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In situ observation and kinetics of the phase transformation under high pressure and stress

高压和应力下相变的原位观察和动力学

基本信息

批准号：
08640606
负责人：
YAMANAKA Takamitsu
金额：
$ 1.47万
依托单位：
Osaka University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1996
资助国家：
日本
起止时间：
1996 至 1997
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-08640606/
关键词：
kinetics of structure change pressure induced phase transition metastable state Plastic and elastic deformation bulk moduli and elastic velocity diamond anvil high prssure cell Single crystal x-ray diffraction molecular dynamical calculation

项目摘要

Present investigation aims to discuss the kinetics of the phase transformation of silicates and hydrates constituting earth crust and mantle. It has been known that the phase change often stays in the metastable or even unstable state by the Ostwald step rule, when the thermal energy is not large enough to supply the proper activation energy for the phase transformation. For the purpose of understanding the above mentioned mechanical process, quantitative kinetic investigations have been undertaken by the simulation of physico-chemical process found in the earth interiors as a function of temperature, pressure and stress. The following research projects have been performed :(1) X-ray diffraction study of the phase transition of Ca(OH)2, which is an analog material to mafic hydrates such as serpentine, has been carried out using the single crystal under hydrostatic pressure condition at 300K with diamond-avil cell (DAC). The compression induced a high density amorphous state but never b … More rought a CaCl2 type high pressure stable phase. This pressure-induced amorphization was caused by elastic deformation of the lattice and it is a reversible transformation.(2) An internal Pt heating system installed in the DAC enable to simulate the more precise phase transformation in the earth mantle in consideration of the geothermal gradient. Kinetics study of the structure change from quartz to coesite under various pressures and temperatures was undertakek by the time resolved diffraction study, Their physical properties such as thermal expansibity, bulk moduli and elastic constants were observed. It has clarified that the various compression paths and heating processes bring a different threshold transition critical pressure and temperature.(3) The present Raman spectroscopic study and EXAFS experiment accounts for the elastic or plastic lattice deformation causes the amorphization under high pressure. The investigation of the local structure of glass and high density amorphous phase of GeO2 could explain the different mechanism of the pressure-induced amorphization.(4) Simulation of structure change of SiO2, GeO2, SnO2 and PbO2 having a rutile structure has been executed under variable stress field through the molecular dynamical calculation using optimized pair potential and molecular orbital calculation based on DX-Xalpha method. Less

本文旨在讨论构成地壳和地幔的硅酸盐和水合物的相变动力学。根据Ostwald阶跃规则，当热能不足以提供相变所需的激活能时，相变通常停留在亚稳态甚至不稳定状态。为了理解上述力学过程，通过模拟地球内部的物理化学过程作为温度、压力和应力的函数，进行了定量动力学研究。（1）采用金刚石衍射盒（diamond-avil cell，DAC），在300 K静水压力条件下，对镁铁质水合物（如蛇纹石）的模拟材料Ca（OH）_2的相变进行了X射线衍射研究。压缩诱导了高密度的非晶态，但从未诱导出B ...更多信息形成了CaCl 2型高压稳定相。这种压力诱导的非晶化是由晶格的弹性变形引起的，是一种可逆的转变。(2)在DAC中安装的内部Pt加热系统能够考虑地热梯度来更精确地模拟地幔中的相变。利用时间分辨衍射技术研究了石英到柯石英在不同温度和压力下结构变化的动力学过程，观测了它们的热膨胀率、体积模量和弹性常数等物理性质。阐明了不同的压缩路径和加热过程会产生不同的临界转变压力和温度。(3)目前的拉曼光谱研究和EXAFS实验解释了在高压下晶格的弹性或塑性变形导致的非晶化。对玻璃和高密度非晶相GeO 2的局域结构的研究可以解释压力诱导非晶化的不同机理。(4)通过优化对势的分子动力学计算和基于DX-Xalpha方法的分子轨道计算，模拟了具有金红石结构的SiO2、GeO 2、SnO 2和PbO 2在可变应力场下的结构变化。少