JPH0346438B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION FIELD OF INDUSTRIAL APPLICATION The present invention relates to a method for synthesizing diamond by combustion flame.

Prior Art Conventionally, the following method is known as a diamond synthesis method using a vapor phase synthesis method that does not use high temperature and high pressure.

(1) The so-called ion beam evaporation method or ion plating method, in which carbon ions or hydrocarbon ions are created by electric discharge, accelerated by a potential gradient, and collided with a substrate to deposit diamond.

(2) The so-called plasma method, which uses plasma, heat, and light to activate a mixed gas of hydrocarbon and hydrogen to deposit diamond on the substrate surface, thermal tungsten filament method, optical CVD method, high-frequency thermal plasma method, and direct current arc. Law. etc.

However, in the above-mentioned methods other than the high-frequency thermal plasma method and the direct current arc method, not only the diamond formation rate is slow at 0.1 to 1 μm/hr, but also the resulting precipitation area is small. The equipment is also very expensive. Although the high-frequency thermal plasma method and the DC arc method produce diamonds at a high rate of several μm/min, they have the problem that the equipment is extremely expensive.

Purpose of the Invention The present invention was made to solve the problems in the conventional method, and its purpose is to use a simple and inexpensive device, and to increase the diamond production rate to several μm/min.
and to provide a fast diamond synthesis method.

Composition of the Invention As a result of intensive research to achieve the above object, the present inventor has discovered that organic compounds or charcoal can be used in a high-temperature combustion flame of 600°C or higher obtained by combustion of hydrocarbons, hydrogen, or a mixed gas thereof and oxygen or air. The material is decomposed, evaporated, and dissociated to excite carbon, and a gas mixed with hydrogen in an amount more than 50 times the volume of carbon is added.
They succeeded in depositing diamond on a substrate held at 600° to 1200°C or in its gas, and found that diamond could be synthesized at a production rate of 0.1 to several μm/min using this method. Obtained. The present invention was completed based on this knowledge.

The gist of the present invention is to excite carbon by decomposing, evaporating, and dissociating an organic compound or carbon material in a combustion flame of 600°C or more of hydrocarbon, hydrogen alone or a mixed gas, and oxygen gas or air. A method for synthesizing diamond, which is characterized by applying a gas mixture containing 50 times more hydrogen than carbon to a substrate kept at 600° to 1200°C, or precipitating diamond in the gas phase.

As a method for decomposing, evaporating, and dissociating organic compounds or carbon materials in a high-temperature combustion flame in the method of the present invention, a high-temperature combustion flame may be generated and the organic compound or carbon material may be introduced into it, or the organic compound or carbon material may be introduced into the flame. An organic compound or carbon material may be introduced simultaneously with the raw material.

Hydrocarbons, hydrogen, or a mixed gas thereof, and oxygen or air are used as the gas for generating the high-temperature combustion flame of the present invention. The combustion flame temperature can be adjusted by introducing the type and concentration of the gas used, a sheath gas, a cooling gas such as hydrogen, an inert gas, or a mixture thereof. The temperature of the combustion flame must be at least 600°C; if the temperature is lower than this, monatomic carbon cannot be produced and diamond cannot be synthesized.

The organic compound may be in any form of gas, liquid, or solid as long as it can be decomposed during combustion and generate carbon-containing ionic species or radical species. For example, nitrogen in molecules such as hydrocarbons such as methane, ethane, propane, butane, ethylene, and benzene, alcohols such as methanol, ethanol, and propanol, polymeric substances such as polyethylene and polypropylene, oils and fats, pyridine, and thiophene, It may also contain sulfur or the like.

Examples of the carbon material include graphite for electrodes.

H ₂ is introduced into the excited carbon atmosphere and mixed in an amount more than 50 times the volume of carbon. This hydrogen stabilizes the carbon single atom and acts to maintain the excited state of ^Sp3 . If the amount of hydrogen is less than 50 times the capacity of carbon, graphite will result, so the amount needs to be greater than that. However, if the amount is too large, hydrogen will be wasted, so it is preferable that the amount is about 50 to 100 times the capacity.

The temperature of the substrate is maintained between 600° and 1200°C. Below 600°C, diamond does not precipitate, and when it exceeds 1200°C, it becomes a gas and diamond does not precipitate. It is also possible to remove the substrate and deposit diamond as a powder in the gas phase.

The method of the present invention will be explained based on the drawings. FIG. 1 is a schematic diagram of one implementation of the method of the present invention. In the figure, 1 is a concentric triple tube, 2 is a reaction vessel, 3 is a substrate, 4 is a cooling gas inlet, 5 is an ignition plug,
6 is a sheath gas blowing ring, 7 is an exhaust gas treatment device, and 8 is a vacuum pump.

A raw material gas for combustion or an organic compound or a carbon material is introduced into the reaction vessel 2 through each tube of the concentric triple tube 1 (made of quartz) at the same time or after this, and is ignited by the ignition plug 5 to produce a high-temperature combustion flame. It also decomposes, evaporates, and dissociates organic compounds or carbon materials. Hydrogen in an amount more than 50 times the capacity of carbon is introduced into this from the sheath gas blowing ring 6. During diamond film synthesis, the substrate 3 is placed inside the reaction vessel 2, and cooling gas is introduced from the cooling gas inlet 4 to maintain the temperature of the substrate 3 at 600° to 1200°.
The temperature is adjusted to .degree. C., and the substrate 3 is applied with the substrate 3 to deposit a diamond film. When synthesizing diamond powder, the substrate 3 is removed and the temperature inside the reaction vessel 2 is controlled by introducing cooling gas from the cooling gas inlet 4.
The diamond powder is precipitated in the gas phase by adjusting the temperature to the above-mentioned temperature in the diamond production region.

Effects of the Invention According to the method of the present invention, a combustion flame of hydrocarbon, hydrogen alone or a mixed gas and oxygen is used to decompose, evaporate, and dissociate organic compounds or carbon materials to produce excited carbon. Therefore, there is no need to use conventional expensive equipment. Furthermore, the diamond production rate is as fast as 0.1 to several μm/min.

Example 1 Using the apparatus shown in Figure 1, oxygen was flowed at 10/min from the center of a triple-walled quartz tube, propane gas at 10 ml/min from the middle, and methane at 2 ml/min from the outer tube to ignite the tube. A combustion flame of ℃ was generated. Additionally, 50% hydrogen is used as sheath gas (outlet 6).
/min. 20mm diameter on water-cooled holder
A molybdenum substrate was placed and placed at a position where the surface of the substrate reached a temperature of 1200°C using an optical thermometer for 10 minutes to allow the reaction to occur. After the reaction, the molybdenum substrate, which had cooled to room temperature, was taken out and examined, and it was found that a gray polycrystalline film of approximately 10 μm had formed.
It was confirmed by X-ray diffraction and Raman scattering spectrum that it was cubic diamond.

Example 2 Oxygen 2/min from the center, hydrogen 10 from the middle
/min, 100ml/min of methane was flowed through the outer tube and ignited to generate a combustion flame of over 1500℃. Furthermore, hydrogen was flowed at 5/min as a sheath gas. A molybdenum substrate with a diameter of 20 mm was placed on a water-cooled holder, and the substrate surface was placed at a temperature of 1000° C. using a photothermometer for 10 minutes to allow the reaction to occur. After the reaction,
When I took out the board that had cooled to room temperature and examined it,
It was confirmed that a 35 μm diamond film was obtained.

Example 3 Oxygen at 4/min from the center, hydrogen at 10/min from the middle tube, and methane at 40 ml/min from the outer tube were ignited to generate a combustion flame of 1500°C or higher. A space was found in advance where the temperature would be 1200°C when the substrate was placed, and without placing the substrate, hydrogen was blown at 10/min as a cooling gas from the inner wall of the space in a circumferential manner. After one hour of reaction, 0.03 g of grayish powder deposited on the walls and bottom of the reaction vessel was collected and examined, and it was confirmed to be cubic diamond with a diameter of approximately 0.1 μm.

[Brief explanation of drawings]

The drawing is an embodiment of an apparatus for carrying out the method of the invention. 1: Concentric triple tube, 2: Reaction vessel, 3: Substrate, 4: Cooling gas inlet, 5: Ignition plug,
6: Sheath gas blowing ring, 7: Exhaust gas treatment device, 8: Vacuum pump.

Claims (1)

[Claims] 1 Excite carbon by decomposing, evaporating, and dissociating organic compounds or carbon materials in a combustion flame of hydrocarbon, hydrogen alone or mixed gas, and oxygen gas or air at 600°C or higher, and then excite carbon with a capacity 50 times that of carbon. A diamond synthesis method characterized by applying a gas containing a mixture of the above hydrogens to a substrate maintained at a temperature of 600° to 1200°C, or precipitating diamond in the gas phase.