Synthesis Of Boron-doped Diamond Single Crystal And Thermal Characterization

Boron-doped diamond has excellent corrosion resistance, thermal conductivity and semiconductor properties. It is widely applied in such fields as military and space technology and excellent results have been achieved; boron-doped diamond has excellent abrasion resistance performance and is very suitable to be used for grinding hard and ductile materials, with promising industrial application prospect. Flaky iron-based catalyst is prepared with cheap raw materials and simple methods and then high-quality boron-doped diamond is synthesized under HPHT. After that, further analysis was conducted for their semiconductor property, which is of great practical significance for improving the structure and performance of synthetic diamond crystals, expand its application range and improve the usage effects.Based on the boron source substance and the variety of trace elements, the quantity of influencing factors in the experiment is reasonably designed, the adding amount of many kinds of boron sources and trace elements is determined and then the boron-doped iron-based catalyst was prepared; meanwhile, compounding experiments of various compositions were carried out, which not only reduces the influence of environmental factors but also saves the cost, achieving excellent application effects. Thermal analysis method was adopted to characterize the synthesized diamond single crystalline, determine the relation between the thermal effects & weightlessness and heating temperature of the sample and calculate the apparent activation energy of radically oxidized diamond mono-crystalline. A comparative analysis can be conducted to sturdy the influence of adding amount of boron to the thermal stability of boron-doped diamond single crystal so as to provide theoretical analysis basis for the design of catalyst composition.This paper takes elementary metal as the main raw materials to prepare flaky boron-doped iron-based catalyst for powder metallurgy and prepare high-quality boron-doped diamond single crystal through optimized diamond synthesis technology. Then thermal analysis was conducted for the boron-doped diamond single crystal; then multiple scanning rate method was adopted to calculate the apparent activation energy when radical oxidization occurred and the relevancy between boron content and thermal stability of diamond single crystal is discussed.Boron-doped iron-based catalyst for powder metallurgy took elementary metal as the main raw materials and the experiments selected elementary iron powder, elementary nickel powder, graphite powder and a variety of boron-doped agent. Main constitutes of powder materials were analyzed via chemical analysis methods; D/max-yc model X ray diffractometer was adopted to determine the phase composition of powder materials and IRO-â…¡model infrared oxygen analyzer was adopted to determine the oxygen content of powder materials. The powder materials were tested to be in conformity with the related national standards and can be used for preparing boron-doped iron-based catalyst for powder metallurgy.According to the experiment requirement, the thickness ratio between the carbon film and catalyst is between 2.4 and 2.7, boron was added in trace amount according to the flaky catalyst preparation technological process to prepare the boron-doped iron-based catalyst for powder metallurgy. Through the reformation to the control system of synthetic diamond press, the pressure lifting was accurately suspended for two times; the pre-heating, synthesis pressure and power achieve dynamic matching. The pressure and temperature within the synthesis chamber were controlled to be ideal for the growth of diamond so as to synthesize high-quality boron-doped diamond.After the DAT experimental data of diamond single crystal was determined, Kissinger dynamic model was adopted to calculate out that the apparent activation energy of conventional diamond single crystal and boron-doped radically oxidized diamond single crystal is 165.34 KJ/mol and 428.37KJ/mol, respectively. Ozawa dynamic model was adopted to calculate out that the apparent activation energy of both kinds of radically oxidized diamond single crystal is 170.37KJ/mol and 423.20KJ/mol, respectively. It is proved that the apparent activation energy of boron-doped diamond single crystal is significantly higher than conventional diamond single crystal and therefore, the former has higher thermal stability. The calculation results of both kinds of dynamic models are similar, which displays that the calculation results of the apparent activation energy are basically reliable.According to the determination of apparent activation energy of radically oxidized diamond single crystals with different boron content, the DTA and TG data is in conformity with the calculation results of apparent activation energy. The sample with low boron content has the poorest thermal stability; however, the variation of thermal stability is not directly proportional to the boron content and a relatively optimal boron-doping quantity exists. When the boron-doped diamond single crystal is radically oxidized, the apparent activation energy decreases with the increasing amount of boron and the excess boron-doping is detrimental to the oxidation resistance performance of diamond single crystal. Therefore, the doping amount of boron carbide in the iron-based catalyst shall be further optimized so as to synthesize boron-doping diamond single crystal with higher thermal stability.