Al2O3 Layer Research Articles

Role of Re additions on hot corrosion behaviors of a Co–Al–W superalloys

The hot corrosion behaviors of Co–Al–W superalloys with Re additions were investigated at 900 °C. The results showed that the addition of Re improved the hot corrosion resistance significantly. The alloys developed multi-layer oxidation and corrosion products, which located from surface to substrate were: the CoO and Co3O4 layer, the CoWO4 and CoAl2O4 layer, the Al2O3 layer, and the Co3W layer. The addition of Re promotes the formation of the α-Al2O3 scale, which is stable and dense. The thickness the α-Al2O3 scale in 1Re alloy is 1.9 μm, which is much thicker than that of the base alloy. The well-developed α-Al2O3 scale leads to the improvements in hot corrosion resistance.

Proton Permeable, Oxygen Blocking, Ultrathin Al2O3 Layers for Electrocatalytic Applications

Operating zero-gap electrolyzers at current densities above 1 Acm-2 is very challenging because ohmic losses associated with ion transport across the ion exchange membrane become predominant.[1] Technically, we can reach current densities up to 10 Acm-2. However, even a 100 micrometer thin nafion membrane would lead to cell voltages over 3 V [2] due to ohmic losses. Therefore, research and experimental development efforts are still needed to enable and increase the cell efficiency at elevated current densities.Implementing an ultrathin membrane of only a few nanometers in electrolyzers will minimize ion transport (i.e. protons) losses and will enable high-throughput electrolysis at low temperatures. However, to date, there is no concept available to perform electrochemical conversions using membranes of only of a few nanometers thickness that can block molecules but permeate protons.Multiple reports have demonstrated that dense ultrathin oxide layers, i.e. SiO2, can be used as electrocatalyst coatings to increase selectivities by blocking undesired ions/molecules from reaching the electrode.[3,4] The properties of such dense ultrathin oxide layers in principle fulfil the requirements of a proton exchange membrane, being only a couple of nanometer thin.To implement a nanometer thin proton exchange membrane into an electrolysis setup and enable mechanical integrity we envision a 3D-nanotube array design as shown in Figure 1a. In the ‘inside’ of the tube we perform the Hydrogen evolution reaction, and on the ‘outside’ the water oxidation reaction. Cathode and anode are separated only by a dense ultrathin oxide layer that permeates protons but blocks oxygen.Herein, we discuss the performance of ultrathin dense and amorphous Al2O3 layers made via pulsed laser deposition (2.5 nm, 3 nm, and 5 nm) with regard to proton and oxygen permeability. Electrochemical impedance spectroscopy allows us to determine diffusion coefficients and charge transfer resistances (Figure 1b). We use state-of-the-art operando FT-IR reflection-absorption spectroelectrochemistry that enables us to probe the dynamic structural and morphological changes of the dense alumina layer over time vs. applied potential (Figure 1c). In fact, we observe that proton permeation improves over time while we can exclude dissolution of the Al2O3 layer.

Precision Interface Engineering of CuNi Alloys by Powder ALD Toward High Thermoelectric Performance

The main bottleneck in obtaining high-performance thermoelectric (TE) materials has been identified as how to decouple the strong interrelationship between electrical and thermal parameters. Herein, we present a precise interface modification approach based on the powder Atomic Layer Deposition (pALD) technology to enhance the performance of CuNi alloys. Single-layer ZnO and Al2O3 layers have been deposited on the surface of powders, typically in 10-100 cycles, and their effect on the TE performance of bulks has been thoroughly investigated. A standard model is proposed and experimentally confirmed to build the relationship between the ALD oxide cycle numbers and Zn and Al content, which could be easily adapted to other pALD processes. The enhancement of the Seebeck coefficient, caused by the energy filtering effect, compensates the electrical conductivity deterioration due to the low electrical conductivity of oxide layers. Furthermore, the oxide layers may significantly increase the phonon scattering. Therefore, to reduce the resistivity of coating layers, a multiple-layer structure is deposited on the surface of powders by inserting Al2O3 into ZnO is constructed on. The atom probe tomography shows that after pressing, the Al atoms diffused into ZnO and realized the doping effect. Al diffusion has the potential to increase the electrical conductivity and complexity of coating layers. In comparison to pure CuNi, zT increased by 227.6% as a result of the decrease in resistivity and stronger phonon scattering in phase boundaries. The study demonstrates that ALD-based interface modification may be a versatile method for decoupling TE parameters and precisely modifying phase boundaries, which is practical for other thermoelectric materials.

Molecular Relays in Nanometer Scale Alumina: Effective Protection Layers for Water-Submersed Halide Perovskite Photocathodes

Halide perovskite (HaP) solar cells have an excellent voltage efficiency (>70%) and a low electron-affinity conduction band minimum, making them prospective candidates to be used as photocathodes in integrated low-cost solar fuel generators. However, halide perovskites are notoriously unstable in aqueous solutions and immediately dissolve upon exposure to liquid water. Ultrathin layers (< 10 nm) of Al2O3 deposited by atomic layer deposition are suitable encapsulants to prevent water ingression but are also electronically insulating. Embedding linear conjugated organic molecules (‘molecular relays’) that transverse the insulating layer enables selective electron transport across the insulating encapsulating layer. The electronic functionality of the embedded molecular relays is verified by conductive probe atomic force microscopy and photo-electrodeposition of metal particles (Pt and Ag) from ethanolic solutions. Lastly, the encapsulated HaP photoelectrodes were submersed in a CO2-saturated aqueous electrolyte and a photocurrent of ~100 µA/cm2 (at ~ -0.32 V vs. Ag/AgCl) was measured. This work demonstrates a way for stabilizing semiconductors in polar and protonic electrolytes as photoelectrodes for the generation of solar fuels.

Nanoscale Periodic Modulation of Doping over Large Areas with Block Copolymer Lithography and Ion Implantation

Whenever periodic patterning at the nanoscale over a large surface is required, block-copolymers (BCPs) represent an extremely attractive alternative for lithography1 and nano-templating,2 because of the low cost, if compared to conventional photolithography,3 and the high throughput, if compared to serial lithographic processes, such as electron beam lithography (EBL).4 Despite the relatively simple structure of BCPs, two different linear homopolymers linked to each other at one end by a covalent bond, when annealed above the glass transition temperature, they spontaneously microphase separate generating a variety of periodic nanostructures. The periodicity (L0 ) of the microdomains can be varied in the 10 – 100 nm range by properly adjusting the molecular weight and the interaction parameter of the two blocks.5 In this work, the combination of BCP lithography and ultra-low energy implantation of phosphorus ions at high fluences is investigated to promote a periodic modulation at the nanoscale of the concentration of dopant impurities over the near-surface layer of a silicon substrate.For the fabrication of the masks, two different poly(styrene-b-methyl methacrylate) (PS-b-PMMA) BCPs were used, to obtain two different geometries: the first with out of plane hexagonally packed PMMA cylinders, with an average diameter of 22 nm and center-to-center distance of 35 nm (Figure 1A) , and the second with out of plane lamellae having a periodicity of 28 nm (Figure 1B). The thickness of the BCP films was 35 nm thick. In addition, a graphoepitaxy protocol was implemented to obtain different sets of perfectly aligned 20 μm long parallel lamellae. A mesoporous soft mask can be readily obtianed by selective removal of PMMA cylinders with UV light and acetic acid. Conversely, a different process is required to avoid the collapse of the PS lamellae. Using Sequential Infiltration Synthesis (SIS),6 Al2O3 is incorporate into the PMMA phase of the BCP film. Upon the removal of the organic material by a mild O2 plasma cleaning, a nanostructured Al2O3 layer, that perfectly matches the PMMA pattern, remains on the substrate (Figure 1B).Phosphorus ions were implanted through the soft masks into the Si substrate operating at ultra-low energy (3 keV) to prevent the degradation of the polymeric film and reduce P penetration (10 nm) into the Si substrate. Additionally, high implantation doses are considered, to induce local amorphization of the silicon substrate. In this way Solid Phase Epitaxial Regrowth (SPER) can be exploited to recover the crystallinity of the substrate by thermal treatments at relatively low temperatures.7 During the SPER process the phosphorus atoms are substitutionally incorporated into the silicon lattice preserving their spatial confinement.AFM morphological analysis and ToF-SIMS depth profiling of the mask confirm the capability of the PS and alumina matrix to properly shield the low energy phosphorus ions in the dose range under investigation. AFM and ToF-SIMS characterization of the samples upon removal of the mesoporous template demonstrated that the P ions were effectively implanted into the Si substrate through the mask, leading to localized implantation (Figure 1C - 1E). Raman spectra suggested the presence of a thin layer of amorphous Si in the implanted samples and subsequent recrystallization after the annealing. By specific SPM measurements, it was possible to compare the morphology, the map of surface potential and the map of conductivity of the samples. The analysis of the Si surface after implantation through the mask with cylindrical pores and activation of the P is reported (Figure 1F, 1G). Small variations of the surface potential that perfectly match the implanted regions were obtained, suggesting a local modification of the electrical properties of Si. This result is also supported by conductivity measurements and finite element method (FEM) simulations. Further results will be presented, to investigate the electrical properties of the samples as a function of the implanted P dose and of the geometry of the mask.(1) Feng, H. et al., Nat. Mater. 21, 1426–1433 (2022).(2) Chai, J. & Buriak, J. M., ACS Nano 2, 489–501 (2008).(3) Levinson, H. J., Jpn. J. Appl. Phys. 61, (2022).(4) Yang, X. M. et al., ACS Nano 3, 1844–1858 (2009).(5) Seguini, G. et al. Soft Matter 16, 5525–5533 (2020).(6) Tseng, Y. C. et al. J. Phys. Chem. C 115, 17725–17729 (2011).(7) Luce, F. P. et al., Nucl. Instruments Methods Phys. Res. Sect. B Beam Interact. with Mater. Atoms 370, 14–18 (2016). Figure 1

Modified MnO2-Based Cathode for Zinc-Ion Batteries Using Facile Processing and Easily Available Materials

With the fast development of diverse electronics, the demand for safe energy storage systems with high energy density and high stability has increased rapidly. So far, lithium-ion batteries (LIBs) have dominated the market, from small smart electronics to electric vehicles. Nevertheless, LIBs have several limitations, such as high cost, limited raw material resources, high flammability, and harsh environmental impact. Therefore, novel rechargeable batteries which can mitigate these shortcomings must be explored. Aqueous zinc-ion batteries (ZIBs) have shown a promising future. Zinc with high theoretical volumetric capacity (5855 mAh cm-3) and high stability in aqueous electrolytes should enable high-performing, safe, and low-cost batteries. Additionally, the simple assembly of ZIBs in the ambient environment results in low capital costs. Despite these attractive merits, developing cathode materials with high capacity, rate performance, and stability in order to build commercial high-performing ZIBs, remains a great challenge.Cathode materials directly influence the electrochemical performance of ZIBs. Manganese oxide (MnO2) has been investigated as a promising cathode in ZIBs research due to its good specific capacity, low cost and high safety. However, the low ionic conductivity, slow diffusion kinetics, and low stability of MnO2 severely deteriorate the electrochemical performance and cycling stability of zinc-ion batteries. Recently, a series of studies have revealed the high effectiveness of coating on improving MnO2 cathode stability, including polymer coatings, carbon-based material coatings, artificial cathode-electrolyte interfaces, and metal oxide coatings.[1] Nevertheless, the improvement of other parameters, such as the rate performance, could be further improved for practical usage. In this research, we develop a novel modification method combining coating and doping strategies to induce MnO2 cathode with high capacity, high rate performance and low capacity decay after long-term operation. First, we utilize a facile one-step hydrothermal synthesis for Ag-doped α-MnO2. Different amounts of AgNO3 are added into reactors with KMnO4 and MnSO4 (n(Ag):n(Mn)=1:100-4:100) to investigate the influence of doping on capacity and rate performance. Subsequently, the doped tunnel-type MnO2 cathodes are mixed with precursor solutions of Al2O3 and then thoroughly stirred. Finally, an annealing process is conducted to achieve a nanoscale Al2O3 coating on the tunnel type MnO2. The coating configurations influence the electrochemical performance of cathodes;[2] thus, we test precursor solutions with different concentrations (1-3 wt% Al2O3) and annealing temperatures (500-700 °C) to investigate the influence of coating thickness and annealing treatment.With the assistance of scanning and transmission electron microscopes, the nanoscale Al2O3 layer coating on the doped active material is verified. The stable Al2O3 coating protects active materials from dissolution and structural collapse, improving cycling stability and resulting in high capacity retention after long-term operation. Moreover, a significant improvement in rate performance compared to unmodified MnO2 is verified through electrochemical tests. The X-ray photoelectron spectroscopy (XPS) and EPR spectra showed that the doped Ag+ ions lead to oxygen vacancies due to the formation of Ag-O-Mn.[3] The abundant vacancies act as active sites, significantly improving conductivity and ion insertion rates. The ex-situ X-ray diffractometer (XRD) and electrochemical tests are used to investigate the ion insertion mechanism during charging/discharging operations. The Ag-MnO2 @ Al2O3 cathode is synthesized through a facile methodology with environment-friendly materials. The modified cathode exhibits promising performance, especially regarding cycling stability and rate performance, which will be a crucial step for developing high-performing cathodes in aqueous zinc-ion batteries.Reference:[1] Shi, W., Lee, W. S. V., & Xue, J. (2021). Recent development of Mn‐based oxides as zinc‐ion battery cathode. ChemSusChem, 14(7), 1634-1658.[2] Zhou, A., Xu, J., Dai, X., Yang, B., Lu, Y., Wang, L., ... & Li, J. (2016). Improved high-voltage and high-temperature electrochemical performances of LiCoO2 cathode by electrode sputter-coating with Li3PO4. Journal of Power Sources, 322, 10-16.[3] Pu, X., Li, X., Wang, L., Maleki Kheimeh Sari, H., Li, J., Xi, Y., ... & Wu, Y. (2022). Enriching Oxygen Vacancy Defects via Ag–O–Mn Bonds for Enhanced Diffusion Kinetics of δ-MnO2 in Zinc-Ion Batteries. ACS Applied Materials & Interfaces, 14(18), 21159-21172. Figure 1

Revisiting the Anodic Stability of Aluminum Current Collectors in High-Voltage Li-Ion Batteries

High-voltage Li-ion batteries are anticipated to play a crucial role in the present transition towards electric vehicles, owing to their high energy density. However, a big challenge is the anodic stability (often referred to as corrosion) of the positive electrodes current collector, aluminum (Al), at potentials > 3.0 V vs. Li+/Li). In this work, we present a systematic study on the corrosion of 12 µm-thick Al foil (©Gränges, Sweden) up to 5.0 V vs. Li+/Li in a series of carbonate electrolytes containing lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl) imide (LiFSI) or lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) salts. The selection of the 12 µm foil was motivated by the need to decrease the mass or volume of the dead weight components (i.e., current collector) to increase the energy density of the battery.The electrochemical behavior was investigated using voltammetric techniques, and the results indicated that the anodic oxidation of the 12 µm Al foil was similar to that of the conventionally used 20 µm-thick Al foil. Notably, the first anodic oxidation scan exhibited a two-step oxidation after 3.5 V vs. Li+/Li, suggesting carbonate solvent oxidation and a liberation of H+ ions attacking the native surface Al2O3 layer followed by oxidation of metallic Al. A passivation was observed on the subsequent scans in 1.0 M LiPF6 solutions due to formation of surface layer of AlF3, as confirmed by X-ray photoelectron spectroscopy (XPS) analyses. [1,2]However, in 1.0 M solutions of the imide salts (i.e., LiFSI or LiTFSI) a continuous anodic oxidation of aluminum was seen between 3.5 and 5.0 V vs. Li+/Li on the first few scans. After this the magnitude of the anodic current decreased significantly. The latter observations can be attributed to formation of soluble Al(TFSI) x or Al(FSI) x complexes [3] and a gradual saturation of the electrolyte. The voltammetric experiments showed that the magnitude of the anodic current increased when increasing the volume of the used imide electrolyte, supporting the saturation hypothesis.Results and analyses regarding the anodic oxidation of Al in a series of carbonate solvents and using different salt concentration, as well as effect of the use of carbon coated Al will also be presented.

Atomic Layer Deposition of HfAlOx for High-k Gate Dielectrics

Nowadays, the downscaling of CMOS devices requires continued effort to propose high performance components with extremely compact size. Surely, this trend is not achievable without extremely enhanced High-k gate stack materials, inter alia. For years, HfO2-based dielectrics deposited using ALD (Atomic Layer Deposition) technique are perfect dielectrics of choice for various devices and applications (Memristor, resistive random access memory, ferroelectric random access memory, antiferrolectric capacitances, ferroelectric FET...).As such, HfAlOx films present a good compromise between HfO2 and Al2O3 in term of coupling properties and insulating capabilities in comparison with both single HfO2 and Al2O3 films. The purpose of this work is to evaluate binary high-k HfAlOx dielectrics deposited by ALD technique. ALD is well suited for deposition of ultrathin films with exceptional capabilities enabling precise thickness, stoichiometry control and conformal growth at atomic scale. In this work, we focused on Al2O3/HfO2 films fabricated using two approaches: (i) repeatedly alternating the deposition of two different and separate extremely thin oxides (Al2O3 and HfO2; particular focus on HfO2/Al2O3/HfO2/Al2O3/HfO2 multilayer stack with equivalent Al fraction around 30%); (ii) combination of ALD super cycles allowing the formation HfAlOx layers. We analyze the general performance and the behavior of the binary high-k HfAlOx dielectrics (10 nm thin layers deposited at 300°C using TiCl4-TMA-H2O precursors) using physico-chemical (X-ray photoelectron spectroscopy XPS, X-ray reflectometry XRR, wavelength dispersive X-ray fluorescence WDXRF) and electrical measurements (Hg probe measurements, MIM capacitance).The incorporation of Al2O3 in the composition of the HfO2 gate dielectrics allows a perfect monitoring of physico-chemical properties varying from HfO2 layers to Al2O3 layers by controlling the number of Al2O3 and HfO2 ALD cycles. In this respect, we were able to monitor the Al fraction in the range of 5% to ~86% in the mixed binary dielectrics (Figure 1: XRR density of mixed binary layers vs Al/[Al+Hf] ratio, Figure 2: Al and Hf fractions in the mixed layer determined by WDXRF and XPS analysis).The electrical characteristics of the HfAlOx dielectrics confirm the influence of the Al fraction in the HfO2 layer. The leakage currents of the mixed layers decreases with increasing the Al fraction (Figure 3: J/E characteristics of mixed and stacked HfAlOx layers). The breakdown voltages for all mixed HfAlOx layers are greater than that of reference HfO2 layer. On the other hand, the shown multilayer presents an intermediate leakage currents profiles between the two mixed HfAlOx (25%Al and 40%Al). Thus, the incorporation of Al in the construction of HfAlOx system is likely to decrease the number of defects. Furthermore, the fully integrated MIM structures exhibit areal capacitance in the range 10-15 nF/mm2 of ALD-based high-k HfAlOx (10 to 12 nm) depending on the Al fraction. Thus, ALD-HfAlOx with various composition highlight the potential tremendous for high-κ capacitances stack for CMOS semiconductor devices. Figure 1

Nanoarray of Vivaldi Rectenna for Infrared-energy Harvesting

This article presents the design of an array of rectennas operating at 28.3 THz for infrared (IR) energy harvesting applications. The basic element of the array consists of a Vivaldi-dipole rectenna composed of two arms made with different conductors (gold and titanium). A metal-insulator-metal (MIM) tunnel diode is used to rectify the THz ac current. The proposed MIM diode consists of a very thin layer of Al2O3 sandwiched between the two metal electrodes. Arrays of two, three, and four rectennas are investigated. The improvement of the energy captured by coupling several elements in the same structure with a common gap is also investigated. This array architecture, without feeding network, may reduce the number of rectifying diodes and, therefore, decrease losses and increase the overall efficiency. Finally, it has been found that the four-elements rectenna array has a maximum electric field intensity of 62.4 × 104 V/m at 28.3 THz.

Compositional Grading of Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;/ZrO&lt;sub&gt;2&lt;/sub&gt;/SUS304 Hybrid Materials Using Centrifugal Slurry Methods and Spark Plasma Sintering

Ceramic/ metal functionally graded materials (FGMs) have been promising to sustain coating structures working under super high temperature as well as high temperature gradient conditions. Compositional gradients in the FGMs can be engineered according to functional performance requirements. This study aims to fabricate Al2O3/ZrO2/SUS304 hybrid FGMs with continuous compositional gradient manners using a combination of centrifugal slurry methods and spark plasma sintering (SPS). The compositional gradients in the FGMs were investigated on microstructures with elemental distributions and hardness on the cross sections of the FGMs. It was demonstrated that the compositions of ZrO2 and SUS304 continuously varied in the FGMs, while Al2O3 resided only on ZrO2-rich sides, which can effectively enhance the fracture toughness of the ZrO2-rich layer. Ball milling treatments can make the Al2O3 layer more formed in the ZrO2-rich layer. With increasing the amount of Al2O3, the Al2O3 layer resided closer to the top of the ZrO2 surfaces in the FGMs subject to ball milling treatments, which can prevent the crack propagation from the ZrO2 top surfaces.

Effect of Cu addition on the tribological properties and oxidation behavior of nanomultilayered AlTiN/Cu coatings

As a soft metal, the addition of Cu has an important influence on the high-temperature tribological properties and oxidation behavior of nanomultilayered AlTiN/Cu coatings. At room temperature (RT), due to abrasive wear, the AlTiN coating exhibited a high friction coefficient of 0.97 and low wear resistance. After adding Cu layer, the friction coefficient gradually decreased to 0.59 at 18.4 at.% Cu due to the lubricating effect of soft metal Cu and CuO, and the best wear resistance was achieved at 2.9 at.% Cu. At 800 °C, the oxidation resistance sharply reduced after adding Cu layer, and exhibited oxidation delamination. At low Cu contents (≤4.5 at.%), by the inward diffusion of O, a mixed oxide layer of Al2O3, TiO2, and CuO formed. At 18.4 at.% Cu, by the outward diffusion and oxidation of Cu, double-layer oxides formed, and the top layer of CuO contributed to a low friction coefficient of 0.53, but also caused a reduce in the wear resistance.

Effect of exposure temperature on the corrosion behavior of a FeNiCrCuAl high entropy alloy in supercritical water

The corrosion behavior of a FeNiCrCuAl high entropy alloy exposed to supercritical water at 380–650 °C and 25 MPa was investigated. The weight gain exhibited a nearly parabolic kinetics. At 380 °C, Al2O3 precipitated on Fe3O4 particles in FeCr-rich regions and intensified as the temperature increased to 650 °C, eventually resulting in an Al2O3 particle. A mixed Fe3O4 and NiAl2O4 outer layer developed on NiAl-rich regions at 380 °C, whereas an Al2O3 layer formed at 650 °C. Cu2O formed along the boundaries of NiAl-rich regions, regardless of exposure temperatures. The corrosion mechanism at different temperatures was elucidated.

Precursor Induced Assembly of Si Nanoparticles Encapsulated in Graphene/Carbon Matrices and the Influence of Al2O3 Coating on their Properties as Anode for Lithium-Ion Batteries.

The theoretical capacity of pristine silicon as anodes for lithium-ion batteries (LIBs) can reach up to 4200 mAh g-1, however, the low electrical conductivity and the huge volume expansion limit their practical application. To address this challenge, a precursor strategy has been explored to induce the curling of graphene oxide (GO) flakes and the enclosing of Si nanoparticles by selecting protonated chitosan as both assembly inducer and carbon precursor. The Si nanoparticles are dispersed first in a slurry of GO by ball milling, then the resulting dispersion is dried by a spray drying process to achieve instantaneous solution evaporation and compact encapsulation of silicon particles with GO. An Al2O3 layer is constructed on the surface of Si@rGO@C-SD composites by the atomic layer deposition method to modify the solid electrolyte interface. This strategy enhances obviously the electrochemical performance of the Si as anode for LIBs, including excellent long-cycle stability of 930 mAh g-1 after 1000 cycles at 1000mA g-1, satisfied initial Coulomb efficiency of 76.7%, and high rate ability of 806 mAh g-1 at 5000mA g-1. This work shows a potential solution to the shortcomings of Si-based anodes and provides meaningful insights for constructing high-energy anodes for LIBs.

Synergistic Improvement of Dielectric and Thermal Conductivity Properties for Polymers Filled with Multifunctional Modified Nanowires.

Dielectric composites are widely used in power electronics, power systems, aerospace, and other fields due to their extremely high power density. However, if their energy density can be further increased, the application range will be greatly improved. Improving the dielectric constant of composites is one of the most effective ways to increase the energy density. In this study, a preparation method for copper calcium titanate nanowires (CCTO-NWs) with adjustable aspect ratio was investigated. Upon incorporation of these CCTO-NWs into the polymer matrix, the nanocomposites exhibit a significantly higher dielectric constant and a lower dielectric loss. In addition, a thin layer of Al2O3 with excellent thermal conductivity is coated on the surface of the CCTO-NWs to form a core-shell structure nanowire CCTO-NW@Al2O3. The introduction of the thermal conductive layer of Al2O3 not only creates a continuous heat transfer path within the dielectric composite, increasing the thermal conductivity of the composite from 0.11 W/(m·K) of pure HIPS to 1.12 W/(m·K), but also serves as a buffer layer between HIPS and CCTO-NWs, effectively alleviating the electric field distortion caused by the large difference in the dielectric constant between them, thereby optimizing the dielectric properties of the composite and reducing the dielectric permeability threshold from 30 to 20 vol %. This work provides an effective strategy for synergistically improving the dielectric constant and thermal conductivity of dielectric composites while also taking into account the good flexibility of polymer/ceramic nanocomposites.

Macroencapsulation of sodium chloride by a double layer strategy for high temperature phase change thermal storage over 800 °C

To solve the key problems of high corrosiveness, easy leakage and low thermal conductivity of sodium chloride as phase change material (PCM) for high-temperature heat storage, this study reports a double-shell coating method to prepare centimeter-sized macrocapsules. The capsules are made of powder raw materials with the help of organic adhesives such as polyvinyl pyrrolidone and carboxymethyl cellulose for shape formation, in which the inner expanded graphite (EG) layer and the outer Al2O3 layer are coated on the salt core spheres and finally are sintered formed at high temperatures. The double-shell capsules can prevent salt from leakage because the inner EG layer is repellent to liquid salt, in contrast, the single Al2O3 shell is penetrated by liquid salt due to their wettability. After 100 cyclic tests, the double-shell capsules have good stability and high durability for long-term use. In order to improve the heat storage density of the capsules, the method of isostatically pressing the cores to increase the compactness is studied. At 200 MPa, the capsules in size of 20@2@2 show a high heat storage capacity of 1024.54 J/cm3 and 551.56 J/g from 600 to 900 °C. The double-shell encapsulated salt PCM can be widely used in high-temperature heat storage over 800 °C in solar thermal power plants and industrial waste heat recovery.

A New Al2 O3 -Protected EB-PVD TBC with Superior CMAS Resistance.

Calcium-magnesium-aluminium-silicate (CMAS) attack is a longstanding challenge for yttria stabilized zirconia (YSZ) thermal barrier coatings (TBCs) particularly at higher engine operating temperature. Here, a novel microstructural design is reported for YSZ TBCs to mitigate CMAS attack. The design is based on a drip coating method that creates a thin layer of nanoporous Al2 O3 around YSZ columnar grains produced by electron beam physical vapor deposition (EB-PVD). The nanoporous Al2 O3 enables fast crystallization of CMAS melt close to the TBC surface, in the inter-columnar gaps, and on the column walls, thereby suppressing CMAS infiltration and preventing further degradation of the TBCs due to CMAS attack. Indentation and three-point beam bending tests indicate that the highly porous Al2 O3 only slightly stiffens the TBC but offers superior resistance against sintering in long-term thermal exposure by reducing the intercolumnar contact. This work offers a new pathway for designing novel TBC architecture with excellent CMAS resistance, strain tolerance, and sintering resistance, which also points out new insight for assembly nanoporous ceramic in traditional ceramic structure for integrated functions.

Numerical Analysis of Williamson-Micropolar Ternary Nanofluid Flow Through Porous Rotatory Surface

This research introduces an advanced nanofluid model for optimizing the rate of heat transmission. The trihybrid nanofluid is constructed by suspending three distinct nanoparticles in a base fluid with diverse physical and chemical affinities. This study confronts the heat transfer characteristics of TiO2, Al2O3, and SiO2 boundary layer flow involving thermal radiation and slip scenarios. The controlling boundary layer equations are modified through an array of ordinary differential equations employing suitable similarity transformations, which have been solved by using bvp4c algorithm in MATLAB. As of yet, no prior investigation has ever been conducted on the flow of tri-hybrid nanofluid TiO2, Al2O3, and SiO2/H2O via rotatory surface. As a result, the current investigation has been undertaken to fill this gap, and the primary objectives of this work is to look into the aspects that optimise the heat transfer of base fluid (H2O) dissolved with tri-hybrid nanoparticles (TiO2, Al2O3, and SiO2) past a rotatory surface with slip conditions. The figures indicate that the presence of distinct nondimensional parameters in this analysis has a tremendous impact on the fluid motion inside the boundary layer. The plots obtained reveal that the diminution in particle movement is addressed simply by raising the Williamson parameter, magnetic parameter, and Forchheimer parameter. While the temperature profiles of the magnetic parameter, rotation parameter, and Williamson parameter demonstrate a reverse pattern. The findings are visualized in graphical format, and it is predicted that the tri-hybrid nanofluid has a greater thermal conductivity than the hybrid nanofluid and traditional fluid.

Hindered Aluminum Plating and Stripping in Urea/NMA/Al(OTF)3 as a Cl-Free Electrolyte for Aluminum Batteries

Conventional electrolytes for aluminum metal batteries are highly corrosive because they must remove the Al2O3 layer to enable plating and stripping. However, such corrosiveness impacts the stability of all cell parts, thus hampering the real application of aluminum-metal batteries. The urea/NMA/Al(OTF)3 electrolyte is a non-corrosive alternative to the conventional [EMImCl]: AlCl3 ionic liquid electrolyte (ILE). Unfortunately, this electrolyte demonstrates poor Al plating/stripping, probably because (being not corrosive) it cannot remove the Al2O3 passivation layer. This work proves that no plating/stripping occurs on the Al electrode despite modifying the Al surface. We highlight how urea/NMA/Al(OTF)3 electrolyte and the state of the Al electrode surface impact the interphase layer formation and, consequently, the likelihood and reversibility of Al plating/stripping. We point up the requirement for carefully drying electrolyte mixture and components, as water results in hydrogen evolution reaction and creation of an insulating interphase layer containing Al(OH)3, AlF3, and re-passivated Al oxide, which finally blocks the path for the possible Al plating/stripping.

Antiferroelectric nano-heterostructures filler for improving energy storage performance of PVDF-based composite films

Incorporating high permittivity inorganic ferroelectric in polymer dielectrics is the most prevalent and straightforward approach to improve their energy storage capacity, which has an extensive application prospect in power electronic circuits owing to their higher power density. However, the discharged energy density attained with these materials are mainly restrained by the high remnant electric displacement of ferroelectric and the large discrepancy in permittivity between inorganic and organic substance. Herein, we proposed a novel antiferroelectric (Pb0.875La0.05Sr0.05)(Zr0.595Sn0.4Ti0.005)O3@Al2O3 (PLSZST@AO) nano-heterostructure as fillers to fabricate nanocomposite films, wherein the Al2O3 layer with wide band gap and dielectric constant close to that of the PVDF matrix was encapsulated onto the antiferroelectric nanoparticle PLSZST to alleviate the discrepancy in permittivity and enhance the breakdown strength. Especially, the experimental results and computational simulations confirmed that the presence of Al2O3 layer is capable of effectively enhancing the electric displacement and breakdown strength, while reducing the remnant displacement and impeding the formation of electrical trees. As a result, the nanocomposite films exhibited an impressive discharged energy density of 18.2 J/cm3 along with a remarkably enhanced energy storage efficiency of 70 % near the high electrical breakdown strength of 594.7 MV/m when the fillers content was 3 wt%, which was far surpassed the pristine PVDF (Ud = 5.34 J/cm3 and η = 51.8 %). Together with its excellent mechanical strength, the monolayer film was verified to be an outstanding performance dielectric material, outperforming the current PVDF-based composite dielectrics for high-power energy storage capacitors. This work allowed for more versatility in designing and manufacturing flexibility nanocomposite films, which can contribute to improving their performance and practicality.

Stable and wide spectrum response Zn3As2/Al2O3 photocatalyst for photocatalytic overall water splitting

Constructing highly efficient and durable non-noble-metal photocatalysts with a broad spectral response for promoting sluggish photocatalyticover water splitting reaction is very desirable but still challenging. To realize scalable hydrogen production, an energy conversion efficiency of 10 % and stable photocatalysts with broad light-absorption are required. To this end, a wide spectrum response Zn3As2/Al2O3 has been successfully synthesized by a layer-by-layer coating method as a photocatalyst utilized in the hydrogen evolution reaction (HER) for the first time, which gave the HER rate of 92.5 μmol·g−1·h−1. The HER activity did not decline obviously after three runs. Characterization results and photocatalytic performance confirmed that the Al2O3 layer could protect Zn3As2 from photocorrosion, which exhibited preeminent stability and outstanding photocatalytic performance. In addition, Zn3As2/Al2O3 showed light response extending to ∼1300 nm, and more efficient separation capability of photogenerated charges benefited from the built-in electric field between Al2O3 and Zn3As2, which were verified by UV–Vis–NIR DRS and electrochemical measurements. Our research results may provide a new route of design and construction of stable and efficacious photocatalysts to realize solar energy conversion to hydrogen.