Hours In Air Research Articles

Effect of Excess Na Contents in Precursor on the Property of Na2Zn2TeO6 Ceramic Solid Electrolyte

P2-type layered sodium (Na) ion conducting oxide Na2M2TeO6 (M = Mg, Zn, etc.) have attracted much attention for the application to all-solid-state Na-based batteries with high safety and lower cost, because of the high ionic conductivity above 10-4 S/cm at room temperature range and excellent chemical and electrochemical stability [1, 2]. Generally, Na in precursor materials is easy to volatilize in high temperature processing, so that the excess Na in precursors must be added to compensate the Na loss and suppress the composition shift in final products and undesired secondary phase formation. In this work, we investigated the effect of excess Na contents in precursor on the property of Na2Zn2TeO6 (NZTO) solid electrolyte synthesized via a conventional solid state reaction method.Na2CO3, ZnO and Te2O3 were used as precursor materials and the excess Na contents were adjusted to 3, 7 and 10% over the stoichiometric composition. They were pulverized and mixed for 3 hours by planetary ball milling and then calcined at 850ºC for 6 hours in air using a SiC crucible. Calcined powders were ground again and then pelletized by cold isostatic pressing at 300 MPa. Finally, the pellets with different excess Na contents were sintered at 850ºC for 12 hours in air using a SiC crucible.From XRD analysis, P2-type layered NZTO phase were mainly confirmed in all sintered samples, but only the sample with 3% excess Na in precursor contained small amount of secondary phases, which is attributed to the Na volatilization during high temperature processing. From SEM observation, it was confirmed that all sintered samples have porous structures. The relative densities were in the range from 80 to 83% and nearly independent of the excess Na contents.Au film was formed on both the end surfaces of each sintered NZTO sample as an ion-blocking electrode and electrochemical impedance was measured at 27-202ºC to investigate the ionic conducting property. As results, the ionic conductivity of NZTO samples strongly depends on the excess Na contents in precursor. The sample with 3% excess Na showed the lowest total (grain + grain boudary) conductivity of 0.5 x 10-4 S/cm at room temperature, while the conductivity for the samples with 7 and 10% excess Na was well above 10-4 S/cm. In our experiment, 7% excess Na in precursor is the best and the highest total conductivity of 3.8 x 10-4 S/cm at room temperature and low activation energy of 0.27 eV were obtained. Since the relative density of our NZTO samples are not so high and the contribution of grain-boudary resistance is large at present, the total conductivity could be improved further by densification via optimizing sintering processing.This work was partly supported by Iketani Science and Technology Foundation.[1] Y. Li, et al., Chem. Eur. J. 24, 1057-1061 (2018).[2] Y. Li, et al., ACS Appl. Mater. Interfaces 10, 15760−15766 (2018). Figure 1

Fabrication and characterization of ethanol gas sensor based on hydrothermally grown V2O5 nanorods

Vanadium Pentoxide (V2O5) nanorods (NRs) were grown on corning glass substrate for ethanol gas sensing application. The NRs were annealed at 500 °C for one hour in air. Structural characteristics of as-grown and annealed NRs were examined by using X-ray diffraction (XRD) system. The analysis of the (XRD) diffraction patterns revealed an increase in the crystallinity of NRs after annealing along with their preferred orientation towards (001) plane. The density and length of V2O5 NRs were also increased after annealing as shown by the field emission SEM. The Raman spectroscopy result revealed stretching vibrational modes of V2O5. The photoluminescence spectroscopy displayed green emission of V2O5 NRs at 538 nm. For the fabrication of an ethanol gas sensor, Ag electrodes were deposited on the annealed V2O5 NRs by RF reactive sputtering. The current-time measurements were made to observe the gas sensing response of the device at 2 V. The device exhibited remarkable ethanol gas sensing performance with a fast recovery time of 12 s at low working temperature. These findings depicted that the V2O5 NRs can be efficiently used for gas sensing application.

Quantitative Characterization of Surface Polarity Dependence of Wetting Properties of V-Doped SiC Using a Novel Image Analysis Technique

Vanadium doped semi-insulating (SI) 6H-SiC {0001} substrates and their wetting properties were characterized using precisely dispensed de-ionized (DI) water drops. Radius, contact angle, width (chord), height and cap volume of a DI water drop on the SiC surface were quantitatively determined by analyzing sideview images of DI water drop in contact with SI 6H-SiC {0001} substrates using image processing software. The average of ten (10) contact angle measurements showed approximately 4 ° difference between the Si-face (48.48°) and the C-face (44.33º). Contact angle on the Si-face (0001) measured after native oxide removal showed significant decrease of contact angle, from 55° to 25° and recovered over time by room temperature oxidation in air. In contrast, contact angle on the C-face (000-1), measured after native oxide removal, showed significant increase of contact angle, from 40° to 54°, and continue to increase contact angle up to 71° after room temperature oxidation for 24 hours in air. Contact angle is found to be very sensitive to SiC surface polarity and specific surface conditions. Contact angle measurement, using image analysis techniques, can be applied as an in-line identification and surface condition characterization technique for SiC polytypes of specific surface polarities.

High Temperature Oxidation Study of Nano-Y2O3 Dispersed Ferritic Alloys Synthesized by Mechanical Alloying and Sintering

This study concerns mechanism and kinetics of isothermal oxidation of four Fe-Cr-Al-Ti ferritic alloys in the range 700 °C to 900 °C for up to 50 hours in air. These four alloys with nominal compositions of 83.0Fe-13.5Cr-2.0Al-0.5Ti (alloy A), 79.0Fe-17.5Cr-2.0Al-0.5Ti (alloy B), 75.0Fe-21.5Cr-2.0Al-0.5Ti (alloy C), and 71.0Fe-25.5Cr-2.0Al-0.5Ti (alloy D) each with 1.0 wt pct nano-Y2O3 dispersion were synthesized by mechanical alloying and sintering at 1000 °C by hot isostatic pressing, high pressure sintering, hydrostatic extrusion and pulse plasma sintering techniques. A detailed characterization of the phase aggregate, microstructure and micro-composition of the oxide scale was carried out by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy, respectively. Oxidation kinetics appear to follow a parabolic rate with an activation energy of 135 to 234 kJ/mol, which depend on alloy composition (i.e., Cr content). Oxidation mostly occurred by counter-ionic diffusion of oxygen from air to the interior and cations (Cr+3 or Fe+3) from the bulk toward the surface. Alloy D sintered by hot isostatic pressing offered the highest resistance to oxidation.

Stretchable Perovskite Solar Cells with Recoverable Performance

AbstractPerovskite solar cells (PSCs) are a promising photovoltaic technology for stretchable applications because of their flexible, light‐weight, and low‐cost characteristics. However, the fragility of crystals and poor crystallinity of perovskite on stretchable substrates results in performance loss. In fact, grain boundary defects are the “Achilles’ heel” of optoelectronic and mechanical stability. We incorporate a self‐healing polyurethane (s‐PU) with dynamic oxime–carbamate bonds as a scaffold into the perovskite films, which simultaneously enhances crystallinity and passivates the grain boundary of the perovskite films. The stretchable PSCs with s‐PU deliver a stabilized efficiency of 19.15 % with negligible hysteresis, which is comparable to the performance on rigid substrates. The PSCs can maintain over 90 % of their initial efficiency after 3000 hours in air because of their self‐encapsulating structure. Importantly, the self‐healing function of the s‐PU scaffold was verified in situ. The s‐PU can release mechanical stress and repair cracks at the grain boundary on multiple levels. The devices recover 88 % of their original efficiency after 1000 cycles at 20 % stretch. We believe that this ingenious growth strategy for crystalline semiconductors will facilitate development of flexible and stretchable electronics.

Effects of wettability and flow direction on gas retention and flow resistance of water flowing through carbon felts with thermally induced gas evolutions

Owing to superior properties and low cost, carbon felts are widely used in flow batteries as versatile porous electrodes, through which liquid electrolyte is usually pumped to transport reactants/products. In operation, electrochemically/physically induced gas evolution occurring inside the carbon felt is almost inevitable which, even though seems trivial in most cases, may lead to significant reduction in liquid saturation and permeability. To study the impact of the carbon felt wettability and the flow direction on this in-situ generated liquid-gas two-phase flow, we experimentally visualize gas distributions and measure average gas saturations and liquid permeabilities in hydrophobic/hydrophilic carbon felts and in upward/downward/horizontal flows, which is a continuation of our recent work exploring the thermally induced evolution of dissolved air in water flowing through a carbon felt sample. After being heated at 500°Cfor 7 hours in air, the carbon felt becomes rather hydrophilic, as indicated by its capability of water-droplet sucking. As expected, the gas saturation measured in this hydrophilic felt is lower and the liquid relative permeability is higher than those measured in the un-treated hydrophobic felt. It is also found that the buoyancy force is non-negligible in this flow, which is confirmed by the fact that both the liquid phase saturation and the permeability are considerably lower in the down-ward flow compared with those in the upward and horizontal flows.

Ce-Doped Sns Quantum Dots Sensitized SnS2 Nanocomposites for NO2 Monitoring

IntroductionMetal sulfides have been proved to be highly sensitive to low concentration NO2 due to their unique structure and electrical properties, among which SnS2 has been widely studied to make use of its narrow band gap, large surface-to-volume ratio and large electronegativity. However, it has been proved that the low sensitivity of pure SnS2 to NO2 at the room temperature is still far from sufficient practical values. Therefore, the fabrication of nanocomposites based on SnS2 with heterojunctions have been studied as promising candidate materials for gas sensors with practical applications. For instance, Gu and his coworkers reported that the sensing properties of formed SnO2/SnS2 nanohybrids improved obviously compared with commercial pristine SnS2 nanosheets and Hao further promoted the progress by decorating the surface of SnS2 nanoflowers with SnO2 nanoparticles.Under the inspiration from the above studies, herein cerium was later introduced into the one-step synthesis process of SnS2/SnS heterostructures to effectively modulate the sensing property. In previous studies, Ce-doped SnS2 nanoflakes were successfully synthesized and exhibited higher photocatalytic efficiency than that of un-doped SnS2 due to the porous architecture and reduced energy bandgap after Ce-doping. Ce-doped SnS2 nanoflowers were also studied as anode electrodes materials for lithium ion batteries, whose reversible capacities and cycling performance is the best among the synthesized Ce SnS2 compounds because of larger lattice space provided by the larger-radius cerium ions replacement of Sn4+ for lithium intercalation and deintercalation. Besides, it has been found that Ce dopants can effectively tune the optical gaps and produce the magnetic ground state. Experimental Synthesis of SnS@SnS2 nanoparticles The pure SnS@SnS2 nanoparticles were synthesized by a hydrothermal reaction. In experiment, 0.902 g of SnCl2·2H2O and 1.805 g of thiourea were dissolved in a stoichiometric ratio of 1:3 in 32ml Milli-Q water under vigorous stirring to form a white homogeneous solution. Then, the obtained homogeneous solution was transferred into a 50 mL Teflon-lined stainless-steel autoclave and kept at 200 °C for 8 h. Then, the autoclave was allowed to cool down to room temperature naturally. The formed SnS@SnS2 nanoparticles were washed with ethanol and water by centrifugation (8 000 rpm) three times, respectively, then dried at 60 °C for several hours in air to obtain the final product named SnS@SnS2-0. Synthesis of Ce3+ doped SnS@SnS2 nanoparticles The Ce3+ doped SnS@SnS2 nanoparticles are synthesized in the same method. The only difference is that different amounts of Ce(OOCCH3)3·5H2O were added with SnCl2·2H2O and thiourea to obtain the homogeneous solution. The synthesized Ce3+ doped SnS@SnS2 with molar ratios of Ce3+ to tin (Ce/Sn) in the precursors of 0.005, 0.01, 0.02 and 0.04 were named SnS@SnS2-0.5, SnS@SnS2-1, SnS@SnS2-2 and SnS@SnS2-4 respectively. Results and Conclusions In this study, the synthesized SnS2 bulk nanocomposites are randomly arranged with a great many SnS quantum dots dispersing on the surface. At the interfaces between SnS2 and SnS phases, accumulation layers are formed and p-n heterojunctions come into existence. Besides, it has been proved that cerium is mainly found in SnS quantum dots to achieve the lowest formation energy. Therefore, the number of SnS quantum dots can be modulated by the doping concentration. Furthermore, the number of heterojunctions, the baseline resistance and the sensing properties can be effectively controlled. In conclusion, the pristine SnS@SnS2 nanocomposites and Ce-doped SnS@SnS2 nanocomposites with different doping proportions were all synthesized by a simple one-step hydrothermal method. Due to the combined action of SnS@SnS2 p–n heterojunctions and high specific surface, 1at.% Ce-doped SnS@SnS2 sensor had obviously improved sensing sensitivity with lower baseline resistance compared to pristine SnS@SnS2 and exhibited the best gas sensitivity of 31 with response/recovery time of 19s/63s to 10 ppm NO2 at room temperature. The reason was that Ce-doping could effectively modulate the number and size of SnS quantum dots, thereby regulating the number of the SnS@SnS2 p-n heterojunction and specific surface to enhance the gas sensitivity, which was consistent with the DFT calculating results. The replacement of some Sn2+ by Ce3+ also increased the electron concentration and made contributions to the decrease of baseline resistance. By changing the proportion of Ce precursors, the sensing performance can be effectively modulated and finally achieve the ideal sensing material for NO2 gas sensing at room temperature.

Improvement of Hydrogen Sensing Performances of Sol-Gel Derived Platinum Doped Tungsten Trioxide Gasochromic Films

Introduction Various hydrogen sensitive gasochromic materials, such as V2O5 [1], MoO3 [2], and Y-Mg [3], have been reported. Among them, Catalyst-loaded WO3 film has been intensively studied to apply to smart windows or optic hydrogen sensors. Although there are many fabrication methods of WO3, sol-gel method [4, 5] is relatively cost-effective, does not need a large-scale apparatus, can be operated easily, and makes it possible to fabricate metal oxide film on complex shape surface. However, the gasochromic performance and its long-term stability sensitively depends on fabrication conditions. In this study, the effect of calcination temperature on crystalline structure, chemical state and hydrogen response of Pt-loaded WO3 (Pt/WO3) fabricated by sol-gel method were evaluated. Then, degradation behaviors were tested under various conditions. Principle In the presence of hydrogen, Pt/WO3 is reduced into tungsten bronze through reactions (1) and (2). Hydrogen molecules dissociate on the surface of catalyst into hydrogen adatoms even at room temperature. Consequently, they react with WO3 through spill-over mechanism. In the recovery process, tungsten bronze is oxidized into initial WO3 by oxygen gas in air following reaction (3). With exposure to hydrogen gas, it is well known that WO3 turns into dark blue color. In this study, transmission loss is focused as a tool for evaluating the hydrogen sensing properties of tested materials. Method WO3 precursor solution was prepared by ion-exchange method. This solution was added to the Pt containing solution which was composed of H2PtCl6, ethanol, and surfactant to make molar ratio of Pt:W about 1:5. After mixing, Pt/WO3 precursor solution was spin-coated onto the quartz glass substrates at 500 rpm for 300 seconds. The film was dried for over 1 hour. Then, the films were calcined for 1 hour in air. Calcination temperature was set in the range from 250°C to 500°C. X-ray diffraction measurements of the hydrogen sensing films were performed with CuKα radiation. The accelerating voltage and current were 40 kV and 45 mA, respectively. Fig. 1 represents the experimental set-up of transmitted light intensity measurement. The fabricated Pt/WO3 film was set into a homemade gas chamber. The one end of fiber cable was coupled with 1.3 µm LED light source. The light transmitting through the film was monitored by the optical power meter. 4 vol.% H2 gas balanced with N2 gas was used as test gas in order to evaluate hydrogen sensitivity of the film. Air as recovery gas was fed into the chamber by using an air compressor. Results and Conclusions The results of XRD measurement of Pt/WO3 films calcined at various temperature are shown in Fig. 2. The broad peak around 21° appears in all results comes from the quartz glass substrate. A sharp peak appeared at 24.0° in the film calcined at 500°C. This peak indicates formation of crystalline WO3. This peak became smaller for film calcined at 400°C and disappeared below 350°C. It indicates that crystal structure of WO3 films calcined below 350°C were amorphous. On the other hand, any peak related to Pt did not appeared. It is surmised that Pt exists in the form of microcrystalline and is well dispersed in the WO3 film. Fig. 3 represents the optical transmittance changes of the fabricated Pt/WO3 films calcined at various temperature with exposure to hydrogen containing gas. The transmitted light intensity sensitively responded to hydrogen gas and immediately reached steady states. The recovery reaction by air readily proceeded. Although the sensitivity increased with increasing calcination temperature, the response speed became slower. It would be closely related to amount of Pt° formed as a result of decomposition reaction of H2PtCl6. In order to evaluate long-term stability of Pt/WO3 film in severe condition, the effect of sodium addition to Pt/WO3 film was tested. In this experiment, Pt/WO3 coated substrate covered with small NaCl salt particles was calcined at 500°C in air at 500°C for 1 hours. Fig. 4 represents the result of hydrogen sensing test of Na-doped Pt/WO3 film. No variation in optical transmittance was observed. XPS studies suggested that catalyst-poisoning compounds generated and therefore gasochromic property of the film was considerably degraded.

Study of the magnetic properties of Zn doped Cobalt ferrite (CoZnxFe2-xO4)

Zinc substitution is proposed as an efficient way to improve the performance of the ferrite. In this work, Zinc doped cobalt ferrite with the generic formula CoZnxFe2-xO4, with x = 0.0, 0.1, 0.3 and 0.4 were prepared by conventional ceramic technique, sintered at 1000ο C for 4 hours in air. The effect of zinc concentration on the initial permeability, Curie temperature, saturation magnetization, magnetic moment, coercivity and magnetic susceptibility was investigated. Contrary to most of the work in this subject, here Co is maintained fixed and Fe is progressively varied along with Zn. Curie temperature is found to increase initially up to 459 0C for Zn content of x = 0.1 and then decreased to 1480C for further increase of Zn content (x = 0.4). Effect of Zn on the frequency dependent initial permeability, loss factor and relative quality factor was studied. The maximum value of saturation magnetization (51.37emu/gm) was found for the sample x = 0.1 and then decreases with the increase of Zn content. Morphological and magnetic properties of the samples were studied using scanning electron microscope (SEM) and vibrating sample magnetometer (VSM) respectively. The Zn-doped cobalt-ferrite (x = 0.1) having a high strain derivative could be a potential material for stress sensor application.

Joining of SiC, alumina, and mullite by the Refractory Metal—Wrap pressure‐less process

AbstractThe aim of this work was to discuss the suitability of the joining process called “RM‐Wrap” (RM = Refractory Metals, ie, Mo, Nb, Ta, Zr) as a pressure‐less and tailorable technique to join several different ceramics such as SiC, alumina, and mullite (3Al2O3.2SiO2). In the RM‐Wrap joining technique the refractory metal foil is used as a wrap containing one or more silicon foils. It is performed at 1450°C, under flowing argon, and the resulting joining materials are in situ formed composites made of refractory metal disilicides (MoSi2, NbSi2, TaSi2, or ZrSi2) embedded in a silicon‐rich matrix; their coefficient of thermal expansion has been calculated and the Laser Flash Method was used to measure the thermal diffusivity of one of them (MoSi2/Si) in 25°C‐1000°C range, then to calculate its thermal conductivity. All the obtained joints are uniform, continuous, and crack free. Some preliminary oxidation tests were carried out on all joints at 1100°C, 6 hours in air, giving unchanged morphology of the interface and the joining materials itself; the joint strength of RM‐Wrap joined SiC was measured at room temperature using three different mechanical tests: (a) single lap (SL), (b) single lap off‐set (SLO) and (c) torsion on hourglass‐shaped samples (THG) (on Mo‐wrap joined SiC).

Synthesis of Hercynite from Aluminium Dross at 1550°C: Implication for Industrial Waste Recycling

Aluminium dross is a waste from aluminium melting process, containing approximately 70 wt% of Al2O3. Disposal of dross in landfill causes soil and ground water pollutions, leading to the difficulty of waste management. This work aims to utilize aluminium dross as a source of Al2O3 for the synthesis of hercynite (FeAl2O4). Aluminium dross was heated at 1200°C for 1 hour in air and then compacted into a substrate using a hydraulic press. The substrate was brought into contact with two different types of iron chip at 1550°C in air for 6 hours. Pure iron chip and iron chips containing 0.8 wt% carbon were employed in this experiment in order to investigate the effect of carbon content in the iron chip on the formation of hercynite. The samples after reactions were characterized using XRD, SEM and EDS techniques. It was found that the final product is hercynite having a dark grey solid phase. The formation of hercynite was due to the interaction of Al2O3 in the dross with Fe and/or FeO in the system. FeO came from the oxidization of iron chip due to the excess of oxygen in the system. Carbon content in the iron was found to effect the formation of FeO in the system, which in turn effect the formation of hercynite. This research is one of the possible way to recycling aluminium dross instead of bury in a landfill.

Change of structural and magnetic property due to zinc substitution and sintering temperature of nano-crystalline Cobalt ferrite

ABSTRACTCo1–xZnxFe2O4 (x = 0.2, 0.4, 0.6 and 0.8) were synthesized using typical wet chemical co-precipitation technique. The ferrite specimen have been sintered at 700°C and 900°C for three hours in air. X-ray diffraction (XRD) diffractogram and Mössbauer spectroscopy technique were employed to describe the nano-ferrites. The single-phase spinel cubical structure was confirmed from XRD studies. Employing vibrating sample magnetometer (VSM), saturation magnetization, remanent magnetization, etc. have been determined. The value of coercivity confirmed that all the samples were soft ferrites. Ferromagnetic to superparamagnetic transition has been seen by Mössbauer spectroscopy. Complex permeability has been determined using an impedance analyzer. The real and imaginary part of initial permeability along with loss tangent was, and loss tangent was calculated within the frequency range 1 kHz to 120 MHz. It shows the constant value at the high-frequency range that is identical properties for the ferrite samples to apply the materials for storage device applications.

Li‐insertion into sol‐gel Na0.44MnO2 cathode material for higher structure and electrochemical performance of batteries

AbstractStability of electrolyte with higher electrochemical and structural performance is a key aspect for achieving greater longevity of cycle life of battery. In this article, we investigated the electrochemical performance of sol‐gel Na0.44MnO2 (SG‐NMO) as cathode material in lithium batteries within nonaqueous lithium electrolyte. The SG‐NMO was prepared by the two‐step of the sol‐gel method: a transparent gel was obtained by a stirring of precursors (Na2CO3, Mn(CH3COOH)2 and acid citric) at 80°C; then gel was calcinated at 400°C for 6 hours and 800°C for 9 hours in air. The structure and morphology were characterized by X‐ray diffraction, SEM, and Raman spectroscopy. The XRD pattern exhibited a high crystallization of orthorhombic phase and SEM images showed the well‐crystalline grains in submicrometric scale. Following charge‐discharge profile and ex‐situ XRDs result, SG‐NMO showed 0.22 ion Na+‐extraction at the end of first cycle and a reversible Li‐migration from second cycle without a phase transition. The specific capacity at rate C/10 was about 180 mAh/g with a capacity retention of 95% upon 50 cycles. Moreover, a good electrochemical performance in rate capability (from C to 3C) indicated a highly kinetic Li‐transportation.

Morphological changes of the PVD coatings after isothermal annealing

The main of this work is to investigate the impact of the isothermal annealing on the structure and morphological changes on the PVD hard coatings. Three different coatings based on the AlTiN system were deposited onto cemented carbide substrates containing 6 wt% of Co. Two coatings AlTiN/TiAlN and AlTiN/TiN with an initial thickness of 3 μm has a coarse-grained columnar structure with a chemically graded nanomultilayering consisting of alternating Ti-rich and Al-rich layers. In the case of the AlTiN/TiAlN coating, a total of 20 layers were applied. Ten layers had a thickness of 200 nm (AlTiN) and 10 layers with the thickness of 100 nm (TiAlN). The same number of nanolayers was also retained for the AlTiN/TiN multilayer coating. The TiN layers were 100 nm thick. The third coating was a nanocomposite sandwich coating formed by a TiSiN adhesive layer (50nm), a functional nanocomposite AlTiSiN layer (2 μm) and a top functional TiSiN layer with a thickness of 1 μm. The coatings were prepared by cathodic arc evaporation using the LARC® technology. After deposition, the samples were annealed at high temperatures (700 °C, 800 °C, 900 °C, 1000 °C) for one hour in air. With X-ray diffraction and scanning electron microscopy, the morphology, structure and phase composition of coatings and oxide layers after annealing were evaluated.After the heat-treatment at 800 °C, cross-sectional and surface morphology images revealed, that an oxide layer has grown on top of the all coatings. EDS analysis showed that the oxide layers on the multilayers coatings had a layered structure, which was found to be the consequence of the high diffusion rate of Al. The interface with the coatings was very rough. It was depleted of Al, which diffused to the upper surface of the oxide. The oxidation process of nanocomposite AlTiSiN/TiSiN coating started by forming an oxide layer of ternary Ti–Si–O at the interface. This system segregated into two phases of TiO2 and SiO2. The nanocomposite coating remained stable even after annealing at 1000 °C. The surface of the multilayers was accompanied by a network of cracks at this temperature. An interesting phenomenon was also observed on the substrates itself during the annealing. As a result of oxidation, unprotected sides of the substrates expanded. Globular oxides based on tungsten and cobalt were also formed on the surface of the samples at the places where the coating was peeled off. The reasons for the differences are discussed.

Structural and Mechanical Properties of Chitosan Doped with Zirconium Oxide

Abstract In this work, chitosan (CTS) powder has been doped with zirconium oxide (ZrO2) at different wt.% in order to improve the mechanical strength of the composites for biomedical applications. The composites have been prepared by ball milling method and the sintering has been done at three temperatures 100°C, 150°C and 180°C for 3 hours in air. The crystalline structure of the composites was confirmed by X-ray diffraction (XRD) pattern and the crystallite size of the composites decreases with increasing the percentage of ZrO2 and sintering temperature. The improvement of mechanical strength of the composites with the addition of ZrO2 in CTS polymer matrix has been investigated using micro-Vickers hardness tester and observed that the hardness of the prepared composite increased to 536 MPa when 90 wt.% CTS doped with 10 wt.% ZrO2 at 180°C of sintering temperature, demonstrating that the composites can be a potential candidate in bone tissue engineering.

High Temperature Oxidation of Slurry Aluminized Deformable Austempered Ductile Iron (DADI)

This work reports on the aluminization and oxidation behaviour of a new class of cast iron (deformable austempered ductile iron, DADI). The slurry aluminization resulted in uneven coatings due to the lack of wettability of molten aluminium to the graphite inclusions of the substrate. In spite of this, the isothermal tests at 650 °C for 100 hour in air revealed a drastic reduction of oxygen uptake related to the formation of mixed Al-containing spinels compared to the very unprotective iron oxides formed in the absence of coating. It derives that deposition of thicker aluminide layers by precoating with, e.g. nickel would be a promising way to protect further DADI cast iron.

The interpretability of stable hydrogen isotopes in modern herbivore tooth enamel

Stable hydrogen isotopes (δD values) in animal organic tissues such as collagen and keratin typically correlate with local meteoric water, but little is known about δD in tooth enamel apatite. In this study, we analyzed comminuted tooth enamel for oxygen isotopes (δ18O) of the CO3 component and for δD of bulk enamel. We find positive correlations between enamel δD and δ18O (R2 = 0.70) and between enamel δD and local precipitation δD (R2 = 0.53). However, the slopes of these relationships are much shallower (less variation in tooth enamel δD) than expected from studies of other tissues. Based on mass spectrometric peak areas, H2 contents for enamel are 2–5 times higher than expected from chemical compositions, and we interpret as much as 50–90% of measured hydrogen from tooth enamel may be adsorbed water derived from laboratory water vapor. We tested this hypothesis by equilibrating tooth enamel with very high and very low δD values of water vapor, then exposing to laboratory air for different periods of time ranging from minutes to 8 hours. These experiments show that the apparent δD value of enamel converges to a nearly constant δD value in 1 to 2 hours. The large amount of adsorbed water and rapid approach to equilibrium will make it difficult to infer provenance from δD measurements alone, or to reproduce measured tooth enamel δD values among laboratories with different water vapor compositions. Heating at 70 °C for 48 hours in air does not remove adsorbed hydrogen, but does reduce δD values by c. 10‰ compared to unheated samples. Differences in δD values for heated vs. unheated enamel may reflect either a different, temperature-dependent partition coefficient between adsorbed water (on apatite) and water vapor, exchange of structural H at elevated temperatures, or subtle changes to crystal structure, such as loss of structural H.

Effect of post deposited annealing ambience and temperature on the longer visible absorption of zinc oxide films

Zinc oxide films were deposited on heated glass substrates at different substrate temperature 450°C and 500°C. After the deposition, some samples were heat treated at 500°C for one hour in air and some samples in vacuum for one hour at the same temperature. Absorbance analysis revealed that as deposited samples and post heat treated samples are showing intense absorption near 1.5eV apart from that corresponding to band gap of ZnO. The absorption coefficient variation with incident energy for the samples annealed in vacuum after deposition at 450° suggested the presence of oxygen vacancy as the native defect for the absorption near 1.5eV. The absorption energy for the samples obtained from (αhν)2 vs energy plot suggested that same kind of defect may be present in all the samples and is around 1.53eV.

The Crystallization Process of Zr-Based Metallic Glass by the Influence of Heating Rate and Alloy Composition

A study of the crystallization process of Zr-based Metallic Glass by the influence of the heating rate and variation of alloy composition was investigated. The alloys used were Zr68Cu14Ni11Al7, Zr64.5Cu17Ni11Al7.5, and Zr69.5Cu12Ni11Al7.5. Thermal stability was analyzed using DSC (Differential Scanning Calorimetry) with a heating rate of 5°C/min and 10°C/min until the temperature reached 500°C. The three samples were heated with temperature variations of 400°C, 425°C, and 450°C for one hour in air. Crystal growth was observed by XRD test. The DSC curve of the three samples shows that the higher the rate of heating, the shift of the crystallization peak temperature shifts to a higher temperature. At higher temperatures, the crystallization process occurs faster than at lower temperatures. The composition of zirconium contributes to the resistance properties of crystallization. The alloy with the highest zirconium composition has a high resistance to crystallization. The crystalline phase formed is ZrO2 tetragonal in all samples heated at a temperature of 450°C, and there is an intermetallic phase of Zr2Ni identified on Zr64.5Cu17Ni11Al7.5

Catalyst-Coated PrBa0.8Ca0.2Co2O5+Δ Cathode with High Cr-Poisoning Tolerance for Intermediate-Temperature Solid Oxide Fuel Cells

Intermediate-temperature solid oxide fuel cells (IT-SOFCs) have potential to be a very promising technology for direct conversion of a wide variety of fuels to electricity. However, the commercialization of IT-SOFCs is hindered by several technical challenges. For example, volatile chromium species from interconnect materials often accumulates on the cathode surface or the cathode/electrolyte interface[1], resulting in degradation in electro-catalytic activity for oxygen reduction reaction (ORR) of the cathode. Further, the presence of water vapor can exacerbate the effect of Cr poisoning[2]. Thus, the development of a cathode material with high resistance to Cr poisoning in the presence of water is urgently needed. Recently, a double perovskite PrBa0.8Ca0.2Co2O5+δ (PBCC) cathode with high ORR activity and excellent tolerance against CO2 has attracted much attention[3]. However, its tolerance to Cr poisoning and long-term durability under realistic operating conditions are yet to be characterized. Inspired by our previous studies [4], a number of catalysts are used to modify the surface of PBCC cathode in order to enhance its tolerance to Cr poisoning. As shown in Figure 1a, the measured apparent ORR activation energy is ~1.09 eV for the bare PBCC cathode, as determined from the slope of the Arrhenius plots of kinetics studies. The apparent activation energies for PBCC cathode infiltrated with Ce0.8Sm0.2O1.9 (SDC), La2NiO4 (LN), Ba0.5Co0.5Ox (BaCo), PrOx, and PrNi0.5Mn0.5O3 (PNM) are 0.98 eV, 0.86 eV, 0.87 eV, 0.91 eV, and 0.91 eV, respectively. PBCC coated with La2NiO4 shows the lowest activation energy. As shown in Figure 1b, PBCC cathodes coated with La2NiO4 and Ba0.5Co0.5Ox also show better durability than bare PBCC and other cathodes towards Cr-poisoning (even when the water content was ~7 v%). For instance, the polarization resistance (Rp) of the bare PBCC cathode increased from 0.056 Ω·cm2 to 0.235 Ω·cm2 after operation at 650℃ for ~220 hours in air with 3 v% H2O and then for 140 hours in air with 7 v% H2O; in contrast, the Rp for the Ba0.5Co0.5Ox-coated PBCC cathode remained less than 0.050 Ω·cm2 under the same testing conditions. Among all electrodes studied, La2NiO4 and Ba0.5Co0.5Ox coated PBCC cathodes show the best durability against Cr-poisoning. Figure 1