| 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.
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