JP2752753B2 - Synthesis method of diamond by combustion flame - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention has characteristics such as wear resistance, corrosion resistance, high thermal conductivity, and high specific elasticity, and is used for optical materials, carbide tool materials, abrasive materials, and sliding materials. The present invention relates to a vapor-phase method for synthesizing film-like or granular diamond useful for a moving material, a corrosion-resistant material, an acoustic vibration material, a member for a cutting edge material, and the like.

<Conventional technology> As a method for synthesizing diamond, under ultra-high pressure conditions,
2. Description of the Related Art A direct conversion method of graphite by a synthesis method using an iron or nickel-based catalyst or an explosive method has been conventionally performed.

In recent years, as a low-pressure CVD method, diamond has been synthesized as an excited state using a mixed gas of hydrocarbon or an organic compound containing nitrogen, oxygen, etc. and hydrogen by hot filament, microwave plasma, high frequency plasma, DC discharge plasma, DC arc discharge, etc. A way was developed.

As an improved method of the CVD apparatus, the inventors of the present application burn a diamond deposition raw material compound so as to have an incomplete combustion region, and deposit diamond on a substrate provided in or near the incomplete combustion region. Developed a diamond synthesis method for the combustion flame method to be deposited, and presented it at the 35th Annual Conference of the Japan Society of Applied Physics (Preliminary Proceedings, Volume 2, p.434, 29a-T-1). Disclosed. Further, in Japanese Patent Application No. Hei 1-246382, an application was made as a method for synthesizing a transparent diamond using a combustion flame method, wherein argon gas is directly introduced into the inner flame portion of the combustion flame separately from the combustion gas. The former is a combustion using oxygen of a single or mixed gas mainly composed of an organic compound, and carbon in the organic compound is almost consumed by the combustion. For this reason, the quality of the produced diamond is not so good, and a particularly high yield cannot be obtained. In the latter, high-quality diamond can be obtained by adding argon as the third component, but the deposition rate is not high and the yield is not high.

<Problems to be Solved by the Invention> In the diamond synthesis method of the combustion flame method, it is possible to deposit diamond on a base material only by forming a combustion flame with a raw material compound. This is a revolutionary method. However, in recent years, with an increase in demand for diamond, there has been an increasing demand for a large amount of high-quality film-like or granular diamond using simple means.

<Means for Solving the Problems> The present inventors have conducted intensive studies on a synthesis method for depositing high-quality diamond at high speed by a combustion flame method,
The present invention was completed by confirming that the object was achieved by directly introducing an organic compound or a mixed gas of an organic compound and argon into the combustion region separately from the combustion flame forming gas.

That is, according to the present invention, an organic compound or an organic compound having a composition different from that of the combustion flame forming gas, argon, or the like is externally supplied to the internal flame portion of the combustion flame, that is, the high temperature plasma portion near the already formed core (white heart). The present invention relates to a method for synthesizing a high-speed deposited diamond by the combustion flame method, wherein the mixed gas is directly introduced separately from the combustion flame forming gas.

As the carbon source for diamond synthesis used in the present invention, methane, ethane, propane, saturated hydrocarbons such as butane,
Unsaturated hydrocarbons such as ethylene, propylene, butylene, and acetylene; aromatic hydrocarbons such as benzene and styrene;
Alcohols such as ethyl alcohol, compounds containing a ketone group such as acetone, ethers such as diethyl ether,
In addition, all aldehyde compounds, nitrogen-containing compounds, carbon monoxide and the like can be used.

In the present invention, the source gas for diamond synthesis or (and / or) the mixed gas is introduced into the non-oxidizing and out-of-flame non-oxidizing and near-flame-excited basin where the diamond can be deposited. It is necessary for the material to be present. Further, the oxygen of the source gas for diamond synthesis is added, and combustion is performed in an atmosphere containing no oxygen or in an atmosphere containing oxygen to generate an incomplete combustion region in which diamond is excited to a precipitated state. In the former example, combustion in an inert gas atmosphere can be exemplified, and in the latter example, combustion in the atmosphere open can be exemplified.

In the vapor phase synthesis of these diamonds, the organic source compound is separated and dissociated by heating and reaction with oxygen in the combustion flame, and further reacts to form, for example, C, C ₂ , CH,
CH ₂ , CH _{3 and the} like are generated. In the method of the present invention, decomposition by high heat by injecting an organic compound into the inner flame portion of the combustion flame,
Tighten performed dissociation, are clustered or radicalized, C radical, C ₂ radical, repeatedly active species and the collision of such CH radical, momentum of radicals is increased, a preferable atmosphere diamond product as a whole. The properties of the precipitated diamond in this atmosphere are significantly improved,
At the same time, the deposition rate is greatly increased.

For example, acetylene, styrene, allene, propane,
Add oxygen to raw material gas such as ethyl alcohol, methyl alcohol, benzene, etc. to form combustion flame in open air system,
It is possible to adjust the volume of the incomplete combustion zone by adjusting the amount of added oxygen.

For example, in the case of oxygen acetylene, O ₂ / C ₂ H
The ratio of ₂ is preferably from 0.75 to 1, more preferably from 0.8 to 0.95.
It is. If it is less than 0.75, soot is likely to occur. In these cases, the temperature of the inner flame, which is the region of incomplete combustion, is
2000-3000 ° C., no auxiliary excitation means required. Generally, the synthesis temperature of diamond is desirably 1500 ° C or higher. The deposition substrate temperature is 500-1200 ° C., more preferably 800
11100 ° C., and can be controlled to this substrate temperature range by cooling.

As a substrate for diamond deposition, a substrate usually used in a low pressure CVD method can be used. That is, Si wafer, SiC sintered body, SiC
In addition to the granular material, shapes and granular materials such as W, WC, Mo, TiC, TiN, cermet, cemented carbide tool steel, and high-speed steel can be exemplified.

The basin where diamonds are deposited is a region of oxygen deficiency, commonly referred to as internal flame in the combustion flame. In general, the oxygen-excess region has a high heat. For example, even if diamond is formed, it is converted into CO and CO ₂ by excess oxygen and disappears. That is, it is considered that diamond does not precipitate in this region. Incidentally, the diamond deposition region is deficient in oxygen and has a relatively low temperature. In this region, it is necessary to excite the raw material gas under conditions for producing hydrocarbon radicals (active species).

Next, the method of injecting the additive such as the organic compound of the present invention in which the combustion state is adjusted as described above will be described with reference to the drawings, taking the case of an oxygen-acetylene system as an example.

FIGS. 1 (a) and 1 (b) show an example of a burner for carrying out the method of the present invention, which is a crater 1 having a spout 2 for an additive made of an organic compound or the like in the center and acetylene in the periphery. Etc. are disposed. Usually, the spout of the additive has a larger diameter than the spout of a raw material gas such as acetylene.

FIG. 2 shows a combustion flame from the burner having the crater 1 described above. The combustion flame is composed of an inner flame 6, an outer flame 7, a white heart 4, and a radical flame (tentative name) 5 at the center. Have been. For radical flame formation, it is necessary that the composition of the additive be different from the combustion forming gas. In particular, it is preferable that oxygen is oxygen-free or very low.

FIG. 3 shows the state of the combustion flame when the combustion flame is blown from the burner crater 1 toward the deposition substrate 9 supported on the water-cooled support 8 because the flame hits the substrate as shown in the figure. The combustion flame flows as shown in the figure, and the excited additive becomes a radical flame 5 enclosed inside the internal flame 6 together with carbon-containing active species such as C ₂ radicals and CH radicals.

In the radical flame, (HC) radical + C ₂ H ₂ → {Diamond precursor}
Reaction of the radical H ₂ is believed to occur.

In addition, {H ・ C} radicals and various kinds of carbon, and the contact between radicals and atomic hydrogen increase the activity. By reaching more substrates, high quality, highly transparent and self-developed diamond can be produced at high speed. It is thought that it will grow in a wide area.

In carrying out the method of the present invention, the installation position of the substrate is 0 to 0 from the tip of the white heart in the case of oxygen-acetylene.
It is preferably set to 10 mm, and in the case of other systems, to a position 2 to 10 mm from the crater.

Further with respect to formation of diamond material is C ₂ H ₂ for additive supplying practicing the present invention method, an organic compound / C ₂ H
₂ is preferably 1 vol% to 10 vol%.

When the amount of organic compounds is small, the amount of diamond deposition decreases,
If it is too much, it is graphitized and diamond cannot be obtained. When Ar gas is mixed into the raw material for addition, a high-quality, highly transparent and self-developed diamond can be obtained. Ar
The mixing ratio of the gas is such that Ar / organic compound is 5 to 70 vol%, preferably 15 to 50 vol%. Although the internal flame of an acetylene / oxygen flame is light blue, generally, when an organic compound is introduced into the internal flame, the radical flame discolors. In the case of methane, it becomes yellow, and in propane, it becomes more and more colored. When Ar is mixed into these, the original color tone becomes soft pale yellow and gradually becomes lighter color, and therefore, the portion having the introduction effect is clearly identified.
It is also effective to add oxygen to promote the decomposition and dissociation of the organic compound introduced into the internal flame, but the entire combustion flame of the raw material and the organic compound for addition may be incomplete due to the adjustment of the oxygen addition amount. It must be within the combustion range.

On the other hand, C, C ₂ , CH, CH ₂ , CH ₃
Such radicals are generated, but it is also effective to add a certain amount of hydrogen gas or H ₂ O to enhance the activation of these radicals. These decompose at high temperatures into atomic hydrogen and OH radicals. Atomic hydrogen is the aforementioned "diamond precursor"
By repeating collisions with radicals, the active lifetime is increased, which greatly contributes to the formation of diamond. OH radicals are thought to remove generated graphite and help to form high-quality diamond.

<Example 1> The acetylene burner crater 1 was fixed downward as shown in Fig. 1 (a). The burner opening has a slit outer diameter of 3.4 mm and a slit inner diameter of 2.9 mm, and the additive outlet at the center has a diameter of 0.9 mm. Next, acetylene 5.0l / min, oxygen 4.6lmin
(Oxygen acetylene ratio 0.92), propane additive 150cc /
The mixture was supplied to the burner at a flow rate of min, and a combustion flame was formed in the atmosphere as shown in FIG. Thereafter, as shown in FIG.
A 20 mm square, 0.5 mm thick Mo substrate 9 was fixed to the water-cooled support 8, moved to a distance of 7 mm from the white center and fixed. The substrate temperature at this time was adjusted to about 1000 ° C. After the reaction for 20 minutes, the substrate deposit was observed with an optical microscope, and it was confirmed that a well-developed, blocky diamond crystal having a good shape was dispersed and distributed over the entire surface of the substrate. Further microscopic Raman spectroscopy analysis of this diamond showed a Raman shift of 13
Only one sharp peak due to the diamond crystal was shown at 33 cm ^-1 . When the particle size was measured, it was found to be transparent and blocky self-shaped diamond particles having an average of about 100 μm, and the yield was 0.03 g.

<Example 2> An acetylene burner crater was fixed downward in the same manner as in Example 1, and a 20 mm square, 0.3 mm thick silicon wafer was placed on a water-cooled support stand at a temperature of 900 ° C at a distance of 7 mm from the burner crater. Fixed. Acetylene to burner, 5.0l / mi
n, introduce oxygen 4.4l / min (oxygen / acetylene ratio 0.88), then form a combustion flame in the atmosphere, further introduce methane 150cc / min, argon 50cc / min from the center hole of the burner, light yellow After a flame was formed and adjusted to 7 mm from the white center of the substrate distance, it was reacted for 20 minutes.

After completion of the reaction, the deposits on the substrate were observed with an optical microscope. As a result, a number of highly transparent grains having a diamond shape were confirmed. 1333cm by Raman spectroscopy
Only one peak due to sharp diamond bonding was recognized at ^-1 . Further, it was found that the half width of this peak was very close to that of a natural diamond single crystal. The particle size of the transparent and well-developed diamond was 60 μm, and 0.02 g was obtained.

<Comparative Example 1> Synthesis was performed for 20 minutes using the same burner, substrate position, and generation method as in Example 1 except that 5.0 l / min of acetylene, 4.6 l / min of oxygen, and propane as an additive were removed. As a result, a yield of 0.004 g of diamond was obtained.

<Example 3> The same burner, substrate position and production method as in Example 2 were used without addition of argon, that is, synthesis was performed for 20 minutes with 5.0 l / min of acetylene, 4.4 l / min of oxygen, and 150 cc / min of methane,
As a result, 0.015 g of a grayish black self-developed diamond having an average particle diameter of 30 μm was obtained.

<Comparative Example 3> Propane was previously mixed with acetylene as a combustion gas by the same burner, substrate position and method as in Example 1 without adding the third component from the center hole. That is, acetylene 5.
0l / min, each with 150cc / min of propane premixed, oxygen
Synthesis was performed at 4.4 l / min for 20 minutes. As a result, 0.002 g of gray-black diamond was obtained, and the yield was reduced.

<Effect of the Invention> By adding a simple means of introducing an organic compound gas separately from the combustion gas into the inner flame portion of the combustion flame in the combustion flame method, it is possible to precipitate the self-shaped well-developed diamond grains at a high speed. It was possible to obtain highly transparent diamond grains by adding argon gas.

By this method, the yield of diamond can be dramatically increased.

[Brief description of the drawings]

1 (a) and 1 (b) show the arrangement of an acetylene outlet and an argon outlet of a burner crater for carrying out the present invention. FIG. 2 shows the structure of a combustion flame formed by the method of the present invention from the burner having the crater of FIG. FIG. 3 is a view showing a flow of a combustion flame when substrates are provided at intervals in a burner crater. In the figure, 1 is a burner crater, 2 is an additive outlet, 3 is a combustion flame forming gas outlet, 4 is a white heart, 5 is a radical flame, 6
Denotes an internal flame, 7 denotes an external flame, 8 denotes a water-cooled support, and 9 denotes a diamond deposition substrate.

Claims (1)

(57) [Claims] A combustion flame characterized in that an organic compound having a different composition from the combustion flame forming gas or a mixed gas of an organic compound and argon is introduced into the inner flame portion of the combustion flame separately from the combustion flame forming gas. Method of diamond synthesis.