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Local structure of high-pressure and high-temperature melts and its correlation to density and viscosity

高压高温熔体的局部结构及其与密度和粘度的相关性

基本信息

批准号：
16340169
负责人：
OHTAKA Osamu
金额：
$ 10.05万
依托单位：
Osaka University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2004
资助国家：
日本
起止时间：
2004 至 2006
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-16340169/
关键词：
liquid germanate local structure of liquid EXAFS sintered diamond x-ray radiography synchrotron radiation multi anvil high-pressure device high-density liquid X線ラジオグラフィーマグマ超高圧

项目摘要

In order to examine the pressure-induced structural change of liquids having locally tetrahedral molecular structure, short range order of liquid germinates have been investigated by means of high-pressure and high-temperature in situ x-ray absorption fine structure (XAFS). Two types of liquid germanates, Li2Ge4O9 and SrGeO3, show a sharp liquid-liquid transition accompanied by fourfold-sixfold coordination change occurs around 3 GPa at 1273 K. The fourfold-sixfold coordination change is completed below 4 GPa and a high-density liquid consisting of octahedrally coordinated germanium is stable up to) GPa. The coordination number change in both liquid germanates occurs within narrow pressure range of less than 1 GPa in spite of a wide visersity in chemical composition. These results suggest that there would be less effect of coexisting cations on the local structural change around Ge comparing with solid state. These results give not only evidence for liquid polymorphism but also some fa … More r-reaching implications for the evolution and dynamics of Earth's interior, when the analogy of germanates to silicates is considered.Using a hot isostatic pressing (HIP) technique, diamond/SiC composites were synthesized from diamond and Si powders. At an HIP condition of 1250℃ and 100MPa, a pressure much lower than that of the diamond stability field, diamond powders react with molten Si to form well-sintered diamond/SiC composites. Cubes of the composites with 15mm edge length were thereby fabricated, and an application to the second stage anvils in a Kawai-type high-pressure apparatus was attempted. The anvils were proved to be hard enough for the generation of pressures up to 40GPa. For high-pressure and high-temperature in-situ X-ray experiments using synchrotron radiation, a hybrid anvil system using 4 cubes of the composites and 4 of conventional WC was introduced and heating experiments up to 1600℃ at 22GPa became possible. Because the diamond/SiC composites are transparent to X rays, the present system is applicable not only to diffraction studies but also to radiographic studies, such as density and viscosity measurements for liquid under high pressure, which need a larger window for an X-ray image Less

为了研究具有局部四面体分子结构的液体在压力作用下的结构变化，采用高压高温原位x射线吸收精细结构（XAFS）对液体萌发物的短程序进行了研究。Li2Ge4O9和SrGeO3两种液态锗酸盐在1273 K温度下，在3gpa左右发生了剧烈的液-液转变，并伴有4 - 6倍配位变化。在4 GPa以下完成4 - 6倍配位变化，八面体配位锗组成的高密度液体在6 GPa以下稳定。两种液体日耳曼酸盐的配位数变化发生在小于1 GPa的狭窄压力范围内，尽管化学成分差异很大。这些结果表明，与固态相比，共存阳离子对Ge周围局部结构变化的影响较小。这些结果不仅为液态多态提供了证据，而且还为地球内部的演化和动力学提供了一些更深远的意义，当考虑到锗酸盐与硅酸盐的类比时。采用热等静压（HIP）技术，以金刚石和硅粉为原料合成了金刚石/SiC复合材料。在远低于金刚石稳定场压力的1250℃和100MPa的HIP条件下，金刚石粉末与熔融Si发生反应，形成烧结良好的金刚石/SiC复合材料。制备了边缘长度为15mm的复合材料立方体，并尝试将其应用于卡哇伊型高压装置的二级顶砧。这些砧被证明足够坚硬，可以产生高达40GPa的压力。在同步辐射的高压高温原位x射线实验中，引入了由4个立方体的复合材料和4个常规WC组成的混合砧系统，实现了高达1600℃、22GPa的加热实验。由于金刚石/SiC复合材料对X射线是透明的，因此本系统不仅适用于衍射研究，也适用于射线学研究，如高压下液体的密度和粘度测量，这些研究需要更大的X射线成像窗口