Accumulation Of Molecular Hydrogen Research Articles

Abiotic Synthesis of Methane and Organic Compounds in Earth’s Lithosphere

Accumulation of molecular hydrogen in geologic systems can create conditions energetically favorable to transform inorganic carbon into methane and other organic compounds. Although hydrocarbons with a potentially abiotic origin have been proposed to form in a number of crustal settings, the ubiquitous presence of organic compounds derived from biological organic matter presents a challenge for unambiguously identifying abiotic organic molecules. In recent years, extensive analysis of methane and other organics in diverse geologic fluids, combined with novel isotope analyses and laboratory simulations, have, however, yielded insights into the distribution of specific abiotic organic molecules in Earth’s lithosphere and the likely conditions and pathways under which they form.

Radiation-heterogeneous processes in stainless steel in contact with seawater

The kinetics of accumulation of molecular hydrogen during γ radiolysis of seawater is studied. The effect of γ radiation on stainless steel (SS)-seawater (SW) systems at T = 300–773 K is investigated. The molecular hydrogen accumulation rates during radiation, thermal-radiation, and thermal processes in the SS-SW system are determined. The contributions of thermal and radiation-heterogeneous processes during accumulation of molecular hydrogen and corrosion of stainless steel in contact with seawater are revealed.

Oxidation and accumulation of molecular hydrogen in a beryllium-water system upon radiation thermal treatment

The kinetics of radiation thermal oxidation of beryllium with water vapor and the accumulation of molecular hydrogen in a Be-H2O system at temperatures of 473–673 K under the effect of gamma radiation is studied. The oxidation is shown to proceed according to a parabolic law and be limited by diffusion. A sharp change (by a factor of 16) in the formation rate of molecular hydrogen and an increase in its concentration by an exponent depending on the oxidation degree and defectiveness of beryllium plates is observed and confirmed by AFM images. The activation energies of the formation of hydrogen are estimated as E a = 12 and 34 kJ/mol.

Effect of inert gas flow on hydrogen underpotential deposition measurements in polymer electrolyte fuel cells

The effect of inert gas flow rate on hydrogen underpotential deposition ( H upd) measurements in polymer electrolyte fuel cells (PEFCs) was investigated using a novel experimental technique. The method combines local voltammetric measurements in PEFCs with the use of sectioned electrodes. The results give experimental proof that the high inert gas flow rate usually employed in voltammetric measurements in PEFCs at the working electrode results in high hydrogen reduction currents in both the cathodic and the anodic sweep, which hampers an accurate determination of the electrochemically active surface area (ECA). Strong spatial inhomogeneities occur at low potentials as a consequence of formation and accumulation of molecular hydrogen along the flow field. The results show that the flow of inert gas should be minimized or even stopped during a measurement to allow molecular hydrogen to accumulate at the working electrode and to provide uniform conditions along the flow field.

Oxidation and Accumulation of H2 in the Aluminum-Water System Under the Radiation-Thermal Action

Using the method of reflection-absorption infrared spectroscopy (RAS), the laws of thermal, radiation-thermal, and radiation transformations of water on an aluminum surface have been investigated. It has been found that water radiolysis in the Al-adsorbed water heterosystem is followed by the formation of surface hydroxides and hydrides and molecular hydrogen, as well as by the formation of an oxide film on the Al surface. The kinetics of aluminum oxidation by water and accumulation of molecular hydrogen (H2) under the action of γ-radiation at temperatures of 300–900 K has been investigated. It has been shown that as the temperature of the aluminum-water contact is increased to T ≤ 873 K, there is an increase in the rates of the surface processes of oxidation and accumulation of H2. On the basis of the results obtained, mechanisms of the processes are proposed.

Hydrogen pressure build-up in blowholes at pickling of interstitial free steel

During continuous casting of Interstitial Free steel occasionally argon bubbles are entrapped in the solidifying shell. Some of these bubbles can be found in the final cold rolled sheet as elongated blisters, so-called blowholes. During processing, the steel is exposed to atomic hydrogen at the pickling process. Exposure to atomic hydrogen can lead to accumulation of molecular hydrogen in the blowholes, making them more apparent. This process is examined in this paper. The hydrogen diffusion behaviour is studied by a permeation technique, accumulation is modelled and the deformation process is studied by loading a blowhole with hydrogen electrochemically. The results and implications for pickling lines are discussed.

Model for Hydrogen Retention, Reemission and H/He Exchange in Beryllium under Ion Irradiation*

In the model two states for accumulated hydrogen (soluble and molecular) are suggested. Under ion irradiation three reactions (events) take place: recombination of soluble hydrogen on irradiated surface; accumulation of molecular hydrogen; molecular percolation. The first reaction describes recombination under and after irradiation. The second reaction describes molecular hydrogen accumulation as statistical packing of the “traps”. The third one describes molecular percolation as a capturing of one more incoming particle in already packed “trap”, that is accompanied by the reemission of H2, by the devastation of the “trap”, and by the increasing of the irradiated surface. Under steady state for molecular accumulation and surface formation, recombination flux approaches the value of incoming flux and no percolation acts take place. Molecular accumulation approaches the steady state prompter than surface formation. The cross sections for (helium/hydrogen) emission changing over hydrogen to helium beam and vice versa were calculated. Simulation of the model coincides with the experimental data of hydrogen retention, reemission, and post-implanted release.

Organic syntheses from CH4-N2 atmospheres: implications for Titan.

Numerous experiments have already been performed, simulating the evolution of gaseous mixtures containing CH4 when submitted to energy flux. From their results, it appears that a variety of organic compounds, including unsaturated hydrocarbons and nitriles such as HCN, can be synthesized into noticeable amounts from CH4-N2 mixtures. In particular, systematic studies of the influence of the composition of the mixture on the nature and amount of synthesized compounds show that organic volatile nitriles, and particularly cyanoacetylene and cyanogen, are formed only in media rich in nitrogen. Those nitriles have been identified very recently in the atmosphere of Titan, and thus, data from such laboratory experiments may provide important indirect information on the organic chemistry occurring at the periphery of this satellite of Saturn. However, during these experiments, there is a continuous formation and accumulation of molecular hydrogen, which does not occur in the atmosphere of Titan, because of H2 escape. In order to reassess the data already available from this type of laboratory studies, experiments on CH4-N2 atmospheres, with and without H2 escape, have been recently performed. The influence of this parameter on the chemical evolution of the atmosphere and on the nature and relative quantities of organic compounds has been studied. After reviewing these experiments, implications of the obtained results on the organic chemistry at the periphery of Titan are discussed.