A method for fabricating low-density, flexible aerogel composites for use as thermal insulation was developed for environments that require insulation materials that can withstand temperatures of up to 1200 °C. This innovation significantly advances the state of the art for composite insulation systems, reducing adherence problems and thermal conductivity limitations of conventional aerogel insulations while improving performance with lower weight, lower density, and higher efficiency. The aluminosilicate aerogel composites are fabricated using a sol-gel technique. A sol is formed by hydrolyzing an alumina dispersion in acid solution; the alumina may be combined with a silicon precursor to create a sol.
Fabrics, papers, and felts are used as reinforcing fibers to form an aerogel composite. The aerogel adheres to the reinforcement without use of sizing or organic binders. Composites can be fabricated in a batch process, impregnating individual layers of paper, felt, or fabric with the precursor sol, or in a roll-to-roll process. The sol is allowed to gel and then ages for several days prior to supercritical drying using liquid CO2. Heat treatment of the super critically dried composites can be used to tailor the alumina or aluminosilicate crystal structure and pore size.
In contrast to commercially available insulations, this material provides extremely low thermal conductivity (60 mW/m-K at 900 °C in argon) at high temperatures. In addition, the unique process provides very good adhesion of the aerogel to its reinforcing fibers in alumina papers and zirconia felts, eliminating the spalling seen in other aerogel composites. Finally, it demonstrates low density and extreme resilience to high temperatures and harsh conditions.
Seven layers of composite material of 1.25 mm/layer produced a temperature drop of 700 °C when tested in a wind tunnel. The technology also has withstood heat tests of up to 1200 °C. In combination with other insulators, it has withstood fluxes of up to 65 W/cm2, producing a temperature drop of 625 °C across 8 mm.