<abstract xml:lang="en" xmlns="http://www.w3.org/1999/xhtml">Aerogels are internally nanostructured materials characterized with a plethora of unique properties. Monoliths with high optical transparency made of silica aerogels were some of the first and still one of the most important classes of aerogels. Experiments and theory indicate that optical transparency and structural integrity of silica aerogels are negatively correlated. Other than optimal combination of processing conditions during aerogel fabrication can result in either highly transparent but cracked or in crack-free but less transparent and even opaque aerogels monoliths. Results are presented from the study of the relationship between the properties of single-step tetramethoxysilane (TMOS) base-catalyzed silica aerogels and the processing conditions, both at the alcogel preparation step and during the supercritical liquid CO2 drying process. Crack-free aerogel monoliths with good optical transparency were obtained with TMOS:methanol (MeOH) molar ratios of 1:16 and TMOS:ammonia (NH4OH) molar ratios of 1:0.05, CO2-MeOH exchange rates of about 1.25 ml/min, and autoclave decompression rates of 70 KPa/min. Adding glycerol in the sol-gel stage had a positive effect on the aerogel monolithicity but, even without glycerol, crack-free silica aerogels can be obtained by reducing the depressurization rate of the autoclave. A strict control and careful selection of the aerogel's processing conditions within the set of parameters identified will enable the fabrication of structurally sound silica aerogels with good optical properties essential for a number of applications.</abstract>

Aerogels are internally nanostructured materials characterized with a plethora of unique properties. Monoliths with high optical transparency made of silica aerogels were some of the first and still one of the most important classes of aerogels. Experiments and theory indicate that optical transparency and structural integrity of silica aerogels are negatively correlated. Other than optimal combination of processing conditions during aerogel fabrication can result in either highly transparent but cracked or in crack-free but less transparent and even opaque aerogels monoliths. Results are presented from the study of the relationship between the properties of single-step tetramethoxysilane (TMOS) base-catalyzed silica aerogels and the processing conditions, both at the alcogel preparation step and during the supercritical liquid CO2 drying process. Crack-free aerogel monoliths with good optical transparency were obtained with TMOS:methanol (MeOH) molar ratios of 1:16 and TMOS:ammonia (NH4OH) molar ratios of 1:0.05, CO2-MeOH exchange rates of about 1.25 ml/min, and autoclave decompression rates of 70 KPa/min. Adding glycerol in the sol-gel stage had a positive effect on the aerogel monolithicity but, even without glycerol, crack-free silica aerogels can be obtained by reducing the depressurization rate of the autoclave. A strict control and careful selection of the aerogel's processing conditions within the set of parameters identified will enable the fabrication of structurally sound silica aerogels with good optical properties essential for a number of applications.

Optically transparent and structurally sound silica aerogels: insights from a process study

Industrial and Manufacturing Engineering Fargo, North Dakota State University, ND 58102, USA

Advances in Materials Science

Aerogels are internally nanostructured materials characterized with a plethora of unique properties. Monoliths with high optical transparency made of silica...

Optically transparent and structurally sound silica aerogels: insights from a process study

Published Online: Aug 07, 2012

Page range: 5 - 16

DOI: https://doi.org/10.2478/v10077-012-0001-8

Keywords
silica aerogel, transparent aerogel monolith

This content is open access.

Optically transparent and structurally sound silica aerogels: insights from a process study

Published Online: Aug 07, 2012

Page range: 5 - 16

DOI: https://doi.org/10.2478/v10077-012-0001-8

Keywordssilica aerogel, transparent aerogel monolith

This content is open access.

Keywords
silica aerogel, transparent aerogel monolith