Synthesis Of Industrial Diamond Single Crystal Using Fluoride And Silicon As Catalyst

Diamond is a functional material with many excellent properties. Now, it has been applied in many fields such as industry, scientific research, national defense, medical treatment etc. It plays an important part in the development of industry.The diamond synthesis technique has been greatly improved due to its extensive application. In the late 1980s, the technique for the high-strength coarse grain diamond crystal synthesized by powder catalyst in a belt apparatus was successfully exploited by Winter Company, Germany, which made a great breakthrough in synthesis of high grade diamond using powder materials. This method had many merits such as increasing the output, decreasing the consumption of raw materials and improving the crystal quality. Therefore, almost all the famous diamond companies in the world employed the method to synthesize high-strength coarse grain diamond and cornered chronically the high grade diamond market since the end of 90's.In the industrial production of diamond, the cost of catalyst and tungsten carbide anvil occupies very large proportion in the total production cost. So it is of great significance to develop cheap catalyst and reduce the cost of anvil in the synthesis of diamond.Strong indicated that the advantages of using metal alloy as catalyst were that the synthesis temperature and pressure were lower than pure metal. The synthesis pressure could be dropped to 5GPa from 7Gpa. The scientific researchers of our country have done a large amount of work on iron-base catalyst too, and have get some comparatively prominent achievement. Now, almost all the domestic producers are using iron-base catalyst to synthesize industrial diamond. However, compared with NiMnCo, the synthesis pressure and temperature of iron-base catalyst are still higher. This undoubtedly lead to the higher anvil consumption in industrialization and higher production cost. So it is necessary to develop new catalyst material to solve the problem described above. XiaoPeng Jia Professor has proposed to develop cheap pure iron catalyst for industrial diamond synthesis, only that it still has following problems: firstly, needing higher pressure and temperature; secondly, the growth region of {100}is narrow, and the crystal is mostly octahedral; thirdly, there is more inclusions in the crystal. So pure iron is unsuitable to be used for synthsizing high grade diamond. Even so, because of the low price of pure iron powder catalyst, numerous scientific research workers are still devoted to research and develop on this respect.In this paper, using china-made cubic high-pressure apparatus, the growth characteristic of industrial diamond in the five different powder systems (NiMnCo+C+FeF₃, Fe+C+FeF₃, FeNi+C+FeF₃, FeNi+C+LiF, Fe+C+Si+FeF₃) were investigated separately under high pressure and high temperature conditions. And the effect of additive FeF₃, Si on the synthesis was also studied. It is found that the introduction of FeF₃ has inhibited the nucleation of diamond to a certain extent, and reduced the growth rate, and expanded the growth region of cubo-octahedral diamond. On the other hand, the introduction of Si has largely reduced the synthesis conditions for pure iron catalyst. There are also some other obvious effects of additive FeF₃ and Si on synthesis, such as the surface morphology, crystal shape and growth rate of diamonds. In this paper, optical microscope, SEM, XRD, Raman, etc. have been used to carry on relevant test and characteristics.In this paper, the growth region of cubo-octahedral diamond crystal was expanded in Fe+C+FeF₃, FeNi+C+FeF₃ system, and the growth rate of diamond was reduced. So the operability of synthesis in the actual course was enhanced, and the quality of crystal could be improved. The crystal with coarse surface and high index crystal surface {311} was successfully synthesized, which probably has some advantage on preparing diamond tools by enhancing the holding ability of the carcass to diamond, lengthening the service life of diamond tools, etc. And the temperature ranges for the synthesis of this crystal in every system was investigated and confirmed under certain pressure conditions for the first time.It is reasonably explained that the effect of additive FeF₃ on catalyst characteristic and its inhibition function on the nucleation. On one hand, the iron in FeF₃ had entered into metal catalyst, changed the already existing catalyst matching, which should lead to the change of the catalyst characteristics, such as melting point, flow ability, surface tension of metal liquid, and dissolving carbon ability of catalyst, etc. That is to say, the catalyst was poisoned. On the other hand, there was CF_x compound in the metal catalyst, so the carbon in diamond must react with CF_x during diamond nucleation and growth. Only if CF_x was excessive, the nucleation will be destroyed, and diamond will be graphitized, forming other compound of fluorum or carbon. These have inhibited the nucleation of diamond in the synthesis using iron, nickel alloy as catalyst.In the Fe-C-Si system, the introduction of Si has reduced the minimum synthesis pressure and temperature. So the growth range of cubo-octahedral diamond was expanded, and then high-quality cubo-octahedral diamonds were synthesized successfully. This takes an important step to develop the cheap pure iron catalyst.