Development of High-Temperature Technique with Diamond Anvil Window Cells for use in Geophysical Sciences

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0132270SaxenaTo obtain high quality data at physical conditions of Earth's core and mantle, we need to modify our present equipment and develop new techniques of heating our samples at ultra-high pressures and for measuring the temperature and pressure. Funds from this grant will fully exploit the diamond-anvil techniques to study materials of geophysical importance at high to ultra-high pressures and temperatures. We will study the nature of the problems in laser heating as related to large temperature gradients (cool diamond to the hot sample), chromatic aberration (use of refractive optical elements, even chromatically corrected, results in the severe temperature errors that vary significantly with the chosen position of a spectral region) and poor knowledge of emissivity (wavelength dependent emissivity, needed for use of the Planck function). A combination of laser-heating systems, optical systems and methods for the determination of emissivity of several metals and oxides will be explored. A new method of temperature determination using a digital imaging camera will also be tested. Additional developments will include: i) the use of moissanite (SiC) anvils at high pressures (~ 50 GPa) to reach temperatures close to 2000 K, ii) design of a cell that provides easy access to the sample for the electrical leads and still maintains all the benefits of the Mao- Bell design and is easily cooled with a good inert atmosphere around the diamonds, and iii) building of cells which can be both electrically and laser heated with in-situ x-ray diffraction of the heated sample at one bar or few bars of pressure to measure thermal expansion and melting temperatures of solids. We will attempt to provide a solution to the key problem of simultaneous measurement of pressure and temperature. ***