Effects of carbonization temperature on structure and mechanical properties of monolithic C/SiO2 aerogels based on ambient pressure dried superhydrophobic resorcinol-formaldehyde/SiO2 aerogels

In general, C/SiO2 aerogels were prepared by pyrolyzing resorcinol-formaldehyde/SiO2 (RF/SiO2) aerogels. However, the synthesis of RF/SiO2 aerogels usually involves high cost and time-consuming supercritical drying process, which seriously restrict their large-scale production. In this study, ambient pressure dried superhydrophobic RF/SiO2 aerogels prepared by our reported facile one-step sol-gel method were used to synthesize crack-free monolithic C/SiO2 aerogels. The structural evolution and mechanical properties of C/SiO2 aerogels during thermal treatment were investigated by X-ray powder diffraction, scanning electron microscopy, Brunauer-Emmett-Teller method and compression test. The results showed that the RF/SiO2 aerogels converted to C/SiO2 aerogels completely until the carbonization temperature over 700 degrees C. The volume shrinkage of the aerogels increased from 52.2 to 73.2%, while BET specific surface areas decreased from 427.2 to 74.2m(2)g(-1) with carbonization temperature increased from 600 to 900 degrees C. X-ray diffraction studies revealed that the aerogels were still amorphous even after heating at 900 degrees C for 2h. Remarkably, the Young's modulus of compression of the aerogels was observed to increase from 2.58 to 34.4MPa with an increase in the density of the aerogels from 0.149 to 0.244gcm(-3).