Advanced Powder Materials最新文献

As a non-toxic copolymer of isobutylene and maleic anhydride, Isobam is successfully used as a dispersant and a gelling agent for fabricating porous Si₃N₄ ceramics by gel casting. The dispersity and rheological properties of the Si₃N₄ slurry are influenced by the pH, milling time, and Isobam content which varies from 0.1 ​wt.% to 0.6 ​wt.%, and these factors are investigated. The slurry with 40 ​vol.% solid content and milled for 4 ​h has a high zeta potential at pH 12 (adjusted by Tetramethyl ammonium hydroxide (TMAH)), which means that the particles are well dispersed. The mechanisms of TMAH are electrostatic repulsion and steric hindrance. The viscosity of the slurry increases with the increase of Isobam content. After pressureless sintering at 1700 ​°C for 2 ​h, a uniform unique interlocking microstructure of rod-like β-Si₃N₄ grains is observed, which may improve the flexural strength of the ceramics by intergranular fracture and particle pullout of β-Si₃N₄ grains. The density and porosity of the samples fluctuate negligibly with the increase of Isobam content, and the Si₃N₄ ceramic with 0.1 ​wt.% Isobam exhibits the highest bending strength of 251.6 ​MPa among all samples.

To study the formation of detrimental phases under the sulfur gas impurity to the long-term degradation in the cathode material, the classic cathode material, (La_0.8Sr_0.2)_0.95MnO₃ (LSM), was prepared, sintered, and annealed at 800, 900, and 1000 ​°C in the sulfur-containing atmospheres, respectively. Through X-ray diffraction, scanning electron microscope, and transmission electron microscopy techniques, as well as the computer coupling of phase diagrams and thermochemistry methodology, the secondary phases, especially the detrimental ones, under different conditions were predicted and experimentally verified correspondingly. Furthermore, sulfur poisoning results indicate that the accelerated tests might have degradation mechanisms different from actual operation conditions. More importantly, comprehensive comparisons among various impurity-containing conditions were also made to recommend better operation parameters.

ZrB₂/SiC–AlN nanoceramic composites were densified at 1950 ​°C by hot pressing using an organic-precursor-derived SiC and commercially available AlN and ZrB₂. A cross-scale microstructure was constructed by distributing the ZrB₂ secondary phase (∼421 ​nm) within the SiC–AlN solid solution matrix. The substructure of the SiC–AlN matrix was agglomerated by nanograins with an average size of only 62 ​nm. ZrB₂ connected around the majority of pores within the SiC–AlN matrix and contributed to the formation of numerous weak interfacial bonding, resulting in improved strength and toughness. The highest flexural strength and fracture toughness of 579 ​± ​52 ​MPa and 6.7 ​± ​0.1 ​MPa ​m^1/2 were obtained from a 10 ​wt%-ZrB₂/SiC–AlN sample, respectively. The high concentration of grain boundaries of the ZrB₂/SiC–AlN nanoceramic composites resulted in heat insulation characteristic. The thermal diffusivity and conductivity were 3.6 ​mm²⋅s⁻¹ and 14.3 ​W·(m·K)⁻¹ at 1400 ​°C, respectively, while the electrical resistivity was 3.9×10³ ​Ω·cm for the 10 ​wt%-ZrB₂/SiC–AlN sample.

Ru-doped NiAlHf coatings were deposited on Ni-based single crystal substrate by arc ion plating technology. The failure mechanism and interfacial diffusion behavior were comparatively investigated with NiAlHf coating using scanning electron microscopy, electron probe micro-analyzer, and transmission electron microscopy. The results indicated that microstructure evolution of oxide scale induced by element diffusion process significantly affected oxidation resistance of NiAlHf/Ru coatings, resulting in formation of cracks and voids, thereby accelerating failure process. The precipitates in interdiffusion zone and secondary reaction zone of the substrate initiated by interfacial element diffusion were P phase and σ phase, respectively. And the discrepancy in content was elucidated from the perspective of thermodynamics and kinetics. Besides, microstructural evolution between NiAlHf/Ru coatings and substrate was also deliberated. The research could not only provide profound understanding of NiAlHf/Ru coatings failure mechanism, but also had significant guidance for suppressing precipitation of topological close-packed phases and facilitating development of single crystal Ni-based superalloys.

The weak visible light harvesting and high charge recombination are two main problems that lead to a low photocatalytic H₂ generation of polymeric carbon nitride (p-CN). To date, the approaches that are extensively invoked to address this problem mainly rely on heteroatom-doping and heterostructures, and it remains a grand challenge in regulating dopant-free p-CN for increasing H₂ generation. Here, we report utilizing the inherent n-π∗ electronic transition to simultaneously realize extended light absorption and reduced charge recombination on p-CN nanosheets. Such n-π∗ electronic transition yields a new absorption peak of 490 ​nm, which extends the light absorption edge of p-CN to approximately 590 ​nm. Meanwhile, as revealed by the photoluminescence (PL) spectra of p-CN at the single-particle level, the n-π∗ electronic transition gives rise to an almost quenched PL signal at room temperature, unravelling a dramatically reduced charge recombination. As a consequence, a remarkably improved photocatalytic performance is realized under visible light irradiation, with a H₂ generation rate of 5553 ​μmol ​g⁻¹∙h⁻¹, ∼ 12 times higher than that of pristine p-CN (460 ​μmol∙g⁻¹∙h⁻¹) in the absence of the n-π∗ transition. This work illustrates the highlights of using the inherent n-π∗ electronic transition to improve the photocatalytic performance of dopant-free carbon nitrides.

The unique deposition manner of additive manufacturing (AM) allows the near-net-shaping of components with multiple materials configurations and complex geometries, which sheds light on the process of high-performance metal matrix composites (MMCs). This work explores laser powder bed fusion (LPBF) AM of SiC-reinforced maraging steel MMCs to consolidate the merits of both ceramics and metal matrix for improving overall properties. The laser processing parameters were systematically optimised based on the density, roughness and hardness of the deposited samples. The effects of SiC content on the microstructures, mechanical properties, tribological performance, and wear resistance are elucidated. SiC particles are refined with uniform distribution in the metal matrix after laser processing. The highest tensile strength reaches 1611 ​MPa together with an elongation of about 10.1% with 3 ​vol% SiC addition. The tribological performance of MMCs is investigated by studying the coefficient of friction (COF), wear rate, and worn morphology. The COF has been slightly reduced with the SiC addition, and the wear rate of MS reduced from 3.25 ​× ​10⁻⁵ to 1.72 ​× ​10⁻⁵ mm³/Nm with the 12 ​vol% SiC addition. The underlying wear mechanisms are also investigated. Besides, the corrosion behaviour of MMCs is also investigated; the addition of SiC (≥6 ​vol%) has improved the corrosion properties of the matrix.

Two-dimensional (2D) materials offer novel platforms to meet the increasing demands of next-generation miniaturized electronics. Among them, the recently emerged 2D Bi₂O₂Se with unique non-van der Waals interlayer interaction, high mobility, sizeable bandgap, and capability to fabricate homologous heterojunction, is of particular interest. In this Review, we introduce recent progress in preparation, transfer, mechanical and electrical properties, and electronic applications of 2D Bi₂O₂Se. First, we summarize methodologies to synthesize and massively produce 2D Bi₂O₂Se, as well as recent advances in transferring them from growth substrate to arbitrary substrates. Then, we review current understandings on the intrinsic mechanical properties of Bi₂O₂Se at 2D thickness limit, and its in-plane and out-of-plane electrical properties. Electronic devices including field-effect transistors, memristors, and sensors based on 2D Bi₂O₂Se for neuromorphic computing, memory, logic, and integrated circuits are discussed. Finally, challenges and prospects for the development of 2D Bi₂O₂Se are proposed.

To improve the corrosion resistance of C_f/SiC composites in a water vapor oxygen coupled environment, the bi-layer Yb₂Si₂O₇/SiC and tri-layer Yb₂Si₂O₇/(SiC_w-Mullite, SM)/SiC environment barrier coatings were designed and prepared on the surface of C_f/SiC composites by chemical vapor deposition and sol-gel method united with air spraying. Results show that the mass loss of bi-layer Yb₂Si₂O₇/SiC coating coated samples was 17.24 ​× ​10⁻³ ​g ​cm⁻² after 200 ​h oxidation at 1673 ​K, and the average compression strength retention rate was only 79.44% due to the formation of wide penetrating cracks. Comparatively, SiC whiskers in SM middle coating can not only increase the crack propagation resistance of mullite middle coating, but also alleviate the difference of coefficient of thermal expansion between Yb₂Si₂O₇ outer coating and mullite middle coating. Therefore, the mass loss of tri-layer Yb₂Si₂O₇/SM/SiC coating coated samples was only 2.93 ​× ​10⁻³ ​g ​cm⁻² after 200 ​h oxidation at 1673 ​K, and the average compression strength retention rate was up to 98.79%.

Simultaneous composition and valence-dependent strain regulation is achieved in lead-free (Bi_0.5Na_0.4K_0.1)_1-2xSm_2xTi_1-xMn_xO₃ (BNKT-SM100x) ceramics by a facile co-doping design with Sm³⁺ and Mn²⁺. By simply controlling the sintering temperature, Mn ions exhibited mixed-oxidation states with different ion radius and electronic structures, further adjusting the crystalline field. The regulated disorder degree finally induced large electro-strain (0.445%) under appropriate doping contents (x ​= ​0.01) and sintering temperature (1150 ​°C). Moreover, the random effect of Mn²⁺ (arising from the different valence and radius comparing with Ti⁴⁺) is stronger than the pinning effect due to the suppressed oxygen vacancies, and the different crystal structures may also affect the role of Mn²⁺. The domain morphologies with mixed nanodomain and ferroelectric domain were observed in the BNKT-SM1 ceramics, further demonstrating the coexistence of random effect and pinning effect. It is believed that the self-strain regulation phenomenon in this work may serve as an effective strategy for designing ferroelectrics with high strain performance.

The development of distinguished photocatalysts with high photo-carrier disassociation and photo-redox power for efficient elimination of pollutants in water is of great significance but still a grand challenge. Herein, a novel Cd_0.5Zn_0.5S/Bi₂WO₆ S-scheme heterojunction was built up by integrating Cd_0.5Zn_0.5S nanoparticles on Bi₂WO₆ microspheres via a simple route. The S-scheme charge transfer mode substantially boosts the high-energetic electrons/holes spatial detachment and conservation on the Cd_0.5Zn_0.5S (reduction) and Bi₂WO₆ (oxidation), respectively, as well as effectively suppresses the photo-corrosion of Cd_0.5Zn_0.5S, rendering Cd_0.5Zn_0.5S/Bi₂WO₆ photocatalysts with superior redox ability. The optimal Cd_0.5Zn_0.5S/Bi₂WO₆ heterojunction achieves exceptional visible-light-driven photocatalytic tetracycline degradation and Cr(VI) reduction efficiency, 3.2 (1.9)-time and 33.6 (1.6)-time stronger than that of neat Bi₂WO₆ (Cd_0.5Zn_0.5S), while retaining the superior stability and reusability. Quenching test, mass spectrometry analysis, and toxicity assessment based on Quantitative Structure Activity Relationships. calculation unravel the prime active substances, intermediates, photo-degradation pathway, and intermediate eco-toxicity in photocatalytic process. This research not only offers a potential photocatalyst for aquatic environment protection but also promotes the exploration of novel and powerful chalcogenides-based S-scheme photocatalysts for environment protection.