Synthesis and anisotropic properties of alumina-silica aerogels constructed by silica sols infiltrated into unidirectional frozen alumina templates

Abstract

Abstract Alumina-silica aerogels (ASAs) were firstly prepared by using alumina aerogels as template via ice-template method and then silica sols infiltrated via vacuum impregnation. Fourier transform infrared (FT-IR) spectra, X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to investigate the microstructures characteristics and phase composites. Compared with the alumina templates (ATs), ASAs presented the porous characteristic of nano-level aerogels. The infiltrated silica can retard phase transformation of alumina. The anisotropic mechanical and thermal conduction properties of ATs in parallel and perpendicular to ice-crystal growth directions were demonstrated, which was related to the anisotropic porous structures of ATs due to the difference of main and secondary skeleton structures forming in unidirectional freeze. After infiltrated silica sols, the mechanical property was increased but the thermal conductivity was decreased. The anisotropic characteristics of ASAs still were maintained. Using ice template as a support, shape-stabilized aerogel composites can be constructed.