JPH02196094A - Method for synthesizing diamond by combustion flame - Google Patents

Abstract

PURPOSE:To continuously synthesize large-area diamond on a substrate at a high rate by contact-sweeping the substrate by the inner flame separated from the outer flame of a premixed flame. CONSTITUTION:The inner flame separated from the outer flame of a premixed flame is brought into contact with the substrate to synthesize diamond on the substrate. To separate the outer flame from the inner flame, the supply of a gaseous oxidizing agent to a combustion flame has to be prevented except when the agent is supplied in premixing. Accordingly, the premixed flame is blown into a space contg. nonoxidizing atmosphere, or the premixed flame is covered with an inert gas. Any materials contg. carbon atom and having >=2000 deg.C flame temp. can be used as a gaseous fuel to be used for the premixed flame. When oxygen is used as the oxidizing gas, acetylene, ethylene, propylene, propane, butane, LP gas, natural gas, or their mixed gas can be used as the gaseous fuel, and acetylene having the highest flame temp. is most preferably used.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for continuously synthesizing diamond over a large area using a combustion flame.

[Prior Art] Various methods are known for diamond synthesis using the vapor phase method. Conventionally, diamond films have been grown in vapor phase using plasma such as microwave methods and high frequency methods, but there have been problems with high-speed film formation, large area growth, etc. It is thought that the atmosphere and reaction on the diamond growth surface created by these methods are essentially the same, and based on this idea, we focused on the plasma in the combustion flame in an open atmosphere system and investigated the synthesis of diamond using the combustion flame. It has also been reported that this combustion flame can This method is a diamond synthesis method in an open atmosphere system, and because the concentration of radicals and ions is high, it is expected to realize high-speed diamond synthesis. However, a combustion flame has an outer flame outside the inner flame where diamonds are synthesized, and there is an essential problem that if diamonds synthesized in the inner flame are taken out by passing through the outer flame, they will burn. It is impossible to synthesize diamond in an area larger than the cross-sectional area, and the combustion flame method is not as practical as methods such as the microwave method and radio frequency method.

[Problems to be Solved by the Invention] The present invention aims at high-speed continuous synthesis and large-area synthesis of diamond on a substrate using a combustion flame.

[Means for Solving the Problems, Effects] The present invention provides a method for synthesizing diamond using a combustion flame, characterized in that an inner flame from which an outer flame of a premixed flame is separated is brought into contact with a substrate, and diamond is synthesized on the substrate. It's a method.

That is, the present invention is capable of high-speed continuous synthesis of diamond on a substrate over a large area by sweeping the inner flame, which is separated from the outer flame of a premixed flame, into contact with the substrate.

The combustion phenomenon is very complex, and it is still not clear what kind of elementary reactions are occurring.Therefore, why is it possible to separate the oxidation flame and create only the reduction flame, as in the present invention, to generate diamonds over a large area at high speed? However, it is not necessarily clear whether such a film can be synthesized.

It can be considered as follows. In the inner flame part of the combustion flame, there is a reaction between the premixed oxygen supplied and the raw material gas, but in the outer flame part, the reaction between the combustion gas and oxygen in the air is progressing, and the oxygen ratio is lower than the theoretical oxygen amount. Alternatively, in the inner flame of a premixed flame that burns at an air ratio, there is a reducing atmosphere lacking oxygen, and it is thought that many carbon and hydrocarbon molecules exist without being oxidized. . On the other hand, in the outer flame part, oxygen diffuses from the surrounding air, resulting in an oxidizing atmosphere, and it is thought that many chemical species such as carbon monoxide are present. Therefore, if oxygen is removed from the combustion atmosphere or if the flame is covered with an inert gas or the like to block the air, the outer flame disappears and only the inner flame remains.

Smithells separation apparatus (Smithells, A, & I
ngle, )1. .

Trans, Chemi, Soc, 61.20418
92), it is possible to separate the inner conical flame and the outer conical flame of the premixed flame. A premixed flame is a flame that is formed when a flammable gas and a gaseous oxidizer are mixed in advance and then combusted. reacts and burns. If the premixed gas is moved toward this flame front at an appropriate speed, the flame will remain stationary. This is the principle behind the formation of the inner conical flame, or inner flame, of the Sumicelle separation device.

At this stage of combustion, the premixed gas contains more fuel, so unreacted fuel remains, and this combustion gas further reacts with oxygen in the air to form a diffusion flame. This is the principle behind the formation of the outer conical flame, or outer flame, of the Sumicelle separation device.

In the present invention, for large-area synthesis, it is necessary to move the substrate or the inner flame while irradiating the substrate with the inner flame.

We found that it is effective to separate external inflammation from internal inflammation. To separate external inflammation from internal inflammation.

Any method can be used as long as it prevents the supply of gaseous oxidizers other than the gaseous oxidizer supplied by premixing to the combustion flame. In particular, there are two methods: one in which the premixed flame is blown into a space with a non-oxidizing atmosphere, and the other in which the premixed flame is prevented from being supplied to the combustion flame. A method of covering with active gas is effective.

The fuel gas used as a raw material for the premixed flame of the present invention may be one containing carbon atoms and having a flame temperature of 2000°C or higher. When the oxidizing gas is oxygen, the fuel gas may be acetylene, ethylene, propylene, Propane, butane, methylacetylene.

LP gas, city gas, natural gas, and a mixture of these gases can be used. Among them, acetylene is preferred because it has the highest flame temperature.The amount of oxygen or air required for complete combustion of the fuel is called the theoretical oxygen amount or theoretical air amount, and the actual amount of oxygen or air mixed during premixing is determined by the oxygen ratio or Although called the air ratio, in the present invention, the oxygen ratio and air ratio are
The flame temperature is approximately 2000℃ in the range of excess fuel where the lower limit is above the lower flammability limit and the upper limit is below the theoretical oxygen amount and theoretical air amount.
Within the range of 0 or more, the lower the oxygen ratio and the air ratio, the faster the diamond formation rate, but the lower the degree of crystallinity.

This is thought to be because the flame temperature is low and the number of excited species such as oxygen atoms that etch non-diamond components is reduced. As the oxygen and air ratios increase during diamond production, the crystallinity of the produced diamond improves, but the production rate decreases. The reason why the production rate decreases is that the supply of carbon that becomes diamond decreases, and the number of excited species such as oxygen atoms increases, causing some of the diamond to be etched as well.

When the excited carbon in the combustion flame touches the substrate, it is rapidly cooled and fixed into the diamond structure. Since diamond growth progresses in this manner, the substrate may be cooled with a coolant such as water as necessary.

A combustion flame consisting only of the inner flame as described above.

By irradiating a substrate that is already coated with diamond, further diamond can be synthetically deposited thereon without damaging the original diamond. Therefore, according to the present invention, it has become possible to synthesize diamond continuously and densely on a substrate of any area by sweeping the combustion flame.

[Examples] Example 1 Diamond was synthesized using a combustion flame in an apparatus schematically shown in FIG. A rotatable circular water cooling stand 2 is installed in a quartz tube 1 having a diameter of 10 cm and a height of approximately 10 cm, and the gap between the quartz tube and the water cooling stand is shielded.

A lid 3 is placed on the top surface of the quartz tube with a hole for a combustion flame supply blowpipe mouthpiece and an exhaust hole. The surface of the substrate is 0.25μ
A mirror-polished tungsten carbide plate (material: old 0) 4 with a thickness of 3 mm and a diameter of 8 cm was used and placed on a water-cooled table.

Gas welder (Tanaka Seisakusho medium size welder 163M, crater No. 100) 5 with acetylene gas 2.5 m/inch,
After supplying a premixed gas with a (0,/C2H2) ratio of 1゜5 Q/win of 0.6 and setting the length of the inner flame to 30 soybeans, turn the inner chamber downward and open the crater. Insert into the quartz tube through the hole in the lid 3.

When the oxygen remaining in the quartz tube is exhausted, the external flame disappears. The flame consisting only of this inner flame is
The distance between the board and the crater is 2 cm on the board located 1 cm apart.
The substrate is rotated at a rate of once per hour while adjusting the water cooling so that the surface temperature of the substrate is 800° C. or higher and 1100° C. or lower as measured by a radiation thermometer. At this time, the gas blown out from the exhaust hole is naturally ignited by the heat of the inner flame to form a diffusion flame 6. After 1 hour, the flame was moved away from the substrate to terminate the irradiation and the substrate was taken out, and the substrate became gray and cloudy without any breaks in the shape of a doughnut, and the width of the discolored band was about 10 square meters. When this part is observed with a scanning electron microscope, (11
1) Diamond particles with a diameter of about 50 μm were densely present and covered by the (ioo) plane.

When the Raman spectrum is measured using a Raman microscope, it is 1332C.
It showed a sharp peak at 11'' and was confirmed to be diamond.

Example 2 Diamond was synthesized using an apparatus schematically shown in FIG. Attach the shielding gas jacket 12 to the gas cutter (cutter 11C-338 manufactured by Nichi Seisakusho, Crater No. 1) 11, and add acetylene gas 3.5Q to the blowpipe used as an underwater cutter.
/win, oxygen gas 2.4 Q /win, (0
, /C,H,) ratio is 0.7 to create a combustion flame with an inner flame length of 30, then argon gas is supplied to the shielding gas jacket at a rate of 5 Q/win. The outer flames around the flame disappeared. As a substrate, the surface is polished to 15 μm, thickness is 5 mm, width is 3 cm, and length is 30 cm.
A tungsten carbide plate (material: old 0) 13 was used. The combustion flame of the underwater cutter is directed downward, the distance between the substrate and the crater is maintained at 2 cm, and cooling water 14 is injected onto the back side of the part of the substrate that is hit by the flame. The substrate was moved in the length direction at a speed of 6 mm per minute while keeping the surface temperature of the substrate in the area hit by the flame at 800° C. or higher and 1100° C. or lower as measured by a radiation thermometer. After 40 minutes, a gray band of haze was formed on the substrate, about 1.5 cm wide and about 25 cm long.

When this part was observed with a scanning electron microscope, it was found that diamond particles with a diameter of about 10 μm were densely present and covered by (111) and (100) planes. When the Raman spectrum was measured using a Raman microscope, it showed a sharp peak at 1332 cm-'', confirming that it was diamond.

[Effects of the Invention] According to the present invention, diamond particles and diamond polycrystalline plates can be continuously synthesized over a large area at high speed under normal pressure.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a diamond synthesis apparatus used in Example 1 of the present invention, and FIG. 2 is a schematic diagram of a diamond synthesis apparatus used in Example 2 of the present invention. l: quartz tube, 2: rotating water cooling stand, 3: lid, 4: substrate,
5: Gas welder, 6: Diffusion flame, 11: Gas cutter,
12: Gas jacket. 13: Substrate, 14: Cooling water.

Claims (1)

[Claims] A method for synthesizing diamond using a combustion flame, characterized in that an inner flame separated from an outer flame of a premixed flame is brought into contact with a substrate, and diamond is synthesized on the substrate.