Carburizing of titanium with plasma jets under reduced pressure

The carburizing of titanium with argon-methane (0.1%) and argon-methane (0.1%)-hydrogen (2%) plasma jets at a pressure of 200 Torr was studied. The carburizing of titanium was not successful with the argon-methane plasma jet because the specimen was covered with graphitic carbon. A hard and thick TiC layer was formed by the argon-methane-hydrogen plasma jet in a short time without the deposition of graphitic carbon. Emission spectra from the plasma jets show that the addition of hydrogen increases the amount of CH radicals as well as decreases the amount of C₂ and C in the plasma jet. The decrease of C₂ and C suppresses the deposition of graphitic carbon and enhances the TiC formation.Partly presented at Gordon Research Conference on Plasma Chemistry, August 11–15, 1986, Tilton, New Hampshire.     

Nitriding of niobium and tantalum with a plasma jet under reduced pressure

The nitriding of niobium and tantalum with argon-nitrogen and argon-nitrogen-hydrogen plasma jets at pressures of 190 and 240 Torr was studied. The reaction kinetics obeyed a parabolic law. Cubic -NbN and cubic -TaN, which were stable phases at high temperature, were easily obtained at higher nitriding rates than those of thermal nitriding at the same temperature. Results obtained are discussed with plasma diagnostics such as emission spectroscopy and electrical double probe techniques.     

Hydrogen/argon plasma jet with methane addition

Spatial distributions of plasma parameters are presented for a H₂/Ar plasma jet with addition of methane. The plasma has been generated at atmospheric pressure by a 200 A (20 kW) nontransferred do arc. Optical emission spectroscopy has been used for the measurements assuming the plasma jet to be optically thin and to have an axial symmetry. Local spectral ernissivity values have been evaluated using a routine Abel inversion procedure. Half- width and emissivity of H spectral line have been measured to determine the electron density and temperature of the plasma. The densities of excited C, CH radicals have been evaluated from the absolute emissivities of relevant molecular emission bands measured in limited spectral intervals in the visible spectrum. The emissivity ratios have been used to fund rotational and vibrational temperatures. The results supply information on methane decomposition and the behavior of molecular radicals in close-to-thermal plasma jets.     

大气压等离子体射流重整CH_4-CO_2制合成气

采用大气压等离子体射流,以CH4和CO2直接作为放电气体进行常压下重整制合成气的实验研究,考察了等离子体射流的放电特征及放电距离、放电功率、原料气配比和流量对反应的影响。结果表明,该等离子体具有放电稳定、均匀的特征。重整反应的主要产物为合成气,只有少量的H2O和积炭生成。优化的反应条件为放电距离为9 mm,CH4和CO2的摩尔比为4/6。当原料气流量为1 000 mL/min,放电功率为88.4 W时,CH4和CO2的最高转化率为分别为94.99%和87.23%。甲烷和二氧化碳的转化率随放电功率的增加而增加,随流量的增加而减少。     

Diagnostics of a thermal plasma jet by optical emission spectroscopy and enthalpy probe measurements

An accurate determination of electron density, temperature, and velocity distributions is of primary interest for the characterization of steady-state thermal plasma spray jets. Our diagnostic capabilities based on optical emission spectroscopy include measurements of absolute emission coefficients and Stark broadening. In addition, enthalpy probe diagnostics has also been used for temperature and velocity measurements. Observation of large discrepancies between temperatures derived from absolute emission coefficients, Stark broadening, and from enthalpy probe measurements indicate that severe deviations from LTE (local thermal equilibrium) exist in various regimes of plasma spray jets. Nonequilibrum characterization of such turbulent thermal plasma jets suggests that diffusion of high-energy electrons into the fringes of plasma jets and deviations from chemical equilibrium due to high velocities in the core of plasma jets and entrainment of cold gas, are the main reasons for these discrepancies. The establishment of a reliable data base, taking these nonequilibrium effects into account, is a prerequisite for meaningful modeling of real plasma jets.     

GDOES,XPS, and SEM with EDS analysis of porous coatings obtained on titanium after plasma electrolytic oxidation

In the paper, the glow discharge optical emission spectroscopy, X‐ray photoelectron spectroscopy, scanning electron microscopy, and energy‐dispersive X‐ray spectroscopy results of a commercial purity titanium grade 2 after plasma electrolytic oxidation (PEO), also known as micro arc oxidation (MAO), are presented. The PEO treatment was performed in the electrolyte containing concentrated (85%) phosphoric acid with copper nitrate at the voltage of 450 ± 10 V for 1 min. For the electrolyte, copper nitrate addition from 300 to 600 g/l was used. Porous coatings of specific properties were obtained. The measurements results allow to state that the copper and nitrogen ions can be introduced into the surface layer formed on pure titanium by the plasma electrolytic oxidation. The distributions of these elements were detected to depend on the electrolyte composition, with the highest amounts revealed in the coating created in the electrolyte containing 600 g Cu(NO₃)₂ in 1 l H₃PO₄. Three sub‐layers of the coating, displayed in this work by two models, were developed in the study. The analysis performed shows that under the PEO treatment in each of the electrolytes used, the formation of coating with the top sub‐layers always enriched in copper compounds was found. Copyright © 2016 John Wiley & Sons, Ltd.     

大气压等离子体射流重整CH4-CO2制合成气

采用大气压等离子体射流,以CH₄和CO^₂直接作为放电气体进行常压下重整制合成气的实验研究,考察了等离子体射流的放电特征及放电距离、放电功率、原料气配比和流量对反应的影响。结果表明,该等离子体具有放电稳定、均匀的特征。重整反应的主要产物为合成气,只有少量的H₂O和积炭生成。优化的反应条件为放电距离为9mm,CH₄和CO₂的摩尔比为4/6。当原料气流量为1000mL/min,放电功率为88.4W时,CH4和CO₂的最高转化率为分别为94.99%和87.23%。甲烷和二氧化碳的转化率随放电功率的增加而增加,随流量的增加而减少。     

电感耦合等离子体原子发射光谱法测定钛合金中锆

建立电感耦合等离子体原子发射光谱法(ICP-AES)测定钛合金中锆元素的含量。采用盐酸-氢氟酸-硝酸溶解钛合金样品,选择357.247 nm为锆的分析谱线,通过基体匹配法消除基体钛的干扰,以电感耦合等离子体原子发射光谱法测定钛合金中锆的含量。锆的质量分数在0%~0.4%范围内与光谱强度呈良好的线性关系,相关系数大于0.999,定量下限为0.21%。测定结果的相对标准偏差小于2%(n=11),样品加标回收率为99.0%~102.7%。该方法快速、准确,能够满足实际生产中钛合金样品的测定要求。     

An overall mechanism for the deposition of plasma polymers from methane in a low-pressure argon plasma jet

An overall mechanism for plasma polymer deposition from a methane-seeded argon plasma jet was established from experimental measurements and a simplified model of reaction kinetics within the plasma jet. Total mass deposition rates were obtained at various substrate positions and methane flow rates. Methane consumption was estimated from residual gas analysis. The influence of substrate coolant temperature on deposition rate was evaluated. The model was based on particle densities, jet temperature, and jet velocity data published previously, and reaction rate constants from the literature were used. No adjustable parameters were employed in this model. Experimental results for total deposition rate and methane consumption were in good agreement with model predictions. The overall deposition mechanism consists of three steps: Penning ionization of methane by excited argon neutrals, followed by dissociative recombination of CN _x ⁺ to yield CH, followed by incorporation of CH into the growing film upon impact. Contributions of species other than CH to the total deposition rate are minor, and adsorption is not a prerequisite for incorporation into the growing film.     

Laser Doppler anemometry under plasma conditions. Part I. Measurements in a d.c. plasma jet

A study is presented on the use of laser Doppler anemometry (LDA) techniques for the measurement of the gas and particle velocities under plasma conditions. Experimental data is presented for a d.c. plasma jet in which alumina particles are injected under different operating conditions. The results reveal that the plasma velocity at the exit of the jet is of the order of 200–300 m/s. The intensity of turbulence is as high as 30 to 40% in the free shear layer and the particle velocity distribution is shown to be asymmetric, with particle dispersion in the plane of injection considerably more important than that in the perpendicular direction. The average particle velocity depends on the composition of the plasma gas, the torch current, and power.     

Particle densities and non-equilibrium in a low-pressure argon plasma jet

Plasma diagnostic techniques have been employed to determine particle densities and temperatures in a low-pressure argon plasma jet generated by a cascade arc. These measurements allow characterization of the extent to which the plasma jet deviates from thermodynamic equilibrium and provide a basis for predicting how reactive gases will interact with the excited and ionized species in the plasma jet. It was found that the distribution of atomic states in the plasma jet is not adequately described by either local thermodynamic equilibrium (LTE) or partial local thermodynamic equilibrium (pLTE), and the jet was optically thick for 3p4s transitions across the jet radius. Excited argon neutrals outnumber ions by a large ratio, and dominate subsequent dissociation/excitation phenomena. The rate of methane destruction in the plasma jet shows that estimates for particle densities, temperature, and jet velocity are self-consistent.     

Diagnostic analysis of styrene plasma polymerization

For studying plasma polymerization of styrene, two in situ diagnostic methods, optical spectroscopy and mass spectroscopy, were used to measure chemical components formed in the discharge volume and their concentrations in plasma column and two sheaths. The synergetic influence of power (W), pressure (p), and monomer flow rate (F) on plasma polymerization was expressed with a composite parameter, W/pF, which is proportional to the energy transferred to styrene monomer molecule. In a certain range of W/pF, the population of C₂H₂ and H₂ produced in the discharge decreased with W/pF, while the concentration of C₈ and C₆ fragments increased, which indicates that different chemical reactions may occur in different intervals of W/pF value. The similarity in change tendency between the deposition rate, the emission intensity of CH and C₄H and mass peak vs. W/pF implies that the polymerization is controlled by the reaction in the gas phase plasma, and supports the view that initial reactive species are produced in plasma, and polymerization is performed on the substrate surface. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 325–330, 1999     

A magnetically excited microwave plasma source for atomic emission spectroscopy with performance approaching that of the inductively coupled plasma

A novel magnetically excited microwave plasma emission source was developed and tested. Unlike previous microwave plasma sources which couple energy from the microwave electric field, this source couples energy from the magnetic field. The resultant plasma shape allows easy entrainment of wet sample aerosol, such as is produced by a conventional inductively coupled plasma (ICP) nebulizer and spray chamber, into the core of the plasma. Plasma support gas can be either nitrogen or air although better sensitivity is achieved using nitrogen. Good stability of operation was observed for both aqueous and organic solvents over a wide range of sample flows. The measured performance when used as a spectroscopic source in conjunction with an echelle polychromator showed detection limits approaching those of commercial ICP sources.     

Single‐phase TiO2 formation by plasma oxidation of titanium thin films

Synthesis of titanium oxide film by plasma oxidization of the metallic films is investigated. Argon/oxygen gas mixture in the pressure range 30 × 10^?2 mbar is used for plasma processing at a frequency of 250 kHz. The plasma‐oxidized films are annealed in a tube furnace in argon atmosphere to establish crystalline‐phase formation. X‐ray diffraction and Raman spectroscopic results manifest peaks corresponding to rutile TiO₂. Ultraviolet‐Visible (UV‐Vis) spectroscopic analysis confirms the bandgap of rutile TiO₂, and photoluminescence spectra exhibit peaks due to oxygen defects. Homogeneity across the film's thickness and the nature of the film substrate interface is studied by depth profiling acquired using secondary ion mass spectrometry. Copyright © 2015 John Wiley & Sons, Ltd.     

Formation of gaseous intermediates in titanium(IV) chloride plasma oxidation

A number of experiments were made to study tire gas phase reactions that precede TiO₂ aerosol formation from TiCl₄ in an O₂/Ar plasma. The gaseous .species from the plasma-aerosol reactor were detected by a high-resolution QP mass spectrometer. The feed ratio of Ar: O₂: TiCl₄ was typically 4. l: 0.1. Under such conditions both titanium oxychlorides and oxides of chlorine could be recognized. In the reactor the decay of oxychlorides from the reactions it-as fast, compared to the decay of chlorine. A rough estimate of the quantities of both ClO(g) and Ti0Cl_x(g) metastable species present is given. TiCl₄ oxidation reaction mechanisms with mentioned oxychlorides as intermediates are discussed The theoretical calculations were conducted in tire temperature range from 800 to 3500°C.     

Surface modifications of PET in argon atmospheric pressure plasma: Gas flow rate effect

The correlation between plasma optical properties and the treated polyethylene terephthalate (PET) surface characteristics have been studied at various Ar flow rate. The rotational T_rot and vibrational T_vib temperatures of APPJ were determined from SPS emission band. The pristine and plasma-treated PET surfaces were characterized by several techniques including X-ray photoelectrons spectroscopy (XPS), Raman spectroscopy, contact angle (CA), and atomic force microscope (AFM). The CA decreased rapidly in the flow rate range 1–3 L/min and weakly dependent as flow rate > 3 L/min. XPS results showed that C 1s % of plasma-treated PET surfaces decreases and has a minimum for samples treated at 3–4 L/min, while O 1s has a maximum at the same flow rate range. The carbon C 1s peak of pristine and plasma treated PET samples resolved into five subcomponents: C–C, C–O, C=O, O–C=O, and π–π bonds with variable percentage ratio accordance to the plasma gas flow rate. Raman data revealed a partial loss in the crystallinity of the treated PET samples and also confirm the incremental of C–O band at Ar flow rate of 3 L/min. AFM images showed that the surface roughness of treated PET films increases as Ar flow rate increases.     

A comparison of experimental measurements and theoretical predictions regarding the behavior of a turbulent argon plasma jet discharging into air

Computed results are presented describing the temperature and concentration fields obtained when an argon plasma jet is being discharged into ambient air. A previously published mathematical model for turbulent plasma plumes is used for the calculations. These predictions are compared with recent), published experimental measurements by Brossa and Pfender, performed with an enthalpy probe. The theoretical predictions appear to agree reasonably well with the measurements of both the temperature and concentration profiles, with a maximum deviation in the 10–20% range.Notation A _max maximum temperature or velocity in the torch exit profile - C ₁ C ₂ C _D constants inK- model - h enthalpy - I torch current - K turbulent kinetic energy per unit mass - m mass concentration of plasma p pressure - Q How rate of argon through the torch - r radial coordinate - r _n nozzle radius (inside) - S source term for dependent variable      

Selective determination of organofluorine compounds by capillary column gas chromatography with an atmospheric pressure helium microwave-induced plasma detector

Fluorinated analogs of compounds typical of those found in metabolic and other biological studies are detected with high selectivity using a gas chromatograph/microwave-induced plasma detector (GC-MIPD), which permits fluorine-selective detection by monitoring the emission at 685.6 nm. Using the described atmospheric pressure helium-sustained plasma detector, the minimum detectable level, fluorine selectivity (relative to carbon), and linear dynamic range of this GC-MIPD system were determined to be 4.8 pg-F/s, 1060, and 5000, respectively. The utility of this GC-MIPD system for the selective detection of organofluorine compounds is demonstrated by its application in the analysis of the metabolic fate of a fluorinated substrate administered to a mixture of wheat germ phosphatase and potato apyrase, as well as by analysis of synthetic mixtures.     

Numerical modeling of titanium carbide synthesis in thermal plasma reactors

Titanium carbide powders synthesized in thermal plasma reactors are virtually always contaminated by soot. Equilibrium modeling predicts a viable process window without soot formation; however, this has not been achieved in practice. A numerical model incorporating chemical kinetics, nucleation and growth, and soot formation mechanisms has been developed to investigate this process. The chemical kinetic scheme teas based on ethylene pyrolysis and methane combustion with additional reactions to account for titanium-based molecules and the free carbon species found at plasma temperatures. Nucleation and .soot formation were based on simple kinetic models. The governing equations were integrated through time using typical temperature-time histories found by computational fluid dynamic (CFD) modeling of a radio frequency plasma torch. The results indicate that the synthesis is governed by interactions between several parallel processes and that there is a delicate balance between reactant stoichiometry, system pressure, cooling rate, product formation, and soot formation. This balance may be a limiting feature of ceramic carbide production in thermal plasma reactors.