Nitrogen Carrier Gas Research Articles

Thermal decomposition reactions of n‐alkylated 2‐aminobiphenyls to carbazole and phenanthridine

Abstractmagnified imageThermal cyclization reactions were examined by passing vapors of N‐alkylated 2‐aminobiphenyls 1a‐c and 2 over calcium oxide at 450‐600°C under nitrogen carrier gas. The reactions yielded 9‐methylcarbazole 3, carbazole 4, phenanthridine 5 and phenanthrene 6. The major product for the reactions of 1a, 1b and 2 was phenanthridine 5 while that of 1c was carbazole 4.

Formation of Cyclopentadienyl Radical from the Gas-Phase Pyrolysis of Hydroquinone, Catechol, and Phenol

The formation of radicals from the gas-phase pyrolysis of hydroquinone, catechol, and phenol over a temperature range of 400-750 degrees C was studied using the technique of low-temperature matrix isolation electron paramagnetic resonance (LTMI EPR). Cooling the reactor effluent from pyrolysis in a nitrogen carrier gas to 77 K produces a cryogenic matrix that exhibits poorly resolved EPR spectra. However, using carbon dioxide as a carrier gas formed a matrix that, upon annealing by slowly raising the matrix temperature followed by rapid recooling to 77 K, yielded more resolved, identifiable spectra. Annealed spectra of all three samples resulted in the generation of EPR spectra above 700 degrees C with 6 lines, hyperfine splitting constant approximately 6.0 G, and peak to peak width approximately 3 G that was readily assignable, based on comparison to the literature and theoretical calculations, as that of cyclopentadienyl radical. Pyrolysis at temperatures below 700 degrees C generated a carbon dioxide matrix isolation spectrum with a high g-value (>2.0040) that is attributed to oxygen-containing radicals such as semiquinone or phenoxyl. Conclusive identification of anticipated semiquinone, phenoxyl, and hydroxycyclopentadienyl radicals was complicated by the ability of these radicals to exist in carbon-centered and oxygen-centered resonance structures that can give different EPR spectra.

Chemical identification using an impedance sensor based on dispersive charge transport

Impedance spectroscopy has been used to identify analytes in semiconducting metallophthalocyanine thin films. Above a critical concentration, the magnitudes of the high frequency conductivity changes are invariant with concentration but distinct for different analytes and can be used for analyte identification. The analyte-induced ac conductivity changes above 5kHz have been converted to frequency shifts in a circuit resonance and used to differentiate methanol, ethanol, and isopropanol vapors in a nitrogen carrier gas. The analyte-induced changes in the conductivity are consistent with analyte-induced changes in the charge relaxation times.

ファインチャネルミスト法によるＺｎＯ透明薄膜の作製とその特性

The fine channel mist (FCM) method has been developed, as a safe and economical growth technology of zinc oxide (ZnO) thin films. This technique utilized aqueous solution of zinc acetate, which is a safe material, as a zinc source, and this solution is supplied to the growth as a form of micro-sized mist by applying ultrasonic-power with the carrier gas of nitrogen. ZnO thin films were grown in an open system, where the mist of zinc acetate reacted with oxygen or water on a glass substrate at the temperature of 270 to 500°C. One of the key technologies was to flow the reactant gases in a micro-channel on the substrate. This allowed effective growth of ZnO by “condensing” the flow to the substrate neighborhood and by rapidly improving collision probability of the source gases, resulting in the high efficiency (as high as 10%) for the zinc source to form ZnO. The ZnO thin film hence grown was transparent with the naked eyes, that is, the optical transmission was higher than 90% in the visible light region. Photoluminescence spectra exhibited near-band edge emission around 3.3eV (375nm) at room temperature, with weak deep level emissions. The surface morphology changed in terms of the growth conditions, reflecting different crystallographic properties. The thickness, the electrical conductivity, and the growth rate were 50-5000nm, 1-5Ωcm, and 1-200nm/min respectively. The overall properties of ZnO thin films grown here suggested the potential of this novel growth technology being utilized to fabricate transparent conducting films, ultraviolet absorbers, and so on.

Crystal growth and characterization of thick GaN layers grown by oxide vapor transport technique

Single-crystal GaN layers of 20–40 μm thickness were grown in an oxide transport process using a mixture of commercially available Ga 2O 3 powder and graphite powder as precursors. Ammonia was used as the source of nitrogen in these experiments. A two-flow design was used to perform these experiments, in which, the nitrogen carrier gas was passed through the powder to transport the resulting gallium suboxide (Ga 2O) towards the seed crystal. The GaN layers thus obtained from the processes were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and reciprocal space mappings. XRD patterns showed that the grown GaN layers are single crystals oriented along c-direction with wurtzite structure.

Numerical investigations on cold gas dynamic spray process with nano- and microsize particles

The particle velocity in cold gas dynamic spraying (CGDS) is one of the most important factors that can determine the properties of the bonding to the substrate. In this paper, the acceleration process of microscale and sub-microscale copper (Cu) and platinum (Pt) particles inside and outside De-Laval-Type nozzle is investigated. A numerical simulation is performed for the gas-particle two phase flow with particle diameter ranging from 100 nm to 50 μm, which are accelerated by carrier gas nitrogen and helium in a supersonic De-Laval-type nozzle. The carrier gas velocity and pressure distributions in the nozzle and outside the nozzle are illustrated. The centerline velocity for two types of particles, Pt and Cu, are demonstrated. It is observed that the existence of the bow shocks near the substrate prevents the smaller size particles (less than 0.5 μm) from penetrating, thus leads to poor coating in the actual practices. Furthermore, the extended straight section may have different optimal length for different size particles, and even may be unnecessary for sub-microsize particles.

Influence of the nucleation layer morphology and epilayer structure on the resistivity of GaN films grown on c-plane sapphire by MOCVD

The influence of hydrogen and nitrogen carrier gases used during the preparation of the nucleation layer on the structural and electrical properties of GaN layers has been investigated. The GaN were grown on sapphire substrates using metal organic chemical vapor deposition. The nucleation layer morphology strongly depends on the carrier gas affecting the electrical properties of GaN epitaxial films through changes of the ratio of edge to mixed and screw-type threading dislocations. X-ray diffractometry, X-ray reflectometry, atomic force microscopy, and defect selective etching were employed to study the structural properties of both the nucleation layer and the GaN epilayers deposited on top of this. It is found that the density of edge-type dislocations determines the resistivity of GaN epilayers and that one key factor for varying the density of these dislocations is the morphology of the nucleation layer, i.e. the morphology of the GaN epilayer can be controlled by the type of carrier gas used in the preparation of the nucleation layer. The electrical resistivity of our GaN epilayers is typically about 0.5 Ω cm and more than 3×10 4 Ω cm with nucleation layers grown using hydrogen and nitrogen carrier gases, respectively.

A Mechanism for the Destruction of CFC-12 in a Nonthermal, Atmospheric Pressure Plasma

The destruction of CFC-12 (CF2Cl2) has been studied in an AC, nonthermal, atmospheric pressure plasma reactor packed with barium titanate beads. The extent of the destruction in air ranges between 8% and 40% depending on the conditions. The decomposition products in air as determined by infrared spectroscopy are CO, CO2, and COF2. It is deduced that the undetected chlorine and fluorine is present as F2 and Cl2. A chemical mechanism for the decomposition is proposed. Large concentrations of NO, NO2, and N2O are also formed. Destruction in a stream of pure N2 is about twice as effective as in air under corresponding conditions. The addition of a small amount of water (∼0.03%) or oxygen (∼0.02%) to the nitrogen carrier gas increases the destruction efficiency but the presence of molecular hydrogen (≤2%) brings about no enhancement. It is suggested that in all cases, the primary decomposition step involves dissociative electron attachment to the CF2Cl2. This is confirmed by the observed differences in the destruction in pure nitrogen and in air.

Deposition and characterization of carbon nitride films from hexamethylenetetramine/N 2 by microwave plasma-enhanced chemical vapor deposition

Carbon nitride thin films were deposited on Si(1 0 0) substrate by microwave plasma-enhanced chemical vapor deposition (PECVD). Hexamethylenetetramine (HMTA) was used as carbon and nitrogen source while N 2 gas was used as both nitrogen source and carrier gas. The sp 3-bonded CN structure in HMTA was considered significantly in the precursor selection. X-ray diffraction analysis indicated that the film was a mixture of crystalline α- and β-C 3N 4 as well as graphitic-C 3N 4 and β-Si 3N 4 which were not easily distinguished. Raman spectroscopy also suggested the existence of α- and β-C 3N 4 in the films. X-ray photoelectron spectroscopy study indicated the presence of sp 2- and sp 3-bonded CN structures in the films while sp 3CN bonding structure predominated to the sp 2 CN bonding structure in the bulk composition of the films. N was also found to be bound to Si atoms in the films. The product was, therefore, described as CN x :Si, where x depends on the film depth, with some evidences of crystalline C 3N 4 formation.

Fiber optic ammonia sensing employing novel thermoplastic polyurethane membranes

Ammonia gas fiber optic sensors have been fabricated using a commercially available thermoplastic polyurethane resin, Tecoflex ®, which entraps a pH indicator that undergoes a color change in presence of ammonia gas. Highly repetitive and reversible sensors have been achieved using simple and short fabrication processes. Evanescent wave absorption has been monitored under exposure to 0.03–1% of ammonia in nitrogen carrier gas, measuring a maximum optical variation of 6 dB at 600 nm. These sensors can work even in extremely dry environments and show recovery times of less than 5 s.

Cryogenic trapping for determination of odor concentration

The sensory testing method applied under Japanese law to measure odor concentration has a lower detection limit of 10 in the specified Odor Index. To measure odor below the limit, a condensing procedure using solid sorbents (Tenax-TA, Unicarbon B and Carbosieve SIII) has been developed and used in Japan. This procedure however cannot condense all odorous substances, and is specifically unsuited to hydrogen sulfide, methyl mercaptan, dimethyl sulfide, ammonia, and other typical odorous substances. In the present study, cryogenic trapping was tested to improve recovery rate. As water in sample air causes choking of the trap tube, vacant pre-columns to condense the water were connected to the Tenax-TA-packed column. The columns were chilled with liquid oxygen before passage of 100 L of sample air. The columns were then heated to 200 degrees C under passage of 50 mL/min of nitrogen carrier gas to desorb odors. The desorbed gases were captured in sampling bags made of polyethylene terephthalate film. The total volume of desorbed gases was approximately 1 L. The method showed good recovery rates for hydrogen sulfide, methyl mercaptan, dimethyl sulfide and ammonia, and was useful for determining low-level odor concentrations during measurement of odor in ambient air at various sites in Osaka City.

Synthesis of Carbazole, Acridine, Phenazine, 4H‐Benzo[def]carbazole and Their Derivatives by Thermal Cyclization Reaction of Aromatic Amines.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Influence of injection mode on properties of DC plasma jets for thermal plasma spraying

In plasma spraying powder particles are transported to the plasma jet with the help of a carrier gas. The influence of this gas was investigated by means of an enthalpy probe system with a mass spectrometer for measuring plasma temperature, velocity and plasma gas composition, and visualized by means of Schlieren optics. The enthalpy probe system does not allow measurements of the plasma flow containing solid particles. Therefore, to establish changes of the jet characteristics the carrier gas was supplied through different ports without addition of any powders. Nitrogen and helium were used as carrier gases. They were supplied into the jet with flow rates from 5 to 20 slpm either directly into the plasma beam through a hole in the nozzle or with help of an external injector positioned at a distance of several millimeters from the exit nozzle. Injection of the carrier gas led to high jet perturbations. Values of the centerline temperature and the velocity were reduced. The higher the carrier gas flow rate the stronger the changes of the jet properties. Nitrogen carrier gas perturbed plasma jet flow more than helium.

Synthesis of carbazole, acridine, phenazine, 4H‐benzo[def]carbazole and their derivatives by thermal cyclization reaction of aromatic amines

AbstractA variety of nitrogen‐containing heterocycles were synthesized by passing vapors of aromatic amines over calcium oxide at 450–650 °C under nitrogen carrier gas. Reaction of 2‐aminobiphenyl 3a at 560 °C gave carbazole 4 in 80% yield. Reaction of 2, 2′‐diaminobiphenyl 3b afforded a mixture of carbazole 4 and 4‐aminocarbozole 6b. In the case of 2‐amino‐2′‐nitrobiphenyl 3c, benzo[c]cinnoline 7 was obtained along with carbazole 4. Reaction of 2‐amino‐2′‐methoxybiphenyl 3d gave four products of carbazole 4,4‐hydroxycarbazole 6e, phenanthridine 8 and dibenzofuran 9. Reaction of 2‐aminodiphenylmethane 5a afforded acridine 10. In the case of 2‐aminobenzophenone 5b, acridone 11 was obtained as a major product. Reaction of 2‐aminobenzhydrol 5c gave acridine 10. When 2‐aminodiphenylamine 5d was reacted, phenazine 12 was obtained in good yield. In contrast, reaction of 2‐aminodiphenyl ether 5e produced only 2‐hydroxydiphenylamine 13. Reaction of 4‐aminophenanthrene 14 produced 4H‐benzo[def]carbazole 15 in 61% yield.

Determination of arsenic species in fish, crustacean and sediment samples from Thailand using high performance liquid chromatography (HPLC) coupled with inductively coupled plasma mass spectrometry (ICP-MS).

Suitable techniques have been developed for the extraction of arsenic species in a variety of biological and environmental samples from the Pak Pa-Nang Estuary and catchment, located in Southern Thailand, and for their determination using HPLC directly coupled with ICP-MS. The estuary catchment comprises a tin mining area and inhabitants of the region can suffer from various stages of arsenic poisoning. The important arsenic species, AsB, DMA, MMA, and inorganic arsenic (As III and V) have been determined in fish and crustacean samples to provide toxicological information on those fauna which contribute to the local diet. A Hamilton PRP-X100 anion-exchange HPLC system employing a step elution has been used successfully to achieve separation of the arsenic species. A nitric acid microwave digestion procedure, followed by carrier gas nitrogen addition- (N2)-ICP-MS analysis was used to measure total arsenic in sample digests and extracts. The arsenic speciation of the biological samples was preserved using a Trypsin enzymatic extraction procedure. Extraction efficiencies were high, with values of 82-102%(As) for fish and crustacean samples. Validation for these procedures was carried out using certified reference materials. Fish and crustacean samples from the Pak Pa-Nang Estuary showed a range for total arsenic concentration, up to 17 microg g(-1) dry mass. The major species of arsenic in all fauna samples taken was AsB, together with smaller quantities of DMA and, more importantly, inorganic As. For sediment samples, arsenic species were determined following phosphoric acid (1 M H3PO4) extraction in an open focused microwave system. A phosphate-based eluant, pH 6-7.5, with anion exchange HPLC coupled with ICP-MS was used for separation and detection of AsIII, AsV, MMA and DMA. The optimum conditions, identified using an estuarine sediment reference material (LGC), were achieved using 45 W power and a 20 minute heating period for extraction of 0.5 g sediment. The stability and recovery of arsenic species under the extraction conditions were also determined by a spiking procedure which included the estuarine sediment reference material. The results show good stability for all species after extraction with a variability of less than 10%. Total concentrations of arsenic in the sediments from the Pak Pa-Nang river catchment and the estuary covered the ranges 7-269 microg g(-1)and 4-20 [micro sign]g g(-1)(dry weight), respectively. AsV was the major species found in all the sediment samples with smaller quantities of AsIII. The presence of the more toxic inorganic forms of arsenic in both sediments and biota samples has implications for human health, particularly as they are readily 'available'.

Effects of carrier gas on the stress of a-plane GaN films grown on r-plane sapphire substrates by metalorganic chemical vapor deposition

The anisotropic stresses of a-plane GaN films were in detail investigated. Nonpolar a-plane GaN films were grown on r-plane sapphire substrates by MOCVD. High resolution X-ray diffraction and polarized Raman scattering measures were performed to characterize the epitaxial films. The full width at half maximum of rocking wave is just 0.25°. Raman spectra provide us evidence that anisotropic stresses exist within the epitaxial GaN films. The effects of carrier gas on the stress states of the films were studied by Raman spectra. The stress was larger in film grown with hydrogen carrier gas than with nitrogen carrier gas.

Formation of “air‐gap” structure at a GaN epilayer/substrate interface by using an InN interlayer

We propose a new technique for “air-gap” formation at a GaN/sapphire interface by using an InN interlayer. This is aimed to grow epitaxial GaN films with reduced stress and cracks. First, an InN interlayer of about 0.2 μm thick is grown at 600 °C in atmospheric pressure. Then a 30 nm-thick GaN buffer layer is grown on the InN layer at 550 °C. The substrate temperature is ramped up to 1000 °C in the NH3 flow, and finally a 1.5 μm-thick GaN epilayer is grown on the annealed GaN buffer layer using nitrogen carrier gas. Consequently, an “air-gap” structure is naturally formed close to the substrate surface. During the ramping period of substrate temperature, the InN layer decomposes due to its thermal instability and metallic In is formed. It is found that metallic In drops as a result of InN decomposition contribute to the air-gap formation. No cracks are found on the GaN surface and a reduced stress in the layer is confirmed by PL and Raman shift measurements. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Study of xα - Fe/sub 2/O/sub 3/ - (1 - x)ZrO/sub 2/ solid solution for low-temperature resistive oxygen gas sensors

A noble type of oxygen-sensitive and electrical-conductive material, ZrO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -based with α-Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> thick-film gas sensor, was investigated for low operating temperature. Amorphous-like solid solutions of xα-Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> -(1-x)ZrO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> powders were derived using the high-energy ball milling technique, and their physical and microstructural properties were characterized from DTA, XRD, TEM, and XPS. The oxygen gas-sensing properties of the screen-printed thick-film gas sensors fabricated from such mechanically-alloyed materials were characterized systematically. Very good sensing properties were obtained with a relative resistance value of 82 in 20% oxygen, and at a low operating temperature of 320°C. AC impedance spectra and thermally stimulated current were characterized to investigate the conduction properties of the solid solution, 0.2α-Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> -0.8ZrO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , in air and nitrogen (carrier gas), respectively. It was found that the Arrhenius plots of ΣT versus 1000/T have two distinct gradients corresponding to two activation energies in the high and low temperature regions. The transition temperature occurs at about 320°C that corresponds to an optimal operating temperature of the gas sensor. It is believed that the high oxygen vacancy concentration present in the solid solution, 0.2α-Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> -0.8ZrO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , and the dissociation of the associated oxygen vacancy defect complexes at 320°C are the critical factors for the high relative resistance to oxygen gas at low operating temperature.

GaInNAs/GaAs Multiple-Quantum-Well Grown by Metalorganic Chemical Vapor Deposition Using Nitrogen Carrier Gas

Using nitrogen as a carrier gas, we have grown a GaInNAs/GaAs three-quantum-well structure by metalorganic chemical vapor deposition (MOCVD). Photoluminescence (PL) intensity of the sample using nitrogen carrier gas was increased by more than one order of magnitude and full-width at half maximum (FWHM) was reduced in comparison with a sample using hydrogen carrier gas at the same PL peak wavelength. Furthermore, the incorporation ratio of nitrogen was increased by using nitrogen carrier gas.

Characterization of carbon-coated silicon: Structural evolution and possible limitations

Carbon-coated silicon has been synthesized by a thermal vapor deposition method using silicon powder and toluene/benzene vapors carried by a nitrogen carrier gas. It has been investigated under different charging/discharging modes. In all cases, the silicon lattice undergoes gradual destruction during lithium insertion/extraction. Lithium ion extraction from the silicon host matrix did not lead to the formation of an ordered silicon structure. In addition, no new ordered phases were detected. Impedance spectroscopy was applied to monitor the changes during the first lithium insertion/extraction. The results suggest that the material behaves differently than the typical single phase well-defined structures, from which is possible to extract the diffusion coefficient at all lithium insertion levels. Impedance spectra rather detected the phase transition and connected changes in the roughness of the phase boundaries between the Si/C and C/electrolyte. Estimation of the diffusion coefficient was possible only after deeper lithium insertion/extraction when the spectra pattern followed the predictions of the Randless model.