2006 Fiscal Year Final Research Report Summary
Local structure of high-pressure and high-temperature melts and its correlation to density and viscosity
| Project/Area Number |
16340169
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Petrology/Mineralogy/Science of ore deposit
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| Research Institution | Osaka University |
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Principal Investigator |
OHTAKA Osamu Osaka University, Graduate School of Science, Associate Professor (40213748)
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| Co-Investigator(Kenkyū-buntansha) |
YOSHIASA Akira Kumamoto Univ., Science, Professor (00191536)
SHIMONO Masaru Ryukoku Univ., Science & Technology, Lecturer (30319496)
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| Project Period (FY) |
2004 – 2006
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| Keywords | liquid germanate / local structure of liquid / EXAFS / sintered diamond / x-ray radiography / synchrotron radiation / multi anvil high-pressure device / high-density liquid |
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| Research Abstract |
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
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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
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