Reactive Gas Flow Rate Research Articles

Catalytic Hydrodesulfurization of a Spent Tire Pyrolysis Oil Distillate over a Ni–Mo Catalyst

This paper reports an experimental investigation into catalytic hydrodesulfurization of a spent tire pyrolysis oil distillate over a Ni–Mo catalyst. The desulfurization efficacy of the catalyst was evaluated over a range of reaction times (1–36 h), temperatures (300–375 °C), pressures (1–4 MPa), H2 concentrations (16.7–33.3% v/v), and reactive gas flow rates (H2 in N2, 45–90 mL min–1). Increasing temperature, pressure, or H2 concentration increased sulfur removal to a maximum of 99.9% w/w at 350 °C, 4 MPa, and 45 mL min–1 33.3% v/v H2. The treatment not only effectively removed sulfur but also reduced oxygenates, nitrogen-bearing compounds, and alkenes. The role of the Ni–Mo catalyst changed from adsorbing sulfur to catalyzing hydrodesulfurization as it was sulfided to Ni3S2 and MoS2. Full catalyst reduction only slightly increased the initial desulfurization activity but had an insignificant influence on subsequent sulfur removal as both the oxidized and reduced Ni and Mo forms could be sulfided to Ni3S2 and MoS2.

Fabrication of spectrally selective tandem stack of HfZrC/HfZrCN/HfZrON/HfZrO by reactive magnetron sputtering for CSP applications

A novel HfZrC/HfZrCN/HfZrON/HfZrO based solar absorber tandem stack was successfully deposited on silicon and stainless steel (SS) substrates by pulsed DC reactive magnetron sputtering using an alloy target of HfZr. The optimized tandem stack was fabricated by varying the deposition parameters like reactive gas flow rates (C2H2, N2, and O2), sputtering power, and deposition time. X-ray diffraction and X-ray photoelectron spectroscopic methods were used to determine the structural and chemical compositions present in the optimized tandem coatings. In the tandem stack, HfZrC, HfZrCN and HfZrON/HfZrO layers act as a main absorber layer, a semi-absorber layer and double layer anti-reflection in the coating structure. The high spectral selectivity was achieved by optimizing the individual layers in the tandem stack, which exhibits 0.947 of optical absorptance in the solar region and 0.14 of low emissivity in the IR region. The optimized tandem stack is stable up to a temperature of 500 °C in a vacuum environment. The present investigation demonstrates that the developed HfZrC/HfZrCN/HfZrON/HfZrO tandem stack exhibited high solar spectral selectivity and good thermal stability, thus it can be used in high-temperature solar concentrated power applications.

Study on properties of silicon nitride film prepared by PECVD for solar cells

Silicon nitride film containing hydrogen is widely used as antireflection layer and passivation layer in the field of solar cell industrial production. Silicon nitride films containing hydrogen were prepared by industrial plasma enhanced chemical vapor deposition (PECVD) equipment. Fourier Transform Infrared Spectroscopy (FTIR) was used to analyze the composition of the film, to study the influence of reaction gas flow rate and high-frequency power on the composition and properties of the film, and to study the influence of silicon nitride film composition on the passivation effect of the silicon wafer through the minority carrier life of the silicon wafer, so as to clarify the direction of process adjustment in actual industrial production.

Electrical Characterization of Hydrogenated Boron Carbon Nitride Thin Films at Cryogenic Temperatures

Compounds in boron-carbon-nitrogen ternary triangle such as diamond (C), cubic boron nitride (c-BN), and boron carbide (B4C) have gained attention due to their covalent bonding, short bond lengths, low atomic mass[1]. These materials exhibit low dielectric values along with excellent mechanical and thermal strength. Boron carbon nitride (BCN) compounds are known to combine unique properties of boron carbide and boron nitride, with the properties being tunable with varying elemental composition and structure. These outstanding properties have made BCN attractive and finds multi-functional applications in anti-wear and protective coatings, supercapacitors, UV detectors, nanobiotechnology and nanomedicine[2]. BCN thin films also find opto-electronic applications in the harsh environments. While addition of small amounts of hydrogen has been proven beneficial for electrical and optical properties in BCN films, the electrical behavior of hydrogenated BCN films at low temperatures is not evaluated. Such evaluations will further expand the use of of hydrogenated BCN for extreme temperature applications.In this study, BCN thin films are deposited using RF magnetron sputtering with varying hydrogen/nitrogen gas flows. Substrate temperature is kept constant at room temperature. Dual target sputtering from B4C and BN targets is performed to deposit BCN thin films. I-V characterization is performed from room temperature to 70 K. The variation in resistivity with reactive gas flow rate at low temperature is reported.

Graded solar selective absorbers deposited by non-equilibrium RF magnetron sputtering

A new approach to deposit graded solar selective absorbers (SSA) is proposed. High entropy composite SSAs with antireflection layers have been prepared by non-equilibrium reactive RF magnetron sputtering. In order to obtain the gradient composition a relaxation process of target poisoning in the reactive O 2 /Ar atmosphere is employed. After introduction of oxygen the target gradually poisoned, resulting in a smooth change of the absorber composition from pure metals to their oxides. The poisoning relaxation time controls the thickness of SSA and the profile distribution of elements, and can be adjusted by selecting the reactive gas flow rate and RF power. Cintered Al:Cr:Nb:Si:Ta:Ti:Y mixture of powders is used as a target material. The graded SSAs demonstrate encouraging results: a coating with maximal selectivity of 13.4 has the solar absorptivity of 0.884 and emissivity of 0.066. In order to test the deposition method, we also try another target materials (AlTi and AlSc), which show better optical properties with the absorptivity of 0.949 (0.978 for textured surface) and selectivity of 18.6. The non-equilibrium reactive sputtering method proposed in this study has the advantages of simplicity and high production yield compared with the existing methods to deposit effective SSAs including double absorbing layer and multilayer coatings. • A new approach to fabricate graded solar selective absorbers (SSA) is developed. • High entropy composite SSAs was synthesized using nonequilibrium RF sputtering. • Graded composition is obtained using a relaxation process of target poisoning. • The relaxation time of the poisoning defines thickness and profile distribution. • Absorbers demonstrate selectivity of 13.4 and absorptivity of 0.909

Reactive pulsed DC magnetron sputtering deposition of vanadium oxide thin films: Role of pulse frequency on the film growth and properties

In this study, vanadium oxide (VOx) thin films were prepared by reactive pulsed DC magnetron sputtering (PDMS). The influence of pulse frequency (Fp) on the deposition process and properties of VOx films was investigated. The obtained results indicate that with the increase of Fp, which not only can enhance the oxidation of vanadium but also can facilitate the formation of a denser microstructure and smoother surface morphology in the films. More importantly, films with composition from metal-rich to maximum stoichiometry can be accessed by tuning the Fp, without varying any other parameters, especially, the flow rate of reactive gas. And temperature dependent electrical properties of the VOx films can also be tailored via the Fp to fall in the desirable range for microbolometer applications. The impacts of Fp on the reaction between V and O, thin film growth and some dynamic processes occurring during reactive PDMS were analyzed. The corresponding underlying mechanisms were discussed in detail. Our present work may provide a practical and effective way to develop the reactive sputtering towards hysteresis-free, and also paves the way for optimizing the reactive sputtered VOx films with desirable properties via Fp.

Grid-Assisted Co-Sputtering Method: Background, Advancement, and Prospect

In this paper, the incorporation of auxiliary grids/electrodes into the design of the sputtering method is scrutinized by studying the impact of factors such as grid size, grid position, grid bias voltage, electrode sheath design, substrate bias voltage, reactive gas partial pressure, and magnetic trap configuration on the discharge condition and thin-film growth. In this regard, utilizing the updated Berg model for reactive sputtering, the authors obtained a formulation for the reactive grid-assisted sputtering. By the newly-developed formulation, the sputtering rate and the reactive gas partial pressure were simulated as a function of the reactive gas flow rate for various grid-to-target distances, argon partial pressures (0.67, 1.6, and 3.6 Pa), and discharge current densities (0.01, 0.015, and 0.02 A/cm2). According to the computation results, with a grid being utilized, the width of the hysteresis loops can be modified in a broader range by changing either the grid-to-target distance, the argon partial pressure, or the discharge current, resulting in better control over the deposition process. Moreover, the novel configuration of anode-spot-assisted sputtering was proposed to significantly ionize sputtered/neutral atoms near the substrate and to simultaneously deposit sputtered species and products produced as the direct result of introducing dust into the dense plasma. Finally, diverse configurations of the grid-assisted co-sputtering method were introduced for two prime purposes: deposition of composite films in any desired ratios of constituents without significantly changing the other co-sputtering parameters, and favorable alternation of a hysteresis loop for one of the guns at shared gas flow rates.

Selective reduction of lead sulfate containing slag using the fluidized bed reactor

Lead sulfate containing residue is a hazardous waste that should be treated cleanly and efficiently for environment protection and resource sustainability. In this work, a novel reduction-sulfurization process using a fluidized bed reactor was investigated for treating lead sulfate containing residue. The effects of temperature, hydrogen ratio, reaction time and gas flow rate on the conversion of PbSO4 and selectivity of PbS were studied. The results showed that reducing the reaction temperature and hydrogen ratio improved the PbS selectivity, while increasing the reaction time and gas flow rate had no significant effect. In the optimal process conditions, i.e., the reaction temperature 650 °C, hydrogen ratio 20%, reaction time 5 min, and gas flow rate 550 mL min−1, the conversion and sulfurization ratios of PbSO4 were 96.2% and 84.8%, which were 2.0% and 40.1% higher than those obtained in a fixed bed reactor, suggesting that enhanced mass transfer in the fluidized bed reactor benefited the phase transformation of PbSO4 to PbS. This work offers a highly potential approach for processing lead sulfate containing wastes in a clean and economical manner.

Use Of Natural Gas Become a Petrochemical with Zeolite Catalyst

Methane is a hydrocarbon compound that can be used for various purposes. Currently, methane is widely used as fuel, and continues to be developed as a synthetic gas material and petrochemical products that have added value, one of which is formaldehyde. This study aimed to study the partial catalytic oxidation reaction of methane to formaldehyde using MoO3/zeolite as a catalyst. Reactant gas stream consisting of pure O2 and CH 4 were contacted with a rate ratio of 1:20, put into Fixed Bed Reactor therein contained 30 grams of catalyst MoO3/zeolite, and the pressure was maintained at 1 atm. The temperature and flow rate of the incoming reactant gas were used as variables. The main product produced was formaldehyde, besides that there were also CH3 OH, CO, CO2, H2O. The results were analyzed using Gas Chromatography, so it was known that the converted methane was 5.18% and the volume fraction of formaldehyde formed was 1.46%.

Influence of Flow Rate on Catalyst Layer Degradation in Polymer Electrolyte Fuel Cells

With the U.S. Department of Energy (DOE) 2020 durability target for transportation applications of 5000 hours in mind [1], several studies have been performed to understand the factors influencing load cycle durability of the cathode catalyst layer subjected to various operating conditions. In general, high upper potential limit (> 1 V vs RHE), high temperature (> 90 °C) and high relative humidity (RH) during potential cycling have been shown to exacerbate degradation [2]. It is known that Electrochemical surface area (ECSA) loss occurs by Pt dissolution attributed to particle size growth via modified Ostwald ripening, crystal migration, detachment from carbon support due to carbon corrosion, and precipitation in the membrane by chemical reduction due to hydrogen crossover [3].Accelerated stress tests (ASTs) are often used to mimic material component degradation similar to real automotive driving conditions. Different cycle profiles have been shown to cause varying rates of degradation depending on the operating conditions. The influence of flow rate of reactant gases on degradation, however, has received little attention. Stariha et al. [4], showed that a relatively high flow rate AST had the highest degradation acceleration factor and resulted in non-uniform decay rates when compared to low flow rate conditions of nitrogen gas (N2) at the cathode. However, this phenomenon has not been further studied in detail.The current study is aimed at elucidating the effect of flow rate on cathode catalyst layer degradation subjected to a standard DOE square-wave AST protocol. Single cell studies with 5-cm2 active area were performed using Nafion® XL membrane (Ion Power Inc.) and SGL-22 BB gas diffusion electrodes (GDEs) as MEA materials and 1-serpentine flow field. All the MEA samples used in the present study had nominally identical Pt loading and were subjected to a consistent conditioning procedure prior to AST. A DOE square-wave cycling protocol [4] was executed: H2/N2 flows at anode/cathode, voltage cycling between 0.6 V and 0.95 V, and 3 seconds hold at each voltage. 30,000 cycles (total test time of 50 hours) were performed at 100% RH, 80°C, and atmospheric pressure. Three different cathode N2 flow rates of 20 sccm, 40 sccm and 80 sccm were used during the AST with fixed H2 flow of 40 sccm at the anode. ECSA loss was tracked using cyclic voltammograms at several intervals during the AST. Complete electrochemical characterization at beginning and the end of life (BOL and EOL), along with ex-situ diagnostic techniques such as TEM and GIXRD, were used to obtain particle size distribution and spatial degradation profiles. The results indicate higher performance loss (at EOL) for 80 sccm flow of N2 at the cathode compared to 20 sccm and 40 sccm flow rates, most likely due to inhomogeneous Pt loss from inlet to the outlet due to variations in local flow conditions by fully saturated N2 flow at different flow rates.

Sputtered ruthenium oxide coatings for neural stimulation and recording electrodes.

We have investigated the deposition and electrochemical properties of sputtered ruthenium oxide coatings for neural stimulation and recording electrodes. A combination of oxygen and water vapor was used as a reactive gas mixture during DC magnetron sputtering from a ruthenium metal target. The sputtering plasma was monitored by optical emission spectroscopy to determine the reactive species present and confirm the control of plasma chemistry by reactive gas flow rates into the deposition chamber. The effect of the O2 :H2 O gas ratio on the microstructure and electrochemical properties of the ruthenium oxide were studied in detail. We employed a combination of surface characterization techniques, including scanning electron microscopy, x-ray diffraction, and x-ray photoelectron spectroscopy, to understand the relationship between plasma chemistry and the microstructure of the films produced under different gas flow conditions. Electrochemical characterization included cyclic voltammetry, electrochemical impedance spectroscopy, and voltage transient measurements, performed on planar ruthenium oxide electrodes with a geometric surface area of 1960 μm2 . At an O2 :H2 O gas flow rate ratio of 1:3, a cathodal charge-storage capacity per unit film thickness of 228.7 mC cm-2 μm-1 (median, Q1 = 134.5, Q3 = 236.6, n = 15) and a charge-injection capacity (0.6 V anodal interpulse bias) of 7.4 mC cm-2 (median, Q1 = 6.9, Q3 = 8.3, n = 15) were obtained in phosphate buffered saline. The charge-injection capacity of ruthenium oxide sputtered with water vapor in the reactive plasma is comparable with sputtered iridium oxide (SIROF) and higher than reported values for porous TiN, a commonly employed high-surface area stimulation electrode coating.

One-step conversion of syngas to light olefins over bifunctional metal-zeolite catalyst

Light olefins (C2–C4) are fundamental building blocks for the manufacture of polymers, chemical intermediates, and solvents. In this work, we realized a composite catalyst, comprising MnxZry oxides and SAPO-34 zeolite, which can convert syngas (CO + H2) into light olefins. MnxZry oxide catalysts with different Mn/Zr molar ratios were facilely prepared using the coprecipitation method prior to physical mixing with SAPO-34 zeolite. The redox properties, surface morphology, electronic state, crystal structure, and chemical elemental composition of the catalysts were examined using H2-TPR, SEM, XPS, XRD, and EDS techniques, respectively. Tandem reactions involved activation of CO and subsequent hydrogenation over the metal oxide catalyst, producing methanol and dimethyl ether as the main reaction intermediates, which then migrated onto SAPO-34 zeolite for light olefins synthesis. Effects of temperature, pressure and reactant gas flow rate on CO conversion and light olefins selectivity were investigated in detail. The Mn1Zr2/SAPO-34 catalyst (Mn/Zr ratio of 1:2) attained a CO conversion of 10.8% and light olefins selectivity of 60.7%, at an optimized temperature, pressure and GHSV of 380 °C, 3 MPa and 3000 h−1 respectively. These findings open avenues to exploit other metal oxides with CO activation capabilities for a more efficient syngas conversion and product selectivity.

Effects of substrate temperature and reactive gas flow rate on the crystalline ceramic phases formation and tribological properties of W–Ti–Co–C–N thin films produced by co-sputtering

The present study investigates the deposition condition of W–Ti–Co–C–N thin films made by magnetron co-sputtering. The central composite design of experiments was applied for analyzing the effect of substrate temperature (X1) and nitrogen gas flow rate (X2) on the mechanical properties. Nanoindentation, sliding wear test (ball-on-disk method), scanning electron microscopy, atomic force microscopy, and X-ray diffraction techniques were employed to evaluate the tribological properties and microstructure of the thin films. The optimum values of variables were found to be in the range of 500 °C < X1 and 6.5 < X2 < 9 sccm, giving a high hardness of 36.5 GPa, while the friction coefficient and wear rate have the lowest amount of 0.10 and 4 × 10−8 mm3/N.m, respectively.

Iridium oxide top electrodes for piezo- and pyroelectric performance enhancements in lead zirconate titanate thin-film devices

Iridium oxide films of various morphologies are produced by manipulating the reactive gas flow rate in a reactive sputtering process. This study explores the benefits of using planar and nanostructured IrOx top electrodes for Pb(Zr0.52Ti0.48)O3 (PZT) devices employed in piezoelectric and pyroelectric applications in comparison with conventional platinum electrodes. For the first time, the Young’s modulus of a planar IrOx thin film was directly measured to be 300 ± 15 GPa. The piezoelectric performance of devices with planar IrOx showed up to 245% more strain compared to those capped with a Pt electrode. Nanostructured, 2D IrOx platelet networks are observed for films deposited with high oxygen flow rates. The compatibility with various cleanroom processes, such as liftoff, ultrasonic cleaning, and deposition on etched surfaces, is tested for the IrOx nanostructured layers. These films are shown to have low optical reflectivity while retaining good PZT thin-film capacitor polarization and dielectric permittivity. An improved pyroelectric energy harvesting figure of merit by a factor of 2.5× was observed for the IrOx compared to Pt films on the same PZT material.

Plasma Diagnostics in Reactive High-Power Impulse Magnetron Sputtering System Working in Ar + H2S Gas Mixture

A reactive high-power impulse magnetron sputtering system (HiPIMS) working in Ar + H2S gas mixture was investigated as a source for the deposition of iron sulfide thin films. As a sputtering material, a pure Fe target was used. Plasma parameters in this system were investigated by a time-resolved Langmuir probe, radio-frequency (RF) ion flux probe, quartz crystal monitor modified for measurement of the ionized fraction of depositing particles, and by optical emission spectroscopy. A wide range of mass flow rates of reactive gas H2S was used for the investigation of the deposition process. It was found that the deposition rate of iron sulfide thin films is not influenced by the flow rate of H2S reactive gas fed into the magnetron discharge although the target is covered by iron sulfide compound. The ionized fraction of depositing particles decreases from r ≈ 40% to r ≈ 20% as the flow rate of H2S, QH2S, changes from 0 to 19 sccm at the gas pressure around p ≈ 1 Pa in the reactor chamber. The electron concentration ne measured by the Langmuir probe at the position of the substrate decreases over this change of QH2S from 1018 down to 1017 m−3

Effect of gas-phase transport in a planar solid oxide fuel cell

Reaction mechanisms and performance improvement in solid oxide fuel cells (SOFCs) have been the major research areas in this field. There are several discrepancies associated with the kinetics of SOFCs due to the contradicting theories proposed by researchers in this area. This work aims at determining the overpotential due to the gas-phase mass transfer resistance at the various electrodes and the possible electrode reaction characteristics using the inert gas step addition (ISA) method proposed by this research group. The ISA method can quantitatively measure the overpotentials due to the mass transfer resistance at each electrode. The ISA method shows an inverse relationship between the overpotential shift and the square root of the reactant gas flow rate according to the boundary layer theory. The overpotential due to the gas-phase mass transfer resistance is expected to be much higher at the anode than at the cathode, indicating the presence of considerable gas-phase mass transfer resistance at the anode.

Influence of N2 flow rate on UV photodetection properties of sputtered p-ZnO/n–Si heterojuctions

Al–N codoped ZnO heterojunction diodes were grown on n–Si (100) substrates using radio frequency (RF) magnetron sputtering with different flow rates of N2 reactive gas (5–18 sccm). X-ray diffraction results revealed that codoped ZnO thin films have wurtzite structure with crystallite size 25–31 nm. Scanning electron micrographs revealed that all thin film samples have agglomerated flakes type surface morphology. The optical band-gap determined using UV–Vis transmission spectra was found increased with increasing the flow rate of N2. The current-voltage (I–V) measurements were performed in dark and illumination condition using UV light (wavelength 365 nm) for photodetection application. The high stability and fast switching UV photoresponse behaviour was obtained for p-ZnO/n–Si. The maximum responsivity 0.16 A/W was obtained at 3.2 mW/cm2 illumination of the UV light (365 nm) at 5 V bias voltage.

Optimization of W/WAlSiN/SiON/SiO2 tandem absorber consisting of double layer anti-reflection coating with broadband absorption in the solar spectrum region

A novel spectrally selective tandem stack of W/WAlSiN/SiON/SiO2 was deposited on stainless steel 304 and silicon substrates using a four-cathode reactive unbalanced magnetron sputtering system. The coatings were deposited by sputtering of W, Al and Si targets in Ar, Ar + N2, Ar + N2 + O2, and Ar + O2 plasmas. The process parameters were optimized by studying the optical properties of the individual layers using UV-VIS-NIR spectrophotometer and Fourier transform infrared spectroscopy measurements. The high spectral selectivity of the tandem stack was achieved by varying the reactive gas flow rates of N2 and O2 and thickness of individual layers. In the tandem stack, W layer acts as an IR reflector, WAlSiN acts as the main absorber layer, SiON, and SiO2 layers act as anti-reflecting layers. The tandem stack was designed based on graded refractive indices of individual layers with a double layer anti-reflection coating. The tandem stack exhibits superior spectral selectivity with a high solar absorptance of 0.955 in the broadband solar spectrum region and low thermal emissivity of 0.10 in the infrared region. The coating was found to be thermally stable up to 600 °C in vacuum for 200 h under cycling heating conditions.

Rapid analytical method of 90Sr in urine sample: Rapid separation of Sr by phosphate co-precipitation and extraction chromatography, followed by determination by triple quadrupole inductively coupled plasma mass spectrometry (ICP-MS/MS)

A rapid analytical method for determining 90Sr in urine samples (1–2 L) was developed to assess the internal exposure of workers in a radiological emergency. Strontium in a urine sample was rapidly separated by phosphate co-precipitation, followed by extraction chromatography, and the 90Sr activity was determined by triple quadrupole inductively coupled plasma mass spectrometry (ICP-MS/MS). Measurement in the MS/MS mode with an O2 reaction gas flow rate 1 mL min−1 showed no tailing of 88Sr at m/z = 90 up to 50 mg L−1 Sr. The interferences of Ge, Se and Zr at m/z = 90 were successfully removed by phosphate co-precipitation, followed by extraction chromatography with a tandem column of Pre-filter, TRU and Sr resin. This analytical method was validated by the results of the analyses of synthetic urine samples (1.2–1.6 L) containing a known amount of 90Sr along with 1 mg of each of Ge, Se, Sr and Zr. The turnaround time for Sr purification from the urine sample and the 90Sr measurement by ICP-MS/MS was about 10 h. The detection limit of 90Sr was approximately 1 Bq per urine sample, which was lower than 15 Bq per urine after a day of intake giving 5 mSv of unplanned exposure of worker limited by Nuclear Regulation Authority of Japan.

Optical, electrical and microstructural properties of SiC thin films deposited by reactive dc magnetron sputtering

In this study, amorphous silicon carbide (SiC) thin films of variable compositions were deposited on Si (100) and glass substrates by reactive direct current magnetron sputtering of high purity silicon target, using CH4 as reactive gas. The composition and the properties of the coatings have been modified by the change in the reactive gas flow rate from 5% to 50%. Spectrophotometer has been used to measure the optical transmittance and reflectance of silicon carbide thin films over the spectral range from 280 to 1000 nm. The optical constants such as refractive indices and the extinction coefficients of the films were calculated. The band gap values of the deposited films were further evaluated with respect to the gas flow rate. Transmittance values of SiC films changed from 85% to almost 0% in the visible light range. The optical band gap values of the films were altered from 1.7 to 2.7 eV. The activation energy was found to increase from 0.16 eV up to 1 eV and dark conductivity decreased from 7.42 × 10−4 to 1.06 × 10−9 Ω−1cm−1 while carbon concentration in the films increased. The results demonstrated that the optical and electrical properties of SiC films could easily be tailored by modifying Si and C concentrations in the coating composition, for the same film thicknesses.