Research On Some Typical Minerals Under High Temperature And Pressure

It is well known that all kinds of substances are in motion on some energy levels and exhibit some intrinsic properties. When the exterior conditions (i.e. pressure or temperature) have the energy levels changed, the physical, chemical and mechanical properties of a matter would also change. The inner matters of many celestial bodies are in high temperature and high pressure (HTHP) conditions. In the depth of the earth, there occurs HTHP surrounding. At present, in addition to HTHP research, there still are the following ways to study the depth of the earth: (1) comprehensive geophysical measurement at global scale. It can provide some physical parameters of the depth of the earth from the mantle to the centrosphere. But we could not get the information on the material component in each layer of the earth using this method. (2) ultra-deep probe-boring. It can reach the depth of 13Km, which is only 2‰of the earth radius. So the obtained data are limited to the scope of the lithosphere. (3) Research on aerolites and mantle rocks. Some information on the depth of the earth can be obtained, but it is not in-situ. In addition, quenching and stress-releasing must be taken into account. So in-situ measurement under HTHP is an irreplaceable mean to explore the component, state, property and evolvement of the inner matter.In the case that it is difficult to get directly the sample from the depth of the earth, HTHP research is one of the most direct way to realize and understand the inner structure of the earth and the properties of the inner matter. Its development makes it possible for geophysicists to realize the structure, component, property, state and evolvement of the depth of the earth, and to test the some kinds of models about the material component of the depth. Meanwhile, the experimental results may inverse and explain the large numbers of observed data, and can be a basis of the extrapolation of the geochemical data about the upper mantle. Many fatal geologic happenings, such as earth-quake, eruption of volcanoes, flow of magma and formation of minerals are tightly relevant to the structure, property and state of the matter in HTHP conditions.By means of the HTHP technology of , geophysicists have found that the structures of many minerals may change with the increase of pressure. So we can deduce the configuration of minerals in the depth of the mantle. The measurement of elasticity, electrical and thermodynamic property on the mantle minerals under the simulation of HTHP conditions in the mantle layer, can deduce the equation of state. This information is very important to explain geophysical data and to study the behavior of the mineral convection and evolvement in the mantle.In this paper, we study mainly the physical property of some typical minerals under ultra-HTHP. It includes XRD of the minerals in the transition layer of the mantle under HTHP in a diamond anvil cell (DAC) heated by laser, Raman spectra at high temperature heated by the resistance-wire, isothermal equation of state, Raman spectra of some sulfate minerals under HTHP in a DAC heated by laser.(1) In-situ energy dispersive X-ray diffraction measurements of enstatite have been studied by using diamond anvil cell (DAC) with synchrotron radiation and laser heating in the range of 0~23 GPa and 293~2000K. We have found that enstatite transform to wadsleyite phase at 15.3GPa and 1600K. At temperatures up to 2000 K and pressure up to 23GPa we have observed mixed phase of ilmenite and perovskite structure. The experiment further demonstrates that the density and seismic-wave velocity jumps are attributed to the phase transition of olivine and enstatite minerals(2) In-situ Raman spectra of Enstatite and Olivine have been studied in a temperatures range from 293K to 1113 K and at ambient pressure using resistance-wire heating. Temperature of the sample was measured by an alumel-chromel thermocouple. The vibration modes of Raman shift were validated at room temperature. We determined the temperature dependences of the Raman bands of Enstatite and investigated the changes of structure during increasing temperature.The Raman spectra of pyrope garnet have been studied. A new Raman peak near 743 cm-1 was observed in a bending vibration of the SiO4 tetrahedra frequency range at pressure about 28 GPa. We suggest that the new Raman peak results from the lattice distortion of the SiO4 tetrahedra. All the Raman frequencies continuously increase with increasing pressure. The average pressure derivative of the high frequency modes (650-1000 cm-1) is larger than that of the low frequency (below 650 cm-1). Based on the above data, the mode Grüneisen parameters for pyrope were obtained.(3)The in-situ synchrotron radiation diffraction of pyrope and olivine under high pressure has been studied with diamond anvil cell (DAC), using methanol - ethanol - water (16:3:1) mixture as transmission medium. We have not found any convincing evidence for a phase transformation or pressure-induced amorphization in the experimental pressure range. The equations of state of pyrope garnet and olivine were determined under pressure. The bulk modulus B0 is 199 GPa and 141 GPa , with B'0 fixed to 4, respectively.(4) The high-pressure and high-temperature behaviors of anhydrite (CaSO4) are studied up to 53.5 GPa and 1800 K using double-sided laser heating Raman spectroscopy and X-ray diffraction in diamond anvil cells. The evidence of phase transition from an anhydrite structure to the monazite type was observed at about 2 GPa under cold compression. Another phase transition and the change in color of sample from transparence to black have been also observed at pressure 33.2 GPa after laser heating. The new phase after laser heating persists till to 53.5 GPa and 1800 K and can only be partially preserved at ambient condition.