Molecular Hydrogen Atmosphere Research Articles

A competetive way to low-viscosity PAO base stocks via heterocene-catalyzed oligomerization of dec-1-ene

Hydrogenated oligomers of higher α-olefins (primarily, dec-1-ene) represent base stocks for high-quality polyolefin oils (PAOs), transmission fluids, lubricants and greases. Competitive advantages of zirconocene catalysts in oligomerization of α-olefins have been already demonstrated and industrially implemented for higher oligomers. However, the problem of the selective synthesis of α-olefin oligomers that have degree of polymerization (DPn) 3 and 4, remains unresolved. A series of –CH2CH2– bridged ansa-zirconocenes derived from 5,10-dihydroindeno[1,2-b]indole, 'heterocenes' Zr4–Zr6, were synthesized and characterized by NMR spectroscopy and X-ray diffraction (XRD) analysis. New complexes Zr4–Zr6 and known –SiMe2– bridged ansa-heterocenes Zr1–Zr3 were investigated in oligomerization of dec-1-ene using MMAO-12 or [PhNMe2H][B(C6F5)4] activators. In the atmosphere of molecular hydrogen, at [dec-1-ene]/[Zr] ratios up to 4·105, rac-forms Zr4r–Zr6r provided more than 85% yields of dec-1-ene oligomers without skeletal rearrangements. In some experiments, at least 50% yields of lightweight oligomers (DPn=3–4) were achieved. After activation of Zr6r by TIBA and [PhNMe2H][B(C6F5)4] and completion of dec-1-ene oligomerization, we isolated new cationic complex Zr6r-Al containing Zr-(μ-Cl)2-Al fragment, as confirmed by XRD. Zr6r-Al alone was inactive against dec-1-ene, but after addition of TIBA oligomerization started. Due to uniform molecular structure of oligomers, complete catalytic hydrogenation of oligo(dec-1-ene)s was conducted using Ni/Al2O3 catalyst under mild conditions (150°C, 3 h, 20 bar). Hydrogenated dec-1-ene oligomers turned out to be high-quality PAO base stocks far exceeding industrial dec-1-ene PAOs in terms of viscosity characteristics.

Theoretical study of the formation of C18H and C18H2 molecules by low energy irradiation with atomic and molecular hydrogen

We study the formation of C18H and C18H2 by irradiating a cyclo [18]carbon molecule with atomic and molecular hydrogen at impact energy, E, in the range of 0.5–25 eV. We utilize the density-functional tight-binding method to perform molecular dynamics simulations to emulate the interaction of a carbon ring when colliding with atomic or molecular hydrogen. From our results, the formation of the C18H molecules is likely to occur upon irradiating by H atoms at E<10 eV and by H2 molecules at 2<E<15 eV center of mass energy. Formation of C18H2 molecules is only observed at around E=2 eV. Our results show that the absorption of hydrogen is more prone in atomic than in molecular hydrogen atmosphere. Thus, we find that the probability of physio-absorption reaches up to 80% for atomic projectiles with E<5 eV but only up to 10% for the molecular ones. Our analysis shows that the deformation of the carbon ring due to the hydrogen bonding produces transition from sp to sp2 hybridization. The angle between the carbon atoms at the locations near to the H bond in the resulting ring is not 120° but instead 110° degrees. No molecular fragmentation of the C18 ring is observed.

Interaction of O2, H2O and H2 with proton-conducting oxides based on lanthanum scandates

An interaction of components from the gas phase, containing gaseous oxygen, hydrogen and water, with the La1–xSrxScO3–α oxides in the temperature range of 300–950 °С and partial pressure of 6.1–24.3 kPa 8.1–50.7 kPa has been studied using a high temperature thermogravimetric analysis. The effects of partial pressure of the gaseous oxygen, water and hydrogen on the apparent uptake level of protons with oxides has been found. The studies of incorporation processes of hydrogen from molecular hydrogen atmosphere into the structure of proton-conducting oxides based on strontium-doped lanthanum scandates were performed in the temperature range of 300–800 °C and hydrogen pressure of 0.2 kPa by means of the isotope exchange method with the equilibration of isotope composition in the gas phase. The protons and deuterons concentrations were determined for the La0.91Sr0.09ScO3–α oxide. The existence of proton defects in the structure of studied oxides after the exposure in H2O and H2-containing atmospheres was revealed using the 1Н NMR. The role of oxygen vacancies in the proton incorporation processes is considered in the present work.

Interaction of H2O, O2 and H2 with Proton Conducting Oxides Based on Lanthanum Scandates

The research uses the method of high-temperature thermogravimetric analysis to study the processes of interaction of the gas phase in the temperature range 300–950 °C in the partial pressure ranges of oxygen 8.1–50.7 kPa, water 6.1–24.3 kPa and hydrogen 4.1 kPa with La1–xSrxScO3–α oxides (x = 0; 0.04; 0.09). In the case of an increase in the partial pressure of water vapor at a constant partial pressure of oxygen (or hydrogen) in the gas phase, the apparent level of saturation of protons is shown to increase. An increase in the apparent level of saturation of protons of the sample also occurs with an increase in the partial pressure of oxygen at a constant partial pressure of water vapor in the gas phase. The paper discusses the causes of the observed processes. The research uses the hydrogen isotope exchange method with the equilibration of the isotope composition of the gas phase to study the incorporation of hydrogen into the structure of proton-conducting oxides based on strontium-doped lanthanum scandates. The concentrations of protons and deuterons were determined in the temperature range of 300–800 °C and a hydrogen pressure of 0.2 kPa for La0.91Sr0.09ScO3–α oxide. The paper discusses the role of oxygen vacancies in the process of incorporation of protons and deuterons from the atmosphere of molecular hydrogen into the structure of the proton conducting oxides La1–xSrxScO3–α (x = 0; 0.04; 0.09). The proton magnetic resonance method was used to study the local structure in the temperature range 23–110 °C at a rotation speed of 10 kHz (MAS) for La0.96Sr0.04ScO3–α oxide after thermogravimetric measurements in an atmosphere containing water vapor, and after exposures in molecular hydrogen atmosphere. The existence of proton defects incorporated into the volume of the investigated proton oxide from both the atmosphere containing water and the atmosphere containing molecular hydrogen is unambiguously shown. The paper considers the effect of the contributions of the volume and surface of La0.96Sr0.04ScO3–α oxide on the shape of the proton magnetic resonance spectra.

PHYSICAL CORROSION PROCESSES IN FERRITE-PEARLITIC STEELS

Background Results of physical corrosion of ferrite-pearlitic steels have been studied. The growth of grains leads to a deterioration in the physical and mechanical properties of steel, is observed with prolonged aging of the steel at certain temperatures: pre-eutectoid steels or hypereutectic steels, with the growth of austenite grains. Upon cooling, a coarse-grained ferrite-pearlite structure forms. Steels with such a structure have low mechanical characteristics. Aims and Objectives To study the influence of the physical influence of the medium on ferrite-pearlitic steels, the mechanisms and processes occurring inside the steel during physical corrosion, the process of destruction of steel caused by decarburization, carburizing, phase transitions, the release of carbides, hydrogen, water and methane on defects, nonmetallic inclusions and grain boundaries and also growth of grains and the formation of eutectic alloys and the decomposition of a solid solution. Results Various manifestations of physical corrosion of ferrite-pearlitic steels have been revealed, which lead to a deterioration in the physicomechanical properties of steel. Vanadium (catastrophic) corrosion is represented. It is noted that the Fe - V2O5 system forms at eutectic alloy (its melting temperature is lower than the melting point of vanadium oxide and steel), which leads to the melting of the metal structure. It is noted that when a number of refineries are operating, the steel is ignited, leading to an increase in strength and a decrease in ductility. This leads to an increase in the probability of brittle failure of the device. In the interaction of oxygen with steel, along with the oxidation of iron, oxidation of the carbon that forms part of the cementite occurs. Decarburization leads to a reduction in the strength of the steel completely or its surface layers. The article presents hydrogen brittleness of steel or hydrogen corrosion, which occurs in an atmosphere of molecular hydrogen at a temperature above 200 °C. Also a scheme for the formation of carbon-bearing corrosion, which occurs when a metal interacts with carbon monoxide at high pressures and elevated temperatures as a result of a reversible reaction, is shown.

Low temperature catalytic reactivity of nanodiamond in molecular hydrogen

In this paper, the reaction dynamics of hydrogen termination of nanodiamond annealed at low temperature (500 °C) in molecular hydrogen atmosphere is reported. In-situ residual gas analysis of nanodiamond particles (4–5 nm) during annealing/hydrogenation indicates C3-radical desorption which incites a free radical reaction through the reduction of molecular hydrogen to atomic hydrogen. Consequently, as released atomic hydrogen facilitates CH adsorption on the surface of nanodiamond which was confirmed using infrared spectroscopy. This explains how nanodiamond particles can play a key role in hydrogen (H2) dissociation and be terminated by the hydrogen (H) at relatively low temperature.

Fabrication and characterization of PbSe nanostructures on van der Waals surfaces of GaSe layered semiconductor crystals

The growth morphology, composition and structure of PbSe nanostructures grown on the atomically smooth, clean, nanoporous and oxidized van der Waals (0001) surfaces of GaSe layered crystals were studied by means of atomic force microscopy, x-ray diffractometry, photoelectron spectroscopy and Raman spectroscopy. Semiconductor heterostructures were grown by the hot-wall technique in vacuum. Nanoporous GaSe substrates were fabricated by the thermal annealing of layered crystals in a molecular hydrogen atmosphere. The irradiation of the GaSe(0001) surface by UV radiation was used to fabricate thin Ga2O3 layers with thickness < 2 nm. It was found that the narrow gap semiconductor PbSe shows a tendency to form clusters with a square or rectangular symmetry on the clean low-energy (0001) GaSe surface, and (001)-oriented growth of PbSe thin films takes place on this surface. Using this growth technique it is possible to grow PbSe nanostructures with different morphologies: continuous epitaxial layers with thickness < 10 nm on the uncontaminated p-GaSe(0001) surfaces, homogeneous arrays of quantum dots with a high lateral density (more than 1011 cm−2) on the oxidized van der Waals (0001) surfaces and faceted square pillar-like nanostructures with a low lateral density (∼108 cm−2) on the nanoporous GaSe substrates. We exploit the ‘vapor–liquid–solid’ growth with low-melting metal (Ga) catalyst of PbSe crystalline branched nanostructures via a surface-defect-assisted mechanism.

The hydrogenic-electron model of accumulation of surface states on the oxide-semiconductor interface under the effects of ionizing radiation

The results obtained in research tests of kinetics of a radiation-induced formation of surface states in a MOS structure in an atmosphere of molecular hydrogen in various field modes are represented. It is found that an important element of the process of accumulation of radiation-induced surface states is the interaction between hydric complexes and electrons of the substrate. The obtained data allow considering hydrogenic and conversion concepts from the perspective of an integral hydrogenic-electron model for the incorporation of surface states. Under the proposed approach, both the existence of positive hydric complexes in the proximity of oxide-silicon interface and the interaction between these complexes and electrons from a substrate are necessary for the formation of the surface states. Both components would be a factor constraining the rate of formation of the surface states, depending on particular conditions.

Aggregation of carbon in an atmosphere of molecular hydrogen investigated by ReaxFF-molecular dynamics simulations

The formation of carbon and hydrocarbon molecules by aggregation of carbon in a H 2 atmosphere was investigated by molecular dynamics simulations based on the Reax force field (ReaxFF). Systems of 500 carbon atoms and 1000 hydrogen molecules were simulated at different densities and temperatures from 1000 K to 2000 K. The majority of hydrocarbons formed during 4 ns of simulation time consist of four carbon atoms and less and a varying number of hydrogen atoms. Their number increases with increasing system temperature. The formation of few large hydrocarbon molecules is observed via formation of linear carbon-rich molecules. These large molecules have mainly branched structures and contain hardly any pentagons to heptagons which are typical structural elements in large hydrocarbons and carbon nanostructures.

Photoinduced changes in UV absorption spectra of nitrogen-doped silica caused by exposure to ArF excimer laser

Abstract Absorption spectra of high-purity silica, in which 1.2% or 3.0% oxygen atoms are replaced by nitrogen, are measured in the spectral interval of 3.0–6.5 eV. Photoinduced changes of these spectra when exposed to 193 nm wavelength excimer laser radiation, pulse intensity being ∼50 mJ/cm2, are examined. Absorption spectra relaxation under subsequent annealing as well as changes brought about by saturation of glass with molecular hydrogen are studied. Parts of graded-index fiber ∼1 mm in length and 200 μm thick transverse slices of a fiber preform served as samples. It is found that exposure of fiber samples to laser irradiation brings about a significant decrease of initially more intense absorption band of Si-ODC in the region of 5.0 eV and an increase of initially less intense band centered at 5.8 eV at a time. In bulk samples correlation of these bands is opposite, photoinduced changes are less expressed against structureless absorption tail increase in the spectral interval of 3.0–6.5 eV. It is shown that subsequent 20 min 700 °С annealing leads to the relaxation of photoinduced changes in absorption spectra in bulk and fiber samples. By placing irradiated samples into molecular hydrogen atmosphere at room temperature absorption bands are suppressed and transparency at shorter wavelengths of UV region is increased. Data obtained is discussed in the context of photosensitivity of nitrogen-doped silica-core fibers, which serve a technological platform for thermoresistant in-fiber Bragg gratings fabrication.

Hydrogen-induced mitigation of O on Ru(101̄0): a density-functional study

The reaction of hydrogen with oxygen adsorbed on an Ru(1010) surface has been studied by density-functional calculations and kinetic Monte Carlo simulations. In agreement with experiment, it has been found that molecular hydrogen does not react with adsorbed O. In contrast, the hydrogenation of oxygen by an atomic H beam occurs spontaneously and results in the formation of adsorbed OH molecules. Subsequent impinging H-atoms can either initiate the formation of water, which readily desorbs at room temperature thus removing the O from the surface, or lead to formation and desorption of H2. It is the latter channel that hinders, at 300 K, a complete removal of O from Ru capping layers on Si/Mo mirrors for extreme ultraviolet radiation. The estimated height of the barrier for the Langmuir-Hinshelwood reaction between adsorbed H and OH, 0.92 eV, and related position of the H2O peak in model desorption spectra (approximately 320 K) are consistent with recent experiments. The H2 desorption peak appears at higher temperature, approximately 350 K, so that in the range from 320 to 330 K adsorbed hydrogen atoms will react predominantly with OH. Hence, the present simulations predict that an efficient removal of the chemisorbed O from Ru capping layers can be achieved by heating the surface to 320-330 K in a molecular hydrogen atmosphere.

Ellipsometric detection of GaAs(0 0 1) surface hydrogenation in H 2 atmosphere

Optical properties of MBE-grown GaAs(0 0 1) surfaces have been studied by spectroscopic ellipsometry under dynamic conditions of ramp heating and cooling after desorption of passivating As-cap-layer with low pressure H 2 atmosphere (14 Torr) applied to the surface. The temperature dependence of GaAs pseudo-dielectric function with atomically smooth (0 0 1) surface carrying the fixed Ga-rich (4 × 2) reconstruction was obtained for the temperature range of 160–600 °C. It is shown ellipsometrically that GaAs(0 0 1) heating in the molecular hydrogen atmosphere results in the formation of hydrogenated layer on the surface.

The effect of atomic hydrogen flow on electrical resistance of the transition metal films

On using of nuclear reaction analysis, X-ray analysis, electron microscopy, the mechanisms of structure and phase composition change of thin vanadium films at treatment in a flow consisting of molecular and atomic hydrogen (AH) have been studied. A comparative analysis on regularities of the film saturation with hydrogen and its resistance changing was carried out. It has been settled that the resistance dependence on hydrogen concentration in the case of thin film hydrogenised in AH flow differs from the analogous dependence for the bulk material hydrogenised in an atmosphere of molecular hydrogen in the conditions of thermodynamic equilibrium. Nevertheless, the found peculiarities of thin film resistance dependence on hydrogenation time, the same as in the case of bulk material, are determined by formation of vanadium hydride β-phase in the film. It is shown that with transient metal films it is possible to measure AH flow densities under reduced pressure of gas (10 −1 to 10 −3 Pa). The principle of measurement is based on dependence analysis of the film resistance increment determined by hydrogen solubilization in the film versus exposure time in AH flow. The suggested measurement method is characterized by high selectivity to AH allowing measurement of partial density of atomic flow over the range from 5×10 13 up to 10 16 at cm −2 s −1 in a mixed atomic–molecular flow. The sensor made on the basis of this method can find applications in microelectronic techniques where semiconductor treatment by atomic hydrogen flows is employed.

Kinetics of Hydrogenation and Variations in Resistance of Vanadium Thin Films Treated in Atomic Hydrogen Flow

Methods of nuclear reactions, x-ray diffraction analysis, transmission electron and nuclear microscopy were used to investigate the mechanism of hydrogenation of thin vanadium films in their treatment in a flow consisting of a mixture of molecular and atomic hydrogen. It has been shown that the main component penetrating into the metal from the gas phase is atomic hydrogen. At a gas pressure of 10–2 Pa and room temperature, the dissolution of particles which, in the gas phase, are in molecular form, occurs at a much lower rate. It has been established that the (initially high) rate of variation of the hydrogen concentration in the film decreases during hydrogenation and gradually approaches zero. As this takes place, the hydrogen concentration in vanadium reaches its limiting value equal to about 42.5 at. %. A mathematical model of the hydrogenation of a vanadium film is proposed which describes experimental results based on the relaxation dependence of the hydrogen concentration on hydrogenation time. Comparative analysis of the variations in hydrogen concentration in a film and in film resistance is performed. It has been established that the dependence of the resistance on hydrogen concentration for a thin film hydrogenated in a flow of atomic hydrogen differs from the similar dependence for a bulk material hydrogenated in the atmosphere of molecular hydrogen under the conditions of thermodynamic equilibrium. The features of the behavior of the resistance of a thin film on hydrogenation time revealed experimentally are caused, as in the case of a bulk material, by the formation of the β phase of vanadium hydride in the film. The possibility of using vanadium thin films for measuring absolute values of the atomic hydrogen flow density is discussed.

Structure and optical properties of amorphous silicon oxide thin films with different porosities

Amorphous silicon oxide thin films were prepared by evaporation of a silicon oxide powder. Samples were prepared under ultrahigh vacuum, under a flow of hydrogen ions or under a molecular hydrogen atmosphere. Two others sets of samples were prepared using deuterium instead of hydrogen. These five groups of samples were then annealed to different temperatures up to 950 °C and were exposed to the ambient air. The samples present different densities and microstructures. The sample prepared under ultrahigh vacuum is dense, hydrogen free and OH-bond free. Samples prepared under atomic hydrogen and deuterium flows contain Si–H and Si–D bonds, respectively, and are OH-bond free. The sample prepared under a molecular hydrogen atmosphere is very similar to that prepared under a molecular deuterium atmosphere. Both samples are porous and contain Si–H bonds and OH-groups coming from the exposure to the air. All the samples show visible photoluminescence attributed to isolated silicon clusters. The photoluminescence intensity increases with thermal annealing post-treatments up to an optimal annealing temperature. This maximum value is equal to 650 °C for the unhydrogenated sample and the sample prepared under an atomic hydrogen flow and to 800 °C for the sample prepared under a molecular hydrogen atmosphere. This difference is correlated to the different microstructures of the samples. Moreover the strongest photoluminescence intensity is obtained for the porous sample.

Effect of hydrogen on the properties of Pd/GaAs/InGaAs diode structures with quantum wells

The effect of hydrogen on photoelectric properties and photoluminescence of Pd/GaAs/InGaAs diode structures with quantum wells (QWs) was investigated. The dependence of the structure characteristics on the thickness of the GaAs anodic oxide layer is revealed, and the optimum oxide thickness for the fabrication of hydrogen sensors is determined. It is established that the existence of metal bridges in a thin oxide layer has a significant influence on the I-V curves of the structures. It is shown that the presence of QWs leads to an increase in the structure’s sensitivity to hydrogen. Using the QWs as local defect probes, formation of the defects resulting from the deposition of a Pd electrode both on natural and on anodized GaAs surface is studied. It is found that defects in the QWs of the diode structures can be passivated by introduction of atomic hydrogen through the Pd electrode upon exposure of the structures to an atmosphere of molecular hydrogen.

Deuterium trapping by carbon materials for tokamak plasma-facing components

The experiments on large tokamaks on measuring the hydrogen isotope pressure in the near-wall or divertor plasma are briefly described. Based on the analysis of exchange fluxes between the plasma and the wall it is stated that the plasma action, with respect to hydrogen sorption by graphite components of the tokamak first wall, is identical to materials exposure in the atmosphere of molecular hydrogen at pressures of 1–10 3 Pa and temperatures of 1200–1700 K. Within these ranges of pressures and temperatures RG-Ti-91 and USB-15 graphites are shown to be impermeable to molecular hydrogen in contrast to easily permeable POCO-AXF-5Q. Sorption capacity of well-treated dense graphites is about 10 2 appm. Sorption capacity of materials is increased to (1–3)×10 4 appm with defects like unsaturated carbon bonds, introduced into the above materials by mechanical treatment, ion irradiation, graphite gasification (exposure at 1200 K, 133 Pa during 1 h). At the same time permeability of graphites is increased to molecular hydrogen. Graphite modification by boron retards the rise of sorption capacity. The hydrogen sorption process is described as the filling of two sets of traps, i.e. weak traps arranged over the boundaries of carbon materials and deep traps arranged in the volume of separate crystallises. Russian-made graphites RG-Ti-91 and USB-15 can be used in large tokamaks as divertor and first wall tiles, respectively.

More progressive technology of GaSb single crystal growth

GaSb single crystals were grown by the Czochralski method without encapsulant in an atmosphere of ionized hydrogen. It has been found that the resistivity increased by more than one order of magnitude (0.8–1.0Ω cm) and free carrier concentration decreased to the value of (1–2) × 1016 cm−3 in comparison with the crystals grown under molecular hydrogen atmosphere. A certain asymmetry in acceptor and donor passivation is assumed because the Hall concentration does not vary along the direction of crystal growth. Donors are passivated more than acceptors, which should be confirmed by increasing resistivity and decreasing mobility.

Study of hydrogen in hydrogenated Pd/semiconductor device by ERDA

The content of hydrogen in Pd nSi , Pd pSi , and Pd pGaAs devices have been measured, both in the semiconducting substrates and the palladium thin film deposited on p-type Si, n-type Si and p-type GaAs, by ERDA (Elastic Recoil Detection Analysis) using 55 Mev Si ions. The samples were hydrogenated by keeping them in the atmosphere of molecular hydrogen at a pressure of 1 atm at room temperature. It is found that there is a fairly large amount of hydrogen in the semiconductor substrates and the palladium overlayers. It seems that the hydrogen absorbed by the palladium overlayers diffuses to the semiconducting substrates through the Pd/Semiconductor interface. It is found that the p-type semiconducting substrates accommodate more hydrogen than n-type semiconducting substrates in such hydrogenated samples.

Properties of Doped GaSb Single Crystals Grown by the Czochralski Method

AbstractThe specific electrical properties and average dislocation density of GaSb crystals are shown and discussed regarding various elements presented as dopant. The single crystals were grown by the Czochralski method without encapsulant in a flowing atmosphere of molecular hydrogen, on the one hand, and of atomic hydrogen, on the other hand. The results are summarized in the Table II.