JPH0151042B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing ferromagnetic metal powder primarily for magnetic recording, useful in magnetic tapes, magnetic disks, magnetic cards, and the like. Specifically, the present invention provides a ferromagnetic metal powder that has high coercive force and high saturation magnetization suitable for high-density magnetic recording media, and has excellent corrosion resistance. Recently, with the increasing density of magnetic recording, magnetic metal powders with high coercive force and high saturation magnetization have begun to be used in place of conventional magnetic oxide powders. This magnetic metal powder is usually pure iron or an iron alloy containing other metals (nickel, cobalt, chromium, etc.). The conventional method for manufacturing magnetic metal powder or magnetic iron alloy powder is to heat metal iron oxide, iron oxyhydroxide, or iron oxyhydroxide or other metals (Co, Ni, etc.) in a reducing gas. There are known ways to restore it. (For example, Special Publication No. 35-3862, Special Publication No. 53-Sho.
No. 11512, JP 54-22838, JP 54-122663
Issues of publications and IEEE Trans Magnetics
Mag-5 317 (1969), Mag-8 430 (1972)
etc. ) However, with these methods, sintering occurs between powder particles, resulting in large changes in particle shape.
As a result, there was a drawback that the coercive force decreased. In order to improve this, a method has been disclosed in which the surface of these iron oxide or iron oxyhydroxide powders is coated in advance with bismuth or a bismuth and silicon compound, and then reduced with hydrogen gas.
(Japanese Patent Publication No. 46-7153, Japanese Patent Publication No. 52-19541, etc.).
However, since all of these methods use water-soluble salts or emulsions, the particle surfaces cannot be sufficiently covered, making it difficult to obtain sufficient effects. Alternatively, there is also known a method in which molybdenum trioxide is dissolved in an aqueous sodium hydroxide solution, cobalt-containing magnetic iron oxide powder is immersed in the solution, filtered, washed with water, dried, and then reduced.
Publication No. 54299). However, in this method, most of the soluble molybdenum salt flows out, and the effect of preventing sintering is weak. Furthermore, the metal powder obtained by the above method has insufficient corrosion resistance and is not preferred for practical use. The present inventors have carried out extensive research to improve the above points, and as a result, have established the method of the present invention. That is, the present invention provides Mg,
reacting a water-soluble salt of Ca, Sr, Ba, Co, Ni, Zn, Zr or Al with sodium peroxoborate, potassium peroxoborate or ammonium peroxoborate to deposit a peroxoborate of these metals; It is then characterized in that it is reduced in a reducing gas such as hydrogen gas. To describe this method more specifically, first, iron oxide, hydrated iron oxide, or Ni, Co, etc. Disperse powder containing other metals. Next, while stirring, Mg, Ca, Sr, Ba, Co, Ni, Zn, Zr
Alternatively, by adding an aqueous solution of a water-soluble salt of Al (denoted as X), iron oxide or hydrated iron oxide (Ni, Co
It may also contain other metals. Insoluble salts or sparingly soluble salts (for example, magnesium peroxoborate, etc.) of these elements are deposited on the particle surfaces of the particles (the same applies hereinafter) to form a uniform film of these salts. Next, these surface-treated iron oxides or hydrated iron oxides are separated, dried, and then heated and reduced in a reducing gas to form metal powder. Of course, the desired metal powder can be obtained in the same manner even if the order of addition of the two types of aqueous salts (X) and (Y) is reversed in the above method. According to the method of the present invention, sintering between iron oxide or hydrated iron oxide particles is effectively prevented during thermal reduction, and a metal powder having a particle shape with a high acicular ratio can be obtained. Furthermore, since the surfaces of these metal powders are protected by a stable coating derived from peroxoborates, metal iron powders that are resistant to corrosion can be obtained. Therefore, the obtained metal powder has high coercive force and saturation magnetization, as well as excellent corrosion resistance, and is extremely valuable as a material for high-density magnetic recording. The Mg, Ca, Sr used in the present invention,
Water-soluble salts (X) of elements such as Ba, Ni, Co, Zn, Zr or Al include formates, acetates, hydrochlorides,
Sulfates, nitrates, (e.g. Mg(HCOO) ₂ .
2H ₂ O, Mg(CH ₃ COO) ₂・4H ₂ O, MgCl ₂・
_6H2O , _MgSO4・_7H2O , Mg( _NO3 ) ₂・_6H2O ,
Ca(CH ₃ COO) ₂ H ₂ O...etc.). Here, it is preferable to use acetate or nitrate because the resulting metal powder has particularly excellent corrosion resistance. In addition, when describing the usage amount of each of these salts in the case of hydrated iron oxide, for example, the usage amount of sodium perborate, potassium peroxoborate, or ammonium peroxoborate is hydrated iron oxide (for example, goethite (α- 1 for FeOOH))
A range of ˜30 weight percent is preferred. On the other hand, the amount of the water-soluble salt of Mg, Ca, Sr, Ba, Ni, CO, Zn, Zr, or Al used is preferably in the range of 0.5 to 20 weight percent based on goethite. In addition, the amount of peroxoborate produced by the reaction of these salts attached to goethite varies slightly depending on the concentration of goethite in water;
[Goethite] is about 50% of the amount of peroxoborate produced when it is about 20. If the amount of adhesion is small, sintering between powder particles cannot be prevented, and the coercive force of the obtained metal powder decreases. If there is too much adhesion,
Even if an attempt is made to promote the reduction by increasing the heating temperature during reduction or by extending the heating time for a long time, the reduction of the raw material powder will be insufficient and the saturation magnetic amount or coercive force of the product will decrease. In this way, Mg, Ca, Sr, Ba, Co, Ni,
The temperature at which the material to be reduced coated with Zn, Zr, or Al peroxoborate is thermally reduced is preferably within the range of 300 to 500°C; if the reduction temperature is too low, the reduction time becomes long. Not only is it time-consuming, but the reduction is insufficient, resulting in a decrease in saturation magnetic capacity or coercive force. If the reduction temperature is too high, particles will sinter and the coercive force of the product will decrease. The content of the present invention will be explained in more detail by giving Examples and Comparative Examples below (% means weight basis). Example 1 _Magnesium acetate [Mg(CH ₃ COO) 2.4H ₂ O〕
100c.c. of X% aqueous solution of (magnesium acetate x/100g
10 g of goethite powder (α-FeOOH with a length of 0.5 to 0.8 μm and a needle-like ratio of about 15) was immersed in the solution (containing 100 g of goethite powder) and dispersed by stirring with a stirrer. Next, a y% aqueous solution of sodium peroxoborate [NaBO ₃ 4H ₂ O]
After adding 100c.c. (containing y/100g of sodium peroxoborate) and stirring and dispersing the powder again,
Separately, dried. After that, this dry cake was put into a reduction furnace and after replacing the air with nitrogen gas, the flow rate was 3/3.
The temperature was raised in a hydrogen gas atmosphere of min., and reduction was performed at 400°C for 2 hours to obtain metallic iron. After lowering the temperature to room temperature and purging with nitrogen gas again, it was immersed in toluene for 20 hours. After that, this metal iron powder is separated in the air,
Stabilized iron powder was obtained by drying. The iron powder obtained in this way was classified according to the concentration of the treatment agent added, and the iron powder was classified into x=0.05 and y=0.1 (equivalent to 0.5% by weight and 1% by weight, respectively, relative to goethite).A2, ( x=0.2,y
=0.4) is A2, (x=0.5, y=1) is A3, and (x=1, y=2) is
Make it A4. Example 2 The same procedure as in Example 1 was carried out except that magnesium nitrate [Mg(NO ₃ ) _{2.6H 2} O] was used instead of magnesium acetate [Mg(CH ₃ COO) ₂ ] in the treatment method of Example 1. The iron powder obtained by
B1, (x=1, y=2) is assumed to be B2. Example 3 Iron powder obtained in the same manner as in Example 1 except that potassium peroxoborate was used instead of sodium perborate was classified according to the concentration of the treatment agent added, and =0.5,y=1)
Let C1 be C1, and C2 be C2, where (x=1, y=2). Example 4 Iron powder obtained in the same manner as in Example 1 except that ammonium peroxoborate was used instead of sodium perborate in Example 1 was used (x=
0.5, y=1) is D1, (x=1, y=
2) is referred to as D2. Comparative Example 1 Iron powder obtained in the same manner as in Example 1 except that sodium perborate was not added was divided according to the treatment concentration of magnesium acetate (X) and x = 0.5, and E1 was obtained. , x=1 is set as E2. Comparative Example 2 Iron powder obtained in the same manner as in Example 1 except that magnesium acetate was not added was divided according to the treatment concentration of sodium perborate (Y), and y = 0.5 and 1.0. are F1 and F2, respectively. Example 5 Regarding iron powder obtained in the same manner as in Example 1 except that calcium acetate Ca (CH ₃ COO) ₂ H ₂ O was used instead of magnesium acetate in Example 1 (x
=0.5, y=1) is G1, (x=1, y
=2) is set as G2. Example 6 Regarding iron powder obtained in the same manner as in Example 1 except that strontium acetate was used instead of magnesium acetate in Example 1 (x = 0.5, y = 1)
Let H1 be the one where the equation is set, and H2 be the one where (x=1, y=2). Example 7 Regarding the iron powder obtained in the same manner as in Example 1 except that barium acetate was used instead of magnesium acetate in Example 1, (x = 0.5, y = 1), I1, (x = 1 , y=2) is set as I2. Example 8 J1, (x=0.5, y=1) for iron powder obtained in the same manner as in Example 1 except that cobalt acetate was used instead of magnesium acetate in Example 1. , y=2) is designated as J2. Example 9 Regarding iron powder obtained in the same manner as in Example 1 except that nickel acetate was used instead of magnesium acetate in Example 1, (x = 0.5, y = 1) was K1, (x = 1, y=2) is K2
shall be. Example 10 For iron powder obtained in the same manner as in Example 1 except that zinc acetate was used instead of magnesium acetate in Example 1, (x = 0.5, y = 1) was set as L1, (x = 1, y=2) is defined as L2. Example 11 In Example 1, zirconium oxynitrate [ZrO(NO ₃ ) _{2.2H 2} O] was used instead of magnesium acetate.
Regarding the iron powder obtained in the same manner as in Example 1 except that (x = 0.3, y = 0.4), M1,
(x=0.5, y=0.6) is defined as M2. Example 12 Regarding the iron powder obtained in the same manner as in Example 1 except that aluminum chloride was used instead of magnesium acetate in Example 1, (x = 0.1, y = 0.3), N1, (x = 0.5 , y=1) is set as N2. Comparative Example 3 Iron powder obtained in the same manner as in Example 9 except that borax Na ₂ B ₄ O ₇ was used instead of sodium peroxoborate in Example 9 was classified according to the concentration of the treatment agent added. (x=0.5, y′=2.3)
Let O2 be O1, (x=1, y′=4.6). Comparative Example 4 10 g of the goethite powder used in Example 1 was immersed in 200 c.c. of an aqueous solution of potassium silicate [K ₂ SiO ³ ],
After stirring and dispersing, it was dried separately. after that,
This dried cake was reduced in the same manner as in Example 1 to obtain metal powder. The iron powder thus obtained was classified according to the treatment concentration of potassium silicate, and P1 was 5wt% and 10wt% of goethite, respectively.
and P2. The magnetic metal powders obtained in the above Examples and Comparative Examples were classified according to the type and amount of goethite surface treatment agent used, and their magnetic properties were summarized in Tables 1 and 2.
Shown in the table. [Table] [Table] [Table] In addition, magnetic metal powders A2, A3, and P2 obtained in Example 1 and Comparative Example 4 were mixed at a temperature of 60°C and relative humidity.
Saturation magnetization amount σm when left in air at 90%
The figure shows the results of examining changes over time in (value at an applied magnetic field of 10 KOe). As is clear from the figure, it can be seen that the iron powder obtained in this example exhibits better oxidation resistance than that of the comparative example. From the above results, the magnetic metal powder produced according to the present invention not only has excellent magnetic properties but also excellent corrosion resistance, and is very industrially advantageous.

[Brief explanation of drawings]

The figure shows magnetic metal powder according to Example 1 of the present invention.
It is a graph showing changes over time in the amount of saturation magnetization at 60° C. and 90% relative humidity for A2 and A3 and P2 according to Comparative Example 4.

Claims (1)

[Claims] 1. A method for producing iron or a magnetic metal powder mainly composed of iron by reducing iron or an oxide or hydrated oxide of a metal mainly composed of iron and containing other elements such as Ni and Co. A peroxoborate of at least one element selected from Mg, Ca, Sr, Ba, Co, Ni, Zn, Zr and Al is attached to the surface of the oxide or hydrated oxide, and then reduced. A method for producing magnetic metal powder, which comprises reducing the powder in a magnetic gas. 2 Mg, Ca, Sr, Ba, Co,
As a method for depositing peroxoborates of Ni, Zn, Zr, or Al, the oxides are added to an aqueous solution containing at least one of sodium perborate, potassium perborate, and ammonium perborate (represented as Y). Alternatively, disperse hydrated oxide powder and add Mg, Ca, Sr,
The method according to claim 1, characterized in that an aqueous solution containing at least one of water-soluble salts of Ba, Co, Ni, Zn, Zr, and Al (hereinafter referred to as X) is added. 3. The manufacturing method according to claim 2, characterized in that the order of addition of the water-soluble salts (X) and (Y) is reversed. 4. The production method according to claim 2 or 3, wherein the water-soluble salt (X) is an acetate or a nitrate.