A Sustainable Processing Route for Open Cell Glass Foams With Hierarchical Pore Structure

Herein, a sustainable direct foaming method for the synthesis of open‐cell sodium‐borosilicate glass foams is presented. For the foaming process, sodium borosilicate (SBS) waste‐glass‐powder is ball‐milled with manganese carbonate and mixed with an aqueous solution containing citric acid (CA), sodium‐waterglass (WG), sodium lauryl ether sulfate (SLES), and guar gum. During mixing, CO 2 gas is released, creating a liquid foam that quickly hardens due to condensation of the dissolved silica. After drying and sintering, the foams are submitted to a thermally induced phase separation and subsequent leaching. At 700°C, a low‐density foam of 0.22 g·cm −3 with a compressive strength of 0.5 MPa is obtained. After leaching, an additional macropore system in the struts with pore diameters ranging from 50 to 200 nm is introduced. The density is almost halved to 0.13 g·cm −3 , and the strut pore volume is increased to 0.7 cm 3 ·g during leaching. The low pressure drop of around 40 Pa·cm −1 at a gas flow velocity of 0.5 m·s −1 of the open‐cell network makes the hierarchically porous silica monoliths suitable as catalyst supports. During the synthesis process, mainly sustainable and nontoxic starting materials are being used, making the whole process environmentally friendly.