| 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 |
Abstract
Structure 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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Folgar_CE_2010.pdf |
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