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.
Department or Program
Department of Mechanical and Materials Engineering
Year Degree Awarded
Copyright 2020, all rights reserved. My ETD will be available under the "Fair Use" terms of copyright law.