In 1993, the international trade groups predicted that the market for superconducting devices will grow 100-fold in the next three decades. ! Some of the growth areas for bulk superconductors are applications that rely on the ability of the superconductor to exclude magnetic fields or shape electromagnetic waves, for example, levitated vehicles, motors, and magnetic shields. Additional research, development, and manufacturing scale-up are needed to achieve full commercialization, especially with high temperature superconductors. Development of bulk superconducting applications relying on the Meissner effect or shielding capability are limited by the mechanical performance, processability, and environmental resistance of high temperature superconductors; however, these problems can be alleviated by making superconductor/polymer composites. One goal of this research is to process high temperature superconductor/polymer composites and to systematically characterize them. A second objective of this research 1s to determine if a superconductor/polymer composite can shield electromagnetic waves and to define the critical composite requirements for effective shielding.
Three types of composite structures, 3-3, 0-3, and 2-3 superconductor/ polymer composites, were processed. The 3-3 composites have continuous ceramic and polymer phases. The 0-3 composites have ceramic particles in a polymer matrix, and the 2-3 composites have ceramic platelets in a polymer matrix. These composites were compared on the basis of mechanical performance, machinability, environmental resistance, diamagnetic strength, electrical resistance, and shielding effectiveness. If the superconductor/polymer 0-3 composites are processed well, they have improved mechanical performance, machinability, and environmental resistance compared to superconductor/polymer 3-3 composites; however, they do not have zero resistance nor provide any shielding capability, and they have a lower diamagnetic strength than superconductor/polymer 3-3 composites. The YBCO/polymer 3-3 composites have lower superconducting properties than 90% dense bulk YBCO, but they have improved machinability and mechanical performance. Unfortunately, the processability of superconductor/ polymer 3-3 composites is not improved compared to bulk superconductors. The superconductor/polymer 2-3 composites combine the formability of the 0-3 composites and the shielding effectiveness of 3-3 composites. This is the first time a discontinuous ceramic phase/polymer composite has demonstrated shielding capability. Superconducting shielding 1s determined to be a result of reflection, dependent on the Meissner effect, and absorption, dependent on the high conductivity, but it does not rely on zero sample resistivity. Based on these results, the critical composite material requirements for effective shielding are 1) that the superconducting phase be of sufficient size and critical current density to absorb electromagnetic waves and 2) that the nonnormal volumes of the superconducting phase overlap. Thus, a superconductor/polymer 0-3 composite can not provide any shielding, but a superconductor/polymer 2-3 composite shields at both low frequencies and microwave frequencies. / Ph. D.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/38246 |
| Date | 06 June 2008 |
| Creators | Namboodri, Shannon Leahy |
| Contributors | Materials Engineering Science, Kander, Ronald G., Gordon, Ronald S., Davis, William A., Kampe, Stephen L., Gibbs, Gerald |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Dissertation, Text |
| Format | xiii, 165 leaves, BTD, application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
| Relation | OCLC# 30935499, LD5655.V856_1994.N363.pdf |
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