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Study on Rheology of the Pyrophyllite&Ultrahigh Pressure Technique for the Cubic Press

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Tutor: WangDaWei; FangXiaoHu; YuZuoJun
School: Central South University
Course: Mineral prospecting and exploration
Keywords: pyrophyllite,ultrahigh pressure technique,rheology,cubic anvil high-pressure app
CLC: TQ164
Type: PhD thesis
Year:  2011
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Pyrophyllite, a kind of phyllosilicate minerals with least water content exhibits alayered structure, this special structure and composition determine its physical and chemical properties. This mineral was characterized by small internal friction coefficients, low expansion coefficient, high refractoriness, low thermal conductivity and wide dewatering temperature, volume stability, internal friction coefficients increases with confining pressure etc. Pyrophyllite is a excellent pressure transmitting medium. It is widely used in metallurgy, building materials, light industry, petroleum, chemical industry, electrical appliance industry and agriculture.Through the study of the flow and deformation pattern of pyrophyllite under high pressure, the author analyzes its mechanism of sealing and pressure transmitting performance in cubic press, and systematically summarizes the researches on technology of cubic press in the past few decades. This paper put forward "the final state symmetry" theory of ultrahigh pressure technique about cubic press, which has improved the process design about ultrahigh pressure cell and pressure transmitting medium and acquired succeed application in dimond synthsis. This research results play a significant role in the development of new pressure transmitting medium and potentials of cubic press. Also, this study is instructive in new synthetic technology of superhard material.The most significant innovations of this research are as follows: 1. For the first time, the ultrahigh pressure cell of cubic press is divided into two regions, and their role is discussed respectively. The pressure-distance curve and pressure-flow weight curve of pyrophyllite under ultrahigh pressure was determined. Also these two curves has been used to study the rheology of pyrophyllite, which revealed the law of plastic flow and static compression of pyrophyllite under ultrahigh pressure.2. For the first time, the relationship between internal friction coefficient and flow weight of pyrophyllite and the structure size of cemented carbide anvil was established, this research analyzes these parameter, providing theory basis and scientific calculation method to design structure of cell in cubic press.3. It was found that pyrophyllite accomplished plastic deformation in the lower pressure, and then entered the elastic compression process. Under the ultrahigh pressure, the density of pyrophyllite is greater than the density under atmospheric pressure. The anvil top size has the greatest influence on sealing of pyrophyllite. Results obtained from the study of flow law of pyrophyllite under the ultrahigh pressure can be used to find the right way for the realization of seal and effective pressure transmission. From theoretical and experimental aspects, it was demonstrated that large cell has a better sealing performance.4. Expressing the principle of shape reinforcement theory and stress reinforcement theory of ultrahigh pressure mold design in a concis mathematical language. And "three centre-in-one point" principle of was studied, whuch offer guidance on equipment design, process, usage and maintenance of cubic press.5."The final state symmetry" theory was raised through the study of pyrophyllite flowing deformation law. The final work state of ultrahigh pressure cell must be able to keep tight and able totransmit pressure. At the same time, in order to meet the needs of static equilibrium, the final work state ultrahing pressure cell must be exactly symmetric, while the initial state might not be symmetric."The final state symmetry" theory serves as theoretical basis for a new ultrahigh pressure cell structure design."The final state symmetry" gave theoretical basis of theory for the design of a new ultrahigh pressure cell structure. And the relationship established between carbide anvil and pyrophyllite structure size provided a calculating method for the design of them.6. Systematically explaination of "the final state symmetry" theory of the cubic ultrahigh pressure technology. This research lays a theoretical fundation for structural design of the pressure transmitting medium and ultrahigh pressure cell. According to this new theory, enlarging the diameter of ultrahigh pressure cell from ¦µ42mm to ¦µ48mm, the capacity would increased by30%with the cubic press which cylinder diameter is ¦µ560mm. Also, the anvils consume was obviously decreased. In this case a new cell designed by this theory is a revolutionary change for the reason that not only it reaches the device potential but also maintain its stability.
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