Fabrication of hierarchically porous silicon carbonitride monolith using branched polysilazane and freeze casting method without crosslinking step: Effect of polymer additive to aligned macropore structure

Abstract

A hierarchically porous SiCN monolith with aligned macropores was prepared using a branch-structured polysilazane, silsesquiazane (SSQZ), as a precursor and polymer additive, through the freeze casting method. As polymer additives, polystyrene (PS) and poly(methyl methacrylate), which have different compatibilities with SSQZ, were used to confirm the effect on the pore formation. In addition, the pore formability according to the molecular weight was investigated using PSs with different molecular weights. When the SSQZ and high-molecular-weight PS (HPS) were used, a porous SiCN with micro/meso/macropore structure could be fabricated because of the structural stability of the SSQZ and high molecular weight of HPS. The hierarchically porous SiCN monolith was successfully manufactured using SSQZ and HPS with 639 m(2)/g of specific surface area, 0.36 cm(3)/g of pore volume, and 2.1 nm of average pore size. The hierarchically porous SiCN monolith with high HPS content has improved dimensional stability to show its compressive fracture energy.