Growth Of Oxide Layer Research Articles

MOCVD growth of gadolinium oxide layers on tubes

In the paper, non-porous and smooth gadolinium oxide layers were synthesized on the inner surfaces of quartz glass tubes using MOCVD (Metalorganic Chemical Vapour Deposition) in the temperature range of 580–800 °C.Commercial Gd(tmhd)3 (Tris(2,2,6,6-tetramethyl-3,5-heptanedionato)gadolinium(III), 99% (99.9%-Gd)) was a basic reactant. Pure argon (99.999%) was used as a carrier gas. Air was applied to eliminate the carbon. It also was a carrier gas. The magnitude of the extended Grx/Rex2 criterion did not exceed the value of 0.01. Other synthesis conditions were established in such a way that this condition was maintained. The evaporation temperature of Gd(tmhd)3 varied in the range of 170–270 °C.The influence of the synthesis conditions on microstructure, structure and transparency of the deposited layers was investigated. Oval-shaped Gd2O3 aggregates and fine crystallites were formed regardless of the synthesis conditions. The conducted research also shows that the lower deposition temperature and the higher evaporation temperature of reactant, causes smaller crystallite sizes and smaller their number.

Temperature‐dependent mechanical and oxidation behavior of in situ formed ZrN/ZrO2‐containing Si3N4‐based composite

AbstractIn this work, Si3N4 and Zr(NO3)4 were used as raw materials to prepare ZrN/ZrO2‐containing Si3N4‐based ceramic composite. The processing, phase composition, and microstructure of the composite were investigated. Hardness and fracture toughness of the ceramics were evaluated via Vickers indentation in Ar at 25°C, 300°C, 600°C, and 900°C. During spark plasma sintering, Zr(NO3)4 was transformed into tetragonal ZrO2, which further reacted with Si3N4, resulting in the formation of ZrN. The introduction of ZrN enhanced the high‐temperature mechanical properties of the composite, and its hardness and fracture toughness reached 13.4 GPa and 6.1 MPa·m1/2 at 900°C, respectively. The oxidation experiment was carried out in air at 1000°C, 1300°C, and 1500°C for 5 h. It was shown that high‐temperature oxidation promoted the formation and growth of porous oxide layers. The microstructure and phase composition of the formed oxide layers were investigated in detail. Finally, it was identified that the obtained composite exhibited a higher thermal diffusivity than that of monolithic Si3N4 in the temperature range of 100°C–1000°C.

Oxidation behavior of AlCoCrFeNiSix high entropy alloy bond coatings prepared by atmospheric plasma spray

To investigate the oxidation resistance of AlCoCrFeNi high entropy alloy coating and the effect of Si modification on oxidation resistance, AlCoCrFeNiSix (x = 0, 0.15, 0.3) coatings were prepared on 316 L stainless steel substrate by atmospheric plasma spray (APS). The evolution process and oxidation kinetics of the thermal grown oxide (TGO) layer at 800 °C for the three coatings were discussed, and the growth model of the TGO layer was established. The results show that the oxides tend to be preferentially generated at the particle boundaries and diffused laterally, but the Al2O3 would hinder them. The TGO layer of the three coatings transformed from the single layer to the double layer with the oxidation process, and the lower oxide layers were continuous and dense Al2O3. Spinel oxides appear in the TGO layers of the Si0 and Si0.3 coatings, but the TGO layer of the Si0.15 coating consists entirely of Al2O3 and which displays the lowest oxidation rate. Although the Si modification reduced the growth rate of the TGO layer, the content of the Si element was not proportional to the improvement of the oxidation resistance of the coating.

Laser-induced electron dynamics and surface modification in ruthenium thin films

We performed the experimental and theoretical study of the heating and damaging of ruthenium thin films induced by femtosecond laser irradiation. We present the results of an optical pump-probe thermoreflectance experiment with rotating sample allowing to significantly reduce heat accumulation in irradiated spot. We show the evolution of surface morphology from growth of a heat-induced oxide layer at low and intermediate laser fluences to cracking and grooving at high fluences. Theoretical analysis of thermoreflectance in our pump-probe experiment allows us to relate behavior of hot electrons in ruthenium to the Fermi smearing mechanism. This conclusion invites more research on Fermi smearing of transition metals. The analysis of heating is performed with the two-temperature modeling and molecular dynamics simulation, results of which demonstrate that the calculated single-shot melting threshold is higher than experimental damage threshold. We suggest that the onset of Ru film damage is caused by the heat-induced stresses that lead to cracking of the Ru film. Such damage accumulates during repetitive exposure to light.

Heat-induced ultrathin oxide layer blocks the current generation of Schottky nanogenerators

Schottky nanogenerators (SNGs) are very simple power generation devices that can generate a direct current with a high current density of 104–107 Am−2 by sliding a metal-coated nanotip on semiconductor wafers. However, the current generation of SNGs has a rapid degradation if the sliding between metal and semiconductor is repeatedly performed over the same area. Although it is widely guessed that the oxidization during sliding on the semiconductor side induces the current attenuation, there is no reported in situ direct characterization of the ultrathin oxide layer (thickness <0.5 nm) in the SNGs as a demonstration of the aforementioned attenuation mechanism, and no reason for the oxidation is given. Here, we performed meticulous characterization and then illustrated that the current attenuation is mainly derived from the growth of an ultra-thin oxide layer in the semiconductor side contact region, which is mainly caused by friction heating and Joule heating. This understanding may guide the design and development of Schottky generators with a high current density as well as sufficient long life.

Influence of microstructure on the oxidation characteristics of conventional and wire arc additive manufactured alloy 625 at 750 ⁰C

Microstructure and the high temperature oxidation performance of the wire arc additive manufactured (WAAM) and wrought alloy 625 was investigated at 750⁰C. Microstructure results showed the solid solution dendrites as WAAM-built alloy and austenite structure was observed on the wrought alloy. Both the alloys are followed the parabolic behavior and the WAAM-built alloy exhibited lower weight gain than wrought alloy. The oxides growth rate was controlled by the formation of protective passive Cr2O3 film, which could avoid the inward oxygen penetration. Oxide layer growth Kinetics are explored in detail based on alloy composition and microstructure.

Oxidation Behavior of Single-Layer Gd2Zr2O7, and Gd2Zr2O7/YbSZ, and Double-Layer YSZ + Gd2Zr2O7/YbSZ Thermal Barrier Coatings

Oxidation is one of the failure mechanisms of gas turbines under operating temperature. Yttria-stabilized zirconia (YSZ) is well-known ceramic topcoat material of thermal barrier coatings (TBCs), but it has some drawbacks. From this point of view, other new materials such as rare earth zirconate are interesting. In the present research, single-layer Gd2Zr2O7 (GZO), and GZO/YbSZ (Gd2Zr2O7 + 50 wt% YbSZ), and double-layer YSZ + GZO/YbSZ (YSZ/Gd2Zr2O7 + 50 wt% YbSZ) topcoats as TBC were deposited by air plasma spraying. To estimate the phase stability of homogeneous mixtures of GZO (pyrochlore) and YbSZ (tetragonal), heat treatment was conducted at 1400 °C and showed complete conversion to a single-cubic (fluorite) phase after 100 h. The as-sprayed TBCs were subjected to oxidation for different times at 900 °C, and their features were investigated by different analysis techniques (SEM and XRD). The microstructural analysis indicated that the thickness of the thermally grown oxide layer was less for GZO coating due to reduced oxygen diffusion. Conversely, because of the lower fracture toughness and lower thermal expansion of GZO, it had a considerably less lifetime. It was concluded that coatings with the new composition GZO/YbSZ exhibited higher oxidation resistance and longer lifetime than GZO coatings.

Study on Room-Temperature Wet Oxidation of Silicon Catalyzed by Copper.

The anomalously fast growth of the silicon oxide layer at room temperature has been reported for the Cu/Si system. However, the systematical exploration of such a reaction under humidity conditions has not yet been carried out. Through one combination of the experiments and first-principle density functional theory (DFT) simulations, here, we investigate the influence of the imparted Cu atoms in Cu/Si on the oxidation of Si with the presence of H2O. The Cu addition causes the geometric distortion of the Si lattice, which alters the charge transfer to absorbed H2O and decreases its dissociation energy. This results in the experimental formation of much defective SiOx for the Cu/Si system than bare Si under humidity conditions. Furthermore, the presence of such an oxide structure and the catalytic effect of Cu provide the suitable diffusion channels and adsorption sites for the H2O transport and its dissociation. This enhances the oxidation rate of Si consequently and results in the fast growth of the oxide layer on Cu/Si at room temperature.

Aluminum Particle Ignition Studies with Focus on Effect of Oxide Barrier

Aluminum particle ignition behavior in open atmosphere rocket propellants fires is of particular interest for preventing accidents for rockets carrying high-value payloads. For nominal motor pressures, aluminum particles oxidize to aluminum oxide in the gas phase and release significant combustion energy while minimizing motor instability. During rocket abort or launch pad malfunction which occur under atmospheric or low pressure, behavior of aluminum particle combustion becomes complex and aluminum appears to melt, agglomerate or form a skeletal structure. Furthermore, an oxide shell of alumina instantly forms on any fresh aluminum surface which is exposed to an oxidizing environment. Aluminum combustion then strongly depends on the oxide layer growth, which is influenced by causative factors, including particle size, environmental gas composition, and heating rate. This work focuses on the effect of the oxide barrier which forms on the surface of aluminum that is recognized to impede combustion of aluminum in solid rocket propellants. Understanding the mechanism for breach of this barrier is deemed to be an important consideration in the overall process. In this discussion, results of various experiments will be discussed which have a bearing on this process. Basically, a recognized criterion is the melting of the oxide layer at 2350 K is sufficient. However, in other situations, depending on the mechanism of oxide formation, there will occur defects in the oxide shell which provide for aluminum ignition at lower temperatures. For slow heating in an oxidizing environment, where the oxide layer can grow thick, then ignition is more difficult. Because there is no uniform model to establish an ignition criterion due to the unknown history of an aluminum particle, this paper reports experimental findings involving oxyacetylene torch, thermogravimetric analysis with differential scanning calorimeter, aluminum particle heating, electric ignition and aluminum powder heating, to address the influence of the oxide layer on the aluminum particle ignition.

The Coupled Thermo-Chemo-Mechanical Peridynamics for ZrB2 Ceramics Ablation Behavior

The ablation of ultra-high-temperature ceramics (UTHCs) is a complex physicochemical process including mechanical behavior, temperature effect, and chemical reactions. In order to realize the structural optimization and functional design of ultra-high temperature ceramics, a coupled thermo-chemo-mechanical bond-based peridynamics (PD) model is proposed based on the ZrB2 ceramics oxidation kinetics model and coupled thermo-mechanical bond-based peridynamics. Compared with the traditional coupled thermo-mechanical model, the proposed model considers the influence of chemical reaction process on the ablation resistance of ceramic materials. In order to verify the reliability of the proposed model, the thermo-mechanical coupling model, damage model and oxidation kinetic model are established respectively to investigate the applicability of the proposed model proposed in dealing with thermo-mechanical coupling, crack propagation, and chemical reaction, and the results show that the model is reliable. Finally, the coupled thermo-mechanical model and coupled thermo-chemo-mechanical model are used to simulate the crack propagation process of the plate under the thermal shock load, and the results show that the oxide layer plays a good role in preventing heat transfer and protecting the internal materials. Based on the PD fully coupled thermo-mechanical model, this paper innovatively introduces the oxidation kinetic model to analyze the influence of parameter changes caused by oxide layer growth and chemical growth strain on the thermal protection ability of ceramics. The proposed model provides an effective simulation technology for the structural design of UTHCs.

Modification of the Ni-NiO-oxidant system by thermo-chemical oxidation with accelerated growth of the p-type dielectric oxide layer, by the action of substituted V2O5 on the system

Nickel is covered with very thin oxide film and is stable against corrosion under normal conditions. Nickel, as Ni-NiO-oxidant system, can make much thicker (even a thousand times) and more corrosion unstable oxides. With certain new oxidation process parameters, nickel can undergo so-called accelerated oxidation. The subject and goal of this work is to find the most favorable conditions for performing of accelerated - catastrophic Ni oxidation process, when substitution of V2O5 is carried out into NiO (2V (Ni)), with significant electron concentration increase and oxygen surplus. Unlimited main and secondary charge carriers transfer is significantly facilitated if oxide film with non-stoichiometric composition and defects is formed. The aim is to avoid compact oxide film formation by chemical-thermal treatments and to obtain porous and defective NiO. By using oxidized system Ni - NiO - oxidant in glass, ceramics and evaporated metal technology, extraordinary usable value of this work is ensured.

Tunable asymmetric magnetoresistance in an Fe3GeTe2/graphite/Fe3GeTe2 lateral spin valve.

van der Waals (vdW) ferromagnetic heterojunctions, characterized by an ultraclean device interface and the absence of lattice matching, have emerged as indispensable and efficient building blocks for future spintronic devices. In this study, we present a seldom observed antisymmetric magnetoresistance (MR) behavior with three distinctive resistance states in a lateral van der Waals (vdW) structure comprising Fe3GeTe2 (FGT)/graphite/FGT. In contrast to traditional spin valves governed by the magnetization configurations of ferromagnetic electrodes (FEs), this distinct feature can be attributed to the interaction between FGT and the FGT/graphite interface, which is primarily influenced by the internal spin-momentum locking effect. Furthermore, modulation of the MR behavior is accomplished by employing the coupling between antiferromagnetic and ferromagnetic materials to adjust the coercive fields of two FEs subsequent to the in situ growth of an FGT oxide layer on FGT. This study elucidates the device physics and mechanism of property modulation in lateral spin valves and holds the potential for advancing the development of gate-tunable spintronic devices and next-generation integrated circuits.

Investigating the thermal effects and oxidation of aluminum alloy 6061 using In-situ spectroscopic ellipsometry

• In-situ spectroscopic ellipsometry on thermal effects of metal alloy • Multi-data analysis to break correlation between refractive index and oxide thickness • Discussion on Drude and interband transition • Growth of surface oxide In-situ spectroscopic ellipsometry was applied to monitor the thermally induced changes in the optical properties of aluminum alloy Al6061 and the growth of the surface oxide layer. Raw data indicate noticeable to accelerated changes at 400°C and 500°C. The simultaneous analysis of multiple data sets broke the correlation typically observed in ellipsometric analysis on metals. Dielectric functions of Al6061 at different temperatures were determined and found to have changed irreversibly after the heat treatment. Evolution of absorption features related to aluminum interband transition and the Drude absorption in the near-infrared were discussed. Morphology of the surface oxide was attributed to the lower than expected refractive index.

Numerical simulation of corrosion phenomena in oxygen-controlled environment for a horizontal lead-bismuth reactor core

In order to explore the core corrosion characteristics of horizontal lead-bismuth reactor in oxygen-controlled environment, a liquid lead-bismuth eutectic (LBE) corrosion model including the growth and removal process of oxide layer was established in this paper. The coupling method of double-layered oxidation model and computational fluid dynamics (CFD) was used to simulate the long-term oxidation corrosion of horizontal LBE reactor core numerically. The results show that the average total oxide layer thickness of fuel rod surface is 1.59 μm, and the thickest oxide layer is 3.48 μm on the fuel rod surface at the core outlet after 20,000 h. The fuel rods maintain a double-layer oxide layer structure. The growth rate and removal rate of the oxide layer on fuel rod surface increase with the increase of inlet temperature and the decrease of inlet flow rate. The growth rate of the oxide layer on fuel rod surface increases with the increase of inlet oxygen concentration, while the removal rate decreases. At higher temperature above 420℃, lower flow velocity below 0.25 m/s and lower oxygen concentration below 2 × 10−8wt%, the magnetite layer will first be completely removed from the surface of the fuel rods at the core outlet. The liquid LBE oxidation corrosion model and coupled CFD method presented in this paper can be used for numerical simulation of oxidation corrosion in different units of LBE cooling system.

Corrosion resistance of Al2O3/FeAl coatings doped with Er2O3 in liquid Pb-15.7Li

Al2O3/FeAl coatings doped with Er2O3 were prepared on CLAM steel by ECX (electrochemical deposition in ionic liquids) and ion injection. The corrosion resistance of samples doped with Er2O3 was investigated in static liquid Pb-15.7Li at 550 °C for 1000 h. After the corrosion test, compared with the sample without Er2O3, the surface of the coating doped with Er2O3 was uniform and smooth, only a few corrosion products could be detected. Such results could be attributed to that: owing to the addition of Er2O3, the inward diffusion of Li and O ions along the coating grain boundaries was moderated, the formation of corrosion products and the growth of oxide layer was reduced. As a consequence, the corrosion resistance of Al2O3/FeAl coatings in liquid Pb-15.7Li was improved by doping Er2O3.

Effect of trace impurity elements on the high-temperature oxidation resistance of a high-purity nickel-based superalloy

This study indicates that the kinetic rate constants of oxidation weight gain and thickening both increase with the increasing content of O, N and S impurities. The oxide layer of the low-purity alloy is not tight and easy to peel off. Internal oxidation becomes more serious with the increase of oxygen solubility. The microscopic mechanism of how impurity atoms affect the oxidation diffusion process was explained, and the models of the oxide layer growth process for high-purity alloys and low-purity alloys were constructed, which provide a reference for the improvement of high-temperature oxidation performance of superalloys in the future.

Structure, electronic properties, and energetics of oxygen vacancies in varying concentrations of SixGe1−xO2

SiGe alloys, widely used in various technological applications, are typically interfaced with a thermally grown oxide layer that is composed of ${\mathrm{Si}}_{x}{\mathrm{Ge}}_{1\ensuremath{-}x}{\mathrm{O}}_{2}$, a composite material which is also used for technological applications in its own right. Point defects in this oxide layer influence the electronic and structural properties, which can detrimentally affect the desired application. In this paper, we use ab initio calculations to investigate the canonical oxygen vacancy in systems of varying compositions of ${\mathrm{Si}}_{x}{\mathrm{Ge}}_{1\ensuremath{-}x}{\mathrm{O}}_{2}$. We find that the electronic structures and geometries of the vacancies remain qualitatively similar to their well-known analogs in ${\mathrm{SiO}}_{2}$ and ${\mathrm{GeO}}_{2}$ regardless of the composition and similar to previous results in the literature on Ge-doped ${\mathrm{SiO}}_{2}$. They show a wide distribution of formation energies and one-electron levels across the various concentrations of ${\mathrm{Si}}_{x}{\mathrm{Ge}}_{1\ensuremath{-}x}{\mathrm{O}}_{2}$. However, our results show that the factor defining their quantitative behavior is not the concentration, rather it is the chemistry of the atoms around the vacancy, each combination of which has its own distribution of properties. The resulting charge transition levels similarly cover a wide range of the band gap. These results aid the understanding of reliability issues in technological applications.

Phase transitions in alumina films during post-sparking anodising of Al alloys

Formation of the high-temperature α-Al2O3 phase during Plasma Electrolytic Oxidation of aluminium at ambient bulk temperatures has been previously attributed to local microdischarge events providing multiple melting-solidification cycles in micro-volumes of the surface oxide layer. In this work, it is demonstrated that the α phase can be formed even if the microdischarge is fully suppressed under specific processing conditions. Oxide layers produced in the post-sparking anodising mode were studied by FIB, TEM, EBSD, EDS and GDOES techniques to reveal microstructural and chemical evolutions that accompany the γ to α alumina transition. Our results provide strong evidence that the α phase can form spontaneously in regions of oxide with the appropriate temperature, grain size and impurity distributions in the γ-Al2O3 matrix that allow sufficient mobility of α/γ grain boundaries. Ionic migration within the oxide and hydrothermal dissolution/precipitation in the associated microporous network that facilitate species mobility at the grain boundaries allow the critical temperature for activation of γ→α transition to be reduced. Overall, it is suggested that oxide layer growth can be considered in terms of a relatively simple Plug Flow Reactor model. This can help predict the phase transition kinetics depending on key processing parameters such as current density and frequency of pulse polarisation, thus enabling optimum control of coating microstructure for specific application requirements.

The use of some sulfonic acids for improving aluminum current collector resistance

The corrosion behavior of aluminum current collectors in the standby and high-load modes was investigated by simulating via immersion and anodization experiments in electrolyte environments. The immersion experiments were carried out using aluminum alloy (AA5754) in camphorsulfonic (CSA), p-toluenesulfonic (PTSA), trifluoromethanesulfonic (TFMSA), and fluorosulfonic (FSA) acid solutions, and the results were compared with those of H 2 SO 4 and methanesulfonic acid (MSA). Corrosion resistance increased in the order of FSA, MSA, TFMSA, PTSA, H 2 SO 4 , and CSA. Thin-film XRD and XPS results revealed sulfonic acid adsorption to Al 2 O 3 . From AFM, the least rough and highest crystalline oxide layer was obtained with CSA, while FSA yielded the opposite. In addition, AA5754 was anodized in 0.1 M CSA, PTSA, and H 2 SO 4 solutions, and its corrosion behavior was examined. R ct values were about one hundred times higher than in the immersion experiments; besides, less rough and thicker layers were obtained on the surface owing to the controlled dissolution. The mixture of CSA:H 2 SO 4 (1:1) was used as an anodization solution, and the maximum resistance (5652 Ω.cm 2 ) was obtained at 20 V, which was a better corrosion behavior according to individual electrolytes. This could be due to the optimum combination of the high acidity of H 2 SO 4 and the ability of CSA to block the surface sites thanks to its larger cyclic structure. Finally, a symmetric supercapacitor cell prepared using a carbon-coated Al current collector in PVA/H 2 SO 4 :CSA gel electrolyte was tested by cyclic voltammetry and GCD. The cell provided 26 Wh.kg -1 and 10.2 kW.kg -1 with 89% efficiency and 64% retention after 5000 cycles over a wide potential range of 1.6 V, exhibiting better capacitive performance than the gel electrolyte without CSA. This increase could be because CSA contributes to the growth of the protective aluminum oxide layer as an anionic surfactant. • Sulfonic acids are adsorbed on aliminum alloy surface during immersion and anodization • Al 2 O 3 has the least rough and highest crystalline in the presence of camphorsulfonic and p-toluenesulfonic acids • The corrosion resistance of AA5754 significantly improves by anodization in the mixtures of sulfonic acids with H 2 SO 4 • Supercapacitor with Al current collector operates in a wide potential range of 1.6 V in PVA/H 2 SO 4 :CSA • The cell provides 26 Wh.kg -1 and 10.2 kW.kg -1 with 89% efficiency

The behavior of plasma sprayed thermal barrier coating with laser microtextured bond coat under high temperature testing

In this work, the laser microtexturing is exploratory studied for controlling the interface between the oxidation resistant metallic bond coat and thermally insulating ceramic top coat in Thermal Barrier Coatings.The 80 to 100 μm thick NiCrAlY layer was deposited by Atmospheric Plasma Spraying over the nickel-based super alloy substrate. Then, the infrared fiber nanosecond laser was used for shaping the topography of bond coat prior to the top coat deposition. The surface geometry was adapted by selecting the laser set-up operational conditions, mainly: (i) laser power, (ii) frequency, (iii) scanning velocity and (iv) inter-pass spacing. The two groove-based patterns were finally selected for further work together with one as-sprayed bond coat, as a reference. The 8 wt% yttria stabilized zirconia (8YSZ) was deposited by means of Suspension Plasma Spraying over all three types of bond coats. The samples were then subjected to isothermal oxidation and thermal cyclic fatigue testing in order to study the influence of bond coat topography on the overall behavior of coatings under high temperature conditions. The microstructural studies revealed that the as-sprayed bond coat topography may be progressively modified by multistep laser microtexturing. The uniform bond coat topography is found to be beneficial in promoting formation of homogeneous, columnar-like top coat. However, the modification of bond coat topography affects the behavior of the bond coat/top coat interface during high temperature testing. The study shows that the microtexture depth should be precisely controlled, otherwise the through bond coat thickness oxidation is observed, which has a detrimental effect on the overall durability of the TBC system. The bond coat asperity width plays also an important role. If it is too narrow, then the failure may propagate locally through the bond coat or the thermally grown oxide layer.