Strong and resilient alumina nanotube and CNT/alumina hybrid foams with tuneable elastic properties

Abstract

Excellent chemical and heat resistance combined with the attractive properties of aerogels, including large surface area and low density makes alumina aerogels an attractive material for high temperature catalysis, thermal insulation, and vibration damping. Brittle behaviour, a high propensity to sinter, and poor moisture stability, however, have drastically inhibited the practical use of alumina aerogels produced using traditional methods. Herein, we report the scalable fabrication of low density, anisotropic carbon nanotube (CNT)/alumina hybrid foams synthesized via atomic layer deposition (ALD) on aligned carbon nanotube foams (CNTFs). Calcination of the hybrid foams in air resulted in removal of the CNTFs, leaving behind a free-standing three-dimensional network of interconnected alumina nanotubes. Both CNT/alumina hybrid foams and pure alumina nanotube foams exhibit unprecedented elastic recovery following 50% compression, and possess values for strength and Young's moduli which exceed those of aerogels with similar densities. The scaling behaviour of Young's modulus to foam density for pure alumina foams exhibits a power-law dependence of n ≈ 1.9, attributed to superb ligament connectivity. These unique structures remain stable to the large capillary forces induced upon liquid infiltration and removal, and can absorb up to 100 times their own weight in water. Furthermore, alumina nanotube foams demonstrate enhanced thermal insulation capabilities at temperature of 1000 °C with no evidence of shrinkage.