高温高压气体的状态方程与热力学性质

本文根据高温高压下气体分子要压缩的观点出发,提出了一个简单实用的高温高压气体状态方程,并用以研究和计算气体在高温高压下的热力学函数与性质.     

高温高压下液态水声速的研究——不同状态方程的准确性验证

 研究水的热力学状态方程,对于理解地球及行星科学等起着重要作用,但由于高温高压区域的实验数据较少,该区域的状态方程主要依赖于由低压部分外延或分子动力学模拟计算得到。采用布里渊散射技术测量熔解曲线附近液态水的声速,低温区采用电加热系统,高温区采用激光加热布里渊散射系统,分析比较了由实验测量得到的声速值与用经验状态方程计算的结果之间的差别。结果表明,在温度不超过673 K、压力不超过6.0 GPa的范围内,Abramson方程的计算结果与实验测量结果在误差范围内一致,而Saul 和IAPWS-95的预言值比实验测量值偏高,并且温度越高偏差越大。在压力为21 GPa、温度为890~1 100 K时,实验测量出的水的声速比状态方程预言的结果偏高。     

高压下发射药燃气的状态方程

 本文从分子运动论出发，考虑到高密度下分子碰撞及高温下分子间作用的特点，提出了简化的三分子碰撞模型，并引进屏蔽效应，给出了描述高压下火药燃气实际状态行为的多项式型状态方程式。在800 MPa的压力范围以内，本文对不同组分的发射药进行了计算，其计算压力与实验有较好的一致性。比目前美国三军所用程序BLAKE编码的计算结果有所改进。     

南丹铁陨石冲击绝热线和状态方程的研究

 用二级轻气炮作为加载工具，对南丹铁陨石进行了冲击压缩线测量，压力范围为62~208 GPa。用阻抗匹配法得出的南丹铁陨石冲击波速度D与粒子速度u之间的关系为：D=3.884+1.840u-0.12267u²（km/s），还据此确定了考虑到晶格非谐振项贡献的南丹铁陨石的三项式Grüneisen状态方程。     

高温高压下硬水铝石状态方程研究

 在金刚石压砧装置上,用氧化铝膜作绝热层,借助同步辐射和双面激光加温系统,分析了硬水铝石在高温高压下的结构变化,并分别用理论和实验的方法得出了其结构参数,得到了样品在不同压力温度下的体模量。这对于人们认识和研究地壳结构和地球内部物质的演化具有重要意义。研究发现,在常温和高温时其压缩率有明显不同,在高温高压范围内,其晶格常数和晶胞体积的变化非常接近样品在高压常温下的情况;而在高温低压范围内,情形和常温时有较大差别。在实验过程中并没有发现相变的产生。     

高温高压下碳的状态方程及相变理论研究

 研究了高温高压下三相碳（石墨、金刚石、液相碳）的状态方程，包括高压下石墨到金刚石的固-固相变以及高温下石墨和金刚石的熔解曲线。计算所得到的金刚石熔解曲线具有正的斜率，石墨-金刚石-液相三相点为4 400 K，14 GPa左右。     

液态CO2高温高密度状态方程研究

 利用二级轻气炮作冲击加载手段，采用自己建立的低温靶，比较系统地研究了液态CO₂的冲击压缩行为。在20～60 GPa压力区获得六个新的Hugoniot数据点。根据这些实验点，采用液体统计力学理论和化学平衡方法，重新优化获得一组CO₂－CO₂，CO₂－O，CO－O作用势参数。分析表明，引起体系在25 GPa以上区域冲击软化现象的主要机制是CO₂离解反应，CO₂—→CO+O。     

利用光分析方法测量液态CO多次冲击Hugoniot状态方程

 结合液氮低温靶技术和光分析方法同时测量液态CO样品的第一、二、三次冲击Hugoniot状态方程,分别在19、60和71 GPa获得3个数据点。样品体积的最大压缩度达到3.5倍,比文献发表的一次冲击最大压缩度提高20%以上。体积测量值比分子流体微扰变分理论的计算结果偏低20%以上,体积发生明显软化现象归因于CO分解反应所致。详述了多次冲击过程的光分析测量方法,该方法应用于其它分子流体可将其物态方程的实验数据点延伸到更高压力和更宽的压缩范围。     

铋的固相及液相多相状态方程研究

铋在高温高压下存在一系列复杂相结构,相变伴随着密度、内能等物理性质的改变.采用半经验三项式Helmholtz自由能表达式,构建了铋的五个固相及液相的多相状态方程,其中离子热振动自由能计算基于经典平均场理论给出的平均场势函数模型开展.研究结果表明,状态方程计算给出的铋的相图、等温压缩线、液相的温度-密度曲线以及冲击Hugoniot线等均与实验测量符合较好,故可认为本文构建的铋的多相状态方程具有良好的参数合理性以及模型适用性.     

Grüneisen系数与铝的高温高压状态方程

基于Gray金属三相状态方程模型,分别采用ργ=常数,Gray,GRIZZLY的Grüneisen系数模型和从头算给出的Grüneisen系数,系统计算了铝的熔化曲线、等熵压缩线、等温压缩线和等熵卸载线,计算结果与实验数据比较表明;在冲击压力约为500GPa的宽广压力范围,GRIZZLY Grüneisen系数模型是最适合描述铝的热力学特性的形式,ργ=常数模型次之,在高压区,Gray和从头算的Grüneisen系数的计算结果与实验值差距较大. 关键词： Grneisen系数 状态方程 铝     

A molecular dynamical study of the equation of state of solids at high temperature and pressure

The molecular dynamics method of computer simulation was used to study the pressure and energy as a function of volume and temperature for f.c.c. neon with 6–12 Lennard-Jones interatomic forces and for b.c.c. iron with Morse interatomic forces. A self-consistent cell model was used to derive analytical formulae which describe the results of the computer experiments. A method for correcting the inherently classical results of the molecular dynamics calculations for the effect of quantum statistics is proposed. The results of the calculations are compared with experimental data and with various approximate methods for calculating the Grüneisen constant.     

Thermal conductivity of hcp iron at high pressure and temperature

Results of steady-state heat transfer experiments on iron in laser-heated diamond anvil cell, combined with numerical simulation using finite-element method are reported. Thermal boundary conditions, dimensions of sample assemblage, heating-laser beam characteristics and relevant optical properties have been well defined in the course of experiments. The thermal conductivity of the polycrystalline hexagonal-iron foil has been determined up to pressure 70 GPa and temperature 2000 K. At these conditions, the conductivity value of 32±7 W/m K was found. Sources of errors arising from uncertainties in input parameters and applied experimental procedures are discussed. Considering results of earlier preferred-orientation studies in diamond anvil cell, an averaging effect of polycrystalline texture on the intrinsic anisotropy is assumed. The obtained conductivity is interpreted as an effective value, falling in between the upper and lower bounds on the average conductivity of a random aggregate of uniaxial crystals.     

Simulated equation of state of CaF2 with fluorite-type structure at high temperature and high pressure

The pressure-volume-temperature (P-V-T) equation of state (EOS), isothermal bulk modulus, and thermal expansivity of CaF₂ with cubic fluorite-type structure are investigated using the constant temperature and pressure shell model molecular dynamics (MD) method with effective pair potentials which consist of the Coulomb, dispersion, and repulsion interaction. It was shown that MD simulation is very successful in accurately reproducing the measured volumes of the CaF₂ over a wide range of pressures. The simulated P-V data matched X-ray diffraction experimental results up to 9.5 GPa at 300 K. In addition, volume thermal-expansion coefficient and isothermal bulk modulus were also calculated and compared with available experimental data and the latest theoretical results at ambient condition. At extended temperature and pressure ranges, The P-V EOS under different isotherms at selected temperatures, T-V EOS under different isobars at selected pressures, thermal expansivity, and isothermal bulk modulus were predicted up to 1500 K and 10 GPa. The detailed knowledge of thermodynamic behavior and EOS at extreme conditions are of fundamental importance to the understanding of the physical properties of CaF₂.     

Equations of state of MgO at high pressure and temperature

Abstract

A synchrotron X-ray diffraction study on MgO has been done at simultaneous high pressure and temperature. The lattice parameter of MgO has been measured up to a static pressure of 6 GPa and a temperature of 1273 K, using a large volume pressure cell and energy-dispersive synchrotron X-ray powder diffraction. The compression was made following six high-temperature isotherms. A Vinet equation of state was used to fit the experimental P-V-T data. The Vinet's model compares very well with the experimental data above the Debye temperature (760 K) and allows the use of MgO as an alternative internal pressure calibrant for experiments at high temperature.     

Test of a high pressure equation of state

An equation of state for shock compressed matter is used to correlate P.V.T. data for Ag, Cu, Mo, Pd and K in the range from 0.05 to 0.95 M bar. Isotherms at 293K are obtained and the results are compared with static experimental data. Very good agreement between calculated and experimental values is generally obtained for all the materials considered. A critical analysis of the data is presented.     

Behaviour of the equation of state of some liquid n-alkanes at high pressures

The equation of state of several liquid n-alkanes is analyzed along a series of isotherms in the liquid region. It is found that, for a substantial range of pressures for each isotherm, the experimental data are well reproduced by an equation of state, which was initially proposed for the high density hard-spheres system and later proved to be valid for several simple and molecular liquids, if we determined an effective excluded volume for each isotherm and provided that, in molecular liquids, we treat rotational degrees of freedom as equivalent translational ones.     

Isochoric measurement of the equation of state of solid argon at high pressure

Isochoric P-T traces have been measured for solid argon at eight different molar volumes by using a capacitance technique which records the radial expansion of the vessel due to pressure. These measurements extend from melting curve temperatures down to 4 °K at pressures ranging up to 7 kbar.Analysis of the data indicates that, for the high temperature region (above 80 °K) the thermodynamic derivative ?P/?T_r is independent of both temperature and density to within experimental errors. Using the fact that ?P/?T_r is constant, it is possible to generate PVT and isothermal bulk modulus data at high temperatures. These data are compared with X-ray diffraction measurements and piston displacement data and are found to be in good agreement with both. The data also agree quite well with current theoretical predictions. The high-temperature bulk modulus data were found to have a simple exponential dependence on the molar volume, prividing another convenient representation of the high-temperature equation-of-state data.     

高温高压下铁热导率的第一性原理研究

铁在高压高温下的热导率是研究地球动力学和热演化的关键参数.在以往的研究中,铁的热导率主要归结于电子热导率,我们发现铁在高压下晶格振动对热导率的贡献不可忽略.本文利用晶格动力学和玻尔兹曼输运理论计算了铁的声子色散、Hugoniot状态方程和热导率.预测了铁在核幔边界附近温度约为3500K,在地球内核边界条件约为6500K.考虑晶格振动的热导率在地球核幔边界附近为112W/m K,在内核边界条件约为200W/mK.