Hydrothermal Stability of Mesostructured Cellular Silica Foams

The hydrothermal stability of mesostructured cellular silica foams (MCFs) was studied in detail for the first time, using a variety of techniques including transmission electron microscopy, nitrogen sorption, small-angle X-ray scattering, 29Si solid-state nuclear magnetic resonance, and Fourier transform infrared spectroscopy. It was found that the high aging temperature, greater microporosity, and high calcination temperature contribute to the stability of MCFs in high-temperature steam. The frameworks of MCFs calcined at 550 °C are stable in 100% steam at 600 °C for 12 h, but cannot withstand more critical conditions of 800 °C steam and collapse completely. By elevating the calcination temperature of MCFs to 900 °C, the polymerization degree of the silica frameworks is further enhanced, and the obtained MCF materials exhibit high hydrothermal stability under steam at 800 °C for 12 h. The results indicate that increasing the calcination temperature is an effective method to improve the hydrothermal stability of MCFs. It is concluded that 3-D disordered MCFs show structural variations during the high-temperature steam treatments different from those of 2-D ordered hexagonal SBA-15 materials. The pore size, window size, and wall thickness were unaltered for the steam-treated MCFs, while the pore size decreased and the pore wall thickness became thicker for SBA-15.