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Effective factors in the kinetics of pressure-induced transformation.

压力诱导转变动力学的有效因素。

基本信息

批准号：
10640463
负责人：
NAGAI Takaya
金额：
$ 2.11万
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：
1998
资助国家：
日本
起止时间：
1998 至 1999
项目状态：
已结题

项目摘要

The kinetics of the quartz-coesite transformation were investigated at 4 GPa and 650, 750 and 850℃ using quartz single crystal and powdered samples. Optical microscopic observations for partly transformed single crystal samples indicate that the coesite heterogeneously nucleates on the surface of the quartz grain and grows into the interior. The growth rate of coesite is independent of crystallographic orientations. The mechanism of incoherent grain-boundary nucleation and interface-controlled growth seems to operate during the transformation. The thickness of the coesite rims increases linearly as a function of time and the growth rate clearly depends on temperature. The activation energy for growth of coesite is determined as 85 (±11) kJ/mol and this value is significantly small in comparison with that determined for powdered samples.Synchrotron x-ray powder diffraction studies were performed on Ca(OH)ィイD22ィエD2 and Mg(OH)ィイD22ィエD2 under room temperature pressurization to 10.4 GPa and 16.0 GPa, respectively. We used the diamond anvil cells technique and the data were collected with an imaging plate detector at BL-18C in Photon Factory at KEK, Japan. The c-axis is much softer than the a-axis and, thus, the c/a ratio decreases with pressure. There is no remarkable discontinuity in the compression curves. The atomic position of O atoms, (1/3, 2/3, z), has been successfully refined using Rietveld analysis of x-ray powder diffraction patterns. In Mg(OH)ィイD22ィエD2, a change of compression mechanism is observed at 11GPa. However, in Ca(OH)ィイD22ィエD2, it is concluded that the shortening of the interlayer spacing controls compression below the amorphization pressure and no change of compression mechanism has occurred. It has been reported that H disorder occurs at a pressure in Mg(OH)ィイD22ィエD2 and the present results clearly suggest that the H disorder has great influence on the compression behavior.

用石英单晶和粉状样品研究了4℃、650、750和850 GPa时石英-柯石英转变的动力学。部分转变单晶样品的光学显微镜观察表明，柯石英不均匀地在石英颗粒表面成核，并向内部生长。柯石英的生长速率与晶体取向无关。非共格晶界形核和界面控制生长机制似乎在相变过程中起作用。柯石英边缘厚度随时间呈线性增加，生长速度明显依赖于温度。测定了Ca(OH)ィイD22ィエD2和Mg(OH)ィイD22ィエD2样品在室温加压至10.4 GPa和16.0 GPa时的同步辐射X-射线粉末衍射谱。我们使用了钻石砧座技术，数据是在日本KEK的光子工厂的BL-18C成像平板探测器上收集的。C轴比a轴软得多，因此，c/a比随着压力的增加而减小。压缩曲线没有明显的间断。利用X-射线粉末衍射谱的Rietveld分析，成功地确定了O原子(1/3，2/3，z)的原子位置。在Mg(OH)ィイD22ィエD2中，在11 GPa时观察到压缩机制的变化。然而，在Ca(OH)ィイD22ィエD2中，层间距的缩短将压缩控制在非晶化压力以下，压缩机制没有发生变化。有报道称，在加压下，Mg(OH)ィイD22ィエD2中发生了H无序现象，目前的结果清楚地表明H无序对压缩行为有很大的影响。