HR: 17:00h
AN: MR24A-05    [Abstracts]
TI: A New Technique for In Situ X-ray Microtomography Under High Pressure
AU: Uchida, T
EM: uchida@cars.uchicago.edu
AF: Consortium for Advanced Radiation Sources, The University of Chicago, 5640 S. Ellis Ave., Chicago, IL 60637 United States
AU: * Wang, Y
EM: wang@cars.uchicago.edu
AF: Consortium for Advanced Radiation Sources, The University of Chicago, 5640 S. Ellis Ave., Chicago, IL 60637 United States
AU: Westferro, F
EM: westferro@cars.uchicago.edu
AF: Consortium for Advanced Radiation Sources, The University of Chicago, 5640 S. Ellis Ave., Chicago, IL 60637 United States
AU: Gebhardt, J
EM: gebhardt@cars.uchicago.edu
AF: Consortium for Advanced Radiation Sources, The University of Chicago, 5640 S. Ellis Ave., Chicago, IL 60637 United States
AU: Rivers, M L
EM: rivers@cars.uchicago.edu
AF: Consortium for Advanced Radiation Sources, The University of Chicago, 5640 S. Ellis Ave., Chicago, IL 60637 United States
AU: Sutton, S R
EM: sutton@cars.uchicago.edu
AF: Consortium for Advanced Radiation Sources, The University of Chicago, 5640 S. Ellis Ave., Chicago, IL 60637 United States
AB: We have developed a new technique for in situ synchrotron microtomography to study texture evolution in multi-phase specimens under high pressure and temperature. Two critical issues in performing tomography experiments under pressure are (1) the limited X-ray access to the sample because of the highly absorbing materials, such as tungsten carbide and tool steel, typically used in the pressure vessel and (2) a high pressure compatible rotation mechanism to collect projections of the sample continuously from 0 to 180$\deg$. We addressed these issues by (1) employing an opposed-anvil high pressure cell, known as the Drickamer cell, with an X-ray transparent containment ring, to allow panoramic X-ray access, and (2) rotating the Dricakmer cell by Harmonic Drive$^{TM}$ gear reducers, with thrust bearings supporting the hydraulic load. The design of the rotation mechanism benefited from the rotational deformation apparatus developed by Yamazaki and Karato (Rev. Sci. Instrum., 72, 4207, 2001). We report results obtained from a test run performed under pressure with monochromatic synchrotron radiation. A sapphire sphere (1.0 mm dia.) was embedded in a powdered mixture of Fe and 9 wt.$%$ S alloy. The diameter of the sample chamber was 2 mm. Under pressure, the entire Drickamer cell was rotated to collect radiographs of the sample at various angles from 0 to 179.5$\deg$ in 0.5$\deg$ step size. Computational reconstruction of these projections provided three dimensional (3D) distribution of linear attenuation coefficient of the sample with a spatial resolution of 6 microns. The shape change in the sapphire sphere during compression was clearly observed. Using the program Blob3d, reconstructed 3D images of the sphere were separated from the surrounding Fe-S alloy. Volumes of the sphere were then accurately determined from the extracted images, by carefully defining the image intensity threshold. The errors in the volume measurement are about 0.3 to 0.7$%$, mostly due to shadowing by anvil deformation. The results, although performed using a solid sample, demonstrate the potential of measuring melt volume. Previous density measurements using X-ray radiography with only one dimensional data assumed that the shape of the sample remained unchanged throughout the experiment. In our new technique, this assumption is no longer required and density of melts can be inferred directly from the sample volume even when the molten sample is distorted. Other applications of this apparatus will be also discussed.
DE: 8429 Lava rheology and morphology
DE: 5104 Fracture and flow
DE: 5112 Microstructure
DE: 5194 Instruments and techniques
DE: 3954 X ray, neutron, and electron spectroscopy and diffraction
SC: Mineral and Rock Physics [MR]
MN: 2004 AGU Fall Meeting