Oxide Layer Research Articles

Effect of the simultaneous addition of lanthanum and nickel on the oxidation behavior and related area-specific resistance of ferritic stainless steels for solid oxide fuel cell interconnects

The effects of simultaneous lanthanum and nickel addition on the oxidation behavior and area-specific resistance (ASR) of stainless steels for fuelcell interconnects were investigated. The La and Ni addition promoted the entire growth of the oxide layer and increased the roughness of the metal/oxide interface. Despite the thicker oxide scale, these alloys prevented the increase of ASR compared to the alloy with only Ni added. The void analysis indicated that simultaneous La and Ni addition could prevent void growth, leading to lower ASR. The above findings can be interpreted in terms of the fast La diffusion and convoluted metal/oxide interface.

Wet chemical surface functionalization of AA2017 powders for additive manufacturing

Laser Powder Bed Fusion (L-PBF) is an important route for processing aluminum alloys, nevertheless, the high laser reflectivity and thermal conductivity and lower powder flowability of the aluminum alloys remain a challenge for their processing. Aiming to overcome these issues, AA2017 powders were surface-functionalized using chemical etchings. The powders' physical and rheological characterization revealed a decrease in the laser reflectance and an improvement in the flowability of the surface-functionalized powders, when compared to the gas-atomized powder. The higher amount of keyhole porosity in the as-printed L-PBF samples using the surface-functionalized powders also suggests an improvement in the laser absorption of these powders. However, the formation of a thick oxide layer on the surface-functionalized powders led to oxidation porosity in the as-printed samples. Therefore, the chemical etching should be improved to avoid the formation of a thick oxide layer on the powder surface and oxidation porosity in the as-printed L-PBF samples.

High-temperature ablation behavior and failure mechanism of (Hf0.25Zr0.25Ti0.25Ta0.25)C high-entropy carbide in wide temperature range

The ablation behavior of (Hf0.25Zr0.25Ti0.25Ta0.25)C was investigated using a plasma flame gun over a wide temperature range of 2070–2600℃. The structural transformation during ablation and the effect of temperature on the failure mechanism were discussed. Results showed a sharp increase in mass and linear ablation rates from 0.23 mg·cm−2·s−1 and 4.6 μm·s−1 at 2070℃ to 4.6 mg·cm−2·s−1 and 37 μm·s−1 at 2600℃. This variation was attributed to the temperature's impact on on the microstructure and composition of the oxide layer. During ablation, Hf/Zr-rich oxycarbides preferentially nucleated within the amorphous Hf-Zr-Ti-Ta-C-O layer, leading to phase separation of the oxide layer. With increasing ablation temperature, the filler and binder oxides with low melting point (e.g., (Hf,Zr)TiO4, TaZr2.75O8) were rapidly consumed. The skeleton oxides (e.g., (Hf,Zr)O2) failed to bond and peeled off. The transiently formed (Hf,Zr,Ti,Ta)Ox layer was repeatedly destroyed and reconstructed, resulting in the continuous damage and eventual failure of the matrix.

Atomic diffusion and electrical reliability of NiAl/SiO2 interconnect: Breakdown voltage and TDDB characteristics

This study reports the effects of post-annealing on the electrical reliability of a NiAl/SiO2 interconnect structure for potential use as post-Cu interconnect. Our materials characterization using transmission electron microscopy and secondary ion mass spectrometry discloses that annealing at elevated temperatures induced the diffusion of Al into SiO2: Al, for a 400 °C-annealed sample, diffused only to a few nanometers from the interface, forming a thin aluminum-rich oxide layer, while samples annealed at higher temperatures show an extensive Al diffusion and interfacial reactions. In a voltage ramp dielectric breakdown test, the 400 °C annealed sample shows the lowest breakdown voltage, possibly, due to the aluminum-rich oxide layer serving as a self-forming barrier while the samples annealed at higher temperatures display a drastic reliability degradation with the annealing temperature increasing. In addition, analyzing data acquired from time-dependent dielectric breakdown tests using the E-model helps us predict the lifetime of the 400 °C sample to be longer than 105 h at 1 MV/cm.

Ball-milled biochar-modified zero-valent aluminum activates peroxodisulfate for phenol degradation: Enhancement of catalysis by membrane-breaking effect

Zero-valent aluminum (ZVAl) is a potential activator for peroxodisulfate (PDS), yet the dense oxide film on its surface hampers electron transfer for the O−O bond cleavage of PDS. We synthesized zero-valent aluminum-biochar (BM-ZVAl@BC) composites through ball milling, which effectively disrupted the native oxide layer on BM-ZVAl@BC. Within the BM-ZVAl@BC/PDS system, biochar (BC) not only suppressed the rapid oxidation of BM-ZVAl@BC but also enhanced the dispersion and electron transfer rate of ZVAl, thereby improving the overall catalytic efficiency. Consequently, the phenol removal efficacy in the BM-ZVAl@BC/PDS system was notably improved. Optimal catalytic performance of the prepared BM-ZVAl@BC was achieved at a charcoal-to‑aluminum mass ratio of 2:1, resulting in 95.7 % phenol removal after 180 min. Quenching experiments and electron paramagnetic resonance (EPR) analysis revealed that both free radicals (SO4•−, •OH, and O2•−) and non-radical species (1O2) contributed to phenol degradation, with SO4•− and •OH playing predominant roles. In summary, the BM-ZVAl@BC/PDS system represented an effective and promising technology for the remediation of phenolic water pollutants.

High-temperature oxidation of oxide-dispersion-strengthened FeCrAl alloys: Influences of Al, Co and Y concentration on the mechanism of oxide scale growth

Oxide-dispersion-strengthened (ODS) FeCrAl alloys with different Al and Co contents were oxidized at 800 °C in air, and the oxidation behavior was investigated. The oxidation mass gain was measured, and the phase and morphology of the oxide scale were characterized using XRD, SEM, and STEM. The elemental distribution of the oxide layer was determined by EPMA. The results demonstrated that protective α-Al2O3 scales were generated on the surface of alloys containing 3 and 5 wt% Al. After 225 h of oxidation, the mass gain of alloys with 5 wt% Al decreased as Co concentration increased, whereas the 3 wt% Al alloys exhibited the reverse tendency. The ferritic matrix and lower oxidation temperature promoted the external Al2O3 scale formation on the 3Al alloys. It is proposed that the balance between matter diffusion blocking through the oxide grain boundary and grain coarsening determines how the Y/Y2O3 concentration affects the oxidation kinetics. The minor addition of Y/Y2O3 decreases the oxidation kinetics of FeCrAl–ODS alloys, whereas excess addition is detrimental to the oxidation behavior of the alloy. A plausible model for analyzing the influence of Co and Y concentration on the oxidation kinetics of FeCrAl alloys containing 3 and 5 wt% Al was proposed. The findings could serve the fundamental alloying design to realize the transformable FeCrAl-ODS alloys for high-temperature applications.

Nanostructured Yb2SiO5/mullite-SiC/Si environmental barrier coating with long-term stability at 1250 °C

In this work, nanostructured Yb2SiO5/mullite-SiC/Si environmental barrier coatings (EBCs) were prepared to investigate the effect of heat treatment on the microstructure and phase transition of nanostructured Yb2SiO5/mullite-SiC/Si coatings. The Yb2SiO5 content and microstructure evolution in the coatings were thoroughly analyzed before and after heat treatment. The results demonstrate a slight decrease in the porosities of nanostructured Yb2SiO5 and mullite-SiC coatings, accompanied by a gradual growth in grain sizes with increasing heat treatment time, indicating the nanostructured EBCs show good resistance to sintering. Moreover, the thickness of thermal growth oxidation layer is only 200 nm at 1250 °C for 500 h of heat treatment. In particular, the presence of the Yb2O3 phase has been observed to exert a favorable influence on the thermal stability of nanostructured EBCs. This work provides an innovative strategy for designing advanced EBCs with excellent high-temperature thermal stability.

The influence of liquid height to bubble size ratio on the boiling crisis in pool boiling

We conducted experiments to analyze water boiling under 10 K subcooling and atmospheric conditions in a horizontal pool boiling test setup, focusing on the effect of liquid height above the heating surface. Our main interest was the transition in boiling crisis mechanisms at liquid heights comparable to bubble size. For pool heights above 4.0 mm, we observed a relatively constant critical heat flux (CHF) of approximately 1.21 MW/m^2. Conversely, CHF significantly dropped to around 0.19 MW/m^2 for liquid heights below 2.5 mm. For depths between 2.5 – 4.0 mm the measured CHF values varied within these limits. Our pool boiling facility featured a stainless-steel chamber filled with deionized water heated by external circulating oil. A ceramic cartridge supported a transparent heater at the cell’s center-bottom, which utilized an indium tin oxide layer on a sapphire substrate for heat dissipation. We monitored bubbles’ footprint dynamics during boiling using infrared and high-speed video cameras. Preliminary high-speed data analysis revealed different hydrodynamic mechanisms corresponding to the obtained CHFs. For heights above 4.0 mm, the formation of an irreversible dry patch is triggered by bubble interactions. Conversely, at heights below 2.5 mm, one of the bubbles nucleating shortly after the onset of boiling failed to detach from the surface shortly. Instead, it grew in size and eventually spread over the entire surface, prematurely triggering a boiling crisis. We attributed this behavior to a lack of buoyancy forces to detach the bubble from the surface as it grew above the liquid level. Pool heights between 2.5 – 4.0 mm showed both behaviors. Further investigations will focus on exploring the transition in boiling mechanisms shifting from buoyancy- to surface-tension-dominated processes by varying bubble dimensions through the introduction of surfactants. Ultimately, we aim to analyze fundamental boiling parameters and heat flux to characterize how boiling dynamics, boiling crisis and CHF value vary with the bubble-to-liquid height ratio.

The Effect of Sulfuric Acid Anodization on the Electrochemical Properties of Aluminum Alloy AlSi10Mg Prepared by Selective Laser Melting

Aluminum alloy, AlSi10Mg, prepared by selective laser melt (SLM) fabrication was anodized in 9.8% sulfuric acid (Type II) at 15 V for a total of 23 min. Experiments were performed to study the potentiostatic anodization process and its effects on the oxide coating morphology, thickness, and electrochemical properties of the alloy. Prior to anodization, the alloy microstructure is composed of aluminum cells encapsulated in a silicon network. Anodizing the abraded and polished AlSi10Mg surface produced a porous oxide layer with a thickness of 5 μm. The oxide coating weight was 698 ± 29 mg/ft2. The oxide coating forms in the aluminum cells that are isolated from one another by the silicon eutectic phase. In electrochemical tests, the anodic and cathodic potentiodynamic polarization currents were suppressed by factors of 15× and 215×, respectively, as compared to the unanodized controls. The data indicate the anodic oxide coating suppresses the cathodic more than the anodic reaction rate. Linear polarization resistance (R p) values increased by 279× after anodization. The corrosion current density values (j corr) decreased by 133× after anodization. Taken together, the electrochemical data indicate the anodic oxide coating (unsealed) increases the corrosion resistance of the SLM alloy by two orders of magnitude.

High-temperature oxidation mechanism and microstructure evolution of Cr-Mn-Si alloyed steel oxidized by Fe2O3 contained in mold flux

The high-temperature oxidation behavior of Cr-Mn-Si alloyed steel by Fe2O3 contained mold flux in high temperatures, and its effect on microstructure evolution were investigated in detail by TEM, EBSD, CLSM, SEM, and XPS. A novel oxidation mechanism was firstly revealed that the Fe2O3 in mold flux melts during high temperatures plays a role of oxidizing alloyed steels by the released free oxygen ions (O2−) from the transformation of Fe2O3 (Fe3+) to FeO (Fe2+). The formed oxidized dots within the oxide layer changed from SiO2 and MnSiO3 to MnCr2O4 spinel phases by increasing the content of Fe2O3 in the mold flux. Notably, the amorphous SiO2 was discovered in the core region of MnSiO3 phase due to its selective oxidative behavior in high temperatures. This research provides conclusive evidence that the small size MnSiO3 oxides can be acted as a nucleation core for the refinement of austenite grains through in-situ observation.

Effect of humidity on the friction and wear behavior of C/C-CuNi composites

The friction behavior and wear performance of C/C-CuNi composites under varying humidity conditions were investigated. Lower levels of humidity (30 %–50 % RH) resulted in the formation of a lubrication layer composed mainly of graphite and CuO, which led to adhesive wear of the composites together with stable and low coefficients of friction (∼0.144) as well as a low wear rate. However, when the relative humidity exceeded 70 %, there was an increased tendency for the formation of a brittle layer predominantly consisting of Cu(OH)2 and Cu2(OH)2CO3 compounds due to tribo-chemical reactions between the composites and H2O and CO2 in humid air. Subsequently, this brittle oxide layer caused abrasive wear accompanied by fluctuations in the coefficient of friction along with increased wear rates.

High-Speed Thermo-Compression Sinter-Bonding Properties in Air of a Paste Containing Dendritic Cu Particles Having Oxalate Skins

To enhance the sinter-bonding speed of Cu dendrite particle-based paste, the particles were surface-treated with oxalic acid solution. This treatment transitioned the particle surface from an oxide layer to a CuC 2 O 4 phase, which suppressed the oxidation of Cu until thermal decomposition between 284-315 °C generating Cu nanoparticles. Using the surface-treated Cu dendrite particle-based paste, sinter bonding at 320 °C under 5 MPa pressure in air provided a sufficient shear strength of 23.4 MPa in just 60 s, reaching the maximum of 28.7 MPa after 180 s. The in situ generated Cu nanoparticles from the thermal decomposition of CuC<sub>2</sub>O<sub>4</sub> directly contributed to the very rapid sintering-bonding behavior at 320 °C. However, the bondings at 300 °C and 350 °C showed poorer bonding characteristics than that of before treatment, indicating that the surface treatment strategy for forming CuC<sub>2</sub>O4 skins is effectively implemented by appropriately setting the following sinter-bonding temperature.

Indium-free nonmetal and Nb co-doped anatase TiO2 transparent conductive oxide materials for photovoltaic applications: From first-principles calculations to macroscopic simulation

Various researchers have attempted to design indium-free transparent conductive materials. This study first employed density functional theory combined with the Hubbard U parameter to predict the photoelectric properties of nonmetal (B, C, N, F, P, and S) and Nb co-doped anatase TiO2. The results indicate that Ti0.875Nb0.125O1.96875N0.03125, Ti0.9375Nb0.0625O1.96875F0.03125, Ti0.875Nb0.125O1.96875P0.03125 and Ti0.9375Nb0.0625O1.96875S0.03125 possess characteristics of n-type semiconductors with high transmittance, exceptional thermal stability and wide bandgap. Notably, Ti0.9375Nb0.0625O1.96875S0.03125 exhibits optimal electronic conductivity due to its lower effective mass and higher electron concentration. Then, we used the SCAPS-1D solar cell simulation software to simulate the macroscopic characteristics of the MASnI3-based perovskite solar cell with Ti0.9375Nb0.0625O1.96875S0.03125 transparent conductive oxide layer based on the microscopic properties computed at the density functional theory level. A maximum efficiency of 27.17 % is obtained by regulating the thickness, electron affinity, and defect density of Ti0.9375Nb0.0625O1.96875S0.03125 layer and the thickness of MASnI3 absorber layer. The findings highlight the tremendous potential of Ti0.9375Nb0.0625O1.96875S0.03125 as an indium-free transparent conductive oxide candidate material for photovoltaic applications.

Characteristics of zero-valent iron surface oxide films under the catalytic interface reactions by assisting ligands in nitrate-contaminated groundwater

The surface passivation layer coating on zero-valent iron (ZVI) particles impedes the electron transfer from ZVI to nitrate. To enhance the efficiency of nitrate reduction by Fe(0), we tested the chemical process and the thickness of the iron oxide film on the surface of Fe(0) particles, utilizing Fe2+aq in aqueous solution and wheat straw as ligands. A novel principal surface catalyzing reaction was formulated as follows: NO3−+0.67Fe2++2.2Fe0+2.33H2O→NH4++1.18Fe3O4+0.64OH−. When Fe2+aq concentration increased from 0 - 200 mg·L−1, the NO3- removal rate increased from 6.95% to 82.6% respectively during 12 h and it was 48%, 72%, 79% and 94% respectively in Fe0/WS ratio of 0, 0.25, 0.5 and 1 system. Uniform surface iron oxide films formed around the Fe(0) particles within 12 h after the adding Fe2+aq or wheat straw to the Fe(0) system. The composition and thickness of these films were dependent on the quantity of added materials. X-ray diffraction (XRD) analysis revealed that surface oxide iron mainly consisted of Fe2+ or Fe3+ oxides, with Fe3O4 being predominant. The X-ray photoelectron spectroscopy (XPS) etching indicated that the addition of Fe(0)/straw at mass ratios of 1 or system with 20 mg·L−1 Fe2+aq resulted in the thinnest surface iron oxide layer. The study demonstrated that reducing the oxide layer’s thickness was achieved through partial catalysis and enhanced complexation capacity. This reduction was facilitated by the introduction of Fe2+aq or wheat straw into the Fe(0) system, potentially improving proton dissociation and promoting the ligand-assisted dissolution of Fe3+ oxides.

Diffusion Nitride Surface Layers on Aluminum Substrates Produced by Hybrid Method Using Gas Nitriding

While gas nitriding of steel is currently used in industry, nitriding of aluminum alloys remains an open challenge. The main obstacle is aluminum’s high susceptibility to passivation. The oxide film provides an effective barrier to nitrogen diffusion. Attempts to overcome this problem have mainly focused on glow discharge nitriding using cathode sputtering of an oxide layer. The produced AlN layers exhibit no diffusion zone and show limited performance properties. In this work, the effect of hybrid treatment aimed at producing diffusion layers of nitrides other than AlN on aluminum alloys was investigated on the model system of iron nitride–aluminum substrate. Hybrid treatment combines an electrochemical process involving the removal of the aluminum oxide layer from the substrate, its subsequent iron plating, and a further gas nitriding in high-purity ammonia. The obtained results prove that the hybrid treatment allows the production, at 530 °C/10 h, of diffusion layers of Fe3N iron nitrides on aluminum substrates with a nitrogen diffusion zone range in aluminum of ca. 12 µm. In alloys containing magnesium, its unfavorable effect on the nitrogen diffusion and the functional properties of the layers was observed. An interesting direction for further research is hybrid treatment of precipitation-hardened alloys without magnesium.

Computational modelling of cylindrical-ferroelectric-dual metal-nanowire field effect transistor (C-FE-DM-NW FET) using landau equation for gate leakage minimization

In order to address and resolve the significant problem of gate-induced drain leakage (GIDL) current and enhance device reliability, band-to-band tunnelling (BTBT), and OFF-state leakages, a computational model of a cylindrical-ferroelectric-dual-metal-nanowire-field effect transistor (C-FE-DM-NW-FET) has been proposed in this manuscript. The proffered structure is a symmetric gate structure with ferroelectric layer sandwiched between the gate terminal and oxide layer which reduces the BTBT which in term reduces the OFF-state leakage hence making the device definitive for low power applications. In this manuscript, there has been a reduction in the leakage current by a magnitude of 104 times in 50 nm and 107 times in 60 nm channel length which translates to a reduction in gate leakage (IGIDL) of more than 100 % in C-FE-NW-FET over C-NW FET. To analyze the Electric Field, Surface Potential, and IGIDL with the proper boundary conditions, the 2D Poisson's equation is solved analytically with Landau-Khalatnikov (LK) equation. The analytical findings are quite similar to the simulated outcomes.

Assessment on oxidation behaviors of high chromium white iron matrix composite in high temperature air environment

Oxidation behaviors of in situ formed TiCx/high chromium white iron (TiCx/HCWI) composite containing trace alloying elements with super hardness were investigated in air at 650 °C and 700 °C for 96 h, respectively. Rich types of oxides appeared on the oxidized surfaces of the TiCx/HCWI composite both at 650 °C and 700 °C. While, MoO3 appeared on the surface only at 650 °C, FeV2O4 turned up only at 700 °C. The various oxides were enriched in diverse regions inside and outside the oxide layer at 700 °C due to the discrepancy of oxidation thermodynamics and oxidation partial pressure. Oxidation thermodynamics, kinetics, and oxidation mechanisms of the TiCx/HCWI composite were discussed. The present work provides enlightenment for the application of the super hard TiCx/HCWI.

Enhanced toughness and ductility of T91 steel after exposure to liquid LBE saturated by oxygen at 350–500 °C

The mechanical tensile properties of T91 steel after being oxidized in liquid LBE saturated by oxygen at 350–500 °C for up to 1000 h are studied. Duplex oxide scales are found on T91 steels after the LBE exposure, and the thickness evolution is revealed. Oxidized T91 steels with surface oxide scale yield enhanced toughness and ductility, which is mainly attributed to the inner oxide layer. We show that the enhancing effect relies on the presence of the oxide scale, not its thickness. The possible enhancing effect of the oxide scale on the toughness of T91 steel by impeding the dislocation from emitting out of the steel surfaces is discussed and qualitatively verified by micro-scale elastoplastic simulations based on a newly proposed discrete dislocation dynamics and peridynamics superposition scheme.

2D MoS2 monolayers integration with metal oxide-based artificial synapses

In this study, we report on a memristive device structure wherein monolayers of two-dimensional (2D) molybdenum disulfide (MoS2) are integrated with an ultrathin yttrium oxide (Y2O3) layer to simulate artificial synapses functionality. The proposed physical simulation methodology is implemented in COMSOL Multiphysics tool and is based on the minimization of free energy of the used materials at the applied input voltage. The simulated device exhibits a stable bipolar resistive switching and the switching voltages is significantly reduced by increasing the number of MoS2 layers, which is key to conventional low-power computing and neuromorphic applications. The device is shown to perform synaptic functionalities under various applied bias conditions. The resulting synaptic weight decreases almost linearly with the increasing number of MoS2 layers due to the increase in the device thickness. The simulation outcomes pave the way for the development of optimised metal oxide-based memristive devices through their integration with semiconducting 2D materials. Also, the 2D MoS2 integration can enable the optoelectronic operation of this memory device.

Controlling splat boundary network evolution towards the development of strong and ductile cold sprayed refractory metals: The role of powder characteristics

Feedstock powder characteristics such as composition (specific alloying elements and concentrations and impurity levels), microstructure, thickness/composition of surface oxide layers, and particle size distribution play a crucial role in determining the overall mechanical properties of cold sprayed deposits. Herein, we report on two deposits consolidated via cold spray processing from differently-sourced batches of nominally identical elemental refractory powders under identical spraying conditions, which exhibit bending strength and ductility values that differ by more than a factor of two – and with the weakest sample displaying negligible effective ductility. Through chemical, microstructural and micromechanical characterization of both the feedstock powders and cold sprayed deposits, we consider the possible influences of feedstock characteristics on the mechanical performance of cold spray consolidated deposits. It is shown that while differences in interstitial oxygen and hydrogen content may result in differences in the intrinsic yield characteristics of the feedstock material, both feedstocks maintain the ductile behavior required to induce good metallurgical bonding upon impact of optimally sized powder particles. We conclude that the deposits formed from the two feedstock powders are indistinguishable and exhibit high ductility when characterized locally within the relatively undeformed bulk of a single particle or splat. However, the two sprayed deposits show low ductility or brittle behavior when loaded in tension across intersplat boundary domains comprising material that has undergone extensive deformation. In addition, one feedstock incorporates a broader particle size distribution, with a long tail of larger-than-optimal particles. These larger particles are accelerated below the critical impact velocity, resulting in observed imperfect metallurgical bonding at splat interfaces and higher porosity at such intersplat boundaries. This result, combined with the overall differences in the morphology of the intersplat boundary network between the two deposits, explains the difference in macroscopic mechanical behavior. We conclude that accurate control of the powder feedstock particle size distribution is essential for optimizing the mechanical integrity of cold sprayed refractory elements and alloys.