Hydrogen Gas Flow Research Articles

Synthesis and Characterization of Fe-Co/mesoHZSM-5 : Effect of Desilication Agent and Iron-cobalt Composition

Synthesis of Fe-Co/meso-HZSM5 catalyst, intended to be applied in Fischer-Tropsch (FT) reaction was investigated. The study emphasized the effect of desilication agents, NaOH and KOH, on the catalyst materials properties. Impregnation composition of active metal (Fe and Co) was also examined. HZSM-5, converted from ammonium ZSM-5 through calcination, was treated with NaOH and KOH for desilication, followed by impregnation with 10% metal loading. Fe composition in the initial mixture was varied at 10-50% from total composition. After impregnation, reduction was applied by flowing hydrogen gas at 400 ℃ for 10 hours. The use of KOH solution induced greater mesoporous volumes; however, it had a detrimental effect on zeolite crystal structure. NaOH solutions, on the other hand, increased mesopore area as high as 100%, indicated from surface area increase from 266.28 m2/g of HZSM-5, to 526.03 m2/g of NaOHdesilicated HZSM-5. In addition, the application of NaOH solution increased pore volume from 0.14 cc/g to 0.486 cc/g. Further, more Fe-Co alloys and less oxide of iron (Fe2O3) as well cobalt (Co3O4) had been commonly observed in the produced catalysts. The largest Fe-Co alloys could be found in 50Fe-50Co/HZSM-5.

Effect of hydrogen and argon shrouding gas flow rate on high-temperature oxidation behavior of NiCrAlY coating by solid shielding shrouded plasma spray (SSPS)

This paper investigates the effect of hydrogen and argon shrouding gas flow rates in solid shielding shrouded plasma spray (SSPS) method on in-flight oxidation, formation and growth of the TGO layer and high-temperature oxidation behavior of NiCrAlY coating. With this in mind, NiCrAlY coating was applied on the Hastelloy X substrate by solid shielding shrouded plasma spray (SSPS) and compared with the conventional atmospheric plasma spray (APS). High-temperature oxidation was carried out at 1000 °C for 200 h. Microstructure of the coatings before and after oxidation was evaluated by scanning electron microscope (SEM) equipped with energy dispersive spectrometer (EDS). To study the effect of solid shielding shrouded plasma spray on the properties of metallic coatings, the variable parameters such as the shroud gas nature (Ar, H2), the gas injection method (internal, external or both) and their flow rates, were examined. The results indicated the better operation of the coatings deposited under the protection of internal argon shroud gas with a flow rate of 75SLPM, which could be due to better protection of the metallic particles against in-flight oxidation. This sample represented the lowest thickness of the TGO layer (2.25 μm). The formation and growth of the TGO layer were higher in APS coating (3.82 μm) than that of SSPS. Consequently, this can prove by the preservation of mono-layered TGO of SSPS coating even after 200 h oxidation without the formation of any CSN clusters.

Design and optimization of electrochemical cell potential for hydrogen gas production

Abstract This study deals with the optimization of best working conditions in molten melt for the production of hydrogen (H2) gas. Limited research has been carried out on how electrochemical process occurs through steam splitting via molten hydroxide. 54 combinations of cathode, anode, temperature and voltage have been investigated for the optimization of best working conditions with molten hydroxide for hydrogen gas production. All these electrochemical investigations were carried out at 225 to 300°C temperature and 1.5 to 2.5 V applied voltage values. The current efficiency of 90.5, 80.0 and 68.6% has been achieved using stainless steel anodic cell with nickel, stainless steel and platinum working cathode respectively. For nickel cathode, an increase in the current directly affected the hydrogen gas flow rate at cathode. It can be hypothesized from the noted results that increase in current is directly proportional to operating temperature and applied voltage. Higher values were noted when the applied voltages increased from 1.5 to 2.5 V at 300°C, the flow rate of hydrogen gas increased from 1.5 to 11.3 cm3 min−1, 1.0 to 13 cm3 min−1 in case of electrolysis @ stainless steel and @ graphite anode respectively. It is observed that the current efficiency of stainless steel anodic cell was higher than the graphite anodic cell. Therefore, steam splitting with the help of molten salts has shown an encouraging alternate to current methodology for H2 fuel production.

Development of a pulsed radio frequency ignited multicusp-free negative hydrogen ion source.

A multicusp-free external antenna based radio frequency (RF) negative hydrogen (H-) ion source was developed to produce 16 mA of H- ion current at -50 kVDC accelerating voltage operated with a pulse width of 2 ms at 2 Hz repetition rate. A pulsed RF igniter system is devised for generating the initial electron and ion pairs required to generate the main plasma in the pulsed mode. This pulsed RF igniter reliably starts ignition with a hydrogen gas flow rate in the range of 18-50 standard cubic centimeter per minute (SCCM). This system eliminates the need of igniter in continuous operation although it is operated in low power mode. This source operating at a low average power and without any moving parts can be expected to have a superior lifetime. This paper describes the development and operational characteristics of the pulsed RF ignited H- ion source.

Spectroscopic study of plasma nitrocarburizing processes with an industrial-scale carbon active screen

The active screen plasma nitrocarburizing technology is an improvement of conventional plasma nitrocarburizing by providing a homogeneous temperature distribution within the workload and reducing soot formation. In this study, an industrial-scale active screen (AS) made of carbon-fibre-reinforced carbon serves as the cathode as well as the carbon source for the plasma-chemical processes taking place. The pulsed dc discharge was maintained at a few mbar of pressure while simultaneously being fed with a mixed gas flow of hydrogen and nitrogen ranging from 10 to 100 slh. Using in situ infrared laser absorption spectroscopy with lead salt tuneable diode lasers and external-cavity quantum cascade lasers, the temperatures and concentrations of HCN, NH3, CH4, C2H2, and CO have been monitored as a function of pressure and total gas flow. To simulate industrial treatment conditions the temperature of the sample workload in the centre of the reactor volume was kept at 773 K by varying the plasma power at the AS between 6 and 8.5 kW. The resulting spectroscopically measured temperatures in the plasma agreed well with this value. Concentrations of the various species ranged from 6 × 1013 to 1 × 1016 cm−3 with HCN being the most abundant species.

Formation of ε-Co nanocrystals in borosilicate and aluminosilicate glasses

Formation of cobalt nanocrystals in durable borosilicate and aluminosilicate glass matrices is studied. Using a hydrogen gas flow treatment, ε-Co nanocrystals precipitate primarily in these glasses. This rare Co allotrope, which so far has mainly been synthetized by organometallic routes is found for the first time in a glass. XRD and TEM results indicate that ε-Co is present in glasses ≥ 500 °C and that it successively transforms into the more stable α- and β-Co allotropes. Primary formation of the ε-Co in glasses is in agreement with the Ostwald-Volmer rule of stage as it yields the lowest density change with respect to the parent glass among the three Co allotropes.

Analytical and numerical predictions of hydrogen gas flow induced by wall and corner leakages in confined space

This contribution addresses a newly developed semi-analytical model coupling the zone model, virtual point source buoyancy plume theory and mirror theory to predict the gas flow behaviors of leaked hydrogen restricted by a wall or a corner in confined space with an opening. The effects of leaked hydrogen mass flux, opening geometry and the leakage location on interface height, outflow velocity and hydrogen molar fraction in upper layer, were thoroughly investigated at steady stage. A computational fluid dynamics tool, FLACS, was employed to simulate the dispersion process in different leakage scenarios and validate the capability of the derived analytical model. The results show that in all center, wall and corner leakage circumstances, the interface height declines with larger leakage mass flux, whereas the outflow velocity and hydrogen molar fraction change inversely. The interface height, outflow velocity and hydrogen molar fraction are positively, negatively and negatively correlated with the opening dimension, respectively. The opening height plays a more important role in determining the interface height and hydrogen molar fraction but hardly affects the outflow velocity. The interface height keeps unchanged with varying leakage locations when other parameters remain constants. However, according to the mirror theory the outflow velocities in corner and wall leakage conditions are 0.63 and 0.4 times of those in center leakage case. Meanwhile, the hydrogen molar fractions of corner and wall leakages are 1.59 and 2.52 times of the ones in center leakage. All these ratios are validated by the corresponding analytical and numerical predictions. The credibility of the analytical model is verified by the good agreement with the numerical estimations.

Deposition of Gallium Oxide Nanostructures at Low Substrate Temperature by Chemical Vapor Deposition

Semiconductor nanostructures (NSs) are usually synthesized at short source-substrate distances where the substrate temperature is high using the chemical vapor deposition (CVD) technique. Herein, we report for the first time the growth of -Ga2O3 NSs at low substrate temperature ∼260 °C in a CVD system when gallium (III) oxide powder was reduced to Ga vapor at 1000 °C under hydrogen atmosphere. The polycrystalline nature of the Ga2O3 NSs was confirmed by high-resolution X-ray diffraction (HR-XRD) analysis. Appearance of additional diffraction planes, increasing X-ray diffraction signal strength and shift of 2θ to smaller angles was observed with increasing hydrogen supply in the reactor. Field-emission scanning electron microscope (FE-SEM) revealed different morphologies with increasing amount of Ga2O3 on the substrate. Elemental analysis by using energy dispersive X-ray spectroscopy (EDX) showed increasing Ga atoms, and Ga/O atomic ratio with increase in hydrogen gas flow rate. Optical reflectance measurements by UV–vis-NIR spectrophotometer revealed optical bandgaps ranging from 4.94 to 4.82 eV, attributed to increasing film compactness, Ga/O and oxygen vacancies on the prepared films.

Activated carbon from bamboo waste: Effect of activation sequences and iron-cobalt impregnation to material properties and catalyst performance

Bamboo "Ori" (Bambusa blumeana) is a potential raw material for activated carbon production due to rapid growth and abundant availability. Raschig ring activated carbon for industrial catalyst, catalyst support and adsorbent in purification process can be made from small diameter bamboo branches. The activated carbon as a support for Fe and Co catalysts in Fischer-Tropsch synthesis provides an opportunity for direct conversion from synthesis gas (CO and H2) to biofuel (C5-C19). The effect of activation sequence on the activated carbon and impregnation product properties was investigated. Activated carbon was obtained from bamboo waste through various activation sequences (steam, phosphoric acid and carbonization), then it was impregnated with 10% metal loading. The Fe composition in the initial metal mixture was varied at 0-40% from total composition. After impregnation, reduction was applied by flowing hydrogen gas at 400°C for 10 hours.These catalysts were performed for Fischer-Tropsch synthesis in a batch reactors. The activation sequences of carbonization-acid and acid-carbonization gave similar surface area (2173 and 2091 m2 /g), much greater than the steam-carbonization-acid and steam-acid-carbonization (427 and 478 m²/g) sequences. Functionalization with nitric acid produced oxygen functional groups of carboxyl, carbonyl, alcohol and phenol.Catalyst reduction gave Fe, Co and Fe-Co alloys as active metal and a little oxides Fe2O3 and Co3O4 . The larger amount of Fe-Co alloys were formed on 30Fe-70Co/Activated Carbon and 40Fe-60Co/Activated Carbon catalyst. Fischer-Tropsch synthesis was performed in batch at H2/CO = 2, Fe-Co/Activated Carbon catalyst, 250°C, 8 bars for 18 hours. The n-paraffin compound is only formed in 40Fe-60Co/Activated Carbon catalyst which contained the highest amount of Fe-Co alloys. The more Fe-Co alloys content was, more n-paraffin was formed. The n-paraffin (OH) compound was only formed in 10Fe-90Co/AC. The more Co content was, more n-paraffin (OH) was formed.

Gas‐solid displacement reactions in the Ti–W–C system

AbstractDisplacement reactions between binary and ternary ceramics in the Ti–W–C system and reactive gaseous atmospheres are investigated in this work. Specifically, WC and 50:50 wt% TiC:WC solid solution powders were exposed to flowing hydrogen gas, or equilibrated against an excess of titanium in the presence of iodine, to form metallic tungsten and TiC solid products. In the case of pure WC reacting with hydrogen, transformation to metallic tungsten occurred as a result of removal of chemically bound carbon as gaseous hydrocarbons. In the case of pure WC reacting with titanium iodide vapors, transformation was accompanied by the appearance of TiC as a solid product formed at the gas‐solid interface. In the case of 50:50 wt% TiC:WC solid solution powders, hydrogen was generally found to be an ineffective displacing reagent, whereas reaction with titanium iodide vapors was observed to proceed virtually to completion, resulting in a two phase product mixture comprising metallic tungsten and TiC. For the latter case, a variety of microstructures could be observed within a given batch, including tungsten platelets and/or lamellae in a TiC matrix, or coarse tungsten grains interspersed with TiC grains. These morphological variations are speculated to arise from compositional variation in the starting material and the occurrence of local rapid coarsening along fast diffusion pathways within reacting agglomerates and polycrystalline primary particles. The observed reaction products and relative efficacy of gaseous reagents to promote displacement reactions in the Ti–W–C system are rationalized on the basis of thermodynamic predictions. The reaction between 50:50 wt% TiC:WC solid solution powders and titanium iodide vapors constitutes the first known report of an internal displacement reaction proceeding via gaseous intermediates in a nonoxide ceramic system.

Spectroscopic method to measure the residual deuterium pressure during vacuum arc discharge with deuterated cathode

The pressure beyond the cathode surface is an important parameter in vacuum arc discharge. However, it is difficult to be measured because of its cramped space. A spectroscopic method using hydrogen gas as a tracer is proposed to measure the temporal residual deuterium pressure in a vacuum arc discharge with deuterated cathode. The principle of this method is that the spectral and chemical characteristics are almost the same for isotopes and atom spectrum intensity is proportional to its pressure. The method is in-situ and does not disturb the discharge. Besides the method could avoid the effect of cathode spot's random jumping. In order to verify the method, an integrated experiment is carried out. Different hydrogen gas flows are used in the experiment. The residual deuterium pressures are almost the same at different hydrogen gas flows, which is about 0.01 Pa when the discharge arc current is 90 A and pulse duration is 5 μs The low pressure may be caused by the large measurement space beyond cathode spots. The method could be used to measure temporal pressure in cramped space.

Boosted Electron-Transfer Kinetics of Hydrogen Evolution Reaction at Bimetallic RhCo Alloy Nanotubes in Acidic Solution.

RhCo alloy nanotubes were synthesized via the reduction of single-phase Co2RhO4 nanotubes. The reduction was conducted by thermal annealing of the Co2RhO4 nanotubes under hydrogen gas flow. The crystallinity of the prepared RhCo alloy nanotubes depended on the reduction temperature: amorphous phase (200 °C reduction) and the crystalline phase (300 °C reduction). The hydrogen evolution reaction (HER) on RhCo alloys was investigated with voltammetry in 1.0 M HClO4 solution. Amorphous RhCo alloys provided lower overpotential than the crystalline counterpart despite their similar morphology and composition. Of great interest, amorphous RhCo alloy nanotubes exhibited an outstanding HER electroactivity verified with a low overpotential at -10 mA cm-2 (-22 mV) and a small Tafel slope (-24.1 mV dec-1), outperforming commercial Pt, pure Rh metal, and the other previously reported Rh-based catalysts. This excellent HER activity of amorphous RhCo nanotubes was attributed to the amorphous structure having a large electrochemical surface area and maximized Rh-Co interfaces in the alloy facilitating HER. Active but expensive Rh alloyed with less active but cheap Co was successfully demonstrated as a potential cost-effective HER catalyst.

In situ synthesis of B4C–SiC, B4C–TiB2, and B4C–ZrB2 composites from organic–inorganic hybrid precursor via a simple bottom-up approach

Boron carbide (B4C) and its in situ composites were synthesized via a simple bottom-up process using low-cost boric acid and a sucrose-based precursor solution with silicon (Si), titanium (Ti), or zirconium (Zr) species. The precursor solution was first dried at 250 °C and then heat-treated at 1650 °C for 90 min under argon and hydrogen gas flow. Free boron oxide phases appeared in the boric acid-rich precursor compositions, whereas free carbon appeared in the sucrose-rich compositions. The B4C particles exhibited a coarser and elongated morphology with boron-rich stoichiometric compositions (B/C:4/1), whereas the particles had a finer equiaxed morphology in carbon-rich compositions (B/C:2/1). As the carbon concentration increased in the precursor solution, the hexagonal lattice parameters of B4C and its corresponding lattice volume decreased. On the other hand, the addition of Si, Ti, or Zr species into the precursor solution resulted in the formation of a silicon carbide (SiC), a titanium diboride (TiB2), or a zirconium diboride (ZrB2) phase along with the B4C phase and was associated with an overall reduction in the average particle size and a more uniform size distribution. Moreover, the addition of these species increased the B4C lattice parameter with a corresponding increase in the lattice volume; this was most likely due to an elemental substitution into the B4C lattice. In addition, the data provide evidence that the formation of an ideal B4C lattice is possible when synthesized from carbon-rich precursors using this method, despite the potential presence of free carbon.

Feasibility studies for hydrogen reduction of ilmenite in a static system for use as an ISRU demonstration on the lunar surface

The ESA-ROSCOSMOS mission, Luna-27, scheduled for launch in 2023, includes a payload known as PROSPECT that is intended for sampling the polar lunar regolith through drilling, with subsequent analyses of the retrieved material. One of the aims of the analytical module, ProSPA, which is being developed at The Open University, is to identify and quantify the volatiles present in the extracted sample that are released by heating from ambient up to 1000 °C and analyzed by the mass spectrometers to assess their potential for in-situ resource utilization. The ProSPA design also includes a provision to test the extraction of water (and its associated oxygen) from lunar regolith by hydrogen reduction. Previous attempts at such extractions generally utilize a flow of hydrogen gas through the feedstock to efficiently extract water. However, in ProSPA, samples would be processed in a static mode, which leads to concerns that the reaction may be suppressed by inefficient removal of water vapor above the regolith. A first order theoretical assessment of the diffusion of gases in such a system was performed and suggested that water can diffuse through the system at an acceptable rate and be collected upon a cold finger thus enabling the reaction to proceed. Proof of concept experiments were successfully performed with a ProSPA breadboard using ilmenite samples up to ∼45 mg heated at 900 °C for 60 min. Subsequent heating of the cold finger, in vacuum, released 17 ± 1 μmol water from a 44.7 ± 0.5 mg sample, equating to a calculated yield of 0.6 ± 0.1 wt % oxygen, and a reduction extent of 5.8 ± 0.4%. A sample of mass 11.2 ± 0.5 mg had the greatest calculated yield of 1.4 ± 0.2 wt % oxygen, and this equates to a reduction extent of 12.9 ± 1.5%. SEM analyses of cross-sections of grains showed evidence of a reduction reaction inside the ilmenite grains with some showing greater reduction than others, indicating the reaction is limited by furnace dimensions, reaction kinetics and geometry. The results suggest that the ProSPA ISRU experiment should be capable of producing water, and therefore oxygen, by hydrogen reduction of ilmenite, ultimately this could be a viable technique for producing oxygen from ilmenite-containing lunar regolith with ProSPA.

Effect of direct ultrasound synthesis via a sesquihydrate route on bismuth‐promoted vanadyl pyrophosphate catalysts

AbstractA series of 1, 3, and 5% Bi‐doped vanadium phosphate catalyst catalysts were prepared via sesquihydrate route using direct ultrasound method and were denoted as VPSB1, VPSB3, and VPSB5, respectively. These catalysts were synthesized solely using a direct ultrasound technique and calcined in a n‐butane/air mixture. This study showed that catalyst synthesis time can be drastically reduced to only 2 hr compared to conventional 32–48 hr. All Bi‐doped catalysts exhibited a well‐crystallized (VO)2P2O7 phase. In addition, two V5+ phases, that is, β‐VOPO4 and αII‐VOPO4, were observed leading to an increase in the average oxidation state of vanadium. All catalysts showed V2p3/2 at approx. 517 eV, giving the vanadium oxidation state at approx. 4.3–4.6. Field‐emission scanning electron microscopy micrographs showed the secondary structure consisting of thin and small plate‐like crystal clusters due to the cavitation effect of ultrasound waves. VPSB5 showed the highest amount of oxygen species removed associated with the V5+ and V4+ species in temperature‐programmed reduction in H2 analyses. TheX‐ray absorption near edge structure (XANES) measurement showed the occurrence of vanadium oxide reductions in hydrogen gas flow, indicating the presence of V4+ and V5+ species. Higher average valence states of V5+, indicating more V5+ phases, were present. The addition of bismuth has increased the activity and selectivity to maleic anhydride.

The hydrogen flow characteristics of the multistage hydrogen Knudsen compressor based on the thermal transpiration effect

Multistage hydrogen Knudsen compressor based on the thermal transpiration effect has very exciting prospect for the hydrogen transmission in the micro devices. Understanding of the hydrogen flow characteristic is the key issue for the designs and applications of the hydrogen energy systems. Firstly, the numerical models of the multistage hydrogen Knudsen compressor are established. The distributions of the rarefaction, velocity and temperature at different stages of the hydrogen flow are calculated and presented. Moreover, the dimensional pressure increases of the hydrogen gas flow are analyzed, and the flow behaviors in the microchannel and the connection channel are discussed. Secondly, the numerical simulation at different connection channel height is implemented, and the hydrogen gas flow characteristics in the connection are analyzed. Especially, the performances of the pressure drop in the connection channel under different channel heights are studied, and the hydrogen gas compression characteristics of different cases are compared and discussed. Also, the effect of the connection channel height on the hydrogen gas pressure increase in the microchannel is investigated. The studies presented in this paper could be greatly beneficial for the hydrogen detection and transmission.

Direct ultrasound synthesis of vanadyl pyrophosphate catalyst for partial oxidation of n-butane to maleic anhydride

Three VPO catalyst were prepared via direct ultrasound technique using organic, sesquihydrate and dihydrate routes, denoted as VPOuo, VPOus and VPOud respectively. These catalysts were synthesised solely on direct ultrasound technique and calcined in n-butane/air mixture. All catalysts exhibited well-crystallised (VO)2P2O7 phase. VPOus and VPOud showed αII-VOPO4, which led to an increase in average oxidation state of vanadium. All catalysts were showing O1s approx. 530 eV, similar P2p value and V2p3/2 at approx. 517 eV, giving vanadium oxidation state of approx. 4.0 – 4.2. FE-SEM micrographs showed the secondary structure consisting of thin plate-like crystals in different sizes agglomerate to each other due to cavitation effect. HR-TEM demonstrated the existence of polycrystalline phase. The nature of the oxidants was investigated by TPR in H2. VPOus showed highest amount of total removal of oxygen species suggesting that it had highest activity compared to VPOuo and VPOud. The XANES measurement of these catalysts showed the occurrence of vanadium oxide reductions in flowing hydrogen gas, which indicates the presence of V4+ and V5+ species. Catalytic tests demonstrated that the activity and selectivity to maleic anhydride increased with direct ultrasound technique. This study showed that catalyst synthesis time can be reduced to only 2 hours and giving polycrystalline particles compared to conventional method.

Estimating leaked hydrogen gas flow in confined space through coupling zone model and point source buoyancy plume theory

A semi-analytical model combining zone model and virtual point source buoyancy plume theory is proposed to predict the gas flow and dispersion behaviors of leaked hydrogen in confined space with an opening. The height of interface between the upper and lower layers, outflow velocity and hydrogen molar fraction in outflow at steady stage are quantitively analyzed to study the effects of leakage mass flux and opening geometry. A computational fluid dynamics (CFD) tool, FLACS, is employed to simulate the interested scenarios and validate the reliability of the developed model. The results show that the interface height declines as the leakage mass flux increases, but the outflow velocity and hydrogen molar fraction exhibit inverse tendencies. The interface height is positively proportional to both opening width and height, but the opening height plays a more important role. At steady stage, the simulated interface height fluctuates within 0.1 m uncertainty range, which is identical to the grid size, and it well fits the analytical estimations. The opening width affects the outflow velocity more greatly than that of opening height. The fluctuation of the simulated interface height enhances the inaccuracy of the predicted outflow velocity in the acceptable range. Meanwhile, it is found that with fixed opening geometry the ratio of outflow velocity with higher leakage mass flux to that with lower leakage mass flux remains at 1.28 when the leakage mass flux is doubled. The variations of opening width and height have little and significant effects on outflow hydrogen molar fraction, respectively. Similarly, for given opening geometry the ratio of hydrogen molar fraction with higher leakage mass flux to that with lower leakage mass flux is about 1.58 when the leakage mass flux is doubled.

Investigation of thermal treatment on improving the performance behavior of Si PIN alpha radiation detectors

The silicon-based PIN-type photodiode was designed and fabricated employing conventional bipolar planar technology using different annealing process to reduce the leakage current and detector energy resolution. In this process the effects of the Annealing and gas flow rate on the detector electrical properties such as capacitance-voltage (C–V) of MOS capacitors and current-voltage (I–V) of diodes and alpha spectral measurement are specified. Silicon PIN radiation detectors are made on four similar fabrication process with different post thermal annealing at constant temperature and different hydrogen gas flow (10 sccm–60 sccm). The study results proves that the detector with 15 sccm hydrogen gas flow shows lower leakage current due to the lower remained interface traps density at the Si/SiO2 interface. Si PIN diodes were fabricated, by considering all the important aspects discussed in this paper, and consequently an excellent spectral response was observed.

Effect of the microchannel obstacles on the pressure performance and flow behaviors of the hydrogen Knudsen compressor

The hydrogen Knudsen compressor has potential applications on the hydrogen transmission for the microdevices and systems. In this paper, the numerical model of the hydrogen Knudsen compressor was established, combining the NS continuity equations with the slip boundary conditions. The effect of structures on the performance of the hydrogen Knudsen compressor is studied by generating different obstacles in the microchannels. This paper is mainly concerned on the rectangular and the triangular obstacles, and the influence of the obstacles length and height are investigated, respectively. The Knudsen number distribution and the rarefaction of the hydrogen gas flow are analyzed. Also, the characteristic of the pressure increase for the compressor under different parameters are investigated and discussed. The effect of the structure parameters on the flow velocity distributions are detailed described, as well as the velocity contour and the vortex distributions. Moreover, the variation of the Knudsen layers of the hydrogen gas flow in the hydrogen Knudsen compressor is presented, and the key factor of the Knudsen layers is analyzed and discussed. The results is significantly beneficial for the applications and designs of hydrogen Knudsen compressor.