Oxygen Penetration Research Articles

Oxidation of TiAl alloy by oxygen grain boundary diffusion

Ti–Al intermetallic alloys have a number of advantages for the manufacture of aviation and car details. The use of these alloys is limited by their oxidation at high temperatures, which is associated with structural features and the presence of micro and nanosized grains. In such materials, grain boundary diffusion of oxygen can be active, which contributes to the acceleration of oxidation upon heating. In this paper, we present a two-dimensional model for research the diffusion which is accompanied by oxidation. The structure of TiAl is specified as symmetrically alternating grains with a clear separation of boundaries and triple junctions between them. Diffusion and chemical properties of grains and boundaries are different. The problem is formulated in a two-dimensional formulation and solved numerically. The influence of changes in the composition over time on the penetration of oxygen is taken into account. For the convenience of numerical research and analysis of the results, dimensionless variables are used. To solve the diffusion equation, an implicit difference scheme of splitting in coordinates is used. The equations of chemical kinetics are solved using an algorithm similar to the implicit Euler method using an iterative procedure. The results demonstrate the influence of different variants of kinetic regimes on the concentration distribution and integral concentrations of reagents and oxides.

Oxidation Effects on Short-Term Creep Response in Air of Commercially Pure Titanium (CP-2 Ti)

The creep response in the air of commercially pure titanium was investigated at 550, 600, and 650 °C to assess the effect of oxidation on the mechanical response. Experiments demonstrated that prolonged exposures at high temperatures produced a marked reduction in the minimum creep rate under a given applied stress. Microhardness measurements showed that a hardened zone formed in proximity to the surface due to oxygen penetration into the metal. A simplified composite model was then used to describe the creep response. In this model, the sample consisted of two zones, the hard case that was enriched in oxygen and the soft pure-titanium core, both creeping with similar strain rates. Calculations led to an estimation of the dependence of the minimum creep rate on stress and temperature for the hard high-oxygen zone. The simplified composite model presented here provided a good description of the experimental creep data for pure titanium, tested in its air, and a reliable picture of the effect of oxidation on complex Ti alloys.

Hydrodynamic Control of Sediment‐Water Fluxes: Consistent Parameterization and Impact in Coupled Benthic‐Pelagic Models

AbstractBenthic oxygen dynamics and the exchange of oxygen and other solutes across the sediment‐water interface play a key role for the oxygen budget of many limnic and shallow marine systems. The sediment‐water fluxes are largely determined by two factors: sediment biogeochemistry and the thickness of the diffusive boundary layer that is determined by near‐bottom turbulence. Here, we present a fully coupled benthic‐pelagic modeling system that takes these processes and their interaction into account, focusing especially on the modulation of the sediment‐water fluxes by the effects of near‐bottom turbulence and stratification. We discuss the special numerical methods required to guarantee positivity and mass conservation across the sediment‐water interface in the presence of rapid element transformation, and apply this modeling system to a number of idealized scenarios. Our process‐oriented simulations show that near‐bottom turbulence provides a crucial control on the sediment‐water fluxes, the oxygen penetration depth, and the re‐oxidation of reduced compounds diffusing upward from the deeper benthic layers especially on time scales of a few days, characterizing oceanic tides, internal seiching motions in lakes, and mesoscale atmospheric variability. Our results also show that the response of benthic‐pelagic fluxes to rapid changes in the forcing conditions (e.g., storm events) can only be understood with a fully coupled modeling approach.

The high temperature oxidation and thermal shock behavior of a dense WSi2–TaSi2 coating on Ta substrate prepared by a novel two-step process

In order to improve the oxidation resistance of the Ta substrate, a novel two-step process including molten salt electrodeposition (Na2WO4-WO3 system) and halide activated pack cementation was adopted to prepare a WSi2–TaSi2 coating on tantalum substrate. During the electrodeposition process, dense tungsten coatings were fabricated at current densities of 30 mA/cm2, 40 mA/cm2 and 50 mA/cm2. It was observed that the grain size exhibited a log-normal distribution. When the current density was 40 mA/cm2, the grain size and flattest surface of the tungsten coating reached 9.50 ± 0.23 μm and 6.792 μm, respectively. When performing the static oxidation test, the WSi2–TaSi2 coating could effectively protect the Ta substrate oxidized at 1600 °C for 30 h. This is attributed to the presence of dense SiO2 and Ta2O5, which acted as a protective layer and suppressed the further penetration of oxygen. Furthermore, due to the matching thermal expansion coefficient between each layer and the sealing ability of semi-molten SiO2, the four-layer SiO2–W5Si3–WSi2–Ta5Si3 coating could successfully pass 721 thermal shock tests from 1600 °C to room temperature.

Oxygen Penetration Through Full-Thickness Skin by Oxygen-Releasing Sutures for Skin Graft Transplantation

The transplantation of full-thickness skin grafts (FTSGs) is important for reconstructing skin barrier and promoting wound healing. Sufficient oxygen supply is closely related to the success of skin grafting. However, full-thickness oxygen delivery is limited by the poor oxygen permeability of skin. Oxygen-releasing sutures (O2 sutures) were developed to facilitate oxygen penetration through full-thickness skin. The O2 sutures delivered 100 times more oxygen than topical gaseous oxygen therapy at a 15 mm depth in the skin model. Under extreme hypoxia (< 0.5% O2, v/v), O2 sutures could also promote endothelial cell proliferation. After the transplantation of FTSGs in mice, O2 sutures accelerated blood re-perfusion and increased the survival area of the skin graft. It is expected that O2 sutures will be adopted in clinical applications to increase the success rate of full-thickness skin transplantation.

Effects of yttrium on the oxidation behavior of Fe13Cr6AlY alloys under 1200 °C steam

FeCrAl alloys are a candidate material for accident-tolerant fuel cladding in nuclear power plants owing to their high-temperature oxidation resistance, which can be further enhanced by the addition of Y. The main objective of this study was to investigate the effects of Y on the oxidation behavior of Fe13Cr6Al alloys in a 1200 °C steam environment with varying Y concentrations. Initially, Y was present as intermetallic particles in the matrix, which were identified as YFe4Al8. Once the oxidation process began, Y-rich intermetallics served as Y reservoirs and caused two conflicting effects: Y segregation at the oxide grain boundaries and Y-rich oxide formation. The Y segregation caused the inward diffusion of oxygen to be dominant, which changed the oxide growth mechanism and led to enhanced oxidation resistance and oxide adherence. On the other hand, Y formed Y2O3 at the grain boundaries near the oxide/metal interface, which eventually became Y3Al5O12. The Y3Al5O12 pegs allowed rapid oxygen penetration into the metal substrate and caused internal oxidation. Therefore, there is an optimal Y content as a result of these conflicting effects of Y addition. The reticular structure was also carefully analyzed to determine any relationship with the Y-rich oxide pegs. The reticular structure observed on the oxidized surface was identified as Y3Al5O12, which was formed at the grain boundaries of the metal or buried in the Al oxide. The size of the reticular structure coincided with the grain size of the metal near the surface. Data AvailabilityThe raw/processed data required to reproduce these findings cannot be shared at this time as the data also form part of an ongoing study.

Potential impacts of seasonal and altitudinal changes on enzymatic peat decomposition in the High Andean Paramo region of Ecuador

The Andean Paramo is a vast ecosystem, characterized by distinct vegetational zones at several altitudinal levels with huge water storage and carbon fixation capacity within its peat-like andosols, due to a slow decomposition rate of organic matter. These characteristics become mutually related as enzymatic activities increase with temperature and are associated with oxygen penetration, restricting the activity of many hydrolytic enzymes according to the enzyme Latch Theory. This study describes the changing activity of sulfatase (Sulf), phosphatase (Phos), n-acetyl-glucosaminidase (N-Ac), cellobiohydrolase (Cellobio), β-glucosidase (β-Glu), and peroxidase (POX) on an altitudinal scale from 3600 to 4200 m, in rainy and dry seasons at 10 and 30 cm sampling depth, related to physical and chemical soil characteristics, like metals and organic elements. Linear fixed-effect models were established to analyze these environmental factors to determine distinct decomposition patterns. The data suggests a strong tendency towards decreasing enzyme activities at higher altitudes and in the dry season up to two-fold stronger activation for Sulf, Phos, Cellobio, and β-Glu. Especially the lowest altitude showed considerably stronger activity of N-Ac, β-Glu, and POX. Although sampling depth revealed significant differences for all hydrolases but Cellobio, it had minor effects on model outcomes. Further organic rather than physical or metal components of the soil explain the enzyme activity variations. Although the levels of phenols coincided mostly with the soil organic carbon content, there was no direct relation between hydrolases, POX activity, and phenolic substances. The outcome suggests that slight environmental changes with global warming might cause important changes in enzyme activities leading to increased organic matter decomposition at the borderline between the paramo region and downslope ecosystems. Expected extremer dry seasons could cause critical changes as aeration increases peat decomposition leading to a constant liberation of carbon stocks, which puts the paramo region and its ecosystem services in great danger.

Oxygen barrier resistance of HfB2-MoSi2-TaB2 coatings in a wide temperature region

HfB2-MoSi2-based ultra-high temperature ceramic (UHTC) coatings have shown remarkable antioxidant effects owing to the formation of silicate glass layers with low oxygen permeability in high-temperature environments, which shows great potential in the antioxidation of carbon structural materials. To further enhance the oxidation resistance of the HfB2-MoSi2-based coating in a wide temperature region, the influence of volume ratio between HfB2 and TaB2 on the antioxidant capacity of the HfB2-MoSi2-TaB2 coatings was investigated. The addition of 15 vol% TaB2 in the 60HfB2-40MoSi2 coating delays the initial oxidation temperature of the 60HfB2-40MoSi2 sample from 300 °C to 500 °C, which decreased the oxidation loss by 75.85% during dynamic oxidation. In oxidation process at 900 °C and 1700 °C, the weight gains of the 45HfB2-40MoSi2–15TaB2 coating reduced by 78.56% and 63.14%, respectively. Due to the coexistence of 45 vol%HfB2 and 15 vol%TaB2, the suitable Ta5+ promoted the homogenization and dispersion of Hf/Ta-oxides, which forms the coral-like Hf/Ta oxides skeleton in the glass layer, thus preventing the oxygen penetration and decreasing the inert factor of the HfB2-MoSi2 coating at 1700 °C by 51.19%. However, excessive TaB2 weakened the self-healing ability of the Ta-Hf-Si-O glass layer and inhibited the oxygen barrier effect of the HfB2-MoSi2-TaB2 coating.

Oxidation ablation resistance of ZrB2-HfB2-SiC-TaSi2 coating prepared on C/C composite surface

In order to improve the oxidation and ablative properties of C/C composites, ZrB2-SiC-HfB2-TaSi2 coating was prepared on the surface of C/C composites by atmospheric plasma spraying. By means of microstructure analysis and phase structure analysis, the difference of the spray powder before and after IPS treatment and the microstructure and oxidation ablation resistance of the coating were studied. The results show that the IPS treated powder has better fluidity and densification. In the coating, part of ZrB2 and HfB2 exist in the form of unmelted particles, another part exists in the form of intermediate solid solution (Zr, Hf)B2, and TaSi2 exists in the particle gap. The linear ablation rate and mass ablation rate of the coating are −1.513 × 10−4 mm/s and 2.842 × 10−4 g/s, respectively, measured under the condition of oxygen acetylene heat flux of 1.8 MW/m2, 180 s were ablated. The coating has good ablative resistance, and TaSi2 can form dense Zr-Ta-O and Hf-Ta-O oxides with Zr and Hf elements. The Ta-Si-O glass phase can effectively seal the holes of the coating to prevent oxygen penetration. During the ablation process, the oxidation of (Zr,Hf)B2 also plays a certain role in the formation of densification zone on the coating surface.

Impact of Novel Active Layer-by-Layer Edible Coating on the Qualitative and Biochemical Traits of Minimally Processed 'Annurca Rossa del Sud' Apple Fruit.

The color changes brought on by the enzymatic interactions of phenolic compounds with released endogenous polyphenol oxidase and the penetration of oxygen into the tissue has a significant impact on the commercialization of fresh-cut fruit, such as apples. This process causes a loss of quality in fresh-cut apples, resulting in browning of the fruit surface. By acting as a semipermeable barrier to gases and water vapor and thus lowering respiration, enzymatic browning, and water loss, edible coatings can provide a chance to increase the shelf life of fresh-cut produce. In this study, the effect of edible coatings composed of carboxymethylcellulose (CMC, 1%), sodium alginate (SA, 1%), citric acid (CA, 1%), and oxalic acid (OA, 0.5%) on fresh-cut 'Annurca Rossa del Sud' apple was studied. Four formulations of edible coatings, A. SA+CMC, B. SA+CMC+CA, C. SA+CMC+OA, and D. SA+CMC+CA+OA, were tested. Fresh-cut apples were dipped into different solutions and then stored at 4 °C, and physicochemical and biochemical analyses were performed at 0, 4, 8, and 12 days of storage. Results demonstrated that all four combinations improved the shelf-life of fresh-cut apple by slowing down the qualitative postharvest decay, total soluble solid, and titratable acidity. The browning index was highest in the control samples (82%), followed by CMC+SA (53%), CMC+SA+CA (32%), CMC+SA+OA (22%), and finally CMC+SA+CA+OA (7%) after 12 days of cold storage. Furthermore, coating application increased the bioactive compound content and antioxidant enzyme activities. Furthermore, the synergistic activity of SA+CMC+CA+OA reduces enzymatic browning, prolonging the postharvest life of minimally processed 'Annurca Rossa del Sud' apples.

Polymer-Based Coating for Steel Protection, Highlighting Metal–Organic Framework as Functional Actives: A Review

Polymer-based coatings are a long-established category of protective coatings for metals and alloys regarding corrosion inhibition. The polymer films can degrade, and when coated on metallic substrates, the degradation facilitates moisture and oxygen penetration, reducing the polymer film’s adhesion to the metallic substrate and exposing the substrate to extreme conditions capable of corrosion. For this reason, pigments, inhibitors, and other compatible blends are added to the polymer coating formulations to enhance adhesion and protection. To prevent the possible deterioration of inhibitor-spiked polymer coatings, inhibitors are encapsulated through diverse techniques to avoid leakage and to provide a controlled release in response to the corrosion trigger. This review discusses polymer-based coating performance in corrosion-causing environments to protect metals, focusing more on commercial steels, a readily available construction-relevant material used in extensive applications. It further beams a searchlight on advances made on polymer-based coatings that employ metal–organic frameworks (MOFs) as functional additives. MOFs possess a tailorable structure of metal ions and organic linkers and have a large loading capacity, which is crucial for corrosion inhibitor delivery. Results from reviewed works show that polymer-based coatings provide barrier protection against the ingress of corrosive species and offer the chance to add several functions to coatings, further enhancing their anti-corrosion properties.

Oxidative Ablation Behavior of W‐Coated C/C Composites Prepared by Chemical Vapor Deposition with Heat Treatment

To improve the ablation resistance of C/C composites, tungsten (W) coating is applied by chemical vapor deposition (CVD) technology on C/C composites. Results show that the coatings are dense, with a thickness of about 400 μm. After heat treatment at a temperature of 1500 °C for 1 h, the main component of coating is W2C. Additionally, a dense WC layer forms on the surface of pyrolytic carbon (PyC). The sample subjected to heat treatment remains relatively intact after ablation at 3000 °C for 60 s, with a mass and linear ablation rate of 1.83 × 10−5 g s−1 and 3.03 × 10−5 cm s−1, respectively. The high‐temperature stability of WC formed on PyC and the filling of fiber gaps to prevent oxygen penetration are the main reasons for the improved ablation resistance of W‐coated C/C composites.

Achieving a thermally stable Eu2+-doped Sr2Si5N8 phosphor via adjusting the lattice defects of oxygen atoms and protection by the graphene-like multilayer

Sr2Si5N8:Eu2+ (258) phosphor has attracted much attention due to its excellent red emission properties. However, its poor thermal stability hinders its further development in electronic display devices. Therefore, it is important to solve this problem in order to produce stable and long life-time WLED devices. In this work, a 258 phosphor was synthesized by a simple solid-phase reaction method, which was then coated by an ultrathin carbon layer by chemical vapor deposition. The carbon-coated powders were further annealed in N2 atmosphere at a high temperature to trigger the carbothermal reaction. On the one hand, the carbothermal reaction resulted in the removal of oxygen in the phosphor particle by a part of the carbon on the surface, which reduced the oxidation of both the luminescent centers and the host lattice. On the other hand, the remaining carbon crystallized, forming a graphene-like multilayer that protected the phosphor particle from the penetration of the external oxygen. This eventually resulted in a significant improvement of the thermal stability and oxidation resistance of the phosphor.

Ediacaran-Cambrian bioturbation did not extensively oxygenate sediments in shallow marine ecosystems.

The radiation of bioturbation during the Ediacaran-Cambrian transition has long been hypothesized to have oxygenated sediments, triggering an expansion of the habitable benthic zone and promoting increased infaunal tiering in early Paleozoic benthic communities. However, the effects of bioturbation on sediment oxygen are underexplored with respect to the importance of biomixing and bioirrigation, two bioturbation processes which can have opposite effects on sediment redox chemistry. We categorized trace fossils from the Ediacaran and Terreneuvian as biomixing or bioirrigation fossils and integrated sedimentological proxies for bioturbation intensity with biogeochemical modeling to simulate oxygen penetration depths through the Ediacaran-Cambrian transition. Ultimately, we find that despite dramatic increases in ichnodiversity in the Terreneuvian, biomixing remains the dominant bioturbation behavior, and in contrast to traditional assumptions, Ediacaran-Cambrian bioturbation was unlikely to have resulted in extensive oxygenation of shallow marine sediments globally.

Enhancing CMAS corrosion resistance of PS-PVD Si/Yb2Si2O7 EBCs via Al-modification

Enhancing the resistance to molten silicate corrosion is crucial for the long service life of environmental barrier coatings (EBCs). In this study, we used the Al-modification technique to enhance the CMAS corrosion resistance of Si/Yb2Si2O7 coatings prepared by plasma spray-physical vapor deposition. The results show that the Al-modified Yb2Si2O7 coating had higher resistance to CMAS corrosion than the Yb2Si2O7 coating annealed at 1300 ℃ for 100 h, which is related to the refractory mullite and Yb2Mg(AlO2)2O3 generated during the CMAS exposure of Al-modified Yb2Si2O7 coating. The Al-modified Yb2Si2O7 coating also exhibited excellent resistance to oxygen penetration. The Al-modification technology provides the direction for the corrosion resistance of Yb2Si2O7 system to CMAS.

The effect of aeration on treatment efficiency and bioenergy generation of septic-tank effluent in constructed wetland-microbial fuel cell

This study examines the effect of different rates and modes of supplementary aeration on the treatment of synthetic septic tank effluent in a lab-scale unplanted constructed wetland-microbial fuel cell (CW-MFC) along with bioenergy generation. The experiment was conducted in 4 sequential phases; 1) the cell was operated with no aeration (NA), 2&3) the cathode layer was continuously aerated under different aeration rates (CA-I and CA-II), and 4) the cathode layer was intermittently aerated (IA). Results showed that the dissolved oxygen gradient caused by IA formed aerobic and anoxic zones in CW-MFC and promoted total nitrogen removal. The best performance was observed with intermittent aeration where the maximum removal efficiencies of COD (96.8 ± 3.3 %), TN (62.3 ± 2.1 %), TKN (68.3 ± 2.0 %), and NH3 (64.8 ± 2.3 %) were achieved. Furthermore, this treatment efficiency corresponded with enhanced bioenergy generation under the IA regime, achieving maximum power output (7.5 mW/m2), highest average voltage output (0.399 ± 0.02 V), Coulombic efficiency (1.94 %), and normalized energy recovery (1.4 Wh/m3). Continuous aeration, however, induced an adverse effect on energy generation due to excessive oxygen penetration into the anode region. Nitrate accumulation was also observed as a sign of an incomplete denitrification process under the continuous aeration regime. Overall, it can be concluded that the intermittently aerated CW-MFC not only lowers operational costs but improves effectiveness in terms of the nitrogen removal process in the treatment of septic tank effluent.

Structure‐property relationships of waterborne polyurethane (WPU) in aqueous formulations

AbstractThis study provides an overview of the rheological properties of aqueous polyurethanes (WPU), as the main component, or as a thickening additive in aqueous formulations. Waterborne polyurethanes (WPU) have been proposed as an environmentally friendly alternative to conventional solvent‐based solutions in a variety of industrial applications such as coatings, adhesives, inks. In all these fields, the control of rheological properties became an important prerogative to determine the quality of the dispersion and its potential applicability. First, the effect of parameters such as components, particle size and content, temperature, and interactions on dispersion viscosity was reported. Then, the effect of two additives, i.e. thickeners and nanomaterials, on structure–property relationships of WPU‐base systems, was described. Thickeners are rheological modifiers, commonly used to stabilize the dispersion and prevent flocculation and sedimentation of the particles, or to change the flow behavior of dispersions from Newtonian to pseudoplastic. These species can interact with water and polymer particles to create a network structure that alters the flow resistance, and thus viscosity. The use of hyperbranched aqueous polyurethane as thickening agent in WPU formulations was also presented. On the other hand, nanostructured fillers (0D/1D/2D) or a combination thereof in waterborne polyurethane led to the formation of specific microstructures that prevented the penetration of water, oxygen, and corrosive substances, also improved mechanical and thermal properties, allowing the development of high‐performance WPU‐based products.

High Hydraulic Loading Rates Favored Mainstream Partial Nitritation: Experimental Demonstration and Model-Based Analysis

Partial nitritation is required to provide nitrite for the anammox reaction in an autotrophic nitrogen removal process, which has been considered crucial to achieving energy-positive mainstream sewage treatment. In this study, three lab-scale reactors were operated to treat wastewaters with low ammonium concentrations at high hydraulic loading rates (nitrogen loading rates of 0.36 kg N/d/m3). Long-term experiments repeatedly demonstrated that a high hydraulic loading rate favored the startup of partial nitritation, as indicated by the nitrite buildup and effluent nitrite accumulation ratio maintained above 95% over 2 months. Despite many advantages of high loading rates, a major drawback resides in the process instability, i.e., unsustained nitrite-oxidizing bacteria (NOB) suppression. To elucidate the occurrence and disappearance of the partial nitritation, mathematical modeling was implemented. An integrated fixed-film activated sludge biofilm model was developed, calibrated, and validated based on the observed coexistence of granules and floccular sludge. Model-based analysis suggested that high hydraulic loading rates suppressed NOB likely via intensifying granule surface sloughing and restricting oxygen penetration. Based on the unraveled mechanisms, operational strategies were proposed and tested with mathematical models. The mechanisms illustrated in this work can guide the development of new operational strategies to facilitate mainstream partial nitritation and the anammox process.

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.

Surface treatment of triple cation mixed perovskite for highly stable lateral photodetectors with low dark current

Owing to their remarkable optoelectronic properties, three-dimensional (3D) organic-inorganic hybrid perovskites are considered as promising candidate materials for highly sensitive photodetectors (PDs). However, intrinsic instability and high dark current of bare 3D perovskite-based PDs are limiting their potential applications. In this paper, we utilized three different ammonium salts, including the alkyl methylammonium iodide (MAI), single-ring aromatic phenylmethylammonium iodide (PMAI), and fused-ring aromatic 1-naphthylmethylamine iodide (NMAI), to treat the 3D triple cation (Cs/FA/MA) mixed perovskite film, respectively. Most notably, the PMAI treatment generates a two-dimensional (2D) (PMA)2PbI4 capping layer on the top of the 3D mixed perovskite film. The 2D layer not only passivates the surface undercoordinated iodide ions defects of the 3D perovskite film, but also protects the film from oxygen and water penetration. As a result, the PMAI-treated perovskite PD exhibits an ultra-low dark current (5.49 × 10−11 A at a 10 V bias), a high on/off ratio (∼4 × 103) and good long-term air stability. The imaging capability is also demonstrated in the bilayer device.