Synthesis and structural evolution of dual-boron-source-modified polysilazane derived SiBCN ceramics

Abstract

Here, we demonstrated a novel synthesis of a polyborosilazane (PBSN) precursor using hydroboration and aminolysis reaction synergies to modify polysilazane (PSN). Specifically, borane·tetrahydrofuran and boron trichloride·hexane were used as dual boron sources, which not only reacted with Si–Vi and Si–N–H functionality respectively to modify multiple active sites of PSN resulting in boron-rich silicon–boron–carbide–nitride (SiBCN) ceramics, but also improved controllability on composition, molecular structure, as well as final features. The resulting structures were characterized by FTIR, solid-state ¹¹B and ²⁹Si magic-angle-spinning NMR and inductively coupled plasma emission spectral (ICP) analysis. These polymers were found to be structurally complex networks composed of tri-coordinate BC_xN_3−x and tetra-coordinate BC_xN_4−x bridges. The resulting polyborosilazanes contained ∼11 wt% higher boron contents than that in the starting polymer. The structural evolution of the resulting polymers was evaluated by means of XPS, FTIR and XRD, and TGA-DSC-QMS was utilized to detail the precursor-to-ceramic conversion.