Temperature and density profiles of magnetically rotating arcs burning in contaminated argon

Spectroscopic measurements on copper vapors emitted by the cathode are presented for magnetically rotating arcs in a coaxial copper electrode geometry. The maximum temperature of a 100-A arc column burning in contaminated argon is shown to be lower than 8000 K. A maximum Cu density of 5 × 10²¹ in m^–3 is observed when argon is contaminated with 1% CO, while it is larger than 10²² m^–3 with 1% nitrogen contamination. The copper vapors emitted by the cathode explain the low temperatures observed. Cases of surface control of the arc velocity at the cathode and radial losses of copper vapors out of the arc column are observed front specific parameters describing the arc profiles. Evidence is given for a copper ion recombination zone extending 2 mm from the cathode in the nitrogen contamination case.     

Some analytical characteristics of an argon—nitrogen d.c. plasma arc for emission spectrometry

A low-power d.c. plasma arc device was used to estimate the analytical characteristics of an Ar—N₂ plasma arc compared to those of an argon plasma arc. When the flow rate of added nitrogen was varied from 0 to 1 l min^-1, the Cd I 228.802-nm line showed a maximum signal-to-background ratio at a nitrogen flow rate of approximately 0.3 1 min^-1 which corresponds to 0.23% of the total argon flow rate. Ratios of the signal intensities with the Ar—0.23%N₂ and argon plasma arcs are given for the spectral lines of seventeen elements. Relatively higher ratios were found for the atom lines of the group VIII through IIIA elements in the periodic table. Better precision and lower detection limits were attained for aluminium and cadmium with the Ar—0.23%N₂ plasma arc than with the argon plasma arc.     

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.     

Numerical Study of a Free-Burning Argon Arc with Copper Contamination from the Anode

The present modeling of a free-burning argon arc accounts for copper vapor contamination from the anode. Simulations are made for an atmospheric arc that has a length of 10 mm and an electric current of 200 amps. Predicted results for two different anode evaporation rates are compared to those from a pure argon arc with no copper vapor contamination. Copper vapor concentration, temperature, electric potential, and current density profiles are presented. Included in this analysis are radiation losses from both the argon and copper by using recently calculated net emission coefficients. It was found that evaporation of copper from the anode results in a cooling of the arc in a region close to the anode, but has an insignificant influence on the arc close to the cathode. Due to the arc flow characteristics most of the copper vapor tends to be confined to the anode region.     

Optical emission diagnostics in cascade arc plasma polymerization and surface modification processes

Optical Emission Spectroscopy (OES) was used to identify reactive species and their excitation states in low-temperature cascade arc plasmas of N₂, CF₄, C₂F₄, CH₄, and CH₃OH. In a cascade arc plasma, the plasma gas (argon or helium) was excited in the cascade arc generator and injected into a reactor in vacuum. A reactive gas was injected into the cascade arc torch (CAT) that was expanding in the reactor. What kind of species of a reactive gas, for example, nitrogen, are created in the reactor is dependent on the electronic energy levels of the plasma gas in the cascade arc plasma jet. OES revealed that no ion of nitrogen was found when argon was used as the plasma gas of which metastable species had energy less than the ionization energy of nitrogen. When helium was used, ions of nitrogen were found. While OES is a powerful tool to identify the products of the cascade arc generation (activation process), it is less useful to identify the reactive species that are responsible for surface modification of polymers and also for plasma polymerization. The plasma surface modification and plasma polymerization are deactivation processes that cannot be identified by photoemission, which is also a deactivation process. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1583–1592, 1998     

Heat transfer from a transferred-arc plasma to a cylindrical enclosure

Hear-transfer rates from an axially enclosed transferred arc to a surrounding water-cooled cylindrical sleeve, 15 cm high, were measured. The arc (argon or nitrogen) was struck between a movable cathode within the sleeve and a bath of molten copper below the sleeve, serving as anode. The distance from the bottom of the sleeve to the surface of the molten copper (L _o) was constant. Variables studied were the diameterD of the sleeve (5, 7.5. and 10 cm), the length of the arc within the sleeveL (5, 10, and 15 cm), the currentI (200, 250, and 300 A) and a tangential flow of gas or vortex within the sleeve (0, ?0, and 50 liters/min). The total power transferred to the sleeve,P _s was measured caloronetrically and was the sure ofP _r the effective power radiated by the arc of lengthL within the sleeve.P _a, the power radiated into the sleeve from the arc of length L_o below the sleeve, andP _o , the power radiated from the melt surface (a constant of small value), minusP _a , the power lost by convection from the sleeve (negligible, except for a strong vortex). BothP _r andP _o were found to be equal to the product of the Joule heat released within their respective arc lengths, IV_gL and IV_g0L₀ (where V_g and V_g0 are the voltage gradients), and dimenonless efliciency factors, η_r and η₀. which are functions ofL/D andL ₀ /D, respectively, for each gas, regardless of the geometry of the sleeve, the current, and the strength of the vortex.     

Condensation of Argon,Monosilane and Their Mixtures in a Pulse Free Jet

Pulse supersonic outflow of Ar, SiH₄ and Ar + SiH₄ gas mixture (where monosilane is a small admixture) was studied experimentally by the method of molecular beam mass-spectrometry. Using argon as an example we have shown that condensation processes at the quasi-stationary region of a pulse flow and within a stationary jet are similar. In the flows of pure gases clusters of argon and silane (hydrogenated silicon) and in the mixture argon – silane complexes were registered. The dependencies of the intensities of monomer and cluster ions on stagnation pressure were investigated. It was shown that in the mixture jet at low stagnation pressures the condensation process with the formation of monosilane clusters takes place and at high pressures mixed argon-silane complexes are formed. The parameters of flow transition into the regime of developed condensation were determined for pure gases and their mixture.     

The behavior of titanium,stainless steel,and copper-nickel alloys as plasma torch cathodes

Cathode erosion continues to be a problem hindering the widespread application of plasma technology. In this work, cathode erosion was studied on titanium, stainless steel 314, copper-nickel 10% and 30%, and copper 122 for magnetically rotated arcs operating in argon, nitrogen, and argon/hydrogen mixtures at a constant magnetic flux density of 0.1 T Titanium and stainless steel gave very low erosion rates in argon (0.2 and 0.3, g/C respectively). Cupronickels were shown to be suitable for nitrogen and hydrogen plasmas. The slope of hydrogen solubility versus temperature in the cathode material was found to be important in determining hydrogen plasma erosion characteristics. When the plasma gas has a high solubility in the cathode material, or can react with the cathode, a negative erosion rate may result. When gas solubility in the cathode is low, oxide stability and mode of electron emission may govern the erosion rate. A high gas solubility in the cathode material, as with hydrogen, can result in mechanical erosion due to micro-explosions near the cathode surface.     

Distribution of metastable argon atoms in the modified Grimm-type electrical discharge

The absorbance by metastable argon atoms of the Ar 696.543 nm line in the modified Grimm-type electrical discharge source was measured at different discharge conditions and at distances varying from 0.25 to 6 mm from the cathode. A uranium/argon hollow cathode lamp was used as primary source, which gave an argon gas temperature of 850 K when run at 12 mA. A maximum absorbance of 0.57 was found 3 mm from the cathode at 600 V, 80 mA. The magnitude of absorbance increases with discharge current while the position of maximum absorbance shifts away from the cathode with increase in discharge voltage. The quenching of metastable atoms by nitrogen is demonstrated.The spatial distribution of the intensity of four different types of spectral lines is shown. The approximate number densities of the different particles are 10¹²cm^?3 for metastable argon atoms, 10¹⁶cm^?3 for neutral argon atoms, 10¹³ cm^?3 for sputtered copper atoms and 10¹⁴cm^?3for electrons.     

A Mathematical Model of the Carbon Arc Reactor for Fullerene Synthesis

A mathematical model of the carbon arc process for the synthesis of fullerenes (C ₆₀ , C ₇₀ ) is developed. The two-dimensional model solves for the velocities, temperature, and total concentration of carbon species. The net emission coefficient method is used for the radiation term. The carbon species conservation equations consider the evaporation of carbon from the anode, cathode surface deposition, and carbon condensation. The thermodynamic and transport properties are calculated as a function of temperature and carbon mass fraction, using the method of Chapman–Enskog. Erosion rates used by the model are determined experimentally. Calculated fields of the velocities, temperatures, carbon mass fraction and current intensity are presented. Comparison is made of the behavior of the arc at 1 and 4 mm interelectrode gaps, and between operation in argon and in helium. The results of simulations provide a justification for the higher yields observed in helium compared to the argon case.     

Decomposition of SiCl4 and deposition of Si in inductively coupled plasmas of H2+SiCl4

The mechanism of homogeneous reactions in plasmas of H₂+5%SiCl₄ was studied by mass spectrometry and was compared to the mechanism observed in plasmas of Ar+H₂+SiCl₄. Contrary to the behavior with Ar, the results indicate that without argon the SiCl₄ molecule undergoes only fragmentation and the deposition proceeds through SiCl₂. No polymerization was observed. The deposition rates of c-Si were lower and the amounts of chlorine incorporated in the films were higher in the plasma of SiCl₄+H₂ than in the argon-containing plasma.     

Thermal and Chemical Nonequilibrium Effects in Free-Burning Arcs

Effects caused by thermal and chemical nonequilibrium in free-burning arcs in argon are presented and discussed. The results cover a range of arc currents between 100 and 200 A, interelectrode distance of 5–10 mm, and a variation of the electrode material and the shape of the cathode tip. The results obtained show that nonequilibrium in the near-electrode regions has a strong impact on the distributions of temperatures, electric conductivity and current density, and the arc voltage. Departure from chemical nonequilibrium in the vicinity of the cathode as a result of transport processes is indicated. Moreover, overpopulation of the atomic ground state close to the arc axis, under population of the excited states in the arc periphery with respect to the equilibrium values, axial dependence of the off-axis maximum of the radial emission coefficient of Ar I at 696.5 nm, and enhanced population of the Ar (1s₄) resonance level due to trapping of resonance radiation in the arc periphery are considered.     

Two-Temperature Chemical-Nonequilibrium Modelling of a High-Velocity Argon Plasma Flow in a Low-Power Arcjet Thruster

A numerical simulation has been performed of a high-velocity argon plasma arc flow in a low power arcjet including a finite-rate chemical kinetic model. Electrons, ions, molecular ions ( $ {\text{Ar}}_{2}^{ + } $ ), neutral atoms including the ground and excited argon atoms (Ar^*) are treated as separate species in the plasma mixture. The chemical reactions considered are excitation, de-excitation, ionization and recombination processes, in which reactions involving excited argon atoms (Ar^*) and molecular ions ( $ {\text{Ar}}_{2}^{ + } $ ) are taken into account. The relative importance of different production and loss processes in determining the densities of excited argon atoms and ions is calculated inside the constrictor and expansion portion of the nozzle. The roles of the excited argon atoms and molecular ions are investigated. It is found that excited argon atoms play an important role in the ionization of argon atoms in the core of plasma arc, while the molecular ions have a significant effect on the recombination process at the arc fringes inside the constrictor and in the arc attachment zone of the anode.     

On the Cu2 bands in the cold cathode discharge in inert gas

The Cu₂ AX and BX bands were obtained in a cylindrical copper cold cathode neon and argon discharges (ref.I) at gas pressure I0–I5 torr and current densities 200 – 300 mA.cm^?2. torr^?2. The result may be of importance for the cathode sputter laser developments and the spectral analysis.     

Penetration of plasma surface modification. II. CF4 and C2F4 low-temperature cascade arc torch

The depth of surface modification by low-temperature cascade arc torch is investigated. A stack of 10 sheets of nonwoven fabrics of polyester fibers is exposed to a low-temperature cascade arc torch containing CF₄ or C₂F₄, and the fluorination effect is examined by ESCA. It is shown that interaction of chemically reactive species, created in a low-temperature cascade arc torch, with the surface is not limited to the surface contacted by the torch (flame). The results indicate that the fluorination effect is observed on surfaces which are shadowed from the torch by overlying fibers. The highest degree of fluorination is found on the second layer, rather than on the first layer which the torch contacts directly. No significant differences in the trends of penetration of CF₄ and C₂F₄ treatment through porous samples are observed. However, ESCA data show principal differences in chemical structures of the surfaces treated with CF₄ (nonpolymer-forming gas) and C₂F₄ (polymer-forming gas). These results indicate that chemically reactive species induced by the excited species of argon rather than primary species created by the ionization process seem to play predominant roles in the surface treatment as well as the low-temperature cascade arc torch polymerization of perfluorinated compounds. © 1994 John Wiley & Sons, Inc.     

Diagnostics of a Radio-Frequency Plasma Expanding Through a Nozzle (PETN) at Low Pressure

The diagnostics of the radio-frequency (induction mode) plasma expanded through a nozzle (PETN) at low pressures (100–1000 Pa) was performed by on-line optical emission spectroscopy (OES) and on line quadrupole mass spectrometry (QMS). The OES was used for evaluating the electronic, vibrational, and rotational temperatures (T_e, T_v, and T_r) along the plasma reactor before and after the nozzle. The PETN gas mixtures analyzed were Ar+N₂, Ar+CO, and Ar+O₂with an addition of 1 vol.% N₂to the last two gas mixtures. For the same conditions in the PETN the values of T_e, T_v, and T_r were found to be different for the different gas mixtures and related to the depopulation of excited N ₂ ⁺ by oxygen atoms. Moreover the Ar+O₂PETN aqueous solutions of lanthanum and manganese nitrates were nebulized for the deposition of LaMnO₃perovskite. The QMS, in real time, measuring the mass species formed before and after the nozzle, explained the reasons in the different values of T_e, T_v, and T_r for the three gas mixtures as well as for the formation of oxides in the PETN from the aqueous nitrate solutions.     

Effect of the presence of iron vapors on the volumetric emission of Ar/Fe and Ar/Fe/HZ plasmas

The net volumetric emission coefficient was calculated using the escape factor method for Ar/Fe and Ar/H₂/Fe plasmas, at atmospheric pressure, over the temperature range from 3000 K to 30,000 K. The calculation involved 712 lines for Ar I, Ar II, and Ar III, 3481 lines for Fe I, Fe II, and Fe III, and 230 lines for H in the Ar/H₂/Fe case. A semiempirical method was used for the determination of line profiles and line broadening. The results show a strong influence of the presence of even traces of iron vapors at low temperatures where the volumetric emission increases by several orders of magnitude. Special attention is given to self-absorption of the argon resonance lines which prevents the radiation from escaping within a few millimeters from the emission source.     

H2/Ar direct current glow discharge mass spectrometry at constant voltage and pressure

The addition of hydrogen to a direct current (dc) - argon glow discharge (GD) coupled to a time of flight mass spectrometer has been studied using a fixed voltage between the electrodes and a fixed discharge pressure. Hydrogen contents investigated were 0.5%, 1% and 10% v/v in the argon discharge and the samples under study consisted of a copper-base, a nickel-base and an iron-base homogeneous materials. Also, the in-depth profile analysis of a tin plate was investigated. Results have shown that hydrogen addition gives rise to significant changes in the slope of the linear relationship between the electrical current and the discharge voltage. Clearly, the electrical resistance of the discharge at the typical operation voltages in the interval 600–1000 V increases with hydrogen added to pure argon.A decrease of the sputtering rates was observed the higher the hydrogen concentrations. Besides, the “reduced sputtering rates”, i.e. the sputtering rates divided by the corresponding electrical current, were also lower for the H₂/Ar discharges than for pure argon. However, the analytical ion signals observed using discharge voltages higher than 900 V turned out to be higher in a 0.5% H₂/Ar discharge than in pure argon for the copper and nickel materials. Besides, for the three samples investigated the ion yields were from 1.5 up to 3 times higher in 0.5% H₂/Ar discharges as compared to the pure argon.Finally, the effect of 0.5% H₂ addition to the Ar discharge on the in-depth profile of a tin plate has also been investigated. As compared to the use of a pure Ar GD, higher sensitivity for major and minor components of the coating were observed without loss of the relative depth resolution achieved.     

Determination of Nd,Ho, Er,Tm and Y in Solutions by Hollow Cathode Discharge with Copper Cathodes

Abstract

A hollow cathode discharge has been applied to the determination of Nd, Ho, Er, Tm and Y in solutions using copper cathodes and argon as a carrier gas. The solutions were evaporated to dryness in the cathodes without a pretreatment. Absolute detection limits for the elements studied here were found to be lower in the copper cathode by about one order than those obtained in previous studies in graphite hollow cathodes.     

Langmuir probe measurements during plasma-activated chemical vapor deposition in the system argon/hydrogen/dicyclopentadienyldimethylhafnium

A Langomir probe investigation of Ar/H₂/Cp₂HfMe₂ plasmas is described. The probe measurements were performed for various discharge conditions. The mean electron energy and electron density were measured for various power, gas flows of argon, and hydrogen and precursor concentrations. Addition of the precursor into the discharge resulted in an appreciable decrease in the electron density and an increase in the mean electron energr. Whereas a transition front the a-mode to the -mode has been observed with power rise in the Ar/H₂ plasmas without precursor, in the presence of the precursor the plasota -mode remained unchanged in the power range investigated.