关键词: 固体介质, 高温高压, 实验容器, 轴压标定, 围压标定

Abstract: Pressure calibration for solid medium vessel under high pressure and high temperature is an important step before apparatus is employed,because precise pressure calibration directly determines the preciseness of measurement of experimental pressure.Sound and effective methods are premises of pressure calibration.Pressure calibration includes confining pressure calibration and axial load calibration.The best way of axial load calibration is to estimate axial friction by multi-cycle of piston-in and piston-out.There are two key points during the test:(1)ensuring the hit-point of piston and sample:The hit-point is determined by an intersection of two beelines,one is the linear fit to the part of load-displacement curve of piston contacting with soft metal,the other is the linear fit to the part of load-displacement curve of sample's elastic deformation;(2)confirming dynamic friction:The dynamic friction which is dependent with displacement is established by the linear fit to the part of load-displacement curve of piston contacting with soft metal.Then,the final axial calibration includes cutting the load-displacement curve before hit-point,and correcting the load-displacement with dynamic friction.The best method for calibrating confining pressure is mineral phase transition,such as quartz-coesite,albite-jadeite + quartz,fayalite + quartz-ferrosilite and farringtonite-Mg₃(PO₄)₂-Ⅱ,because those phase transitions are more stable and the transition equations are widely used in previous calibrating confining pressure.It is proposed that quartz-coesite and albite-jadeite + quartz be used as pressure standards for the piston-cylinder apparatus in the pressure-temperature range of 2.5～3.2GPa,500～1200℃ and 1.6～3.2GPa,600～1200℃.Tests were performed for calibrating the axial friction using 2GPa confining pressure vessel.The sample is gabbro.Two experiments have been performed:(1)a number of cycle-experiments with different piston-rate under 500MPa and 820℃,1000MPa and 900℃,1000MPa and 25℃;(2)under 500MPa and 1000℃,firstly cycle-experiments were conducted,and then piston rate reduced from 2×10^-4mm/s to 5×10^-5mm/s after rock sample's plastic deformation,and the rate dependence of creep observed.The result of the experiment shows that the factors which affect the dynamic friction are confining pressure,temperature and piston rate.Confining pressure is the main factor,dynamic friction increases with the increase of confining pressure.Temperature and piston rate only influence on intercept.Hence,axial calibration should be conducted under specific experimental condition.Finally,axial calibration of an experimental load-displacement curve was conducted.

Key words: solid medium, high-temperature and high-pressure, axial pressure calibration, confining pressure calibration