Heterogeneous Layered Structure Research Articles

Ultrahigh Capacitive Energy Storage in a Heterogeneous Nanolayered Composite

AbstractFerroelectric polymers with robust electrical polarization have been extensively investigated for capacitive energy storage. However, their inherent ferroelectric hysteresis loss limits the discharged energy density and compromises energy efficiency. Here, a heterogeneous nanolayered composite of ferroelectric polymer poly(vinylidene fluoride‐trifluoroethylene) (P(VDF‐TrFE)) and Al2O3 is presented, which effectively mitigates ferroelectric hysteresis loss while maintaining high polarization and enhanced breakdown strength. Phase‐field simulations indicate that the polarization behaviors of the heterogeneous layered structure are jointly influenced by the thickness and dielectric constant of each component, which balances the electrical energy and Landau energy within the heterogeneous system. Guided by the theoretical simulations, optimized polarization behaviors are achieved with a significant reduction in remnant polarization and ferroelectric loss in the P(VDF‐TrFE)/Al2O3 composites through careful control of P(VDF‐TrFE) thickness at nanometer scale. Moreover, the presence of multiple interfaces in the layered composites leads to a remarkable enhancement in polarization and breakdown strength. Consequently, an ultrahigh energy density of about 108 J cm−3 is achieved with a high charge–discharge efficiency of exceeding 80%. This work not only presents a straightforward approach to modify the polarization behaviors of ferroelectric polymers but also demonstrates a promising strategy for developing high‐energy‐density polymer nanocomposites.

Fracture Behavior and Mechanism of Nb-Si-Based Alloys with Heterogeneous Layered Structure.

Novel Nb-Si-based alloys with heterogeneous layers that have the same composition (Nb-16 at.%Si) but different phase morphologies were designed in this work. Heterogeneous layered structure (HLS) was successfully fabricated in Nb-16Si alloys by layering composite powders after various degrees of mechanical alloying (6 h, 12 h, 18 h, and 24 h) alternately and subsequent spark plasma sintering (SPS). The influence of HLS on the fracture behavior at both room and elevated temperature was investigated via single-edge notched bending (SENB) and high-temperature compression, respectively. The results show that the diversified HLS is obtained by combining hard layers containing fine equiaxed crystals and/or soft ones with coarse lamellar niobium solid solution (Nbss). By affecting the crack propagation in SENB, HLS is favorable for improving the fracture toughness and exhibits a significant increase compared with the corresponding homogenous microstructure. Moreover, for the same HLS, a more excellent performance is achieved when the initial crack is located in the soft layer and extended across the interface to the hard one through crack bridging, crack deflection, crack branching, and shielding effect. Fracture starts in the soft layer (from powders of ball-milled for 12 h) of a 12-24 alloy, and a maximum KQ value (14.89 MPa·mm1/2) is consequently obtained, which is 33.8% higher than that of the homogeneous Nb-16Si alloy. Furthermore, the heterogeneous layered alloys display superior high-temperature compression strength, which is attributable to the dislocation multiplication and fine-grained structure. The proposed strategy in this study offers a promising route for fabricating Nb-Si-based alloys with optimized and improved mechanical properties to meet practical applications.

Dependences of the defect, microstructure and properties of 15-5 PH martensitic stainless steel on the laser powder bed fusion process parameters

15-5 PH martensitic stainless steel is widely utilized in the marine, chemical, and aerospace industries owing to its high strength and corrosion resistance properties. The highly tailored samples can be produced via laser powder bed fusion technology, however it is still unknown how to optimize process parameter windows and conduct mechanism research for 15-5 PH steel forming. The results show that fusion defects are mostly concentrated in the region with low laser power (P) of 200 W, and there is no obvious distribution pattern in the pore and porosity defects. Excellent dense samples can be formed mainly at medium P of 260 W and medium scanning speed (V) of 1200 mm/s. The proportion of body center cubic structure reaches 91.7 % for the hatch space (H) of 0.06 mm, and a heterogeneous layered structure with alternating fine and coarse grain layers is formed. The sample exhibits high strength and excellent plasticity, where the ultimate tensile strength, yield strength, elongation to fracture, impact toughness, and hardness are 1161 MPa, 825 MPa, 17.5 %, 122.5 J/cm2, and 34.6 HRC, respectively. The excellent comprehensive property is due to fine-grained strengthening, dislocation strengthening, solid solution strengthening and intrinsic factors/oxide dispersion strengthening.

MXene-Stabilized VS2 Nanostructures for High-Performance Aqueous Zinc Ion Storage.

Aqueous zinc-ion batteries (AZIBs) based on vanadium oxides or sulfides are promising candidates for large-scale rechargeable energy storage due to their ease of fabrication, low cost, and high safety. However, the commercial application of vanadium-based electrode materials has been hindered by challenging problems such as poor cyclability and low-rate performance. To this regard, sophisticated nanostructure engineering technology is used to adeptly incorporate VS2 nanosheets into the MXene interlayers to create a stable 2D heterogeneous layered structure. The MXene nanosheets exhibit stable interactions with VS2 nanosheets, while intercalation between nanosheets effectively increases the interlayer spacing, further enhancing their stability in AZIBs. Benefiting from the heterogeneous layered structure with high conductivity, excellent electron/ion transport, and abundant reactive sites, the free-standing VS2/Ti3C2Tz composite film can be used as both the cathode and the anode of AZIBs. Specifically, the VS2/Ti3C2Tz cathode presents a high specific capacity of 285 mAh g-1 at 0.2 A g-1. Furthermore, the flexible Zn-metal free in-plane VS2/Ti3C2Tz//MnO2/CNT AZIBs deliver high operation voltage (2.0 V) and impressive long-term cycling stability (with a capacity retention of 97% after 5000 cycles) which outperforms almost all reported Vanadium-based electrodes for AZIBs. The effective modulation of the material structure through nanocomposite engineering effectively enhances the stability of VS2, which shows great potential in Zn2+ storage. This work will hasten and stimulate further development of such composite material in the direction of energy storage.

Inorganic salt-assisted hydrothermal synthesis of composite vanadium oxides for stabilization of aqueous zinc ion batteries with low current density cycling

Vanadium-based materials have been widely investigated as cathode materials for aqueous zinc-ion batteries because of their multiple valences, large interlayer spacing and open framework. However, their sluggish reaction kinetics, poor structural stability and cycling stability at low rates still limit their further development. At present, the improvement of vanadium-based materials mostly involves complex processes or expensive materials that are difficult to synthesize on a large scale. In this work, by introducing an inorganic salt (NH4)2HPO4 as an additive and adjusting the reaction temperature of hydrothermal synthesis, a composite vanadium oxide (NVO(210)-2P) with the coexistence of NH4V4O10 and V5O12·6H2O was successfully synthesized. Compared with the surfactant-assisted process, the inorganic salt-assisted hydrothermal synthesis has the advantages of being greener and more environmentally friendly. As a cathode material for aqueous zinc ion batteries, the obtained NVO(210)-2P shows excellent cycle stability at low current density (88.1 % retention over 250 cycles at 0.3 A/g and 80 % after 600 cycles at 0.5 A/g). The excellent electrochemical performance is attributed to the well-structured nanosheets synthesized using (NH4)2HPO4 as an additive. At the same time, the generated V5O12·6H2O provides a large interlayer distance, reduces the structural water molecules of electrostatic interaction and indirectly forms a heterogeneous layered structure with NH4V4O10, which reduces the distribution density of NH4+ and avoids irreversible deamination.

Settling velocity of algal-bacterial granular sludge studied in the sequence batch reactor

Granule settling velocity is critical to biosolids-liquid separation. The settling velocity of algal-bacterial granules versus the diameter of granules was examined as a function of granule diameter in the sequence batch reactor in eleven days of cultivation. Despite granules having an apparently compact and rounded shape and considerable scatter of the data, the results never showed granules are homogeneously dense packed structures in the range of 10 μm to 1.0 mm in diameter. The settling velocity increases with granule size. The estimated fractal dimension was always less than two. The result was interpreted as forming heterogeneous compact layered structures in the shell from the early stage of cultivation rather than rearrangement from a bulk floc into a dense structure. Additional analysis for the cultivation of 150 days confirmed the considerable growth of size and fluffy hair. However, the settleability of small fragments remained relatively the same as heterogeneous compact structures.

Annealing parameters effect on microstructure evolution, tensile properties and deformation behaviors of direct-cold-rolled UNS S32101 duplex stainless steel with heterogeneous layered structure

Microstructure evolution, strain-induced martensite transformation (SIMT) kinetics, tensile properties, deformation behaviors of UNS S32101 duplex stainless steel (DSS) with heterogeneous layered structure (HLS) were investigated. HLS composed of multiscale grains (spanning coarse, fine, and ultrafine grains) was prepared by direct cold rolling in combination with short-time annealing, being dominated by coarse-grained ferrite (CGed α) and fine-grained austenite (FGed γ). A quantitative SIMT kinetics model was established to predict the α′-martensite fraction at various strain/annealing parameters, indicating that increased average grain size (AGS) for γ not only contributed to the SIM formation but also promoted the monotonic increase of SIMT rate until annealing for 10 min. Relatively high stacking fault energy (SFE, 35.89∼39.34 mJ/m2) favored mechanical twinning as the dominant deformation mode of γ accompanied by SIMT and dislocation glide. And α deformation was mainly coordinated by wavy slip. Both SFE and Olson-Cohen parameters were strongly correlated with the γ AGS, which could reasonably interpret the dependence of SIMT on the AGS. The A and B values increased progressively with grain coarsening along with the rapid decline in SFE, facilitating the martensite formation. Further increasing the AGS beyond the peak region severely suppressed SIMT probably due to the low probability of martensite embryo generation at deformation twins (DTs) intersections, coinciding with the sharp decrease A value.

Design of synergistic alloying CoCrFeNi eutectic high entropy alloy based on infinite solid solution

Multivariate synergistic alloying is an effective means to improve the comprehensive mechanical properties of metallic materials. Eutectic high-entropy alloys achieve heterogeneous biphasic layered structures on the micro and nano scale resulting in very good properties, most of the current alloying studies of CoCrFeNi eutectic high-entropy alloys focus on unitary alloying. In this work, the design strategy of CoCrFeNi eutectic high-entropy alloys based on infinite solid solution synergistic alloying is proposed, and a series of eutectic high-entropy alloys consisting of face-centered cubic (FCC) and intermetallic compound (IM) with fine and regular microstructures are successfully designed, and some of the synergistic alloying eutectic high-entropy alloys have very excellent comprehensive mechanical properties.

Heterogeneous layered structure in thermal barrier coatings by plasma spray-physical vapor deposition

The unique columnar structure endows thermal barrier coatings (TBCs) prepared by plasma spray-physical vapor deposition (PS-PVD) with high thermal insulation and long lifetime. However, the coating delamination failure resulting from an intra-column fracture (within a column rather than between columns) is a bottleneck in the solid dust particle impact environment for aero-engine. To clarify the intra-column fracture mechanism, a basic layer deposition model is developed to explore a heterogeneous weak-to-strong layered structure formed by a local transient <i>in-situ</i> deposit temperature. During the PS-PVD, an <i>in-situ</i> deposit surface is continuously updated due to constantly being covered by vapor condensation, showing a transient temperature, which means that the <i>in-situ</i> deposit surface temperature rises sharply in short period of 0.2 s of depositing a thin layer during a single pass. Meanwhile, the increasing temperature of the <i>in-situ</i> deposit surface results in an experimentally observed heterogeneous weak-to-strong structure, showing a continuous transition from a porous weak structure at the bottom region to a dense strong structure at the top region. This structure easily makes the intra-column fracture at the porous weak region. The results shed light on improving TBC lifetime by restraining the intra-column fracture.

Heterogeneous layered multiple transition metal composite electrocatalysts with controlled composition for hydrogen production

The exploration of highly efficient and low-cost bifunctional electrocatalyst is essential for overall water splitting, especially for industrial application under alkaline conditions. Herein, we propose a controllable structural engineering strategy of constructing heterogeneous layered electrocatalyst with wetting surface for hydrogen evolution reaction and oxygen evolution reaction. Heterogeneous layered NiFe LDH (layered double hydroxide)/CoFeP/NF (Ni foam) with superhydrophilic surfaces is successfully fabricated by successive electrodeposition, phosphorization and solvothermal method. The NiFe LDH/CoFeP/NF for hydrogen evolution achieves a low overpotential of 198 mV at 50 mA cm−2 in 1.0 M KOH. An overpotential of 269 mV is required at 50 mA cm−2 for oxygen evolution. Meanwhile, the practical utilization of NiFe LDH/CoFeP/NF as bifunctional electrocatalysts for overall water splitting yields 1.73 V at 50 mA cm−2 in the two-electrode cell. Moreover, NiFe LDH/CoFeP/NF can retain over 50 h without an obvious degradation at 10 mA cm−2. The satisfactory operating stability and high activity of NiFe LDH/CoFeP/NF in alkaline solution can be attributed to the heterogeneous layered structure and excellent hydrophilic surface. The study provides a strategy to engineering heterogeneous layered structures with wetting surface for excellent electrocatalytic activities toward overall water splitting.

Spatial Band Separation in a Surface Doped Heterolayered Structure for Realizing Efficient Singlet Oxygen Generation.

Singlet oxygen (1 O2 ) with electrical neutrality and long lifetime holds great promise in producing high-added-value chemicals via a selective oxidation reaction. However, photocatalytic 1 O2 generation via the charge-transfer mechanism still suffers from low efficiency due to the mismatched redox capacities and low concentration of photogenerated carriers in confined systems. Herein, by taking bismuth oxysilicate (Bi2 O2 SiO3 ) with alternating heterogeneous layered structure as a model, it is shown that iodine doping can facilitate the spatial redistributions of bands on alternated [Bi2 O2 ] and [SiO3 ] layers, which can promote the separation and transfer of photogenerated charge carriers. Meanwhile, the band positions of Bi2 O2 SiO3 are optimized to match the redox potential of 1 O2 generation. Benefiting from these features, iodine-doped Bi2 O2 SiO3 exhibits efficient 1 O2 generation with respect to its pristine counterpart, leading to promoted performance in the selective sulfide oxidation reaction. A new strategy is offered here for optimizing charge-transfer-mediated 1 O2 generation.

The Distribution of the Thermal Field in an Elliptical Electric Conductor Coated with Insulation

The paper determines the stationary thermal field in an elliptical cross-section electric conductor coated with insulation. Heat is generated by the flow of alternating current (AC) through the conducting core, and then dissipated from the insulation surface via convection and radiation. The authors have developed an original method for hybrid (analytical–numerical) modeling of a field. This method has been used to solve the relevant boundary problem of Poisson’s equation. While the eigenfunctions of the Laplace operator were determined analytically, the coefficients of the eigenfunctions were calculated by iteratively solving an appropriate system of algebraic equations. The proposed method enables the analysis of systems with an elliptical geometry and a heterogeneous layered structure (e.g., air, aluminum alloy, PCV), and does not require area discretization (grid). The developed analytical–numerical (AN) method has been positively verified using finite elements (FEs). The determined thermal field is illustrated graphically. The obtained solution has a good physical interpretation.

Layered Structure in the Crystalline Adsorption Layer and the Leaching Process of Poly(vinyl alcohol) Revealed by Neutron Reflectivity.

We investigated the structure of the crystalline adsorption layer of poly(vinyl alcohol) (PVA) in hot water by neutron reflectivity in two cases: when the adsorption layer is exposed on the substrate by leaching the upper bulk layer and when it is deeply embedded between a relatively thick PVA film and substrate. In both cases, the PVA adsorption layer consists of three layers on the Si substrate. The bottom layer, consisting of amorphous chains that are strongly constrained on the substrate, is not swollen even in hot water at 90 °C. The middle layer, consisting of amorphous chains that are much more mobile compared with those in the bottom layer, has no freedom to assume a crystalline form. Only the molecular chains in the top layer are crystallizable in the adsorption layer, leading to a heterogeneous layered structure in the film thickness direction. This layered structure is attributed to the crystallizable chains of PVA during the formation of the adsorption layer driven by hydrogen bonding. However, the structure and dynamics in the adsorption layer may differ in both cases because the molecular chains in the vicinity of the surface seem to be affected by surface effects even in the adsorption layer.

The Interface Characterization of 2-Mercapto-1-methylimidazole Corrosion Inhibitor on Brass

This work presents a detailed surface analytical study and surface characterization, with an emphasis on the X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) analyses of 2‑mercapto‑1‑methylimidazole (MMI) as a corrosion inhibitor for brass. First, the electrochemical measurements demonstrated a corrosion inhibition effect of MMI in a 3 wt.% NaCl solution. Next, the formation of the MMI surface layer and its properties after 1 month of immersion was analyzed with attenuated total reflectance–Fourier-transform infrared spectroscopy, atomic force microscopy, field-emission scanning electron microscopy, and contact angle analysis. Moreover, to gradually remove the organic surface layer, a gas cluster ion beam (GCIB) sputtering source at different accelerated voltages and cluster sizes was employed. After each sputtering cycle, a high-resolution XPS analysis was performed. Moreover, an angle‑resolved XPS analysis was carried out for the MMI-treated brass sample to analyze the heterogeneous layered structure (the interface of the MMI organic/inorganic brass substrate). The interface properties were also investigated in detail using ToF-SIMS for spectra measurements and 2D imaging. Special attention was devoted to the possible spectral interferences for MMI‑related species. The thermal stability of different MMI-related species using molecular-specific signals without possible spectral interferences was determined by performing a cooling/heating experiment associated with ToF-SIMS measurements. It was shown that these species desorbed from the brass surface in the temperature range of 310–370 °C.

Reshaping the Cathodic Catalyst Layer for Anion Exchange Membrane Fuel Cells: From Heterogeneous Catalysis to Homogeneous Catalysis.

In anion exchange membrane fuel cells, catalytic reactions occur at a well-defined three-phase interface, wherein conventional heterogeneous catalyst layer structures exacerbate problems, such as low catalyst utilization and limited mass transfer. We developed a structural engineering strategy to immobilize a molecular catalyst tetrakis(4-methoxyphenyl)porphyrin cobalt(II) (TMPPCo) on the side chains of an ionomer (polyfluorene, PF) to obtain a composite material (PF-TMPPCo), thereby achieving a homogeneous catalysis environment inside ion-flow channels, with greatly improved mass transfer and turnover frequency as a result of 100 % utilization of the catalyst molecules. The unique structure of the homogeneous catalysis system comprising interconnected nanoreactors exhibits advantages of low overpotential and high fuel-cell power density. This strategy of reshaping of the catalyst layer structure may serve as a new platform for applications of many molecular catalysts in fuel cells.

Reshaping the Cathodic Catalyst Layer for Anion Exchange Membrane Fuel Cells: From Heterogeneous Catalysis to Homogeneous Catalysis

AbstractIn anion exchange membrane fuel cells, catalytic reactions occur at a well‐defined three‐phase interface, wherein conventional heterogeneous catalyst layer structures exacerbate problems, such as low catalyst utilization and limited mass transfer. We developed a structural engineering strategy to immobilize a molecular catalyst tetrakis(4‐methoxyphenyl)porphyrin cobalt(II) (TMPPCo) on the side chains of an ionomer (polyfluorene, PF) to obtain a composite material (PF‐TMPPCo), thereby achieving a homogeneous catalysis environment inside ion‐flow channels, with greatly improved mass transfer and turnover frequency as a result of 100 % utilization of the catalyst molecules. The unique structure of the homogeneous catalysis system comprising interconnected nanoreactors exhibits advantages of low overpotential and high fuel‐cell power density. This strategy of reshaping of the catalyst layer structure may serve as a new platform for applications of many molecular catalysts in fuel cells.

Elemental Distribution of Gas-Thermal Coatings with W and Ta Modifiers

Currently, the technology of arc metallization according to technical and economic indicators is a promising way to restore worn parts of equipment. In the coating process the cored wire is melted by an electric arc, and molten particles are accelerated towards the surface parts with high temperature gas flow. On the subsequent formation of strengthening coatings are significantly influenced the technological modes of electric arc metallization. As practice shows, the coatings obtained by electric arc metallization are characterized by a heterogeneous layered structure. The structure of powder coatings, the distribution, composition and properties of the phases affect on the wear resistance, hardness and strength of the machined surface of machine parts and mechanisms. It is therefore necessary a detailed study of the structure of wear-resistant coatings taking into account technological properties of cored wire, and process heating of the particles by arc spraying. In this work the X-ray microanalysis of the elements of the structure of wear-resistant coatings obtained from cored wire with a refractory additives were conducted. The results of the study will be useful for the improvement technology of electric-arc metallization cored wires.

Heterogeneous layered structures for improved terahertz generation.

One of the most effective ways of generating terahertz (THz) radiation involves the conversion of short-pulsed IR or visible laser light into THz pulses at significantly lower frequencies. This conversion can be accomplished using organic crystals with nonlinear optical crystal (NLO) properties for IR to THz conversion through optical rectification. Due to the high refractive indices of organic crystals, pump laser light as well as generated THz radiation is lost from reflections at crystal surfaces. Here we report a structure composed of a layered series of materials with intermediate refractive indices designed to reduce reflective losses and improve the THz generation from organic crystals. This structure increases the transmission coefficients for both infrared pump input and THz output. We combine simple theoretical calculations with experimental data to show that a structure composed of materials with intermediate refractive indices can be used to increase generated THz intensity by nearly 50%.

Termination of local strain concentration led to better tensile ductility in multilayered 2N/4N Al sheet

Multilayered aluminum composites (ARB6-2N/4 N) with alternating layers of commercially purity aluminum (2N–Al) and high-purity aluminum (4N–Al) were fabricated by six cycles of accumulative roll bonding (ARB) processing. The ARB processed specimens were annealed at different temperatures. It was found that heterogeneous lamellar microstructures composed of fine-grained 2 N (hard) layers and coarse-grained 4 N (soft) layers formed in the specimens. The specimen with the heterogeneous layered structure showed a large tensile elongation with a strength following the rule of mixture. Digital image correlation analyses revealed that the deformation bands with high local strains formed in the 4 N layers but were terminated at the interfaces between the 2 N and the 4 N layers in the multilayered aluminum composites, accommodating the deformation between the hard (2 N) layers and the soft (4 N) layers during tensile deformation. Termination of the strain localization delayed macroscopic necking of the materials, leading to a better combination of high strength and good ductility in the multilayered aluminum composites.

Saturated and unsaturated hydraulic conductivity of synthetic gel structures in coarse textured soil substrates

Saturated and unsaturated hydraulic conductivity as a function of a thermodynamic potential (pressure) of soil water K(P) are investigated in the sandy samples with admixtures of strongly swelling polymer hydrogels (SSPHs) in a wide concentration range from 0.01 to 0.3 %SSPHs. The author’s original centrifugation method has been used along with a kinetic model of the water removal process, which enables to determine the function of water conductivity of gel compositions operating in an unsteady state. In saturation state and within the range of low absolute values of soil water pressure |P| = 0.3-20 kPa the SSPHs significantly (2-10 up to 50 times) reduced the hydraulic conductivity in proportion to the dose of a superabsorbent. A heterogeneous layered structure with a layer of pure gel or gel composition 0.1-0.3% SSHP reduces the saturated conductivity by 10-80 times.In the range | P | = 100-3020 kPa, the K(P) function, on the contrary, strongly increased up to 10–20 times under the action of SSPHs. The calculation of K(P) using the Mualem theory disagrees with our experimental estimation, especially in a range of low water content, where such a calculation strongly (up to 100-1000 times) underestimates the values of K(P).