Chemistry of inorganic compounds – Carbon or compound thereof – Elemental carbon
Patent
1994-05-09
1997-08-05
Lewis, Michael
Chemistry of inorganic compounds
Carbon or compound thereof
Elemental carbon
427249, 117 1, 117104, C01B 3106
Patent
active
056539525
DESCRIPTION:
BRIEF SUMMARY
INDUSTRIAL FIELD
The present invention relates to combustion method, i.e., a low pressure vapor phase synthetic process for artificially synthesizing diamond, which comprises, for example, combusting a hydrocarbon fuel gas and an oxidizing agent in a burner and striking the combustion flame on the surface of a substrate being set facing the burner to synthesize diamond. The present invention relates to a process for synthesizing diamond using combustion method, which provides diamond crystals larger than the conventional ones in diameter.
PRIOR ART
Artificial diamonds can be synthesized by either high pressure synthetic process or low pressure vapor phase synthetic process. Recently, there is proposed, as one of the low pressure vapor phase synthetic processes for synthesizing diamond, a combustion method in which combustion flame is used.
The process for synthesizing diamond using combustion method comprises, as shown in FIG. 8(a), combusting a hydrocarbon fuel and the like such as acetylene, ethylene, methane, propane, methanol, and ethanol as the carbon source for depositing diamond in a burner 11, using pure oxygen as the oxidizing agent being mixed at an amount far lower than the stoichiometric mixing ratio. In this manner, a specified flame 12 can be obtained by controlling the conditions for the combustion. Then, as shown in FIG. 8(b), a substrate 15 is placed inside a flame 14 denoted "feather" and which generates at the vicinity of the fire outlet 13, while forcibly cooling the substrate 15 using a cooling means being provided to the substrate holder 16 to maintain the substrate in the temperature range of from 600.degree. to 1,200.degree. C. Diamond can be synthesized in this way on the surface of the substrate 15.
However, most of the conventional processes for synthesizing diamond using combustion method heretofore proposed are in fundamental processes of experimental scale, and hence problems concerning the burners for use in the combustion and the cooling methods remain yet to be solved. The present applicants proposed modified processes for overcoming those problems in Japanese patent application Nos. 2-111263 and 2-43657.
Since then, the present applicants have attempted to synthesize diamond on the surface of a substrate using the above modified synthetic process. As a result, it has been found that the process for synthesizing diamond using combustion method is of best economy among the low pressure vapor phase synthetic processes, but that it is extremely difficult to synthesize large diamond crystals on the surface of a substrate. More specifically, the diamond grains having grown by this process were found to have a maximum size in the range of from about 100 to 300 .mu.m, and when an attempt was made to obtain a diamond grain exceeding this maximum size range, graphite and carbon began to deposit on the surface of the diamond crystals with increasing duration of deposition. Accordingly, it was found that diamond crystals larger than about 100 to 300 .mu.m in size cannot be synthesized by the conventional process for synthesizing diamond using combustion method.
In the light of such circumstances, the present applicants further modified the process for synthesizing diamond using combustion method to newly develop a process capable of synthesizing diamond crystal grains larger in diameter. That is, the substrate for synthesizing diamond thereon was arranged in such a manner that it may cross the axial center of the burner, and the distance between the substrate and the front end of the burner was gradually increased with the passage of time from 5 mm at the initial stage of the synthesis. This process for synthesizing diamond using combustion method was applied for patent as Japanese patent application No. 2-205412.
The above process enabled synthesis of diamond crystals as large as about 500 .mu.m in diameter over two hours of synthesis. However, it was found impossible to obtain larger diamond grains of fine quality by simply controlling deposition conditions such as the distance
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Morinishi Yoshiaki
Suzuki Tomio
Hendrickson Stuart L.
Kabushiki Kaisha Kobe Seiko Sho
Lewis Michael
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