mim-shimi 25686 اشتراک گذاری ارسال شده در 16 فروردین، ۱۳۹۳ [h=1] برای مشاهده این محتوا لطفاً ثبت نام کنید یا وارد شوید. ورود یا ثبت نام [/h] abstract A procedure for the fabrication of monolithic silica aerogels in eight hours or less via a rapid supercritical extraction process is described. The procedure requires 15-20 min of preparation time, during which a liquid precursor mixture is prepared and poured into wells of a metal mold that is placed between the platens of a hydraulic hot press, followed by several hours of processing within the hot press. The precursor برای مشاهده این محتوا لطفاً ثبت نام کنید یا وارد شوید. ورود یا ثبت نام consists of a 1.0:12.0:3.6:3.5 x 10-3 برای مشاهده این محتوا لطفاً ثبت نام کنید یا وارد شوید. ورود یا ثبت نام ratio of tetramethylorthosilicate (TMOS):methanol:water:ammonia. In each well of the mold, a porous silica sol-gel matrix forms. As the temperature of the mold and its contents is increased, the pressure within the mold rises. After the temperature/pressure conditions surpass the supercritical point for the برای مشاهده این محتوا لطفاً ثبت نام کنید یا وارد شوید. ورود یا ثبت نام within the pores of the matrix (in this case, a methanol/water mixture), the supercritical fluid is released, and monolithic aerogel remains within the wells of the mold. With the mold used in this procedure, cylindrical monoliths of 2.2 cm diameter and 1.9 cm height are produced. Aerogels formed by this rapid method have comparable properties (low bulk and skeletal density, high surface area, mesoporous morphology) to those prepared by other methods that involve either additional reaction steps or solvent extractions (lengthier processes that generate more chemical waste).The rapid supercritical extraction method can also be applied to the fabrication of aerogels based on other precursor recipes منبع: jove.com. 1 لینک به دیدگاه
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