Facile synthesis of monolithic carbon/alumina composite aerogels with high compressive strength using different inorganic aluminium salts

Resorcinol-formaldehyde/alumina composite (RF/Al2O3) gels were initially prepared using sol-gel techniques, and then dried to aerogels with supercritical fluid CO2. RF/Al2O3 aerogels were successfully converted to monolithic carbon/alumina composite (C/Al2O3) aerogels after carbonization under flowing Ar at 800 A degrees C. The samples were characterized by Brunauer-Emmett-Teller, scanning electron microscopy, transmission electron microscope and X-ray diffraction, and the compressive strengths were also measured. The results indicated that the resulting C/Al2O3 aerogels prepared from hydrated AlCl3 possessed microstructures containing highly reticulated networks of fibers, 2-5 nm in diameter and of varying lengths, whereas the samples prepared from hydrated Al(NO3)(3) were amorphous with microstructures comprised of interconnected spherical particles with diameters in the 5-15 nm range and the alumina were surrounded by amorphous carbon. The difference in microstructure resulted in each type of aerogels displaying distinct physical and mechanical properties. In particular, the as-prepared C/Al2O3 aerogels with the weblike microstructure were far more mechanically robust than those with the colloidal network. Correspondingly, the compressive strengths are 5.6 and 2.8 MPa, respectively.