Porosity and insulating properties of silica-fume based foams

The synthesis of silica-fume based foams, with a multi-range macroporosity, was obtained by alkalineactivation. Foams were obtained through an in situ foaming process exploiting the gaseous productionof hydrogen caused by the oxidation, in alkaline medium, of metal silicon impurities contained in silicafume. Potassium or sodium alkaline solutions were selected and a temperature of 70◦C was sufficient topromote the development of hydrogen bubbles, the increase of the viscosity and the consolidation of thefoams. The balance of these reactions allowed to entrap hydrogen bubbles inside the structures creat-ing highly porous foams. The foams were characterized in term of macro- and microstructure, porositydistribution, infrared spectroscopy, thermal and acoustic properties achieved. The foams showed ultra-macroporous structures, with a total porosity of ≈80%. The average values of bulk density (0.5 g cm−3),thermal conductivity (0.16 W m−1K−1), and the acoustic behaviors, highlighted a use of the foams aspromising insulating materials