JPH0987857A - Carbide coating method by plasma CVD - Google Patents

Abstract

(57) Abstract: A metal oxide powder surface is coated with a carbide to modify the powder. SOLUTION: A container 7 containing a powder of metal oxide is evacuated, a mixed gas of methane and hydrogen is supplied while rotating the container 7, and the powder has a frequency of 1 MHz to 10 MHz.
By irradiating electromagnetic waves of GHz to generate plasma, methane is decomposed by the plasma, and C of the active group decomposed from methane is replaced with lattice-like oxygen of metal oxide to powder the carbide coating layer having high catalytic activity. It is formed on the surface of body particles. The container 7 containing the powder is 20 to 10 per minute.
Rotate at 0 rpm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for coating the surface of metal oxide powder particles such as titania and zirconia with a carbide.

[0002]

2. Description of the Related Art Diamond films and diamond-like carbon films are used in a wide range of fields as cutting materials, semiconductor protective films, etc. because they exhibit excellent characteristics such as high hardness, wear resistance, and low friction resistance. . A plasma CVD method is often used for synthesizing a diamond film, a diamond-like carbon film and the like.

[0003]

In plasma CVD,
Although a diamond film and a diamond-like carbon film are synthesized on a substrate, there is no example in which metal oxide powder is used as a coating target. However, when coating a metal oxide powder with a diamond film or a diamond-like carbon film, it is considered that new surface characteristics can be imparted to the oxide powder. The present invention has been devised to meet such a demand, and has a high electron density and ionization degree, and by using a low temperature plasma CVD method excellent in stability for a long time,
The purpose is to obtain high-performance powder particles by coating the surface of oxide powder with carbide.

[0004]

In order to achieve the object, the coating method of the present invention is to evacuate a container containing a powder of metal oxide and to mix methane and hydrogen while rotating the container. While supplying gas, the powder is irradiated with electromagnetic waves to generate plasma, and carbon obtained by decomposing methane by the plasma is replaced with lattice oxygen in the powder, and particles of the powder are obtained. Characterized by depositing carbide on the surface. When the container containing the powder of the metal oxide is rotated at a speed of 20 to 100 revolutions per minute, the individual powder particles are uniformly irradiated with plasma, and a uniform carbide coating is applied. Further, in order to efficiently decompose methane to obtain a fibrous carbon-based substance, it is preferable to maintain the frequency of the electromagnetic wave to be irradiated within the range of 1 MHz to 10 GHz.

In the present invention, for example, an electromagnetic wave plasma heating device having the equipment structure shown in FIG. 1 is used. The electromagnetic wave oscillated from the electromagnetic wave oscillator 1 is sent out through the isolator 2 and the output is measured by the power monitor 3. Then, it is fed into the reaction chamber 5 via the three-stub tuner 4. A plunger 6 is provided below the reaction chamber 5. Above the plunger 6, a quartz reaction tube 7 containing the powder to be treated is arranged. The quartz reaction tube 7 is rotatable by a stirrer 8. The inside of the quartz reaction tube 7 is evacuated by a vacuum pump connected via a trap 9, and the internal pressure is measured by a vacuum gauge 11. The powder to be treated includes titania,
In addition to zirconia, etc., Sc, Y, lanthanoid element, H
An oxide such as f, V, Nb, or Ta, a complex oxide, or the like is used. The particle size of the powder particles depends on the purpose of use, but is 1-2.
It is preferably in the range of 000 μm.

An appropriate mixed gas feed pipe is connected to the quartz reaction pipe 7, and a mixed gas of methane and hydrogen is fed into the quartz reaction pipe 7 through this feed pipe. The mixed gas is preferably a mixture of hydrogen and 0.1 to 10% by volume of methane. Methane becomes a carbon-based substance by decomposition, and an effective coating of the carbon-based substance cannot be obtained unless it reaches 1% by volume. But 10
When the blending ratio exceeds volume%, the partial pressure of hydrogen is insufficient and the adverse effects of oxygen and water contained in the atmosphere are likely to appear. In the electromagnetic wave oscillator 1, the frequency is 1 MHz to 10 GH
Generates an electromagnetic wave of z. This electromagnetic wave causes the quartz reaction tube 7
When the powder contained in the powder is irradiated, the powder particles are heated from the inside, and the surfaces of the particles are activated. Further, methane contained in the internal atmosphere of the quartz reaction tube 7 is decomposed,
Highly active carbon is produced. This carbon replaces the lattice-like oxygen of the powder particles to form a carbide coating layer having excellent electrical conductivity.

Observing the carbide coating layer formed on the surface of the powder particles in this way, the coating layer has a dense and uniform layer structure, is excellent in adhesion to the base material, is hard and has high thermal conductivity. Is also excellent. The particles provided with a coating layer are used as a photocatalyst, a gas sensor, etc. because the surface exhibits conductivity and semiconductor characteristics are improved.

[0008]

EXAMPLE Anatase type titania powder having an average particle size of 20 to 60 mesh was used as a raw material, and 10 g of titania powder was used.
Was stored in a quartz reaction tube 7 having a capacity of 200 cc. After evacuating the system with a vacuum pump, plasma was generated with a Tesler coil while irradiating an electromagnetic wave at 500 W. Then, a CH ₄ 1% -H ₂ mixed gas whose flow rate was adjusted to 30 cc / min by a mass flow meter so as to have a predetermined mixing ratio was introduced at a predetermined pressure, and the treatment was started while rotating the quartz reaction tube 7 at 70 rpm. did. After reacting for a predetermined time (2 hours), the electromagnetic wave irradiation was stopped and the treatment was completed. The gas pressure was set to 1, 10, 20, 30, 40 Torr. The plasma generated at an atmospheric pressure of 1 Torr is shown in FIG.
It has an emission spectrum shown in (a), and a highly active decomposition product -CH was produced. The temperature of the plasma gas at this time was about 1000 ° C. The emission spectrum of the plasma changed according to the atmospheric pressure as shown in FIGS. 2 (b) and 2 (c).

Physical properties of the plasma-treated sample were evaluated by powder X-ray diffraction (XRD) and Raman spectroscopy. In addition, active species generated in plasma are analyzed by optical emission spectroscopy (OES).
It was measured at. When anatase type titania was treated with methane hydrogen plasma, only the surface became gray. Also,
As seen in FIG. 3, which shows the result of spectroscopy by Raman spectroscopy, it was confirmed that titanium carbide was formed on the titania surface. This result indicates that CH ₄ is attached to the oxygen lattice of TiO _2.
It is presumed that it was caused by the substitution of the carbons of.
Therefore, in order to investigate the optimal conditions for titanium carbide synthesis, the gas pressure was changed under the reaction conditions to carry out the reaction.

As a result, it can be confirmed by visual observation that the entire surface of the sample treated with 1 Torr is gray, whereas the sample treated with 40 Torr is gray only in a part of the surface. It was When the titanium carbide formed on the titania surface was quantified by Raman spectroscopy, the Raman peak of titanium carbide decreased with increasing gas pressure, as shown in FIG. Originally, even if the electromagnetic wave power is kept constant, the plasma region becomes narrower as the gas pressure becomes higher, the power is concentrated, and the sample temperature rises. Therefore, it is expected that the higher the gas pressure, the faster the film formation rate.
In this example, the exact opposite result was obtained. Therefore, we investigated by emission spectroscopy how the active species such as radicals and ions, which are considered to play an important role in the gas phase reaction in plasma, are affected by the change in gas pressure. The survey results, as shown in Figure 2 above,
At a gas pressure of 1 torr, CH (420 nm), Hα (6
The emission peaks based on 60 nm), Hβ (486 nm), and H ₂ (near 600 nm) were clearly confirmed. But,
As the gas pressure increased to 20 Torr and 40 Torr, all the emission intensity decreased drastically. This indicates that the increase in pressure suppressed the ionization of gas and decreased the concentration of active species in plasma. That is, it can be said that the increase in gas pressure is the primary cause of reducing the production of titanium carbide.

Next, titania whose surface was carbonized was used for the photolysis of acetaldehyde, and the performance as a photocatalyst was investigated. In the test, anatase-type titania which was obtained by hydrolyzing titanium tetraisopropoxide, washed with water, filtered, and calcined in air at 500 ° C. for 2 hours was used as a sample A. Further, CH ₄ 1 Sample A in 1 Torr vacuum atmosphere
While supplying the% -H ₂ mixed gas at a flow rate of 30 ml / min, 5
A sample B plasma-treated with 00W for 2 hours was used. The test was conducted with acetaldehyde concentration of 1000 ppm, reactor volume of 2 liters, and UV intensity of 2.0 mW on the sample surface.
It was performed under the condition of / cm ² . As shown in FIG. 5, which shows the test results, Sample B, the surface of which was coated with TiC by plasma treatment, showed twice the aldehyde photodegradation performance as Sample A.

[0012]

As described above, in the present invention, the surface of the particles is coated with carbide by treating the metal oxide powder particles with the plasma induced by the electromagnetic wave. The formed coating layer is hard and has excellent electrical conductivity, thermal conductivity, etc., so high functionality is given to the powder particles, and abrasion resistance is improved. It can be used as a functional material.

[Brief description of drawings]

FIG. 1 is an electromagnetic wave plasma heating apparatus used in the present invention.

FIG. 2 Effect of gas pressure on emission spectrum of plasma generated by irradiating methane-hydrogen mixed gas with electromagnetic wave

FIG. 3 Raman spectra of titania and titanium carbide

FIG. 4 Changes in Raman spectrum depending on atmospheric pressure

FIG. 5: Effect of presence or absence of plasma treatment on photocatalytic function of titania

[Explanation of symbols]

1: Electromagnetic wave oscillator 2: Isolator 3: Power monitor 4: Three-stub tuner 5: Reaction chamber 6: Plunger 7: Quartz reaction tube 8: Stirrer 9: Trap
10: Vacuum pump 11: Vacuum gauge

Claims (3)

[Claims] 1. A vacuum is applied to a container containing a powder of metal oxide, a mixed gas of methane and hydrogen is supplied while the container is rotated, and a plasma is generated by irradiating the powder with an electromagnetic wave. By replacing the carbon obtained by decomposing methane by the plasma with the lattice oxygen in the powder,
A method for coating a carbide by plasma CVD, which comprises depositing a carbide on the particle surface of the powder. 2. The container according to claim 1 at a rate of 20 to 100 per minute.
A carbide coating method of rotating at a rotation speed. 3. The carbide coating method according to claim 1, wherein electromagnetic waves having a frequency of 1 MHz to 10 GHz are irradiated.