Journal of the American Ceramic Society最新文献

Silica glass plays a significant role in aerospace and laser fusion applications; however, radiation-induced performance degradation severely limits its service life. This study focused on five types of high-purity quartz glass: low-Cl high-OH (S1), low-Cl medium-OH (S2), low-Cl OH-free (S3), high-Cl OH-free (S4), and Cl-free OH-free (7979). All samples underwent prolonged thermal annealing at 1000°C for 20 h to standardize the fictive temperature (T_f) and evacuate residual hydrogen molecules from the silica glass. This step aimed to eliminate the influence of T_f and hydrogen on the optical and radiation-resistant properties, allowing the study to concentrate on the effects of OH and Cl impurities. The hydrogen molecule content was measured using Raman spectroscopy, and the OH content and T_f were determined using Fourier transform infrared spectroscopy. A ⁶⁰Co gamma-ray source provided irradiation with a total dose of 100 kGy. Changes in the optical properties before and after irradiation were analyzed using waveguide-prism coupling instruments, vacuum ultraviolet spectrophotometry, ultraviolet–visible spectrophotometry, and fluorescence spectroscopy. The types of radiation-induced color center defects were identified using fluorescence spectroscopy and continuous-wave electron paramagnetic resonance. Radiation-induced absorption spectra were deconvoluted to determine the evolution of different color center defect concentrations with varying OH and Cl contents. The results indicate that the OH and Cl contents significantly affect the refractive index, ultraviolet (UV) absorption, infrared absorption, and radiation resistance of the quartz glass. Higher Cl content increases the concentrations of radiation-induced defects (Si–E′, POR, ODC(II)), degrading the radiation resistance of silica glass. Higher OH content suppresses Si–E′, POR, and ODC(II) formation, improving UV radiation resistance, but enhances NBOHC defects, worsening performance at 620 nm.

To address the challenge of inefficient synthesis of multi-principal-element transition metal carbides, this study demonstrates an efficient pathway using ultrafast high-temperature sintering (UHS) to convert elemental precursors into dense, 2- to 9-component solid solutions within minutes. Rapid densification results from a synergy between the high heating rate of UHS and the formation of a Cr₃C₂-based liquid phase. The formation of a single-phase solid solution is governed by a thermo-kinetic control mechanism, where thermodynamic drivers are ultimately constrained by kinetic barriers, such as the poor solubility of key components (e.g., ZrC) and the diffusion-facilitating role of carbon vacancies. The resulting solid solutions exhibit excellent hardness (up to 38.6 GPa), but their fracture toughness is limited by process-induced thermal stresses, a drawback partially mitigated by post-sintering annealing. This work presents a promising approach for the high-throughput fabrication and screening of these materials and provides critical insights into their non-equilibrium sintering mechanisms.

Plastic waste (PW) leads to a considerable environmental challenge, highlighting the need for effective recycling strategies. One promising approach is its incorporation into emerging advanced technologies, such as extrusion-based cementitious 3D-printed concrete (3DPC), which can enhance material efficiency while reducing plastic disposal. This paper presents a concise review of recent studies on the incorporation of PW into cementitious 3DPC. Parameters such as the type of PW and particle characteristics, including length, width, or diameter, and their effects on 3DPC properties are critically analyzed. Any surface modification techniques applied to PW are discussed, and maximum and suitable replacement levels of PW are also documented. Incorporating PW aggregates in 3DPC mixes usually enhances the flowability but tends to negatively affect buildability, compressive strength, flexural strength, and interlayer bond strength. The optimum PW aggregate replacement level appears to be ∼5% of the total mix volume or ∼10% of the sand volume. Conversely, using PW fibers lowers flowability while improving buildability and overall mechanical performance. The optimum PW fiber dosage is ∼0.3% of the cementitious materials by weight or 0.3%–1% of the total mix volume, depending on fiber type and dimensions. The review also discusses the influence of PW on durability, sustainability, and cost. Incorporating PW into 3DPC offers a sustainable approach that reduces environmental impact, conserves natural resources, and links waste management with advanced construction technologies, promoting a greener environment. Finally, this review provides a foundational reference for the preliminary optimization of PW in 3DPC and for directing future research.

A synergistic enhancement in bending strength, hardness, and fracture toughness while maintaining low density in B₄C ceramics remains a challenge. Herein, we propose to design a simple three-layer symmetrical sandwich-type laminated structure of B₄C-TiB₂ by imitating the nacre's structure, which effectively minimizes interfacial defects and achieves stronger interfacial bonding via reactive sintering using B₄C, TiC, and B as starting materials. The simple symmetric design generates residual compressive stress in both outer layers and tensile stress in the middle layer. It has been found that the residual compressive stress can counteract external loads and lead to a remarkable improvement in hardness and bending strength. Furthermore, a rising R-curve behavior is observed in the fracture toughness testing of laminated B₄C-TiB₂ ceramics, indicating superior resistance to crack propagation. Compared to monolithic ceramics, the as-synthesized laminated B₄C-TiB₂ ceramic exhibits amazing comprehensive properties with a high hardness of 37.1 ± 0.4 GPa, bending strength of 834.3 ± 62.8 MPa, and fracture toughness of 5.0 MPa·m^1/2. This work provides precise guidance for the design of impact-resistant ceramics by offering an in-depth understanding of how residual compressive stress affects mechanical properties.

Direct nitridation is widely applied for industrial-scale preparation of Si₃N₄, while facing a persistent challenge of incomplete nitridation due to melting and volatilization of Si powder. In this work, a foaming-assisted route, in which the porous Si foams were used as the staring material, was developed to prepare the Si₃N₄ whiskers from the perspective of mass production. A complete nitridation at 1300°C could be achieved, which is lower or comparable to those reported previously for preparation of whiskers. The interconnected “pores” of Si foam not only provided the N₂ pathways, which enabled it to enter the interior efficiently, thus promoting its reaction of Si nitridation regardless of foam sizes, but also provided enough surface for the growth of whiskers. The as-prepared Si₃N₄ whiskers could be potentially used as a thermally conductive filler in resin composites, which enhanced the heat transfer and robustness of the polymer matrix. By simply stacking these Si foams in an industrial nitriding furnace, a scale-up preparation of Si₃N₄ whiskers can be realized without complex operations, anticipating its applicability for industrial production.

With increasing propulsion ratios in next-generation aeroengines, surface temperatures of turbine blade leading edge have reached 1700°C even after active cooling, making long-term thermal protection systems a critical bottleneck for aeroengine advancements. The carbon/carbon (C/C) composites with excellent high-temperature performance present more promising development prospects. However, their viability for aeroengine application lacks experimental verification. In this work, the SiC/TiC ceramic derived from a single-source precursor was incorporated into C/C composites via precursor infiltration and pyrolysis. A (Zr-Ti)C-SiC-Si/SiC-Si double-layered coating was subsequently prepared on the C/C-SiC-TiC composites through slurry dipping-carbonization and gaseous silicon infiltration. Oxidative ablation behavior of co-prepared sample was evaluated under a 1700°C oxyacetylene flame for 2400 s, revealing a superior long-term ablation resistant property with the lowest linear ablation rate of 0.763 µm/s. A (Zr, Ti)O₂ oxide skeleton and SiO₂ healing phase made a joint contribution as an effective oxygen and thermal barrier during initial ablation. Prolonged ablation time led to SiO₂ depletion and (Zr, Ti)O₂ skeleton erosion by oxyacetylene flame, causing coating failure, whereafter the modified substrate provided the effective protection. Thus, dense ZrTiO₄ phase, TiO₂, and SiO₂ healing phase were formed, which can seal the porous surface of the oxide layer, further enhancing ablation resistance. This work affirms that synergistic matrix and coating modification is an effective strategy to significantly improve the long-term ablation resistance of C/C composites in simulated dynamic aeroengine environment.

Mullite fiber aerogel materials have attracted growing interest due to their superior lightweight thermal insulation properties. To ensure optimal performance of the mullite fiber skeleton within the aerogel matrix, precise control of fiber diameter is essential. Kármán vortex solution blow spinning (KV-SBS) is an emerging technique for efficient, low-cost manufacture of mullite fibers, whose quality is influenced by various process parameters. Numerical simulation offers a powerful alternative to traditional experiments, reducing cost and duration while enabling rapid optimization. In this study, a multiphysics coupled numerical model for KV-SBS ceramic fiber fabrication was developed, incorporating KV airflow, solution rheology, solvent evaporation, and fiber formation mechanics. The model reveals intrinsic relationships between process parameters and fiber morphology, with predictions experimentally validated, confirming its accuracy and demonstrating that the diameter of mullite fibers can be precisely controlled with high quality.

The selection of binders in ceramic additive manufacturing plays a high role in determining the feasibility and quality of printed components. This study investigates the performance of sodium carboxymethylcellulose (CMC) and hydroxypropylmethylcellulose (HPMC) as bio-based binders in aqueous alumina suspensions for direct ink writing (DIW). CMC, characterized by its polyelectrolyte nature, demonstrated rapid dissolution, exceptional dispersion stability, and consistent rheological properties, facilitating smooth extrusion and the formation of high-quality surfaces. These characteristics are critical for DIW, where ink homogeneity and stability directly impact printing resolution and part integrity. HPMC, by contrast, exhibited slow dissolution, thermally induced gelation, and printing inconsistencies, likely due to its lack of electrostatic stabilization. Microstructural and mechanical evaluations of sintered parts confirmed that CMC-based systems achieved higher density, homogeneity, and microhardness. This study highlights the significance of CMC as a binder, providing a pathway to overcome common challenges in DIW, such as agglomeration, foaming, and poor sintered properties, while enabling the production of high-performance ceramic components.