Yonggang Liu

A simple external resistance heating diamond anvil cell and its application for synchrotron radiation x-ray diffraction

A simple external heating assemblage allowing diamond anvil cell experiments at pressures up to 34 GPa and temperatures up to 653 K was constructed. This cell can be connected to the synchrotron radiation conveniently. The design and construction of this cell are fully described, as well as its applications for x-ray diffraction. Heating is carried out by using an external-heating system, which is made of NiCr resistance wire, and the temperature was measured by a NiCr-NiSi or PtRh-Pt thermocouple. We showed the performance of the new system by introducing the phase transition study of cinnabar (alpha-HgS) and thermal equation of state study of almandine at high pressure and temperature with this cell.

Note: Measurement method for sound velocity of melts in large volume press and its application to liquid sodium up to 2.0 GPa

Based on large volume press and conventional pulse-echo ultrasonic technique, we have overcome the difficulty in determining the length of liquid specimen under high pressure, and the sound velocity in liquid Na has been measured up to 2 GPa. The P-V data deduced by our sound velocity results through equation of state is in an excellent agreement with previous data directly determined by piezometer method. This new experimental technique is convenient and ready for use, being expected to advance investigation on thermodynamic properties of liquid metals and other melts under high pressure.

A broadband spectroscopy method for ultrasonic wave velocity measurement under high pressure

A broadband spectroscopy method is proposed to measure the ultrasonic wave phase velocity of Z-cut quartz under high pressure up to 4.7 GPa. The sample is in a hydrostatic circumstance under high pressure, and we can get longitudinal wave and shear wave signals simultaneously in our work. By fast Fourier transform of received signals, the spectrum and phase of the received signals could be obtained. After unwrapping the phase of the received signals, the travel time of ultrasonic wave in the sample could be obtained, and the ultrasonic wave phase velocity could also be resolved after data processing. The elastic constant of measurement under high pressure is also compared with previous studies. This broadband spectroscopy method is a valid method to get ultrasonic wave travel parameters, and it could be applied for elasticity study of materials under high pressure.

Hydrostatic pressure and temperature calibration based on phase diagram of bismuth

Under high-temperature and high pressure (HTHP) experiments, materials of small elastic modulus deform easily, and the length of the sample can be hardly predicted which lead to failure of ultrasonic velocity measurement. In this paper, a hydrostatic assembly of the sample for ultrasonic measurements is designed under HPHT, which can prevent plastic deformation. According to the abrupt change of travel time of the sample across the different phase boundaries of bismuth, the correspondent relation of sample pressure and oil pressure of multi-anvil apparatus can be calibrated, and the relation of sample temperature and temperature measured by thermocouple can also be determined. Sample pressure under high temperature is also determined by ultrasonic results. It is believed that the new sample assembly of hydrostatic pressure is valid and feasible for ultrasonic experiments under HTHP.

Measurement on Wave Velocities of Rock Glasses to 900°C at 1.0 GPa and Geophysical Implications

At 1.0 GPa, compressional and shear wave velocities (vp and vs) of seven types of glass were measured as a function of temperature up to 900°C and 730°C, respectively. Experimental runs indicated that with elevating temperature under high pressure, the compression of glass is responsible for the decrease in travel time in sample and the glasses show little change in height during cooling process. When the temperatures are lower than the glass transition temperatures (Tg), it is fitted that the temperature derivatives of velocities of the glasses are between −0.2×10−3 km·s−1·°C−1 and −0.7×10−3 km·s−1·°C−1 for vp and almost −0.1×10−3 km·s−1·°C−1 for vs, respectively. At higher temperatures (T > Tg), vp of the glasses decrease quickly with temperature derivatives between −0.8×10−3 km·s−1·°C−1 and −3.6×10−3 km·s−1·°C−1. According to the change in temperature derivatives of vp, the glass transition temperatures are determined to be between 584°C and 654°C. Using the Voigt-Reuss-Hill (VRH) average method, it is calculated that the wave velocities of the lower crustal rocks decrease with increasing glass content. Because of this, we suggest that the low velocity layer in lower curst is a function of the glass contents in rocks, which results in a decrease in the wave velocity of rocks in lower crust.