Cathode erosion on copper electrodes in steam,hydrogen, and oxygen plasmas

Experimental data are presented for cathode erosion rates on copper cathodes (or magnetically rotated arcs in steam, and mixtures of steam, hydrogen, and oxygen with argon. Measurements were also made of the arc voltage and velocity. The erosion rates for steam and oxygen plasmas were significantly lower than those .16r argon and hydrogen. Pure steam and 10% oxygen in argon gave erosion rates of 2.3 and 6.1 g/ C respectively while pure argon and 70% hydrogen in argon gave rates of 14.8 and 13.0 g/C respectively. Erosion rates decreased with increasing are velocities. The variation of arc velocity with operating conditions is described in terms of both aerodynamic and surface drag on the arc and arc root respectively.     

Cathode erosion in inert gases: The importance of electrode contamination

Experimental results are presented for electrode erosion on copper electrodes in magnetically rotated arcs in argon and helium. Measurements were also made of the arc voltage and velocity. The effects due to the contamination of the electrode surface by either a native contaminant layer (copper oxide and carbon traces) or the continuous injection of very small amounts of various diatomic gases (nitrogen, oxygen, chlorine, and carbon monoxide) into the inert plasma gases were determined. The erosion rates for pure argon were significantly higher than those for pure helium (13.5 g/C for argon and 1 g/C for helium) and with both gases, very high arc velocities were measured initially (>60 m/s for argon and >160 m/s for helium) when a natural contaminant layer was still present on the cathode. The removal of this layer resulted in lower velocities (2m/s for argon and 20m/s for helium) and higher erosion rates. The removal of the layer was much faster with argon, due possibly to higher electrode surface current densities for argon arcs.     

Cathode erosion phenomena in a transferred-arc plasma reactor

Phenomena occurring on file surface of a thoriated tungsten cathode operating in a transferred-arc reactor were investigated. The effects of cathode geometry (pointed-tip vs. flat-tip) and plasma gas composition (argon vs. helium) on the rate and mechanisms of cathode erosion were studied experimentally by examining the morphology of the surface before and after runs of prespecified duration, up to one hour in length. For flat-tip cathodes in argon, the major characteristic was the migration of thoria and its concentration at segregated sites. Both geometries in helium operated at much higher temperatures, around the boiling point of tungsten, giving rise to extensive vaporization of cathode material, followed by apparent redeposition of the ionized species carried by file ionic current, in characteristic ringlike sites on the surface. Erosion rates were low and similar in magnitude, except for pointed-tip cathodes operated in argon, where the formation of a large molten sphere of tungsten and its subsequent release gave rise to a higher rate of erosion.     

Influence of Gas Type on the Thermal Efficiency of Microwave Plasmas for the Sintering of Metal Powders

Microwave plasmas have enormous potential as a rapid and energy efficient sintering technology. This paper evaluates the influence of both plasma atmosphere and metal powder type on the sintering temperatures achieved and the properties of the sintered powder metal compacts. The sintering is carried out using a 2.45 GHz microwave-plasma process called rapid discharge sintering (RDS). The sintering of three types of metal powder are evaluated in this study: nickel (Ni), copper (Cu) and 316L stainless steel (SS). An in-depth study of the effects of the plasma processing parameters on the sintered powder compacts are investigated. These parameters are correlated with the mechanical performance of the sintered compacts to help understand the effect of the plasma heating process. The substrate materials are sintered in four different gas discharges, namely hydrogen, nitrogen oxygen and argon. Thermocouple, pyrometer and emission spectroscopy measurements were taken to determine the substrate and the discharge temperatures. The morphology and structure were examined using scanning electron microscopy and X-ray diffraction. The density and hardness of the sintered compacts were correlated with the plasma processing conditions. As expected higher densities were obtained with powders with lower sintering temperatures i.e. nickel and copper when compared with stainless steel. Under the power input and pressure conditions used, the highest substrate temperature attained was 1,100°C for Cu powder sintered in a nitrogen atmosphere. In contrast under the same processing conditions but in an argon plasma, the temperature achieved with SS was only 500°C. The effect of the plasma gas type on the sintered powder compact chemistry was also monitored, both hydrogen and nitrogen yielded a reducing effect for the metal in contrast with the oxidising effect observed in an oxygen plasma.     

Spectroscopic study of a magnetically rotating arc between opper electrodes in contaminated argon

The effects of N₂ and CO contaminants in atmospheric-pressure argon on an arc rotating between two concentric copper electrodes has been studied using optical spectroscopy of copper lines. The axial temperature of the magnetically driven arc in Ar + %N₂ was determined to be around 10,000 K for arc currents of SO to 200 A. The diffusion process of the copper vapor from the cathode was also studied. A copper density maximum 1 mm from the cathode along the arc column was found in Ar + %N₂. Removal of the contaminated cathode surface layers by the arc when contaminant injection in the plasma gas was stopped was found to be a slow process with a time scale depending on the type of the gas contaminant. The presence of gas contaminant in the electrode material controls the cathode erosion mechanism and the overall arc behavior in the transition between a contaminated to a pure argon arc.     

Basic investigations for laser microanalysis: III. Application of different buffer gases for laser-produced sample plumes

We have measured the diameters and depths of craters in a copper sample and the amount of material ablated by the 1.06-m radiation of a pulsed Nd: YAG laser in the buffer gases argon, neon, helium, air and nitrogen as well as the emission intensities of analyte atoms in dependence on laser power and buffer gas pressure. The results are correlated with corresponding data of the plasma temperatures and the relative electron densities in the plasma. Criteria for the choice of the buffer gas, the buffer gas pressure and the laser power for optical emission spectrometry of microplasmas are given.     

Influence of Gas Entry Point on Plasma Chemistry,Ion Energy and Deposited Alumina Thin Films in Filtered Cathodic Arc

The effect of gas entry point on the plasma chemistry, ion energy distributions and resulting alumina thin film growth have been investigated for a d.c. cathodic arc with an aluminum cathode operated in an oxygen/argon atmosphere. Ions of aluminum, oxygen and argon, as well as ions originating from the residual gas are investigated, and measurements for gas entry at both the cathode and close to the substrate are compared. The latter was shown to result in higher ion flux, lower levels of ionised residual gas, and lower ion energies, as compared to gas inlet at the cathode. These plasma conditions that apply when gas entry at the substrate is used result in a higher film deposition rate, less residual gas incorporation, and more stoichiometric alumina films. The results show that the choice of gas entry point is a crucial parameter in thin film growth using reactive PVD processes such as reactive cathodic arc deposition.     

Radiofrequency Plasma Polymers Containing Ionic Phosphonate Groups: Effect of Monomer Structure and Carrier Gas on Properties and Deposition Rate

Radiofrequency (RF) plasma polymers prepared from perfluoroallylphosphonic acid (PAPA) are hydrophilic and have ionic properties. Unfortunately, deposition rates are low. The current study focuses on RF plasma polymers prepared from PAPA and pentafluoroallyldiethylphosphonate (PADP) with and without argon carrier gas. Plasma polymerized PADP films were similar in composition, structure, and properties to plasma polymerized PAPA films, but were deposited at much higher rates. The addition of argon to the PAPA discharges resulted in a decrease in mean deposition rate from 41.7 Å/min to less than 20 Å/min, while the deposition rate of plasma polymerized PADP increased significantly with the addition of argon to the discharge. PADP derived plasma polymer deposition rates ranged from 136 Å/min to 390 Å/min, depending on position in the reactor and presence or absence of argon carrier gas. PAPA-derived plasma polymers exhibited deposition rates and properties that were uniform throughout the reactor, while PADP-derived plasma polymers had maximum deposition under the upstream induction coil and linearly decreasing deposition rate with downstream distance in the reactor. Additionally, the PADP-derived plasma polymers exhibited downstream changes in atomic composition, structure, and physical properties, such as wettability and hardness. These changes were attributed to a getter effect upstream in the reactor in which ablated hydrogen species scavenge etching fluorine species in the plasma phase.     

Some properties of a microwave boosted glow discharge source using neon as the operating gas

The use of neon as the operating gas for the analysis of aluminium samples with the microwave boosted glow discharge source has been studied. A new type of anode tube allowed the gas to enter the source near the sample surface so that more material was transported into the discharge. Erosion rates have been measured under conditions optimised for high line-to-background ratios and found to be lower than with argon (9 and 21 n/s, respectively). Despite the lower erosion rate the detection limits measured for a number of elements in aluminium are in the range 0.02–1 g/g and comparable to those obtained with argon as the operating gas.     

Temperature Distribution in a Pilot Plasma Tundish: Comparison Between Plasma Torch and Graphite Electrode Systems

Arc, bath, and refractory wall temperatures are measured in a pilot transferred-arc plasma furnace by atomic emission spectroscopy (AES) and multiwavelength pyrometry. Argon plasma torch and graphite electrode with nitrogen as plasma gas are both examined and compared using the steel bath as anode. With argon, a two-slope characteristic curve is measured for arc temperature, which ranges from 9000 to 25,000 K. Another trend is observed with nitrogen for temperatures in the range 8000–12,000 K. In this latter case, the bath temperature is very sensitive to arc length: more than 100 K increase results in arc length rise from 50 to 150 mm. Experimental data shows the variation of heat transfer efficiency between the two configurations, which is supported by results about surface emissivity in the spectral domain 1–15 m.     

不锈钢网阴极微生物燃料电池的产电性能研究

构建了一个以曝气池污泥为阳极接种微生物、碳毡为阳极、无任何修饰的不锈钢网为阴极的双室微生物燃料电池. 通过输出电压、功率密度以及电化学阻抗等考察了阴极面积对电池产电性能的影响,并对电池的长期运行稳定性进行评价. 研究结果表明,不锈钢网作为微生物燃料电池的阴极性能稳定. 当不锈钢网面积为2 × 2 cm²时,最大输出电压达到0.411 V,功率密度为0.303 W•m^-2,内阻841 Ω,极化内阻80 Ω. 增大阴极面积至2 × 4 cm²,最大输出电压能达到0.499 V,内阻减小至793 Ω. 不锈钢网价格便宜,具有长期运行稳定性,适宜做MFCs的阴极.     

Applicability of microwave induced plasma optical emission spectrometry (MIP-OES) for continuous monitoring of mercury in flue gases

The applicability of microwave-induced plasma optical emission spectrometry (MIP-OES) for continuous monitoring of the environmentally hazardous element mercury in flue gases has been studied. Microwave induced plasmas have been sustained using both a TM₀₁₀ cavity (Beenakker resonator) and a so-called Surfatron. The analytical figures of merit for mercury in argon and helium discharges with both types of low-power micro-wave discharges have been examined. To determine mercury in artificial stack gases non-mixed argon/nitrogen discharges have been tested using a tangential flow torch design which allows to introduce a metal-loaded nitrogen gas flow as external gas and argon as internal gas. The addition of main flue gas components such as water vapour (concentration <6 g/m³), oxygen (<4% v/v) and carbon dioxide (<15% v/v) decrease the mercury line intensities to a considerable extent. Trace gases (CO, HCl, SO₂, NO) in concentrations typical to waste incineration processes have been found to have no effect on the mercury and the argon line intensities. The detection limit of mercury in nitrogen is 8 g/m³ using the TM₀₁₀ MIP and 10 g/m³ using the Surfatron. As such low detection limits are below the emission limit values of present-day environmental legislation MIP-OES is useful for on-line monitoring of mercury.Dedicated to Professor Dr. Dieter Klockow on the occasion of his 60th birthday     

等离子体基低能离子注入的光谱诊断

采用发射光谱（ＯＥＳ）技术系统地研究了电子回旋共振（ＥＣＲ）微波等离子体基低能离子注入的等离子体特性。结果表明：纯氮气形成的等离子体中的活性粒子主要是Ｎ２和Ｎ＋２，等离子体中电子与气体分子碰撞使Ｎ２产生激发和电离，而使Ｎ２离解的作用很小；氮氩混合气形成的等离子体中，随着氩气分压的增加，Ｎ２和Ｎ＋２的浓度降低，同时氩气对氮分子离解的贡献很小；直接施加于试样的脉冲负偏压对等离子体特性没有明显影响，但存在着一定的溅射作用。     

Redox Processes in Water,Initiated by Electric Discharge over Its Surface

The yields of oxidation, reduction in a flash corona discharge between a solid cathode andthe water surface are compared. As the cathode was used a system of five aluminum electrodes. As the gasmedium were tested air, oxygen, and nitrogen. The models of processes in the discharge suggest formation of atomic hydrogen in water vapor: H₂O H + OH. However, the reduction yield is equal to the Faraday value irrespective of the gas composition. In the presence of oxygen, oxidation prevails. The yield of Fe^{2 +} oxidation in oxygen is about 190 reaction events per electron passed in the circuit; in air it is lower by a factor of 2, and in nitrogen the yield is equal to the Faraday value.     

Reaction scheme of ammonia synthesis in the ECR plasmas

The reaction scheme of ammonia synthesis in the ECR plasma apparatus teas investigated from both identifications of the species in the plasmas and the adsorbed species on the surface of a steel substrate placed in the plasmas. The adsorbed species were considerably different when different kinds of plasmas are used. NH, species were adsorbed on the steel substrate surface in the nitrogen-hydrogen plasma, and N₂ molecules were adsorbed in the nitrogen plasma. By the application of a negative bias potential on the substrate, the adsorption of N atom or Fe-N bond formation was identified on the steel substrate surface. When the stainless steel wall of the chamber was covered with aluminum foil, the yield of NH,, radicals, which were on both the substrate and in the plasma, decreased. By exposure of the substrate, on which N₂ molecules or N atoms adsorbed, to the hydrogen plasma, N₂ and N disappeared from the steel substrate surface, forming ammonia. Moreover, the adsorption of NH,, radicals disappeared when the stainless steel wall surface was covered with aluminum foil. Thus, the surface of the stainless steel wall acts as a catalyst in ammonia formation. The formation of ammonia in the nitrogen-hydrogen ECR plasma, in which the steel substrate served as the catalyst, is not only through the dissociative adsorption of excited nitrogen molecules but also through the dissociative adsorption of nitrogen molecular ions.     

Electrodeposition of cobalt on stainless steel foils. Preparation of57Co sources for Mössbauer experiments

Conditions for the electrodeposition of⁵⁹Co and⁵⁷Co on stainless steel foils have been studied. A set of electrolytic parameters has been determined to get a reasonably good electrodeposited sample. The⁵⁷Co electrodeposited foil was then introduced in a quartz tube to be annealed in an argon flow. The final product was a 11 Ci Mössbauer source for college experiments which was succesfully tested by obtaining spectra of stainless steel and sodium nitroprusside.     

Determination of arsenic by continuous hydride generation with direct introduction into an O2-argon microwave plasma torch atomic emission spectrometer

The determination of arsenic was studied with a simple and economic method. A continuous hydride generation system is interfaced to a microwave plasma torch atomic emission spectrometer (MPT-AES). Arsenic hydride is transferred directly and continuously by the carrier gas into the plasma torch without separation of hydrogen. When oxygen is introduced into the outer tube of the plasma torch, the plasma is more stable and has a higher tolerance to hydrogen. The detection limit (3σ) is 5.2 μg/L when the forward power is 100 W with argon as support gas. Application to the standard sample coal fly ash showed a comparable result to the certified quantity.     

Conversion electron Mössbauer and XPS study on the effect of polishing of a stainless steel sample

Conversion electron Mössbauer spectroscopy (CEMS) and XPS has been used for the surface analysis of an X10CrNiTi 18/9 (DIN 1.7440)-type stainless steel in order to determine the supposed structural and/or chemical changes in the surface layer caused by polishing. Both, CEMS and XPS results can be associated with the appearance of Fe nitride in the outer layer of steel samples after polishing, while no sign of nitrogen was detected in the bulk material.     

Characterization of surface modifications of stainless steel samples after electron and ion bombardment by SEM, AES, and XPS

The interaction of inert or reactive gas plasmas with the surface of stainless steel has been investigated with the aim, to modify the surface and hence to reduce the outgassing rate of the material, an important factor for the production of an ultrahigh vacuum. The plasma treatments investigated may be an alternative to the common used in situ baking. The samples have been exposed to electrons, argon and oxygen ions either in a DC glow discharge or in a microwave discharge. The DC glow discharge in Ar/O₂, the most effective plasma treatment reduces the outgassing rate by a factor of 10. After this treatment the surfaces of the samples have been investigated with respect to the topography and the chemical composition (depth profile) by Secondary Electron Microscopy (SEM), Auger Electron Spectroscopy (AES) and X-ray Photoelectron Spectroscopy (XPS), respectively. The surface modifications resulting from the different treatments of the samples have been correlated to the outgassing rate.     

Tritium separation from heavy water by electrolysis with solid polymer electrolyte

A tritium separation from heavy water by electrolysis using a solid polymer electrode layer was specified. The cathode was made of stainless steel or nickel. The electrolysis was performed for 1 hour at 5, 10, 20, and 30 °C. Using a palladium catalyst, generated hydrogen and oxygen gases were recombined, which was collected with a cold trap. The activities of the samples were measured by a liquid scintillation counter. The apparent tritium separation factors of the heavy and light water at 20 °C were 2 and 12, respectively.