Effect of catalyst on SiO2 sol-gel
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At present, the preparation of SiO2 aerogel generally adopts the two-step method of first acid and then alkali. A low pH value is conducive to the hydrolysis of TEOS, and a high pH value is conducive to the polycondensation of the sol. The two reactions compete with each other, so the pH is gradually increased in acidic systems Values will result in a sharp reduction in gel time, and even instant gelation. The gelation time decreases relative to the pH value, but decreases towards neutrality. This may have a significant impact on the gel structure. For example, the product under general alkaline conditions has poor transparency and low refractive index, which is considered to be related to the structure and coarse pores.
