Synthesis of silica aerogels: a sol-gel process

Company	Nano Technology Co., Ltd	Alison Aerogel Co., Ltd	Guizhou Aerospace Wujiang Co., Ltd	IBIH Advanced Materials Co., Ltd
Preparation Process	1. Raw materials: acidic silica sol, deionized water, NaOH, H2SO4 Drying method: CO2 supercritical drying	1. Raw materials: TEOS, ethanol, oxalic acid, NH3·H2O, deionized water, n-hexane, 1,2-dimethoxyethane Drying method: CO2 supercritical drying	Raw materials: TEOS, methanol, deionized water, oxalic acid, NH3·H2O, dimethyl silicone oil Drying method: CO2 supercritical drying	1. Raw materials: TMOS, methyltrimethoxysilane, methanol, deionized water, NH3·H2O Drying method: CO2 supercritical drying
	2. Raw materials: alkaline silica sol, deionized water, sodium silicate, HCl, trimethyl chlorosilane Drying method: alcohol supercritical drying	2. Raw materials: TEOS, methanol, HNO3, ammonium carbonate, deionized water, n-hexane, 1,2-dimethoxyethane Drying method: CO2 supercritical drying		2. Raw materials: TEOS, methyltrimethoxysilane, methanol, deionized water, NH3·H2O Drying method: CO2 supercritical drying
	3. Raw materials: methanesiliconicacid sodium salt, sodium silicate, deionized water, H2SO4, sodium perfluorooctane sulfonate Drying method: ambient drying	3. Raw materials: TEOS, acetone, HF, NH3·H2O, deionized water, n-hexane, 1,2-dimethoxyethane Drying method: CO2 supercritical drying		3. Raw materials: TMOS, dimethyldiethoxylsilane, methanol, deionized water, NH3·H2O Drying method: CO2 supercritical drying
Advantages	Low cost Simple process Short production cycle Low equipment input. Three drying methods: ambient drying, CO2 and alcohol supercritical drying	Less solvent volatilization Low cost Low equipment investment Two drying methods: CO2 and alcohol supercritical drying	Quality product Complete equipment and production process package are available One drying method: CO2 supercritical drying	Simple production process Short production cycle Low production cost Two drying methods: CO2 and alcohol supercritical drying

Table 1. Comparison of SiO₂ aerogel preparation processes in several leading Chinese aerogel companies (obtained from publicly available information on these companies) ^[19]

There are many factors that need to be considered in the industrialization of aerogels. Since there are many preparation process pathways, and each has its advantages and disadvantages, each company will choose a suitable process path according to its own characteristics. In terms of the drying method, supercritical drying technology requires a large investment in equipment, but the production cycle is short and the process parameters are easy to control. Therefore, it will show advantages when the production scale is relatively large. At present, supercritical drying techniques mainly involve the use of ethanol and CO₂. The former requires high safety security, but the production cycle is shorter; the latter is safer but has a slightly longer production cycle. The cost for ambient drying processes is low, but they require a long time for surface modification and other production processes. The type of precursor can generally be divided into metal-organics (such as TEOS, etc.) and inorganics (such as water glass, etc.). The cost of metal-organic precursors is relatively high, but the process parameters are easy to control. Inorganic precursors are cheaper, but the process parameter control is relatively complicated. Thanks to the large number of universities, research institutions, and R&D enterprise teams in China, more than 20 aerogel manufacturers in China have adopted different process paths. The general preparation processes of several Chinese leading aerogel companies are listed in Table 1.

Manufacturing This page is part of the collection 'Aerogel Insulation Felt: Silica Aerogel'.

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