H. Daniel Young, Ph.D. (Advisor); Raghavan Srinivasan, Ph.D. (Committee Member); Maher Amer, Ph.D. (Committee Member); Randy Hay (Other)
Master of Science in Materials Science and Engineering (MSMSE)
Fused silica (silica glass) is transparent in the optical and near-infrared and has a low dielectric constant, making it suitable as a window material for radio frequency radiation. However, at high temperatures (>1100C), fused silica will easily creep and lose dimensional stability. Crystallized silica is much more creep resistant than fused silica. Silica crystallizes to many different structures including quartz, tridymite, and α- and β cristobalite. The only cubic polymorph, which is suitable for both optical and radio frequency transmission in polycrystalline form, is β -cristobalite. Unfortunately, this polymorph transforms to α-cristobalite at ~300C, and the volume change during this transformation drastically weakens the material. Consequently β -cristobalite cannot be used for most structural applications unless it is stabilized in the cubic β- phase. When boron phosphate and aluminum phosphate are added to the fused silica, the material crystallizes and results in a stable cristobalite. This stable cristobalite can be used in high temperature and dynamic environments. In order to better understand this stabilization process, X-ray diffraction, Transmission Electron Microscopy, and Scanning Electron Microscopy have been used to identify various polymorphic phases of SiO2-AlPO4-BPO4 under various processing conditions.
Year Degree Awarded
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