Synthesis, inorganic transformation, and high‐temperature evolution of liquid non‐oxygen ultra‐high‐temperature HfSiCN ceramic precursors

Abstract Ultra‐high‐temperature ceramic precursors are crucial for fabricating large, complex‐shaped, high‐performance ceramic matrix composites using a precursor impregnation pyrolysis (PIP) method. A liquid precursor composed of non‐oxygen polyhafniumnitrocarbosilane was successfully synthesized from tetrakis(diethylamino)hafnium and self‐made liquid polycarbosilane using a one‐pot process. The precursor's composition, structure and properties were analysed using Fourier‐transform infrared (FTIR) spectroscopy, nuclear magnetic resonance and viscosity testing, revealing the presence of Si–N–Hf structures. The synthesised precursor remained liquid at 25°C with a tunable viscosity range of 38.8–136.1 mPa·s. The precursor's inorganic transformation was examined using thermogravimetry–FTIR–mass spectrometry, elemental analysis, and scanning electron microscopy (SEM), achieving a ceramic yield of 71.62 wt% under argon at 1000°C. The resulting inorganic product was amorphous with low oxygen content (≤2.84 wt%), no detectable HfO 2 phase, and an adjustable Hf content of 16.28–42.90 wt%. The high‐temperature evolution of the inorganic product from 1600 to 2400°C in argon was studied using X‐ray diffraction, Raman spectroscopy, SEM, and transmission electron microscopy. This product exhibited a thermal weight loss of 10.60–19.67 wt%. The product contained HfC x N 1− x and SiC phases with grain sizes of 17.4–114.9 nm and an adjustable HfC x N 1− x phase content of 21.6–69.4 wt%. This novel precursor, characterised by its non‐oxygen composition, adjustable room‐temperature viscosity, high ceramic yield, and substantial HfC content, demonstrates strong potential as an ideal raw material for the PIP method in preparing ultra‐high‐temperature ceramic composites, exhibiting a favourable outlook for aerospace applications.