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'Aerogel' is magical, but not mysterious
- Time of issue:2022-07-18 16:32
'Aerogel' is magical, but not mysterious
What is aerogel
Aerogel is a special gel that replaces the liquid in the gel with gas without changing the network structure or volume of the gel itself. It has the characteristics of nano-scale porous structure and high porosity. one of the solid materials. It is also sometimes called "solid smoke" or "frozen smoke" because of its translucent color and ultra-light weight. Aerogels (aerogels) and dry gels (xerogels) are not the same concept. Wet gels obtained by supercritical drying are aerogels, and those obtained by atmospheric drying are xerogels. Strictly speaking, aerogels should be bulk structures, while xerogels are generally powders or granules.
Due to its cumbersome and lengthy preparation process, high price and brittleness, etc., it has not attracted the attention of the industry for a long time. It was not until the advent of supercritical drying that aerogels caught the attention of researchers. The supercritical drying method can quickly and mass produce aerogel materials with precise size, arbitrary shape and complete structure. This new material looks fragile, but it is actually very strong and durable. Aerogels of different compositions can withstand different temperatures. Common silica aerogels can be used in the range of absolute zero to 650 °C. Some types of aerogels The glue can withstand high temperatures up to 1400°C. It is gratifying that, unlike other new materials, the industrialization level of aerogel materials in my country is almost synchronized with the world, and it shows a good trend of catching up and surpassing. The first commercial aerogel company in my country was established in 2004.
Aerogels can be divided into three categories according to their components: inorganic aerogels, organic aerogels and composite aerogels. The most typical and most studied aerogels are single-component SiO2 aerogels and carbon aerogels (organic aerogels).
Characteristics of Silica Aerogels
1. The porosity is very high, up to 99.8%; scientists say that because it has millions of pores and wrinkles, if you take 1 cubic centimeter of aerogel apart, it will fill a football field. big place. Its tiny pores not only trap pollutants like a sponge, but also act as air pockets. The researchers believe that some forms of aerogels made of platinum could be used to accelerate hydrolysis and hydrogen production. In this way, aerogels can be used to produce hydrogen-based fuels.
2. Nano-scale holes and three-dimensional nano-framework particles;
3. High specific surface area;
4. Low density;
5. The unique structure of aerogel determines its extremely low thermal conductivity, which can be as low as 0.013W/(m·K) at room temperature, which is lower than the thermal conductivity of air.
Silica Aerogel applications
1. Super insulation material
The thermal conduction of materials is determined by gaseous conduction, solid conduction and thermal radiation conduction. Due to the nanoporous structure of aerogel materials, the gaseous thermal conductivity λg under normal pressure is very small, and the thermal conduction in vacuum is determined by solid-state conduction and thermal radiation conduction. Compared with glassy materials, the high porosity of nanoporous materials limits the propagation of local excitation of chains in the sparse framework, so that the solid-state thermal conductivity λs is only about 1/500 of the thermal conductivity of non-porous glassy materials. It is the solid material with the best thermal insulation performance at present.
1. Solar water heater. The efficient thermal insulation of solar water heaters and other heat collecting devices has become a key factor in whether to further improve the energy utilization rate of solar energy devices and further improve their practicality. Applying nanoporous super-insulation materials to water heater storage tanks, pipes and collectors will more than double the heat collection efficiency of existing solar water heaters, while heat loss drops to less than 30% of the existing level.
2. Application on hot battery. It can prolong the working life of the thermal battery and prevent the heat generated from affecting the components around the thermal battery.
3. Military and aerospace fields. Compared with traditional thermal insulation materials, nanoporous aerogel superinsulation materials can achieve equivalent thermal insulation effects with lighter mass and smaller volume. This feature makes it have a pivotal advantage in the field of aviation and aerospace applications. If it is used as a thermal insulation material for aero-engines, it not only has excellent thermal insulation effect, but also reduces the weight of the engine. It also has good application prospects as a super-insulation material on outer space exploration tools and vehicles. The application of gel in aerospace is far more than that. NASA's "Stardust" space probe has taken it to complete a very important mission in space - collecting comet particles.
4. Industrial and building insulation fields. Nanoporous super-insulation materials have a wide range of potential applications in industrial and civil fields. First of all, in the electric power, petrochemical, chemical, metallurgy, building materials industry and other industrial fields, thermal equipment is ubiquitous. In industrial energy saving, nanoporous super-insulation materials also play a very important role. Some special parts and environments are in urgent need of high-efficiency super-insulation materials due to the limitation of weight, volume or space.
2. Application in catalyst and catalytic carrier
Silica Aerogel is a solid material composed of ultrafine particles, which has the characteristics of small particle size, high specific surface area and low density, which makes the activity and selectivity of SiO2 aerogel catalyst far higher than that of conventional catalysts, and it can also Effectively reduce the occurrence of side reactions. However, its application is limited due to the small thermal conductivity and low permeability that affect the heat and mass transfer of aerogels in catalytic reactions.
3. The application of aerogel in daily life
Silica Aerogels are also entering our daily life. Sports equipment company Dunlop has created a line of squash and tennis racquets reinforced with aerogels that unleash more power. Bob Stocker, 66, of Nottingham, England, has become the first Briton to own a house insulated with aerogel. "Insulation is greatly improved," he says. Climbers are also beginning to benefit from aerogels. A British climber, Anne Parmantle, climbed Mount Everest in boots with aerogel insoles, which are even added to her sleeping bags.
4. Application in Electrochemistry
In the field of energy storage devices, carbon aerogels will be obtained after organic aerogels are treated by a sintering process. This conductive porous material is a new type of carbon material developed after fibrous activated carbon. high specific surface area and high electrical conductivity, and a wide range of density variations. If a suitable electrolyte is filled into its micro-holes, a new type of rechargeable battery can be made. Repeated charge and discharge performance is good.
5. Hydrogen storage materials
Hydrogen energy has a high calorific value, and the product after combustion and energy release is water, which is non-polluting to the environment. In addition, hydrogen energy is a renewable energy source that will not be exhausted, so it is known as a green new energy source in the 21st century. Carbon aerogels have high specific surface area, low density, continuous network structure, small pore size and communication with the outside world, and have excellent hydrogen absorption and desorption properties.
6. Gas or liquid adsorption
Silica Aerogels can also be used as adsorption materials, such as adsorption of CO2 gas, adsorption of some chemical toxic vapors, adsorption of explosive waste water, etc.