The effect of annealing at 1400 °C on the structural evolution of porous C-rich silicon (boron)oxycarbide glass

A precursor SiBOC glass was annealed at 1400 °C for 1, 3, 5 and 10 h and then it was HF etched in order to dissolve the SiO2/B2O3 phase and to obtain a porous C-rich oxycarbide glass. The porous material was studied by N2 absorption. The pore diameter of the porous C-rich SiBOC glass ranges between 2 and 5 nm and continuously increases with increasing annealing time. The pore volume also increases with the annealing time up to ≈1.0 cm3/g which is close to the pore volume estimated from the chemical composition (1.04 cm3/g) assuming complete dissolution of the silica-based phase.