热固性酚醛树脂-羟甲基三聚氰胺经历聚合反应、溶胶-凝胶、超临界干燥和裂解过程生成了有机和炭气凝胶.比较了超临界石油醚干燥(240 ℃、6.0 MPa下1 h)和超临界二氧化碳干燥(60 ℃、10.0 MPa下7 d)在制备有机和炭气凝胶过程中的作用.结果发现:超临界石油醚干燥时间比超临界二氧化碳的显著短,虽然前者制备的有机气凝胶的BET比表面和中孔孔容比后者小,但前者制备的有机气凝胶在热裂解过程中的热稳定性比后者好,因此,超临界石油醚干燥制备的炭气凝胶的BET比表面和中孔孔容均比超临界二氧化碳的大.超临界石油醚干燥可以替代超临界二氧化碳干燥来制备炭气凝胶.
Organic and carbon aerogels were synthesized from sol-gel polymerization of phenolic resole and methylolated melamine followed by supercritical drying and pyrolysis. Supercritical petroleum ether (30 ℃-60 ℃) drying (SPD) and supercritical carbon dioxide drying (SCD) were employed and compared for the preparation of organic and carbon aerogels. It was found that SPD, which was carried out at 240 ℃ and 6.0 MPa for 1 h, produced organic aerogels with lower BET surface areas and mesopore volumes than SCD, which was carried out at 60 ℃ and 10.0 MPa for 7 d. However, the porous structure of SPD organic aerogels is more stable during pyrolysis than that of SCD organic aerogels, and as a result, BET surface areas and mesopore volumes of SPD carbon aerogels are all larger than those of SCD carbon aerogels, indicating that SPD, whose drying process is substantially shorter than with SCD, can be used as an alternative method for the preparation of carbon aerogels.
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