Original Paper: Nano- and macroporous materials (aerogels, xerogels, cryogels, etc.)
Silica aerogel is the archetypal thermal superinsulator and commonly applied to improve the thermal performance of on- and off-shore industrial infrastructure and buildings. Hitherto, the main products on the market are silica aerogel based blankets fabricated by casting a silica sol into a porous or fiber matrix, followed by gelation, hydrophobization, and (supercritical) drying. Considering the diffusion efficiency of the reagents and solvents used in the preparation, a reduced size of the gel bodies may accelerate and simplify the sol-gel, hydrophobization, and drying processes. Thus, particle based products, derived from silica aerogel granulate and powder additives and semi-finished products, are an attractive solution towards inexpensive aerogel applications. Here, we optimized the process parameters for silica aerogel powder production from three common silica precursors: waterglass (WG), ion-exchanged waterglass, and tetraethoxysilane (TEOS), including gelation pH, hydrophobization procedure, solvent system, processing temperatures, and ambient pressure drying protocol. Successful hydrophobization is confirmed by elemental analysis, FTIR and quantitative solid-state NMR spectroscopy. All three routes lead to silica aerogel powders with similar type IV isotherms, and BET surface areas above 700 m2/g. Importantly, the thermal conductivity of the packed powder beds does not exceed 20 mW/(m⋅K) for all three routes, implying even lower thermal conductivities of the aerogel phase itself. Total processing time, including gelation, aging, surface modification, and ambient pressure drying is between 2 and 4 h, depending on the selected route. Given that high quality silica aerogel powders can be produced from all investigated silica precursors and hydrophobization agents, the process selection for industrial upscaling can be based entirely on engineering and economic considerations.
Silica aerogel powder was produced from waterglass, ion-exchanged waterglass and TEOS.
All precursors lead to surface areas above 700 m2/g and thermal conductivities below 20 mW/(m·K).
The precursor can thus be selected based on availability, cost and process complexity.
Silica aerogel powder Thermal insulation Hydrophobization Process comparison
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We thank Daniel Rentsch for maintaining and providing access to the NMR spectrometer, which was funded in part by grant 150638 from the Swiss National Science Foundation, and are grateful to Olivier Emery for his assistance with some of the synthesis experiments.
Compliance with ethical standards
Conflict of interest
A patent on the production of silica aerogel powders from non-ion-exchanged waterglass has been filed.
Eur-Lex (2012) Directive 2012/27/EU of the European Parliament and of the Council of 25 October 2012 on energy efficiency, amending Directives 2009/125/EC and 2010/30/EU and repealing Directives 2004/8/EC and 2006/32/EC Text with EEA relevanceGoogle Scholar
Schwertfeger F, Frank D (2001) Organically modified aerogels, processes for their preparation by surface modification of the aqueous gel, without prior solvent exchange, and subsequent drying, and thier use. US20010034375A1Google Scholar
Chakraborty S, Pisal AA, Kothari VK, Venkateswara Rao (2016) A synthesis and characterization of fibre reinforced silica aerogel blankets for thermal protection. Adv Mater Sci Eng. https://doi.org/10.1155/2016/2495623.