| Measurement techniques for in-situ rheological investigations under high pressure allow insight into the phenomena governing the microstructural modifications. The conventional mechanical methods can not be operated to this aim due to their inherent limitations. This is why ultrasonic methods for the measurement of the viscosity of liquids under high pressure were introduced. Among them, the methods using SH surface acoustic waves are the most sensitive. To this end, the authors have applied new ultrasonic methods, i.e., the Love wave method and the Bleustein-Gulyaev (B-G) wave method. The measurements of the viscosity of liquid (castor oil) were carried out in function of hydrostatic pressure up to 800 MPa. During the measurement we stated the phase transformation of castor oil and the presence of the hysteresis of the dependence of viscosity on pressure. To the authors’ knowledge, the measurement of the viscosity of liquids under high pressure during the phase transition and during the decompression process is the novelty. |