Sufficient Hydrogen Research Articles

The crack tip strain field of AISI 4340 Part III Hydrogen influence

This paper studied the influence of hydrogen and water vapour environments on the plastic behaviour in the vicinity of the crack tip for AISI 4340. Hydrogen and water vapour (at a pressure of 15 Torr) significantly increased the crack tip opening displacement. The crack tip strain distribution in 15 Torr hydrogen was significantly different to that measured in vacuum. In the presence of sufficient hydrogen, the plastic zone was larger, was elongated in the direction of crack propagation and moreover there was significant creep. These observations support the hydrogen enhanced localised plasticity model for hydrogen embrittlement in this steel. The strain distribution in the presence of water vapour also suggests that SCC in AISI 4340 occurs via the hydrogen enhanced localised plasticity mechanism.

Insulated pressure vessels for hydrogen storage on vehicles

Probably the most significant hurdle for hydrogen vehicles is storing sufficient hydrogen onboard. Three viable technologies for storing hydrogen fuel on cars are: compressed gas, metal hydride adsorption, and cryogenic liquid. However, each of these has significant disadvantages: volume, weight, boiling losses, or energy to compress or liquefy the hydrogen. Insulated pressure vessels can reduce these problems for hydrogen-fueled light-duty vehicles. Insulated pressure vessels can be fueled with liquid hydrogen (LH 2), with low-temperature (80 K) compressed hydrogen (CH 2) or with ambient-temperature CH 2. In this analysis, hydrogen venting losses are calculated for insulated pressure vessels fueled with LH 2 or with low-temperature CH 2, and the results are compared to those obtained in low-pressure LH 2 tanks. Hydrogen losses are calculated as a function of daily driving distance during normal operation, as a function of time during long periods of vehicle inactivity and as a function of initial vessel temperature during fueling. The number of days before any venting losses occur is also calculated as a function of the daily driving distance. The results show that insulated pressure vessels with packaging characteristics comparable to those of conventional, low-pressure LH 2 tanks (low weight and volume), have greatly improved dormancy and much lower boil-off. Insulated pressure vessels used in a 17 km/l (40 mpg) car can hold the hydrogen indefinitely when the car is driven at least 15 km/day in average. Nearly all cars are driven for greater distances, so most cars would never need to vent hydrogen. Losses during long periods of parking are also relatively small. Due to their high-pressure capacity, these vessels would retain about a third of their full charge even after a very long dormancy, so that the owner would not risk running out of fuel. If an insulated pressure vessel reaches ambient temperature, it can be cooled down very effectively by fueling it with LH 2 with no losses during fueling. The vessel has good thermal performance even when inexpensive microsphere insulation is used. Finally, the vessel eases fuel availability and infrastructure requirements, since it would be compatible with both compressed and cryogenic hydrogen refueling.

What Is the Geometry at Trigonal Nitrogen?

Organic texts invariably depict aliphatic amines as pyramidal but anilines as planar presumably because of contributions from resonance forms with double bonds from carbon to nitrogen. Other evidence relies on comparisons made from aqueous basicities and dipole moments. Subsequent developments using data from gas-phase acidities, computational modeling and X-ray diffraction contradict these old premises. Ab intio calculations pyramidal anilines to be more stable than planar in the gas phase. Single crystal structures show both planar and pyramidal anilines exist. The latter, including aniline itself and halo or methyl substituted anilines, have C-N lengths near single bonds. the former contain nitro-substituents which help delocalize the nitrogen lone pair density to produce C-N bond orders between 1.5 and 2. Planarity is also induced by attaching very electronegative groups directly to nitrogen as well as by sufficient intermolecular hydrogen bonding between amino and nitro groups to overcome energy differences between planar and pyramidal forms.

Role of Hydrogen for Microcrystalline Silicon Formation

ABSTRACTThe role of hydrogen atoms in the formation process of hydrogenated microcrystalline silicon (μc-Si:H) by plasma enhanced chemical vapor deposition method has been investigated. Under the present conditions, the etching and the permeation of hydrogen atoms in the subsurface region do not cause the crystallization. The kinetics study of surface morphology and structure in the initial growth of μc-Si:H on an atomically flat substrate indicates that the onset thickness of island coalescence reduced under μc-Si:H formation condition. The results support the ‘surface diffusion model’ in which the surface diffusion of film precursors is enhanced by the sufficient hydrogen coverage of surface and by hydrogen atom recombination energy on the growing surface of the film.

Hydrogen Evolution in Concrete Due to Free Silicon Metal in Microsilica

Abstract Many millions of cubic meters of microsilica concrete have been placed over the years. Still, concern has been raised over possible risks related to the formation of hydrogen due to free silicon metal (silicon) contained in microsilica (silica fume, condensed silica fume). The paper addresses this question from four different viewpoints: • Chemical reaction mechanism and theoretical amounts of hydrogen that can be generated. • Definition of explosion limits on hydrogen content in the air. • Test method for silicon-metal content in microsilica in one laboratory and comparison between laboratories. • Hydrogen development in practical situations, that is, in tests with mortar in an isolated chamber and in simulation tests of hollow-core elements. From the present study it is concluded that only in extreme cases, with very high silicon-metal contents and with heat curing, can sufficient hydrogen be developed to cause an explosive mixture of gases. Further, the limit of 0.4% metallic silicon, as determined by the recommended method, will remove even these concerns.

Mass-balance analysis of reactive transport and cation exchange in a plume of wastewater-contaminated groundwater

Mass-balance calculations were used to quantify reactive transport processes and cation exchange in a plume of groundwater contaminated with septage-effluent wastewater on Cape Cod, Massachusetts. Of the chloride mass recharged to the aquifer in effluent, as much as 72% was accounted for using spatial moment analysis and finite-element integration of groundwater concentrations, which were sampled at ≤69 wells and supplemented by borehole electromagnetic-induction logging. Comparison of chloride transport and mass balances with transport and mass balances of other species indicated that reactive processes substantially altered concentrations of all major chemical constituents. Calcium in effluent was exchanged for magnesium on aquifer sediments. Potassium also was attenuated, possibly through exchange with magnesium, sodium, and/or hydrogen ions. Sufficient hydrogen ions were generated by microbial nitrification in the unsaturated zone to consume effluent alkalinity and lower the effluent pH from 7.2 to 5.0 in the recharged groundwater; the resultant acid conditions may have facilitated anion adsorption and silicate-mineral dissolution. Retardation factors ( R) calculated from breakthrough curves indicated that calcium ( R = 1.4−2.2) and boron ( R = 1.3−2.1) were similarly retarded, whereas potassium experienced greater retardation ( R = 1.8−5.2). Retardation of calcium, boron, and potassium was greater in the unsaturated zone than in the saturated zone; this may have resulted from spatial heterogeneity in exchange properties and preferential saturated-zone flow through coarse-grained sediments not present in the unsaturated zone. Although concentrations may stabilize and chemical reactions reach equilibrium at fixed points along paths in the plume, the mass-balance analysis illustrated that steady-state conditions will not be established throughout the aquifer and the cumulative mass of reacted constituents in the plume will increase until the plume reaches its discharge area. The analysis also indicates that retrospective study of dissolved concentrations in an established plume after many years of transport may not identify reactive transport and attenuation of plume constituents, if precise data on source concentrations (or masses) and the spatial distribution of solutes during plume development are not available. Finally, transport of the effluent-contaminated groundwater also altered the geochemistry of the aquifer, for example, through cation exchange, such that the introduction of clean, uncontaminated water into the aquifer will not immediately restore pre-plume conditions.

Transient-state and steady-state kinetics of the oxidation of aliphatic and aromatic thiols by horseradish peroxidase

In the course of oxidation of thiols by peroxidases thiyl radicals are formed which are known to undergo several free-radical conjugative reactions, among others leading to hydrogen peroxide formation. The present paper for the first time presents a comparative transient-state and steady-state investigation of the reaction of 15 aliphatic and aromatic mono- and dithiols with horseradish peroxidase (HRP). Both sequential-stopped-flow spectrophotometric investigations of the reaction of HRP intermediates Compound I ( k 2) and Compound II ( k 3) with thiols and measurements of the overall thiol oxidation and the simultaneous oxygen consumption in the presence and absence of exogenously added hydrogen peroxide (10 μM) have been performed. With HRP as thiyl radical generator it was shown that three groups of thiols have to be distinguished: (i) Aromatic thiols (e.g. thiophenol, 2-mercaptopurine) were excellent electron donors of both Compounds ( k 2: 10 4–10 7 M −1 s −1 and k 3: 10 3–10 6 M −1 s −1); however, the overall reaction was shown to depend on addition of hydrogen peroxide, indicating insufficient peroxide regeneration by arylthiyl radicals. (ii) Aliphatic thiols which were extremely bad substrates ( k 3 <10 M −1 s −1) for HRP (e.g. homocysteine, glutathione) and/or have a p K a,SH >9.5 (e.g. N-acetylcysteine, α-lipoic acid) were also shown to depend on exogenously added H 2O 2 to maintain the peroxidasic reaction, whereas (iii) with those thiols with rates of k 3 between 11 and 1600 M −1 s −1 (e.g. cysteine, cysteamine, cysteine methyl ester, cysteine ethyl ester) and/or with a p K a,SH <8 (penicillamine) thiol oxidation was independent of exogenously added hydrogen peroxide, indicating sufficient hydrogen peroxide regeneration.

Review of Australian phosphate rock research

Summary. Most of the research on the effectiveness of phosphorus (P) fertilisers in Australia has involved comparing phosphate rock (PR) or partially acidulated PR (PAPR) with superphosphate (SP) or other water-soluble P fertilisers. There are many estimates of effectiveness (current relative effectiveness or CRE) which compared freshly-applied (current) PR and freshly-applied (current) SP. The CRE values for PR range from &lt;0.1 to 2.5, with a mean value for apatite PR of 0.26 and 0.43 for calcined calcium iron aluminium PR (Calciphos). As measured in field experiments in the years after application, and using current SP as a basis for comparison, the residual effectiveness of PR (residual value or RV) is low and constant for up to 11 years after application. Phosphate rock is 5–30% as effective as current SP. The average value of RV for SP declines by about 40% in the first year after application, followed by a further 15% in the second year, and a further 30% over the remaining 6 years. Values of relative effectiveness and RV, and the rate of decline in RV differ substantially between sites and sometimes between plant species. Laboratory studies of reactions between PR and soil have shown that the poor effectiveness of PR is primarily due to the limited extent and rate of dissolution of these fertilisers compared with the almost complete and rapid dissolution of water-soluble P fertilisers. Many Australian soils are only moderately acid (pH in water &gt;5.5) with low pH buffering capacities and they cannot quickly contribute a large supply of hydrogen ions to promote rapid dissolution of PR. Soils are commonly sandy and have low water-holding capacities; in the strongly seasonal Mediterranean climate of south-western and southern Australia, the fertilised surface soil rapidly dries between rains thereby restricting PR dissolution. This restricted dissolution contributes to the poor agronomic effectiveness of PR fertilisers. Studies in Western Australia have shown that the effectiveness of current and residual PR relative to current SP generally decreases with increasing level of application. Therefore, relative to current SP, PR fertilisers become less effective per unit of PR as more is applied to the soil. Consequently, PR fertilisers frequently cannot support the same maximum yield as current SP. Published work indicates that PR fertilisers cannot be regarded as economic substitutes for SP for most agricultural applications in Australia. However, much Australian research has used low reactive PRs in conditions that are not likely to favour even highly reactive PRs. The soils dry out between rains during the growing season and have insufficient hydrogen ions to cause rapid, extensive dissolution of even reactive PR. Research elsewhere has suggested that reactive apatite PRs can be as effective as SP for suitable soils and environments. These are soils that remain wet for the whole growing season and which contain sufficient hydrogen ions to cause rapid dissolution of reactive PR. Laboratory studies, in which there is no P leaching, on 254 different soils collected from throughout south-western Australia showed that 29 soils, all collected from &gt;800 mm average annual rainfall areas, dissolved &gt;40% highly reactive North Carolina PR, suggesting that in the field these soils could be suitable for highly reactive PRs. Insufficient research has been conducted in the high rainfall areas of Australia, where the environment is more likely to favour highly reactive PR, and PAPR made from highly reactive PR. Therefore, a national program was undertaken in 6 Australian states to identify circumstances under which PRs, including reactive PR and PAPR made from reactive PR, may be economic fertilisers for acidic soils in the high rainfall areas of Australia where agricultural production is largely based on pasture production.

The Role of HO2− in SC-1 Cleaning Solutions

The RCA Standard Clean, developed by W. Kern and D. Puotinen in 1965 and disclosed in 1970 [1] is extremely effective at removing contamination from silicon surfaces and is the defacto industry standard.[2]. The RCA clean consists of two sequential steps: the Standard Clean 1 (SC-1) followed by the Standard Clean 2 (SC-2). The SC-1 solution, consisting of a mixture of ammonium-hydroxide, hydrogen-peroxide, and water, is the most efficient particle removing agent found to date. This mixture is also referred to as the Ammonium- Hydroxide/Hydrogen-Peroxide Mixture (APM). In the past, SC-1 solutions had the tendency to deposit metals on the surface of the wafers, and consequently treatment with the SC-2 mixture was necessary to remove metals. Ultra-clean chemicals minimize the need for SC-2 processing. SC-I solutions facilitate particle removal by etching the wafer underneath the particles; thereby loosening the particles, so that mechanical forces can readily remove the particles from the wafer surface. The ammonium hydroxide in the solution steadily etches silicon dioxide at the boundary between the oxide and the aqueous solution (i.e., the wafer surface). The hydrogen peroxide in SC-I serves to protect the surface from attack by OH" by re-growing a protective oxide directly on the silicon surface (i.e., at the silicon/oxide interface). If sufficient hydrogen peroxide is not present in the solution, the silicon will be aniostropically etched and surface roughening will quickly occur. On the other hand, hydrogen peroxide readily dissociates and forms water and oxygen. If the concentration of the resulting oxygen is too high, bubbles will appear in the solution. The gas liquid interfaces that result from the bubble formation act as a “getter” for particles that can re-deposit on the wafer surface if a bubble comes in contact with the wafer.

The role of hydrogen in stress-corrosion cracking of austenitic stainless steel in hot MgCl2 solution

The role of hydrogen in stress-corrosion cracking (SCC) of austenitic stainless steel was investigated in boiling chloride solution. The tests in the mixed melted salt verified that hydrogen-induced cracking (HIC) could occur at 160 °C if sufficient hydrogen could be supplied continuously. It was found that the threshold SCC intensity factors of both 321 and 310 steels were lower than those of HIC during dynamic charging at high fugacity at 40 °C and 160 °C. In addition, anodic polarization decreased hydrogen concentration and promoted SCC in hot LiCl solution, while cathodic polarization increased hydrogen concentration and restrained SCC. Hydrogen could be introduced into the specimen and be concentrated at the crack tip during SCC. It could promote anodic dissolution and SCC remarkably, although it was not enough to produce cracking.

Solid-state NMR characterization of Mowry shale from the Powder River Basin

Solid-state 13C NMR measurements were carried out on a suite of petroleum source rocks from the Mowry shale of the Powder River Basin in Wyoming. The objectives of this study were to use CP/MAS 13C NMR measurements to monitor changes in the carbon structure of the kerogen that result from depth of burial. NMR measurements were made on a suite of samples covering a present-day depth interval of 3000–11,500 ft. Because total organic carbon values were mainly in the range of 1–2 wt%, a large-volume sample spinner was used for the 13C NMR measurements. Washing the samples with HCl was found to improve the quality of the 13C spectra. The carbon aromaticity of the kerogen increased with depth of burial, and at depths greater than ∼10,000 ft the kerogen showed little capacity to generate additional oil because of the small fraction of residual aliphatic carbon remaining in the kerogen. By combining NMR and Rock-Eval measurements, an estimate of the hydrogen budget was obtained. The calculations indicated that ∼20% of the kerogen was converted to hydrocarbons, and that sufficient hydrogen was liberated from aromatization and condensation reactions to stabilize the generated products.

The pH-lowering ability ofSphagnum magellanicumBrid.

AbstractThe classic explanation of the low pH in bogs attributes this phenomenon to the H+ exchange capacity of Sphagnum. However, recent researchers have challenged this theory, arguing instead that such exchange could not account for the ions measured and that organic acids were a more likely explanation. We have attempted to determine if Sphagnum can exchange sufficient hydrogen to account for the low pH of the bog surface zone. To determine cation exchange capability of Sphagnum magellanicum in relation to the common cations of natural habitats, distilled and deionized water and different concentrations of Mg2+, Ca2+, K+, and Rudolph's Sphagnum nutrient medium were tested. In these experiments Sphagnum changes the pH of a surrounding liquid medium in the pH range of 3 to 7. The cation exchange capacity of Sphagnum magellanicum follows the series K+<Mg2+<Ca2+. Rudolph's medium consists of many compounds that resulted in much less hydrogen being released than from solutions of single compounds. Differen...

Dissolved uranyl complexed species in artificial seawater

The distribution of dissolved uranyl species was calculated on the basis of the stability constants published elsewhere and compared with the results obtained from the experiments performed in artificial seawater. According to the distributions calculated and electrochemical and spectrophoto-metrical measurements performed in model electrolytes and artificial seawater (pH=8.2) in the presence of sufficient hydrogen peroxide, uranium most probably predominates in the form of a mixed uranyl-dicarbonato-hydrogenperoxo complex. The results obtained could be applied to the natural marine photic zone. The mixed complex has to be taken into account as an additional form of dissolved uranium species influencing their cycle in natural water systems. Recent discovery of the presence of hydrogen peroxide in the surface waters of seas has challenged a long-held notion of the prevalence of uranyl-carbonato complexes in seawater.

The possible role of organic matter in transport and accumulation of metals exemplified at the Permian Kupferschiefer formation

The Permian Kupferschiefer in the Central European Zechstein Basin has been deposited under anoxic sedimentary conditions. The shale contains on average about 5% of organic matter which is classified as kerogen Type II. In areas where an ore-grade mineralization of the Kupferschiefer is not observed (i.e. NW Germany), the organic matter follows solely a temperature-induced transformation process. Copper and silver enrichment in the Kupferschiefer is associated with the occurrence of Rote Fäule. At those places where Rote Fäule came in contact with or very close to the Kupferschiefer, secondary alteration reactions are detectable in the solvent-extracted organic matter as well as in the kerogen. This effect is pronounced in the Kupferschiefer of the Konrad mine investigated in the present study. The analysis of solvent extracts has been carried out using methods such as gas chromatography coupled to mass spectrometry (GC/MS). For the investigation of the kerogen pyrolysis experiments (“Rock-Eval”) have been undertaken. In a closely sampled Kupferschiefer profile from the Konrad mine (SW Poland), significant depletion of the organic matter and the hydrogen content of the organic matter is found in the bottom part of the section approaching the Rote Fäule horizon. The precipitation of copper from ascending oxidizing solutions occurred primarily in the inner part of the Kupferschiefer section, where sufficient hydrogen for abiotic thermochemical sulphide production was still available. Thus, the organic matter acted as a reducing barrier mediating the metal accumulation from upwards migrating metal-bearing brines (ascending brine theory). The determination of the maturity parameters indicates, that the organic matter was mature when oxidation occurred.

Hydrogen compatibility of Femnal alloys

Five Femnal alloys with various ferrite/ austenite were prepared by mainly adjusting the carbon content. Hydrogen compatibility of these alloys was investigated. A slow extension rate tensile test in one atmosphere of hydrogen gas showed that hydrogen embrittlement (HE) increased with the content of ferrite in the alloys. The alloy with a full austenite phase was strong, ductile, and essentially immune to HE, whereas the one with full ferrite was weaker, very brittle, and suffered serious damage in hydrogen. A sustained load test was further conducted in hydrogen gas at 25°C to 75 °C for the alloys with 10, 35, and 65 pct ferrite. No subcritical crack growth occurred in the alloy with 10% ferrite. Typical three-stage environment-assisted crack growth was observed for the alloys with 35 and 65 pct ferrite. A kinetics study of the subcritical crack growth indicated that the cracking rate was basically controlled by hydrogen transport through the ferrite grains. Austenite phase could be embrittled provided sufficient hydrogen was dissolved. To reduce HE in Femnal alloys, the content of ferrite should be reduced; this can be achieved mainly by controlling the carbon content in the alloys.

The suggestion that the yeast cell Saccharomyces cerevisiae may absorb sufficient hydrogen ions to increase ruminal fluid pH is untenable

The suggestion that the yeast cell <i>Saccharomyces cerevisiae</i> may absorb sufficient hydrogen ions to increase ruminal fluid pH is untenable

Formation of cathode plasma in a magnetically insulated high-current diode to generate negative hydrogen ions with current densities up to 200 A/cm2

High-power pulsed beams of neutral atoms may be useful for CTR as alternative ways to drive the target. They can be obtained by stripping high-current negative ion beams. Experiments are described on cathode plasma formation with sufficient negative hydrogen ion concentration to obtain H− current density up to 200 A/cm2. The plasma was formed by a surface discharge on a dielectric initiated by a bipolar prepulse or by laser illumination. It is shown that the electron current density flowing through the cathode plasma needs to be greater than 104 A/cm2 to create H− continuously in the outer region of the plasma and thereby produce H− current densities up to 200 A/cm2.

The role of stress state on hydrogen cracking in Fe-Si single crystals

While state-of-stress effects have long been known to play a major role in hydrogen embrittlement, there has been little direct evidence outside of thickness effects on threshold stress intensities. Also, there have been recent mechanisms proposed suggesting that enhanced plasticity effects may be more dominant than enhanced decohesion effects. If true, this would mandate different state of stress effects. The goal here was to settle this issue in at least one material, that being a semi-ductile, iron base single crystal. This was achieved by examining the crack initiation site under various loading and hydrogen interaction conditions in precracked Fe-3wt.%Si single crystals oriented in {001}<010> and {001}<110>. A strong dependency of hydrogen-induced cracking on the state of stress was evidenced by the consistent nature of a mid-section initiation stage and tunneling behaviour during crack propagation. This plane stress vs plane strain effect was quantified by analysing both small scale yielding and discretized dislocation computer solutions of the stress field. It was shown that the former did not provide sufficient stress and hydrogen in the local sense while the latter provided both high stress and hydrogen enrichment to cause decohesion. Finally, an assessment is made as to whether surface observations are helpful in sorting out the micromechanical aspects of cracking. This is addressed by examining surface plasticity with respect to the interior crack profile.

Fungicides and photochemistry. Photodehalogenation of captan

Photodegradation ( λ > 280 nm) of the fungicide captan (N-(trichloromethylthio)-cis-4-cyclohexene-1,2-dicarboximide) is more efficient in an olefinic (cyclohexene) as well as in an alcoholic (isopropanol) medium than in a saturated hydrocarbon medium (cyclohexane). Photolysis leads to the homolytic dissociation of a C-Cl bond. In the presence of sufficient hydrogen donors N-(dichloromethylthio)-cis-4-cyclohexene-1,2-dicarboximide results, a new photometabolite of captan. On further uv irradiation, the photometabolite is rapidly photodecomposed via Norrish-type-II cleavage yielding tetrahydrophthalimide by loss of thiophosgene. The results are discussed as compared to those obtained with folpet (W. Schwack, 1987).

Thermochemical production of methanol from biomass in Hawaii

Sufficient trees or grasses can be grown in Hawaii and converted into enough methanol to replace all of the gasoline and diesel fuel consumed in the State for ground transportation. A recent Hawaii Natural Energy Institute study shows that methanol can be produced from biomass via partial oxidation for $0·16 liter −1 (wholesale price at the plant gate), based on a 760 million liter per year (MLPY) methanol plant processing 7000 tonnes day −1 of biomass feedstock (50% moisture content) from a recurring annual harvest of approximately 36 000 hectares of intensively managed, short-rotation energy crops. The capital cost of this methanol-from-biomass facility would be roughly $280 million. Sufficient hydrogen added to the synthesis gas to convert all of the biomass carbon into methanol carbon would more than double the methanol produced from the same biomass base, yielding 1700 MLPY at $0·28 liter −1 at a capital cost of $335 million.