Effect Of Oxygen Partial Pressure Research Articles

The influence of oxygen partial pressure on the properties of sputtered vertical NiO/β-Ga2O3 heterojunction diodes

In this work we present studies on the influence of oxygen partial pressure on the properties of sputtered vertical NiO/β-Ga2O3 heterojunction diodes. Obtained results shows substantial effect of oxygen partial pressure on the electrical properties of NiO/β-Ga2O3 heterojunction diodes. The diodes with NiO layers deposited in pure Ar shows Schottky-like I-V characteristics with low ideality factor of 1.05 and barrier height of 1.27 eV as well as low turn-on voltage close to 1V. On the other hand, diodes with NiO layer deposited in oxygen containing atmosphere shows typical p-n diode characteristics. The best electrical characteristics i.e. low on-state resistance of 2.85 mΩcm2, lack of defects and low ideality factor down to 1.07 at RT along with high breakdown voltage close to 900V without any junction termination, were obtained for diodes with NiO layers deposited at 50 % oxygen content. We have demonstrated that by optimization of oxygen partial pressure, the properties of NiO/β-Ga2O3 heterojunction diodes can be tuned and excellent electrical performance in terms of low-on state resistance, high breakdown voltage, low-leakage current and low ideality factor, can be obtained.

Kinetics of Vanillin and Vanillic Acid Production from Pine Kraft Lignin

Vanillin (4-hydroxy-3-methoxybenzaldehyde) is the main component of natural vanilla and a relevant substance in the flavoring and aromatic industries. This study presents a kinetic model to explain both vanillin and vanillic acid concentrations achieved in the alkaline oxidation of pine kraft lignin. Considering that they come from the same precursors, this approach allows an understanding of vanillin production with reaction conditions that minimize the vanillic acid pathway directly from the lignin oligomers, thus maximizing vanillin production. This study involves the effects of oxygen partial pressure, temperature, and the presence or absence of a catalyst (CuSO4 and Fe2(SO4)3 mixture) on the vanillin and vanillic acid yields. An adapted reactor (M/K Systems Inc., Williamstown, MA, USA) with a recirculation and spray liquids system was used in the experiments. The experiments were performed using one liter of a solution of NaOH 2 M and 60 g of lignin. During the lignin oxidation reaction, liquid samples were analyzed at different times (from 0 to 200 min). The oxidation products were quantified by liquid chromatography (HPLC). The catalyzed experiments presented higher maximum vanillin yields than the non-catalyzed ones (39.2–39.6% on nitrobenzene oxidation) achieved at 150 °C. A kinetic model is proposed where the kinetic parameters were estimated using Monte Carlo methods, fitting satisfactorily to the experimental results. The statistical analysis of the kinetic parameters showed that all the studied variables significantly affect the vanillin yield.

Effects of H2 on microstructures of Cr2O3 scales grown in water vapour and consequences for breakaway

Model alloy, Fe-20Cr (wt%), was exposed in Ar-(5, 20)H2O, Ar-(5, 20)H2O-5H2 and Ar-20O2 (vol%) at 750 and 850 °C. The alloy formed Cr2O3 scales plus Fe-rich oxide nodules in H2O-containing gases, but a Cr2O3 scale in Ar-20O2 at 750 °C. The alloy formed an outer (Cr,Fe)-rich oxide layer and an inner, porous Cr2O3 layer in Ar-5H2O-5H2, whereas a dense Cr2O3 scale grew in Ar-5H2O at 850 °C. Application of Wagner’s theory successfully differentiated effects of oxide grain sizes and oxygen partial pressures of gases on scaling rates. Chemically inert SiO2 markers showed that Cr2O3 scales grew by outward metal diffusion.

Effect of sputtering power and oxygen partial pressure on structural and opto-electronic properties of Al-doped ZnO transparent conducting oxides

This paper presents the results of electrical, optical and structural properties, along with studies of the surface morphology and cross sections of aluminium-zinc oxide (AZO) thin films. The thin films were fabricated by reactive magnetron sputtering using the two-element Zn-Al disk. The properties of the thin films prepared using different sputtering power densities and different oxygen partial pressures in the working chamber were discussed. To control the partial pressure of oxygen, a characteristic parameter of the magnetron power supply, called the circulating power, was used. The best properties of prepared AZO thin film as a transparent oxide conducting thin film were found for the film prepared using the ratio of circulating to effective power equal to 0.5. For that thin film, the electron concentration of about 6·1020 and the band gap properties (bandgap width equal to 3.14 eV, work function equal to 3.75 eV) were determined.

Effects of Oxygen Partial Pressure and slag Basicity on the Behavioral Characteristics of Ni in Slag Drying Smelting

This study was intended to investigate the effects of basicity and oxygen partial pressure on the distribution behavior of Ni in the nickel smelting process using nickel oxide ore, the raw material of nickel, among natural ores. Experiments were conducted in a vertical tube furnace using Fe-Ni metal and FeO-MgO-SiO2 ternary slag, which simulated the composition of natural ore. An equilibrium experiment was conducted to observe the distribution ratio of Ni, and thermodynamic data required for this experiment was calculated through Factsage. As a result, it was found that as the oxygen partial pressure increased, the Ni content in the slag increased linearly. The Ni content in the slag increased as the basicity moved away from 0.60.

Cu metallization of Al2O3 ceramics via CuO reduction: Role of SiO2 additive and sintering atmosphere

A Cu-coated Al2O3 substrates which can be used for power modules are prepared via sintering and reduction of CuO–SiO2 film onto the surface of Al2O3 ceramic without precious metal brazing filler or high-vacuum equipment. This method has a significant cost advantage over the existing technology. Effects of oxygen partial pressure from sintering atmosphere and SiO2 content on microstructure and mechanical properties of Cu/Al2O3 interface are systematically investigated. Phase compositions and morphologies of sintered Cu2O layer, reduced Cu layer and reactive layer are characterized via X-ray diffraction and scanning electron microscopy. In addition, physicochemical changes within CuO–SiO2 during sintering are characterized by thermogravimetry-differential scanning calorimeter. It is found that oxygen and SiO2 can promote the generation of Cu2O–CuO–SiO2 eutectic phase with low melting point upon sintering, which increases the thickness of reaction layer and the densification of Cu layer. The shear strength between the Cu layer and the Al2O3 substrate is enhanced with the increase in Cu layer densification degree, while varying in irregular manner with the thickness of reaction layer. In particular, the highest shear strength of 62.70 MPa is obtained at oxygen partial pressure of 0.02 atm and SiO2 content of 1.5 wt%.

Effect of Temperature-Dependent Low Oxygen Partial Pressure Annealing on SiC MOS.

Oxygen post annealing is a promising method for improving the quality of the SiC metal oxide semiconductor (MOS) interface without the introduction of foreign atoms. In addition, a low oxygen partial pressure annealing atmosphere would prevent the additional oxidation of SiC, inhibiting the generation of new defects. This work focuses on the effect and mechanism of low oxygen partial pressure annealing at different temperatures (900-1250 °C) in the SiO2/SiC stack. N2 was used as a protective gas to achieve the low oxygen partial pressure annealing atmosphere. X-ray photoelectron spectroscopy (XPS) characterization was carried out to confirm that there are no N atoms at or near the interface. Based on the reduction in interface trap density (Dit) and border trap density (Nbt), low oxygen partial pressure annealing is proven to be an effective method in improving the interface quality. Vacuum annealing results and time of flight secondary ion mass spectrometry (ToF-SIMS) results reveal that the oxygen vacancy (V[O]) filling near the interface is the dominant annealing mechanism. The V[O] near the interface is filled more by O2 in the annealing atmosphere with the increase in temperature.

The effect of temperature and oxygen partial pressure on the concentration of iron and manganese ions in La1/3Sr2/3Fe1-xMnxO3-δ.

The oxygen content was measured in cubic perovskite-type La1/3Sr2/3Fe1-xMnxO3-δ (x = 0.1, 0.17, 0.25, and 1/3) in the range of oxygen partial pressure from 10-22 to 0.5 atm at 750-950 °C with a step of 50 °C by coulometric titration. Gradual removal of oxygen from the oxides during the measurements was carried out until the stability limit was achieved and the reductive decomposition began. An increase in manganese content was shown to lead to a decrease in the stability of La1/3Sr2/3Fe1-xMnxO3-δ under reducing conditions. The obtained data on oxygen content were used for defect chemistry modeling in the oxides. The enthalpy of the Fe3+ to Fe4+ and Mn3+ to Mn4+ oxidation reactions (ΔHox0) was determined to be -103.2 ± 0.3 and -250 ± 2 kJ mol-1, respectively, for the x = 0.1 composition, and increased slightly with increasing manganese content. The large difference in ΔHox0 determines a strong distinction between the behavior of iron and manganese in perovskite-type oxides. An increase in manganese content in La1/3Sr2/3Fe1-xMnxO3-δ was found to lead to a decrease in the concentration of Fe4+ ions, but did not affect the concentration of Fe2+ ions. The impact of La/Sr ratio was evaluated by comparison of the obtained data with that for La0.5Sr0.5Fe1-xMnxO3-δ, and found to be different for iron and manganese. An increase in lanthanum fraction causes a decrease in the concentration of Fe2+ ions and an increase in the concentration of Mn2+ under reducing conditions.

Evaluation of Hydrogen Crossover in Pemfcs at Intermediate Temperature (80 - 120 °C)

Proton Exchange Membrane Fuel Cells (PEMFCs) are promising for heavy-duty vehicles (HDV) in the strive to make the transportation sector more sustainable. However, because of the small temperature gradient between the cell (typically run around 80°C) and the ambient temperature, these cells require a large cooling system. Raising the operating temperature to an intermediate temperature range (IT: 80 – 120 °C) would reduce the cooling system size required in HDVs and improve the tolerance towards contaminants, although higher temperature may accelerate degradation [1,2]. To be able to withstand IT operation, reinforcements and chemical modifications have been implemented in commercial PFSA polymers. Unfortunately, most of the data available for PEMFCs are referred to non-reinforced membranes and only few studies analysed the latter under realistic operating conditions. Among some possible issues regarding proton exchange membranes (PEMs), hydrogen crossover is an undesirable, but inevitable phenomenon. The membrane is not perfectly impermeable to hydrogen gas and this results in a safety concern, lower cell efficiency and can lead to faster cell degradation.This work investigates the influence of the reinforcement in a PEM on the hydrogen crossover. Specifically, Nafion HP (reinforced) and Nafion 211 (non-reinforced) are compared under different operating conditions. The purpose of the reinforcement is to improve thermo-mechanical stability, and its physical properties can differ from the rest of the membrane, which can influence hydrogen crossover.Using electrochemical methods, the hydrogen crossover is measured in-situ in a PEMFC with hydrogen on one side and inert gas on the other side. The measurements have been performed between 80 and 120 °C, at different cell relative humidity (RH) conditions (20-90 %) and multiple levels of pressure for both reinforced and non-reinforced membranes. Particular attention has been paid to the case in which the hydrogen side of the cell is more pressurized than the inert side, as this is most often the case in HDV applications. In such conditions, hydrogen permeation increases considerably as a result of the total pressure gradient over the membrane, although this factor is rarely considered in the literature [3]. By adapting the methodology established in our previous work [4], here the effects of the differential total pressure and hydrogen partial pressures are decoupled through a systematic dilution of the hydrogen gas stream. Special points are measured in which the hydrogen partial pressure is kept equal to the ambient case, while the total pressure on the hydrogen side is increased by adding the inert gas, as shown in Figure 1, plot I.Results show that the presence of a reinforcement affects the amount of hydrogen that crosses through the membrane, as seen in Figure 1. Moreover, among the different conditions tested, higher total pressures, especially on the hydrogen side of the cell, are affecting hydrogen crossover the most, while a more modest change is observed for different RH and cell temperatures.The observation that pressure is the most important factor for hydrogen crossover has noteworthy implications and should have an influence when deciding at which pressure the PEMFC is operated in transportation applications. Minimizing hydrogen crossover, while still ensuring adequate cell performance, should be a priority to improve the overall fuel consumption and the electric power obtained from the fuel cell.Figure 1: Hydrogen crossover due to concentration gradients and, in certain conditions, to a differential total pressure. Three different conditions are used to measure crossover, whose results are reported in the right figure: I) the total pressure on the hydrogen side is increased by diluting with inert gas, while the hydrogen partial pressure is kept constant, the inert side is unvaried; II) the total pressure is increased symmetrically on both sides, the hydrogen side is not diluted; III) the total pressure on the hydrogen side is increased and no dilution is employed.[1] Cullen et al., “New roads and challenges for fuel cells in heavy-duty transportation,” Nat. Energy, 2021, doi:10.1038/s41560-021-00775-z.[2] Akitomo et al., “Investigation of effects of high temperature and pressure on a polymer electrolyte fuel cell with polarization analysis and X-ray imaging of liquid water,” J. Power Sources, 2019, doi:10.1016/j.jpowsour.2019.04.115.[3] Kreitmeier et al., “Investigation of membrane degradation in polymer electrolyte fuel cells using local gas permeation analysis,” J. Power Sources, 2012, doi:10.1016/j.jpowsour.2012.03.071.[4] Butori et al., “The Effect of Oxygen Partial Pressure and Humidification in Proton Exchange Membrane Fuel Cells at Intermediate Temperature,” J. Power Sources, 2023, doi:10.1016/j.jpowsour.2023.232803. Figure 1

Effect of oxygen partial pressure on phase, local structure and photoluminescence properties of Hf(1-x)YxO2 thin films prepared by pulsed laser deposition

Hf(1-x)YxO2 (x = 0, 0.10, 0.15, 0.20) epitaxial thin films on YSZ(100) substrate were prepared at different oxygen (O2) partial pressures (100, 70, 30, and 10 sccm) by pulsed laser deposition. The effect of oxygen partial pressure on crystalline and local structure was investigated using X-ray diffraction (XRD), Fourier Transform Infrared (FTIR) and X-ray absorption spectroscopy (XAS). The surface composition was determined by X-ray photoelectron spectroscopy. The XRD and FTIR studies reveal that undoped HfO2 thin films remain in monoclinic phase, and the Hf0.85Y0.15O2 & Hf0.80Y0.20O2 films stabilize in cubic phase at all oxygen pressures, whereas the structure of Hf0.90Y0.10O2 films changes from orthorhombic to cubic as oxygen pressure reduces from 100 sccm. The XAS at Hf-L3 edge and O K-edge shows the changes in bond distances, disorder and hybridization. In monoclinic HfO2 films the Hf–O bond distance and disorder increases and Hf–Hf bond decreases as the O2 partial pressure decreases, whereas disorder in doped films shows anomalous behaviour. The oxygen vacancies are evident from both XAS and photoluminescence studies. The results enlighten a deeper understanding of phase change, local structure, optical properties and pave a way to stabilize and identify different technologically important HfO2 phases for dielectric and ferroelectric applications.

Evaluating the influence of Ar/N2 flow rate and pressure on the conversion efficiency of a solar-assisted Fe2O3 – FeO WS cycle for hydrogen production: A thermodynamic approach

A thermodynamic analysis is carried out to evaluate the effects of oxygen partial pressure (PO2) and molar flow rate of reduction agents (m˙N2/Ar) on the performance of Fe2O3−FeO solar thermochemical cycle (STC|Fe2O3−FeO). The chemical equilibrium and efficiency analysis parameters such as enthalpy, Gibbs free energy and entropy are calculated as a function of thermal dissociation temperature (TH). The chemical equilibrium analysis suggests that the thermal dissociation step is feasible above 1250 K while the re-oxidation step is practicable at 550 K. The efficiency analysis revealed that the highest value of conversion efficiency (ηsolar−to−fuel) reached up to 44.42% for N2 based cycle and 45.46% for Ar based cycle without using the recuperation technique. However, the conversion efficiency (ηsolar−to−fuel) attained the highest value of 57.84% for N2 based cycle and 59.14% for Ar based cycle with 50% heat recuperation.

Corrosion Behaviors of Ni–Cr Alloys in O2, H2O and H2O + O2 Gases at 700°C and the Effect of Temperature

Pure nickel and four binary Ni–Cr (5, 10, 20 and 30 wt%) alloys were exposed to Ar–20O2, Ar–20O2–20H2O and Ar–20H2O (vol.%) at 700°C. In dry and wet O2, three Ni–Cr alloys (5, 10 and 20 wt%) formed a three-layered structure: an external NiO layer, an inner oxide layer of NiO + Cr2O3 and an internal oxidation zone (IOZ) with Cr2O3 dispersed. The Ni–30Cr alloy formed a continuous chromia layer, with locally outer NiO islands. In pure water vapor, all alloys underwent internal oxidation, nickel metal expulsion and NiO formation. Compared with the results at 650°C, increasing the temperature to 700°C did not alter the morphology of the oxide scale, but enhanced the scale growth kinetics. A significant difference between these two temperatures was that the strong retarding effect of water vapor on NiO formation in oxygen at 650°C became insignificant at 700°C. However, in water vapor only condition, NiO formation remained much slower at both temperatures. The effects of water vapor and oxygen partial pressure on NiO formation of different alloys and the effect of temperature on scale growth kinetics and morphology were discussed.

Assessing the Impact of BaZr0.7Y0.3-YPryO3- d Composition on Water Splitting Kinetics in Composite Pr2NiO4+Δ-BaZr0.7Y0.3-YPryO3- d Electrodes in Proton-Conducting Electrolysis Cells

Protonic-ceramic electrolysis cells (PCECs), with proton-conducting oxide electrolytes, provide high current densities between 500-700°C because electrolytes such as BaCe0.8-xZrxY0.1Yb0.1O3-δ (BCZYYb) have protonic conductivities in this temperature range. The protonic conductivities of BCZYYb are almost an order of magnitude higher than oxide-ion conductivities in conventional solid-oxide electrolytes. To convert such high ionic fluxes in PCECs into efficient hydrogen production, robust positive electrodes (positrodes) must be developed with reduced overpotentials associated with water-splitting kinetics and proton incorporation [1]. The positrodes with Ruddlesden-Popper oxides like Pr2NiO4+δ(PNO) have demonstrated effective water-splitting kinetics as well as mechanical and chemical compatibility with barium zirconate electrolytes [2]. As a mixed conductor, PNO conducts polarons, oxide ions, and protonic defects (OH●) into the crystal structure [3]. However, its relatively low proton and oxide-ion conductivities limit charge transfer reaction near three-phase boundaries with the electrolyte, which increases positrode overpotentials. To improve the surface conductivity in PNO-based positrodes, our team, in collaboration with West Virginia University [4], has explored the impact of very thin overlayers of mixed ion-conducting BaZr0.7Y0.15Pr0.15O3- d (BZYP) on PNO positrode layers. Electrochemical characterization showed that the BZYP overlayers reduce the area-specific resistance of the PNO positrodes by ≈50% at 550-700°C: this suggests the extension of the electrochemically active surface area required for the water-splitting reaction beyond three-phase boundaries. The present study focuses on optimizing composite PNO-BZYP porous positrodes in conventional negatrode-supported PCECs to understand the water-splitting reaction mechanism for efficient electrolysis.Composite PNO-BaZr0.7Y0.3-yPryO3- d (BZYP) positrodes were fabricated for a range of Y/P cation ratios. The 22 mm diameter negatrode-supported button cells included 1 mm thick porous negatrodes of BaCe0.4Zr0.4Y0.1Yb0.1O3-δ(BCZYYb4411)-NiO and a spray-coated 5-10 μm thick BCZYYb4411 electrolytes as shown in figure 1. These negatrode-electrolytes were sintered at 1550°C for 6 h. The PNO and BZYP positrode powders were synthesized by solid-state reaction at 1350°C and 1500°C, respectively. PNO was identified as an orthorhombic crystal structure, and BZYP as a tetragonal crystal structure. Reactivity tests PNO and BZYP (1:1 wt ratio) at 1050°C, 1150°C, and 1250°C for 5 h showed no phase change. After negatrode-electrolyte sintering, both single-phase PNO (reference), and composite PNO-BZYP slurries were painted on the exposed electrolyte layers and sintered at 1150°C for 5 h to provide porous positrodes.Electrochemical impedance spectroscopy (EIS) and current-voltage measurements on BZYP-PNO positrode were compared with PNO positrode in the temperature range of 550-700°C. During these measurements, steam, and oxygen partial pressures were varied by 3-50%. EIS measurements informed the resistances associated with the different processes in the water-splitting reaction mechanism. The impact of both proton/oxygen ion and electron conductivity on the water-splitting kinetics could be identified based on different BZYP compositions by investigating the effects of temperatures, steam, and oxygen partial pressures. Different Y/P cation ratios in BZYP supported the investigation of how different (proton/oxygen ion and electron) conductivities in the BZYP impact the electrochemical water-splitting reaction. Figure 1

Effects of glucose concentration and oxygen partial pressure on the respiratory metabolism of sheep temporomandibular joint disc cells.

Temporomandibular joint (TMJ) disc degeneration is a common disease characterized by a decrease in metabolic function. The present study aimed to investigate the pathogenesis of TMJ disc degeneration by analyzing the effects of oxygen and glucose concentrations on metabolism in a simulated TMJ disc cell growth environment. Cell samples were divided into 10 groups and cultured in different nutritional environments, including 21 and 2% O2 partial pressures and various glucose concentrations (0, 0.5, 3, 5.5 and 22.5 mmol/l). Cell proliferation, extracellular matrix content, mitochondrial function, and cell metabolism were subsequently analyzed. The results demonstrated that hypoxia and a low glucose concentration inhibited cell growth, and low glucose concentration inhibited extracellular matrix synthesis and adenosine 5'-monophosphate-activated protein kinase expression. Hypoxic conditions also induced a compensatory increase in the number of mitochondria, whereas mitochondrial deformation and swelling were observed in the absence of glucose. According to this study, the primary metabolic pathway of TMJ disc cells is glycolysis. It was concluded that hypoxic conditions and normal glucose concentrations are needed for the growth of TMJ disc cells. Glucose is necessary to ensure cell survival, extracellular matrix synthesis and mitochondrial function. Glucose deficiency may be related to disc degeneration, aging and disease mechanisms.

Oxidation of accident tolerant fuels models based on Cr-doped UO2 for the safety of nuclear storage facilities

Oxidation of Accident-Tolerant Fuels (ATF) is important from the nuclear safety point of view because it could provoke the release of radioactive material. Despite of the use of ATFs in current nuclear reactors, no studies regarding their oxidation are available. Thus, we propose here an experimental study on Cr2O3-doped UO2 samples, which were subjected to a thermal treatment ranging from room temperature up to 973 K in oxidant conditions. The aim is to assess the potential oxidation resistance of Cr-doped UO2 based model systems. Next, the effect of oxygen partial pressure and the influence of Cr2O3 dopant concentration concentrations on fresh UO2 fuel oxidation were evaluated. Two oxygen compositions (1% and 21%O2) were used to further evaluate the impact of Cr2O3 concentrations on UO2 oxidation. The results show that, despite no effect of the dopant is found in air (21% O2), there is a clear decrease in the oxidation degree at 1%O2. These results are intended to provide a fundamental reference for future investigations of Cr2O3-doped UO2 corrosion behavior and performance to be accounted in new designs of storage facilities.

Continuous Hot‐Dip Galvanizing of Medium‐Manganese Third‐Generation Advanced High‐Strength Steels

The effects of process atmosphere oxygen partial pressure (pO2) on the preimmersion surface structures, interfacial reactive wetting products, and reactive wetting mechanisms of two prototype (0.15–0.20)C–(5.6–5.9)Mn–(0.4–1.9)Al–(1.1–1.5)Si–(0–0.6)Cr (wt%) third‐generation advanced high‐strength steels during continuous hot‐dip galvanizing are determined. In this study, the two‐stage thermal processing routes employed comprise an austenitization anneal followed by flash pickling and an intercritical anneal. All annealing treatments are conducted in a N2–5 vol% H2 process atmosphere with a controlled dew point. The substrates are austenitized at dew points of –30 or –10 °C, intercritically annealed at a dew point of –30, –10, or +5 °C, and then galvanized using a conventional 0.2 wt% Al (dissolved) bath. The preimmersion surfaces comprise a near‐pure Fe layer with dispersed nanoscaled oxide nodules. The primary reactive wetting mechanism is the direct wetting of the surface Fe, while oxide wetting, oxide cracking and liftoff, and oxide bridging by the liquid metal bath are secondary reactive wetting mechanisms. Zn ingress into the substrate via pores in the oxide network from selective dissolution during flash pickling is also noted. A well‐developed Fe2Al5–xZnx interfacial layer is observed for all metallic coating conditions. The resultant coatings show outstanding adherence after ASTM three‐point bend testing.

Controlling the optical properties of hafnium dioxide thin films deposited with electron cyclotron resonance ion beam deposition

The effects of reactive and sputtering oxygen partial pressure on the structure, stoichiometry and optical properties of hafnium oxide (HfO2) thin films have been systematically investigated. The electron cyclotron resonance ion beam deposition (ECR-IBD) technique was used to fabricate the films on to JGS-3 fused silica substrates. The amorphous structure of HfO2 films were determined by X-ray Diffraction. Energy-dispersive X-ray Spectroscopy and Rutherford Backscattering Spectrometry were carried out for the composition and stoichiometry analysis, where this suggests the formation of over-stoichiometric films. The data suggests that the O:Hf ratio ranges from 2.4 – 4.45 to 1 for the ECR-IBD fabricated HfO2 films in this study. The transmission and reflectance spectra of the HfO2 films were measured over a wide range of wavelengths (λ = 185 – 3000 nm) by utilizing a spectrophotometer. The measured spectra were analyzed by an optical fitting software, which utilizes the model modified by O'Leary, Johnson and Lim, to extract the optical properties, refractive index (n) and the bandgap energy (E0). By varying the reactive and sputtering oxygen partial pressure, the optical properties were found to be n = 1.70 – 1.91, and E0 = 5.6 – 6.0 eV. This study provides a flexible method for tuning the optical properties of HfO2 coatings by controlling the mixture of reactive and sputtering gas.

Hypoxia Altitude Simulation and Reduction of Cerebral Oxygenation in COPD Patients

BACKGROUND: Chronic obstructive pulmonary disease (COPD) is highly prevalent and often associated with chronic hypoxia. Previous studies have shown alterations of cerebral oxygenation and cardiac repolarization in COPD patients (GOLD stage II-IV). Airplane travel is common in patients with COPD; however, the clinical effects of a diminished oxygen partial pressure in aircraft cabin environments at cruising altitude remain elusive. The aim of this study was to assess changes of cerebral oxygenation as well as parameters of cardiac repolarization during a hypoxia altitude simulation combined with mild physical activity in these patients.METHODS: Patients with COPD and healthy subjects (10 per group) randomly selected from the Charité outpatient clinic conducted a hypoxia altitude simulation test which consisted of three phases. The regional cerebral oxygen saturation (rSO₂) of the frontal cortex was measured at rest using near-infrared spectroscopy (NIRS). Furthermore, oxygen saturation (SpO₂), blood pressure, and heart rate values, as well as a 12-lead-ECG, were recorded. Subsequently, a mild treadmill exercise program (25 W) was divided into 10 min of normoxia (pre-hypoxia), 30 min of mild hypoxia (FIO₂ = 0.15), followed by a second 10-min period of normoxia (post-hypoxia). Meanwhile, mentioned parameters were recorded in 2-min intervals. P, PQ, QRS, QT, QTc, QTd, T-peak-T-end interval (TpTe), and corrected TpTe (TpTec) were measured on three ECG complexes, each at baseline, at the end of the normoxic phase, and at the end of the hypoxic phase.RESULTS: A total of 10 patients with COPD and 10 control subjects were included in this study. SpO₂ was significantly lower in COPD patients throughout the whole test. Frontal cerebral rSO₂ was significantly lower in the left hemisphere during hypoxia altitude simulation in COPD patients (59.5 ± 8.5 vs. 67.5 ± 5.7).CONCLUSIONS: We show reduced left frontal cerebral oxygenation during hypoxia and mild exercise in patients with COPD, suggesting diminished altitude resilience and altitude capabilities. Preflight hypoxia assessment might be recommended to patients with severe COPD.Dehe L, Hohendanner F, Gültekin E, Werth G, Wutzler A, Bender TO. Hypoxia altitude simulation and reduction of cerebral oxygenation in COPD patients. Aerosp Med Hum Perform. 2023; 94(3):102-106.

The effect of oxygen partial pressure and humidification in proton exchange membrane fuel cells at intermediate temperature (80–120 °C)

The integration of proton exchange membrane fuel cells (PEMFCs) in heavy-duty vehicles would be facilitated if operating temperatures above 100 °C were possible. In this work, the effect of temperature in the intermediate range of 80–120 °C is investigated for a commercial membrane electrode assembly (MEA) through polarization curves and electrochemical impedance spectroscopy. The importance of oxygen partial pressure on voltage is systematically studied by decoupling it from humidity and temperature. The results show that adequate operation at intermediate temperature is achievable if the oxygen partial pressure is sufficient. Although the cathode kinetics is faster with rising temperatures, the voltage gain is counteracted by the decreasing equilibrium potential. At intermediate temperature, the water transport is enhanced, levelling out the relative humidity difference between anode and cathode. However, ionic conductivity in the polymer can become limiting at high currents, due to a smaller relative humidity increase at these temperatures. To conclude, a higher operating temperature does not inherently cause a decrease in obtained current density. Rather, the difficulty to simultaneously have sufficient oxygen partial pressure and high relative humidity causes limitations within the cathode that to some extent can be solved by pressurizing the cell.

New insights into the process of intrinsic point defects in PuO2.

Intrinsic point defects are known to play a crucial role in determining the physical properties of solid-state materials. In this study, we systematically investigate the intrinsic point defects, including vacancies (VPu and VO), interstitials (Pui and Oi), and antisite atoms (PuO and OPu) in PuO2 using the first-principles plane wave pseudopotential method. Our calculations consider the whole charge state of these point defects, as well as the effect of oxygen partial pressure. This leads to a new perspective on the process of intrinsic point defects in PuO2. We find that the antisite atoms OPu and PuO are more likely to appear in O-rich and O-deficient environments, respectively. Interestingly, the most energetically favorable type of Schottky defect is {2VPu3-: 3VO2+} in an O-rich environment, while {4VO1+: VPu4-} is preferred in an O-deficient environment. These results differ from the commonly known {VPu4-: 2VO2+} type of Schottky defect. Moreover, under O-deficient conditions, we predict that the stable cation Frenkel defect is {VPu4+: Pui4+}, while the most stable anion Frenkel defect is {VO2+: Oi2-} under O-rich conditions. Lastly, we find that the only two types of antisite pairs that can appear are {OPu5-: PuO5+} and {OPu6-: PuO6+}, with the latter being the more stable configuration. These unconventional defect configurations provide a new viewpoint on the process of intrinsic point defects in PuO2 and lay theoretical foundations for future experiments.