Type of Document Dissertation Author Folgar, Carlos Eduardo URN etd-05192010-013744 Title Structure Evolution of Silica Aerogel under a Microwave Field Degree PhD Department Materials Science and Engineering Advisory Committee
Advisor Name Title Clark, David E. Committee Chair Pickrell, Gary R. Committee Member Suchicital, Carlos T. A. Committee Member Viehland, Dwight D. Committee Member Keywords
- silica gel
- single mode microwave oven
- dielectric measurements
- microwave process
Date of Defense 2010-05-10 Availability unrestricted AbstractStructure evolution of silica aerogel was studied in microwave- and conventionally processed samples over the temperature range from 25 to 1200⁰C. The samples were produced using sol-gel processing and dried under carbon dioxide supercritical conditions. After drying, the monolithic samples received a thermal treatment at different programmed temperatures in two different ovens, conventional and microwave. The microwave process was performed using a single mode microwave oven at 2.45GHz. Dielectric properties were measured using the cavity perturbation method, and structural characterization was carried out using a variety of techniques, including absorption surface analysis, Helium pycnometry, Archimedes principle, Fourier transform infrared spectroscopy, X-ray diffraction, and high resolution microscopy. The data obtained revealed that structural differences do exist between microwave- and conventionally processed samples.
Three different regions were identified from the structural characterization of the samples. Regions I exhibited a structure densification at temperatures between 25 and 850⁰C. Region II was characterized by a bulk densification in the temperature range from 850 to 1200⁰C. Region III was represented by the onset of crystallization above 1200⁰C. Explanation and possible causes behind the structural differences observed in each region are provided. In general, the structure evolution observed in microwave- and conventionally processed samples followed the same order, but occurred at lower temperature for the microwave process.
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