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

摘要： 固体介质压力标定一般分为2方面。其一是轴压标定,最有效的方法是轴压活塞反复前进和后退,根据活塞循环来获得摩擦力的大小,其中有2个关键环节:1)活塞和样品接触点的确定;2)动摩擦力的确定。其二是围压标定,最有效的方法是利用矿物相变,适用于固体压机压力标定的相变有:石英-柯石英相变、钠长石-硬玉+石英相变,其适合温压范围分别为:500～1200℃、2.5～3.2GPa,600～1200℃、1.6～3.2GPa。我们对2GPa固体介质高温高压实验设备进行了轴压标定,在不同温度、围压、活塞速率等条件下进行了实验,结果表明:围压、温度、活塞运动速率等因素都对动摩擦力有不同程度的影响。因此,轴压标定应该针对不同的实验条件分别进行。

关键词: 固体介质, 高温高压, 实验容器, 轴压标定, 围压标定