What is the aerogel thermal insulation coating that has been very popular recently? Is it an IQ tax? Or is it a truly practical product?
1. Thermal insulation mechanism of aerogel
Aerogel is the solid thermal insulation material with the lowest known thermal conductivity and density, which is only 0.012~0.016W/(m·K), which is 1/8~1/2 of traditional thermal insulation materials. It fits the general trend of energy conservation and emission reduction, and has the advantages of long service life (about 20 years), waterproof (water repellency>99%), high and low temperature resistance (operating temperature -200℃~650℃), pressure resistance, and breathability. The cost of use throughout the life cycle is very competitive. Aerogel is a national basic strategic frontier new material, which is of great strategic significance to reducing carbon emissions and achieving the "dual carbon" goal. As an energy-saving material, aerogel is expected to shine in the fields of construction, industry, environmental protection, new energy, etc.
So why does aerogel have good thermal insulation? From a thermodynamic point of view, heat transfer includes three pathways: heat conduction, heat radiation, and heat convection. Aerogel is a three-dimensional mesh nanoporous material. The gas inside it can be regarded as bound gas molecules. Gas conduction and convection are almost zero. In addition, the solid conductive skeleton is infinitely long, resulting in an infinitely long conduction path, as shown in the following figure:

2. What principle does aerogel thermal insulation coating use to insulate?
From the thermal insulation mechanism of aerogel, it can be seen that aerogel uses its own three-dimensional nanostructure to achieve thermal insulation. What if aerogel is added to the coating?
Due to its fragile three-dimensional network structure, aerogel is very brittle and easy to crush, so that the structure is destroyed. Then it must be added to the coating as powder particles. Assuming that it can be added to the coating resin (assuming that it can be well dispersed and there is no problem with nano-agglomeration), high-speed dispersion and shearing are required during the coating preparation process, and the aerogel structure is further destroyed. Finally, only the destroyed aerogel structure is left in the resin, and only the solid phase particles with further increased thermal conductivity. Then the aerogel thermal insulation coating only relies on the broken aerogel particles for thermal insulation.
By testing the thermal conductivity of aerogel thermal insulation coatings on the market, it is roughly distributed between 0.03-0.05w/mk, which is still higher than traditional thermal insulation materials, including polyurethane insulation, EPS insulation, glass wool, rock wool, etc.
The primary function of coatings is corrosion resistance and beautiful decoration, followed by functionality. Due to its characteristics, the dry film thickness is generally only a few hundred um or less (for special static occasions, its thickness can be several mm), and it is also necessary to take into account issues such as impact, toughness, and cost. According to the calculation method of thermal resistance: R=L/K, R is thermal resistance, L is the thickness of the insulation material, and K is the thermal conductivity of the material itself. It can be theoretically deduced that the thermal resistance of the insulation material is at least 3 orders of magnitude higher than that of the aerogel coating. Therefore, in thermal insulation occasions, the preferred choice is the insulation material rather than the aerogel insulation coating. Of course, in some special occasions, such as static narrow spaces, a thicker aerogel insulation coating can be selected.

3. Is aerogel reflective coating reliable?
Reflective insulation coatings are currently relatively mature. The most important thing in reflective insulation coatings is the structure and characteristics of the inorganic particles that reflect sunlight. Glass beads are commonly used. The structure and processing technology of glass beads have a relatively large impact on the final result.
First, let's look at the working principle of reflective heat-insulating coatings: when sunlight shines on the coating, the glass beads in the coating will emit most of the energy in the sunlight, and only a small part will enter the coating, and then after a long period of diffuse scattering, the heat in the sunlight will gradually dissipate, thereby achieving a small reflection effect.
Among them, the processing technology of glass beads is very important. According to the processing and reflection methods of glass beads described by the reflective industry, they are:

So do aerogel particles have this reflective effect? From the current relevant information, this feature has not been seen yet, which means that aerogel coatings still use their thermal resistance effect to insulate heat, rather than reflect.