JPS6260804A - Production of ferromagnetic powder - Google Patents

Abstract

PURPOSE:To produce ferromagnetic powder for an electric-wave absorbing material having superior characteristics by mixing iron oxide powder contg. wustite and magnetite as principal components with a carbon source and by heating the mixture at a specified temp. CONSTITUTION:Iron oxide powder contg. wustite and magnetite as principal components is mixed with a carbon source such as graphite powder, coke breeze or mineral oil. The mixture is heat treated at 300-650 deg.C in a flow of gaseous nitrogen or the like. By this method, ferromagnetic powder contg. metallic Fe and Fe3O4 without losing the state of fine particles and having uniform quality can be produced at a low cost.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention is directed to magnetite (Fe304) and metallic iron CM, F
e) The present invention relates to a method for producing a ferromagnetic powder containing e).

[Conventional technology]

Radio wave absorbing materials can prevent electromagnetic waves from reflecting on the inside surfaces of buildings, obstructing communication, or leaking electromagnetic waves from electromagnetic wave generating devices and affecting other digital devices! The demand for radio wave absorbers is increasing with the development of communications and electronics.Usually, radio wave absorbers are made of ferromagnetic powder such as ferrite and dielectric materials such as resin. A desirable property of radio wave absorbers, often used in the form of composites, is that they absorb radio waves at a wide range of frequencies in as thin a material as possible. For this reason, the condition that the ferromagnetic powder must satisfy is to maintain high magnetic permeability over a wide frequency range.

As mentioned above, ferrite (including magnetite) is the most common ferromagnetic powder. however,
The problem with ferrite is that it is difficult in principle to maintain high magnetic permeability at frequencies higher than 10 GHz. By changing the composition of the ferrite, it is possible to increase the magnetic permeability at low frequencies. However, the frequency characteristics are bound to deteriorate as a result, and in the end, the S transmittance in the high frequency range (10 GHz or higher) decreases.
l, there is no.

To compensate for this, if ferromagnetic powder of metal such as iron is used in combination, radio wave absorption in the high frequency range can be improved. In this case, the limit frequency that can be absorbed is inversely proportional to the square of the particle size, and 5 pm particles can absorb up to 10 GHz, and IJLm particles can absorb up to about 250 GHz.

However, it is not easy to obtain such fine metal powder at low cost, which has hindered the expansion of practical use.

[Problem that the invention seeks to solve]

The inventors of the present invention have studied to solve these problems and obtain a ferromagnetic powder having excellent properties for use in radio wave absorbing materials, and as a result, they have achieved the objective using the manufacturing method described below.

[Means for solving problems]

In order to solve the above problems, the present invention mixes iron oxide powder containing wustite and/or magnetite as one component with a powder and/or liquid serving as a carbon source.
The technical means is to heat it to 650°C.

[Effect]

The main point of the unreleased January report is that if it is iron oxide rather than metallic iron, it can be easily made into fine particles at low cost by crushing, etc., and if it is heat-treated under appropriate conditions, it can be made into fine particles while maintaining its fine particle state. , Fe3O4, M2, and Fe can be obtained. This makes it possible to produce at low cost a radio wave absorbing material that absorbs a wide frequency range of electromagnetic waves.

Hereinafter, the configuration of the present invention will be explained in detail together with its operation.

Firstly 1. One of the reasons why iron oxide powder containing FeO and/or Fe3O4 as a main component is used as a raw material is that oxides are brittle and can be easily ground into fine particles. In addition, these oxides are easily incorporated as magnetite hanite or mill scale.

Furthermore, by heating FeO and Fe3O4 in a reducing atmosphere, it is relatively easy to make ferromagnetic powder containing M, Fe, and Fe3O4. °Maybe,
In this case, the fine particle size of the raw material can be substantially maintained.

Second, when heating the raw material iron oxide, the powder or liquid serving as the carbon source is mixed for the following reason.In the present invention, a so-called composite powder containing M, Fe and Fe3O4 at the same time is obtained. Therefore, in principle, the raw material powder is heated in a reducing atmosphere to dissolve FeO and/or
or Fe3O4, M, Fe and Fe3O4
It is also possible to create a reducing atmosphere by adjusting the composition of the atmospheric gas, but if you rely on gas for reduction, the contact situation with the gas may vary depending on the location of the powder layer. Due to the difference, the ferromagnetic powder M, Fe
% and Fe3O4 often vary greatly depending on the location of the layer. Mixing and heating carbon sources improves this point.
By using this carbon source as a reducing agent, it plays the role of uniformly progressing the reduction reaction within the layer. In this case, an inert gas may be used as the atmosphere, or the powder layer is removed in some way.

Graphite powder with low ash content is excellent as a carbon source, but
In addition, powders such as coke powder, coal powder, carbon black powder, and resin powder, and liquids such as mineral oil and alcohol may also be used.

The reason why the heating temperature is limited to 300 to 650°C is as follows. At temperatures below 300°C, the reduction reaction does not proceed, and M
, Fe is not generated on top and the raw material is Fe.
When O is included in large quantities, FeO is M, Fe or Fe3
The reaction to decompose into O4 does not proceed, and as a result, the ferromagnetic phase (
Only low contents of M, Fe and Fe304) can be obtained.

On the other hand, when the temperature exceeds 650°C, FeO becomes a stable phase, so that FeO-q in the heated powder increases, resulting in a decrease in the content of the ferromagnetic phase.

Therefore, the heating temperature range is set at 300 to 650°C. However, the heating temperature range mentioned here does not prohibit heating outside the range; for example, if heated at a temperature exceeding 650°C and then kept heated inside, the same effect can be obtained. can get.

As described above, since the present invention is characterized by heating at a relatively low temperature, the fine particle size of the raw material powder can be almost maintained, and it can be applied to radio wave absorbing materials with a wide absorption frequency range as mentioned above. It can be done.

〔Example〕

Example 1 The raw material, the wustite-containing powder, was obtained by pulverizing mill scale in a vibrating ball mill for 10 hours, cutting the coarse powder by air classification, and obtaining a powder with an average particle size of 8. OILm was used. X
The wustite content according to line diffraction is about 79w%,
In addition, about 19 wt% magnetite and about 2 wt% hematite.
% was detected. T, Fe content by wet analysis is 73.9 wt%, impurity is 5i02:0.22
wt%, MnO: 0, 35 wt%, P: 0.0
1wt%, S: 0.01wt%, CaO: 0.05wt
%Met.

Graphite powder (fixed carbon 99.5%, ash content 0.
5%, average particle size 6. 4 wt% of Og, m) was mixed, 200 g was placed on an alumina tray, and the mixture was kept at each temperature for 20 hours in a tube furnace through which N2 gas was flowed.

For comparison, oxide powder without graphite was also subjected to the same heat treatment.

Table 1 shows the composition of the powder after 8 millings.

As is clear from Table 1, in the case where graphite is added, more M and Fe appear than in the case where graphite is not added.
Since 3O4 is kept low, the ferromagnetic phase (M, Fe and F
e304) has significantly increased. However, even if graphite is added, FeO
decomposition is incomplete, and graphite also remains unreacted and becomes an impurity. On the other hand, if the heating temperature exceeds 650°C, FeO will increase;
℃ heating is found to be appropriate.

Example 2 Here, in order to investigate the composition variation of powder containing magnetite and metallic iron, the powder that was heat-treated at 600°C with 3% graphite powder added in Example 1 was divided into 5 parts, and M
, Fe was measured.

For comparison, powder was also made by a method of generating metallic iron using H2 gas without adding any graphite powder, and M
, F e was analyzed. In this case, the raw material powder and heating container were the same as in the example, but the heating atmosphere, temperature, and time were as follows: for the first 4 hours in N2 + H2 (H2 10%) mixed gas, and for the next 6 hours in N2 gas. ℃ for a total of 10 hours.

As a result, in the case of the graphite mixed powder according to the present invention, M,
Fe is 7.9.9.6.8, 3.10.5.10.1
While the variation in wt% is small, in the comparative example, M
, F e is 15.3.10. O19,6,7,1,5
, 9wt%, which showed a large variation.

〔Effect of the invention〕

As described above, according to the method of the present invention, fine particles and M
, Ferromagnetic powder containing Fe and Fe3O4 at the same time can be produced at low cost and with small variations in quality, and can be used to improve the characteristics of radio wave absorbers and the like.

Claims (1)

[Claims] 1. Magnetite and metal characterized by mixing powder and/or liquid serving as a carbon source with iron oxide powder mainly composed of wustite and/or magnetite, and heating the mixture to 300 to 650°C. A method for producing ferromagnetic powder containing iron.