Fabrication and Characterization of Nano-porous beta-Sialon Ceramic Articles Prepared via Gel-casting

Antenna protection against external factors (e. g. wind، rain، and objects colliding) is done by radome. In addition to acceptable mechanical properties، radome should satisfy suitable electrical properties such as dielectric constant and loss tangent to prevent negative effect on antenna performance. In order to build radome to be utilizing at high temperatures (over 1000 °C)، for flying objects with hypersonic speed (5 to 10 Mach)، engineering ceramics are used. Porosity affects the electrical and mechanical properties of articles. It simultaneously reduces the dielectric constant and flexural strength. In this study porous ceramic articles of beta-Sialon were fabricated by ball milling beta-Sialon powder، monomers and water for 10 hours and under 20 MPa uniaxial pressure. Average porosity size of this sample is 200 nm with 30% of its porosities are below 100 nm. Dielectric constant and loss tangent of this sample with 20% porosity in 8-12 GHz is 5. 3 and 0. 04، respectively.