DEVIATORIC STRESS IN A DIAMOND-ANVIL CELL USING SYNCHROTRON-RADIATIONWITH 2 DIFFRACTION GEOMETRIES

Deviatoric stress in a diamond anvil cell with gold as a pressure and stress indicator is measured by two complementary techniques using syn chrotron radiation. The first method employs a white X-ray beam using energy dispersive X-ray diffraction. The incident X-ray beam is parall el to the load axis and the diffraction pattern is recorded at a low t wo-theta angle. Using powder diffraction patterns of polycrystalline g old, we measured the elastic strain of two crystal planes oriented nor mal to the diffraction vector. Stresses nearly parallel and perpendicu lar to the load axis can be calculated by stress-strain tensor relatio nship. The other method uses a monochromatic wiggler X-ray beam. In th is case, the diamond cell is oriented so that the incident beam is per pendicular to the load axis. The diffraction pattern is recorded on an image plate area detector. Elastic strains responding to stresses per pendicular and parallel to the load axis can be measured and stresses of the same orientations can be calculated from the strain data. These measurements provide a lower bound of the actual differential stresse s in a diamond cell. With these techniques, we can measure stress dist ribution in a less deviatoric gasketted sample and determine yield str ength of mantle materials at high pressures and temperatures.