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Abstract

Transparent glass sponges are a new class of materials that can potentially be used for effective light dispersion in photobioreactors. In this work, transparent glass sponges are prepared by the polymer replica technique employing polyurethane sponges with cell sizes of 20 pores per inch as templates and commercially available nanoscaled SiO2 powders. Necessary conditions for obtaining transparent open-celled glass sponges are presented. Topics such as slurry stabilization, temperature for burning-out the polymer and subsequent sintering of the remaining SiO2 structure to transparent cellular bodies are discussed. It was found, that concentrated suspensions at around pH 10 offer suitable properties for both, bringing enough particles onto the polymer template for the formation of a stable and self-supporting SiO2 shell and for successful sintering of the particulate framework to transparent bodies. Therefore, an adjusted burning-out process and an adequate sintering regime is presented. Furthermore, the resulting sponge structure is characterized employing X-Ray diffractometry, light, and scanning electron microscopy. In addition, volume image analysis was performed using magnetic resonance imaging. This method allows the calculation of geometrical parameters like cell-size and specific surface area of the resulting structure, required for application of the new material.