JPS59155106A - Manufacture of magnetic metal powder - Google Patents

Abstract

PURPOSE:To improve the oxidational stabilization of a surface protective film of the magnetic metal powder by a method wherein a liquid, which is the mixture of a copper-salt aqueous solution and a complexing agent, is added to powdery alkaline suspension having iron oxyhydroxide, ferrous oxide or metal iron as a main ingredient. CONSTITUTION:A liquid, consisting of a copper-salt aqueous solution and a complexing agent, is added to an alkaline suspension of the powder consisting of ironoxy hydroxide, ferrous oxide or metal iron as a main ingredient, the above is neutralized and a copper complex compound is adhered to the grain surface of the powder. This is reducibly processed by heat, and magnetic metal powder consisting of the magnetic metal powder composed of iron as a main ingredient and the magnetic metal powder consisting of a surface protective layer having copper formed on the grain surface as a main ingredient are obtained. When a complexing agent is added to the copper-salt aqueous solution, a water-soluble copper complex compound is formed, and as the compound is stable for alkali, no crystal deposition is generated when said compound is added to alkaline suspension, and crystal deposition is generated for the first time when the liquid is neutralized, thereby enabling to form a uniform surface protective layer.

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to a method for producing metal magnetic powder mainly useful for magnetic recording.

Metallic magnetic powder, mainly made of iron, has a high coercive force and is prized for high-density recording, but it has inferior oxidation stability compared to oxide-based magnetic powder, and its magnetic properties deteriorate over time. It has the disadvantage of being easy. In order to avoid such drawbacks, the inventors added a copper salt aqueous solution to an alkaline suspension of powder such as iron oxyhydroxide to adhere copper hydroxide to the particle surface of the powder, and then heated the powder. A method has already been proposed for obtaining a metal magnetic powder consisting of a metal magnetic powder mainly composed of iron and a surface protection layer mainly composed of copper formed on the surface of the particle by reduction treatment.

The metal magnetic powder obtained by this method has improved oxidation stability due to the surface protective layer mainly composed of copper, and has low deterioration of magnetic properties over time. This invention was made with the aim of further improving the method proposed above to obtain a metal magnetic powder with even better oxidation stability. 0 That is, this invention is characterized by adding a complexing agent to an aqueous copper salt solution in an alkaline suspension of powder mainly composed of iron oxyhydroxide, iron oxide, or metallic iron. After adding a liquid consisting of iron, the powder is neutralized to adhere a copper complex compound to the particle surface of the powder, and then heated and reduced to form a metal magnetic powder mainly composed of iron and copper formed on the particle surface. The present invention relates to a method for producing a metal magnetic powder, which is characterized by obtaining a metal magnetic powder comprising a surface protective layer.

In this invention, when a complexing agent is added to a copper salt aqueous solution, a water-soluble copper complex compound is formed, and since this compound is stable against alkali, when it is added to an alkaline suspension of powder such as iron oxyhydroxide, However, it is not used for crystallization, but only when the liquid is neutralized by blowing carbon dioxide gas etc. into it, crystals precipitate and adhere to the surface of the particles of the powder. The copper complex compound that deposits and adheres in this way has a very uniform coating on the particle surface, so a surface protective layer mainly composed of copper is also formed by final heat reduction treatment. It becomes homogeneous, which leads to better oxidative stability.

Examples of the powder mainly composed of iron hydroxide, iron oxide, or metallic iron used as a starting material in this invention include α-Feool-1, p-FeoOH.

7 Fe 0011- (1! Fe 203-7
In addition to F e 203- F e 304 and those corresponding to the intermediate type of Kowara, and metal iron, Ni
, Go, Cr, Mn, MW, Ca, Zn, Sn
Examples include those containing metal components such as , Si, etc., and those with good acicularity are particularly preferably used.

In this invention, first, an alkaline suspension of the above-mentioned powder with a P f-] of 11 or more is prepared, and a solution obtained by adding a complexing agent to an aqueous solution of a copper salt such as copper sulfate, copper nitrate, or copper chloride is added to the suspension. Added. As the complexing agent, an alkali metal salt such as citric acid or tartaric acid is used, and an aqueous solution thereof is prepared in advance and the mixture is mixed with an aqueous copper salt solution. By this mixing, a corresponding copper complex compound is rapidly formed, and this compound is stably dissolved in the alkaline suspension even after being added.

Next, when carbon dioxide gas is blown into the alkaline suspension or acid such as hydrochloric acid is added to neutralize the liquid, the copper complex compound crystallizes and adheres to the surface of the powder particles such as iron oxyhydroxide. . It is preferable that the amount of the coating be 0.1 to 10% by weight relative to metallic iron in terms of metallic copper.

In addition, after or during the deposition of the copper complex compound, water-soluble silicic acids such as sodium orthosilicate, sodium metasilicate, potassium metasilicate, and water glass of various compositions are added to the alkaline suspension. In particular, it is preferable to add a salt or various water-soluble aluminum salts and neutralize and precipitate the same as in the case of copper complex compounds to deposit silicic acid or aluminum compounds on the powder surface together with the copper complex compounds, especially a silicic acid coating. prevents sintering between powder particles during the heat reduction treatment in the subsequent process, and improves the particle shape of the starting material (
Since it has the function of maintaining the acicularity (acicularity), it gives good results to the magnetic properties of the finally obtained metal magnetic powder. As for the amount of adhesion, the weight of silicon atom equivalent to metal iron C is 0.
．． It is desirable that the weight is 1 to 15% by weight.

After depositing the copper complex compound and preferably the silicic acid coating as described above, a heat reduction treatment is performed, but it is usually preferable to carry out a heat treatment at a temperature of 300 to 1,000° C. prior to this reduction treatment. °The hydroxide is converted into an oxide by this heat treatment. Thermal reduction treatment after heat treatment is generally carried out at a temperature of 300 to 600°C in hydrogen gas, and when the starting material is mainly composed of iron oxyhydroxide or iron oxide, it is converted into powder mainly composed of iron. While being reduced, the copper complex compound attached to its surface is reduced to metallic copper, and when the starting material is made of metallic iron, the copper complex compound attached to its surface is similarly reduced.

The metal magnetic powder obtained in this way consists of a metal magnetic powder mainly composed of iron and a surface protective layer mainly composed of copper formed on the particle surface, and this protective layer is extremely uniform and dimensional. Since it is in the form of a thin film, it has better oxidation stability and good initial magnetic properties.

In addition, in order to further improve the oxidation stability of the metal magnetic powder of the present invention obtained in this way, after the heat reduction treatment described above, it is dispersed in an organic solvent such as toluene, and air is blown into the powder. It is desirable to provide a fine oxide film on the powder surface by a method such as the following.

EXAMPLES Below, examples of the present invention will be described in more detail.

Example 1 24.8 ml of an aqueous 0.2 mol copper sulfate solution was added to 800 mt of an alkaline suspension (pF 111 or higher) containing α-Ogishi iron hydroxide powder 101 with an average particle size of 0.5 μm and an axial ratio of 15 while stirring. Cu is equivalent to 5 parts of Fe) and 0.2 mol of sodium citrate aqueous solution 2
A mixed solution of 4.8 mt was added. While stirring, carbon dioxide gas was blown into the solution to neutralize it to a level where the PI''l of the solution was 8 or less, and a complex compound of copper and citric acid was precipitated and adhered to the surface of the α-iron hydroxide particles.

Next, the α-oxyhydroxide powder to which the complex compound was attached was washed with water, dried, and then heat-treated in air at a temperature of 300° C. for 2 hours to obtain iron oxide powder. Add this iron oxide powder to 80% (
The suspension was suspended in 1 mt of water, and a 1 mol/l aqueous solution of sodium orthosilicate (Na4SiO4) ismz was added thereto and mixed, and then carbon dioxide gas was blown in to neutralize the pH to 8 or lower.

After that, the suspended matter was washed with water and dried, and then 800%
℃ for 2 hours, and then heated and reduced in a hydrogen stream at 500℃ for 2 hours. The reduced product was immersed in toluene and air was blown into it while stirring to form a fine oxide film.

The metal magnetic powder of the present invention thus obtained has an average particle diameter of 9.3 μm, an axial ratio of 10, and a saturation magnetization of 13.
1 emu/'? The coercive force was 1475 oersted, and the square shape was 0.52.

Example 2 Instead of using a mixed solution of 0.2 mol copper sulfate aqueous solution and 0.2 mol sodium citrate aqueous solution, 24.8 mt of 0.1 mol copper sulfate aqueous solution (24.8 mt of 0.1 mol copper sulfate aqueous solution (Cu: 2 ，
5) and 0.1 mol sodium tartrate aqueous solution 24
．． A metal magnetic powder of the present invention was produced in exactly the same manner as in Example 1, except that a mixed solution with 8mt was used. This powder had an average particle diameter of 0.3 μm, an axial ratio of 1' O-saturation magnetization of 1308 mu/l', a coercive force of 1500 oersted, and a square shape of 0.52.

Example 3 An alkaline suspension (PI
(11 or more) 01 to this while stirring soomz
A mixture of 24.8 ml of a molar aqueous copper sulfate solution and 24.8 mt of a 0.1 molar aqueous sodium citrate solution was added. Then, 1 mol/l sodium orthosilicate aqueous solution x
smt was added and mixed, and 3N hydrochloric acid was gradually added to this to adjust the pH of the liquid to 4 to 5.Then, the suspension was washed with water, dried, and then dissolved in air at 80C.
Heat treated at a temperature of 0°C for 2 hours, and then heated for 50 hours in a hydrogen stream.
Heat reduction treatment was performed at 0°C for 2 hours.

The reduced product was immersed in toluene and air was blown into it while stirring to form a fine oxide film.

The metal magnetic powder of the present invention thus obtained has an average particle diameter of 0.3 μm, an axial ratio of 10°, a saturation magnetization of 127 emu/17', a coercive force of 1490 oersted, and a square shape of 0.52. Met.

Example 4 Commercially available metallic iron powder (average particle size 0.35 μm, axial ratio 10
) 6.3? Alkaline suspension containing CPH11
The metal magnetic powder of the present invention was obtained in the same manner as in Example 3 except that 500 mt (above) was used as the starting material. The average particle diameter of this powder is 0.30μm, the axial ratio is 8%, and the saturation magnetization is 1
It was 32 emu/g, the coercive force was 1520 Oersted, and the square shape was (1.52).

Comparative Example 1 Instead of using a mixture of 0.2 mol copper sulfate aqueous solution and 0.2 mol sodium citrate aqueous solution, 24.8 mt of 0.2 mol copper sulfate aqueous solution was gradually added, and Except that the subsequent neutralization by blowing carbon dioxide gas was not carried out.
Metal magnetic powder was obtained in the same manner as in Example 1. The average particle diameter of this powder is 0.3 μm, the axial ratio is 10%, and the saturation magnetization is]
, 34 emu, / f, coercive force was 1440 oersted, and square shape was 0.52.

Comparative Example 2 Instead of using a mixture of 0.1 mol copper sulfate aqueous solution and 0.1 mol sodium citrate aqueous solution, 24.8 ml of 0.1 mol copper sulfate aqueous solution was gradually added. A metal magnetic powder was obtained in the same manner as in Example 3 except for the following. The average particle diameter of this powder is 0.3 μm, and the axial ratio is ]0. Saturation magnetization is 130 emu/ffb coercive force is 1490
Ersted and square shape were 0.51.

Comparative Example 3 Step of depositing and forming a complex compound of copper and citric acid on the particle surface of α-oxidized iron hydroxide powder, subsequent washing with water, drying,
A metal magnetic powder was obtained in exactly the same manner as in Example 1, except that the heat treatment step (to form iron oxide powder) was omitted. The average particle size of this powder was 0.3 μm.

The axial ratio was 10, the saturation magnetization was 12 gemu/l, the coercive force was 1530 oersted, and the square shape was 0.52.

The metal magnetic powder according to each of the above examples and comparative examples was heated at 60°C.
Deterioration rate of saturation magnetization after being left in an atmosphere of %90 coefficient 1f-1 for 7 days: [(initial saturation magnetization - saturation magnetization after oral administration)/initial saturation magnetization] X10n91. The results of the investigation were as follows.

Deterioration rate of saturation magnetization Example 1 4.3% Example 2 4.6 Example 3 4.8% Example 4 4.8% Comparative example 1 4.8 Comparative example 25.1 Comparative example 3 '10.9% As is clear from the above results, the metal magnetic powder of the present invention has excellent oxidation stability and shows little deterioration in magnetic properties after storage over time.

Claims (1)

[Claims] (1) A solution prepared by adding a complexing agent to an aqueous copper salt solution is added to an alkaline suspension of powder mainly composed of iron oxyhydroxide, iron oxide, or metallic iron, and then neutralized to surface the particles of the powder. A copper complex compound is attached to the particle, and then heat reduction treatment is performed to obtain a metal magnetic powder consisting of a metal magnetic powder mainly composed of iron and a surface protective layer mainly composed of copper formed on the surface of the particle. A method for producing metal magnetic powder.