The New Technology Of Temperature-pressure Measurement And Pressure Relaxation In Diamond Anvil Cell

As a widely used high pressure generating device,diamond anvil cell is an effective tool to obtain physical and chemical properties of materials under extreme pressure conditions.With the development of technology,in-situ detection technology under high pressure based on DAC continues to expand,which makes high-pressure science to cover more scientific fields.However,high-pressure technology in DAC still faces some basic problems to solve,such as the elimination of pressure gradient in the case of no pressure transmission medium and accurate calibration of pressure,temperature loading and accurate detection of samples.The reliability and accuracy of high-pressure physical property measurement are directly affected by these basic problems which also limit the application field of DAC.In this paper,a series of new methods for pressure gradient processing,temperature loading and test are proposed for the basic problems of DAC devices.The authors study the pressure variation trend and stability conditions in DAC,and give some methods to eliminate the pressure gradient.A new technology and device for coaxial dual-pressure chamber DAC for temperature-loading and in-situ measurement under high pressure was invented.The results were showed as follows:1.Pressure relaxation in DAC pressure chamberUnder the non-hydrostatic pressure,we have systematic studied the experiments of the radial / axial pressure distribution,pressure release and equilibrium,the effect of temperature on the release and equilibrium of axial pressure,and the electrical impedance measurement and contrast experiment of olivine powder crystal sample under stable pressure in the DAC chamber.The results showed that the radial/axial pressure in the chamber were presents a regular gradient distribution when the powder sample was pressed instantaneously in the DAC without pressure transfer medium,and this phenomenon would be more pronounced with increasing of pressure.When the initial pressure increased,the pressure gradient became more significant.In the radial direction,the pressure at the edge point can reach 9.2 GPa when the center point of the chamber was pressurized to 6.1 GPa.In axial direction,when the pressure surface was 12.9 GPa,the pressure at the bottom of the chamber was 10.2 GPa.The pressure gradient continued to slow down and finally reached the pressure equilibrium in the pressure chamber,at the same time,the overall pressure in the pressure chamber decreased significantly.In the pressure range studied in this paper,the maximum pressure dropped after relaxation reached 32.6% in radial direction and 34.9% in axial direction.The pressure balancing process would continue for tens of hours at room temperature.As the initial pressure increased,the time required for pressure balance also increased.The time for pressure balancing could be reduced to tens of minutes under the condition of properly heating the sample.Heating the sample immediately after applying pressure could lead to the pressure reduce nearly 30%.However,the maximum pressure drop was less than 6% after pressure balance.The heating of sample was an effective method to speed up the process of pressure equilibrium and maintain pressure stability without causing sample phase transformation.In-situ olivine impedance test under high pressure results showed that: in the process of pressure relaxation,the impedance spectra of different periods were significantly different.As the pressure gradually approached equilibrium,the impedance spectrum gradually approached a certain value.The results showed that the changes of pressure distribution caused by pressure relaxation in the pressure chamber had a significant influence on the experimental results.2.New method of DAC heating and temperature measurementFor the problem of temperature measurement of DAC,we have completed the design and preparation of temperature measuring composite gasket,pressure chamber heating composite gasket and heating temperature measuring composite gasket through the design of composite gasket.Preparation and actual test proved that the heating condition of the sample can be improved effectively by the temperature measuring composite gasket,the heating composite gasket and the heating temperature measuring composite gasket.Comparing with existing technology,the heating temperature measuring composite gasket greatly reduced the complexity of preparation process,and it can achieve stable heating temperature field in the pressure chamber,and measure the stable real-time temperature of the sample chamber while heating.Because the inert platinum was used as heater,the gasket can effectively inhibit sample contamination,and effectively improve the success rate of the experiment.In this paper,the composite gasket had a rapid temperature response and stable process,the heating effect was obvious,and the temperature could be raised stably to 1400 K.3.Diamond anvil cell with double coaxial chambersAccording to the pressure measurement problems faced by the high-pressure heating experiment,a novel DAC device was designed and fabricated in this paper.The main body of this DAC was composed of sample module,pressure transmitting water cooling module and calibration pressure module.The design of sample and calibration pressure module refer to the large window design of four column DAC,which can provide a large operating space for electrical and lateral XRD detection tests.Inner part adopted the way of matching spherical cushion seat with parallel seat,which was helpful to quickly complete the disassembly and leveling.Pressure transfer water cooling module with water cooling chamber combined with the module of supporting water cooling to refrigerate DAC and ensured that the calibration pressure module can't be influenced by the heating of sample chamber.The innovation of the new DAC was embodied in the design of coaxial double pressure chamber.The calibration and sample modules worked together by sharing a set of guidance systems.It not only realized the measurement of the pressure of the heated sample chamber at room temperature,but also realized the space separation between the sample and the standard pressure material(such as ruby,etc.),which effectively eliminated the pressure measurement error caused by the pyrolysis of the calibration-pressure material or the reaction with the sample or the sample contamination.4.Comprehensive application test of new DAC and gasket preparation technologyIn order to study the comprehensive performance of the experimental measurement system composed of DAC with double coaxial chambers and heating temperature measurement technology,we took the temperature and pressure characteristics of SiO2-H2 O system as the entry point of research,and completed the measurement and analyzed of cooperativity and stability between realization of temperature and pressure with test measurement.According to the analysis of the experimental process and results: SiO2-H2 O as a simple mineral fluid binary system,the solubility temperature of solid SiO2 in the miscible component gradually decreased with the increase of ambient pressure,and the resistance of miscible material decreased first and then increased with the increase of temperature under constant pressure,indicating that the transport properties of active ions in miscible materials tended to change with temperature.The study also showed that the experimental measurement system composed of DAC with double coaxial chambers and heating temperature measurement technology not only had good coordination in temperature loading,temperature measurement and pressure calibration,but also had excellent compatibility with spectral and electrical detection.