New route for producing crack-free xerogels: Obtaining uniform pore size

Aluminum hydroxide microstructural units in gelled media aged, or nonaged, with alcohol and water

“…2. In agreement with previous studies [8][9][10][11][12][13], the alcoholic gelled media give xerogels with higher specific surface area than the ones obtained from aqueous gelled media.…”

“…These samples, which from here onward will be referred to as ES (ethanol samples), were stored at room temperature in dark glass bottles and taken as starting material for the subsequent experiments. Portions of them were subjected to drying at 8 • C and 1.3 Pa for 24 h. These temperature and pressure conditions were selected to ensure a slow liquid vaporization rate, which is needed to obtain the dispersed and the dried microstructure fairly equal at the microlevel [11,20]. A thermostatic bath was used to keep the temperature constant and to avoid any freezing phenomena that might introduce stresses into the solid matrix [21].…”

“…Thus, the beneficial action of alcohol was demonstrated experimentally, and nowadays alcohol washing is commonly used to obtain ultrafine dispersed powders [9]. To explain the effect of ethanol washing on precipitates, a number of authors argued that, since it has a surface tension less than water, the maximum capillary tension inside the network of the evaporating gel is kept at a minimum level; accordingly, the resulting dried xerogels are crack-free and have larger specific surface area [5,10,11]. According to other authors [7,9], assuming that the formation of agglomerates is the result of bridging among individual particles due to surface hydroxyl groups [12,13], alcohol washing would prevent or limit such a bridging action by substitution of hydroxyls by ethoxy groups.…”

New Consolidant-Hydrophobic Treatment by Combining SiO2 Composite and Fluorinated Alkoxysilane: Application on Decayed Biocalcareous Stone from an 18th Century Cathedral

“…In the last years, we have prepared crack-free nanomaterials for stone conservation [7][8][9][10][11][12][13][14][15][16][17][18]. Specifically, the addition of an aqueous solution of n-octylamine to an alkoxysilane produces inverse micelles, which act as nanoreactors, generating silica seeds.…”

Potential of PVA templated Silica Xerogels as Adsorbents for Rhodamine 6G

“…[3][4][5] The overall process involves hydrolysis and polycondensation reactions of the organometallic (silicon alkoxides) or inorganic (silicic acid) compounds. Polymerization followed by condensation of siloxane bonds results in the formation of a gel which is described as a continuous solid frame work embedded in a large volume of fraction-liquid phase.…”