MRI: Development of Multi-Field Resonant Ultrasound Spectroscopy
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Elastic constants are fundamental properties of any solid material and knowing their changes with temperature and/or under applied magnetic or electric field is essential for understanding different physical processes that take place in different materials. However, measurement of elastic constants using conventional techniques is not always a trivial task. It usually requires large number of samples and/or numerous time-consuming tests, especially if the measurements are performed at low and high temperatures and/or under various external stimuli such as electric and magnetic fields. Multi-field Resonant Ultrasound Spectroscopy (MF-RUS) apparatus under development in this project will allow rapid experimental determination of the full set of elastic constants of any solid from the single test using only one sample as small as 1 mm3 in the wide temperature range, with or without applied electric or magnetic fields. The broad capabilities of the MF-RUS will enable comprehensive characterization of different solids, and enhance research in many fields, including materials science and engineering, physics, and chemistry. By allowing rapid and easy evaluation of elastic properties of different materials, utilization of MF-RUS will further foster development of new materials for widely varying applications including energy harvesting, storage and conversion, defense, and transportation systems. Once developed, this unique instrument will be available to researchers from other academic institutions, industry and laboratories through a well-established Materials Characterization Facility''s users program at Texas A&M University. Eighteen research projects at Texas A&M University and other academic institutions, including two minority serving institutions, currently supported by NSF and other federal agencies will benefit immediately from the development of MF-RUS.Elastic constants, as the second derivatives of the free energy with respect to strain, not only relate stress and strain tensors, but also provide fundamental information about the character of atomic bonding in solids, and thus they are considered to be one of the most fundamental materials properties. While the elastic constants represent primarily equilibrium thermodynamic properties, the attenuation is direct manifestation of irreversible processes related to energy absorption by various physical processes in the material. Resonant Ultrasound Spectroscopy (RUS) is a simple, inexpensive and elegant experimental technique that can be used to determine simultaneously Young''s and shear moduli of isotropic solids, or a full set of elastic constants (Cij) of single crystals, as well as ultrasonic attenuation, using single crystal or polycrystalline sample as small as 1 mm3. Currently, commercially available RUS instruments are limited to room temperature measurements while some existing custom-made RUS systems allow measurements up to 1320ÂºC in controlled environments, in magnetic fields up to 7T from cryogenic temperatures to 327ÂºC, or under an electric field but only at room temperature. A Multi-Field Resonant Ultrasound Spectroscopy (MF-RUS) system under development in this project will be unique since it will allow simultaneous measurements of elastic constants and ultrasonic attenuation of solid materials from liquid helium temperature up to 1900ÂºC, with or without electric fields of up to 1000 V/mm or magnetic fields of up to 7T, and in various atmospheres (air, high vacuum, inert gases, etc.) This RUS system will be modular and will be developed in stages over the 3-year project period with partial functionality as each module is added. This instrument will provide a powerful new tool to observe and quantify changes in elastic coefficients and ultrasonic attenuation as a result of various physical processes in the solid, such as first- and second-order phase transformations or different inelastic relaxation mechanisms due to different processes such as thermoelastic relaxation and motion of point defects (e.g. interstitial and vacancy hopping), linear defects (e.g. dislocations) or planar defects (e.g. domain walls or martensitic transformation phase interfaces, etc.).