Design and performance of foamed ceramics with ultra–low permittivity and thermal conductivity

Abstract

To meet the requirements for materials with ultra–low permittivity and thermal conductivity in cutting–edge fields, the feasibility of preparing foamed ceramics (FCs) with high porosity by high–temperature sintering using desalinated sea sand as the primary raw material and aluminium nitride (AlN) as a blowing agent was investigated. The preparation of FCs is achieved through the blowing up of the molten ceramic body by the oxidation–derived nitrogen from AlN during sintering. The FCs sintered at 1100 °C from the material system of 11 wt% Na₂CO₃ and 3 wt% AlN exhibit a high porosity of 94.6 %, a low density of 0.138 g/cm³, and a compressive strength of 0.24 MPa. The FCs sintered at 1050 °C from the material system of 11 wt% Na₂CO₃, 3 wt% AlN and 0.5 wt% MnO₂ have a high porosity of 94.2 %, a low density of 0.149 g/cm³, and a compressive strength of 0.35 MPa. The high porosity, independent and uniform pore structure, coupled with a simple phase composition, enables the FCs to exhibit a thermal conductivity as low as 0.043–0.051 W/(m·K) in the temperature range of 10–80 °C and a mean permittivity as low as (1.61–1.64) + j(0.0031–0.0037) in the X–band, resulting in FCs with excellent thermal insulation and microwave penetration.