Processing, properties and microstructure of SiC foam derived from epoxy-modified polycarbosilane

SiC foams having controlled porosity were fabricated using epoxy modified polycarbosilane (EMPCS). The EMPCS was synthesized by refluxing adequate amount of epoxy and polycarbosilane (PCS) in THF solution at 150 °C. The EMPCS having epoxy content of 0%, 10% and 20% by weight were termed as PCS, 10EMPCS and 20EMPCS respectively. Thermal foaming of the EMPCS was carried out at 1000 °C under inert atmosphere followed by ceramization at 1200, 1400 and 1600 °C under vacuum. The cell size of the ceramized SiC foam was found to be varying between 100 and 700 µm. The ceramized SiC foams were characterized for their density, porosity and compressive strength. Total porosity was found to be 81.8 ± 3.9, 87 ± 4.1 and 90.6 ± 4.6% for the PCS, 10EMPCS and 20EMPCS based SiC foams while their bulk densities were found to be 0.6 ± 0.03, 0.4 ± 0.02 and 0.3 ± 0.01 g/cc respectively. Compressive strength was found to be the highest for the SiC foams ceramized at 1600 °C for all the types of EMPCS. The compressive strength of the 10EMPCS is found to be 2.2 ± 0.2 MPa, 2.5 ± 0.2 MPa and 3.8 ± 0.3 MPa for the foams pyrolyzed at 1200 °C, 1400 °C and 1600 °C respectively while the strength was 1.9 ± 0.1 MPa, 2.1 ± 0.2 MPa and 2.9 ± 0.2 MPa for the 20EMPCS based SiC. The 20EMPCS based SiC foam of thickness 10 mm was exposed to oxy-acetylene flame for 120 s, back face temperature was found to be around 300 °C. Microstructure and phase analysis was carried out to understand the effect of epoxy content and ceramization temperature on physical, mechanical and thermal properties of different types of the SiC foams.