposed in which the oxide film layer is densified by applying heat treatment after providing the oxide layer.

Methods belonging to (1) include a method in which the oxidation layer is formed by a gas phase contact reaction and a method in which the oxidation layer is formed by a liquid phase reaction.
-127701, 52-85054, 55-164
001.57-85901, 57-93504, 5
8-110433.58-159311 and the like.

Furthermore, as a method belonging to (2), a method of depositing a protective layer of an organic material is a method of depositing a low molecular weight organic material with a special surfactant characteristic such as silicone, for example, JP-A No. 46-5057. .50-104164.51-
122655.51-140860, 52-1553
98.53-5798, 53-76958, 54-2
4000, 55-39660, 55-39661
, 55-39662 , 56-29841.56-54
013.56-148726 and the like.

Furthermore, as a method for applying a protective layer of resin, JP-A-53-13906.53-78099.54-1395
08.56-130831 etc. In addition, as a method of depositing inorganic salt, Japanese Patent Application Laid-Open No. 53-8798.56-984
01.57-9802.57-63601.58-15
9306, 58-159307, 58-15930
8.58461708, 58-161709.

58-161725 and the like.

In addition, as a method of using a volatile rust preventive agent,
4565, and a method using amine and mineral oil to form a protective layer is disclosed in JP-A No. 53-7.
8096.53-7809 and Japanese Patent Application No. 60-292875 proposed by the present inventors.

Further, as a method of utilizing an inorganic gas, there is a method proposed by the present inventors, such as Japanese Patent Application No. 60-29287.

A method belonging to (3) includes Japanese Patent Application No. 59-273711 proposed by the present inventors.

The problem that we are trying to solve today Stability has been imparted to the surface of ferromagnetic metal powder particles by the method described above, but (1)
The method of providing the metal powder's own oxide on the surface layer of the ferromagnetic metal powder fine particles is more stable than metal powder without an oxide layer, but this method alone is not sufficient to prevent oxidation. I couldn't have it. Also (2)
For example, the method of depositing a special low-molecular-weight surfactant such as silicone is characterized by blocking oxygen and moisture, which cause deterioration, with an organic layer. The effect of preventing the deterioration of fine particles is significantly improved compared to the above-mentioned oxide film alone, and a similar example is a method of applying a resin or the like. However, since low molecular weight surfactants, resins, etc. are larger than the molecules of oxygen and hydrogen gas, it is necessary to use them in relatively large amounts. Furthermore, when used as a magnetic recording medium, ferromagnetic metal powder is always mixed with a binder resin. In this case, as in the above method, the ferromagnetic metal powder is covered with the binder resin, and the effects of such organic matter and resin treatment are reduced.

In addition, methods of depositing inorganic salts include methods of depositing metal soaps, metal alkoxides, and metal hydroxides, but in this case, the molecular weight is smaller than the organic substances mentioned above, and oxygen, water vapor, etc. are the cause of deterioration. Although it is relatively difficult for molecules to pass through, the effect of improving stability is still low because the bonding force with the ferromagnetic metal fine particles is weak.

Furthermore, as a method described in JP-A-58-120704, a metal alkoxide is dissolved in a solvent that is inert to ferromagnetic metal powder and can dissolve the metal alkoxide, and the resulting solution is used to wet the ferromagnetic metal powder. Then, by gradually hydrolyzing the metal alkoxide present on or near the surface of the metal powder, a film of complete or incomplete hydrolysis of the metal alkoxide is formed on the surface of the metal powder, and then a solvent is added to the metal powder. A method for stabilizing ferromagnetic powders by evaporating or sterilizing them has been proposed. In this method, a film of metal hydrate is formed on the surface of the ferromagnetic powder; Since it did not have binding strength, it had little effect on improving stability. In addition, Al43. A method of dissolving and depositing hydroxides such as Ti", Zn", etc. in an organic polar solvent is described in Japanese Patent Application Laid-Open No. 61-40005.
It is known as proposed in . In this method, the metal hydroxide is dissolved in an organic polar solvent, and the polar solvent is evaporated to precipitate and deposit the metal hydroxide. However, in this method, segregation is avoided during drying of the organic solvent. However, it was difficult to form a uniform film, and the metal hydroxide that remained after evaporation of the organic polar solvent did not have a strong bond with the ferromagnetic metal, so it had little effect as a film to improve oxidation stability. .

Furthermore, the method of using a volatile rust preventive agent does not fundamentally improve stability, similar to the use of organic substances described above. Also, in the method of using amine or mineral oil, the basic stability cannot be improved like the above-mentioned use of organic substances. Also, as a method of using inorganic gases, SO□ has a strong bonding force, but it has a drawback in stability against oxidation by water vapor, and CO□ has the effect of reducing the oxidation rate, but
Due to its weak binding strength, stability was still a problem when replaced with oxygen and water vapor.

As method (3), the method of forming an oxide layer on the surface layer of the fine particles and then applying heat treatment to make the oxide layer denser is an effective method for forming a dense oxide layer on the surface layer of the fine particles. Even if the ferromagnetic metal oxide film was made denser, it was still not able to completely prevent corrosion by oxygen and water vapor by itself.

In addition, a method described in Japanese Patent Publication No. 56-28967 is known in which a ferromagnetic metal powder is produced by depositing an AI compound before reduction. In this case, since the AI compound is deposited before reduction, the film formed on the metal surface by the reducing gas such as hydrogen cannot necessarily exist uniformly, and the effect of improving stability is poor.

In order to solve the above-mentioned problems, the inventors of the present invention have made intensive studies and found that ferromagnetic metal powder is immersed in an organic solvent in which an organometallic compound is dissolved. Hydrolyzing an organometallic compound to form a metal hydrate, depositing the metal hydrate on the surface of the ferromagnetic metal particles, and then reducing the metal hydrate under an inert gas atmosphere or using hydrogen gas or hydrogen as the main component. The inventors have discovered that extremely stable ferromagnetic metal powder can be obtained by heat-treating the ferromagnetic metal particles in a magnetic gas atmosphere, and have thus arrived at the present invention.

The present invention will be explained in detail below.

The organometallic compound that can be used in the present invention is one that is soluble in general organic solvents that are difficult to bond with ferromagnetic metal powders, such as toluene and heptane, as described below, and that is easily hydrolyzed. Hydrolysis produces highly stable hydrates. Furthermore, the hydrate obtained in this manner is heat-treated in an inert gas atmosphere or in a hydrogen gas or a reducing gas atmosphere mainly composed of hydrogen to form a ferromagnetic metal surface. It is like changing into an oxide that has binding strength. Metals that provide such hydrates and oxides include ^1. S
Organometallic compounds of metals such as i+B+Ti+Zn and Zr can be suitably used. Further, preferred examples of compounds that are soluble and easily hydrolyzed and whose hydrates are converted into oxides by heat treatment include metal alkoxide compounds and metal alkyl compounds.

As such a metal alkoxide compound, 81 (O
C2H5)3, AI (iso-OC3H9) 3, 81 (sec-OC4H7)3.5i (OCHa)a
, 5t (OCJs)a, Si (iso-OCJ7)a
, St (sec-OCJ,)a, B(OCH3)3,
B(OCzHs)+, B(iso-0-C+H1)+,
B (sec-OCJ,) 3, Ti (OCH3) 4,
Ti (OC, H5)4, Ti (iso-OCJ7)
a, Ti (sec-OCJ,)4, Zn (OCR
+) 3, Zn (OCJs) 3, Zn (iso-
OC+H7) 3, Zn (sec-OCJ,)s, Z
r(OCHz)n, Zr(OCzHs)4, Zr(i
so-OCJ7) 4, Zr(sec-OCJq) 4, etc., and metal alkyl compounds include AI (CL) 3, AI (C2H5) 3, Al
(iso-CJ7) :+, AI (sec-CJq)
x, Si (CH3) a, Si (C2H5)
a, 5t(iso-CJ'+)n, 5i(sec-C
J,)4,B(C1h)i,B(CzHs)3,
B (iso-CJt) 3, B (sec-C4H7)
3, Ti (CH3) 4, Ti (C2H5) a
, Ti (iso-C3Ht) < , Ti (sec
-CaI2)4, Zn(CHs)3, Zn(CJs)3
, Zn(iso-CJ7)3, Zn(sec-CJq)
a, Zr(CH3)4, Zr(C2Hs)4, Zr(
Examples include iso-CJ7)4, Zr(sec-CJ, )4, and the like.

Of course, the above-mentioned organometallic compounds exhibit sufficient effects even when used alone, but there is nothing to prevent them from being used in combination of two or more types, if desired.

The present invention involves immersing a ferromagnetic metal powder in an organic solvent solution of the organometallic compound, hydrolyzing the organometallic compound to deposit the metal hydrate on the surface of the ferromagnetic metal particles, and then The ferromagnetic metal particles are heat-treated in an inert gas atmosphere or in an atmosphere of hydrogen gas or a reducing gas mainly composed of hydrogen. A ferromagnetic metal powder for magnetic recording obtained by a catalytic reduction reaction with hydrogen or a reducing gas mainly composed of hydrogen using a ferromagnetic metal compound as a starting material (usually with an average particle diameter of 2 to 0.05 μm along the long axis, preferably is 1
The adhesion and heat treatment method will be described by taking as an example a material having a diameter of about 0.1 .mu.m and a long axis/minor axis ratio of about 5 to 20, preferably about 10 to 15.

Examples of solvents that can be used in the present invention include benzene,
Aromatic hydrocarbons such as toluene and xylene; aliphatic hydrocarbons such as hexane, heptane, octane, nonane, decane, and undecane; acetone, MEK, M
Preferred examples include ketones such as IBK; alcohols such as ethanol and isopropanol; and esters such as ethyl acetate and butyl acetate.

First, an organometallic compound, such as a metal alkoxide compound or alkyl compound as described above, is dissolved in an organic solvent as described above, such as toluene, and a ferromagnetic metal powder as described above is immersed in this solution. The ferromagnetic metal powder may be one that has not been slowly oxidized immediately after reduction, or may be one that has been slowly oxidized by known means to provide an oxidized layer on the surface.

The ferromagnetic metal powder soaked in the solution is preferably mixed in the form of a slurry or paste, for example, at about 10M1n to 10Hr, so that the metal powder and the solution are brought into sufficient contact. At this time, just to be sure, the powder may be left immersed for several minutes to several tens of hours. Thereafter, an appropriate amount of water is added to the solution to hydrolyze the dissolved organometallic compounds such as metal alkoxide compounds and metal alkyl compounds, and deposit metal hydrates on the ferromagnetic metal powder. It is to dress them up. In order to make the deposition as complete as possible, an additional 10M1
It is preferable to mix using a kneader or the like for about 10 hours.

Note that the amount of metal deposited is 0.05 for ferromagnetic metal.
-20%, preferably about 0.1-10% (Wtχ). In addition, the amount of water added is 0.00% of the organometallic compound.
It is preferably about 5 to 10 times the molar amount. If it is less than this, the hydrolysis yield will be low, and if it exceeds this, problems such as agglomeration and rusting of the magnetic metal will occur.

Furthermore, for convenience of handling, the slurry is filtered or dried in nitrogen or air as it is to obtain a ferromagnetic metal powder which has been precipitated and coated with the above metal.

In addition, when actually carrying out the operation, a disilver or homogenizer can be suitably used as a mixer for processing in slurry or paste form, and a disilver or homogenizer can be suitably used when processing in slurry form. In this case, Neegoo etc. can be suitably used.

The ferromagnetic metal powder on which the metal hydrate thus obtained is precipitated and deposited is heat treated, and the heat treatment method is as previously proposed by the present inventors in Japanese Patent Application No. 59-273711. It is preferable to perform heat treatment in an atmosphere of a gas inert to iron, such as nitrogen, argon, helium, or methane. In addition, the same effect can be achieved by heat treatment in an atmosphere of hydrogen or a reducing gas mainly composed of hydrogen (a mixed gas of hydrogen and the above-mentioned inert gas). The temperature of the heat treatment is preferably in the range of 300°C to 700°C. If the temperature is less than 300°C, as shown in Examples and Comparative Examples later, the metal hydrate will not change to metal oxide, and the effect of heat treatment will not be fully exhibited, and if it exceeds 700°C, the magnetic recording Since the ferromagnetic metal powder used is usually fine particles of 1 μm or less, sintering progresses excessively, making the metal powder unsuitable for magnetic recording. The heat treatment time may vary depending on the temperature, but is usually about 30M1n to LOHr.

The operation of the present invention will be explained in detail. In the present invention, ferromagnetic metal powder is immersed in an organic solvent in which an organometallic compound is dissolved, the organometallic compound is hydrolyzed to form a metal hydrate, and the metal hydrate is coated on the surface of the ferromagnetic metal particles. coated with
The ferromagnetic metal particles are then heat-treated in an inert gas atmosphere or in an atmosphere of hydrogen gas or a reducing gas mainly composed of hydrogen, but the organometallic compound is dissolved in an organic solvent. In this state, even if the ferromagnetic metal powder is immersed, the organometallic compound will not be deposited on the surface of the ferromagnetic metal powder because it is dissolved in the organic solvent. However, when a metal hydrate is generated by hydrolysis, the metal hydrate is precipitated in an organic solvent such as toluene and adheres to the surface of the ferromagnetic metal particles.

Since the metal hydrate is precipitated from the solution, it is presumed that it is inevitably precipitated substantially evenly on the surface of the metal particles that are in contact with the solution to form a uniform film. By further applying heat treatment to the metal particles having the metal hydrate film, the dehydration reaction of the metal hydrate constituting the film progresses, and the film made of metal hydrate becomes more It transforms into a film made of metal oxide that is strong, dense, and stable, and has a bonding force to the ferromagnetic metal surface. In this way, the coating has the effect of improving the stability of the ferromagnetic metal particles against oxidation.

The method and effects of the present invention will be explained in more detail with reference to Examples and Comparative Examples below.

Example 1 100 g of a ferromagnetic metal powder mainly composed of iron having an average particle diameter of 0.15 μm along the long axis of primary particles and an axial ratio of 10 was prepared. When the magnetic properties were measured using a vibrating sample magnetometer (VSM) in an external magnetic field of 10 kOe, Hc = 13800e, σs = 1
It was 68 emu/g, Rs=0.493. AI(
iso-OC+H7): + 22.7g to toluene 15
Dissolved in 0g. AI/Fe=3/100 (wt ratio)
And so. The metal powder was immersed in the above solvent and left overnight just to be sure. After adding 6.0 g of pure water (3 times the molar amount of isopropoxide) to the soaked material for hydrolysis, kneading was performed for 4 hours using a kneader to ensure sufficient adhesion. Continuing,
It was air-dried in the air. When the magnetic properties of this were measured, t(c・14850e, σS・135 emu/
g, Rs=0.501. The heat-treated metal powder was heat-treated at 400°C for 12 hours in a nitrogen gas atmosphere by the method described in Japanese Patent Application No. 59-273711, and the magnetic properties of the heat-treated metal powder were measured, and Hc=15450e.

σs = 132 emu/g, Rs = 0.502. The heat-treated metal powder was immersed in toluene and then air-dried. The nucleic acid-treated metal powder was left in a constant temperature and humidity chamber at 50°C and 980χRH to perform a deterioration test. After 60 hours had elapsed, the treated metal powder was taken out from the constant temperature chamber and its magnetic properties were measured, and the saturation magnetization (σS) was 122em
It was u/g. Also, after a week had passed, the acid-treated metal powder was removed from the constant temperature and humidity chamber and its magnetic properties were measured.
It was mu/g. It was found that the deterioration did not progress.

As a result, it was found that the powder had extremely sufficient stability as a metal magnetic powder for magnetic recording.

Example 2 The same ferromagnetic metal powder as in Example 1 was used.

AI (iso-OCJ,)3 was dissolved in toluene,
The same method as in Example 1 was followed until adding pure water and coating the ferromagnetic metal powder.

The treated metal powder was heat treated at 400° C. for 2 hours in a hydrogen atmosphere. When the magnetic properties of the treated metal powder were measured, Hc = 1370'Oe, a s = 159em
u/g, Rs=0.490. The treated metal powder was immersed in toluene and then taken out into the air as an air-dried powder. When the magnetic properties of the metal powder were measured, Hc=1
4500e, a s=137emu/g, Rs=
It was 0.502. A deterioration test was conducted in the same manner as in Example 1. After 60 hours, the σS value of the nucleic acid powder was 120.
emu/g. Moreover, the σS value after -week had passed was also 120 emu/g. As a result, it was found that heat treatment in a hydrogen atmosphere also has the effect of greatly increasing stability.

Example 3 The same ferromagnetic metal powder as in Example 1 was used.

8I (iso-OCJt) 3 to AI (C2H5)
The same method as in Example 1 was carried out except that 3 was used.

The amount of AI (Czl(s) z added was set to 3/100 in the ratio of AI to ferromagnetic metal powder as in Example 1. Ethane gas was generated at the same time as 6.0 g of pure water was added. In air. When the magnetic properties were measured after air drying, Hc=148
50e, σs=135emu/g, R5-0,
It was 501. The treated iron powder was heat treated by the method described in Example 1. When the magnetic properties of the heat-treated metal powder were measured, Hc=15500e, σs=132e
mu/g, Rs=0.503. Further, after being immersed in toluene and air-drying, a deterioration test was conducted using the method described in Example 1. The saturation magnetization value after 60 hours is
It was 121 emu/g. Also - σs after a week has passed
(i was 120 emu/g.) As a result, it was found that the use of the AI alkyl compound also had a great effect of increasing stability.

Example 4 The ferromagnetic metal powder described in Example 1 was used for deposition treatment using Ti alkoxide as the organometallic compound. As Ti alkoxide, Ti [0CR(CHs
)z) a was used, and the amount added was set at a ratio of Ti to ferromagnetic metal of 3/100. In addition, pure water is Ti (0CR(C
H3) 2) 4.5 g, which was 4 times the molar amount of a, was added. Thereafter, in the same manner as in Example 1, 4
Kneaded for hours. The magnetic properties of the transferred metal powder that had been air-dried were measured: Hc = 14850e, σs
= 134 emu/g, Rs = 0.501. After the adhesion treatment, heat treatment was applied by the method described in Example 1. When the magnetic properties of the heat-treated metal powder were measured, Hc=15
400e, σs=131emu/g, Rs=0.5
It was 03. Further, after being immersed in toluene and air-drying, a deterioration test was conducted using the method described in Example 1. The saturation magnetization value after 60 hours was 118 emu/g.

Moreover, the σS value after -week had passed was 117 emu/g. As a result, it was found that Ti alkoxide also has the effect of increasing stability.

Example 5 Using the ferromagnetic metal powder described in Example 1, a deposition treatment was performed using Zr alkoxide as the organometallic compound. As Zr alkoxide, Zr (OCJ,)
A is used, and the amount added is 3/1 in the ratio of Zr to ferromagnetic metal.
It was set as 00. Further, 2.4 g of pure water was added, which was 4 times the molar amount of Zr(OCJt) a. Thereafter, the mixture was kneaded for 4 hours in the same manner as in Example 1 using a Ni-Goo. Transfer treated metal powder subjected to air drying treatment The magnetic properties of transferred treated metal powder subjected to air drying treatment were measured and Hc = 14
900e, σs=133emu/g, Rs・0.50
It was 1. After the adhesion treatment, heat treatment was applied by the method described in Example 1. When the magnetic properties of the heat-treated metal powder were measured, )Ic = 15400e, σs = 130em
u/g, Rs=0.503. Further, after being immersed in toluene and air-drying, a deterioration test was conducted using the method described in Example 1. The saturation magnetization value after 60 hours is 1
It was 16 emu/g. Further, the σS value after -week had passed was 115 emu/g. As a result, it was confirmed that Zr alkoxide also exhibits the effect of increasing stability.

Example 6 The ferromagnetic metal powder described in Example 1 was used.

AI (iso-OCsl(+) By changing the amount of a, further A
The deposition process was carried out in the same manner as in Example 1, except that the amount of pure water added was changed depending on the amount of I(iso-OCJ7)3.

Figure 1 shows the results of a deterioration test on metal powder heat treated at 400°C for 2 hours in a nitrogen atmosphere. Here, O is the value after 60 hours, and Δ is the value after one week.

Example 7 The ferromagnetic metal powder described in Example 1 was used.

15.1 g of AI (iso-OCsHl) s and T
i (,0CR(CH:+)z) 8.6 g of a was dissolved in 150 g of toluene. 100 g of ferromagnetic metal powder was immersed in this solution. - After standing overnight, 5.5 g of pure water was added and the coating treatment was carried out by the method described in Example 1. When the magnetic properties of the treated metal powder were measured, Hc=14850e,
σs=135emu/g, Rs=0.501. Thereafter, heat treatment was applied using nitrogen gas using the method described in Example 1. When the magnetic properties of the heat-treated metal powder were measured, Hc=15450e, σs=132emu/g,
Rs=0.502. Further, after being immersed in toluene and air-drying, a deterioration test was conducted using the method described in Example 1. The saturation magnetization value after 60 hours is 121 emu/g
Met. Moreover, the σS value after − weeks has passed is 120 emu
/g. As a result, it was confirmed that, as a matter of course, the use of two types of metal alkoxides also had the effect of greatly improving stability.

Comparative Example 1 The ferromagnetic metal powder described in Example 1 was immersed in toluene and air-dried to obtain a ferromagnetic metal powder. As a result of measuring the magnetic properties of the metal powder, Hc=15000e, σS=131
emu/g, Rs=0.502. A deterioration test was conducted in the same manner as in Example 1. After 60 hours
The value was 95 emu/g, and the σS value after -week had passed was 9 Qe+no/g. The stability was significantly inferior to that of the ferromagnetic metal powder obtained by the method described in the Examples.

Comparative example 2 The ferromagnetic metal powder described in Example 1 was used.

Dissolve AI (iso-OC3Hma)3 in toluene,
The deposition process was carried out in the same manner as in Example 1 until the ferromagnetic metal powder was immersed. The soaked material was air-dried as it was in the air to obtain ferromagnetic metal powder. As a result of measuring the magnetic properties of the metal powder, Hc=14950e, σs=132
emu/g, Rs.0.502. The treated metal powder was subjected to a deterioration test using the method described in Example 1. 6
The saturation magnetization value after 0 hours was 98 emu/g.

Moreover, the σS value after -week had passed was 90 emu/g. As a result, although the adhesion treatment had a slight effect of improving initial stability, it was not possible to achieve a completely satisfactory stability imparting effect in the long term.

Comparative Example 3 The ferromagnetic metal powder described in Example 1 was used. A ferromagnetic metal powder was prepared in the same manner as in Example 1 except that the heat treatment with nitrogen was not performed. As a result of conducting a deterioration test in the same manner as in Example 1, the σS value after 60 hours was 10106 e/g, but the σS value after − weeks had rapidly decreased to 95 emu/g. From this result, we found that the method of wetting ferromagnetic metal powder in an aluminum alkoxide solution, adding water to hydrolyze it, and depositing an aluminum alkoxide hydrolyzate has the role of reducing the initial deterioration rate to some extent, but it has a long-lasting effect. It cannot be an effective measure against the deterioration of For this reason, it was found that results that were completely unsatisfactory as a ferromagnetic metal powder for magnetic recording were obtained.

Example 8, Comparative Example 4 The ferromagnetic metal powder described in Example 1 was used. The method of Example 1 was followed except that the heat treatment temperature with nitrogen gas was changed. The results of the deterioration test of the ferromagnetic metal powder after treatment are shown in the second
As shown in the figure. Here, O is the value after 60 hours, and △
is the value after one week.

As a result, it was found that when the heat treatment temperature was less than 300°C, the σS value after one week was significantly lower than the S value after 60 hours, and it was not effective in stopping the progress of deterioration. This is not a problem especially at temperatures below 200°C. That is, it was found that a heat treatment temperature of at least 300° C. or higher is effective. In addition, the heat treatment temperature is 200℃
It was experimentally confirmed that in the following cases, the formed film was aluminum hydroxide, whereas in the case of 300° C. or higher, it was a strong oxide (alumina).

As is clear from the results of the examples above, ferromagnetic metal powder is immersed in an organic solvent in which an organometallic compound is dissolved, the organometallic compound is hydrolyzed to form a metal hydrate, and the ferromagnetic metal powder is The metal hydrate is deposited on the surface of the particles, and then the ferromagnetic metal particles are heat-treated in an inert gas atmosphere, hydrogen gas, or a reducing gas atmosphere mainly composed of hydrogen to make the coating stronger. By forming a dense coating, it is possible to provide extremely stable ferromagnetic metal powder for magnetic recording.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between the amount of AI compound deposited and the stability of ferromagnetic metal powder. It is a graph showing the relationship between processing temperature and stability. Patent applicant: Mitsui Toatsu Chemical Co., Ltd. Figure 1: Coating amount: Figure 2: Temperature

Claims (4)

[Claims] (1) Ferromagnetic metal powder is immersed in an organic solvent in which an organometallic compound is dissolved, the organometallic compound is hydrolyzed to form a metal hydrate, and the metal hydrate is coated on the surface of the ferromagnetic metal particle. 1. A method for stabilizing ferromagnetic metal powder, which comprises depositing a ferromagnetic metal powder on the ferromagnetic metal particles and then heat-treating the ferromagnetic metal particles in an inert gas atmosphere or in an atmosphere of hydrogen gas or a reducing gas mainly composed of hydrogen. (2) The metal of the organometallic compound is Al, Si, B, Ti
, Zn, and Zr. (3) The method for stabilizing ferromagnetic metal powder according to claim 1, wherein the organometallic compound is an alkoxide compound or an alkyl compound. (4) The method for stabilizing ferromagnetic metal powder according to claim 1, wherein the temperature range of the heat treatment is 300°C to 700°C.