Al2O3 Layer Research Articles

Influence of the mechanical activation process on the corrosion of Ti2⁠AlN MAX phase obtained by hot pressing

The Ti2AlN MAX phase is known for its unique blend of metallic and ceramic properties, including high electrical and thermal conductivity and excellent oxidation and corrosion resistance. This study focuses on the influence of the mechanical activation process on the electrochemical properties of Ti2AlN in a saline environment. High-purity powders of AlN and Ti were mechanically activated or mixed and sintered to synthesize the Ti2AlN MAX phase. The electrochemical behavior was assessed through potentiodynamic curves and electrochemical impedance spectroscopy, while surface characteristics were analyzed using SEM-EDS and XPS post-exposure to a 3.5% NaCl solution. Results reveal that Ti2AlN forms protective Al2O3 and TiO2 layers, enhancing its corrosion resistance. Mechanically activated samples (MAP) displayed different corrosion behavior than non-activated samples (NMAP), with MAP showing reduced corrosion resistance. This discrepancy is attributed to differences in oxide formation and microstructural changes due to mechanical activation. This research not only elucidates the corrosion mechanisms of MAX phases in chloride-rich environments but also analyzes the effect of mechanical processing on their properties, contributing to developing Ti2AlN applications where high durability and resistance are critical.

Electrodeposition of Sacrificial Layer, Al2O3/ZnTPP film, onto NiTi Orthodontic Wire: Surface Characterizations and Electrochemical Investigations

Background: NiTi (nickel-titanium) alloy wires are widely used in orthodontics due to their unique properties, such as shape memory and superelasticity. However, these wires can be susceptible to corrosion in the oral environment, which can compromise their mechanical performance and longevity. Zinc tetraphenyl porphyrin (ZnTPP) is a corrosion inhibitor that forms a protective layer on the aluminum oxide (Al2O3) surface, acting as a barrier against corrosive agents. Objective: The electrodeposition of a sacrificial layer of Al2O3 with ZnTPP was carried out onto Ni- Ti orthodontic wire to enhance the corrosion resistance. Methods: 10 mM aluminum nitrate was dissolved in 10 mL of 0.1 M phosphate buffer solution (PBS), which was used as an electrolyte. Firstly, electrodeposition of Al2O3 on NiTi wire was carried out by using cyclic voltammetry by potential scanning between 0 and -2.0 V at a scan rate of 50 mV/s for 50 cycles. Secondly, 10 mL of 1 mM ZnTPP in 0.1 M PBS and ethanol (1:1) was prepared and used as an electrolyte. Electrodeposition of ZnTPP onto Al2O3/NiTi wire was achieved by cyclic voltammetry through the potential window of 0 to -2.0 V at a scan rate of 50 mV/s for 50 cycles. Results: The ZnTPP/Al2O3/NiTi wire displayed a potentiodynamic polarization resistance of 412931 Ω, with high stability compared to the bare NiTi wire (396421 Ω). Additionally, the corrosion rate for the ZnTPP/Al2O3/NiTi wire was measured as 0.254 mm/year, which was notably lower than that of the bare NiTi wire (0.540 mm/year). This decrease in corrosion rate can be attributed to the presence of the ZnTPP/Al2O3 film, which renders the NiTi wire electrically insulative and significantly increases its impedance compared to the bare NiTi wire. Conclusion: The bilayer coating of Al2O3 and ZnTPP has proven to significantly improve the corrosion resistance and stability of the wires. Thus, these materials can be considered for coating orthodontic archwires with improved corrosion stability.

Insight into the oxidation behavior and excellent internal oxidation and nitridation resistance of Fe71.5-x(Ni, Cr, Ti)28.5Alx complex concentrated alloys by advanced characterization

For precipitate-strengthened alloys, the decomposition of the precipitates at the subsurface during high-temperature oxidation is detrimental to mechanical properties. In this study, we adjusted Al concentrations in Fe71.5-x(Ni, Cr, Ti)28.5Alx (x = 8, 12, and 16 at. %) complex concentrated alloys (CCAs) to precipitate elongated cuboidal L21 with higher density and Al concentration, as well as reduced inter-precipitate spacing. This is more conducive to the rapid diffusion of Al to the matrix and grain boundaries, promoting the formation of a continuous and compact Al2O3 layer with random crystallographic orientation at 800 °C in air. This not only inhibits the further decomposition of the L21 phase but also avoids internal oxidation and nitridation.

Study on the High-Temperature Oxidation of AlCrFeCoNi-Based High-Entropy Alloys with Trace Si Additions

This research investigates the isothermal oxidation behavior of AlCrFeCoNiSix (x = 0, 0.04, 0.08, 0.12at.%) at 900°C for 96hours from multiple aspects, including the oxidation surface, the oxide layer microstructure, and the oxidation mechanisms. The oxidation kinetics curves of the alloys follow the parabolic oxidation law. After 96hours of oxidation at 900°C, the oxide films of the AlCrFeCoNi and AlCrFeCoNiSi0.04 alloys are primarily composed of Al2O3. In contrast, the oxide films of the Si8 and AlCrFeCoNiSi0.12 alloys consist of an outer layer of Cr2O3/spinel oxides and an inner layer of Al2O3.The results show that the third element effect triggered by the addition of Si can promote the generation of an Al2O3 layer, which has a positive effect on the antioxidant of high-entropy alloys.

Structural modification of MgO/Au thin films by aluminum Co-doping and related studies on secondary electron emission

The secondary electron emission (SEE) has the potential applications in electron multiplication, mass spectrometer, scanning electron microscope, photomultiplier tubes and so on. Among these, the electron multiplier (EM) based on MgO/Au thin film has attracted great attention over the past few years. Here, we design a new kind of MgO thin film by co-doping of gold and aluminum elements based on the structural modification through reactive magnetron sputtering method. The doping of Al into MgO/Au film gives a rise to the maximum SEE coefficient (δmax) between 9.02 and 10.23 while the optimal decay rate is around 10.4 % after 2 h of consistent electron bombardment. Herein, we also improved the stability of the film stored in air by sputtering Al2O3 layer on it. For the sample sputtered with the protecting layer Al2O3, its SEE coefficient (δ) at the incident electron energy of 200 eV still kept at a relatively high level that exceed 4.5 after stored in air for 72 h. The film properties after Al and Au co-doping are investigated in detail by the SEM, AFM, XPS and UV-VIS spectroscopy. Our results provide a new candidate for SEE layer in the application of long lifespan vacuum electron devices.

Antioxidant Behavior of Carbon/Carbon Composites with Hot Dip Plating and Electroplating for Single-Crystal Furnaces

In the Czochralski single-crystal silicon manufacturing industry, single-crystal furnaces often experience corrosion from silicon vapor, which reduces their operational lifespan. However, the preparation of metal coatings on the surface of C/C composites is challenging due to their low coefficient of thermal expansion and the intricate structure of carbon fibers. To address this issue and achieve high-quality alloy coatings, Ni-Al and Ni-Al/Si composite coatings are successfully prepared on the surface of C/C composites through a combination of electroplating and hot-dip plating, and their oxidation behavior at elevated temperatures is thoroughly investigated. The experimental results indicate that the Ni-Al composite coatings exhibit superior antioxidant properties compared to Ni coatings following thermal shock experiments, thereby significantly enhancing the antioxidant performance of C/C composites. This improvement is attributed to the preferential oxidation of surface aluminum, which forms a dense Al2O3 layer in aerobic and high-temperature environments, effectively preventing oxygen from reaching the underlying matrix. During the oxidation process, coating elements migrate outward along the concentration gradient, while oxygen molecules diffuse inward. Simultaneously, aluminum atoms diffuse inward, and Ni atoms diffuse outward, where they partially dissolve with oxygen. The inner coating’s Ni enhances the bonding of the coating by connecting the substrate to the outer layer. Meanwhile, the added Si in the Ni-Al/Si composite coating further improves the antioxidant properties of the coating.

High temperature properties of nichrome resistant heaters – A systematic comparison of APS, suspension and filament HVOF sprayed coatings

This study investigates the performance of Nichrome coatings, a nickel‑chromium alloy containing 20 wt.-% chromium, applied using three thermal spray techniques: powder plasma spray, suspension HVOF, and filament HVOF. Thin, homogeneous coatings approximately 35 μm thick were deposited onto steel substrates pre-coated with an insulating Al2O3 layer. The oxide content in the coatings varied based on the spraying technique and parameters, ranging from 57 to 64 vol.-% for plasma spraying, 42 to 54 vol.-% for filament HVOF, and 9 to 43 vol.-% for suspension HVOF. The coating's heating performance was evaluated over a temperature range of room temperature (RT) to 700 °C. Analytical techniques such as X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Energy Dispersive X-ray Spectroscopy (EDS) were employed to investigate the mechanisms affecting temperature-dependent resistivity in relation to the coating microstructure. The results indicate that increased oxidation leads to a decrease in specific resistivity at RT (ρ0). In example, plasma sprayed coatings exhibited lower specific resistivity ρ0 of 0.80 Ωmm2/m. In contrast, suspension HVOF reaches values up to 2.75 Ωmm2/m. At the same time coatings with higher oxidation levels demonstrate an elevated dependence of resistivity as compared to less oxidized coatings. Both can be attributed to changes in the phase composition of the conductive phase as the dominating factor, primarily driven by the preferential oxidation of chromium during the spraying process. Notably, the results provide valuable information for adjusting the coating properties to suit specific needs, such as self-regulating or high-temperature heating applications.

Effect of Al2O3 on the operation of SiNX-based MIS RRAMs

The role of a 3 nm Al2O3 layer on top of stoichiometric LPCVD SiNx MIS RRAM cells is investigated by using various electrical characterization techniques. The conductive filament formation is explained, and a compact model is used to fit the current–voltage curves and find its evolution during each operation cycle. The conduction in SiNx is also studied.

Effect of Al doping on structural and electrical properties of HfO2/ZrO2 layered structures for high-k applications

ZrO2 films with ultrathin Al2O3 layers have effectively contributed to the miniaturization of dynamic random access memory (DRAM) capacitors for many years. However, as memory devices continue to shrink, higher dielectric constants are required to maintain cell capacitance. To address this challenge, research has explored the use of tetragonal HfO2 layers, which theoretically possess a higher dielectric constant than ZrO2, as dielectrics. However, the thermodynamically stable phase of HfO2 is monoclinic with a lower dielectric constant, necessitating a phase transition to the tetragonal form for DRAM capacitor applications. Although attempts have been made to induce this phase transition to achieve high dielectric constants by applying an HfO2/ZrO2 layered structure or doping HfO2 with elements such as Zr, Al, and Si, significant challenges remain in completely eliminating the monoclinic phase or implementing a pure tetragonal phase of HfO2. In this study, we systematically investigated the crystallinity changes and improved the electrical properties of HfO2/ZrO2 layered structures with Al doping in the HfO2 layers. Our findings demonstrate that optimizing the partitioning of the ZrO2 and HfO2 layers, combined with Al doping, effectively achieves equivalent oxide thickness scaling.

Influence of Nitrogen Content on the Microstructure Evolution and Oxidation Resistance toward Ambient Air of CrAlSiN Coatings Deposited by FCVAD Technique.

In this study, CrAlSiN coatings with nitrogen contents ranging from approximately 42 to 54 at. % were deposited and subsequently exposed to temperatures of 700 or 900 °C for 2 h in ambient air to investigate the impact of nitrogen content on the microstructure evolution and high-temperature oxidation resistance. It was found that the CrAlSiN coating with nitrogen content of 42-45 at. % exhibited an amorphous/nanocrystalline hybrid structure, comprising pure metallic Cr and (Al,Cr)N phases within the matrix, as determined by the TEM, XRD, and XPS analysis. In contrast, as the nitrogen content exceeded 52 at. %, the coatings transformed to a dominantly columnar structure featuring solely Cr(Al)N phase. The CrAlSiN coating with a nitrogen content of ∼52 at. % retained amorphous fraction of around 20% but demonstrated superior oxidation resistance with the lowest parabolic rate constant of 1.1 × 10-14 cm2/s at 900 °C compared to other coatings. This enhanced performance was primarily attributed to the high stability of Cr(Al)N phase and formation of a fine-columnar/amorphous microstructure devoid of metallic Cr, resulting in a significantly thin (∼60 nm) yet dense Al2O3-rich monolayer atop the coating surface during the oxidation. Conversely, substoichiometric CrAlSiN coatings with N content ≤45 at. % would form a thick Cr2O3 outer layer over an underlying Al2O3 layer. Additionally, elemental segregation of Cr, Si, and Al was observed in all CrAlSiN coatings after exposure to 900 °C for 2 h, which was induced by the spinodal decomposition of the ternary nitride phases.

Intercomparison of Indexable Cutting Inserts' Wear Progress and Chip Formation During Machining Hardened Steel AISI 4337 and Austenitic Stainless Steel AISI 316 L.

This article deals with a mutual comparison of indexable cutting inserts of the CNMG 120408 type from two different manufacturers during the machining of hardened steel AISI 4337 and austenitic stainless steel AISI 316 L. The main goal is to analyse the different wear processes depending on the difference in the manufacturer's design and also depending on the properties of the different machined materials. The progress of the wear of the main spine of the tool, the types of wear and the service life of the cutting edge were monitored, with the achievement of the critical value VBmax = 300 µm being the standard. In addition to the wear of the inserts, the production of chips was monitored in terms of their shape, average size and number of chips per 100 g of chips produced. In order to understand the relationships arising from the obtained data, an SEM equipped with an elemental analyser was used to analyse the coating layers and the substrate of the unworn inserts and the types of wear and the intensity of the surface damage of the worn inserts. A several-fold difference in the lifetime of the cutting edge was found, both in terms of design and in terms of the selected machined material, while in both cases the cutting edge with Al2O3 and TiCN layers of half thickness achieved a better result in liveness. From the point of view of chip formation, very similar results in shape and average length were observed despite the different designs of chip breakers. Cutting inserts with half the thickness of the coating layers achieved longer cutting edge life in the non-primary material application compared to the target workpiece material. At the same time, it was observed that a thinner coating layer has a positive effect on chip formation in terms of its length and shape.

Substantial improvement of InGaN/GaN visible-light polarization-induced self-depletion phototransistor by thermally oxidized Al2O3

Atomic layer deposited (ALD) Al2O3 acting as gate dielectric and surface passivation is widely adopted in power electronics but seldom used in optoelectronic fields for its sophisticated and expensive technology. Herein, a simple but efficient Al2O3 passivation is used in the fabrication of InGaN/GaN visible-light (VL) polarization-induced self-depletion field effect phototransistors (FEPTs), for suppressing the surface leakage and recombination. The Al2O3 layer obtained by thermal oxidation (TO) of 2-nm-thick thermally evaporated metal Al shows high electrical insulation and even better passivation effect than the ALD-Al2O3. As a result, the dark current of TO-Al2O3 passivated device decreases by about 2 orders of magnitudes; meanwhile, the photoresponse increases by about 65%. Under a weak VL illumination of 6.8 μW/cm2, the InGaN/GaN FEPT exhibits a large photo-to-dark current ratio of 3.1 × 108 and an ultrahigh shot-noise-limited detectivity of 1.9 × 1018 jones. In addition, the FEPTs exhibit a strong wavelength selectivity with a 600 nm/400 nm spectral response rejection ratio exceeding 5 × 105. All these performances show huge potential in emerging VL applications that are limited by the insufficiencies of current Si photodetectors.

Improved Thermal Dissipation in a MoS2 Field-Effect Transistor by Hybrid High-k Dielectric Layers.

Transition metal dichalcogenides like MoS2 have been considered as crucial channel materials beyond silicon to continuously advance transistor scaling down owing to their two-dimensional structure and exceptional electrical properties. However, the undesirable interface morphology and vibrational phonon frequency mismatch between MoS2 and the dielectric layer induce low thermal boundary conductance, resulting in overheating issues and impeding electrical performance improvement in the MoS2 field-effect transistors. Here, we employed hybrid high-k dielectric layers of Al2O3/HfO2 to simultaneously reduce the interfacial thermal resistance and improve device electrical performance. The enhanced contact, greater vibrational phonon overlapping region, and stronger interfacial bonding force between the top Al2O3 layer and MoS2 promote the heat removal efficiency across the interface to the substrate. Under the same input power density, the temperature profile of the MoS2 transistor on the Al2O3/HfO2 has been largely reduced compared to that of the device on HfO2, with a maximum reduction of 49.5 °C. In addition, the field-effect mobility and current of MoS2 devices on the Al2O3/HfO2 high-k dielectric layers have been significantly improved, attributed to the depressed electron scattering and trap states at the interface. The design of the hybrid high-k dielectric layers provides an efficient solution to simultaneously improve the thermal and electrical performance of the two-dimensional devices.

An automatic multi-precursor flow-type atomic layer deposition system

Designs for two automated atomic layer deposition (ALD) flow reactors are presented, and their capabilities for coating additively manufactured (AM) metal prints are described. One instrument allows the coating of several AM parts in batches, while the other is useful for single part experiments. To demonstrate reactor capabilities, alumina (Al2O3) was deposited onto AM 316L stainless steel by dosing with water (H2O) vapor and trimethylaluminum (TMA) and purging with nitrogen gas (N2). Both instruments are controlled by custom-programmed LabVIEW software that enables in situ logging of temperature, total pressure, and film thickness using a quartz crystal microbalance. An initial result shows that 150 ALD cycles led to a film thickness of ∼55 nm, which was verified with Rutherford backscattering spectroscopy. This indicates that the reactors were indeed depositing single atomic layers of Al2O3 per ALD cycle, as intended.

Study on the anti-ablation behavior of (Ti,W)3AlC2 under oxyacetylene flame above 2500 K

To evaluate the reliability of (Ti,W)3AlC2 in aerospace ablation conditions, the ablation behavior of (Ti,W)3AlC2 ceramic is investigated by using oxyacetylene flame above 2550 K. Results show a four-stage process exists with the formation of TiO2-Al2TiO5-Al2O3. Once the central ablation temperature exceeds 2350 K, the innermost Al2O3 layer melts and collapses, exposing the decomposed TiCx-Al matrix directly to the flame with rapid oxidation and a remarkable increase of the linear ablation rate. The melt finally flows out with the flame from the ablation center and solidifies into a stripe-like TiO2-Al2TiO5 eutectic oxide above the protective oxide layer. The refractory W particles detected in the eutectic TiO2-Al2TiO5 may retard the flowing rate of the fluid by increasing its viscosity, resulting in a better ablation resistance performance in the later period of the ablation process, making the linear ablation rate lower from 10.30 μm/s of Ti3AlC2 to 9.01 μm/s of (Ti,W)3AlC2.

Constructing Long and Stable Ag‐Al2O3 Core–Shell Nanowires for Humidity Sensing and Triboelectric Energy Generation

Silver nanowires (AgNWs) are a promising alternative material to indium tin oxide as flexible transparent electrodes owing to their excellent optoelectrical properties and mechanical performance. However, the main challenge is the poor stability under diverse environments, ranging from high humidity, chemical exposure, and dynamic mechanical deformation. Herein, ultralong AgNWs (≈100 μm) have been synthesized via controlling growth kinetics by a facile acetic acid‐assisted solvothermal method, further decorated with a thin Al2O3 layer by electrodeposition to form a core–shell architecture. The resultant films based on Ag‐Al2O3 core–shell nanowires (NWs) possess a higher conductivity while preserving the optical transparency due to the enhanced NWs contact. More importantly, the constructed films exhibit strong resistance to various conditions, such as exposure to high temperature/humidity and immersion in NaCl, HCl, and Na2S solutions. The laser‐etched interdigital electrodes based on the chemically stable AgNWs are further integrated with graphene oxide layer for humidity sensing and respiration monitoring. Furthermore, the developed NWs with superior mechanical stability are constructed as triboelectric nanogenerators for electricity generation, and reliable output performance has been demonstrated. This work provides a convenient, scalable, and cost‐effective solution that offers great potential for designing robust, transparent electrodes for next‐generation flexible electronics.

Design of a PIT biosensor based on plasmonic-graphene-black phosphorous hybrid for hypercholesterolemia detection

Cardiovascular diseases are the primary and fundamental reasons of people death around the world. Precise, fast responding, compact and integrable biosensors are considered as the most important prevention or treatment devices. In this work, remarkable absorbers based on graphene-plasmonic-black phosphorous hybrid structures are proposed. These devices are utilized for bio-sensing applications. The presented device is consisted of different quarter-cylindrical and plate shaped layers of graphene, black phosphorous, Ag, Au and Al2O3. In order to improve functionality of the presented absorber (improving the absorption’s peak value), effects of structural parameters and chemical potential (Ef) on the absorption spectrum are being considered. The proposed structure will be considered as a biosensor for detection of cholesterol concentrations in blood samples (this would help physicians in diagnosis of hypercholesterolemia and prevention of cardiovascular diseases), after improving its characteristics. Finally, it is expected for this biosensor the following remarkable sensitivity, figure of merit, quality factor and detection limit of 6045.6 nm/RIU, 237.61 RIU− 1, (80.3–90.1) and (2.1e-4–2.26e-5) RIU, respectively. Therefore, the proposed device can be an appropriate candidate for bio-sensing applications in optical integrated circuits.

High-temperature oxidation behavior of GH4169 superalloy repair by wire-fed electron beam directed energy deposition

This study systematically examines the high-temperature oxidation behavior of GH4169 nickel-based superalloy repaired via wire-fed electron beam directed energy deposition (EB-DED). The analysis focuses on two distinct regions: the deposited zone and substrate zone. After exposure to 850 °C for 120 h, the oxidation films consisted of an outer layer of Cr2O3 and an inner layer of Al2O3 and TiO2. The deposition zone exhibits lower oxidation resistance, attributed to more pronounced element segregation resulting from the EB-DED process condition. This investigation establishes a clear correlation between element segregation and oxidation resistance, demonstrating that severe element segregation leads to poor oxidation resistance.

“Cocktail-like” double-layered polyimide/alumina composite aerogels via side-direction freezing method as designable high-temperature thermal insulations

The extremely low thermal conductivity, low density, and high-temperature stability of polyimide (PI) aerogels are promising candidates for thermal insulation applications. In this work, the layered PI/Al2O3 composite aerogels (PACAs) were developed, inspired by the biomimetic idea of a “cocktail” layered structure to enhance the service temperature of PI. By exploiting the density difference between the water-soluble polyimide acid (PAA) solution and Al2O3 slurry, we successfully fabricated PACAs with a macro-scale layered structure through side-direction freezing and thermal imidization processes. The PACAs exhibit significant anisotropic structural characteristics, with pore channels presenting a honeycomb structure in the Z-direction, effectively suppressing heat transfer along this direction. Both PI and Al2O3 aerogels demonstrate anisotropic properties in different directions, with the PI aerogel achieving excellent thermal insulation with a thermal conductivity of 0.0197 W/(m·K) along the Z-direction. By adjusting the relative thickness of the PI and Al2O3 layers, optimal thermal insulation performances were achieved at temperatures of 300 °C, 600 °C, and 900 °C. These results showcase the innovative advantages of the layered structure in enhancing thermal insulation while leveraging the low thermal conductivity of PI and the high-temperature tolerance of Al2O3.

Durability improvement of electrochromic WO3 thin films by deposition of an ultra-thin Al2O3 layer via atomic layer deposition

Introduction of an ultra-thin Al2O3 protective layer via atomic layer deposition (ALD) significantly enhances the durability and performance of amorphous tungsten trioxide (a-WO3) thin films for electrochromic devices. The Al2O3 layer, despite being less than 4 nm thick, effectively suppresses the dissolution of WO3 that typically occurs through hydration reactions forming WO3·H2O and tungstic acid (H2WO4). XRD and XPS analyses confirmed the presence of Al2O3 and its minimal impact on the amorphous structure of WO3 thin films. Optical transmittance measurements showed that the Al2O3-protected a-WO3 thin films maintained a higher transmittance modulation (ΔT) compared to bare a-WO3 thin films, with the ALD30 sample retaining 87.9 % of its initial transmittance modulation after 1000 cycles, in contrast to the rapid degradation observed in unprotected films. Microstructural analysis revealed significantly fewer surface cracks and reduced thickness loss in Al2O3-coated films after 100 cycles. Additionally, ICP-MS analysis indicated a much lower W concentration in the electrolyte for Al2O3-protected samples, confirming reduced dissolution.