Sintering of different silica aerogels

Abstract

This work reports on isothermal sintering experiments, conducted with silica aerogel samples in a broad density range (∼0.025–0.277 kg/m³) made by the same process by varying the solvent-to-sol ratio, as well as samples made by different formulations used by several aerogel manufacturers. The latter comparison is deficient in the literature. Low-density (<0.05 kg/m³) aerogels were found to be significantly more resilient to sintering, which is consistent with established sintering theories. Unexpectedly large variability in the susceptibility to sintering was observed in similar density (∼0.1 kg/m³) aerogels made by different formulations and by different producers. All material made by utilizing a CO₂ solvent exchange step prior to supercritical drying exhibited effects attributable to residual original solvent in the micropores. This alludes to an incomplete solvent exchange process. The materials were examined in the context of devising a methodology for producing an ultra-pure silica aerogel, a substance free of organic constituents, intended to serve NASA life detection mission needs.