Journal of the American Ceramic Society

Dong, Honglei; Li, Shujing; Wang, Hailu; Li, Yuanbing; Zhan, Hongxing

doi: 10.1111/jace.70494pmid: N/A

Despite their high‐temperature stability, alumina crucibles used in industries exhibit poor thermal shock resistance. To improve the comprehensive performance of alumina crucibles, the effects of different silica sources and sintering temperatures on the mechanical properties and thermal shock resistance of alumina ceramics are studied. The experimental results show that the addition of 5 wt% silica sol (30 wt%) and sintering at 1550°C improves the comprehensive properties of alumina–mullite composite ceramics, achieving a bulk density of 3.56 g/cm3, compressive strength of 260.5 MPa, and flexural strength of 373.68 MPa. After five cycles of thermal shock tests, the highest residual strength ratio is 56.18%, indicating improved thermal shock resistance. These results are significant for the production of new alumina crucible materials for the smelting of alloys.

Zhang, Maoru; Liang, Shiou; Huang, Haoyu; Jiang, Jinyang; Wang, Zengmei

doi: 10.1111/jace.70557pmid: N/A

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.

Andrea, Christine; Boyd, Daniel

doi: 10.1111/jace.70537pmid: N/A

The precise regulation of the dissolution and ion release of borate‐based glasses is essential for optimizing their potential in various applications, including antimicrobial materials, angiogenesis, and resorbable medical uses. However, the multicomponent interactions among network modifiers that govern these behaviors remain insufficiently resolved. In this study, a composition‐response mapping strategy was employed to systematically evaluate 16 multicomponent borate networks. Utilizing a design‐of‐mixture (DoM) approach, the individual and interaction effects of the modifiers were examined with respect to mass loss and ion release kinetics under simulated physiological conditions. This approach delivers a composition‐response map for the studied system and a mechanistic foundation to expedite the development of borate‐based formulations. The extent of dissolution varied from 20%–72% at 10 min to between 85% and 100% at 24 h. Statistical modeling indicated that dissolution is governed by modifier synergy rather than by concentration alone. For example, Ca2+ moderated reactivity, F− suppressed long‐term mass loss, and Ag+ accelerated ion exchange. The distinct kinetic profiles for the release of B, Ca, Ag, and F demonstrated compositionally adjustable transitions between transient and relatively more stabilized dissolution states. Collectively, these data establish a comprehensive map linking composition to function, enabling precise control over the degradation and ion‐release behavior. This framework enables the rational engineering of borate‐glass biomaterials that resorb with defined kinetics and can be functionally tailored for various therapeutic applications.

Mariani, Marco; Isachenkov, Maxim; Bertolini, Francesco; Galassi, Carmen; Grande, Antonio Mattia; Sala, Giuseppe; Lecis, Nora

doi: 10.1111/jace.70595pmid: N/A

Binder jetting has emerged as a compelling approach for processing lunar regolith, as it is well‐suited for low‐energy environments and requires lower amounts of organic binder, compared to the competitive technologies. This study investigates the feasibility of binder jetting lunar regolith simulants from micrometric particles, focusing on the interplay between sintering conditions, especially atmosphere and temperature, and the resulting microstructural and mechanical properties. Sintering was explored across a range of conditions to elucidate the evolution of porosity and phase composition. Microstructural characterization revealed void morphologies varying due to progressive coalescence, while energy‐dispersive x‐ray (EDX) and x‐ray diffraction (XRD) identified the primary presence of bytownite with other minor oxides, partially subjected to redistribution and reduction as in the case of ilmenite and pyroxene. Mechanical testing revealed the influence of sintering conditions on mechanical properties. While the compression samples, sintered at 1150°C, yielded 228.7 ± 100.9 MPa of strength, the performance of the samples sintered at 1200°C in air degraded down to 180.6 ± 53.7 MPa.

Wilke, Stephen K.; Ishikawa, Takehiko; Koyama, Chihiro; Benmore, Chris J.; Kastengren, Alan L.; Al‐Rubkhi, Abdulrahman; Rafferty, Jared; Weber, Richard

doi: 10.1111/jace.70573pmid: N/A

The thermophysical properties and atomic structure of molten oxides are crucial data for advancing our understanding of the glass transition and for optimizing melt processes of advanced functional glasses. We report a variety of measurements on ten binary and ternary fragile liquid oxides selected from two compositional families, the CaO–Al2O3–SiO2 and R2O3–Al2O3 (R = Y, La, and/or Yb) systems, using imaging techniques on droplets levitated and laser beam heated in microgravity. The liquids’ densities, thermal expansion coefficients, viscosities, and surface tensions are measured up to 2800 K, spanning several hundred kelvins above and below the equilibrium melting points. For binary and ternary rare‐earth aluminate melts, the molar volumes follow approximately a linear trend with the mean cube of the cation radii, consistent with their unary oxide endmembers. Melt‐quenched glasses are further characterized with x‐ray tomography and diffraction to assess internal porosity and structure. Glasses prepared in microgravity have atomic structures that are indistinguishable from terrestrially prepared analogues. Internal bubbles are occasionally present, and in microgravity, the bubbles do not migrate to external surfaces as is common for terrestrial processing of such high‐temperature, inviscid liquids. These findings provide useful insights into the nature of fragile oxide liquids and glass formation, with implications for space‐based manufacturing.

Kumar, Basina Veera Naveen; Erasmus, Lucas J. B.; Kroon, Robin E.

doi: 10.1111/jace.70544pmid: N/A

Tm3+ and Yb3+ co‐doped yttrium pyrogermanate (Y2Ge2O7) phosphors were synthesized via the conventional solid‐state reaction method. The structural properties, optical properties for upconversion luminescence, and optical thermometric properties were studied. Phase analysis using powder x‐ray diffraction confirmed the formation of a single‐phase tetragonal structure without any secondary phases. The scanning electron microscopy revealed irregular, agglomerated grains of micrometer size range. The diffuse reflectance spectroscopy showed characteristic absorption bands for absorption from the ground state 3H6 of Tm3+ ions to excited states 3F2,3 (684 nm) and 3H4 (797 nm), as well as the 2F7/2 → 2F5/2 transition of Yb3+ ions (∼980 nm), confirming successful incorporation of dopant ions into the host lattice. Photoluminescence spectra under 355 nm excitation exhibited strong blue emission at ∼453 nm (1D2 → 3F4), alongside weaker blue, red, and near infrared emissions at 475, 650, and 792 nm, respectively. The upconversion luminescence emissions under 980 nm excitation produced characteristic blue (∼475 nm; 1G4 → 3H6) and near infrared (∼797 nm; 3H4 → 3H6) bands. Notably, the blue emission showed a stronger power‐dependent enhancement compared to the near infrared emission, attributed to multiphoton energy transfer upconversion involving Yb3+ sensitizers. The maximum intensity was observed in the 2% Tm3+ doped sample co‐doped with 5% Yb3+, confirming efficient Yb3+→Tm3+ energy transfer. Further, temperature‐dependent upconversion luminescence studies demonstrated thermally modulated emission intensity, with calculated activation energies of 0.35 eV (blue emission) and 0.43 eV (near infrared emission). Optical thermometry based on the ratio of emission intensities for 797 and 475 nm exhibited excellent sensitivity, with absolute sensitivity (Sa) of 156.42 × 10−2 K−1 and relative sensitivity (Sr) of 13.4% K−1 at 673 K. These results highlight Y2Ge2O7:Tm3+/Yb3+ as a promising phosphor for blue upconversion‐based photonic and high‐sensitivity ratiometric thermometry applications.

Löffler, M.; Abreu, D. A.; Habermann, A.; Lepple, M.; Fabrichnaya, O.

doi: 10.1111/jace.70538pmid: N/A

Phase equilibria in the Y2O3–Ta2O5 system play an important role in the development of new materials for thermal barrier coating (TBC) applications, with higher thermal stability resulting in more efficient gas turbines with reduced exhaust gas emissions. Therefore, the development of a consistent thermodynamic database for this oxide system is invaluable for faster and more sustainable material development. In this work, four different sample compositions were prepared by co‐precipitation reactions, and the heat capacities of the orthorhombic Y3TaO7 (Y1‐xTaxO1.5+x with x = 0.26 and x = 0.29) and the hexagonal YTa7O9 phases, both with homogeneity ranges, were experimentally measured in the temperature range from 200 to 1373 K using differential scanning calorimetry (DSC). The obtained results, together with literature data on phase equilibria and experimental thermodynamic values, have been used to assess the thermodynamic description of the Y2O3–Ta2O5 system applying the CALPHAD approach.

Qin, Qixian; Xu, Shuang; Mei, Hai; Wang, Dangqiang; Lai, Xin; Liu, Lisheng

doi: 10.1111/jace.70529pmid: N/A

The microstructural changes and spallation damage behavior of silica glass under shock loading at different levels of lateral compressive stress were investigated by molecular dynamics (MD) simulations. At the shock compression stage, higher lateral compressive stress promotes an increase in the proportions of five‐ and six‐coordinated silicon atoms, particularly at elevated impact velocities, where the structure transitions from tetrahedral to octahedral configurations. Furthermore, lateral compressive stress amplifies the shock stress, though its effect saturates beyond a critical threshold. At the reflected tension stage, lateral compressive stress enhances the spall strength of silica glass, with pronounced improvements at stress levels lower than 4 GPa. However, when lateral compressive stress exceeds 6 GPa, the enhancement in spall strength diminishes. With the increase of impact velocities, failure behaviors of silica glass change from classical spallation to micro‐spallation, accompanied by significant expansion of the damage region. This study further elucidates the spallation damage behavior of silica glass under varying lateral compressive stress levels, including transitions in spallation modes and propagation of the damage zone. These findings offer novel insights into the mechanical performance of compressed silica glass under impact and provide a strategy for strengthening glass performance in application.

Gao, Xinyu; Wang, Ziyu; Luo, Yixiu; Sun, Luchao; Wang, Jingyang

doi: 10.1111/jace.70533pmid: N/A

Multi‐rare‐earth‐principle‐component disilicates ((nREx)2Si2O7) are advanced candidates for the environmental barrier coatings (EBCs) materials, wherein the multicomponent design strategy is used to achieve synergistic optimization on various material properties. In this study, two (nREx)2Si2O7 materials, that is, β‐(Gd0.15Ho0.15Yb0.35Lu0.35)2Si2O7 and γ‐(Gd0.15Ho0.35Yb0.35Lu0.15)2Si2O7 with distinct polymorphic structures are designed by exquisitely tuning the relative ratio of the four constituent rare‐earth elements. The two samples exhibit good stability of β or γ phase, low thermal conductivity, and coefficients of thermal expansion in good compatibility with the silicon carbide fiber‐reinforced silicon carbide ceramic matrix composites. The corrosion depth of β‐(Gd0.15Ho0.15Yb0.35Lu0.35)2Si2O7 and γ‐(Gd0.15Ho0.35Yb0.35Lu0.15)2Si2O7 samples after the completeness of CMAS corrosion process at 1300°C are approximately 428.33 and 239.70 µm, respectively. Such different corrosion behaviors have been attributed to the increased concentration of active elements (e.g., Ho), which serves multiple functions by accelerating apatite formation, consuming molten CMAS, decreasing the Ca/Si ratio, and significantly mitigating the activity of corrosion reactions. These results are expected to enlighten the synergistic optimization of thermo‐physical properties and corrosion resistance of (nREx)2Si2O7 materials by compositional modulation, and provide important guidelines for the design and screening of advanced EBC materials.

Huang, Shiwei; Li, Hejun; Guo, Lingxiang; Ou, Hongkang; Zhang, Shuo; Wu, Keke; Zhang, Yuyu; Zhang, Xuemeng; Fan, Kaifei; Huang, Qizhong; Hu, Dou; Xu, Yang; Sun, Jia

doi: 10.1111/jace.70536