Reactive Gas Flow Research Articles

(Digital Presentation) Fabrication and Characterization for Vanadium Oxynitride Thin Films By Magnetron Sputtering

Vanadium oxynitride (VNxOy, x+y=1) is a metallic compound between vanadium oxides (VO, V2O3, V2O5) and vanadium nitride (VN) which would have interesting properties and functions that potentially can be supplied for different applications. In this study, vanadium nitride and oxynitride thin films were obtained by reactive magnetron sputtering using vanadium targets, Ar as plasma carrier, and a mix of N2 and O2 as reactive gas. The ratio of mass flow between the two gases is maintained around O2:N2=1:20 during the process. To obtain crystalline phases of oxynitrides a post rapid thermal annealing (RTP) in Ar atmosphere at 600ºC and 700ºC for 5 minutes was done. The purpose of the study is to define the effect of the magnetron sputtering parameters, such as reactive gas flow rates, and annealing temperature on the composition, microstructure, and optical properties of the obtained vanadium oxynitride thin films. The characterization of obtained films includes the examination of thickness and morphology by the surface profiler and SEM; identifying crystal structures and further microstructural vibration modes of molecular polarizability by X-ray diffraction and Raman spectroscopy, respectively; evaluation of the chemical composition of films by XPS analysis; assessing of optical transmittance, reflectance, and absorbance by the UV-visible- NIR spectrometer. Experimental data reveal that the annealed films can be oxynitrides when the oxygen flow rate is below 0.25 sccm and the ratio of oxygen/nitrogen ≤1/20. The annealed vanadium oxynitride films in terms of their properties are closer to vanadium nitrides than to oxides: more metallic than semi-conductive with dark appurtenance and high optical absorbance across the spectrum between 200 and 900 nm. The optical absorbance reaches almost 90% around 300 nm and then slowly reduces to 70% at 900 nm. Thus, these films could be good optical shields. For practical usage, the deposition of O2:N2=1/20, O2<0.25 sccm, and 600ºC annealing are recommended because of the truly low transmittance (<10%) through films.

A computational study of the double hysteresis phenomenon during reactive sputtering

When process parameters such as the reactive gas partial pressure or the discharge voltage are studied as a function of the reactive gas flow during reactive magnetron sputtering, the obtained curve has an S-shape. A direct consequence of this behaviour is that process control based on the reactive gas flow exhibits hysteresis. Under specific conditions, it is possible to observe two S-shaped curves: one when the reactive gas pressure is increased, the other during the return to the initial state by decreasing the reactive gas pressure. This behaviour has been described as double hysteresis behaviour. The origin of the double hysteresis behaviour is computationally studied by high-throughput calculations using a previously developed model. The influence of different process and material parameters were evaluated based on newly developed measures to characterize the calculated process curves. This high-throughput analysis reveals that the double hysteresis behaviour is linked to the difference in the removal rate of non-reacted implanted ions during the increase and decrease of the reactive gas pressure. Within the parameter space a region can be defined for which the double hysteresis behaviour is strong. The latter can not only assist further experiments to study this behaviour but also defines conditions to limit its impact. For Al, a discharge current density of approximately 0.025 A cm−2 was found to maximize double hysteresis.

Comparative Study on the Influence of Reactive Gas Flow Rate on the Growth and Properties of P-doped TiAlN Coatings Prepared by DcMS and HiPIMS

Comparative Study on the Influence of Reactive Gas Flow Rate on the Growth and Properties of P-doped TiAlN Coatings Prepared by DcMS and HiPIMS

One-Dimensional Model and Numerical Solution to the Viscous and Heat-Conducting Reactive Micropolar Real Gas Flow and Thermal Explosion

One-Dimensional Model and Numerical Solution to the Viscous and Heat-Conducting Reactive Micropolar Real Gas Flow and Thermal Explosion

Busemann diffuser for supersonic ramjet engine with detonation combustion of hydrogen-air mixture

The expediency of using a Busemann diffuser in a scramjet engine with detonation combustion of hydrogen-air mixtures is studied. A method is developed for calculating an air intake that provides spontaneous initiation of oblique detonation in a hydrogen-air mixture under conditions of rarefied atmosphere at hypersonic freestream Mach numbers. The geometry of the Laval nozzle (convergent-expanding) with the Busemann diffuser for the free flow Mach number 9 is determined. It is shown that at an altitude of about 40 km, the detonation combustion of the hydrogen-air mixture in this nozzle can provide more than 0.4 tons of thrust and more than 35% efficiency. The mathematical model is based on unsteady two-dimensional Euler equations for axisymmetric multicomponent reacting gas flow. To simulate chemical transformations, the detailed kinetic scheme is used that takes into account 33 non-equilibrium reactions for nine components of the mixture. The heat capacity, enthalpy, and entropy of a mixture are calculated using the reduced Gibbs energy of the gas components. Numerical modeling is carried out according to the modified Godunov scheme of the second order of approximation in spatial variables.

CFD modelling and simulation of a zeolite catalytic membrane reactor for low temperature water-gas shift reaction

In this work, a catalytic membrane reactor is proposed to couple water-gas shift reaction with selective separation of H2 product to improve the overall conversion. A 3D isothermal CFD model of this catalytic membrane reactor is developed with COMSOL Multiphysics software. The effects of reaction temperature, pressure, sweep gas flow rate and reactor geometry on CO conversion and H2 recovery are analysized in details. Based on the results, the coupling mechanism of reaction, and H2 permeation is proposed. It is found that that the catalyst bed could be divided into active and less-active volume and reducing less-active volume helps improve the utilization efficiency of catalyst. As a conclusion, H2 permeation directly affects H2 mole fraction in near-membrane area, and the effect is spreaded to the rest part to boost the local reaction rate. However, the effect is neutralized by the improved H2 production and permeation affecting volume is mainly less-active volume while active volume is hardly to be affected. Our study indicates that H2 permeation tends to deplete H2 fraction in catalyst volume but the consequent improved reaction rate acts as a resistance and tends to move back to a new steady state.

Electrode reaction properties using a reactant gas addition method in a commercial 100 cm2 class solid oxide fuel cell

This work investigates the reaction characteristics of the anode and cathode by overpotential analyses in 100 cm2 class planar anode-supported SOFCs. The reactant gas addition (RA) technique was applied to analyse the overpotential, which uses the reactant gas flow rate and partial pressure as parameters due to their variation upon adding a reactant species to an electrode. The anodic overpotential was determined to be made up of mass transfer-induced overpotentials of H2 and H2O species. The H2O species account for the majority of the anodic overpotential at the measured current range i.e., 0–150 mA cm−2. Thus, the anodic reaction is under an extreme H2O-induced mass-transfer resistance compared with H2. The RA method showed that the cathodic overpotential was mainly due to a deficiency of O2 species in the mass transfer through the gas phase rather than the solid phase. Furthermore, both cathodic and anodic overpotentials depended on gas flow rate and utilisation, indicating a significant gas-phase mass transfer effect.

Effect of reactive gas condition on nonpolar AlN film growth on MnS/Si (100) by reactive DC sputtering

The effects of reactive gas flow conditions on nonpolar AlN film growth on MnS/Si (100) substrates using reactive DC magnetron sputtering were investigated. During AlN deposition at a substrate temperature of 750 °C, the MnS surface can be unintentionally nitrided, resulting in a decrease in the crystallinity of the AlN. Low-temperature growth of the AlN layer at 300 °C prevents this nitridation and results in the crystallization of nonpolar AlN. A N2 flow equal to 30% of the Ar sputtering gas flow was found to improve the crystallinity of the nonpolar AlN and to reduce nitrogen defects, which play an important role in interfacial reactions. Nitrogen defects promote the formation of alloys such as AlMn and MnSi that degrade the interface and can significantly decompose the MnS. A higher proportion of N2 improves the nonpolar AlN crystallinity, reduces the concentration of defects and suppresses reactions at the AlN/MnS interface.

Hydrogen PEMFC stack performance analysis through experimental study of operating parameters by using response surface methodology (RSM)

Although many studies have been done on finding operating conditions of hydrogen-fed fuel cells before, it remains one of the most critical points in determining its parameters in the process. So this paper aims to investigate experimentally the reactant gases flow rate and cell voltage which have a significant impact on the current density of a 3-cell Proton Exchange Membrane fuel cell stack having a 150 cm2 active layer. In this case, to determine the optimum values, Design of Experiment and Response Surface Methodology was applied to the experimental system at low 1.5 V, medium 1.8 V, and high 2.1 V. Then, they were compared with each other. In this context, keeping the hydrogen flow rate low and obtaining high current density is one of the main targets; at low voltage values, it was concluded that the flow rate should be increased due to the reaction rate increases with temperature. In general, the effect of humidification and cell temperature on performance was seen more prominently at 1.8 V. The highest current density values that were 313.66 mA/cm2, 336.75 mA/cm2, and 323.48 mA/cm2, respectively, were reached at flow rates of 1 L/min,1.3 L/min,1.6 L/min.

Bipolar high‐power impulse magnetron sputtering synthesis of high‐entropy carbides

AbstractIn this study, we report high‐entropy carbides synthesis with reactive bipolar high‐power impulse magnetron sputtering (HiPIMS). Uncontrolled microstructure and stoichiometry development with reactive gas flow rate are major limitations of conventional direct current (DC) and radio frequency (RF) magnetron sputtering of multicomponent carbides. With HiPIMS these chemically disordered crystals structurally and compositionally transform from a carbon‐deficient metallic (C/M &lt; 1), to a stoichiometric ceramic zone (C/M ∼ 1), and to a nanocomposite embodiment (C/M &gt; 1), as a function of the carbon content during HiPIMS deposition. X‐ray diffraction, X‐ray photoelectron spectroscopy, Raman spectroscopy, scanning electron microscopy, and nanoindentation hardness measurements are combined to demonstrate the three regions of synthesis domain. HiPIMS provides access to metallic, ceramic, and composite carbides with great control over the microstructure and stoichiometry, which is elusive in case of conventional DC and RF magnetron sputtering. Notably, the stoichiometric ceramic zone maintains a constant carbon to metal ratio (C/M ∼ 1) over an extended amount of methane flow before transitioning to a nanocomposite microstructure (C/M &gt; 1). The transition zone breadth depends on materials affinity for carbon that correlates with valence electron concentration (VEC). As such, synthesis conditions for new high‐entropy carbides can be understood and predicted based on VEC.

Numerical Simulation of Heat and Mass Transfer in an Open-Cell Foam Catalyst on Example of the Acetylene Hydrogenation Reaction

In the present work, based on numerical simulation, a comparative analysis of the flow of a chemically reacting gas flow through a catalyst is performed using the example of selective hydrogenation of acetylene in a wide range of flow temperatures variation. Catalyst models are based on open-cell foam material. A comparison is also made with calculations and experimental data for a granular catalyst. The porosity and cell diameter were chosen as variable parameters for the porous catalyst. The results of numerical studies were obtained in the form of component concentration fields of the gas mixture, vector fields of gas movement, values of conversion, and selectivity of the reaction under study. The parameters of the porous material of the catalyst are determined for the maximum efficiency of the process under study.

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.

Local existence for viscous reactive micropolar real gas flow and thermal explosion with homogeneous boundary conditions

In this paper, we prove that the one-dimensional model of reactive micropolar real gas flow and thermal explosion has a solution locally in time. We first define the notion of a generalized solution for the governing initial-boundary value problem. We prove the claim of local existence by deriving a sequence of approximate problems obtained by Faedo-Galerkin projections. A priori estimates allow us to choose small enough time interval of existence, and show that the sequence of approximations is bounded in certain functional spaces, and therefore has a convergent subsequence. In the end, we show that it is precisely this limit that is the solution to the observed problem.

The identification of optimal operating parameters under high energy efficiency conditions for a single polymer electrolyte membrane (PEM) fuel cell

The performance of PEM fuel cells is influenced by several factors such as: the operating temperature of the cell, the reactant gas flow, work pressures, the reaction gas humidity. In the present work we aimed to identify the optimal values of these parameters for operation of a PEM cell to achieve maximum power in conditions of high efficiency; the technological possibilities of its use in a portable energy application have been evaluated. Experimental measurements regarding the integrating polymeric membrane in three different fuel cell construction designed were performed. The influence of the mechanical compression of the GDL diffusion layer on the total internal resistance of the cell was achieved by comparative analysis of the polarization curves. It was found that as the deformation level of the MEA increases, the power generated by the battery increases progressively. The resulting experimental data subsequently allowed the design and implementation of a PEM fuel cell assembly, fully functional at power level, corresponding to the number of constituent elements.

One-pot microwave synthesis of Pd modified titanium dioxide nanocrystals for 3D aerogel monoliths with efficient visible-light photocatalytic activity in a heated gas flow reactor

We present a one-pot microwave synthesis of Pd modified titanium dioxide nanocrystals for macroscopic aerogel monoliths, which are efficient visible-light photocatalysts for methanol oxidation in a heated gas flow reactor.

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.

Tantalum-Titanium Oxynitride Thin Films Deposited by DC Reactive Magnetron Co-Sputtering: Mechanical, Optical, and Electrical Characterization

The possibility to tune the elemental composition and structure of binary Me oxynitride-type compounds (Me1Me2ON) could lead to attractive properties for several applications. For this work, tantalum-titanium oxynitride (TaTiON) thin films were deposited by DC reactive magnetron co-sputtering, with a –50 V bias voltage applied to the substrate holder and a constant substrate temperature of 100 °C. To increase or to decrease in a controlled manner, the Ti and Ta content in the co-sputtered films, the Ti and Ta target currents were varied between 0.00 and 1.00 A, in 0.25 A steps, while keeping the sum of the currents applied to the two targets at 1.00 A. The reactive gases flow, consisting of a nitrogen and oxygen gas mixture with a constant N2/O2 ratio (85%/15%), was also kept constant. The single-metal oxynitrides (TaON and TiON) showed a low degree of crystallinity, while all the other co-sputtered films revealed themselves to be essentially amorphous. These two films also exhibited higher adhesion to the metallic substrate. The TaON film showed the highest hardness value (14.8 GPa) and the TiON film a much lower one (8.8 GPa), while the co-sputtered coatings exhibited intermediary values. One of the most interesting findings was the significant increase in the O content when the Ti concentration surpassed the Ta one. This significantly influenced the optical characteristic of the films, but also their electrical properties. The sheet resistivity of the co-sputtered films is strongly dependent on the O/(Ta + Ti) atomic ratio.

Hybrid reactive sputtering of transition metal aluminum oxynitrides

Transition metal aluminum nitrides like CrAlN and TiAlN coatings are widely used to improve performances of cutting tools. Incorporation of oxygen leads to the transition metal aluminum oxynitrides CrAlON and TiAlON, resulting in reduced friction against steel compared to nitride coating and further improved cutting performance. In previous studies, over stoichiometric chemical compositions with increased non-metal to metal ratios of z > 1 were observed in oxynitride CrAlON and TiAlON coatings. Nevertheless, the reason for the non-metal to metal ratios of z > 1 is not clarified yet. The current study aims to contribute to this issue. For this purpose, CrAlON and TiAlON coatings were deposited with four different oxygen to reactive gas flow ratios jO2/(jO2+jN2) using a direct current magnetron sputtering (dcMS) / high power pulsed magnetron sputtering (HPPMS) hybrid process. The plasma composition was investigated at the substrate side in front of both, the dcMS and HPPMS cathode. Subsequently, the chemical and phase composition of the deposited coatings was examined. It can be concluded that a higher oxygen content of reactive gas mixture jO2/(jO2+jN2) increases non-metal to metal ratios z in the plasma. This results in higher non-metal to metal ratios z in the coating. The findings reported in this study expand the understanding of the reason for over stoichiometric chemical composition of transition metal aluminum oxynitrides.

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.

Ni-Fe-Ce hydrotalcite-derived structured reactor as catalyst for efficient steam reforming of toluene

Development of the efficient and inexpensive catalyst for steam reforming of biomass tar plays a significant role in the wide application of biomass gasification. In the present study, the long, through, but distorted channels with a low tortuosity of wood, which are preserved after carbonization and the Ni-Fe-Ce hydrotalcite-derived catalyst deposition, were employed for the catalytic steam reforming of biomass tar. Outstanding catalytic activity was achieved as the reactant gases flow through the Ni-Fe-Ce hydrotalcite-derived structured reactor (NiFeCe-HTc/WC), with over 98.5% toluene conversion and good stability observed at 550 °C. Moreover, the NiFeCe-HTc/WC catalyst exhibited much better catalytic performance compared to the NiFe-HTc/WC catalyst and the Ni-Fe-Ce hydrotalcite-derived catalyst supported on traditional activated carbon (NiFeCe-HTc/AC). This was because of the presence of Ce, the open but distorted channels of monolithic wood, and the graphitic carbon layer covering the active sites, which could improve the dispersion of Ni species and the mass transfer efficiency, and prevent coke formation. This work demonstrated that the Ni-Fe-Ce hydrotalcite-derived structured reactor is potentially cost-effective for a range of high-temperature applications.