Solvents evacuation

The effect of the Zr/Si molar ratio is studied both for aerogels and xerogels, and a comparison allows to determine the effect of solvent evacuation procedure on the textural properties of silica supported sulfated zirconia samples. 

Thus, europium loaded gels were prepared. Some of them were dried by solvent evacuation at CO2 supercritical conditions to obtain the Eu-organic aerogeh After pyrolysis at 1050 °C a Eu-carbon aerogel was obtained (entries 2-4 of Table 5.7). The materials were tested as catalysts in Michael additions (Scheme 5.11). We performed the reaction of ethyl 2-oxocyclopentanecarboxylate and 3-buten-2-one... 

POLYMERIZATION Solvent evacuation (SE) method and intrinsic nonsolvent (INS)... 

The second amnioniation does not lead to completion, as an N/CI ratio of only 1.33 is reached. A similar phenomenon was observed in the gas-phase synthesis route, where an N/Cl ratio of 1.5 was found. In the gas-phase synthesis route, a higher uptake of Cl is observed during the third and fourth chlorosilylations than in the liquid phase. This is certainly due to the presence of the solvent in the liquid case, which leads to a sterically unfavorable situation. Therefore, chlorosilylation is expected only at the most easily reached sites. From the third reaction cycle on, the ammoniation leads to a complete modification of the SiCI groups in the liquid-phase synthesis route, whereas the gas-phase synthesis route never leads to an N/CI ratio of 2. After the solvent evacuation in the liquid case, there is enough space left for NH3 to reach and react with all the =SiCl groups. The general trend of... 

Recently, sulfated zirconia aerogels were also doped with cerium. In order to optimize the catalytic performances of these materials, prepared by the sol-gel method, Mejri et al. [48] studied the impact of the solvent evacuation mode on their properties. The xerogel solids (XZC) obtained by ordinary gel drying and calcined at different temperatures exhibit a very low surface areas. On the contrary, the aerogels (AZC) obtained by solvent evacuation under supercritical conditions show a more developed surface areas (Table 6.2). 

Macquet C, Thomassin J H, Woignier T (1994) Archaeological glass drying during hypercritical solvent evacuation method. Journal of Sol-Gel Science and Technology, 2 285-291... 

Subrenat Packtex offers customised non woven packaging solutions. They use a wide variety of nonwovens (spunbonded, drylaid, wetlaid, airlaid) and also converted nonwoven materials. These materials are often marketed as resistant and reusable protective packs, for example, to prevent surface scratching without fibre release (linting) lifting, or to allow rapid solvents evacuation, etc. 

The intrinsic nonsolvent (INS) polymerization protocol [34], where solvent is never employed, is a technique that is closely related to the solvent evacuation method. In a typical experiment, neat AlEt3 was dropped into neat Ti(OBu)4 in a Schlenk flask at 0°C. The catalyst was aged for 1 h at room temperature and then further aged for another hour at 150° C. The flask was degassed and rotated to coat its walls with the catalyst solution. The system was then cooled to —78°C and acetylene was added. The reaction was allowed to proceed for 30-60 min before quenching. The resulting PA film was washed with toluene at — 78°C and dried under vacuum. 

The conductivity of PA films produced by the INS method was measured as a function of the Al/Ti ratio. No general trend was found, but the highest conductivity was achieved when the Al/Ti ratio was 4. On an iodine-doped stretched sample, the conductivity ranged between 2.2 x Kf and 4.3 x 10 S/cm. These values are twice that found for Agaki-type PA films synthesized by the solvent evacuation method. By comparison, the PA obtained using toluene as the solvent has a maximum conductivity when the Al/Ti ratio is 2 [31, 33, 35]. Researchers proposed that the properties of the INS PA are optimized at an Al/Ti ratio of 4 because the excess AlEt3 served as a solvent to stabilize the titanium catafyst. (The dielectric constant of Al t3 is 2.005, which is similar to that of toluene at 2.237.)... 

Prassas M., Phalippou J., Zarzycki J. Synthesis of monolithic sihca gels by hypercritical solvent evacuation. J. Mat. Sci. 1984 19 1656-1665... 

Interpenetrating Composite Aerogels by Supercritical Solvent Evacuation A related procedure was reported for the preparation of highly porous, low-density composites. This process relies on the selection of a cosolvent that is suitable for the preparation of interpenetrating organic-inorganic composites, and can also be replaced by carbon dioxide under supercritical... 

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