Kalwall In The News
Silica Aerogel Nearing Commercialization
Environmental Building News, Product News & Reviews, July/August 2002
Invented in the 1930s and widely touted in the energy-conscious 1970s and 1980s, silica aerogel has promised glazings that transmit light yet insulate as well as the best rigid foams. Finally, commercial production of this almost-magic material is just around the corner. The Cabot Corporation, headquartered in Boston, Massachusetts, has completed a silica aerogel factory in Frankfurt, Germany. Following commissioning of that plant, manufacturing of NanogelTM will begin this fall, said Nanogel sales manager Jim Litrun.
Silica aerogel is a very light, highly porous form of silica that is 97 percent air. Cabot makes it by producing a hydrogel that is treated to make it hydrophobic before drying at atmospheric pressure. "Imagine a Jello® made from sand, then getting rid of the water–you're left with a solid foam with cells so tiny they prevent air molecules from transferring heat to their neighbors," explained Litrun. While early efforts to produce silica aerogels focused on a monolithic end-product that made for great press photos, Cabot has focused on a less glamorous but more practical granular product. The granular aerogel can be poured into a translucent glazing panel and packed to prevent settling; in this way, problems of cracking that occurred with the monolithic aerogel products are eliminated. The density of the material is just 6.5 lb/ft3 (100 kg/m3).
The amazing thing about silica aerogel is how well it insulates–even while transmitting (diffused) light. A 1-inch thick (25 mm) layer of Nanogel insulates to R-8 (RSI-1.4)–without any of the ozone-depleting substances found in most high-R-value foam insulation materials. Aerogels insulate well for two reasons: first, silica is a poor conductor of heat, and second, the aerogel contains a large number of tiny pores (about 20 nanometers in diameter) which are small enough to retard heat transfer. By way of explanation; consider fiberglass insulation; it is the air that provides the actual insulation, based on its gas-phase conductivity. If kept perfectly still, air would insulate to about R-5.5 per inch (38 m.°/C/W). Fiberglass insulation does not achieve that high an R-value because the air spaces are large enough for convection to occur and because the glass fibers conduct heat fairly effectively. With silica aerogels, the silica has lower conductivity than glass, there is less solid material, free air movement is effectively restricted by the small pores, and gas-phase conductivity is restricted because the pore sizes of the aerogel are smaller than the average free path length of the air molecules in the pores. "It's the very, very small pore size that's the secret," said Litrun.
Testing of Nanogel has been very successful, according to Litrun. In accelerated aging tests, there is no discoloration due to ultraviolet light. Because the material is permanently hydrophobic, there is no risk of it absorbing moisture. Settling is not a problem if the material is packed as panels are filled. ("You can actually put the material under compression," noted Litrun.) And the friability problem that existed with earlier generations of aerogels has apparently been eliminated because of Nanogel's elasticity. "The elasticity is enhanced by the hydrophobic treatment, which is one of the unique aspects of the Nanogel manufacturing process," Litrun said.
Probably the first company that will actually put Nanogel to work in a glazing product (at least in the U.S.) is the Kalwall Corporation. Their glazing products are ideally suited to an aerogel fill because they are translucent to start with (fiberglass-reinforced polyester). Also, the company has long been a leader in advancing energy and daylighting performance. Kalwall has offered glazing panels filled with lightweight fiberglass insulation for a number of years, but the more fiberglass insulation they add, the lower the transmissivity. "We've exhausted that option," said Bruce Keller, vice president for sales and marketing.
Nanogel allows Kalwall to achieve the insulation levels they want (about R-20/RSI-3.1) in their standard 70 mm-thick (2-3/4 inch) glazing panel while blocking far less light than occurs with their current insulated skylight panels. "We've partnered with Cabot to try to become the first to come out with a product," Keller told EBN. As soon as Nanogel becomes available from Cabot's new Frankfurt plant, Kalwall will be using it in a pool-enclosure building in the company's hometown of Manchester, New Hampshire. The high humidity and harsh conditions in this building will make it an ideal test case for the product, according to Keller. "If it's going to work and it's manufacturable, then Kalwall will be out front with the least expensive product," he said.
Costs of Nanogel are dependent on thickness, but Litrun said that Nanogel should add "less than $ 10/ft2 ($ 110/m2) to the cost of a 1-inch thick (25 mm) skylight glazing system." Keller doesn't know what the cost impacts will be for Kalwall products. EBN will keep you posted on developments with this exciting product. - AW
For more information:HOME | ABOUT KALWALL | REQUEST MORE INFORMATION | CONTACT KALWALL