No description available.

No description available.

No description available.

Sand casting is the most widely used casting process for both ferrous and non-ferrous alloys; however, the process is marred by large grain size structures and long solidification times. The coarser microstructure has a negative effect on the mechanical properties of the cast components and the long processing time affects the overall productivity of the process. The research reported herein addresses these problems for aluminum sand castings by enhancing the rate of heat extraction from the casting by replacing air, which is typically present in the pores of the sand mold and has a relatively low thermal conductivity by helium which has a thermal conductivity that is at least five times that of air in the temperature range of interest. The effect of (1) the flow rate of helium, (2) the way in which it is introduced into the mold, and (3) the mold design on (a) the average grain size, (b) the secondary dendrite arm spacing, and (c) the room temperature tensile properties of castings is investigated and compared to their counterparts produced in a typical sand casting process. In addition, a cost analysis of the helium-assisted sand casting process is performed and an optimum set of parameters are identified. It is found that when the helium-assisted sand casting process is performed with close to the optimum parameters it produces castings that exhibit a 22 percent increase in ultimate tensile strength and a 34 percent increase in yield strength with no significant loss of ductility, no degradation in the quality of the as-cast surfaces, and no significant increase in the overall cost.

Thermal transport in nanowires and nanotubes has attached much attention due to their use in various functional devices and their use as a model system for low dimensional transport phenomena. The precise control of the crystal structure, defects, characteristic size, and electronic properties of nanowires has allowed for fundamental studies of phonon and electron transport in a variety of nanoscale systems. The thermal conductivity in nanostructured materials can vary greatly compared to bulk values owing to classical and quantum size effects. In this work, two model systems for investigating fundamental phonon transport were investigated for potential use in thermoelectric and thermal management applications. The thermoelectric properties of twin defect indium arsenide nanowires and the thermal conductivity of polythiophene nanofibers with improved polymer chain crystallinity were measured with a microfabricated measurement device. The effects of twin planes on reducing the mean free path of phonons in indium arsenide and the effects of improved chain alignment in increasing the thermal conductivity in polymer fibers is discussed. / text

Not available / text

Thesis (Ph.D)--Chemical Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Teja, Amyn S.; Committee Member: Abdel-Khalik, Said I.; Committee Member: Meredith, Carson; Committee Member: Nair, Sankar; Committee Member: Skandan, Ganesh. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Thesis (Ph. D.)--University of Texas at Austin, 2004. / Supervisor: John B. Goodenough. Vita. Includes bibliographical references.

Made available in DSpace on 2014-10-09T12:23:53Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:06:51Z (GMT). No. of bitstreams: 1 00972.pdf: 1471018 bytes, checksum: 69f6c23b7bae93be019dc24069488410 (MD5) / Dissertacao (Mestrado) / IEA/D / Escola Politecnica, Universidade de Sao Paulo - POLI/USP

Made available in DSpace on 2014-10-09T12:25:57Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:06:48Z (GMT). No. of bitstreams: 1 11281.pdf: 11270615 bytes, checksum: 7ab921002ca47b9d45181b99f34235e4 (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP