Journal of the American Ceramic Society最新文献

SiAlON ceramic cutting tools are well suited for high-speed machining of heat-resistant superalloys. The ever-rising demands for higher productivity require the development of new SiAlON grades with better wear and fracture resistances. This investigation systematically studied the effects of Yb₂O₃/Y₂O₃ ratio and La₂O₃ content on the phase evolution, microstructure, elemental segregation, and mechanical properties of Y‒Yb‒La co-doped SiAlON ceramics for the first time. Vickers hardness and fracture toughness were evaluated, while the precipitated phases and microstructural features were characterized using X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The critical role of La₂O₃ in optimizing multication-doped α‒β-SiAlON was revealed. The addition of La₂O₃ enhanced the elongation of columnar β-SiAlON grains, suppressed the devitrification of intergranular phases and weakened the interfacial bonding particularly at low levels (0‒0.4 mol%), leading to higher fracture toughness due to more frequent bridging and grain pull-out during crack propagation. The replacement of Y₂O₃ by Yb₂O₃ consistently increased hardness but reduced fracture toughness, attributed to the higher α-SiAlON content and more isotropic grain morphology. Furthermore, an increase in the α-SiAlON content was observed at higher synthesis temperatures for a given composition. This multication doping strategy offers a promising route to tailor the balance between hardness and toughness for advanced ceramic cutting tool applications with HV10 over 18 GPa and K_1C over 8 MPa/m².

There is a tremendous demand for noncontact temperature sensing technologies due to their fast response and accurate testing. In this work, Ba₃LaNb₃O₁₂:Sm³⁺/g-C₃N₄ mixed phosphors with various compositional ratios were synthesized via a high-temperature solid-state reaction. Over the temperature range of 313–573 K, the luminescent intensity of g-C₃N₄ exhibited a decreasing trend. In contrast, the luminescent intensity of Ba₃LaNb₃O₁₂:Sm³⁺ demonstrates an antithermal quenching phenomenon due to the high structural rigidity of Ba₃LaNb₃O₁₂. To achieve high temperature sensitivity, Ba₃LaNb₃O₁₂:0.08Sm³⁺ and g-C₃N₄ were mixed at an optimal 15:1 ratio, leveraging their contrasting thermal responses. The composite exhibits tunable emission, with its color shifting from cyan to orange as the temperature rises. This property enables a dual-mode temperature sensing based on fluorescence intensity ratio (FIR) and Commission Internationale de l'Éclairage (CIE) chromaticity coordinates, achieving maximum relative sensitivities of 1.63% K⁻¹ at 313 K and 0.34% K⁻¹ at 573 K, respectively. Besides, the repeatability of the optimal mixed phosphors reaches 98% across variable temperature cycles. These results indicate that the Ba₃LaNb₃O₁₂:Sm³⁺/g-C₃N₄ mixed phosphor exhibits high sensitivity and exceptional repeatability, demonstrating its potential for application in self-calibrated optical thermometry.

Ceramic materials are essential in aerospace, medical, automotive, energy, and semiconductor industries due to their exceptional mechanical, optical, electrical, and thermal properties. However, their fabrication is often time-consuming, particularly in binder-based systems where binder removal is a critical bottleneck. In this study, we explored strategies to accelerate the debinding process using additive manufacturing (AM) by tailoring particle size distribution to induce a capillary gradient from the core to the surface. Two microscale models with distinct particle arrangements were studied: Random and Gradient. The results show that the Gradient model debound 1.3× faster than the Random model due to enhanced capillary-driven binder transport. Particle motion affected binder migration pathways, increasing their tortuosity compared to models without particle movement. These findings demonstrate the role of spatially tailored particle distributions in meaningfully accelerating binder removal while expanding design possibilities for more complex, high-performance architectures in ceramic AM.

Zirconium titanate (ZrTiO₄) is a technologically important ceramic that is difficult to synthesize by conventional sintering, typically requiring several hours of heat treatment at temperatures around 1500°C. It undergoes a sluggish order–disorder transition near 1125°C. At low temperatures, Zr⁴⁺ and Ti⁴⁺ ions occupy ordered lattice sites, whereas heating above 1200°C causes these cations to exchange positions randomly, transforming the material into a disordered, symmetric phase. Although the disordered phase is stable above 1200°C, achieving homogeneity at lower temperatures requires prolonged or repeated annealing treatments. Here, we demonstrate that zirconium titanate can be rapidly synthesized by reactive flash sintering (RFS), in which mixed oxide powders simultaneously densify and react to form a single phase within 30 s at a furnace temperature of 800°C. Experiments were carried out at nominal current densities of 60, 100, and 140 mA/mm². Unlike conventional flash sintering, which typically occurs in stage II near the flash onset, sintering in this case initiated in stage III, followed by the formation of the ZrTiO₄ phase. This phase formation was accompanied by a measurable volume expansion. By carefully controlling furnace temperature, current density, and hold time, two distinct phases—ZrTiO₄ and Zr₅Ti₇O₂₄—were successfully stabilized. In summary, dense ZrTiO₄ with ∼95% relative density and a hardness of ∼11 GPa was obtained by optimizing the electrical parameters. Rapid cooling of the specimen immediately after flash termination effectively suppressed the order–disorder transition. A small amount of residual TiO₂ remained due to the use of an equivolumetric initial powder mixture.

The transition toward sustainable energy requires safe and efficient storage systems. Sodium-ion batteries are a promising alternative to lithium-based systems, with Na₃PS₄ solid electrolytes gaining attention for their safety, processability, and ionic conductivity. This study investigates how synthesis parameters (e.g., heat treatment time) affect the conductivity of pristine and Cl⁻/Br⁻-doped Na₃PS₄. Electrolytes with nominal compositions Na₃PS₄, Na_3.0PS_3.8Cl_0.2, and Na_3.0PS_3.88Br_0.12 were synthesized via ball milling and heat treatment, and characterized by X-ray diffraction (with Rietveld refinement), scanning electron microscopy, and electrochemical impedance spectroscopy. Cl⁻ doping with moderate heat treatment introduces Na⁺ vacancies, enhancing ionic conductivity fourfold (4.8×10⁻⁵ Scm⁻¹) without compromising phase stability. In contrast, Br⁻ doping results in NaBr precipitation and reduced conductivity. These findings provide insights into the effect of halogen doping and synthesis conditions to understand structure–transport relationships, guiding the development of Na₃PS₄-based solid electrolytes. Based on that, future work should refine synthesis conditions and doping level to deepen the understanding and further improve ionic transport in solid-state sodium-ion batteries.

Electroplating sludge (ES), a hazardous waste containing heavy metals, poses significant environmental challenges. This study presents a sustainable strategy for transforming chromium-rich ES into high-value uvarovite (Ca₃Cr₂(SiO₄)₃) green pigments via an optimized solid-state synthesis route. Guided by thermodynamic analysis using FactSage software, the Ca/Si and Ca/Cr molar ratios were optimized to 1.6 and 1.2, respectively, to compensate for the variability in sludge composition. Borax was identified as the optimal mineralizer, enhancing crystallinity while suppressing secondary phase formation. The introduction of carbon effectively reduced the hexavalent chromium content. The synthesized pigments exhibited excellent green coloration and maintained structural stability up to 1200°C. Leaching tests confirmed Cr(VI) concentrations below 0.1 mg/L, complying with regulatory standards. When incorporated into commercial glazes at 3–6 wt.%, the pigments demonstrated coloration performance comparable to conventional Cr₂O₃-based alternatives. This work establishes a technically viable pathway for the valorization of ES, addressing both waste management and circular economy objectives.

Understanding the rheological behavior of ceramic suspensions is crucial for optimizing shaping technologies, including slip casting, injection molding, and additive manufacturing. Classical models often fail to account for temperature effects, interfacial phenomena, and nonlinear concentration effects, thereby limiting their applicability to real processing conditions. This study introduces a new empirical rheological model based on a hyperbolic sine formulation, incorporating three physically interpretable parameters: the effective Einstein limit offset (A), the mixing viscosity factor (β), and the interaction viscosity factor (C), verified in the concentration range 0–40 vol.%. Unlike conventional viscosity–concentration relationships, the proposed model captures the first measurable deviation from the dilute Einstein regime and describes the progressive nonlinear rise of relative viscosity using a compact analytical expression. The parameter β captures the effects of interfacial tension, liquid viscosity, and effective particle number density under isothermal conditions, as confirmed by its temperature and shear-dependent decrease and by its reduction in dispersant-stabilized suspensions, where steric layers diminish particle interactions. Therefore, parameter β provides a physically grounded link between the suspension structure and its rheological response. The model demonstrates excellent agreement with experimental data, outperforming five established rheological models across multiple systems and measurement conditions. These findings highlight the novelty of the proposed formulation as both a flexible fitting tool and a physically meaningful descriptor of early-stage viscosity evolution.

Garnet-structured (A₃B₅O₁₂) transparent ceramics show promising applications in fields such as lasers, phosphors, and scintillators. The introduction of high-entropy design into transparent ceramics offers a new pathway to expand the regulatory space of structure and properties in garnet materials. However, conventional powder sintering methods used for preparing high-entropy transparent ceramics face several challenges, including stringent requirements for high-quality powders, dependence on high temperature and pressure, and consequently grain coarsening. In this study, we innovatively employed the full glass crystallization method to fabricate high-entropy transparent ceramics. Through pressureless crystallization of glassy bulk at a relatively low temperature (1000°C, 2 h), a high-entropy transparent (Eu_0.2Gd_0.2Y_0.2Yb_0.2Lu_0.2)₃Al₅O₁₂-Al₂O₃ (HEAG-Al₂O₃) garnet-based nanoceramic was successfully synthesized. Crystallization kinetics analysis revealed that the bulk glass precursor of the HEAG-Al₂O₃ nanoceramic exhibits a high activation energy, with a crystallization mechanism of three-dimensional crystal growth mode accompanied by volume nucleation. The obtained high-entropy transparent ceramic consists of a HEAG primary phase and an in-situ formed Al₂O₃ secondary phase. The resulting dense three-dimensional network nanostructure, combined with nanoscale grains (< 30 nm), endow the biphasic HEAG-Al₂O₃ nanoceramics possessing excellent optical transmittance (81.4% at 780 nm) and mechanical properties even comparable to those of single crystal.

For potentially wider applications of ceramics with dislocation-tuned mechanical and functional properties, it is pertinent to achieve dislocation engineering in polycrystalline ceramics. However, grain boundaries (GBs) in general are effective barriers for dislocation glide and often result in crack formation when plastic deformation in ceramics is attempted at room temperature. To develop strategies for crack suppression, it is critical to understand the fundamental processes for dislocation–GB interaction. For this purpose, we adopt a model system of bi-crystal SrTiO₃ with a 4° tilt GB, which consists of an array of edge dislocations. Room-temperature Brinell indentation was used to generate a plastic zone at the mesoscale without crack formation, allowing for direct assessment of GB-dislocation interaction in bulk samples. Together with dislocation etch pits imaging and transmission electron microscopy analysis, we observe dislocation pileup, storage, and transmission across the low-angle tilt GB. Our experimental observations reveal new insight into dislocation–GB interaction at room temperature at the mesoscale.