Effect of carbothermal reduction temperature on microstructure of fiber reinforced silicon carbide porous monoliths with high thermal resistance

The objective of this work is to develop fiber reinforced silicon carbide porous monoliths (FRSiCs) with high thermal resistance at low carbothermal reduction temperature. FRSiCs were prepared by carbothermal reduction of fiber reinforced resorcinol-formaldehyde/silica (FR-RF/SiO₂) aerogel at different temperatures starting at 1 300 °C The evolution of phase composition, morphology and pore structure of FRSiC with carbothermal reduction temperature were investigated by X-ray diffractometer (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM),N₂ adsorption/desorption analyzer and mercury intrusion porosimeter (MIP). The results reveal that FRSiCs consist of β-SiC and mullite fibers transformed from aluminium silicate fibers. Along with the increase of carbothermal reduction temperature, SiC nanocrystals aggregate to lump and transform to whiskers, and pore size becomes larger.Thermalanalyses of FRSiCs indicate that FRSiCs have excellent thermal stability in air up to 1 300 °C. FRSiCs have a high porosity more than 89%, and their apparent densities and thermal conductivities are 0.345~0.330 g·cm-3 and 0.06~0.07 W·m^-1·K^-1, respectively.