Working Gas Pressure Research Articles

Optimization of Electrical and Morphological Properties of MCrAlY thin films deposited by DC magnetron sputtering using Taguchi method

The objective of the research work was to optimize and standardize sputtering parameters based on physical parameters and electrical properties of the coatings. The experimental and statistical investigation was conducted for optimizing the sputtering parameters. The sputtering parameters were selected as sputtering power, working gas pressure, substrate temperature and deposition time. For coating of MCrAlY thin film on a borofloat glass substrate, the electrolytic MCrAlY target was used based on a design of experiment layout. The thin film coatings were characterized for film thickness and surface roughness. The optimum conditions for maximum thickness and minimum surface roughness are sputtering power (17.57 W), working gas pressure (5x10-3mbar), substrate temperature (100˚C) and deposition time (32 min). The ANOVA results for film thickness showed the contribution of deposition time (93.92) followed by working pressure (3.26 %), substrate temperature (2.052 %) and power (0.646%)

Features of the discharge ignition in the trigger unit of the cold-cathode thyratron

The sealed-off cold-cathode thyratron TPI1-10k/50 type with a newly developed trigger unit based on auxiliary glow discharge is investigated. As distinct from the commercially produced sealed-off thyratrons, in the thyratron under investigation the high-emissivity tablet is not used. Features of ignition of the trigger discharge are considered. It has been revealed that the delay time to breakdown in the trigger unit and a jitter in the delay time decrease with an increase in working gas pressure. The delay time can be significantly decreased due to availability of the so-called parasitic current in the electrode system of trigger unit. A capability of the thyratron operation with a stability in delay time no more than 4 ns is demonstrated.

Energy and gas dynamic characteristics of ionization nitrogen installations of industrial type

The work provides the analysis of power characteristics of the industrial equipment – ionic nitriding applications – with different types of vacuum chambers – with hot and cold walls. The calculations results and experimental researches of thermal balance of the system “melt-wall chamber” at the process of plasma nitration for industrial applications are given. The work examines the influence of heat-shielding screens quantity in the applications with cold walls on the internal screen temperature and power of thermal losses at warming up parts melt and at its isothermal endurance. It has been displayed the significant influence of the discharge chamber geometry on the discharge power value which is necessary for the melt warming up and its exposition at the certain temperature – the less are geometrical sizes of the chamber (diameter and height), the smaller is the power of the smoldering discharge which is required for ensuring necessary melt temperature. It is shown that at sufficient melt parts distance from the chamber walls, the voltage drop on the skeleton of the smoldering discharge can be tens volts that causes the decrease of cathodic falling potential and, respectively, the increase of the electric power which is required to maintain necessary melt temperature in comparison to melt which is as close as possible to chamber walls. It leads to the fact that at more dense loading, smaller specific consumption of the electric power to ensure the necessary depth of the nitrated layer is required; at the same time the specific energy consumptions by the melt temperature of 525–530 °C are 0.6–1.6 kW∙h/kg, depending on the loading extent of the chamber. It has been displayed that at ionic nitration, the value of working gas pressure must provide the deviance of the smoldering discharge i. e. the whole area the cathode –melt must be captured by the discharge luminescence.

Three-dimensional Particle-In-Cell simulation of ion characteristics in anode layer ion source

Ion characteristics in cylindrical anode layer ion source (ALIS) with an outlet diameter of 80 mm (D80) are experimentally investigated. The ion beam current in the high-current and low-voltage mode is higher than that in the low-current and high-voltage mode and divergence half angle of ion beam is up to 42°. Numerical simulation by three-dimensional Particle-In-Cell with Monte Carlo collisions method (PIC-MCC) is performed to demonstrate the ion characteristics in different operational conditions. The simulation results reveal that ion density distribution and ion energy and ion divergence half-angle is mainly affected by discharge voltage which induce the formation and movement of ions. About 52% ions have divergence half-angle range from 30°to 45°, meanwhile this kind of ion source has a wide range of ion energy distribution which is helpful for application. Therefore, according to specific process, keeping the balance of a relatively large ion divergence angle and a concentrated ion energy distribution and choosing a proper working gas pressure is the key to improve the processing effect.

Asymmetric Bipolar Plasma Power Supply to Increase the Secondary Electrons Emission in Capacitive Coupling Plasmas

Power supplies have played crucial role to improve and extend plasma applications. Several dc, pulsed, and radio frequency (RF) stabilized power supplies have been developed over a wide range of frequencies and voltage waveforms. However, the influence of voltage waveform on the plasma densification, mainly due to the secondary electrons emission from the electrodes, has not been quite explored. This paper proposes an asymmetric pulsed bipolar power supply, adjustable in frequency, amplitude, pulsewidth, and number of pulses for generation of cold plasmas. Short period positive pulses, between longer negative pulses, increase greatly the secondary electron emission from the electrodes and, consequently, the plasma ionization rate. Short pulses (ns) are obtained by the phase shift between each carrier, and the high-intensity pulses are obtained by cascading the cell submodules in a half-bridge cascade topology, using a modular half-bridge converter configuration. The intensity of the positive and negative pulses can be varied independently. There is no unintended dc voltage level between the electrodes, which appear in RF plasmas. The plasma generated in this way is free of electric arc and can be kept stable within a broader range of operating parameters, mainly the voltage and the working gas pressure.

In-operando stress measurement and neutron imaging of metal hydride composites for solid-state hydrogen storage

Solid-state hydrogen storage in metal hydrides offers highest volumetric energy storage densities and low working gas pressures at the same time. Recently developed metal hydride composites (MHC) consist of a hydride-forming metal alloy and a secondary phase, typically graphite, to realize form-stable composites and short loading and unloading times (<5 min). Hydride formation causes a volume expansion of the storage material. Thus, it is mandatory to characterize this behavior for the sake of system safety.This work focuses on the in-operando characterization of the volume expansion of MHC that could trigger mechanical stresses acting on the walls and internal assemblies of the storage container. MHC with different metal particle shapes (flakes and powder) were studied. In-operando neutron imaging of axially freely expanding MHC was applied to analyze the time-resolved and spatial concentration of hydrogen, reaction fronts and the evolution of volume expansion and stability of the MHC. Stress measurements revealed that stresses of up to 330% of the respective operating gas pressure occur for confined MHC. Both techniques combined deliver crucial information and implications for the design of safe (according to ISO 16111), efficient and dynamic metal hydride storage systems.

Comparison of measured pinch parameters versus pressure for SABALAN1 plasma focus facility against computed values using Lee model code

In this paper, we have studied the effect of working gas pressure on plasma pinch properties in a Mather type plasma focus (2 kJ, 20 kV, 10 μF), named SABALAN1. Argon at the various operating pressures ranging from 0.1-1.2 Torr has been used as working gas. The total current waveform has been measured for different pressures. Also, a numerical simulation was done using Lee model code to perform numerical experiments in SABALAN1. The numerical simulation was used to compute argon soft x-ray yield as a function of pressure, to anticipate the maximum soft x-ray efficiency at optimum operating gas pressure. The Lee model was configured for SABALAN1, by fitting a simulated discharge current waveform against a measured discharge current waveform was obtained by numerically integrating the output of a dI/dt calibrated Rogowski coil. The experimental and simulation curves for plasma pinch properties have been plotted. Some of the dynamic parameters of the plasma and the characteristics of the plasma pinch have been displayed at different argon pressures in two tables. In addition, the chart of the normalized parameters of the plasma pinch has been plotted in terms of pressure. The results of experimentally measured and numerical simulation show that better pinches with attention to their plasma pinch characteristics, generally were dependent on pressure and the best pinch is obtained at 0.6-0.7 Torr for argon at 14 kV in SABALAN1. Furthermore, in high pressures (higher than 0.7 Torr in our experiments), the discharge current can behave as short circuit discharge and resembles that of a simple L-C-R discharge which is a damped sinusoidal. Comparison of the experimental and numerical curves shows sensible agreement in some plasma pinch properties such as the time to pinch and depth of focus. The results from charts and tables have been discussed.

Systematic research on the performance of self-designed microwave plasma reactor for CVD high quality diamond

Abstract Optical grade diamond, in particular, high-end products, are mainly used for aerospace and defense purposes. How to manufacture them with higher quality and lower cost was critical technology. Systematic research on the performance of Self-designed plasma reactor with higher power for synthesizing diamond film was carried out. Microwave input power can reach up to 10 kW, the plasma reactor has good adaptability for the deviation of microwave frequency f at 2.45 GHz ± 20 MHz. The secondary plasma could be eliminated by adjusting the working gas pressure and the cylinder adjustment structure, it is helpful to improve the deposition rate with less energy loss. The concentrated and steady plasma could be obtained device with higher gas pressure and relative lower microwave input power. Gas supply modes and inlet gas flow rate were optimized, which would be beneficial to synthesize the film with good quality.

A solar pressurizable liquid piston stirling engine: Part 1, mathematical modeling, simulation and validation

This paper describes the comprehensive mathematical modeling, simulation and finally validation the developed dynamic equations of a pressurizable liquid piston Stirling engine. The proposed system comprises of the main following components: solar fresnel lens, hot, cold and tuning liquid columns, regenerator, solid pressure intensifier, liquid power piston and output water column. The mathematical modeling of the proposed system is divided into distinct parts, including dynamic of working gas pressure, hot, cold and tuning liquid columns and dynamic of the output part of the system. The obtained dynamic differential equations are rewritten to nine first order differential equations and solved employing 4th order Runge-Kutta numerical method. The pumping head of 1.5 m, the hot and cold side temperature of 100 °C and 20 °C, respectively and zero dead volumes are considered. It is obtained that the working gas pressure has the oscillatory behavior between two upper and lower points, frequently. According to the oscillatory dynamic of working gas pressure, when the working gas pressure is high enough, it can push the liquid power piston to overcome the static pressure of the output column of the pump and finally the water pumping occurs.

Varying the Composition of Ferroelectric Films during Ion-Plasma Sputtering: Simulation and Experiment

Varying the elemental composition of ferroelectric thin films of barium strontium titanate, barium zirconate titanate, and barium stannate titanate solid solutions obtained by ion-plasma sputtering of ceramic targets at different pressures of the working gas is studied through simulation and experimentally. The experimental results are interpreted based on statistical simulation of the transport processes for fluxes of sputtered Ba, Sr, Sn, Zr, and Ti atoms in a gas medium. It is shown that the simulation results describe variations in the elemental composition satisfactorily (within 5%) in a wide range of working gas pressures. Theoretical and experimental studies enable us to choose the optimum values of technological parameters for obtaining ferroelectric thin films with specified elemental compositions that determine their electrophysical properties.

Study of Cold-Cathode Thyratron Triggering Stability at High Anode Voltages

The delay time to breakdown of a cold-cathode thyratron with a trigger unit based on an auxiliary steady-state low-current glow discharge was studied experimentally. The device was connected into the electric circuit according to the circuit of a classical thyratron. The main experiments were carried out at low working gas (deuterium) pressures and high anode voltages of about 40 kV. It is found that, during the triggering current pulse or commutation of the main discharge current, the auxiliary discharge in the trigger unit passes from the stable segment of the current-voltage characteristic into the regime with a reduced operating voltage. Spontaneous reverse transitions from this regime are also possible. On the other hand, the initial conditions of the auxiliary discharge affect the delay time to thyratron breakdown and lead to the jitter in the total delay time to breakdown relative to the triggering pulse. The total delay time amounts to 100 ns, the jitter in delay time being within 15 ns.

Tribo-Mechanical and Electrochemical Properties of Carbonitrided 316 Austenitic Stainless Steel by rf Plasma for Biomedical Applications

AISI 316 austenitic stainless steel was carbonitrided using rf plasma with purpose of using low-cost orthopedic implant materials in biomedical applications besides the manufacturing requests. The plasma treatment process was accomplished at low working gas pressure of 0.075 mbar in nitrogen-acetylene gaseous mixture. The plasma-processing time was fixed at 10 min while the plasma-processing power was varied from 450 to 650 watt. The effect of plasma treatment power on the structure, tribological, mechanical, electrochemical and biocompatibility of AISI 316 has been investigated. The structural results demonstrated the formation of nitrogen and carbon solid solutions, chromium nitride, iron carbide and iron nitride phases in the treated samples. The microhardness of the treated layer increases with increasing the processing power to reach a maximum value of approximately 1300 HV0.1 at 600 W which represents more than 6-folds increase in microhardness in comparison with the untreated matrix. The wear and corrosion resistance of the treated AISI 316 were enhanced compared to the untreated one. The friction coefficient was reduced from nearly 0.5 for the untreated substrate to nearly 0.3 for the carbonitrided sample. The surface energy and wettability of the carbonitrided samples were augmented as the plasma-processing power increased. Furthermore, the numbers of grown mesenchymal stem cells are higher for carbonitrided samples compared to the untreated one. The formation of nitrogen and carbon solid solution, chromium nitride, iron nitride and iron carbide hard phases after carbonitriding process is responsible for achieving good mechanical, tribological, biocompatibility and electrochemical properties for AISI 316 alloys.

Ozone Production Influenced by Increasing Gas Pressure in Multichannel Dielectric Barrier Discharge for Positive and Negative Pulse Modes

ABSTRACTThis paper describes the influence of gas pressure on the conversion of O2 to O3 and the ozone production efficiency in a multichannel dielectric barrier discharge (DBD) reactor utilizing positive and negative pulses. Results show that conversion of O2 to O3 is continuously enhanced by the increase of gas pressure (0.1–0.24 MPa) while the rising speed of oxygen conversion with the increasing gas pressure at fixed specific input energy is reduced above 0.15 MPa. The maximum ozone generation efficiency is increased with increasing gas pressure (0–0.2 MPa) while positive pulse exhibits higher energy efficiency. The maximum ozone generation efficiency is suppressed with further increase of gas pressure (0.2–0.24 MPa) while no significant difference in ozone generation efficiency is observed for two unipolar pulse modes. Results also show that 0.2 MPa is the optimal working gas pressure to obtain the maximum ozone generation efficiency and increasing gas pressure would lead to remarkable increase of ozone generation efficiency for ozone production at high energy densities in multichannel DBD.

Measurement of Temperature and Density Profiles of the Plasma at PR-2 Facility

A new system of probe diagnostics at linear plasma simulator PR-2 is described, allowing us to measure the profiles of plasma temperature and density in different cross sections of the plasma column. The Langmuir probe fixed to the movable part of the two-coordinate positioning system built into the PR-2 passes the region of the discharge area during the process of measuring plasma parameters. The overall dimensions of the positioning system make it possible to mount electrical probes (magnetic probes, optical fibers, and other diagnostic equipment) covering almost the entire volume of the vacuum chamber between the magnetic mirrors of the device. We present the measurement results of local plasma parameters of the beam-plasma discharge (BPD) for different values of the input power and working gas pressure. The boundaries of appearance of discharge of three types were determined: the diffusive BPD mode, the BPD mode, and the arc mode. Dependences of the plasma concentration and temperature on the input power for different values of pressure have been also determined.

Sahand Plasma Focus Emitted More Than 35 J in Yield Neon Soft X-ray

X-ray emission from neon plasma produced in Sahand Filippov type plasma focus device is investigated. Detecting system used in our experiments is a five channel pin diode detector. Soft X-ray emissions from neon gas at different charging voltages and working gas pressures are studied and optimum condition for production of soft X-ray for Sahand plasma focus facility is obtained. Results show that for every working pressure there is a charging voltage at which the average soft X-ray yield is maximum and this optimum charging voltage increases with increasing gas pressure. For 0.25, 0.50 and 0.75 Torr neon the optimum voltages are 12, 13 and 16 kV respectively. The highest average soft X-ray yields produced at 0.50 Torr which is about 35.87 ± 1.18 J. Also soft X-ray production decreased after a certain pressure which for our experiments is 0.50 Torr. The variation of relative hard X-ray yield with charging voltage and working gas pressure is also investigated. The results show that 0.50 Torr is also the best operating gas pressure for optimum hard X-ray production in Sahand Filippov type plasma focus device.

Switching of 100-kV pulses in a planar “open” discharge with generation of counterpropagating electron beams

Some results of studying a planar “open” discharge with generation of counterpropagating electron beams at high voltages and appreciable working gas pressures up to atmospheric one are presented. The possibility of its functioning in helium at a voltage above 100 kV is demonstrated, and an increase in the working voltage does not prevent fast breakdown with characteristic switching times of ~1 ns. A specific feature of this type of discharge is the existence of a gas-pressure region, where the discharge-development delay time nonmonotonically depends on the voltage due to the competition between emission processes leading to breakdown.

Dependence of the constitution, microstructure and electrochemical behaviour of magnetron sputtered Li–Ni–Mn–Co–O thin film cathodes for lithium-ion batteries on the working gas pressure and annealing conditions

AbstractLi(Ni1/3Mn1/3Co1/3)O2as a cathode material for lithium ion batteries shows good thermal stability, high reversible capacity (290 mAh g−1), good rate capability and better results in terms of environmental friendliness. In this paper thin film cathodes in the material system Li–Ni–Mn–Co–O were deposited onto silicon and stainless steel substrates, by non-reactive r.f. magnetron sputtering from a ceramic Li1.18(Ni0.39Mn0.19Co0.35)O1.97target at various argon working gas pressures between 0.2 Pa and 20 Pa. A comprehensive study on the composition and microstructure was carried out. The results showed that the elemental composition varies depending on argon working gas pressure. The elemental composition was determined by inductively coupled plasma optical emission spectroscopy in combination with carrier gas hot extraction. The films showed different grain orientations depending argon working gas pressures. The degree of cation order in the lattice structure of the films deposited at 0.5 Pa and 7 Pa argon working gas pressure, was increased by annealing in an argon/oxygen atmosphere at different pressures for one hour. The microstructure of the films varies with annealing gas pressure and is characterized using X-ray diffraction and unpolarized micro-Raman spectroscopy at room temperature. Electrochemical characterization of as-deposited and annealed films was carried out by galvanostatic cycling in Li–Ni–Mn–Co–O half-cells against metallic lithium. Correlations between process parameters, constitution, microstructure and electrochemical behaviour are discussed in detail.

Oxygen Reduction Reaction Activity of Platinum Thin Films with Different Densities

Polymer electrolyte membrane fuel cells (PEMFCs) have gained significant attention as alternative power sources, especially for automotive applications due to their high energy conversion efficiency, low operating temperature and being environmentally friendly compared to the other types of fuel cells. However, sluggish kinetics of oxygen reduction reaction (ORR) on the cathode requires a high loading of platinum (Pt), which increases the cost of the fuel cell. In addition, dissolution and agglomeration of Pt nanoparticles and oxidation of the carbon support are among the major factors that cause electrode degradation and performance loss. Therefore, extensive efforts are focused on developing high performance, durable, and low-cost electrocatalysts. Extended surfaces such as nanostructured thin films are good candidate for non-conventional catalysts due to their high surface area and having no need for a support material. In this work, a new density-modulated platinum thin film (Pt-TF) design was fabricated by high pressure sputtering deposition (HIPS) and was investigated as potential electrocatalysts for the ORR in PEMFCs using cyclic voltammetry and rotating disk electrode techniques in aqueous perchloric acid electrolyte. Scanning electron microscopy and X-ray diffraction methods were used to study morphological and crystallographic properties of the density-modulated Pt-TF electrocatalysts. The Pt-TF catalyst was produced by changing working gas pressure from low to high values during film growth, which results in denser film bottoms and more porous tops. Low-density film top provides effective transportation of oxygen, which could enhance catalyst utilization and result in reduced Pt-loading and enhanced activity. Porous yet interconnected network of Pt atoms in the low-density Pt-TF surface can also eliminate the agglomeration and dissolution problems. In addition, high-density film bottom provides a strong adhesion to the substrate leading to enhanced physical and electrochemical stability of the Pt-TF. Stronger bonds along with self-protection against the acidic environment due to the dense-packing of Pt atoms at the interface with the substrate can hinder leaching of Pt and avoid the detachment of large regions of Pt-TF from the substrate as a whole. In addition, high-density layer can reduce contact resistance and enhance the electronic conductivity. This presentation will focus on electrochemically active surface area, area specific activity, and mass activity of density-modulated Pt-TFs during accelerated stability tests and compare them to conventional high-density Pt-TF and Pt/C electrocatalysts.

Analysis of high-frequency processes in an electric-discharge chamber of a three-phase plasma torch at high working gas pressure

The paper deals with electrophysical processes in an electric-discharge chamber of a three-phase AC plasma torch with nitrogen as working gas. The frequency characteristics of voltage pulsations depending on current, gas mass flow rate, power, and pressure are obtained. Photos of arc burning processes in the plasma torch discharge chamber at different parameters are presented. It is shown that two arcs burn simultaneously in the plasma torch chamber and the third one either extinguishes or arises. These investigations might be useful when creating various technological processes by applying three-phase AC plasma torches operating on inert gases.

Influence of gas pressure on electron beam emission current of pulsed cathodic-arc-based forevacuum plasma electron source

We describe our experimental investigation of the effect of background gas pressure on the emission parameters of a pulsed cathodic-arc-based forevacuum-pressure plasma-cathode electron source. We find that increased gas pressure over the range 4–16 Pa significantly reduces the beam current rise-time and significantly increases the emission current amplitude. For example, at a discharge current of 20 A, increasing the working gas pressure from 4 Pa to 16 Pa increases the emission current from 8 A to 18 A and shortens the beam rise-time from 50 μs to 20 μs. This influence of gas pressure on the electron beam parameters can be explained by the effect of arc discharge current switching from the anode to emission. In our case, the current switching effect is caused by increased working gas pressure. In the forevacuum pressure range, the increase of the electron emission current with the growth of gas pressure is due to a rise in the emission plasma potential which is caused by ion back-streaming from the plasma formed in the electron beam transport region. A model describing the influence of gas pressure on the electron emission from the plasma is presented.