JPS58147502A - Manufacture of ferromagnetic metallic powder - Google Patents

Abstract

PURPOSE:To manufacture ferromagnetic metallic powder having increased saturation magnetizability while almost preventing the deterioration of the squareness ratio by reducing iron-base oxyhydroxide or oxide and heat treating it at a specified temp. in an inert gas. CONSTITUTION:Iron oxyhydroxide such as alpha-FeOOH or oxide prepared by heat treating the iron oxyhydroxide is used as a starting material. The starting material is reduced at about 200-500 deg.C in a flow of a reducing gas, and the resulting iron-base metallic powder is heat treated at the reducing temp. -1,000 deg.C, preferably 400-800 deg.C in an inert gaseous atmosphere. Thus, ferromagnetic metallic powder with increased saturation magnetizability and a superior squareness ratio is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to a method for producing ferromagnetic metal powder, and more particularly, to a method for producing ferromagnetic metal powder and a magnetic recording medium using the ferromagnetic metal powder.

Magnetic recording as a recent magnetic recording medium! ! In order to improve the station and playback output, magnetic tape is used using gold metal powder, which is a magnetic material with high saturation magnetization (σ taste and coercive force). The following method is generally used to produce the powder.

(υ III Magnetism 1!!1 A method of thermally decomposing a metal M balate and reducing it with a reducing gas.

(2) Acicular oxyhydroxide or other gold 11
A method of reducing nine-acicular iron oxide obtained from these O oxyhydroxides with a reducing gas.

(3) Ferromagnetic gold 114t - method of evaporation in low pressure inert gas.

(4) A method in which a ferromagnetic material is produced by reducing a metal salt using a reducing agent (such as borohydride, hypophosphite, etc.) in a water bath solution.

(5) A method of thermally decomposing a metal carbonylated metal.

The present invention relates to method (2).

Several drawbacks can be pointed out regarding conventional methods belonging to this method.

Unfortunately, reduction is usually carried out in a high-temperature hydrogen stream, which causes sintering and makes it difficult to obtain desirable magnetic properties.

In order to suppress this sintering, the fi lightning is set at a lower temperature of reduction, but the ferromagnetic gold produced in that case.
The final layer is porous and has a large specific surface area. Metallic materials are extremely susceptible to oxidation in the atmosphere, so it is necessary to form an oxide mat on the particle surface 1io in order to make it cheaper. On the other hand, when the particle size of the starting material oxyhydroxide or oxide is small, the specific surface area becomes very large when a porous powder is produced as described above. Therefore, the proportion of oxide formed in the stabilizing tin layer increases, and the overall saturation magnetization decreases, which is an undesirable result.

On the other hand, the coercive force of the ferromagnetic metal powder produced in this way varies depending on the size of the crystallites formed in the hollow particles described above. Therefore, in order to obtain a ferromagnetic metal powder having a desired coercive force from a certain raw material, it is necessary to control the bore size or the degree of crystal growth during the heat treatment process. However, if the bore is suppressed or the crystal growth is promoted in a 1-reducing waste flow as in the conventional method, sintering occurs at lWj and the structure collapses, resulting in an angular effect on lWI# even if the coercive force #a can be controlled. The type ratio (residual magnetization/saturation magnetization) decreases, making it impossible to obtain desirable magnetic properties.

The present invention solves the above-mentioned drawbacks. That is, Motoya-
The purpose of this is to provide TiE/ with a ferromagnetic metal powder with large saturation magnetization and excellent squareness ratio, and to provide the desired coercive force without deteriorating the squareness ratio. The purpose is to provide nine ferromagnetic metal powders.

In order to combine the above objects, the inventors of the present invention conducted research on all types of products, and as a result, produced oxyhydrides or saponified products containing iron as a product.
One-dimensional imitation, 'l! The fist is heated in an inert gas (kl)
It was found that the saturation magnetization increased with almost no deterioration in the squareness ratio, and the book was rated good by -1.

The starting material for the present invention is α-FeOOH.

β-F*OOH, iron oxyhydroxide with r-Fe00HIk and these with Ni, Go, Mn, Zn, Cu
, Al.

One or more of metals such as Cr and Ti are added, and iron oxides, etc., which are made by heating and destroying round or thick pieces, are used. These starting materials tRyc 1
In the middle of the day ao o @C-j o o @Ce) @ML
, lovable し(l;2J j O@C−j 00 ”C
011j[rl1 element 0 In the present invention, ζ can be obtained, and iron is the generated component! The 41m powder is further heat treated in an inert gas atmosphere.

If the heat treatment temperature IL0 is too low, the heat treatment will not be effective.
On the other hand, if the temperature is too high, sintering will occur even in an inert gas, which is undesirable. The ferromagnetic metal powder used in the present invention is obtained by heating reduction in an H2 stream. However, the already mentioned 1
In fact, in the heating process in an inert gas, the diffusion and movement of atoms is much slower than in the heating process in a reducing gas.

Therefore, if the heat treatment temperature in an inert gas is as low as 9 temperature t↓9 experienced during reduction, the heat treatment effect U will hardly be observed within a practical time. On the other hand, the temperature at which sintering occurs during heating depends on the nature of the ferromagnetic metal powder before the tin salt.

It also depends on the nature of the iron oxyhydroxide starting material, and at the same time, sintering begins at a sufficiently low temperature for reduction even in the case of powder obtained from the same starting material. Based on the above considerations, I performed a roaring sleep experiment.11! The temperature of the fruit and heat treated salt is between the reducing temperature and 1ooo"c.

It turns out that it is best to perform the test at a temperature of preferably between *oo'C and too much °C.

The ferromagnetic metal powder obtained by this method is stabilized in the heat exchanger, and then released into the air. As a method of slow oxidation, it is immersed in 11 organic solvents, then it is t! The town will apply either method, such as drying in two atmospheres or increasing the partial pressure of air little by little with a mixed gas of air and nitrogen.

The sum magnetization of the resulting ferromagnetic metal powder is higher than before the heat treatment, but it depends on the heat treatment temperature; the higher the heat treatment temperature, the hotter the saturation magnetization becomes. At the same time, the thermal sensitivity temperature decreases and the crystallite size increases. It is known that coercive force depends on particle size. In addition, the coercive force is maximum when the particle size is a certain size (J-9), and the coercive force decreases even if the particle size becomes large or small (obtained with the present invention). The coercive force of saa powder varies depending on the crystallite size according to the above trend. - Although the squareness ratio has a large coercive force, there is no noticeable deterioration due to the large diameter.

The method of the present invention can be considered to have the following reasons for obtaining a ferromagnetic metal powder with a high saturation magnetization and a good squareness ratio.

It can be considered that the process of heat treatment in a hydrogen stream causes a reduction reaction and crystal growth of the metal crystal part generated by the reaction. Even if the reduction reaction is almost completed,
If crystal growth is insufficient, the metal powder produced will have many bores and small crystallites, resulting in an increase in the proportion of monoxide that is produced to make it stable in air as described above. Saturation magnetization becomes small.

However, if crystallization is carried out in a reducing atmosphere, sintering tends to proceed at the same time, impairing the magnetic properties of the ferromagnetic metal powder. In the method of the present invention, since the crystal growth is performed in an inert gas, the ciJ ability is to promote only the crystal growth while being transparent to the sintered material. The result is magnetic''
It is possible to obtain particles with a small bore size and a somewhat large condensate size without impairing A-temperature, and the saturation magnetization increases. On the other hand, since the coercive force changes with the amount of crystals, it is possible to control the coercive force while suppressing sintering by appropriately selecting the salt temperature in an inert gas and the JP-A. In general, if the particle size of the starting material is small, it is easy to sinter, so the effect of the present invention is not so great for fine particles, and a ferromagnetic gold M with a large saturation magnetization and an excellent t-square ratio can be obtained. .

The present invention will be specifically explained below according to examples.

Implementation Inuoukan 40. Is, acicular ratio 0"t'5iiQ, jatm duck-containing acicular α-F e 00Hf N s in air flow 10
The mixture was heated and dehydrated at 0oC to obtain s+@4α-FesO,@ powder. This was obtained as a black ferromagnetic metal powder that is extremely easy to oxidize due to the i * o ``c-c4 * sekim heat in the tH, fi flow. Tokikaku heating I
IJI place - After giving the pill, immerse it in toluene and release it in the air *o
Dry toluene with @C! ! A ferromagnetic metal powder (sample i>) stable in aA was obtained.

Example 3 A magnetic starch II4 powder (sample λ) stable in 9 atmospheres was swallowed in exactly the same manner as in Example 1 except that the N after reduction and medium heating salt temperature 1L were *oo'c. .

The procedure was exactly the same as in Example 1, except that the reduction was ON and the medium heating temperature was 60°C.
A metal powder (sample J) was prepared.

Example 4 The heat treatment in N8 after reduction is roo@c except for ◆? Exactly the same procedure as l11 - stable in air! la
A metal powder (sample reference) was obtained.

Example 5 A ferromagnetic metal powder (sample j) stable in air was produced using the following procedure: .

Comparative Example 1 and N after reduction of N medium heat treatment temperature k was 1xoo"c.

Comparative Example 2 Except for the case where reduction was ON and medium heat treatment was not performed, the food was the same as Example 1. (Stable tkg in air using the same procedure!) ! I [Obtain a sample of magnetic metal.

Example - The drag α-F・OOH used in Example 1 was exposed to N in an air stream.
Heat and dehydrate at @c to give 81 degrees α-k e
Nine points. This was a black O strong aS metal composite which is extremely easy to oxidize due to 4# threshold heating in ITO@C in H3 air flow.

This was heat-treated for J hours at
% air/N mixed gas was pumped. Then, the O8 concentration was doubled every 10 minutes in the layer, and finally, by passing only air, it was gradually densified by 1p to obtain a black powder (sample 1) that was stable in air.

Example 1 A ferromagnetic metal powder stable in air (sample Fat-Fu Jiu) was prepared using exactly the same procedure as *M-Gar, except for ◆ where the temperature of the medium-heated salt was turned on after the rhinoceros was turned on. .

In the implementation process, a ferromagnetic metal cart (sample 10) stable in air was obtained by following the same procedure as in Example 1, except for one thing: ON after reduction, medium heat treatment temperature f was 40''c.

Example: Example: N after reduction, medium heating temperature was too@c.
Obtain the metal test material (sample //).

Example 1: A stable metal powder (sample 1) in 9 atmospheres was obtained using the same procedure as in Example except that the reduction was 1 tON and the medium heat treatment temperature was 1 ooo@c. .

Ground assembly 1 After reduction, N, medium heating m and iii were not performed, and except for 9, the same procedure was used as in Example 4.

Comparative Example 4 Dehydration and reduction proceeded in the same procedure as 夷'mf11.
! ! KH, J#@C in an air stream for J hours of thermal reduction, the IL was subjected to slow oxidation treatment HILt of Example- and Oka- to produce 9IA magnetic metal powder stable in air (see Sample I). ) Meeting nine.

As can be seen from the results shown in Table 1, the gII-containing gold R'llll powder obtained by the method of the present invention is lower than that of the conventional method.
Compared to K, the saturation magnetization is increased without deteriorating the square shoe ratio. Shimazu salt has no effect if it is below 1000C, and if it exceeds 1000C, the squareness ratio will deteriorate.9
It becomes useless after 1. Furthermore, Hc changes depending on the temperature of the p-heat treatment shown in Table C).
It is possible to obtain a ferromagnetic gold MS wheel with a coercive force of .

Claims (1)

[Claims] A ferromagnetic metal powder containing iron as a product obtained by adding an oxyhydroxide or oxide containing iron as a main component in a reducing gas is heated at the same temperature as above in an inert gas. More than 1oo
A method for producing ferromagnetic metal powder, which involves heat treatment at a temperature below o.C.