| At present,in-situ measurements of material dynamics,optics,electricity,magnetism,etc.have been achieved and physical parameters such as atomic arrangement structure,lattice vibration mode and electronic energy level structure have been obtained under the extreme environment of diamond anvil cell(DAC),which provide important data and scientific rules for many fields such as earth science,materials science,and physics.However,there are still many problems need to be overcome for the in-situ thermal transport properties measurements based on DAC under high temperature and high pressure.It can be imagined that if the in-situ detection of all physical quantities such as force,heat,light and electricity can be realized in DAC,it is bound to provide a broader vision for experimental scientific research,and more strange phenomena will be revealed,thus promoting the development of high temperature and high pressure science.In this paper,a set of schemes for in-situ thermal conductivity measurement is proposed based on DAC under the constant temperature conditions.The temperature of the designated experimental point is measured under the actual extreme environment,and the measured temperature data is substituted into the finite element analysis as a constraint condition.The finite element analysis method is used to calculate the temperature field distribution of the DAC and obtain the computational temperature data at the same position as the experimental measurement point.Finally,the thermal conductivity of the sample is determined by comparison with the actual measured temperature data.In order to provide a stable and controllable temperature gradient field in the DAC,modification was performed on the DAC.Two ceramic resistance-heating rings were introduced in the DAC.One of the rings was located inside the groove of the plate seat,and the other was located on the platform of the spherical seat.Mica slices were introduced to effectively reduce the influence of environment factors on the measurement and the design of the spherical seat and spherical seat base facilitated the thermal insulation and adjustments of the device.An external water cooling system was introduced to achieve fine control of temperature and avoidance of the pressure loss under high temperature.In addition,in order to minimize the effect of thermal exchange and thermal convection of air,the whole system was placed inside a vacuum chamber during the measurement.The temperature gradient inside the DAC was generated and controlled by independently tuning the power of the heating rings.The new thermal conductivity measurement scheme is based on the temperature distribution of diamond anvil,the measurement precision is dependent on the geometrical dimensions and thermodynamic parameters of each component,therefore,reasonable experimental parameters are crucial to the experimental scheme.In order to reduce unnecessary experimental period,finite element simulation is adopted in this paper.The geometric and thermodynamic parameters of samples,gaskets and anvil were systematically analyzed and compared to obtain the most reasonable experimental parameters,and the experimental process was optimized.Furthermore,large vertical and horizontal diamond anvil was designed to ensure the accurate measurement of thermal conductivity.Under this designation,the calibration of the anvils and gasket’s thermal conductivity is the key step to achieve in situ thermal conductivity measurement in a DAC under high pressure.The thermal conductivity of diamond anvil is significantly different with different types and impurities,and the difference of anvil will affect the accuracy of the measurement of the thermal conductivity of samples,therefore,it is necessary to in-situ calibrate the thermal conductivity of anvil in DAC.The thermal conductivity of diamond anvils with different nitrogen content have been calibrated using the method of calculated temperature field,from the test,we were able to calibrate the thermal conductivity of diamond anvils for future in-situ thermal conductivity measurements in DAC.In addition,the feasibility of the groundbreaking experimental design needs to be verified,even if the feasibility of this method was tested by enforcing in-situ thermal conductivity measurements on diamond anvils.In order to make the experiment more convincing,we measured the thermal conductivity of some typical materials at extreme temperature and pressure,the comparison with the literature data further proves that the thermal conductivity measurement method designed is efficient,accurate and easy to implement.To sum up,we proposed a new method for in situ thermal conductivity measurements in DACs using FEA calculation constrained by experimentally measured temperature;Independently developed and designed a set of high temperature and high pressure transport property measurement system device,optimize the heating system preparation process,simplify the experimental operation process;The factors affecting the thermal field and thermal conductivity measurement were systematically studied by using the temperature field calculation,and the research scheme of the thermal conductivity measurement in DAC was optimized.The accurate thermal conductivity calibration of the anvil and the metal gasket used in the experiment was carried out,and the feasibility of the experiment scheme was further verified.Except to the above main work,in the experimental simulation,we found that contact temperature measurement experiment error is significant,for which we propose a set of sample temperature correction program;In addition,through the anvil high-pressure thermal conductivity calibration,it is confirmed that the pressure regulation is conducive to improve the thermal conductivity of diamond,providing a possibility to explore the cognitive upper limit of human thermal conductivity.The research results of this paper are created on the original basis of the tutor and the research group to make up for many gaps in the measurement of high temperature and high pressure heat transport properties. |
PDF Full Text Request