Axial Friction Calibration for 3 GPa Molten Salt Medium Triaxial Pressure Vessel under High Pressure and High Temperature

The axial friction calibration of 3 GPa molten salt medium triaxial pressure vessel under high pressure and high temperature is performed based on the calibration of the temperature and confining pressure of the apparatus, which mainly analyses the effects from different experimental conditions, such as the confining pressure, the temperature, and type of salt cell used around the sample. The results show that the axial friction includes static friction, squeezing friction and sliding friction between the piston and the surrounding material. Three types of friction play different roles in axial stress, in which sliding friction is the main factor that affects axial stress precision, while static fiction and squeezing friction have little effects on axial stress. The static and sliding frictional force has a positive correlation to the confining pressure. The axial piston velocity has a positive effect on static friction, too, but the effect is not significant, while it has no effect on sliding friction. Both static and sliding friction has a negative correlation to the experimental temperature, and the effect of temperature is significant. The type of salt cell has a great effect on axial friction. The axial friction drops dramatically as the experimental temperature approaches the melting point of the salt. The procedure of calibrating axial friction is made based on the results, and the axial friction calibration is applied to stress-strain curves for deformation experiments of amphibole. It is found that it is more reliable that the deformation curve with the calibration of axial friction than the curve without calibration.