Oxygen Tension Research Articles

Comparative effects of variable versus conventional volume-controlled one-lung ventilation on gas exchange and respiratory system mechanics in thoracic surgery patients: A randomized controlled clinical trial

BackgroundMechanical ventilation with variable tidal volumes (V-VCV) has the potential to improve lung function during general anesthesia. We tested the hypothesis that V-VCV compared to conventional volume-controlled ventilation (C-VCV) would improve intraoperative arterial oxygenation and respiratory system mechanics in patients undergoing thoracic surgery under one-lung ventilation (OLV). MethodsPatients were randomized to V-VCV (n = 39) or C-VCV (n = 39). During OLV tidal volume of 5 mL/kg predicted body weight (PBW) was used. Both groups were ventilated with a positive end-expiratory pressure (PEEP) of 5 cm H2O, inspiration to expiration ratio (I:E) of 1:1 (during OLV) and 1:2 during two-lung ventilation, the respiratory rate (RR) titrated to arterial pH, inspiratory peak-pressure ≤ 40 cm H2O and an inspiratory oxygen fraction of 1.0. ResultsSeventy-five out of 78 Patients completed the trial and were analyzed (dropouts were excluded). The partial pressure of arterial oxygen (PaO2) 20 min after the start of OLV did not differ among groups (V-VCV: 25.8 ± 14.6 kPa vs C-VCV: 27.2 ± 15.3 kPa; mean difference [95% CI]: 1.3 [−8.2, 5.5], P = 0.700). Furthermore, intraoperative gas exchange, intraoperative adverse events, need for rescue maneuvers due to desaturation and hypercapnia, incidence of postoperative pulmonary and extra-pulmonary complications, and hospital free days at day 30 after surgery did not differ between groups. ConclusionsIn thoracic surgery patients under OLV, V-VCV did not improve oxygenation or respiratory system mechanics compared to C-VCV.Ethical Committee: EK 420092019.Trial registration: at the German Clinical Trials Register: DRKS00022202 (16.06.2020).

Oxygen diffusion in β-Ga2O3 single crystals under different oxygen partial pressures at 1375 °C

Abstract The monoclinic β-polymorph of gallium oxide is a semiconductor with an ultra-wide bandgap. It is becoming increasingly significant for various technological applications. We have investigated the tracer self-diffusion of oxygen in β-Ga2O3 single crystals as a function of the oxygen partial pressure (2, 20 and 200 mbar) at a temperature of 1375 °C. Isotopically enriched 18O2 gas was used as a tracer source and secondary ion mass spectrometry to analyze depth profiles. We observed that, with decreasing oxygen partial pressure, the diffusivities at a given temperature increase significantly. We suggest that this behaviour can be explained by a change in the diffusion mechanism from oxygen interstitials to oxygen vacancies.

Apneustic anesthesia ventilation improves pulmonary function in anesthetized bottlenose dolphins (Tursiops truncatus).

Use of mechanical ventilation during general anesthesia is a necessary practice in the anesthetization of small cetaceans as spontaneous ventilation fails to provide adequate gas exchange. Currently available methods of ventilation do not account for the intermittent breathing strategy of representative species within this infraorder of fully aquatic mammals and may have a significant effect on cardiac and respiratory physiology. To understand the impact of mechanical ventilation on cardiopulmonary function in one small species of cetacean, the bottlenose dolphin (Tursiops truncatus), we compared controlled mechanical ventilation (CMV) to a novel ventilation method known as apneustic anesthesia ventilation (AAV). AAV simulates the normal inspiratory breath-hold pattern of dolphins. Ten anesthetic procedures (dental procedure, n = 9; bronchoscopy, n = 2) were performed on nine dolphins (age range: 10-42 years; mean = 32 years; median = 37 years; female = 3, 40%; male = 6, 60%). In a cross-over study design, dolphins were instrumented and randomly assigned to AAV or CMV as the initial mode of ventilation, then switched to the alternate mode. Baseline cardiopulmonary data were collected and again after 30 min on each mode of ventilation. Cardiac index, stroke volume index, systemic vascular resistance, alveolar dead space, alveolar-arterial oxygen tension gradient, arterial oxygen content, oxygen delivery index, and dynamic respiratory system compliance index were calculated at each of the four time points. During AAV, dolphins had higher arterial oxygen tension, higher mean airway pressure, reduced alveolar dead space ventilation and lower alveolar-arterial oxygen difference. Cardiovascular performance was not statistically different between the two modes. Our study suggests AAV, which more closely resembles the conscious intermittent respiratory pattern phenotype of dolphins, improves ventilation and pulmonary function in the anesthetized dolphin. Future studies should evaluate the cardiopulmonary effects of neutral buoyancy and cardiopulmonary sparing drug protocols to reduce the need for hemodynamic support of current protocols.

A Recruitment Maneuver After Apnea Testing Improves Oxygenation and Reduces Atelectasis in Organ Donors After Brain Death.

Hypoxemia is the main modifiable factor preventing lungs from being transplanted from organ donors after brain death. One major contributor to impaired oxygenation in patients with brain injury is atelectasis. Apnea testing, an integral component of brain death declaration, promotes atelectasis and can worsen hypoxemia. In this study, we tested whether performing a recruitment maneuver (RM) after apnea testing could mitigate hypoxemia and atelectasis. During the study period, an RM (positive end-expiratory pressure of 15cm H2O for 15s then 30cm H2O for 30s) was performed immediately after apnea testing. We measured partial pressure of oxygen, arterial (PaO2) before and after RM. The primary outcomes were oxygenation (PaO2 to fraction of inspired oxygen [FiO2] ratio) and the severity of radiographic atelectasis (proportion of lung without aeration on computed tomography scans after brain death, quantified using an image analysis algorithm) in those who became organ donors. Outcomes in RM patients were compared with control patients undergoing apnea testing without RM in the previous 2years. Recruitment maneuver was performed in 54 patients after apnea testing, with a median immediate increase in PaO2 of 63mm Hg (interquartile range 0-109, p = 0.07). Eighteen RM cases resulted in hypotension, but none were life-threatening. Of this cohort, 37 patients became organ donors, compared with 37 donors who had apnea testing without RM. The PaO2:FiO2 ratio was higher in the RM group (355 ± 129 vs. 288 ± 127, p = 0.03), and fewer had hypoxemia (PaO2:FiO2 ratio < 300mm Hg, 22% vs. 57%; p = 0.04) at the start of donor management. The RM group showed less radiographic atelectasis (median 6% vs. 13%, p = 0.045). Although there was no difference in lungs transplanted (35% vs. 24%, p = 0.44), both better oxygenation and less atelectasis were associated with a higher likelihood of lungs being transplanted. Recruitment maneuver after apnea testing reduces hypoxemia and atelectasis in organ donors after brain death. This effect may translate into more lungs being transplanted.

Methemoglobinemia as a Cause of Unexplained Hypoxia in Neurosurgical Patients: A Report of Two Cases

AbstractIn methemoglobinemia, ferrous iron in the hemoglobin is oxidized to a ferric state. Hemoglobin in this state cannot carry oxygen resulting in hypoxemia, which manifests as low peripheral oxygen saturation (SpO2). Bedside co-oximetry can identify this condition. We present here two cases of methemoglobinemia. Our experience with the first case enabled swift diagnosis of the second case. This also enabled us to prepare ourselves better in the second case if worsening of hypoxemia had occurred. Therefore, we learn here that whenever there is low SpO2 with a normal partial pressure of oxygen, methemoglobinemia should be suspected and diagnosis should be confirmed using co-oximetry.

High-flow nasal oxygen in resource-constrained, non-intensive, high-care wards for COVID-19 acute hypoxaemic respiratory failure: Comparing outcomes of the first v. third waves at a tertiary centre in South Africa.

High-flow nasal oxygen (HFNO) is an accepted treatment for severe COVID-19-related acute hypoxaemic respiratory failure (AHRF). To determine whether treatment outcomes at Groote Schuur Hospital, Cape Town, South Africa, during the third COVID-19 wave would be affected by increased institutional experience and capacity for HNFO and more restrictive admission criteria for respiratory high-care wards and intensive care units. We included consecutive patients with COVID-19-related AHRF treated with HFNO during the first and third COVID-19 waves. The primary endpoint was comparison of HFNO failure (composite of the need for intubation or death while on HFNO) between waves. A total of 744 patients were included: 343 in the first COVID-19 wave and 401 in the third. Patients treated with HFNO in the first wave were older (median (interquartile range) age 53 (46 - 61) years v. 47 (40 - 56) years; p<0.001), and had higher prevalences of diabetes (46.9% v. 36.9%; p=0.006), hypertension (51.0% v. 35.2%; p<0.001), obesity (33.5% v. 26.2%; p=0.029) and HIV infection (12.5% v. 5.5%; p<0.001). The partial pressure of arterial oxygen to fraction of inspired oxygen (PaO2 /FiO2 ) ratio at HFNO initiation and the ratio of oxygen saturation/FiO2 to respiratory rate within 6 hours (ROX-6 score) after HFNO commencement were lower in the first wave compared with the third (median 57.9 (47.3 - 74.3) mmHg v. 64.3 (51.2 - 79.0) mmHg; p=0.005 and 3.19 (2.37 - 3.77) v. 3.43 (2.93 - 4.00); p<0.001, respectively). The likelihood of HFNO failure (57.1% v. 59.6%; p=0.498) and mortality (46.9% v. 52.1%; p=0.159) did not differ significantly between the first and third waves. Despite differences in patient characteristics, circulating viral variant and institutional experience with HFNO, treatment outcomes were very similar in the first and third COVID-19 waves. We conclude that once AHRF is established in COVID-19 pneumonia, the comorbidity profile and HFNO provider experience do not appear to affect outcome. What the study adds. This study adds to the body of evidence demonstrating the utility of high-flow nasal oxygen (HFNO) in avoiding invasive mechanical ventilation (IMV) in patients with severe COVID-19 hypoxaemic respiratory failure, and shows that this utility remained consistent across different waves of the COVID-19 pandemic.Implications of the study. In resource-constrained settings, HFNO is a feasible non-invasive alternative to IMV and can be employed with favourable and consistent outcomes outside traditional critical care wards. It also confirms that the degree of gas exchange abnormality, and not pre-existing patient-related factors, circulating wave variant or provider experience, is the main predictor of HFNO failure.

Equivalent uniform aerobic dose in radiotherapy for hypoxic tumors

Objective. Equivalent uniform aerobic dose (EUAD) is proposed for comparison of integrated cell survival in tumors with different distributions of hypoxia and radiation dose. Approach. The EUAD assumes that for any non-uniform distributions of radiation dose and oxygen enhancement ratio (OER) within a tumor, there is a uniform distribution of radiation dose under hypothetical aerobic conditions with OER = 1 that produces equal integrated survival of clonogenic cells. This definition of EUAD has several advantages. First, the EUAD allows one to compare survival of clonogenic cells in tumors with intra-tumor and inter-tumor variation of radio sensitivity due to hypoxia because the cell survival is recomputed under the same benchmark oxygen level (OER = 1). Second, the EUAD for homogeneously oxygenated tumors is equal to the concept of equivalent uniform dose. Main results. We computed the EUAD using radiotherapy dose and the OER derived from the 18F-Fluoromisonidazole PET (18F-FMISO PET) images of hypoxia in patients with glioblastoma, the most common and aggressive type of primary malignant brain tumor. The 18F-FMISO PET images include a distribution of SUV (Standardized Uptake Value); therefore, the SUV is converted to partial oxygen pressure (pO2) and then to the OER. The prognostic value of EUAD in radiotherapy for hypoxic tumors is demonstrated using correlation between EUAD and overall survival (OS) in radiotherapy for glioblastoma. The correction to the EUAD for the absolute hypoxic volume that traceable to the tumor control probability improves the correlation with OS. Significance. While the analysis proposed in this research is based on the 18F-FMISO PET images for glioblastoma, the EUAD is a universal radiobiological concept and is not associated with any specific cancer or any specific PET or MRI biomarker of hypoxia. Therefore, this research can be generalized to other cancers, for example stage III lung cancer, and to other hypoxia biomarkers.

Anesthesia experience in an adult Silver-Russell syndrome: a case report

BackgroundThere are no reports of anesthesia use in adult patients with Silver-Russell syndrome (SRS). Here, we report our experience with anesthesia in an adult patient with SRS complicated by chronic respiratory failure.Case presentationA 33-year-old woman was clinically diagnosed with SRS. She had severe chronic respiratory failure, complicated by superior mesenteric artery syndrome. Percutaneous gastrostomy was scheduled for nutritional management under epidural anesthesia; however, soon after esophagogastroduodenoscopy was started, she lost consciousness and spontaneous respiration. The patient was urgently intubated and converted to general anesthesia. The end-tidal carbon dioxide tension was > 90 mmHg at intubation.ConclusionsAdult SRS patients with chronic respiratory failure have a risk of CO2 narcosis. SRS also requires preparation for difficult airway management during the perioperative period.

Venous blood gas and lactate values in adult giraffe trained for voluntary jugular phlebotomy.

Blood gas analyses have previously been performed for giraffe under anesthesia and with physical restraint in a chute; however, reference values for giraffe that are trained to participate in venipuncture without chemical or physical restraint have not previously been described. Using a point-of-care blood gas and lactate analyzer and 20 giraffe trained for voluntary phlebotomy, values were determined for venous blood gasses and plasma lactate concentration. Ninety-five percent confidence in the mean values for venous pH (7.34-7.46), partial pressure of carbon dioxide (PCO2; 28.5-37.8 mmHg), partial pressure of oxygen (PO2; 56-102 mmHg), bicarbonate (HCO3 -; 18.9-21.0 mmol/L), base excess (BE; -6.0 to -3.6 mmol/L), total carbon dioxide (TCO2; 19.9-22.0 mmol/L), and lactate (0.32-0.56 mmol/L) were calculated. This is the first report on venous blood gas analysis values for giraffe without chemical or physical restraint. These data will provide a reference for clinical interpretation of venous blood gas and lactate values in giraffe and demonstrate some of the potential diagnostic benefits to training giraffe and other zoo species for voluntary medical procedures.

Effect of TRPV4 Antagonist GSK2798745 on Chlorine Gas-Induced Acute Lung Injury in a Swine Model.

As a regulator of alveolo-capillary barrier integrity, Transient Receptor Potential Vanilloid 4 (TRPV4) antagonism represents a promising strategy for reducing pulmonary edema secondary to chemical inhalation. In an experimental model of acute lung injury induced by exposure of anesthetized swine to chlorine gas by mechanical ventilation, the dose-dependent effects of TRPV4 inhibitor GSK2798745 were evaluated. Pulmonary function and oxygenation were measured hourly; airway responsiveness, wet-to-dry lung weight ratios, airway inflammation, and histopathology were assessed 24 h post-exposure. Exposure to 240 parts per million (ppm) chlorine gas for ≥50 min resulted in acute lung injury characterized by sustained changes in the ratio of partial pressure of oxygen in arterial blood to the fraction of inspiratory oxygen concentration (PaO2/FiO2), oxygenation index, peak inspiratory pressure, dynamic lung compliance, and respiratory system resistance over 24 h. Chlorine exposure also heightened airway response to methacholine and increased wet-to-dry lung weight ratios at 24 h. Following 55-min chlorine gas exposure, GSK2798745 marginally improved PaO2/FiO2, but did not impact lung function, airway responsiveness, wet-to-dry lung weight ratios, airway inflammation, or histopathology. In summary, in this swine model of chlorine gas-induced acute lung injury, GSK2798745 did not demonstrate a clinically relevant improvement of key disease endpoints.

Boosting the electrocatalytic activity of NdBaCo2O5+δ via calcium co-doping as bifunctional oxygen electrodes for reversible solid oxide cells

The oxygen electrode of the solid oxide cells (SOCs) operates under an oxidizing atmosphere. Lattice shrinkage in a high oxygen partial pressure environment results in cation misalignment, leading to a decline in performance. Addressing the drawbacks associated with A-site cation mismatch in LnBaCo2O5+δ double perovskite oxides for reversible solid oxide cells (RSOCs) oxygen electrodes, a novel calcium ion co-doping strategy is proposed. This approach effectively mitigates A-site cation segregation and enhances stability. The glycine-nitrate method was employed to synthesize Nd0.8Ca0.2Ba1−xCaxCo2O5+δ (x = 0–0.2) layered double perovskites oxides co-doped with calcium ions, denoted as NCBCC. NCBCC exhibits excellent compatibility with commonly used electrolytes. The doping of calcium co-doped in NdBaCo2O5+δ decreases the thermal expansion coefficient and improves the electron transfer characteristics. The sample with x = 0.1 exhibited an area-specific resistance (ASR) of 0.024 Ω cm2 when operated at a temperature of 800 °C in air. In the solid oxide fuel cell mode, employing x = 0.1 as an oxygen electrode, the maximum power density achieved was 766 mW cm−2 at 800 °C. In the solid oxide electrolysis cell mode, operating with CO2 and steam at an electrolysis voltage of 1.5 V and a temperature of 800 °C, the corresponding current densities were −1.51 and −1.85 A cm−2, respectively. The incorporation of calcium ions into layered perovskite oxides offers a promising strategy to enhance the performance of oxygen electrodes in RSOCs.

Prediction and simulation of PEEP setting effects with machine learning models

ObjectiveTo establish a new machine learning-based method to adjust positive end-expiratory pressure (PEEP) using only already routinely measured data. DesignRetrospective observational study. SettingIntensive care unit (ICU). Patients or participants51811 mechanically ventilated patients in multiple ICUs in the USA (data from MIMIC-III and eICU databases). InterventionsNo interventions. Main variables of interestSuccess parameters of ventilation (arterial partial pressures of oxygen and carbon dioxide and respiratory system compliance) ResultsThe multi-tasking neural network model performed significantly best for all target tasks in the primary test set. The model predicts arterial partial pressures of oxygen and carbon dioxide and respiratory system compliance about 45 min into the future with mean absolute percentage errors of about 21.7%, 10.0% and 15.8%, respectively. The proposed use of the model was demonstrated in case scenarios, where we simulated possible effects of PEEP adjustments for individual cases. ConclusionsOur study implies that machine learning approach to PEEP titration is a promising new method which comes with no extra cost once the infrastructure is in place. Availability of databases with most recent ICU patient data is crucial for the refinement of prediction performance.

Electrochemical Technique to Characterize the High Temperature Oxidation Behavior of Materials

This work demonstrates an approach using solid state electrochemical cells to study the long-term oxidation of materials at 800 °C. The capability of zirconia-based cells to control the oxygen partial pressure was first evaluated using an empty chamber. For most voltages applied to the pump cell, the steady state sensor voltage matches the pump voltage, leakage rates are low, and response times are short, allowing precise and prompt control over the chamber atmosphere. The technique was validated by measuring the oxidation of niobium and nickel. Niobium was oxidized at pump voltages ranging from 0 mV to +500 mV; decreasing the oxygen partial pressure around the specimen reduces the oxidation rate. Comparing the integrated oxidation rate with the weighed mass gain showed good agreement. Measured oxidation rates for nickel were of order 1 μg h−1, illustrating the sensitivity of this technique. For higher oxidation rates, a depression in oxygen partial pressure was observed around the specimen. Improved control over the oxidation potential was achieved by using a sensor cell to dynamically tune the pump voltage. Rates for both metals are compared to literature reports using other techniques.

Gulf toadfish (Opsanus beta) gill neuroepithelial cells in response to hypoxia exposure.

Neuroepithelial cells (NECs) within the fish gill contain the monoamine neurochemical serotonin (5-HT), sense changes in the partial pressure of oxygen (PO2) in the surrounding water and blood, and initiate the cardiovascular and ventilatory responses to hypoxia. The distribution of neuroepithelial cells (NECs) within the gill is known for some fish species but not for the Gulf toadfish, Opsanus beta, a fish that has always been considered hypoxia tolerant. Furthermore, whether NEC size, number, or distribution changes after chronic exposure to hypoxia, has never been tested. We hypothesize that toadfish NECs will respond to hypoxia with an increase in NEC size, number, and a change in distribution. Juvenile toadfish (N = 24) were exposed to either normoxia (21.4 ± 0.0kPa), mild hypoxia (10.2 ± 0.3kPa), or severe hypoxia (3.1 ± 0.2kPa) for 7 days and NEC size, number, and distribution for each O2 regime were measured. Under normoxic conditions, juvenile toadfish have similar NEC size, number, and distribution as other fish species with NECs along their filaments but not throughout the lamellae. The distribution of NECs did not change with hypoxia exposure. Mild hypoxia exposure had no effect on NEC size or number, but fish exposed to severe hypoxia had a higher NEC density (# per mm filament) compared to mild hypoxia-exposed fish. Fish exposed to severe hypoxia also had longer gill filament lengths that could not be explained by body weight. These results point to signs of phenotypic plasticity in these juvenile, lab-bred fish with no previous exposure to hypoxia and a strategy to deal with hypoxia exposure that differs in toadfish compared to other fish.

Analysis of slag chemistry in WEEE smelting using experimental and modelling study of the “CuO0.5”-ZnO-FeO-FeO1.5-CaO-SiO2-AlO1.5 system in equilibrium with Cu metal

The variability of the composition of recycled copper-containing materials requires enhanced control and understanding of slag chemistry in the secondary pyrometallurgical processing, when compared to primary copper smelting. In the black copper route for recycling waste electronic and electrical equipment (WEEE), slags exhibit high concentrations of alumina and zinc oxide. The simplest system governing phase equilibria at the reducing smelting stage of the black copper process is “CuO0.5”-ZnO-FeO-FeO1.5-CaO-SiO2-AlO1.5. In the present study, slags within this system were equilibrated with liquid copper Cu and solid Fe metallic alloys, quenched and characterized by the Electron Probe X-ray Microanalysis (EPMA). The range of compositions was selected based on the information about the process available in literature. The study focused on the liquidus and proportion of solid spinel in the temperature range from 1100 to 1300 °C. Precise control of the proportion of solids can enhance the stability of refractory materials against corrosive slags while maintaining entrained metal droplets at reasonably low level. Additionally, experimental correlations between the solubility of copper in the oxide liquid and the partial pressure of oxygen were developed for the Zn-free slags in equilibrium with metallic copper at 1200 and 1300 °C. All experimental results were compared to thermodynamic predictions using recent models and FactSage® software. Uncertainties were identified to be used in further model improvement.

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.

Simulated Abrupt Shifts in Aerobic Habitats of Marine Species in the Past, Present, and Future

AbstractThe physiological tolerances of marine species toward ambient temperature and oxygen can jointly be evaluated in a single metric: the metabolic index. Changes therein characterize a changing aerobic habitat tailored to species‐specific thermal and hypoxia sensitivity traits. If the geographical limits of marine species as indicated by critical thresholds of the metabolic index shift abruptly in response to ocean warming and deoxygenation, aerobic habitat could potentially be lost abruptly. Here, we assess the spatio‐temporal detectability of abrupt shifts in potential habitats for selected marine species within the Shared Socioeconomic Pathway 5–8.5 (SSP5‐8.5) scenario run with the fully coupled Norwegian Earth System Model version 2 (NorESM2‐LM). We use an environmental time series changepoint detection routine and analyze the number and timing of these abrupt changes over the past, present and future. We construct nine ecophysiotypes with low, medium, and high resting vulnerability to hypoxia and sensitivity of hypoxia vulnerability to temperature, respectively, with six different thresholds for minimal oxygen demand. For all ecophysiotypes with positive temperature sensitivity to hypoxia, the volume of non‐viable habitat in the upper ocean expands between 1850 and 2100. Changepoints in the metabolic index are detected in 49.0 ± 9.2% of the volume that eventually becomes non‐viable for all ecophysiotypes over the course of the 21st century. More than 75% of these abrupt shifts occur in response to warming close to the surface, while at depth, the abrupt shifts driven by changes in oxygen partial pressure become more important, with potentially severe consequences for marine species, populations, and ecosystems.

Increasing thermodynamic stability and electrochemical performance of IT-SOFC cathodes based on Ln2MO4 (Ln = La, Pr; M = Ni, Cu)

La2-xPrxNi1-yCuyO4+δ (x=0.5, 1, 1.5, y=0.4, 0.6, 0.8) were synthesized by a citrate-nitrate method and studied as cathode materials for IT-SOFCs by Electrochemical Impedance Spectroscopy (EIS) in symmetrical cells based on the Ce0.8Sm0.2O2-δ (SDC) and La28-zW4+zO54+1.5z (z = 0.85, LWO) electrolytes. Phase identification and crystal structure analysis by means of X-ray powder diffraction (XRPD) shows that solubility of copper y decreases with the increase in praseodymium content x due to increasing structural distortions. Thermodynamic stability of La2-xPrxNi1-yCuyO4+δ at intermediate temperatures in air tends to decrease with praseodymium doping level x and increases with copper substitution for nickel y. Oxides with x=0.5 and 0.6≤y≤0.8 are shown to be thermodynamically stable at 700 °C in air. Electrochemical performance of the La2-xPrxNi1-yCuyO4+δ electrodes improves with praseodymium and copper doping. The results of EIS measurements at different temperatures and oxygen partial pressures (P(O2)) reveal that the rate-determining step of the overall electrochemical process is charge transfer, which can be a combination of surface diffusion and bulk diffusion. EIS studies in dry and wet air indicate the presence of proton conduction in the studied electrodes. The area-specific resistances (ASRs) for La2-xPrxNi1-yCuyO4+δ with x=0.5, y=0.6 and y=0.8 in contact with SDC are comparable with those reported for Pr2NiO4+δ and equal to 0.07 and 0.065 Ω cm2 at 800 °C.

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%.

A high temperature engine materials test facility.

Gas turbine engines subject materials to extreme conditions. Their high temperature materials and co-developed coatings must survive combustion gas temperatures currently approaching 1800 °C, large thermal gradients, severe thermal shock, and static and fatigue inducing applied stresses, all the while operating in highly reactive, high-pressure, high-speed combustion gas flows containing significant partial pressures of water vapor, oxygen, and other reactive species for many tens of thousands of hours. We describe the design and development of a test facility for the study of materials under individual and combinations of test parameters similar to those experienced within legacy and future engines. A hydraulic load frame capable of applying static or cyclic tension-compression stresses up to 400 MPa to flat-dog bone-shaped test specimens is integrated within an environmental test chamber capable of sustaining gas pressures from 0.1 to 1.2 MPa (1-12 atm). An adjustable0.1-2 kW power CO2 laser whose 10.6 µm wavelength radiation is strongly absorbed by ceramic coating materials is used to heat sample surfaces to temperatures of 1800 °C and above, while rear surface air jet cooling establishes through-thickness thermal gradients. Rapid laser heating in conjunction with transiently applied front and/or rear-side air cooling is used to create hot or cold thermal shock effects. This is accompanied by the impingement of a high pressure (up to 1.3 MPa) reactive gas jet upon the sample with speeds up to 300m/s by preheating dry air, mixing it with steam to the desired humidity, heating to 850 °C, and then expanding it through a converging nozzle. Thermal imaging pyrometers measure specimen front and back surface temperature fields, while environmental test chamber view ports permit digital image correlation and strain mapping.