Aerogels possess unique microstructural characteristics, such as high surface area and high porosity. They are chemically stable, have low thermal conductivity, are resistant to high temperatures, have a wide operating temperature range, and have a long lifespan. In recent years, researchers in China, the United States, Europe, and other countries and regions have developed a variety of new aerogels, including biomass-based aerogels, by improving aerogel preparation processes.
Aerogel is a metamaterial that is so light that even a piece placed on a flower's pistil would not bend it. Currently, a variety of aerogels have been developed, ranging from soft to hard, conductive to insulating, and suitable for a wide range of applications. Steam pipelines have extremely high requirements for corrosion protection and thermal insulation. The Xinxiang Steam Pipeline Project in Henan Province uses a composite insulation material of high-temperature centrifugal glass wool and nano-aerogel. Wang Xing, the project's technical lead, stated that nano-aerogels offer two to five times the insulation of traditional insulation materials, significantly improving construction quality and efficiency while reducing costs.
As the solid material with the lowest known thermal conductivity and density, aerogel is considered the "king of thermal insulation" and has been applied in aerospace, petrochemical, and other fields. For example, aerogels are used in the Tianwen-1 rover's engine and Mars rover surface, in the thermal insulation of the high-temperature gas system of the Long March 5 Yao-4 carrier rocket's engine, and in the thermal battery protection of the Chang'e-4 rover. Since my country's announcement of its "dual carbon" goals, and with continuous technological innovation, the application of aerogels has further expanded.
It exhibits properties such as high-temperature resistance, high elasticity, and strong adsorption.
Aerogel is a new nanoscale porous solid material. The combined volume of all pores accounts for the vast majority of the aerogel's volume, even up to 99%. It possesses unique microstructural characteristics such as high specific surface area, high porosity, nanoscale pores, and low density. It boasts stable chemical properties, low thermal conductivity, high-temperature resistance, high elasticity, strong adsorption, excellent water repellency, a wide operating temperature range, and a long lifespan.
"Aerogel can be thought of as a nanoscale version of a porous sponge," said Wang Beier, a technical expert in the aerogel field. Its pore size ranges from 20 to 50 nanometers. Air molecules are approximately 70 nanometers in size, larger than the diameter of aerogel pores. Therefore, air flow efficiency through aerogel is extremely low. Furthermore, aerogel's inherently high specific heat capacity minimizes heat radiation transfer, resulting in excellent thermal insulation properties.
Aerogels are primarily classified into three categories: inorganic aerogels, organic aerogels, and organic-inorganic hybrid aerogels. Inorganic aerogels are primarily inorganic and include simple aerogels, oxide aerogels, and sulfide aerogels. Organic aerogels are primarily organic and include phenolic aerogels, cellulose aerogels, polyimide aerogels, chitosan aerogels, and chitosan-cellulose aerogels. Organic-inorganic hybrid aerogels leverage the respective strengths of organic and inorganic materials to achieve specialized functionalization.
Science magazine listed aerogels as one of the top ten hottest scientific technologies in 2021, calling them "a multifunctional new material that could change the world." Wang Beier stated that aerogel is the only one of the top ten new materials selected by Science magazine that has been widely deployed in commercial applications.
The aerogel production process consists of two main steps: preparing the gel through a sol-gel process, and then using a specific drying method to replace the liquid material within the gel with a gaseous state, thus producing the aerogel.
Data shows that manufacturing costs account for approximately 45% of the aerogel industry's cost structure. Zheng Song, Assistant to the Chairman of Suzhou Jinfu Technology Co., Ltd., stated that reducing aerogel costs is a direction the industry is currently striving to address. One of the main approaches currently is the implementation of automated production lines, and lowering costs will open up more application scenarios.
Biomass-based aerogels have become a research hotspot.
According to an assessment by the China Petroleum Pipeline Technology Research Center, for example, in the insulation of 350°C steam pipelines, aerogels can reduce the insulation layer thickness by two-thirds compared to traditional insulation materials, saving over 40% energy consumption and reducing carbon dioxide emissions by 125 tons per kilometer of pipeline per year.
Data shows that in 2021, demand for aerogels in the oil and gas sector accounted for 56% of total demand, with an additional 18% used for industrial insulation, 9% for building construction, and 8% for transportation. The National New Materials Industry Development Strategy Advisory Committee stated in its "2022 Aerogel Industry Research Report" that the use of aerogel flame-retardant materials in new energy vehicle battery core modules can increase the battery pack's high-temperature tolerance to over 800°C. With the development of the new energy vehicle industry and other sectors, aerogels are finding widespread application in new energy vehicles and energy storage, and demand is expected to continue to grow.
Aerogels are developing rapidly. Li Weike, an analyst at the Institute of International Technology and Economics at the Development Research Center of the State Council, stated that in recent years, researchers in China, the United States, Europe, and other countries and regions have developed a variety of new aerogels, including biomass-based aerogels, graphene aerogels, and polymer aerogels, by improving aerogel preparation processes. It is worth noting that biomass raw materials are widely available, low-cost, and rich in carbon sources. Using biomass raw materials to produce environmentally friendly porous carbon fiber aerogels is an economical and sustainable production method, making biomass-based aerogels a hot research topic.
For example, a team led by Academician Yu Shuhong of the University of Science and Technology of China has developed a superelastic cellulose aerogel. This cellulose aerogel exhibits temperature-invariant superelasticity and excellent fatigue resistance from room temperature to -196°C, offering significant thermal insulation potential in harsh environments. Furthermore, the materials used in its preparation are all biomass-based, potentially addressing environmental pollution issues caused by energy-intensive technologies and petrochemical materials, making it an ideal alternative to traditional, non-renewable aerogels.
A team led by Researcher Lu Yun of the Institute of Wood Industry, Chinese Academy of Forestry, has pioneered the development of third-generation lignocellulose aerogels by combining inorganic and organic aerogels with a wood skeleton matrix. By manipulating cellulose from wood and biomass waste, they have increased the specific surface area of cellulose by seven orders of magnitude, achieving an oil adsorption capacity of 75 to 300 times its own mass, reducing volume requirements by 50% to 75%, and making it biodegradable and renewable.
Aerogel development is entering the fast lane.
The development of aerogels continues to receive support from national policies. In 2014 and 2015, the National Development and Reform Commission included aerogel in the "National Key Energy-Saving and Low-Carbon Technology Promotion Catalogue" for two consecutive years, beginning the initial promotion and application of aerogel. In June 2018, aerogel was included in the emerging building materials industry. In September of the same year, the first national standard for aerogel, "Nanoporous Aerogel Composite Insulation Products," was released. In 2020, the "Technical Standard for Aerogel Thermal Insulation Coating Systems" came into effect. In 2021, the "Opinions of the CPC Central Committee and the State Council on Completely, Accurately, and Comprehensively Implementing the New Development Concept and Doing a Good Job in Achieving Carbon Peak and Carbon Neutrality" proposed promoting the research and application of new materials such as aerogel.
As aerogel application technology continues to mature, aerogel development has entered a fast lane. However, Li Weike stated that aerogel research still faces some challenges, such as the rapid increase in thermal conductivity of aerogel at high temperatures and poor adhesion to reinforcing matrix materials such as fibers; the use of numerous organic solvents in the production process, which can easily cause environmental pollution; and the difficulty of recycling aerogel, which is not conducive to sustainable development.
Furthermore, aerogel production is costly, resulting in a high price tag. The "2022 Aerogel Industry Research Report" points out that aerogel production costs are primarily concentrated in the raw material silicon, equipment depreciation, and energy consumption. Effective cost reduction relies not only on breakthroughs in preparation processes but also on the large-scale industrialization of low-cost raw materials.
Aerogel is a rare material that can simultaneously meet multiple requirements, including fire protection, waterproofing, thermal insulation, and sound insulation. Li Weike stated that the development and application of aerogels are still under continuous exploration, with future research focusing on developing new aerogels such as cellulose aerogels, graphene aerogels, perovskite aerogels, and non-metallic aerogels.