Changes In Hydrogen Concentration Research Articles

ChemInform Abstract: THE EFFECT OF HYDROGEN CONTENT ON THE PHOTOVOLTAIC PROPERTIES OF AMORPHOUS SILICON

Hydrogenated amorphous silicon (a‐Si:H) films were deposited from an rf electrodeless glow discharge in silane, and the dependence of the hydrogen concentration on substrate temperature, silane pressure, and rf power was studied by means of secondary ion mass spectroscopy (SIMS). The photovoltaic properties of the a‐Si:H films were also studied as a function of the same deposition parameters. The observed photovoltaic behavior appears to be mainly due to variations in the optical gap caused by changes in the hydrogen concentration of the films.

Dissolution Ratio of Hydrogen Generated by Small-Leak Sodium-Water Reaction

A study, both theoretical and experimental, was undertaken on the hydrogen dissolution ratio in liquid sodium, with the view of estimating the quantity of hydrogen that dissolves into sodium before reaching the free surface, following the occurrence of sodium-water reaction in a steam generator. Superheated steam was injected into the sodium in a reaction vessel of configuration simulating the steam generator. The hydrogen dissolution ratio was determined from analysis of the responses obtained on a hydrogen detector installed downstream of the reaction vessel. The hydrogen dissolution ratio was found to vary from o to 15% over a leak rate ranging of 3~10 g/sec, as determined both from the transient response data given by the hydrogen detector and from the corresponding data obtained from tests on changes in hydrogen concentration upon complete mixture with the entire sodium inventory. A theoretical model was assumed for estimating the hydrogen dissolution ratio, which yield results in good agreement with...

The Leakage of Water into Sodium in Steam Generators and Test Rigs

When water and sodium react, hydrogen is released to enter cover gas spaces and become absorbed into the sodium. Changes in hydrogen concentration are measured with suitable instruments to monitor ...

Elucidation of gas chromatographic fractions in hydrogenation and oxidation reactions

Several methods for determining the components of gas chromatographic fractions were developed. The compounds underwent hydrogenolysis in a post-column reactor and only highly volatile reaction products were detected. The method enabled the alkoxyl groups present, their amounts and structure to be determined, and the alkyl chains cleaved by the hydrogenolysis of the carboncarbon bond to be established. The hydrogenation, dehydrogenation and hydrogenolysis reactions were applied to the gas chromatographic effluents in argon carrier gas, which contained 5–30% of hydrogen. The results were recorded in the form of changes in hydrogen concentration. The dependence of reaction kinetics on the nature of the functional group (hydroxyl, carbonyl, ether, unsaturation), its position in the molecule and on the structure of the carbon skeleton was investigated. The oxidation of hydrocarbons and oxygen-containing compounds was studied by measuring the consumption of oxygen (in the helium stream containing oxygen) in a post-column reactor. The dependence of the oxidation kinetics on the structures of compounds and the nature of catalysts was investigated. A reaction gas chromatographic method for ultimate oxygen determination is presented, as well as a technique for the determination of the C:O ratio of compounds in gas chromatographic fractions.

A Hydrogen Monitor for Detection of Leaks in LMFBR Steam Generators

A monitoring system has been developed for detecting leaks in LMFBR steam generators by the detection of the hydrogen produced in the sodium-water reaction. The principal capabilities of this detection system are rapid response, high sensitivity, and high stability and reliability. The monitoring system is based on the detection of a change in hydrogen concentration in sodium by measurement of the change in the rate of hydrogen diffusion through a nickel membrane immersed in the sodium. A vacuum is drawn on the membrane by an ion pump, and the partial pressure of hydrogen on the vacuum side, a measure of the hydrogen flux and the hydrogen activity in the sodium, is determined by the measurement of the current to the ion pump.The response time of the monitor depends chiefly on the hydrogen-diffusion properties of the nickel membrane. Transient-diffusion calculations indicate that 10 sec after a sudden change in the hydrogen concentration in the sodium, the change in the hydrogen flux from the membrane would be 70% of the eventual total change in flux for a 10-mil-thick nickel membrane at 500°C. With a stable high-voltage power supply, the noise on the recorded ion pump signal was <0.2% of the signal output for a hydrogen concentration in sodium of 0.1 to 1.0 ppm. This level of sensitivity and stability are adequate to detect a water leak from the steam generator into the LMFBR secondary sodium of 10−4 lb/sec at a sodium flow of 107 Ib/h in <1 min, if the hydrogen concentration in the secondary sodium is ∼0.1 ppm.

The Permeation of Electrolytic Hydrogen through Platinum

The absorption and permeation of electrolytically generated hydrogen through thin platinum foils have been observed directly by an electrochemical method. The diffusion coefficient and the associated apparent energy of activation were determined. The concentration of absorbed hydrogen was obtained, and it was shown that atomic hydrogen tends to concentrate in areas of high strain in the metal where it can be in a lower energy state. Hydrogen embrittlement phenomena similar to those found in iron and steel were observed. The variation of cathodic overpotential with time was explained in terms of the change in hydrogen concentration in the bulk of the metal near the cathodic surface.

Statistical Model for the Beta Zirconium Hydrides

It appears reasonable to consider the hydrogen as bonded covalently to zirconium in the zirconium hydrides. After consideration of the known structure of ZrH2, the hypothesis is made that the nonstoichiometric ``beta'' (bcc) Zr–H phases have four symmetrical (tetrahedral) hydrogen sites on each face of the unit cell, with simultaneous occupancy restricted to pairs not closer than the shortest H–H distance in ZrH2. The complex configurational problem is solved for all concentrations by developing a simple process of building up the lattice, after making tests of the amount of detail required for accurate solutions in one and two dimensions. The total entropy, when decreased by the corresponding configurational entropy, corresponds to values of the hydrogen vibration frequency averaging 1440 cm—1 and showing no consistent trend with temperature or with a fourfold change in hydrogen concentration. A semiempirical energy model is constructed by introducing the hypothesis that zirconium bonded to no hydrogen is ``abnormally stable,'' and the two energy parameters are derived from the experimental data. The agreement with the curves derived from thermodynamic data is fairly good for the partial molal entropy and energy of hydrogen, and excellent for the hydrogen equilibrium pressures. Alternative models, however, are not eliminated unambiguously.