Aerogel pore size

According to the small size of aerogel pores we expect to prepare a nanocomposite by a very simple process. The size of actinides domains will depend on the aerogel pore size and actinides content in liquid. 

It is less well known, but certainly no less important, that even with carbon dioxide as a drying agent, the supercritical drying conditions can also affect the properties of a product. Eor example, in the preparation of titania aerogels, temperature, pressure, the use of either Hquid or supercritical CO2, and the drying duration have all been shown to affect the surface area, pore volume, and pore size distributions of both the as-dried and calcined materials (34,35). The specific effect of using either Hquid or supercritical CO2 is shown in Eigure 3 as an iHustration (36). 

Fig. 7. The effect of preparation on the pore size distribution (a), titanium dispersion (b), and the activity for epoxidation of cyclohexene (c) of titania—siUca containing 10 wt % titania and calcined in air at 673 K. Sample A, low-temperature aerogel Sample B, high-temperature aerogel Sample C, aerogel.

Both xerogels and aerogels are characteristically high surface area materials (surface areas normally exceed 500 m2/g). Unlike wet gels, many uses exist for dried gels due to their high surface areas and small pore sizes (typically, < 20 nm diameters). Examples include catalyst supports (12.). ultrafiltration media (18), antireflective coatings (19-20), and ultra-low dielectric constant films. (Lenahan, P. M. and Brinker, C. J., unpublished results.)... 

Figure 16. The pore-size distribution for sol—gel-derived birnessite Na(5Mn02 20 as processed into three pore-solid nanoarchitectures xerogel, ambigel, and aerogel. Distributions are derived from N2 physisorption measurements and calculated on the basis of a cylindrical pore model. (Reprinted with permission from ref 175. Copyright 2001 American Chemical Society.)...

Aerogels are highly porous materials where the pore sizes are truly on a molecular level, less than 50 nm in diameter. This gives a material with the highest known internal surface area per unit weight. The surface area of 1 oz. is equal to 10 football fields, over 1000 m in 1 g. 

The pore size of aerogels varies. The International Union of Pure and Applied Chemistry classifies materials with pore sizes of less than 2 nm as micropores, 2-50 nm are called mesopores, and those greater than 50 nm in diameter are called macropores. While aerogels have some pores that fall within the micropore region, the majority of pores are in the mesopore region. 

Figure 2. Pore size distributions in titania-sulfate aerogels before (a) and after calcination (b).

Figure 3. Pore size distributions of Vacac-doped aerogel samples V33A. The modified C-parameters C " are given in the legends.

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