Autoclave treatment effect on silica alcogel texture

Porous Materials

“…Pauthe et al [toO] subjected wet gels to a pressure and temperature at which the solvent became a superfluid and then cooled to room temperature without evacuating the solvent as is usually done in supercritical drying. They found that the above treatment led to a loss of microporosity and a decrease of macroporosity while the size and volume of mesopores increased significantly (Figure 4 thought to be due to syneresis [100]. Leboda et al [101] showed a dramatic decrease in surface areas as a function of hydrothermal treatment of various silica gels (Figure 4.42) as a result of dissolution and reprecipitation.…”

“…Textural properties of aerogels have been investigated by thermoporometry, BET adsorption-desorption, small angle neutron or X-ray scattering techniques, etc. [100,[232][233][234][235][236][237][238][239]. Schaefer [237] pointed out that the structure of the aerogels can be controlled by manipulating the polymerization conditions in solution precursors and pH is the dominant factor that determines structure.…”

“…ml TEOS in100 ml ethyl alcohol at room temperature under vigorous stirring for 1 h followed by the dropwise addition of deionized water (pH = 5.5) and 2N HCl to give molar ratios ofH20/TEOS = 1 and HCl/TEOS of 0.01. The addition of water and HCl was finished within 15 min followed by 2 h of mixing under…”

Thermal aging of silica gels in water

“…The results derived from the sorption data taken for the aerogels (Table 2) yield a loss as a result of the heat treatment of both external surface area -consistent with the observed change in particle size d as determined from SAXS data -and microporosity. Pauthe et al have also observed a disappearance of microporosity upon thermal treatment of silica alcogels at conditions at which the alcoholic pore fluid became supercritical [24]. Comparing the SAXS data of the untreated aerogel (Fig.…”

Evolution of the Mechanical Properties During the Gel–Glass Process

“…The total porous volume in a gel consists of the macroporosity (R > 50 nm), the mesoporosity (R = 2-50 nm), and the microporosity (R < 2 nm). A previous study (Pauthe 1991) has shown that, for the two sets of material (alcogel and aerogel), the microporous and mesoporous volumes are not strongly affected by the TMOS%. On the other hand, the macroporous volume decreases strongly and the pore size distribution changes.…”