Double-layer Oxide Research Articles

Effect of H2S on the corrosion behavior of austenitic and martensitic steels in supercritical CO2 at 550 °C and 20 MPa for Brayton cycle system

Corrosion of alloy materials significantly influences the stability and efficiency of the supercritical carbon dioxide (S-CO2) Brayton cycle. In this study, we investigated the corrosion behavior of the austenitic alloy SP2215 and the martensitic alloy X19CrMoNbVN11-19 (X19) in S-CO2 at 550°C and 20 MPa. The effect of impurities, H2S, on corrosion behavior was studied. After 900 hours, SP2215 formed a 1.1 μm thick oxide layer (Cr2O3). X19 formed a loose and porous double oxide layer of 4.1 μm (outer: Fe3O4, inner: FeCr2O4). After H2S doping, SP2215 had an oxide layer of 6.2 μm (FeS, SiO2, and Cr2O3), while X19 was 9.8 μm (outer: Fe3O4, SiO2, FexSy and Fe2O3, inner: FeCr2O4, Fe2SiO4 and Cr2S3). Metal sulfides formed and the corrosion layer thickened. This indicates that H2S not only changes the corrosion mechanism but also aggravates the corrosion. However, the corrosion of CO2 is dominant. SP2215 has better corrosion resistance than X19.

Optimization of the Synchronous Pressurization Process for the Elimination of Double-Layer Oxide Film Defects

Optimization of the Synchronous Pressurization Process for the Elimination of Double-Layer Oxide Film Defects

Effect of Y on Oxidation Behavior of Directionally Solidified Ni-Based Single-Crystal Superalloy

The effect of yttrium (Y) addition on the oxidation behavior of a Ni-based directionally solidified single-crystal superalloy is investigated in this study. Isothermal oxidation tests for samples with different levels of Y addition are conducted at 1100 °C in air. The Y content of the samples is determined by the actual pickup amount obtained from an Inductively Coupled Plasma-Atomic Emission Spectrometry test. It is discovered that the addition of Y increases the oxide resistance by the scale of an adhesive double-layer oxide, which is composed of Al2O3 and spinel Ni(Cr,Al)2O4. With 70 ppm of Y addition, the oxidation mass gain decreases from 12.6 g/m2 for the alloy without Y addition to 5.3 g/m2, and the oxidation rate decreases significantly. In addition, the internal nitride disappears after Y doping because of an increase in oxidation scale adherence and a decrease in oxidation products. In this study, the alloy with 660 ppm Y addition demonstrates the best oxidation resistance.

Superior Activity of Carbon Felt Coated with PEDOT and Titanium Oxide Double Layers Towards V(II)/(VIII) Reaction in Redox Flow Batteries

Energy consumption has become a great problem in the last few decades due to the dramatic increment in population and solo dependence on fossil fuels to fulfill energy requirements. The intense consumption of these limited non-renewable resources had harmful effects on humanity, making the adoption of renewable energy resources compulsory. High-efficiency storage systems are necessary for the integration of renewable energy sources into the electrical grid and for the provision of that energy when needed. For this application, all-vanadium redox flow batteries (VRFBs) hold great promise because of their high energy storage capacity, extended operational life, and long-life reusable solutions1. The enhancement of RFBs should be taken from many perspectives such as the enhancement of electrodes, membranes, or even the design of the cell. Enhancing the electrode performance is one of the important challenges that attracted the attention of researchers, with a variety of electrode modifications that have been studied such as using carbon, metals, and metal oxide materials2,3. Over a large number of metal oxides, TiO2 possesses interesting catalytic properties as it has been used in sensors, Li-ion batteries, and electrocatalysis, in addition to its ability to suppress the hydrogen evolution reaction (HER) which was a stumbling block for the negative side of VRFBs4.The goals of this work are to suppress the parasitic reaction of hydrogen evolution and improve the kinetics of the VRFBs' negative half-cell reaction (V(II)/V(III)). To achieve this goal, coating carbon felt (CF) with poly(3,4-ethylenedioxythiophene) (PEDOT) and Titanium Oxide double layers was proposed. The underlayer of PEDOT is expected to enhance the TiOx conductivity, and hence its electrocatalytic activity, but without enhancing the parasitic HER5. The PEDOT layer was formed using chronopotentiometric electropolymerization method, followed by the deposition of a TiOx layer using a solvothermal method. To understand the effect of the PEDOT and TiOx layers on the final electrode activity towards V(II)/V(III) redox reaction, several electrodes (CF\\PEDOT, CF\\G-PEDOT, CF\\TiOx CF\\PEDOT\\TiOx, and CF\\G-PEDOT\\TiOx) were fabricated. The physical and chemical properties of the synthesized electrodes were characterized using XRD, FESEM, EDX, UV-vis DRS, Raman spectroscopy, FTIR, contact angle measurements, and XPS. The performance of the fabricated electrodes towards V(II)/V(III) redox reaction was evaluated in 3-electrode and 2-electrode setups, using cyclic voltammetry, electrochemical impedance spectroscopy, and charging/discharging methods. The addition of an underlayer of PEDOT is found to generally enhance the TiO2 activity as a negative electrode in VRFB. References R. K. Sankaralingam, S. Seshadri, J. Sunarso, A. I. Bhatt, and A. Kapoor, J. Energy Storage, 41, 102857 (2021).Z. Huang, A. Mu, L. Wu, and H. Wang, J. Energy Storage, 45, 103526 (2022).Y. Lv et al., J. Mater. Sci. Technol., 75, 96–109 (2021).J. Vázquez-Galván et al., ChemSusChem, 10, 2089–2098 (2017).M. Heydari Gharahcheshmeh et al., Adv. Mater. Interfaces, 7, 2000855 (2020).

Revealing the Relationship between Critical Inlet Velocity and a Double-Layer Oxide Film Combined with Low-Pressure Casting Technology

In the context of low-pressure casting, an excessive inlet velocity may result in the introduction of an oxide film and air into a liquid metal, leading to the formation of a two-layer film structure within the casting. Such defects can significantly degrade the mechanical properties of the castings. In order to optimize the advantages of low-pressure casting, an empirically designed equation for the inlet velocity was formulated and the concept of critical inlet velocity was further refined. A comprehensive numerical simulation was conducted to meticulously analyze the liquid metal spreading phase within the cavity. Subsequently, low-pressure casting experiments were carried out with actual castings of an A357 alloy, using two different entrance velocities—one critical and the other exceeding the critical entrance velocity. Tensile test specimens were extracted from the castings for the comparative evaluation of mechanical properties. It was observed that the average tensile strength of specimens cast at the critical inlet velocity exhibited a notable 16% enhancement. In contrast, specimens cast at velocities exceeding the critical inlet velocity manifested the presence of double oxide film defects. This evidence suggests that casting at a velocity faster than the critical inlet velocity leads to the formation of double oxide film defects, which in turn reduces the mechanical properties of the castings.

High-Temperature Oxidation and Phase Stability of AlCrCoFeNi High Entropy Alloy: Insights from In Situ HT-XRD and Thermodynamic Calculations.

The high-temperature oxidation behaviour and phase stability of equi-atomic high entropy AlCrCoFeNi alloy (HEA) were studied using in situ high-temperature X-ray diffraction (HTXRD) combined with ThermoCalc thermodynamic calculation. HTXRD analyses reveal the formation of B2, BCC, Sigma and FCC, phases at different temperatures, with significant phase transitions observed at intermediate temperatures from 600 °C-100 °C. ThermoCalc predicted phase diagram closely matched with in situ HTXRD findings highlighting minor differences in phase transformation temperature. ThermoCalc predictions of oxides provide insights into the formation of stable oxide phases, predominantly spinel-type oxides, at high p(O2), while a lower volume of halite was predicted, and minor increase observed with increasing temperature. The oxidation behaviour was strongly dependent on the environment, with the vacuum condition favouring the formation of a thin, Al2O3 protective layer, while in atmospheric conditions a thick, double-layered oxide scale of Al2O3 and Cr2O3 formed. The formation of oxide scale was determined by selective oxidation of Al and Cr, as further confirmed by EDX analysis. The formation of thick oxide in air environment resulted in a thick layer of Al-depleted FFC phase. This comprehensive study explains the high-temperature phase stability and time-temperature-dependent oxidation mechanisms of AlCrCoFeNi HEA. The interplay between surface phase transformation beneath oxide scale and oxides is also detailed herein, contributing to further development and optimisation of HEA for high temperature applications.

Ni segregation in the oxide film of 15–15Ti austenitic steel at high-temperature CO2

A double-layer oxide film was formed on 15–15Ti exposed to high-temperature CO2, with outer Fe-rich layer and Cr/Ni-rich inner layer comprising Ni-poor and Ni-rich zones. The Ni-poor zone contained Fe-Cr spinel oxides and numerous nanopores, whereas the Ni-rich zone consisted of Fe-Cr spinel oxides and Ni-rich phases with austenite structure. The Ni segregation showed a specific evolution with exposure time and temperature: Ni-poor zones grew up and evolved into a laminar structure as the oxide film thickened. The formation and evolution mechanism of Ni-poor zones and the effect of Ni segregation on the oxidation were discussed in present work.

Effect of Microstructure on Oxidation and Micro-mechanical Behavior of Arc Consolidated Mo-Ti-Si-(B) Alloys

AbstractThe present study deals with the development and characterization of Mo-35Ti-10Si and Mo-35Ti-10Si-2B (wt.%) alloy for ultra-high temperature applications beyond the temperature limit of existing super alloys. The microstructural characterization using scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), electron back scattered diffraction (EBSD), x-ray diffraction (XRD) revealed that the Mo-35Ti-10Si-2B alloy was consisted of three phases, namely, (Mo, Ti)ss, (Mo, Ti)5SiB2 and (Ti, Mo)5Si3; whereas, Mo-35Ti-10Si alloy was found to be consisting of (Mo, Ti)ss, and (Mo,Ti)3Si phases. Since quantification of boron is difficult by EDS, Particle Induced Gamma-ray Emission (PIGE), a nuclear reaction analysis technique was used for chemical composition analysis of boron. The oxidation behavior of the Mo-35Ti-10Si-2B alloy in the temperature regime of 825-1250 °C was studied in detail and compared with boron-free Mo-35Ti-10Si alloy. Mo-35Ti-10Si-2B alloy exhibited superior oxidation behavior at intermediate temperatures of 825 °C, and excellent oxidation resistance at higher temperatures between 1000 and 1250 °C due to the formation of the protective borosilica and double oxide layers (TiO2 and duplex borosilica-TiO2), respectively. High-temperature oxidation mechanisms were discussed using detailed microstructural cross section analysis of the oxidized alloy samples. The micro-mechanical behavior of constitutive phases of the Mo-35Ti-10Si-2B alloy were studied by microhardness, nano-indentation and micropillar compression testing. The micropillar compression of (Mo, Ti)ss phase showed fairly ductile behavior with the evidence of activation of dislocation in the form of slip lines revealed through the post-deformation fractography. Deformation studies of (Mo, Ti)5SiB2 and (Ti, Mo)5Si3 phases were also carried out which showed large strain bursts indicating possibility of activation of dislocation activities even at room temperatures imparting low level of ductility.

Corrosion characteristics of Fe, Ni and Ti based alloys near the critical point of water and during supercritical water gasification and oxidation of municipal sludge

Supercritical water gasification (SCWG) and oxidation (SCWO) were promising technologies for treating municipal sludge; however, corrosion hindered their development. To obtain the candidate material for preheaters, corrosion characteristics of 316, 316 L, Incoloy 800, 825, and TA-10 were investigated at 350 °C and 400 °C. For SCWG and SCWO reactors, corrosion behaviors of 316, Incoloy 800, 825, Inconel 600, 625, and Hastelloy C276 were explored at 450 °C and 520 °C, with and without oxidants. Near the critical point of water, corrosion rates of all materials were below 0.4 mm·a−1, with 316 L being the candidate material. According to the pH variation, materials underwent activation (350 °C) and passivation (400 °C) pathways. During SCWG and SCWO, Incoloy 825 and Inconel 625 were prioritized at 450 ℃ and 520 ℃, exhibiting corrosion rates below 0.40 mm·a−1 and 0.50 mm·a−1, respectively. Chemical corrosion dominated and double-layer oxide films (Fe3O4-FeCr2O4 and NiO-Cr2O3) formed.

Investigations on supercapacitor performance of novel ZnO-CeO2-rGO nanohybrid prepared via hydrothermal method for energy storage applications and their charge storage mechanism

Nanohybrids which can utilize the synergistic effect to enhance the electrochemical activity as an electrode material for supercapacitor has gained immense interest recently.Here,we report a ZnO-CeO2-rGO ternary nanohybrid synthesized via hydrothermal method which can combine the pesuedocapacitance nature of transition metal oxide and electric double layer behavior of reduced graphene oxide. The electrochemical activity was thoroughly investigated using cyclic voltammometry(CV) and galvanostatic charge discharge for the ternary using a two electrode set up with 2 M KOH as the electrolyte. Cyclic stability analysis was done and impedance analysis was carried out using electrochemical impedance spectroscopy. Among the samples the best electrochemical performance was observed for ZnO –CeO2-rGO (Ter-2) with weight ratio 85:10:5. Ter-2 exhibited specific capacitance of 26 F/g from CV in the 2-electrode setup and a capacity retention as high as 93 % even after 5000 cycles of charge-discharge. It was observed that the addition of rGO improved the cyclic stablity as well as specific capacitance. Systematic analysis of charge storage mechanism was done using Dunn's and Trasatti's method. The results substantiate that Ter-2 is a potential supercapacitor electrode material with excellent electrochemical activity.

Optimizing Factors affecting gas porosity in GDC of Al-Si (A356) Alloy using Taguchi’s DOE

Aluminium alloys find extensive use in various applications because of its advantage of strength-to-weight ratio,. However, the casting process introduces susceptibility to defects, and managing all parameters proves to be a complex task. Casting rejections often stem from one or more defects, with mold parameters, filling, and solidification processes being key contributors. When the molten metal of the Al-Si (A356) alloy is exposed to the atmosphere in a holding furnace, it develops an oxide layer on its surface. Turbulence in the molten metal leads to the formation of a double oxide layer, also known as bifilms. Gas entrainment occurs due to the turbulent movement of metal, resulting in the entrapment of gas in the molten metal and ultimately causing gas porosity in the final casting. Gas entrapment during the filling process leads to gas porosities during the solidification phase.This study aims to comprehend the factors influencing the formation of gas entrapment during the casting of the aluminium alloy Al-Si (A356). The experimental investigation utilizes Taguchi’s Design of Experiments (DOE) to explore the impacts of parameters such as pouring temperature (PoT), degassing time (DgT), and volume in the holding furnace (VoH) on the formation of gas porosity in casting [8].An experimental setup was created to produce tensile test rods and reduced pressure test (RPT) samples. The results were validated using the mechanical properties of the tensile test samples and the density of the Reduced Pressure Test (RPT) samples. Better the mechanical properties, fewer will be the defects in castings. Taguchi’s DOE is applied to analyse the results. The experimental findings indicate that a pouring temperature at level 1 (710°C), degassing time at level 1 (10 minutes), and volume in the holding furnace at level 1 (>450 kg) yield favourable castings. Confirmatory tests were conducted to validate the results, and they aligned with the experimental data.

A bacterial cellulose/polyvinyl alcohol/nitro graphene oxide double layer network hydrogel efficiency antibacterial and promotes wound healing

In this study, graphene oxide (GO) was chemically modified utilizing concentrated nitric acid to produce a nitrated graphene oxide derivative (NGO) with enhanced oxidation level, improved dispersibility, and increased antibacterial activity. A double-layer composite hydrogel material (BC/PVA/NGO) with a core-shell structure was fabricated by utilizing bacterial cellulose (BC) and polyvinyl alcohol (PVA) binary composite hydrogel scaffold as the inner network template, and hydrophilic polymer (PVA) loaded with antibacterial material (NGO) as the outer network. The fabrication process involved physical crosslinking based on repeated freezing and thawing. The resulting BC/PVA/NGO hydrogel exhibited a porous structure, favorable mechanical properties, antibacterial efficacy, and biocompatibility. Subsequently, the performance of BC/PVA/NGO hydrogel in promoting wound healing was evaluated using a mouse skin injury model. The findings demonstrated that the BC/PVA/NGO hydrogel treatment group facilitated improved wound healing in the mouse skin injury model compared to the control group and the BC/PVA group. This enhanced wound healing capability was attributed primarily to the excellent antibacterial and tissue repair properties of the BC/PVA/NGO hydrogel.

Effect of Gating System Design on the Quality of Aluminum Alloy Castings

In this paper, a naturally pressurized gating system has been designed to reduce the turbulence of the melt during casting. The influence of gate dimensions, foam filters, a trident gate and a vortex element were evaluated. Their effect on melt velocity, flow characteristics, number of oxides, casting properties and mechanical properties were observed. ProCAST Simulation software v.2023 and a water flow test were also evaluated to assist in the experimental evaluation of the castings. Melts showed a relationship between melt velocity and porosity of castings. Quantitative evaluation of the surface porosity showed a trend of decreasing porosity with decreasing melt velocity. The greatest reduction in the melt velocity was achieved by a M4 design, which was associated with the highest reduction in the oxides. The pores analyzed proved the presence of oxide layers on their inner surface and a possible theory of pore formation when the initiator of porosity is entrained double oxide layers. The best metal yield was achieved with M1, but the difference between M2 and M4 was negligible (2–5% yield difference), so it can be stated that the beneficial effect of the M4 design in providing the best quality castings is not negated by the increase in metal yield.

Comparison and mechanism research of corrosion behavior of materials used in supercritical water-cooled reactors

In this study, the corrosion characteristics of essential materials used in supercritical water-cooled reactors (SCWRs) were investigated. Austenitic stainless steels 304 SS and 316 SS and nickel-based alloys 625 and 800 were exposed to supercritical water (SCW) at 500 °C and 25 MPa. The results showed that 304 SS, 316 SS, and Alloy 800 formed a double oxide layer, with the outer and inner layers enriched in Fe and Cr/Ni, respectively. Alloy 625 formed outer Ni-rich oxides (mainly NiO) and inner Cr-rich oxides and Ni-Cr oxides (mainly Cr2O3 and NiCr2O4, respectively). The results indicated that the difference in the protective performance of the corrosion products was mainly due to the Cr content, and the order of corrosion resistance was Alloy 625 > Alloy 800 > 304 SS > 316 SS. In addition, a corrosion mechanism model was established, which lays a good foundation for corrosion prediction and protection in SCWRs.

Lead-bismuth eutectic corrosion resistance of TiAlN coating after N5+ ion irradiation

In this study, a Ti0.33Al0.67N coating with Cr as the transition layer was prepared by cathodic arc-ion plating. After irradiation with N5+ ions, the coating was exposed to lead-bismuth eutectic (LBE) at 450 °C for 3000 h. The effect of irradiation on the corrosion resistance of the coatings was also investigated. No evidence of an LBE corrosion attack was observed in either the irradiated or unirradiated coatings. Transmission electron microscopy images revealed that the nanoscale oxide layer on the surface of the titanium aluminum nitride coating was the main barrier to LBE corrosion. The unirradiated coating had a single oxide layer, whereas the irradiated coating had a double oxide layer. Irradiation also affects the coating adhesion by inducing stress. However, after the corrosion test, the adhesion of all coating samples unexpectedly increased and were almost at the same level. The coating exhibited excellent properties after irradiation and LBE corrosion; therefore, the coating can be applied in future nuclear reactors.

Enhancing oxidation resistance of ferritic heat-resistant stainless steel in air atmosphere at 1100 °C by self-repairing oxide layer

The oxidation behaviors of Al-free and 1Al ferritic heat-resistant stainless steels (FHSSs) at 1100 °C were investigated. After oxidation for 100 h, the Al-free FHSS had triple oxide layers of a first layer Fe2O3 + MnCr2O4, a second layer MnCr2O4 + Cr2O3 + MnO, a third layer SiO2 and oxides of Nb and Ti. The 1Al FHSS had double oxide layers of a first layer Ti-bearing (Al, Cr)2O3 particles, a second layer dense (Al, Cr)2O3. The (Al, Cr)2O3 layer with self-repairing feature can reduce the thickness of oxide layer by 515 times, and reduce the oxidation weight gain rate of the FHSS by 5 orders of magnitude.

Toughening mechanism and oxidation resistance of SiC whisker-toughened SiAlCN ceramics

Mechanical alloying and spark plasma sintering were used to prepare dense SiCw/SiAlCN ceramics. The effects of whisker content on the mechanical properties and oxidation resistance were investigated. Compared with SiAlCN ceramic, the fracture toughness of 5 wt% SiCw/SiAlCN ceramic increased by 31.8 % to 5.8 MPa m1/2, which was attributed to crack deflection/branch and SiCw bridging/pull-out. Based on quantitative calculation, SiCw bridging/pull-out increased fracture toughness by 27.8 %. The flexural strength of 5 wt% SiCw/SiAlCN ceramic was 523.2 MPa, which was 26.9 % higher than that of SiAlCN ceramic. The residual strengths of the SiCw/SiAlCN ceramic after 50 h isothermal oxidation at 1500 °C and 50 times thermal cycles from room temperature to 1500 °C were 292.5 and 449.7 MPa. Because of SiAlCN matrix passive oxidation and SiCw active oxidation, a double-layer oxide scale composed of glassy scale and porous scale was formed on SiCw/SiAlCN ceramics. The unoxidized whiskers could remain original morphology and were available to strengthening and toughening.

Effect of co on mechanical and electrochemical properties of powder synthesized cellular Ti-Al alloy

ABSTRACT This work describes the effect of Co content on the compressive and electrochemical behaviour of cellular Ti4AlxCo (x = 2%, 4%, 6% and 8 wt%) alloy. Cellular products were prepared through powder metallurgy route by adding 70 v% of ammonium bicarbonate as space holder in Ti4AlxCo powder mixture. Relative density of the final products slightly upsurged due to increment of Co amount and it was found in the range of 0.32–0.35. Microstructure represented the interconnecting pores which will be advantageous to circulate the body fluid, if used as a bone implant. Plastic collapse stress of Ti4Al8Co was about 45% higher than Ti4Al2Co. Also, the elastic modulus was under the range of modulus of natural bone (11 ± 1 GPa). In Tafel plot, value of corrosion current density shifted from 8 μA/cm2 to 15 μA/cm2 by increasing the Co content from 2 wt% to 8 wt% which indicates the hampering of corrosion resistance. Corrosion rate followed the linear relationship with Co content. Best fitted electrochemical circuit showed the double layer oxide formation during corrosion. Micrographs of corroded cellular samples also represent that the surface of material is more prone to corrosion containing higher amount of Co.

Atomic-level mechanism of CO2-promoted oxidation of alumina-forming alloys

The high-temperature oxidation of the NiAl alloy in the CO2 and O2 atmospheres is comparatively studied by a combination of electron microscopy characterization and first-principles calculations. It is shown that CO2 accelerates the oxidation of NiAl alloy by the formation of a highly porous γ-Al2O3 scale that is non-protective and follows the linear growth law. By contrast, the NiAl oxidation in O2 results in a double-layered oxide scale consisting of an outer columnar γ-Al2O3 layer and an inner equiaxed α-Al2O3 layer, which is protective and follows parabolic growth law. Our first-principles calculations show that this accelerated NiAl oxidation in the CO2 can be attributed to more ready decomposition of adsorbed CO2 than adsorbed O2 into atomic oxygen on defective γ-Al2O3 surfaces, which leads to the inward γ-Al2O3 growth by the infiltration of gaseous CO2 through the cracked oxide scale toward the exposed NiAl alloy. These results provide new insights into the atomic origin of CO2-promoted alloy oxidation.

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

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