JPS587337B2 - Oxide reduction method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for reducing oxides using hydrogen plasma generated by electron cyclotron resonance.

First, a method for generating hydrogen plasma using electron cyclotron resonance method will be described.

A static magnetic field in a vacuum (the magnitude is B tesla).

) and introduce hydrogen gas into it to create a low-pressure hydrogen gas atmosphere.

When a strong electromagnetic wave with a frequency f (hertz) given by f = eB/2πme is applied, the free electrons created due to cosmic rays become electrons because the period of the cyclotron motion around the magnetic field matches the period of the electromagnetic wave. is resonantly accelerated by the electric field of the electromagnetic wave and absorbs the energy of the electromagnetic wave.

These electrons ionize the surrounding neutral gas, and the electrons generated here are also resonantly accelerated and ionize gas atoms one after another, generating plasma.

This plasma is called electron cyclotron resonance (ECR) plasma.

The characteristics of ECR plasma are that it does not require an anode or cathode to generate it, the lifetime of the generator is extremely long, and its electron temperature (T
e) is 0.1ev by changing the gas pressure and electromagnetic wave power density.
It can be varied over a wide range of ~1 kev.

The purpose of the present invention is to provide an inexpensive and easy-to-handle method for reducing metal oxides by irradiating hydrogen plasma generated in this manner onto metal oxides on the metal surface. do.

The present invention will be explained in detail below with reference to the accompanying drawings.

FIG. 1 is a diagram showing the principle of the metal oxide reduction apparatus according to the present invention.
A metal discharge tube 2 is inserted into a DC magnetic field generation coil 1,
The discharge tube 2 is evacuated using a vacuum pump.

After that, while evacuating the discharge tube 2, hydrogen gas is introduced from the inlet 3, and the pressure inside the discharge tube 2 is set to 10-5 to 10-2 Torr.
Maintain the required pressure between r.

A direct current is passed through the coil 1 to generate an electron cyclotron resonance magnetic field, and high-power microwaves are sent from the waveguide 5 through the vacuum-tight window 6 to generate hydrogen BCR plasma 7.

A metal oxide 9 to be reduced is mounted on a pedestal 8, and hydrogen plasma is irradiated onto it.

There are two types of particles that participate in the reduction reaction: hydrogen atoms H° and hydrogen ions H+ in the plasma.

H° is generated when hydrogen molecules H2 are dissociated by electrons in the plasma in the process H2+e→2 H°+e, and H+ is generated in the process H°+e→H++2e when H° is ionized.

Since H° is electrically neutral, it reaches the metal oxide without being affected by an electric field.

Chemically, H゜ has extremely high activity, so it reduces metal oxide MOx with the reaction MOX + 2XH゜ = M + 2XH20, and easily removes oxygen in metal oxides, which cannot be easily released due to its large binding energy, from the base metal. Converts to water that can be eliminated.

On the other hand, since H+ has a plasma charge, the ion sheath 1 formed between the plasma 7 and the metal oxide 9 shown in FIG.
It is accelerated by the electric field that exists in zero, reaches the surface of the metal oxide, recombines with electrons, becomes H°, and participates in the same reaction as the reduction reaction described above.

Here, the potential difference φ5 applied to the ion sheath is the electron temperature of the plasma in electron volts, and if Te electron volts is used, φs=T
It is e.

In the case of H+, since it is accelerated by the ion sheath, it collides with the H20 molecules generated by the reduction and gives its energy to the H2O molecules, which helps to promote their desorption from the surface of the oxide 9.

The desorbed H2O molecules reach the vacuum pump 4 and are exhausted.

As the reduction progresses, the above-mentioned H° diffuses within this reduction layer and reaches the internal oxidation layer, causing the above-mentioned reduction reaction.

The generated water molecules diffuse within the reduced layer, reach the surface, and are released and exhausted.

Therefore, in order to increase the reduction rate, it is necessary to heat 9 through the pedestal 8 to increase the diffusion rate of hydrogen atoms and water in the reduction layer.

FIG. 3 shows the experimental results when reduction was performed without heating using cuprous oxide as the sample.

Here, the plasma uses 4.4 GHz microwave (resonance magnetic field 1.57 KG) 200 W and hydrogen pressure is 2 x 10-4.
Generated under Torr.

The electron temperature and ion density of the plasma are 12 ev and 4 x 1010 cm-3, respectively.

The horizontal axis represents plasma irradiation time, and the vertical axis represents reduction thickness.

Table 1 shows the results of reduction experiments regarding metal oxides that are much more difficult to reduce than copper (having a large bonding energy with oxidation).

Note that the metal oxide sample was formed on the surface of a metal plate by heating it in air.

The thickness of the oxide layer causes the interference color of light to be a secondary blue (as the thickness of the oxide layer increases, the interference color changes from violet to red, and once the first change is completed, the color changes from violet to red again) .

Secondary blue means that the interference color exhibits blue in the second change.

). In air oxidation, it is difficult to identify the oxide, and therefore the refractive index is unknown, and the thickness of the oxide layer cannot be given quantitatively, but assuming the refractive index is 2, the thickness is approximately 230 nm.

According to this result, it becomes possible to reduce titanium, etc., which cannot normally be reduced in a hydrogen furnace.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an ECR plasma generator used in carrying out the present invention. FIG. 2 is an explanatory diagram of the oxide reduction method according to the present invention. FIG. 3 shows experimental results regarding the progress rate of reduction of cuprous oxide according to the present invention. In the figure, 1... vacuum container, 2... electromagnet for magnetic field generation, 3... hydrogen gas introduction tube, 5...
...Microwave waveguide, 6...Dielectric window for vacuum sealing, 7...Hydrogen plasma, 8...
- Frame, 9... Metal oxide to be reduced, 10...
...Ion sheath.

Claims (1)

[Claims] 1. An oxide reduction method characterized by reducing the oxide by irradiating the oxide with electron cyclotron resonance plasma of hydrogen.