Preliminary study on the synthesis of diamond by using graphite-encapsulated nickel nanoparticles at high pressure and high temperature
Date Issued
2005
Date
2005
Author(s)
Hsiao, Tun-Jen
DOI
zh-TW
Abstract
Since 1955 when Tracy Hall had first successfully synthesized diamond by using a belt high-pressure apparatus from a mixture of troilite (FeS) and graphite raw materials, many scientists have been studying on the formation mechanism of diamond and have gained some significant progress. The raw materials used in modern diamond synthesis technology are usually micrometer sized graphite powder and metal catalyst. This research, however, uses a new raw material, the graphite-encapsulated metal nanoparticle (GEM), as the carbon source and metal catalyst in the synthesis of diamond. GEM is a composite material, whose grain size is 10-100 nm and with a core/shell structure, i.e., the core is metal, and the shell is graphite. The three possible advantages of using GEM to synthesize diamond are: its large specific area, the already existed catalytic core metal, and the close contact of core/shell structure.
Though the comparing section of the sample that was composed of industrial graphite and metal catalyst had successfully produced diamonds, in the experiment-section of the sample it was a surprise that we could not find any diamond with either XRD or Raman spectrum analysis, only by TEM that we found some nanodiamonds. The possible formation mechanisms of nanodiamond are: first, the nickel core melts and the nickel precipitates outside of the graphitic shells. Second, graphite shells become disintegrated and forming many crystallized graphite flakes. Third, the graphite flakes are catalyzed by the nickel catalyst and transformed into nanodiamond. In addition, we found a well-crystallized graphite single crystal by TEM. This may indicate that first, the pressure during the experiments was actually lower than the required high pressure. Second, because the graphite pieces that used in the experiments to prevent any contamination have a higher resistance, they would probably produce more heat and create a higher temperature. Thus, the relatively lower pressure and higher temperature experimental conditions would lead to the recrystallization of graphite, and produce the hexagon graphite crystal observed.
In summary, the nanostructure of the GEM nanopaticles may probably have deviated the required experimental temperature and pressure. As a result, we cannot find any larger sized diamond other than nanodiamond.
Subjects
石墨包裹鎳奈米晶粒
合成鑽石
graphite-encapsulated nickel nanoparticles
the synthesis of diamond
Type
thesis
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