NON-CRYSTALLINE SOLIDS Pore structure evolution in ,silica gel during aging/drying. III. Effects of surface tension *
نویسندگان
چکیده
A two-step acid/base-catalyzed silica gel has been aged in alcohol and water baths followed by various aprotic solvents with a wide range of surface tensions. Low temperature (CO 2) and high temperature (ethanol) aerogels were also prepared. The physical and chemical structures of gels dried from aprotic solvents were studied by a series of techniques (29Si MAS-NMR, nitrogen adsorption, SAXS, elemental analysis, TGA). The aprotic solvents isolated the effects of pore fluid surface tension during drying since they do not participate in condensation and other reactions. For aprotic solvents, a linear decrease in xerogel surface area was observed with increasing surface tension. Pore volume and pore size distribution followed a similar trend. Depending upon whether the gel had been washed in ethanol or water prior to the aprotic solvent, the final pore volume was changed significantly for a given surface tension. This indicates that both surface area and pore volume may be independently controlled.
منابع مشابه
NON-CRYSTALLINE SOLIDS Pore structure evolution in silica gel during aging/drying II. Effect of pore fluids
A two-step acid-base-catalyzed silica gel has been aged in a series of alcohol and water baths and some chemical and physical structures of the gel were measured using several techniques (low-field NMR, 29Si and 13C MAS-NMR, IR, Raman, nitrogen adsorption) on gels in wet and dry states. When the gel was placed in alcohol, the surface area increased as a result of esterification and depolymeriza...
متن کاملPore structure evolution in silica gel during aging/drying. IV. Varying pore fluid pH
In an effort to understand the various phenomena which occur during aging of silica gels at different pH, silica particles prepared by three routes distinguished principally by their silicon coordination (Qn distributions) (St6ber silica spheres, Ludox and Cab-O-Sil) were employed. In situ techniques were used including proton spin-latt ice relaxation, SAXS and zeta potential for the wet state ...
متن کاملPore structure evolution in silica gel during aging/drying I. Temporal and thermal aging
Low field NMR spin-lattice relaxation measurements of pore fluids contained in silica gels are employed as a pore structure probe to ascertain the changes that occur in a two-step acid/base-catalyzed silica gel during aging in its mother liquor. It has been shown that both a narrowing of pore size distribution and an increase in mean pore size is obtained for a gel aged at 303 K over a time per...
متن کاملPore surface fractal dimension of sol-gel derived nanoporous SiO2-ZrO2 membrane
In this work, SiO2 –ZrO2 mixed oxides was prepared by the polymeric sol–gel route. The characterization of pore structure, which determines the permeation process of membrane, is of great importance. So far, most investigations have focused on such pore structure as specific surface area and pore size distribution, but the surface fractal, the important parameter reflecting the roughness of por...
متن کاملThe role of the DCCAs in the preparation of crack-free Xerogel
Sol–gel chemistry is an efficient tool to control the morphology and reactivity of solids. Drying is the crucial step due to the capillary forces exerted during the classic ambient drying process, which induces the collapse of the wet gel porosity. The use of N, N-dimethylformamide (DMF), a newly found DCCA were found to be effective in the sol–gel synthesis of crack-free silica gel monolith fr...
متن کامل