Reoxidation Time Research Articles

Environmentally relevant copper concentrations stimulate photosynthesis in Monoraphidium sp.

Microalgae require copper (Cu) in trace levels for their growth and metabolism, it is a vital component of certain metalloproteins. Although this element has been widely studied concerning microalgae physiology, the effects of environmentally relevant levels have been less studied. We studied the photosynthesis and growth of the Chlorophyte Monoraphidium sp. exposed to Cu ranging from low (1.7nM) to high (589.0nM) free Cu ions (Cu2+) concentrations. The growth rate was unaffected by Cu concentrations in the range of 1.7-7.4nM Cu2+, but decreased beyond it. The relative maximum electron transport rate (rETRm), saturation irradiance (Ek), photochemical quenching (qP and qL), and PSII operating efficiency [Formula: see text] were stimulated in the 3.4-7.4nM Cu2+ range, concentrations slightly higher than the control, whereas non-photochemical quenching (NPQ) gradually increased with increasing Cu2+. The photosystem II antenna size [Sigma (II)440] increased under high Cu (589.0nM), which resulted in a decrease in the quinone A (QA) reduction time (tau). In contrast, the QA re-oxidation time was unaffected by Cu exposure. These findings show that a slight increase in Cu stimulated photosynthesis in Monoraphidium sp., whereas high Cu reduced photosynthesis and increased the dissipation of captured light energy. This research is a contribution to the understanding of the dynamic photo-physiological responses of Monoraphidium sp. to Cu ions.

Influence of Ba/Ti ratio on PTCR effect of Bam(Ti1−xNbx)O3 ceramics prepared by the reduction sintering-reoxidation method

In this work, we investigate the influences of Ba/Ti ratio and sintering conditions on the characteristics of positive temperature coefficient of resistance (PTCR) and electrical properties of Ba[Formula: see text](Ti[Formula: see text]Nb[Formula: see text])O3 (BTN) ceramics. The ceramics were fired at 1190[Formula: see text]C for 0.5–6.0 h in a reducing atmosphere and then reoxidized at 600–650[Formula: see text]C for 0–8 h. The Ba/Ti ratio [Formula: see text] affected the electrical properties and PTCR effect of the BTN specimens. The room-temperature (RT) resistance of the BTN samples initially decreased [Formula: see text] and then increased [Formula: see text] as the Ba/Ti ratio increased. Moreover, BTN ceramics exhibit a pronounced PTCR effect, with a resistance jump greater by 3.0 orders of magnitude and a low 0.1 [Formula: see text] RT resistance at a low reoxidation temperature of 600[Formula: see text]C after sintering under a reducing atmosphere. Furthermore, the average sample grain size increased along with the Ba/Ti ratio. In addition, the influence of the sintering time and the reoxidation time on the electrical properties and the PTCR effect were also investigated.

Elemental Stoichiometry and Photophysiology Regulation of Synechococcus sp. PCC7002 Under Increasing Severity of Chronic Iron Limitation.

Iron (Fe) is an essential cofactor for many metabolic enzymes of photoautotrophs. Although Fe limits phytoplankton productivity in broad areas of the ocean, phytoplankton have adapted their metabolism and growth to survive in these conditions. Using the euryhaline cyanobacterium Synechococcus sp. PCC7002, we investigated the physiological responses to long-term acclimation to four levels of Fe availability representative of the contemporary ocean (36.7, 3.83, 0.47 and 0.047 pM Fe'). With increasing severity of Fe limitation, Synechococcus sp. cells gradually decreased their volume and growth while increasing their energy allocation into organic carbon and nitrogen cellular pools. Furthermore, the total cellular content of pigments decreased. Additionally, with increasing severity of Fe limitation, intertwined responses of PSII functional cross-section (σPSII), re-oxidation time of the plastoquinone primary acceptor QA (τ) and non-photochemical quenching revealed a shift in the photophysiological response between mild to strong Fe limitation compared with severe limitation. Under mild and strong Fe limitation, there was a decrease in linear electron transport accompanied by progressive loss of state transitions. Under severe Fe limitation, state transitions seemed to be largely supplanted by alternative electron pathways. In addition, mechanisms to dissipate energy excess and minimize oxidative stress associated with high irradiances increased with increasing severity of Fe limitation. Overall, our results establish the sequence of physiological strategies adopted by the cells under increasing severity of chronic Fe limitation, within a range of Fe concentrations relevant to modern ocean biogeochemistry.

Influence of Reoxidation Time on Electrical Properties of Y2O3-doped BaTiO3 Ceramics Sintered in a Reducing Atmosphere

The influence of the reoxidation time on electrical properties and the positive temperature coefficient of resistance (PTCR) effect in multilayer Y2O3-doped BaTiO3 (BTO) ceramics were investigated. The BTO ceramics were sintered at 1160 °C−1270 °C for 2 h in a reducing atmosphere and then reoxidized at 500 °C–900 °C for 0 h−4 h. Results indicated that the room-temperature resistance of BTO ceramics reoxidized at 750 °C for 2 h after sintering at 1160 °C−1270 °C for 2 h decreased with the increasing of the sintering temperature. As the reoxidation time increased, the room-temperature resistance of the BTO samples slightly increased. In addition, the effect of the reoxidation time on the PTCR effect of the ceramics was also studied. The BTO ceramics had a low room-temperature resistance of 0.3 Ω and a resistance jump greater than 3.0 orders of magnitude.

Redox-Stable High-Performance Thin-Film Solid Oxide Fuel Cell

An anode-supported Solid Oxide Fuel Cell (ASC) consists of a mechanically supporting, thick, and highly porous anode substrate, coated on top with thin films of a fine-structured porous anode, a dense electrolyte, and a fine-structured cathode. Both, the anode substrate and the anode are made of a cermet of nickel and yttria-stabilized zirconia (YSZ). An increase of the oxygen partial pressure at the anode side will lead to a reoxidation of the nickel and to microstructural changes. This may result in a macroscopic expansion of the anode substrate and in a complete cell failure, due to cracking of the YSZ electrolyte. In this work, a redox-stable SOFC with a thin-film sol-gel electrolyte is presented. Using tailored suspensions and polymeric sols of varying target particle size, a 1 µm thick, three layer sol-gel electrolyte is coated on top of a tape cast anode substrate and a screen printed anode by spin-coating and dip-coating techniques. With this sol-gel electrolyte a power output larger than 1.25 W/cm2 at 0.7 V and an operating temperature of 600 °C could be demonstrated. In this study, half cells (anode substrate, anode, and electrolyte) are reoxidized in excess air, in order to test the redox stability of these SOFCs. Afterwards the electrolyte is investigated ex situ using optical microscopy and SEM. No cracks are found in the sol-gel electrolyte after reoxidation for 4 hours at 600 °C and 15 minutes at 800 °C, respectively, whereas a lot of cracks are visible in a standard ASC with a 10 µm thick, screen printed electrolyte for both reoxidation conditions. This means the sol-gel electrolyte can tolerate higher degrees of oxidation (DoO) of the anode substrate than the screen printed electrolyte. The residual compressive stresses of both electrolytes are measured to about 600 MPa using XRD and are therefore not responsible for the higher stability against reoxidation of the sol-gel electrolyte. In contrast, the energy release rate has to be larger than a critical value for the creation of cracks in a thin-film on a thick substrate. Due to the fact, that the energy release rate is proportional to the thickness of the thin-film, a thinner film is more stable against cracking than a thicker film at constant tensile stresses. After reoxidation of 8 hours at 600 °C and 60 minutes at 800 °C, respectively, cracks are also found in the sol-gel electrolyte. However, the SOFC with the thin-film sol-gel electrolyte can be considered as stable against reoxidation, because the long reoxidation time of 4 hours at an operating temperature of 600 °C is unlikely to happen under real conditions.

Redox-Stable High-Performance Thin-Film Solid Oxide Fuel Cell

In this work, a mechanically redox-stable SOFC with a 1 µm thin-film sol-gel electrolyte is presented. With this electrolyte a power output larger than 1.25 W/cm2 at 0.7 V and an operating temperature of 600 °C could be demonstrated. Half cells were re-oxidized in excess air, in order to test the redox stability of these SOFCs. No cracks were found in the sol-gel electrolyte after re-oxidation for 4 hours at 600 °C and 30 minutes at 800 °C, respectively. Due to the fact, that the energy release rate is proportional to the thickness of the thin-film, a thinner film is more stable against cracking than a thicker film at constant tensile stresses. The SOFC with the thin-film sol-gel electrolyte can be considered as stable against re-oxidation, because the long re-oxidation time of 4 hours at an operating temperature of 600 °C is unlikely to happen under real conditions.

Effect of reoxidation annealing on the PTCR behaviour of multilayer Nb5+-doped BaTiO3 ceramics with a Ni internal electrode

The effects of reoxidation annealing on the electrical properties and the positive temperature coefficient of resistance (PTCR) effects of multilayer Ba1.005(Ti1−x Nbx)O3 (BTN) ceramics sintered at different temperatures from 1100 to 1160 °C for 2 h in a reducing atmosphere and reoxidized at various temperatures in the range 500–900 °C were investigated. The results indicated that the room-temperature (RT) resistance of the BTN ceramics reoxidized at different temperatures first increased slowly and then quickly with the increase in the reoxidation temperature. Meanwhile, the resistance jump of the samples increased first and then decreased with the increase in the reoxidation temperature. In addition, the PTCR effect could be improved by prolonging the reoxidation time. Finally, the samples reoxidized at a low temperature of 600 °C after sintering at 1160 °C in a reducing atmosphere exhibited a significant PTCR effect, with a resistance jump of 3.5 orders of magnitude, along with a low RT resistance of 0.38 Ω. Additionally, the influences of the reoxidation temperature and time on the grain resistance and grain-boundary resistance were investigated using complex-impedance spectroscopy.

The Electrochemical Behavior of the Rehealing Oxide Scales After Pitting Corrosion

The electrochemical behaviour of the rehealing oxide scales on the K52 nanocrystalline coatings had been studied by polarization curves. The results indicated that the oxide scales formed on the nano-coating exhibited rehealing ability after pitting corrosion, and the coating still had excellent corrosion resistance. The rehealing ability was enhanced with prolonged re-oxidation time. EDX analyses revealed that the oxide scales within the pits were composed of mixed-oxides (Cr2O3, Al2O3 and TiO2). The mixed-oxides were made up of two layers: the external oxide layer was composed of Cr2O3 and TiO2 and the internal oxide layer was Al2O3.

Reoxidation Effects of Ba‐Excessive Barium Titanate Ceramics for Laminated Positive Temperature Coefficient Thermistors

Using tape casting technique Ba‐excessive BaTiO3 ceramics were prepared, and their reoxidation effects for laminated positive temperature coefficient thermistors are investigated. These ceramics exhibit fine grains of size ~1.15 μm. A resistivity of 727 Ω·cm and a PTCR jump about 3.3 orders of magnitude can be observed when the sample was sintered in reducing atmosphere at 1150°C and successively reoxidized at 850°C for 15 min. The influences of reoxidation on ceramic characteristics are discussed. The correlation of room temperature resistivity against reoxidation temperature showed an anomalous trend. This anomaly can be explained by the enhancement of ferroelectricity led by annihilation of oxygen vacancies. The influences of reoxidation time on ceramic characteristics were found to be limited. The impedance analysis revealed that the resistance of grain boundary is more likely to be influenced during reoxidation compared to that of grain bulk. The low acceptor‐state densities of 2 × 1012–6 × 1012 cm−2 at grain boundaries were also estimated.

Sm을 첨가한 BaTiO3계의 재산화 온도 및 시간에 따른 PTC 특성 변화

We investigated the effects of the re-oxidation temperature and time on the positive temperature coefficient (PTC) of resistivity characteristics of Sm-doped BaTiO₃ sintered at 1200~1260℃ for 2 h in a reducing atmosphere (3% H₂/N₂), followed by re-oxidization processes in air, in which re-oxidization temperature and time were 600~1000℃ and 1~10 h, respectively. The result reveals that Smdoped (Ba,Ca)TiO₃ ceramics fired in a reducing atmosphere exhibit low PTC characteristics, whereas the sample re-oxidized at 800℃for 1 h in air exhibit pronounced PTC characteristics. The room-temperature resistivity and jumping characteristics of resistivity (ρmax/ρ 25℃ ) decrease with Sm contents. The PTC characteristics with reoxidization time at 800℃ have improved about 2~3 orders of magnitude whereas differed according to the sintering temperature. The 0.7 at% Sm-doped (Ba,Ca)TiO₃ samples reveal the best PTC characteristics in the present range of formula and processes.

Evaluation of the redox stability of segmented-in-series solid oxide fuel cell stacks

Abstract The tolerance for the reduction and oxidation (redox) reactions of the segmented-in-series solid oxide fuel cells (SIS-SOFCs) has been investigated. In conventional anode-supported solid oxide fuel cells (SOFCs), the anode and the substrate are typically prepared from Ni–YSZ-based materials which exhibit a significant dimensional change because of the redox reaction and cannot retain their structure. The substrate of the SIS-SOFCs is prepared from Ni-doped MgO-based material, which has a high redox tolerance, and the SIS-SOFC exhibits a good performance after the redox cycles. The degradation rate is approximately 0.15% per cycle in a redox condition of start-and-stop operation without fuel supply. In the other redox condition (when the fuel supply is interrupted for 1.5 min), the voltage of the SIS-SOFCs remains almost constant. However, the voltage of SIS-SOFCs decreases with an increase in the reoxidation time of the interruption in the fuel supply. The high redox tolerance is attributed to the fact that the diffusion coefficients, mean free path, and existence of the Ni particles in the substrate can effectively deter the oxidation of the anode.

Redox Reaction of Catalytic Layer in the Electrochemical Reactor for NOx Decomposition

The influence of reduction and re-oxidation reactions on NOx decomposition properties of an electrochemical reactor with a catalytic layer (NiO/YSZ) has been studied. To clarify the correlation between the NOx decomposition properties and the redox reactions of NiO in the catalytic layer, we carried out the measurements of re-oxidation time (interval) dependence of electric current at between 350 and 600{degree sign}C. The electrochemical reactor with the catalytic layer was shown the highly effective NOx decomposition properties in the presence of excess oxygen. Even if the interval increases, the current efficiency for NOx decomposition was not deteriorated at less than 400{degree sign} C. However, the current efficiency has been decreased according to an increase in temperature and/or interval at over 450{degree sign}C. The deterioration of current efficiency occurs with the volume expansion of the catalyst layer by the re-oxidation of NiO.

Advanced measurement techniques to characterize thermo-mechanical aspects of solid oxide fuel cells

Advanced characterization methods have been used to analyze the thermo-mechanical behaviour of solid oxide fuel cells in a model stack. The primarily experimental work included contacting studies, sealing of a model stack, thermal and re-oxidation cycling. Also an attempt was made to correlate cell fracture in the stack with pore sizes determined from computer tomography. The contacting studies were carried out using pressure sensitive foils. The load to achieve full contact on anode and cathode side of the cell was assessed and applied in the subsequent model stack test. The stack experiment permitted a detailed analysis of stack compaction during sealing. During steady state operation thermal and re-oxidation cycling the changes in open cell voltage and acoustic emissions were monitored. Significant softening of the sealant material was observed at low temperatures. Heating in the thermal cycling loop of the stack appeared to be less critical than the cooling. Re-oxidation cycling led to significant damage if a critical re-oxidation time was exceeded. Microstructural studies permitted further insight into the re-oxidation mechanism. Finally, the maximum defect size in the cell was determined by computer tomography. A limit of maximum anode stress was estimated and the result correlated this with the failure strength observed during the model stack testing.

Reduction and Reoxidation Reaction of Catalytic Layers in Electrochemical Cells for NOx Decomposition

The influence of reduction and reoxidation reactions on decomposition properties of an electrochemical cell with a catalytic layer (NiO/yttria stabilized zirconia) has been studied. To clarify the correlation between the decomposition properties and the redox reactions of NiO in the catalytic layer, we carried out the measurements of reoxidation time dependence of electric current in the temperature range of . The electrochemical cell with the catalytic layer was shown for the highly effective decomposition properties in the presence of excess oxygen. Even if the reoxidation time increases, the current efficiency for decomposition was not deteriorated at less than . However, the current efficiency has been decreased according to an increase in temperature and/or reoxidation time at over . The deterioration of current efficiency occurs with the volume expansion of the catalyst layer by the reoxidation of NiO.

Preparation of conductive polyaniline fibers by a continuous forming-drawn processing routine

Polyaniline fibers were prepared with a continuous forming-drawn processing routine that better met practical production requirements. The continuous forming drawing of the fibers was conducted successfully with the following methods. A reducing agent was added to a polymer solution during the dissolution of a polyaniline emeraldine base in N-methyl-2-pyrrolidinone (NMP). After the entire wet-spinning process was finished, the fibers were reoxidized and doped to obtain electric conductivity. The as-spun fibers were predrawn at a low drawing ratio in a warm water bath before a plasticization drawing process on a hot plate. After the fibers were predrawn, some solvent was still kept in the fibers and used as a plasticizer of the fibers so that the plasticization drawing process would be performed successfully. The spinning conditions that affected the mechanical properties and conductivity of the fibers were the content of NMP in the coagulation bath, the coagulation-bath temperature, the warm-water-bath temperature, the predrawing ratio, the hot-plate temperature, the plasticization drawing ratio, and the reoxidation and protonation treatment time. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 956–960, 2004

The effect of reoxidation time during the preparation of Ni-loaded CsLa 2Ti 2NbO 10 on the photocatalytic hydrogen production in water decomposition reaction

The photocatalytic decomposition of water for H 2 evolution over 1 wt.% Ni/CsLa 2Ti 2NbO 10 was investigated according to the reoxidation time during the preparation. The dependence of photocatalytic activity on the reoxidation time was examined by XRD, UV-Vis, TEM and TPR. With the increase in the reoxidation time, the H 2 evolution increased gradually. The maximum H 2 evolution (212 μmol/h g-cat) was observed when the catalyst was reoxidized at 200 °C for 2 h. It is because of the small particle size of 10 nm and homogenous Ni/NiO distribution. The drastic decrease of photocatalytic activity for samples reoxidized for 4 h was due to the partial formation of NiO bulk phase and the growth of nickel particles.

Interplay between photochemical activities and pigment composition in an outdoor culture of Haematococcus pluvialis during the shift from the green to red stage

The transfer of laboratory cultures of H. pluvialis to high irradiance outdoors caused a substantial decline in the maximum quantum yield of photosystem II (PSII), from 0.65 in the morning to 0.45 at midday, as measured by the ratio of variable to maximum fluorescence yields (Fv/Fm), and a steep rise in non-photochemical quenching (NPQ). Chlorophyll fluorescence induction curves of morning samples showed a clear I-step, reflecting a certain PSII heterogeneity. Single turnover flash measurements on samples taken from the outdoor photobioreactor in the middle of day showed an increase in the reoxidation time constant of the reduced plastoquinone QA−, i.e., the time required for electron transfer from the primary plastoquinone acceptor of PSII QA− to the secondary plastoquinone acceptor QB. Photosynthesis rates were almost constant during the day. Along with the increase in non-photochemical quenching, there was a slight increase in zeaxanthin and antheraxanthin contents and decrease in violaxanthin, showing the presence of an operative xanthophyll cycle in this microalga. A marked increase of secondary carotenoids was found at the end of the first day of exposure to sunlight, mainly astaxanthin monoester, which reached 15.5% of the total carotenoid content. Though cells turned reddish during the second day, the decline in the fluorescence parameter Fv/Fm in the middle of the day was less than during the first day, and there was no further increase in the value for NPQ. Similar behaviour was observed during the third day when the culture was fully red. After four days of exposure to sunlight, the dry weight reached 800 mg L−1 and the concentration of secondary carotenoids (81% astaxanthin monoester) reached 4.4% dry weight.

Highly Reliable Liquid-Phase-Deposited SiO2 with Nitrous Oxide Plasma Post-Treatment for Low-Temperature-Processed Polysilicon Thin Film Transistors

Low-temperature (∼300°C) N2O-plasma post-treatment for liquid-phase-deposited (LPD) gate oxide has been proposed for the first time. This treatment successfully takes the place of conventional furnace annealing in O2 ambient. Results of physicochemical and electrical characteristics show that N2O-plasma post-treated LPD-SiO2 has a high electrical breakdown field and low interface state density. In addition, N2O-plasma treatment also improves the Si-rich phenomenon of LPD-SiO2. From the comparison with pure N2O-plasma oxidation film, LPD-SiO2 with its short re-oxidation time in N2O plasma plays an important role in relieving interfacial stress. Finally, the novel technology is applied to the gate oxide of low-temperature-processed (LTP) polysilicon thin film transistors (poly-Si TFTs). The device performance reveals excellent electrical characteristics, and the reliability shows a satisfactory result, as well as the gate oxide reliability. It is believed that the N2O-plasma post-treatment not only improves the oxide quality, but also effectively passivates the trap states of poly-Si TFTs.

Effect of oxygen pressure on the structure and thermal stability of ultrathin Al2O3 films on Si(001)

Al 2 O 3 /Si(001) surfaces and interfaces were investigated using scanning reflection electron microscopy, reflection high-energy electron diffraction, x-ray photoelectron spectroscopy, and Auger electron spectroscopy. A uniform, stoichiometric and ultrathin Al2O3 film of about 0.6 nm was grown on an atomically flat Si(001)-2×1 surface, and the resulting Al2O3/Si(001) interface was atomically abrupt. An intentional reoxidation of the Al2O3/Si(001) system under low oxygen pressure (2×10−6, 5×10−6, and 2×10−5 Torr O2) showed that the ultrathin Al2O3 film stoichiometry and the interface abruptness were maintained with progress in reoxidation time. Furthermore, the film and the interface showed no degradation under low-pressure reoxidation at various temperatures (400–750 °C). A high-pressure reoxidation of the Al2O3/Si(001) system at 5×10−5 Torr O2 resulted in the formation of an interfacial SiO2 layer which grew in a layer-by-layer mode with atomic-scale uniformity and had an atomically abrupt interface with Si(001) substrate up to 700 °C. Additionally, a very weak temperature dependence of the growth of interfacial SiO2 was observed. A high-pressure reoxidation at 750 °C led to the formation of crystalline ultrathin Al2O3 film and also caused degradation of the film by formation of SiO2 in the near-surface region, where a slight decrease in the Al2O3 film thickness was observed. This was attributed to the formation of interstitial Si in the interfacial SiO2 layer and the subsequent mobility of Si and Al under this growth condition. Under low-pressure reoxidation, the Si and Al were immobile because of the absence of an interfacial SiO2 layer at the Al2O3/Si(001) interface. These results indicate that the oxygen pressure of the ambience plays an important role in the oxidation of the Al2O3/Si(001) interface, and the mobility, transport, and chemical reactions at various oxidation temperatures (400–750 °C).

A systematic study of the initial electrical and radiation hardness properties of reoxidized nitrided oxides by rapid thermal processing

The initial electrical and radiation hardness properties of MOS capacitors with reoxidized nitrided oxides (RNO) structures are systematically investigated by changing the pressure, temperature, and times of nitridation and reoxidation in rapid thermal processes. It was found that the initial flat-band voltage (V/sub fb/) and midgap interface trap density (D/sub itm/) are strongly dependent on the growth conditions and show concave or convex "turnaround" dependency on some process parameters. This may be explained by the hydrogen evaporation and oxygen passivation mechanisms. The radiation induced flat-band voltage shift (/spl Delta/V/sub fb/) and midgap interface trap density shift (/spl Delta/D/sub itm/) are also growth-condition dependent and show different "turnaround" dependencies on some process parameters from those observed in initial properties. This may be explained by the variations of the amount of hydrogen-related species such as Si-NH, Si-H, or Si-OH, and nitrogen-related species, such as Si-N, in the oxide bulk and at the Si/SiO/sub 2/ interface. Finally, the sample with a reoxidation pressure of 250 torr, a reoxidation temperature of 1050/spl deg/C, and a reoxidation time of 100 s is suggested to be the most radiation-hard together with good initial properties for RNO devices.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>