Silica aerogels; a review of synthesis, applications and fabrication of hybrid composites

Silica aerogels are gaining significant importance and have attracted considerable interest due to their extraordinary properties and numerous applications. Silica aerogels are highly porous with high surface area and very low density and thermal conductivity. Usually they are prepared and synthesized via sol-gel technique, which involves making a sol containing a precursor, a solvent and a catalyst. The properties possessed by the final product depend upon numerous factors such as ratio of precursor to solvent and the drying method employed. Due to the flexibility of synthesis methods and the production of aerogels with tailored properties, silica aerogels have found numerous commercial applications and are being investigated of their suitability in several areas, such biomedical and aerospace engineering. Despite having exceptional properties, silica aerogels come with drawbacks such as brittleness and low mechanical strength, which can be resolved by fabricating composites extending the potential applications. This paper reviews the synthesis of silica aerogels via sol-gel technique, and the applications where this extraordinary material has shown promising results. The different materials used for the fabrication of composites to improve and enhance the physical and chemical properties of silica aerogels are also presented.