纳米聚晶金刚石的高温高压制备
发布时间：2018-07-15 18:32
【摘要】：金刚石是自然界中最硬的材料。由于其优异的力学性质,而被广泛应用在工业加工、航空航天、地质勘探、国防建设等领域。由于金刚石单晶具有各向异性和较高的脆性,在受到外力冲击时容易沿(111)解理面解离,从而限制了单晶金刚石在自身加工和抗冲击等方面的应用。纳米聚晶金刚石(NPD)具备优于天然金刚石的各向同性、良好的韧性、耐磨性和热稳定性等,以及硬度不低于天然金刚石,具有更广阔的的应用空间。无添加剂石墨在高温高压下直接转变为纳米聚晶金刚石是获得优异力学性质NPD的最理想的途径。然而,利用石墨直接合成NPD需要极高的压力和温度,在较低的温度和压力下,石墨只能部分转化为金刚石。此外,制备NPD的前驱物中,包括玻璃碳、洋葱碳、炭黑、石墨等,以石墨为前驱物制备出的NPD所需要的条件最为苛刻,但制备出的NPD硬度最高,并且具有较高的断裂韧性和高温抗氧化性。因此,制备优质的纳米石墨前驱物、探索由石墨直接转化成NPD的实验条件及其机理,不仅优化合成条件使其能在工业化生产具有重要的意义,而且对研究石墨与金刚石的相变路径具备重要的科学意义。为了研究纳米聚晶金刚石的合成,本论文首先对国产六面顶液压机高压装置和Walker型六-八压机的样品腔体进行压力和温度的标定,并设计出一套适用于国产六面顶高压装置的高压样品腔体高温组装,温度可达2000℃以上,提高了六面顶合成腔极端条件下的稳定性能;确定了国产六面顶和Walker型六-八压机系统油压与合成样品腔压力之间的关系,获得了油压与实际腔体压力的曲线关系;标定了六-八压机高压样品腔的温度。为后续实验的进行提供了压力和温度的参考依据。利用高能球磨制备出纳米石墨粉,作为合成纳米聚晶金刚石的前驱物,得到了不同的球磨条件与纳米石墨粉粒径之间的关系。利用得到的纳米石墨粉,在六-八高压装置中,高温高压合成方法在18 GPa,2100℃到2300℃之间实现了石墨到金刚石的转变,合成出了纳米聚晶金刚石体材料。样品微区XRD测试结果显示:高温高压下,前驱物烧结后的样品在2100℃和2300℃均合成出了立方相的金刚石;前驱物未烧结的样品,虽有立方相金刚石的产生但是XRD测试结果表明样品转化不完全。拉曼测试结果表明样品中在1330 cm-1处均有拉曼峰,为金刚石一阶拉曼谱线。通过扫描电镜分析结果显示合成出的纳米金刚石的颗粒在15 nm左右,维氏硬度仪测量结果表明前驱物烧结过的样品维氏硬度高达140GPa。这一结果大于单晶金刚石最大值(120 GPa)近17%。这一结果再次证实,NPD是一种性能优异的超硬材料。
[Abstract]:Diamond is the hardest material in nature. Because of its excellent mechanical properties, it has been widely used in industrial processing, aerospace, geological exploration, national defense construction and other fields. Due to the anisotropy and high brittleness of diamond single crystal, it is easy to dissociate along (111) cleavage surface when it is impacted by external force, which limits its application in self-processing and impact resistance. Nanocrystalline diamond (NPD) is superior to natural diamond in isotropy, good toughness, wear resistance and thermal stability, and its hardness is no less than that of natural diamond. The direct transformation of graphite without additives to nanocrystalline diamond at high temperature and high pressure is the best way to obtain NPD with excellent mechanical properties. However, the direct synthesis of NPD from graphite requires very high pressure and temperature. At low temperature and pressure, graphite can only be partially converted into diamond. In addition, among the precursors for the preparation of NPD, including glass carbon, onion carbon, carbon black, graphite and so on, the conditions required for the preparation of NPD with graphite as precursor were the most severe, but the hardness of NPD was the highest. It also has high fracture toughness and high temperature oxidation resistance. Therefore, it is of great significance to prepare high quality nano-graphite precursors and explore the experimental conditions and mechanism of direct transformation from graphite to NPD, which not only optimizes the synthetic conditions, but also can be used in industrial production. Moreover, it is of great scientific significance to study the phase transition path between graphite and diamond. In order to study the synthesis of nanocrystalline polycrystalline diamond, the pressure and temperature of the high pressure device and the sample chamber of Walker type 6-8 press were calibrated firstly in this paper. A set of high-pressure sample cavities suitable for domestic six-sided top-high pressure device is designed, which can be assembled at a temperature of more than 2000 鈩，
本文编号：2125005
[Abstract]:Diamond is the hardest material in nature. Because of its excellent mechanical properties, it has been widely used in industrial processing, aerospace, geological exploration, national defense construction and other fields. Due to the anisotropy and high brittleness of diamond single crystal, it is easy to dissociate along (111) cleavage surface when it is impacted by external force, which limits its application in self-processing and impact resistance. Nanocrystalline diamond (NPD) is superior to natural diamond in isotropy, good toughness, wear resistance and thermal stability, and its hardness is no less than that of natural diamond. The direct transformation of graphite without additives to nanocrystalline diamond at high temperature and high pressure is the best way to obtain NPD with excellent mechanical properties. However, the direct synthesis of NPD from graphite requires very high pressure and temperature. At low temperature and pressure, graphite can only be partially converted into diamond. In addition, among the precursors for the preparation of NPD, including glass carbon, onion carbon, carbon black, graphite and so on, the conditions required for the preparation of NPD with graphite as precursor were the most severe, but the hardness of NPD was the highest. It also has high fracture toughness and high temperature oxidation resistance. Therefore, it is of great significance to prepare high quality nano-graphite precursors and explore the experimental conditions and mechanism of direct transformation from graphite to NPD, which not only optimizes the synthetic conditions, but also can be used in industrial production. Moreover, it is of great scientific significance to study the phase transition path between graphite and diamond. In order to study the synthesis of nanocrystalline polycrystalline diamond, the pressure and temperature of the high pressure device and the sample chamber of Walker type 6-8 press were calibrated firstly in this paper. A set of high-pressure sample cavities suitable for domestic six-sided top-high pressure device is designed, which can be assembled at a temperature of more than 2000 鈩，
本文编号：2125005
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