JPH0250964B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for producing metal magnetic powder, and more specifically, it relates to a method for producing metal magnetic powder, and more specifically, it is suitable for high-density recording and has a coercive force (Hc) of 700.
The present invention relates to a method for producing iron-based metal magnetic powders of ~1200 Oe. [Prior Art] The magnetic recording media currently in use are extremely diverse, and the characteristics required of the magnetic powder used are also different. The ferromagnetic powder conventionally used in magnetic recording media is γ-
Fe ₂ O ₃ , Co-doped γ-Fe ₂ O ₃ , Fe ₃ O ₄ , Co-doped
There are Fe ₃ O ₄ , Fe ₃ O ₄ -γ-Fe ₂ O ₃ , CrO ₂ , etc.
Since these magnetic powders have limitations in coercive force, saturation magnetic flux density, etc., ferromagnetic metal powder (metal powder) has recently attracted attention due to its high coercive force, saturation magnetic flux density, etc. [Problem to be solved by the invention] The coercive force of these metal magnetic powders is usually 1100 to 1300.
Oe range, and because of its high holding power, it has the disadvantage that it cannot be used in audio equipment, video equipment, digital equipment, etc. that are not compatible with metal. Furthermore, magnetic recording is trending toward higher density, and in order to achieve higher density magnetic recording, it is necessary to further miniaturize magnetic powder. However, conventional metal magnetic powders are usually needle-shaped and have a major axis length of 1 to 10 microns, which is insufficient to achieve high density. Therefore, if this metal magnetic powder is made finer and higher density is not achieved, the coercive force will further increase and the surface properties will deteriorate, resulting in poor dispersibility, making it impractical. [Means for Solving the Problems] The present inventors have solved the above-mentioned drawbacks, and have developed a metal magnetic material that can be used in audio equipment, video equipment, digital equipment, etc. other than those compatible with metal, and can achieve high-density recording. They conducted extensive research to produce powder and were able to complete the present invention. Conventionally, the following methods have been considered for producing metal magnetic powder. (1) A method of thermally decomposing metal organic acid salts (mainly oxalates) and reducing them with reducing gas. (2) A method of reducing iron oxyhydroxide, or iron oxyhydroxide containing other metals, or iron oxide or ferrite composition oxide with a reducing gas. (3) A method of vaporizing a ferromagnetic metal alloy in an inert gas. (4) A method for decomposing metal carbonic compounds. (5) A method in which Hg is separated after ferromagnetic metal powder is electrodeposited by hydroxyl electrolysis. (6) A method in which a ferromagnetic metal salt is wet-reduced in its solution using sodium borohydride, sodium hypophosphite, etc. (7) A method in which ferromagnetic powder is produced by discharge explosion through a large impact current. Among these methods, method (2) is particularly promising when considering industrial efficiency and economic efficiency, and the method for producing the metal magnetic powder of the present invention also belongs to this production method. That is, the present invention involves mixing an aqueous solution containing sodium carbonate with a ferrous salt solution, blowing air to precipitate seed crystals, and then adding an aqueous caustic soda solution and blowing air to grow crystals.
A method for producing a metal magnetic powder characterized by depositing a Si compound and/or an Al compound and then reducing the powder at a temperature of 300 to 600°C in a hydrogen stream, and adding an aqueous solution containing caustic soda to a ferrous salt solution. After mixing and blowing air to precipitate seed crystals, and then adding an aqueous sodium carbonate solution and growing crystals by blowing air, a Si compound and/or an Al compound was deposited on the α-FeOOH. The present invention provides a method for producing metal magnetic powder, which is characterized by reducing the metal magnetic powder at a temperature of 300 to 600°C in a hydrogen stream. Next, a preferred embodiment of the method of the present invention will be described in detail. First, ferrous chloride, ferrous sulfate, etc.
Adding soda carbonate or caustic soda to the iron salt solution,
Seed crystals are precipitated by blowing air into the α-FeOOH, and then caustic soda is added if sodium carbonate is used, or soda carbonate is added if caustic soda is used, and air is blown into the α-FeOOH to grow crystals. compound and/or Al compound with SiO ₂ and/or
Alternatively, 0.05 to 5 wt% of Al ₂ O ₃ is deposited. For adhesion, the effect can be seen just by sufficient contact with the Si compound or Al compound, but to further increase the effect, after suspending, if the water-soluble Si compound or Al compound is alkaline, use an acid or Conversely, if these compounds are acidic, a method of total or partial neutralization with an alkali should be adopted. Also α-
The effect can be further improved by using a surfactant such as sodium oleate or sodium alginate to improve the dispersibility of FeOOH. In addition, water-soluble Si compounds that can be used include sodium silicate, silica sol, colloidal silica, etc.
Examples of the compound include alumina sol, sodium aluminate, aluminum chloride, and aluminum sulfate. The α-FeOOH produced by the above method is filtered, washed and dried, and then reduced in a hydrogen stream at a temperature not exceeding 600°C, preferably 500°C or less. There is no practical lower limit for the reduction temperature, but at low temperatures the reaction proceeds very slowly and the reaction time becomes too long, which is undesirable.
It is appropriate to reduce at temperatures above ℃. After reduction, the reducer is cooled, and a mixed gas of, for example, 1% air and 99% nitrogen is introduced into the reducer, the air content is gradually increased, and after 4 to 5 hours, the gas is switched to only air and taken out from the reducer. The metal magnetic powder of the present invention can be produced by the method described above. In addition, in the present invention, the size and morphology of the crystals are controlled by manufacturing α-FeOOH in two steps: generation of seed crystals and growth of crystals, so that the coercive force is kept within a specific range and It has the characteristic that the squareness ratio (σ _r /σ _s ) can be maintained at a high level. [Example] The present invention will be explained in detail with reference to Examples below. Examples and Comparative Examples 0.5 mol/Na ₂ CO ₃ aqueous solution 24 and 0.5 mol/
Put an aqueous solution of _FeCl2 into a reactor at 50 °C and 40 °C.
After raising the temperature to
Add 4 mol/NaOH aqueous solution 2, further oxidize until the oxidation rate reaches 100%, and separate the generated α-FeOOH.
Washed and dried. This was designated as sample 1. Samples 2 and 3 were obtained by adding NaOH aqueous solution when the oxidation rate reached 50% and 75% in the above method, and Sample 4 was carried out until the oxidation rate reached 100%, that is, without adding NaOH. Next, 1.0 mol/NaOH aqueous solution 24 and
A 0.5 mol/FeCl ₂ aqueous solution 16 was placed in a 50°C reactor, heated to 40°C, air was blown at 15/min to perform an oxidation reaction, and when the oxidation rate reached 25%, 2 mol/Na ₂ CO _3Aqueous solution 2 was added, and the oxidation reaction was further carried out to an oxidation rate of 100%, resulting in α-
The FeOOH was separated, washed, and dried. Sample 5
And so. In addition, in the above method, when the oxidation rate reached 50% and 75%, Na ₂ CO ₃ aqueous solution was added to sample 6,
Sample 8 was obtained by increasing the oxidation rate to 100%, that is, without adding Na ₂ CO ₃ . Samples 1 to 8 above were suspended in 89 g each in 6 portions of water, 40 ml of 100 g/(SiO ₂ equivalent) aqueous sodium silicate solution was added, neutralized with hydrochloric acid, filtered, and washed.
Dry at a temperature not exceeding 150°C. Each 50 g of α-FeOOH thus obtained was reduced at 420° C. for 6 hours in a hydrogen flow of 3/min. After the reduction is complete, the reactor is cooled to room temperature and air 1
% and 99% nitrogen into the reactor, approximately
Gradually increase the amount of air in the mixed gas at 30 minute intervals.
After 5 hours, the atmosphere was switched to air only, the magnetic powder was taken out from the reactor, and its magnetic properties were measured with an applied magnetic field of 10 KOe. The results are shown in Table 1.

〔Effect of the invention〕

According to the method of the present invention, the coercive force is 700 to 1200 Oe.
It is possible to easily obtain a metal magnetic powder suitable for high-density recording with a high squareness ratio.

Claims (1)

[Claims] 1. α which is prepared by mixing an aqueous solution containing soda carbonate with a ferrous salt solution, blowing air to precipitate seed crystals, and then adding a caustic soda aqueous solution and blowing air to grow crystals. - A method for producing metal magnetic powder, which is characterized by depositing a Si compound and/or an Al compound on FeOOH and then reducing it in a hydrogen stream at a temperature of 300 to 600°C. 2. Mixing an aqueous solution containing caustic soda with a ferrous salt solution, blowing air to precipitate seed crystals, and then adding a sodium carbonate aqueous solution and blowing air to grow crystals. and/or a method for producing metal magnetic powder, which comprises depositing an Al compound and then reducing the powder at a temperature of 300 to 600°C in a hydrogen stream.