The Investigation On The Effect Of B, N And H On The Synthesis Of Diamond In The Iron-based Catalyst System

Diamond as a multifunctional material has been widely used in the high-technology applications stems from its exceptional physical and chemical properties. Although a series of synthesis methods for the diamond crystal has been developed, high temperature and high pressure (HPHT) is still the main method to manufacture synthetic diamond. The participation of catalysts not only reduces the synthesis conditions of diamond single crystal, but also affects the properties of synthetic diamond under HPHT conditions. With the exploitation of new catalyst, many diamond crystals with excellent properties were synthesized, which greatly enriched the diamond application fields. Although the exploitation technology for many new catalysts has been more and more mature in the developed countries, they are not open. Because the synthesis of diamond in our contury is mainly based on the china-type large volume cubic high-pressure apparatus, the disadvantage P-T conditions of equipment prevents the development of new catalysts. Therefore, the research on the new type of catalyst adapting to the situation of our country can promote the improvement of the level of science and technology, and enhance the diamond market competitiveness.At present, some transition metals and alloys are the mainly domestic catalysts used for the synthesis of diamond, such as Fe, Ni, Mn and Co, etc. The elements of Ni, Mn, Co can be easily incorporated into the internal of diamond crystal under HPHT. However, iron element is difficult to get into the diamond. Thus the research of new iron-based catalyst for the synthesis of high quality diamond has become an important development direction. In our work, we study the effect of non-metal elements on the traditional iron-based catalyst, and exploit the new catalysts for the diamond synthesis. Our works are divided into the following sections: 1. We research the effect of the non-metal hydrogen element on diamond crystallization by adding ferrocene to the system of carbon and Fe-based solvent/catalyst.Besides nitrogen, hydrogen is also considered to as an important role in the genesis of diamond. Furthermore, a large number of theoretical and experimental studies have shown that the thermal and electronic properties of diamond can be changed by hydrogen impurity. To investigate the effect of hydrogen element on diamond crystallization, the diamond crystals are synthesized by adding ferrocene to the system of carbon and Fe-based solvent/catalyst. We found that the growth region of{111} face becomes wider, while the region of{100} face becomes narrower and almost disappears with the increasing concentration of ferrocene. The result of Fourier transform infrared absorption and Raman reveals that the changing of the diamond growth habits can be explained by the effect of hydrogen from the decomposition of ferrocene on the diamond crystallization. In addition, the hydrogen doped diamond with low nitrogen contentration can be synthesized in the high concentration ferrocene additive system.2. We investigate the diamond crystallization using iron-nickel alloy as catalyst with C3N6H6additive, to study the synergistic effect of nitrogen and hydrogen on the diamond synthesis under HPHT conditions.Experimental and theoretical studies show that the established changes of diamond in the growth, morphology, and main characteristics are induced by the impurities, especially nitrogen and hydrogen. It is interesting to note that nitrogen and hydrogen usual simultaneously exist in the natural diamond. Moreover, one of the most feasible methods to tailor the electrical properties of diamond is by co-doping. The simultaneous incorporation of nitrogen and hydrogen into diamonds have more potential semiconducting properties and can be applied in many fields. Hence, it is an interesting subject to explore the synergistic effect of nitrogen and hydrogen on the general features and peculiarities of diamond crystallization under HPHT. To investigate the effect of nitrogen and hydrogen element on diamond crystallization, the diamond crystals are synthesized by adding C3N6H6to the system of carbon and Fe-based solvent/catalyst. We found that the distributions of nitrogen and hydrogen are non-uniform in the synthesized diamond, which is similar as natural diamond. As the C3N6H6additive increases, the nitrogen and hydrogen co-doped strip shape diamonds are preponderated with the production of slice shape crystals.3. We examined the catalytic effect of boron, nitrogen on the synthesized diamond. The two different forms of nitrogen boron co-doped diamond were synthesized.Compared with the cubic B-C-N crystal, the diamond crystals doped with B and N atoms under HPHT is easier to be obtained with more structurally stable. Thus, the new "BCN" diamond will be more attractive in future studies on the cubic B-C-N alloys. We study the synergistic effect of nitrogen and boron in the crystallization medium on the growth processes and real structure of diamond crystals. The two kinds of B and N co-doped diamond with different precursors have been synthesized. The first used additive is hexagonal boron nitride, another is sodium azide and boron powder. We studied the effect of boron and nitrogen on diamond crystal structure. We found the synthesized diamonds from the hexagonal boron nitride additive are strip-shaped diamond. However, when the boron and nitrogen sources from a variety of additives, the synthesized diamonds have traditional hexoctahedron shapes with nonuniform colors. Two forms of nitrogen boron doped diamond will be widely used in many different areas.