Porous Reaction-Bonded Silicon Nitride Ceramics: Fabrication Using Hollow Polymer Microspheres and Properties

Abstract

A process has been proposed for the preparation of porous reaction-bonded silicon nitride (RBSN) via the addition of a pore former, uniaxial pressing, and subsequent reaction sintering in a vacuum furnace. As a pore former, we used a commercially available powder consisting of hollow polymer microspheres (Akzonobel) with an average diameter of 9 μm. We have studied the effect of pore former content in green compacts on the mechanical, dielectric, and thermophysical properties of the ceramics. The proposed process allows one to prepare porous RBSN with the following properties: σ_b = 48 MPa, ε = 3.2, tan δ = 35 × 10^–4 at a frequency of 10 GHz, and λ = 0.96 W/(m K) at 1100°C. The ceramic obtained in this study is potentially attractive for industrial application as a radar-transparent structural material with reduced thermal conductivity.