The 1980’s: Aerogel Gets Going
The 1980’s brought forth safer techniques for producing aerogels, ways of making aerogels 30 times lighter than had ever been accomplished before, and a new class of organic and carbon aerogels that would demonstrate aerogels of different substances could do amazing and very different things.
Safer Aerogel Production
In the 1980’s, the alkoxide sol-gel process was made less toxic by using a safer alkoxide compound and the supercritical drying technique was made safer by replacing supercritical alcohol with supercritical carbon dioxide. With these developments, interest in commercializing aerogels emerged again, along with scientific interest from a large body of scientists intrigued by what aerogels coul do and what substances they could make aerogels out of.
In his article in the New Scientist (January 30, 1993), Prof. Jochen Fricke discusses how the efficient alkoxide processing technique developed in the 1970’s led to interest in recommercializing aerogels for superinsulation (reproduced with permission from the New Scientist):
Cherenkov detectors require only relatively small amounts of the rather expensive aerogel tiles. If they could be mass-produced cheaply, aerogels would have enormous potential. Beginning with Kistler, scientists working with aerogels recognised that their unique structure gives them unusual thermal properties, making them ideal insulators. Their main advantage over other insulators is their high thermal resistance and their stability – they do not melt at temperatures as high as 600°C, and they do not burn.
Following the international oil crisis in the 1970s, a new impetus to save energy led to research at the German company BASF. Scientists there developed a way to produce aerogel pellets instead of tiles. Their aim was to make aerogels suitable for use as insulating spacer material in windows and in solar panels.
Until now, drying alcogels at high temperature and pressure had been a necessary but risky procedure. In 1984 a gasket failed in the 3000 litre autoclave at the laboratory of Airglass, ejecting 1000 litres of methanol and causing an explosion that destroyed the entire facility.
Scientists at BASF aimed to modify this part of the process to make the production of aerogels safer, and to devise a cheaper means of producing the wet gels. Liquid carbon dioxide (CO2), which is nonflammable and nontoxic, seemed an ideal substitute for methanol, and the wet gels would be produced as pellets rather than tiles. The pellets are made by spraying waterglass and acid from a mixing jet to give droplets that gel while falling into a flask. After washing, the water in the aquagel pellets is exchanged for acetone, then liquid CO2. The resulting gels can be dried at around 31°C and at a pressure of 74 bars.
Here is where a bit of historical debate arises. Although it is true that scientists at BASF developed CO2-based supercritical drying, the American aerogel community largely attributes this discovery to Dr. Arlon Hunt at Lawrence Berkeley National Laboratory, who many believe applied it first.
Arlon Hunt and Mike Ayers provide their perspective on the development of the CO2 technique:
After th[e] discovery [of the alkoxide sol-gel approach for producing aerogels], new developments in aerogels science and technology occurred rapidly as an increasing number of researchers joined the field. Some of the more notable achievements are:
The first pilot plant for the production of silica aerogel monoliths using the TMOS method was established by members of the Lund group in Sjobo, Sweden. The plant included a 3000 liter autoclave designed to handle the high temperatures and pressures encountered for supercritical methanol (240°C and 80 atmospheres). However, in 1984 the autoclave developed a leak during a production run. The room containing the vessel quickly filled with methanol vapors and subsequently exploded. Fortunately, there were no fatalities in this incident, but the facility was completely destroyed. The plant was later rebuilt and continues to produce silica aerogels using the TMOS process. The plant is currently operated by the Airglass Corp.
In 1983 Arlon Hunt and the Microstructured Materials Group at Berkeley Lab found that the very toxic compound TMOS could be replaced with tetraethylorthosilicate (TEOS), a much safer reagent. This did not lower the quality of the aerogels produced.
At the same time the Microstructured Materials Group also found that the alcohol within a gel could be replaced by liquid carbon dioxide before supercritical drying without harming the aerogel. This represented a major advance in safety as the critical point of CO2 (31°C and 1050 psi) occurs at much less severe conditions than the critical point of methanol (240°C and 1600 psi). Additionally, carbon dioxide does not pose an explosion hazard as does alcohol. This process was put to use in making transparent silica aerogel tiles from TEOS.
BASF in Germany simultaneously developed CO2 substitution methods for the preparation of silica aerogel beads from sodium silicate. This material was in production until l996 and was marketed as “BASOGEL”.
With newfound possibilities for efficient aerogel production, a large number of scientists became interested in the field and along with them came new types of aerogels and new entrepreneurship. Among them were scientists at Lawrence Livermore National Laboratory and NASA. Starting around 1985, Lawrence Livermore quickly became a leader in aerogel technology development and would produce numerous breakthroughs in processing, application, and synthesis of aerogels. Arlon Hunt and Mike Ayers report:
In the late 1980s, researchers at Lawrence Livermore National Laboratory (LLNL) led by Larry Hrubesh prepared the world’s lowest density silica aerogel (and the lowest density solid material). This aerogel had a density of 0.003 g/cm3, only three times that of air.
Shortly thereafter, Rick Pekala, also of LLNL, extended the techniques used to prepare inorganic aerogels to the preparation of aerogels of organic polymers. These included resorcinol-formaldehyde and melamine-formaldehyde aerogels. Resorcinol-formaldehyde aerogels could be pyrolyzed to give aerogels of pure carbon. This opened a completely new area in aerogel research.
Thermalux, L.P. was founded in 1989 by Arlon Hunt, and others, in Richmond California. Thermalux operated a 300 liter autoclave for the production of silica aerogel monoliths from TEOS using the carbon dioxide substitution process. Thermalux prepared a large quantity of aerogels, but, unfortunately, ceased operations in 1992.
The invention of carbon aerogels would become a cornerstone of future energy applications. Combing the ultrahigh surface area of aerogels with tunable electrical conductivity, carbon aerogels would enable the production of revolutionary “supercapacitors” in the 1990’s–capacitors that store energy as electric charge in high enough density they could be used in place of batteries in some applications. These devices would pave the way for a new generation of energy storage systems and, more importantly, a new way of thinking about energy storage, both essential in the development of the hybrid and electric vehicles of the 21st Century.
By the end of the 1980’s, the theoretical knowledge, fundamentals of processing, and characterization tools needed to really understand and develop aerogels were all in place, ready to enable breakthroughs in possible compositions and manufacturing in the 1990’s.