The Application Of α-β Quartz Transition To Pressure Calibration In The High Temperature And High Pressure Experimental System

As a significant branch of modern geophysics, experimental research at high temperatures and high pressures is an important approach to explore substance deep in the earth and to discover secret in the earth interior. Measuring the physical characteristics of rocks or minerals in situ, petrophysical experiments can provide effective constraints on the interpretation of geophysical surveys.The piston-cylinder type device with solid confining pressure medium, by which some complex settings deep in earth could be simulated, is popular in experiments on natural rock samples. In the laboratory of petrophysics under the high temperature and high pressure, the upper limits of pressure and temperature of this type of device are 1.5 GPa and 1200℃, respectively. In recent years, the lab has been changed and advanced a lot. The precision of data collection as well as the experimental control program have been improved. Furthermore new sample chambers are used in which the pressure loss, the temperature distribution and displacement are unknown. Therefore, experiments should be prepared and carried out for the experimental system calibration.The experimental system calibration includes three aspects: displacement calibration, temperature calibration and pressure calibration.1. Displacement calibration. In the experimental design and assemblage, natural pyrophylite has been used as the solid confining pressure medium. The experimental results have shown that natural pyrophylite is well fit for pressure confining. The two soft materials, pyrophylite and the experimental sample, are the main body of experimental compression bearing the pressure loaded. Thus, the experiment was carried out with corundum as the sample to determine the displacements of pyrophylite assembly under pressure. The values could be used as a reference to estimate the compression or length of the experimental sample in future experiments, and thus revise the velocity preliminarily.The experimental results show that the curve of load pressure (L) and displacement (D) can be divided into two segments:One is the cranny closure and pressure-deduced compression segment with the load pressure upper limit 2.0MPa. The curve is a conic, and its expression is: D=-90.55L~2+881.27L-4529.76,R~2=0.9994.Another is the pressure-deduced compression segment with the load pressure over 2.0MPa.The curve is an excellent line, and its expression is:...