Silicon-boron-carbon-nitrogen monoliths with high, interconnected and hierarchical porosity

Silicon-boron-carbon-nitrogen (Si-B-C-N) monoliths with high, interconnected and hierarchical porosity have been prepared by spark plasma sintering (SPS) of ordered mesoporous powders with a P6mm hexagonal symmetry at low temperature without any sintering additives. The ordered mesoporous Si-B-C-N powders derived from boron-modified polycarbosilazanes displayed a mesopore population centred on 4.6 nm, a total pore volume of 0.78 cm³ g ^-1 and a specific surface area of 544 m² g^-1. They have been partially sintered in the temperature range 800-1000 °C under nitrogen to lead to robust meso-/macroporous Si-B-C-N monoliths with surface areas of 123-171 m² g^-1, mesopore diameters centred on 6.2-6.5 nm and total pore volumes varying from 0.25 to 0.35 cm³ g^-1 measured by nitrogen adsorption experiments. As-obtained crack-free Si-B-C-N monoliths displayed porosities from 59 to 69% and a relatively large pore size distribution as determined by helium pycnometry and confirmed by mercury porosimetry. TEM observations and low angle X-ray diffraction (LA-XRD) confirmed the formation of monoliths that maintained a mesoporosity organization in comparison to starting powders while SEM experiments showed a microstructure in which necks are formed around the area of contact between particles. With a thermal stability extending up to 1400 °C in flowing nitrogen and a heat conductivity of 0.647 W m^-1 K ^-1 for the most porous component, these new materials display the necessary intrinsic properties required as porous supports working in a harsh environment.