FAQs - Aerogel Technologies, LLC

Aerogels are a diverse class of ultralow density solids that combine multiple disparate and extreme materials properties into a single material envelope. Aerogel materials generally exhibit a high degree of porosity, high specific surface area, and superlative energy damping (thermal, acoustic, and impact) properties. The term aerogel refers to the sparse, porous solid backbone of a gel isolated from the liquid component of the gel and similar porous solid materials with mesoporosity, that is, primarily containing pores ranging from about 2-50 nm. The name aerogel may be misleading at first, as aerogels are dry, rigid or elastic foam-like materials and are not wet or wobbly. The name originates from the fact that aerogels are typically made by replacing the liquid component of a gel—think something physically similar in consistency to edible gelatin—with a gas or a vacuum in a way that preserves the structural integrity of gel’s sparse solid, porous backbone.

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Historically, the most commonly researched and commercially available type of aerogel has been the holographic-looking “blue” silica type. Today, aerogels of numerous different substances can be prepared, including:

• Silica, both hydrophilic (water-absorbing) and hydrophobic (water-repelling)
• Transition metal oxides, lanthanide oxides, actinide oxides, main group oxides, and mixed matrix oxides
• Synthetic polymers such as phenolics, polyureas, polyurethanes, polyimides, and polyamides
• Biopolymers such as cellulose, alginate, and lignin
• Carbon allotropes such as amorphous carbon, graphitic carbon, carbon nanotubes, graphene, and diamond
• Metal chalcogenides and quantum dots
• Metals, carbides, and nitrides

Each of these different types of aerogels provides unique properties, which can include electrical conductivity (carbon and metal aerogels), extreme (up to 80%) elastic return (nanotube and graphene aerogels), catalytic functions (various oxide and metal aerogels), photoluminescence (quantum dot and metal chalcogenide aerogels), water repulsion and oil sorption (hydrophobic silica and polymer aerogels), and more.

The insulating ability (or thermal conductivity) of an aerogel material depends on its composition, form factor, and density, as well as the temperature of its environment. Silica aerogel-based materials are typically used for insulating applications, although Airloy® and other polymer aerogels such as BASF’s Slentite® are beginning to be used as well. For a typical silica aerogel monolith with a density of ~100 mg/cc, the thermal conductivity is usually between 10-20 mW/m-K, or about 2-3 times more insulating per unit thickness than polyurethane foam (PUF) or Styrofoam® (expanded polystyrene), which have thermal conductivities of 29-35 mW/m-K typically. Composite aerogel blankets such as Aspen Aerogels’ Spaceloft® typically have a thermal conductivity of ~14-21 mW/m-K. Cabot Aerogel’s Lumira® aerogel particles used for daylighting applications similarly have a thermal conductivity of ~9-12 mW/m-K. Cabot Aerogel’s Thermal Wrap™ blankets, used in construction, daylighting, and low-dust insulating applications, has a thermal conductivity of ~23 mW/m-K. In general, the thermal conductivity of an aerogel decreases (that is, its insulating ability increases) as its density decreases. While aerogels are available in a wide range of densities, from as low as 0.001 g/cc up to ~0.55 g/cc, in general only materials with densities in the range of 0.06-0.55 are practical for industrial applications. Thermal conductivity of non-silica aerogels depends on composition and density, with some materials being equal to or better than silica aerogels at the same density, and others exhibiting higher thermal conductivity at the same density.

Aerogels are extremely good thermal insulators for several reasons. First, it is important to understand how heat is transported through materials. Heat is transported through a material three different ways: through conductive transport, that is, through the solid part of the material; through convective transport, that is, by being carried by gas diffusing through a material; and through radiative transport, that is, by electromagnetic energy like infrared energy penetrating through the material.

Aerogels are extremely low-density materials, typically 50-99.98% air by volume. This means aerogels have very little mass through which heat can conduct. Additionally, the solid part of an aerogel is highly disordered and thus makes conduction of heat through the little solid that is there inefficient.

Additionally, aerogels have extremely tiny pores, typically between 2-50 nm in diameter. These pores are actually so tiny that they are smaller than the mean free path of air at room temperature and pressure, that is, the average distance a molecule of air can travel before hitting another air molecule is greater than the width of the pores in a typical aerogel. As a result, air has an extremely difficult time diffusing through and thus carrying heat energy through an aerogel by convection. This phenomenon, called the Knudsen effect, differentiates aerogels from traditional foams, which typically have pore sizes of tens to thousands of microns in diameter and thus allow more heat through by convection.

Aerogels are not necessarily good at stifling radiative transport, however, and so at high temperatures, heat can pass through aerogels in the form of infrared energy. As a result, commercial aerogel insulation products include additional materials called IR opacifiers embedded in the aerogel to reflect and/or absorb infrared energy. This helps limit radiative transport, making aerogel insulators excellent insulators at high temperatures as well as room temperature.

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First, not all aerogels are easy to break!  Classic (or “legacy”) aerogels exhibit extremely high strength-to-weight ratios and are able (in principle) to hold thousands of times their weight in applied force, however also typically exhibit extremely low fracture toughness, that is, the ability to resist propagation of flaws in the material. As a result, it is possible for a classic aerogel block that is 96% air by volume to hold a brick thousands of times its own weight, but only if the weight is placed on the monolith gently and there are no major cracks in the aerogel.

New mechanically strong and machinable aerogels such as Airloy® strong aerogels made by Aerogel Technologies fix this problem. Airloy aerogels are hundreds of times stronger and stiffer than classic aerogels and simultaneously durable and fracture tough. Unlike legacy aerogels, Airloy aerogels can be machined (drilled, tapped, turned, milled) and bent without breaking. The strength, stiffness, thermal conductivity, and other properties of Airloy aerogels depend on the product series. See our page about Airloy materials properties for specific information about the mechanical properties of different Airloy products.

Aerogel materials vary in price depending on form factor and composition. Once very costly due to specialty manufacturing processes and lack of commercial availability, today aerogel materials of various types are produced commercially on massive scales at prices that are in many instances competitive with traditional materials technologies. Aerogel particles such as Cabot Aerogel’s Lumira® aerogel, used in the daylighting panels in office buildings, gyms, and sports arenas around the world, while composite aerogel blankets such as Aspen Aerogels Spaceloft® and Cabot Aerogel’s Thermal Wrap™ insulate subsea oil pipelines, refineries, and residential apartments. Strong aerogel panels such as Airloy® strong aerogels from Aerogel Technologies are making planes, cars, and rockets lighter, more energy efficient, and cheaper to operate. Sub-bulk pricing for these and other aerogel products is available at BuyAerogel.com. Please contact us for bulk pricing requests.

by Nick Gromicko, CMI®Aerogel is a class of porous, solid materials that exhibits an impressive array of extreme properties. Invented in and used for decades in scientific applications, aerogel is becoming increasingly feasible as a building insulation, largely due to a decrease in the price of the material.Aerogel is still prohibitively costly for most homeowners, and the few who can afford it probably don’t know what it is. At expensive properties with environmentally friendly features, however, inspectors should be prepared to encounter the material. Also, the prevalence of aerogel is likely to increase in the coming years as it becomes more affordable and widely known.Physical Properties and Identification Aerogel holds 15 world records for material properties, a few of which are listed below. Aerogel is:

• lightweight. It is, in fact, the lowest-density solid on the planet. Some types are composed of more than 99% air, yet they still function as solids;
• extremely high in surface area. It can have a surface area up to 3,000 square meters per gram, meaning that a cubic inch of aerogel, if flattened out, could cover an entire football field; and
• strong. It can support up to 4,000 times its own weight. In the picture at right, a 2-gram piece of the material is supporting a  5-pound brick.

The following qualities will also assist with identification. Aerogel:

• appears blue due to Rayleigh scattering, the same phenomenon that colors the sky;
• feels like Styrofoam® to the touch. Although a slight touch will not leave a mark, pressing more firmly will leave a lasting depression or even produce a catastrophic breakdown in the structure, causing it to shatter like glass; and
• is rigid. Despite its name, it is hard and dry, little resembling the gel from which it was derived.

ProductionAerogel is derived from gels, which are substances in which solid particles span a liquid medium. The first aerogel was produced from silica gels, although later work involved alumina, chromia, carbon and tin oxide. Through a process called super-critical drying, the liquid  component of the gel is removed, leaving behind the hollow, solid framework. The resulting aerogel is a porous, ultra-lightweight lattice composed of more than 90% air. Ordinarily, drying of a gel results in its shrinkage and collapse (think of Jell-O left out for a few days), but super-critical drying is performed under intense heat and pressure that preserve the structure of the gel.  

Manufacturers offer the material in a variety of forms, such as the granules pictured at right, made by Cabot, which are sometimes used as insulation in skylights. Aspen Aerogel® offers 57-inch wide rolls of the material in 0.2- and 0.4-inch thicknesses, while Thermoblok® comes in 1.5-inch wide strips that are used to cover framing studs and help prevent thermal bridging at a cost of about $1.99 per foot. 

Safety

Aerogel safety is dependent on the safety of the gel from which it was made; it will be carcinogenic, for instance, if the gel from which it was derived had this quality. Fortunately, silica-based aerogel is not known to be dangerous, although it may irritate skin, mucous membranes, eyes, the respiratory tract, and the digestive system. Aerogel is hydroscopic and extremely dry to the touch, which can, in turn, cause it to dry out unprotected skin. Gloves and goggles are recommended for inspectors and contractors who must handle the material.

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Aerogel does not seem to be an environmental threat. Aspen Aerogel’s® website states: “Aerogel blankets do not meet any of the characteristics of a U.S. EPA hazardous waste,” and further notes that scrap aerogel may be disposed of in landfills that are approved to accept industrial waste.In summary, aerogel is a safe, remarkably effective thermal insulator whose use should become more widespread as it becomes more affordable.