The plasma column in a metal inert gas welding process is investigated by optical emission spectroscopy and high-speed imaging. The concentration and repartition of iron vapours are measured and ...correlated with the plasma and electrode geometric configuration. Plasma temperatures and electron densities are also measured for each studied position in the plasma. The temperatures are calculated using two different methods, allowing validation of the local thermodynamic equilibrium state of the plasma. The results show a maximum temperature of 12 500 K in the upper part of the arc, away from the arc axis. The iron concentration reaches a maximum of 0.3% close to the anode and strongly decreases along both the vertical and radial directions.
The plasma thermophysical properties, calculated from this plasma composition, are then discussed regarding the metal transfer mode.
Metal Active Gas (MAG) welding in presence of Argon and CO
2
mixture as shielding gas is a largely developed process allowing the transfer of the liquid metal from the consumable wire anode to the ...workpiece according to various modes (short-arc, globular, spray-arc). The CO
2
presence in the shielding gas leads to the formation of an oxide layer, or gangue, wrapping the droplet, limiting the access to the spray-mode transfer, taking into account the low conductivity and the high viscosity of this layer. Several electrodes of various compositions have been tested thanks to Flux Cored Arc Welding, to limit the gangue formation or its negative contribution, based on Ti, La, Zr and alkali metals addition or reduction in silicon content. The results are interpreted considering the metal transfer mode for a given current intensity (330 and 410 A), with various CO
2
concentrations in the shielding gas. Finally, the role of the gangue, compared to the other factors governing the droplet detachment, is discussed. A decrease in silicon content limits significantly the gangue formation and gives access to spray arc transfer up to 30 vol.% of CO
2
at 330 A. Titanium addition leads to the same results. The tests in presence of zirconium proved the conductivity improvement of the gangue. The addition of alkali allows to stabilize the spray arc up to the noteworthy value of 60 vol.% of CO
2
at 330 A, supporting the hypothesis of a strong influence of viscosity on droplets detachment in the process.
The gas metal arc welding (GMAW) process is strongly influenced by the composition of the shielding gas. In particular, addition of CO2 increases the threshold current for the transition from ...unstable globular to more stable spray transfer mode. We report on the diagnostics-using optical emission spectroscopy-of a GMAW plasma in pure argon and in mixtures of argon, CO2 and N2 while operated in spray and globular transfer modes. The spatially resolved plasma parameters are obtained by applying the Abel transformation to laterally integrated emission data. The Stark widths of some iron lines are used to determine both electron density and temperature, and line intensities yield relative contents of neutral and ionized iron to argon. Our experimental results indicate a temperature drop on the arc axis in the case of spray arc transfer. This drop reduces with addition of N2 and disappears in globular transfer mode when CO2 is added. Despite the temperature increase, the electron density decreases with CO2 concentration. The highest concentration of iron is observed in the plasma column upper part (close to the anode) and for GMAW with CO2. Our results are compared with recently published works where the effect of non-homogeneous metal vapour concentration has been taken into account.
The lattice Boltzmann modeling of immiscible multiphase flows needs to be further validated, especially when density variation occurs between the different flow phases. From this perspective, the ...goal of this research is to introduce the multiple-relaxation-time operator into a lattice Boltzmann model in order to improve its numerical stability in the presence of large density and viscosity ratios. Essentially, this research shows that the introduction of this operator greatly improves the numerical stability of the approach compared to the original single-relaxation-time collision operator. In many lattice Boltzmann research studies, multiphase lattice Boltzmann methods are validated using a reduced number of test cases, and unsteady flow test cases are frequently omitted before much more complex flow configurations are simulated. In this context, several test cases are proposed to evaluate the behavior of a lattice Boltzmann method for simulating immiscible multiphase flows with high density and viscosity ratios. These are: (1) two-phase Couette flow; (2) three-phase Laplace law; (3) three-phase Zalesak disk; (4) two-phase flow between oscillating plates; (5) two-phase capillary wave; and (6) the two-phase oscillating cylindrical bubble. The first two involve a steady regime, and the remaining four an unsteady regime.
Study of glasses with a high content of rare earth elements has a particular interest due to their use in nuclear waste storage. New glass matrices are required to immobilize even higher ...concentrations of high-level waste in comparison to borosilicate glasses already used. We study the effect of aluminum/boron substitution on the structure of peraluminous lanthanum-rich sodium aluminoborosilicate glasses of 55SiO2-(25-x)Al2O3-xB2O3-15Na2O-5La2O3 composition, where lanthanum simulate all the lanthanides as well as the minor actinides typical for the high-level waste. We have here chosen a chemical composition of a model glass that can accept the presence of minor actinides among the fission products generated by the new reactors of the fourth generation.
Transmission Electron Microscopy, Differential Scanning Calorimetry, X-ray diffraction and Infrared spectroscopy showed the existence of phase separation at high boron oxide concentrations, and finely characterized the structure of the major vitreous network.
•We investigated a composition of glasses with a high content of rare earth elements.•This composition is a particular interest due to their use nuclear waste storage with the presence of minor actinides among the fission products generated by the new reactors of the 4th generation.•The TEM shown the domain of homogeneity of the matrices extends over a narrow range of composition.•Infrared spectroscopy gave a better discerption of the silicates, aluminosilicates and borates units in the aluminoborosilicate glasses.
Part of the Research and Development program concerning high level nuclear waste (HLW) glasses aims to assess new glass formulations able to incorporate a high waste content with enhanced properties ...in terms of thermal stability, chemical durability, and process ability. This study focuses on peraluminous glasses of the SiO2 – Al2O3 – B2O3 – Na2O – Li2O – CaO – La2O3 system, defined by an excess of aluminum ions Al3+ in comparison with modifier elements such as Na+, Li+ or Ca2+. To understand the effect of composition on physical properties of glasses (viscosity, density, Tg), a Design Of Experiments (DOE) approach was applied to investigate the peraluminous glass domain. The influence of each oxide was quantified to build predictive models for each property. Lanthanum and lithium oxides appear to be the most influential factors on peraluminous glass properties.
•A Design of Experiment approach to link composition and glass properties.•Adding alkali decreases glass transition temperature.•Adding La2O3 strongly decreases glass melt viscosity.•Adding La2O3 increases density.
Considering the interest of developing new glass matrices able to immobilize higher concentration of high level nuclear wastes than currently used nuclear borosilicate compositions, glasses ...containing high rare earth contents are of particular interest. This study focuses on a peraluminous aluminoborosilicate system SiO2–B2O3–Al2O3–Na2O–CaO–Nd2O3 defined by a peralkaline/peraluminous ratio RP=(Na2O+CaO)/(Na2O+CaO+Al2O3)<0.5. Samples with various contents of Nd2O3 from 0 to 10mol% were studied using DSC, XRD, SEM, TEM, STEM and EMPA methods. The glasses present a high thermal stability even after a slow cooling treatment from the melt. Only a slight mullite crystallization is detected for low Nd2O3 content (≤2.3mol%) and crystallization of a neodymium borosilicate crystalline phase combined to a phase separation occurred at high Nd2O3 content (≥8mol%). The solubility of neodymium in the presence of aluminum is demonstrated, with higher neodymium incorporation amounts than in peralkaline glasses.
•Peraluminous glasses present a very large domain of homogeneity.•Enhancement of neodymium solubility compared to peralkaline glasses•Boron, aluminum and neodymium play synergic roles for network stabilization.•Above neodymium solubility limit, crystallization and/or phase separation occur.
The combined effects of noise and temperature on environmental perception and acceptability were studied on 18 lightly clothed subjects (0.6 clo), individually exposed for 2 h in a climatic chamber. ...Three homogeneous climatic conditions were chosen (air temperature at 18, 24 or 30 degrees C, air velocity =0.1 m/s). For each of them, three different noise levels were continuously maintained (35, 60, 75 dBA, recorded fan noise). The 18 subjects were divided into three groups and each group experienced only one single thermal condition, at each level of noise, during three different experimental sessions. Subjective answers about perception and comfort were obtained at t = 30 and 120 min. Main results indicate that acoustic perception decreases when thermal environment is far from thermoneutrality. Although the combined effects of noise and temperature did not influence the physiological data, our results show that whatever the ambient temperature, thermal unpleasantness is higher when noise level increases. Finally, equivalence between acoustic and thermal sensations is proposed for short-term exposure (1 degree C = 2.6 dBA) and for steady state (1 degrees C = 2.9 dBA). In conclusion, this study strongly suggests that interactions between environmental components do exist, right from perceptual level, and might explain some combined effects on cognitive performance.
The trade-off between noise and temperature and their combined effects on discomfort were studied on 108 lightly clothed subjects (0.6 clo), individually exposed for 2 h in a climatic chamber. Every ...10 min of the first hour, subjects could modify the experimental conditions by deciding a change in temperature or noise. However, any change in one parameter was experimentally associated with a fixed change in the other parameter according to eight predetermined designs and all trials for thermal improvement were detrimental to acoustic comfort and conversely. Four initial exposures started at thermoneutrality (24 °C) in a noisy environment (85 dBA, recorded fan noise), the reduction of noise being linked to a temperature change towards cool or warm climates. The other four conditions started at a low noise level (35 dBA) but in a cool (14 or 19 °C) or warm (29 or 34 °C) environment, the reduction of thermal discomfort towards 24 °C leading to a louder noise. After six possible voluntary changes, the environment was kept constant for 1 h. Ambient parameters, skin temperatures, and subjective estimates were recorded.
Results showed that females accepted noisier environments than males, suggesting that thermal comfort is dominant for women. Noise was rated as the most unpleasant factor when initial conditions were noisy whereas temperature was the most disturbing factor when subjects began the experiment with thermal conditions far from thermoneutrality. Finally, although the combined effects of noise and temperature did not influence the physiological data, our results suggest that noise may alter thermal pleasantness in warm conditions.
The nature of the applied shielding gas has a strong influence on arc stability and transfer metal mode of the welding process. In particular, increase of the percentage of carbon dioxide in argon ...induces the increase of the transition current value from the globular to spray metal transfer mode. This work shows that these effects are linked to the chemical and microstructural modifications of the anode tip during the gas metal arc welding process. The microstructure of the anode is investigated for various experimental conditions. Transition between the two transfer modes is linked to the existence and disappearance of a rather insulating oxide “gangue” at the wire extremity whose nature depends of the shielding gas. Chemical reactions at high temperature such as oxidation–reduction reactions between shielding gas and melted metal govern the transition of the spray-arc to globular transfer mode.
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