Experimental design and teaching application of SiZrBC ceramic precursor synthesis

Ultrahigh-temperature ceramics (UHTCs) are essential materials for aerospace thermal protection systems, including nose caps and wing leading edges, due to their excellent high-temperature mechanical properties, resistance to antioxidant ablation, and appropriate thermal expansion coefficients. However, their inherent brittleness results in low fracture toughness and poor thermal shock resistance, which limits their widespread use. Fabricating ceramic matrix composites through continuous fiber reinforcement and the precursor infiltration and pyrolysis method offers an effective solution, with ceramic precursors playing a key role in defining the final composite properties.

This study provides a comprehensive experiment on synthesizing and optimizing SiZrBC ceramic precursors, combining cutting-edge UHTC research with educational practices to address the high costs and low yields associated with traditional precursors. The experiment utilized a one-pot polymerization method with zirconium tetrachloride, tetraethyl orthosilicate (TEOS), boric acid, and boron phenol resin (BPR) as raw materials. It systematically examined the effects of precursor preparation temperature (80 ℃-120 ℃), Si source (TEOS), B source (boric acid), and C source (BPR), along with the influence of different pyrolysis atmospheres on the properties of the resulting ceramics. Characterization techniques included Fourier Transform Infrared Spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS).

The results showed that the best overall properties were achieved at a synthesis temperature of 80 ℃, with the addition sequence starting with the Si source, then the B source, followed by the C source. Pyrolysis was performed at 1550 ℃ in an argon atmosphere. This addition order significantly affected ceramic yield and microstructure. Specifically, initial addition of the Si source helped form a Si–O–Zr network, providing stable attachment sites for subsequent components, while early B source addition facilitated B–O bonds in the polymer backbone, acting as strong cross-linking points. The precursor was pyrolyzed at 1550 ℃ in an argon atmosphere to produce composite ceramic powder with optimal properties. After pyrolysis at 1000 ℃ in argon, the ceramic achieved a high yield of 64.7%, with fine grains averaging approximately 65.61 nm, and exhibited relatively low toxicity and low raw material costs. The pyrolysis atmosphere greatly influenced the final product: argon favored higher ceramic yields and finer grains by slowing gas diffusion and promoting network formation, while a vacuum atmosphere encouraged complete oxide reduction but accelerated boron loss via B₂O₃ evaporation and grain growth beyond 106 nm. Vacuum pyrolysis removed ZrO₂ impurities but resulted in lower ceramic yields and larger grains.

This experimental approach effectively integrates core materials science concepts with practical laboratory work, covering all stages from material synthesis and structural characterization to performance analysis. By systematically exploring processing-structure-property relationships, students develop a deeper understanding of ceramic precursor chemistry, pyrolysis mechanisms, and advanced characterization methods such as FTIR, XRD, SEM, and EDS. The use of low-toxicity, cost-effective raw materials ensures safety and accessibility in educational settings. This experiment improves the quality of materials chemistry education, enhances students’ practical skills in data analysis and problem-solving, and promotes innovative thinking vital for scientific research. Through project-based learning, students acquire critical research skills, recognize the importance of parameter optimization, and understand the connection between laboratory experiments and real-world aerospace applications, preparing them for careers in materials science and engineering.