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Nagaiyar Krishnamurthy - One of the best experts on this subject based on the ideXlab platform.
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Effect of aluminum on Hydrogen Absorption kinetics of tantalum
Journal of Alloys and Compounds, 2015Co-Authors: Manju Taxak, Nagaiyar KrishnamurthyAbstract:Abstract The isothermal Hydrogen Absorption kinetics of Ta 1 − z Al z alloys ( z = 0, 1, 1.6 and 2.4 atom%) has been investigated in the temperature range of 673–973 K. The reacted fractions of Hydrogen as well as reaction rate constant have been determined from time dependent Hydrogen Absorption curves using pressure drop method. The variation in rate constant with respect to temperature has been observed for all the alloys. Three-dimensional diffusion processes seems to be the intrinsic rate limiting step of Hydrogen Absorption. The apparent activation energy of Hydrogen Absorption has been calculated using Arrhenius equation. With increasing aluminum concentration, the Hydrogen Absorption kinetics slows down. Consequently, the rate constant decreases and the apparent activation energy of Hydrogen Absorption increases. The apparent activation energy of Hydrogen Absorption increases from 53.7 to 57.7 kJ/mol with increasing Al concentration from 0 to 2.4 atom% in tantalum.
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Synthesis and Hydrogen Absorption kinetics of V_4Cr_4Ti alloy
Journal of Thermal Analysis and Calorimetry, 2013Co-Authors: Sanjay Kumar, Manju Taxak, Nagaiyar KrishnamurthyAbstract:V_4Cr_4Ti alloy is synthesized by aluminothermy process followed by electron beam refining. Hydrogen Absorption characteristics of the alloy have been evaluated by measuring the pressure composition isotherm (PCIT) at 57 °C temperature. Two plateau pressures are observed in the PCIT curve. Substantial decrease in the Hydrogen Absorption capacity of the alloy as compared to vanadium has been recorded. Hydrogen Absorption kinetics of the alloy was investigated in the temperature range of 200–500 °C. Three-dimensional diffusion appears to be the rate controlling step of the Hydrogen Absorption. The apparent activation energy was calculated as 0.16 eV/atom-Hydrogen.
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SYNTHESIS AND Hydrogen Absorption KINETICS OF V4Cr4Ti ALLOY
Journal of Thermal Analysis and Calorimetry, 2012Co-Authors: Sanjay Kumar, Manju Taxak, Nagaiyar KrishnamurthyAbstract:V4Cr4Ti alloy is synthesized by aluminothermy process followed by electron beam refining. Hydrogen Absorption characteristics of the alloy have been evaluated by measuring the pressure composition isotherm (PCIT) at 57 °C temperature. Two plateau pressures are observed in the PCIT curve. Substantial decrease in the Hydrogen Absorption capacity of the alloy as compared to vanadium has been recorded. Hydrogen Absorption kinetics of the alloy was investigated in the temperature range of 200–500 °C. Three-dimensional diffusion appears to be the rate controlling step of the Hydrogen Absorption. The apparent activation energy was calculated as 0.16 eV/atom-Hydrogen.
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Hydrogen Absorption kinetics of V4Cr4Ti alloy prepared by aluminothermy
International Journal of Hydrogen Energy, 2012Co-Authors: Sanjay Kumar, Manju Taxak, Nagaiyar KrishnamurthyAbstract:Abstract The Hydrogen Absorption kinetics of V4Cr4Ti alloy, synthesized by aluminothermy process has been investigated in the temperature range of 373–773 K. The obtained Hydrogen Absorption kinetic curves were linearly fitted using a series of mechanism function to reveal the kinetics parameter and reaction mechanism. Nucleation and growth, one dimensional diffusion and three-dimensional diffusion processes are the intrinsic rate limiting steps of Hydrogen Absorption at 373 K. It was found that nucleation and growth processes disappear between 413 K–473 K. However at higher temperatures (>473 K), nucleation and growth as well as one dimensional diffusion process disappear. In the temperature ranges investigated (473 K–773 K), three-dimensional diffusion process was the intrinsic rate limiting step. The apparent activation energy was calculated using Arrhenius equation and found to be 6.1 kJ/mol. This value appears to be relatively higher which can be attributed to the presence of aluminium, which has blocked the Absorption sites and increased the activation energy.
Th. Kannengiesser - One of the best experts on this subject based on the ideXlab platform.
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Hydrogen Absorption And Diffusion in different welded Duplex Steels
Welding in The World, 2011Co-Authors: Stephan Brauser, Th. KannengiesserAbstract:In this study, Hydrogen Absorption and diffusion were investigated for various high-alloyed ferritic-austenitic duplex steels. On account of the specific transformation and solidification behaviour, respectively, of duplex steels as compared to single-phase ferritic and austenitic steels, special conditions have to be considered concerning Hydrogen Absorption which may ultimately lead to microstructure-dependent Hydrogen-assisted weld metal cracking. Hydrogen Absorption during welding may occur via the shielding gas, moisture from Qthe surroundings or via the welding filler material. As a contribution to the interpretation and prediction of “ Hydrogen-induced cracking in welded duplex steels, the actual Hydrogen Absorption via the arc as well as the weld metal Hydrogen diffusion was investigated for the first time in a duplex steel DS (1.4462), a super duplex steel SDS (1.4501) and in a lean duplex steel LDS (1.4162). Isothermal heat treatment using carrier gas hot extraction enabled quantification of the amounts of Hydrogen trapped in the respective microstructure areas. The Hydrogen diffusion coefficients were determined by analytical and numerical calculation. The total Hydrogen concentrations and the diffusion coefficients were found to be nearly identical. Trapped Hydrogen was however observed to be dependent on the material and on the microstructure condition. The influence of Hydrogen on the mechano-technological properties of the weld metal was characterized with the help of tensile tests. In addition, the Hydrogen embrittlement effect was detected in scanning electron microscopic analyses
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Hydrogen Absorption of different welded duplex steels
International Journal of Hydrogen Energy, 2010Co-Authors: Stephan Brauser, Th. KannengiesserAbstract:In this study, Hydrogen Absorption and storage was investigated for various high-alloyed ferritic-austenitic duplex stainless steels. On account of the specific transformation and solidification behaviour, respectively, of duplex stainless steels as compared to single-phase ferritic and austenitic steels, special conditions have to be considered concerning Hydrogen Absorption which may ultimately lead to microstructure-dependent Hydrogen-assisted weld metal cracking. Hydrogen Absorption during welding may occur via the shielding gas, moisture from the surroundings or via the welding filler material. As a contribution to the interpretation and prediction of Hydrogen-induced cracking in welded duplex stainless steels, the actual Hydrogen Absorption via the arc as well as the weld metal Hydrogen diffusion was investigated in a duplex stainless steel DSS (1.4462) and in a lean-duplex stainless steel LDS (1.4162). Isothermal heat treatment using carrier gas hot extraction enabled quantification of the amounts of Hydrogen trapped in the respective microstructures. The total Hydrogen concentrations were found to be nearly identical. Trapped Hydrogen was however observed to be dependent on the material and on the microstructure condition. The influence of Hydrogen on the mechanical properties of the weld metal was characterized with the help of tensile tests. In addition, Hydrogen embrittlement was detected in scanning electron microscopic analyses.
Kiyoshi Aoki - One of the best experts on this subject based on the ideXlab platform.
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Hydrogen Absorption and desorption in the binary Ti–Al system
Journal of Alloys and Compounds, 2001Co-Authors: K. Hashi, Kazuhiro Ishikawa, Kiyonori Suzuki, Kiyoshi AokiAbstract:Abstract Binary Ti 1− x Al x alloys were Hydrogenated at 5 MPa H 2 pressure at room temperature for 173 ks. Structures and thermal stability of the Hydrogenated alloys were investigated by XRD and DSC. The Hydrogen Absorption and Hydrogen desorption behavior were investigated by means of a Hydrogen analyzer, DSC and XRD. An fcc type (CaF 2 type) hydride formed for x =0, 0.20 and 0.25 and an amorphous hydride for x =0.30 and 0.35. That is, off-stoichiometric (Al-rich) Ti 3 Al ( α 2 ) amorphized by Hydrogen Absorption. The amount of Hydrogen Absorption under the quoted conditions decreased with increasing Al concentration, but the 50% Hydrogen desorption temperature T d increased. The hcp solid solution alloy Ti 0.80 Al 0.20 showed the best Hydrogen Absorption and desorption properties of the Ti 1− x Al x alloys investigated.
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Amorphous phase formation by Hydrogen Absorption
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2001Co-Authors: Kiyoshi AokiAbstract:Abstract This article describes our recent investigations on the amorphous phase formation by Hydrogen Absorption, i.e. Hydrogen-induced amorphization (HIA) of intermetallic compounds. HIA for D0 19 and C15 Laves compounds is demonstrated at first. Next, chemical compositions and crystal structures of amorphizing compounds are reviewed. Subsequently, we focus on HIA of the C15 Laves compounds. HIA of C15 Laves phase TbFe 2 compounds investigated by DTA, DSC, XRD, TEM, Mossbauer spectroscopy, magnetic measurements and Hydrogen analysis, the factors controlling HIA are presented. DTA curves of C15 Laves RFe 2 (R=a rare-earth metal) in a Hydrogen atmosphere show exothermic peaks resulting from Hydrogen Absorption, Hydrogen-induced amorphization, precipitation of RH 2 and crystallization of amorphous phases. As the melting temperature T m of the C15 Laves phase RFe 2 increases, Hydrogen Absorption temperature T h , HIA temperature T a and crystallization temperature T x increase. On the contrary, T h / T m , T a / T m and T x / T m are nearly constant, being 0.28, 0.4 and 0.5, respectively, suggesting that HIA occurs by the diffusion of metallic atoms over a short distance. In addition, the enthalpy change and the activation energy for the thermal reactions of TbFe 2 during heating in a Hydrogen atmosphere are evaluated by DSC. Finally the mechanism of HIA for the C15 Laves RM 2 phases is discussed on the basis of the experimental data.
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Trends in Hydrogen Absorption Alloys.
DENKI-SEIKO[ELECTRIC FURNACE STEEL], 2001Co-Authors: Kiyoshi AokiAbstract:This article reviews the recent progress in Hydrogen Absorption alloys. Firstly, the mechanism of the Hydrogen storage in Hydrogen Absorption alloys is briefly described. Secondly, the chemical composition, crystal structures, Hydrogen Absorption properties of typical binary intermetallic compounds are summarized. Finally, the merits and the demerits of novel Hydrogen Absorption alloys, i.e. BCC solid solution alloys, Mg-based alloys and compounds and PuNi3-type ternary compounds, are discussed.
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Hydrogen Absorption in an icosahedral ZnMgY alloy
Journal of Alloys and Compounds, 1997Co-Authors: An Pang Tsai, Kiyoshi Aoki, A Niikura, T. MasumotoAbstract:Abstract Hydrogen Absorption in a stable icosahedral (i-) Zn 50 Mg 42 Y 8 alloy has been studied by X-ray diffraction, transmission electron microscopy and differential scanning calorimetry. The i-phase decomposed to a hexagonal Zn 2 Mg Laves phase, YH 3 and MgH 2 after Hydrogenation under 3 MPa Hydrogen pressure at 573 K for 259.2 ks. Two stages of Hydrogenation for the i-phase were identified; i-ZnMgY+ x H 2 →i-ZnMgYH 2 x in the initial stage and then i-ZnMgYH 2 x +H 2 →Zn 2 Mg+YH 2 +MgH 2 . DSC curve of the fully Hydrogenated (3 MPa, 573 K, 259.2 ks) sample revealed an endothermic peak around 730 K corresponding to the Hydrogen desorption. The transformations between the icosahedral and crystalline phases due to Hydrogen Absorption and desorption are reversible.
Sanjay Kumar - One of the best experts on this subject based on the ideXlab platform.
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Synthesis and Hydrogen Absorption kinetics of V_4Cr_4Ti alloy
Journal of Thermal Analysis and Calorimetry, 2013Co-Authors: Sanjay Kumar, Manju Taxak, Nagaiyar KrishnamurthyAbstract:V_4Cr_4Ti alloy is synthesized by aluminothermy process followed by electron beam refining. Hydrogen Absorption characteristics of the alloy have been evaluated by measuring the pressure composition isotherm (PCIT) at 57 °C temperature. Two plateau pressures are observed in the PCIT curve. Substantial decrease in the Hydrogen Absorption capacity of the alloy as compared to vanadium has been recorded. Hydrogen Absorption kinetics of the alloy was investigated in the temperature range of 200–500 °C. Three-dimensional diffusion appears to be the rate controlling step of the Hydrogen Absorption. The apparent activation energy was calculated as 0.16 eV/atom-Hydrogen.
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SYNTHESIS AND Hydrogen Absorption KINETICS OF V4Cr4Ti ALLOY
Journal of Thermal Analysis and Calorimetry, 2012Co-Authors: Sanjay Kumar, Manju Taxak, Nagaiyar KrishnamurthyAbstract:V4Cr4Ti alloy is synthesized by aluminothermy process followed by electron beam refining. Hydrogen Absorption characteristics of the alloy have been evaluated by measuring the pressure composition isotherm (PCIT) at 57 °C temperature. Two plateau pressures are observed in the PCIT curve. Substantial decrease in the Hydrogen Absorption capacity of the alloy as compared to vanadium has been recorded. Hydrogen Absorption kinetics of the alloy was investigated in the temperature range of 200–500 °C. Three-dimensional diffusion appears to be the rate controlling step of the Hydrogen Absorption. The apparent activation energy was calculated as 0.16 eV/atom-Hydrogen.
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Hydrogen Absorption kinetics of V4Cr4Ti alloy prepared by aluminothermy
International Journal of Hydrogen Energy, 2012Co-Authors: Sanjay Kumar, Manju Taxak, Nagaiyar KrishnamurthyAbstract:Abstract The Hydrogen Absorption kinetics of V4Cr4Ti alloy, synthesized by aluminothermy process has been investigated in the temperature range of 373–773 K. The obtained Hydrogen Absorption kinetic curves were linearly fitted using a series of mechanism function to reveal the kinetics parameter and reaction mechanism. Nucleation and growth, one dimensional diffusion and three-dimensional diffusion processes are the intrinsic rate limiting steps of Hydrogen Absorption at 373 K. It was found that nucleation and growth processes disappear between 413 K–473 K. However at higher temperatures (>473 K), nucleation and growth as well as one dimensional diffusion process disappear. In the temperature ranges investigated (473 K–773 K), three-dimensional diffusion process was the intrinsic rate limiting step. The apparent activation energy was calculated using Arrhenius equation and found to be 6.1 kJ/mol. This value appears to be relatively higher which can be attributed to the presence of aluminium, which has blocked the Absorption sites and increased the activation energy.
Stephan Brauser - One of the best experts on this subject based on the ideXlab platform.
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Hydrogen Absorption And Diffusion in different welded Duplex Steels
Welding in The World, 2011Co-Authors: Stephan Brauser, Th. KannengiesserAbstract:In this study, Hydrogen Absorption and diffusion were investigated for various high-alloyed ferritic-austenitic duplex steels. On account of the specific transformation and solidification behaviour, respectively, of duplex steels as compared to single-phase ferritic and austenitic steels, special conditions have to be considered concerning Hydrogen Absorption which may ultimately lead to microstructure-dependent Hydrogen-assisted weld metal cracking. Hydrogen Absorption during welding may occur via the shielding gas, moisture from Qthe surroundings or via the welding filler material. As a contribution to the interpretation and prediction of “ Hydrogen-induced cracking in welded duplex steels, the actual Hydrogen Absorption via the arc as well as the weld metal Hydrogen diffusion was investigated for the first time in a duplex steel DS (1.4462), a super duplex steel SDS (1.4501) and in a lean duplex steel LDS (1.4162). Isothermal heat treatment using carrier gas hot extraction enabled quantification of the amounts of Hydrogen trapped in the respective microstructure areas. The Hydrogen diffusion coefficients were determined by analytical and numerical calculation. The total Hydrogen concentrations and the diffusion coefficients were found to be nearly identical. Trapped Hydrogen was however observed to be dependent on the material and on the microstructure condition. The influence of Hydrogen on the mechano-technological properties of the weld metal was characterized with the help of tensile tests. In addition, the Hydrogen embrittlement effect was detected in scanning electron microscopic analyses
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Hydrogen Absorption of different welded duplex steels
International Journal of Hydrogen Energy, 2010Co-Authors: Stephan Brauser, Th. KannengiesserAbstract:In this study, Hydrogen Absorption and storage was investigated for various high-alloyed ferritic-austenitic duplex stainless steels. On account of the specific transformation and solidification behaviour, respectively, of duplex stainless steels as compared to single-phase ferritic and austenitic steels, special conditions have to be considered concerning Hydrogen Absorption which may ultimately lead to microstructure-dependent Hydrogen-assisted weld metal cracking. Hydrogen Absorption during welding may occur via the shielding gas, moisture from the surroundings or via the welding filler material. As a contribution to the interpretation and prediction of Hydrogen-induced cracking in welded duplex stainless steels, the actual Hydrogen Absorption via the arc as well as the weld metal Hydrogen diffusion was investigated in a duplex stainless steel DSS (1.4462) and in a lean-duplex stainless steel LDS (1.4162). Isothermal heat treatment using carrier gas hot extraction enabled quantification of the amounts of Hydrogen trapped in the respective microstructures. The total Hydrogen concentrations were found to be nearly identical. Trapped Hydrogen was however observed to be dependent on the material and on the microstructure condition. The influence of Hydrogen on the mechanical properties of the weld metal was characterized with the help of tensile tests. In addition, Hydrogen embrittlement was detected in scanning electron microscopic analyses.
