Effect of Viscosity on Preparation of Foamed Silica Ceramics by a Rapid Gelation Foaming Method

An environmentally benign preparation method for silica foam (the rapid gelation foaming method) was developed by combining sol-gel reactions and mechanical foaming without using organic polymers or monomers, in order to generate less CO₂ and harmful gases from the decomposition of organic compounds contained in the raw material. The viscosity of the silica sol during foaming affects the porous properties of the silica foam, i.e. the porosity and average pore size decrease with increasing viscosity. The pore structure of the silica foams depend on the viscosity of silica sol, two types of pore structure being formed. An open-pore structure is obtained by foaming low-viscosity sols, while a closed-pore structure is obtained by foaming high-viscosity sols. Since the viscosity of the silica sol affects the stability and foaming ability of the foam, the porous properties of the product can be controlled by controlling the viscosity of the silica during foaming.