Aerogel: A new material track with a $10 billion space

Aerogel Overview
Aerogel is a solid material with excellent thermal insulation, with special microstructures such as high ratio surface area, nanoscale holes, low density, etc., based on which the thermal performance is excellent. Its thermal conductivity of 0.012mw/mk, density of 0.16mg/cm3, than the surface area of 400-1000m2 /g, porosity rate of 90-99.8%, its chemical properties are stable, the internal volume of 99% is composed of gas, is currently the least known density of solids.
1.1. The industrialization of aerogels is becoming more and more mature
aerogels have experienced three industrializations since their discovery, and are now in the rapid development of the

. Aerogel was born in 1931, and the discovery of aerogels was marked by Steven.S. Kistler's publication of Co-diffusion Aerogels and Jelly in Nature magazine. It was also the first time kistler had produced the world's first aerogel, SiO2 aerogel, using ethanol supercritical drying technology.
first industrialization took place in the early 1940s, but the first industrialization failed because of the high cost. Monsanto Corp. In collaboration with Kistler, we produce aerogel powders called Santocel for cosmetics, silicone rubber additives, solidified gasoline thickeners, etc. But Monsanto ended its aerogel program in the 1970s because of high manufacturing costs and lagging application development.
the second wave of industrialization, there are typical representatives of different technical directions. (1) In 1984, The Swedish company Airglass used methanol supercritical technology for the Cherenkov detector; In 2003, Tongji University began publishing research papers on normal pressure drying, and Chinese technicians gradually increased their investment in the field of normal pressure drying by producing aerogel powders with normal pressure drying technology to promote their use in insulation coatings, anti-lighting agents and other fields.
third industrialization took place in the early 2000s, when the famous Aspen Aerogel and Cabot companies were born. In 1999, Aspen Systems of the United States undertook a NASA project to successfully prepare a fiber composite aerogel super insulation material. Aspen Aerogel was formally established in 2001 to commercialize aerogels and began to apply aerogel insulated felts to aerospace military and petrochemical industries. Thus opened the third wave of industrialization of aerogel materials, aerogel finally found a good commercial product model. In 2003, Cabot, the world's leading specialty chemicals and high-performance materials company, acquired the production technology for the preparation of SiO2 aerogel materials for normal pressure drying through the merger of Hoechst, Germany, and established Aerogel Professional, which mainly produces aerogel powder particles as a filling layer application in coating additives or lighting glass. In 2004, domestic enterprises engaged in the industrialization of aerogel materials began to appear.
the fourth industrialization mainly occurred in China, with the reduction of aerogel process costs and the expansion of industrial scale, some emerging applications continue to develop, aerogel market is becoming more and more mature. Beginning in 2010, the first batch of domestic aerogel production enterprises have successfully opened up industrial equipment pipeline energy conservation, new energy vehicle safety protection, rail carriers and hull fire insulation application market. In 2017, China issued the "nano-hole aerogel composite insulation products" (GB/T34336-2017) national standards; In 2019, China's aerogel production of 782,000 cubic meters, in 2019 China's aerogel market size of about 1.123 billion yuan.
1.2. The domestic aerogel industry is rising against adversity
the aerogel industry is rising in adversity, and the domestic industry is constantly paying attention to and developing rapidly. In 2016, Aspen Aerogels filed a 337-investigation application with the U.S. International Trade Commission (ITC), alling that products from two companies in China infringe patents related to their composite aerogel insulation materials and manufacturing methods, and requesting the ITC to issue general exclusion orders (or limited exclusion orders) and prohibitions. In 2018, the ITC conducted a 337-part investigation into aerogel insulation composites and their manufacturing processes: it ruled that two Chinese companies had violated intellectual property rights. The investigation has aroused the domestic aerogel industry and scientific researchers to the aerogel patent property rights attach great importance to.
number of patents and applicants has grown rapidly since 2010. From the patent search data, the number of new applicants in aerogel patent applications increased rapidly year by year, with a large number of new applicants pouring into the aerogel field each year. According to the ranking of domestic aerogel patent applicants, two-thirds of the top 20 are universities and research institutes, relatively few enterprise applicants, and the average number of patent applications is less than 50, the number of authorized inventions is even smaller. From the technical direction of the invention patent, it is mainly concentrated in the aerogel preparation process and equipment, which is also the direction of the need for aerogel industrialization to focus on breakthrough. From the domestic aerogel patent application situation, aerogel industry is currently in the early stage of industrialization, there have been a large number of enterprises and research and development institutions into this field.
policy support gradually clear, aerogel pushers frequently out. In issue 250, Science, one of the top international academic journals, listed aerogels as one of the top ten popular science and technology, calling them versatile new materials that could change the world. In 2014 and 2015, the NDRC listed aerogel materials as a "national key energy-saving low-carbon technology promotion catalog" for two consecutive years, and began the initial promotion and application of aerogel materials. In June 2018, aerogels were included in the building materials industry, the first national standard for aerogel materials was issued in September of the same year, and in December 2019 the National Development and Reform Commission issued a document encouraging aerogel energy-saving materials, 2020 In November, the "Aerogel Insulation Insulation Coating System Technical Standard" was launched, which is conducive to regulating the application of aerogel insulation coatings in construction projects, and provides technical guarantee for the design, construction and acceptance of aerogel applications in new construction, expansion and existing construction projects.
According to the China Petroleum Pipeline Science and Technology Research Center, taking the insulation application of 350 degrees C steam pipe as an example, compared with traditional insulation materials, aerogel insulation thickness is reduced by 2/3, energy consumption savings of more than 40%, per kilometer of pipeline can reduce CARBON emissions by 125 tons per year.
With the aerogel industry into the growing number of enterprises, product applications continue to expand, the market scale is expanding, technology research and development speed is accelerating, product prices significantly reduced, industry-leading companies into the rapid growth stage, at present, no domestic enterprises have formed a solid leading position, master low-cost core technology and a certain market resources of enterprises will get huge development space, the entire industry will enter a rapid development window.
1.3. Types of aerogels
Aerogels can be divided into inorganic aerogels, organic aerogels, mixed aerogels and composite aerogels. Common aerogels are mainly silicon aerogels, carbon aerogels and silicon dioxide aerogels, and the newly developed aerogels are mainly graphene oxide aerogels, Fullerene aerogels and fiber/silicon dioxide aerogels.
common on the market and more research can be divided into oxide aerogel materials, carbon aerogel materials (high temperature resistance up to 3000 degrees C) and carbides aerogel materials.
1.3.1. Oxide aerogel material
oxide aerogel material in the high temperature zone (>1000 degrees C) prone to crystal transformation and particle sintering, its temperature resistance is relatively poor, but in the medium and high temperature zone (<1000 degrees C) has a lower thermal conductivity. Oxide aerogel materials are mainly SiO2, Al2O3, TiO2, ZrO2, CuO and so on.
1) SiO2 aerogel material
SiO2 aerogel is currently the most mature research in the field of thermal insulation is a kind of high temperature aerogel, its porosity rate of up to 80% to 99.8%, the typical size of the hole is 1 to 100nm, than the surface area of 200 to 1000m2 / g, and density can be as low as 3kg/m3, room temperature thermal conductivity can be as low as 12m. W/(m〃K)。 SiO2 aerogel materials are typically composited with infrared gels and enhancers to improve the thermal and electrical properties of SiO2 aerogels, making them both practical nano-hole super insulation materials and good insulation and regeneration properties, mainly used in aerospace, military, electronics, construction, home appliances and industrial pipes. Commonly used infrared phosphorescies are silicon carbide, TiO2 (golden redstone and sharp titanium), carbon black, potassium hexatinate, etc., commonly used reinforcing materials are ceramic fiber, alkali-free microglass fiber, polycrystalline molybric fiber, aluminum silicate fiber, zirconia fiber and so on.
2) ZrO2 aerogel material
Compared with SiO2 aerogel material, ZrO2 aerogel has lower high temperature thermal conductivity, is more suitable for high temperature segment insulation applications, in the high temperature insulation material has great potential for application. ZrO2 aerogel material aperture is less than the average free range of air molecules, there is no air conflow in aerogel, pore rate is very high, solids account for a very low volume ratio, so that aerogel thermal conductivity is very low. At present, there are relatively few reports on the application of ZrO2 aerogels in the field of insulation, and the researchers are mainly engaged in the research of ZrO2 aerogel preparation process.
3) Al2O3 aerogel material
Alumina aerogel material has nano-porous structure, making it lighter mass, smaller volume to achieve the equivalent heat insulation effect, while with high pore rate, high ratio surface area and open weaving structure, in catalysts and catalytic carriers have potential application value. Alumina aerogels can also be used as high-pressure insulation, substrates for high-speed or overspeed integrated circuits, isolation media for vacuum electrodes, and super capacitors.
1.3.2. Carbon aerogel and carbide gel material
carbon aerogel is the biggest characteristic of its inert and vacuum atmosphere up to 2000 degrees C temperature resistance, graphite resistance can even reach 3000 degrees C, and carbon nanoparticles in carbon aerogel itself have excellent absorption properties for infrared radiation, resulting in a similar effect to infrared gel. However, under aerobic conditions, carbon aerogels are oxidized at more than 350 degrees C, which greatly limits their use in the field of high temperature insulation. With the development of high antioxidant coatings such as SiC, MoSi2, HfSi2 and TaSi2, the application of dense antioxidant coatings on the surface of carbon aerogel materials to prevent further diffusion of oxygen will make the material have great application prospects.
carbide material has excellent antioxidant properties, but its own thermal conductivity is high, it is made into an aerogel containing a three-dimensional vertical network structure, which can greatly reduce the thermal conductivity of the material, and further improve the thermal insulation of the material. At present, there are relatively few studies on carbid aerogels at home and abroad, especially for block carbides aerogels with good forming properties are still in the initial stage, and the research on them as high-efficiency insulation materials is also relatively scarce, limited to the preparation and normalization of the material.
1.4. Preparation of SiO2 aerogels
Since SiO2 aerogels are by far the most mature products in the industry, the preparation of such aerogels consists of two methods: drying and sol-gel. At present, the main technology used in industrialization is drying technology.
1.4.1. Drying technology
The main technologies used in the current industrialization are supercritical drying technology and normal pressure drying technology, and other batch production technology has not yet been realized, such as vacuum freeze drying, subcritical drying and so on.
supercritical drying technology is the earliest to achieve batch preparation aerogel technology, has been more mature, but also at home and abroad aerogel enterprises to adopt more technology. Supercritical drying enables the gel to maintain a well-maintained skeleton structure during the drying process.
new aerogel preparation process with normal pressure drying technology is the most active research and the most promising aerogel batch production technology. The principle is to use hydrophobic groups to modifie the gel skeleton, to avoid the silicon hydroxyl on the surface of the gel hole and improve elasticity, while using a low surface pressure liquid
compared with supercritical drying technology, normal pressure drying technology has significant cost advantages in equipment input and silicon source, there is a certain threshold in technology, suitable for large-scale mass production of later aerogels.
1.4.2. The sol-gel method
obtains a SiO2 gel with a three-dimensional network structure through hydrolysing and shrinking of silicon-sourced substances, reacts to produce polymers with ≡Si-O-Si≡ as the main body, and then, after aging, a gel of the network structure. During the formation of the gel, a partially hydrolysed silicone is condensed, and the unhydrated substumps on the condensed silicon oxygen chain can continue to hydrolyze. The gel structure can be obtained by adjusting the acidity and alkalinity of the reaction solution and controlling the phase-to-phase rate of the hydrolytic reaction and the condensation reaction during hydrolytic-shrinking process. Under acidic conditions (pH-2.0-5.0), the hydrolytic rate is relatively fast, which is conducive to the formation of more nucleases in nuclear reactions, and under alkaline conditions, it is beneficial to the growth and cross-linking of nuclear cores, making it easy to form dense colloidal particles. The solubility of SiO2 increases under strong alkaline or high temperature conditions, resulting in the formation of glial aggregates in the final gel structure.
1.4.3. Aerogel correction gives it greater performance
the aerogel material itself has low strength and high brittleness