Dry Synthetic Air Research Articles

Ozone Production Using a Power Modulated Surface Dielectric Barrier Discharge in Dry Synthetic Air

The measurements of electrical and optical characteristics of the discharge and concentrations of produced ozone and nitrogen oxides were performed to evaluate the efficiency of ozone production in an AC surface dielectric barrier discharge in dry synthetic air at atmospheric pressure. The discharge was driven in an amplitude-modulated regime with driving AC frequencies of 1, 5 and 10 kHz, variable discharge duty cycle of 0.02–0.8 and synthetic air flow rate of 2–10 slm. The experimental results show that ozone and nitrogen oxides concentrations increased with increasing AC high-voltage amplitude, increasing discharge duty cycle and with increasing residence time. The highest calculated ozone production yield reached ~90 g/kWh with a corresponding energy cost of about 20 eV/molecule. The production yield was found to be independent of the driving AC frequency and specific energy density in the 10−4–10−2 Wh/l range.

Heterotermetallic Indium Lithium Halostannates: Low‐Temperature Single‐Source Precursors for Tin‐Rich Indium Tin Oxides and Their Application for Thin‐Film Transistors

The syntheses and structural elucidation of dimeric [Sn(OCyHex)(2)] (1), its corresponding (cyclohexoxy)alkalistannates(II) [{M(OCyHex)(3)Sn}(2)] (M = Li (2), Na (3), K (4)), and of the first heteroleptic heterotermetallic Li/In/Sn-haloalkoxide clusters [X(2)In{LiSn(2)(OCyHex)(6)}] (X = Br (5), Cl (6)) with a double seco-norcubane core are reported. They represent suitable precursors for new amorphous indium tin oxide (ITO) materials as transparent conducting oxides with drastically reduced concentrations of expensive indium, while maintaining their high electrical performance. In fact, compounds 5 and 6 were successfully degraded under dry synthetic air at relatively low temperature, resulting in new semiconducting tin-rich ITOs homogeneously dispersed in a tin oxide/lithium oxide matrix. The obtained particles were investigated and characterised by different analytical techniques, such as powder XRD, IR spectroscopy, SEM, TEM and energy-dispersive X-ray spectroscopy (EDX). The analytical data confirm that the final materials consist of tin-containing indium oxide embedded in an amorphous tin oxide matrix. The typical broadening and shift of the observed indium oxide reflections to higher 2θ values in the powder XRD pattern clearly indicated that tin centres were successfully incorporated into the In(2)O(3) lattice and partially occupied In(3+) sites. Investigations by EDX mapping proved that Sn was homogeneously distributed in the final materials. Thin-film field-effect transistors (FETs) were fabricated by spin-coating of silicon wafers with solutions of 5 in toluene and subsequent calcination under dry air (25-700 °C). The FETs prepared with precursor 5 exhibited excellent performances, as shown by a charge-carrier mobility of 6.36×10(-1) cm(2) V(-1) s (calcination at 250 °C) and an on/off current ratio of 10(6).

Synthesis of Stannyl-Substituted Zn4O4 Cubanes as Single-Source Precursors for Amorphous Tin-Doped ZnO and Zn2SnO4 Nanocrystals and Their Potential for Thin Film Field Effect Transistor Applications

The first heterobimetallic alkyl(trimethylstannoxy)zinc clusters with the formula [Me3SnOZnR]4 (R = Me 1, Et 2) are facile accessible by the Bronsted acid−base reaction of trimethyltin hydroxide with the respective zinc dialkyls ZnR2 (R = Me, Et). The resulting products 1 and 2 can be isolated as white solids in high yields (>95%) and were characterized by multinuclear NMR, elemental analysis, FTIR spectroscopy, mass spectrometry, and single-crystal X-ray diffraction analyses. They proved to serve as unprecedented low-temperature single source precursors (SSPs) for the fabrication of tin-containing ZnO as well as zinc stannate semiconducting materials and could be successfully utilized in field effect transistor (FET) applications. The thermal degradation of 1 and 2 under dry synthetic air, monitored by thermogravimetric analysis (TGA and TGA-IR), indicates high volatility of the trimethylstannyl group, which turned out to be the key parameter to control the tin concentration in the final semiconducting p...

Unprecedented Alkylzinc-Magnesium Alkoxide Clusters as Suitable Organometallic Precursors for Magnesium-Containing ZnO Nanoparticles

The synthesis and characterization of the first heterobimetallic methylzinc-magnesium alkoxide clusters [Me(6)MgZn(6)(OR)(8)] [R=Et (1 a), n-Pr (1 b), nBu (1 c)] with a bis-cubane-shaped MgZn(6)O(8) core is described. The thermal degradation of 1 a-c and mixtures of 1 a and the homometallic MeZn-alkoxide cubane [{MeZnOtBu}(4)] (2) in dry synthetic air led to wide-band-gap semiconducting Mg(x)Zn(1-x)O nanoparticles at temperatures below 500 °C. The final materials were characterized by different analytical techniques such as PXRD, REM, TEM, EDX, and IR spectroscopy. The morphology of the as-prepared magnesium-containing ZnO samples is influenced by the different organo groups (alkoxo) in the precursors. EDX mapping showed that magnesium is uniformly distributed in the ZnO matrix. The incorporation of magnesium led to a distortion of the ZnO lattice with increased a axis and decreased c axis parameters. Room-temperature photoluminescence (PL) spectra reveal that the near-band-edge (NBE) emission of Mg(2+)-doped ZnO is shifted to higher energies relative to that of pure ZnO.

Microstructure–property relations of reactively magnetron sputtered VCxNy films

VCxNy films with a wide range of chemical composition were grown onto silicon and high-speed steel substrates using reactive unbalanced magnetron sputtering from V targets in an Ar/N2/C2H2 atmosphere at a substrate temperature of 500°C. A nanocomposite structure is formed, consisting of a VN–VC solid solution and an amorphous carbon phase. While an increase in hardness is observed for low carbon contents due to solid solution hardening, raising the amorphous carbon phase fraction results in a hardness reduction. Dry-sliding ball-on-disk tests yield low friction coefficients with values of 0.22 for those films with the highest content of an amorphous carbon phase, while the lowest wear is observed for films with dominating vanadium carbonitride solid solution. The low friction behavior is attributed to the formation of tribo-layers with easy-shearable C―H bonds formed in humid atmospheres, and is not observed in dry nitrogen and synthetic air.

Bi-layer nanostructures of CuPc and Pd in SAW and resistance hydrogen sensor

Bi-layer nanostructures of copper phthalocyanine (CuPc ∼ 80nm, ∼100nm and ∼200nm) with a very thin film of palladium (Pd ∼18nm) on the top, have been studied for hydrogen gas-sensing application at ∼30-38°C, and medium (0,5 – 4%), and low (0,01-0,08%) hydrogen concentrations in synthetic dry air. The structures were obtained by vacuum deposition (first the CuPc and then the Pd film) onto a LiNbO3 (Y- cut Z-propagating) and glass substrates and were tested by means of the Surface Acoustic Wave (in a dual channel delay line configuration) and resistance methods. Very repeatable results have been observed for these three nanostructures with changes in frequency on the level of 100 to 600Hz, for hydrogen concentration from 0,5 to 4% in air. The absolute response value depends on the CuPc film thickness, the interaction temperature and hydrogen gas concentration and is greater for the bi-layer nanostructure with a medium (100nm) CuPc film.

Unusual decrease in conductivity upon hydration in acceptor doped, microcrystalline ceria

The impact of hydration on the transport properties of microcrystalline Sm(0.15)Ce(0.85)O(1.925) has been examined. Dense, polycrystalline samples were obtained by conventional ceramic processing and the grain boundary regions were found, by high resolution transmission electron microscopy, to be free of impurity phases. Impedance spectroscopy measurements were performed over the temperature range 250 to 650 °C under dry, H(2)O-saturated, and D(2)O-saturated synthetic air; and over the temperature range 575 to 650 °C under H(2)-H(2)O atmospheres. Under oxidizing conditions humidification by either H(2)O or D(2)O caused a substantial increase in the grain boundary resistivity, while leaving the bulk (or grain interior) properties unchanged. This unusual behavior, which was found to be both reversible and reproducible, is interpreted in terms of the space-charge model, which adequately explains all the features of the measured data. It is found that the space-charge potential increases by 5-7 mV under humidification, in turn, exacerbating oxygen vacancy depletion in the space-charge regions and leading to the observed reduction in grain boundary conductivity. It is proposed that the heightened space-charge potential reflects a change in the relative energetics of vacancy creation in the bulk and at the grain boundary interfaces as a result of water uptake into the grain boundary core. Negligible bulk water uptake is detected under both oxidizing and reducing conditions.

Structural and gas-sensing properties of CuO–Cu xFe 3− xO 4 nanostructured thin films

Nanocrystalline CuO–Cu x Fe 3− x O 4 thin films were developed using a radio-frequency sputtering method followed by a thermal oxidation process. Thin films were deposited applying two very different conditions by varying the argon pressure and the target-to-substrate distance. Structural, microstructural and gas-sensing characteristics were performed using grazing incidence X-ray diffraction (GXRD), Raman spectroscopy, atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and electrical measurements. Their sensing properties were examined using hydrogen gas in dry synthetic air. The shortest response and recovery times were observed between 280 and 300 °C independently of the deposition conditions.

Mid-infrared absorption cross sections for acetone (propanone)

Infrared absorption cross sections for acetone (propanone) have been determined in the 830–1950 cm −1 spectral region from spectra recorded using a high-resolution FTIR spectrometer (Bruker IFS 125HR) and a multipass cell with a maximum optical path length of 19.3 m. The spectra of mixtures of acetone with dry synthetic air were recorded at 0.015 cm −1 resolution (calculated as 0.9/MOPD using the Bruker definition of resolution) at a number of temperatures between 194 and 251 K and pressures appropriate for atmospheric conditions. Intensities were calibrated using three acetone spectra (recorded at 278, 293 and 323 K) taken from the Pacific Northwest National Laboratory (PNNL) IR database. The new absorption cross sections have been combined with previous high spectral resolution results to create a more complete set of acetone absorption cross sections appropriate for atmospheric remote sensing. These cross sections will provide an accurate basis for upper tropospheric/lower stratospheric retrievals of acetone in the mid-infrared spectral region from ACE and MIPAS satellite data.

Infrared absorption cross sections for acetone (propanone) in the 3 μm region

Infrared absorption cross sections for acetone (propanone), CH 3C(O)CH 3, have been determined in the 3 μm spectral region from spectra recorded using a high-resolution FTIR spectrometer (Bruker IFS 125 HR) and a multipass cell with a maximum optical path length of 19.3 m. The spectra of mixtures of acetone with dry synthetic air were recorded at 0.015 cm −1 resolution (calculated as 0.9/MOPD using the Bruker definition of resolution) at a number of temperatures and pressures (50–760 Torr and 195–296 K) appropriate for atmospheric conditions. Intensities were calibrated using three acetone spectra (recorded at 278, 293 and 323 K) taken from the Pacific Northwest National Laboratory (PNNL) IR database.

Identification of Organic Nitrates in the NO3Radical Initiated Oxidation of α-Pinene by Atmospheric Pressure Chemical Ionization Mass Spectrometry

The gas-phase reactions of nitrate radicals (NO3) with biogenic organic compounds are a major sink for these organics during night-time. These reactions form secondary organic aerosols, including organic nitrates that can undergo long-range transport, releasing NOx downwind. We report here studies of the reaction of NO3 with alpha-pinene at 1 atm in dry synthetic air (relative humidity approximately 3%) and at 298 K using atmospheric pressure chemical ionization triple quadrupole mass spectrometry (APCI-MS) to identify gaseous and particulate products. The emphasis is on the identification of individual organic nitrates in the particle phase that were obtained by passing the product mixture through a denuder to remove gas-phase reactants and products prior to entering the source region of the mass spectrometer. Filter extracts were also analyzed by GC-MS and by APCI time-of-flight mass spectrometry (APCI-ToF-MS) with methanol as the proton source. In addition to pinonaldehyde and pinonic acid, five organic nitrates were identified in the particles as well as in the gas phase: 3-oxopinane-2-nitrate, 2-hydroxypinane-3-nitrate, pinonaldehyde-PAN, norpinonaldehyde-PAN, and (3-acetyl-2,2-dimethyl-3-nitrooxycyclobutyl)acetaldehyde. Furthermore, there was an additional first-generation organic nitrate product tentatively identified as a carbonyl hydroxynitrate with a molecular mass of 229. These studies suggest that a variety of organic nitrates would partition between the gas phase and particles in the atmosphere, and serve as a reservoir for NOx.

Infrared absorption cross sections for propane (C 3H 8) in the 3 μm region

Infrared absorption cross sections for propane have been measured in the 3 μm spectral region from spectra recorded using a high-resolution FTIR spectrometer (Bruker IFS 125 HR). The spectra of mixtures of propane with dry synthetic air were recorded at 0.015 cm −1 resolution (calculated as 0.9/MOPD using the Bruker definition of resolution), at a number of temperatures and pressures appropriate for atmospheric conditions. Intensities were calibrated using two propane spectra (recorded at 278 and 293 K) taken from the Pacific Northwest National Laboratory (PNNL) IR database.

Infrared absorption cross sections for ethane (C 2H 6) in the 3 μm region

Infrared absorption cross sections for ethane have been measured in the 3 μm spectral region from spectra recorded using a high-resolution FTIR spectrometer (Bruker IFS 125/HR). Results are presented for pure ethane gas from spectra recorded at 0.004 cm −1 resolution and for mixtures with dry synthetic air from spectra obtained at 0.015 cm −1 resolution (calculated as 0.9/MOPD using the Bruker definition of resolution), at a number of temperatures and pressures appropriate for atmospheric conditions. Intensities were calibrated using three ethane spectra (recorded at 278, 293, and 323 K) taken from the Pacific Northwest National Laboratory (PNNL) IR database.

Water vapor effect on high-temperature oxidation behavior of Fe3Al intermetallics

Fe3Al intermetallics (Fe3Al, Fe3Al-Zr, Fe3Al-Zr,Mo and Fe3Al-Zr, Mo, Nb) were oxidized at 950 °C in dry and humid (11 vol% water) synthetic air. Thermogravimetric measurements showed that the oxidation rates of the tested intermetallics were lower in humid air than in dry air (especially for Fe3Al-Zr, Mo and Fe3Al-Zr, Mo, Nb). The addition of small amounts of Zr, Mo or Nb improved the kinetics compared with that of the undoped Fe3Al. Fe3Al showed massive spallation, whereas Fe3Al-Zr, Fe3Al-Zr, Mo and Fe3Al-Zr, Mo, Nb produced a flat, adherent oxide layer. The rapid transformation of transient alumina into alpha alumina may explain the decrease in the oxidation rate in humid air.

A Microdrop Generator for the Calibration of a Water Vapor Isotope Ratio Spectrometer

Abstract A microdrop generator is described that produces water vapor with a known isotopic composition and volume mixing ratio for the calibration of a near-infrared diode laser water isotope ratio spectrometer. The spectrometer is designed to measure in situ the water vapor deuterium and oxygen (17O and 18O) isotope ratios from the low troposphere up to the lower stratosphere with a high temporal resolution, and is based on ultrasensitive optical-feedback cavity-enhanced absorption spectroscopy. To calibrate the spectrometer, a commercial microdrop generator (Microdrop GmbH) is used to inject water droplets of known size at a preset repetition frequency into a stream of dry nitrogen or synthetic air. Complete evaporation of the small droplets ensures that there is no isotopic fractionation between the liquid phase and the generated moist “air.” The water mixing ratio of the synthetic air is controlled by the repetition rate and gas flow. The current system spans a water mixing ratio range from about 10 to 5000 ppmv, representing the range of conditions expected in the lower to upper troposphere. Both lower and higher mixing ratios can be produced after small modifications to the injector’s operating conditions or the system’s design.

CO ppb sensors based on monodispersed SnOx:Pd mixed nanoparticle layers: Insight into dual conductance response

This study reports the modifications in CO sensing of SnOx nanoparticle layers by utilizing monodispersed Pd nanoparticles. The distinct advantage of monosized particles and contaminant-free samples with open porosity in addition to size effects resulted in improved CO sensing with decrease in Pd nanoparticle size to 5 nm, decreasing the lowest detection levels of CO using SnOx-based sensor technology down to 10 ppb (parts per billion) in dry synthetic air. The homogeneously mixed nanoparticle layers also exhibit discrimination capability between CO and ethanol in dry air as a manifestation of the dual conductance response. Detailed x-ray photoelectron spectroscopy studies clearly reveal “Mars–van Krevelen” as the key mechanism responsible for the observed sensing in mixed nanoparticle layers. The interfacial/surface PdO formed upon pretreatment in air is continuously “consumed” and “reformed” upon exposure, respectively, to CO and synthetic air. In contrast to the case of ethanol exposure with n-type response, the Pd aided reduction of tin oxide surface in CO ambient leads to p-type response. The sensors of the present study have a wide range of promising applications from air quality control to food and fuel industries.

Effect of oxidation on the performance of low-temperature petroleum cokes as anodes in lithium ion batteries

The effect of an oxidative treatment on the electrochemical performance of various low-temperature cokes as anodes in lithium ion batteries was examined in order to optimize their chemical composition and textural properties. Annealing in a stream of dry synthetic air over short time and temperature ranges was found to result in substantially increased cell capacity and improved capacity retention during cycling in coke oxidized at 350 °C for 1 h, which exhibited a capacity as high as 385 mAh g−1 after 20 cycles at C/50. However, raising the oxidation temperature to 500 °C resulted in undesirably increased irreversible capacity and polarization between the charge and discharge branches, the effect being confirmed by the high impedance values obtained after only a few cycles. 7Li MAS NMR spectroscopy was used to assess covalency in lithium bonds and its relationship to electrochemical performance in the studied batteries.

Fluctuation enhanced gas sensing on functionalized carbon nanotube thin films

AbstractThin films of functionalized carbon nanotubes were deposited on silicon chips by drop‐coating and inkjet printing. These sensors were exposed to 50 ppm N2O, CO, H2S and H2O vapour in dry synthetic air. We have found relatively small changes in the electrical resistance of the films exposed to the different test gases. However it is shown that chemical classification of the test gases could still be achieved. To this end pattern recognition technique (Principal Component Analysis) was applied on the acquired power spectral density of the stationary resistance fluctuations of the sensors. The method, whereby fluctuations are used to increase the chemical selectivity of electronic sensors, is called fluctuation enhanced sensing. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

A comparison of the oxidation behaviours of Al 2O 3 formers and Cr 2O 3 formers at 700 °C – Oxide solid solutions acting as a template for nucleation

The oxidation behaviour of a number of ferritic iron based commercial steels and model alloys containing 6 and 9 wt% Cr and 0–2.5 wt% Al have been studied at 700 °C. The oxidation time ranged from 5 min to 500 h and the atmosphere consisted of flowing dry synthetic air. The oxide layers formed were analysed by SEM, GI-XRD and ToF-SIMS. The material without Al formed a (Cr,Fe) 2O 3 film with an Fe enrichment in the outer part of the layer. The Al containing alloys showed more complex oxidation behaviour. The oxidation started initially by formation of (Cr,Fe) 2O 3 with an Cr enriched inner part. With time Al was oxidized and dissolved in the inner Cr rich part of the oxide. This process continued until it eventually was transformed into α-Al 2O 3 with minute amount of Fe in the outer and Cr in the inner part of the oxide. The thickness of all oxide films ranged from 20 to 400 nm apart from the material that contained 9% Cr and no Al, which experienced breakaway oxidation after 500 h at 700 °C. This means that materials alloyed with small amounts of Al must also be considered to be protective at 700 °C, as the thicknesses of the Al 2O 3 oxides was comparable with the ones not containing Al, and as they do not experience breakaway corrosion.

Optical gas sensitivity of a metaloxide multilayer system with gold-nano-clusters

Abstract In this paper we report on the optical gas sensitivity of a sputtered multilayer system consisting of InxOyNz thin films and gold-nano-clusters. This system shows a reversible change in the optical absorption (increase or decrease of absorbance) during exposure to reducing or oxidizing gases in air. The gold-nano-clusters are randomly distributed on and inside the multilayer system. Here, we demonstrate the optical gas sensitivity at a temperature of 400 °C and three exemplary gas samples: carbon monoxide in dry synthetic air, nitrogen dioxide in dry synthetic air and hydrogen in dry synthetic air. We show that the incorporation of the gold-clusters leads to a broad absorption peak in the range of visible light due to the excitation of localized surface plasmons. The corresponding resonance wavelength is shifted by gas exposure that in turn changes the optical behavior of the multilayer system.