The Experts below are selected from a list of 243 Experts worldwide ranked by ideXlab platform
Michael De Podesta - One of the best experts on this subject based on the ideXlab platform.
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correction of npl 2013 estimate of the boltzmann constant for Argon isotopic composition and thermal conductivity
Metrologia, 2015Co-Authors: Michael De Podesta, R Underwood, D.f. Mark, G Sutton, Inseok Yang, Graham MachinAbstract:In 2013, a team from NPL, Cranfield University and SUERC published an estimate of the Boltzmann constant based on precision measurements of the speed of sound in Argon. A key component of our results was an estimate of the molar mass of the Argon gas used in our measurements. To achieve this we made precision comparison measurements of the isotope ratios found in our experimental Argon against the ratios of Argon isotopes found in atmospheric air. We then used a previous measurement of the atmospheric Argon isotope ratios to calibrate the relative sensitivity of the mass spectrometer to different Argon isotopes. The previous measurement of the atmospheric Argon isotope ratios was carried out at KRISS using a mass spectrometer calibrated using Argon samples of known isotopic composition, which had been prepared gravimetrically.We report here a new measurement made at KRISS in October 2014, which directly compared a sample of our experimental gas against the same gravimetrically-prepared Argon samples. We consider that this direct comparison has to take precedence over our previous more indirect comparison. This measurement implies a molar mass which is 2.73(60) parts in 106 lighter than our 2013 estimate, a shift which is seven times our 2013 estimate of the uncertainty in the molar mass.In this paper we review the procedures used in our 2013 estimate of molar mass; describe the 2014 measurement; highlight some questions raised by the large change in our estimate of molar mass; and describe how we intend to address the inconsistencies between them. We also consider the effect of a new estimate of the low pressure thermal conductivity of Argon at 273.16 K. Finally we report our new best estimate of the Boltzmann constant with revised uncertainty, taking account of the new estimates for the molar mass and the thermal conductivity of the Argon.
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preparation of Argon primary measurement standards for the calibration of ion current ratios measured in Argon
International Journal of Mass Spectrometry, 2010Co-Authors: S. Valkiers, D. Vendelbo, M. Berglund, Michael De PodestaAbstract:In this work a procedure is described to prepare SI-traceable Argon isotope amount ratios in high purity Argon. Following a gravimetric approach, a total of three synthetic isotope mixtures have been prepared, from Argon gases enriched in (36)Ar, (38)Ar and (40)Ar, close to the natural isotopic composition of Argon. These synthetic mixtures serve as reference gases to calibrate ion current ratio measurements in Argon. In this way SI-traceable measurements of Argon isotope amount ratios can be performed without any assumptive correction. On a high purity Argon gas separated from air the absolute Argon isotope amount ratios R(36/40) = 0.00334774 (93) and R(38/40) = 0.00063529 (57) were measured. From these ratios, the average molar mass of Argon gas can be determined with a total relative combined uncertainty of 0.09 x 10(-6). (C) 2010 Elsevier B.V. All rights reserved.
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Preparation of Argon Primary Measurement Standards for the calibration of ion current ratios measured in Argon
International Journal of Mass Spectrometry, 2010Co-Authors: S. Valkiers, D. Vendelbo, M. Berglund, Michael De PodestaAbstract:In this work a procedure is described to prepare SI-traceable Argon isotope amount ratios in high purity Argon. Following a gravimetric approach, a total of three synthetic isotope mixtures have been prepared, from Argon gases enriched in 36Ar, 38Ar and 40Ar, close to the natural isotopic composition of Argon. These synthetic mixtures serve as reference gases to calibrate ion current ratio measurements in Argon. In this way SI-traceable measurements of Argon isotope amount ratios can be performed without any assumptive correction. On a high purity Argon gas separated from air the absolute Argon isotope amount ratios R36/40 = 0.00334774 (93) and R38/40 = 0.00063529 (57) were measured. From these ratios, the average molar mass of Argon gas can be determined with a total relative combined uncertainty of 0.09×10-6.JRC.D.3-Knowledge Transfer and Standards for Securit
M Suban - One of the best experts on this subject based on the ideXlab platform.
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experimental research of the effect of hydrogen in Argon as a shielding gas in arc welding of high alloy stainless steel
International Journal of Hydrogen Energy, 2000Co-Authors: J Tusek, M SubanAbstract:Abstract The paper treats the effect of hydrogen in Argon as a shielding gas in arc welding of austenitic stainless steel. The studies were carried out in TIG (Tungsten Inert Gas) welding with a non-consumable electrode and MIG (Metal Inert Gas) welding with a consumable electrode, in both cases with different volume additions of hydrogen to the Argon shielding gas, i.e., 0.5, 1.0, 5.0, 10 and 20%. The studies showed that hydrogen addition to Argon changes the static characteristic of the welding arc. The hydrogen addition to Argon increases arc power and, consequently, the quantity of the material melted. In TIG welding a 10% addition of hydrogen to Argon increases the quantity of the parent metal melted by four times. The hydrogen addition increases thermal and melting efficiencies of the welding arc too. The process stability in TIG welding in the mixture of hydrogen and Argon is very good. Also in MIG welding, the hydrogen addition to Argon increases melting rate and melting efficiency of the arc, but the increase is much smaller than in TIG welding. Since hydrogen is a reducing gas, the weld surface produced by hydrogen addition to Argon is in both cases very clean and without oxides.
Graham Machin - One of the best experts on this subject based on the ideXlab platform.
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correction of npl 2013 estimate of the boltzmann constant for Argon isotopic composition and thermal conductivity
Metrologia, 2015Co-Authors: Michael De Podesta, R Underwood, D.f. Mark, G Sutton, Inseok Yang, Graham MachinAbstract:In 2013, a team from NPL, Cranfield University and SUERC published an estimate of the Boltzmann constant based on precision measurements of the speed of sound in Argon. A key component of our results was an estimate of the molar mass of the Argon gas used in our measurements. To achieve this we made precision comparison measurements of the isotope ratios found in our experimental Argon against the ratios of Argon isotopes found in atmospheric air. We then used a previous measurement of the atmospheric Argon isotope ratios to calibrate the relative sensitivity of the mass spectrometer to different Argon isotopes. The previous measurement of the atmospheric Argon isotope ratios was carried out at KRISS using a mass spectrometer calibrated using Argon samples of known isotopic composition, which had been prepared gravimetrically.We report here a new measurement made at KRISS in October 2014, which directly compared a sample of our experimental gas against the same gravimetrically-prepared Argon samples. We consider that this direct comparison has to take precedence over our previous more indirect comparison. This measurement implies a molar mass which is 2.73(60) parts in 106 lighter than our 2013 estimate, a shift which is seven times our 2013 estimate of the uncertainty in the molar mass.In this paper we review the procedures used in our 2013 estimate of molar mass; describe the 2014 measurement; highlight some questions raised by the large change in our estimate of molar mass; and describe how we intend to address the inconsistencies between them. We also consider the effect of a new estimate of the low pressure thermal conductivity of Argon at 273.16 K. Finally we report our new best estimate of the Boltzmann constant with revised uncertainty, taking account of the new estimates for the molar mass and the thermal conductivity of the Argon.
Ulrich Kroll - One of the best experts on this subject based on the ideXlab platform.
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the role of metastable atoms in Argon diluted silane radiofrequency plasmas
Journal of Physics D, 1994Co-Authors: L Sansonnens, A A Howling, Christoph Hollenstein, J L Dorier, Ulrich KrollAbstract:The evolution of the Argon metastable states density has been studied by absorption spectroscopy in power-modulated plasmas of Argon and a mixture of 4% silane in Argon. A small concentration of silane suppresses the Argon metastable states density by molecular quenching. This molecular quenching adds to the electronic collisional dissociation to increase the silane dissociation rate as compared with pure silane plasmas. Using time-resolved emission spectroscopy, the role of metastable states in excitation to the Argon 2P2 state has been determined in comparison with production from the ground state. In silane plasmas, emission from SiH* is due essentially to electron impact dissociation of silane, whereas in 4% silane-in-Argon plasmas, emission from SiH* seems to be due to electron impact excitation of the SiH ground state. These studies demonstrate that Argon is not simply a buffer gas but has an influence on the dissociation rate in plasma-assisted deposition of amorphous silicon using Argon-diluted silane plasmas.
Xuan Liu - One of the best experts on this subject based on the ideXlab platform.
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The role of ultrasound in hydrogen removal and microstructure refinement by ultrasonic Argon degassing process
Ultrasonics Sonochemistry, 2017Co-Authors: Xuan Liu, Zhiqiang Zhang, Cheng Zhang, Jilai XueAbstract:Abstract In this work, the role of ultrasound in hydrogen removal and microstructure refinement by the ultrasonic Argon degassing has been fully investigated by the experimental work in water and AZ91-0.4Ca magnesium melt, respectively. Ultrasound is able to break up Argon gas into numbers of small bubbles and drive them diving deeply to the bottom of water, which are responsible for the efficient degassing regime of ultrasonic Argon process. The Argon flowrate plays a dominant role in promoting hydrogen removal effect. Meanwhile, the increasing Argon flowrate can suppress the microstructure refinement, due to the subdued ultrasonic cavitation under a large Argon flowrate. Mechanical properties of AZ91-0.4Ca alloy can be much promoted by the ultrasonic Argon degassing process. Ultrasound is the key to achieve not only efficient degassing regime, but also microstructure refinement as well as mechanical properties promotion.
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Study on hydrogen removal of AZ91 alloys using ultrasonic Argon degassing process
Ultrasonics Sonochemistry, 2015Co-Authors: Xuan Liu, Lei Bao, Jianzhong Cui, Zhiqiang Zhang, Jiajia JiangAbstract:Abstract Argon degassing, ultrasonic degassing and a novel ultrasonic Argon degassing treatment were applied for the hydrogen removal of AZ91 magnesium alloy. The hydrogen concentration, microstructures and mechanical properties have also been investigated. AZ91 alloys contains a high hydrogen concentration. The mechanical properties of the as-cast alloy are much improved using degassing process, which should be mainly attributed to the hydrogen removal. Among the three degassing process, the ultrasonic Argon treatment is a high efficient process both for hydrogen removal and microstructure refining. One hand, ultrasonic wave could break up the purged Argon bubble to improve the degassing efficiency of these bubbles. On the other hand, ultrasound could also generate many cavitation bubbles in the melt, which should account for the microstructure refinement. The ultrasonic Argon treatment involves dynamics between the ascending Argon bubbles and ultrasonic effects, such as cavitation and streaming, etc.
