Improvement of mechanical strength of ultralight resorcinol–formaldehyde/silica aerogel by addition of zirconia

In the present work, RF/SiO2 aerogels reinforced by zirconia (ZrO2) were fabricated by a sol–gel process combined with N2-ethanol supercritical drying. The physical properties and microstructures of the aerogels were investigated by uniaxial compression, X-ray diffraction, N2 physico-adsorption, scanning electron microscopy, X-ray photoelectron spectroscopy, and infrared spectrum. The compressive strengths of the aerogels were improved obviously with the addition of ZrO2. The composite aerogels remained amorphous state even the percentage of ZrO2 reached up to 6.77 wt%. The pore sizes of the aerogels with various ZrO2 were hierarchical and the Brunauer-Emmett-Teller surface area increased distinctly with the increase of ZrO2. On the contrary, the aerogel particle sizes decreased as the increase of ZrO2. In our opinion, the enhanced compressive strengths derive from both of the varied pore structures and the decrease of the particle sizes.