| Diamond is a representative production of superhard materials. It is a limiting functional material with many exceptional physical and chemical properties. Now, it has been applied in many fields such as industry, scientific research, national defense, medical treatment etc. Diamond plays an important part in the development of industry. China is not rich in natural diamond, so that independently holding high-level diamond synthesis technique is of realistic strategic significance.Recently, in the field of diamond synthesis, powder catalyst technique has gradually replaced the traditional slice catalyst depending on its advantages of high unit yield, low raw material consumption and good synthesis quality. Especially, with the extensive application and popularization of the large-scale cubic high pressure apparatus and indirect heating technique, the level of Chinese diamond synthesis using powder catalyst has made a great step forward in, and china is gradually stepping in the ranks of strong country on diamond synthesis.Natural diamonds are usually hosted by kimberlites and lamproites, which contain sulfur. Sulphides are the most common syngenetic inclusions in natural diamonds. Study on the influence of sulfur on diamond growth will contribute to understanding the formation of natural diamonds. This research will also be helpful to explore new type catalyst, and synthesize special type diamond.In this paper, the uniformly mixed technique for catalyst-graphite powder system was improved. For several important assembling departments(heating cube, insulating cube, etc.), the selection of raw materials and the preparation were studied and improved. And then the stable growth of industrial diamond single crystal was realized. Regard solvent theory as guidelines, the diamond synthesis craft was further improved.We have respectively investigated the growth characteristics of industrial diamonds in four kinds of sulfur-added powder system (NiMnCo-C-FeS, NiMnCo-C-S, Fe-C-S, FeNi-C-S). The influences of additive sulfur on the synthesis have been studied. It was found that the introduction of additive sulfur have made the diamond forming condition rise, and inhibited the spontaneous nucleation with a certain degree. Additive sulfur has obviously influenced the growth of diamond from several aspects such as surface morphology, growth rate and inclusions. Optical microscope, SEM, XRD and XPS were used for detection and characterization.In our research, high-quality golden octahedral industrial diamonds have been successfully synthesized. The granularity of the crystals are uniform, transparency is high, and the excellent crystal ratio can be more than 90%. This product has very good application prospect, and has been approved in the trade. Utilize the inhibitory nucleation character of additive sulfur, we have further improved the diamond synthesis craft, made the synthesis cycle shorten, improved the production efficiency.In the end of this paper, the experimental phenomenon and the growth mechanism of industrial diamond was discussed in light of the solvent theory. It was found that there was certain correlation between diamond synthesis conditions and the electronegativity value of additive. This has some important guiding significance for the selection of additive for diamond synthesis. We also investigated the effect of diamond surface dangling bond on the morphology of diamond, and crystal growth rate on inclusion distribution. Using these mechanism, the correlative experimental phenomenon was explained rationally. |
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