Presence Of Hydrogen Gas Research Articles

Studies on Ru/3C-SiC Schottky Junctions for High Temperature Hydrogen Sensors

The sensor response behavior of the Ru/3C-SiC (epilayer on Si substrate) Schottky junctions was studied at different temperatures in presence of hydrogen gas with concentrations varying from 5,000 ppm to 20,000 ppm. The output signal of the sensors, the response time, and the reversibility were investigated from the transient response characteristics of the sensors. The sensor parameters were found to improve with higher operating temperature, up to 400°C, above which they degrade due to the influence of thermally generated carriers in the Si substrate. The sensitivity was found to be a function of applied bias across the junction. As compared to the Pd/3C-SiC junctions, the Ru/3C-SiC Schottky sensors showed better resolution in the hydrogen concentration range between 10,000 and 20,000 ppm. Also, the Ru/3C-SiC sensors showed better reversibility. The secondary ion mass spectrometry study indicates that the Ru/3C-SiC Schottky sensors can be operated at 400°C without any significant degradation of the interface. © 2003 The Electrochemical Society. All rights reserved.

Missing row formation induced by unidirectional field evaporation of hydrogen-covered Rh{1 1 0}

We have studied the interaction of hydrogen with Rh tips under imaging conditions of field ion microscopy. In electric fields of 2.4 V/Å, in the presence of hydrogen gas at 10−5 mbar and at cryogenic temperatures, discrete events of field evaporation were found to form (1×2) patterns on Rh{110} due to the removal of Rh atoms along [011] the direction of densely packed atomic chains. This is different from the usual field evaporation mechanism which occurs by a shrinkage of layers from the edge to the center. Corroborating evidence for this interpretation is obtained from ab initio cluster calculations based on density functional theory.

Palladium mesowire arrays for fast hydrogen sensors and hydrogen-actuated switches.

Arrays of mesoscopic palladium wires prepared by electrodeposition form the basis for hydrogen sensors and hydrogen-actuated switches that exhibit a response time ranging from 20 ms to 5 s, depending on the hydrogen concentration. These devices were constructed by electrodepositing palladium mesowires on a highly oriented pyrolytic graphite surface and then transferring these mesowires to a cyanoacrylate film supported on a glass slide. The application of silver contacts to the ends of 10-100 mesowires, arrayed electrically in parallel, produced sensors and switches that exhibited a high conductivity state in the presence of hydrogen and a low conductivity state in the absence of hydrogen. After an initial exposure to hydrogen, 15-50 nanoscopic gaps are formed in each mesowire. These nanoscopic gaps or "break junctions" close in the presence of hydrogen gas and reopen in its absence as hydrogen is reversibly occluded by the palladium grains in each wire, and the palladium lattice expands and contracts by several percent. The change in resistance for sensors and switches was related to the hydrogen concentration over a range from 1 to 10%.

Sensing of carbon monoxide gas in reducing environments

The change in resistance of thin-films of CuCl upon exposure to carbon monoxide is developed as the basis for sensing CO gas in reducing environments. Several methods of preparation of thin films of CuCl films were examined. Films prepared by solvent evaporation under ambient conditions showed good sensitivity for CO in the presence of hydrogen gas. The optimum sensing temperature was found to be 50 °C. We propose a hole conduction mechanism for CO sensing by CuCl films.

A novel silica trap for lead determination by hydride generation atomic absorption spectrometry

A novel silica trap for lead determination at concentration levels of ng/l was developed using hydride-generation atomic absorption spectrometry. The device consists of a 7.0-cm silica tubing which is externally heated to a desired temperature. The lead hydride vapor is generated by a conventional hydride-generation flow system. The trap is placed between the gas–liquid separator and silica T-tube; the device traps analyte species at 500 °C and releases them when heated further to 750 °C. The overall efficiency is 49%. The presence of hydrogen gas is required for revolatilization; O 2 gas must also be present. The analytical plot is linear up to 2.0 ng/ml for a collection period of 60 s. The response is also linear with respect to increasing collection periods up to 4 min. For 60-s trapping, the detection limit is 19 ng/l.

Indium tin oxide films prepared by radio frequency magnetron sputtering method at a low processing temperature

Low temperature deposition of thin films of indium tin oxide (ITO) prepared by radio frequency magnetron sputtering method have been developed. This involved introducing hydrogen into the sputtering gas mixture during the film preparation. The surface morphology of the ITO films was sensitive to the hydrogen partial pressures used in the gas mixture. ITO films with a root mean square roughness of 1.13 nm over an area of 300×300 nm were obtained at the hydrogen partial pressure of 7.0×10 −6 torr. The presence of hydrogen gas in the sputtering processes was also shown to increase the number of charge carriers in the ITO films. At optimal deposition conditions, thin films of ITO with a resistivity of 4.66×10 −4 Ω cm and an optical transmission of over 86% in the visible spectrum range were achieved. The ITO films fabricated by this method do not require substrate heating during the film preparation or any additional post-deposition annealing treatment.

A Synthetic Route to a New Surface-Active Phosphine Ligand: 12-DPDP (12-Diphenylphosphinododecylphosphonate)

A water-soluble phosphonate-functionalized phosphine ligand Na 2[Ph 2P(CH 2) 12PO 3] ( 8), was prepared in eight steps from cyclododecanone. Phosphine 8 reacts with [Rh(COD)Cl] 2 in methanol to give the new complex Na 2[Rh(COD)(Ph 2P(CH 2) 12PO 3)Cl] ( 9). Complex 9 is inactive in the catalytic hydrogenation of 1-hexene and cyclohexene due to the decomposition of 9 to rhodium metal in the presence of hydrogen gas. Hydrogenation of decene using [Rh(COD) 2]BF 4 and 3 equiv. of 8 in an aqueous emulsion was achieved using 1 atm H 2. 31P NMR studies on 8 suggest a lack of well-defined aggregation in water, which has been ascribed to the steric bulk of the diphenylphosphino group.

Effect of anions on catalytic and electrocatalytic hydrogenations and on the electrocatalytic oxidation and evolution of hydrogen on platinum

The hydrogenation reaction of maleic acid, catalyzed by platinized platinum, was investigated in the presence and in the absence of gaseous hydrogen, and with/without an external control of platinum potential, in different acid supporting electrolytes. The intrinsic catalytic activity of platinum, used as a catalyst and as an electrode, was measured at different potentials. A promotion of the catalytic activity of platinum, induced by an external control of its potential, in the presence of gaseous hydrogen, was found only in a perchloric acid supporting electrolyte. No promotion effect was obtained in the presence of strongly adsorbed anions (HSO 4 −, Cl −). Moreover strongly adsorbed anions induce a decrease in the catalytic activity of platinum, whereas they do not affect the electrocatalytic activity of platinum catalyst-electrode. The observed anion effects on the hydrogenation of maleic acid were compared with those obtained in the electrocatalytic hydrogen oxidation (h.o.r.) and evolution (h.e.r.) reactions studied on a rotating disk platinum electrode. In electrocatalytic oxidation of hydrogen the current densities depend on the nature of the supporting electrolyte and decrease in the order, j(HClO 4)> j(H 2SO 4)> j(HCl). However, the hydrogen evolution reaction, studied in underpotential and in low overpotential regions, does not depend on the nature of the supporting electrolyte. The ensemble of results is discussed in connection with the nature of active hydrogen species and/or active platinum sites involved in these reactions.

Optimized indium tin oxide contact for organic light emitting diode applications

This work aimed to develop indium tin oxide (ITO) coatings with optimum optoelectronic properties required for applications in organic light emitting diode (OLED) devices on flexible thin glass substrates. This involved introducing hydrogen in gas mixture during ITO film preparation using radio frequency magnetron sputtering method. Uniform ITO films with resistivity of 2.7×10; −4 Ω cm and transparency of 85% over the visible wavelength region was achieved. The presence of hydrogen gas in the sputtering processes was shown to increase the number of charge carriers in the ITO films. The feasibility of using the ITO films with high carrier concentration was examined and tested in OLED devices composing a fluorene based polymeric hole transporting layer (HTL) and green-emitting polymer, benzothiadiadzole-fluorene. The devices made with different ITO substrates had an identical configuration of ITO/HTL/emitter polymer/Ca (6 nm)/Ag (200 nm). The device showed that a maximum luminance of 4.36×10 4 cd/m 2 and an efficiency of 4.14 cd/A were achieved when an optimal ITO layer was used. These results are comparable with that of devices made with the best commercially available ITO products operated at the same conditions.

Comparison of Superacid-Catalyzed Depolymerization and Thermal Depolymerization of Bituminous CoalCatalysis by Superacid HF/BF3 and Synthetic Pyrite

Depolymerization of bituminous coal by conventional thermal reaction, both with and without a synthetic pyrite catalyst, and a superacid-catalyzed reaction using a mixture of hydrogen fluoride and boron trifluoride were examined to study differences between radical and ionic reactions in coal depolymerization. All reactions took place under hydrogen without any solvent. Depolymerization of bituminous Miike coal was comparatively homogeneous following the superacid-catalyzed reaction with HF/BF3, but was heterogeneous following the thermal reaction using the synthetic pyrite catalyst. Because a reaction temperature of 440 °C was required to cleave the linkages between the coal molecules, the thermal reaction probably promoted dealkylation (removal of alkyl side chains) as well as simultaneously promoting negative reactions such as condensation. In contrast, the superacid-catalyzed reaction at 150 °C predominantly promoted coal depolymerization and did not cause significant dealkylation, providing a highly soluble product. The synthetic pyrite catalyst accelerated deoxygenation of coal, resulting in higher extractability than that following the thermal reaction without a catalyst although the synthetic pyrite catalyst does not have substantial hydrogenation catalytic activity in the presence of gaseous hydrogen.

Effect of ion irradiation on hydrogen gas sensitivity of polymer

In search of economical hydrogen gas sensor material, polymer blend with polyvinyl chloride (PVC) and polyester (PET) has been investigated as sensor material. The polymer blend were irradiated with 50 MeV Li 3+ ions at different fluences. The changes in conductivity of the ion irradiated blend in the presence of hydrogen gas were studied. The sensitivity, response time and recovery time were studied as a function of ion fluences on exposing the sensor material to the H 2 gas at ambient condition. Preliminary results observed are encouraging.

Temperature-induced reflectivity changes and activation of hydrogen sensitive optically thin palladium films on silicon oxide

The optical properties of several thin metal film palladium-silicon oxide structures are examined at room temperature before and after annealing to 200 °C and also at 90 °C—in all cases in the presence of hydrogen gas. Multicycling sample activation is shown to occur in the presence of hydrogen at room temperature with an increase in reflectivity on exposure to hydrogen, in contrast to thicker 80 Å films. The reflectivity change increases with increasing film thickness (1–10 Å). The surface activation at room temperature, before and after annealing to 200 °C, is compared with the performance at 90 °C, where it is shown that heat treatment strongly influences the behavior of the metal film.

IRAS study of π-bonded ethylene on a Pt(111) surface in the presence of gaseous ethylene and hydrogen

Adsorption of ethylene on Pt(111) in the presence of gaseous ethylene up to 1300 Pa was investigated using infrared reflection absorption spectroscopy (IRAS). Ethylene was reversibly adsorbed on bare Pt(111) at 1300 Pa and 150–180 K giving an IRAS peak at 954 cm −1 which was assigned to the out-of-plane bending mode of CH of the π-bonded ethylene. Adsorption of ethylene on Pt(111) covered by ethylidyne was next examined. It was found that ethylene was adsorbed on ethylidyne-covered Pt(111) in the presence of gaseous ethylene at 1300 Pa and 150 K but the adsorption was weaker than that on bare Pt(111). Adsorption of ethylene on bare Pt(111) from the mixture of ethylene and hydrogen ( 1 1 , v/v) was also investigated. In the presence of hydrogen gas, the adsorption of the π-bonded ethylene was also slightly inhibited.

A New Probe Reaction for Studying the Hydrogen Spillover Phenomenon

It was found by FTIR measurement that pyridine strongly adsorbed on acid sites of ZSM-5 was hydrogenated over Pt/H-ZSM-5 (0.5 wt%) and a Pt-hybrid catalyst (a physically mixed catalyst with a weight ratio of Pt/SiO2(2.5 wt%)/H-ZSM-5=1:4) to adsorbed piperidine in the presence of gaseous hydrogen at around 473 K, whereas no such phenomena were observed on either H-ZSM-5 or Pt/SiO2. The phenomenon revealed the occurrence of hydrogen spillover from Pt sites to zeolite acid sites (Brønsted and Lewis). A quantitative description of this reaction was attained by calculating and measuring the amount of zeolite acid on the basis of pyridine chemisorption and hydrogen consumption. In connection with this finding, the dehydrogenation of adsorbed piperidine in correlation with reverse hydrogen spillover was also observed on Pt/H-ZSM-5 catalyst in the temperature range from 623 to 723 K.

Visible photoluminescence from hydrogenated amorphous carbon films prepared by pulsed laser ablation of polymethyl methacrylate (PMMA)

Visible photoluminescence (PL) has been observed from the hydrogenated amorphous carbon (a-C:H) films prepared by ArF pulsed laser ablation of polymethyl methacrylate (PMMA) in the presence of hydrogen gas (H2). With increasing hydrogen concentration the PL intensity increases and the intensity maximum blue-shifted. The PL intensity also increases after hours of light illumination, exhibiting a light soaking enhancement. Increasing the deposition temperature decreases the PL and increases the ratio of sp3/sp2 bonds.

Hydrocracking and Hydroisomerization of Long-Chain Alkanes and Polyolefins over Metal-Promoted Anion-Modified Zirconium Oxides

A method of cracking a feedstock by contacting the feedstock with a metal-promoted anion-modified metal oxide catalyst in the presence of hydrogen gas. The metal oxide of the catalyst is one or more of ZrO2, HfO2, TiO2 and SnO2, and the feedstock is principally chains of at least 20 carbon atoms. The metal-promoted anion-modified metal oxide catalyst contains one or more of Pt, Ni, Pd, Rh, Ir, Ru, (Mn & Fe) or mixtures of them present between about 0.2% to about 15% by weight of the catalyst. The metal-promoted anion-modified metal oxide catalyst contains one or more of SO4, WO3, or mixtures of them present between about 0.5% to about 20% by weight of the catalyst.

Isomerization of alkylaromatic hydrocarbons on nickel-boron-alumina catalysts

The activity of alumina and silica-alumina modified with nickel and/or boron trifluoride etherate in the transformations of o-xylene and α-methylnaphthalene in the presence of gaseous hydrogen has been measured. Dependence between the yields of isomerization reaction and the concentration of Bronsted acid centers on the surface of the catalysts investigated was observed.

水素酸化脱窒細菌の比脱窒速度に及ぼす諸因子の検討

Autotrophic denitrification was studied using hydrogen gas as the hydrogen donor. It was confirmed that microorganisms which have the ability of autotrophic denitrification using hydrogen gas are distributed widely. It was concluded that Alcaligenes eutrophus (ATCC 17697), Paracoccus denitrificans (IFO 13301) and Pseudomonas pseudoflava (ATCC 33668) can reduce nitrate to nitrogen gas in the presence of hydrogen gas. The effect of pH value for autotrophic denitrification of these bacteria was not significant within the range of 7 to 8. The effect of temperature on the specific denitrification rate was also examined and the calculated Arrhenius constant was within the range of 44.1 to 63.2 kJ·mole-1. The specific denitrification rate of A. eutrophus and P. pseudoflava was above 1 mgN·mgSS-1·d-1 at 15 degree centigrade. The specific denitrification activity was constant above 10 kPa of partial pressure of hydrogen gas and the Michaelis-Menten half-velocity constant for hydrogen gas was found to be less than 3% of saturation.

Deposition and characterization of zinc oxide thin films for hydrogen sensor devices

Polycrystalline zinc oxide thin films with thicknesses in the range 0.3 μm-1 μm were deposited on silicon and alumina substrates by a spray chemical vapour deposition method. The film was characterized for crystallinity, resistivity and carrier concentration. A modified heterostructure Pd/ZnO(0.38 μm)/p-Si device was fabricated. The current-voltage characteristics of the device were studied both in the absence and in the presence of hydrogen gas.

Hydrogen in RF Reactive Magnetron Sputtered Silicon Nitride Films

ABSTRACTABSTRACT: Silicon nitride films (a-SixN1−x:H) have been prepared by rf reactive magnetron sputtering from a silicon target in a mixture gas of Ar, N2, and H2. The effects of the presence of hydrogen gas have been related to the refractive index, deposition rate, etch rate, and the Si-H and N-H bonding in the films. Hydrogen contents were measured by a quadrupole secondary ion mass spectrometer (SIMS) using deuterium implanted samples as reference standards. The deuterium implanted samples were annealed at 900°C for various periods of time to study the diffusion behavior of deuterium and hydrogen in a Si-rich and a nearly stoichiometric silicon nitride film.