Nitrogen Arc Research Articles

Spectroscopic measurement of temperature and gas composition in Ar-N2 shielded TIG welding

Demixing causes changes in the composition and thermal transport in a mixed-gas arc. Thus, the temperature and gas composition of argon–nitrogen arc plasma are measured to analyze the effect of demixing in both direct-current tungsten inert gas (DC-TIG) and pulsed TIG (P-TIG) welding. The arc image acquisition system is developed; this system includes two monochromatic imaging devices, which are triggered synchronously by software. The presented system is an efficient approach to capture monochromatic images simultaneously with high temporal and spatial resolutions. It is applied to obtain monochromatic images of the Ar I and N I spectra. Using the modified Fowler–Milne method, the radial profiles of temperature and gas composition are measured. For DC-TIG in 80 % Ar + 20 % N2, the argon concentration is decreased in the arc centre, relative to the original gas mixture, and then gradually increases with the radius. This is attributed to frictional forces. As the radius increases further, the argon mass fraction decreases again, which is attributed to diffusion of argon toward the arc periphery. For P-TIG using 80 % Ar + 20 % N2, the demixing effect in the peak-current phase is stronger than that in the base-current phase due to the higher current in the peak-current phase. This phenomenon helps control the heat input into the workpiece.

Nitrogen loss and effects on microstructure in multipass TIG welding of a super duplex stainless steel

Nitrogen loss is an important phenomenon in welding of super duplex stainless steels. In this study, a super duplex stainless steel was autogenously TIG-welded with one to four bead-on-plate passes with low or high heat inputs using pure argon shielding gas. The goal was to monitor nitrogen content and microstructure for each weld pass. Nitrogen content, measured by wavelength dispersive X-ray spectrometry, was after four passes reduced from 0.28wt% in the base metal to 0.17wt% and 0.10wt% in low and high heat input samples, respectively. Nitrogen loss resulted in a more ferritic structure with larger grains and nitride precipitates. The ferrite grain width markedly increased with increasing number of passes and heat input. Ferrite content increased from 55% in base metal to 75% at low and 79% at high heat inputs after four passes. An increasing amount of nitrides were seen with increasing number of weld passes. An equation was suggested for calculation of the final nitrogen content of the weld metal as functions of initial nitrogen content and arc energy. Acceptable ferrite contents were seen for one or two passes. The recommendation is to use nitrogen in shielding gas and proper filler metals.

Enthalpy modulation of a laminar pulsed nitrogen arc jet: time-resolved diagnostics and model

In most studies, plasma spraying of liquid feedstock for ceramic coating elaboration requires limiting the arc motion to obtain stable plasma and to favour homogeneous treatment of nanomaterials. In this chapter, an alternative approach is proposed and consists of using a pulsed arc jet modulating the specific enthalpy in time. The momentum and heat transfers can be controlled provided a synchronous injection of materials is associated with it. The rotational temperatures of the nitrogen arc jet are measured by means of time-resolved optical emission spectroscopy synchronized with the arc voltage. The enthalpy modulation ratio (hmax/hmin) is shown to be close to 2.68. A simplified model of the dynamics of heat transfers is used to interpret diagnostics and highlights a time delay between arc voltage and enthalpy at the nozzle exit due to the characteristic time of heat transfers and residence time of plasma.

The Study on Microstructure and Wear Resistance of In-situ Synthesis of TiAl(CN)/Fe Cermet Composite Coating

With Ti powder, Al powder and graphite powder as the coating material, and with industrial N2 as the shielding gas and reactive gas, the TiAl(CN)/Fe Cermet Composite Coating were prepared on the surface of Q235 steel base on Reactive Nitrogen Arc cladding by the TXII500 argon arc welding machine. The microstructure, phases and micro-hardness were investigated by means of scanning electron microscope (SEM), X-ray diffraction (XRD) and MH-6 micro-hardness instrument. The wear loss of TiAl(CN)/Fe coating and 65Mn steel were analyzed and compared by HSR-2M friction and wear testing machine under room temperature dry sliding wear. The experiments show that the coating and the substrate forms metallurgical bond without stomata andcrack; the coating are composed of TiAl(C0.51N0.12) phase, AlFe3 phase,FeC phase; the micro-hardness of TiAl(CN)/Fecoating is 1110HV0.5 high, about 4 times of base metal; comparing with the 65Mn,the wear weight loss of TiAl(CN)/Fe coating is about 1/2 times, the wear resistance of TiAl(CN)/Fe coating is excellent. KeywordsIn-Situ Synthesis; Reactive Nitrogen Arc Cladding; Tial(CN) Cermet; Microstructure; Wear Resistance

Spectroscopic Characteristics of Supersonically Expanding Nitrogen Arc-Jet Plume—Strong Atomic Lines and Weak Molecular Band Spectra

We generate recombining nitrogen plasma plume by expansion of nitrogen arc into lower pressure vessel with a weak longitudinal magnetic field in a steady state. Spectroscopic observation reveals that the plasma has almost no component of molecular band spectra. Meanwhile, atomic nitrogen lines are observed with considerable intensity. The reason for this spectroscopic peculiarity is discussed in terms of chemical thermodynamics of the nitrogen thermal arc plasma and of nonequilibrium characteristics.

Axial evolution of radial heat flux profiles transmitted by atmospheric pressure nitrogen and argon arcs

Axial evolutions of radial heat flux profiles in argon and nitrogen plasma jets from an atmospheric pressure dc non-transferred arc plasma torch are determined using a double calorimetric technique. Results are presented for power levels suitable for the processing of high temperature ceramic oxides, where the heat flux data reported in the literature is rare. Variations of the profile widths and profile maxima are presented as a function of axial distance as well as power. Relatively uniform profile width over prolonged axial distance for nitrogen plasma compared to argon is an important observation which has the potential to offer a much longer dwell time of the injected particles inside the plasma, avoiding the problem of unmelts, especially for ceramics. A comparative study of the heat flux profiles for argon and nitrogen plasma is presented. The obtained results are compared with the data reported in literature.

Functionalization and Characterization of Carbon Nanohorns (CNHs) for Hydrotreating of Gas Oils

Improvement in the functionality of carbon nanohorns (CNHs), a novel carbon nanomaterial, for hydrotreating applications is investigated in the present work. The current work was carried out by using pristine CNHs synthesized by the submerged arc in liquid nitrogen and their corresponding physicochemical properties were investigated. The surface area, pore diameter and pore volume of the pristine CNHs are 129 m2/g, 23.1 nm, and 0.64 cm3/g respectively. Functionalizing the CNHs with 30 wt% HNO3 under reflux for 15 min to 4 h at 110 °C modified the physical and chemical properties. 30 min functionalization duration was found to be the best and a co-impregnation method was used to load Ni (2.5 wt%) and Mo (13 wt%) onto the support. Techniques used to thoroughly characterize the properties of pristine CNHs, functionalized CNHs and NiMo/CNHs catalyst include: Brauner-Emmett-Teller (BET), Fourier Transform Infrared (FTIR) and Raman Spectroscopy. Type II isotherm and mesoporous pore diameter was observed for CNHs in it’s pristine, functionalized or catalyst form. An increase in surface area of over 500 m2/g was also attained under optimum functionalized conditions. The pore volume of acid treated CNH samples for hydrotreating increased by ~10 % as compared to the pore volume of the pristine CNHs. FTIR results revealed the presence of carboxylic acid (–COOH) groups on the functionalized CNHs and ID/IG ratios from Raman spectroscopy was used to assess the increase in defects (nanowindow) on functionalized CNHs. The enhanced properties of functionalized and catalyst-supported CNHs offers prospect for hydrotreating gas oils.

Experimental study of the near-electrode plasma-tungsten cathode system in high-current atmospheric-pressure nitrogen arcs

Results of spectroscopic and pyrometric studies of the near-electrode plasma-tungsten cathode system are presented. The 2D-spectra of radiation of the multiply ionized nitrogen plasma of electric-arc discharge under atmospheric pressure are obtained at different current values. The axial electron temperature in this plasma is determined depending on the distance from the cathode tip, and the temperature distribution over the current-collecting surface of the cathode is found. The high-speed visualization of the cathode-near-cathode plasma region made it possible to observe phase transitions on the cathode surface and processes of crack formation and detachment of its fragments. The power released at the cathode is analyzed including the contribution of the arc column resonance emission, and the peculiarities of phase transitions on the cathode surface are revealed. The densities of the electron emission current at the cathode are estimated theoretically and compared with the data obtained in the experiment. Possible causes of the difference between the theoretical values of the emission current density and those found experimentally are discussed.

Effect of Cladding Current on the Properties of Ti (CN) Ceramic Coating

In order to study the properties of Ti (CN) ceramic coating, nitrogen arc cladding technology was carried out using TXII500 argon arc cladding machine in nitrogen gas atmosphere, and TiCN based composite coating was preparated on the Q235B specimen surface which is precoated titanium powder and graphite powder. The molten coating was tudied under the cladding current respectively in 200 A, 220 A and 240A. The microstructure, phase composition, micro hardness and wear resistance were investigated by scanning electron microscope (SEM), X-ray diffraction (XRD), microhardness tester and reciprocating friction testing machine. The results show that the generation of the Ti (CN) phase is the most when the cladding current is 200A, The microscopic hardness of the coating is reduced with the increase of current, which provides a theoretical basis for the optimization of the process further.

Volt-ampere characteristics of a nitrogen DC plasma arc with anode melting

The characteristics of a nitrogen arc using a graphite cathode and a melting anode in a pilot-scale plasma furnace are investigated. The voltage is examined as a function of current and apparent plasma length. The voltage increases non-linearly with the increase of apparent plasma length, with the current fixed. The experimental data so obtained are compared with the predictions of the Bowman model for the electric arc, and with numerical simulations as well. The level of agreement between the experimental data at the melting anode and the numerical predictions confirms the suitability of the proposed the Bowman model. These characteristics are relevant to the engineering design and evaluation of a DC plasma furnace and reactor for the treatment of hazardous fly ash waste.

Study on TiAl(CN) Particle Reinforce Composites Coating Prepared by Reaction Nitrogen Arc Welding Cladding Process

Particle reinforce composites coating of TiAl(CN) was made on the surface of Q235B steel substrate by reaction nitrogen arc welding cladding process, which take the titanium powder, aluminum powder and the graphite powder as original material. The microstructures, structure and the phase of the coatings were investigated by scanning electronic microscope, X-ray diffract instrument, micro-hardness, reciprocating friction testing machine. The result indicated that the TiAl(CN) coating has a metallurgy union with the substrate, the phase of the coatings are mainly composed of TiAl(C 0.51 N 0.12), AlFe3 and FeC. The microhardness and anti-abrasive performance of the TiAl(CN) coating is better than the Ti(CN) coating processed by tungsten nitrogen arc surfacing welding process.

Process Optimization of Reaction Nitrogen Arc Welding Cladding TiCN/Fe Metal Ceramic Composite Coating

In order to research the technique of reaction nitrogen arc cladding, the 5 factors 4 levels orthogonal experiments have been designed, and the effects of process parameters (such as cladding current, tungsten polar diameter, nitrogen flow, cladding speed and precoated thickness) on coating wear resistance performance were discussed. The process parameters were optimized as follows: cladding current 200 A, tungsten polar diameter 1.6 mm, nitrogen flow 12L. min-1, cladding speed 2 mm.s-1, precoated thickness 1.5 mm.

Microstructural characterization and mechanical properties of nitrided layers on aluminum substrate prepared by nitrogen arc

The present work explores the feasibility of nitrided layers prepared on the aluminum substrate by nitrogen arc discharge at atmospheric pressure. The composite nitrided layers consisted of AlN and aluminum solid solution phases were obtained by the nitrogen arc discharge at the different nitrogen to argon gas flow ratios. The effect of the nitrogen gas contents in the gas mixture on microstructures, hardness and wear resistance of the nitrided layers was investigated. There were lamellar microstructures of AlN and aluminum solid solution distributed alternately at the upper portion of the nitrided layer and the AlN dendrites mainly distributed at the middle and bottom of the layer. It was found that the nitrided layers had high hardness, good wear resistance. With increasing the nitrogen to argon gas flow ratios, the thickness, hardness and wear resistance of the layers were enhanced significantly.

Discharge and optical characteristics of long arc plasma of direct current discharge

Arc discharge with argon and nitrogen was generated across the long electrode gap distance of 400mm to produce a stable thermal plasma and large volume with low power under atmospheric pressure. In the case of nitrogen as plasma forming gas, an increase of the gas flow rate increases the arc voltage, thus the center temperature of the arc column reached higher. For the argon arc, the arc voltage decreases with increasing gas flow rates. Due to the arc constriction in both cases of nitrogen and argon, the center temperature of the arc column increases under the constant current. The result of emission intensity distribution across nitrogen arc column reveals that the arc column diameter increases with increasing gas flow rate because of the increase of the input power. On the other hand, in the argon arc, the diameter decreases by strong thermal pinch in large flow rate of argon. The measured excitation temperature is uniform along with axial direction of the arc column which is an important feature for waste materials processing due to the long direct current arc plasma that provides long residence time for injected materials.

Design of Welding with Trailing Peening System for Reaction Nitrogen Arc Welding Cladding

In order to reduce welding stress, decreased welding crack and improve coating performance, a set of complete computer control system was designed and applied to prepare TiCN cermet composite coating by process. The system, which consists of PC, SCM (AT89C52), sensor, interface circuit, pneumatic rammer, corresponding mechanism and valves, can peen the welded seam by a pneumatic rammer which is controlled by the signal from data acquisition card. The system can easily adjust the peening frequency, force, distance, and angle able. The result show that the system can make coatings more inseparable and compacter, less weld defect, and the coatings have an excellent mechanical property.

TiCN Cermet Composite Coating Prepared By Reaction Nitrogen Arc Welding Cladding Process

A TiCN cermet composite coating was fabricated on 45# steel substrate by reaction nitrogen arc welding cladding technique. The mixture powder of titanium and graphite was preplaced onto the 45# steel substrate after intensive mixing by star ball-mill and gluing with starch binder. The microstructures and phase of the coatings, interracial behavior between coatings and the substrate were investigated by scanning electronic microscope, X-ray diffractometer. The microhardness distribution of the coating section, frictional coefficient, abrasion loss and wearing surface morphology were investigated by microhardness tester, abrasion machine and scanning electronic microscope. The results show that an excellent bonding between the coatings and the 45# steel substrate is ensured by the strong metallurgical interface and phase of the coatings are mainly composed of TiCN. The highest microhardness of the coatings reaches HV 0.5 810, which is about 3 times more than that of the 45# steel substrate. The anti-abrasive test results show the coating has better anti-abrasive performance than the 45# steel substrate.

Effective preparation of SiC nanoparticles by the reaction of thermal nitrogen plasma with solid SiC

It is well known that SiC nanoparticles are mainly prepared by a gas phase reaction involving thermal decomposition or by precursor methods. In this paper, we propose a new process of effectively preparing SiC nanoparticles through a reaction between nitrogen arc plasma and a solid SiC block or a mixture compact of Si and C powders. The solid SiC block is irradiated with nitrogen arc plasma containing various nitrogen partial pressures at a total pressure of 0.1MPa. The generation rate of SiC nanoparticles in 100% Ar plasma is negligible. However, the generation rate of SiC nanoparticles increases with increasing the nitrogen concentration in Ar. In the case of 100% nitrogen plasma, the generation rate has the highest value.

Study on <i>In Situ</i> Ti(CN) Particle Reinforce Composites Coating Processed by Nitrogen Shielded Arc Welding Technique

An in-situ Ti(CN) particle reinforce composites coating was fabricated on Q235 steel substrate by nitrogen arc shielded welding technique which take the titanium powder and the graphite powder as original material. The microstructures, interracial behavior and phase of the coatings were investigated by scanning electronic microscope, X-ray diffractometer, microhardness tester, abrasion machine. The results show that an excellent bonding between the coatings and carbon steel substrate is ensured by the strong metallurgical interface and phase of the coatings are mainly composed of TiC0.51N0.12.The highest microhardness of the coatings reaches HV0.5810, which is about five times more than that of the base metal .The anti-abrasive test results show the coating has better anti-abrasive performance than base steel.

Finite element analysis of GTAW arc under different shielding gases

The aim of this work is to use COMSOL software as a tool for solving the 2-D Magnetohydrodynamics (MHD) problem in the Gas Tungsten Arc Welding (GTAW) arc under the shielding gases argon, helium, nitrogen and argon+10% hydrogen. COMSOL 3.5a worked perfectly for solving multiphysics phenomena, including the Navier–Stokes flow equation, the heat transfer equation and the Maxwell Equation. COMSOL software can be utilized to simulate the temperature and velocity profile in the GTAW arc after some validation procedures. Cumbersome experimental work can be avoided by using this numerical instrument.For our study, we compared the numerically calculated temperature profile and maximum plasma velocity under argon shielding gas and maximum temperature of a nitrogen arc with experimental results found in the literature. We also compared the numerically calculated velocity profile with another numerical solution found in the literature. Our comparisons showed good agreement. The highest temperature was in the nitrogen arc, while the highest voltage was in the helium arc. The highest total energy was in the helium arc similar to the voltage value. The highest plasma velocity values were obtained in the nitrogen and helium arcs. The most constricted arc was calculated in the nitrogen arc.

Current Interruption Using Electromagnetically Convolved Electric Arcs in Gases

Measurements were described as current, voltage, and local dielectric strength for a current interrupter which utilized a novel form of electromagnetically convolved electric arc in air. Experiments have been performed with various interrupter structures and operational conditions. Precurrent zero-voltage extinction peaks and post-arc local breakdown voltages have been measured and are compared with values for nonconvoluted arcs in nitrogen and SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> . An empirical relationship between the extinction peak voltage and various design and operational parameters is presented. Signatures for the various interrupter structures under different operational conditions have been obtained by using a chromatic methodology and embodying the extinction peak and a local breakdown voltage.