【作者】 吕世杰；

【导师】 洪时明；

【作者基本信息】 西南交通大学 ， 一般力学与力学基础， 2010， 博士

【摘要】 高压物理学是研究物质在高压作用下物理性质的一门学科,属于极端条件下的凝聚态物理学,其研究内容包括物质在高压下的力学、热学、光学、电学、磁学性质,以及物质的微观结构,状态方程,相变等等,也为发现新现象、新规律、高压下合成新材料提供理论和实验依据。高压研究依赖各种高压设备,在大腔体静态高压设备中,六含八多压砧高压装置能获得的温压条件范围较广,各种原位测量技术的配备,使其在材料学、地球与行星物理学、矿物学、岩石学等研究领域扮演着越来越重要的作用。本论文共分为两个部分,第一部分为滑块式六含八大腔体高压装置的调试和标定工作；第二部分为高压合成金刚石新触媒体系的探索和发现。(一)滑块式六含八大腔体高压装置调试和标定。以本实验室新建的滑块式六含八大腔体高压装置为对象,介绍了其独特的机体构架和高压模具的设计特点,一级压砧优异的同步性及实验的重复性,以及六含八式二级增压系统的样品组装。根据压砧的定位因素和挤压块受力形变特点,探索出快速校准一级压砧的方法,使得更换和校准压砧快捷而准确。并使用本实验室开发的加工夹具,成功地制作出叶腊石八面体传压介质、密封边等部件,还总结出用于高温高压实验的叶腊石的焙烧工艺条件。在此基础上,成功地利用金属Bi丝和半导体粉末ZnTe材料对12.5／8(八面体边长／二级压砧截角边长)样品组装进行了压力标定,标定点对应压力分别为2.55,7.7,9.6和12.0GPa；进而,在10GPa压力下,利用WRe3-WRe25热电偶将温度标定到1560℃,结合铁碳二元高压相图以及堵头处石墨加热炉转变为金刚石的温度点,验证了标定结果的正确性,给出样品腔内的轴向平均温度梯度约为21℃／mm。这些工作为本实验室六含八高压装置的应用打下了基础,可以对10mm3的样品在12.0GPa,2000℃的条件以内开展高温高压实验。(二)高压合成金刚石新触媒体系的探索和发现。金刚石具有多种优异的物理和化学特质：最高硬度,最高热导率,最宽的透光波段,禁带宽度宽,介电常数小,抗强碱和强酸腐蚀等等,使它成为不可替代的功能材料,被广泛应用在工业、科技、国防、装饰等许多领域。人工合成金刚石的方法有许多种,目前,高温高压触媒法仍然是主要的合成方法。在过去的几十年里所发现的触媒体系有多种类型,不同体系需要的温度压力条件也不相同,迄今报道的触媒的最高压力为8.5GPa。我们认为在更高压力条件下可能还存在新的触媒体系。于是,使用滑块式六含八大腔体高压装置,在压力9.0-9.6GPa,温度1600-1850℃的条件下,对锡(Sn)铅(Pb)合金、锑(Sb)、铋(Bi)、硒(Se)、碲(Te)等添加物与石墨共存体系展开了金刚石触媒探索实验。发现在9.6GPa,1800-1850℃的高压高温条件下,单质元素硒(Se)和碲(Te)分别对石墨转变成金刚石具有明显的触媒作用。保持条件不变,当合成时间由30min延长到60min时,金刚石成核量有明显增加,粒度平均尺寸提高近一倍,合成晶体形貌多为八面体。而Sn-Pb合金和Sb,Bi在相近实验范围内都没有这种作用。根据这些结果,参考理论计算值和相关参数,提出了关于Ⅵa族元素对石墨转变为金刚石的触媒机理的一种解释：氧族元素(O、S、Se、Te)具有相同的外壳层电子结构,有利于它们在高温高压下和碳原子发生氧化反应,生成碳的化合物(CX或CX2),反应是可逆的,还原分解出的碳原子以金刚石相成核并生长,随着反应的持续,亚稳态石墨相的碳原子可以通过这种氧化-还原过程不断转化为金刚石相碳原子,促进金刚石的晶体生长。更多还原

【Abstract】 High pressure physics is a special subject to investigate physical behaviors of substance under high pressure, and belongs to the condensed matter physics under extreme condition. It includes mechanics, optics, electricity, magnetism, microstructure, equation of state and phase transformation of materials under high pressure. High pressure researcher can provide a great of theoretical and experimental evidence to discover the new phenomena or new principle, and to synthesize new materials. High pressure research relies on a variety of equipments. In the static high-pressure equipments, the 6/8 mult-anvil large volume apparatus has powerful capability to generate pressure and temperature, combined with synchrotron radiation measurement techniques it plays an important role in Material Science, Earth and Planetary Physics, Mineralogy, Petrology and other fields. This dissertation is divided into two parts, one is about the debugging and calibration of a slide-type 6/8 multianvil large volume high-pressure apparatus, and another is an exploration and discovery of new catalyst system for diamond synthesis under high-pressure and high-temperature.In the first part, regarding to the slide-type 6/8 multianvil large volume high-pressure apparatus, we introduce the unique design about main framework and high-pressure mold, excellent synchronicity and reproducibility of the first-stage anvils and assembly of second-stage anvils with sample for HP-HT experiments. The first-stage anvils are linked respectively with slide blocks, they can move and construct a cubic space with the three upper and three down symmetrical distributions. According to positioning factors of the anvils and character of the test block, we found a practical method to calibrate the first-stage anvils, which made the process of replacement and adjustment of anvils quick, easy and exact. By using a series of special holders in lathe we produced pyrophyllite gasket, including octahedral bulk, sealing pieces etc., and also set up the appropriate condition and program for the heat treatment of pyrophyllite pressure medium. The cell pressure was calibrated successfully at room temperature for 12.5/8 (octahedron edge-length/truncation edge-length of two-stage anvil) sample assembly by using known phase transition of bismuth and semiconductor powder of ZnTe at pressure of 2.55,7.7,9.6 and 12.0GPa, respectively. Under the pressure of 10GPa, the cell temperature was calibrated up to 1560℃by a WRe3-WRe25 thermocouple. Combined with the high pressure phase diagram of Fe-C and the observation of diamond formed on the interface between graphite heater and steel plug, we not only reconfirmed the temperature calibration result, but also estimated the axial temperature gradient (～21℃/mm) in cell. This work showed that the apparatus can be applied for high pressure experiments within the range of the sample size of 10mm3, high-pressure and high-temperature conditions of 12.0GPa and 2000℃.Second part is the exploration and the discovery of new catalyst system for diamond synthesis under high-pressure and high-temperature. Diamond has unique physical and chemical properties, such as highest hardness and thermal conductivity, wide band gap, high insulativety, resisting to alkali and acid, etc., and so as an irreplaceable functional material it is widely applied in the industry, science and technology, national defense, decoration and others. Many kinds of methods have been used in diamond synthesis, at present the main method is to add catalyst into graphite for converting to diamond at HP-HT. Many catalyst systems have been found in the past several decades, they are active in the different pressure and temperature conditions respectively. Up to now the highest pressure for synthesis diamond by adding catalyst was 8.5GPa. Considering latent catalyst system exists possibly at higher conditions, we investigated five systems:tin (Sn)-lead (Pb) alloy, antimony (Sb), bismuth (Bi), selenium (Se), tellurium (Te) with graphite under high-pressure of 9.0-9.6GPa and high-temperature of 1600-1850℃by using the slide-type 6/8 large volume press. The results showed that elements selenium (Se) and tellurium (Te) have obvious catalytic action for diamond synthesis under pressure at 9.6GPa, and temperature 1800 and 1850℃respectively, but Sn-Pb alloy, Sb and Bi do not. In the new catalyst systems, when reaction time extended from 30 to 60 min at the determinated synthetic conditions, the nucleation of diamond advanced and the average size increased remarkably. The morphology of the euhedral crystals obtained from the new systems was mostly octahedron. According to the experimental results, theoretic calculation and correlative thermodynamic data, the catalytic mechanism of group VI elements for conversion from graphite to diamond is suggested as follows:the group VI elements (O, S, Se, Te) have a similar outer shell electron configuration, which helps them react easily with carbon (graphite) to form some carbides (CX or CX2) under HP-HT conditions. With the reversible reaction, the carbides can also decompose into the thermodynamic stable diamond phase. Therefore, metastable graphite can convert to diamond crystals in the systems, and the diamond grows continuously with the reaction time.更多还原