Structure Evolution of Silica Aerogel under a Microwave Field

dc.contributor.authorFolgar, Carlos Eduardoen
dc.contributor.committeechairClark, David E.en
dc.contributor.committeememberViehland, Dwight D.en
dc.contributor.committeememberSuchicital, Carlos T. A.en
dc.contributor.committeememberPickrell, Gary R.en
dc.contributor.departmentMaterials Science and Engineeringen
dc.description.abstractStructure evolution of silica aerogel was studied in microwave- and conventionally processed samples over the temperature range from 25 to 1200â °C. 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 850â °C. Region II was characterized by a bulk densification in the temperature range from 850 to 1200â °C. Region III was represented by the onset of crystallization above 1200â °C. 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.en
dc.description.degreePh. D.en
dc.publisherVirginia Techen
dc.rightsIn Copyrighten
dc.subjectsilica gelen
dc.subjectsingle mode microwave ovenen
dc.subjectdielectric measurementsen
dc.subjectmicrowave processen
dc.titleStructure Evolution of Silica Aerogel under a Microwave Fielden
dc.typeDissertationen Science and Engineeringen Polytechnic Institute and State Universityen D.en


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