JP2786721B2 - 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 abrasion resistance, touch resistance, high thermal conductivity, and high specific elasticity, and includes optical materials, carbide tool materials, abrasive materials, The present invention relates to a vapor-phase method for synthesizing film-like and granular diamonds useful for sliding materials, acoustic vibration materials, and cutting edge materials.

<Conventional technology> As a method for synthesizing diamond, under ultra-high pressure conditions,
Conventionally, a synthesis method using an iron or nickel-based catalyst or a direct conversion method of graphite using an explosive method has been practiced.

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 method, the inventors of the present application burn a raw material compound for diamond deposition 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, and presented it at the 35th Annual Conference of the Japan Society of Applied Physics (Preliminary Proceedings, 2nd Volume, 434 pages, 29a-T-1) and applied for Japanese Patent Application No. 63-71758. did. Further, in Japanese Patent Application No. Hei 1-246382, an application was filed 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. In Japanese Patent Application No. 1-343229, it has been proposed that an organic compound having a different composition from the combustion flame forming gas, argon alone or a mixed gas, be introduced separately from the combustion flame forming gas into the inner flame portion of the combustion flame. An application was filed as a synthesis method of a high-speed deposition diamond characterized by the combustion flame method.

In a method of obtaining a high-speed or high-quality diamond by adding a third component using a combustion flame, a method of increasing a radical component in a plasma space in an inner flame portion of the combustion flame has been required.

<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, with the recent increase in demand for diamond, there has been an increasing demand for a large amount of high quality film or granular diamond with 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,
It has been confirmed that it is necessary to directly introduce an organic compound, hydrogen or argon alone or a mixed gas into the combustion area in order to achieve the purpose, but the plasma space in the inner flame portion of the combustion flame has been further advanced. The present invention has been completed by developing a method of appropriately penetrating the above-mentioned third component into the plasma space and increasing the radical component in the plasma space composed of both components.

That is, an organic compound which is a third component having a different composition from the combustion flame forming gas from the outside to the internal flame portion of the combustion flame of the present invention, 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 a combustion flame method, wherein a single gas or a mixture gas of hydrogen and argon is introduced as a cross flow having a certain angle or more separately from a 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, it is necessary that the diamond synthesizing source gas be present in a non-oxidizing region outside the flame or in a region near the flame that is excited so that diamond can be precipitated, in the incomplete combustion region. It is. In addition, oxygen is added to the source gas for diamond synthesis to generate an incomplete combustion region in which diamond is excited into a precipitated state in an atmosphere containing no oxygen or an atmosphere containing oxygen. The former can be exemplified by combustion in an inert gas atmosphere, and the latter can be exemplified by combustion in open air.

In the vapor phase synthesis of these diamonds, the organic raw material compounds are separated and dissociated by heating and the reaction with oxygen in the combustion flame, and further react, from radicalized active species, for example, C, H, C ₂ ,
CH, CH ₂ , CH _{3 and the} like are generated. In the method of the present invention, a third component gas having a composition different from that of the combustion flame forming gas penetrates into the inner flame portion of the combustion flame so as to intersect, thereby causing decomposition and dissociation by high heat, and clustering or radicalization. , 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 remarkably improved, and at the same time, the precipitation roughness is also greatly increased.

The region where diamond is deposited is a region of oxygen deficiency, which is usually 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 hydrocarbon 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.

FIG. 1 shows an example of an outlet of a burner for carrying out the method of the present invention, in which a concentric double hole and an outer peripheral hole are an outlet of a mixed gas of a raw material gas and oxygen and have an outer diameter of 3.2 mm. The inside diameter is 2.8 mm. The outer diameter of the third component and the outlet of the carrier gas is 1.4 mm and the inner diameter is 1.0 mm in the inner peripheral hole at the center.

Figure 2 is a commercially available burner with a spout at the center,
There is a concentric outer peripheral hole. The gas outlets are set in parallel, and the ejected gas flows hardly cross each other. In this method, it is difficult to effectively inject the third component into the high-temperature plasma of the combustion flame.

FIG. 3 conceptually shows a state in which the flow of the gas flow injected from the third component injection port in the circumferential hole intersects with the flow of the combustion gas in the outer circumferential hole. In such a cross flow, the two gas flows intersect sharply, so that the gas flow of the third component penetrates into the high-temperature plasma portion near the core of the raw material gas, and the plasma composed of both these components flows. It can be expected to increase the radical component of the space. Certainly, the crossing pattern based on the conceptual diagram is patterned as described above, but the actual combustion plasma flame is a moving body of high-temperature, plasmanized ions that form a constant steady flow, so that a homogeneous combustion flame is close to the combustion flame. If they do not keep a certain crossing angle, they will repel each other. Normal,
The intersection angle between the combustion gas and the third component is 10 ° to 60 °, more preferably 20 ° to 45 °.

The flow rate of the third component is preferably in the range of 3% to 130% of the combustion gas. If it is less than this, the third component of the raw material will be diluted and its effect will not be exhibited, and if it exceeds this, the plasma density of the combustion flame will decrease.

This promotes the radicalization of the third component and increases the probability of collision with each component in the combustion flame. For example, it is considered that the following radical chemical reaction occurs.

{H • C} radical + C ₂ H ₂ → {Diamond precursor} Radical + H ₂ or {HC} radical, various carbon-containing radicals, and atomic hydrogen increase the activity and reach more substrates By doing so, it is considered that a diamond having a high quality and high transparency and a self-developed diamond grows quickly and in a wide area.

Example 1 As shown in FIG. 3, the acetylene burner crater was fixed downward. The outer opening is 3.4 mm in outer diameter, 2.8 mm in inner diameter,
The center third component injection port has an outer diameter of 1.4 mm and an inner diameter of 1.0 mm.
The central jet gas crosses the combustion gas flow at a 30 ° angle. Next, acetylene 4.5mm / min, oxygen 4.3 / min
(Oxygen / acetylene ratio 0.93), propane 100c as the third component
c / min and 200 cc / min of hydrogen were mixed in advance and supplied to the burner from the central port to form a combustion flame in the atmosphere. Thereafter, as shown in FIG. 3, a 20 mm square, 0.5 mm thick Mo substrate was fixed to a water-cooled support, moved to a distance of 7 mm from the white heart, and fixed. When the substrate temperature at this time was observed with an optical microscope, it was confirmed that a self-shaped and well-developed blocky diamond crystal was dispersed over the entire surface of the substrate. Further, the diamond was subjected to Raman spectroscopic analysis under a microscope. As a result, only one sharp peak due to the diamond crystal was shown at a Raman shift of 1333 cm ^-1 . When the particle size was measured,
At 150 μm, transparency was found especially at the center, and the yield was 20 mg.

[Comparative Example 1] A burner set so that the third component ejection gas and the combustion gas flow at the center shown in Fig. 2 flow in parallel without intersecting with each other was used. The substrate position and generation method were the same as in Example 1, and acetylene 4.5 / min, oxygen 4.2 / min, and argon as a third component were supplied to the burner at 100 cc / min, and synthesis was performed for 30 minutes. When taken out and observed, a diamond of 20 to 30μ was seen around the precipitation area, and the central part was slightly annealed. The yield was 5.0 mg.

[Comparative Example 2] In the same manner as in Comparative Example 1, the acetylene was 4.5 / min and the oxygen was 4.3 / mi with the burner, substrate position, and generation method set in parallel flow.
n, The third component propane was synthesized at 100 cc / min for 30 minutes. As a result, formation of graphite was observed in some places on the substrate although polyhedral diamond of 30 to 60μ was deposited.

[Comparative Example 3] Acetylene 4.5 / min, oxygen 4.2 / mi with a burner, substrate position and generation method set in parallel flow as in Comparative Example 1.
n, 4 propane of the third component at 100 cc / min and 200 cc / min of hydrogen
Synthesis was performed for 0 minutes. As a result, polyhedral diamond crystals of 30 to 40 μm were obtained, but diamond-like carbon particles were formed around the deposition portion on the substrate, and graphite was partially generated.

<Effect of the Invention> A large amount of diamond films or grains can be produced with high quality, high homogeneity, high speed, and relatively easily by the diamond synthesis method according to the present invention.

[Brief description of the drawings]

FIG. 1 is a bottom view and a sectional view of a burner used in an embodiment of the present invention. FIG. 2 is a conceptual diagram showing a parallel flow as a comparative example, and FIG. 3 is a conceptual diagram showing a cross flow as an example.

Claims (1)

(57) [Claims] The present invention is characterized in that a combustion flame forming gas and a third component gas are cross-penetrated into a plasma space of an inner flame portion of a combustion flame to generate a plasma space in which both components are mixed with each other. Diamond synthesis method.