Journal of the American Ceramic Society最新文献

This study presents the first systematic experimental determination of phase equilibria in the Er₂O₃–Al₂O₃–SiO₂ system at 1600°C in air, employing the high-temperature isothermal equilibration method followed by rapid drop-quenching to preserve high-temperature phase assemblages. The mineralogy and chemical compositions of the equilibrated samples were analyzed by x-ray diffraction (XRD), scanning electron microscopy (SEM), and electron probe x-ray microanalysis (EPMA). One single liquid equilibria, five two-phase equilibria (liquid–SiO₂, liquid–Er₂Si₂O₇, liquid–Er₃Al₅O₁₂, liquid–Al₂O₃, and liquid–mullite) and seven three-phase equilibria (liquid–SiO₂–Er₂Si₂O₇, liquid–Er₂Si₂O₇–Er₂SiO₅, liquid–Er₂SiO₅–Er₃Al₅O₁₂, liquid–Er₃Al₅O₁₂–Al₂O₃, liquid–Al₂O₃–mullite, Er₂O₃–Er₂SiO₅–Er₄Al₂O₉, Er₃Al₅O₁₂–Er₂SiO₅–Er₄Al₂O₉) were observed in the equilibrium ternary system. The 1600°C isothermal section of the Er₂O₃–Al₂O₃–SiO₂ phase diagram in air (pO₂ = 0.21 atm) was constructed based on the present experimentally determined equilibrium phase compositions. The liquid area and the primary fields of SiO₂, Er₂Si₂O₇, Er₃Al₅O₁₂, Al₂O₃, and mullite were constructed. The comparison of the present experimental results deviate significantly from the modelling by FactSage (version 8.3) using its “FactPS” and “FToxid” databases, suggesting that FactSage underestimated the stability of the liquid phase under the present experimental conductions.

Brittle oxides, such as α-Al₂O₃, i.e., sapphire, are traditionally unsuitable for ductile applications, yet exhibit enhanced plasticity at nanoscale. This study explores the mechanical behavior of c-plane-oriented, dislocation-free monocrystalline α-Al₂O₃ via molecular dynamics (MD) simulations and experiments, including nanoindentation and post-indentation TEM analysis. The results demonstrate high strength with homogeneous, extensive deformation without failure. Plasticity is dominated by basal (0001) dislocations and rhombohedral [10$�\overline{1}$2] twins, which nucleate at deformation onset, as confirmed by MD and TEM. Generalized stacking fault energy (GSFE) and twinning fault energy (TFE) calculations elucidate mechanisms that mitigate crack initiation and propagation on the c-plane, aligning simulations with observations. These insights advance the understanding of nanoscale ductility in oxides, broadening the utility of sapphire in load-bearing micro/nano devices.

This study presents a novel process for the synthesis of MoO₂ and Mo₂C particles. It consisted of waste polyethylene (PE) pyrolysis and MoO₃ reaction with pyrolytic gas in a furnace with two-independently controlled zones. The gaseous species such as H₂ and CH₄ were in situ generated from the waste during heating to the temperatures ranging from 670 to 800 K. The resultant pyrolytic gas was carried to the MoO₃ powder bed by Ar flow to obtain MoO₂ at 900 K. Mo₂C was synthesized in the temperature range 1000–1300 K by the reaction of pre-reduced MoO₂ with the pyrolytic gas. Mo₄O₁₁, MoO₂, and Mo₂C phases sequentially formed during the reduction and carburization of the MoO₃ powder. Mo₄O₁₁ phase played an intermediate role in the reduction, as predicted by the thermodynamics. MoO₂ and Mo₂C phases were obtained at PE/oxide reactant ratios higher than those predicted. The discrepancy was discussed in terms of essential characteristics of the thermodynamics and the experiments. Mo₂C powders consisted of fine platelet-shaped crystals similar to those of MoO₂. Mo₂C crystallite size decreased, whereas microstrain increased as the carburization temperature decreased. This study demonstrates that waste PE can be recycled as alternative H₂ and C resources in reduction/carburization processes.

Magnesium oxychloride cement (MOC) is recognized for its superior mechanical performance and environmental benefits. Yet, the phase evolution of MOC in aggressive environments, particularly with chloride and sulfate exposure, remains insufficiently understood. A novel thermodynamic database with self-consistency is constructed in this study to reveal the degradation mechanism of hardened MOC paste exposed to solutions of NaCl, CaCl₂, Na₂SO₄, MgSO₄, and natural brine environments, accounting for both chemical attack and leaching effects. The predicted phase assemblages are validated through x-ray diffraction data from published sources and additional experiments. The results reveal that MOC degradation in saline media is governed by three interrelated factors: (i) leaching dominates the degradation process, with chemical attack playing a secondary role; (ii) chloride/sulfate concentrations dictate the thresholds for phase transformation; and (iii) reaction pathways and secondary phase evolution are shaped by the competition between Ca²⁺/Na⁺ and Mg²⁺ ions. The present work delivers novel thermodynamic perspectives on MOC degradation and lays a theoretical foundation for its optimization in marine and saline environments.

The zirconia (ZrO₂)-based electrolyte with fine grain size obtained from nanoscale powders is of crucial importance for high-performance intermediate-temperature solid oxide fuel cells (SOFC). Although the sol‒gel method for obtaining the nanoparticles of ZrO₂-based electrolyte has been extensively studied, the detailed crystallization process of this method has not been systematically investigated. Here, we prepared scandia-doped zirconia (10ScSZ) nanoparticles by a sol‒gel method employing nitrate as the precursor, ethylene glycol as the solvent, and acetic acid as the catalyst. The chemical reactions between metal nitrates and ethylene glycol are described by the theoretical calculation of enthalpy of formation, which is firstly reported for the sol‒gel preparation of ZrO₂-based nanoparticles. The decomposition of the residual solvents, organics and carbon as well as the generation of CO₂, ZrO₂·xH₂O, and Zr‒O during the calcination from 200°C to 800°C are carefully determined through Thermogravimetric and differential scanning calorimetry and Fourier transform infrared characterizations. X-ray diffraction (XRD) refinements with the analyses of crystallinity and grain growth activation energy confirm the crystallized temperature of 750°C with the average grain size of 13.91 nm. Notably, the grain growth activation energy was determined to be as low as 0.28 eV, significantly lower than values typically reported for solid-state or co-precipitation methods, highlighting the advantage of the sol–gel route. The detailed lattice features of 10ScSZ nanoparticles by transmission electron microscopy measurements are consistent with those obtained from XRD refinements. Finally, the spherical and well-dispersed 10ScSZ nanoparticles synthesized by our sol‒gel method are confirmed by scanning electron microscopy observations, with the average particle size of 86.43 nm at the crystallized temperature of 750°C.

Layered-KVO₃ anode material has recently emerged as a promising candidate due to its structural flexibility and tunable ion-transport mechanisms. The KVO₃ sample was synthesized through solid-phase calcination and then comprehensively characterized. This study focuses on understanding thermal properties of the layered-KVO₃ from experimental measurements and first-principles calculations combined with anharmonic phonon renormalization, and quasi-harmonic approximation (QHA). KVO₃ exhibits strong anisotropic thermal conductivity dominated by low-frequency acoustic phonons along the c-axis, with minimal four-phonon scattering at room temperature, indicating good thermal stability for energy applications. The molar heat capacity (Cp) of KVO₃ for temperatures ranges 4–300 K and 300–750 K was experimentally measured through Physical Property Measurement System (PPMS) and differential thermal analysis (DTA). Various Cp expressions were used to fit the experimental data, reflecting the physical character in various temperature ranges. The third-law entropy at 298.15 K was derived as 133.1 ± 4 J·mol⁻¹·K⁻¹, and thermodynamic properties at elevated temperatures were calculated. The systematic trend on the heat capacity for all alkali metavanadates RVO₃ (R = Li, Na, K, Rb, and Cs) is observed, which can be further used to predict thermodynamic properties of complex compounds and solid solutions with unknown experimental data. The thermal properties of the KVO₃ offer valuable insights into the design, synthesis, and evaluation of its service performance.

The automated computational package SLUSCHI, originally interfaced with the first-principles package VASP, has demonstrated effectiveness but remains computationally demanding for accurately calculating melting temperatures. This study leverages machine learning potentials via the efficient molecular dynamics simulator LAMMPS, utilizing pre-trained LASP neural network potentials derived from first-principles data. Tests on 30 diverse material systems—including simple metals, transition metals, alloys, oxides, and carbides—demonstrate that this approach significantly cuts computational costs, often by more than one order of magnitude compared to conventional DFT simulations. Approximately 60% of the calculated melting temperatures, prior to applying any DFT-based correction, fall within 200 K of experimental values. Focusing specifically on single-element systems, where direct comparison with DFT is possible, the percentage of melting temperatures within 200 K of experimental data improves from 53% to 82% following a DFT correction. This substantial improvement in computational efficiency, without sacrificing accuracy, facilitates high-throughput materials screening and accelerates material design consistent with the materials genome paradigm.

To enhance the mechanical properties of Ti(C,N)-based cermets cutting tools for high-speed cutting applications, this study incorporated five types of metal powders into Ti(C,N) powder, followed by uniform dispersion and high-energy ball milling. Subsequently, spark plasma sintering was employed to in situ synthesize high-entropy alloy (HEA)-toughened Ti(C,N)-based cermets cutting tools [HEA-Ti(C,N)]. Compared with the conventional method of directly adding pre-fabricated HEAs, the in situ generation of HEAs ensured a more uniform distribution of the HEA phase within the ceramic matrix, while also eliminating the need for a separate HEA preparation process. The results indicated that the in situ synthesized NiMoCoAlTi HEA-reinforced Ti(C,N)-based cermets exhibited a core‒shell microstructure composed of Ti(C,N)‒(Ti,Mo)(C,N) multiple solid solution. The HEA phase and ceramic matrix exhibited grain boundary anchoring effect, which enhanced interfacial bonding strength and significantly improved flexural strength and fracture toughness. The Vickers hardness, flexural strength, and fracture toughness of the material reached 15.12 ± 0.11 GPa, 1653 ± 21 MPa, and 13.78 ± 0.33 MPa·m^1/2. Dry cutting test on 40Cr steel revealed that the cutting life of the HEA-Ti(C,N) tool exceeded 20 000 m, representing a 43.2% improvement over conventional Ti(C,N) cermet tools, with a surface roughness of only 0.89 µm. Analysis indicated that the enhanced cutting performance of the HEA-Ti(C,N) tools was primarily attributed to grain boundary anchoring effect of the HEA phase and multiple solid solution, which improved mechanical properties. Furthermore, during the cutting test, the surface of the cutting tool was consistently protected by a dense film of metal oxide, which slowed down the wear of the tool and improved microchipping.

While phase transformations had been reported during the preparation of (Mg)AlON transparent ceramics, their impact on sintering remained insufficiently understood. In this study, Mg_0.27Al_2.58O_3.73N_0.27 green bodies were sintered under tailored thermal schedules designed to induce varying degrees of transient α-Al₂O₃ precipitation. Phase analysis revealed α-Al₂O₃ formation within 1250–1600°C, reaching a maximum of 7.83 wt% at 1500°C after 2 h of soaking, followed by redissolution at 1650°C. Microstructural characterization and phase analysis confirmed that the crystallization and subsequent dissolution of α-Al₂O₃ followed a time–temperature-dependent nucleation-growth model. Dilatometry results indicated that the effect of transient α-Al₂O₃ vanished once the relative density exceeded 61.5% (continuous heating) or 65.9% (2 h soaking at 1500°C) before final stage of sintering. The pore size decreased from 210 to 187 nm during α-Al₂O₃ precipitation and returned to 208 nm after redissolution. Despite the intentionally varied degrees of precipitation introduced by different sintering schedules, the final ceramics exhibited convergent microstructures and comparable in-line transmittance (∼65%), highlighting the minimal influence of transient decomposition on the ultimate transparency.

This study pioneers the cross-disciplinary application of garnet-type solid-state electrolyte Li₇La₃Zr₂O₁₂ (LLZO) in microwave dielectric ceramics. LLZO was synthesized via solid-state reaction, achieving optimized microwave dielectric properties at 900°C: ε_r = 8.13, Q × f = 31 735 GHz, τ_f = −44.3 ppm/°C. Direct cofiring experiments with Ag electrodes validated its compatibility with low-temperature cofired ceramic (LTCC). X-ray diffractometer (XRD)/scanning electron microscope (SEM)–energy-dispersive X-ray spectroscopy (EDS) confirmed interfacial stability and chemical inertness, overriding standalone thermal expansion parameter considerations. A Beidou antenna prototype on LLZO substrates demonstrated 59.2 MHz bandwidth at 1.57 GHz with 4.33 dBi gain and >97% radiation efficiency. By synergizing low-loss microwave response with inherent Li⁺ conductivity and thermal robustness, LLZO emerges as a multifunctional platform for integrated energy-communication systems. It enables future designs of LTCC based self-powered modules and real-time structural health monitoring devices. This work bridges solid-state electrolytes and microwave ceramics, offering a paradigm for material innovation in fifth-generation (5G)/sixth-generation (6G) networks and intelligent electronics.