JPH02267193A - Method for synthesizing diamond by combustion flame method and gas burner for synthesis - Google Patents

Abstract

PURPOSE:To promote increase in deposition surface of diamond and improvement in homogenization by flowing an inert gas on the outside of an outer flame of a combustion flame using a burner of a specific shape. CONSTITUTION:Oxygen is added to a raw material compound for depositing diamond and a combustion flame is formed so as to provide an existing incomplete combustion region. Diamond is then synthesized on a substrate installed in the incomplete combustion region. In the process, a gas burner for synthesizing diamond by a combustion flame method having a gas blowoff outlet 1 for forming the combustion flame surrounded with an inert gas blowoff pipe (nozzle) 2 or many inert gas blowoff pipes (nozzles) 5 arranged around the gas blowoff outlet 1 for forming the combustion flame is used. Thereby, the length and thickness of an inner flame 3 are increased. An outer flame 4 disappears in a part near the gas blowoff outlet 1 due to the inert gas and is formed from a part near the apex of the inner flame 3. As a result, a diamond crystal, excellent in homogeneity and having a large area can be readily deposited.

Description

[Detailed Description of the Invention] <Industrial Application Fields> The present invention has excellent properties such as abrasion resistance, corrosion resistance, high thermal conductivity, high electrical insulation, and wide-area optical transparency, and is suitable for use as an abrasive and grinding material. The present invention relates to a method for synthesizing film-like diamond using a gas phase combustion flame method, which is useful for materials, carbide tool materials, members for optical materials, etc., and a gas burner suitable for carrying out the synthesis method.

<Prior Art> Conventionally, methods for synthesizing diamond include a synthesis method using an iron, nickel-based catalyst, etc. under ultra-high pressure and high temperature conditions, and a direct conversion method of graphite using an explosive method.

In recent years, low pressure +1. The VD method is a method of synthesizing diamond by excitation of a mixed gas of hydrocarbon or organic compound containing nitrogen, oxygen, etc., and hydrogen using a hot filament, microwave plasma, high frequency plasma, DC discharge plasma, DC arc discharge, etc. being developed.

More recently, the applicant has developed a method for synthesizing diamond in the non-oxidizing region of combustion flame,
No. 8, and the present invention relates to a method that further develops this method and a gas burner for generating a combustion flame to realize the method.

<Problems to be solved by the invention> The invention of Japanese Patent Application No. 1983-71758 is a vapor phase synthesis method that is simpler than conventional methods and can also produce a large area of diamond film. The key point is to burn a carbon-containing raw material compound for diamond precipitation so that it has an incomplete combustion region, and to place a substrate for diamond precipitation in a non-oxidizing atmosphere in or near the incomplete combustion region. In this method, diamond is deposited on the base material by maintaining the base material temperature at the diamond precipitation temperature.

This method allows diamond to be deposited on a substrate simply by forming a combustion flame using a raw material compound containing carbon, and is a revolutionary method compared to the conventional CVD method, but it is difficult to put it into practical use. There is a strong desire to further increase the diamond precipitate area and control the homogeneity of the precipitates.

The present invention aims to increase the area of diamond precipitation and promote homogenization.

Means for Solving the Problems> The present inventors have conducted various studies regarding the low-pressure CVD method, particularly regarding excitation means, and have found that thermal plasma is used for hot filaments, microwave plasma is used for microwaves, and arc discharge plasma is used for direct current arc discharge. It was concluded that the plasma state is greatly involved in diamond synthesis in all cases, and since the combustion flame caused by combustion is also in the plasma state, it is easier to synthesize diamonds by using this combustion flame than with conventional methods. It was determined that it could be synthesized, and a patent application was filed in 1983-7175.
I applied as No. 8.

Furthermore, as a result of research aimed at expanding the diamond precipitation area and homogenizing the precipitated diamond, the present invention was completed by discovering that the objectives could be achieved by circulating an inert gas outside the outer flame section of the combustion flame.

That is, the present invention adds oxygen to a raw material compound for diamond precipitation, forms a combustion flame so that an incomplete combustion region exists, and in a non-oxidizing atmosphere in or near the incomplete combustion region, By installing a base material for diamond precipitation and maintaining the temperature of the base material at the diamond precipitation temperature, an inert gas flow is formed around the combustion flame to reduce the diffusion of oxygen and cause diamond precipitation. A method for synthesizing diamond using a vapor phase method, which is characterized by increasing the area, and an inert gas blowing pipe is double-layered so that the combustion flame generating gas blowing port used in the method is surrounded. The present invention relates to a gas burner for combustion flame diamond synthesis, which is arranged in a combustion flame method, and a gas burner for combustion flame diamond synthesis, in which a large number of inert gas blow-off pipes are arranged around a combustion flame generation gas blow-off port.

Note that the diamond synthesized by the method of the present invention contains diamond-like carbon.

First, the raw material gas for diamond synthesis will be explained.

Various compounds shown below can be used as carbon sources.

Saturated hydrocarbons such as methane, ethane, propane, butane,
Unsaturated hydrocarbons such as ethylene, propylene, butylene and acetylene; aromatic hydrocarbons such as benzene and styrene;
Alcohols such as ethyl alcohol, compounds containing ketone groups such as acetone, ethers such as diethyl ether,
Other aldehyde compounds, nitrogen-containing compounds, -carbon oxide, etc. can all be used. Further, the above-mentioned compounds can be used alone or in combination of two or more.

These carbon source compounds are mixed with oxygen and non-oxidizing gases such as N2, Ar, N2, C01C02, N20, etc., if necessary, and burned.

Furthermore, it is also possible to use solid carbon, graphite, etc. as a carbon source through reactions such as vaporization, combustion, and hydrogenation in a combustion flame of a mixed gas of the compound, hydrogen, and oxygen.

In the present invention, the raw material gas for diamond synthesis is combusted so that an incomplete combustion region exists to form a combustion flame, and non-oxidizing diamonds in the incomplete combustion region or outside the flame and in the vicinity of the flame are used. In the region excited to be able to precipitate,
It is necessary to always have a diamond precipitation growth surface.

Next, the gas burner of the present invention for carrying out the combustion flame diamond synthesis method and the combustion method of the present invention using the gas burner will be explained with reference to the drawings. The burner itself has a well-known structure, and since the gas outlet is unique, only that part is illustrated.

Figures 1 and 2 are explanatory diagrams showing how the combustion flame of the present invention is formed using a typical gas burner of the present invention, and Figure 3 is an explanatory diagram showing how a combustion flame of the present invention is formed using a conventional gas burner using a conventional method. The explanatory diagrams, Figures 4 and 5, are A-'A of Figure 1, respectively.
2 shows a cross-sectional view taken along line B-Bm in FIG.

In the figure, 1 and 1' are gas outlets, 2 is an annular inert gas nozzle, 3 and 3' are the inner flame of the combustion flame, 4 and 4' are the outer flames, and 5 are multiple units arranged around the outlet. Shows an inert gas outlet pipe.

The annular inert gas nozzle 2 shown in FIG. 1 is preferably a slit. Furthermore, as is clear from the drawing, the gas burner shown in FIG. 1 has double inert gas blow-off pipes so that the combustion flame-generating gas blow-off port is surrounded.

As shown in FIG. 3, a normal combustion flame has a short circular segment 3' within an elongated outer flame 4'. In this case, there is no inert gas flow.

In FIGS. 1 and 2 showing the present invention, for example, argon is flowing through the inert gas nozzle 2 and the inert gas blowing pipe 5 in the direction of the arrow. For this reason, the length of the inner flame 3 has increased significantly, and its thickness has also increased. On the other hand, external inflammation 4
Due to the inert gas, it disappears near the gas outlet, and is formed near the top of the inner flame as shown in the figure. The shapes of the inner flame and outer flame shown in FIGS. 1 and 2 are merely examples, and the shapes are determined by the combustion flame formation conditions, the type of inert gas, the flow rate, etc. In the combustion flame synthesis method of the present invention, as in the conventional combustion method, it is necessary to place the substrate so that at least a portion thereof exists within the inner flame.

As the base material for diamond precipitation, those commonly used in low pressure CVD methods can be used. That is, in addition to the s1 wafer, SiC sintered body, and SiC granules, W, WC, Mo, TiC, and Ti
Examples include shaped objects and granular objects such as N, cermet, cemented carbide tool steel, alloy tool steel, and high-speed steel.

The region where diamonds are deposited is an oxygen-deficient region of the combustion flame, commonly referred to as the inner flame.

- Numerically, even if a diamond is formed under high heat in an oxygen-excessive region, the excess oxygen turns into co and co□ and disappears. That is, the diamond precipitation region is oxygen deficient and relatively low temperature. In this region, it is necessary to excite the raw material gas to conditions that produce hydrocarbon radicals and carbon radicals (active species).

In the method of the present invention, the temperature of the flame is 300 to 3000°C, and the temperature of the substrate for diamond precipitation is 300°C to 1400°C.
It is preferable to keep it within the range of .

If the excitation is insufficient in this state, a heating element using electrical heating, high-frequency induction heating, a heating method using laser light, infrared heating, heating using arc discharge, or the like is used as an auxiliary heating source.

Specifically, the heating area temperature is 800°C or higher, preferably 1000°C or higher, and the base material temperature is 300°C or higher.
Just keep it above ℃.

<Example> Next, the present invention will be explained with reference to Examples and Comparative Examples.

Example Acetylene oxygen burner gas outlet (outer diameter 12 mm
A gas burner of the present invention as shown in FIG. 1 was manufactured by fixing a copper tube with an inner diameter of 14 mmφ to the outer circumference of the cylinder φ) so that an inert gas could flow between the burner blow-off tube and the outer peripheral steel tube.

Acetylene and oxygen, which are raw materials for diamond synthesis, are supplied to this burner at a flow rate of 50 p/min and 4517 min (oxygen acetylene flow rate ratio 090), respectively, and argon is supplied between the steel pipe and the gas outlet at a flow rate of 5 N/min. It was supplied in parallel with the raw material gas for synthesis.

As a substrate, a 20 mm x 20 mm x 3 mm carbide bit WC-Go sintered chip was placed perpendicular to the combustion flame and at a distance of 7 mm from the gas outlet. After burning for 30 minutes, it was cooled and the state of diamond precipitation on the substrate was observed using an optical microscope. A film-like precipitate with a diamond shape is observed over the entire substrate, and the crystallite diameter is 10 to 15 LLm from the center to 15 mmφ, and at the outer periphery, it is about 6 to 12 μm over the entire surface of the substrate, and the edges of the substrate are well attached. Met.

Raman shift of 1333 by microscopic Raman spectroscopy of the deposited film
One diamond beak of cm-' and 1550cm-
A very broad low peak was observed near '. From the above, it was confirmed that the precipitate was diamond. Further, the film thickness was about 40 μm.

Comparative Example j Combustion was performed for 30 minutes under the same conditions as in Example except that the Ar gas flow rate was set to 0, and the precipitates were observed in the same manner.

As a result, there are 8
A film-like diamond including euhedral shapes consisting of crystallites of about 14 LLm was precipitated. However, no diamond precipitation was observed at the outer periphery. Further, Raman spectroscopy was also the same as in Example 1. The film thickness was approximately 251 tm.

That is, the amount of diamond precipitated was smaller than in the example.

Comparative Example 2 In a reaction vessel with an inner diameter of 30 cmφ, a height of 35 cm, and an internal volume of 25 liters, an acetylene-oxygen burner with an outer diameter of 12 mmφ was placed, and an acetylene-oxygen burner with an outer diameter of 12 mmφ was placed, and an acetylene-oxygen burner with an outer diameter of 7 mm was placed perpendicular to the combustion flame formed by the burner and 7 mm from the banner opening. 2 at intervals
A carbide cutting tool WC-Co sintered tip measuring 0 mm x 20 mm x 3 mm was installed.

After reducing the pressure inside the reaction vessel, argon gas was introduced into the reaction vessel and the pressure was adjusted to 730 torr.

Next, acetylene and oxygen were supplied to the burner in the same manner as in Example 1, and the mixture was burned for 30 minutes. After the combustion stopped, the inside of the reaction vessel was replaced with air.

The precipitates on the substrate were observed using an optical microscope.

Diamond crystallites having an euhedral shape of 8 to 1.5+ and Lm were precipitated at the center of the substrate over a diameter of 17 mm, and diamond crystallites of 3 to 9 μm were precipitated around the diamond crystallites.

Further, the film thickness was approximately 32 μm, and the film quality was confirmed to be the same as in Example 1 by Raman spectroscopy.

That is, compared to Example 1, there was less diamond precipitation.

<Effects of the Invention> The combustion flame method of the present invention makes it easier to precipitate large-area diamond crystals with excellent homogeneity compared to conventional combustion flame methods. In particular, since the gas burner of the present invention is small and compact, a diamond synthesis apparatus using this gas burner is also compact and easy to move.

Furthermore, in the combustion flame method of the present invention, if S diamond is deposited while moving the gas burner of the present invention, it is easier to deposit diamond on a long or large-area substrate compared to a synthesis method in which the burner is fixed. It is.

[Brief explanation of drawings]

Figures 1 and 2 are explanatory diagrams showing how a combustion flame is formed by the method of the present invention using a gas burner, which is a typical example of the present invention, and Figure 3 is an illustration showing how a combustion flame is formed by a conventional method. The explanatory drawings, FIGS. 4 and 5, are cross-sectional views taken along the line AA and line B-B in FIGS. 1 and 2, respectively. In the figure, 1 and 1' are the gas outlet, 2 is the annular inert gas nozzle, 3.3' is the inner flame of the combustion flame, 4.4' is the outer flame,
Reference numeral 5 indicates a plurality of inert gas blow-off pipes arranged around the blow-off port.

Claims (3)

[Claims] (1) Adding oxygen to the raw material compound for diamond precipitation,
A combustion flame is formed so that an incomplete combustion zone exists, a substrate for diamond precipitation is placed in a non-oxidizing atmosphere in or near the incomplete combustion zone, and the temperature of the substrate is adjusted to the temperature required for diamond precipitation. 1. A method for synthesizing diamond using a combustion flame method, which comprises arranging an inert gas flow around a combustion flame when synthesizing diamond on a substrate by maintaining the temperature. (2) A gas burner for combustion flame diamond synthesis, in which inert gas blow-off pipes are arranged in duplicate so that the combustion flame-generating gas blow-off port is surrounded. (3) A gas burner for combustion flame diamond synthesis, in which a large number of inert gas blow-off pipes are arranged around the gas blow-off port for combustion flame generation.