Oxygen Diffusion Research Articles

A mathematical model of tissue axial and radial diffusion in the microvasculature for intravascular microscopy and phosphorescence quenching data

This study aims to extend earlier Krogh Cylinder Models of an oxygen profile by considering axial diffusion and analytically solving Fick's Law Partial Differential Equation with novel boundary conditions via the separation of variables. We next prospectively collected a total of 20 animals, which were randomly assigned to receive either fresh or two-week-old stored red blood cell (RBC) transfusions and PQM oxygen data were measured acutely (90 min) or chronically (24 h). Transfusion effects were evaluated in vivo using intravital microscopy of the dorsal skinfold window chamber in Golden Syrian Hamsters. Hamsters were initially hemorrhaged by 50% of total blood volume and resuscitated 1-h post hemorrhage. PQM data were subsequently collected and fit the derived 2D Krogh cylinder model. Systemic hemodynamics (mean arterial pressure, heart rate) were similar in both pre and post-transfusion with either stored or fresh cells. Transfusion with stored cells was found to impair axial and radial oxygen gradients as quantified by our model and consistent with previous studies. Specifically, we observed a statistically significant decrease in the arteriolar tissue radial oxygen gradient after transfusion with stored RBCs at 24 h compared with fresh RBCs (0.33 ± 0.17 mmHg μ m-1 vs, 0.14 ± 0.12 mmHg μ m-1; p = 0.0280). We also observed a deficit in the arteriolar tissue oxygen gradient (0.03 ± 0.01 mmHg μ m-1 fresh vs. 0.018 ± 0.007 mmHg μ m-1 stored; p = 0.0185). We successfully derived and validated an analytical 2D Krogh cylinder model in an animal model of microhemodynamic oxygen diffusion aberration secondary to storage lesions.

Mechanisms of Hysteresis and Reversibility across the Voltage-Driven Perovskite-Brownmillerite Transformation in Electrolyte-Gated Ultrathin La0.5Sr0.5CoO3-δ.

Perovskite cobaltites have emerged as archetypes for electrochemical control of materials properties in electrolyte-gate devices. Voltage-driven redox cycling can be performed between fully oxygenated perovskite and oxygen-vacancy-ordered brownmillerite phases, enabling exceptional modulation of the crystal structure, electronic transport, thermal transport, magnetism, and optical properties. The vast majority of studies, however, have focused heavily on the perovskite and brownmillerite end points. In contrast, here we focus on hysteresis and reversibility across the entire perovskite ↔ brownmillerite topotactic transformation, combining gate-voltage hysteresis loops, minor hysteresis loops, quantitative operando synchrotron X-ray diffraction, and temperature-dependent (magneto)transport, on ion-gel-gated ultrathin (10-unit-cell) epitaxial La0.5Sr0.5CoO3-δ films. Gate-voltage hysteresis loops combined with operando diffraction reveal a wealth of new mechanistic findings, including asymmetric redox kinetics due to differing oxygen diffusivities in the two phases, nonmonotonic transformation rates due to the first-order nature of the transformation, and limits on reversibility due to first-cycle structural degradation. Minor loops additionally enable the first rational design of an optimal gate-voltage cycle. Combining this knowledge, we demonstrate state-of-the-art nonvolatile cycling of electronic and magnetic properties, encompassing >105 transport ON/OFF ratios at room temperature, and reversible metal-insulator-metal and ferromagnet-nonferromagnet-ferromagnet cycling, all at 10-unit-cell thickness with high room-temperature stability. This paves the way for future work to establish the ultimate cycling frequency and endurance of such devices.

Corrosion of Old Overhead Lines: Insights into Aluminum-Steel Galvanic Couple Using Electrochemical Techniques

In order to explain the corrosion inside 20th century power lines, the galvanic corrosion of steel and aluminum from 1949 was examined. In this investigation, 0.1 M Na2SO4 + 1 mM NaCl was used as moderately corrosive medium. Various electrochemical methods were applied to determine the corrosion potential and the different reactions involved in the corrosion process. The thickness of the oxide layer that regulates the corrosion of aluminum was obtained from impedance measurements and it was shown that the diffusion of oxygen through a porous oxide layer is the governing stage for the reaction occurring at the steel electrode. Finally, the corrosion of steel regulates the corrosion of both metals when they are in electrical contact.

Oxidation resistance and thermal insulation performance of Al–Cr–O/Zr–O + NiCoCrAlSiY and Al–Cr–O + NiCoCrAlSiY coatings prepared by arc ion plating

Al–Cr–O/Zr–O multilayer coating + NiCoCrAlSiY bond layer and Al–Cr–O single-layer coating + NiCoCrAlSiY bond layer were deposited on superalloy by arc ion plating, and subsequently they were heat treated at 1000–1200 °C. Scanning electron microscope and X-ray diffractometer were used to analyze the microstructure and phase of the coatings. The results showed that both the Al–Cr–O/Zr–O multilayer coating and Al–Cr–O single-layer coating exhibited a compact spherical structure. After heat treatment, cracks occurred on the surface of Al–Cr–O/Zr–O coating. Cracks increased and widened with rising the temperature. However, the surface cell clusters of Al–Cr–O coating after heat treatment were changed to tightly connected granular structures, and the granular structures grew up significantly with the increase of annealing temperature. Owing to the oxygen ion conductor and lower densification of t-ZrO2 than α-Al2O3, t-ZrO2 in the Al–Cr–O/Zr–O coating provided an access for the inward diffusion of oxygen. Therefore, the high temperature oxidation resistance of the Al–Cr–O coating + NiCoCrAlSiY layer was superior to that of the Al–Cr–O/Zr–O multilayer coating + NiCoCrAlSiY layer. The thermal insulation performance of Al–Cr–O/Zr–O multilayer coating + NiCoCrAlSiY layer was better than that of Al–Cr–O coating + NiCoCrAlSiY layer due to the large thickness and low thermal conductivity of t-ZrO2 phase and the heat reflection of interlayer interface.

Study on the Thermal Stability of Molybdenum Oxide‐Passivated Silicon Solar Cells

Dopant‐free heterojunction (HJ) solar cells are known for their simple process conditions and low parasitic absorption. However, stability issues remain one of the major obstacles for further development of cells with transition metal oxides (TMOs). Therefore, this research demonstrates the mechanism of thermal annealing degradation effects on TMOs/silicon (Si) HJ, namely, the infiltration of oxygen from air and the bidirectional diffusion of oxygen from TMOs, by investigating a typical molybdenum oxide (MoOx)/Si contact. A dense Au interlayer is introduced to block the interdiffusion of oxygen from the MoOx/Si interface and its surrounding environment. As a result, the dense layer slows down the interfacial oxidation of MoOx/Si and the degradation of the MoOx work function, thus improving the stability of the MoOx/Si HJ to 200 °C. The diffusion of oxygen from MoOx to the MoOx/Si interface will be critical to further promote the thermal stability of the devices thereafter, especially for the cells with i‐a‐Si:H layer as the passivation layer. To attain stable dopant‐free cells with MoOx, it is crucial to prevent oxygen diffusion into Si while maintaining a high MoOx work function and a thin SiOx layer at the interface.

High-temperature oxidation characteristics of 20CrMnTi electroplated with copper

During high-temperature forming and phase change heat treatment, the steel surface is susceptible to oxidation. This can negatively affect the surface quality of steel parts. The production of antioxidant coatings on the surface of steel parts is important for high-temperature precision forming and heat treatment. In this paper, the high-temperature oxidation tests of 20CrMnTi steel, copper, and 20CrMnTi electroplated with copper are conducted. The 20CrMnTi samples showed varying degrees of mass gain above 900 °C; the copper samples showed varying degrees of mass gain above 700 °C; and the process of mass gain for copper-plated 20CrMnTi followed the same trend as for copper during heating and holding. For heated samples of 20CrMnTi plated with copper, the copper coating was oxidized and residual copper was observed in the oxide layer. The distance between the residual copper and the surface of the sample is greater than between the residual copper and the junction of the plating layer and the substrate. Oxygen diffuses through internal defects in the material at a higher rate than copper oxidation. In this study, an oxygen diffusion model and an antioxidant protective layer model at high temperatures were suggested. The protective layer against oxidation recommended in this research is a dense coating consisting of single crystals or fine grains free of porosities and cracks.

Composite LaNi0.6Fe0.4O3-δ - La0.9Sr0.1Sc0.9Co0.1O3-δ cathodes for proton conducting solid oxide fuel cells: Electrode kinetics study

Composite LaNi0.6Fe0.4O3-δ - La0.9Sr0.1Sc0.9Co0.1O3-δ (LNF-LSSCo) electrodes with the compositions 50/50, 60/40, and 80/20 wt% LNF/LSSCo are successfully applied for La0.9Sr0.1ScO3-δ proton conducting electrolyte. Electrochemical activity of the electrodes is studied by impedance spectroscopy, depending on temperature and oxygen partial pressure. The best performance is observed for 60/40 LNF/LSSCo electrodes. Detailed analysis of impedance data is performed using non-linear least squares and distribution of relaxation times methods taking into account the shunt effect of electronic conductivity of La0.9Sr0.1ScO3-δ electrolyte. Two main rate-determining stages of the electrode reaction are determined, which are assigned to oxygen ion diffusion in the bulk of the electrode and oxygen interphase exchange with the gas phase. The application of the LNF current collector layer improves the electrochemical activity of the electrodes without changes in the electrode reaction mechanism, while the modification of the electrodes with Pr6O11 leads to a sufficient decrease in the resistance of the stage, corresponding to oxygen interphase exchange, resulting in a twice-improved electrochemical activity of the electrodes.

Tailored SrFeO3-δ for chemical looping dry reforming of methane

Chemical looping dry reforming of methane (CL-DRM) is a highly efficient process that converts two major greenhouse gases (CH4 and CO2) into syngas ready for the feedstock of liquid fuel production. One of the major obstacles facing this technology now is creating oxygen carriers that are stable and reactive. We fabricated high-performance Sr0.98Fe0.7Co0.3O3-δ perovskite-structured oxygen carrier by combining A-site defects and B-site doping of SrFeO3-δ. During isothermal CL-DRM tests at 850 °C, Sr0.98Fe0.7Co0.3O3-δ achieved 87% CH4 conversion and 94% CO selectivity in the CH4 partial oxidation reaction, followed by a syngas yield of 8.5 mmol/g, and CO yield of 4.2 mmol/g in CO2 decomposition. A-site defect engineering of the perovskite creates abundant oxygen vacancies and enhances oxygen storage capacity (OSC). Co-doping of the B-site of Sr0.98FeO3-δ increases oxygen mobility and CH4/CO2 activation, resulting in high activity in the CL-DRM process. This methodology resulted in high ionic mobility and facilitated the rapid diffusion of oxygen in the bulk phase, thereby increasing the redox properties of SrFeO3-δ. The oxygen carrier exhibits excellent structural stability and regeneration ability in successive redox cycles. This strategy offers a simple but very effective pathway to tailor OSC, oxygen mobility, and oxygen vacancies of perovskite-structured materials for chemical looping or redox-involved processes.

Impact of molten salts composition on the corrosion behavior of NiMoCr and CoNiCrAl coatings on L-PBF 316L stainless steel for CSP plants

The high-temperature corrosion performance of NiMoCr and CoNiCrAl coatings produced by high velocity oxy-fuel (HVOF) on laser powder bed fusion (L-PBF) 316L stainless steel substate has been evaluated in presence of three different molten salts used as thermal energy storage (TES) materials for concentrated solar power (CSP) plants. The coatings have an excellent oxidation resistance at 700 °C, showing a percentage of affected thickness lower than 2 %, due to the formation of a protective layer of Cr2O3 and Al2O3 in both NiMoCr and CoNiCrAl coatings, respectively. The carbonates-based molten salt accelerates the corrosion of the NiMoCr coating, affecting around 43 % of the coating thickness, due to the formation of chromates and the high depletion of Mo in the coating. In contrast, the effective protection shown by the CoNiCrAl coating is explained because the grown LiAlO2 after the lithiation process has a high capacity to act as a strong diffusion barrier for metal ions and inhibited the formation of chromates. In the presence of two different ZnCl2 and MgCl2-rich molten salts, the CoNiCrAl coating behaved worse than NiMoCr coating due to the breakage of the (Al,Cr)-rich oxide layer as a consequence of an active oxidation mechanism and due to the formation of voids along the entire thickness, which were identified in 100 % of the coating thickness. The superior corrosion resistance of the NiMoCr coating in presence of the chloride rich molten salts was attributed to the presence of Mo, which fixed the Cr and inhibited the diffusion of oxygen.

Oxygen permeation mass transfer modeling and onion-like micromechanical modeling to predict the effect of multilayered interface on oxidation resistance and mechanical properties of composites

To predict oxidative damage of interfaces and fibers under high temperature aerobic environment and mechanical strength of composites before and after oxidation, oxygen permeation mass transfer modeling and onion-like micromechanical modeling of multilayered interface were proposed. The oxygen mass transfer theory and oxidation damage theory of PyC interface were used to establish the two models. The oxidative damage of PyC interface was extended to (PyC-SiC)n multilayered interface, and transformation of SiC phase and microcracks caused by thermal mismatch were also considered. The law of oxygen permeation mass transfer and the evolution of fiber oxidative damage in the “Carbon fiber/(PyC-SiC)n multilayered interface” region were revealed. The mechanical strength of composites under different interface layers was researched, resembling an onion-like wrapping in layers from the core outwards. Furthermore, Cf@(PyC-SiC)n/SiC(n = 1/2/3/4) composites were prepared by chemical vapor infiltration (CVI) method. The mechanical properties of the composites were tested before and after oxidation. A comparison was made between the experimental and predicted tensile strengths before and after oxidation. The predicted results of tensile strength were found to be in good agreement with the experimental ones. In addition, the results show that PyC-SiC multilayered interface has a positive effect on the tensile strength of the composites, mainly as the cracks are deflected and branched by the multilayered interface to promote the multistage pull-out of the fibers. With the increase of interface number, the oxygen diffusion path was lengthened and zigzagged, reducing the oxidative damage of fiber and interface.

Study on a novel Al-B-Li alloy powder with high enthalpy of combustion

ABSTRACT To develop aluminum-based alloy fuels with high energy release levels and good storage stability, the series of Al-B-Li alloy powders were prepared using high-temperature gas atomization. Al-4B-5Li meets the batch preparation requirements, with the mass combustion enthalpy of 31,101 J/g, exceeding the theoretical value of pure Al powder. XRD, SEM/EDS, XPS, TG-DTA, and other methods were used to characterize the alloy powder. The results showed that at 680℃~800°C, “channels” favorable for oxygen diffusion are formed inside the particles, which promotes the complete oxidation of Al-4B-5Li at 1300°C. Al-4B-5Li exhibits a total heat release of 6317 mJ/mg and an oxidation weight gain ratio of up to 95.0%, compared to just 8.39% for pure Al powder. In addition, Al-4B-5Li has good storage stability and lower energy attenuation compared to Al-5Li. After being placed in air for two weeks, the mass combustion enthalpy still exceeds 29,500 J/g, with a decay rate of only 4.52%. And the attenuation rate of Al-5Li is 10.17%. Al-4B-5Li has excellent combustion heat, thermal oxidation performance, and storage stability, and has good application prospects in the field of energetic materials.

Pressureless sintering behavior of ZrC ceramic particles encapsulated by nano-sized carbon layer

The typical high-density zirconium carbide (ZrC) ceramic requires high temperature and high pressure, leading to high manufacturing cost for complex shapes. Herein, nano-sized carbon layer encapsulated ZrC particles were pressureless sintered to achieve near-net preparation of high-density and complex-shape ZrC ceramic. The results indicate that reaction between carbon layer and the ZrCxOy phase in ZrC was improved because the carbon layer shortened the oxygen diffusion pathway. The oxygen content decreased from 3.52 wt% to 0.82 wt% while the thickness of carbon layer decreased from 4.0 nm to 0.75 nm after sintering at 1950 °C for 1 h. Furthermore, the migration of oxygen from ZrCxOy phase to the carbon layer effectively facilitate the formation and growth of the sintering neck. The resulting ZrC ceramic exhibited a high relative density of 92.3 % and excellent mechanical properties. The Vickers hardness, indentation fracture toughness, micro hardness, elastic modulus, and flexural strength were 17.3 ± 0.7 GPa, 4.0 ± 0.5 MPa m1/2, 22.2 ± 2.4 GPa, 429.9 ± 20.7 GPa, and 324 ± 8 MPa, respectively. This work provides a novel perspective to fabricate near-net, high-density and complex-shape ZrC ceramic at lower temperature without pressure.

Soil dependence of biochar composts in mitigating greenhouse gas emissions: An overlooked biophysical mechanism

Biochar-manure co-compost (BM) has garnered considerable attention as a promising soil amendment for improving nutrient retention and mitigating the emission of greenhouse gases (GHGs). However, its efficacy often varies largely from one soil to another. By comparing soil CO2 and N2O effluxes, solution chemistry, enzyme activities, and the abundances of N-cycle genes between BM and manure compost (M) across three soils of different texture classes through microcosm incubations, we aimed to develop biophysical mechanics to untangle the soil-dependent efficacy of BM in mediating soil carbon and nitrogen transformation processes. Compared to M addition, BM addition significantly reduced soil CO2 and N2O emissions, but its effectiveness was soil texture-dependent, being strongest for CO2 and N2O in fine-textured clay loam and coarse-textured sand, respectively. Such soil texture-dependent effects of BM versus M were also observed in soil enzyme activities and gene copy numbers of ammonia-oxidizing bacteria and denitrifiers. Our datasets suggest that BM interacted strongly with soil texture to modulate the pore scale-based diffusion of oxygen, thereby creating divergence in the aeration status among soils. Sequentially, soil phenol oxidase activity was greater in BM than in M under more aerobic conditions but no difference between BM and M in oxygen-limited soils. The balance between oxygen depletion due to microbial respiration of organic amendments and oxygen diffusion through soil/biochar pores also shaped the activities of nitrifying and denitrifying prokaryotes differently between coarse- and fine-textured soils. This logic model well-explained the magnitude of change in soil-dependent CO2 and N2O emissions from organic amendments. The knowledge gained in this work will likely have profound practical ramifications for optimizing BM efficacy in mitigating the GHGs emission.

Investigation of the Effect of Stress on Oxygen Diffusion in Pure Titanium Using a Phase-Field Model.

Diffusion plays a vital role during the fabrication of many materials. It is a well-known fact that stress can influence diffusion behavior. In order to optimize material processing techniques, a quantitative evaluation of the effect of stress on diffusion is essentially required. By analyzing the free energy change in a Ti-O system during diffusion, a phase-field model was developed to address this issue. Using this model, the diffusion of oxygen atoms in pure titanium under different stress states was investigated. It was observed that the true equilibrium concentration of oxygen was proportional to its hydrostatic pressure. Tensile stress can increase the oxygen concentration. This raise in concentration decreased with temperature. However, the promotion of diffusion can be attained in deeper regions at a higher temperature. On the contrary, compressive stress inhibited the diffusion of oxygen in pure titanium. Under a certain compressive stress, the decrease in the oxygen concentration at the surface layer was more significant at a lower temperature, while a decrease could be observed at a deeper distance from the surface at a higher temperature. A thermodynamic explanation of the effect of stress on diffusion was given based on the proposed phase-field model.

Atomic Diffusivities of Yttrium, Titanium and Oxygen Calculated by Ab Initio Molecular Dynamics in Molten 316L Oxide-Dispersion-Strengthened Steel Fabricated via Additive Manufacturing.

Oxide-dispersion-strengthened (ODS) steels have long been viewed as a prime solution for harsh environments. However, conventional manufacturing of ODS steels limits the final product geometry, is difficult to scale up to large components, and is expensive due to multiple highly involved, solid-state processing steps required. Additive manufacturing (AM) can directly incorporate dispersion elements (e.g., Y, Ti and O) during component fabrication, thus bypassing the need for an ODS steel supply chain, the scale-up challenges of powder processing routes, the buoyancy challenges associated with casting ODS steels, and the joining issues for net-shape component fabrication. In the AM process, the diffusion of the dispersion elements in the molten steel plays a key role in the precipitation of the oxide particles, thereby influencing the microstructure, thermal stability and high-temperature mechanical properties of the resulting ODS steels. In this work, the atomic diffusivities of Y, Ti, and O in molten 316L stainless steel (SS) as functions of temperature are determined by ab initio molecular dynamics simulations. The latest Vienna Ab initio Simulation Package (VASP) package that incorporates an on-the-fly machine learning force field for accelerated computation is used. At a constant temperature, the time-dependent coordinates of the target atoms in the molten 316L SS were analyzed in the form of mean square displacement in order to obtain diffusivity. The values of the diffusivity at multiple temperatures are then fitted to the Arrhenius form to determine the activation energy and the pre-exponential factor. Given the challenges in experimental measurement of atomic diffusivity at such high temperatures and correspondingly the lack of experimental data, this study provides important physical parameters for future modeling of the oxide precipitation kinetics during AM process.

The Roles of Impurities and Surface Area on Thermal Stability and Oxidation Resistance of BN Nanoplatelets.

This study considers the influence of purity and surface area on the thermal and oxidation properties of hexagonal boron nitride (h-BN) nanoplatelets, which represent crucial factors in high-temperature oxidizing environments. Three h-BN nanoplatelet-based materials, synthesized with different purity levels and surface areas (~3, ~56, and ~140 m2/g), were compared, including a commercial BN reference. All materials were systematically analyzed by various characterization techniques, including gas pycnometry, scanning electron microscopy, X-ray diffraction, Fourier-transform infrared radiation, X-ray photoelectron spectroscopy, gas sorption analysis, and thermal gravimetric analysis coupled with differential scanning calorimetry. Results indicated that the thermal stability and oxidation resistance of the synthesized materials were improved by up to ~13.5% (or by 120 °C) with an increase in purity. Furthermore, the reference material with its high purity and low surface area (~4 m2/g) showed superior performance, which was attributed to the minimized reactive sites for oxygen diffusion due to lower surface area availability and fewer possible defects, highlighting the critical roles of both sample purity and accessible surface area in h-BN thermo-oxidative stability. These findings highlight the importance of focusing on purity and surface area control in developing BN-based nanomaterials, offering a path to enhance their performance in extreme thermal and oxidative conditions.

Overcoming equilibrium constraints in the reverse water gas shift with counter-current gas–solid flow and oxygen transport in La0.75Sr0.25Cr0.5Mn0.5O3-δ

Utilizing carbon dioxide in the reverse water gas shift (RWGS) reaction (CO2+H2→CO+H2O) is a potential pathway for mitigating CO2 emissions, as the resulting CO can be used to produce valuable products, such as chemicals and fuels. Here, we explore the implementation of the RWGS reaction by solid-oxide redox cycling in a two-reactor moving-bed process with counter-current gas–solid flow. We also develop a method for obtaining design diagrams from the thermodynamic data of the solid oxide utilized for redox cycling. Using this tool and screening the previous literature for relevant thermodynamic data, we identify the perovskite La0.75Sr0.25Mn0.5Cr0.5O3-δ as a highly promising candidate material, and we experimentally determine its non-stoichiometry under conditions relevant for the RWGS. The reaction kinetics are also obtained for its reduction in H2 and its reoxidation in CO2. We observe that the inward diffusion of oxygen into the perovskite grains during reoxidation in CO2 is likely to determine the minimum feasible temperature at which this process can be operated, and we estimate an effective diffusion coefficient of D = 7.7−1.4+1.8 *10−14 cm2 s−1 at T = 550 °C, with an activation energy of 122±4.4 kJ mol−1. Implementing the RWGS with this material in counter-current gas–solid flow is expected to significantly improve the RWGS process by decreasing the operating temperature, enabling continuous gas production, and increasing the gas conversion.

The Influence of Environmental Temperature on the Passive Oxidation Process in the C/SiC Composite

The C/SiC composite plays a crucial role in providing thermal protection for hypersonic vehicles. The SiO2 oxide layer formed via passive oxidation during ablation constitutes a typical porous medium with self-similarity. Given its significant impact on the thermal protection of the material, accurately predicting the variation in the SiO2 oxide layer thickness is of paramount importance. The growth of the oxide layer impedes the diffusion of oxygen within the material. This study considered microstructural parameters of the oxide layer based on high-temperature gas oxidation tests of the C/SiC composite. Fractal theory was utilized to construct a fractal diffusion-reaction kinetics model describing oxygen diffusion within the oxide layer and the evolution of the oxide layer under varying environmental conditions. The finding demonstrated that the existence of the oxide layer significantly influences the passive oxidation of the composite. This study underscored the significance of predicting the impact of environmental parameters on passive oxidation in the practical application of the C/SiC composite and the study result offers a valuable reference for evaluating the thermal resistance of the C/SiC composite.

Effects of Al and Si elements on oxidation behavior in 1000–1200 °C steam for PEO/CrAlSi composite coating on Zr alloy

A PEO/CrAlSi composite coating of ~10 μm thick on Zr–2 alloy was prepared by duplex plasma electrolytic oxidation (PEO) and filtered cathode vacuum arc deposition (FCVAD) techniques. The high temperature steam oxidation behavior of bare and PEO/CrAlSi–coated Zr alloys was performed in 1000–1200 °C. Their morphologies, microstructures, compositions and phase components were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X–ray diffraction (XRD) and glow discharge optical emission spectrometer (GDOES). The effects of Al and Si elements on multilayers microstructure evolution of coated Zr–2 alloy at steam atmosphere were discussed. It was found that the composite coating significantly improved the high–temperature steam oxidation resistance of Zr–2 alloy. The mass gains of the PEO/CrAlSi–coated Zr–2 alloy after 3600 s exposure in 1000 °C, 1100 °C and 1200 °C steam were 28 %, 29 % and 44 % of the bare alloy. Through the oxidations, Al diffused both inward and outward to the substrate and the surface regions, respectively. Formation of a top oxide layer (Al2O3, Cr2O3) greatly suppressed the inward oxygen diffusion. The Si enrichment in the PEO interlayer formed a Zr2Si layer, which inhibited the Cr-Zr interdiffusion at 1000 °C and 1100 °C. At 1200 °C, the Zr2Si layer was oxidized and the CrZr2 phase was formed in the Zr alloy substrate especially at the β–Zr/α–Zr(O) interface.

COMPUTATIONAL MODELING OF A FOOD PACKAGING USING FINITE ELEMENTS

Food packaging has, among others, the main function of protecting food from external biochemical contamination. Nowadays, packages can be formed by different combinations of materials in order to maximize the barrier against external agents, so ensuring food safety. This naturally leads to understand modern packages as multilayer objects, with different characteristics and purposes. In this work, it’s intended to simulate the diffusion of oxygen (responsible for the oxidation of food) in a package consisting of three polymeric materials (in ABA and ABC format) by means of a mathematical model, which resulted in a partial differential equation to be solved, along with initial and boundary conditions. Then, a Finite Element Method (FEM) implementation was devised using Fortran 77, not only to get results for the firstly chosen materials, but also to try other polymer combinations, thus generating different sets of data that could be compared further.