In 1931, Steven.S.Kistler from College of the Pacific, United States, expected to prove that a solid ‘gel’ with a continuous network structure of the same size has the same shape as the wet gel, and it would be direct and effective by proving that it is possible to replace the liquid in the gel with gas without changing the solid structure. Based on the speculation that the solid composition of the gel was porous, and when the liquid evaporates, there was a larger surface tension at the liquid-gas interface, which leaded to the collapse of the channel, ‘Kistle prepared hydrogels using sodium silicate as silicon source and hydrochloric acid as catalyst, and then prepared silica aerogel for the first time through solvent replacement and ethanol supercritical drying.’[4]