Lightweight ceramic aerogel stands up to high heat

In the world of materials, aerogels are lightweights. Air accounts for almost all their volume, with a fine network of material holding the structures together. Ceramic aerogels are ideal components for heat shields on spacecraft because they are chemically stable and can maintain their structures in corrosive environments. But aerogels made from typical ceramic materials, such as silica, become fragile at high temperatures or when subjected to dramatic temperature swings. Now, researchers report a new ceramic aerogel that maintains its strength when heated above 1,400 °C in a vacuum or when it is repeatedly heated to 900 °C and rapidly cooled to –198 °C (Science 2019, DOI: 10.1126/science.aav7304). A team led by the University of California, Los Angeles’s Yu Huang and Xiangfeng Duan and the Harbin Institute of Technology’s Hui Li created the material using a previously reported method to build a graphene aerogel template that can be compressed without breaking or bulging, thanks to its architecture. They deposited a thin layer of hexagonal boron nitride (h-BN, the compound’s most stable crystalline form) on this template and oxidized the graphene away, leaving behind a network of h-BN with double-pane walls. This architecture helps the h-BN aerogel stay strong even after experiencing high temperatures. In addition to its heat tolerance, the h-BN aerogel is virtually weightless—it can be placed atop a flower’s delicate stamen without deforming or damaging it.