Chemical Reaction Of Hydrogen Research Articles

Calculation of Start-Up Time of Passive Catalytic Hydrogen Recombiner of Localization Safety System of a Nuclear Power Plant Equipped with VVER

The hydrogen removal system ensures hydrogen safety. At a VVER nuclear power plant, it consists of passive catalytic hydrogen recombiners. The calculation of devices is of great importance for safety justification, since the complex conditions of an accident at a power unit are not reproducible in experiments. The recombiner consists of a casing and a cassette with catalytic elements, the design of which ensures the passage of a gaseous medium through the device. Upon contact with the catalyst, a chemical reaction of hydrogen and oxygen compounds occurs, accompanied by the release of heat; as a result, the concentration of hydrogen under the shell decreases. The problem is starting from a cold state since the activity of the cold catalyst is low, and the thrust is not observed until the catalyst is heated and a column of warm gas is formed inside the device. The transition from the cold state to the working state takes a certain time, during which the recombiner performance is below nominal. The start-up time is a parameter that is important in terms of safety. The article calculates the start-up time of a hydrogen recombiner with a catalytic block in the form of equidistant parallel catalytic plates. Local cross-sectional averages and transmission coefficients are used, the latter taking into account the influence of free convection and chemical reaction. The gas velocity is determined by the balance of buoyant and resistance forces. The calculated data and the data known from the scientific and technical literature coincide satisfactorily. As a conservative estimate of the start-up time of the recombiner, it is recommended to use the value of 300 s. An increase in temperature practically does not affect the start of the recombiner with an active catalyst, an increase in the concentration of hydrogen accelerates the start, and a decrease in pressure slows it down. The results obtained in the study can be used in the justification of the safety of VVER nuclear power plants and the examination of reports on the justification of the safety of power units.

A systematic analysis of distribution and sources of various types of water on the earth

Water is essential part of nature because in nature all types of mechanism are proceeds by the use of water. It is a chemical substance which is made of by the chemical reaction of hydrogen and oxygen. It’s molecular formula is H2O with tetrahedral geometry. It is found in mainly three different physical state i.e. solid, liquid and gaseous state. Solid state is found as ice, liquid state is present as water and gaseous state is found in vapour form. These physical form of water are distributed in surroundings as oceans water, ground water and surface water. Oceans water is non-drinkable due to the presence of high concentration of salts containing Ca+2, Mg+2, Na+, K+ etc. There are many sources of water on earth like oceans, springs, well, gysers, artesian well, lakes, rivers, rain, snow fields, glaciers etc.. It is very necessary to know about the distribution and sources of water on earth so that we can usefully utilize and manage the very important part of nature i.e. water.

INCREASING EFFICIENCY BY INTEGRATING THERMOLECTRIC MATERIALS INTO FUEL CELL

PEM (Polymer Membrane Fuel Cell) is a technology that emits electricity from the chemical reaction of hydrogen and oxygen gases. The material is also capable of generating electricity due to the temperature difference applied to both surfaces. In this study, it is aimed to establish a mechanism to evaluate the waste heat produced by the fuel cell by using peltier. The fuel cell is designed to facilitate heat transfer to the Thermoelectric Coolant. One side of the Thermoelectric Coolant was mounted on the heat exit surface of the fuel cell and a fan was used to remove heat from the other surface. As a result of the experiments, it was seen that the most efficient working range of PEM fuel cell was limited to 70-80 o C, thus the surface temperature difference required for the efficient operation of the peltier was not fully formed. However, it has been determined that the energy obtained from the PEM fuel cell can be increased by 10% in these conditions.

Simulation of Liquid Level, Temperature and Pressure Inside a 2000 Liter Liquid Hydrogen Tank During Truck Transportation

Hydrogen is an ultimate energy source because only water is produced after the chemical reaction of hydrogen and oxygen. In the near future, a large amount of hydrogen, produced using sustainable/renewable energy, is expected to be consumed. Since liquid hydrogen (LH2) has the advantage of high storage efficiency, it is expected to be the ultimate medium for the worldwide storage and transportation of large amounts of hydrogen. To make a simulation model of the sloshing of LH2 inside a 2000 liter tank, simulation analyses of LH2 surface oscillation, temperature and pressure inside the tank during a truck transportation have been carried out using a multipurpose software ANSYS CFX. Numerical results are discussed in comparison with experimental results.

Enhanced Internal Quantum Efficiency and Light Extraction Efficiency of Light-emitting Diodes with Air-gap Photonic Crystal Structure Formed by Tungsten Nano-mask

We demonstrate the blue InGaN/GaN multiple quantum wells light-emitting diodes (LEDs) with an embedded air-gap photonic crystal (PC) which was fabricated by the lateral epitaxial overgrowth of GaN layer on the tungsten (W) nano-masks. The periodic air-gap PC was formed by the chemical reaction of hydrogen with GaN on the W nano-mask. The optical output power of LEDs with an air-gap PC was increased by 26% compared to LEDs without an air-gap PC. The enhanced optical output power was attributed to the improvement in internal quantum efficiency and light extraction efficiency by the air-gap PC embedded in GaN layer.

Role of molybdenum in increasing the resistance of steel to the breaking effect of hydrogen at elevated temperatures and pressures (hydrogen corrosion)

The physicochemical nature and the mechanism of the breaking effect of hydrogen on steel at elevated temperatures and pressures (hydrogen corrosion) are studied. This phenomenon is found to be based on the chemical reaction of hydrogen with carbon on the inner surface of closed micropores in the steel volume. Methane accumulates gradually in these micopores, and they transform into microcracks at a certain critical methane pressure. As a result, the metal embrittles catastrophically and undergoes cracking. When methane accumulates in micropores (incubation period of hydrogen corrosion), the mechanical properties of the steel remain almost unchanged. Alloying of steel up to 2.0 wt % (the upper limit of the concentration range under study) is shown not to affect the thermodynamics of carbon in steel in the pearlitic temperature range. However, this alloying element strongly affects the incubation period of hydrogen corrosion. Thus, prerequisites formed for a preliminary (before steel is put into operation) determination of the conditions of the absolute and relative (within the incubation period) hydrogen resistance of steel.

Chemisorption of Molecular Hydrogen on Carbon Nanotubes: A Route to Effective Hydrogen Storage?

The energetics of the chemisorption of molecular hydrogen on small-diameter armchair carbon nanotubes has been investigated using first-principles density functional theory (DFT). The adsorption of hydrogen was examined at a range of coverages, from low to full monolayer coverage. Several pathways for hydrogenation were investigated, and those that could lead to energetically favorable, stable structures of fully saturated nanotubes were identified. For these routes, the calculations indicate that the addition of hydrogen, apart from at the very onset, is exothermic and also becomes increasingly more favorable with increasing degree of coverage. Carbon nanotubes of sufficiently small diameter are shown to have the capacity to store a full monolayer of hydrogen effectively via chemisorption. In addition, kinetic barriers for the dissociative chemisorption of H2 and thermal equilibration of the system were considered. These were found to be quite large for admolecules on an otherwise-clean nanotube, but to drop substantially in the vicinity of preadsorbed hydrogen; that is, the adsorbed hydrogen acts as an autocatalyst for further hydrogenation. On the basis of these findings, the chemical reaction of hydrogen with carbon nanotubes is expected to become increasingly exothermic and also to proceed more rapidly at higher coverages.

Some aspects of SiC CVD epitaxy

A brief comparative analysis of techniques for the CVD epitaxy of SiC is made. Two tendencies in the use of inner reactor equipment are distinguished. Irrespective of the design features and the active gases used, chemical reactions of hydrogen with the interior of the reactor occur concurrently with the epitaxial growth. These reactions control the actual [C]/[Si] ratio in the gas phase and in part determine the background impurity concentration in pure epilayers.

A CONTINUUM DAMAGE RELATION FOR HYDROGEN ATTACK CAVITATION

A continuum damage relation (CDR) is proposed to describe the failure process of hydrogen attack, i.e. grain boundary cavitation of steels under conditions of high temperature and high hydrogen pressure. The cavitation is caused by the chemical reaction of hydrogen with grain boundary carbides forming cavities filled with high pressure methane. The micromechanisms described are the grain boundary cavitation and the dislocation creep of the grains. The CDR is based on two extreme cavitation rate distribution modes. In the first mode, the cavitation rate along the facets is uniform, resulting in a hydrostatic dilatation while the creep deformations remain relatively small. In the second mode, cavitation proceeds predominantly on grain boundary facets transverse to the principal macroscopic stress. This part of the CDR builds on Tvergaard's constituitive relation for intergranular creep rupture [Tvergaard, V., Acta metallurgica, 1984, 32, 1977] where the facet cavitation is constrained by creep of the surrounding grains. The mode corresponding to the highest cavitation rate is the active mode. The two-dimensional version of the CDR is verified against detailed finite element analyses of hydrogen attack in planar polycrystalline aggregates. Finally, the generalization to a three-dimensional CDR is discussed. © 1997 Acta Metallurgica Inc.

特集 水素と材料機能 金属と金属酸化物表面への水素の吸着と化学反応

特集 水素と材料機能 金属と金属酸化物表面への水素の吸着と化学反応

Reactive scattering of H and D atoms. II. isotope effect on the angular distribution of H, D + NO 2

The chemical reactions of hydrogen and deuterium atoms with nitrogendioxide (NO 2) have been studied with crossed molecular beams. Angular and velocity distributions have been measured. The angular distribution peaks at small angles and shows a pronounced isotope effect; only 2̃4% of the available energy goes into translation. Al-though four very deep potential wells (2.1 eV) exist in the potential hypersurface no statistical complex is formed. The reaction can probably be described as intermediate between direct and complex scattering.

Reactive scattering of H and D atoms. II. Isotope effect on the angular distribution of H, D + NO 2

Abstract The chemical reactions of hydrogen and deuterium atoms with nitrogendioxide (NO 2 ) have been studied with crossed molecular beams. Angular and velocity distributions have been measured. The angular distribution peaks at small angles and shows a pronounced isotope effect; only 24% of the available energy goes into translation. Al-though four very deep potential wells (2.1 eV) exist in the potential hypersurface no statistical complex is formed. The reaction can probably be described as intermediate between direct and complex scattering.

Infrared Spectra of Free Radicals and Chemical Intermediates in Inert Matrices

Free radicals have played a significant role in the development of chemistry during the twentieth century. Since Gomberg's (1) preparation in 1900 of the first free radical, triphenylmethyl-and along with it a challenge to the understanding of valence-free radicals have been used increasingly to explain reaction mechanisms. As early as 1918 Nernst suggested (2) that the photo­ chemical reaction of hydrogen and chlorine involved the individual atoms as intermediates. Further important work of Paneth & Hofeditz in 1929 (3) postulated that alkyl free radicals, produced by thermal decomposition of metal alkyls, were responsible for removing a metal film in the famous metal mirror experiments. Following this early work, the appearance of free radical intermediates in the literature became itself a chain reaction. Free radicals were subsequently proposed as reaction intermediates by numerous prominent scientists. Steacie has reviewed much of this early work (4) in his book Atomic and Free Radical Reactions. Recently Pryor (5) has discussed the mechanistic, synthetic, and industrial significance of free radicals in contemporary organic chemistry. Obviously, the validity of a proposed mechanism is improved by the direct observation of the free radical from a related chemical process. Furthermore, free radicals provide unique tests for theories of chemical bonding. The presence of an unpaired electron in a half-filled orbital supplies an excellent opportunity for electronic interaction with neighboring atoms and groups. Knowledge of the vibrational spectrum of simple free radicals provides insight into the structure and bonding of these interesting chemical species. Free radicals are most simply defined as species containing one or two unpaired electrons. Examples include methyl CH3, the chlorine atom CI, and the lithium atom Li, as well as the stable molecules nitric oxide NO and nitrogen dioxide NOz, each of which contains a single unpaired electron. Diradicals, such as triplet CH2, contain two unpaired electrons. In this dis­ cussion we will use the term radical to refer to species containing a single