There has long been a fascination in the design industry with aerogel, the ultimate space material: super light, super stiff, super insulator. At one time it heralded the future of advanced material applications. Then it didn’t really get very far. While there are new and exciting applications, there may be a much more compelling take on the story of aerogel. Let’s reanimate this sometimes forgotten, other times cast aside, novel material in the service of finding new applications and inspiring the next generation of designs and processes.
It is not known precisely how aerogel was developed or when, exactly, it was first produced, though it was somewhere between the end of the 1920s and the early 1930s. In 1931, S.S. (Steven) Kistler wrote the first description of aerogel. The short article primarily describes the ‘procedure’ for producing an aerogel before elaborating on the already long list of possible applications. Kistler was actively teaching at College of the Pacific at the time (pursuing a doctoral degree at Stanford University and eventually teaching at the University of Illinois), and there is a possibly apocryphal tale that he and a colleague at Stanford, Charles Learned, had made a gentleman’s wager to see who could replace the liquid in a jar of jam with a gas, while leaving the size, structure and shape of the jam intact.
An ultra-light, self-organising structure was born, the first of its kind and a predecessor to, and in some ways still more advanced than, many current additive manufacturing processes. In the most common form of aerogel, the first step is to catalyse a silica solution into a gel. While it gels, the solution undergoes a hydrolysis reaction creating nanoparticles that agglomerate into a regular structure. The next step is to remove all liquid and gas from the material, leaving only the structure of nanoparticles. Kistler originally executed the last step in aerogel production with a supercritical drying process. This means placing the liquid under high pressure and high temperature so that its liquid and gaseous states are interchangeable (i.e., the states have the same density), then rapidly dropping the pressure so that gas very quickly replaces the supercritical liquid. Later in the development of aerogels, they were produced with the more resource efficient method of solvent exchange.
In the past 30 years the most popular commercial use of aerogel has been as insulation. Current products on the market are more than 15 times lighter and have approximately three times lower thermal conductivity. And, as opposed to the typical insulation-on-a-roll start that is layered to 250mm thickness, aerogel starts at a thickness of 10mm. Given that, it’s clear that aerogel insulation can save a significant amount of weight and volume. The value is evident in upfront and long-term energy use and, in the case of the superyacht industry, fuel efficiency. These products are widely available, and don’t require any much, if any, training to install.
Throughout his career, our hero Kistler went on to evangelise and distribute the technology and processes of aerogel. Perhaps the most romantic of his undertakings, while he was with the Norton Company, was the effort, employing techniques similar to those used to create aerogel, to be the first to synthesise diamonds. This line of luxurious research led to the less glamorous invention of a scratch-resistant polymer for eyeglasses. Over the years, though, there have been more fascinating and nefarious uses of aerogel. Monsanto’s Santocel, an aerogel that was developed as a thickening agent for animal medications, was later used as a thickening agent for napalm, the notorious firebombing gel. Then there is FOGBANK, a material classified to this day, speculated to be silica aerogel doped with beryllium that acts as a kind of superinsulator used in two-stage nuclear weapons to prevent the second stage from exploding prematurely in a smaller, ‘conventional’ heat explosion.
These applications are all compelling, but this is not the most valuable thing about aerogel. The value lies in the concept and creation process of aerogel. A process for creating superlight designed materials (from any base: plastic, metal, etc.) is more important than the material itself. It is one of, if not the first, ‘designed’ modern material. A material created not to solve an industrial problem or societal ill, but one created as pure speculation, which is wonderful and rare in science. Parts of this process are now used in other industries, for instance, a cousin of the supercritical drying process is used in ‘light water’ nuclear reactors. In this case, the water transitions from liquid to gas at high temperature and pressure, without boiling and goes on to turn a steam turbine. Thus, it saves volume and reduces energy loss in the process.
Clearly, Kistler and Learned knew aerogel would have some implicit value, but it took many years of tacking up the R&D winds to achieve this value. Without aerogel would 3D printing even exist? This is a simplification, of course, but its concept is the same as that of SLA printing, and is still more material-efficient that most other printing types. The next aerogel paradigm may come when we can control the outward shape of an aerogel object—to mould it or print it.
In fact, 3D printed aerogel already exists: graphene can be 3D printed, as of 2017, in layers more resembling the thickness of ink than the typical 3D printing tolerances of plastics and metals. Aerogel 3D printing is a two-step dematerialisation: first an optimised macro structure is printed, then that structure is dried, leaving the graphene aerogel microstructure. This is the ultimate in dematerialisation, an idea that is beginning to permeate this series of articles.
So now what do we do with this? How about combining aerogel with active coatings  ? Essentially, one could coat an aerogel nano-structure to create an ultra-high surface area (and ultra-lightweight) wall that filters harmful chemicals out of the air. It’s lighter, healthier and energy efficient. Soon metals will be printed via a similar ‘drying’ process and the next race for the world’s lightest, most efficient structure, building or boat hull will be on.
Thank you to Dr. Valerie Hayez of Dow for her insight and technical support on aerogel insulation.
Check back soon for the next instalment: Thin glass
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