Decrease In Hydrogen Content Research Articles

In Situ XRD Study of La2Ni7Hx During Hydrogen Absorption–Desorption

Structural changes of La2Ni7H(x) during the first and second absorption-desorption processes along the P-C isotherm were investigated by in situ X-ray diffraction (XRD). Orthorhombic (Pbcn) and monoclinic (C2/c) hydrides coexisted in the first absorption plateau, but only a monoclinic (C2/c) hydride was observed in the first desorption plateau. Phase transformation of La2Ni7H(x) was irreversible between the first as well as the second absorption-desorption process. The lattice parameters and expansion of the La2Ni4 and LaNi5 cells during the absorption-desorption process were refined using the Rietveld method. The lattice parameters a and b of the orthorhombic hydride (Pbcn) decreased, while the lattice parameter c increased with increasing hydrogen content in the first absorption. During the first absorption, the volume of the orthorhombic La2Ni4 cell expanded by more than 50%, while the expansion of the LaNi5 cell was below 10%. The monoclinic La2Ni4 cell expanded to approximately four times the size of the LaNi5 cell in the first absorption. The lattice parameters a, b, and c of the monoclinic hydride (C2/c) decreased with decreasing hydrogen content in the first desorption. These La2Ni4 and LaNi5 cells contracted isotropically in the first desorption.

Tribological properties of hard a-C:H:F coatings

Hydrogenated amorphous carbon thin films containing fluorine (a-C:H:F) have been produced by radio-frequency plasma enhanced chemical vapor deposition by using different F/H ratios in the gas phase. The introduction of fluorine from 0 to 19at.% resulted in a decrease of hydrogen content and to the formation of CF and CF2 bonds. For all the films, Raman analysis showed a typical diamond-like carbon response with an evolution of the structure to larger sp2 clusters with less hydrogen while fluorine content increased. The drop in hardness generally observed in the literature with fluorine introduction was less abrupt here: for a fluorine content up to 6.5at.%, the measured hardness was 28GPa, and for 19at.% of fluorine, value was 20GPa. These are quite high values for a-C:H:F thin films. Moreover, fluorine improved tribological behavior in dry conditions with friction coefficient slightly reduced at low fluorine content and wear rate significantly reduced: divided by two to four than the fluorine free reference coating.

Low-temperature deposition of µc-Si : H thin films by a low-frequency inductively coupled plasma for photovoltaic applications

Low-temperature depositions of Si films from hydrogenated amorphous silicon (a-Si : H) to highly crystallized hydrogenated microcrystalline silicon (µc-Si : H) were realized by the low-frequency inductively coupled plasma (LF-ICP) technique, with low hydrogen dilution (50%) and without any intentional substrate heating. µc-Si : H films with a thin incubation layer (<100 nm), a small grain size (<14 nm), a weak [1 1 1] or [2 2 0] preferred orientation, and a low hydrogen content (4–8%) were obtained (at deposition rates ∼0.4–0.7 nm s−1). The increased crystallinity due to the increasing rf power is accompanied by the improved structural order, lowered impurity contamination and decreased hydrogen content. The compactness of the µc-Si : H film is positively related to crystallinity and independent of the high microstructure factor (>0.8). Low-temperature growth of µc-Si : H is attributed to high atomic H flux and suppression of high-energy ion bombardment due to the high density of low-temperature electrons in the plasma. A µc-Si : H solar cell with a less dense intrinsic layer (on a SnO2 : F glass substrate) exhibits a high Voc (584 mV), showing great potential for photovoltaic applications.

Linear antenna microwave plasma CVD diamond deposition at the edge of no‐growth region of CHO ternary diagram

AbstractThe process parametric window for diamond deposition using the chemical vapor deposition at low pressures is quite limited where addition of oxygen in the gas phase broadens this window. The lower boundary of the lens‐shaped domain in CHO ternary diagram concurs with the H2CO tie‐line (C/(C + O) = 0.5). In this work, we present the set of experiments where the ratio of C/(C + O) was kept at a constant value 0.385. The effect of hydrogen concentration (ratio O/(O + H) varied from 0.047 to 0.364) on plasma characteristics and deposited NCD films were investigated. Raman spectroscopy confirmed the diamond character of all deposited coatings while scanning electron microscopy showed transformation from not closed to continuous film and further decrease of grain size and finally growth of diamond nanowires while decreasing hydrogen concentration in a gas mixture.

Surface Modification of DLC Film Due to Oxygen-Plasma Exposure, Observed by IR Absorption Spectroscopy in Multiple-Internal-Reflection Geometry

We investigated the surface modification of diamond-like carbon film during its exposure to oxygen plasma, at different substrate temperatures. Observation of infrared spectral changes reveals that, during plasma exposure, OH groups are formed in the film. With increasing substrate temperature, OH formation suppresses, and hydrogen content decreases. Thus, we speculate that, with increasing temperature during the exposure, insertion of oxygen into C-H bonds decreases, and hydrogen abstraction from the film increases.

Effect of powder granulation on hydrogen transport rate and hydrogen solubility in LaNi5-paraffin composite material

On the basis of potentiostatic discharge method, the diffusion rate of atomic hydrogen as well as its solubility in LaNi5 crystal lattice have been evaluated for three LaNi5 powder - paraffin composite electrodes, with different LaNi5 powder particle diameters: 0 - 20 μm, 20 - 50 μm and 50 - 100 μm. The chronoamperommetric tests have been carried out in strong alkaline (6 M KOH), deaerated solution, at 25°C. Apparent hydrogen diffusion coefficients have been determined using Crank’s spherical diffusion model. It has been shown, that increase of particle size is prone to increase of hydrogen apparent diffusion coefficient and to decrease of hydrogen concentration in the solid phase. To explain the granulation effect on hydrogenation ability parameters, the inhibition of hydrogen transport by surfacial corrosion products present on powder particles has been assumed.

Investigating the role of hydrogen in silicon deposition using an energy-resolved mass spectrometer and a Langmuir probe in an Ar/H2 radio frequency magnetron discharge

The plasma parameters and ion energy distributions (IED) of the dominant species in an Ar-H2 discharge are investigated with an energy resolved mass spectrometer and a Langmuir probe. The plasmas are generated in a conventional magnetron chamber powered at 150 W, 13.56 MHz at hydrogen flow rates ranging from 0 to 25 sccm with a fixed argon gas flow rate of 15 sccm. Various Hn+, SiHn+, SiHn fragments (with n = 1, 2, 3) together with Ar+ and ArH+ species are detected in the discharge. The most important species for the film deposition is SiHn (with n = 0, 1, 2). H fragments affect the hydrogen content in the material. The flux of Ar+ decreases and the flux of ArH+ increases when the hydrogen flow rate is increased; however, both fluxes saturate at hydrogen flow rates above 15 sccm. Electron density, ne, electron energy, Te, and ion density, ni, are estimated from the Langmuir probe data. Te is below 1.2 eV at hydrogen flow rates below 8 sccm, and about 2 eV at flow rates above 8 sccm. ne and ni decrease with increased hydrogen flow but the ratio of ni to ne increases. The formation of H+ ions with energies above 36 eV and electrons with energies greater than 2 eV contributes to the decrease in hydrogen content at hydrogen flow rates above 8 sccm. Analysis of the IEDs indicates an inter-dependence of the species and their contribution to the thin film growth and properties.

Films thickness effect on structural and optoelectronic properties of hydrogenated amorphous germanium (a-Ge:H)

Thin films of hydrogenated amorphous germanium (a-Ge:H) deposited at high growth rate by radiofrequency (RF) glow discharge with 1sccm GeH4 diluted in 40sccm H2 have been studied. The effect of the films thicknesses on the defect density and on the structural parameters was carefully investigated by means of infrared spectroscopy, optical transmission measurements, and the photothermal deflection spectroscopy (PDS) technique. The results of this investigation show that when the films thicknesses increase, the total hydrogen content (CH) decreases and the hydrogen-bonding configuration changes. The results of these changes appear clearly on the defects density and on the microstructure parameter of the films, while the disorder parameter EOV and the optical gap ET remain practically constant (EOV≈45±2meV,ET=1.08±0.02eV). The improvement of these parameters is mainly due to the incorporation of the hydrogen in the bulk of the material as the monohydride groups (Ge-H) rather than the polyhydride groups (Ge-H2 and Ge-H2n) when the films thicknesses increase.

Halogenated Benzene Cation Radicals

The halogenated benzenes C(6)HF(5), 2,4,6-C(6)H(3)F(3), 2,3,5,6-C(6)H(2)F(4), C(6)F(6), C(6)Cl(6), C(6)Br(6), and C(6)I(6) were converted into their corresponding cation radicals by using various strong oxidants. The cation-radical salts were isolated and characterized by electron paramagnetic resonance (EPR) spectroscopy and by single-crystal X-ray diffraction. The thermal stability of the cation radicals increased with decreasing hydrogen content. As expected, the cation radicals [C(6)HF(5)](+) and 2,3,5,6-[C(6)H(2)F(4)](+) had structures with the same geometry as C(6)HF(5) and 2,3,5,6-[C(6)H(2)F(4)]. In contrast, the cation radicals [C(6)F(6)](+), [C(6)Cl(6)](+), and possibly also [C(6)Br(6)](+) exhibited Jahn-Teller-distorted geometries in the crystalline state. In the case of C(6)F(6)(+)Sb(2)F(11)(-), two low-symmetry geometries were observed in the same crystal. Interestingly, the structures of the cation radicals 2,4,6-[C(6)H(3)F(3)](+) and C(6)I(6)(+) did not exhibit Jahn-Teller distortions. DFT calculations showed that the explanation for the lack of distortion of these cations from the D(3h) or D(6h) symmetry of the neutral benzene precursor was different for 2,4,6-[C(6)H(3)F(3)](+) than for [C(6)I(6)](+).

The influence of thermal stabilization stage on the molecular structure of polyacrylonitrile fibers prior to the carbonization stage

Structural transformation from a linear chain structure to crosslinked chain structure, occuring during the thermal stabilization stage of carbon fiber manufacture, was followed through the use of infrared spectroscopy, differential scanning calorimetry (DSC), elemental analysis and gel-fraction measurements. The results obtained from the analysis of IR spectroscopy showed the gradual and continuous loss of intensity of the nitrile (C≡N) vibration at 2242 cm -1 closely associated with the cyclization reactions whereas the intensity loss of the methylene (CH2) groups vibration around 2920- 2939 cm −1 has been attributed to the loss of hydrogen atoms as part of the dehydrogenation reactions. The dehydrogenation index, evaluated using the absorbance ratio of A1452/A1368, also indicated the gradual loss of hydrogens in agreement with decreasing hydrogen content with progressing stabilization process. IR spectroscopy also showed the emergence of new absorption bands attributed to the formation of crosslinked ladder-like structure in the 1590-1600 cm -1 region. The amount of newly formed crosslinked structure was characterized using DSC conversion index, IR conversion index and gel-fraction measurements. The results are compared and discussed in detail.

Pyrolysis Characteristics of Oil Shale of Six Density Sections

In this paper, Huadian oil shale was divided into six density sections through the use of a float–sink method. By utilizing thermogravimetric analyzer (TGA) etc. analytic methods, a study was conducted of industrial and elementary analysis, pyrolysis characteristics, kinetic property of oil shale of different densities. The results of the proximate and ultimate analysis show that with an increase in density of oil shale, an increase of ash content in oil shale, fixed carbon content, a decrease of volatile, element hydrogen, organic carbon and nitrogen content. The main minerals of oil shale are quartz, clay and calcite. The pyrolysis characteristics of oil shale of different densities are various, which due to the distinctive of the organic matter and mineral matter. The pyrolysis curves of oil shale of six densities indicate that oil shale in the range 1.50∼1.60g/cm3 assumes a most intense pyrolysis and the maximum decomposition rate in the low temperature step. The weight loss of six density fractions becomes ever weaker with an increase of density.

Effects of Microporosity on the Tensile Properties of Aluminum Alloy

The influences of cooling rate, hydrogen inflating time, degassing time, inclusion content on the distribution of pores within the ingot , hydrogen content and the mechanical properties of 1050 aluminum alloy were investigated by tensile test, optical microscope(OM), scanning electron microscope(SEM). With the increasing inflating hydrogen time, the hydrogen content increases, while, the strengths and elongation decrease. With the increasing degassing time, the hydrogen content decreases, while, the strengths and the elongation increase. With increasing cast temperature, the hydrogen content remains constant at first and increases obviously from 7200C to 7600C, while the strengths and the elongation decrease gradually. The crack is mainly originated at outcrop of slip step, inclusion and porosity.

Characterization of bio-oil, syn-gas and bio-char from switchgrass pyrolysis at various temperatures

Pyrolitic conversion of lignocellulosic biomass, such as switchgrass and other agricultural residues, to bio-fuels is being considered for national energy security and for environmental advantages. Bio-oil, syn-gas and bio-char were produced and characterized from switchgrass at 400, 500 and 600 °C by pyrolysis. Bio-oil yield increased from 22 to 37%, syn-gas yield increased from 8 to 26%, and bio-char yield decreased from 48 to 25% with increases of pyrolysis temperatures from 400 to 600 °C. Bio-oil heating value was 36.3 MJ/kg, density was 920 kg/m 3 and viscosity was 10 cST. GC–MS study indicated that the bio-oil contained 37% oxygenates that can be upgraded to transportation fuel in future research. Syn-gas compositional analysis shows that, with increasing pyrolysis temperature, CO 2, CO, C 2H 4 and C 2H 6 contents increased, whereas H 2 and CH 4 contents decreased. Part of the syn-gas consisting of H 2, CO and CO 2, when converted to syn-fuel, can be beneficial to the environment; sulfur free, presence of oxygenates results in less CO emissions and ozone to the atmosphere. Bio-char may be used as a co-product to enhance soil quality, and for carbon sequestration. Analysis of elemental composition and physical properties of bio-char show increase in carbon content, decrease in oxygen, hydrogen, and nitrogen content, and increase in surface area and pore volume with increases of pyrolysis temperature. The optimized pyrolysis process for bio-oil production in this study will help meet future goals of oil upgrading to produce transportation fuel.

Er3+ and Si luminescence of atomic layer deposited Er-doped Al2O3 thin films on Si(100)

Atomic layer deposition was used to deposit amorphous Er-doped Al2O3 films (0.9–6.2 at. % Er) on Si(100). The Er3+ photoluminescence (PL), Er3+ upconversion luminescence, as well as the Si PL and associated surface passivation properties of the films were studied and related to the structural change of the material during annealing. The PL signals from Er3+ and Si were strongly dependent on the annealing temperature (T = 450–1000 °C), but not directly influenced by the transition from an amorphous to a crystalline phase at T &amp;gt; 900 °C. For T &amp;gt; 650 °C, broad Er3+ PL centered at 1.54 μm (4I13/2) with a full width at half maximum of 55 nm was observed under excitation of 532 nm light. The PL signal reached a maximum for Er concentrations in the range of 2–3 at. %. Multiple photon upconversion luminescence was detected at 660 nm (4F9/2), 810 nm (4I9/2), and 980 nm (4I11/2), under excitation of 1480 nm light. The optical activation of Er3+ was related to the removal of quenching impurities, such as OH (3 at. % H present initially) as also indicated by thermal effusion experiments. In contrast to the Er3+ PL signal, the Si luminescence, and consequently the Si surface passivation, decreased for increasing annealing temperatures. This trade-off between surface passivation quality and Er3+ PL can be attributed to an opposite correlation with the decreasing hydrogen content in the films during thermal treatment.

Effect of the Soft X-rays on Highly Hydrogenated Diamond-Like Carbon Films

The effect of soft X-ray irradiation of diamond-like carbon films in vacuum was investigated using synchrotron radiation (SR). Etching and the desorption of hydrogen upon SR exposure in vacuum occurred in highly hydrogenated diamond-like carbon (H-DLC) films; these processes were not observed in the irradiation of a low-hydrogenated DLC film. The extent of decrease in hydrogen content due to SR exposure was found to decrease with increasing the etching ratio of the H-DLC film. This indicates that hydrogen desorption from the H-DLC films competed with the etching process. Namely, the modified surface, in which hydrogen content was decreased by SR exposure, was immediately removed from the H-DLC film that had a high etching rate.

Impedance Behavior of SOFC at High Fuel Utilization and a Way of Evaluating Diffusion Contribution

A quantitative evaluation method of gas diffusion resistance is proposed in which measurement of V-I characteristics under constant fuel utilization (Uf) and ac impedance were combined to separate diffusion and electromotive force change contributions from the low frequency semi-circle observed in complex impedance diagrams. Diffusion resistance was evaluated using various hydrogen content mixture diluted with nitrogen, Uf , hydrogen flow rate and current as parameters. From the measurement under various Uf, it was found that the diffusion resistance at low Uf originates mainly from the diffusion of H2O. Also, from the measurement under various hydrogen concentration in inlet fuel, the diffusion resistance was found to become significantly large with decreasing hydrogen content.

Role of OH bonding in catalytic activity of Nb2O5 during the course of dehydrogenation of MgH2

AbstractThe hydrogen desorption reaction of MgH2, MgH2 → Mg + H2, is accelerated by the addition of metal oxide catalysts (e.g., Nb2O5). From our theoretical calculation of electronic structure, it was predicted that the catalytic activities of metal oxides are related closely to the OH interaction operating at the interface between oxide catalyst and MgH2. In this study, the OH vibration on the Nb2O5‐catalyzed MgH2 was investigated experimentally using FTIR spectroscopy. The broad absorption band due to the OH stretching mode was observed in the region of 2,800–3,600 cm−1 in the FTIR spectra of the specimens when hydrogen desorption reaction was in progress. The absorbance of the band decreased monotonously with decreasing hydrogen content in the specimen during the course of dehydrogenation of MgH2. This experimental result was in agreement with our prediction for the existence of OH interaction in the hydrogen desorption process. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011

Effect of CH 4/H 2 plasma ratio on ultra-low friction of nano-crystalline diamond coating deposited by MPECVD technique

Nano-crystalline diamond coatings were deposited on the silicon substrate using Microwave Plasma Enhanced Chemical Vapor Deposition (MPECVD). Experiments were performed by varying the H 2 content in CH 4/H 2 plasma during synthesis. Raman spectral analysis revealed that with decrease in hydrogen content in the CH 4 plasma, the I D/ I G ratio decreases with the formation of smaller crystallites. Such a film possesses a large grain boundary fraction containing hydrogenated amorphous carbon (a-C:H). During tribological test, sufficient amount of hydrogen present in the grain boundary passivates the dangling σ-bond causing ultra-low friction and extremely low wear evident by improvement in microstructure.

SIMS analysis of hydrogen content in near surface layers of AISI 316L SS after electrolytic polishing under different conditions

Hydrogen concentration in AISI 316L stainless steel samples was monitored perpendicularly to the flat sample surface up to the depth of 0.8 μm, using secondary ion mass spectrometry (SIMS). Depth profile analysis was performed on the samples after electrolytic polishing under different conditions. Analyses were performed on SAJW-05 apparatus with quadrupole Balzers QMA-410 analyzer and Physical Electronics 06-350E ion gun. 5 keV Ar + primary ion beam of 100 μm diameter was scanned over 1 mm × 0.8 mm area. Positive (H +, C +, CH +, O +, Cr +, Fe +) and negative (H −, C −, CH −, O −, OH −, CrO −, FeO −) secondary ion emission was registered from central part of the scanned area (10% of area) during primary ion beam sputtering. Results of hydrogen depth profile analysis were compared for the samples after a conventional electrochemical polishing (EP), and magnetoelectropolishing (MEP). Both EP and MEP processes were carried out under the electrochemical conditions regarding also natural and forced convection. The steel samples taken of a hot-rolled sheet, as received (AR), and after abrasive polishing (MP), were used as a reference. Results show that the increased current density (up to 200 A/dm 2) and electrolyte stirring during electropolishing cause lowering of the hydrogen content in the samples, with the best result regarding hydrogen content decrease obtained on MEP200 sample. In fact, within the MEP process, characteristic with the self-contained electrolyte whirling, the contents of hydrogen are significantly decreased.

712 水素またはケイ素を含有したDLC被膜の熱電特性評価(OS7-(4)オーガナイズドセッション《精密/微細加工と評価》)

This paper presents an investigation of the influence of the Hydrogen or Silicon addition to thermoelectric performance of DLC films on glass substrates using RF plasma CVD method. The DLC films were prepared using CH_4 + HMDSO gas mixture, CH_4 and C_6H_6 as the source gas. The respective thermoelectric performance of the DLC films were evaluated and compared. The Seebeck coefficients of the DLC films decreased with decreasing Hydrogen and increasing the Silicon concentration at the range from 0% to 14.5%. Resistivity of the DLC films was creased with increasing Hydrogen and Silicon concentration at temperatures from 25℃ to 150℃. The power factor of the DLC films was decreased with decreasing Hydrogen concentration at temperatures from 100℃ to 150℃ and increasing the Silicon concentration at temperatures from 25℃ to 150℃.