Because the supercritical fluid has no surface tension, there is no additional pressure in the gel capillary pores due to surface tension. Therefore, the use of the gel under supercritical fluid conditions for boring, will not occur by the additional pressure caused by the gel structure of the collapse field, thus avoiding the gel in the boring process of contraction, adhere to the gel network framework structure, made with a high ratio surface.
ultrafine aerogels with uniform particle size distribution and large pore volume. The dry path to complete the gel: There are two main types of dry media commonly used: one is organic alcohols such as methanol and ethanol, and the other is CO2. Summarize the literature, the existing SCFD skills can be divided into the following three categories: 2-1, high temperature supercritical organic solvent dry: sol-gel method to prepare the catalyst is usually carried out in aqueous solution. Because the critical temperature of water, the critical pressure
are relatively large, so the hydrogel is not suitable for direct supercritical fluid drying. The high-temperature supercritical organic solvent drying method is to replace the water obtained by the reaction with an organic solvent to obtain an organic sol or directly obtain an organic sol by other methods, and the organic sol is then aged into an organic gel. Then the organic gel is placed in a high-pressure dryer that has been put into an appropriate solvent, and the organic solvent is heated and pressurized to make the organic solvent reach a supercritical state, the supercritical nature of the organic solvent is used for the purpose of driving off the solvent in the gel.