Aerogels have special microstructure characteristics such as high specific surface area, high void ratio, stable chemical performance, low thermal conductivity, high temperature resistance, wide temperature range and long service life. In recent years, researchers in China, the United States, Europe and other countries and regions have developed a variety of new aerogels such as birth material based aerogels by improving the preparation process of aerogels.
Aerogel is a kind of super material. It is very light, and even if a piece of aerogel is placed on the stamen, it will not be bent. At present, all kinds of aerogels have been developed. They are soft or hard, conductive or insulating, and have a wide range of applications. The steam pipe network has very high requirements for corrosion prevention and thermal insulation. High temperature centrifugal glass wool and nano aerogel composite thermal insulation materials are selected for the pipeline of Xinxiang Steam Pipe Network Project in Henan Province. Wang Xing, the technical director of the project, said that the thermal insulation effect of nano aerogel is 2-5 times that of traditional thermal insulation materials, which can greatly improve the construction quality and efficiency and reduce the construction cost.
As a known solid material with the lowest thermal conductivity and minimum density, aerogel is the "king of insulation" in the field of materials and has been applied in aerospace, petrochemical and other fields. For example, aerogel is applied to the engine and the surface of the Mars rover of the "Tianwen 1" probe, the high-temperature gas system insulation of the engine of the "Long March 5" remote four carrier rocket, and the thermal battery protection of the Chang'e-4 probe. After China put forward the goal of "double carbon", with the continuous innovation of technology, the application scenario of aerogel is also further expanded.
Has characteristics such as high temperature resistance, high elasticity, and strong adsorption
Aerogel is a new type of nano porous solid material. The volume of all pores together accounts for the vast majority of the volume of the entire aerogel, even up to 99%. It has special microstructure characteristics such as high specific surface area, high void ratio, nano pores, low density, etc. It has stable chemical performance, low thermal conductivity, high temperature resistance, high elasticity, strong adsorption, good waterproof effect, wide temperature range and long life.
"Aerogel can be understood as a nano version of porous sponge." Wang Beier, a technical expert in the field of aerogel, said that its pore diameter is between 20 nm and 50 nm. The size of the air molecule is about 70 nm, which is larger than the diameter of the pores of the gel, so the air flow efficiency on the gel is extremely low. In addition, the specific heat capacity of the gel itself is very high, and the heat radiation transfer energy is minimized, so it has good heat insulation performance.
Aerogels can be divided into three categories: inorganic gel, organic gel and organic-inorganic hybrid gel. Among them, inorganic gel are mainly composed of inorganic materials, including simple matter aerogels, oxide aerogels gel and sulfide aerogels gel. Organic aerogels are mainly organic compounds, including phenolic gel, cellulose aerogels, polyimide aerogels, chitosan aerogels, and chitosan cellulose aerogels gel. Organic inorganic hybrid aerogels can utilize the advantages of organic and inorganic materials to realize the special functionalization of aerogels.
In 2021, Science magazine listed aerogel as one of the top ten popular science and technology, and called it "a multi-functional new material that can change the world". Wang Beier said that aerogel is the only one of the top ten new materials selected by Science magazine that has been widely used in actual business scenarios.
The preparation process of gel is mainly divided into two steps, that is, the gel is prepared through the sol gel process, and then the liquid matter in the gel is replaced by the gas by a certain drying method, so as to prepare the aerogel.
Data shows that the manufacturing cost accounts for about 45% of the cost structure of the aerogel industry. Zheng Song, assistant to the chairman of Suzhou Jinfu Technology Co., Ltd., said that reducing the cost of aerogel is a direction the industry is striving for. At present, one of the main paths is the landing of automated production lines, and cost reduction will open more application scenarios.
Research hotspot of biomass based aerogels
According to the assessment of China Petroleum Pipeline Science and Technology Research Center, taking the thermal insulation application of 350 ℃ steam pipeline as an example, compared with traditional thermal insulation materials, the thickness of the thermal insulation layer of aerogel can be reduced by 2/3, saving more than 40% of energy consumption, and reducing 125 tons of carbon dioxide emissions per kilometer of pipeline every year.
Data shows that in 2021, the demand for aerogel in the oil and gas field will account for 56% of the total demand, with another 18% for industrial insulation, 9% for building construction and 8% for transportation. The National New Material Industry Development Strategy Advisory Committee pointed out in the 2022 Aero gel Industry Research Report that the use of aero gel flame retardant materials in battery cell modules of new energy vehicles can improve the high temperature resistance of battery packs to more than 800 degrees Celsius. With the development of new energy vehicle industry, aerogel is widely used in new energy vehicles and energy storage industry, and the demand is expected to continue to increase.
Aerogels have developed rapidly. Li Weike, an analyst at the International Institute of Technology and Economics of the Development Research Center of the State Council, said that in recent years, researchers in China, the United States, Europe and other countries and regions have developed a variety of new aerogels such as biogenic gel, graphene gel, and polymer gel by improving the preparation process of aerogels. It is worth mentioning that biomass raw materials have a wide range of sources, low cost, and rich carbon sources. It is an economic and sustainable production method to use biomass raw materials to prepare environmentally friendly porous carbon fiber aerogels. Therefore, at present, biomass based aerogels have also become a research hotspot.
For example, Yu Shuhong, an academician from the University of Science and Technology of China, has developed a super elastic cellulose aerogel. From room temperature to minus 196 degrees Celsius, this cellulose aerogel shows super elasticity that does not change with temperature, excellent fatigue resistance, etc., and has great heat insulation potential in harsh environments. The materials used in the preparation are all biomass raw materials, which is expected to solve the environmental pollution problems caused by energy intensive technology and petrochemical materials, and is an ideal substitute for traditional non renewable gel.
Lu Yun, a research team from the Wood Industry Research Institute of the Chinese Academy of Forestry Sciences, took wood as the matrix, compounded inorganic and organic aerogels with wood matrix, and pioneered the third generation of lignocellulose aerogels. By regulating wood and biomass waste cellulose, the specific surface area of cellulose has been increased by 7 orders of magnitude, and its ability to adsorb oil pollution is 75 to 300 times its own mass. The volume consumption has been reduced by 50% to 75%, making it biodegradable and renewable.
The development of aerogel has entered the "fast lane"
The development of aerogel has been continuously supported by national policies. In 2014 and 2015, the National Development and Reform Commission listed aerogels in the National Key Energy Saving and Low Carbon Technology Promotion Catalog for two consecutive years, and began to preliminarily promote and apply aerogels; In June 2018, aerogel was listed in the emerging industry of building materials; In September of the same year, the first national standard for aerogels, Nanoporous Aerogel gel Composite Thermal Insulation Products, was released; In 2020, the Technical Standard for Aerogel Thermal Insulation Coating System will be launched; 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 Carbon Peak and Carbon Neutralization was put forward to promote the research, development and application of new materials such as aerogels.
With the continuous maturity of aerogel application technology, aerogel has entered the "fast lane" of development. However, Li Weike said that at present, there are still some problems in the research of aerogels. For example, the thermal conductivity of aerogels increases rapidly at high temperatures, and their adhesion to fiber and other reinforced matrix materials is poor; Many organic solvents are used in the production process, which can easily cause environmental pollution; It is difficult to recycle aerogel, which is not conducive to sustainable development.
In addition, the production cost of aerogel is high, and the product price is expensive. The 2022 Aerogel Industry Research Report points out that the production cost of aerogel is mainly concentrated in the raw material silicon source, equipment depreciation and energy consumption. Effective cost reduction depends 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 the needs of fire prevention, waterproof, heat insulation, sound insulation and other needs. Li Weike said that the development and application of gel are still in the process of continuous exploration, and the future research direction is mainly focused on the development of cellulose aerogels, graphene aerogels, perovskite structure aerogels, non-metallic elemental aerogels gel and other new aerogels.