Journal of the American Ceramic Society最新文献

The impact of corrosion on pharmaceutical glasses has received significant attention in the pharmaceutical industry. In this study, the evolution of chemical structure and nanomechanical properties of a commercial pharmaceutical borosilicate glass with a medium boron content was investigated upon static corrosion in sodium citrate solution, which has been widely used as stabilizers in modern pharmaceutical products. Experimental results reveal that the dissolution of glass network dominates the corrosion of the pharmaceutical glass during the initial corrosion, and nanomechanical properties of the pharmaceutical glass surface decrease firstly and then increase. As the corrosion time further extends, the ion-exchange and Na ion in-diffusion as well as the precipitation formation dominate the corrosion behavior, accompanied by a significant decrease in nanomechanical properties of glass surface. These findings and previously published works suggest that the nanomechanical properties of corroded pharmaceutical glass surfaces need more attention and it can reveal more information about the corrosion behavior of glass surface.

The development of radionuclide-containing matrix materials, for ceramic-based high-level nuclear wasteforms or neutron absorbent fuel components, requires both a robust matrix material and a neutron absorbent isotope. Here, we fabricated a series of compounds Gd₂(Ti_1-xZr_x)O₅ (x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5) using the conventional oxide route of mixing oxide precursors, pressing, and sintering in air to various maximum temperatures. Crystal structure refinement of x-ray diffraction data indicates zirconium-containing compounds to be of the defect-fluorite form, Fm-3m space group. There is sequential decrease in the cell parameter with increasing titanium content from Gd₂Ti_0.5Zr_0.5O₅, a = 5.27795 (4) Å to Gd₂Ti_0.8Zr_0.2O₅, a = 5.2475 (4) Å. However, electron diffraction analysis highlights greater crystal structure complexity, including a 4× fluorite superstructure and additional diffuse diffraction features. The Argonne National Laboratory IVEM-Tandem in situ irradiation facility has been utilized to characterize the 1 MeV krypton irradiation response for this system of compounds. The addition of zirconium has improved the radiation response, increasing the fluence required for amorphization and lowering the temperature for maintaining the crystalline structure. For the Gd₂Ti_0.8Zr_0.2O₅, a critical temperature of 936 K was found, while for Gd₂Ti_0.5Zr_0.5O₅, the T_c was 565 K.

Femtosecond laser ablation is widely used as a high-efficiency, high-precision, and non-contact machining technology for fabricating surface microstructure of silicon nitride (Si₃N₄) ceramic. Nevertheless, the thermal damage caused by laser spot overlap unavoidably leads to crack generation, impaired surface quality, and reduced service life of Si₃N₄ workpieces. Thermal damage reduction is the key to improving the performance of laser-machined Si₃N₄ workpieces. In our previous research, we found that low temperature could improve machining quality, but its interaction mechanism was complicated, causing difficulty in selecting the appropriate temperature to obtain high surface quality. To determine the optimal processing temperature, a series of time-consuming and labor-intensive experiments must be conducted at various temperatures to identify the appropriate low-temperature range. In this study, a 3D multi-physics thermal–mechanical model was established to elaborate the ablation mechanism and predict ablation characteristics. Then, the formation of surface morphology was simulated, the temperature evolution was computed, and the thermal stress was quantified. The results were analyzed to assess the phenomena occurring during the ablation process. Variations in surface integrity with different temperatures were revealed utilizing this numerical model. Besides that, control experiments were performed. The finite element analysis results are in agreement with experimental data so that the precision of simulation has been verified. This work could provide a theoretical reference for cryogenic laser machining, a valuable machining technology that improves micromachining quality.

Rare earth molybdates have emerged as promising candidates for thermal barrier coatings owing to their high melting points, excellent chemical and thermal stability, and good ductility. In this work, we employ density functional theory to systematically investigate the influence of strain on the crystal structure, mechanical properties, and thermal conductivity of Dy₂MoO₆ and Lu₂MoO₆. Our results indicate that both molybdates retain good structural stability under strains ranging from –6% (compressive) to +10% (tensile). A moderate compressive strain is found to enhance the elastic constants and moduli of both compounds. Moreover, applied strain leads to a reduction in the minimum thermal conductivity. Specifically, under a tensile strain of 10%, the minimum thermal conductivity of Dy₂MoO₆ (Lu₂MoO₆) decreases by approximately 23% (40%) relative to the unstrained case. The thermal conductivity exhibits a monotonic decline with increasing both compressive and tensile strain. Further analysis reveals that strain-mediated reduction in thermal conductivity is achieved predominantly through weakened interatomic bonding rather than enhanced lattice anharmonicity. This study offers valuable insights for the strain-engineered design of materials with low thermal conductivity.

To address the challenges of thermal insulation and service lifetime in traditional yttria-stabilized zirconia (YSZ) coatings, this study proposes a novel YSZ/SiO₂ composite coating design based on Mie-scattering theory. The SiO₂-embedded YSZ composite coating was successfully deposited by an optimized air plasma spraying process, enabling the construction of a tailored microstructural architecture. The spherical SiO₂ particles, possessing a lower refractive index, intensified Mie scattering within the coating and effectively suppressed radiative heat transport. The composite coating deposited via the optimized spraying process exhibited a significantly improved interfacial bonding strength of 38 MPa. Specifically, at 5 wt% SiO₂, the composite coating showed the highest reflectivity in the 3–5 µm and achieved a minimum thermal conductivity of 1.27 W/(m·K). Long-term oxidation at 1000°C revealed that moderate interfacial diffusion of Si in the bond-coat region promoted the formation of Ni₂SiO₄, which strengthened the coating–substrate interface adhesion. The composite coating exhibited a 50% improvement in durability compared with the YSZ sample, extending the service life extended to 900 h. These findings highlight a promising strategy to concurrently enhance the thermal insulation efficiency and long-term stability of YSZ-based thermal barrier coatings under demanding service environments.

In response to the growing demand for low-loss and thermally stable LTCC dielectrics suitable for 5G Sub-6 GHz applications, a series of W⁶⁺-substituted NaSrYb(Mo_1−xW_xO₄)₃ (NM_1−xW_x, x = 0.02–0.10) ceramics was synthesized through a conventional solid-state reaction route, and the influence of W⁶⁺ incorporation on the crystal structure, microstructural evolution, and microwave dielectric behavior was comprehensively examined. XRD confirmed that all compositions were stabilized in a single-phase tetragonal scheelite lattice (space group I4₁/a). SEM and density revealed that moderate W⁶⁺ substitution facilitated homogeneous grain development and enhanced densification. Among the investigated samples, the x = 0.06 composition exhibited superior dielectric performance, characterized by ε_r = 10.12, Q×f = 98 018 GHz, and τ_f = –8.67 ppm/°C. Raman spectroscopy was utilized to investigate the lattice vibrational modes, while the P–V–L approach was applied to clarify structure–property correlations. FTIR spectra further substantiated ionic displacement polarization as the principal dielectric mechanism. The materials maintained low-loss characteristics even in the terahertz regime, and a microstrip patch antenna constructed on an NM_0.94W_0.06 ceramic substrate successfully operated within the 5G Sub-6 GHz frequency range, thereby validating its strong applicability in next-generation communication technologies.

To reduce the oxidation loss of ZrB₂–SiC ceramic coatings in the early stage of oxidation and minimize coating oxidation defects, a Hf-Ta-Si-B-O outer layer glass film was coated on the surface of ZrB₂–SiC coatings by the slurry brushing method, and oxidation tests were conducted. The experimental results showed that the coating with the Hf-Ta-Si-B-O outer layer glass film formed a continuous protective layer in the early stage of oxidation, and the final weight gain in the wide temperature range from 600 to 1600°C was suppressed to 4.60% of that of the pure ZrB₂–SiC coating. The Hf-Ta-Si-B-O/ZrB₂–SiC coating with 10 wt.% Ta₂O₅ addition had the best oxidation protection effect, with an average oxygen permeation rate of only 0.34%, a final carbon loss rate of only 0.12 × 10⁻⁶ g·cm⁻²·s⁻¹, and a final protection efficiency of 99.97% after oxidation at 1700°C for 100 min. The Hf-Ta-Si-B-O/ZrB₂–SiC coating showed a dual protection mode of “low-temperature dense barrier + high-temperature dynamic healing” during cyclic oxidation in the wide temperature range from 600 to 1700°C.

This work presents the first steps in using Eu³⁺ as a structural probe using photoluminescence (PL) emission spectra. The sol–gel synthesis of four Eu³⁺-doped powders encompassing seven phases of the yttrium silicate phase system is detailed. Following heat treatment at 1100 and 1400°C, the powders were then interrogated using x-ray diffraction (XRD), Rietveld refinement, electron dispersive spectroscopy, and thermal analysis techniques. The following Eu³⁺-doped phases were identified and assigned in the PL-emission spectra: cubic Y₂O₃; X1-Y₂SiO₅; X2-Y₂SiO₅; Y_4.67(SiO₄)₃O and the α, β, and y polymorphs of Y₂Si₂O₇. A validation of the assigned peak database is achieved through the prediction of the major and minor phases present in an Eu³⁺-doped yttrium disilicate powder synthesized through coprecipitation synthesis from its PL-emission spectra alone, with outputs corroborated through XRD analysis.

SiC fiber-reinforced SiC ceramic matrix composites (SiC_f/SiC CMCs) are promising for aero-engine hot-end components due to their excellent high-temperature strength and corrosion resistance. However, they are prone to damage during service, highlighting the need for efficient, low-cost repair technologies. This study proposes a gelcasting repair method for SiC_f/SiC composites. By optimizing bimodal SiC powder distribution and employing a N,N-dimethylacrylamide (DMAA)-based gel system, a repair slurry with high fluidity and strong gel-curing ability was developed. This slurry effectively infiltrated pores at the fiber/matrix interface and within fiber bundles. Subsequent silicon infiltration produced β-SiC through reaction with residual carbon, strengthening interfacial bonding. Postrepair characterization showed porosity reduction from 38.01% to 0.85% and density increase from 1.46 to 2.61 g/cm³. Flexural strength improved from 29.51 to 125.33 MPa, a 324.7% enhancement. After oxidation at 1200°C for 2 h, the repaired composite retained 91.4% of its original flexural strength. This technique provides a rapid, low-cost pathway for repairing CMCs in aero-engine applications.

Inter-diffusion coefficient and viscosity of borosilicate glass are critical parameters in the recently proposed revised model of oxidation of MeB₂‒SiC ultra-high temperature ceramic (UHTC) materials. Inter-diffusion in the glass controls the mode and the kinetics of oxidation, including the development of the internal depletion zone. The viscosity of the glass controls the shearing of the external glass layer and the oxide scale on MeB₂‒SiC UHTC materials under conditions of high temperatures and high rates of air flow. In this work, the available literature data on these two related parameters have been critically reviewed and evaluated. The viscosity and inter-diffusivity of borosilicate glass exhibit significant deviation from the “ideal” log-linear behavior across the compositional and temperature domains relevant to oxidation of MeB₂‒SiC UHTC materials in service and/or testing. Based on the available data, an empirical thermodynamic model is proposed that allows for the calculation of the inter-diffusion coefficient and viscosity of borosilicate glass across the entire composition and temperature range of interest for modeling of the oxidation kinetics of silicon carbide-containing refractory diborides.