Fragility and brittleness have always been flaws of delicate three-dimensional aerogel structures. Especially when exposed to harsh conditions (e.g. in aerospace applications), their frailty has limited the broad application of aerogels in such fields. A Chinese team of researchers from the Beijing Jiaotong University has now attended to this matter. By equipping a ZrO2–SiO2 aerogel with Polycrystalline ZrO2 fibers (ZrO2f), aerogels possessing high thermal and mechanical resilience have been devised. Astonishingly, these monolithic aerogels do not only excel in terms of stability, but also show low bulk densities and thermal conductivities.
The idea of adding a fibrous agent to the aerogel matrix is that, when dispersed evenly throughout the matrix, the fibers act as an additional mechanical backbone. This means that the fibers hinder fracturing and irreversible deformation through fiber-bridging and crack-deflection (see Figure below) when the monolithic structure is being strained. Furthermore, due to the even dispersion of the fibers in the aerogel matrix, the contribution of heat conduction through the fibers is minimized and hence the overall heat conductivity increases only marginally upon addition of the fibrous ZrO2.
In summary, these effects lead to highly insulating aerogels possessing compressive strengths 3-10 times higher than previously reported. Therefore, applications in very demanding environments are facilitated, which might prove to be significant in aerospace engineering and other fields in which stable and highly insulating materials are essential.
More details: Xianbo Hou, Rubing Zhang and Daining Fang; An ultralight silica-modified ZrO2–SiO2 aerogel composite with ultra-low thermal conductivity and enhanced mechanical strength, Scripta Materialia Volume 143, 15 January 2018, Pages 113-116. http://doi.org/10.1016/j.scriptamat.2017.09.028