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

Abstract

AbstractMetallopolymers 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°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.