Name: Preparing Silica Aerogel Monoliths via a Rapid Supercritical Extraction Method (Video) | JoVE Journal
Uploaded: 2014-02-28T14:15:00.000+00:00
Duration: 6 min 54 s
Description: Learn rapid supercritical extraction to fabricate monolithic silica aerogels using a hydraulic hot press. This efficient method reduces processing time to eight hours or less for advanced materials applications.

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5 minutes

The authors thank undergraduate students Lutao Xie, for physical characterization of the aerogel materials, and Aude Bechu, for testing the draft procedure. We are grateful to the Union College Engineering Laboratory for machining the stainless steel mold. The Union College Aerogel Laboratory has been funded by grants from the National Science Foundation (NSF MRI CTS-0216153, NSF RUI CHE-0514527, NSF MRI CMMI-0722842, NSF RUI CHE-0847901, NSF RUI DMR-1206631, and NSF MRI CBET-1228851). This material is based upon work supported by the NSF under Grant No. CHE-0847901.

Safety Considerations: Safety glasses or goggles should be worn at all times during the preparative work with solutions and the hydraulic hot press. Laboratory gloves should be worn when preparing the chemical reagent solution and when pouring the solution into the mold in the hot press. TMOS, methanol and concentrated ammonia, and solutions containing these reagents, must be handled within a fume hood. The supercritical extraction process releases hot methanol, so it is necessary both to vent the hydraulic hot press, and to ensure that there are no ignition sources within the vent path of the hot press. In addition, we recommend installation of a safety shield around the hot press. In the event of a gasket failure, the shield will help contain the resulting gasket pieces and thereby protect anyone working near the hot press.
1. Prepare Reagents and Other Supplies
<ol>
	<li>Gather the reagents needed for the recipe: tetramethylorthosilicate, methanol, deionized water, and ammonia.</li>
	<li>Make 100.0 ml of a 1.5&#160;M ammonia solution. To do so, dilute 10.1 ml of 14.8 M concentrated ammonia to 100 ml with deionized water.</li>
	<li>Acquire a square stainless steel mold, 12.7 cm x 12.7 cm x 1.9 cm high, with 9 circular wells of 2.2 cm diameter (see Figure 3). Wipe the mold with a clean, damp rag to remove any surface oil or dust. Spray inside of each circular well with high-temperature mold release spray to ease in removal of aerogels from the mold after processing.</li>
	<li>Prepare three sets of sealing gaskets from 1/16 in&#160;(1.6 mm) thick graphite sheet and 0.0005 in&#160;(0.012 mm) thick stainless steel foil. Cut three pieces of each material sufficient to cover the mold completely (&#62;12.7 cm x &#62;12.7cm).</li>
</ol>
2. Prepare Instruments
<ol>
	<li>Program the hot press sealing and extraction programs. First set up a sealing program that will be used to seal the bottom of the open mold. See Table 1 for the necessary program values. Next set up the extraction program with the correct parameters for the silica aerogels using the mold described above. See Table 2 for these parameters.</li>
	<li>Prepare glassware. To avoid contamination, four glass beakers will be needed, one 250&#160;ml beaker labeled &#39;precursor solution,&#39; one 100&#160;ml beaker labeled &#39;methanol,&#39; one 20&#160;ml beaker labeled &#39;DI water,&#39; and one 10&#160;ml beaker labeled &#39;1.5&#160;M ammonia.&#39; Make sure all beakers are clean and dry.</li>
	<li>Prepare pipettes. Digital pipettes should be used for ease. A 10&#160;ml digital pipette and a 1,000&#160;&#956;l&#160;pipette will be used. Make sure multiple pipette tips are available.</li>
	<li>Prepare sonicator by adding water to the fill line.</li>
</ol>
3. Seal Mold Bottom
<ol>
	<li>Place mold and gasket material in hot press. First center a graphite sheet on the lower platen, add a sheet of stainless steel foil and place the mold on top of the stainless steel foil. Add another set of gasket material (stainless steel then graphite) on top of the mold. (Note: used gasket material can be used on the top in this step, but new gasket material must be used on the bottom.)</li>
	<li>Start the hot press sealing program, using the parameters shown in Table 1. This program seals the bottom of the mold to prevent the liquid precursor chemicals from leaking when the mold is filled with precursor solution.</li>
</ol>
4. Make Precursor Solution
The recipe for TMOS-based silica aerogels is shown in Table 3. All solution preparation work is performed in a fume hood.
<ol>
	<li>First pipette aliquots of TMOS totaling 17.0 ml from the reagent bottle into the 250&#160;ml&#160;glass beaker labeled &#39;precursor solution&#39;.</li>
	<li>Pour some methanol into the 100&#160;ml glass beaker and then pipette aliquots of methanol totaling 55.0 ml into the 250&#160;ml glass beaker labeled &#39;precursor solution.&#39;</li>
	<li>Pour some deionized water into the 20&#160;ml beaker labeled &#39;DI water&#39; and from that beaker pipette 7.2 ml of water into the 250&#160;ml beaker.</li>
	<li>Lastly, pour some 1.5&#160;M NH3 into the 10&#160;ml beaker and from that beaker pipette 270 &#181;l&#160;of the solution into the 250&#160;ml beaker.</li>
	<li>Seal the beaker with plastic paraffin film.</li>
	<li>Mix reagents to ensure that hydrolysis occurs by sonicating the precursor solution for at least 5 min. Prior to sonication, two liquid layers are sometimes visible in the precursor mixture. Following 5 min of sonication, the solution should appear to be monophasic. If it does not, sonicate the mixture for an additional 5 min.</li>
</ol>
5. Pour Precursor Solution into the Mold in the Hot Press
<ol>
	<li>At the end of the mold sealing program the hot press platens will open. Remove the top-side gasket material and set aside. Leave the mold as is in the hot press so that the bottom side of the mold remains sealed.</li>
	<li>Fill each well of the mold completely with the precursor solution. (Note: there will be about 10 ml of aerogel precursor solution left over after filling the mold. This can be discarded or processed under ambient conditions to make xerogels.)</li>
	<li>Put fresh gasket material on the top of the mold: the stainless steel foil first and then the graphite on top.</li>
	<li>Run the hot press extraction program (shown in Table 2). This program seals the mold, heats the contents to a supercritical state, performs the supercritical extraction and then cools the mold.</li>
</ol>
6. Remove the Aerogels from the Mold
<ol>
	<li>When the extraction process is complete, remove the mold and gasket material from the hot press.</li>
	<li>Remove the top gasket material from the mold. Set this aside.</li>
	<li>Gently loosen the mold from the bottom gasket material.</li>
	<li>Carefully remove each aerogel from the mold, one at a time, by firmly pushing them through from one side with a gloved finger.</li>
	<li>When the aerogels are removed from the mold, the process is complete.</li>
</ol>

<ol><li>Aegerter, M. A., Leventis, N., Koebel, M. M. <a target="_blank" href="http://scholar.google.com/scholar?hl=en&safe=off&q=author%3aAegerter%2C+MA+%22Aerogels+Handbook%22">Aerogels Handbook</a>. , Springer. New York, New York, USA. (2011).</li>
<li>Gurav, J. L., Jung, I. -K., Park, H. -H., Kang, E. S., Nadargi, D. Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Silica+aerogel%3A+Synthesis+and+applications%5BTitle%5D)+AND+%22J.+Nanomater%22%5BJournal%5D)">Silica aerogel: Synthesis and applications.</a> J. Nanomater. , Forthcoming.</li>
<li>Kistler, S. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Coherent+expanded+aerogels%5BTitle%5D)+AND+%22J.+Phys.+Chem%22%5BJournal%5D)">Coherent expanded aerogels.</a> J. Phys. Chem. 13, 52-64 (1932).</li>
<li>Phalippou, J., Woignier, T., Prassas, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Glasses+from+aerogels%5BTitle%5D)+AND+%22J.+Mater.+Sci%22%5BJournal%5D)">Glasses from aerogels.</a> J. Mater. Sci. 25 (7), 3111-3117 (1990).</li>
<li>Danilyuk, A. F., Gorodetskaya, T. A., Barannik, G. B., Lyakhova, V. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Supercritical+extraction+as+a+method+for+modifying+the+structure+of+supports+and+catalysts%5BTitle%5D)+AND+%22React.+Kinet.+Catal.+Lett%22%5BJournal%5D)">Supercritical extraction as a method for modifying the structure of supports and catalysts.</a> React. Kinet. Catal. Lett. 63 (1), 193-199 (1998).</li>
<li>Pajonk, G. M., Rao, A. V., Sawant, B. M., Parvathy, N. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Dependence+of+monolithicity+and+physical+properties+of+tmos+silica+aerogels+on+gel+aging+and+drying+conditions%5BTitle%5D)+AND+%22J.+Non-Cryst.+Solids%22%5BJournal%5D)">Dependence of monolithicity and physical properties of tmos silica aerogels on gel aging and drying conditions.</a> J. Non-Cryst. Solids. 209 (1-2), 40-50 (1997).</li>
<li>Poco, J. F., Coronado, P. R., Pekala, R. W., Hrubesh, L. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((A+rapid+supercritical+extraction+process+for+the+production+of+silica+aerogels%5BTitle%5D)+AND+%22Mat.+Res.+Soc.+Symp%22%5BJournal%5D)">A rapid supercritical extraction process for the production of silica aerogels.</a> Mat. Res. Soc. Symp. 431, 297-302 (1996).</li>
<li>Tewari, P. H., Hunt, A. J., Lofftus, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Ambient-temperature+supercritical+drying+of+transparent+silica+aerogels%5BTitle%5D)+AND+%22Mater.+Lett%22%5BJournal%5D)">Ambient-temperature supercritical drying of transparent silica aerogels.</a> Mater. Lett. 3 (9), 363-367 (1985).</li>
<li>Van Bommel, M. J., de Haan, A. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Drying+of+silica+aerogel+with+supercritical+carbon+dioxide%5BTitle%5D)+AND+%22J.+Non-Cryst.+Solids%22%5BJournal%5D)">Drying of silica aerogel with supercritical carbon dioxide.</a> J. Non-Cryst. Solids. 186, 78-82 (1995).</li>
<li>Pajonk, G. M., Repellin-Lacroix, M., Abouarnadasse, S., Chaouki, J., Klavana, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((From+sol-gel+to+aerogels+and+cryogels%5BTitle%5D)+AND+%22J.+Non+Cryst.+Solids%22%5BJournal%5D)">From sol-gel to aerogels and cryogels.</a> J. Non Cryst. Solids. 121, 66-67 (1990).</li>
<li>Kalinin, S., Kheifets, L., Mamchik, A., Knot'ko, A., Vertigel, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Influence+of+the+drying+technique+on+the+structure+of+silica+gels%5BTitle%5D)+AND+%22J.+Sol-Gel+Sci.+Technol%22%5BJournal%5D)">Influence of the drying technique on the structure of silica gels.</a> J. Sol-Gel Sci. Technol. 15 (1), 31-35 (1999).</li>
<li>Prakash, S. S., Brinker, C. J., Hurd, A. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Silica+aerogel+films+at+ambient+pressure%5BTitle%5D)+AND+%22J.+Non-Cryst.+Solids%22%5BJournal%5D)">Silica aerogel films at ambient pressure.</a> J. Non-Cryst. Solids. 190 (3), 264-275 (1995).</li>
<li>Prakash, S. S., Brinker, C. J., Hurd, A. J., Rao, S. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Silica+aerogel+films+prepared+at+ambient+pressure+by+using+surface+derivatization+to+induce+reversible+drying+shrinkage%5BTitle%5D)+AND+%22Nature%22%5BJournal%5D)">Silica aerogel films prepared at ambient pressure by using surface derivatization to induce reversible drying shrinkage.</a> Nature. 374 (6521), 439-443 (1995).</li>
<li>Haereid, S., Einarsrud, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Mechanical+strengthening+of+TMOS-based+alcogels+by+aging+in+silane+solutions%5BTitle%5D)+AND+%22J.+Sol-Gel+Sci.+Technol%22%5BJournal%5D)">Mechanical strengthening of TMOS-based alcogels by aging in silane solutions.</a> J. Sol-Gel Sci. Technol. 3 (3), 199-204 (1994).</li>
<li>Bhagat, S. D., Oh, C. S., Kim, Y. H., Ahn, Y. S., Yeo, J. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Methyltrimethoxysilane+based+monolithic+silica+aerogels+via+ambient+pressure+drying%5BTitle%5D)+AND+%22Microporous+Mesoporous+Mater%22%5BJournal%5D)">Methyltrimethoxysilane based monolithic silica aerogels via ambient pressure drying.</a> Microporous Mesoporous Mater. 100 (1-3), 350-355 (2007).</li>
<li>Leventis, N., Palczer, A., McCorkle, L., Zhang, G., Sotiriou-Leventis, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Nanoengineered+silica-polymer+composite+aerogels+with+no+need+for+supercritical+fluid+drying%5BTitle%5D)+AND+%22J.+Sol-Gel+Sci.+Technol%22%5BJournal%5D)">Nanoengineered silica-polymer composite aerogels with no need for supercritical fluid drying.</a> J. Sol-Gel Sci. Technol. 35 (2), 99-105 (2005).</li>
<li>Gauthier, B. M., Bakrania, S. D., Anderson, A. M., Carroll, M. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((A+fast+supercritical+extraction+technique+for+aerogel+fabrication%5BTitle%5D)+AND+%22J.+Non-Cryst.+Solids%22%5BJournal%5D)">A fast supercritical extraction technique for aerogel fabrication.</a> J. Non-Cryst. Solids. 350, 238-243 (2004).</li>
<li>Gauthier, B. M., Anderson, A. M., Bakrania, S. D., Mahony, M. K., Bucinell, R. B. Method and Device for Fabricating Aerogels and Aerogel Monoliths Obtained Thereby. , (2008).</li>
<li>Gauthier, B. M., Anderson, A. M., Bakrania, S. D., Mahony, M. K., Bucinell, R. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Method+and+Device+for+Fabricating+Aerogels+and+Aerogel+Monoliths+Obtained+Thereby%5BTitle%5D)+AND+%22%22%5BJournal%5D)">Method and Device for Fabricating Aerogels and Aerogel Monoliths Obtained Thereby.</a> , (2011).</li>
<li>Carroll, M. K., Anderson, A. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Use+of+a+rapid+supercritical+extraction+method+to+prepare+aerogels+from+various+precursor+chemistries%5BTitle%5D)+AND+%22Polymer+Preprints%22%5BJournal%5D)">Use of a rapid supercritical extraction method to prepare aerogels from various precursor chemistries.</a> Polymer Preprints. 52 (1), 31-32 (2011).</li>
<li>Pierre, A. C., Rigacci, A. SiO aerogels. <a target="_blank" href="http://scholar.google.com/scholar?hl=en&safe=off&q=author%3aPierre%2C+AC+%22Aerogels+Handbook%22">Aerogels Handbook</a>. Aegerter, M. A., Leventis, N., Koebel, M. M. , Springer. New York, New York, USA. (2011).</li>
<li>Anderson, A. M., Wattley, C. W., Carroll, M. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Silica+aerogels+prepared+via+rapid+supercritical+extraction%3A+Effect+of+process+variables+on+aerogel+properties%5BTitle%5D)+AND+%22J.+Non-Cryst.+Solids%22%5BJournal%5D)">Silica aerogels prepared via rapid supercritical extraction: Effect of process variables on aerogel properties.</a> J. Non-Cryst. Solids. 355 (2), 101-108 (2009).</li>
<li>Anderson, A. M., Carroll, M. K., Green, E. C., Melville, J. T., Bono, M. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Hydrophobic+silica+aerogels+prepared+via+rapid+supercritical+extraction%5BTitle%5D)+AND+%22J.+Sol-Gel+Sci.+Technol%22%5BJournal%5D)">Hydrophobic silica aerogels prepared via rapid supercritical extraction.</a> J. Sol-Gel Sci. Technol. 53 (2), 199-207 (2010).</li>
<li>Brown, L. B., Anderson, A. M., Carroll, M. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Fabrication+of+titania+and+titania-silica+aerogels+using+rapid+supercritical+extraction%5BTitle%5D)+AND+%22J.+Sol-Gel+Sci.+Technol%22%5BJournal%5D)">Fabrication of titania and titania-silica aerogels using rapid supercritical extraction.</a> J. Sol-Gel Sci. Technol. 62 (3), 404-413 (2012).</li>
<li>Bono, M. S., Anderson, A. M., Carroll, M. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Alumina+aerogels+prepared+via+rapid+supercritical+extraction%5BTitle%5D)+AND+%22J.+Sol-Gel+Sci.+Technol%22%5BJournal%5D)">Alumina aerogels prepared via rapid supercritical extraction.</a> J. Sol-Gel Sci. Technol. 53 (2), 216-226 (2010).</li>
<li>Dunn, N. J. H., Carroll, M. K., Anderson, A. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Characterization+of+alumina+and+nickel-alumina+aerogels+prepared+via+rapid+supercritical+extraction%5BTitle%5D)+AND+%22Polymer+Preprints%22%5BJournal%5D)">Characterization of alumina and nickel-alumina aerogels prepared via rapid supercritical extraction.</a> Polymer Preprints. 52 (1), 250-251 (2011).</li>
<li>Plata, D. L., Briones, Y. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Aerogel-Platform+Optical+Sensors+for+Oxygen+Gas%5BTitle%5D)+AND+%22J.+Non-Cryst.+Solids%22%5BJournal%5D)">Aerogel-Platform Optical Sensors for Oxygen Gas.</a> J. Non-Cryst. Solids. 350, 326-335 (2004).</li>
<li>Roth, T. B., Anderson, A. M., Carroll, M. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Analysis+of+a+rapid+supercritical+extraction+aerogel+fabrication+process%3A+Prediction+of+thermodynamic+conditions+during+processing%5BTitle%5D)+AND+%22J.+Non-Cryst.+Solids%22%5BJournal%5D)">Analysis of a rapid supercritical extraction aerogel fabrication process: Prediction of thermodynamic conditions during processing.</a> J. Non-Cryst. Solids. 354 (31), 3685-3693 (2008).</li>
</ol>

The authors declare that they have no competing financial interests.

The RSCE method produces consistent batches of monolithic silica aerogels using an automated and simple process. The method as presented here requires an eight-hour processing step. It is possible to speed up the heating and cooling steps to make monolithic aerogels in as little as 3 hr22; however, when an 8 hr procedure is employed, more consistent batches of aerogel monoliths result. Small variations in the process parameters do not affect the physical properties of the resulting aerogels, indicating that th...

Silica aerogel materials have low density, high surface area, and low thermal and electrical conductivity combined with a nanoporous structure with excellent optical properties. The combination of these properties in one material makes aerogels attractive in a large number of applications1. In a recent review article, Gurav et al. describe in detail the current and potential applications of silica aerogel materials, both in scientific research and in development of industrial products2. For example, silica aerogels have been used as absorbents, as sensors, in low-dielectric materials, as storage media for fuels, and for a wide array of thermal insulating applications2.
Aerogels are typically fabricated using a two-step process. The first step involves mixing appropriate chemical precursors, which then undergo condensation and hydrolysis reactions to form a wet gel. To prepare silica gels, the hydrolysis reactions occur between water and a silica-containing precursor, in this case tetramethylorthosilicate (TMOS, Si(OCH3)4), in the presence of acid or base catalyst. 
Si(OCH3)4 + H2O <img alt="Vector arrow symbol, indicating direction or movement; used in physics and mathematics diagrams." fo:content-width=".2in" src="/files/ftp_upload/51421/arrow.jpg" width="20" data-altupdatedat="1787630408000" data-alt="arrow"> Si(OCH3)4-n(OH)n + n CH3OH
TMOS is insoluble in water. In order to facilitate hydrolysis, it is necessary to include another solvent, in this case methanol (MeOH, CH3OH), and to stir or sonicate the mixture. Base-catalyzed polycondensation reactions then occur between the hydrolyzed silica species:
R3SiOH + HOSiR3 <img alt="Vector arrow symbol, indicating direction or movement; used in physics and mathematics diagrams." fo:content-width=".2in" src="/files/ftp_upload/51421/arrow.jpg" width="20" data-altupdatedat="1787630408000" data-alt="arrow"> R3Si-O-SiR3 + H2O
R3SiOH + CH3OSiR3 <img alt="Vector arrow symbol, indicating direction or movement; used in physics and mathematics diagrams." fo:content-width=".2in" src="/files/ftp_upload/51421/arrow.jpg" width="20" data-altupdatedat="1787630408000" data-alt="arrow"> R3Si-O-SiR3 + CH3OH
The polycondensation reactions result in the formation of a wet gel, comprised of a porous SiO2 solid matrix, in which the pores are filled with the solvent byproducts of the reaction, in this case methanol and water. The second step involves drying the wet gel to form an aerogel: removing the solvent from the pores without altering the solid matrix. The drying process is critically important to the formation of the aerogel. If not carried out correctly the fragile nanostructure collapses and a xerogel is formed as illustrated schematically in Figure 1.
There are three basic methods for drying sol-gel materials to produce aerogels: supercritical extraction, freeze drying and ambient pressure drying. The supercritical extraction methods avoid crossing the liquid-vapor phase line so that surface tension effects do not cause the nanostructure of the gel to collapse. Supercritical extraction methods can be performed at high temperature (250-300 °C) and pressure with direct extraction of the alcohol solvent byproduct of the condensation and hydrolysis reactions3-7. Alternatively, one can perform a set of exchanges and replace the alcohol solvent with liquid carbon dioxide, which has a low supercritical temperature (~31 °C). The extraction can then be performed at relatively low temperature8,9, albeit at high pressure. Freeze drying methods10,11 first freeze the wet gel at low temperature and then allow the solvent to sublimate directly to a vapor form, again avoiding crossing the liquid-vapor phase line. The ambient pressure method uses surfactants to reduce the surface tension effects or polymers to strengthen the nanostructure, followed by drying of the wet gel at ambient pressure12-16.
The Union College Rapid Supercritical Extraction (RSCE) process is a one-step (precursor to aerogel) method17-19. The method employs high-temperature supercritical extraction, which allows fabrication of monolithic aerogels in hours, rather than the days to weeks required by other methods. The method utilizes a confined metal mold and a programmable hydraulic hot press. Chemical precursors are mixed and poured directly into the mold, which is placed between the platens of the hydraulic hot press. The hot press is programmed to close and apply a restraining force to seal the mold. The hot press then heats the mold at a specified rate to a temperature, Thigh, above the critical temperature of the solvent (see Figure 2 for a plot of the process). During the heatup period the chemicals react to form a gel and the gel strengthens and ages. As the mold is heated the pressure also rises, eventually reaching a supercritical pressure. Upon reaching Thigh, the hot press dwells at a fixed state while the system equilibrates. Next the hot press force is decreased and the supercritical fluid escapes, leaving behind a hot aerogel. The press then cools the mold and its contents to room temperature. At the end of the process (which can take 3-8 hr) the press opens and monolithic aerogels are removed from the mold.
This RSCE method offers significant advantages over other aerogel fabrication methods. It is fast (&lt;8 hr total) and not very labor intensive, typically requiring only 15-20 min preparation time followed by 3-8 hr processing time. It does not require solvent exchanges, which means that relatively little solvent waste is generated during the process.
In the section that follows, we describe a protocol for preparing a set of cylindrical silica aerogel monoliths via the Union RSCE method from a precursor mixture comprised of TMOS, methanol, and water with aqueous ammonia employed as the catalyst for the hydrolysis and polycondensation reactions (with a TMOS:MeOH:H2O:NH3 molar ratio of 1.0:12:3.6:3.5 x 10-3). We note that the Union RSCE method can be used to prepare aerogels of various different sizes and shapes, depending on the metal mold and hydraulic hot press employed. This RSCE method has also been used to prepare other types of aerogels (titania, alumina, etc.) from different precursor recipes20.

<table><tbody><tr><td>Tetramethylorthosilicate&amp;nbsp; (TMOS)</td><td>Sigma Aldrich</td><td>218472-500G</td><td>98% purity, CAS 681-84-5&amp;nbsp;</td></tr><tr><td>Methanol&amp;nbsp; (MeOH)</td><td>Fisher Scientific</td><td>A412-20</td><td>Certified ACS Reagent Grade, &amp;ge;99.8%</td></tr><tr><td>Ammonium Hydroxide (aqueous ammonia)</td><td>Fisher Scientific</td><td>A669S212</td><td>Certified ACS Plus, about 14.8 N, 28.0-20.0 w/w%</td></tr><tr><td>Deionized Water</td><td>on tap in house</td><td></td><td></td></tr><tr><td>Flexible Graphite Sheet</td><td>Phelps Industrial Products</td><td>7500.062.3</td><td>1/16 in thick</td></tr><tr><td>Stainless Steel Foil</td><td>Various</td><td></td><td>0.0005 in thick, 304 Stainless Steel</td></tr><tr><td>High Temperature Mold Release Spray</td><td>various (for example, CRC Industrial Dry PTFE Lube)</td><td></td><td>Should be able to withstand high temperatures.</td></tr></tbody></table>

preparing silica aerogel monoliths via a rapid supercritical extraction method

Preparing Silica Aerogel Monoliths via a Rapid Supercritical Extraction Method

A procedure for the fabrication of monolithic silica aerogels in eight hours or less via a rapid supercritical extraction process is described. The procedure requires 15-20 min of preparation time, during which a liquid precursor mixture is prepared and poured into wells of a metal mold that is placed between the platens of a hydraulic hot press, followed by several hours of processing within the hot press. The precursor solution consists of a 1.0:12.0:3.6:3.5 x 10-3 molar ratio of tetramethylorthosilicate (TMOS):methanol:water:ammonia. In each well of the mold, a porous silica sol-gel matrix forms. As the temperature of the mold and its contents is increased, the pressure within the mold rises. After the temperature/pressure conditions surpass the supercritical point for the solvent within the pores of the matrix (in this case, a methanol/water mixture), the supercritical fluid is released, and monolithic aerogel remains within the wells of the mold. With the mold used in this procedure, cylindrical monoliths of 2.2 cm diameter and 1.9 cm height are produced. Aerogels formed by this rapid method have comparable properties (low bulk and skeletal density, high surface area, mesoporous morphology) to those prepared by other methods that involve either additional reaction steps or solvent extractions (lengthier processes that generate more chemical waste).The rapid supercritical extraction method can also be applied to the fabrication of aerogels based on other precursor recipes.

Following the procedure described here results in consistent batches of monolithic silica aerogels. Figure 4 shows images of typical silica aerogels made via this process. Each aerogel takes on the shape and size of the well in the processing mold with no shrinkage. The images show that the silica aerogels are translucent.
The physical properties of these aerogels are summarized in Table 4. They are comparable to those of silica aerogels produced from similar ...

This article describes a rapid supercritical extraction method for fabricating silica aerogels. By utilizing a confined mold and hydraulic hot press, monolithic aerogels can be made in eight hours or less.

A procedure for the fabrication of monolithic silica aerogels in eight hours or less via a rapid supercritical extraction process is described. The ...

The overall goal of the following experiment is to make monolithic silica aerogels via a rapid one-step extraction process. This is achieved by first mixing the precursor chemicals and pouring the mixture into a metal mold. As a second step, the mold is sealed in a hydraulic hot press in which the chemicals are processed to produce aerogels.During this process, the chemical precursors gel and age, the solvent within the pores of the salt gel reaches a supercritical state, and the hot press releases the solvent as a supercritical fluid and cools the mold. At the end of the process, monolithic silica aerogels are removed from the mold. The main advantage of this technique over other methods for aerogel preparation is that the entire process from mixing precursors to obtaining monolithic aerogels requires only a few hours.We came up with the idea for this hot press based method. When an undergraduate student wanted to make aerogels for a senior project, we didn't have access to a critical point dryer, so we improvised and used a hot press. Visual demonstration of this method is critical due to the importance of the proper use of the metal mold and hot press.If the wells are not filled with a precursor solution or the hot press is not programmed properly, the resulting aerogels will be of subpar quality. First dilute 10.1 milliliters of 14.8 molar, concentrated ammonia to 100 milliliters with deionized water to make a 1.5 molar ammonia solution. After acquiring a square stainless steel mold, wipe it with a clean damp rag to remove any surface oil or dust.Then spray the inside of each circular well with high temperature mold release spray to ease and arrow gel removal from the mold After processing, prepare three sets of ceiling gaskets by cutting a one 16 inch thick graphite sheet and a 0.0005 inch thick stainless steel foil to the appropriate sizes. To program the hot press ceiling and extraction programs, set up a ceiling program that will be used to seal the bottom of the open mold. Next, set up the extraction program with the correct parameters for the silica aerogels.Using the mold described to seal the mold bottom, center a graphite sheet on the lower PLA of the hot press and add a sheet of stainless steel foil. Then place the mold on top of the stainless steel foil and add another cent of gasket material on top of the mold. Following this, start the hot press ceiling program using the previously described parameters.At this point, pipette aliquots of tetraethyl ortho silicate, totaling 17.0 milliliters into a 250 milliliter glass beaker labeled precursor solution. Then pipette aliquots of methanol totalling 55.0 milliliters into the beaker pipette 7.2 milliliters of water into the beaker, and then add 270 microliters of 1.5 molar ammonia. Seal the beaker with plastic paraffin film.Mix the reagents to ensure that hydrolysis occurs by syndicating the precursor solution for at least five minutes if the solution is not monophasic. After five minutes of mixing, sonicate the mixture for five additional minutes. Once the mold ceiling program has finished and the hot press PLAs have opened, remove the top side gasket material and set aside.Leave the mold as is in the hot press so that the bottom side of the mold remains sealed. Next, fill each well of the mold completely with the precursor solution. Place fresh gasket material on the top of the mold with a stainless steel foil first followed by a graphite sheet.Following this, run the hot press extraction program. When the extraction process is complete, remove the mold and gasket material from the hot press. Remove the top gasket material from the mold and set aside.Then gently loosen the mold from the bottom gasket material. Finally, carefully remove each aerogel from the mold one at a time by firmly pushing them through from one side with a gloved finger. Following the described procedure results in consistent batches of monolithic silica aerogels shown Here are images of typical silica aerogels made via this process.Each aerogel takes on the shape and size of the well in the processing mold with no shrinkage. The images show that the silica aerogels are translucent. The physical properties of these aerogels are summarized here.They are comparable to those of silica aerogels produced from similar precursor recipes using low temperature supercritical extraction. Shown here is a typical pore distribution prepared by BJH analysis of the Desorption isotherm acquired with a micro metics accelerated surface area and por symmetry system.2010. The air gels are meso porous with a peak in poor diameter near 20 nanometers Once mastered, this technique can be used to prepare silica aerogels in fewer than 15 minutes of preparation time and eight hours of processing time.By adapting this procedure to different precursor chemistries, many types of aerogels can be fabricated. These include Illumina, titania, titania, silica, vania, silica, nickel, Illumina, cobalt, Illumina, and hydrophobic silica aerogels. Don't forget that working with tetraethyl, orthos, silicate, methanol, and the hydraulic hot press can be hazardous.The following precautions should always be taken where safety glasses and gloves, and work in a fume hood for the precursor solution preparation, provide sufficient ventilation of the hot press and avoid wearing loose fitting clothing when performing the procedure.

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JoVE Journal

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Learn rapid supercritical extraction to fabricate monolithic silica aerogels using a hydraulic hot press. This efficient method reduces processing time to eight hours or less for advanced materials applications.

Preparing Silica Aerogel Monoliths via a Rapid Supercritical Extraction Method

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