JPH0753299A - Method for synthesizing diamond - Google Patents

Abstract

PURPOSE:To synthesize diamond with a less expensive producing equipment than the conventional equipment at a rational rate. CONSTITUTION:A reactor 1 with a pressure regulating mechanism is filled with graphite 2, water and inevitably contained air, at least the graphite 2 set part of the reactor 1 is heated to >=1,000 deg.C and diamond is synthesized at the part kept at 600-1,200 deg.C in the reactor 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diamond synthesizing method for synthesizing high-quality diamond crystals at high speed and at low cost without using high temperature and high pressure or plasma as in the prior art.

[0002]

2. Description of the Related Art Conventionally, most industrial diamonds are artificially manufactured under high temperature and high pressure of about 50,000 atm and 1500 ° C. This method is based on the method invented in the United States in 1945, in which graphite is converted into diamond by using a metal catalyst such as Fe, Co and Ni under high temperature and high pressure. At present, this method is the mainstream for diamond synthesis, but since the apparatus for generating high temperature and high pressure is expensive, the diamond grains produced using this are also very expensive. Separately from this, it is also produced by an impact compression method in which graphite is directly converted into diamond by using gunpowder to generate a very high impact force for a short time of about one millionth of a second. This method is also a method invented in the United States in 1956.

Both of the above-mentioned two methods convert graphite into diamond under high temperature and high pressure, and then a method of synthesizing diamond in a gas atmosphere was found,
This method is called a vapor phase synthesis method in contrast to the above two methods and is used for vapor deposition of a diamond film or production of a diamond plate. The first synthesis by the gas phase synthesis method goes back to the study of the former Soviet Union in 1968, but here, graphite and hydrogen are enclosed in a sealed reaction vessel, and this vessel is heated to the side opposite to the graphite. It is said that diamond was synthesized on the placed diamond seed crystal by the chemical transport method. Similar research has also been conducted in the United States, and there are patents such as those shown in USP. 3,030,187 and 3,030,188. However, the development of this method has been discontinued at present due to its slow synthesis rate and poor reproducibility. In recent years, this has been further advanced, and hydrocarbon gases, alcohols, acetone, and other gases are generally used as raw materials for diamond.
However, although the present vapor phase synthesis method is convenient for coating diamond on a substrate in a film form, it has a disadvantage in the production of diamond grains as compared with the high pressure synthesis method because of its slow synthesis rate.

[0004]

As described above, diamond has been artificially mass-produced, but a high temperature and high pressure generator is very expensive and is necessary for synthesizing diamond. The cost of industrial diamonds was still high because the cost of various consumables was also high. An object of the present invention is to provide a method for synthesizing diamond, which solves the above-mentioned problems, and which can synthesize diamond at a reasonable rate with less expensive manufacturing equipment.

[0005]

Therefore, the present invention has solved the above-mentioned problems of the prior art by providing a method for synthesizing diamond as set forth in the claims. The inventor has found that the diamond can be synthesized at a higher speed than the conventional method by improving the conventional chemical transport method. Instead of the method of synthesizing diamond by the chemical transport method in the system of graphite and hydrogen gas performed after 1968, the synthesis of diamond was tried by focusing on the system of graphite and water. As a result, it was found that by using the graphite and water system of the present invention, diamond can be synthesized at a higher speed and with better reproducibility than in the past. That is, graphite and water are placed in a reaction vessel, the remaining space in the reaction vessel is evacuated or hydrogen gas or air is used, and at least the portion of the reaction vessel where the graphite is installed is heated to 1000 ° C. or higher to transform the graphite into diamond. Was found to be generated.

The synthesis rate of diamond increases as the temperature of the graphite portion in the container increases and as the pressure increases. However, when the reaction container is heated, water existing in the reaction container is vaporized and further thermally expanded, so that the pressure in the container is increased in the case of the closed structure. Therefore, the reaction container must have a structure that takes into account the increase in pressure. The higher the heating temperature of graphite, the higher the synthesis rate, but the upper limit is determined by the heat resistance of the container. Although lowering the pressure in the vessel slows down the rate of diamond synthesis, attaching a vacuum device or pressure control valve to the reaction vessel to adjust the pressure in the vessel simplifies the design of the reaction vessel. The pressure range in which the synthesis rate is appropriate and the pressure in the reaction vessel is easy is 1 atm or more and 1000 atm or less. Further, it is well known that diamond grows easily on the diamond grains, but in the method of the present invention as well, the diamond grain seed crystal is similarly put in a pressure vessel to promote the growth of diamond. By using this as a seed, it is possible to grow diamond grains having a large diameter.

(Function) It is considered that in a conventional chemical transport method, that is, in a system using graphite and hydrogen, methane is produced by the reaction of graphite and hydrogen, and diamond is deposited when this is decomposed. However, in this system, the rate of producing methane from graphite and hydrogen is slow, and a large amount of graphite is produced together with diamond.Therefore, in order to remove this graphite, a graphite removal step must be placed during diamond synthesis. I had to do it. Therefore, the synthesis rate of diamond is extremely slow, and this method has never been used practically.

Although the present invention utilizes the reaction of graphite and water,
This reaction is called a water gas reaction and is generally performed at 1000 ° C. or higher. Hydrogen and carbon monoxide are mainly produced, but carbon dioxide and methane are also produced in a small amount. It is believed that the method of the present invention produces diamond when these carbon-containing gases decompose at high temperatures. At this time, graphite is generated together with diamond, but since water and hydrogen present in this system selectively etch graphite, the result is that only diamond can be obtained without a graphite removal step. Is generated.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the attached FIGS. 1 to 4 are block diagrams showing the construction of an apparatus for carrying out the diamond synthesizing method of each embodiment of the present invention. [Embodiment 1] As shown in FIG.
mm cylindrical reaction vessel 1 made of alumina with a length of 400 mm
12 g of graphite 2 and 2 cc of water are placed at the bottom of the pressure relief valve 3 which releases the inner end of the container 1 at an internal pressure of 1.1 atm.
Attached. Put this container 1 in the tubular electric furnace 4,
Arrange so that the part where graphite 2 is placed is near the center,
Next, while measuring the temperature with a thermocouple, the center of the tubular electric furnace is 12
It heated so that it might be set to 00 degreeC. In the initial stage of heating, the pressure of the gas inside rises with heating and is released from the pressure relief valve 3, but the pressure in the container 1 gradually stabilizes. After synthesizing for 10 hours in this state, an investigation was conducted to find that diamond grains 5 were formed on the inner wall of the reaction vessel. The place where the diamond was formed was in the range of about 120 mm from the part where the graphite 2 was placed to the other end, and the temperature of this part was 600 ° C. to 1200 ° C. during the synthesis process. It was found that the particle size of diamond was about 100 μm in the vicinity where graphite 2 was installed, and gradually decreased toward the lower temperature.

Example 2 As shown in FIG. 2, 12 g of granular graphite 2 and 2 cc of water were put in the bottom of a cylindrical reaction vessel 1 made of alumina and having a closed inner diameter of 22 mm and a length of 400 mm on one side. A partition plate 7 made of nickel was placed at a position 50 mm from the bottom, and 0.1 g of diamond powder seed crystal 6 having an average particle size of 50 μm was placed outside the partition plate 7. A pressure relief valve 3 for releasing the internal pressure to 1.1 atm was attached to the reaction vessel 1, and heated in the tubular electric furnace 4 in the same manner as in Example 1 to perform synthesis for 10 hours. When the inside of the container was observed after completion of the synthesis, diamond was also synthesized in the reaction container as in Example 1, but the growth of the initially encapsulated diamond grains was noticeable. Observation of the grain size of the diamond revealed that the original grains had grown to 100 to 200 μm. Although the total amount produced is unknown, it was found from the grain size that the amount of diamond increase was 8 to 64 times.

[Embodiment 3] As shown in FIG.
mm, thickness 6 mm, length 250 mm, and a reaction vessel 11 made of SUS310S, filled with a mixture 16 of 10 g of graphite, 1 cc of water and 0.1 g of diamond seed crystals having an average particle size of 50 μm, and then replaced with hydrogen. Then, the reaction container 11 was closed. Then, the closed reaction vessel 11 is placed in the horizontal tubular electric furnace 4
It heated at 100 degreeC and performed the process for 8 hours. After cooling the closed reaction vessel 11, the diamond grains inside were taken out and the average grain size was measured.
It had grown to a size of μm to 250 μm. This means that the amount of diamond increased to 27 times to 125 times the initial filling amount. Although the pressure in the closed reaction vessel 11 is unknown, it is estimated to be about 200 atm.

[Embodiment 4] As shown in FIG.
mm, wall thickness 6 mm, length 250 mm made of SUS310S reaction vessel 11 having an outer diameter of 14 mm containing 0.2 g of diamond grain seed crystals 6 having an average particle size of 50 μm and 1 cc of water,
After placing a graphite container 8 having an inner diameter of 8 mm and a length of 180 mm and sealing the reaction container 11, this was placed in the annular electric furnace 4 and kept at 1100 ° C. for 8 hours. After cooling the closed reaction vessel 11 and extracting the diamond grains inside, measuring the grain size 1
It had grown to 100 to 200 μm. Also, the shape of the diamond had changed from its original angular shape to a rounded shape. The increase rate was calculated to be 8 to 64 times or more from the change in the particle size of the diamond particles before and after the reaction.

[0013]

EFFECTS OF THE INVENTION According to the method of the present invention, it is possible to synthesize diamond from graphite and water as raw materials at a reasonable production rate and at a reasonable rate as compared with the conventional method, and thus to scale up the method. As a result, a diamond synthesizing method capable of producing diamond powder at low cost is provided.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an apparatus for carrying out a diamond synthesizing method according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of an apparatus for carrying out a diamond synthesizing method according to a second embodiment of the present invention.

FIG. 3 is a block diagram showing a configuration of an apparatus for carrying out a diamond synthesizing method according to a third embodiment of the present invention.

FIG. 4 is a block diagram showing a configuration of an apparatus for carrying out a diamond synthesizing method according to a fourth embodiment of the present invention.

[Explanation of symbols]

 1. ． ． Reaction vessel 2. ． ． Graphite 4. ． ． Tubular electric furnace 5. ． ． Diamond grains 8. ． ． Graphite container 11. ． ． Closed reaction vessel

Claims (3)

[Claims] 1. A reaction vessel equipped with a pressure adjusting mechanism is charged with graphite and water, the remainder is made air inevitably introduced, and at least a portion of the reaction vessel in which the graphite is installed is heated to 1000 ° C. or higher, A method for synthesizing diamond, which comprises synthesizing diamond in a portion of the reaction vessel at a temperature of 600 ° C. or higher and 1200 ° C. or lower. 2. The pressure inside the reaction vessel is 1 atm or more and 100 atm.
The method for synthesizing diamond according to claim 1, wherein the pressure is 0 atm or less. 3. Graphite and water are enclosed in a closed reaction vessel, and at least a portion of the closed reaction vessel where the graphite is installed is 1
Heating to 000 ° C or higher, 600 ° C or higher in the reaction vessel 1
A method for synthesizing diamond, which comprises synthesizing diamond at a temperature of 200 ° C. or lower.