JPS61136608A - Corrosion resistant treatment of magnetic metallic powder - Google Patents

Abstract

PURPOSE:To produce magnetic metallic powder having excellent corrosion resistance by subjecting an alkaline suspension of acicular iron oxide and hydroxide of Co, Ni or Cr to a hydrothermal treatment in an autoclave in which a high temp. and high pressure are maintained. CONSTITUTION:The acicular iron oxide obtd. by heat-treating acicular goethite at 300-700 deg.C is slurried by an aq. NaOH soln. and water soluble metallic salts of >=1 kinds among Co, Ni, Cr, Cu, Sn, Mn, Al, Zn and Cd are added at about 0.05-15wt% thereto by which the alkaline slurry mixture composed of the iron oxide and metallic hydroxide is obtd. Such slurry is subjected to the high- temp. and high pressure hydrothermal treatment at about 150-350 deg.C and about 4-150 atm in the stainless steel autoclave. The iron oxide particles having the smooth particle surfaces are thus obtd. Such particles are reduced and the magnetic metallic powder which has high corrosion resistance, maintains the initial magnetic characteristics without deterioration and decreases deterioration with age is obtd.

Description

BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a method for producing magnetic powder for magnetic tapes, particularly metal magnetic powder, which has excellent corrosion resistance.

BACKGROUND OF THE INVENTION In recent years, recording devices have become smaller and lighter and more sophisticated, and as a result, the demand for higher density recording media has increased significantly. For this reason, recording materials also include γ-Fe203, Co
-y-Fe2 From the oxide system represented by Q3, Fe
, With the appearance of metal magnetic powders such as Fe-Go, the 6 particles that need to be made finer and more dispersed become even more unstable, resulting in lower oxidation resistance and chemical stability. There is even a danger of ignition in metal magnetic powder. Therefore, when manufacturing metal magnetic powder, oxidation-resistant treatment is essential.

The conventional oxidation-resistant treatment gradually forms an oxide film on the surface layer of metal magnetic powder to prevent dangers such as fire caused by rapid oxidation.

In these methods, since the surface oxide layer is a nonmagnetic layer,
There are drawbacks such as not only a decrease in magnetic properties but also unavoidable changes over time.

HObject of the invention In the present invention, acicular iron oxide, Co, Hi, Cr, C
u.

with a hydroxide of one or more metals selected from the group consisting of Sn, Mn, Al, Zn and Gd,
Corrosion-resistant treatment of metal magnetic powder, in which the alkaline suspension is hydrothermally treated in a high-temperature, high-pressure autoclave, and the metal magnetic material produced by reduction treatment has excellent corrosion resistance and its magnetic properties do not deteriorate over time. The present invention provides a method.

These objects are achieved by the invention described below.

That is, the present invention uses acicular goethite in the range of 300 to 70
Acicular iron oxide obtained by heat treatment at 0°C, Go, N
i, Or, Cu, Sn, Mn, Al, Zn
Provided is a method for treating metal magnetic powder with corrosion resistance, the method comprising hydrothermally treating an alkaline suspension with one or more hydroxides selected from the group consisting of Cd and Cd in an autoclave at high temperature and high pressure. It is.

■ Specific structure of the invention Metal magnetic powder is thought to be very active due to pores existing on the particle surface generated during heat treatment. Metal magnetic powder with excellent corrosion resistance is produced by reducing the number of pores on the particle surface or smoothing the surface of each particle to eliminate unevenness, and at the same time modifying the surface of iron oxide with metal hydroxide. We have found a processing method to do this.

The method for improving the corrosion resistance of metal magnetic powder according to the present invention will be described in detail as follows.

Acicular iron oxide obtained by heat treating acicular goethite (
5 wt% ~ 20 wt%), NaOH (0.5 wt% ~
(30 wt%) aqueous solution to form a slurry, Co, Xi.

An aqueous solution of one or more water-soluble metal salts (0.05 wt% to 15 wt%) selected from the group consisting of Cr, Cu, Sn, Mu, Al, Zn, and Cd is added to form iron oxide and metal water. Make a mixed slurry of oxides.

Thereafter, the slurry was placed in a toning container (50 layers x φ) and hydrothermally treated in a stainless steel autoclave at a temperature range of 150 to 350°C and a pressure of 4 to 150 atm, until the amount of metal added was 0. If it is lower than 05 wt%, no corrosion resistance effect will be observed, if it is higher than 15 wt%, it will cause a decrease in σS, if it is lower than 150°C, the effect of hydrothermal treatment will not be recognized, and if it exceeds 350°C, hexagonal plate-like oxidation will occur. Iron is produced, which is undesirable.

It has been confirmed by a transmission electron microscope that the surfaces of the acicular iron oxide particles obtained by the treatment according to the present invention are smooth.

It was also confirmed that the added metal hydroxide was uniformly deposited on the particle surface, as shown in FIG.

The method according to the present invention not only has an anti-corrosion effect due to the smoothing of the particle surface, but also has an anti-corrosion effect due to the deposition of metal hydroxide, and is a very useful means.

Goethite is not suitable as particles for treatment because it changes into plate-shaped hematite (MIO) when hydrothermally treated in an alkaline aqueous solution, and α-Fe203, Fe304
Those obtained by thermally decomposing acicular a-Fe0OH are suitable.

Moreover, as the metal salt, water-soluble metal salts such as chlorides, sulfates, and nitrates are preferable.

(2) Effects of the Invention The iron oxide particles obtained by the present invention have a smooth surface, and when the iron oxide is reduced to form a metal magnetic powder, it has excellent corrosion resistance.

Moreover, not only does the magnetic property not deteriorate as compared to conventional corrosion-resistant treatment methods, but there is also less deterioration over time.

Next, the present invention will be specifically explained with reference to Examples.

[Example 1] CO metal ions were converted into Co/cc-Fe203
00-2.8? After adding 10 g of iron oxide (α-Fe203) to 100 mjL of water containing (%) (1.078 g as CoC12.6H20), 100 mjL of 1% aqueous sodium hydroxide solution was added to form a slurry. Place the above slurry in a silver autoclave container and heat at 250°C.
Then, hydrothermal treatment was carried out at 50 atm for 2 hours to obtain a hydrothermally treated sample.

[Example 2] Hydrothermal treatment was performed under the same conditions as in Example 1, except that Ni was used as the additive metal, to obtain a hydrothermal treated sample.

[Examples 3 to 9] Additive metals were Cr, Cu, Sn, Mn, Al,
Hydrothermal treatment was performed under the same conditions as in Example 1, except that Zn and Cd were used to obtain a hydrothermal treated sample.

The sample obtained in the above example was heated at 450°C for 6 hours.
Magnetic properties of metal magnetic powder obtained by reduction treatment and 1. Metal magnetism obtained by the conventional method (gradually forming an oxide film on the surface layer of metal magnetic powder by air oxidation) without carrying out the treatment according to the present invention. The magnetic properties of the powder are shown in Table 1 as a comparative example.

In Table 1, ΔσS% is the change in σS measured after 168 hours at a temperature of 60° C. and a humidity of 90%.

[Brief explanation of drawings]

Figure 1 is an electron micrograph of the metal structure. 3000 of the iron oxide particles of Example 2 treated by the method of the present invention.
This is a 0x transmission electron micrograph. FIG. 1

Claims (1)

[Claims] Acicular iron oxide obtained by heat-treating acicular goethite at 300 to 700°C, Co, Hi, Cr, Cu, Sn, M
Corrosion-resistant treatment of metal magnetic powder, characterized by hydrothermally treating an alkaline suspension with one or more hydroxides selected from the group consisting of Zn, Al, Zn, and Cd in a high-temperature, high-pressure autoclave. Method.