An overview on alumina-silica-based aerogels

• Published in: Advances in colloid and interface science 2020-08, Vol.282, p.102189-102189, Article 102189
• Main Authors: Almeida, Cláudio M.R., Ghica, Mariana E., Durães, Luísa
• Format: Article
• Language: English
• Subjects: Alumina; Catalysis; Hybrid aerogel; Silica; Thermal insulation
• ISSN: 0001-8686; 1873-3727
• DOI: 10.1016/j.cis.2020.102189

Silica aerogels are remarkable materials with excellent physicochemical properties, such as high porosity and surface area, along with low density and thermal conductivity. In addition to their outstanding properties, these materials are quite interesting due to the possibility to change their chemistry according to intended applications. However, they also show some disadvantages, like low mechanical strength and poor dimensional stability under high temperatures (above 600 °C). Although these aerogels are frequently used as thermal insulators, for high temperature environments some of their properties need to be improved. The mixing with other ceramic thermally resistant phases is a viable approach. Thus, this work presents an overview on alumina-silica-based aerogels, describing their synthesis, processing and properties. The improvement on their properties will be discussed as a function of the amount of refractory phase (alumina) in the silica matrix. The introduction of the alumina phase makes them stable until 1200–1400 °C, maintaining low values of thermal conductivity at very high temperature (below 81 mW m−1 K−1). Finally, a brief survey on the most promising applications of these materials is presented, with several examples. In catalysis, alumina-silica aerogels have shown equivalent performance when compared to reference catalysts. In the field of thermal insulation, these materials show great potential, especially in high temperatures environments, due to their thermal dimensional stability and inherent low thermal conductivity. As adsorbents, higher stability and adsorption capacity were obtained with the incorporation of the alumina phase in silica aerogels, and these materials can be reused for repeated adsorption/desorption cycles. Indeed, a significant improvement of the aerogel performance by the synergetic effect of combining silica and alumina phases is usually obtained, supporting the expectation of the extension of their fields of application. [Display omitted] •Overview on the most recent synthesis methods of alumina-silica-based aerogels.•Microstructure dependent on selected silica and alumina precursors type and ratio.•Mineral & waste materials can be used as Si & Al sources with simple pre-treatments.•Aerogel composite properties may be tailored according to the intended application.•Suitable materials for catalysis, thermal insulation and adsorption.