Hydrogen-containing Species Research Articles

Abnormal Oxidation of Stabilized Ferritic Stainless Steels in Water Vapor

The influence of water vapor on the high temperature oxidation of several stabilized ferritic stainless steels with various Si and Cr contents has been studied by thermogravimetry at 900°C in pure water vapor or dry oxygen, followed by the characterization of the oxide scales formed. Oxidation of Fe-Cr steels in pure water vapor was characterized by a non-protective breakaway oxidation due to the formation of iron oxide nodules on the sample surface. Decreasing the H 2 O partial pressure or increasing the Si or Cr content enhanced the oxidation resistance of the alloy by delaying the breakaway appearance. This abnormal oxidation is thought to be initiated by the arrival of oxygen- and hydrogen-containing species on the chromium depleted metal/oxide interface. The mechanism of the effect of water vapor is discussed and some assumptions proposed.

Formation and characterization of neutral krypton and xenon hydrides in low-temperature matrices

A family of rare-gas-containing hydrides HXY (where X=Kr or Xe, and Y is an electronegative fragment) is described. These molecules are experimentally prepared in low-temperature matrices by photodissociation of a hydrogen-containing HY precursor and thermal mobilization of the photodetached hydrogen atoms. The neutral HXY molecules are formed in a concerted reaction H+Y→HXY. Experimental evidence for the formation of these species is essentially based on strong infrared absorption bands that appear after annealing of the photolyzed matrices and are assigned to the H-X stretch of the HXY molecules. Computationally, the formation of these HXY molecules decreases the H-X distance by a factor of ⩾2 from its van der Waals value, which emphasizes their true chemical bonding, possessing both covalent and ionic contributions. The estimated dissociation energies vary from 0.4 to 1.4 eV and hold promise for forthcoming observation of these molecules in the gas phase. The experiments with the HXY molecules widen our knowledge on solid-state photolysis dynamics of hydrogen-containing species. In particular, the photolysis of small HY hydrides in solid Xe seems to be a quite local process, and the accompanying losses of H atoms play a minor role.

Role of prior cathodic polarization in the pitting corrosion of pure aluminium in acidic chloride solution

Role of prior cathodic polarization in the pitting corrosion of pure aluminium (Al) has been investigated in aqueous 1 M HCl solution (pH 0) using a potentiostatic current transient technique combined with an electrochemical quartz crystal microbalance technique, impedance spectroscopy and scanning electron microscopy (SEM). From the analysis of the first period of combined cathodic current transient and electrogravimetric curves, it is suggested that the hydrogen evolution current starts obeying the Tafel relation via proton absorption, formation of such hydrogen-containing species as OH − ions and/or H 2 O molecules within the native oxide film and proton reduction at the metal/oxide interface. During the second period appearing at potentials −1.5 and −1.7 V SCE (SCE, saturated calomel electrode) hydrogen evolution may occur at an enhanced rate at the bottom of micro-pits, formed due to local breakdown of the oxide film. This breakdown was ensured by the more abrupt decrease in oxide film resistivity ρ ox values with increasing prior cathodic polarization, calculated at −1.5 and −1.7 V SCE , from the analysis of the measured impedance spectra as compared to that reduction in ρ ox calculated at −1.0 V SCE . The surface area of the pitted specimens was quantitatively estimated from the measured capacitance values to increase with rising prior cathodic polarization, as evidenced by SEM. This means that the exposed metal surface at the bottom of micro-pits formed during prior cathodic polarization serves as a preferential site for Cl − ion attack during the following anodic polarization. Hence, a sufficient prior cathodic polarization for the formation of the micro-pits is a necessary condition for the promotion of pitting corrosion of pure Al.

Operational experience with the JET Impurity Processing system during and after DTE1

The hydrogen-containing gases generated during operation and maintenance of a fusion machine need to be detritiated prior their discharge to the environment. The amounts of gaseous impurities with their chemical and isotopic compositions which were decontaminated in the JET impurity processing system during and after Deuterium–Tritium Experiment, DTE1, are presented. Two different techniques for impurities detritiation were tested. The first technique is based on catalytic oxidation of hydrogen-containing species followed by water decomposition in reaction with uranium at elevated temperature. The second technique is based on direct decomposition of impurities with molecular hydrogen liberation in reactions with uranium at elevated temperatures. The results of the impurity detritiation using both techniques are given.

On self-limitation of UV photolysis in rare-gas solids and some of its consequences for matrix studies

UV photolysis of small molecules embedded in rare-gas matrices is examined. We demonstrate that photolysis can be self-limited when products absorb the photolysing radiation. As a result of the rising absorption, in-situ detected luminescence of the photolysis product saturates faster than its concentration. In particular, the present study supports the conclusion that 193 nm photolysis of hydrogen-containing species in Xe matrices produces hydrogen atoms in amounts comparable with the other dissociating part of the precursor. Also, we show that 193 nm radiation activates mobility of hydrogen atoms in annealing, accelerating photochemical processes related to hydrogen mobility.

Effects of low-energy electron irradiation on submonolayer ammonia adsorbed on Pt(111)

The effects of electron impact on ammonia-covered Pt(111) have been studied using temperature-programmed desorption (TPD) and electron-stimulated desorption (ESD). For coverages below one monolayer, ammonia adsorbs on the surface in two distinct TPD states: the α-state is broad and desorbs over the temperature range 150–350 K, and the β-state appears as a sharper peak at 150 K. The β-state was seen to be damaged by electron-beam impact much more readily than the α-state, resulting in the formation of atomically adsorbed N on the surface. The mass 28 recombinative nitrogen desorption TPD peak appearing at 550 K exhibited second-order desorption kinetics, further confirming the presence of atomically adsorbed nitrogen. The ESD kinetic energy distributions (KEDs) were obtained for m/e=1 amu, which exhibited broad peaks generally. The H+ KEDs were analyzed using empirical curve fits, with the resulting conclusion that the H+ KEDs contain contributions from at least three different hydrogen-containing surface species. We believe that these three H+ KED peaks are due to ESD from adsorbed NH3, NH2 and H. The ESD cross-section for NH3 removal was measured in three different ways, all of which were found to be in general agreement, and which gave an averaged cross-section value of Qtot=4×10−17 cm2. © 1998 John Wiley & Sons, Ltd.

Effects of low‐energy electron irradiation on submonolayer ammonia adsorbed on Pt(111)

The effects of electron impact on ammonia-covered Pt(111) have been studied using temperature-programmed desorption (TPD) and electron-stimulated desorption (ESD). For coverages below one monolayer, ammonia adsorbs on the surface in two distinct TPD states: the α-state is broad and desorbs over the temperature range 150–350 K, and the β-state appears as a sharper peak at 150 K. The β-state was seen to be damaged by electron-beam impact much more readily than the α-state, resulting in the formation of atomically adsorbed N on the surface. The mass 28 recombinative nitrogen desorption TPD peak appearing at 550 K exhibited second-order desorption kinetics, further confirming the presence of atomically adsorbed nitrogen. The ESD kinetic energy distributions (KEDs) were obtained for m/e=1 amu, which exhibited broad peaks generally. The H+ KEDs were analyzed using empirical curve fits, with the resulting conclusion that the H+ KEDs contain contributions from at least three different hydrogen-containing surface species. We believe that these three H+ KED peaks are due to ESD from adsorbed NH3, NH2 and H. The ESD cross-section for NH3 removal was measured in three different ways, all of which were found to be in general agreement, and which gave an averaged cross-section value of Qtot=4×10−17 cm2. © 1998 John Wiley & Sons, Ltd.

Burning velocities of CO flames

Asymptotic and computational methods are employed to investigate premixed laminar burning velocities of planar adiabatic flames in ideal gas mixtures containing carbon monoxide, oxygen, an inert, and trace amounts of hydrogen-containing species. The chemical-kinetic steps that control the burning velocity are identified, and the dependence of the burning velocity on composition, pressure, and temperature is determined. A lower limit to the burning velocity that is greater than 5 mm/s, independent of pressure, is established for totally dry stoichiometric mixtures at 300 K. The results contribute to understanding of CO flame structure.

Should the standard basis sets be augmented with diffuse functions on hydrogens to provide a reasonable description of the lowest Rydberg state of hydrogen-containing molecules?

Augmentation of the standard basis sets with the diffuse functions, which were optimized for non-Rydberg anions on the heavy atoms only, may not be adequate for calculating Rydberg states of molecules. Addition of diffuse functions on the hydrogens to such a basis set used for calculations of Rydberg states of hydrogen-containing species can make up for this deficiency and lead to a reasonable description. This gives the possibility of using the standard basis sets (e.g., the 6-31G(d,p) and 6-311G(d,p) basis sets) augmented by diffuse functions, both on the heavy atoms and on the hydrogen atoms, for these calculations and, therefore, provides an alternative to optimizing diffuse functions specifically to describe Rydberg orbitals. Inclusion of diffuse s functions on hydrogens is less important in calculations of non-Rydberg hydrogen-containing anions.

Analytical approximations for structures of wet CO flames with one-step reduced chemistry

Since hydrogen-containing species catalyze CO oxidation, at small H/C and H/O ratios steady-state approximations for reaction intermediaries should be accurate and should produce a good one-step reduced-chemistry approximation for describing the flame structure. Such an approximation is complicated, however, because of the many elementary kinetic steps involved. In the present work simplifications are introduced into a one-step approximation that enable analytical expressions to be obtained for the burning velocities of premixed laminar flames by asymptotic methods. The resulting burning velocities are shown to be in good agreement with experiment and with detailed numerical predictions, and qualitative aspects of the internal flame structure are shown to agree with those deduced from full-chemistry numerical calculations. Estimates are given of the ranges of conditions over which the approximations can reasonably be employed and of flammability limits controlled by chemical kinetics.

Rotational excitations of partially deuterated ammonia NH3− nDn in argon matrices

The rotational dynamics of NH 3, NH 2D and NHD 2 molecules isolated in Ar matrices at a concentration of 1.1% are investigated by high-resolution inelastic neutron spectroscopy at a temperature of 5 K. The one-dimensional almost-free rotor lines of hydrogen-containing species are observed in the high-resolution spectra. The transition energies of the respective lines scale with the rotational constants around the molecular symmetry axis. However, the intensities do not correspond to a binomial distribution of the various partially deuterated species for reasons so far unknown. One-dimensional almost-free rotation has been observed previously in 1.1% concentrations of NH 3 in Ar and microscopically related to substitutional dimeric sites. This interpretation is now confirmed using partially deuterated ammonia NH 2D and NHD 2.

Neutron thermodiffractometry and synchrotron energy-dispersive diffraction studies of zirconium hydroxide calcination

Neutron [l-31 and X-ray [4,5] techniques have been used to study the formation of zirconia from zirconium hydroxide. Synchrotron radiation can now, using dynamic energy-dispersive diffraction (DEDD), shed light on the kinetics of both the hydroxide-to-oxide crystallization and tetragonal-to- monoclinic conversion. Furthermore, different rates of crystallization and conversion have been linked [5] to the preparative conditions of the hydroxide; in particular the final pH of the solution coexisting with the precipitate of zirconium hydroxide. The results here represent an important extension of our dynamic studies. The special advantage of neutron thermodiffractometr!~ (NTD) [6] is that the high scattering/diffraction background associated with incoherent scattering by hydrogen is an effec- tive monitor of the chemical composition of the hydroxide; the scattering background reflects the amount of hydrogen-containing species in the sam- ple. Zirconium hydroxide can be considered as an intermediate between a hydroxide and a hydrated oxide [7]. One possible model [H] depicts the hydroxide as an open polymer in which individual units are linked by double h!.droxy bridges (Fig. 1). Clearly, if such a model were essentially correct, NTD would be expected to monitor the combined loss of H,O and OH during calcination. Zirconium hydroxides were prepared under care- fully controlled conditions [9] at pH 8.37 and 10.35, since these preparations display extremes of crystal- lization behaviour [5]. Aqueous ammonia solution was added to an aqueous suspension of zirconium basic sulphate (Magnesium Elektron Ltd, Man- chester, UK) to the desired pH. the suspension was filtered and washed with distilled water. The sam- ples were dried at 130 "C to produce zirconium hydroxide. Thermal analysis was carried out in both samples at a heating rate of 2 "C min-' in static air. Synchro- tron experiments were undertaken at Daresbury Laboratory, station 9.7, using pellets of thickness approximately 0.5 mm. The pellets were heated at a rate of 20 "C min-' to 400 "C, and the ramp then reduced to 5

Electrical characteristics and hydrogen concentration of chemical vapor deposited silicon dioxide films: Effect of water treatment

The effect of exposing chemical vapor deposited silicon dioxide directly to water has been investigated. Unlike the effect of the water-related traps in thermally grown silicon dioxide, the capacitance-voltage (C-V) shift due to diffused-in water molecules is directly observed without using the method of avalanche injection. The resonate nuclear reaction technique with 15N ion beam has been used to measure the hydrogen concentration of water-boiled, as-deposited, and rapid thermal-annealed silicon dioxide films. These depth profiles show that the hydrogen-containing species, that are most likely water molecules, diffuse in and out and redistribute in the as-deposited and rapid thermal-annealed films. These hydrogen depth profiles also indicate that the amount of diffused-in water molecules in the oxide is limited by the solubility of the water in the oxide. The solubility of water in the oxide annealed at high temperatures is found to be significantly lower than that in the as-deposited oxide. It is found that diffused-in water molecules, in order to satisfy the water solubility of the oxide, play a compensating role in controlling the oxide charges. Water molecules would continue to diffuse in, and interact with oxide charges and produce charges with reverse polarity that compensate the existing oxide charges until water solubility is satisfied.

Nitrogen containing species as intermediates in the oxidation of ammonia over silica supported molybdena catalysts

The behaviour of ammonia and oxygen over silica supported molybdena catalysts has been studied by means of thermal analysis techniques, such as thermo-gravimetry and heat-flow calorimetry. The composition of the reactants and products was determined by means of mass spectrometric analysis. Nitrogen- and hydrogen-containing species were observed to be present on the catalyst surface after reduction of the catalysts by ammonia and subsequent flushing in helium. Additional evidence for the presence of these species was provided by experiments in which labelled molecules were used as well as by means of X-ray photo-electron spectroscopy. The nitrogen- and hydrogen-containing species could be removed from the surface by O 2. or NO. The reaction products were found to be N 2 and H 2O. In the light of these results, a working model is proposed that describes the adsorption of ammonia on; and the oxidative production of nitrogen and water from ammonia over, silica-supported molybdena catalysts.

The effect of deposition conditions on carbon films prepared by laser ablation

Hydrogen-free diamond-like carbon films (DLCF) were deposited by excimer pulsed laser ablation of graphite at q ≈ 1GW/cm 2 in high-vacuum conditions with a deposition rate of several μm/h. The plasma formation in the vapors is essential for DLCF formation. Films with n = 2.6, k = 0.1 and E g = 1.4eV were deposited at room temperature. Surface coverage by hydrogen-containing species results in a strong influence of the surface temperature T on hydrogen incorporation and, finally, on the properties of the DLC films deposited by laser ablation in moderate vacuum conditions.

Development of a gas chromatographic system for hydrogen isotope separation

Abstract Ontario Hydro Research Division has carried out an experimental program co-funded by Canadian Fusion Fuels Technology Project to develop the gas chromatographic technique to separate hydrogen isotopes. Two novel GC techniques were optimized or developed in the pilot system, namely, the heart-cutting technique for removing the hydrogen-containing species from a fusion fuel and the temperature programming technique for separating all six hydrogen isotope species. The experimental results showed that these techniques improved not only the separation but also the throughput significantly for these applications and will be discussed in detail in the paper.

Structures of wet CO flames with full and reduced kinetic mechanisms

Flame structures and deflagration velocities are calculated for CO-O 2 -N 2 mixtures containing H 2 and H 2 O with small H/C ratio, initially at 300 K and 1 atm. The calculations are completed with full chemical kinetics and with reduced mechanisms that retain fewer steps. Calculated burning velocities are in good agreement with experiment. The studies of reduced mechanisms reveal various aspects of the chemical-kinetic processes. Above a crossover temperature of about 1000 K, at which the rates of H+O 2 →OH+O and H+O 2 +M→HO 2 +M are equal, the O-atom and all hydrogen-containing species achieve steady states, so that a one-step approximation is obtained, from which burning velocities can be calculated more simply.

Concentration profiles of hydrogen in technical oxidic thin films and multilayer systems

The hydrogen concentration, C(H), of oxidic thin films (SiO2, WO3, Ta2O5, TiO2, ITO) produced by reactive evaporation has been determined by means of nuclear reaction analysis. For comparison Ta2O5 layers deposited by reactive ion plating were investigated. The results show differences in the time-dependent behaviour of the H uptake for various single film materials and layer combinations. For single layers the kinetics for the hydrogen absorption is as follows: WO3 > Ta2O5 > SiO2 > ITO. An appreciable amount of hydrogen-containing species is found only in the layers created by evaporation.

Inert pyrolysis of stoker-coal fines

This study provided information on the relative stability of nitrogen-, sulphur-, carbon- and hydrogen-containing species retained in the char during pyrolysis of the stoker fines. The presence of these principal constituents was determined by elemental analyses on the remaining char; this allowed a simple (but effective) means of correlating the loss of sulphur and nitrogen species against a variety of pyrolysis conditions. Inert pyrolysis experiments were performed in a CF-IR Lindberg tube furnace. Furnace temperatures studied ranged from 700 °C to 1300 °C while the residence time ranged from 1 to 40 minutes. The coal fines from typical stoker-sized coal included three size ranges (i.e. d < 0.16, 0.16 < d < 0.28 and 0.28 < d < 0.40 cm). The experimental results indicated the relative stability of the carbon species. Carbon evolution was least affected by an increase in temperature and relatively insensitive to changes in coal rank, although the highest-rank coal evolved the least carbon and the lignite coal evolved the most. Hydrogen evolution was also relatively insensitive to coal rank; however, the extent of evolution was large under all conditions tested and increased significantly with increasing temperature. Carbon evolution clearly approached a fixed, asymptotic value with increasing time and temperature, but hydrogen evolution was almost complete at 1100 °C. Nitrogen and sulphur both exhibited behaviour generally intermediate to that observed for carbon and hydrogen. Sulphur evolution consistently exceeded that of carbon but the dependence on temperature was essentially identical for both species. In contrast, nitrogen evolution at 700 °C was almost identical to that of carbon and relatively insensitive to coal rank. However, nitrogen evolution exhibited a stronger temperature dependence and at 1100 °C it far exceeded the evolution of the carbon species. Particle size was shown to have little influence on the evolution of the various species over the range tested in this study; therefore, the conclusions are relevant to stoker-coal fines in general.

Correlation between electron trap density and hydrogen concentration in ultrathin rapidly reoxidized nitrided oxides

Ultrathin nitrided oxides (8 nm) were reoxidized for the first time by lamp-heated rapid thermal annealing in dry oxygen at 900–1150 °C for 15–200 s. Extensive measurements of hydrogen concentration [H] using secondary ion mass spectroscopy were performed. Electron trapping was monitored by flatband voltage shift ΔVfb under high-field stress. Both [H] and the ΔVfb decrease monotonically as reoxidation proceeds in the present experimental conditions. We have found for the first time that the ΔVfb is correlated with the [H] by a single proportional relation regardless of the fabrication condition. This fact gives evidence that the electron traps in the (reoxidized) nitrided-oxide system originate from hydrogen-containing species.