Aerogel cloth is a kind of solid material with three-dimensional nano-porous structure. It has the characteristics of low density, high porosity, high specific surface area and ultra-low thermal conductivity. It can be divided into inorganic and organic categories. At present, the industrial aerogel on the market is SiO2 aerogel which has been studied at the earliest time. The figure below is a typical structure diagram of it
Thermal conductivity is a parameter to measure the thermal insulation effect of materials. The lower the parameter is, the better the thermal insulation effect is. SiO2 aerogel is one of the materials with the lowest thermal conductivity in the world, and its thermal conductivity at room temperature can reach 0.018w /m·K.
Then, why its thermal conductivity can be so low, then we need to analyze from the heat transfer. The transfer mode of heat includes 1. Radiation: the temperature balance between objects is achieved by radiating and absorbing the infrared rays of each other. 2. Conduction: Direct contact between objects transmits heat in the form of atomic vibration, from the high temperature to the low temperature; Convection: The transfer of heat between objects in the medium of fluids such as air and water. For the first time, radiation heat transfer was almost negligible at room temperature, and there was no convection in aerogels, so heat conduction became the main factor that dominated the heat transfer of aerogels. Heat conduction can be divided into gas-phase heat conduction and solid-phase heat conduction. Since the mesoporous size of aerogel is mainly distributed within the range of 2-50nm, and the average free path of air molecules is 70nm, such a mesoporous structure of aerogel greatly restricts the heat conduction of gas phase caused by the collision of gas molecules. The specific surface area of aerogel is as high as 1200m2/g. Therefore, the contact degree of SiO2 particles in aerogel is very low. Moreover, the three-dimensional framework also increases the propagation path of the solid phase heat conduction to some extent. As a result, aerogels present barriers to all heat transfer pathways, almost to the limit, so this is why their thermal conductivity is so low.
Thermal insulation test
Thermal conductivity is used to quantify the thermal insulation effect of materials. So there are three main thermal conductivity tests at present, plate method, heat flow meter method and laser flash method. The first two can be used to measure thermal conductivity at room temperature and low temperature. Generally, samples above 5cm are needed. The laser flash method has been used many times by me and is not suitable for measuring aerogel materials at present. These tests, the basic universities or related research institutes can do, if you want to give an authoritative test report will need to find a professional organization to do.
There is also a kind of device to evaluate the thermal insulation effect of materials, that is, the cold surface temperature meter. Under a constant temperature, the sample is put on and the temperature of the upper surface is measured, and the temperature rise curve and equilibrium temperature are recorded.
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