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Energetics of Nanomaterials

Description: This project, "Energetics of Nanomaterials," represents a three-year collaboration among Alexandra Navrotsky (UC Davis), Brian Woodfield and Juliana Boerio-Goates (BYU), and Frances Hellman (UC Berkeley). It's purpose has been to explore the differences between bulk materials, nanoparticles, and thin films in term of their thermodynamic properties, with an emphasis on heat capaacities and entropies, as well as enthalpies. the three groups have brought very different expertise and capabilities to the project. Navrotsky is a solid-state chemist and geochemist, with a unique Thermochemistry Facility emphasizing enthalpy of formation measurements by high temperature oxide melt and room temperatue acid solution calorimetry. Boerio-Goates and Woodfield are calorimetry. Hellman is a physicist with expertise in magnetism and heat capacity measurements using microscale "detector on a chip" calorimetric technology that she pioneered. The overarching question of our work is "How does the free energy play out in nanoparticles?", or "How do differences in free energy affect overall nanoparticle behavior?" Because the free energy represents the temperature-dependent balance between the enthalpy of a system and its entropy, there are two separate, but related, components to the experimental investigations: Solution calorimetric measurements provide the energetics and two types of heat capacity measurements the entropy. We use materials that are well characterized in other ways (structurally, magnetically, and chemically), and samples are shared across the collaboration.
Date: January 28, 2005
Creator: Navrotsky, Alexandra; Woodfield, Brian; Boerio-Goates, Juliana & Hellman, Frances
Partner: UNT Libraries Government Documents Department

Properties of salt-grown uranium single crystals.

Description: Recently single crystals of {alpha}-uranium were grown from a liquid salt bath. The electrical, magnetic and thermal properties of these crystals have been surveyed. The ratio of the room temperature resistivity of these crystals to the saturation value at low temperature is three times larger than any previously reported demonstrating that the crystals are of higher purity and quality than those in past work. The resistive signatures of the CDW transitions at 43, 37 and 22 K are obvious to the naked eye. The transition at 22 K exhibits temperature hysteresis that increases with magnetic field. In addition the superconducting transition temperature from resistivity is 820 mK and the critical field is 80 mT. Contrary to earlier work where the Debye temperature ranged from 186 to 218 K, the Debye temperature extracted from the heat capacity is 254 K in good agreement with the predicted value of 250 K. Magnetoresistance, Hall effect and magnetic susceptibility measurements are underway. In time, measurements made on these crystals may help us to understand the origin of superconductivity and its relation to the CDW transitions in pure uranium.
Date: January 1, 2001
Creator: Cooley, J. C. (Jason C.); Hanrahan, R. J. (Robert J.); Hults, W. L. (William L.); Lashley, J. C. (Jason C.); Manley, M. E. (Michael E.); Mielke, C. H. (Charles H.) et al.
Partner: UNT Libraries Government Documents Department