Microwave absorbing performance and temperature resistance of multifunctional foamed ceramics prepared by the sintering method

Abstract

To develop multifunctional microwave absorbing (MA) materials, foamed ceramics (FCs) with adequate MA performance that can withstand temperatures up to 1000 °C were prepared by sintering at 1200 °C with Si3N4 as the foaming agent and steel wires (alloy designation 0Cr18Ni9) as the absorber. The FCs with 0.2 vol% wires of 100 μm diameter and 3.0–4.0 mm length showed excellent MA performance in the 8.0–18.0 GHz frequency range. The entire reflectivity–versus–frequency curve was below –10 dB and contained a mean reflectivity as low as –15.3 dB and a minimum reflectivity of –22.4 dB at 17.7 GHz, indicating that more than 97.0% of the 8.0–18.0 GHz microwave was absorbed and the 17.7 GHz microwave was absorbed by about 99.4%. The FCs exhibited a high total/closed porosities of 87%/85%, low density of 0.36 g/cm3, relatively high compressive strength of 6.3 MPa, low thermal conductivity of 0.124 W/mK, and microstructure with uniformly–distributed pores with diameters less than 0.5 mm. After 100 h of heat–treatment at 1000 °C, the FCs remained largely unchanged in MA performance and physical–mechanical properties owing to their almost unchanged wire distribution, phase composition, and foam structure, implying that the FCs are a promising multifunctional MA material with the advantages of light weight, thermal insulation, and temperature resistance.