Influence Of Hydrogen Partial Pressure Research Articles

SIMS studies of hydrogen interaction with the TiFe alloy surface: hydrogen influence on secondary ion yields

Secondary ion mass spectrometry is a powerful analytical tool that offers great capabilities for studying hydrogen interaction with metallic materials. Yet its utilization for the in situ studies of hydrogen interaction with a sample has not been well established. In this research we study the influence of hydrogen partial pressure (5 × 10−9 – 5 × 10−5 Torr) in the sample chamber, the sample temperature (305–900K), and primary ion current density on the emission intensity of various secondary ions for the hydrogen-storage TiFe alloy sample bombarded with 12 or 20 keV Ar+ primary ions. Presence of chemisorbed hydrogen on the alloy surface results in the presence of a variety of positive and negative hydrogen-containing secondary ions in mass spectra. Analysis of the influence of the varied experimental parameters has shown that the secondary ion yield changes reflect only changes of hydrogen concentration regardless of which varied parameter induced a concentration change. The yield dependences on concentration in general are different for different ions and tend to be more substantial for the ions containing a larger number of hydrogen atoms. The ions containing one hydrogen atom have similar and likely linear yield dependences when the concentration is low. At higher concentrations, the yield dependences for these ions diverge: their relation to concentration is discussed. For not hydrogen-containing secondary ions, hydrogen saturation of the surface resulted in an 80-400% increase of the yields of Ti+ and Ti-containing positive secondary ions, no yield change for other positive ions, and 2–3-times decrease of yields of negative ions. As for hydrogen interaction processes with the alloy surface, the obtained dependence of the ion yields only on hydrogen concentration indicates that the alloy surface is rather homogeneous i.e. without large parts that have different characteristics of interaction with hydrogen and different ratios of secondary ion yields. The results of the sample temperature influence indicate that the chemisorption probability of hydrogen molecules is temperature independent at least in the ∼300-500 K range. The substantial decrease in concentration at temperatures above 450 K is a result of associative desorption of hydrogen, although a possible contribution of other processes is not excluded by the presented results.

Thermogravimetric Investigations of Modified Iron Ore Pellets for Hydrogen Storage and Purification: The First Charge and Discharge Cycle

The reaction of iron with steam produces pure hydrogen, which can be directly used in polymer electrolyte fuel cells for power generation. Therefore iron, in its elemental form, can be used as a hydrogen storage and purification material. Besides thermodynamic properties, the hydrogen reception and release rate of the process are of special interest. To determine the reaction characteristics of iron contact mass for the first charging and discharging cycle, thermogravimetric analysis was used in the temperature range of 500−1000 °C. The influences of contact mass composition, reaction temperature, and gas composition on the redox reactions were determined. Contact masses with highly alkaline composition show faster reaction with steam at elevated temperatures. Acidic sample compositions accelerate the reduction with hydrogen at lower temperatures. The influence of hydrogen partial pressure and the suitability of methane, carbon monoxide, and synthesis gas for the contact mass reduction have been investiga...

Investigation of Hydrogen Cross-leak Behaviors in a Polymer Electrolyte Membrane by Direct Gas Mass Spectroscopy and Magnetic Resonance Imaging

Hydrogen permeability of polymer electrolyte membranes is of great importance since hydrogen cross-leak plays a major role in degradation of the membrane and/or catalyst layers in polymer electrolyte membrane fuel cells (PEMFCs). In this study, the hydrogen cross-leak mechanism was investigated using direct gas mass spectroscopy (DGMS) to monitor hydrogen in the cathode exhaust and magnetic resonance imaging (MRI) technique to monitor membrane water content. The DGMS measurement revealed that hydrogen permeability increased with humidity, temperature and hydrogen partial pressure in the anode. MRI visualization verified that hydrogen permeability was strongly affected by membrane hydration. Influence of hydrogen partial pressure was a key factor influencing permeation rates over a wide range of relative humidity. Reduced hydrogen permeation was observed under fuel cell operating conditions presumably due to hydrogen consumption in the anode. These observations suggest that dissolution and diffusion of hydrogen in the membrane play an important roll in hydrogen cross-leak in the PEMFC.

Influence of hydrogen partial pressure on growth and properties of nanocrystalline SiC by magnetron sputtering

Hydrogenated nanocrystalline silicon carbide (nc-SiC:H) thin films were prepared by reactive magnetron sputtering. Deposition was achieved in a plasma of argon (Ar) and an hydrogen (H 2 ) gas mixture with various H 2 dilution percentages (10–80% H 2 ) at a fixed substrate temperature of 500 °C. In order to describe the local bonding and the relative proportion of the different complexes formed during growth, the films were investigated by means of Fourier Transform Infrared absorption and Raman spectroscopy. Other structural features were analyzed by AFM measurements, electron diffraction and high resolution transmission electron microscopy observations. Optical and electrical properties of the films were also characterized. This study shows that hydrogen dilution plays an important role on the microstructure of the films as well as on their properties. The highest refractive index was obtained for a 60% ratio of hydrogen in the plasma and the highest dark conductivity found was 2.03 × 10 −4 Ω −1 cm −1 . A close relationship between the Si-H bond content and the conductivity is confirmed.

Oxidation kinetics of ZrNbO in steam: Differences between the pre- and post-transition stages

The oxidation by water vapour of a zirconium based alloy, a ZrNbO alloy containing 1% of Nb, has been studied between 500 and 550 °C, the water vapour partial pressure ranging in 13–80 h Pa, using isothermal and isobaric thermogravimetry, and calorimetry. During gravimetry experiments, sudden changes (jumps) in temperature or water vapour pressure have also been performed. It comes out that the kinetic behaviour is different before and after the transition, even though the approximations of steady-state and rate-limiting step are justified in both stages: the influence of temperature jumps is greater in pre-transition, whereas the effect of water vapour partial pressure is more pronounced in post-transition (nevertheless, an accelerating effect is also observed before the transition). No influence of hydrogen partial pressure has been observed. Besides, the higher the Nb content in the alloy, the higher the oxidation rate (in pre-transition). A mechanism has been proposed to account for the results obtained in pre-transition, involving the diffusion of adsorbed species in the porous part of the oxide layer as rate-determining step. The transition is accompanied by a change in the oxidation mechanism: in the post-transition stage, the kinetic curves being linear, the oxidation may be controlled by an interface step, which is probably different from the steps proposed for the pre-transition mechanism.

Influence of hydrogen partial pressure on hydrodenitrogenation of pyridine, aniline and quinoline

Influence of hydrogen partial pressure on hydrodenitrogenation (HDN) of pyridine, aniline and quinoline was examined over Ni–Mo–P/alumina catalyst. Pyridine, aniline and quinoline are representative nitrogen compounds found in coal-derived liquids. HDN of aniline was more enhanced by increasing hydrogen partial pressure than HDN of pyridine. The greater the adsorption strength of nitrogen compounds onto catalyst surface, the lesser is the effect of partial pressure of hydrogen. When the hydrogen partial pressure increased, quinoline HDN improved further with hydrogen sulfide than without hydrogen sulfide. The differences in the influence of hydrogen partial pressure on the quinoline HDN reactions were also interpreted in terms of the differences in the adsorption strengths of nitrogen compounds produced in HDN reactions onto catalysts.

Chemistry and kinetics of chemical vapor deposition of pyrocarbon — IV pyrocarbon deposition from methane in the low temperature regime

Pyrocarbon deposition from methane was studied at ambient pressure and 1100 °C using a vertical hot-wall deposition reactor; the methane initial partial pressure was varied up to 75 kPa and the residence time up to 1 second. The influence of hydrogen partial pressure was studied at constant methane partial pressure. Steady-state pyrocarbon deposition rates and corresponding compositions of the gas-phase were determined. Reaction models of homogeneous gas-phase and heterogeneous pyrocarbon deposition reactions were derived and used for simulation of pyrocarbon deposition kinetics influenced by residence time, initial partial pressures of methane and hydrogen, and concentrations of active sites. The importance of active sites and their blocking by hydrogen is discussed with special emphasis.

Iron-doped semi-insulating InP grown by chloride VPE with nitrogen mixed with hydrogen as carrier gas

Iron-doped semi-insulating InP has been grown by chloride vapour-phase epitaxy (VPE) using nitrogen mixed with hydrogen as carrier. Reducing hydrogen partial pressure by the introduction of nitrogen greatly improves the transport of FeCl2. The influence of hydrogen partial pressure on the Fe transport, and therefore on the Fe incorporation, has been studied theoretically and experimentally. With a relatively slow growth rate, InP film with a high Fe concentration is easily obtained. Quantum-well laser diodes with semi-insulating InP(Fe) stripe-confinement have been fabricated successfully.

Influence of Hydrogen Partial Pressure on Hydrodenitrogenation of Coal-derived Liquid.

The influence of hydrogen partial pressure on hydrodenitrogenation (HDN) of nitrogen compounds, found in the coal-derived naphtha fraction, was examined using a continuous flow reactor. The HDN reaction of coal-derived naphtha was not enhanced by increasing the hydrogen partial pressure from 2.4 to 5.3 MPa. The influence of hydrogen partial pressure on HDN of pyridine, pyrrole, and aniline was also investigated. Although HDN of pyridine was not improved by increasing hydrogen partial pressure, HDN of aniline was improved. The HDN rate of pyridine was constant during the experiment, however, the HDN rate of aniline gradually decreased with increasing space time. Properties of pyrrole HDN were somewhat between those of pyridine and aniline. The difference in the HDN properties was interpreted in terms of the difference in the adsorption strengths of nitrogen compounds on the catalyst surface.

Fixed-bed pyrolysis of coal under hydrogen pressure at low heating rates

Fixed-bed hydropyrolysis has been investigated by treating 100 g coal up to 900°C and 10 MPa. The devolatilization rate of Beringen coal (32.8 wt% volatile matter) treated on a fixed bed approximates to that obtained by flash hydropyrolysis. However, the oil yield is smaller because of the slower heating of the coal and the rather longer residence time of the primary volatile matter in the reaction space. The product gas is mainly methane. The oil composition depends on the temperature of pyrolysis. The benzene content of the oil rises with temperature. At constant temperature, the influence of hydrogen partial pressure is important between 0–1 MPa. At higher pressure, the yields and compositions vary only slightly with pressure. It has also been shown that from 580°C pyrolysis under hydrogen yields an additional quantity of water, when compared with pyrolysis under inert atmospheres or under atmospheric pressure. This additional water comes from the hydrogenation reactions of the hydroxyl functions of heavy phenols and xylenols. This implies a hydrogen consumption (from 0.2–0.3 wt% of the coal), varying with the pyrolysis temperature.

Investigations of the Kinetics of Hydrogen and Oxygen Reactions on a Platinum Electrode in Acid Solution Using Pulse and Decay Techniques

The influence of hydrogen partial pressure, current density, and temperature on the anodic oxidation of sorbed H and the anodic generation of sorbed O were determined. Electrode processes were evaluated and separated to give the following quantities: (a) the amount of H associated with a Pt surface and its immediate vicinity, (b) the extent of reaction of H atoms, absorbed in the metal interior, that migrate to the surface of the metal and are either ionized or react with O atoms, (c) the extent of reaction of H2 from the solution phase, (d) the amount of O adsorbed on the Pt surface, and (e) the amount of O absorbed in the Pt surface layers (skin).The kinetics of the open‐circuit reaction of galvanostatically determined amounts of sorbed O with H2 were determined. This investigation showed that absorbed O in Pt significantly affects coulometric measurements at pulse lengths longer than about 1000 µsec. The presence of absorbed O in the Pt can also materially affect the reaction rate of chemisorbed O with H2. Under the experimental conditions, transport of reactants on the solution side was fast enough so that diffusion did not limit processes in either the H ionization or O sorption regions. The data indicated that migration of adsorbed species on the Pt surface to active sites was rate controlling in the O sorption region, except in the case of reaction of adsorbed O with H2 when significant amounts of O were absorbed in the skin of the Pt. In this case the chemical reaction rate between adsorbed O and H2 was retarded so that this chemical step appeared to be rate determining. Reaction rates of the adsorbed O and H2 reaction under open‐circuit conditions were determined at varying temperatures, adsorbed and absorbed O concentrations, and H2 partial pressures.