JPH038083B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing acicular magnetic alloy powder, and the acicular magnetic alloy powder is particularly suitable as a magnetic material for high-output and high-density magnetic recording. Magnetic materials for high-output and high-density magnetic recording have large saturation magnetization (σ _S ) and coercive force (H _c ).
is required to be high. Conventionally widely used magnetic powders include γ-Fe ₂ O ₃ , Fe ₃ O ₄ or solid solutions thereof, CrO ₂ or Co-containing iron oxide-based magnetic powder, but γ-Fe ₂ O ₃ , Fe ₃ O ₄ or their solid solutions as well as CrO ₂ have saturation magnetization (σ _S )
is 70 to 90 emu/g, coercive force (H _c ) is 250 to 600 O _e
In addition, Co-containing iron oxide magnetic powder has a low level of
Although its coercive force is as high as H _c = 600 to 1000 O _e ,
On the other hand, the saturation magnetization (σ _S ) is as low as 60 to 80 emu/g, which is not satisfactory as a magnetic powder for high output and high density magnetic recording. Therefore, in recent years, so-called magnetic alloy powders with large saturation magnetization (σ _S ) and high coercive force (H _c ) have been actively developed. Fe, Fe−Co,
Various methods have been proposed for producing magnetic powders such as Fe-Co-Ni, but a typical method uses acicular hydrated iron oxide particles or acicular iron oxide particles as a starting material. There is a dry reduction method in which a substance is reduced in a reducing gas to obtain acicular magnetic alloy powder, and a solution containing a ferromagnetic metal salt is reduced with sodium hypophosphite or sodium borohydride. There is a wet reduction method to obtain neckless magnetic alloy powder. Note that a method is known in which Co-containing goethite is obtained by a conventional oxygen blowing method, and then dehydrated, heated, and reduced to obtain an acicular Fe--Co magnetic alloy powder. The Co-containing goethite obtained by this method tends to have branched crystals (twins), and the magnetic alloy powder obtained using such goethite as a starting material undergoes significant sintering during heating and reduction treatments, making it difficult to achieve the desired results. It is difficult to ensure the magnetic properties of Therefore, magnetic tapes made using such magnetic powders have poor electromagnetic conversion characteristics and are therefore undesirable. The present invention provides an acicular magnetic alloy powder suitable as a magnetic material that can be used particularly for high-output and high-density magnetic recording. The acicular magnetic alloy powder obtained by the method according to the present invention is an acicular magnetic alloy powder doped with Co and/or Ni, and has a large saturation magnetization (σ _S ) and a coercive force (H _c ).
It has a high value. The production method according to the present invention involves mixing a solution containing a ferric salt and a Co and/or Ni salt with a strong alkaline solution to produce a suspension containing a colloidal substance of ferric hydroxide containing Co and/or Ni. Obtain a cloudy liquid;
This suspension is thermally formed at a temperature from below its boiling point to 30°C to obtain acicular goethite doped with Co and/or Ni, which is dehydrated and heated and reduced at a temperature of 330 to 450°C. ing. The ferric salts used in the method of the present invention include:
There are no limitations on the materials as long as they are used to produce acicular goethite, which is the starting material for magnetic particles used in magnetic recording media. Examples include ferric sulfate, ferric chloride, and ferric nitrate. Examples include 2 iron. The amount of the ferric salt used is preferably such that the ferric ion concentration in the resulting suspension is within the range of 0.40 to 0.80 mol/liter.
If its concentration becomes too low, the crystals become thinner,
This is not preferable because only crystals with short long axes and poor heat resistance are produced. On the other hand, if the concentration is too high, the particles produced tend to aggregate, which is not appropriate. In addition, the Co salt and Ni salt used are:
Examples include halogenated salts such as sulfuric acid, nitrates, chloride salts, and bromide salts. The amount of Co salt and/or Ni salt added is preferably 5 at% or less.
When adding Co salt and Ni salt alone,
Co/Fe+Co and Ni/Fe+Co are each 5at%
Also, when using Co salt and Ni salt together, make sure that Co+Ni/Fe+Co+Ni is 5 at% or less. If the amount of Co salt and/or Ni salt added is large, the suspension is not completely doped and amorphous Co and/or Ni-containing colloids are precipitated and mixed in, making it unsuitable as a magnetic powder. It is. Note that a liquid containing a ferric salt and a Co and/or Ni salt can be created by dissolving each salt in a solvent such as water. Further, examples of the strong alkali used as the strong alkaline solution include alkali metal hydroxides such as sodium hydroxide, potassium hydroxide, and lithium hydroxide. These strong alkalis are dissolved in a solvent such as water to form a solution. In the present invention, the temperature at which the suspension is aged is lower than the boiling point of the suspension and above 30°C, because when the aging temperature is set above the boiling point, α-hematite containing Co and/or Ni is This is because precipitation occurs, which is undesirable, and if it is too low, it becomes difficult to crystallize Co and/or Ni-containing goethite particles, and amorphous colloids become mixed, which is undesirable. Regarding the reduction temperature, if the temperature is too high, the resulting metal particles tend to sinter, which is undesirable, and if it is too low, reduction does not occur and magnetite is produced, which is inappropriate in terms of magnetic properties. Note that the pH concentration of the suspension is preferably 11.0 to 14.0. When the PH concentration becomes too high, it is produced
Goethite particles doped with Co and/or Ni tend to aggregate, and conversely, if the PH concentration becomes too low, this is undesirable as it impedes crystallization of the goethite particles. In addition, in the present invention, it is preferable to keep the obtained suspension at room temperature and stir it for an appropriate time to make the concentration of Co and/or Ni-containing ferric hydroxide uniform. . By performing such pretreatment, Co and/or
This is advantageous because the crystals of Ni-doped goethite particles can be made uniform. Note that the solution containing the ferromagnetic metal salt and the strong alkaline solution are preferably mixed at room temperature, but the method of adding each solution is not particularly limited. It may be added dropwise or vice versa. Regardless of the addition method, a final product with no significant difference in particle state can be obtained. Furthermore, the ripening time is related to the ripening temperature, and the ripening time can be shortened by increasing the ripening temperature, but it can be arbitrarily adjusted while taking into account the amount of ripened product to the extent that it does not adversely affect the particle morphology of the goethite produced. do it. Moreover, Co obtained by the method according to the present invention
The dehydration and heating of the acicular goethite doped with Ni and/or Ni can be carried out in accordance with a conventional method, and it is convenient for processing operations if it is carried out at a temperature that will be applied in the subsequent reduction treatment. In addition, reduction is carried out for an appropriate period of time after dehydration and heating.
It is preferable to carry out the reaction at 330 to 450°C according to a conventional method. The acicular magnetic alloy powder obtained by the method according to the present invention as described above particularly has a saturation magnetization (σ _S ).
It has a large coercive force (H _c ) of 150 emu/g or more.
It has a high strength of 1000 Oe or more, and is suitable as a magnetic material for high-output and high-density magnetic recording. The acicular magnetic alloy powder used in the present invention is doped with Co and/or Ni when the magnetic alloy powder is produced using goethite as a starting material which is not doped with Co and/or Ni. This is because crystal growth within the grains becomes insufficient, making it difficult to obtain desired magnetic properties.This is to eliminate such difficulties and enable easy and sufficient crystal growth. Hereinafter, the present invention will be explained in more detail with reference to Examples. Example 1 100g of ferric sulfate and 7.39g of cobalt sulfate were dissolved in distilled water to form a mixed solution of 0.5 mol/0.5 mol/mol/cobalt sulfate and 0.0263 mol/cobalt sulfate, respectively.
Prepare 1000 ml and drop 560 ml of a 25 mol sodium hydroxide solution obtained by dissolving 100 g of sodium hydroxide in distilled water into it while stirring to create a suspension of Co-containing ferric hydroxide colloid. did. The Fe ³⁺ concentration and PH in this mother liquor were 0.321 mol/and 12.7, respectively. The amount of Co added is
It was 5at% (Co/Fe+Co). The obtained mother liquor was stirred and mixed at room temperature for 12 hours, and then
Co-containing acicular α-
Got FeOOH. Next, after washing this α-FeOOH, it was stirred in 3 liters of water and α-FeOOH was washed.
The surface of the dispersed FeOOH particles was treated with a silane coupling agent to prevent sintering of the particles during the subsequent heat treatment process. Surface treated α-
After drying FeOOH at below 100℃ for an appropriate time,
Co-containing α-Fe ₂ O ₃ particles were produced by heating and dehydrating at 700°C for 2 hours in the air, and hydrogen reduction was performed at 350°C for 3 hours to obtain Fe-Co magnetic alloy powder. This Fe−Co
After immersing the metal powder in toluene at room temperature and _N2 atmosphere, the alloy powder was air-dried at room temperature and in the atmosphere to obtain acicular Fe-Co magnetic alloy powder. Example 2 100 g of ferric sulfate, 4.35 g of cobalt sulfate, and 2.89 g of nickel sulfate were dissolved in distilled water, and 0.5 mol of ferric sulfate, 0.0155 mol of cobalt sulfate, and 0.0103 mol of nickel sulfate were mixed, respectively. Prepare 1000 ml of solution and dissolve 100 g of sodium hydroxide in distilled water while stirring to obtain 2.5
A suspension of ferric hydroxide colloid containing Co and Ni was prepared by dropping 585 ml of a mol/mol sodium hydroxide solution. The Fe ³⁺ concentration and PH in this mother liquor were 0.316 mol/and 13.0, respectively. The amount of Co added is 3at% (Co/Fe+Co),
The amount of Ni added was 2at% (Ni/Fe+Ni).
Thereafter, the mother liquor was stirred and mixed at room temperature for 12 hours, and then aged at an aging temperature of 60°C for 72 hours to obtain acicular α-FeOOH containing Co and Ni. This acicular α-FeOOH was treated in the same manner as in Example 1 to produce acicular Fe-Co-Ni magnetic alloy powder. Comparative Example 1 83.4 g of ferrous sulfate and 2.61 g of cobalt sulfate were dissolved in distilled water to create a mixed solution of 0.3 mol/0.3 mol/mol/cobalt sulfate and 0.0093 mol/cobalt sulfate, respectively.
1000 ml of Co-containing solution was prepared by adding 1000 ml of a 1.2 mol sodium hydroxide solution obtained by dissolving 48 g of sodium hydroxide in distilled water dropwise while stirring in a non-oxidizing atmosphere of _N2 . 1st hydroxide of
A suspension of iron colloid was prepared. In this mother liquor
The amount of Co added was 3 at% (Co/Fe+Co). Then, after stirring and mixing the mother liquor thoroughly in an _N2 atmosphere,
Air was bubbled through the mother liquor at a rate of 7/min at a reaction temperature of 50° C., and the reaction was carried out for a reaction time of 15 hours while stirring and mixing, to obtain Co-containing acicular α-FeOOH. This acicular α-FeOOH was treated in the same manner as in Example 1 to produce acicular Fe-Co alloy powder. Comparative Example 2 150 g of ferric sulfate was dissolved in distilled water to prepare 1000 ml of a 0.75 mol/ferric sulfate solution, and while stirring, 150 g of sodium hydroxide was dissolved in distilled water to obtain 3.75 mol. 490 ml of sodium hydroxide solution was added dropwise to create a suspension of ferric hydroxide colloid. The Fe ³⁺ concentration and PH in this mother liquor were 0.503 mol/and 12.0, respectively. After that, the mother liquor was stirred and mixed at room temperature for 12 hours, and then aged for 24 hours at an aging temperature of 60°C to form an acicular α-
Got FeOOH. This acicular α-FeOOH was treated in the same manner as in Example 1 to produce acicular Fe-Co alloy powder. The properties of α-FeOOH and alloy powder obtained in the above Examples and Comparative Examples are shown in the table below.

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Claims (1)

[Claims] 1 Second iron salt and Co salt and/or Ni
Co by mixing a salt-containing solution and a strong alkaline solution.
and/or a suspension containing a colloidal material of Ni-containing ferric hydroxide is obtained, and this suspension is aged at a temperature below its boiling point and above 30°C to
and/or a method for producing acicular magnetic alloy powder, characterized in that acicular magnetic alloy powder is obtained by obtaining acicular goethite doped with Ni, dehydrating and heating it, and reducing it at a temperature of 330 to 450°C.