Al2 O3 Research Articles

Research on the microstructure and diffusion behavior of CVD aluminide coatings on inconel 718 superalloy

Coating performance fundamentally depends on the microstructure, which is further closely related to the diffusion behavior, especially for the diffusion coatings. Present work investigated the diffusion behavior and microstructure of the aluminide coating prepared by chemical vapor deposition (CVD) on the Inconel 718 superalloy. It was shown that the aluminide coating had a significant layered characteristic influenced by the alloy elements, where the outer layer was β-NiAl, and the beneath inter-diffusion layer consisted of TCP phases (Fe2Nb, Nb(Cr, Fe) and Cr3(Fe, Ni)2) and carbides (Nb6C5). The Y-modified coating additionally contained Y-rich phase in the outer layer, which will transform into (Y, Al)2O3 when exposed to air. Furthermore, a concentration gradient of Al in the outer layer was found, which can be associated with the outward diffusion of the alloying elements, and this phenomenon was effectively alleviated due to Y modification. The results of first-principles calculations further revealed the inhibition of Al diffusion by the substrate elements, whereas the case was opposite for Y.

AlN reinforced Fe activated sintered tungsten matrix composites: Mechanical properties, fracture behaviors and reinforcement mechanisms

In this study, AlN particles were proposed as the reinforcement to prepare Fe activated sintered tungsten matrix composites. The results indicated that the AlN particles stably existed inside the W(Fe) matrix and exhibited a significant strengthening and toughening effect. Compared with the W(Fe) material, the maximum microhardness, flexural strength and fracture toughness of the composites were increased by 101.42%, 66.29% and 64.63%, respectively. An AlN content-AlN particle size-composite fracture mode map was constructed to classify the four fracture modes of the composites. In addition to the fine grain strengthening and residual stress strengthening, a novel “oxygen purification strengthening effect” was found, which resulted from the thin (Fe,Al)2O3 reaction layer formed at the AlN/W(Fe) matrix interface.

The Relation between Nature and Stability of H2‐Dissociating Sites and Propene Selectivity in Silica‐Supported (Ga,Al)2O3 Mixed Oxide Propane Dehydrogenation Catalysts

AbstractColloidal solutions of gallia‐alumina (Ga,Al)2O3(x:y) solid‐solution nanoparticles with nominal atomic Ga : Al (x:y) ratios of 1 : 6, 1 : 3, 3 : 1, and 1:0 were used to prepare silica‐supported catalysts for propane dehydrogenation (PDH). A comparison of the unsupported and silica‐supported catalysts reveals that the dispersion on silica increases the Ga‐normalized PDH rates for all catalysts, albeit with a notably lower propene selectivity for (Ga,Al)2O3(1:6)/SiO2. Fourier transform infrared (FTIR) spectroscopy allows contrasting the H2 dissociation sites in the calcined and H2‐treated (Ga,Al)2O3(x:y)/SiO2, indicating a transformation of Ga3+ surface sites with Al (mainly) and Ga atoms in the second coordination sphere (Ga(Al/Ga) sites) in the calcined (Ga,Al)2O3(1:6)/SiO2 to predominantly Ga(Ga/Si) surface sites in the H2‐treated material. The resulting sites are similarly unselective as in amorphous gallia on silica. H2 produced during the PDH reaction can cause a similar transformation as H2 pretreatment in (Ga,Al)2O3(1:6)/SiO2, rapidly resulting in a notably lowered selectivity. The stable and selective Ga(Al/Ga) surface sites in (Ga,Al)2O3(1:3)/SiO2 yield a Ga−H band at ca. 1990 cm−1 under H2 dissociation conditions while the less selective surface sites, observed for the other Ga : Al ratios, give Ga−H bands at ca. 2040 and 2060 cm−1.

Phase formation, structure and properties of quaternary MAX phase thin films in the Cr-V-C-Al system: A combinatorial study

Tailoring of individual atomic layers via alloying to synthesize quaternary MAX phases allows for expanding their chemical diversity and fine-tuning of their properties. In this study, Cr-V/C/Al multilayered precursors were deposited via combinatorial magnetron sputtering, creating nanostructured architectures with periodic stacking of nanolayers and varying Cr:V ratios. Their phase transformation and underlying reaction mechanisms during subsequent thermal annealing in argon towards the prospective quaternary solid solution (CrV)n+1AlCn MAX phases formation was systematically studied. Crystallization of (CrV)2AlC starts at approximately 500°C, while growth of higher-ordered (CrV)4AlC3 is observed from 960°C. Notably, intergrowth of (CrV)2AlC and (CrV)4AlC3 structures with coherent interface suggests that (CrV)2AlC acts as template for nucleation of (CrV)4AlC3. Thermal stability and high-temperature oxidation tests found that (CrV)2AlC exhibits higher thermal stability compared to (CrV)4AlC3 and films with Cr72.7V27.3 displayed good oxidation resistance at 1000°C, forming a protective bilayer oxide scale consisting of (Cr,Al)2O3 and Al2O3.

Carrier gradient core-double shell structure with heterojunction transition layer for significantly enhancing dielectric properties

In this work, to prohibit the undesirable large dielectric loss and electric-field distortion of the conductive fillers/polymer with a high dielectric constant, TiO2 (TO) and Al2O3 (AO) shells were successively coated on the surface of amorphous carbon (C) to prepare the C@TO@AO core-double shell nanoparticles. This novel design of gradually varying the multilayer hierarchical interface achieved the gradient reduction of carrier concentration from the C core to the TO and AO layers. And the introduction of the multilayer hierarchical interface was advantageous to the enhancement of interface polarization. Moreover, the excellent integrated dielectric properties could be effectively achieved by adjusting the layer thickness and crystal structure of the TO layer. It was worth noting that the TO transition layer with anatase and rutile heterojunctions (HTO) had a significant enhancement in the dielectric constant of the composites induced by the strength of interfacial polarization and built-in electric field inside the HTO layer. Furthermore, the simulated electric field distribution inside the composites was further investigated to reveal the mechanism of enhanced dielectric properties. This work exerts important guiding significance for the reasonable structure design and the elaborate regulation of the shell micro-structures to improve the dielectric properties of composites.

Enhanced dielectric properties of nanocomposites with cyanoethyl cellulose and core‐shell structured BaTiO3@Al2O3 fillers

AbstractThe interface between the polymer matrix and inorganic fillers plays a determinative role in dielectric properties of the composites. In this work, dielectric composites containing core‐shell structured BaTiO3@Al2O3 (BT@AO) nanoparticles and cyano functionalized cellulose (cyanoethyl cellulose, CEC) were prepared to achieve enhanced interface and dielectric properties. With the wide bandgap Al2O3 (AO) shell, the carrier motion inspired by elevating electric filed and temperature was significantly impeded in the composites. Meanwhile, the moderate dielectric constant and surface energy of AO shell between CEC and BaTiO3 (BT) alleviated the inhomogeneous local electric field distribution and improve the interfacial compatibility between inorganic filler and CEC matrix. As a result, enhanced dielectric properties including restrained dielectric loss (0.23 for BT@AO/CEC versus 0.51 for BT/CEC at 100 Hz), suppressed conductivity, increased breakdown strength and improved dielectric constant were accessed in the BT@AO/CEC composites. The excellent thermal conductivity of AO also offered the composites with additional advantage of low electrical conductivity at high temperature of 100°C (1.56 × 10−10 S/cm) exhibiting two orders of magnitude smaller than that of pure CEC.Highlights Core‐shell structured BaTiO3@Al2O3 were prepared and incorporated into cyanoethylated cellulose to yield flexible nanocomposites. Carrier motion was significantly restricted by the wide band gap of Al2O3 shell. Enhanced interfacial compatibility was accessed in the BaTiO3@Al2O3/CEC composite. Improved dielectric properties and thermal conductivity were achieved.

Si-doped (AlGa)2O3 growth on a-, m- and r-plane α-Al2O3 substrates by molecular beam epitaxy

We reported the growth of (AlGa)2O3 layers on (11 2¯ 0), (10 1¯ 0), and (10 1¯ 2) α-Al2O3 substrates using MBE, and the electrical characterization of Si-doped (AlGa)2O3 layers. The Ga2O3 layers grown on (10 1¯ 0) and (10 1¯ 2) α-Al2O3 were α-phase single crystals, while the Ga2O3 layer grown on (11 2¯ 0) α-Al2O3 consisted of (11 2¯ 0) α-Ga2O3 and ( 2¯ 01) β-Ga2O3. The Al composition of the (11 2¯ 0) and (10 1¯ 0) (AlGa)2O3 layers was controlled by varying the Al flux. The Si-doped (10 1¯ 0) α-(Al x Ga1-x )2O3 layers with x = 0–0.41 were electrically conducting.

Solution-Processable Route for Large-Area Uniform 2D Semiconductor Nanofilms.

The semiconductor thin film engineering technique plays a key role in the development of advanced electronics. Printing uniform nanofilms on freeform surfaces with high efficiency and low cost is significant for actual industrialization in electronics. Herein, a high-throughput colloidal printing (HTCP) strategy is reported for fabricating large-area and uniform semiconductor nanofilms on freeform surfaces. High-throughput and uniform printing rely on the balance of atomization and evaporation, as well as the introduced thermal Marangoni flows of colloidal dispersion, that suppresses outward capillary flows. Colloidal printing with in situ heating enables the fast fabrication of large-area semiconductor nanofilms on freeform surfaces, such as SiO2/Si, Al2O3, quartz glass, poly(ethylene terephthalate) (PET), Al foil, plastic tube, and Ni foam, expanding their technological applications where substrates are essential. The printed SnS2 nanofilms are integrated into thin-film semiconductor gas sensors with one of the fastest responses (8 s) while maintaining the highest sensitivity (Rg/Ra = 21) (toward 10ppm NO2), as well as an ultralow limit of detection (LOD) of 46 ppt. The ability to print uniform semiconductor nanofilms on freeform surfaces with high-throughput promises the development of next-generation electronics with low cost and high efficiency.

Interface Engineering Enables Wide-Temperature Li-Ion Storage in Commercial Silicon-Based Anodes.

Silicon-based materials have been considered potential anode materials for next-generation lithium-ion batteries based on their high theoretical capacity and low working voltage. However, side reactions at the Si/electrolyte interface bring annoying issues like low Coulombic efficiency, sluggish ionic transport, and inferior temperature compatibility. In this work, the surface Al2 O3 coating layer is proposed as an artificial solid electrolyte interphase (SEI), which can serve as a physical barrier against the invasion of byproducts like HF(Hydrogen Fluoride) from the decomposition of electrolyte, and acts as a fast Li-ion transport pathway. Besides, the intrinsically high mechanical strength can effectively inhibit the volume expansion of the silicon particles, thus promoting the cyclability. The as-assembled battery cell with the Al2 O3 -coated Si-C anode exhibits a high initial Coulombic efficiency of 80% at RT and a capacity retention ratio up to ≈81.9% after 100 cycles, which is much higher than that of the pristine Si-C anode (≈74.8%). Besides, the expansion rate can also be decreased from 103% to 50%. Moreover, the Al2 O3 -coated Si-C anode also extends the working temperature from room temperature to 0 °C-60 °C. Overall, this work provides an efficient strategy for regulating the interface reactions of Si-based anode and pushes forward the practical applications at real conditions.

2Memristor-1Capacitor Integrated Temporal Kernel for High-Dimensional Data Mapping.

Compact but precise feature-extracting ability is core to processing complex computational tasks in neuromorphic hardware. Physical reservoir computing (RC) offers a robust framework to map temporal data into a high-dimensional space using the time dynamics of a material system, such as a volatile memristor. However, conventional physical RC systems have limited dynamics for the given material properties, restricting the methods to increase their dimensionality. This study proposes an integrated temporal kernel composed of a 2-memristor and 1-capacitor (2M1C) using a W/HfO2/TiN memristor and TiN/ZrO2/Al2O3/ZrO2/TiN capacitor to achieve higher dimensionality and tunable dynamics. The kernel elements are carefully designed and fabricated into an integrated array, of which performances are evaluated under diverse conditions. By optimizing the time dynamics of the 2M1C kernel, each memristor simultaneously extracts complementary information from input signals. The MNIST benchmark digit classification task achieves a high accuracy of 94.3% with a (196×10) single-layer network. Analog input mapping ability is tested with a Mackey-Glass time series prediction, and the system records a normalized root mean square error of 0.04 with a 20×1 readout network, the smallest readout network ever used for Mackey-Glass prediction in RC. These performances demonstrate its high potential for efficient temporal data analysis.

Direct In- and Out-of-Plane Writing of Metals on Insulators by Electron-Beam-Enabled, Confined Electrodeposition with Submicrometer Feature Size.

Additive microfabrication processes based on localized electroplating enable the one-step deposition of micro-scale metal structures with outstanding performance, e.g., high electrical conductivity and mechanical strength. They are therefore evaluated as an exciting and enabling addition to the existing repertoire of microfabrication technologies. Yet, electrochemical processes are generally restricted to conductive or semiconductive substrates, precluding their application in the manufacturing of functional electric devices where direct deposition onto insulators is often required. Here, the direct, localized electrodeposition of copper on a variety of insulating substrates, namely Al2O3, glass and flexible polyethylene, is demonstrated, enabled by electron-beam-induced reduction in a highly confined liquid electrolyte reservoir. The nanometer-size of the electrolyte reservoir, fed by electrohydrodynamic ejection, enables a minimal feature size on the order of 200nm. The fact that the transient reservoir is established and stabilized by electrohydrodynamic ejection rather than specialized liquid cells can offer greater flexibility toward deposition on arbitrary substrate geometries and materials. Installed in a low-vacuum scanning electron microscope, the setup further allows for operando, nanoscale observation and analysis of the manufacturingprocess.

Analysis of dislocation defects in compositionally step-graded α-(Al x Ga1-x )2O3 layers.

The ultra-wide bandgap semiconductor α-Ga2O3 can be heteroepitaxially grown on a sapphire substrate. However, due to a lattice mismatch of about 4.6% with a sapphire substrate, many dislocation defects occur in α-Ga2O3 films. To reduce the dislocation density, compositionally step-graded α-(Al x Ga1-x )2O3 layers were fabricated on a c-plane sapphire substrate using mist CVD. TEM measurements revealed few dislocations in the initial layer of α-(Al0.96Ga0.04)2O3, but numerous dislocations were observed in the subsequent layer of α-(Al0.84Ga0.16)2O3. However, the step-graded α-(Al x Ga1-x )2O3 layers exhibited bending of the dislocations under both compressive and tensile strains due to compositional differences of α-(Al x Ga1-x )2O3, resulting in about 50% reduction of the dislocation density in the high-Ga-composition layer of α-(Al x Ga1-x )2O3. The introduction of multiple 50 nm α-Ga2O3 layers into the compositionally step-graded α-(Al x Ga1-x )2O3 layers resulted in a notable reduction in dislocation defects at the interface between the sandwiched α-Ga2O3 layers. It is assumed that the dislocations were bent by the strain caused by the composition change, resulting in a decrease in the number of dislocations. It is anticipated that further reduction of dislocation density will be achieved by optimizing the composition change and thicknesses of layers that provide effective strain for dislocation bending, and by stacking these layers.

Unifying and Suppressing Conduction Losses of Polymer Dielectrics for Superior High-Temperature Capacitive Energy Storage.

Superior high-temperature capacitive performance of polymer dielectrics is critical for the modern film capacitor demanded in the harsh-environment electronic and electrical systems. Unfortunately, the capacitive performance degrades rapidly at elevated temperatures owing to the exponential growth of conduction loss. The conduction loss is mainly composed of electrode and bulk-limited conduction. Herein, the contribution of surface and bulk factors is unified to conduction loss, and the loss is thoroughly suppressed. The experimental results demonstrate that the polar oxygen-containing groups on the surface of polymer dielectrics can act as the charge trap sites to immobilize the injected charges from electrode, which can in turn establish a built-in field to weaken the external electric field and augment the injection barrier height. Wide bandgap aluminum oxide (Al2 O3 ) nanoparticle fillers can serve as deep traps to constrain the transport of injected or thermally activated charges in the bulk phase. From this, at 200 °C, the discharged energy density with a discharge-charge efficiency of 90% increases by 1058.06% from 0.31 J cm-3 for pristine polyetherimide to 3.59 J cm-3 for irradiated composite film. The principle of simultaneously inhibiting the electrode and bulk-limited conduction losses could be easily extended to other polymer dielectrics for high-temperature capacitive performance.

"Soggy-Sand" Chemistry for High-Voltage Aqueous Zinc-Ion Batteries.

The narrow electrochemical stability window, deleterious side reactions, and zinc dendrites prevent the use of aqueous zinc-ion batteries. Here, aqueous "soggy-sand" electrolytes (synergistic electrolyte-insulator dispersions) are developed for achieving high-voltage Zn-ion batteries. How these electrolytes bring a unique combination of benefits, synergizing the advantages of solid and liquid electrolytes is revealed. The oxide additions adsorb water molecules and trap anions, causing a network of space charge layers with increased Zn2+ transference number and reduced interfacial resistance. They beneficially modify the hydrogen bond network and solvation structures, thereby influencing the mechanical and electrochemical properties, and causing the Mn2+ in the solution to be oxidized. As a result, the best performing Al2 O3 -based "soggy-sand" electrolyte exhibits a long lifeof 2500 h in Zn||Zn cells. Furthermore, it increases the charging cut-off voltage for Zn/MnO2 cells to 2V, achieving higher specific capacities. Even with amass loading of 10 mgMnO2 cm-2 , it yields a promising specific capacity of 189 mAh g-1 at 1 A g-1 after 500 cycles. The concept of "soggy-sand" chemistry provides a new approach to design powerful and universal electrolytes for aqueous batteries.

Adhesive Performance of Resin Cement to Glass-Ceramic and Polymer-Based Ceramic CAD/CAM Materials after Applying Self-Etching Ceramic Primer or Different Surface Treatments.

Ensuring optimum bond strength during cementation is vital for restoration success, with the practicality of the process being crucial in clinical practice. This study analyzed the effect of a single-step self-etching ceramic primer (MEP) and various surface treatments on the microshear bond strength (µSBS) between resin cement and glass-ceramic or polymer-based ceramic CAD/CAM materials. Specimens were fabricated from leucite-based glass-ceramic (LEU), lithium disilicate glass-ceramic (LDC), resin nanoceramic (RNC), and polymer infiltrated ceramic network (PICN) (n = 160). They were then classified based on the surface treatments (n = 10): control (no treatment); sandblasting with Al2O3 (AL); etching with hydrofluoric acid (HF); and MEP application. Scanning electron microscopy was used to evaluate the surface topography. µSBS was measured after cementation and thermocycling procedures. Failure modes were examined with a stereomicroscope. Statistical analysis involved two-way analysis of variance and Tukey HSD tests with a significance level of 0.05. µSBS was significantly influenced by both surface treatment and CAD/CAM material type. The most enhanced µSBS values for each material, regarding the surface treatment, were: LEU and LDC, HF; RNC, AL; PICN, AL or HF. MEP significantly increased the µSBS values of CAD/CAM materials except RNC, yet it did not yield the highest µSBS values for any of them.

Dual Interface Compatibility Enabled via Composite Solid Electrolyte with High Transference Number for Long-Life All-Solid-State Lithium Metal Batteries.

The development of solid-state electrolytes (SSEs) effectively solves the safety problem derived from dendrite growth and volume change of lithium during cycling. In the meantime, the SSEs possess non-flammability compared to conventional organic liquid electrolytes. Replacing liquid electrolytes with SSEs to assemble all-solid-state lithium metal batteries (ASSLMBs) has garnered significant attention as a promising energy storage/conversion technology for the future. Herein, a composite solid electrolyte containing two inorganic components (Li6.25Al0.25La3Zr2O12, Al2O3) and an organic polyvinylidene difluoride matrix is designed rationally. X-ray photoelectron spectroscopy and density functional theory calculation results demonstrate the synergistic effect among the components, which results in enhanced ionic conductivity, high lithium-ion transference number, extended electrochemical window, and outstanding dual interface compatibility. As a result, Li||Li symmetric battery maintains a stable cycle for over 2500h. Moreover, all-solid-state lithium metal battery assembled with LiNi0.6Co0.2Mn0.2O2 cathode delivers a high discharge capacity of 168mAhg-1 after 360 cycles at 0.1C at 25°C, and all-solid-state lithium-sulfur battery also exhibits a high initial discharge capacity of 912mAhg-1 at 0.1C. This work demonstrates a long-life flexible composite solid electrolyte with excellent interface compatibility, providing an innovative way for the rational construction of next-generation high-energy-density ASSLMBs.

Revealing the Deposition Mechanism of the Powder Aerosol Deposition Method Using Ceramic Oxide Core-Shell Particles.

The powder aerosol deposition (PAD) method is a process to manufacture ceramic films completely at room temperature. Since the first reports by Akedo in the late 1990s, much research has been conducted to reveal the exact mechanism of the deposition process. However, it is still not fully understood. This work tackles this challenge using core-shell particles. Two coated oxides, Al2 O3 core with a SiO2 shell andLiNi0.6 Mn0.2 Co0.2 O2 core with a LiNbO3 shell, are investigated. Initially, the element ratios Al:Si and Ni:Nb of the powder are determined by energy-dispersive X-ray spectroscopy (EDX). In a second step, the change in the element ratios of Al:Si and Ni:Nb after deposition is investigated. The element ratios from powder to film strongly shift toward the shell elements, indicating that the particles fracture and only the outer parts of the particles are deposited. In the last step, this work investigates cross-sections of the deposited films with scanning transmission electron microscopy (STEM combined with EDX and an energy-selective back-scattered electron (EsB) detector to unveil the element distribution within the film itself. Therefore, the following overall picture emerges: particles impact on the substrate or on previously deposited particle, fracture, and only a small part of the impacting particles that originate from the outer part of the impacting particle gets deposited.

Ultra-Low Current 10 nm Spin Hall Nano-Oscillators.

Nano-constriction based spin Hall nano-oscillators (SHNOs) are at the forefront of spintronics research for emerging technological applications, such as oscillator-based neuromorphic computing and Ising Machines. However, their miniaturization to the sub-50 nm width regime results in poor scaling of the threshold current. Here, it shows that current shunting through the Si substrate is the origin of this problem and studies how different seed layers can mitigate it. It finds that an ultra-thin Al2 O3 seed layer and SiN (200 nm) coated p-Si substrates provide the best improvement, enabling us to scale down the SHNO width to a truly nanoscopic dimension of 10 nm, operating at threshold currents below 30 A. In addition, the combination of electrical insulation and high thermal conductivity of the Al2 O3 seed will offer the best conditions for large SHNO arrays, avoiding any significant temperature gradients within the array. The state-of-the-art ultra-low operational current SHNOs hence pave an energy-efficient route to scale oscillator-based computing to large dynamical neural networks of linear chains or 2Darrays.

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.

Multi-step differential transform method for both Hall currents and mixed convection effects on MHD flow of non-Newtonian fluid with Al2 O3 nanoparticles

Multi-step differential transform method for both Hall currents and mixed convection effects on MHD flow of non-Newtonian fluid with Al2 O3 nanoparticles