| Summary: | 碩士 === 國立東華大學 === 材料科學與工程研究所 === 87 === The synthesis of metastable diamond via liquid metal process at low pressures combines some of the diamond growth mechanisms and methods of both HTHP(high temperature and high pressure) and low pressure CVD. It could be the third major method, which could produce diamond at large-scale and at low cost. The work is to study the metastable diamond synthesis using various powder mixtures as the starting material in pure H2 and 0.8﹪CH4 in H2 at low pressures, to understand the importance of temperature and reduction processes, to enhance the growth rate, and to understand the effect of solubility of carbon in metal. A hot filament chemical vapor deposition (HFCVD) reactor was used to excite and disengage the gases, and to heat starting powder mixtures. The powder mixtures included various combinations of graphite, diamond, Co, Ni and Mn metal powders. Samples were heated to the range of metal or alloy melting point, and heated for 5 hrs. The XRD patterns of samples with diamond seeds, Co and Ni metal powders processed in CH4/H2 showed an small increases in diamond peak intensities, and their corresponding SEM photos also indicated the growth of diamond seeds into single-crystals and poly-crystals. The size of these crystals are 2~3 times larger than grown on Si substrate under comparable CVD conditions. In this results, the synthesis rate of metastable diamond via liquid metal process still in the range of that via gas phase process. If we use graphite powder under 99.2 H2 and 0.8﹪CH4 , the synthesis rate showed decreases. In condition of metal/graphite/diamond seeds/pure H2 (liquid metal process), the solubility of C and H2 for synthesis rate increasing has positive affection.
|
|---|
