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Microstructure and transmittance of silica gels for application as transparent heat insulation materials

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Abstract

Transparent heat insulation materials (TIMs) exhibit great potential for different solar applications. Despite this fact, they are not used widely, since they are either very expensive (aerogel) or made from organic materials and, thus, are not resistant to higher temperatures. Xerogel, obtained from silica gel by drying at ambient pressure, is a promising material for the production of TIMs. This study investigates different treatments applied during the production of silica gel and their influence on its optical and structural properties. To this end, silica sol was gelled and the resulting silica gel was aged before it was either hydrothermally treated or fired. Subsequently, radiation transmission measurements from 400 to 2700 nm as well as porosity, specific surface area, and scanning electron microscopic/transmissions electron microscopic measurements were conducted. It was found that under certain conditions, the transmittance can be improved by firing as well as by hydrothermal treatment. Firing at 600 °C with 10-min dwell time and hydrothermal treatment at 120 °C with 5-h dwell time resulted in the silica gels with the highest transmittance of 63 up to 66 %. The porosity (24–76 %), the pore radii (3–26 nm), and the specific light absorption by embedded water and SiOH molecules could be adjusted over a wide range.

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Acknowledgments

The authors are grateful to Dr. G. Schmidt from the Institute of Ceramic, Glass and Construction Materials for conducting scanning electron microscopy measurements as well as to Dr. V. Klemm from the Institute of Material Science, for the transmission electron microscopy measurements, both at TU Bergakademie Freiberg. Furthermore, Dr. R. Dittrich from the Institute Electronic and Sensor Materials is gratefully acknowledged for conducting the nitrogen adsorption and desorption measurements, also from TU Bergakademie Freiberg. The authors would like to gratefully acknowledge the financial support of the European Commission through the European Social Fund (ESF) and the Saxon State Ministry of Science and the Arts for the project ANWan (No. SAB 100109651).

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Authors and Affiliations

  1. Institute of Ceramic, Glass and Construction Materials, TU Bergakademie Freiberg, Freiberg, Germany

    Friederike Klenert, Jens Fruhstorfer & Christos G. Aneziris

  2. Institute of Thermal Engineering, TU Bergakademie Freiberg, Freiberg, Germany

    Ulrich Gross, Dimosthenis Trimis, Iris Reichenbach, Dig Vijay & Anja Horn

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  1. Friederike Klenert
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  2. Jens Fruhstorfer
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Correspondence to Friederike Klenert.

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Klenert, F., Fruhstorfer, J., Aneziris, C.G. et al. Microstructure and transmittance of silica gels for application as transparent heat insulation materials. J Sol-Gel Sci Technol 75, 602–616 (2015). https://doi.org/10.1007/s10971-015-3731-3

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  • DOI: https://doi.org/10.1007/s10971-015-3731-3

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