Hydrogen permeation of tungsten phosphate glass thin films

Thin films of tungsten phosphate glasses were deposited on a Pd substrate by a pulsed laser deposition method and the flux of hydrogen passed thorough the glass film was measured with a conventional gas permeation technique in the temperature range 300–500 °C. The glass film deposited at low oxygen pressure was inappropriate for hydrogen permeation because of reduction of W ions due to oxygen deficiency. The membrane used in the hydrogen permeation experiment was a 3-layered membrane and consisted of Pd film (~ 20 nm), the glass film (≤ 300 nm) and the Pd substrate (250 µm). When the pressure difference of hydrogen and thickness of the glass layer were respectively 0.2 MPa and ~ 100 nm, the permeation rate through the membrane was 2.0 × 10^? 6 mol cm^? 2 s^? 1 at 500 °C. It was confirmed that the protonic and electronic mixed conducting glass thin film show high hydrogen permeation rate.     

The reaction of 2,5-dimethylfuran with hydrogen atoms – An experimental and theoretical study

The kinetics of the reaction of hydrogen atoms with 2,5-dimethylfuran (25DMF), a promising liquid transport biofuel, was experimentally studied in a shock tube at temperatures between 970 and 1240 K and pressures of 1.6 and 4.8 bar. The hydrogen atoms were produced by pyrolysis of ethyl iodide and monitored by atom resonance absorption spectrometry. From the hydrogen atom concentration–time profiles, overall rate coefficients for the reaction H + 25DMF → products (R1) were inferred. The results can be expressed by the Arrhenius equation k₁ = 4.4 × 10^?11 exp(?1180 K/T) cm^?3 s^?1 with an estimated uncertainty of ±30%. A significant pressure dependence was not observed. The results were analyzed in terms of statistical rate theory with molecular and transition state data from quantum chemical calculations. Three different compound methods were used to characterize the potential energy surface: CBS-QB3, CBS-APNO, and G3. It is found that reaction (R1) mainly (>75%) proceeds via an addition–elimination mechanism to yield 2-methylfuran + CH₃. Kinetic parameters for the most important competing channels of the net reaction (R1) were calculated.     

A structural study of premixed hydrogen-air cellular tubular flames

Two dimensionally spatially resolved structural measurements are reported for cellular phenomena in lean laminar premixed hydrogen-air tubular flames. Laser-induced Raman scattering and chemiluminescence imaging are combined to investigate low Lewis number lean hydrogen-air flames. The strong effect of thermal-diffusive imbalance is observed in radial profiles interpolated through the centers of reaction and extinction zones. In the flame cell, the equivalence ratio is ～80% higher than the inlet mixture, resulting in a peak flame temperature of 1600 K that is 550 K above the adiabatic flame temperature of the inlet mixture (1055 K). In the adjacent extinction zone, the temperatures are ～900 K lower than the peak flame temperature and the equivalence ratio is similar to the inlet mixture. Despite doubling the global stretch rate from 200 s^?1 to 400 s^?1, the enhancement of local equivalence ratio and peak temperature in the flame cell remain similar. This enhancement seems dependent on the local cellular flame curvature, that is similar between both cases. With strong preferential diffusion effects, cellular flames offer unique validation data to improve the accuracy of current molecular transport modeling techniques.     

Improvement of piezoelectric coefficient of cellular polypropylene films by repeated expansions

Pressure expansion can be used to improve the piezoelectric d₃₃-coefficients of customary cellular polypropylene (PP) films. In the present paper, the experimental procedure for a double expansion process is described and experimental results of d₃₃-coefficients that can be achieved by choosing expansion pressures from 0.2 to 2 MPa and expansion temperatures from 20 to 120 °C for the two processes are discussed. For example, expansion pressures of 2 MPa, a temperature of 90 to 100 °C for the first expansion and 60 °C for the second expansion, and exposure times of the order of 1 h result in quasistatic d₃₃-coefficients of more than 1000 pC/N which are relatively stable at room temperature.     

Polarization-independent rapidly tunable optical add-drop multiplexer utilizing non-polarizing beam splitters in Ti:LiNbO3

A polarization-independent four-port wavelength-tunable optical add drop multiplexer (OADM) that utilizes non-polarizing relaxed beam splitters has been analyzed and demonstrated in Ti:LiNbO₃ at the 1530 nm wavelength regime. The design utilizes an asymmetric interferometer configuration with strain induced index grating for polarization coupling along its arms that are shifted in position relative to each other. Experimental results of the filter response agree with theoretical predictions. Electrooptic tuning over a range of 15.7 nm at a rate of 0.08 nm/V has been measured. A temporal response < 46 ns to a 20 V step change in tuning voltage has been demonstrated. Fiber-to-fiber insertion loss is ~ 6.5 dB.     

2D soot concentration and burning rate of a vertical PMMA slab using Laser-Induced Incandescence

In the field of fire studies, it is interesting to provide useful data for the validation of soot production and radiation models. 2D soot concentration in the flame and burning rate of the solid surface have been determined in the case of the combustion of a vertical PMMA slab. The local soot concentration has been measured with the Laser-Induced Incandescence method. This one has been calibrated with in situ extinction measurements performed simultaneously (at 1064 nm). The interference signals of LII caused by laser scattering and Laser-Induced fluorescence have been considered and eliminated by a well suited detection. The flat field effect caused by the ICCD camera has also been corrected. The trapping effect on the LII signal has also been considered. The flame grows on the slab after the ignition, and after 1500 s a steady state of combustion appears. During this period, the soot profiles in the boundary layer have been measured at two heights in the flame and their main features will be discussed. It has been possible to determine the burning rate of the PMMA slab from the observation of the displacement of soot profiles in the camera field. The values at both heights are respectively 5.55 and 6.95 g/s/m². These values will be compared with results obtained in other studies.     

Ignition of non-premixed cyclohexane and mono-alkylated cyclohexane flames

Ignition temperatures of non-premixed cyclohexane, methylcyclohexane, ethylcyclohexane, n-propylcyclohexane, and n-butylcyclohexane flames were measured in the counterflow configuration at atmospheric pressure, a free-stream fuel/N₂ mixture temperature of 373 K, a local strain rate of 120 s^?1, and fuel mole fractions ranging from 1% to 10%. Using the recently developed JetSurf 2.0 kinetic model, satisfactory predictions were found for cyclohexane, methyl-, ethyl-, and n-propyl-cyclohexane flames, but the n-butylcyclohexane data were overpredicted by 20 K. The results showed that cyclohexane flames exhibit the highest ignition propensity among all mono-alkylated cyclohexanes and n-hexane due to its higher reactivity and larger diffusivity. The size of mono-alkyl group chain was determined to have no measurable effect on ignition, which is a result of competition between fuel reactivity and diffusivity. Detailed sensitivity analyses showed that flame ignition is sensitive primarily to fuel diffusion and also to H₂/CO and C₁–C₃ hydrocarbon kinetics.     

An experimental and numerical investigation of the hetero-/homogeneous combustion of fuel-rich hydrogen/air mixtures over platinum

The hetero-/homogeneous combustion of hydrogen/air mixtures over platinum was investigated experimentally and numerically in a channel-flow configuration at fuel-rich equivalence ratios ranging from 2 to 7, pressures up to 5 bar and wall temperatures 760–1200 K. Experiments involved in situ one-dimensional Raman measurements of major gas-phase species concentrations over the catalyst boundary layer and planar laser induced fluorescence (LIF) of the OH radical, while simulations included an elliptic 2-D model with detailed heterogeneous and homogeneous reaction mechanisms. The employed reaction schemes reproduced the measured catalytic reactant consumption, the onset of homogeneous ignition, and the post-ignition flame shapes at all examined conditions. Although below a critical pressure, which depended on temperature, the intrinsic gas-phase kinetics of hydrogen dictated lower reactivity for the fuel-rich stoichiometries when compared to fuel-lean ones, homogeneous ignition was still more favorable for the rich stoichiometries due to the lower molecular transport of the deficient oxygen reactant that resulted in modest catalytic reactant consumption over the gaseous induction zone. Above the critical pressure, the intrinsic gaseous hydrogen kinetics yielded higher reactivity for the rich stoichiometries, which resulted in vigorous gaseous combustion at pressures up to 5 bar, in contrast to lean stoichiometry studies whereby homogeneous combustion was altogether suppressed above 3 bar. Computations at fuel-rich stoichiometries in practical channel geometries indicated that homogeneous combustion was not of concern for reactor thermal management, since the larger than unity Lewis number of the deficient oxygen reactant confined the flames to the core of the channel, away from the solid walls.     

Ultrasonically improved semi-hydrogenation of alkynes to (Z-)alkenes over novel lead-free Pd/Boehmite catalysts

This paper reports the application of ultrasound in the semi-hydrogenation of alkynes over two novel Pd/Boehmite catalysts. The semi-hydrogenations of phenylacetylene, diphenylacetylene and 2-butyne-1,4-diol have either been investigated in an ultrasonic bath under atmospheric hydrogen pressure, or in an ultrasonic horn reactor under 0.1–0.5 MPa hydrogen pressure. Alkyne hydrogenation was suppressed by sonication under atmospheric hydrogen pressure, but promoted by sonication under 0.1 MPa of hydrogen pressure. Sonication increased selectivity towards the semi-hydrogenated products in both cases. Catalyst loading, hydrogen pressure, temperature and the presence of quinoline, all impacted on hydrogenation rate, activity and selectivity to semi-hydrogenated products. Palladium leaching from the catalyst was evaluated in ethanol and hexane both under plain stirring and sonication.     

The thermodynamic and kinetic properties of hydrogen dimers on graphene

The thermodynamic and kinetic properties of hydrogen adatoms on graphene are important to the materials and devices based on hydrogenated graphene. Hydrogen dimers on graphene with coverages varying from 0.040 to 0.111 ML (1.0 ML = 3.8 × 10¹⁵cm^? 2) were considered in this report. The thermodynamic and kinetic properties of H, D and T dimers were studied by ab initio simulations. The vibrational zero-point energy corrections were found to be not negligible in kinetics, varying from 0.038 (0.028, 0.017) to 0.257 (0.187, 0.157) eV for H (D, T) dimers. The isotope effect exhibits as that the kinetic mobility of a hydrogen dimer decreases with increasing the hydrogen mass. The simulated thermal desorption spectra with the heating rate α = 1.0 K/s were quite close to experimental measurements. The effect of the interaction between hydrogen dimers on their thermodynamic and kinetic properties was analyzed in detail.     

Ultrasonic assisted synthesis of Bikitaite zeolite: A potential material for hydrogen storage application

Li containing Bikitaite zeolite has been synthesized by an ultrasound-assisted method and used as a potential material for hydrogen storage application. The Sonication energy was varied from 150 W to 250 W and irradiation time from 3 h to 6 h. The Bikitaite nanoparticles were characterized by X-ray diffraction (XRD), infrared (IR) spectral analysis, and field-emission scanning electron microscopy (FESEM) thermo-gravimetrical analysis and differential thermal analysis (TGA, DTA). XRD and IR results showed that phase pure, nano crystalline Bikitaite zeolites were started forming after 3 h irradiation and 72 h of aging with a sonication energy of 150 W and nano crystalline Bikitaite zeolite with prominent peaks were obtained after 6 h irradiation of 250 W sonic energy. The Brunauer–Emmett–Teller (BET) surface area of the powder by N₂ adsorption–desorption measurements was found to be 209 m²/g. The TEM micrograph and elemental analysis showed that desired atomic ratio of the zeolite was obtained after 6 h irradiation. For comparison, sonochemical method, followed by the hydrothermal method, with same initial sol composition was studied. The effect of ultrasonic energy and irradiation time showed that with increasing sonication energy, and sonication time phase formation was almost completed. The FESEM images revealed that 50 nm zeolite crystals were formed at room temperature. However, agglomerated particles having woollen ball like structure was obtained by sonochemical method followed by hydrothermal treatment at 100 °C for 24 h. The hydrogen adsorption capacity of Bikitaite zeolite with different Li content, has been investigated. Experimental results indicated that the hydrogen adsorption capacities were dominantly related to their surface areas as well as total pore volume of the zeolite. The hydrogen adsorption capacity of 143.2 c.c/g was obtained at 77 K and ambient pressure of (0.11 MPa) for the Bikitaite zeolite with 100% Li, which was higher than the reported values for other zeolites. To the best of our knowledge, there is no report on the synthesis of a Bikitaite zeolite by sonochemical method for H₂ storage.     

New experimental evidence and modeling study of the ethylbenzene oxidation

A study of the oxidation of ethylbenzene has been performed in a jet-stirred reactor (JSR) at quasi-atmospheric pressure (800 Torr), at temperatures ranging 750–1100 K, at a mean residence time of 2 s and at three equivalence ratios ? (0.25, 1, and 2). Reactants and 25 reaction products were analyzed online by gas chromatography after sampling in the outlet gas. A new mechanism for the oxidation of ethylbenzene was proposed whose predictions were in satisfactory agreement with the measured species profiles obtained in JSR and with flow reactor data from the literature. A flow rate analysis has been performed at 900 K showing the important role of the combinations with HO₂ radicals of resonance stabilized radicals obtained from ethylbenzene by H-atom abstractions. Other important reactions of ethylbenzene are the ipso-additions of H- and O-atoms and of methyl radicals to the aromatic ring.     

Ultrasound response of viscoelastic changes of cellulose hydrogels triggered with Sono-deviced rheometer

Sono-deviced rheometer,which enabled viscoelastic properties under ultrasound operation, was used to investigate for cellulosic hydrogels. The viscoelastic behavior was compared in cellulosic hydrogels prepared at 0.5, 1 and 2 wt% concentration in the DMAc/LiCl solution. The sono-deviced equipment could measure the effect of changes in storage modulus G’ and loss modulus G” under 43 kHz ultrasound exposure. It was noted that the 43 kHz ultrasound significantly changed the values of the G′, meaning that the hydrogel was soften under the exposure within few seconds. When the ultrasound exposed 50 W of the out-put power at 1% strain, the G′ value of 4.2x10⁴ Pa was reduced to 4.0x10³ Pa during 5 min of the US interval. The declined lowering value of G’ then returned to the original moduli value when ultrasound was stopped. The values of both G’ and G” values were measured at applied strain % during viscoelastic measurements of the cellulosic hydrogels without and with ultrasound exposure. The comparison indicated that the ultrasound has reinforced the effect of the mechanical deformation of the hydrogel structure at the smaller mechanical strain values applied during the ultrasound operation. The ultrasound soften effect on the viscoelastic change efficiently occurred in the 0.5 wt% sample and easily induced the structural deformation probably due to the breakage of hydrogen bonds in the cellulose hydrogels.     

Synergistic effects of combining ultrasound with the Fenton process in the degradation of Reactive Blue 19

The decoloration of reactive dye C.I. Reactive Blue 19 (RB 19) using combined ultrasound with the Fenton process has been investigated. The effect of varying the concentrations of hydrogen peroxide and iron sulfate, initial pH, ultrasonic power, initial dye concentration and dissolved gas on the decoloration and degradation efficiencies was measured. Calibration of the ultrasound systems was performed using calorimetric measurements and oxidative species monitoring using the Fricke dosimeter and degradations were carried out with a 20 kHz probe type transducer at 2, 4, 6 and 8 W cm⁻² of acoustic intensity at 15, 25, 50 and 75 mg L⁻¹ initial dye concentrations. First order rate kinetics was observed. It was found that while the degradation rate due to ultrasound alone was slow, sonication significantly accelerated the Fenton reaction. While the results were similar to those reported for other dyes, the effects occurred at lower concentrations. The rate and extent of decoloration of RB 19 increased with rising hydrogen peroxide concentration, ultrasonic powers and iron sulfate concentration but decreased with increasing dye concentration. An optimum pH value of pH = 3.5 was found. The rate of decoloration was higher when dissolved oxygen was present as compared with nitrogen and argon confirming the solution phase mechanism of the degradation.     

Modeled quenching limits of spherical hydrogen diffusion flames

Hydrogen–air diffusion flames were modeled with an emphasis on kinetic extinction. The flames were one-dimensional spherical laminar diffusion flames supported by adiabatic porous burners of various diameters. Behavior of normal (H₂ flowing into quiescent air) and inverse (air flowing into quiescent H₂) configurations were considered using detailed H₂/O₂ chemistry and transport properties with updated light component diffusivities. For the same heat release rate, inverse flames were found to be smaller and 290 K hotter than normal flames. The weakest normal flame that could be achieved before quenching has an overall heat release rate of 0.25 W, compared to 1.4 W for the weakest inverse flame. There is extensive leakage of the ambient reactant for both normal and inverse flames near extinction, which results in a premixed flame regime for diffusion flames except for the smallest burners with radii on the order of 1 μm. At high flow rates H + OH(+M) → H₂O(+M) contributes nearly 50% of the net heat release. However at flow rates approaching quenching limits, H + O₂(+M) → HO₂(+M) is the elementary reaction with the largest heat release rate.     

The effect of confining pressure on specific energy in Nd:YAG laser perforating of rock

For many years, the oil and gas industry were looking for an alternative method that could significantly reduce the primary drawbacks of using explosives. Perforating oil and gas wells using lasers as a new method is currently under research. In laser perforating, many parameters influence the essential factor of specific energy (i.e. the required energy to remove the unit weight of rock). One of these parameters is the confining pressure. Here, a core sample is placed in the Hoek cell and a new frame is designed to fix them. A small circular part of top side of the cylindrical sample is open in order to interact with the laser beam while the mechanical pressure exerted with the Hoek cell confines the other sides. The results show that the main disparity in specific energy and rate of penetration (ROP) occurs in the range 8–16 MPa of confining pressure. It is found that the amount of specific energy is constant at pressures higher than 16 MPa and consequently, micro cracks that appeared on sample surface at low pressure are absent at higher pressures.     

Propagation and extinction of cyclopentadiene flames

Laminar flame speeds and extinction strain rates of cyclopentadiene/air mixture were determined in the counterflow configuration at atmospheric pressure, unburned mixture temperature of 353 K, and for a wide range of equivalence ratios. The experiments were modeled using recently developed kinetic models. Sensitivity analyses showed that both flame propagation and extinction of cyclopentadiene/air mixtures flames depend notably on the fuel kinetics and subsequent intermediates such as cyclopentadienyl, cyclopentadienone, and cyclopentadienoxy. Analyses of the computed flame structures revealed that the high temperature oxidation of cyclopentadiene depends in general on the kinetics of first few intermediates in the oxidation process following the fuel consumption. The potential reaction pathways of the consumption of cyclopentadienyl radicals were discussed and further investigation and validation is recommended for two relevant reactions that could improve the high temperature oxidation kinetic model of cyclopentadiene. The experimental flame data of this study are the first ones to be reported.     

Interface strain profiling in ultrathin SiO2 gate oxides with medium energy ion scattering spectroscopy

Medium energy ion scattering spectroscopy (MEIS) could identify ∼1 nm interface layer with compressive strain, which depends sensitively on the interface treatment conditions such as oxynitridation, ozone oxidation, tilt of Si(0 0 1) substrates. The interface strain relaxation always shows improvements in gate oxide reliability. Atomic scale investigations of strain profiles with MEIS are reviewed for SiO₂/Si(0 0 1) interfaces.     

A novel polarization splitter in ZnTe tellurite glass three-core photonic crystal fiber

A kind of polarization splitter in ZnTe tellurite glass three-core photonic crystal fiber has been proposed. The polarization splitter is based on the phenomenon of resonant tunneling. We use the finite element method and the full-vector beam propagating method to analyze the characteristics of three-core photonic crystal fiber. Compare with the silica glass three-core PCF, the ZnTe tellurite glass three-core PCF have higher extinction ratios and lower coupling loss, the extinction ratios ERA = ? 164.2681 dB and ERC = ? 37.1742 dB at the wavelength λ = 1.55 μm, and the coupling loss is lower than 0.02 dB. The 8.7983-mm-long splitter is proposed to achieve extinction ratio better than ? 20 dB and a bandwidthof 20 nm.     

Multi-species time-history measurements during high-temperature acetone and 2-butanone pyrolysis

High-temperature acetone and 2-butanone pyrolysis studies were conducted behind reflected shock waves using five species time-history measurements (ketone, CO, CH₃, CH₄ and C₂H₄). Experimental conditions covered temperatures of 1100–1600 K at 1.6 atm, for mixtures of 0.25–1.5% ketone in argon. During acetone pyrolysis, the CO concentration time-history was found to be strongly sensitive to the acetone dissociation rate constant k₁ (CH₃COCH₃ → CH₃ + CH₃CO), and this could be directly determined from the CO time-histories, yielding k₁(1.6 atm) = 2.46 × 10¹⁴ exp(?69.3 [kcal/mol]/RT) s^?1 with an uncertainty of ±25%. This rate constant is in good agreement with previous shock tube studies from Sato and Hidaka (2000) [3] and Saxena et al. (2009) [4] (within 30%) at temperatures above 1450 K, but is at least three times faster than the evaluation from Sato and Hidaka at temperatures below 1250 K. Using this revised k₁ value with the recent mechanism of Pichon et al. (2009) [5], the simulated profiles during acetone pyrolysis show excellent agreement with all five species time-history measurements. Similarly, the overall 2-butanone decomposition rate constant k_tot was inferred from measured 2-butanone time-histories, yielding k_tot(1.5 atm) = 6.08 × 10¹³ exp(?63.1 [kcal/mol]/RT) s^?1 with an uncertainty of ±35%. This rate constant is approximately 30% faster than that proposed by Serinyel et al. (2010) [11] at 1119 K, and approximately 100% faster at 1412 K. Using the measured 2-butanone and CO time-histories and an O-atom balance analysis, a missing removal pathway for methyl ketene was identified. The rate constant for the decomposition of methyl ketene was assumed to be the same as the value for the ketene decomposition reaction. Using the revised k_tot value and adding the methyl ketene decomposition reaction to the Serinyel et al. mechanism, the simulated profiles during 2-butanone pyrolysis show good agreement with the measurements for all five species.