Journal of Materials Science最新文献

This study examines the continuous phase transition of NaBr-doped Li₄Ti₅O₁₂ during calcination, focusing on the migration and evolution of Li⁺, Na⁺, and Br⁻ and their impact on the transition. Results from high-temperature in situ X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations indicate that NaBr incorporation increased the TiO₂–Li₂TiO₃ transition temperature and reduced the Li₂TiO₃–Li₄Ti₅O₁₂ transition temperature. An appropriate amount of Li⁺ was doped into TiO₂ at low temperatures. Notably, with increasing temperature, Na⁺ was doped into the TiO₂ cell through the gap, while Br⁻ was adsorbed on the surface of TiO₂ without entering the TiO₂ cell. With the continuous increase in the temperature and doping of Li⁺, TiO₂ transforms into Li₂TiO₃. Na⁺ and Br⁻ gain more energy, Na⁺ enters the Li₂TiO₃ unit cell for gap doping, and Br⁻ enters the Li₂TiO₃ unit cell to replace O²⁻, promoting the transformation of Li₂TiO₃ to Li₄Ti₅O_12. Overall, this research provides an intrinsic connection between the microscopic properties of anions and cations during NaBr-doped Li₄Ti₅O₁₂ phase transition, clarifies the states of Li⁺, Na⁺, and Br⁻ in this transition, and offers a theoretical basis for the states of anions and cations during continuous Li₄Ti₅O₁₂ phase transition.

The passive-corrosion mechanism of passive film for steel rebar in a simulated concrete medium was investigated. The effects of Cl⁻ and SO₄²⁻ on the passivation films were analyzed by electrochemical methods and further verified by visually characterizing the structural changes of the passivated films in combination with XPS, SPM, and TEM techniques. The results revealed a significant discrepancy in defect density between the outer and inner layers of the passive film, while the impact of SO₄²⁻ concentrations on the film composition was relatively minimal. Additionally, the competitive adsorption mechanism between Cl⁻ and SO₄²⁻ was identified as the primary factor determining the protection of the passive film. At a concentration of 0.4 M SO₄²⁻, the non-uniform corrosion dissolution at the junction between matrix and film accelerated the depassivation process of the steel reinforcement. However, the detachment of Cl⁻ occurred at a higher concentration of SO₄²⁻, which reduces the dissolution rate of the passive film and enhances its protective properties on the substrate.

The anisotropic nature and distortion hardening characteristics of inherent in rolled sheet metal pose challenges in accurately predicting forming limits. Anisotropy introduces variations in forming limit curves, while distortion hardening alters both the magnitude and scope of these curves. Neglecting these factors can lead to significant inaccuracies in forming limit predictions. In this study, an orthotropic model for predicting forming limits is proposed. Drawing from Swift's diffuse instability theory and Hill’s localized instability theory, the proposed model comprehensively incorporates the influences of anisotropy and distortion hardening. To validate the approach, Nakajima tests utilizing semi-circular rigid punches were conducted on DC06 deep-drawing steel and DP590 high-strength steel. The results demonstrate that the proposed model rectifies overstated limit strains, narrows the predicted range of theoretical forming limit diagrams, aligns theoretical predictions more closely with experimental data, and enhances overall prediction accuracy. This research contributes valuable theoretical insights into the sheet metal forming industry.

A “large thick base layer + thin functional multi-layer” structure was proposed to enhance the hardness and corrosion resistance of CrSiN films by breaking the CrSiN columnar growth by Al₂O₃ intercalation. The Al₂O₃/CrSiN multilayer films (–1 μm) with different modulation periods (3, 8, 15) were deposited on CrSiN (–2 μm) films by magnetron sputtering. The CrSiN layer consisted mainly of fcc-CrN and a small amount of Si₃N₄, while the Al₂O₃ layer was in an amorphous form. The insertion of Al₂O₃ changed the orientation of film, and the grains on the surface of film were refined. With the increase in the multi-layer period, the modulus tended to stabilize at about 211GPa, and the hardness increased reaching a maximum of 20.7 GPa at period 3. The nitride/alumina interface prevented the diffusion of corrosion species and improved the corrosion resistance of the film. In 3.5 wt% NaCl solution, the multilayer film possessed better corrosion resistance than CrSiN monolayer film. The multilayers showed superior corrosion potentials and ultra-low corrosion current densities (E_corr = -0.566 V, i_corr = 0.67 μA·cm²) at period 8.

Tailoring the performance of supercapacitors (SCs) by design is a critical challenge in high-performance energy storage. Herein, density functional theory (DFT) was utilized to analyze the potential of a sulfur-cobalt–nickel composite material as a supercapacitor. Specifically, heterogeneous NiCo₂S₄@ZnS hollow spheres with disulfide vacancies (V-NiCo₂S₄@V-ZnS) were produced by reducing the Ni/Co-LDH@ZIF-8 precursor. The electrochemical performance of the composites is significantly enhanced by the synergistic effect of the NiCo₂S₄@ZnS hetero-interface, hollow structure, and disulfide vacancy. The V-NiCo₂S₄@V-ZnS heterostructures demonstrate superior specific capacitance, excellent rate capability, and long cycle life (retaining 88.60% after 10000 cycles at 10 A/g), surpassing pure NiCo₂S₄ and ZnS materials. Notably, an asymmetric supercapacitor composed of these heterostructures achieves a maximum energy density of 47.9 Wh/kg at 4000 W/kg and maintains good cycle stability (90.24% after 10000 cycles), presenting promising prospects for future energy storage developments.

A hot-forged Fe-30Mn-11Al-1C-10Ni (wt.%) low-density steel was developed, possessing a comparable strength–ductility synergy to those subjected to prior cold rolling and aging treatment. The initial microstructure after hot forging contained austenite matrix (~ 70 vol.%) and a large fraction of B2 phases (~ 30 vol.%) owing to the addition of high content of Al and Ni. The resultant dual-phase morphology effectively blocked the grain growth during hot forging, resulting in extremely fine grain size of both austenite (< 3 μm) and B2 phases (< 2 μm). In addition, dual precipitation of nano-sized κ-carbides and DO₃ particles was formed during air cooling within austenite and B2 grains, respectively. Consequently, an excellent combination of strength (yield strength of 1250 MPa, ultimate tensile strength of 1381 MPa) and ductility (total elongation of ~ 25%) was achieved in the hot-forged specimens owing to the synergy of the multiple strengthening mechanisms and excellent strain hardening capability. Particularly, the sequentially activated slip-band refinement in austenite and B2 phases and the hindering effect on dislocation movement of B2 phase provided a consistently high strain hardening rate, contributing to the superior strength–ductility balance. However, further aging treatment resulted in a gradual increase in strength but a severe loss in ductility, due to the formation of coarse intergranular κ-carbides. The present study suggests that an excellent strength–ductility synergy in Ni-alloyed low-density steel could be achieved through simple hot forging followed by air cooling.

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Photodetectors (PDs) employing inorganic, organic, low-dimensional, and hybrid materials are making significant advances in photodetection technology, each presenting unique benefits and challenges. Inorganic materials, including silicon and III-V semiconductors, prevail in the domain because of their intrinsic stability, scalability, and established fabrication methods, but their spectrum response is frequently restricted. Organic materials, characterized by tunable optical properties and flexibility, provide a viable alternative, but they are impeded by challenges related to stability and sensitivity. Low-dimensional materials, comprising 0D, 1D, and 2D systems, demonstrate remarkable electrical and optical characteristics, facilitating the creation of ultrathin, very sensitive PDs. Nonetheless, extensive production and longevity continue to pose significant hurdles. Hybrid structures, which amalgamate the advantages of inorganic, organic, and low-dimensional materials, exhibit significant potential for improving essential performance parameters such as responsivity, spectrum range, and response time but encounter challenges related to integration and complexity. This review examines the advancements, limitations, and prospective directions of PDs in the range from ultraviolet (UV) to infrared (IR), utilizing various material systems, emphasizing the significance of hybrid and low-dimensional materials in the development of next-generation PDs.

Graphical Abstract

It is considerably significant and challenging to prepare platinum (Pt)-based catalysts with high activity and stability for the development of direct methanol fuel cells (DMFCs). On that account, we used Pt nanoparticles (NPs) as the core, coated zeolitic imidazolate framework-8 (ZIF-8), silicon dioxide (SiO₂) and Pt NPs on their surfaces. Afterward, the SiO₂ was etched away to prepare Pt-based nanomaterials with core-shell structure, which were named Pt@ZIF-8/Pt. Simultaneously, the electrocatalytic properties of Pt@ZIF-8/Pt nanomaterials catalyzing methanol oxidation reaction (MOR) and oxygen reduction reaction (ORR) were tested under alkaline conditions. The mass and specific activities of Pt@ZIF-8/Pt-12 for MOR were 3285.07 mA mg_Pt⁻¹ and 1.12 mA cm⁻² correspondingly. The limiting current densities (LCD), initial potentials (E_onset) and half-wave potentials (E_1/2) for the catalytic ORR of sample Pt@ZIF-8/Pt-12 were 6.24 mA cm⁻², 1.04 V and 0.83 V, respectively. Last but not least, zinc-air battery was assembled utilizing the Pt@ZIF-8/Pt-12 catalyst. The open circuit potential and maximum power density of the zinc-air battery were 1.48 V and 120.8 mW cm⁻². As evidently demonstrated by our research findings, it still maintained excellent stability after 600 h of cyclic charge and discharge tests. As a result, this research not only provides enlightening guidance for catalyst design for DFMCs and zinc-air batteries, but also accelerates the development of new battery catalyst materials.

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The rapid development of radar systems has led to a surge in demand for low-dielectricity specialty paper’s mechanical, dielectric, and heat-resistant property. Poly (p-phenylene benzobisoxazole) (PBO) fiber is highly promising for the production of low-dielectricity specialty paper due to its excellent mechanical, heat-resistant and low dielectric property. The surface modification and nanosizing of PBO fiber have been applied to the reinforcement of PBO paper, however, these techniques have potential drawbacks, including lengthy preparation cycles and harsh conditions. Resin reinforcement is the simplest way, but suffers from weak interfacial strength. In this work, we creatively introduced the fluorine and benzoxazole ring into the bismaleimide (BMI) resin, based on the idea of homogenous reinforcement, to enhance the interaction between the PBO fiber and the resin. With the strong interfacial interaction and stable chemical structure, the composite paper has outstanding mechanical and heat-resistant property, its tensile strength and T_d reach 78.8 MPa and 389 °C, respectively. Furthermore, the dielectric constant (ε) and dielectric loss (tan δ) of the composite paper are as low as 1.66 and 0.004 at 10⁶ Hz, respectively. We anticipate that this work will offer a viable approach to PBO paper preparation.

Graphical Abstract

MoO₂ is a promising material for efficient and cost-effective electrocatalytic water splitting, particularly for the oxygen evolution reaction (OER) in alkaline media. Modifying the morphology, composition, or oxidation state of MoO₂ can enhance its active surface area and performance. In this study, Mo-coated carbon paper was used as a substrate to synthesize well-organized MoO₂ nanowires and nanosheets via a one-step CVD method without any catalyst. The nanosheets and nanowires grow perpendicularly to the substrate. MoO₂ nanowire arrays exhibit superior OER performance, characterized by a lower onset potential (1.54 V), a smaller Tafel slope, and enhanced durability compared to nanosheets. This improvement is likely attributed to the increased number of exposed active sites, reduced presence of oxidized Mo⁴⁺, and smaller crystalline size.

Graphical abstract

Here, well-organized MoO₂ nanowires and nanosheets have been fabricated on carbon paper using a one-step CVD method by reducing MoO₃ with Mo powder to investigate the intrinsic relationship between morphology, elemental composition and state, and their electrocatalytic properties. The obtained nanosheets presented as a flower-like structure, while nanowires formed into well-aligned arrays. MoO₂ nanowires contained higher amounts of Mo⁴⁺, were composed of smaller crystal grains, and possessed a lower onset potential for OER (oxygen evolution reaction) at about 1.54 V, a smaller Tafel slope at about 110 mV/dec, and better durability when compared to MoO₂ nanosheets.