Oxygen Partial Pressure Range Research Articles

Exploring the defect equilibrium and charge transport in electrode material La0.5Sr0.5Fe0.9Mo0.1O3-δ.

Perovskite-type La0.5Sr0.5Fe0.9Mo0.1O3-δ synthesized via glycine nitrate combustion and sintered at 1350 °C was found to have an orthorhombic lattice, which transforms upon heating into a rhombohedral and then a cubic one. The oxygen content and electrical conductivity in this oxide were measured in the range of oxygen partial pressures from 10-20 to 0.5 atm at 750-950 °C by coulometric titration and four-probe dc techniques, respectively. The oxygen content data were used to model the defect equilibrium in the oxide. Oxidation, charge disproportionation and electron exchange reactions between iron and molybdenum were assumed by the model to be involved in the formation of defects. The experimental data were well approximated with the model and the concentrations of charge carriers in La0.5Sr0.5Fe0.9Mo0.1O3-δ were determined to be used for the electrical conductivity analysis. The average mobility of oxygen ions and n- and p-type charge carriers was determined to be about 10-5, 0.007, and 0.07 cm2 V-1 s-1 with an activation energy of 0.80 ± 0.02, 0.34 ± 0.01, and 0.23 ± 0.01 eV, respectively. Comparison with La0.5Sr0.5FeO3-δ shows that 10% Mo substitution provides a substantial increase in both the concentration and mobility of n-type carriers, which results in an almost threefold increase in electron conductivity under reducing conditions, while maintaining a high level of ionic conductivity.

Ni–Fe–Co alloy – magnesia-iron-silicate slag equilibria and the behavior of minor elements Cu and P in nickel slag cleaning

The increasing demand for metals and the tightening environmental restrictions on industries have led to a situation where improvements of new and existing process technologies for higher metal recoveries from primary and secondary resources are needed. This, in turn, requires a better understanding of process chemistry. The present study provides important fundamental information on the equilibrium reduction path and the formation of metal alloy in an electric furnace under nickel slag cleaning conditions, as well as the chemical properties of Ni, Co, Cu and P at these conditions. High-temperature equilibration experiments were conducted on magnesia-iron-silicate slags at silica saturation at 1400 ˚C (1637.15 K) and in the oxygen partial pressure range of 10 −11 –10 −7 atm (1.01325 × 10 −6 –10 −2 Pa). The samples were analyzed by electron microprobe (EPMA) for major and minor elements and laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS) for trace element compositions. Initially the slag contained 2 wt% Ni and 1 wt% Cu, Co and P each, added as oxides, and at P O2 = 10 −7 atm, these metals were only present in the slag with no metal alloy formed. At lower partial pressures, the alloy formed and its composition changed from 90wt-% Ni-rich to 50 wt-% Ni – 40 wt% Fe alloy as the P O2 decreased. Copper vaporized to a great extent at all conditions. The minor metals were shown to be present as NiO, PO 2.5 , CoO and CuO 0.5 species in slag over the P O2 = 10 −8 –10 −10 atm range.

Influence of sintering activators on electrical property of BaZr0.85Y0.15O3-δ proton-conducting electrolyte

In this study, the influence of CuO and ZnO sintering activators on the densification behavior, distribution of sintering activators, and electrical properties of Y-doped BaZrO 3−δ proton conducting oxide were examined over a wide range of oxygen and water vapor partial pressures. With the use of 1 mol% CuO and 4 mol% ZnO, a relative density above 97% was achieved at sintering temperatures of 1500 °C and 1300 °C, respectively. The bulk and grain boundary conductivities of fully sintered BaZr 0.85 Y 0.15 O 3−δ , Ba(Zr 0.84 Y 0.15 Cu 0.01 )O 3−δ , and Ba(Zr 0.81 Y 0.15 Zn 0.04 )O 3−δ were assessed using electrochemical impedance spectroscopy. The amount of sintering activators incorporated into the bulk was investigated using an energy dispersive spectrometer equipped with a high-resolution transmission electron microscope, whereas the equilibrium concentrations of proton and oxygen vacancies as a function of water vapor pressure were estimated by thermogravimetric analysis. Using these results, the total electrical conductivities of the three compositions at 800 °C over a wide range of oxygen and water vapor partial pressures were analyzed via a non-linear fitting based on the defect structure of Y-doped BaZrO 3−δ . As a result, the proton, oxygen ion, and hole partial conductivities were calculated, and the proton transference numbers of the three compositions were compared. • Additions of CuO and ZnO in BZY effectively lower a sintering temperature • Cu was evenly distributed, whereas most of Zn was presented at grain boundaries • Concentration and mobility of proton in BZY-Cu and BZY-Zn were lower than BZY • Transference number of proton is in the order of BZY-Zn > BZY-Cu ≈ BZY

Defect and Structural Properties of Pr-Doped Strontium Cerate as a Mixed Conductor

Proton conducting membranes that are designed for mixed ionic and electronic conductivity are often limited by their low electronic conductivity. Improving the electronic conductivity of these membranes would increase their hydrogen permeation flux. One of the most promising classes of materials for ceramic proton conductors, perovskites, have highly-tunable compositions that allow for the optimization of both ionic and electronic conductivity. Many of these perovskites that act as mixed conductors, such as SrCeO3, are primarily limited by their electronic conductivity, which becomes a bottleneck for overall hydrogen permeation. In this work Pr-doped SrCeO3 was studied over a wide range of oxygen partial pressures (pO2’s) and temperatures to determine its defect properties and conductivity. Under reducing conditions Pr-doped SrCeO3 was found to be chemically and structurally stable, with the optimal doping level being 10%. This composition also shows greater conductivity compared to previous reported Eu-doped SrCeO3. In the low pO2 region, Pr-doped SrCeO3 exhibited primarily n-type behavior as its conductivity dramatically increased in reducing atmosphere, suggesting that the electronic conductivity of SrCeO3 is significantly enhanced by Pr doping. Under high pO2 conditions, Pr-doped SrCeO3 showed a considerable improvement in conductivity in the presence of water, affirming its high protonic conductivity. This validates the use of Pr as a means of enhancing electronic conductivity in perovskites. Figure 1

Specific interrelations of magnetic, thermodynamic and structural properties in highly non-stoichiometric PrBaMnFeO6−δ double perovskite

The complex oxide PrBaMnFeO6−δ (PBMF) was successfully synthesized through the organo-metallic precursor’s combustion. At high temperatures the obtained perovskite was shown to crystallize either in cubic or in tetragonal phase depending on external conditions applied. Magnetic studies additionally confirmed the significant difference of these phases. The coulometric titration method was carefully implemented in order to define the equilibrium values of oxygen content in PBMF as a function of oxygen partial pressure in a 973–1223 K temperature region. The obtained data revealed the existence of the transitory area between cubic and tetragonal phases enabling their mutual presence in a narrow range of oxygen partial pressures. The comprehensive analysis of defect structure was carried out by the development of independent thermodynamic models involving different sets of defect formation processes. As a result, the defect structure of the tetragonal phase was shown to be governed by averaged B-site cation reduction and oxygen disordering while independent iron and manganese reduction reactions occur to be dominant in the highly-symmetric cubic oxide. Based on the obtained data the equilibrium concentrations of point defects, as well as thermodynamic functions of weakly-bonded oxygen were calculated. Defect concentrations determined were further used to explain chemical deformation of manganites studied which revealed a positive impact of iron doping on lattice expansion of PBMF at reduction. A combination of elevated stability of the reduced phase and high values of stored heat compared to analogous oxides suggests PBMF can be considered as perspective oxygen and energy storage material.

Defect and Structural Properties of Pr-Doped Strontium Cerate as a Mixed Conductor

Proton conducting membranes that are designed for mixed ionic and electronic conductivity are often limited by their low electronic conductivity. Improving the electronic conductivity of these membranes would increase their hydrogen permeation flux. One of the most promising classes of materials for ceramic proton conductors, perovskites, have highly-tunable compositions that allow for the optimization of both ionic and electronic conductivity. Many of these perovskites that act as mixed conductors, such as SrCeO3, are primarily limited by their electronic conductivity, which becomes a bottleneck for overall hydrogen permeation. In this work Pr-doped SrCeO3 was studied over a wide range of oxygen partial pressures (pO2’s) and temperatures to determine its defect properties and conductivity. Under reducing conditions Pr-doped SrCeO3 was found to be chemically and structurally stable, with an optimal doping level of 10%. This composition also shows greater conductivity compared to previous reported Eu-doped SrCeO3. In the low pO2 region, Pr-doped SrCeO3 exhibited primarily n-type behavior as its conductivity dramatically increased in reducing atmosphere, suggesting that the electronic conductivity of SrCeO3 is significantly enhanced by Pr doping. Under high pO2 conditions, Pr-doped SrCeO3 showed a considerable improvement in conductivity in the presence of water, affirming its high protonic conductivity. This validates the use of Pr as a means of enhancing electronic conductivity in proton conducting perovskites.

Effect of oxygen partial pressure on microstructure, optical and electrical property of C-Al co-doped ZnO films

C-Al co-doped ZnO films with superior optical and electrical property have been deposited at oxygen partial pressure range 1–7 Pa by pulse laser deposition. The influences of oxygen pressure on crystalline, optical and electrical property have been investigated. The C-Al co-doped ZnO films exhibit a superior crystallinity and greater grain size in the range of 1 Pa–3 Pa compared to AZO films. Furthermore, carbon doping at various oxygen partial pressure significantly improves the optical and electrical property. C-Al co-doped ZnO film reaches the lowest resistivity of 3.1×10-4 Ω cm at 1 Pa. The average transmittance is higher than 85% and attains the optimal value of 89.9 %.

18O/16O isotope exchange for yttria stabilised zirconia in dry and humid oxygen

The oxygen surface kinetics and mechanism of oxygen interaction between oxygen from the gas phase and yttria-stabilised zirconia nano-sized powder have been studied by pulse 18O/16O isotope exchange (PIE) in dry (O2) and humid (mixture O2 + H2O with pH2O = 2.6 kPa at T = 22 °C) oxygen atmospheres in comparison with micro-sized powder. Dependences of the heterogeneous oxygen exchange rate (rH) in the temperature range from 550 to 900 °C, and oxygen partial pressure range in the carrier gas and pulses of 5–19% have been obtained. It has been established that the presence of water causes a decrease in the heterogeneous oxygen exchange rate due to the presence of strongly bound hydroxyl groups in the nanopores of the sample. Differences between the mechanisms of isotopic exchange for dry and humid atmospheres have been found in this temperature range (550–700 °C). The observed differences are associated with the interaction of the gas phase and hydroxyls in the adsorbed layer of the oxide. An original method for the separation of the contributions of three types of oxygen exchange for dry and humid atmospheres has been proposed.

A new analytical model for predicting the thermal oxidation kinetics of composite organic m atrices. Application to diamine cross-linked epoxy

The system of differential equations derived from the so-called “closed-loop” mechanistic scheme was solved analytically by applying realistic proportionality assumptions between the different concentrations of reactive species during the entire course of the thermal oxidation. This new method of analytical resolution allowed obtaining a sounder kinetic model accurately describing the three first stages of the thermal oxidation kinetics: the induction period, the auto-acceleration of the oxidation kinetics at the end of the induction period, and the steady-state regime. This kinetic model was used to identify the thermal oxidation behavior at 120 and 150°C in a large range of oxygen partial pressures (typically between 0.21 and 10 bars) of two epoxy-diamine (EPO-DA) matrices. In addition, the kinetic model was used to determine the accelerated aging conditions representative of the cruising flight of a commercial airliner. It was found that the oxygen partial pressure must be increased much more than the temperature to avoid any deformation of the structural degradation state in the two EPO-DA matrices, thus leading to the definition of extreme environmental conditions very difficult to access in practice.

Utilization of Promising Calcium Manganite Oxygen Carriers for Potential Thermochemical Energy Storage Application

In this study, oxygen release/consumption behavior of calcium manganese-based oxides (CaMn1–xBxO3, where B: Cu, Fe, Mg and x = 0.1 or 0.2) used in a chemical looping oxygen uncoupling (CLOU) application was investigated. The effect of B-site dopants such as Fe, Mg, and Cu on the oxygen release behavior was also investigated with the aim to use these materials in thermal energy storage (TES). Previous literature studies about CLOU performance of doped calcium manganites were taken into consideration for dopants selection. Calcium manganite-based oxides have been used in chemical looping oxygen uncoupling (CLOU) applications owing to their oxygen release behavior to the gas phase. Studies have revealed that calcium manganite-based oxides show a promising nonstoichiometry over a range of temperatures and oxygen partial pressures, which makes them useful for thermochemical energy storage applications. However, the related literature studies have been mainly focused on their nonstoichiometric characteristics related to temperature and oxygen partial pressure and thermodynamic properties. In this work, thermal analysis and fluidized bed tests were carried out as complementary techniques. CaMn0.8Cu0.2O3 showed the highest oxygen release performance in fluidized bed tests, while CaMn0.9Mg0.1O3 had the best cyclic stability overall among the samples used in the study.

Impact of oxygen content on preferred localization of p- and n-type carriers in La0.5Sr0.5Fe1-xMnxO3-δ.

The oxygen content in La0.5Sr0.5Fe1-xMnxO3-δ, measured by coulometric titration in a wide range of oxygen partial pressure at various temperatures, was used for defect chemistry analysis. The obtained data were well approximated by a model assuming defect formation in La0.5Sr0.5Fe1-xMnxO3-δvia Fe3+ and Mn3+ oxidation reactions and charge disproportionation on Fe3+ and Mn3+ ions. The partial molar enthalpy and entropy of oxygen in La0.5Sr0.5Fe1-xMnxO3-δ obtained by statistical thermodynamic calculations were found to be in satisfactory agreement with those obtained using the Gibbs-Helmholtz equations, thus further confirming the adequacy of the model. The impact of manganese substitution on defect equilibrium in La0.5Sr0.5Fe1-xMnxO3-δ was shown to be attributed to a lower enthalpy of Mn3+ oxidation reaction (vs. for the oxidation of Fe3+) and the charge disproportionation reaction on Mn3+ (vs. for that on Fe3+). The former makes Mn4+ ions more resistant to reduction than Fe4+. The latter favors the presence of Mn2+, Mn3+, and Mn4+ ions in oxides in comparable concentrations. The distribution of charge carriers over iron and manganese ions was determined as a function of oxygen content in La0.5Sr0.5Fe1-xMnxO3-δ.

Portable Oxygen-Sensing Device for the Improved Assessment of Compartment Syndrome and other Hypoxia-Related Conditions.

Measurement of intramuscular oxygen could play a key role in the early diagnosis of acute compartment syndrome, a common condition occurring after severe trauma leading to ischemia and long-term consequences including rhabdomyolysis, limb loss, and death. However, to date, there is no existing oxygen sensor approved for such a purpose. To address the need to improve the assessment of compartment syndrome, a portable fiber-optic device for intramuscular oxygen measurements was developed. The device is based on phosphorescence quenching, where the tip of an optical fiber was coated with a poly(propyl methacrylate) (PPMA) matrix containing a brightly emitting Pt(II)-core porphyrin. The optoelectronic circuit is highly portable and is based on a microspectrometer and a microcontroller readout with a smartphone. Results from an in vivo tourniquet porcine model show that the sensor is sensitive across the physiological oxygen partial pressure range of 0-80 mmHg and exhibits an appropriate and reproducible response to changes in intramuscular oxygen. A commercial laboratory oxygen sensor based on a lifetime measurement did not respond as expected.

(Invited) Effects of Cobalt Co-Doping on Mixed Ion Conductivity in La(Sr)Ga(Fe)O3 for Oxygen Separation

Mixed ion conductor shows oxide ion and electronic conduction simultaneously and expecting for application to oxygen separation membrane from air. Because of significant volume change depending on oxygen partial pressure, oxygen separation membrane using mixed ion conductor has disadvantage of narrow range of oxygen partial pressure resulting in the limited permeation rate. Therefore, increased oxide ion conductivity and mechanical strength have been required for mixed ion conducting membrane for oxygen separator. In our previous study, we found that Fe doped LaGaO3 shows reasonably high oxide ion conductivity and chemical stability. In particular, La0.7Sr0.3Ga0.6Fe0.4O3 (LSGF) shows largest oxide permeation rate from air to He. In this study, for further increase in oxygen permeation rate, effects of dopant to Ga site in LSGF was investigated. Application to CH4 partial oxidation was also studied. All LSGF sample was prepared with conventional solid state reaction method using oxide as source materials. Partial substitution was performed for Ga site in LSGF and dense sample without impurity phase was confirmed by XRD measurement. For oxygen permeation measurement, La0.6Sr0.4CoO3 catalyst was coated on the surface of LSGF disk (Φ17mm diameter, 0.5mm thickness) It was found that the oxygen permeation from air to He was sensitively influenced by dopant and the oxygen permeation rate was increased as the following order, Co>Al>In>Ni>Mn at 1273 K. On the other hand, in case of Ru and Ir which is easily reduced to metallic state decreased the oxygen permeation rate significantly. Therefore, it was found that addition of 10 mol % of Co or Al is effective for increasing oxygen permeation rate of LSGF. Effects of Co in LSGF was further studied from oxygen permeation rate and the highest oxygen permeation rate was achieved at 3 mol% in Ga site of LSGC. On this optimized composition, La0.7Sr0.3Ga0.57Fe0.4Co0.03O3, shows 225 μmol min-1 cm-2 at 1273 K and this value is almost 2.5 times larger than that of LSGF. Effects of small amount of Co on electrical conductivity in LSGF were also studied. Although LSGF shows high hole conduction like log(σ/Scm-1)=0.6, the conductivity was increased by Co doping, in particular, at lower temperature. In contrast, Al doping decreases total conductivity and so, increase in oxygen permeation rate could be assigned to the increased mobility of oxide ion in LSGF. Application of Co doped LSGF to CH4 partial oxidation was further studied. Although optimized amount of Co doped for Ga site in LSGF is 3 mol%, the membrane was broken when 3 mol% doped LSGF was used for oxygen membrane. 1% Co doped LSGF was applied for oxygen permeation membrane and it was found that amount of oxygen permeation rate was 1.5 times increased comparing with LSGF. In addition, no crack was formed in membrane. The amount of oxygen permeation was achieved 364μmol cm2 min-1 which is corresponded to 8.9ml/min cm2 at 1273K. In summary, this study reveals that doping small amount of Co to Ga site of LSGF is highly effective for increasing oxygen permeation rate without decreasing chemical stability.

Signature of Oxide-Ion Conduction in Alkaline-Earth-Metal-Doped Y3GaO6.

We have studied alkaline-earth-metal-doped Y3GaO6 as a new family of oxide-ion conductor. Solid solutions of Y3GaO6 and 2% −Ca2+-, −Sr2+-, and −Ba2+-doped Y3GaO6, i.e., Y(3–0.06)M0.06GaO6−δ (M = Ca2+, Sr2+, and Ba2+), were prepared via a conventional solid-state reaction route. X-ray Rietveld refined diffractograms of all the compositions showed the formation of an orthorhombic structure having the Cmc21 space group. Scanning electron microscopy (SEM) images revealed that the substitution of alkaline-earth metal ions promotes grain growth. Aliovalent doping of Ca2+, Sr2+, and Ba2+ enhanced the conductivity by increasing the oxygen vacancy concentration. However, among all of the studied dopants, 2% Ca2+-doped Y3GaO6 was found to be more effective in increasing the ionic conductivity as ionic radii mismatch is minimum for Y3+/Ca2+. The total conductivity of 2% Ca-doped Y3GaO6 composition calculated using the complex impedance plot was found to be ∼0.14 × 10–3 S cm–1 at 700 °C, which is comparable to many other reported solid electrolytes at the same temperature, making it a potential candidate for future electrolyte material for solid oxide fuel cells (SOFCs). Total electrical conductivity measurement as a function of oxygen partial pressure suggests dominating oxide-ion conduction in a wide range of oxygen partial pressure (ca. 10–20–10–4 atm). The oxygen-ion transport is attributed to the presence of oxygen vacancies that arise from doping and conducting oxide-ion layers of one, two-, or three-dimensional channels within the crystal structure. The oxide-ion migration pathways were analyzed by the bond valence site energy (BVSE)-based approach. Photoluminescence analysis, dilatometry, Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy studies were also performed to verify the experimental findings.

Defect chemistry and charge transport in LaSr3Fe3−xMoxO10−δ

Molybdenum containing solid solution LaSr3Fe3−xMoxO10−δ with triple-layer Ruddlesden-Popper structure is considered a promising mixed conducting material for high-temperature electrochemical applications. Oxygen content and electrical conductivity in the compositions with x=0.1 and 0.2 were measured in the range of oxygen partial pressure from 10−20 to 0.5 atm at temperatures 750-950°C. Experimental data were employed for the simulation of defect equilibrium and charge transfer in oxides. The defect distribution over two B-sublattices and four anion sublattices was determined depending on oxygen partial pressure and temperature. The main transport pathways of electrons, holes, and oxygen ions were found to be spatially separated in these oxides between B1, B2, and O4 sublattices, respectively. An increase in the molybdenum content was found to result in higher electron and oxygen ion conductivity. The enhancement of electron conductivity is explained by partial molybdenum reduction and involvement of Mo5+ ions in electron transport. As for ion conductivity, its improvement is suggested to be attributed to oxygen mobility increase due to a decrease in a fraction of tetrahedrally coordinated iron ions in the B1 sublattice and respective vacancy disordering in the O4 sublattice.

Experimental Study of the Individual Effects of Al2O3, CaO and MgO on Gas/Slag/Matte/Spinel Equilibria in Cu-Fe-O-S-Si-Al-Ca-Mg System at 1473 K (1200 °C) and p(SO2) = 0.25 atm

The individual effects of Al2O3, CaO and MgO on gas/slag/matte/spinel equilibria in the Cu-Fe-O-S-Si-(Al, Ca, Mg) system at 1473 K (1200 °C) and p(SO2) = 0.25 atm. have been experimentally measured for a range of oxygen partial pressures and matte compositions. The experimental methodology has included the high temperature equilibration of individual samples on a spinel primary phase substrate under controlled gas atmospheres (CO/CO2/SO2/Ar), followed by rapid quenching of the equilibrium condensed phases and direct measurement of the phase compositions using electron probe x-ray microanalysis. The experimental results show that the presence of Al2O3, CaO and MgO reduce the iron, sulphur and copper concentrations in the slag phase. Present study is undertaken as part of an integrated approach involving thermodynamic modelling and experimental measurements. The experimental data are compared with predictions obtained using the current thermodynamic database for the Cu-Fe-O-S-Si-(Al, Ca, Mg) system in order to further improve thermodynamic parameters.

Redox-structure dependence of molten iron oxides

The atomic structural arrangements of liquid iron oxides affect the thermophysical and thermodynamic properties associated with the steelmaking process and magma flows. Here, the structures of stable and supercooled iron oxide melts have been investigated as a function of oxygen fugacity and temperature, using x-ray diffraction and aerodynamic levitation with laser heating. Total x-ray structure factors and their corresponding pair distribution functions were measured for temperatures ranging from 1973 K in the stable melt, to 1573 K in the deeply supercooled liquid region, over a wide range of oxygen partial pressures. Empirical potential structure refinement yields average Fe–O coordination numbers ranging from ~4.5 to ~5 over the region FeO to Fe2O3, significantly lower than most existing reports. Ferric iron is dominated by FeO4, FeO5 and FeO6 units in the oxygen rich melt. For ferrous iron under reducing conditions FeO4 and FeO5 units dominate, in stark contrast to crystalline FeO.

Iron activity measurements and spinel-slag equilibria in alumina-bearing iron silicate slags

Alumina is a common substance deporting in copper smelting slags when various secondary copper fractions, e.g. e-scrap or WEEE, are used as feedstock as such or along with primary sulphide concentrates. Properties of iron-silicate slags at high alumina concentrations, in the iron-alumina spinel saturation, have been studied at 1300 °C by a high temperature equilibration-quenching method combined with EPMA (electron probe microanalysis) phase composition data from the polished sections. The equilibrations were performed in fixed oxygen activity with platinum or palladium powder, which dissolved iron from the slag and generated a heterogeneous equilibrium system, characterised by the general equilibrium criterium in isothermal and isobaric conditions, as.μalloy(Fe) = μslag(Fe) = μspinel(Fe).This criterium was used for measuring experimentally iron activities of molten silicate slags. The locations of the spinel-liquid slag tie-lines were also determined in the oxygen partial pressure range of 10−6–10−10 atm. A comparison with the recent critical thermodynamic assessments of the Fe–O–Al2O3 system indicates that the iron-alumina spinel-corundum phase boundary in silica-containing systems as a function of oxygen partial pressure is too steep and thus the assessed databases do not match with the experimental data of this study. The liquid slag domain from silica to iron oxide saturation is also smaller than expected earlier, as the spinel primary phase boundary locates at higher silica concentrations than e.g. obtained in the assessments of the Mtox database.

Oxygen adsorption of molten Ag[sbnd]Cu eutectic alloy and its associated surface modification

The surface tension of liquid AgCu eutectic alloy has been measured in a wide range of oxygen partial pressures using two different methods: the constrained drop method and the electromagnetic levitation method. In order to investigate the influence of oxygen potential on the surface tension of the Ag40Cu (at.%) eutectic alloy, the oxygen partial pressure was varied between 8.62 × 10−15 and 2.42 Pa. At low oxygen partial pressure, the surface tension of the AgCu eutectic alloy measured in the temperature range of 1223–1476 K, shows temperature dependence in a good agreement with previously reported results. At higher oxygen partial pressures, the decrease in surface tension is more pronounced and the oxygen adsorption on the surface accordingly increases. Moreover, at high oxygen partial pressure, the oxygen adsorption on the AgCu eutectic alloy was found to be far greater than the expected saturation limit taking into account the theoretically calculated surface concentration of Cu in the AgCu eutectic alloy and the surface excess of oxygen on the molten Cu at saturation. This phenomenon can be explained with a model where the surface of the AgCu eutectic alloy undergoes Cu-substitution at the Ag sites during the oxygen adsorption process.

Ionic conductivity and thermal expansion of anion-deficient Sr11Mo4O23 perovskite

Transport properties of perovskite-type Sr11Mo4O23 and composite Sr11Mo4O23 - 1 wt% Al2O3 were studied at 400–1300 K in the oxygen partial pressure range from 0.21 down to 10−19 atm. The electromotive force and faradaic efficiency measurements, in combination with the energy-dispersive spectroscopy of the fractured electrochemical cells, unambiguously showed prevailing role of the oxygen ionic conductivity under oxidizing conditions. At temperatures above 600 K, protonic and cationic transport can be neglected. The oxygen ion transference numbers vary in the range of 0.95–1.00 at 973–1223 K. At temperatures lower than 550 K, the total conductivity of Sr11Mo4O23 - 1 wt% Al2O3 composite measured by impedance spectroscopy tends to increase in wet atmospheres, thus indicating that hydration and protonic transport become significant. Reducing oxygen partial pressure below 10−10–10−9 atm leads to a significant increase in the n-type electronic conduction. The average thermal expansion coefficients in oxidizing atmospheres are (14.3–15.0) × 10−6 K−1 at 340–740 K and (18.3–19.2) × 10−6 K−1 at 870–1370 K.