JPH0255294A - Method for synthesizing diamond by vapor process - Google Patents

Abstract

PURPOSE:To synthesize diamond on the surface of a substrate according to a vapor process by separately preheating a carbon-containing gas and O2 gas, mixing and burning both so as to form an incomplete combustion zone and arranging a specific substrate in the incomplete combustion zone. CONSTITUTION:A carbon-containing gas, such as acetylene, styrene or propane, especially acetylene gas as a raw material for synthesizing diamond and O2 gas are separately preheated at 50-400 deg.C in a preheater 3, then fed to an acetylene burner 1 and burned. The ratio of O2/acetylene is 0.75-1.0 to form an incomplete combustion zone, i.e. acetylene feather at 2000-3000 deg.C on the inside of an outer flame in an acetylene flame. Thereby, synthetic diamond is homogeneously deposited on the surface of a substrate 2, such as SiC, W, WC, Mo or TiC, at 600-1200 deg.C by vapor reaction using decomposition of the acetylene.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention has characteristics such as wear resistance, corrosion resistance, high thermal conductivity, and high specific elasticity, and is suitable for use in abrasive materials, abrasive materials, optical materials, and cemented carbide tools. wood,
This invention relates to a vapor phase synthesis method for diamond in the form of a single particle in the form of a film useful for sliding materials, corrosion-resistant materials, acoustic vibration materials, cutting edge materials, etc.

[Conventional technology]

Conventional methods for synthesizing diamond include a synthesis method using an iron- or nickel-based catalyst under ultra-high pressure conditions, and a direct conversion method of graphite using an explosive method.

In recent years, as a low-pressure CVD method, a mixed gas of hydrogen and a hydrocarbon or an organic compound containing nitrogen, oxygen, etc. is heated through a hot filament.
Methods have been developed for synthesizing diamond in an excited state using microwave plasma, high-frequency plasma, DC discharge plasma, DC arc discharge, and the like.

Furthermore, recently, the applicant has developed a method for synthesizing diamond in the non-oxidizing region of combustion flame, and filed a patent application No. 63-7175
No. 8 has been filed, and the present invention corresponds to this improvement method.

[Problem to be solved by the invention]

The invention of Japanese Patent Application No. 83-71758 is a gas phase synthesis method that is simpler than conventional methods and can also produce a large area of film-like diamond. A raw material compound is combusted so as to have an incomplete combustion region, a substrate for diamond precipitation is placed in the non-oxidizing atmosphere in or near the incomplete combustion region, and the temperature of the substrate is set to the diamond precipitation temperature. This is a method in which diamond is deposited on the base material by holding the base material at a certain 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 precipitation rate and control the properties of the precipitates.

The object of the present invention is to promote an increase in the diamond precipitation rate and precipitation area.

[Means to solve the problem]

As a result of intensive research into the invention filed as Japanese Patent Application No. 71758/1983, namely the combustion flame method,
By preheating at least one of the carbon-containing raw material gas used as a raw material compound for diamond precipitation, or the gas mixed therein, and then introducing it into the incomplete combustion region, the diamond precipitation rate increases and high-quality diamonds are precipitated. This discovery led to the completion of the present invention.

In other words, 1. The gist of the present invention is a method for synthesizing vapor-phase diamond by burning a carbon-containing raw material compound for diamond precipitation so as to have an incomplete combustion region, in which a carbon-containing raw material gas for diamond precipitation or mixed therewith is used. At least one of the gases is preheated and then introduced into the incomplete combustion zone.

A substrate for diamond precipitation is installed in the incomplete combustion region or in a non-oxidizing atmosphere in the vicinity of the region, and diamond is deposited on the substrate by maintaining the temperature of the substrate at the diamond precipitation temperature. The present invention is characterized by a vapor phase diamond synthesis method, and the diamond synthesized by the method of the present invention contains diamond-like carbon.

The present invention will be explained in detail below.

Carbon sources for diamond synthesis used in the present invention include saturated hydrocarbons such as methane, ethane, propane, butane, ethylene, propylene, and butylene.

Unsaturated hydrocarbons such as 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 a non-oxidizing gas such as HAt, 82, CO1CO2, H2O2', etc., if necessary, and burned in an oxygen-containing or non-oxygen-containing atmosphere.

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. Moreover, at that time, a non-oxidizing gas can also be mixed.

In the present invention, the raw material gas or (and) mixed gas for diamond synthesis is preheated and combusted so that an incomplete combustion region exists to form a combustion flame. It is necessary that the substrate for diamond precipitation be non-oxidizing and present in a region near the flame that is excited to allow diamond precipitation.

Further, a specific example of adding oxygen to the raw material gas for diamond synthesis to generate an incomplete combustion region excited to a diamond precipitation state in an oxygen-free atmosphere or an oxygen-containing atmosphere is as follows: For example, the former can be exemplified by combustion in an atmosphere such as argon, and the latter can be exemplified by combustion in open air.

In the gas phase synthesis of these diamonds, in the present invention, at least one of the raw material gas or mixed gas is preheated, and preheating promotes decomposition and dissociation from the carbon-containing raw material compound through reaction with oxygen in a combustion flame! 2. It is estimated that radicalized active species such as C, C2, C01C02, CH3, etc. are suitable for forming a diamond phase. In addition, hydrogen atoms and oxygen atoms are also formed and are thought to be involved in the diamond precipitation reaction. It is considered that the formation of radicalized active species, hydrogen atoms, and oxygen atoms is further increased by the preheating of the raw material gas or mixed gas, resulting in an increase in the diamond precipitation rate and qualitative improvement.

For example, a raw material gas such as acetylene, styrene, propane, ethyl alcohol, methyl alcohol, benzene, etc. is preheated, and preheated oxygen is added thereto as necessary.
It is possible to form a combustion flame in a system open to the atmosphere and control the volume of the incomplete combustion zone by adjusting the amount of oxygen added. The incomplete combustion region of the acetylene-oxygen flame in this case is called an acetylene feather, and its volume can be controlled by changing the oxygen/acetylene ratio, total gas amount, and preheating temperature. In particular, the oxygen/acetylene ratio can range from 0.5 to 2, but is preferably from 0.75 to 1.0.

The preheating temperature is preferably in the range of 50 to 400°C, 50'C
! If it is less than 20, the effect of the present invention is insufficient.
If the temperature exceeds 0°C, safety measures such as explosion are required. Therefore, the preheating temperature depends on the raw materials, but if the preheating temperature is 200° C. or higher, it is desirable to preheat at a temperature about 30'0 below the ignition point.

The temperature of the acetylene feather region in these cases is 200
0-3000°C and does not require auxiliary excitation means,
Generally, the diamond synthesis temperature is preferably 1500'C or higher, and the substrate temperature is suitably 800-1200'0, and the substrate temperature can be controlled within this range by cooling.

In addition to the above method, a method may be used in which the raw material gas for diamond synthesis is preheated and burned in an oxygen-containing atmosphere without adding oxygen.

As the base material for diamond precipitation, those commonly used in low pressure CVD methods can be used. That is, Si wafer SiC sintered body,
Besides SiC granules, W, WC, No, Tic, T
Examples include shaped objects and granular objects such as iN, 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. In general, even if diamond is formed in an oxygen-excessive region under high heat, the diamond becomes C01C02 due to the excess oxygen and disappears. In other words, it is considered that diamond does not precipitate in this region. Note that the diamond precipitation region is oxygen deficient and has a relatively low temperature. In this region, it is necessary to excite the raw material gas to conditions that generate hydrocarbon radicals (active species). It is preferable to leave it there.

In the present invention, the excitation of the diamond precipitation region is promoted by preheating the raw material gas, etc., and almost no auxiliary heating source is required. Heating by arc discharge or the like may also be used.

The present invention will be explained in more detail below with reference to Examples and Comparative Examples.

[Example 1] As shown in the schematic diagram shown in Fig. 1, the acetylene burner l is fixed downward, and the acetylene burner l is fixed at a distance of loI from the burner mouth by 8mm.
A substrate made of carbide tool (WC-Go) 2 having a square thickness of 2 mm was fixed to a water-cooled support stand.

Acetylene 2.017 +*in, oxygen 1.5fL/
A flow rate of 5 inches (oxyacetylene ratio 0.75) was preheated to 140° C. by a separate electric preheater 3 and then supplied to a burner to form a combustion flame in the atmosphere. The substrate temperature is 105
It was 0°C. Burning was continued in this state for 20 minutes.

After the reaction was completed, the substrate deposit was observed using a metal microscope, and it was confirmed that the substrate was covered with a film having euhedral diamond crystals. Furthermore, the coverage of the diamond film at the end was also good. Furthermore, as a result of microscopic laser Raman spectroscopy analysis of this diamond film,
A sharp peak due to diamond bonding was shown at a Raman shift of 1333 cm-1. Also, when the film thickness was measured, it was approximately 4
It was recognized that the membrane was completely defective and of good quality.

[Comparative example]

Combustion tests and various measurements were conducted using the same equipment as in the example construction except for the preheater, and under the same conditions except that the temperature of the acetylene gas and oxygen gas supplied to the burner was set to room temperature (25°C). Ta.

The deposit on the substrate was in the form of a film with a diamond shape, and the end member rotation was almost the same as in the example, but the film quality was inferior to that in Example 1.

In addition, laser Raman spectroscopy revealed a diamond peak at 1333 cm-' and a broad low peak around 1550 cm-', which confirmed that the film contained a small amount of i-carbon component. The thickness of the diamond film was approximately 34 mm.

[Example 2] A dedicated propane burner was fixed downward as in the example, and a carbide bib was placed at a distance of 12vs from the burner mouth) 13
A substrate measuring 3 mm square and 3 mm thick was fixed to a water-cooled support.

Propane in burner 3.3 liters/1in, oxygen 7 liters/I
IIn (oxygen/propane ratio = 2:1) was heated to 170 °C in each preheater and then introduced into the burner, and heated in the atmosphere for 2
Burned for 0 minutes.

After the combustion was completed, the deposit on the substrate was observed with a metallurgical microscope, and it was found to be a film-like precipitate with a diamond euhedral shape. In addition, by X-ray diffraction and Raman spectroscopy measurements, i
- It was confirmed that the diamond contained a very small amount of carbon. The thickness of this film-like precipitate was 25 ILm, and it spread well to the edge of the substrate.

〔Effect of the invention〕

The method of the present invention makes it possible to synthesize diamond by a gas phase method using extremely simple equipment, and it is also easy to scale up. Therefore, it became possible to deposit homogeneous diamond over a large area. In addition, the diamond precipitation rate is fast, and diamond can be deposited on a single plate in the same way even if the plate surface is curved. Compared to the conventional gas-phase combustion flame method, it is now possible to easily melt high-quality diamond in the form of a film.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of the method of Example 1, which is a typical apparatus for carrying out the present invention. 1...Burner, 2...Substrate 3
・・・・・・Preheater diagram 1 is a beggar line.

Claims (1)

[Claims] 1. In a method for synthesizing vapor-phase diamond by burning a carbon-containing raw material compound for diamond precipitation so as to have an incomplete combustion region, the raw material gas for diamond precipitation containing carbon or mixed therein; At least one of the gases is preheated and then introduced into an incomplete combustion region, a substrate for diamond precipitation is placed in a non-oxidizing atmosphere in or near the incomplete combustion region, and the substrate temperature is increased. A vapor phase diamond synthesis method characterized by depositing diamond on a base material by maintaining the diamond at a diamond precipitation temperature. 2. The vapor phase diamond synthesis method according to claim 1, characterized in that oxygen is added to a carbon-containing raw material compound for diamond precipitation, and the mixture is burned in an oxygen-free atmosphere. 3. The vapor phase diamond synthesis method according to claim 1, characterized in that oxygen is added to a carbon-containing raw material compound for diamond precipitation, and the mixture is burned in an oxygen-containing atmosphere. 4. The vapor phase diamond synthesis method according to claim 1, characterized in that the raw material compound for diamond precipitation containing carbon is burned in an oxygen-containing atmosphere without adding oxygen.