Different Partial Pressures Of Oxygen Research Articles

Generation of singlet oxygen by porphyrin and phthalocyanine derivatives regarding the oxygen level

Background. The principle of photodynamic effect is based on the combined action of photosensitiser, molecular oxygen and light, which produce various reactive oxygen species and are associated with significant cellular damage. Singlet oxygen is one of the most serious representatives, which is characterised by powerful oxidising properties. Moreover, concomitant hyperbaric oxygen treatment can support these effects. Therefore, the subject of our study was to compare the yields of singlet oxygen for four different photosensitizers in dependency on the oxygen concentration. Material and methods. Four different photosensitizers 5,10,15,20-tetrakis(1-methyl-4-pyridinio)porphyrin tetra(p-toluenesulfonate), tetramethylthionine chloride, 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin zinc(II) and zinc phthalocyanine disulfonate were investigated to determine the yield of singlet oxygen in PBS by Singlet Oxygen Sensor Green reagent under different partial pressures of oxygen (0.4 and 36 mg/l). Results. There were no noticeable shifts in the excitation and emission fluorescence spectra regarding the oxygen concentration. Concerning the same molar concentration of photosensitizers the production of singlet oxygen was highest for 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin zinc(II), where the rate of the fluorescence change was more than 3 times higher than that obtained for 5,10,15,20-tetrakis(1-methyl-4-pyridinio)porphyrin tetra(p-toluenesulfonate). On the other hand, zinc phthalocyanine disulfonate showed the lowest yield in singlet oxygen production. Conclusions. Singlet oxygen production, within the range of oxygen concentrations achievable in tissues under normoxia or hyperoxia, does not depend on these concentrations. However, the singlet oxygen generation is significantly influenced by the type of photosensitizer, with the highest yield belonging to 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin zinc(II).

Influence of oxygen partial pressure on the strain behaviour of reactively co-sputtered Ga doped ZnO thin films

Gallium doped ZnO films (GZO) were deposited by reactive co-sputtering of Zn and GaAs at different partial pressures of oxygen in Ar-O2 mixture. The GZO films were deposited at 375 °C, with GaAs area coverage of 0 - 3 % and 4 - 10 % O2 in sputtering atmosphere. The composition of GZO films was studied by X-ray photoelectron spectroscopy, which showed that the films deposited at 4 % and 5 % O2 display Ga/Zn ratio of ∼ 0.1 and contain oxygen vacancies, while those deposited at 6 % and 7 % O2 display Ga/Zn ratio of ∼ 0.01 and contain chemisorbed/interstitial oxygen. X-ray diffraction measurements supported by Raman studies revealed that undoped ZnO films are strongly c-axis oriented and display decrease of crystallite size along c-axis, along with substantial increase of hydrostatic tensile strain with increase of O2 percentage, which are attributed to the presence of interstitial oxygen. In sharp contrast, GZO films deposited at 4 % and 5 % O2 under limited oxygen availability, display smaller and mis-oriented crystallites along c-axis and large compressive strain, which is also hydrostatic, owing to the incorporation of Ga. The GZO films deposited at 6 % and 7 % O2 display improved crystallinity and decrease of compressive strain, which are attributed to reduced Ga content of the films and sufficient availability of oxygen during deposition. This study reveals the critical influence of the partial pressure of oxygen on the stoichiometry, doping concentration, crystallinity and the nature of strain in reactively sputtered GZO films.

Titanium Suboxide-Based Composite Electrocatalysts: Physico-Chemical and Semiconductor Properties

Titanium dioxide is one of the main products of chemical industry. Due to its optical properties, it is most widely used in the paint and varnish industry and the production of pigments. Its sensory, adsorption, optical, electrical, and catalytic properties are widely recognized as the objects of close attention of researchers [1].Due to its high chemical inertness, lack of toxicity and low cost, titanium dioxide is increasingly used as a photocatalyst, while it has a number of significant disadvantages: low quantum efficiency of the process due to weak separation of the electron-hole pair, limited absorption spectrum in the ultraviolet region, which makes it impossible to use the energy of sunlight [2,3]. Scientists in all leading countries of the world are engaged in solving these problems.It is known that nanosized TiO2 particles (<50 nm) have the highest photocatalytic activity; therefore, the preparation of TiO2 nanoparticles is one of the ways to reduce the degree of charge recombination and increase the active surface area of the oxide [4].We propose to use a combined electrochemical-pyrolytic method of nanotube synthesis. This method will allow one to create a porous developed surface of the matrix for electrodeposition of catalytic layers of platinum and palladium; and their subsequent heat treatment at different partial pressures of oxygen will allow one to design composites with different composition. The high number of cationic vacancies in the matrix and the deficiency of oxygen ions will significantly increase the mobility of platinum and palladium atoms during heat treatment, and the resulting composite will have practically metal conductivity, high catalytic activity, selectivity and extended service life.Naked Ti/TiO2 contain a significant amount of X-ray amorphous compounds on the surface, which are most likely hydrated titanium oxides. The main crystalline phase is titanium dioxide in the allotropic anatase form. Metallic titanium is present on the surface in trace amounts. Thermal treatment of this material at a temperature of 500 ºC for 3 hours in an air atmosphere leads to an increase in the proportion of the crystalline phase. The content of metallic titanium increases significantly, reaching about a third. A partial electrochemical reduction of nanotubes allows one to obtain more electrically conductive titanium suboxides. After cathodic reduction of nanotubes for one hour, a galvanic coating with metallic platinum is uniformly deposited on the surface of the material. Thermal treated Ti/TiO2 nanotubes is an n-type semiconductor with a flat-band potential equal to –0.589 V and a carrier concentration of 6×1020 cm-3. Such a high concentration of carriers is obviously due to the small thickness of the oxide film and its nonstoichiometry, as a result of which the surface is not very depleted in electrons, since titanium metal acts as their donor.An original technique was developed for the deposition of platinized Ti/TiO2 nanotubes, including the stage of thermal treatment of the coating in an air atmosphere. It has been shown that the deposition of platinum on the previously reduced surface of nanotubes allows one to obtain composite coatings with a higher electrical conductivity, and the heat treatment of such a coating is characterized by the content of a larger fraction of TiO2, increased adhesion to the current collector, and an increase in the crystallinity of the coating. At the same time, the internal stresses of the coating are reduced by several times. References V.R.A. Ferreira, P.R.M. Santos, C.I.Q. Silva, M.A. Azenha. Latest developments on TiO2-based photocatalysis: a special focus on selectivity and hollownes for enhanced photonic efficiency, Appl. Catal., A, 623, 118243 (2021).S. Palmas, L. Mais, M. Mascia, A. Vacca. Trend in using TiO2nanotubes as photoelectrodes in PEC processes for wastewater treatment, Curr. Opin. Electrochem., 28, 100699 (2021).E. Brillas. A critical review on ibuprofen removal from synthetic waters, natural waters, and real wastewaters by advanced oxidation processes, Chemosphere, 286, 131849 (2022).M. Bellardita, A. Di Paola, L. Palmisano, F. Parrini, G. Buscarino, R. Amadelli, Preparation and photoactivity of samarium loaded anatase, brookite and rutile catalysts, Appl. Catal., B, 104, 291-299 (2011).

Controlling the Oxygen Defects Concentration in a Pure BiFeO3 Bulk Ceramic.

BiFeO3 is a multiferroic material with a perovskite structure that has a lot of potential for use in sensors and transducers. However, obtaining pure single-phase BiFeO3 ceramic with a low electrical conductivity via solid-state reactions remains a problem that limits its application. In this work, the suppression of secondary phases in BiFeO3 was studied by varying the compositional parameters and the sintering temperature. The addition of 1% Bi2O3 to the stoichiometric precursor mixture prevented the formation of secondary phases observed when sintering stoichiometric precursors. The pure phase ceramic had a p-type conductivity and a three-decade lower electrical conductivity as measured by impedance spectroscopy. Annealing of optimally synthesized material at different partial pressures of oxygen in an oxygen–nitrogen gas atmosphere showed that the reason for this type of conductivity lies in the high concentration of defects associated with oxygen. By annealing in various mixtures of nitrogen and oxygen, it is possible to control the concentration of these defects and hence the conductivity, which can go down another two decades. At a pO2 the conductivity is determined by intrinsic charge carriers in the material itself.

Towards more realistic simulations of microstructural evolution in oxidic systems

High temperature oxidic systems are encountered in nature (magma chambers) and pyrometallurgical processes. In these systems, the solidification of the oxidic liquids influences the flow, the cooling after tapping, the viscosity and rheological behaviour within the reactor and also the freeze lining behaviour. On the mesoscale, the phase field concept has proved to be a very powerful tool for modeling crystallizing microstructures. However, application of the method to slag solidification is still challenging. In this work, we present a phase field model to simulate the faceted crystallization of Fe3O4 in a quaternary FeO–Fe2O3–Cu2O–SiO2 melt under different partial pressures of oxygen to solve certain problems encountered related to more realistic simulations in oxidic systems. The ratio of FeO/Fe2O3 at the upper boundary is in equilibrium with the oxygen fugacity of the atmosphere, while conserving Fe. Two-dimensional simulations are performed with different varying oxygen fugacity in the atmosphere. For the considered composition range, the growth velocities of the spinel crystals increase with decreasing oxygen fugacity. One of the focus points in creating more realistic phase field models is the incorporation of the thermodynamic driving forces in multicomponent multiphase-field models by coupling to thermodynamic databases. The first part of this work used a tabular method. However, as the number of components in the system increases, the number of thermodynamic data points also increases exponentially, and so do the computational and memory requirements. A possible solution for this might be the use of a canonical polyadic decomposition of the tensors containing the thermodynamic data. In this way, the huge tensors are approximated well by compact multilinear models or decompositions. This promising solution has been applied in the second part of this work on the same oxidic liquid-solid system.

Investigation of La2-XSrxNi0.8Co0.2O4+d (0.0 ≤ x ≤ 0.2) Materials as Oxygen Electrodes for Solid Oxide Cells

Lanthanide Nickelate Ln2NiO4+δ (Ln = La, Pr or Nd) has drawn significant attention as an oxygen electrode for solid oxide cells (SOCs) due to its mixed ionic and electronic conductivity (MIEC) property. They exhibit very good electro-catalytic activity as well as high oxygen diffusion coefficient (D*) and surface exchange coefficient (k*) values [1]. Earlier reported results [2, 3] show that the partial substitution of Co2+ at B-site in La2Ni1−xCoxO4+δ (LNCO) lead to an enhancement in the transport and electrochemical properties of the material. The present study aims to investigate the effect of Sr2+ substitution at A-site in LNCO i.e. La2-xSrxNi0.8Co0.2O4+δ (LSNCO) in order to further investigate the structural, physico-chemical and electrochemical properties of the materials. Three different compositions i.e. LSNCO5, LSNCO10 and LSNCO20 were studied with x = 0.05, 0.10 and 0.20 respectively. First the materials were characterized by XRD, TGA and SEM. Then, the electrochemical characterizations were carried out by fabricating the symmetrical half-cells (8YSZ//GDC//LSNCO) as well as single cells (NiO-YSZ//8YSZ//GDC//LSNCO) using Electrochemical Impedance Spectroscopy (EIS) in 700 – 900 °C temperature range.All these materials exist with orthorhombic structure and a decrease in the cell volume as well as oxygen content (4+δ) is observed with Sr-substitution. The TGA analyses as a function of temperature reveals that these materials show reversible oxygen exchange and are always over-stoichiometric in 25-1000 °C temperature range. However, the loss of oxygen with increasing temperature is decreased with increasing Sr-content. The EIS data analysis of the symmetrical half-cells shows an increase in polarization resistance (Rp) with increasing the Sr-content. For instance, the Rp values of 0.047 and 0.88 Ω.cm2 are observed for LSNCO5 and LSNC20 respectively at 800 °C under air at OCV conditions. The EIS measurements under different partial pressure of oxygen reveals that four electrode processes (as fitted by 4R//CPE along with a series resistance Rs) are involved in the oxygen reduction/evolution mechanism. The observed electrode processes are; ionic transfer of oxide ion through electrode electrolyte interface (R1), charge transfer process (R2), adsorption/desorption of atomic species (R3) and molecular gas diffusion process (R4). The impedance data analysis under polarization (-0.2 to +0.2 V) reveals a decrease in the exchange current density with the increase of Sr-content. For instance, the io value is 0.040 A.cm-2 for LSNCO5 which is decreased to 0.003 A.cm-2 for LSNCO20 at 800 °C. Current-Voltage characteristics obtained from the single cell measurements show a decrease in the current density with increasing Sr-content.The detailed structural, physico-chemical and electrochemical properties of these materials will be presented and discuss in detail.

Effects of zinc porphyrin and zinc phthalocyanine derivatives in photodynamic anticancer therapy under different partial pressures of oxygen in vitro

Photodynamic therapy (PDT) is gradually becoming an alternative method in the treatment of several diseases. Here, we investigated the role of oxygen in photodynamically treated cervical cancer cells (HeLa). The effect of PDT on HeLa cells was assessed by exposing cultured cells to disulphonated zinc phthalocyanine (ZnPcS2) and tetrasulphonated zinc tetraphenylporphyrin (ZnTPPS4). Fluorescence microscopy revealed their different localizations within the cells. ZnTPPS4 seems to be mostly limited to the cytosol and lysosomes, whereas ZnPcS2 is most likely predominantly attached to membrane structures, including plasmalemma and the mitochondrial membrane. Phototoxicity assays of PDT-treated cells carried out under different partial pressures of oxygen showed dose-dependent responses. Interestingly, ZnPcS2 was also photodynamically effective at a minimal level of oxygen, under a nitrogen atmosphere. On the other hand, hyperbaric oxygenation did not lead to a higher PDT efficiency of either photosensitizer. Although both photosensitizers can induce a significant drop in mitochondrial membrane potential, ZnPcS2 has a markedly higher effect on mitochondrial respiration that was completely blocked after two short light cycles. In conclusion, our observations suggest that PDT can be effective even in hypoxic conditions if a suitable sensitizer is chosen, such as ZnPcS2, which can inhibit mitochondrial respiration.

X-ray absorption spectroscopy study of Ga-doping in reactively sputtered ZnO films

Ga-doped ZnO (GZO) films were grown by reactive co-sputtering of a Zn-GaAs target (3% area coverage of Zn by GaAs) at 375 °C with different partial pressures of oxygen. The resistivity of GZO films increases drastically from ≲10−3 Ω-cm to ~ 0.2 Ω-cm as the O2 in the sputtering atmosphere is changed from 5 % to 6 %. The films grown at 5% or lower O2 have the Ga/Zn ratio of ~ 0.1 and display low resistivity with carrier concentration ~ 1021 cm−3, while the films grown at 6% or higher O2 have lower Ga/Zn ratio of ~ 0.01 and display high resistivity with carrier concentration ~ 1019 cm−3. Extended X-ray absorption fine structure (EXAFS) measurements at Zn and Ga K-edges reveal substitutional incorporation of Ga in low resistivity films. X ray photoelectron spectroscopy (XPS) studies reveal a substantial decrease in oxygen vacancies together with increase in oxygen interstitials, in high resistivity GZO films. EXAFS measurements of the high resistivity films show a substantial increase in Ga-O and Ga-Zn bond distances and Ga-O coordination, indicating incorporation of oxygen interstitials in the vicinity of Ga. The comparison of measured and simulated X–ray absorption near edge spectra at O K-edge, together with XPS and EXAFS results, provides adequate experimental evidence of the presence of acceptor type (GaZn+Oi) defect complex, which cause carrier compensation in high resistivity films.

Oxidation behaviour of coarse and fine SiC reinforced ZrB2 at re-entry and atmospheric oxygen pressures

ZrB2 composites reinforced with SiC of two different particle sizes (coarse ~30 μm and fine ~5 μm) were processed using spark plasma sintering. The oxidation behaviour of the synthesised composites was investigated at 1500 °C under two different partial pressures of oxygen. At higher oxygen partial pressure of 0.21 atm, coarse SiC reinforced ZrB2 composite developed thicker oxide layers as compared to that of fine SiC reinforced ZrB2 composite. The thicker silica layer provides an enhanced oxidation resistance for extended exposure periods of greater than 3 h. However, at lower oxygen partial pressure of 2 × 10−5 atm, fine SiC reinforced ZrB2 composite showed better oxidation resistance due to segregation of finer ZrO2 particles on the surface, which prevented inward transportation of oxygen.

Effect of Oxygen Partial Pressure and Temperature on the Oxidation Behavior of SiB6

The oxidation kinetics of silicon hexaboride (SiB6) was studied at different partial pressures of oxygen. The specific weight gain was measured at 1173 K, 1223 K, and 1273 K for $$ P_{{{\text{O}}_{2} }} $$ = 0.1, 0.23, and 0.33 atm using thermogravimetric analysis. The conventional empirical expressions for oxidation were observed at all selected oxygen partial pressures and temperatures. The structural characterization of the oxidation product was characterized using XRD and FT-IR, with SiB6, SiO2, B, and amorphous B2O3 observed after oxidation for 25 hours. The oxidation surface morphology was also characterized to obtain the oxidation product size, ranging from 4.54 to 24.69 µm with increasing $$ P_{{{\text{O}}_{2} }} $$ and temperature. The diffusional activation energy for the oxidation process was also calculated from the empirical constant, obtained from the mathematical fitting of the specific weight gain with time. The oxidation activation energies for SiB6 are 250.72, 235.64, and 232.65 kJ/mol at $$ P_{{{\text{O}}_{2} }} $$ = 0.1, 0.23, and 0.33 atm, respectively.

Hydrogen Production During Ethylene Glycol Photoreactions Over Ag-Pd/TiO2 at Different Partial Pressures of Oxygen.

The reaction of ethylene glycol has been studied over Ag–Pd/TiO2 (anatase) under photo-irradiation while monitoring the reaction products (in the gas and liquid phases) as a function of time and at different partial pressures of molecular oxygen. The catalyst contained metal particles with a mean size of about 1 nm, most likely in the form of alloy (TEM, STEM, and XPS). The complex reaction network involves hydrogen abstraction, C-C bond dissociation, de-carbonylation and water gas shift ultimately yielding hydrogen and CO2. The two main competing reactions were found to be, photo reforming and photo-oxidation. Based on our previous study, Ag presence improves the reaction rate for hydrogen production, most likely via decreasing the adsorption energy of CO when compared to pure Pd. At high ethylene glycol concentrations, the rate of hydrogen produced decreased by a factor of two while changing O2 partial pressure from 0.001 to 0.2 atm. The rate was however very sensitive to oxygen partial pressures at low ethylene glycol concentrations, decreasing by about 50 times with increasing oxygen pressures to 1 atm. The order of reaction with respect to O2 changed from near zero at high oxygen partial pressure to ½ at low partial pressure (in 0.008–0.2 atm. range). Liquid phase analysis indicated that the main reaction product was formaldehyde, where its concentration was found to be higher than that of H2 and CO2. The mass balance approached near unity only upon the incorporation of formaldehyde and after a prolonged reaction time. This suggests that the photo-reforming reaction was not complete even at prolonged time, most likely due to kinetic limitations.

Annealing Conditions’ Influence on the Oxidation of Silicon‐Aluminium‐Alloys in Combinatorial Thin‐Film Libraries

Alloys containing aluminium and silicon are of wide use. Due to their abundance, these elements are promising contributors to technical materials. A combinatorial thin‐film approach (silicon content within 27 at.% and 65 at.%, and aluminium between 35 at.% and 73 at.%, deposited by simultaneous co‐sputtering) is chosen for systematic investigations of reactions and compositions of high‐silicon containing alloys with aluminium. As the melting points of silicon and aluminium are far from each other and, furthermore, the binary system comes along with a eutectic point, high‐temperature stability oxidation of these alloys is of interest. Moreover, due to the high oxygen affinity of both, silicon and aluminium, the stability under different annealing conditions is explored. These annealing conditions provide different partial pressures of oxygen while leaving the remaining parameters constant in order not to superimpose the effect of the annealing atmosphere. Surface imaging, together with chemical analysis and contact potential difference (CPD) by Scanning Kelvin Probe along and across libraries provide an insight into the influence of annealing atmosphere onto the surface properties. However, determining an influence of the deposition method on the results is not subject to this investigation.

Oxidation of ablated silicon during pulsed laser deposition in a background gas with different oxygen partial pressures

We have analysed changes in the oxidation state of SiOx films produced by pulsed laser deposition in a background gas with different partial pressures of oxygen. The optical properties of the films in IR range are shown to be close to those of SiO2 while the total oxidation degree is considerably less than 2. It is suggested that the film consists of oxidized and unoxidized regions due to preferential oxidation of the periphery of the silicon ablation plume during expansion. These regions are overlapping in the film if the laser beam is scanned on the target.

In situ oxidation and reduction of cerium dioxide nanoparticles studied by scanning transmission electron microscopy

Cerium dioxide nanocubes and truncated octahedra were reduced and oxidized in the scanning transmission electron microscope. The reduction process was stimulated by the electron beam and oxidation was supported by background gases in the microscope environment. High-angle annular dark field imaging is sensitive to local lattice distortions that arise as oxygen vacancies are created and cerium cations reduce enabling high spatial resolution characterization of this process with temporal resolution on the order of seconds. Such measurements enable us to differentiate and infer that the observed behavior between the nanocubes and truncated octahedra may be due to the difference in crystallographic termination of surfaces. In situ measurements taken with different partial pressures of oxygen reveal the cerium oxidation state and the dose rate threshold for the onset of beam reduction are influenced by the environment. Increasing oxygen partial pressure reduces the Ce3+ content and decreases susceptibility to electron beam driven reduction.

Influence of Oxygen Partial Pressure Variation on Oxidation Resistance of Ti-46.7Al-1.9W-0.5Si at 750, 850 and 950 °C

γ-TiAl intermetallic alloys can be potentially employed as structural materials for many industries where high temperature and access of atmosphere with variable oxygen partial pressures are often met. Different partial pressures of oxygen may influence oxidation behavior and induce different oxide scale phase constitutes. This study investigated the influences of oxygen partial pressures on the oxidation resistance of a γ-TiAl alloy, Ti-46.7Al-1.9W-0.5Si (at.%), in Ar-O2 environments (5%O2, 20%O2 and 80%O2) at 750, 850 and 950 °C, respectively. The oxidation products were characterized using scanning electron microscopy, energy-dispersive x-ray analysis, x-ray diffraction and transmission electron microscopy. The oxidation kinetic results achieved by a discontinuous gravimetric method revealed that the alloy oxidized following a parabolic rate law. The oxidation resistance of the alloy was enhanced with increasing the oxygen partial pressures at all three experimental temperatures. Multilayered oxide scales of TiO2/Al2O3 were developed during the oxidation process. The enhancement of oxidation resistance was resulted from preferential generation of Al2O3 and the reduction in defects in TiO2 with increasing the oxygen partials pressures.

P-1.14: The Influence of Dual-channel on the Performance of Self-Align Top-Gate IGZO Thin Film Transistors

In this work, fully transparent dual-layer channel self-aligned top-gate amorphous indium gallium zinc oxide thin-film transistors (a-IGZO TFTs) are fabricated on glass substrates. Dual-layer channel is consist of indium gallium zinc oxide with different partial pressure of oxygen while sputtering. An oxygen-rich IGZO was deposited to control the threshold voltage and an oxygen-poor IGZO was then deposited to modulate device mobility. The device exhibited the excellent performances, including: a field effect mobility of 5.33 cm2/Vs, a suitable threshold voltage of 1.68V, a sub-threshold swing of 0.54V/dec and a high on/off current ratio. Furthermore, the devices also shows great stability under bias stress.

Dinitrosyl iron complexes: Formation and antiradical action in heart mitochondria.

Mitochondria are widely known as a major source of reactive oxygen and nitrogen species for the cardiovascular system. Numerous studies established that superoxide anion radical production by heart mitochondria is only slightly suppressed under conditions of deep hypoxia, but is completely blocked under anoxia. It was found also that dinitrosyl iron complexes (DNIC) compare favourably with other physiologically active derivatives of nitric oxide (NO). DNIC with glutathione effectively scavenge superoxide radicals generated by mitochondria at different partial pressures of oxygen. Under conditions of simulated hypoxia, the synthesis of thiol-containing DNIC takes place in mitochondria and is concomitant with a significant decrease in the concentration of NO metabolites at the reoxygenation step. Free NO required for DNIC synthesis is generated in the reaction of S-nitrosothiols with superoxide or during single-electron oxidation of the nitroxyl radical (HNO) by coenzyme Q. Plausible mechanisms of antiradical effects of DNIC and their protective role in oxidative stress induced by hypoxia/reoxygenation of myocardial tissues are considered. © 2018 BioFactors, 44(3):237-244, 2018.

Hot corrosion behavior of ZrB2-HfB2 solid solutions in KCl and K2SO4 at 1500 °C

Novel electrode coating materials are needed for coal-fired magnetohydrodynamic (MHD) direct-current extraction power plants. Addition of potassium salt to increase the conductivity of coal plasma combined with high temperature render the service conditions extremely arduous. Therefore, the electrode coating materials must possess certain properties including high-temperature corrosion resistance, high-temperature oxidation resistance, and adequate electrical conductivity. In this work, those very properties of three different compositions of transition metal diboride solid solutions of HfB2-ZrB2 are studied. Two main approaches of oxidation mitigation methods were employed: adding chemical dopants, such as Hf and La, and performing pre-anodization on the samples to create a protective oxide coating. Thermogravimetric experiments were run at different partial pressures of oxygen to determine the high-temperature oxidation resistance of these boride ceramics. In addition, two different salt coatings (KCl and K2SO4) were applied to the surface of the samples to test their hot corrosion resistance. High-temperature polarization resistance tests were also conducted to measure the electrical resistivity. The addition of lanthanum aided in long term oxidation and corrosion protection, with a parabolic rate constant, Kp = 1.33 × 10−5kg2/m4s, a 40% improvement over the sample without the addition of lanthanum under the same conditions. Anodization, however, proved disadvantageous when combined with either lanthanum or a corrosive environment.

Effects of acute and chronic hypoxia on acid-base regulation, hematology, ion, and osmoregulation of juvenile American paddlefish.

Despite the increasing prevalence of hypoxia in natural habitats occupied by the American paddlefish, basal bony fish, and ram ventilator, information about its response to hypoxia is scarce. To understand the physiological and biochemical responses of juvenile paddlefish (~150g) to acute (<24h) and chronic hypoxia (≥24h), blood oxygen transport, blood acid-base balance, and metabolic stress were evaluated under four different partial pressures of oxygen [pO2; normoxia (148mmHg), mild hypoxia (89mmHg), moderate hypoxia (59mmHg), and extreme hypoxia (36mmHg)], all at 21 °C. Arterial blood samples were collected from paddlefish after they had been exposed to treatments for 0.25, 2, 6, 24, and 72h, and analyzed for hematocrit, pO2, total oxygen content, oxygen saturation, pCO2, pH, hemoglobin, Na+, K+, Ca2+, Cl-, glucose, and lactate. Mild hypoxia only caused a reduction in blood pO2 and oxygen saturation. Both acute and chronic moderate and extreme hypoxia caused a decrease in blood pH, pO2, total oxygen content, plasma Na+, and Cl- at all time points. Acute moderate and extreme hypoxia resulted in an increase in blood pCO2, plasma glucose, lactate, and hematocrit. Chronic exposure to moderate hypoxia resulted in an increase in plasma lactate, red blood cell count, and hemoglobin. This study shows that paddlefish are able to physiologically compensate for mild hypoxia, but exhibit secondary stress responses and are unable to return to homeostasis when exposed to both acute and chronic moderate hypoxia, and die after 3-8h of extreme hypoxia.

Interfacial effects on electrical conductivity in ultrafine-grained Sm0.2Ce0.8O2−δ electrolytes fabricated by a two-step sintering process

Ultrafine-grained (∼148 nm) and microcrystalline (∼1.5 μm) Sm0.2Ce0.8O2−δ (SDC20) ceramic pellets with relatively high density are fabricated by two-step sintering (TSS) and the conventional sintering (CS) method. The electrical conductivity was studied at intermediate temperatures in the range of 300–600 °C, and concentration cell measurements were employed to investigate the interfacial effect at or near the grain-boundaries of ultrafine-grained SDC20. The results show that ultrafine-grained SDC20 has a remarkable enhancement in the total conductivity of about one order of magnitude greater than that of conventional microcrystalline SDC20 mainly due to the predominance of increased grain-boundary conduction with decreasing grain size. Concentration cell measurements under different partial pressure of oxygen (PO2) prove that the enhanced grain-boundary conductivity of ultrafine-grained SDC20 is mainly attributed to purely ionic charge carriers but not electronic contribution. The interfacial effect is due most likely to enhanced mobility of oxygen vacancies at or near the grain boundaries. Two-step sintering of SDC20 electrolytes provides an effective approach for further development of high performance, low operation temperature solid oxide fuel cells.