Elevated Oxygen Partial Pressure Research Articles

Prediction of central nervous system oxygen toxicity symptoms using electrodermal activity and machine learning

ObjectiveBreathing elevated oxygen partial pressures (PO2) prior to SCUBA diving increases the risk of developing central nervous system oxygen toxicity (CNS-OT), which could impair performance or result in seizure and subsequent drowning. We aimed to study the dynamics of electrodermal activity (EDA) while breathing elevated PO2 in the hyperbaric environment (HBO2) as a possible means to predict impending CNS-OT. To this end, we used machine learning to automatically detect and predict the onset of symptoms associated with CNS-OT in humans by using features derived from EDA in both time and frequency domains. MethodsWe collected electrodermal activity (EDA) data from forty-nine exposures to HBO2 while subjects were undergoing cognitive load and exercise in a hyperbaric oxygen chamber. Four independent experts were present during the experiment to monitor and classify any symptoms associated with hyperbaric oxygen toxicity. We computed a highly sensitive time varying spectral EDA index, named TVSymp, and extracted informative features from skin conductance responses (SCRs). Machine learning algorithms were trained and validated for classifying features from SCRs and TVSymp as CNS-OT related or non-CNS-OT related. Machine learning models were validated using a subject-independent leave one subject out (LOSO) validation scheme. ResultsOur machine learning model was able to classify EDA dynamics related to CNS-OT with 100 % sensitivity and 84 % specificity via LOSO validation. Moreover, the median prediction time for CNS-OT symptoms was ∼ 250 s preceding the occurrence of actual symptoms. SignificanceThis study shows that EDA can potentially be used for early prediction of CNS-OT in divers with a high sensitivity and sufficient prediction time for countermeasures. While the study results are promising, independent validation datasets are warranted to confirm the findings. However, the current results are well corroborated in an animal study, which consistently showed seizure prediction time of 2 min prior to seizure.

Oxygen-enriched air reduces breathing gas consumption over air.

Owing to the unfamiliar environment, recreational and professional diving is confronted with several challenges. Usage of self-contained under-water breathing apparatuses during the dive provides the indispensable breathing gas supply for the diver. Instead of air, oxygen-enriched breathing gases (EANx or nitrox) are used with increasing frequency. Unfortunately, their usage implies negative effects because the elevated oxygen partial pressure (pO2) increases oxidative stress. As a result, the increased formation of reactive oxygen species exerts negative effects on the central nervous system, lungs, vasculature and eyes. However, these disadvantages can be avoided if appropriate rules are followed, e.g. a pO2<1.4bar. EANx breathing gases have, on the other hand, major advantages as they help reducing narcotic nitrogen effects and bubble formation. Several land-based studies had proven a reduced ventilation of exercising subjects if EANx was used instead of air. As breathing gas is the most valuable under-water good, we wanted to translate the on-land results into under-water results. Appropriate studies now demonstrate a novel EANx property as under-water ventilation is also reduced with EANx. In this short communication, we present this additional advantage of EANx-breathing. This benefit seems to be of particular importance as it delays unforeseen running-out-of-gas and thus, contributes to further improving diving safety.

Extracorporeal Hyperoxygenation Therapy (EHT) for Carbon Monoxide Poisoning: In-Vitro Proof of Principle.

Carbon monoxide (CO) poisoning is the leading cause of poisoning-related deaths globally. The currently available therapy options are normobaric oxygen (NBO) and hyperbaric oxygen (HBO). While NBO lacks in efficacy, HBO is not available in all areas and countries. We present a novel method, extracorporeal hyperoxygenation therapy (EHT), for the treatment of CO poisoning that eliminates the CO by treating blood extracorporeally at elevated oxygen partial pressure. In this study, we proof the principle of the method in vitro using procine blood: Firstly, we investigated the difference in the CO elimination of a hollow fibre membrane oxygenator and a specifically designed batch oxygenator based on the bubble oxygenator principle at elevated pressures (1, 3 bar). Secondly, the batch oxygenator was redesigned and tested for a broader range of pressures (1, 3, 5, 7 bar) and temperatures (23, 30, 37 °C). So far, the shortest measured carboxyhemoglobin half-life in the blood was 21.32 min. In conclusion, EHT has the potential to provide an easily available and effective method for the treatment of CO poisoning.

Time-varying Spectral Index of Electrodermal Activity to Predict Central Nervous System Oxygen Toxicity Symptoms in Divers: Preliminary results.

The most effective method to mitigate decompression sickness in divers is hyperbaric oxygen (HBO2) pre-breathing. However, divers breathing HBO2 are at risk for developing central nervous system oxygen toxicity (CNS-OT), which can manifest as symptoms that might impair a diver's performance, or cause more serious symptoms like seizures. In this study, we have collected electrodermal activity (EDA) signals in fifteen subjects at elevated oxygen partial pressures (2.06 ATA, 35 FSW) in the "foxtrot" chamber pool at the Duke University Hyperbaric Center, while performing a cognitive stress test for up to 120 minutes. Specifically, we have computed the time-varying spectral analysis of EDA (TVSymp) as a tool for sympathetic tone assessment and evaluated its feasibility for the prediction of symptoms of CNS-OT in divers. The preliminary results show large increase in the amplitude TVSymp values derived from EDA recordings ~2 minutes prior to expert human adjudication of symptoms related to oxygen toxicity. An early detection based on TVSymp might allow the diver to take countermeasures against the dire consequences of CNS-OT which can lead to drowning.Clinical Relevance-This study provides a sensitive analysis method which indicates a significant increase in the electrodermal activity prior to human expert adjudication of symptoms related to CNS-OT.

Risks from Breathing Elevated Oxygen.

INTRODUCTION: Effects of breathing gas with elevated oxygen partial pressure (Po₂) and/or elevated inspired oxygen fraction (FIo₂) at sea level or higher is discussed. High FIo₂ is associated with absorption problems in the lungs, middle ear, and paranasal sinuses, particularly if FIo₂ > 80% and small airways, Eustachian tubes, or sinus passages are blocked. Absorption becomes faster as cabin altitude increases. Pulmonary oxygen toxicity and direct oxidative injuries, related to elevated Po₂, are improbable in flight; no pulmonary oxygen toxicity has been found when Po₂ < 55 kPa [418 Torr; 100% O₂ higher than 15,000 ft (4570 m)]. Symptoms with Po₂ of 75 kPa [520 Torr; 100% O₂ at 10,000 ft (3050 m)] were reported after 24 h and the earliest signs at Po₂ of 100 kPa (760 Torr, 100% O₂ at sea level) occurred after 6 h. However, treatment for decompression sickness entails a risk of pulmonary oxygen toxicity. Elevated Po₂ also constricts blood vessels, changes blood pressure control, and reduces the response to low blood sugar. With healthy lungs, gas transport and oxygen delivery are not improved by increasing Po₂. Near zero humidity of the breathing gas in which oxygen is delivered may predispose susceptible individuals to bronchoconstriction.Shykoff BE, Lee RL. Risks from breathing elevated oxygen. Aerosp Med Hum Perform. 2019; 90(12):1041-1049.

Association between hyperoxemia and mortality in patients treated by eCPR after out-of-hospital cardiac arrest

ObjectiveAssess whether elevated oxygen partial arterial pressure (PaO2) measured after the initiation of extra-corporeal cardiopulmonary resuscitation (eCPR), is associated with mortality in patients suffering from refractory out-of-hospital cardiac arrest (rOHCA). MethodsRetrospective cohort study including rOHCA admitted to the ICU. Patients were divided into 3 groups, defined according to the PaO2 measured from arterial blood gas analysis 30 min after the initiation of eCPR. Hyperoxemia was defined as PaO2 ≥ 300 mmHg, hypoxemia as PaO2 ≤ 60 mmHg and normoxemia, as 60 < PaO2 < 300 mmHg.The main outcome was the mortality rate on day 28 after hospital admission. ResultsSixty-six consecutive rOHCA, 77% male, with a mean age of 51 ± 14 years, were admitted to the ICU. rOHCA were mainly due to acute coronary syndrome (67%), hypertrophic cardiomyopathy (8%) and cardiotoxic overdose (8%). Mortality at day 28 reached 61%.In the overall population, the mean PaO2 was 227 ± 124 mmHg.An association between mortality and PaO2 was observed (OR = 1.01 [1.01–1.02]). The AUC for PaO2 after starting eCPR was 0.77 [0.65–0.89].After adjustment for witnessed arrest, bystander's CPR, location, no-flow, low-flow, lactate and pH, age, and PaCO2, hyperoxemia had an ORa of 1.89 (CI95 [1.74–2.07]). ConclusionWe found an association between mortality and hyperoxemia in patients admitted to the ICU for rOHCA requiring eCPR. These data underline the potential toxicity of high dose of oxygen and suggest that controlled oxygen administration for these patients is crucial.

Pulmonary effects of repeated six-hour normoxic and hyperoxic dives.

This study examines differential effects of immersion, elevated oxygen partial pressure, and exercise on pulmonary function after series of five daily six-hour dives at 130 kPa (1.3 ATA), with 18 hours between dives. Five cohorts of 10 to 14 divers participated. The exposure phases were resting while breathing O2 or air in the water (“wetO2”, “wetAir”) or O2 in the hyperbaric chamber (“dryO2”), and exercise in the water while breathing O2 or air (“wetO2X”, “wetAirX”). Respiratory symptoms were recorded during and after each dive, and pulmonary function (forced flow-volume) was measured twice at baseline before diving, after each dive both immediately and on the following morning, and three days post diving (“Day+3”). The incidences of symptoms and of flow volume changes from baseline greater than normal limits (“ΔFV”) were assessed, as were mean ΔFV. The parameters examined were forced vital capacity (FVC), forced expired volume in 1 second (FEV1), and forced expired flow from 25% to 75% volume expired (FEF25–75). The phases ranked from greatest to least fraction of diver-days with symptoms were wetO2X (56%) > dryO2 (42%) > wetO2 (13%) > [wetAir (2%) or wetAirX (1%)] (p<0.05). FEV1 and FEF25–75 were depressed in the morning following wetO2 and wetO2X and on Day+3 after and wetO2X, but increased immediately following each wetAirX dive. O2 exposures caused symptoms and ΔFV suggestive of pulmonary oxygen toxicity,exacerbated by exercise. Indices of small airway function showed late (17-hour) post-O2 exposure deficits, but, particularly with exercise, improvement was evident early after exposure with or without O2. FEF25–75 and FEV1 remained depressed on Day+3 after wetO2 and wetO2X.

Highly conductive AZO thin films obtained by rationally optimizing substrate temperature and oxygen partial pressure

ABSTRACTIn this work, an optimal procedure was proposed to prepare aluminum-doped zinc oxide (AZO) thin films with a sheet resistance of 17.03 Ω/sq by rationally optimizing oxygen partial pressure and substrate temperature. The results showed that increased temperature has an improving trend in the resistivity of AZO thin films while elevated oxygen partial pressure exhibited a deteriorating trend. With rising of substrate temperature in an oxygen-rich atmosphere, oxygen adsorption phenomenon gets stronger. Adsorbed oxygen atoms or molecules suppress the formation of oxygen vacancy and trap electrons, which is responsible for the increase of resistivity. Besides, atomic force microscope analysis indicated that surface roughness of AZO thin films decreases as increase of substrate temperature.

Investigation on SO2, NO and NO2 release characteristics of Datong bituminous coal during pressurized oxy-fuel combustion

The release behaviors of SO2, NO and NO2 of Datong bituminous coal during the pressurized oxy-fuel combustion were studied by pressurized thermogravimetric analyzer combined with Fourier transform infrared spectroscopy, which mainly focused on the effect of pressure to the emission characteristics. The experimental results demonstrated that more pyrite could be converted to the sulfur precursors and then oxidized to SO2 with increasing pressure up to 2 MPa. However, because the conversion of SO2 to SO3 probably was accelerated at 3 MPa, the conversion rate of fuel-S to SO2 decreased to some extent. Along with the increase of volatiles yield at elevated pressure, more volatile-N released during devolatilization converted into NO which led to an increase of NO emission. With increasing pressure from 0.1 to 2 MPa, the conversion value of fuel-N to NO2 increased gradually due to the elevated oxygen partial pressure. But the NO2 emission declined somewhat at 3 MPa due to the accelerated decomposition rate of NO2 at higher combustion temperature. The NOx (NO and NO2) emission under pressurized oxy-fuel atmosphere monotonously increased with increasing pressure.

Microstructure evolution of SiC-ZrB2-ZrC coating on C/C composites at 1773 K under different oxygen partial pressures

The oxidation behavior of SiC-ZrB2-ZrC coating on C/C composites was investigated, basing on the microstructure evolution of oxide scale under different oxygen partial pressures at 1773 K. Similar experiments were conducted in SiC coatings, ZrB2 and ZrC ceramic sheets for comparison. The multiphase coating showed the better oxidation resistance at a higher oxygen partial pressure, and its mass change was 1.34% after isothermal oxidation for 6 h at an oxygen partial pressure of 80,000 Pa. With the increase of the oxygen partial pressure, ZrO2 particles with fibrous denticles were replaced by the aggregations of ZrO2 particles and more SiO2 glass was formed in a short time. The formed SiO2 glass could effectively heal the microcracks of oxide scale. Moreover, the ZrB2 and ZrC phases played an important role in deflecting cracks and restraining the propagation of cracks during oxidation. As the oxygen partial pressure increased, the oxide scale of SiC-ZrB2-ZrC coating became denser, presenting a two-layered structure composed of a SiO2 layer and a Si-O-Zr layer at the elevated oxygen partial pressure.

Nitric oxide and hyperoxic acute lung injury

Hyperoxic acute lung injury (HALI) refers to the damage to the lungs secondary to exposure to elevated oxygen partial pressure. HALI has been a concern in clinical practice with the development of deep diving and the use of normobaric as well as hyperbaric oxygen in clinical practice. Although the pathogenesis of HALI has been extensively studied, the findings are still controversial. Nitric oxide (NO) is an intercellular messenger and has been considered as a signaling molecule involved in many physiological and pathological processes. Although the role of NO in the occurrence and development of pulmonary diseases including HALI has been extensively studied, the findings on the role of NO in HALI are conflicting. Moreover, inhalation of NO has been approved as a therapeutic strategy for several diseases. In this paper, we briefly summarize the role of NO in the pathogenesis of HALI and the therapeutic potential of inhaled NO in HALI.

Comparison of the chemical corrosion resistance of magnesia-based refractories by stainless steelmaking slags under vacuum conditions

This study evaluates commercially available magnesia–chromite, magnesia–carbon and magnesia–doloma bricks for their use in a Vacuum Oxygen Decarburisation ladle. The corrosion behaviour of these bricks by stainless steelmaking slags is, therefore, investigated through crucible tests in a vacuum induction furnace at elevated temperatures (1650 and 1750°C) and low oxygen partial pressures (5.3 and 3.0×10−11atm). The results reveal that magnesia–carbon bricks are severely corroded due to the high dissolution of MgO, while magnesia–chromite and magnesia–doloma refractories exhibit an excellent corrosion resistance. The MgO enrichment in the slag is believed to be the reason of the low wear rate of the MgO–doloma refractories. Rebonded and direct-bonded MgO–chromite refractories show similar corrosion resistance against the slags because of the ‘secondary chromite inactivation’. Decreasing the slag basicity enhances the dissolution of MgO into the slag, thereby increasing the corrosion of the magnesia-based refractories.

Elastoplastic Properties of (Pr, Ce)O2-δ Thin Films

Solid oxide fuel cells (SOFCs) rely on long term, consistent operation of non-stoichiometric oxide components under elevated temperatures and oxygen partial pressure gradients. Materials that exhibit the desired ion transport and reactivity properties generally also exhibit electro-chemo-mechanical coupling that can affect mechanical stability in operando. The importance of chemomechanical coupling such as chemical expansion of SOFC electrodes is increasingly relevant to the goal of reduced operating temperatures enabled by thin film electrodes. Here, we explore this coupling experimentally and computationally, for the model SOFC cathode material, (Pr, Ce)O2-δ. We quantified the Young’s elastic modulus E of (Pr, Ce)O2-δ thin films at temperatures up to 600ºC and oxygen partial pressures pO2 below 10-3 atm via environmentally controlled nanoindentation. The observed decrease in E with increased temperature or decreased pO2 correlated with the changes in oxygen vacancy concentration and lattice parameter expected due to chemical expansion. We compared these results with those we calculated for several compositions of bulk (Pr, Ce)O2-δ via density functional theory, and found that the experimentally observed reduction in mechanical stiffness of reduced (Pr, Ce)O2-δ thin films exceeded that predicted computationally for bulk counterparts. These results demonstrate that the in operando mechanical properties of non-stoichiometric oxides used in thin film SOFCs can differ significantly from those expected from characterization of bulk forms or at standard temperature and pressure. Thus, this chemomechanical coupling must be considered when designing mechanically robust SOFCs with thin film electrode components.

Oxygen-sintered (Pr,Ca) MnO3: Structure and magnetism at high Ca concentrations

Polycrystalline Pr1-xCaxMnO3 (PCMO), a perovskite manganite, was synthesized at high Ca doping levels, 0.5⩽x⩽1.0, by the ceramic method complemented by a final oxygen sintering. The experimental focus was on finding out whether such an oxygen treatment is beneficial in terms of structural and magnetic properties. Except for x=1.0, whose formation required the oxygen treatment, the unit cells of the samples were largely unaffected by the additional oxygen pressure. The materials x=0.8 and x=0.9 exhibited a reproducible crystalline phase separation, which was directly observed at all experimentally accessible temperatures (from 83K to 683K), and a related magnetic phase separation at lower temperatures regardless of the oxygen treatment. What the oxygen sintering did cause was a systematic relaxation of residual crystal strains. This was seen as a consequence of better crystallite homogeneity due to reduced oxygen vacancies. Unexpectedly, the pattern of magnetic transitions shown by PCMO was also found to be insensitive to elevated oxygen partial pressure during sintering. Other synthesis parameters had therefore to be considered in order to explain the comparatively high charge-ordering temperatures found in this study. To summarize, we found that air sintering is sufficient for producing polycrystalline bulk PCMO of good quality, except at x=1.0, where a final oxygen treatment is recommendable in order to avoid magnetostructural defects.

Effects of elevated oxygen and carbon dioxide partial pressures on respiratory function and cognitive performance.

Hyperoxia during diving has been suggested to exacerbate hypercapnic narcosis and promote unconsciousness. We tested this hypothesis in male volunteers (12 at rest, 10 at 75 W cycle ergometer exercise) breathing each of four gases in a hyperbaric chamber. Inspired Po2 (PiO2 ) was 0.21 and 1.3 atmospheres (atm) without or with an individual subject's maximum tolerable inspired CO2 (PiO2 = 0.055-0.085 atm). Measurements included end-tidal CO2 partial pressure (PetCO2 ), rating of perceived discomfort (RPD), expired minute ventilation (V̇e), and cognitive function assessed by auditory n-back test. The most prominent finding was, irrespective of PetCO2 , that minute ventilation was 8-9 l/min greater for rest or exercise with a PiO2 of 1.3 atm compared with 0.21 atm (P < 0.0001). For hyperoxic gases, PetCO2 was consistently less than for normoxic gases (P < 0.01). For hyperoxic hypercapnic gases, n-back scores were higher than for normoxic gases (P < 0.01), and RPD was lower for exercise but not rest (P < 0.02). Subjects completed 66 hyperoxic hypercapnic trials without incident, but five stopped prematurely because of serious symptoms (tunnel vision, vision loss, dizziness, panic, exhaustion, or near syncope) during 69 normoxic hypercapnic trials (P = 0.0582). Serious symptoms during hypercapnic trials occurred only during normoxia. We conclude serious symptoms with hyperoxic hypercapnia were absent because of decreased PetCO2 consequent to increased ventilation.

Physical Properties of Particulate Matter Emitted from Combustion of Coals of Various Ranks in O2/N2 and O2/CO2 Environments

This work examined the particulate emissions from pulverized coals burning under either conventional or oxyfuel combustion conditions. Oxyfuel combustion is a process that takes place in O2/CO2 environments, which are achieved by removing nitrogen from the intake gases and recirculating large amounts of flue gases into the boiler; this is done to moderate the high temperatures caused by the elevated oxygen partial pressure therein. In this study, combustion took place in a laboratory laminar-flow drop-tube furnace (DTF) in environments containing various mole fractions of oxygen in either nitrogen or carbon dioxide background gases. A bituminous coal, a sub-bituminous coal, and a lignite were burned at a DTF temperature of 1400 K. Trimodal ash particle size distributions were observed with peaks in the submicrometer region (∼0.2 μm), as well as in the supermicrometer region (∼5 μm and >10 μm). Both submicrometer and supermicrometer particulate emission yields of all three coals were typically lower in O2/CO2 than in O2/N2 environments. Emission yields typically increased with increasing oxygen concentration in the furnace, with an exception noted at moderate oxygen mole fractions (20%–30%) in CO2, where significant amounts of unburned carbon were detected. Submicrometer particulate yields were found to be comparable in the effluents of all three coals, independently of their ash contents, whereas supermicrometer particulate yields were nearly analogous to the ash contents of the three coals. Scanning electron microscopy (SEM) revealed that submicrometer particles were spherical, whereas supermicrometer particles were often of irregular shapes, fractured spheres, and spheres with small particles attached to their surface.

Structure and lattice dynamics of heterostructures based on bismuth ferrite and barium strontium titanate on magnesium oxide substrates

Bismuth ferrite films doped with neodymium on MgO single-crystal substrates with an epitaxial barium strontium titanate thin (1–2 nm) sublayer have been prepared by rf sputtering of ceramic targets at an elevated oxygen partial pressure and at temperatures below the ferroelectric and magnetic transition temperatures. It has been revealed using X-ray diffraction and Raman scattering spectroscopy that, in these bismuth ferrite films, a new phase (not observed in bulk samples) is formed. The symmetry of this phase is monoclinic, the unit cell contains two formula units, and the spontaneous polarization vector deviates from the [111]cub direction and can have different components along the x, y, and z axes.

Stability of MnCr2O4 spinel and Cr2O3 in high temperature carbonaceous environments with varied oxygen partial pressures

Abstract In this investigation, Cr 2 O 3 and MnCr 2 O 4 were comparatively tested at 1050 °C in carbonaceous environment with varied oxygen partial pressures. MnCr 2 O 4 exhibits much better resistance to carbonaceous attack than Cr 2 O 3 . The carburization rate of MnCr 2 O 4 decreases sharply with increasing oxygen partial pressures. The oxygen partial pressures have less effect on the carburization resistance of Cr 2 O 3 . The increased resistance of MnCr 2 O 4 to carburization is attributed to the dissolution of MnO into Mn–Cr–O spinel lattices with elevated oxygen partial pressures, which retards the decomposition and carburization of Mn–Cr–O spinel. The thermodynamic equations defining the carburization stability of MnCr 2 O 4 and Cr 2 O 3 are modified.

Equilibriums between Cu, Fe, and Zn sulfides and oxides in chloride solution: A thermodynamic study

The results of thermodynamic modeling of equilibriums between Cu, Fe, and Zn sulfides and oxides pertaining to the Cu-Fe-Zn-S-O2 system in water and aqueous chloride solution are presented. The system comprises solid phases of constant composition: pyrite, pyrrhotite, hematite, magnetite, wustite, γ-iron, chalcocite, covellite, cuprite, native copper, chalcopyrite, and bornite, as well as more than 100 ions, complexes, and molecules in an aqueous solution. The GIBBS program with the UNITHERM thermodynamic dataset used in calculations allows numerical analysis of phase assemblages in a dry system and in equilibrium with an aqueous solution. How the temperature, pressure, and the composition of the solution in the system opened for oxygen and sulfur affects the composition of phase assemblages was considered in temperature and pressure ranges of 50–350 C and 100–1000 bar, respectively. Decrease in temperature leads to a shift in stability fields of the studied phases toward the region of elevated oxygen and sulfur partial pressures. Variation of temperature is an important factor affecting precipitation of ore minerals, primarily, Cu- and Zn-bearing. The calculation results are presented in tables and diagrams. Each point in the $$ (\log m_{S_{tot} } - \log f_{O_2 } ) $$ diagram is characterized by a single possible assemblage of phases equilibrated with a solution of the given composition within the considered temperature and pressure range. Since the composition of the mineral assemblage is controlled by physicochemical conditions at the moment of mineral formation, comparison of the calculation results with mineral assemblages at ore deposits makes it possible to estimate the parameters of ore deposition at the early stage of investigation, including oxygen and sulfur activity and, occasionally, the composition and salinity of the solution. These parameters control the formation of such assemblages.

Phase diagram features and solidification behaviour of CoCu 2O 3 at elevated oxygen pressure

A unique behaviour of the phase CoCu 2O 3 was found both from CALPHAD calculations and directional solidification experiments. For elevated oxygen partial pressure the solidification mode changed from double-peritectic to a congruent melting behaviour with respect to the metals (Cu, Co) and to the oxygen content. This transition predicted by the phase diagram calculations was confirmed by microstructure and phase analyses of samples solidified at oxygen pressures up to 60 bar. A DTA analysis has verified basic features of the phase diagram at normal pressures.