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Aaron M Appel - One of the best experts on this subject based on the ideXlab platform.
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thermodynamic hydricity of transition metal Hydrides
Chemical Reviews, 2016Co-Authors: Eric S Wiedner, Matthew B Chambers, Catherine L Pitman, Morris R Bullock, Alexander J M Miller, Aaron M AppelAbstract:Transition metal Hydrides play a critical role in stoichiometric and catalytic transformations. Knowledge of free energies for cleaving metal hydride bonds enables the prediction of chemical reactivity, such as for the bond-forming and bond-breaking events that occur in a catalytic reaction. Thermodynamic hydricity is the free energy required to cleave an M–H bond to generate a hydride ion (H–). Three primary methods have been developed for hydricity determination: the hydride transfer method establishes hydride transfer equilibrium with a hydride donor/acceptor pair of known hydricity, the H2 heterolysis method involves measuring the equilibrium of heterolytic cleavage of H2 in the presence of a base, and the potential–pKa method considers stepwise transfer of a proton and two electrons to give a net hydride transfer. Using these methods, over 100 thermodynamic hydricity values for transition metal Hydrides have been determined in acetonitrile or water. In acetonitrile, the hydricity of metal Hydrides sp...
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Thermodynamic Hydricity of Transition Metal Hydrides
Chemical reviews, 2016Co-Authors: Eric S Wiedner, Matthew B Chambers, Catherine L Pitman, Alexander J M Miller, R. Morris Bullock, Aaron M AppelAbstract:Transition metal Hydrides play a critical role in stoichiometric and catalytic transformations. Knowledge of free energies for cleaving metal hydride bonds enables the prediction of chemical reactivity, such as for the bond-forming and bond-breaking events that occur in a catalytic reaction. Thermodynamic hydricity is the free energy required to cleave an M-H bond to generate a hydride ion (H(-)). Three primary methods have been developed for hydricity determination: the hydride transfer method establishes hydride transfer equilibrium with a hydride donor/acceptor pair of known hydricity, the H2 heterolysis method involves measuring the equilibrium of heterolytic cleavage of H2 in the presence of a base, and the potential-pKa method considers stepwise transfer of a proton and two electrons to give a net hydride transfer. Using these methods, over 100 thermodynamic hydricity values for transition metal Hydrides have been determined in acetonitrile or water. In acetonitrile, the hydricity of metal Hydrides spans a range of more than 50 kcal/mol. Methods for using hydricity values to predict chemical reactivity are also discussed, including organic transformations, the reduction of CO2, and the production and oxidation of hydrogen.
M R Daymond - One of the best experts on this subject based on the ideXlab platform.
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microstructure characterization of a hydride blister in zircaloy 4 by ebsd and tem
Acta Materialia, 2017Co-Authors: Fei Long, David Kerr, G Domizzi, Q Wang, M R DaymondAbstract:Abstract This paper presents a detailed microstructural characterization by EBSD and TEM techniques of a hydride blister grown on a Zircaloy-4 plate. The Hydrides formed are found to be of δ-type, and exhibit an increasing volume fraction from alloy matrix, across matrix-blister boundary, and into the blister. The microstructure of the blister mainly consists of δ-hydride platelets, however there is still un-transformed α-Zr phase inside the blister. The orientation relationship between the hydride and alloy matrix has been analyzed. In addition to the commonly observed ( 0001 ) α − Z r / / { 111 } δ orientation relationship, we found Hydrides with a secondary ( 0001 ) α − Z r / / ( 100 ) δ orientation relationship. A correlation was drawn between the formation of Hydrides with the two orientation relationships and the parent grain orientation. TEM observation revealed the distribution of the remnant α-Zr phase inside the blister, which had either a nodular shape or appeared as thin nano-sized layers among the hydride platelets. The microstructure of the Hydrides has been characterized by HRTEM, exhibiting a uniform atomic structure with high dislocation density. Lastly, δ-hydride embryos obeying the primary orientation relationship were found within untransformed α-grains, indicating a consistent nucleation mechanism during blister growth.
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zirconium Hydrides and fe redistribution in zr 2 5 nb alloy under ion irradiation
Journal of Nuclear Materials, 2016Co-Authors: Yasir Idrees, Zhongwen Yao, J Cui, G K Shek, M R DaymondAbstract:Abstract Zr-2.5%Nb alloy is used to fabricate the pressure tubes of the CANDU reactor. The pressure tube is the primary pressure boundary for coolant in the CANDU design and is susceptible to delayed hydride cracking, reduction in fracture toughness upon hydride precipitation and potentially hydride blister formation. The morphology and nature of Hydrides in Zr-2.5%Nb with 100 wppm hydrogen has been investigated using transmission electron microscopy. The effect of Hydrides on heavy ion irradiation induced decomposition of the β phase has been reported. STEM-EDX mapping was employed to investigate the distribution of alloying elements. The results show that Hydrides are present in the form of stacks of different sizes, with length scales from nano- to micro-meters. Heavy ion irradiation experiments at 250 °C on as-received and hydrided Zr-2.5%Nb alloy, show interesting effects of hydrogen on the irradiation induced redistribution of Fe. It was found that Fe is widely redistributed from the β phase into the α phase in the as-received material, however, the loss of Fe from the β phase and subsequent precipitation is retarded in the hydrided material. This preliminary work will further the current understanding of microstructural evolution of Zr based alloys in the presence of hydrogen.
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in situ study of hydride precipitation kinetics and re orientation in zircaloy using synchrotron radiation
Acta Materialia, 2010Co-Authors: Kimberly B Colas, M R Daymond, A T Motta, Jonathan Almer, M Kerr, A D Banchik, P Vizcaino, J R SantistebanAbstract:The orientation and distribution of Hydrides formed in zirconium alloy nuclear fuel cladding can strongly influence material behavior and in particular resistance to crack growth. The hydride microstructure and hydride platelet orientation (whether in-plane or radial relative to the cladding tubes) are crucial to determining cladding failure limits during mechanical testing. Hydride formation is normally studied by post-facto metallography, performed at room temperature and in the absence of applied stress. This study uses synchrotron radiation to observe in situ the kinetics of hydride dissolution and precipitation in previously hydrided Zircaloy samples. The experiments allow the direct observation of hydride dissolution, re-precipitation, and re-orientation, during heating and cooling under load. The solubility limits and the hydride-matrix orientation relationship determined from in situ experiments were in good agreement with previous post-facto examinations of bulk materials. The present measurements performed under stress and at temperature showed a characteristic diffraction signature of reoriented Hydrides. The results suggest a threshold stress for hydride re-orientation between 75 and 80 MPa for the microstructure/texture studied. These results are discussed in light of existing knowledge.
Eric S Wiedner - One of the best experts on this subject based on the ideXlab platform.
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thermodynamic hydricity of transition metal Hydrides
Chemical Reviews, 2016Co-Authors: Eric S Wiedner, Matthew B Chambers, Catherine L Pitman, Morris R Bullock, Alexander J M Miller, Aaron M AppelAbstract:Transition metal Hydrides play a critical role in stoichiometric and catalytic transformations. Knowledge of free energies for cleaving metal hydride bonds enables the prediction of chemical reactivity, such as for the bond-forming and bond-breaking events that occur in a catalytic reaction. Thermodynamic hydricity is the free energy required to cleave an M–H bond to generate a hydride ion (H–). Three primary methods have been developed for hydricity determination: the hydride transfer method establishes hydride transfer equilibrium with a hydride donor/acceptor pair of known hydricity, the H2 heterolysis method involves measuring the equilibrium of heterolytic cleavage of H2 in the presence of a base, and the potential–pKa method considers stepwise transfer of a proton and two electrons to give a net hydride transfer. Using these methods, over 100 thermodynamic hydricity values for transition metal Hydrides have been determined in acetonitrile or water. In acetonitrile, the hydricity of metal Hydrides sp...
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Thermodynamic Hydricity of Transition Metal Hydrides
Chemical reviews, 2016Co-Authors: Eric S Wiedner, Matthew B Chambers, Catherine L Pitman, Alexander J M Miller, R. Morris Bullock, Aaron M AppelAbstract:Transition metal Hydrides play a critical role in stoichiometric and catalytic transformations. Knowledge of free energies for cleaving metal hydride bonds enables the prediction of chemical reactivity, such as for the bond-forming and bond-breaking events that occur in a catalytic reaction. Thermodynamic hydricity is the free energy required to cleave an M-H bond to generate a hydride ion (H(-)). Three primary methods have been developed for hydricity determination: the hydride transfer method establishes hydride transfer equilibrium with a hydride donor/acceptor pair of known hydricity, the H2 heterolysis method involves measuring the equilibrium of heterolytic cleavage of H2 in the presence of a base, and the potential-pKa method considers stepwise transfer of a proton and two electrons to give a net hydride transfer. Using these methods, over 100 thermodynamic hydricity values for transition metal Hydrides have been determined in acetonitrile or water. In acetonitrile, the hydricity of metal Hydrides spans a range of more than 50 kcal/mol. Methods for using hydricity values to predict chemical reactivity are also discussed, including organic transformations, the reduction of CO2, and the production and oxidation of hydrogen.
J R Santisteban - One of the best experts on this subject based on the ideXlab platform.
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microstructure and texture analysis of δ hydride precipitation in zircaloy 4 materials by electron microscopy and neutron diffraction
Journal of Applied Crystallography, 2014Co-Authors: Zhiyang Wang, Ulf Garbe, Y B Wang, Andrew J Studer, Guangai Sun, Robert P Harrison, Xiaozhou Dr Xiaozhou Liao, M Vicente A Alvarez, J R SantistebanAbstract:This work presents a detailed microstructure and texture study of various hydrided Zircaloy-4 materials by neutron diffraction and microscopy. The results show that the precipitated δ-ZrH1.66 generally follows the δ(111)//α(0001) and δ[1{\overline 1}0]//α[11{\overline 2}0] orientation relationship with the α-Zr matrix. The δ-hydride displays a weak texture that is determined by the texture of the α-Zr matrix, and this dependence essentially originates from the observed orientation correlation between α-Zr and δ-hydride. Neutron diffraction line profile analysis and high-resolution transmission electron microscopy observations reveal a significant number of dislocations present in the δ-hydride, with an estimated average density one order of magnitude higher than that in the α-Zr matrix, which contributes to the accommodation of the substantial misfit strains associated with hydride precipitation in the α-Zr matrix. The present observations provide an insight into the behaviour of δ-hydride precipitation in zirconium alloys and may help with understanding the induced embrittling effect of Hydrides.
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in situ study of hydride precipitation kinetics and re orientation in zircaloy using synchrotron radiation
Acta Materialia, 2010Co-Authors: Kimberly B Colas, M R Daymond, A T Motta, Jonathan Almer, M Kerr, A D Banchik, P Vizcaino, J R SantistebanAbstract:The orientation and distribution of Hydrides formed in zirconium alloy nuclear fuel cladding can strongly influence material behavior and in particular resistance to crack growth. The hydride microstructure and hydride platelet orientation (whether in-plane or radial relative to the cladding tubes) are crucial to determining cladding failure limits during mechanical testing. Hydride formation is normally studied by post-facto metallography, performed at room temperature and in the absence of applied stress. This study uses synchrotron radiation to observe in situ the kinetics of hydride dissolution and precipitation in previously hydrided Zircaloy samples. The experiments allow the direct observation of hydride dissolution, re-precipitation, and re-orientation, during heating and cooling under load. The solubility limits and the hydride-matrix orientation relationship determined from in situ experiments were in good agreement with previous post-facto examinations of bulk materials. The present measurements performed under stress and at temperature showed a characteristic diffraction signature of reoriented Hydrides. The results suggest a threshold stress for hydride re-orientation between 75 and 80 MPa for the microstructure/texture studied. These results are discussed in light of existing knowledge.
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evidence of stress induced hydrogen ordering in zirconium Hydrides
Acta Materialia, 2009Co-Authors: Axel Steuwer, Matthew J Peel, J R Santisteban, M Preuss, T Buslaps, M HaradaAbstract:The formation of Hydrides in zirconium alloys significantly affects their mechanical properties and is considered to play a critical role in their failure mechanisms, yet relatively little is known about the micromechanical behavior of Hydrides in the bulk. This paper presents the result of in situ uniaxial mechanical tensioning experiments on hydrided zircaloy-2 and zircaloy-4 specimens using energy-dispersive synchrotron X-ray diffraction, which suggests that a stress-induced transformation of the delta-hydride to gamma-hydride via ordering of the hydrogen atoms occurs, akin to a Snoek-type relaxation. Subsequent annealing was found to reverse the ordering phenomenon. (C) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. (Less)
Matthew B Chambers - One of the best experts on this subject based on the ideXlab platform.
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thermodynamic hydricity of transition metal Hydrides
Chemical Reviews, 2016Co-Authors: Eric S Wiedner, Matthew B Chambers, Catherine L Pitman, Morris R Bullock, Alexander J M Miller, Aaron M AppelAbstract:Transition metal Hydrides play a critical role in stoichiometric and catalytic transformations. Knowledge of free energies for cleaving metal hydride bonds enables the prediction of chemical reactivity, such as for the bond-forming and bond-breaking events that occur in a catalytic reaction. Thermodynamic hydricity is the free energy required to cleave an M–H bond to generate a hydride ion (H–). Three primary methods have been developed for hydricity determination: the hydride transfer method establishes hydride transfer equilibrium with a hydride donor/acceptor pair of known hydricity, the H2 heterolysis method involves measuring the equilibrium of heterolytic cleavage of H2 in the presence of a base, and the potential–pKa method considers stepwise transfer of a proton and two electrons to give a net hydride transfer. Using these methods, over 100 thermodynamic hydricity values for transition metal Hydrides have been determined in acetonitrile or water. In acetonitrile, the hydricity of metal Hydrides sp...
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Thermodynamic Hydricity of Transition Metal Hydrides
Chemical reviews, 2016Co-Authors: Eric S Wiedner, Matthew B Chambers, Catherine L Pitman, Alexander J M Miller, R. Morris Bullock, Aaron M AppelAbstract:Transition metal Hydrides play a critical role in stoichiometric and catalytic transformations. Knowledge of free energies for cleaving metal hydride bonds enables the prediction of chemical reactivity, such as for the bond-forming and bond-breaking events that occur in a catalytic reaction. Thermodynamic hydricity is the free energy required to cleave an M-H bond to generate a hydride ion (H(-)). Three primary methods have been developed for hydricity determination: the hydride transfer method establishes hydride transfer equilibrium with a hydride donor/acceptor pair of known hydricity, the H2 heterolysis method involves measuring the equilibrium of heterolytic cleavage of H2 in the presence of a base, and the potential-pKa method considers stepwise transfer of a proton and two electrons to give a net hydride transfer. Using these methods, over 100 thermodynamic hydricity values for transition metal Hydrides have been determined in acetonitrile or water. In acetonitrile, the hydricity of metal Hydrides spans a range of more than 50 kcal/mol. Methods for using hydricity values to predict chemical reactivity are also discussed, including organic transformations, the reduction of CO2, and the production and oxidation of hydrogen.
