Journal of the American Ceramic Society最新文献

Widespread implementation of portland limestone cements (PLC) in industry has raised new questions about their carbonation resistance due to higher initial limestone content than ordinary portland cement. While carbonation of portland cement and each of its hydrate phases has been studied at a fundamental level, the integral role of how limestone fillers interact chemically or physically during carbonation necessitates further study. In this study, a C-S-H binder comprised of a highly reactive zeolite pozzolan and lime was used to evaluate the effect of varying calcite additions on carbonation behavior at a microstructural level. Fundamental insight into hydration kinetics and carbonation mechanisms of hydraulic binders was obtained via analysis of the C-S-H and calcite microstructure. X-ray microcomputed tomography (X-ray CT) was used to quantify microstructural changes, and the results showed a decrease in shrinkage for increased calcite dosages, with a ∼50% reduction observed for a 45% wt. calcite replacement level. Crystallographic and thermal analyses measured compositional changes in the binder and confirmed that shrinkage was related to the decalcification of C-S-H. The addition of calcite to the C-S-H binder effectively reduced the liquid-to-solid ratio, porosity, and amount of C-S-H present in these binders. Ultimately, these results help elucidate how the carbonation risks of PLC can be mitigated by proportioning the mixture water only to the reactive component of the binder.

Thanks to their excellent capacity, affordability, and eco-friendly characteristics, transition metal oxides (TMOs) hold promise as lithium-ion battery anodes. Nevertheless, serious challenges, including low electrical conductivity and considerable volume variation during charge–discharge cycles, hinder their commercial viability. Here, Zn-Co bimetallic metal–organic frameworks (MOFs) precursors with distinct morphologies were fabricated through a solvothermal approach by employing three different organic ligands (2-aminoterephthalic acid, 2-methylimidazole, and terephthalic acid). After calcination, the obtained ZnCo₂O₄ nanocomposites retained the morphology and porous features of their MOF precursors. Notably, the ZnCo₂O₄ derived from terephthalic acid (BDC-ZCO) exhibited an ultrathin lamellar structure, which effectively shortened ion/electron transport paths, facilitated charge transport kinetics and accelerated ionic migration, and mitigated volume variation. Benefiting from this unique structure, the BDC-ZCO electrode maintained 695.1 mAh g⁻¹ after 200 cycles at 0.1 A g⁻¹, and 510.9 mAh g⁻¹ after 300 cycles at 0.5 A g⁻¹, along with excellent rate performance and cycling stability. This study demonstrates that structure-oriented regulation through ligand selection is an effective strategy for optimizing the anode characteristics of MOFs-derived TMOs for advanced lithium storage.

To achieve quantitative analysis of cracks in different regions for C_f/SiC composites, this study proposes an automated, multi-scale crack segmentation and quantitative analysis framework for composites with complex backgrounds. This framework is based on the ResNet50-Unet model, which achieves accurate segmentation of fibers and matrix. In addition, adaptive grayscale thresholding combined with multi-scale morphological pore elimination effectively suppresses the influence of pseudo-cracks (defects or pores) while extracting cracks. Moreover, a KD-Tree-based crack connection algorithm module repairs micro-crack fractures, significantly improving crack connectivity. The results demonstrate that the machine learning model achieves a segmentation accuracy of 97%. Following the pore elimination process, the crack line density, area density, and average width were significantly reduced from 18.8 mm/mm², 7.2 mm²/cm², and 6.8 µm to 1.1 mm/mm², 0.2 mm²/cm², and 2.2 µm, respectively. Subsequent to the crack connection procedure, the crack line density, area density, and total crack length increased from 1.1 mm/mm², 0.23 mm²/cm², and 1.8 cm to 1.6 mm/mm², 0.31 mm²/cm², and 2.1 cm, respectively. These findings validate the effectiveness of the proposed crack extraction framework in enabling precise crack quantification and offer a novel methodology for crack analysis in ceramic matrix composites.

Lithium aluminosilicate (Li₂O–Al₂O₃–SiO₂, LAS) glass-ceramics are commercially established as protective covers for smartphones and personal electronic devices. However, quantitative relationships between heat treatment parameters, phase evolution, and optical–mechanical properties remain incompletely resolved. This work systematically maps the influence of nucleation (560–620°C/0.1–8 h) and crystal growth (700–800°C/0.1–4 h) heat treatment parameters on dual-phase LiAlSi₄O₁₀/Li₂Si₂O₅ nanostructures in LAS glass-ceramics. Rietveld refinement shows that the combination of 580°C/4 h nucleation and 740°C/1 h crystal growth steps achieves an equal volume phase ratio (1:1) and 86.1% total crystallized volume fraction, yielding balanced performance: 86.4% visible-light transmittance, 106.2 GPa Young's modulus, 7.6 GPa Vickers hardness, and 1.03 MPa·m^1/2 indentation fracture toughness. Increasing the crystallization temperature to 800°C enhances toughness to 1.21 MPa·m^1/2 via β-quartz solid solution formation but reduces visible transmittance to 11.4% as a result of grain coarsening (> 170 nm). Chemically strengthened surfaces reach a 219 MPa Na⁺ compressive stress layer (5× that of pristine glass) through a double ion exchange process (first in mixed NaNO₃/KNO₃ molten salt, then in pure KNO₃ molten salt at 450°C), though crystallized volume fraction > 80% confines stress layers to 110–135 µm. These quantified relationships establish fundamental phase evolution-property linkages in LAS glass-ceramics, advancing predictive control of optical–mechanical performance.

Femtosecond mode-locked lasers (MLLs) with hundreds of megahertz repetition rate are of broad interest due to the relatively large longitudinal mode interval. The performance of MLL is dominated by the active fiber, and candidates with both high gain and high compatibility with inactive silica fiber are urgently required. Herein, we propose and demonstrate an Er-doped hybridized silicate glass fiber (EHSGF) for nonlinear polarization rotation-based high-repetition-rate MLL. The fiber is derived from silica and hybridized with Y and Al elements, which enables providing a rich chemical environment for the active Er dopant. As a result, EHSGF with heavily doped Er³⁺ ions and a high gain coefficient of 2 dB/cm can be realized. In addition, it exhibits excellent chemical affinity with the Si-O, and the fiber can be directly fused with commercial silica fiber without a bridge component. We design and build a stable MLL device with a fundamental repetition rate up to 318.94 MHz by using only 9.5 cm EHSGF without any special integrated devices. The central wavelength is around 1565 nm with a 3 dB width of 32 nm, and the direct output pulse duration is 87 fs, which is close to the transform limit. The measured root mean square power fluctuation remains below 0.039% during continuous 12-h operation. We believe this research provides a new strategy for the development of highly doped Er-doped fibers and high-repetition-rate laser systems.

Ultra-high-temperature ceramic precursors are crucial for fabricating large, complex-shaped, high-performance ceramic matrix composites using a precursor impregnation pyrolysis (PIP) method. A liquid precursor composed of non-oxygen polyhafniumnitrocarbosilane was successfully synthesized from tetrakis(diethylamino)hafnium and self-made liquid polycarbosilane using a one-pot process. The precursor's composition, structure and properties were analysed using Fourier-transform infrared (FTIR) spectroscopy, nuclear magnetic resonance and viscosity testing, revealing the presence of Si–N–Hf structures. The synthesised precursor remained liquid at 25°C with a tunable viscosity range of 38.8–136.1 mPa·s. The precursor's inorganic transformation was examined using thermogravimetry–FTIR–mass spectrometry, elemental analysis, and scanning electron microscopy (SEM), achieving a ceramic yield of 71.62 wt% under argon at 1000°C. The resulting inorganic product was amorphous with low oxygen content (≤2.84 wt%), no detectable HfO₂ phase, and an adjustable Hf content of 16.28–42.90 wt%. The high-temperature evolution of the inorganic product from 1600 to 2400°C in argon was studied using X-ray diffraction, Raman spectroscopy, SEM, and transmission electron microscopy. This product exhibited a thermal weight loss of 10.60–19.67 wt%. The product contained HfC_xN_1−x and SiC phases with grain sizes of 17.4–114.9 nm and an adjustable HfC_xN_1−x phase content of 21.6–69.4 wt%. This novel precursor, characterised by its non-oxygen composition, adjustable room-temperature viscosity, high ceramic yield, and substantial HfC content, demonstrates strong potential as an ideal raw material for the PIP method in preparing ultra-high-temperature ceramic composites, exhibiting a favourable outlook for aerospace applications.

This study investigated the influence of TaC additions on the densification, mechanical properties, and ablation behavior of HfC–SiC composites fabricated via pressureless sintering. Incorporating TaC shows a measurable improvement in thermo-mechanical performance. At 20 wt.% TaC, hardness increased from 13.0 ± 1.7 GPa to 18.0 ± 2.1 GPa, while flexural strength rose from 303 ± 30 MPa to 377 ± 18 MPa. Ablation testing using an oxyacetylene torch at ∼2400°C for 10 min further demonstrated improved thermal stability: thickness change improved from –0.05 ± 0.01 mm (0 wt.% TaC) to +0.24 ± 0.001 mm, while mass loss decreased from –0.20 ± 0.05 g to –0.15 ± 0.01 g for 20 wt.% TaC. Post-ablation characterization revealed specific microstructural effects: TaC promoted silicon retention at the surface and facilitated the formation of protective oxides, notably HfSiO₄ and Hf₆Ta₂O₁₇, together with Ta₂C nanoparticles. These nanoparticles were found embedded within interlaced Hf-rich and Si-rich amorphous regions. This refined microstructure suppressed SiO volatilization, sealed surface porosity, and limited oxygen ingress, by developing a dense and adherent protective layer. The interplay of solid solution strengthening, oxide-scale stabilization, and a network of finely distributed phases collectively accounts for the improved ablation resistance of HfC–SiC–TaC composites compared to baseline HfC–SiC. These findings set the stage for a deeper discussion of the context and significance within the field of ultra-high-temperature ceramics.

The environmental conical nozzle levitator system enables cooling trace experiments above 4000 K. These cooling trace experiments were used to determine the melting points through observation of thermal arrest of group IV and V transition metal diborides (TiB₂, T_m = 3313 ± 33 K; ZrB₂, T_m = 3404 ± 38 K; HfB₂, T_m = 3529 ± 33 K; and TaB₂, T_m = 3284 ± 10 K; note: mean ± 2 standard error). Temperature measurements were conducted utilizing dual single-color pyrometers at wavelengths of 0.9 and 0.65 µm. This system utilizes aerodynamic levitation and dual laser heating to achieve temperatures approaching 4000 K. The samples were synthesized from commercial powders using ceramic gel-casting to produce high-density spherical components. The measurements obtained were compared to previously reported melting temperature values and were generally found to be in agreement with most of the published values.

Dielectric capacitors with high power density are fundamental and essential components in advanced electric and electrical systems. However, poor energy storage property at low electric fields is a long-term challenge limiting their applications. In this work, the BiMeO₃-based compound Bi(Ni_1/2Hf_1/2)O₃ (BNH) is used to modify BNT-based ceramics to strengthen their dielectric and ferroelectric properties. The pseudo-cubic phase BNT-based ceramics exhibit clear grain and grain boundary, and the grain size grows as BNH content increases. Dielectric constant at dielectric peak and corresponding transition temperature T_m decrease, and energy density increases in BNH-modified BNT-based ceramics with increasing BNH content. 20% mol BNH-modified (Ba_0.3Sr_0.7)_0.35(Bi_0.5Na_0.5)_0.65TiO₃ (BNBST) ceramics achieve a high recoverable energy density of 3.3 J/cm³ at a low electric field of 210 kV/cm, which is 2.2 times that of pure BNT-based ceramics. Moreover, energy storage properties of BNBST-0.2BNH ceramics exhibit robust stability and good reliability. This work demonstrates that BNH modification is a useful way to enhance dielectric energy density of BNT-based relaxor ferroelectrics at low electric field, and further expands the use of the BiMeO₃-based compound(s) on influencing polarization behavior of BNT-based relaxor ferroelectrics.

We investigate the role of CoTiO₃-TiO₂ template geometry on the microstructural evolution and growth kinetics associated with the formation of a product phase, CoTi₂O₅, in this reaction–diffusion system. For this purpose, the CoTi₂O₅ transformation pathways for three templates having distinct reactant-phase grain sizes were compared and contrasted using X-ray diffraction, scanning electron microscopy, electron backscatter diffraction, and atomic force microscopy, and described by Johnson and Mehl, Avrami, and Kolmogorov kinetic analyses. Measurement of the relative magnitude of diphasic (CoTiO₃-TiO₂) boundary energies was carried out via thermal grooving experiments. These analyses indicated that interphase boundary energy and template geometry dictate product-phase nucleation and microstructural evolution in dramatic fashion. The stark differences in the nucleation behavior were consistent with classical nucleation theory and the significant difference in the diphasic boundary energies of template structures with differing duplex grain size. These findings offer a new perspective for understanding the relationship between initial reactant structure and final product microstructure, highlighting the role of template parameters as effective kinetic “knobs” that may be adjusted to create a desired product microstructure. Importantly, this capability to tune product-phase morphology and transformation kinetics via templating opens new avenues for controlled microstructural design in advanced ceramic systems.