Preparation of hierarchical directional porous alumina microspheres with high porosity, low density, and low thermal conductivity via spray freeze drying with heat treatment

Abstract

Hierarchical structure materials have been widely applied in various fields due to their unique structure. However, pores collapse at high temperatures may cause the properties loss of materials. Fortunately, the thermal stability of alumina could maintain the structure stable at high temperatures. In this research, Al(NO3)3·9H2O was selected as the alumina source, using spray freeze drying combined with heat treatment to fabricate hierarchical directional porous alumina microspheres (HDPAMs). The alumina microspheres fabricated by this method have the advantage of high porosity, low density, low thermal conductivity, and high-temperature structure stability. Furthermore, the relationship between the condition of fabrication and the parameters of HDPAMs was explored and the thermal conductivity of HDPAMs was investigated. Moreover, simulations using COMSOL Multiphysics have been conducted to explore the superiority of hierarchical directional porous structures in terms of thermal insulation.