For the wide application as thermal protection materials, it is very necessary for mullite ceramics to improve fracture toughness. In this paper, the laminated and stitched carbon fiber cloth preform reinforced mullite (C/mullite) composites were prepared through the route of sol impregnation and heat treatment using the Al₂O₃—SiO₂ sol with a high solid content as raw materials. The C/mullite composites showed a flexural strength of 228.9 MPa that was comparable to that of dense monolithic mullite although the total porosity reached 13.4%. Especially, a fracture toughness of 11.2 MPa·m^1/2 that was 4–5 times that of dense monolithic mullite was obtained. Strength deterioration due to the carbothermal reduction between carbon fiber and the residual SiO₂ in matrix was found above 1200 °C. A pyrolytic C (PyC) coating was deposited on carbon fibers as interfacial coating. The chemical damage to carbon fibers was obviously alleviated by the sacrifice of PyC coating. Accordingly, the C/PyC/mullite composites kept strength unchanged up to 1500 °C, and showed much higher strength retention ratio than C/mullite composites after annealing at 1600 °C.

Four kinds of sugar (glucose, fructose, sucrose, and maltose) were selected as carbon precursors, and corresponding dense carbon products were prepared using a novel hydrogel carbonization method. The carbonization processes of sugar–polyacrylamide (sugar–PAM) hydrogels were studied in detail. The molecular structures in the raw materials were analyzed by proton nuclear magnetic resonance spectroscopy (¹H NMR). Samples prepared at different temperatures were characterized by thermogravimetry analysis (TGA) and Fourier-transform infrared (FTIR) spectroscopy. The morphology and microstructure of sugar-derived carbons were confirmed by field-emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD). The results indicated that the sugar solution was surrounded by PAM with a three-dimensional network structure and formed hydrogels in the initial stage. The sugar solution was considered to be separated into nanocapsules. In each nanocapsule, sugar molecules could be limited within the hydrogel via walls formed by PAM chains. The hydroxyl group in the sugar molecules connected with PAM by the hydrogen bond and intermolecular force, which can strengthen the entire hydrogel system. The self-generated pressure of hydrogel constrains the foam of sugar during the heat treatment. Finally, dense carbon materials with low graphitization instead of porous structure were prepared at 1200 °C.

As turbine inlet temperatures in advanced aeroengines and heavy-duty gas turbines continue to rise, conventional thermal and environmental barrier coatings (TBCs/EBCs) are increasingly confronted with critical operational bottlenecks. They are increasingly plagued by deleterious high-temperature phase transformations, thermal expansion mismatch with substrates, and catastrophic degradation induced by molten calcium–magnesium–aluminosilicate (CMAS) and water vapor corrosion. To decisively break these inherent limitations, high-entropy rare-earth oxides (HEREOs) have rapidly emerged as a revolutionary materials paradigm. Driven by configurational entropy stabilization, severe lattice distortion, and sluggish diffusion effects, HEREOs uniquely synchronize ultralow thermal conductivity, tailorable thermal expansion coefficients, and exceptional chemical inertness within a single crystal lattice. This comprehensive review systematically navigates the cutting-edge advancements of HEREOs for next-generation hot-section protection. It first demystifies the intricate process–microstructure relationships during coating deposition, highlighting the nonequilibrium phase evolution induced by thermal spraying. Subsequently, it critically dissects high-temperature phase stability, multiscale defect-engineered thermophysical properties, and intricate failure mechanisms under CMAS and water vapor attack. Notably, to counteract the intrinsic brittleness and improve the inferior fracture toughness of HEREOs, advanced structural engineering—incorporating multiphase synergistic toughening and gradient architectures—is highlighted as a crucial strategy for enhancing thermal shock durability. Finally, transitioning from empirical trial-and-error to a predictive framework, this review envisions a machine-learning-empowered inverse design paradigm, offering a data-driven roadmap for multiobjective optimization and lifetime prediction of highly robust HEREO coatings. This contribution also statistically outlines the latest research trends, offering researchers forward-looking guidance and evidence-based references.