Journal of the American Ceramic Society最新文献

This work presents a novel tape-casting method for producing flexible, graphene-enhanced diatomite ceramic sheets. These sheets target dielectric substrates for applications in the critical yet under-explored, high-frequency range. Structural and morphological analyses confirmed the incorporation of graphene nanoplatelets into the ceramics matrix, validating the efficiency of the tape-casting process. The results show the crucial role of the composite's crystalline structure in its dielectric response, where oxygenated functional groups within the graphene nanoplatelets act as intrinsic barriers to restrict leakage current, resulting in low dielectric loss. Doping of flexible ceramic plates with graphene nanoplatelets led to significant dielectric variations of approximately 100% over a wide frequency range. The capacitance increased by 215.35$�\%$ with the addition of 10 wt.$�\%$ graphene compared to pure diatomite. Our results demonstrate the ability to adapt the framework's structural, morphological, and dielectric properties through doping with graphene in diatomite, offering promising prospects for applying flexible ceramic sheets at high frequency.

Photocatalytic H₂ production is considered as a promising method to solve the energy crisis, and how to increase the photocatalytic efficiency is an urgent issues that need to be addressed. In this work, Bi–Bi₂S₃/Zn_0.5Cd_0.5S (BBS/ZCS) composites were successfully prepared by a simple hydrothermal method. By electrostatic attraction, Zn_0.5Cd_0.5S (ZCS) nanoparticles were loaded on the surface of Bi–Bi₂S₃ (BBS) microtubes, facilitating the formation of heterojunctions. Although BBS showed little activity in H₂ production, it largely enhanced the photocatalytic performance of ZCS. After optimizing the amount of BBS cocatalyst, it was found that 10% BBS/ZCS had the best H₂ production performance of 10.18 mmol g⁻¹ h⁻¹, which was 30 times higher than that of ZCS (0.34 mmol g⁻¹ h⁻¹). The enhanced photocatalytic performance could be ascribed to the formation of interfacial heterojunctions, as the photogenerated electrons of ZCS migrate to the Bi⁰ while photogenerated holes transfer to the valence band (VB) of Bi₂S₃. With BBS as the bridge to accept the photogenerated electrons and holes of ZCS, the fast recombination of photogenerated charge carriers (PCCs, including photogenerated electrons and holes) for ZCS was improved. This work not only promotes the separation of PCCs, but provides a new idea for the design of catalysts.

Given the significant oxidation challenges and reciprocal diffusion reactions that occur under the operating conditions of solid oxide fuel cells (SOFC) anodes, it is crucial to develop thin protective coatings that possess a dense structure, appropriate conductivity, good chemical and mechanical compatibility for metallic interconnectors (MIC). Except for the mainly studied cathode environments, the fuel streams during the real stack operation will also inevitably confront the MIC with oxidation and interfacial reaction issues, giving a potential contribution to the overall stack degradation. However, there is relatively little research on these service stability issues induced by the anode operating atmospheres. This research emphasizes the continuity of sputtered CeO_x coatings of different thicknesses during the initial oxidation phase and seeks to optimize the coating thickness. By varying the sputtering powers, CeO_x coatings with thicknesses of 110, 380, and 600 nm are deposited on laboratory-made ferritic stainless steel (AMIC 21). The chemical states of the sputtered Ce ions, the microstructure evolution, and the interfacial reaction mechanism for the CeO_x-coated MIC are successively explored under a simulated anode environment. After isothermal exposure to SOFC anode-reducing atmosphere (90%H₂/10%H₂O) at 800°C for 50–300 h, the CeO_x coatings exhibit good structural stability with uniform grains tightly arranged on the surface. The interfacial reaction layers detected for the CeO_x-coated AMIC 21 samples are less than 1.6 µm after exposure for 300 h, indicating the effectiveness of CeO_x coatings for SOFC interconnector application.

Traditional fiber-reinforced composites with single-layered electrical conductivity (EC) face limitations with respect to electromagnetic wave absorption (EWA) bandwidth and strength. This study introduces a novel C_f/SiC_f/Si₃N_4f layered composite (multifiber layered composite, MFLC), prepared via fiber alignment and curing, which capitalizes on the distinct ECs of carbon fibers (C_f), silicon carbide fibers (SiC_f), and silicon nitride fibers (Si₃N_4f) to address these limitations. The Si₃N_4f layer enhances the impedance matching, deepening EW penetration and curtailing reflection. The conductive C_f and SiC_f layers lead to substantial energy dissipation through conduction loss. Electric field simulations confirmed the regulatory effect of Si₃N_4f layer on EC, thereby facilitating the optimization of impedance matching. MFLCs achieved a minimum reflection loss of −68.52 dB and an effective absorption bandwidth of 8.23 GHz in the X–Ku band. The optimally matched composites demonstrated exceptional EWA performance, attaining the radar cross section reduction of up to 149.9%. The MFLCs hold significant promise as a novel class of lightweight, highly efficient, and wide-bandwidth EW absorbers.

The correlation between the glass-forming ability (GFA) of Metal–Organic Frameworks (MOFs) and their structural characteristics remains poorly understood. To address this gap, we analyze over 20,000 MOFs from the MOF database, comparing geometric and electronic order parameters between zeolitic imidazolate frameworks (ZIFs) and other MOFs. Our findings reveal a set of order parameters that effectively capture the thermal stability, and GFA of MOFs, acting as structural genes to predict glass formation. Through molecular dynamics simulations on representative ZIFs structures, we validate the reliability of these order parameters, particularly the total bond-order density (TBOD) and the largest cavity diameter (LCD), for screening potential melt-quenched MOFs. Furthermore, we predict that external pressure and electric fields can control the TBOD of MOFs, expanding our understanding of their thermal stability. This work identifies structural genes associated with the melt stability of MOFs, and contributes valuable insights into the prediction and understanding of MOFs glass-forming ability.

In this work, we have investigated the mechanical and thermal properties of rare earth sesquioxides A/B/C-RE₂O₃ (RE = La to Lu) by using the first-principles calculation. It is shown that the lattice parameters of RE₂O₃ generally decrease with the rare earth atomic number owing to the lanthanide contraction. Compared to [REO₆] polyhedrons, all [REO₇] polyhedrons present the longer RE-O bonds and the lower energies in spite of different polymorphs. Meanwhile, the elastic moduli show clear increasing tendency from A-RE₂O₃ to C-RE₂O₃ and from La₂O₃ to Lu₂O₃, which may originate from the stronger covalancy or weaker ionicity according to P-V-L chemical bond theory. In addition, the theoretical minimum thermal conductivity is predicted in range of 0.57–0.61 W·m¹·K⁻¹, 0.68–0.72 W·m⁻¹·K⁻¹, and 0.59–0.73 W·m⁻¹·K⁻¹ for A-, B-, and C-RE₂O₃, respectively. Further analysis about temperature-dependent thermal conductivity indicates that the chemical bonds dominate the increasing thermal conductivity with RE elements while the structural complexity determines the difference between three phases. This work provides a comprehensive database on structural, mechanical and thermal properties of RE₂O₃, but also shields light on the exploration of rare-earth-containing oxides with complex structure for potential applications including thermal/environmental barrier coatings.

Exposure to ionizing radiation has been known to affect the mechanical properties of solids; however, the exact mechanisms remain debated. In this study, we test the hypothesis that long lived metastable states formed by trapping of charges within defects influence subcritical cracking (SCC). Crack propagation rates were measured in 5 mol% Yttria-stabilized zirconia samples, with and without prior exposure to Co-60 gamma radiation (10 kGy absorbed dose). Crack growth was followed in situ by employing a double cantilever beam specimen inside an environmental scanning electron microscope (ESEM). In comparison with the unirradiated samples, an increased energy release rate of ∼10 J/m² was required to maintain SCC in the irradiated samples conforming to an increase in SCC fracture resistance. Raman and x-ray studies preclude any phase transformation and volume change due to irradiation; however, there was a significant change in optical absorption characteristics observed as the darkening of the irradiated sample. Thermally and optically stimulated luminescence measurements suggest that sample darkening is caused by metastable states that form due to charge trapping during radiation exposure. A closer examination of the SEM images demonstrates an increased number of microcracks ahead of the main crack in the irradiated specimens. We conclude that charge trapping in defects due to irradiation, and subsequent detrapping during crack propagation by mechanical stresses, initiate the formation of these microcracks. Consequently, energy is consumed during the interactions between the main crack and the developing microcracks, ultimately ensuing an overall increase in fracture resistance in the SCC regime.

A large amount of wastewater containing Cr(VI) is highly toxic and harmful to the environment, which requires effective treatment. In this study, an adsorbed ceramsite was prepared from dredged sludge (DS) and reed powder (RP). Then the prepared ceramsite was introduced Fe₃O₄ magnetic functional groups by a simple hydrothermal method to enhance the adsorption of Cr(VI) from wastewater. Batch adsorption experiments of Fe₃O₄-modified ceramsite (FCS) to remove Cr(VI) were studied systematically. Effects of different contact time, adsorbent mass and initial Cr(VI) concentration on Cr(VI) removal efficiency were investigated and optimized by a response surface methodology. The results show that when the loading content of Fe₃O₄ is 30% (FCS-0.3), the highest removal efficiency of Cr(VI) reached 88.48%, and the Cr(VI) adsorbed process can be well described by pseudo-second-order kinetics and Langmuir model, indicating that adsorption process is a chemisorption and monolayer adsorption. Moreover, the FTIR, XPS and Zeta potential analysis further revealed the mechanism of efficient removal of Cr(VI) by Fe₃O₄ loaded onto the ceramsite to increase the specific surface area and functional groups to adsorb Cr(VI). This study provides an effective method to convert solid waste such as DS and RP into a highly efficient magnetic adsorbent to adsorb and remove Cr(VI) from wastewater.

In this work, a novel two-step joining method was developed to join alumina ceramics for high-temperature applications. First, alumina ceramics were bonded using Al₂O₃ powder at 1550°C. Subsequently, the Dy₂O₃–Al₂O₃–SiO₂ glass was infiltrated into the interlayer at 1450°C to obtain the alumina/alumina joints with dense composite interlayer composed by Al₂O₃, Dy₂Si₂O₇, and few glass phase. The content of Al₂O₃ in the composite interlayer reached 52.7%. As a result, the coefficient of thermal expansion mismatch between the interlayer and the alumina ceramic was reduced to only 2%. The flexural strength of the joints at room temperature was equivalent to that of the alumina ceramic. Furthermore, the flexural strength of the joints at 1000°C reached about 90% of that of alumina ceramics under the same conditions. After the thermal cycles from room temperature to 1000°C for 50 times, there was no significant change in the flexural strength of the joints.