JPS5919164B2 - Manufacturing method of acicular iron-based ferromagnetic metal powder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing acicular ferromagnetic metal powder containing iron as a main component.

Acicular ferromagnetic metal powder used as a powder material for magnetic recording has higher coercive force and saturation magnetization than conventional oxide-based ferromagnetic material powders, so it can improve the recording density and sensitivity of magnetic recording. is expected to increase, and a large market value is expected.
Up until now, the method for producing acicular ferromagnetic metal powder has been to use acicular iron oxyhydroxide as a starting material, to which Co3Ni, Sn
, Ti, Zn, Sb, Bi, Ag, Mn, and other elements to which compounds are attached or doped are thermally reduced. In this method, depending on the heating temperature, fusion or sintering between particles may occur, and the acicularity of the starting material may be impaired. In addition, if the reduction rate is lowered in an attempt to prevent this, the reduction is likely to be insufficient and unstable, and the reduction will take a long time, which is undesirable from the viewpoint of productivity. In order to solve this sintering problem in the thermal reduction method, silicic acid, silicate compounds, or
A treatment method is known in which a substance that prevents sintering between particles, such as a Si compound such as silicone oil, Cr hydroxide, or Cr oxide, is attached and then reduction is performed. However, when thermal reduction is carried out in the presence of silica, for example, pores due to dehydration remain in the grains of the metal powder, and the particles themselves tend to be air- and voids, leading to deterioration in magnetic properties. Further, when thermally reduced in the presence of Cr hydroxide or Cr oxide, the reaction rate is extremely slow, and a large amount of additional elements such as Co that accelerate the reduction rate are required, resulting in an increase in the cost of the rope product. Also, silicone oil etc. are expensive.
Furthermore, it is difficult to deposit a certain amount. The present inventors have developed various anti-sintering agents in order to prevent sintering between particles and decrease in reduction rate, which are the drawbacks of these conventional techniques, and to produce metal powder with high coercive force and high square shape. As a result of investigation, it was found that tungstic acid compounds have good effects.

According to the present invention, Co, Ni, Sn, Ti, Zn, Sb
, Bi, Ag, Mn, etc., in a method for producing an acicular iron-based ferromagnetic metal powder by thermally reducing acicular iron oxyhydroxide or iron oxide powder containing or not containing metals such as Bi, Ag, Mn, etc. A needle-like material to which a tungstic acid compound is attached at a ratio of 0.01 to 5% by weight (W/Fe+W) by adding iron oxyhydroxide or iron oxide powder to a solution of the tungstic acid compound and immersing it. Provided is a method characterized by thermally reducing iron oxyhydroxide or iron oxide powder. The tungstic acid compounds used in the method of the present invention include tungsten isopoly acids (including salts) and heteropolyacids (including salts), the former having the general formula
R2O.YWO3.ZH2O, where R is hydrogen, a monovalent metal, a cation such as ammonium, X, y, and z are integers, and z may be O.

The typical one is, where R is a monovalent metal,
It is a cation of hydrogen and ammonium.

Generally, paratungstates and metatungstates are used. Tungstate decomposes at reducing temperature,
A compound in which R is a hydrogen ion or an ammonium ion, which does not leave any influence on the metal powder obtained by volatilization, is preferable. The latter is a tungsten heteropolyacid, such as cobalt tungstic acid, phosphotungstic acid, and silicotungstic acid, in which the hetero atom is a divalent to tetravalent metal, and like the former, its salt is preferably an ammonium salt. In order to attach such a tungstic acid compound to acicular iron oxyhydroxide or iron oxide (hereinafter referred to as an iron compound), these iron compounds are suspended in an aqueous solution of a tungsten compound, thoroughly stirred and dispersed, and the tungsten This is carried out by attaching the compound to the surface of the iron compound particles and then drying them in a Sawabetsu manner.

The amount to be deposited is 0.01 to 5% as (W/Fe+W)XlOO ((6)).

If it is less than 0J1%, there is no effect of preventing sintering, and if it exceeds 5%, there is no change in the effect of preventing sintering, but rather the magnetization is reduced.

The amount to be deposited can be easily achieved by adjusting the concentration of the tungsten compound solution as a suspending medium. Next, the present invention will be specifically explained using Examples and Comparative Examples.

Example 1 Goethite (αFeOO
H? The powder 266r was mixed with ammonium metatungstate ((NH4)2.O.4W03.8H20) at a concentration of 1.
Suspend in 10 t of aqueous solution at 0 f/t and thoroughly stir to disperse.

This was separated from P, dried and pulverized to obtain a powder of 50f, which was treated in a hydrogen stream at a reduction temperature of 390°C to obtain a metal powder. This is packed in a magnetic field of 15k0e with a packing density of 0.7f/0
As a result of magnetic measurement at d, the saturation magnetization was 160 emu/1
, a square shape of 51%, and a coercive force of 13300e. The w content of this metal powder is 0.65% in W/Fe+W weight%.
It was hot.

Example 2 Using the same αFeα old 266f as in Example 1, the ammonium metatungstate concentration was 0.5, 2, 3,
Table 1 shows the magnetic measurement results of powders that were dispersed in 10 tons of an aqueous solution with a change in velocity of 9 f/t, dried in Sawabetsu, pulverized, and then subjected to reduction treatment under the same conditions.

Example 3 Using the same αFeOOH533l as in Example 1, ammonium paratungstate (5(NH4)20.12W03
-5H20) It was dispersed in 20 tons of aqueous solution with a concentration of 1,07/t, dried in Sawabetsu, and pulverized. 100 tons of powder was taken and subjected to water bottle reduction treatment at 400° C. to obtain metal powder.

The magnetic properties of this metal powder are saturation magnetization of 155 emu/11
It had a square shape of 51% and a coercive force of 13500e. Example 4 Using the same αFeOOH as in Example 1, 5y and 10y of silicotungstic acid (SlO2.12W03.26H20) were dissolved in 10 tons of water, and after dispersing and suspending αFeOOH266y, drying and pulverization were performed according to f.

This powder 50V was subjected to hydrogen reduction at 390°C. Table 2 shows the magnetic properties of the obtained metal powder. Example C0 2
．． 5m01% αFe with major axis 0.7μ (axial ratio 11)
266 liters of OOH was dispersed in 10 t of an aqueous solution having an ammonium paratungstate concentration of 1.0 f/t, dried in Sawabetsu, and then subjected to hydrogen reduction treatment at 390°C to obtain metal powder.

The magnetic properties of the powder are saturation magnetization 160em square shape 51%,
The coercive force was 13,700e. αF used in Example 1
eOOH was heated and dehydrated at 350° C. to obtain red iron oxide of αFe2O3, and its 240y was suspended and dispersed in 10t of an aqueous solution of ammonium paratungstate at a concentration of 0.5y/t, followed by drying separately.

Powder 501 was taken and reduced by heating at 400° C. in a hydrogen stream to obtain a metal powder. The magnetic properties of the obtained powder were a saturation magnetization of 160 emn/9-sided 49% and a coercive force of 13,000 e. Comparative example 1 αFeOOH2667 same as Example 1
was subjected to hydrogen reduction at 390°C to obtain metal powder.

The magnetic properties of this powder were a saturation magnetization of 160 emn/Fl, a square shape of 40%, and a coercive force of 9700 e. Comparative Example 2 αFeα elbow containing the same CO2.5mOl% as in Example 5 was
The magnetic properties of the powder obtained by thermal reduction in a hydrogen stream at 90°C are: saturation magnetization 162 emuj, square shape 41%, coercive force 1.
It was 1000e.

Claims (1)

[Claims] 1 Co, Ni, Sn, Ti, Zn, Sb, Ag, Mn
A method for producing acicular iron-based ferromagnetic metal powder by thermally reducing acicular iron oxyhydroxide or iron oxide powder containing or not containing metals such as acicular iron oxyhydroxide or iron oxide. Acicular iron oxyhydroxide or iron oxide to which a tungstic acid compound is attached at a ratio of 0.01 to 5% by weight (W/Fe+W) by adding the powder to a solution of the tungstic acid compound and immersing it. A method characterized by reducing powder by heating.