Syntactic Closed-cell Foams Based on Silicon Carbide

Abstract

ABSTRACTClosed cell foams were fabricated by incorporating two different grades of hollow alumino-silicate spheres (cenospheres) into a silicon carbide matrix. The silicon carbide matrix was formed by the pyrolysis of a preceramic polymer, and multiple polymer infiltration and pyrolysis (PIP) cycles were employed to minimize the open voids in the material. The physical, mechanical and thermal properties of the fabricated foams were characterized as functions of the number of reinfiltration cycles. The open- and closed-void volume fractions were determined by measurements of bulk and skeletal densities. Mechanical properties, including strength and modulus, were evaluated using four-point bend and compression tests. Finally, thermophysical (thermal conductivity) values of the material were determined using laser-flash technique. This processing technique results in closed-cell syntactic foams with low density (≤ 1.8g/cm3), reasonable mechanical strength (∼ 30 MPa) and very low thermal conductivity (≤ 1 W/m-K). In this manner, this process can be used for the low-cost and net-shape fabrication of closed-cell silicon carbide syntactic foams for high temperature applications.