Synthesis and pyrolysis of Hf-N-B backbone polymer precursor for HfC/HfB2 composite ceramics

Metallopolymers containing refractory metal in the main chain are highly desired but rarely reported as oxygen-free single-source precursors for preparing ultrahigh-temperature ceramics. Herein, a novel single-source precursor of poly-hafnium-borocarbosilane (PHBCNS) with an Hf-N-B backbone molecular structure was synthesized through the dehalogenation reaction between HfCl4 and B(NHCH3)(3). The polymeric Hf-N-B chain with large bond angle and conjugated molecular structure endowed the PHBCNS precursor to be relatively stable, dissolvable, and meltable. Subsequent precursor pyrolysis up to 1800 degrees C resulted in an HfC/HfB2 nanocomposite comprising an Hf content of 87.54 wt%, with the average grain size of HfC and HfB2 to be 34.9 and 74.1 nm, respectively. The ceramization mechanism and phase evolution from the PHBCNS precursor to HfC/HfB2 composite ceramics were thoroughly investigated. This work not only highlights a novel Hf-N-B backbone polymer with high metal content and good shaping properties but also provides fresh insights of designing single-source precursors for ultrahigh-temperature composite ceramics.

Automated summary

In this study, a novel metallopolymers containing poly-hafnium-borocarbosilane (PHBCNS) as an oxygen-free single-source precursor for preparing ultrahigh-temperature ceramics was successfully synthesized. The ceramization mechanism and phase evolution from the PHBCNS precursor to HfC/HfB2 composite ceramics were thoroughly investigated, providing fresh insights for designing single-source precursors for ultrahigh-temperature composite ceramics.