自支撑硼掺杂超细金刚石单晶颗粒合成新工艺

CVD boron-doping diamond powders are a new kind of super-hard abrasive, which have advantages over that of the powders obtained from crushing the large-size HPHT diamonds in the quality and manufacturability, and those synthesized by CVD directly without doping in the growth rate, antioxidant property, and so on. Hence, to study on the synthesis of CVD boron-doping diamond powders have already become a spotlight of research on abrasives. In the present work, on the basis of the method of hot filament chemical vapor deposition (HFCVD), a creative technology of the boron-doping combined with electrostatic device is proposed to achieve a dynamic growth for the free-standing microcrystalline diamonds, and then to explore the variation law and reason of quality, growth rate, and difficulty of crystals fall off from the substrate for the diamonds in the deposition process. Subsequently, the several deposition physical fields and CVD deposition parameters are optimized to promote the synthesis of a great many of microcrystalline diamonds simultaneously and homogenously but independently, by which novel technologies are obtained for fabricating the well-faceted microcrystalline diamonds with the various concentrations of boron-doping in a quantity production. Finally, the performances of boron-doping diamond powders, such as the crystal morphology, antioxidant capacity, machining properties, are evaluated. In this work, the research method integrating simulation calculations, theoretical analyses, and experimental preparations with properties characterization is adopted to perform the multi-disciplinary investigation (e.g., material, chemistry and mechanics) for researching the new method for fabricating free-standing boron-doping microcrystalline diamonds with the CVD. Therefore, this work lays foundations for the industrialized production of high-grade diamond powders synthesized by CVD, and also provides the new way for applying such diamond powders on the processing of iron group metals.

CVD掺硼金刚石微粉作为新型超硬磨料，克服了传统机械粉碎法金刚石微粉品级低、制备工艺性差的难题，有望解决无掺杂CVD金刚石微粉合成速率低、抗氧化性差等问题，探索其合成方法已成为超硬磨料领域的研究热点。本项目以热丝CVD法为基础，创新提出了掺硼与静电振荡相结合的工艺，突破颗粒静止生长模式，研究CVD自支撑金刚石单晶颗粒生长质量、速率、及与衬底脱附等参数的变化规律及原因；优化适合多颗掺硼金刚石颗粒同时均质生长的物理场以及CVD沉积工艺参数，获得适合不同浓度硼掺杂自支撑超细金刚石单晶颗粒的批量合成新技术；进而对其晶形质量、抗氧化性、加工性能等进行评价。本项目采用工艺实验、仿真模拟、理论分析、性能检测相结合的方法，开展材料、化学、机械等多学科交叉研究，探寻自支撑掺硼超细金刚石单晶颗粒制备新方法，为CVD高品级金刚石微粉的产业化应用打下基础，同时也为金刚石微粉在铁族金属加工领域的应用提供新的思路。

传统机械粉碎法制备的金刚石微粉 (<38 μm)品级低、制备工艺性差，利用CVD技术直接合成金刚石颗粒是解决上述问题的有效途径；然而CVD合成超细颗粒在国内外均属于一个较新的课题，其合成颗粒的各项性能都尚存在很大优化空间，探索提高CVD颗粒的合成质量、性能、及生产速率的新技术，以及开发其配套的自支撑新方法是非常有必要的。.本项目基于热丝化学气相沉积法，提出了新型栅状衬底，显著增加金刚石颗粒的有效沉积面积，相较于传统平面衬底，金刚石颗粒的单次沉积量提高5-7倍；采用双面氧化硅基衬底，利用化学腐蚀快速去除1000 nm 的SiO2过渡氧化层，再辅以高速离心技术，可获得自支撑 CVD金刚石单晶颗粒。本项目在氢气-丙酮反应体系中引入硼酸三甲酯（B(OCH3)3）作为硼源，分别针对有籽晶、无籽晶两种金刚石单晶颗粒生长模式，揭示掺硼工艺对CVD金刚石单晶颗粒生长特性的影响：硼元素的加入可提高单晶颗粒的生长速率约1.2-2倍（当[B]/[C]gas=10000 ppm时，单晶的生长速率约为本征条件下的2倍左右）；对于无籽晶，重掺易引起颗粒多发二次形核，但颗粒整体仍呈现较高的圆度，仍属于优质颗粒晶形；对于有籽晶，随着硼浓度的增加，修复后的籽晶形貌变化不显著，但基体的自发形核率明显增多，造成颗粒粒径分布不均匀的问题。在此基础上，利用有限容积法和多次仿真，探索适用于栅状衬底的热丝及进出气口排布方式，优化结果可有效保证衬底各处硼掺杂单晶颗粒金刚石生长粒度和质量的均匀性，结合沉积参数优化，获得了适合于CVD硼掺杂单晶金刚石微粉批量合成的新技术。最后，本项目对CVD硼掺杂单晶金刚石微粉的粒度分布及晶形质量进行了测试研究，并与JB/T 7990-2012金刚石微粉行业标准相比，CVD无籽晶掺硼颗粒在晶形质量和粒度分布范围上均满足或高于标准规定，CVD有籽晶掺硼微粉中80%的颗粒都具有高品级单晶晶体形态，但粒度分布范围过大，无法满足标准需求，需辅以粒度筛选工艺。本项目的研究内容有利于进一步明确硼元素对CVD金刚石生长性能的影响，并为CVD硼掺杂金刚石微粉的产业化应用打下基础。