The Experts below are selected from a list of 255 Experts worldwide ranked by ideXlab platform
Claudine Buess-herman - One of the best experts on this subject based on the ideXlab platform.
-
The two-Phase model of structure microheterogeneity revisited by the study of the CMS cation exchange membrane
Desalination, 2009Co-Authors: Le Xuan Tuan, Denis Mertens, Claudine Buess-hermanAbstract:The chronopotentiometric study of the CMS membrane in contact with 0.05M NaCl shows a chronopotentiometric response at over-limiting currents typical of homogeneous membranes. Based on the two-Phase model, the fraction of the Interstitial Phase in presence of NaCl was determined from the conductivity of the CMS membrane conditioned in NaCl solution; the Interstitial volume fraction value was 13%. In addition, we have determined the sorbed amount of NaCl in the CMS membrane in contact with NaCl solution at different concentrations by the many-stage desorption method. The NaCl sorbed molality in the overall membrane varied linearly as a function of the molality of the NaCl external solution. It is noted that the majority of NaCl sorbed remains in the Interstitial Phase. The equilibrium partition between the external solution and the Interstitial solution was estimated to be 0.89. It is shown in this work that the consideration of an equilibrium partition of the electrolyte between the external solution and the Interstitial Phase strengthens the two Phase model of Zabolotsky and Nikonenko.
-
Cation exchange membranes based on grafted PS/DVB–ETFE films: An investigation of their electrochemical characteristics in sulfuric acid
Electrochimica Acta, 2009Co-Authors: Le Xuan Tuan, Boulehdid Hanae, Mérida Vargas Lara, Claudine Buess-hermanAbstract:Abstract The electrochemical characteristics of lab-made cation exchange membranes based on a PS/DVB–ETFE film with different degrees of grafting (37% and 44%, respectively) have been evaluated in presence of sulfuric acid by means of current–voltage, chronopotentiometric and conductivity measurements. The transport number of the hydrogen ion in the membranes is estimated by resorting to the Sand equation. The chronopotentiometric curves of the membranes in contact with 0.1 M H2SO4 solution present the typical shape of overall homogeneous membranes. The validity of the two-Phase model (Interstitial solution and gel Phase) has therefore been tested with the aim of contributing to provide a better description of the membrane microheterogeneity. According to the two-Phase model, the volume fraction of the Interstitial Phase in the membranes is determined from the membrane and solution conductivity data. Furthermore, the relationship between the Interstitial Phase volume fractions and the water content of the membranes is discussed on the basis of the polyelectrolyte theory.
-
Study of water content and microheterogeneity of CMS cation exchange membrane
Chemical Physics Letters, 2007Co-Authors: Le Xuan Tuan, Claudine Buess-hermanAbstract:Influences of the concentration of different electrolyte solutions on the water content of the CMS cation exchange membrane were studied. Based on the microheterogeneous model of electromembrane, we determined the fraction of the Interstitial Phase in presence of NaCl and H2SO4 solutions by using the conductivity results obtained from impedance spectroscopy. The polyelectrolyte theory was applied to explain the dependence of the water content and the fraction of the Interstitial Phase on the nature of the counter ions. © 2006 Elsevier B.V. All rights reserved.info:eu-repo/semantics/publishe
-
Study of water content and microheterogeneity of CMS cation exchange membrane
Chemical Physics Letters, 2006Co-Authors: Le Xuan Tuan, Claudine Buess-hermanAbstract:Abstract Influences of the concentration of different electrolyte solutions on the water content of the CMS cation exchange membrane were studied. Based on the microheterogeneous model of electromembrane, we determined the fraction of the Interstitial Phase in presence of NaCl and H 2 SO 4 solutions by using the conductivity results obtained from impedance spectroscopy. The polyelectrolyte theory was applied to explain the dependence of the water content and the fraction of the Interstitial Phase on the nature of the counter ions.
-
Properties of CMV cation exchange membranes in sulfuric acid media
Journal of Membrane Science, 2006Co-Authors: Le Xuan Tuan, Claudine Buess-herman, M. Verbanck, H.d. HurwitzAbstract:Properties of CMV cation exchange membranes used for electrodialysis of sulfuric acid solutions were investigated. Membrane characterization has led to determine the ion-exchange capacity and the hydrogen ion transport number in sulphuric acid media. The membrane electrical conductivities were measured as a function of the acid concentration. These data were used to check the applicability of the micro-heterogeneous model which describes the inner membrane microstructure as consisting of a joint gel Phase and an Interstitial Phase. The derived value of the Interstitial Phase volume fraction is large (20%). This value has been correlated to the membrane water content in terms of a model taking into consideration the molecular conformation of polyvalent (polystyrene sulfonate) macro-ions located in the joint gel Phase. The behaviour of membranes placed respectively in their acid and salt forms have been studied and discussed. In the interpretation of membrane swelling and acid absorption, emphasis has been put on the role of polyelectrolyte morphological modifications as a function of the concentration in the equilibrating solutions. The overall membrane homogeneity has been tested by using chronopotentiometric measurements at different current densities.
Anthony E Williamsjones - One of the best experts on this subject based on the ideXlab platform.
-
magmatic evolution and controls on rare metal enrichment of the strange lake a type peralkaline granitic pluton quebec labrador
Lithos, 2018Co-Authors: Karin Siegel, O V Vasyukova, Anthony E WilliamsjonesAbstract:Abstract Although it is well known that A-type granites are enriched in the rare earth elements (REE) and other high field strength elements (HFSE), the magmatic processes that concentrate these elements are still poorly understood. The 1.24 Ga Strange Lake pluton in northern Quebec-Labrador provides an extraordinary example of hyper-enrichment in the REE, Zr, and Nb in a peralkaline A-type granite. The pluton consists of two hypersolvus granite units (southern and northern) and a transsolvus granite, all of which contain perthitic alkali feldspar as the earliest major mineral; the transsolvus granite also contains separate albite and microcline crystals. Arfvedsonite, a sodic amphibole, occurs exclusively as phenocrysts in the transsolvus granite, whereas in the hypersolvus granite it is present as a late, Interstitial Phase. The primary HFSE minerals are zircon, monazite-(Ce), gagarinite-(Ce) and the pyrochlore group minerals. Magma evolution was monitored by the alumina content in the bulk rock, which decreases from the southern to the northern hypersolvus granite and is lowest in the transsolvus granite. Alkalinity indices and bulk Si, Fe, Rb, REE, Zr, Nb concentrations show the opposite trend. Alkali feldspar compositions mirror the trend shown by the bulk rock, i.e., decreasing Al contents are accompanied by increasing Si, Fe3+, REE, Zr and Nb contents. The major driving forces for the evolution of the hypersolvus magma prior to emplacement were the early separation of a fluoride melt from the silicate melt and the crystallization of alkali feldspar and HFSE-rich Phases (zircon, monazite-(Ce), pyrochlore group). An alkali feldspar-rich crystal-mush containing LREE-fluoride melt droplets was emplaced as the least evolved southern hypersolvus granite. Massive fractionation of alkali feldspar led to a sharp increase in ƒH2O and F− activity in the magma chamber that triggered the crystallization of arfvedsonite and was followed by emplacement of the northern hypersolvus granite, which contained a higher proportion of LREE-fluoride melt droplets. Further evolution in the magma chamber led to a transition from a miaskitic to an agpaitic composition. The transsolvus granite was intruded in the form of a low viscosity crystal mush of alkali feldspar, quartz, arfvedsonite (after appreciable crystallization of arfvedsonite) and LREE-fluoride melt droplets. Upon emplacement, arfvedsonite (and gagarinite-(Ce)) crystals segregated as cumulates in response to a combination of flow differentiation and gravity settling. The immiscible fluoride melt accumulated in a volatile-rich residual silicate magma, which migrated to the top of the pluton where it formed the F-REE-rich cores of highly mineralized pegmatites.
-
the amphiboles of the ree rich a type peralkaline strange lake pluton fingerprints of magma evolution
Lithos, 2017Co-Authors: Karin Siegel, Anthony E Williamsjones, Vincent J Van HinsbergAbstract:Abstract Major and trace element compositions of amphibole in igneous environments commonly reflect evolving magma compositions. In this study, we use the amphibole-group minerals from the Strange Lake, REE-enriched peralkaline granitic pluton to gain insights into the evolution of the magma. This 1240 Ma old pluton consists of two main intrusive facies, an early hypersolvus granite, which occurs as separate northern and southern intrusions, and a more evolved transsolvus granite. In the hypersolvus granite the amphibole is a late Interstitial Phase, whereas in the transsolvus granite, it is present as phenocrysts. The amphibole compositions vary from calcic–sodic (ferro–ferri-katophorite) in the southern hypersolvus granite to sodic (arfvedsonite, ferro–ferri-leakeite) in the other, more evolved granitic units. High Na, Si, Li, and low Al and Ca concentrations in the amphibole phenocrysts of the transsolvus granite indicate formation from a more evolved magma compared to the hypersolvus granite, despite the fact that these crystals formed early. We interpret the increasing Fe 3+ /Fe 2+ ratios in the amphibole of the hypersolvus granite to reflect crystal chemical effects (Na/Ca-ratio) and increasingly oxidizing conditions in the magma, whereas in the phenocrysts of the transsolvus granite, the increasing ratio was the product of increasing proportions of F − and OH − in the melt. The amphiboles of all the granite units have elevated Nb, Zr, Hf and REE concentrations compared to the bulk rock, suggesting that these elements are compatible in amphibole. By contrast the much lower Ti concentration was due to saturation of the magma in sodium-titanosilicates. The amphibole REE concentrations vary greatly among the granite units. Amphibole of the southern and northern hypersolvus granite contains 0.16 and 0.07 wt.% ∑ REE + Y, on average, respectively, and in the transsolvus granite, the average ∑ REE content is only 0.01 wt.%, despite the more evolved nature of its host transsolvus granite. We intrepret this compositional difference to be due to the fact that the latter represents phenocrysts, which crystallized early, whereas the hypersolvus arfvedsonite is a late Interstitial Phase. Chondrite-normalized REE profiles emphasise the wide range in LREE-, and the narrow range in HREE-concentrations of the amphiboles. The variations in the LREE-profiles reflect the variable crystallization of primary LREE-bearing Phases, including monazite-(Ce), pyrochlore group minerals and gagarinite-(Ce), prior to or contemporaneous with the amphibole, as well as the exsolution of a LREE-rich fluoride melt. The LREE are incompatible in the amphibole structure (apparent D D > 1). Owing to their small ionic radius and their compatibility with the amphibole structure, HREE concentrations were more controlled by partitioning (crystal chemical effects) than by the concentrations in the corresponding magma. Large proportions of the bulk HREE content (up to 70%) reside in the amphibole, and their later release through hydrothermal replacement helps to explain the extreme and unusual HREE enrichment of the Strange Lake pluton.
Karin Siegel - One of the best experts on this subject based on the ideXlab platform.
-
magmatic evolution and controls on rare metal enrichment of the strange lake a type peralkaline granitic pluton quebec labrador
Lithos, 2018Co-Authors: Karin Siegel, O V Vasyukova, Anthony E WilliamsjonesAbstract:Abstract Although it is well known that A-type granites are enriched in the rare earth elements (REE) and other high field strength elements (HFSE), the magmatic processes that concentrate these elements are still poorly understood. The 1.24 Ga Strange Lake pluton in northern Quebec-Labrador provides an extraordinary example of hyper-enrichment in the REE, Zr, and Nb in a peralkaline A-type granite. The pluton consists of two hypersolvus granite units (southern and northern) and a transsolvus granite, all of which contain perthitic alkali feldspar as the earliest major mineral; the transsolvus granite also contains separate albite and microcline crystals. Arfvedsonite, a sodic amphibole, occurs exclusively as phenocrysts in the transsolvus granite, whereas in the hypersolvus granite it is present as a late, Interstitial Phase. The primary HFSE minerals are zircon, monazite-(Ce), gagarinite-(Ce) and the pyrochlore group minerals. Magma evolution was monitored by the alumina content in the bulk rock, which decreases from the southern to the northern hypersolvus granite and is lowest in the transsolvus granite. Alkalinity indices and bulk Si, Fe, Rb, REE, Zr, Nb concentrations show the opposite trend. Alkali feldspar compositions mirror the trend shown by the bulk rock, i.e., decreasing Al contents are accompanied by increasing Si, Fe3+, REE, Zr and Nb contents. The major driving forces for the evolution of the hypersolvus magma prior to emplacement were the early separation of a fluoride melt from the silicate melt and the crystallization of alkali feldspar and HFSE-rich Phases (zircon, monazite-(Ce), pyrochlore group). An alkali feldspar-rich crystal-mush containing LREE-fluoride melt droplets was emplaced as the least evolved southern hypersolvus granite. Massive fractionation of alkali feldspar led to a sharp increase in ƒH2O and F− activity in the magma chamber that triggered the crystallization of arfvedsonite and was followed by emplacement of the northern hypersolvus granite, which contained a higher proportion of LREE-fluoride melt droplets. Further evolution in the magma chamber led to a transition from a miaskitic to an agpaitic composition. The transsolvus granite was intruded in the form of a low viscosity crystal mush of alkali feldspar, quartz, arfvedsonite (after appreciable crystallization of arfvedsonite) and LREE-fluoride melt droplets. Upon emplacement, arfvedsonite (and gagarinite-(Ce)) crystals segregated as cumulates in response to a combination of flow differentiation and gravity settling. The immiscible fluoride melt accumulated in a volatile-rich residual silicate magma, which migrated to the top of the pluton where it formed the F-REE-rich cores of highly mineralized pegmatites.
-
the amphiboles of the ree rich a type peralkaline strange lake pluton fingerprints of magma evolution
Lithos, 2017Co-Authors: Karin Siegel, Anthony E Williamsjones, Vincent J Van HinsbergAbstract:Abstract Major and trace element compositions of amphibole in igneous environments commonly reflect evolving magma compositions. In this study, we use the amphibole-group minerals from the Strange Lake, REE-enriched peralkaline granitic pluton to gain insights into the evolution of the magma. This 1240 Ma old pluton consists of two main intrusive facies, an early hypersolvus granite, which occurs as separate northern and southern intrusions, and a more evolved transsolvus granite. In the hypersolvus granite the amphibole is a late Interstitial Phase, whereas in the transsolvus granite, it is present as phenocrysts. The amphibole compositions vary from calcic–sodic (ferro–ferri-katophorite) in the southern hypersolvus granite to sodic (arfvedsonite, ferro–ferri-leakeite) in the other, more evolved granitic units. High Na, Si, Li, and low Al and Ca concentrations in the amphibole phenocrysts of the transsolvus granite indicate formation from a more evolved magma compared to the hypersolvus granite, despite the fact that these crystals formed early. We interpret the increasing Fe 3+ /Fe 2+ ratios in the amphibole of the hypersolvus granite to reflect crystal chemical effects (Na/Ca-ratio) and increasingly oxidizing conditions in the magma, whereas in the phenocrysts of the transsolvus granite, the increasing ratio was the product of increasing proportions of F − and OH − in the melt. The amphiboles of all the granite units have elevated Nb, Zr, Hf and REE concentrations compared to the bulk rock, suggesting that these elements are compatible in amphibole. By contrast the much lower Ti concentration was due to saturation of the magma in sodium-titanosilicates. The amphibole REE concentrations vary greatly among the granite units. Amphibole of the southern and northern hypersolvus granite contains 0.16 and 0.07 wt.% ∑ REE + Y, on average, respectively, and in the transsolvus granite, the average ∑ REE content is only 0.01 wt.%, despite the more evolved nature of its host transsolvus granite. We intrepret this compositional difference to be due to the fact that the latter represents phenocrysts, which crystallized early, whereas the hypersolvus arfvedsonite is a late Interstitial Phase. Chondrite-normalized REE profiles emphasise the wide range in LREE-, and the narrow range in HREE-concentrations of the amphiboles. The variations in the LREE-profiles reflect the variable crystallization of primary LREE-bearing Phases, including monazite-(Ce), pyrochlore group minerals and gagarinite-(Ce), prior to or contemporaneous with the amphibole, as well as the exsolution of a LREE-rich fluoride melt. The LREE are incompatible in the amphibole structure (apparent D D > 1). Owing to their small ionic radius and their compatibility with the amphibole structure, HREE concentrations were more controlled by partitioning (crystal chemical effects) than by the concentrations in the corresponding magma. Large proportions of the bulk HREE content (up to 70%) reside in the amphibole, and their later release through hydrothermal replacement helps to explain the extreme and unusual HREE enrichment of the Strange Lake pluton.
Xuexu Gao - One of the best experts on this subject based on the ideXlab platform.
-
improvement of bending strength via regenerated Interstitial Phase at the triple junction Phase on sintered nd fe b alloy
Intermetallics, 2019Co-Authors: Shuo Gao, Xiaoqian Bao, Xuexu GaoAbstract:Abstract Understanding the mechanical properties of sintered Nd-Fe-B magnets is critical for improving the rate of finished products in grinding and cutting. During the preparation of sintered Nd-Fe-B magnet, carbon elements inevitably remain in the magnet. In this paper, the effect of carbon on the bending strength of sintered Nd-Fe-B was investigated and the fracture mechanism was analyzed. In the case of the sample having a high carbon content, the bending strength was significantly increased. Observation of the microstructure shows that the carbon content does not affect the grain size of the main Phase. Stress concentration is applied by pre-cracking. It is directly observed that the sintered Nd-Fe-B crack source is located at the triple junction Phase (TJP). It was found that almost all the carbon elements were concentrated in the TJP using electron probe microanalyzer (EPMA). At the same time, the formation of neodymium carbide contributes to strengthening TJP, which improves the difficulty of crack nucleation and the resistance of crack propagation.
Le Xuan Tuan - One of the best experts on this subject based on the ideXlab platform.
-
Cation exchange membranes based on grafted PS/DVB–ETFE films: An investigation of their electrochemical characteristics in sulfuric acid
Electrochimica Acta, 2009Co-Authors: Le Xuan Tuan, Boulehdid Hanae, Mérida Vargas Lara, Claudine Buess-hermanAbstract:Abstract The electrochemical characteristics of lab-made cation exchange membranes based on a PS/DVB–ETFE film with different degrees of grafting (37% and 44%, respectively) have been evaluated in presence of sulfuric acid by means of current–voltage, chronopotentiometric and conductivity measurements. The transport number of the hydrogen ion in the membranes is estimated by resorting to the Sand equation. The chronopotentiometric curves of the membranes in contact with 0.1 M H2SO4 solution present the typical shape of overall homogeneous membranes. The validity of the two-Phase model (Interstitial solution and gel Phase) has therefore been tested with the aim of contributing to provide a better description of the membrane microheterogeneity. According to the two-Phase model, the volume fraction of the Interstitial Phase in the membranes is determined from the membrane and solution conductivity data. Furthermore, the relationship between the Interstitial Phase volume fractions and the water content of the membranes is discussed on the basis of the polyelectrolyte theory.
-
The two-Phase model of structure microheterogeneity revisited by the study of the CMS cation exchange membrane
Desalination, 2009Co-Authors: Le Xuan Tuan, Denis Mertens, Claudine Buess-hermanAbstract:The chronopotentiometric study of the CMS membrane in contact with 0.05M NaCl shows a chronopotentiometric response at over-limiting currents typical of homogeneous membranes. Based on the two-Phase model, the fraction of the Interstitial Phase in presence of NaCl was determined from the conductivity of the CMS membrane conditioned in NaCl solution; the Interstitial volume fraction value was 13%. In addition, we have determined the sorbed amount of NaCl in the CMS membrane in contact with NaCl solution at different concentrations by the many-stage desorption method. The NaCl sorbed molality in the overall membrane varied linearly as a function of the molality of the NaCl external solution. It is noted that the majority of NaCl sorbed remains in the Interstitial Phase. The equilibrium partition between the external solution and the Interstitial solution was estimated to be 0.89. It is shown in this work that the consideration of an equilibrium partition of the electrolyte between the external solution and the Interstitial Phase strengthens the two Phase model of Zabolotsky and Nikonenko.
-
Study of water content and microheterogeneity of CMS cation exchange membrane
Chemical Physics Letters, 2006Co-Authors: Le Xuan Tuan, Claudine Buess-hermanAbstract:Abstract Influences of the concentration of different electrolyte solutions on the water content of the CMS cation exchange membrane were studied. Based on the microheterogeneous model of electromembrane, we determined the fraction of the Interstitial Phase in presence of NaCl and H 2 SO 4 solutions by using the conductivity results obtained from impedance spectroscopy. The polyelectrolyte theory was applied to explain the dependence of the water content and the fraction of the Interstitial Phase on the nature of the counter ions.
-
Properties of CMV cation exchange membranes in sulfuric acid media
Journal of Membrane Science, 2006Co-Authors: Le Xuan Tuan, Claudine Buess-herman, M. Verbanck, H.d. HurwitzAbstract:Properties of CMV cation exchange membranes used for electrodialysis of sulfuric acid solutions were investigated. Membrane characterization has led to determine the ion-exchange capacity and the hydrogen ion transport number in sulphuric acid media. The membrane electrical conductivities were measured as a function of the acid concentration. These data were used to check the applicability of the micro-heterogeneous model which describes the inner membrane microstructure as consisting of a joint gel Phase and an Interstitial Phase. The derived value of the Interstitial Phase volume fraction is large (20%). This value has been correlated to the membrane water content in terms of a model taking into consideration the molecular conformation of polyvalent (polystyrene sulfonate) macro-ions located in the joint gel Phase. The behaviour of membranes placed respectively in their acid and salt forms have been studied and discussed. In the interpretation of membrane swelling and acid absorption, emphasis has been put on the role of polyelectrolyte morphological modifications as a function of the concentration in the equilibrating solutions. The overall membrane homogeneity has been tested by using chronopotentiometric measurements at different current densities.
