Journal of the American Ceramic Society最新文献

This study develops a moderate-temperature (<1100°C) glass filler in the Al₂O₃-B₂O₃-SiO₂ system, modified with K₂O/Li₂O, for joining reaction-bonded silicon carbide (RB-SiC). The optimized composition (2.5 wt% Al₂O₃, B/Si = 1:2) achieves a coefficient of thermal expansion (CTE) of 3.25×10⁻⁶/K, closely matching that of RB-SiC (ΔCTE < 0.05×10⁻⁶/K), and yields a superior shear strength of 44 MPa when joined at 900°C. Contrary to conventional wisdom, maximum joint strength was achieved not under conditions of optimal wettability (which occurred at higher temperatures) but where interfacial reactions were optimally controlled to prevent defect formation. Comprehensive characterization reveals the bonding mechanism: the in-situ formation of a nanoscale interfacial layer comprising a silica-rich region and alkali carbonates, facilitating strong covalent bonding between the glass and the substrate. This work demonstrates that controlling interfacial chemistry, rather than solely pursuing optimal wettability, is the key to developing robust glass-to-ceramic joints, offering a promising joining solution for high-performance RB-SiC components.

Graded multilayer zirconias exhibit a microstructural gradient based on yttria content, but the transition zone between layers remains poorly characterized. This study evaluated the fracture energy required to create new surfaces in multilayer zirconias. Brazil-nut specimens were tested under different loading angles to induce tensile, shear, or mixed failure modes, using 3Y-TZP and 5Y-PSZ as controls. Groups were defined by zirconia type, loading angle, and hydrothermal aging. Fractured specimens underwent fractographic analysis, failure classification, scanning electron microscopy, and energy-dispersive X-ray spectroscopy characterization. Two-way analysis of variance revealed significant differences between loading angles but not aging. At 25°, where shear forces predominated, fracture energy was significantly higher [baseline: 964.74 (± 202.43); aged: 1389.12 (± 978.47) N/m] compared with most groups, except 15°. Multilayer zirconia showed intermediate fracture energy values between 5Y-PSZ and 3Y-TZP. Importantly, the transition zone presented a heterogeneous interphase rather than a smoothly graded structure. Shear stresses required higher energy release than tensile stresses. These results reveal the microstructural discontinuity and distinct fracture behavior of multilayer zirconias, providing new insights into the structure–property relationships of this class of ceramics.

Aluminum oxynitride (AlON) ceramics, valued for their superior mechanical properties and optical transparency, are promising candidates for advanced armor protection. However, their mechanical response under varying loading rates remains insufficiently understood, constraining reliability-based design and performance optimization for impact conditions. In this study, quasi-static and dynamic indentation tests were conducted to elucidate the strain rate–dependent response of AlON ceramics. The results reveal a pronounced strain-rate hardening effect, with dynamic Vickers hardness markedly exceeding quasi-static values. Correspondingly, crack morphology transitions from simple radial cracks to complex crack networks with secondary branching. Microstructural analysis further shows that dynamic loading activates multiple plastic-related deformation processes within the indentation region, including high-density dislocation structures, slip-band interactions, dislocation-free zones, and deformation twins. These features help explain both the enhanced hardness and the evolution of crack patterns and demonstrate that AlON ceramics exhibit a brittle–plastic coexisting failure mode at high strain rates. This work provides new insight into the strain rate–dependent indentation response and microstructural evolution of AlON ceramics, offering valuable guidance for the design of high-performance transparent armor materials.

A glass series with constant ∼30 mol% BaO in the BaO–B₂O₃–SiO₂ system was studied as a function of SiO₂/B₂O₃ ratio. This system has been studied in-depth to reveal the structure, Part 1, and its relationship to the mechanical properties, Part 2. Both the B coordination and network polymerization are quantified both experimentally, using Raman, IR, and ¹¹B NMR spectroscopies, and theoretically, using classical molecular dynamics (MD) simulations with effective partial charge potentials with composition dependent boron parameters. These results show that ^IIIB, threefold-coordinated boron, increases linearly with increasing boron, at the expense of ^IVB. The Q³ equilibrium constant decreases slightly with boron addition up to 37 mol%, whereas at greater B₂O₃ contents, the silica tetrahedra become more polymerized. These trends are reinforced by MD simulation results, which show that the average connectivity, polymerization, and ring size are directly related. The glass transition temperature increases with increasing silica content, where the range of temperatures follows the packing density. The BaO–B₂O₃–SiO₂ system shows systematic trends from high to low oxygen packing between the binary borate glasses to the binary silicate glasses, indicating a high degree of predictability for properties controlled by density.

Resolving the inherent conflict between high porosity and superior mechanical properties in porous silicon nitride (Si₃N₄) ceramics is critically important for their structural applications. This study presents a novel strategy to simultaneously enhance flexural strength and fracture toughness without compromising porosity. By introducing a small amount of silicon (Si) powder into the starting composition (α-Si₃N₄ and Y₂O₃), a network of in situ Si₃N₄ nanowires was formed via a gas-phase reaction and vapor–solid mechanism under a nitrogen atmosphere. These nanowires eventually transform into nanoscale crystal nuclei, providing abundant heterogeneous nucleation sites for β-Si₃N₄ crystal grains. This process resulted in a refined and uniform microstructure characterized by significantly reduced grain size and pore diameter, while maintaining a high aspect ratio (∼10) of the β-Si₃N₄ grains. Consequently, at a constant high porosity of ∼56%, the flexural strength and fracture toughness were remarkably improved from 171.2 to 234.9 MPa and from 2.41 to 3.33 MPa·m¹/², respectively. The evolution of nanowires and the phase transformation were systematically characterized, and the underlying strengthening and toughening mechanism involving microstructure refinement and Hall–Petch strengthening is thoroughly discussed.

Reactive sintering offers an advantageous route to produce high-performance ceramics from coarse and cheap precursor powders; however, impurities in these sources often prevent the desired product composition from being achieved even when the raw materials are proportioned according to the reaction stoichiometry. This study employed a thermodynamics-guided approach to predict phase evolutions during the consolidation of TiB₂-AlN ceramics (TA) within the TiN–Al–B system. Although oxygen impurities (B₂O₃, Al₂O₃) exist in the raw powders, the formation of undesirable phases in TA could be highly suppressed through a proper composition design. Thermodynamic calculations revealed that excess Al compensates for the reduction of B₂O₃, while a TiN deficiency below a critical threshold is essential to inhibit the formation of hBN. Guided by these insights, stoichiometric, Al-excess (TA5: 5 mol% excess Al) and dual-optimized (T5A5: 5 mol% excess Al and 5 mol% deficient TiN) were consolidated by spark plasma sintering at 1800°C/60 MPa for 5 min. Whereas TA and TA5 contained residual TiN and hBN, T5A5 achieved near-phase purity with refined microstructures and exhibited better mechanical properties.

The high cost and carbon emissions associated with traditional ordinary Portland cement (OPC) coupled with the poor consolidation of superfine tailings (ST) have become serious problems in the cemented superfine tailings backfill (CSTB). To avert this, using industrial by-products as a low-carbon, low-cost alternative binder to OPC is regarded as a promising solution. In this study, a novel steel-making by-product based quaternary binder (SQB) was developed using ladle slag (LS), calcium hydroxide (CH), dihydrate gypsum (DG), and ground granulated blast furnace slag (GGBFS) based on orthogonal protocols. The fresh and hardened properties of the CSTBs were evaluated at different SQB proportions, and the optimal ratio of SQB was determined using the TOPSIS method. The hydration mechanism and microstructural evolution of SQB were further systematically investigated using isothermal calorimetry analysis (ICA), x-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetry and differential thermogravimetry (TG−DTG), and scanning electron microscope (SEM). The results indicated that the proportion of each component in the SQB significantly affected the rheological properties of fresh CSTB slurries. Afterward, the optimal proportion of SQB was determined to be LS:CH:DG:GGBFS = 20:5:15:60, and its uniaxial compressive strengths (UCS) at 1, 3, 7, and 28 days were 1.11, 2.82, 6.23, and 9.45 MPa, respectively, which met the requirements of mine backfill. Moreover, the quaternary SQB system demonstrates more pronounced advantages, with significantly superior performance across all curing stages compared to the corresponding ternary system (without CH). The hydration mechanism and microstructural development of SQB revealed a synergistic reaction between sulfate-activated LS and alkali–sulfate-activated GGBFS, resulting in the formation of a large amount of ettringite (AFt) and calcium silicate hydrate (C–S–H) gels and a denser microstructure. Overall, the synthesized SQB offers an eco-friendly and economical alternative for CSTB, which has notable engineering application prospects.

Nuclear waste glass vitrification furnaces are lined with refractory ceramic blocks to contain the molten glass. The refractory liner is susceptible to corrosion and has a finite service lifetime. For this reason, predicting the refractory corrosion in contact with molten glass is integral to estimating melter service lifetime. Standardized laboratory tests varying time and temperature are commonly performed to estimate refractory material loss as a function of glass composition. These data are time and resource-intensive to collect and are susceptible to considerable measurement error. In order to accelerate glass formulation and design for nuclear waste vitrification, methods are needed to increase laboratory-scale throughput while maintaining data quality. In this work, a method to remove the residual glass from a corroded coupon using hydrofluoric acid is presented that accelerates the throughput of sample analysis while simultaneously facilitating more accurate measurements.

Dense nano-infiltration and transient eutectic phase (NITE)-SiC_f/SiC composites are prepared through low-temperature sintering technology at 1650°C. The densification of SiC matrix, as well as effects of BN interphase thickness and fiber volume fraction on the morphology and mechanical properties of SiC_f/SiC composites are investigated. AlN‒Y₂O₃‒SiO₂ can fully wet SiC at 1650°C and the matrix of SiC_f/SiC composites can be densified via 40 wt% sintering aids. A thick BN interphase layer can reduce stress on the fiber and the interphase in stress concentration regions, but may exacerbate stress concentration in non-concentrated regions. A moderate fiber volume fraction is necessary to balance the content and damage of reinforcement to obtain SiC_f/SiC composites with high mechanical property. The optimum volume density, open porosity, and flexural strength of SiC_f/SiC composites is 2.98 ± 0.05 g/cm³, 3.5 ± 1.7%, and 430 ± 34.2 MPa. This work can provide conduction for fabrication and optimization of low-temperature sintering NITE-SiC_f/SiC composites.

Understanding the thermodynamic equilibria in the Al₂O₃‒Na₂O‒ZrO₂ system is essential for the design of refractory and ceramic materials. Using reliable phase diagram and thermodynamic property data, thermodynamic optimizations of the Al₂O₃‒ZrO₂, Na₂O‒ZrO₂, and Al₂O₃‒Na₂O‒ZrO₂ systems were performed using the Calculation of Phase Diagrams (CALPHAD) method. The liquid phase was described by using the ionic two-sublattice model with the formulation (Al⁺³, Na⁺¹, Zr⁺⁴)_P(O⁻², AlO₂⁻¹)_Q. The species AlO₂⁻¹ was introduced to model pure liquid Al₂O₃, ensuring compatibility with the latest thermodynamic optimization of the Al₂O₃‒Na₂O‒SiO₂ system. A new set of self-consistent thermodynamic parameters for the Al₂O₃‒Na₂O‒ZrO₂ ternary system was obtained. Comprehensive comparisons between calculated results and experimental data demonstrate that the present thermodynamic descriptions accurately reproduce the experimental data.