Abstract
The complex refractive index of ceria has been determined at ambient temperature using variable angle spectroscopic ellipsometry for two chemical states-fully oxidized and partially reduced. The ellipsometric model is corroborated with complementary measurements of thickness, surface roughness, and chemical composition. Partially reduced ceria is shown to have a larger absorption index over a broad spectral range than fully oxidized ceria, including the visible and near IR regions. We use a simple model of a directly irradiated particle entrained in a gas flow to demonstrate the consequences of accounting for changes in chemical state when modeling ceria-based thermochemical process.
Highlights
Cerium(IV) dioxide has garnered recent attention as a promising exchange material for high-temperature thermal processing, for synthetic fuel production [1,2]
Marabelli and Wachter characterized a reduced ceria sample using optical reflectivity measurements, but the reduction state of the sample was not identified. It was likely in a reduction state beyond the reach of the solar thermochemical systems motivating the present study since they were heated to 2275°C for two hours
The model we present here is simple enough to clearly demonstrate the importance of the chemical state on the energy and mass transfer to and from ceria, but complete enough to include the important mechanisms present in a directly irradiated dilute fluidized bed reactor
Summary
Cerium(IV) dioxide (ceria) has garnered recent attention as a promising exchange material for high-temperature thermal processing, for synthetic fuel production [1,2]. Marabelli and Wachter characterized a reduced ceria sample using optical reflectivity measurements, but the reduction state of the sample was not identified It was likely in a reduction state beyond the reach of the solar thermochemical systems motivating the present study since they were heated to 2275°C for two hours. These two data sets demonstrate the wide variation in optical properties reported in the literature for ceria due to differences in material composition/morphology or (possibly) the characterization approach. It exhibits behavior important enough to warrant its own section
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