Mechanistic insights into graphitic carbon-induced devitrification suppression in polymer-derived SiCN/C nanocomposites for extreme temperature applications

Abstract

Silicon carbonitride (SiCN)-based polymer-derived ceramics (PDCs) hold promise for ultra-high temperature applications, but their thermal stability is often compromised by devitrification-prone deterioration. Although carbon (C) incorporation has been reported to influence SiCN evolution, the mechanistic role of graphitic carbon in suppressing crystallization remains unclear. Here, we elucidate the role of carbon in high-temperature structural stabilization via modulated incorporation of divinylbenzene (DVB)-promoted graphitic carbon into SiCN PDCs, pyrolyzed at 1600 ◦C in argon atmosphere. SiCN/C nanocomposites synthesized with 0-50 wt% DVB exhibit progressively enriched graphitic domains (ca. 46-72 at.%), producing turbostratic architectures characterized by reduced coherence length, elevated microstrain, and lowered stacking-fault energy. This defect-engineered framework inhibits β-SiC crystallization, retards atomic mobility, decelerates thermodynamic phase transition and stabilizes the amorphous phase under extreme thermal loads. Microstructural analyses (William-Hall, Warren-Averbach, SEM), phase characterization (XRD, Raman Spectroscopy), and compositional studies (EDX, carbon analysis) reveal that increasing carbon content drives a transition from partial to near-complete devitrification suppression. Thermal analysis (TGA-MS/FTIR) further shows enhanced hydrogen and hydrocarbon evolution during polymer-to-ceramic conversion, followed by stabilization at ceramisation temperatures. Our studies establish a quantitative connection between nanoscale disorder and macroscopic thermal resilience that could provide a design approach for next-generation PDCs capable of transcending the intrinsic stability limit of pristine SiCN. Tailored graphitic phases therefore emerge as potent structural modifiers that may enable ceramics to withstand extreme temperature environments without catastrophic phase transitions.