Directly growing nanowire-assembled nanofibrous ceramic foams with multi-lamellar structure via freeze-casting process

Abstract

Herein, a novel and simple approach for directly growing nanowire-built nanofibrous ceramic foams with tunable hierarchical pores has been put forward, where silicon particles, Ludox® and carbon black are selected as the initial materials. Firstly, cellular green bodies were constructed by freeze casting method, and their oriented pores provided sufficient but designated space for the generation of nanowires during carbothermal reduction nitridation process, meanwhile ensured the adequate nitrogen supply. The prepared multi-laminate ceramic foams assembled by nanowires with low density of 0.40 g/cm3 exhibit excellent heat insulation performance with low thermal conductivity of W/(m·K) and outstanding dielectric properties with low dielectric constant of 2.35 at frequency of 10.0 GHz, which could be attributed to the hierarchical porous structure built by nanowires level by level, and they would have promising applications in the thermal insulators, absorptions, catalyst supports, filters for gas or liquid as well as wave-transparent materials.