【作者】 代福；

【导师】 龚自正；

【作者基本信息】 西南交通大学 ， 理论物理， 2003， 硕士

【摘要】 冲击波动态压缩技术已成为人们研究、认识地球内部物质组成、状态及性质的重要手段和方法之一，在固体地球科学研究中发挥着重要作用。本学位论文以冲击压缩技术为手段，从测量其Hugoniot物态方程入手，结合高压物理和热力学理论分析，较深入地研究了下地幔中的一种主要候选组分顽火辉石(Mg_0.92，Fe_0.08)SiO₃在与下地幔大致相当的温度压力条件下的相态-钙钛矿型结构的相稳定性。这一问题的研究对确定下地幔真实的矿物学组成有十分关键的影响。 本文研究取得的认识主要有以下几点： （1）用阻抗匹配法和电探针技术在80～115GPa压力范围内对平均初始密度为3.05g/cm³的顽火辉石样品进行了5发Hugoniot状态实验测量。实验结果表明，在80～115GPa压力范围内本文所用顽火辉石的冲击波速度D与粒子速度u可用线性关系：D=3.247+1.626u来描述。从实验Hugoniot线来看，在80～115GPa压力范围内钙钛矿型顽火辉石无相变的迹象。 （2）在Hugoniot线的实验测量中，由于客观条件的限制，不同的人所使用的样品的初始密度不同，这使所得的Hugoniot数据的分散性较大，也给Hugoniot数据的分析、应用带来很大不便，甚至存在一些疑问，这就影响到数据的物理解释。特别对岩石材料，很难获得初始密度完全一致的实验样品，使这一问题更加突出。因此，对不同初始密度样品的Hugoniot数据统一进行分析修正（比如都修正到密实密度之下），对Hugoniot数据的进一步分析是十分必要的。 本文通过对不同初始密度样品冲击压缩Hugongiot数据的系统分析显示，对每种物质而言在其Hugongiot线上均存在一个经验常数β：β=(ρ₀-ρ₀₀P_H/P_H^′)/(ρ₀ρ₀₀（1-P_H/P_H^′）)，其中ρ₀,ρ₀₀为同种材料的两种不同初始密度，P_H及P_H^′为压缩到同一密度下的冲击压力。β的数值随材料而异。对金属材料还存在β_金属=1.217ρ₀^-0.884，式中ρ₀为密实密度。利用常数β，可很方便的用公式： 西南交通大学硕士研究生学位论文 第11页 一 凡一4（二一F川——二月）对不同初始密度的Hugongiot数据进行＿ 产 厂。 换算。Grhneisen参数厂与密度产的关系可通过p简单表示为： y＝V加河小文中还对卢值为常数的适用范围作了讨论。这是本 文的重要创新点之一。 （3）用（2）中提出的新方法，对前人和本文的顽火辉石 Hugongiot 实验数据进行了初始孔隙度修正。结果显示，不同研究者所得 的Hugongiot数据的分散性大大减小。在50—160GPa的冲击压 力范围内，将不同研究者的实验数据修正到密实密度产。一3．273 g儿m’下所得的 P－p Hugongiot关系具有较好的一致性，基本位 于同一条曲线上。可以认为，从 P－p Hugongiot 数据看，在 50～160GPa 范围内，顽火辉石的高压相是稳定的。对应于密实 密度产。＝ 3．273 g／cm3 的顽火辉石（Mg。0。，Fe。。s）SO。在 50～140GPa内的D－u关系为： D＝3．7刀十1．516U （4）用混合物 Hugongiot线的叠加性原理计算了 MgO（Mw）和引。（St） 混合体系的Hugongiot线，经过与顽火辉石实验Hugongiot数据 对比，无论是从＊心关系还是从＊一产关系上看两者均有较大差 距。可以认定，在80－140GPa压力范围内，实验Hugongiot数 据所对应的物相不可能是MgO（MW）与SIOZ（St）的混合物。换句 话说，在80—140GPa压力内，顽火辉石的高压相是稳定的，不 可能发生由（咐，刊）引0。叩v 向 吨0你叫个引0。（SO的化学分 解相变。 3）根据本文顽火辉石 Hugoniot实验数据(结合前人的实验数据L 用欧拉有限应变理论计算得到的顽火辉石零压炸弹性模量及其 对压力的一阶导数为：K叮一266GPa，K；，二 4．05。这与众多静压＿ 下测量到的数据 KN＝262 GPa，厂i。＝4．0非常吻合。考虑到静高 压下的数据是在实验中未发现顽火辉石高压相有相变的情况下 得到的。因此，动高压与静高压实验数据的一致性支持了在 80—140GPa压力内预火辉石的高压相保持稳定的观点。更多还原

【Abstract】 Shock wave compression technique has play an important role in the understanding of the material composition thermodynamic state and physical properties of the Earth’s ulterior. In this article, the stabling of high-pressure phase of one of the main candidate materials of the Earth’s lower mantle ?enstatite (Mg0.92,Fe0.08)SiO3 were investigated through the experimented measurement of Hugoniot equation of state, and together with thermodynamic calculation and analysis. This is the key problem for the constraint on the possible composition of lower mantle.The main work and achierement are as following:(1) By using shock impedance matching technique and electric probe method, 5 shots of impact experiments were conducted to measure the Hugoniot equation of state for enstatite (Mg0.92,Fe0.08)SiO3 with the average initial density 3.05g/m3 from shock pressure 50 GPa to 115GPa, using two stage light gas gun. The linear relationship between shock wave velocity D and particle velocity u of our samples were obtained:D=3.701+1.527uThere the unit of relocity is km/s. No phase transition shows for enstatite with perovskite structure according to the experimental linear D-u line upto 110Gpa.(2) Because of different initial density of samples were always used in shock wave experimental measurement by different researchers, the Hugoniot data always shows contradiction sometimes. This is inconvenience for the advanced analysis and application of Hugoniot data. So, it is very necessary and important to modify the Hugoniot data for porosity.A new material parameter, where ρis density and subscript 0 and 00 represent different initial density, and PH and PH represent Hugoniot pressure of ρ0 and ρ00 which compressedto the same density ρ, was find out to keep in constant along Hugoniot. For different materials, the value of β is different. For metal βmetal=1.217ρ0-0.884, where ρ 0 is the no-porous density. By using β, Hugoniot data of different initial density samples can be simply convertedby: . The limitation of this empirical material constant β is discussed.(3) By using the new method put out in (2), Hugoniot data of no-porous samples of enstatite (Mg0.92,Fe0.08)SiO3 which initial density is 3.273g/m3, were reduced and the modified Hugoniot data shows very small dispersivity. The relationship between Shock wave velocity and particle velocity of no-porous enstatite can be expressed as:D=3.771+1.516u Where the unit of velocity is km/s. There is no evidence to shows phasetransition of the high-pressure phase of enstatite between 50-140GPa.(4) The Hugoniot of the mixture of MgO(Mw) and SiO2(St) were calculated by the additire principle of Hugoniot for mixture, and compared with the experimental Hugoniot of enstatite.The results shows that there exists large difference between both D-u relationship and P-n curve for the two Hugoniot. This means that the phase which being measured between 50 to 140Gpa of enstatite is not likely to be the mixture of MgO(Mw) and SiO2(St). So it is impossible for enstatite to decompose to oxides between 50 to 140GPa.(5) The bulk modulus K0S and its first derivative of pressure K0S’ were calculated from the experimental Hugoniot data, by using Eularian limit strain theory. Our value of K0s=266GPa and K0s’=4.05 are very consistant with the value of static high pressure experiments. Considering that no phase transition of enstatite with perovslite structure were found during these static high pressure experiments, the consistence of the bulk modulus also supports that the high pressure phase of perovskite structure of enstatite is stability between 50-140GPa.更多还原