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

A triaxial deformation apparatus with 3 GPa molten salt medium pressure vessel was developed. It is based on the conventional Griggs design and the molten salt cell concept modified. There is a huge difference between apparent confined pressure and true confined pressure due to the friction in the assembly and the strength of the confined medium under high temperature and pressure. In this study, we used the partially molten method of LiCl-KCl to make the confined pressure calibration on the basis of the temperature calibration. We successfully observed the simultaneous variation of confined pressure displacement, axial stress and temperature disturbance when the specimen molten initially, then we calculated the true confined pressure by the given equation. Finally, we obtained a series of true confined pressure under different apparent confined pressure of 300~1 400 MPa. Additionally, we gave a interpretation about the friction in the pressure vessel. When the pressure is at 300~500 MPa, the friction percentage changed from 52% to 31.2% gradually. When the pressure is 700~1 200 MPa, the friction percentage dropped about 11.4%. When the pressure is 1 400 MPa, the friction percentage showed a slightly rise from 11.4% to 15.5%. The true confined pressure of the new pressure vessel is not only more accurate than the old one, it has reached the same level with the similar apparatus in other laboratories of the world.