JPH04136172A - Method for coating inside with diamond - Google Patents

Abstract

PURPOSE:To deposit diamond on only the desired part of the inner wall of a tubular or spherical body made of a nonmetallic material by arranging metal wires in a prescribed shape in a microwave cavity resonator when the surface of the inner wall is coated with diamond by plasma CVD. CONSTITUTION:Holes are pierced in a cavity resonator causing H1 mode resonance in a direction perpendicular to the H face. The inside of a transparent quartz pipe is activated, Nichrome wires are wound around the central part of the pipe and the pipe is put in the holes. A gaseous mixture of hydrogen with 2.5% methane is fed into the pipe from one end, the other end is connected to a rotary oil pump and microwaves are applied to the resonator while keeping 50Torr pressure. After the lapse of 30min, the application of microwaves is stopped. Diamond has been densely deposited on the central part of the inner wall of the pipe at 700 deg.C.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention is directed to the use of a microwave plasma CVD method to coat the inner wall surface of a pipe-shaped or spherical object made of a non-metallic material such as alumina, silica, silicon nitride, or silicon carbide. This invention relates to a method of coating diamond to improve corrosion resistance and wear resistance in specific locations.

(Prior art) A method for coating diamond has already been disclosed in patent No. 1272928.1272929゜1332452.
．． 1332457, etc., and recently, methods capable of high-speed precipitation, such as a direct current plasma method and a combustion flame method, have been developed. Diamond itself has excellent chemical resistance and has the highest hardness in nature, so it is widely used as a corrosion-resistant and wear-resistant material, but the coated diamond mentioned above has almost the same ability.

Since it was confirmed that it exhibits these properties, it has been used as a coating tool. However, these coatings are applied on a flat surface, and a unique example is one described in JP-A-1-138110 in which the coating is deposited on the outer surface of a pipe or the like.

(Problems to be Solved by the Invention) Conventional methods have been able to coat only flat surfaces or outer surfaces, but when expanding to a wider range of applications, it becomes necessary to coat the inner wall surfaces of pipes. For example, corrosive fluids, An example is a pipe carrying an abrasive slurry. The coated diamond film has good translucency, so it has the advantage of allowing you to see the inside clearly. Also, by actively utilizing its good translucency, it is possible to make a durable viewing window.

When coating the inner surface of a pipe or sphere with diamond using the CVD method, high-speed deposition methods such as the plasma torch method 1 and the combustion flame method have limitations such as the inability to excite microscopic parts and the inability to maintain thermal balance due to equipment limitations. Rather, relatively mild methods such as the thermal filament method and the microwave CVD method are suitable. In the case of the hot filament method, it is possible to coat the pipe by placing the filament inside the pipe, but it is not practical due to the problem of deformation of the filament. The microwave CVD method was considered as the last remaining method.

The microwave CVD method is a method in which a reduced pressure reaction space is excited by non-polar discharge using microwaves, so if the inside of the pipe is used as the exciting space, it can be said to be a method that meets the purpose. However, if the conventional method is followed as it is, the entire space in the pipe where microwaves can be excited becomes a space in which deposition can occur, making it impossible to deposit in any intended location. If it is allowed to precipitate as it is, the precipitation will be highly uneven.

(Means for Solving Problem 1) It is said that in order for diamond to precipitate, it is necessary to broadly divide the reaction gas, substrate temperature, excited state, and surface activation for nucleation. Among these, we focused on controlling the excitation space and selectively heating the deposition location in order to deposit diamond as uniformly as possible at any location.

Regarding the control of the excitation space, it is possible to make some adjustment by increasing the pressure inside the reaction vessel, but if it becomes too high, the plasma state cannot be maintained. The reason why we say "to a certain extent" here indicates that when the reaction space becomes smaller, the wall effect comes into play and plasma is not generated at the intended location.

For selective heating of the deposition site, it is possible to attach auxiliary heaters to the necessary areas, but inserting a metal heater in a place where microwaves are flowing is dangerous because a large amount of microwaves will leak through the metal. be. This can be prevented to some extent by shielding the heater, but for safety reasons it is preferable not to use an auxiliary heater.

Figure 1(a) shows the state of the electric field when microwaves are traveling through a waveguide in HI11 mode.When plasma is actually generated and reacted, it is in a resonant state. Therefore, as shown in Figure 1(b), 1/4 from the reflective surface
The strongest electrical vibrations occur at the wavelength. The reaction container is placed in this part, and the present invention is designed to do so. In other words, if an independent heat-resistant metal that is not electrically connected to an external power supply is placed in a place where this electric field is strong, the Joule heat generated by the eddy current flowing within the metal will heat the necessary parts of the reaction vessel placed nearby. be able to. Plasma can also be confined by forming this metal into a loop.

In this way, diamond can be deposited on the inner wall of a hollow object with a diameter of about 3 cm within the limited space of a microwave cavity (6 cm x 12 cm at a frequency of 2.45 GHz).

The usual way to use a cavity resonator using H@+ mode is 8.
A hole is made on the side (long side) and a reaction vessel is inserted, but in the case of the present invention, a hole is made on the H side (short side) and a reaction vessel is inserted. This has the advantage of making it easier to control the location where plasma is generated.

Kanthal wire or nichrome wire is suitable as the heat-resistant metal considering the usage atmosphere and temperature.

In addition to wire rods, mesh or plate shapes may also be used.

The base material must be free of pores in order to reduce internal pressure. Transparent quartz and alumina are the most suitable materials, but other materials may be used as long as they have very few pores or can be sealed. It can be used even if

For activation of the surface of the base material, scratching with fine diamond particles, which has been used in the past, is suitable, but when the coating film layer is thin, it is used by making dense scratches.

(Function) It was difficult to apply diamond coating to the inner wall surfaces of pipes, inner walls of spheres, etc. as there was no suitable means to simultaneously excite the source gas and maintain the temperature of the deposition surface in a well-balanced manner.
This was made possible by skillfully using the characteristics of microwaves as in the present invention.

The temperature of the base material is maintained by Joule heat generated by an eddy current generated by microwaves in a heat-resistant metal body near the base material, and the raw material gas is excited by microwaves. The diamond precipitation mechanism is the same as in the case of ordinary vapor phase diamond. Examples are introduced below.

(Example 1) A hole is made perpendicularly through the H-plane of a cavity resonator that resonates in HII+ mode (Fig. 2-a), and a 12 mm outer diameter inner surface is wrapped with nichrome wire in the center as shown in Fig. 2-b. 2.5% methane from one side through an activated transparent quartz pipe
A hydrogen mixed gas containing 20 cc/min was flowed through the pump, and the other end was connected to an oil rotary pump, and the pressure was kept at 50 Torr, and 150 W microwaves were sent to the cavity resonator section. The length of the plasma generated at that time was 50 mm. When the microwave was stopped after 30 minutes, diamonds with a thickness of 1 μm were deposited densely at a 30 mm length in the center of the inner wall of the pipe. At this time, the temperature of the base material pipe is 700 at the center.
It was ℃.

(Example 2) The shape of the nichrome wire is different as shown in Figure 3, and the power is 1
When diamond was deposited under the same conditions as in Example 1 except that the power was 30 W, plasma with a length of 30 mm was generated and a diamond precipitate with a length of 25 mm was obtained at the center of the inner wall of the pipe. The temperature of the base material at this time was 700°C.

(Example 3) Diamond was deposited under the same conditions as in Example 2 except that the quartz pipe was tilted at 30 degrees in the plane of the cavity resonator E and the power was 120 W. Diamond was deposited under the same conditions as in Example 2. A diamond precipitate with a length of 20 mm was obtained at the center of the inner wall of the pipe. The substrate temperature at this time was 700°C. Among the examples shown here, in the case of Example 3, the areas where diamond was precipitated and the areas where diamond was not precipitated could be most clearly distinguished.

(Comparative Example 1) Diamond was deposited under the same conditions as in Example 1 except for the absence of a nichrome wire and a power of 180 W. When diamond was deposited, a plasma with a length of 100 mm was generated and a length of 50 m was generated.
A diamond precipitate of m was obtained. The base material temperature at this time is 7
It was 00℃.

(Comparative Example 2) When diamond was deposited under the same conditions as in Example 1 except for penetrating the E plane at right angles, a plasma with a length of 60 mm was generated and a diamond precipitate with a length of 40 mm was obtained. The substrate temperature at this time was 700°C.

(Effects of the Invention) As shown in the above embodiments, by arranging the metal wires in a predetermined shape within the microwave cavity, diamond can be deposited only in the required predetermined locations. can.

[Brief explanation of the drawing]

Figure 1 shows the electric field when microwaves travel in the H [I+ mode in the waveguide. Figure 2 shows the relationship between the base material and the device according to the method of the present invention. Figure 3 shows the base material of a heat-resistant metal body. This is an example of how to place it. (If you want to go to 10 heel mushrooms.

Claims (1)

[Claims] A method of coating diamond anywhere on the inner wall surface of a pipe-shaped or spherical base material by placing a metal body on the base material placed in a microwave cavity resonator using the microwave plasma CVD method.