Surrounding Gas Atmosphere Research Articles

X-ray photoelectron spectroscopy (XPS) study of surface oxidation of UO2 doped with Gd2O3 at different temperatures and atmospheres

In this work, the influence of GdIII doping on the surface oxidation of UO2 has been investigated in situ by XPS. The samples were put in contact with either hydrogen, argon or synthetic air streams saturated with water and were heated at different temperatures (60, 200 and 350 °C). The results indicated that, in absence of porosity, doping UO2 with Gd2O3 completely inhibited the oxidation of UO2. Such behaviour could be explained by the matrix stabilization effect of gadolinia (Gd2O3). However, for porous samples, the oxidation of UO2 in presence of Gd2O3 depends strongly on the surrounding gas atmosphere. In presence of hydrogen, the oxidation was significantly supressed, particularly above 200 °C, due to the hydrogen reducing effect. At 350 °C and in the presence of argon, the reactivity of the samples increased slightly when comparing to H2, whereas in contact with synthetic air, the complete oxidation of the samples could not be prevented by Gd2O3. These results could be explained by assuming that the porosity might favour the oxidation of the samples. Therefore, the presence of porosity in the samples is an important parameter to consider when studying the surface oxidation of UO2 doped with Gd2O3.

Investigation of gasification reactivity and properties of biocarbon at high temperature in a mixture of CO/CO2

Understanding the conversion behaviors of biocarbon under conditions relevant to industrial conditions is important to ensure proper and efficient utilization of the biocarbon for a dedicated metallurgical process. The present work studied the reactivity of biocarbon by using a Macro-TGA at 1100 °C in a gas mixture of CO2 and CO to simulate the conditions in an industrial closed submerged arc manganese alloy furnace. The conversion residues from the Macro-TGA tests were collected for detailed characterization through a combination of different analytical techniques. Results showed that biocarbons produced under various conditions have different reactivities under the studied conditions. The biocarbon produced in an atmospheric fixed bed reactor with continuous purging of N2 has the highest reactivity. Its fixed carbon loss started as the gas atmosphere shifted from the inert Ar to a mixture of CO and CO2 at 1100 °C. And only 450 s was needed to reach a desired fixed-carbon loss of 20%. The high reactivity of the biocarbon is mainly related to its porous structure and high content of catalytic inorganic elements, which favor gasification reactions of the carbon matrix towards the surrounding gas atmosphere and consumption of carbon consequently. In contrast, biocarbon produced under constrained conditions and from wood pellets and steam exploded pellets have more compact appearance and dense structures. Significant fixed carbon loss for these biocarbons started 80–200 s later than that of the biocarbon produced at atmospheric conditions with purging of N2. Additionally, it took longer time, 557–1167 s, for these biocarbons to realize the desired fixed-carbon loss. SEM-EDX analyses results revealed clear accumulation and aggregation of inorganic elements, mainly Ca, on the external surface of the residues from gasification of biocarbon produced in the fixed bed reactor with purging of N2. It indicates more intensive migration and transformation of inorganic elements during gasification at this condition. This resulted in formation of a carbon matrix with more porous structure and active sites on the carbon surface, promoting the Boudouard reaction and conversion of carbon.

Self-powered/self-cleaned atmosphere monitoring system from combining hydrovoltaic, gas sensing and photocatalytic effects of TiO2 nanoparticles

A new self-powered/self-cleaned atmosphere monitoring system has been fabricated from TiO2 nanoparticles through combining hydrovoltaic, gas sensing and photocatalytic effects. The TiO2 nanoparticle film can convert natural thermal energy into electricity (hydrovoltaic effect) by the spontaneous water evaporation. The hydrovoltaic/gas-sensing coupling effect of TiO2 nanoparticle offers the water-evaporation-powered gas detection performance, and the outputting voltage/current has a good response to the surrounding gas atmosphere, directly acting as the gas sensing signal. The zeta potential of TiO2 is changed by the surface adsorption of gas molecules, and thus affects the electricity output of the system. The outputting electricity can directly power a wireless transmitter for transmitting the sensing information to external platform, and the whole system can work independently without electricity power supply. The rainwater can be used as the fuel of the system, and thus the system can be used outdoors without scheduled maintenance. Moreover, the photocatalytic activity of TiO2 can effectively degrade the organic pollutants on the film under photo illumination, leading to a self-clean behavior of the system. The system can probably promote the development of green sensing techniques with evaporation-induced ability.

The Effect of the Gaseous Environment on the Electrical Conductivity of Multi-Walled Carbon Nanotube Films over a Wide Temperature Range.

The surrounding gas atmosphere can have a significant influence on the electrical properties of multi-walled carbon nanotube (CNT) ensembles. In this study, we subjected CNT films to various gaseous environments or vacuum to observe how such factors alter the electrical resistance of networks at high temperatures. We showed that the removal of adsorbed water and other contaminants from the surface under reduced pressure significantly affects the electrical conductivity of the material. We also demonstrated that exposing the CNT films to the hydrogen atmosphere (as compared to a selection of gases of inert and oxidizing character) at elevated temperatures results in a notable reduction of electrical resistance. We believe that the observed sensitivity of the electrical properties of the CNT films to hydrogen or vacuum at elevated temperatures could be of practical importance.

Self-powered smelling electronic-skin based on the piezo-gas-sensor matrix for real-time monitoring the mining environment

A flexible self-powered smelling electronic-skin (e-skin) for real-time monitoring the mining environment has been fabricated from piezo-gas-sensor matrix of ZnO-based composite nanowires (NWs) via soft photolithography technique. The e-skin includes four sensing units (relative humidity: bare ZnO NWs, ethanol: Pd/ZnO NWs, hydrogen sulfide: CuO/ZnO NWs, and methane: TiO2/ZnO NWs) and can cross-reactively detect relative humidity (RH), ethanol, hydrogen sulfide (H2S) and methane (CH4) in the surrounding gas atmosphere without external electrical power supply or battery. The e-skin attached on human body can be driven by body motions, and the piezoelectric impulse of the piezo-gas-sensior matrix serves as the power supply. The responses of the four sensing units are 87.76% against 90% RH, 59.82% against 1000 ppm ethanol, 79.27% against 500 ppm H2S and −87.50% against 500 ppm CH4, respectively. High response, selectivity and stability have been achieved from the sensing units. The present results could provoke a possible new research direction for promoting the practical application of flexible self-powered smelling electronic-skin in specific occasion.

Detailed Study of the Nanocasting Process by in Situ X-ray Scattering and Diffraction

The nanocasting method is a valuable tool for producing metal oxides with a well-defined nanostructure. However, the precise details on how the metal oxide is developed inside the mesoporous silica template remain unclear. In this study, we clarify how nickel nitrate species are evolving to nickel oxide and how they are redistributed inside mesoporous SBA-15 particles as a function of heating temperature and surrounding gas atmosphere by a combination of in situ small-angle X-ray scattering, X-ray diffraction and thermogravimetric techniques as well as ex situ transmission electron microscopy and nitrogen physisorption measurements. The SBA-15 template was initially impregnated with Ni(NO3)2·6H2O using the wet infiltration method. The results indicate an initial redistribution of the nickel nitrate salt located outside the pore system into the mesopores due to dissolution, while at temperatures of 110–150 °C (depending on which type of gas flow is used) the mobility of the salt is lost due to drying of th...

Agglomerate fragmentation in high-intensity acoustic standing wave fields

The potential of high intensity ultrasound to cause fragmentation of agglomerated solid particles in air is investigated. The dispersion of single functionalized particulate agglomerates was achieved by application of a standing acoustic wave field. The particle trajectories indicate that the levitated agglomerates initially move in a sinusoidal pattern through the standing acoustic field due to their irregular shape. The frequency of the particle movement is orders of magnitude lower than the base frequency of the applied wave field and thus the agglomerates experience alternating external and internal stresses while moving through the field. Specific energy dependent agglomerate breakage probabilities are investigated by variation of the primary particle size, the degree of particle surface functionalization of the primary particles and the humidity of the surrounding gas atmosphere.

The Influence of Gas Atmosphere Composition on Formation of Surface Films in Self-propagating High-temperature Synthesis of Porous Ti3SiC2

In the present work, the structure and composition of the surface layer formed during self-propagating high-temperature synthesis (SHS) of porous ternary carbide Ti3SiC2 from the initial mixture of powders 3Ti+1.15Si+2C in the surrounding gas atmosphere of different compositions were investigated. Using X-ray analysis, scanning electron microscopy and energy dispersive analysis, it was shown that a porous composite material, consisting of the main phases Ti3SiC2 and TiC, is synthesized under these conditions. During the synthesis in atmospheres of air and nitrogen, a film of 2-3 microns thickness consisting of TiO2 and TiN is formed on the surface of the porous material. During the SHS process in an inert argon atmosphere and in vacuum, this film is not formed. In nitrogen atmosphere, conglomerates of TiN particles are formed on the film as well.

Solid-Gas Interactions of Nanoscaled La0.6Sr0.4CoO3-δ and Their Impacts

Degradation of SOFC cathodes is the result of microstructural and/or chemical alterations taking place during operation [1,2]. The latter originate either from impurities or secondary phases that segregate or form at the electrochemical active solid/gas interface or from compositional changes of the cathode material itself. On the one hand, the cathode material can react with species from adjacent or nearby solid materials within the multi-layer cell setup. On the other hand, surrounding gas species or impurities can initiate the formation of secondary phases on the surface of the cathode material or the decomposition of the cathode material itself.This contribution will focus on the solid/gas interaction between nanoscaled La0.6Sr0.4CoO3-δ (LSC) thin films and the surrounding gas atmosphere in terms of gas composition and partial pressures and discusses the resulting influence on the electrochemical properties. The thin-film cathodes were derived by a sol-gel process based on metal organic precursors and were directly deposited onto Ce0.9Gd0.1O1.95electrolyte pellets [3]. Differently designed experiments and thermodynamic calculations were performed in order to investigate the influence of water-vapor or carbon dioxide in the surrounding atmosphere and of the oxygen partial pressure on the cathode performance. The latter plays an important role during the cathode fabrication process. Low oxygen partial pressures occur during the thermal decomposition of the metal organic precursors of the cathode material, which lead to the formation of a beneficial hetero-interface of (La,Sr)2CoO4± δ and La0.6Sr0.4CoO3- δ, as could be shown by thermodynamic calculations [4]. The influence of H2O(g) and CO2 on the electrochemical performance was investigated experimentally in a temperature range of 400 … 650 °C [5]. Both gases negatively affect the solid/gas electrochemistry of the cathode (cf. Figure 1). CO2 leads to poisoning of the cathode, which is reversible at temperatures above 500 °C. At temperatures below 500 °C a regeneration of the cathodes could only be achieved by a treatment in pure oxygen. In contrast to this behavior, H2O leads to an irreversible and continuously increasing degradation. A detailed analysis of electrochemical impedance spectroscopy data disclosed, which polarization processes are majorly affected. CO2 mainly affects the surface-exchange reaction, whereas H2O – in the time frame of the test – impedes the oxygen ion diffusion within the cathode.The results demonstrate the changeability of the solid-gas electrochemistry at mixed conducting cathodes. Based on these results operation strategies in terms of optimal operation temperature and required gas preprocessing (e.g. drying of oxidant gas) can be deduced, potentially decreasing the degradation during operation.

Numerical and experimental investigations on the breakup of particle laden liquid jets in the centrifugal field

The breakup of a particle laden viscous liquid jet, emitted from a cylindrical nozzle in a rotating cup and thus elongated by centrifugal force is studied by means of perturbation theory and experiments. In perturbation theory the flow of the jet is decomposed into a steady state motion and the transient motion of the small perturbations visible by the oscillation of the jet radius, which leads to breakup. The steady state equations of motion providing the contour as well as the trajectory of the unperturbed jet are derived by balances of forces and mass. The influence of the surrounding gas atmosphere is considered by a drag coefficient which is derived by means of computational fluid dynamics. The transient motion of the perturbations is studied by means of linear stability analysis. The equations of motion for the particle laden liquid jet are based on balances of mass and impulse in the Eulerian formulation. Hence each phase is treated as a continuum. The pressure oscillation in the surrounding gas is considered by treating the gas motion as potential flow. Both, temporal and spatial stability analysis is implied. Jet stability is also investigated experimentally. The curvature, breakup length and the resulting drops are analyzed using shadow imaging. The experimental findings are compared to the numerical model.

APPLICATION HYBRID STRUCTURE BASED ON POROUS SILICON FOR CREATING ELEMENTS SENSOR DEVICES

A multilayer sensory structures of conjugated polymers - porous silicon has been created. The influence of water molecules adsorption on high frequency (1 MHz) conductivity and capacity of hybrid structures based on porous silicon has been studied. It is registered essential changing the electrical conductivity and capacity as functions of humidity. For estimation of sensor properties of the structures it is calculated the adsorption sensitivity of hybrid structures. It is revealed the formation of photosensitive electrical barriers in hybrid structure poly(3,4-ethylenedioxythiophene) - porous silicon, whose parameters are largely dependent on the surrounding gas atmosphere. The obtained results make it possible to optimize the fabrication of selective sensors based on porous silicon. The obtained results make it possible to optimize the fabrication of highly sensitive and selective gas sensors based on porous silicon.

Single Suspended CuO Nanowire for Conductometric Gas Sensing

Abstract We present a novel method for integrating single CuO nanowires as gas sensing components in a suspended configuration. In these devices, the nanowire surface area that is actually exposed to the surrounding gas atmosphere is increased, which is favourable when operating the nanowire as conductometric gas sensor. CuO nanowires bridging two adjacent Cu structures were contacted using a thermal oxidation process leading to growth of copper oxide around the nanowire. By this method, linear IV characteristics could be achieved showing the Ohmic contact properties. The sensitivity of the suspended CuO nanowire devices towards humidity and CO was investigated. High signal changes up to 60% were measured in the presence of humidity while small concentrations of CO down to 1 ppm could be detected validating the excellent sensing performance of the presented devices.

Synthesis of High-Aspect-Ratio CuO Nanowires for Conductometric Gas Sensing

Cupric oxide (CuO) nanowires were synthesized by thermal oxidation of resistively heated copper wires in ambient air conditions. Aspect ratios up to 1000 have been achieved with this easy growth method that requires only standard laboratory equipment. The as-synthesized nanowires were subsequently transferred to silicon substrates and contacted by a structured metallization layer. These devices were used for conductometric gas sensing as nanowire conductivity is strongly dependent on the surrounding gas atmosphere. The sensitivity of a single CuO nanowire towards water vapour and hydrogen sulfide (H2S) was investigated regarding a possible application in hydrogen fuel cells.

Vanadia doped tungsten–titania SCR catalysts as functional materials for exhaust gas sensor applications

Urea-SCR systems (selective catalytic reduction) are required to meet future NO x emission standards of heavy-duty and light-duty vehicles. It is a key factor to control the SCR systems and to monitor the catalysts’ functionalities to achieve low emissions. The novel idea of this study is to apply commercially available SCR catalyst materials based on vanadia-doped tungsten–titania as gas sensing films for impedimetric thick-film exhaust gas sensor devices. The dependence of the impedance on the surrounding gas atmosphere, especially on the concentrations of NH 3 and NO 2, is investigated, as well as cross interferences from other components of the exhaust. The sensors provide a good NH 3 sensitivity at 500 °C. The sensor behavior is explained in light of the literature combining the fields of catalysts and semiconducting gas sensors.

Influence of atmosphere on photoluminescence properties of Eu-doped ZnO nanocrystals

We have fabricated Eu 3+-doped ZnO (ZnO:Eu) nanocrystals (NCs) by a reverse micelle method, and have studied their photoluminescence (PL) properties in vacuum, nitrogen gas, and oxygen gas atmospheres. The ZnO:Eu NCs exhibit the exciton, defect and Eu 3+ PL under the inter-band photoexcitation of the ZnO host NCs. The intensity ratio among the three PL peaks is sensitive to the atmosphere for the PL measurements. We discuss the influence of the surrounding gas atmosphere to the PL properties.

Effects of Rice Straw on the Color and Microstructure of Bizen, a Traditional Japanese Stoneware, as a Function of Oxygen Partial Pressure

The effects of oxygen partial pressure during thermal treatment on the color and microstructure of Bizen, a traditional Japanese stoneware, were studied through model experiments using clay pellets covered lightly with rice straw as a coloring assistant. When heated in flowing nitrogen, the model pellet turned blackish owing to the formation of α-Fe particles coated with graphite. However, schreibersite (Fe3P), which is also blackish, was formed specifically on the pellet surface in direct contact with the straw. The rice straw seems to have generated a strongly reducing atmosphere, strong enough for the metallization to α-Fe, and also to have provided phosphorus through contact. When oxygen content in the surrounding gas atmosphere was raised to N2/O2=99/1, the pellet surface turned yellowish brown because the main coloring material was Fe3+-containing mullite. At oxygen contents of N2/O2=98/2 or more, the formation of hematite (α-Fe2O3) pushed the color to deep red.

Characterization studies of physicochemical modifications conceded by equimolar-mixed chromia and barium carbonate powders as a function of temperature

Occurrence and products of solid/solid interactions in equimolar-mixed BaCO 3 and Cr 2O 3 powders were examined isothermally (700–1000 °C) and non-isothermally (25–1200 °C) under different gas atmospheres, employing thermogravimetry, X-ray diffractometry, infrared and Raman spectroscopies, scanning electron microscopy, and energy dispersive X-ray spectroscopy. Irrespective of the gas atmosphere, a non-catalytic decomposition of the barium carbonate commenced at 570 °C, a temperature that is much less than the decomposition temperature (≥970 °C) of separate BaCO 3. Characteristics and distribution of the yielding products were found to be quite sensitive to the surrounding gas atmosphere. Under N 2 atmosphere, the interactions were thermochemical in nature, leading eventually to the formation of barium chromite (BaCr 2O 4) spinel as the sole detectable product. Under O 2 atmosphere, however, the oxygen molecules contributed oxidatively to the chromite thermal genesis course, thus imposing a topochemical nature to the reaction, leading to formation of BaCrO 4, as the major product, and barium chromites (BaCr 2O 4 and Ba 3Cr 2O 6), as minor products. Proposed reaction pathways and characteristics of products have been presented and discussed.

Infrared integrated optical evanescent field sensor for gas analysis: Part I: System design

A concept for an integrated optical gas measuring system using a free-standing single crystal silicon integrated optical waveguide as an integrated optical gas analysis sensor working in the middle infrared region is presented and the attainable resolution is estimated for practical applications. The cross-section of the waveguide is designed with respect to a pronounced evanescent optical field, which interacts with the surrounding gas atmosphere. The silicon waveguide has an optical transparency from about 1.3 to 6.3 μm thus allowing to monitor pollutants like CO, CO 2, NO, N 2O, NO 2, e.g. emitted in combustion processes as well as CH 4 and H 2O. The light at the waveguide output contains qualitative and quantitative information about the gases present. The high step in refractive index from the silicon core to gas allows very small bending radii so that a sufficiently long waveguide can be realised on a small chip area (about 1 m on 1 cm 2) by arranging it as a spiral or meander in the wafer plane.

Infrared integrated optical evanescent field sensor for gas analysis: Part II. Fabrication

A free-standing single crystal silicon integrated optical waveguide was developed for an integrated optical gas analysis sensor working in the middle infrared region. The cross section was designed to generate a pronounced fraction of evanescent optical power which interacts with the surrounding gas atmosphere field. The silicon waveguide has an optical window from about 1 to 6.3 μm thus allowing the measurement of pollutants like CO, CO 2, NO, N 2O, NO 2 emitted, e.g. in combustion processes as well as CH 4 and H 2O. The light at the waveguide output contains quantitative information about the gases present in a mixture. The high step in refractive index between silicon core and gas allows very small bending radii so that a sufficiently long waveguide can be realised on small chip area (about 1 m on 1 cm 2). The waveguide is patterned as a spiral or a meander in the wafer plane. A suitable freestanding cross section profile is realized by a sequence of anisotropic dry etching, oxidation and isotropic dry etching of crystalline silicon bulk material.

Effect of Temperature and Boron Contents on the Autocausticizing Reactions in Sodium Carbonate/Borate Mixtures

The autocausticizing reactions of sodium carbonate/borate mixtures have been studied by simultaneous TG/DTA. The main reaction occurs in a molten state of the salts, where the carbonate and borate react to form CO2 and more sodium-rich borates. The extent of decarbonation of Na2CO3 is dependent on the amount of added boron, the temperature, and the composition of the surrounding gas atmosphere. At an overall molar ratio of B/Na < 1 and at temperatures of 900−1000 °C, the borate composition of the melt is intermediate to NaBO2 and Na3BO3. The decarbonation reaction is favored by high temperatures and low CO2 contents in the gas phase. The composition of the borate components in the melt shifts toward the Na3BO3 composition at high temperatures, low CO2 partial pressures, and low boron additions. If the surrounding gas contains CO2, the salt melt will be recarbonated as the temperature is lowered and the melt crystallizes.