Studies On Equation Of State And Gr(?)neisen Parameter For Metals At High Pressures And Temperatures

In this article, the content and significance of high-temperature and high-pressure equation-of-state (EOS) is introduced at first. And then a comparatively comprehensive review and analysis are made for the research progresses of both universal isothermal EOS (OK isotherm in the strict sense) that is related to the "cold contribution" and the Griineisen parameter y that is related to the "thermal contribution", which are involved with the compression property of solid materials. Based on the results mentioned-above, two main research goals of this article are projected, which are related to the existing problems in the high-temperature and high-pressure EOS investigations. The first is to find a reasonable method to accurately determine the isothermal bulk modulus B0K, its first pressure derivative B'0K and the specific volume V0K at zero pressure and OK temperature, and then using them as input parameters to search for an isothermal EOS with appropriate functional form that could accurately predicate the OK isotherm for metals applicable to TPa pressure region. The second is to reveal the evolution behavior of Gruneisen parameter y at high pressures and temperatures by applying the isothermal EOS determined above.A method, independent of the functional form of the isothermal EOS, is proposed to determine the values of B0K, B'0K and V0K directly from the experimental Hugoniot data, without any assumption on the behavior of Gruneisen parameter y at high pressures and temperatures. Comparisons with the corresponding experimental and theoretical data demonstrate that the values of B0K, B'0K and V0K calculated from this method is rational and more precisely. With the input parameters determined above, a comparative study is performed among ten kinds of universal isothermal EOSs with different functional forms, including the Born-Meyer EOS. It demonstrates that the Born-Meyer EOS has an excellent agreement with the experimental data up to several hundred GPa, and with theoretical calculation data even up to 1~2TPa for some representative metals.Based on the definition of Gruneisen parameter y defined by Gruneisen EOS, the evolution law of y along Hugoniot locus, denoted by y GB, is deduced in the article directly from the experimental Hugoniot data and the OK isotherm EOS or Born-Meyer EOS that could well describe the OK isothermal EOS as mentioned above. On the other hand, a thermodynamic Gruneisen parameter r, hereafter denoted by rth , is deduced from a generalized specific heat function that is suggested in this article, and a Gruneisen parameter r, hereafter denoted by r mfv is deduced from the "modified free volume theory" that isproposed by Stacey et al. A comparative study is again carried out for the above three y s. It demonstrates that rth accurately predicts the violent change behavior of rGB in the low-pressure region and rmfv successfully describes the gradual change behavior of rGB in the high-pressure region. So good consistent relation with each other among yGB, rth and shows that the evolution low of rGB derived in this article is rational.