These aerogels are most commonly made out of organic polymers. The building blocks can be Resorcinol and Formaldehyde for example, and their gel can range from light orange to dark red to black in color, depending on the density. They are not as fragile as their inorganic counterpart, traditionally prepared by aqueous poly-condensation under alkaline conditions, dried and, depending on the application, ground into particles. This results in a broad particle size and shape distribution and is unusable without additional filtering steps. Alternatively, emulsion-gelation methods can be used to directly fabricate microparticles by slowly adding the RF sol towards rapeseed oil.
RF aerogels can be used as binding material for foundry application by combining it with aluminium oxide and quartz sand as mould material, silylized to become more hydrophobic, or carbonized to produce carbon aerogels.
Images: Resorcinol-formaldehyse aerogel as cylinder (top left) and as monolith (botton left), bend (top right) with an SEM image (bottom right).