The Experts below are selected from a list of 142338 Experts worldwide ranked by ideXlab platform
Huijun Zhao - One of the best experts on this subject based on the ideXlab platform.
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zirconium metal organic frameworks based dgt technique for in situ measurement of dissolved reactive phosphorus in waters
Water Research, 2018Co-Authors: Wenxiu Qin, Haimin Zhang, Guozhong Wang, Yunxia Zhang, Xiaoxian Tang, Huijun ZhaoAbstract:Abstract In an effort to provide early warnings for the occurrence of eutrophication, it is highly desirable to develop an accurate and efficient technique to ensure continuous monitoring of dissolved reactive phosphorus (DRP) in the aquatic environment from the viewpoint of environmental management. Herein, a new diffusive gradient in thin film (DGT) technique was developed and evaluated for in situ measurement of DRP in waters, in which Zr-based metal organic frameworks (MOFs, UiO-66) were utilized as aqueous Binding agent (abbreviated as UiO-66 DGT). As expected, the UiO-66 DGT demonstrated high uptake capacity towards phosphorus (20.8 μg P cm−2). Meanwhile, an excellent linearity between the accumulated DRP mass and deployment time over 5 d (R2 = 0.996) was obtained regardless of high or low phosphate solution. In addition, effective diffusion coefficients (D) of DRP increased exponentially with increasing ionic strengths (R2 = 0.99). Based on the rectified D, the performance of the UiO-66 DGT was independent of solution pH (6.5–8.5) and ionic strengths (ranging from 0.01 to 100 mmol L−1). Furthermore, field deployments of the UiO-66 DGT were undertaken in a natural eutrophic lake (Lake Chaohu, China). It was noteworthy that DRP could be continually accumulated by the UiO-66 DGT for more than 14 d and good agreements were obtained between the concentrations measured by DGT (CDGT) and those by ex situ chemical extraction method in solution (Csol), as reflected by CDGT/Csol of 0.9–1.1. In situ determination of DRP speciation was also carried out at different sites across Lake Chaohu. Overall, this study contributed to a better constructing of liquid Binding Phase DGT for the measurement of DRP in waters, facilitating the widespread application of the UiO-66 DGT as a routine monitoring technique and for large-scale environmental analysis.
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micro nanostructured porous zno as a new dgt Binding Phase for selective measurement of cu ii in water
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2018Co-Authors: Shengwen Liu, Weiping Cai, Guozhong Wang, Huijun Zhao, Xianbiao Wang, Jared G Panther, Fazhi XieAbstract:Abstract Micro/nanostructured porous ZnO was first utilized as a new Binding Phase in DGT (diffusive gradients in thin film) devices for selective measurement of Cu(II) in water, on the basis of its selective adsorption performance. In this case, the accumulated heavy metal ions onto the Binding Phase could be easily determined by a simple complete acid-dissolution elution process without the complicated elution experiments including measurement of elution efficiency. The selective adsorption performance of the micro/nanostructured porous ZnO towards Cu(II) was evaluated in single- and ternary-component metal solutions [Cu(II), Ni(II) and Cd(II) ions]. It was found that the adsorption amount and adsorption rate of Cu(II) ions onto the porous ZnO were the highest by comparing with that of Ni(II) and Cd(II) ions, exhibiting strong adsorption and good selectivity toward Cu(II) ions. The adsorption of heavy metal ions on the ZnO can be well described by Pseudo-second-order model, implying chemical bonding related interaction between the porous ZnO and heavy metal ions. Importantly, the ZnO was utilized as Binding Phase of DGT device for heavy metal ions measurement, the diffusion coefficient of Cu(II) in the diffusive gel was calculated to be 6.13 × 10−6 cm2 s−1, implying such ZnO could be a new potential Binding Phase towards trace Cu(II) ions detection.
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determination of mercury in aquatic systems by dgt device using thiol modified carbon nanoparticle suspension as the liquid Binding Phase
New Journal of Chemistry, 2017Co-Authors: Guozhong Wang, Huijun Zhao, Yunxia Zhang, Mingguang KongAbstract:A diffusive gradients in thin films technique (DGT) device using thiol-modified carbon nanoparticle (SH-CNP) suspension as the liquid Binding Phase and cellulose acetate membrane as the diffusive layer was evaluated for determination of Hg2+ in water. Laboratory DGT validation experiments gave linear mass uptake over time (R2 ≥ 0.99) for Hg2+ in solutions of different concentrations. The effect of pH, ionic strength and potential interfering ions on Hg2+ Binding with DGT devices was investigated. The results showed that the gathering amount of SH-CNPs-DGT for Hg2+ reached the maximum when the pH of solution was close to neutral and the ionic strength of solution and co-existing potential interfering ions such as Cd2+, Cr3+, Cu2+ and Pb2+ had no significant effect on gathering of SH-CNPs-DGT for Hg2+. Finally, validation of the SH-CNPs-DGT devices was undertaken for Hg2+ in spiked local water systems (Dongpu Reservoir and Nanfei River). For in situ measurements in Nanfei River water, the average labile Hg concentrations were 0.091 ± 0.009, 0.053 ± 0.003, and 0.071 ± 0.006 μg L−1 for three, six and seven days, respectively, which were lower than the value obtained by using ICP-MS, as DGT only measures ionic mercury and labile mercury species but direct measurement measures total mercury including inert organic species and large colloids.
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a nanoparticulate liquid Binding Phase based dgt device for aquatic arsenic measurement
Talanta, 2016Co-Authors: Shengwen Liu, Nannan Qin, Jieyao Song, Ya Zhang, Weiping Cai, Haimin Zhang, Guozhong Wang, Huijun ZhaoAbstract:A nanomaterials-based DGT device constructed with commercial dialysis membrane as diffusive layer and nanoparticulate Fe3O4 aqueous suspension as Binding Phase is developed and validated for in situ aquatic arsenic measurement. The Fe3O4NPs Binding Phase is capable of quantitatively accumulated both As(III) and As(V) species. As(III) and As(V) species coexist in the vast majority of environmental water samples. The large difference in diffusion coefficients of As(III) (DAs(III)=3.05×10(-7)cm(2)s(-1)) and As(V) (DAs(V)=1.63×10(-7)cm(2)s(-1)) makes the accurate DGT determination of total arsenic concentration of samples containing both species difficult. An effective diffusion coefficient (DAs¯=DAs(III)[1/(1+x)]+DAs(V)[x/(1+x)],where,x=As(V)/As(III)) approach is therefore proposed and validated for accurate DGT determination of total arsenic when As(III) and As(V) coexist. The experimental results demonstrate that for samples having As(V)/As(III) ratios between 0.1 and 0.9, the DGT determined total arsenic concentrations using DAs¯are within ±93-99% of that determined by ICP-MS. The general principle demonstrated in this work opens up a new avenue of utilizing functional nanomaterials as DGT Binding Phase, paving a way for developing new generation nanomaterials-based DGT devices that can be readily produced in massive numbers at low costs, facilitating the widespread use of DGT for large-scale environmental assessment and other applications.
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comparing dissolved reactive phosphorus measured by dgt with ferrihydrite and titanium dioxide adsorbents anionic interferences adsorbent capacity and deployment time
Analytica Chimica Acta, 2011Co-Authors: Jared G Panther, Peter R Teasdale, William W Bennett, David T Welsh, Huijun ZhaoAbstract:Two adsorbents (Metsorb and ferrihydrite) used in Binding layers with the diffusive gradients in a thin film technique were evaluated for the measurement of dissolved reactive phosphorous (DRP) in synthetic and natural waters. Possible interferences were investigated with Cl(-) (up to 1.35 mol L(-1)) and SO(4)(2-) (up to 0.056 mol L(-1)) having no affect on either DGT Binding layer, and HCO(3)(-) (up to 5.7 mmol L(-1)) having no effect on Metsorb-DGT, over 4 days. However, HCO(3)(-) interfered with the ferrihydrite-DGT measurement at concentrations typical of many natural waters (≥0.7 mmol L(-1)) after a deployment period of 1-2 days. The capacity of the Metsorb Binding Phase for DGT response was ∼37,000 ng P, whereas the capacities of a low-mass (17.8 mg of adsorbent per DGT sampler) and high-mass (29.2mg of adsorbent per DGT sampler) ferrihydrite Binding Phase were substantially lower (∼15,000 ng P and ∼25,000 ng P, low-mass and high-mass, respectively). Increasing the capacity of the ferrihydrite adsorbent allowed the ferrihydrite-DGT to be utilized for up to 3 days before interference by HCO(3)(-) was observed. Seawater deployments demonstrated that even high-capacity ferrihydrite-DGT devices underestimated the DRP concentration by 37%, whereas Metsorb-DGT measurements were accurate. The Metsorb-DGT is superior to the ferrihydrite-DGT for determining DRP over deployment times greater than 1 day and in waters with ≥0.7 mmol L(-1) HCO(3)(-). Based on the experience obtained from this detailed validation process, the authors propose a number of key requirements that need to be considered when developing new DGT Binding layers, with testing the performance over longer deployment times being critical.
El Bakkali Abdellatif - One of the best experts on this subject based on the ideXlab platform.
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Contribution to the study of the corrosion of SiC refractories in aluminum electrolysis cells
2009Co-Authors: El Bakkali AbdellatifAbstract:L’aluminium est fabriqué en Phase liquide à 1000°C dans une cuve à électrolyse par réduction de l’alumine dissoute dans un bain fluoré contenant essentiellement de la cryolithe Na3AlF6. Les parois latérales des cuves d’électrolyse sont revêtues par des briques réfractaires, dites « dalles de bordure », à base de SiC lié par Si3N4. Ces dalles, qui déterminent en grande partie la durée de vie de la cuve d’électrolyse, sont soumises à la corrosion par le bain, l’aluminium liquide et les gaz fluorés dégagés. Afin de contribuer à une meilleure connaissance des mécanismes de corrosion de ces dalles, l’étude des échantillons « post-mortem » prélevés des cuves industrielles a été effectuée. La mise au point d’un dispositif de simulation de corrosion en laboratoire a permis de suivre l’évolution du matériau en fonction de la composition de l’agent de corrosion. Ces études ont permis de mettre en évidence la forte réactivité de la Phase liante de la dalle dans tous les zones de la cuve. Le rôle majeur de sodium, qui provient du bloc cathodique et la pâte de brasque, comme accélérateur de la corrosion de la dalle a été confirmé. La corrélation entre l’oxydation et la corrosion a été démontrée. La dissolution de SiO2 dans le bain fluoré a été étudiée par RMN haute température in situ et par RMN MAS à température ambiante sur les échantillons solidifiés. Nous avons montré la formation de Phases aluminosilicatées (albite et néphéline) qui ont une solubilité non négligeable dans la cryolithe.Aluminum is produced in liquid Phase at 1000 °C in an electrolysis cell by reduction of alumina dissolved in a bath containing essentially cryolite Na3AlF6. The sidewalls of the electrolysis cells are lined with refractory bricks, called « edge slabs », based on Si3N4 bonded SiC. These slabs, which largely determine the lifetime of the electrolysis cell, are submitted to corrosion by the bath, the liquid aluminum and fluoride gas released. To contribute to a better understanding of the corrosion mechanisms of these slabs, the study of postmortem samples from industrial cells has been completed. A specific furnace for corrosion measurements in molten fluorides has been developed in order to characterize the evolution of the refractory with the composition of the corrosion agent. These studies highlight the high reactivity of the Binding Phase of the slab in all parts of the cell. The role of sodium, which comes from the cathode block and the ramming paste, and acts as an accelerator of corrosion has been confirmed. The correlation between oxidation and corrosion has been demonstrated. The dissolution of SiO2 in the cryolitic bath has been studied in situ by NMR at high-temperature and by NMR MAS on solidified samples at room temperature. We have shown the formation of aluminosilicate Phases (albite and nepheline) which have a significant solubility in cryolite
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Contribution à l'étude de la corrosion des réfractaires à base de SiC dans les cuves d'électrolyse de l'aluminium
HAL CCSD, 2009Co-Authors: El Bakkali AbdellatifAbstract:Aluminum is produced in liquid Phase at 1000 °C in an electrolysis cell by reduction of alumina dissolved in a bath containing essentially cryolite Na3AlF6. The sidewalls of the electrolysis cells are lined with refractory bricks, called « edge slabs », based on Si3N4 bonded SiC. These slabs, which largely determine the lifetime of the electrolysis cell, are submitted to corrosion by the bath, the liquid aluminum and fluoride gas released. To contribute to a better understanding of the corrosion mechanisms of these slabs, the study of postmortem samples from industrial cells has been completed. A specific furnace for corrosion measurements in molten fluorides has been developed in order to characterize the evolution of the refractory with the composition of the corrosion agent. These studies highlight the high reactivity of the Binding Phase of the slab in all parts of the cell. The role of sodium, which comes from the cathode block and the ramming paste, and acts as an accelerator of corrosion has been confirmed. The correlation between oxidation and corrosion has been demonstrated. The dissolution of SiO2 in the cryolitic bath has been studied in situ by NMR at high-temperature and by NMR MAS on solidified samples at room temperature. We have shown the formation of aluminosilicate Phases (albite and nepheline) which have a significant solubility in cryolite.L’aluminium est fabriqué en Phase liquide à 1000°C dans une cuve à électrolyse par réduction de l’alumine dissoute dans un bain fluoré contenant essentiellement de la cryolithe Na3AlF6. Les parois latérales des cuves d’électrolyse sont revêtues par des briques réfractaires, dites « dalles de bordure », à base de SiC lié par Si3N4. Ces dalles, qui déterminent en grande partie la durée de vie de la cuve d’électrolyse, sont soumises à la corrosion par le bain, l’aluminium liquide et les gaz fluorés dégagés. Afin de contribuer à une meilleure connaissance des mécanismes de corrosion de ces dalles, l’étude des échantillons « post-mortem » prélevés des cuves industrielles a été effectuée. La mise au point d’un dispositif de simulation de corrosion en laboratoire a permis de suivre l’évolution du matériau en fonction de la composition de l’agent de corrosion. Ces études ont permis de mettre en évidence la forte réactivité de la Phase liante de la dalle dans tous les zones de la cuve. Le rôle majeur de sodium, qui provient du bloc cathodique et la pâte de brasque, comme accélérateur de la corrosion de la dalle a été confirmé. La corrélation entre l’oxydation et la corrosion a été démontrée. La dissolution de SiO2 dans le bain fluoré a été étudiée par RMN haute température in situ et par RMN MAS à température ambiante sur les échantillons solidifiés. Nous avons montré la formation de Phases aluminosilicatées (albite et néphéline) qui ont une solubilité non négligeable dans la cryolithe
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Contribution à l'étude de la corrosion des réfractaires à base de SiC dans les cuves d'électrolyse de l'aluminium
2009Co-Authors: El Bakkali Abdellatif, Bessada Catherine, Poirier JacquesAbstract:L aluminium est fabriqué en Phase liquide à 1000C dans une cuve à électrolyse par réduction de l alumine dissoute dans un bain fluoré contenant essentiellement de la cryolithe Na3AlF6. Les parois latérales des cuves d électrolyse sont revêtues par des briques réfractaires, dites dalles de bordure , à base de SiC lié par Si3N4. Ces dalles, qui déterminent en grande partie la durée de vie de la cuve d électrolyse, sont soumises à la corrosion par le bain, l aluminium liquide et les gaz fluorés dégagés. Afin de contribuer à une meilleure connaissance des mécanismes de corrosion de ces dalles, l étude des échantillons post-mortem prélevés des cuves industrielles a été effectuée. La mise au point d un dispositif de simulation de corrosion en laboratoire a permis de suivre l évolution du matériau en fonction de la composition de l agent de corrosion. Ces études ont permis de mettre en évidence la forte réactivité de la Phase liante de la dalle dans tous les zones de la cuve. Le rôle majeur de sodium, qui provient du bloc cathodique et la pâte de brasque, comme accélérateur de la corrosion de la dalle a été confirmé. La corrélation entre l oxydation et la corrosion a été démontrée. La dissolution de SiO2 dans le bain fluoré a été étudiée par RMN haute température in situ et par RMN MAS à température ambiante sur les échantillons solidifiés. Nous avons montré la formation de Phases aluminosilicatées (albite et néphéline) qui ont une solubilité non négligeable dans la cryolithe.Aluminum is produced in liquid Phase at 1000 C in an electrolysis cell by reduction of alumina dissolved in a bath containing essentially cryolite Na3AlF6. The sidewalls of the electrolysis cells are lined with refractory bricks, called edge slabs , based on Si3N4 bonded SiC. These slabs, which largely determine the lifetime of the electrolysis cell, are submitted to corrosion by the bath, the liquid aluminum and fluoride gas released. To contribute to a better understanding of the corrosion mechanisms of these slabs, the study of postmortem samples from industrial cells has been completed. A specific furnace for corrosion measurements in molten fluorides has been developed in order to characterize the evolution of the refractory with the composition of the corrosion agent. These studies highlight the high reactivity of the Binding Phase of the slab in all parts of the cell. The role of sodium, which comes from the cathode block and the ramming paste, and acts as an accelerator of corrosion has been confirmed. The correlation between oxidation and corrosion has been demonstrated. The dissolution of SiO2 in the cryolitic bath has been studied in situ by NMR at high-temperature and by NMR MAS on solidified samples at room temperature. We have shown the formation of aluminosilicate Phases (albite and nepheline) which have a significant solubility in cryolite.ORLEANS-SCD-Bib. electronique (452349901) / SudocSudocFranceF
Guozhong Wang - One of the best experts on this subject based on the ideXlab platform.
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zirconium metal organic frameworks based dgt technique for in situ measurement of dissolved reactive phosphorus in waters
Water Research, 2018Co-Authors: Wenxiu Qin, Haimin Zhang, Guozhong Wang, Yunxia Zhang, Xiaoxian Tang, Huijun ZhaoAbstract:Abstract In an effort to provide early warnings for the occurrence of eutrophication, it is highly desirable to develop an accurate and efficient technique to ensure continuous monitoring of dissolved reactive phosphorus (DRP) in the aquatic environment from the viewpoint of environmental management. Herein, a new diffusive gradient in thin film (DGT) technique was developed and evaluated for in situ measurement of DRP in waters, in which Zr-based metal organic frameworks (MOFs, UiO-66) were utilized as aqueous Binding agent (abbreviated as UiO-66 DGT). As expected, the UiO-66 DGT demonstrated high uptake capacity towards phosphorus (20.8 μg P cm−2). Meanwhile, an excellent linearity between the accumulated DRP mass and deployment time over 5 d (R2 = 0.996) was obtained regardless of high or low phosphate solution. In addition, effective diffusion coefficients (D) of DRP increased exponentially with increasing ionic strengths (R2 = 0.99). Based on the rectified D, the performance of the UiO-66 DGT was independent of solution pH (6.5–8.5) and ionic strengths (ranging from 0.01 to 100 mmol L−1). Furthermore, field deployments of the UiO-66 DGT were undertaken in a natural eutrophic lake (Lake Chaohu, China). It was noteworthy that DRP could be continually accumulated by the UiO-66 DGT for more than 14 d and good agreements were obtained between the concentrations measured by DGT (CDGT) and those by ex situ chemical extraction method in solution (Csol), as reflected by CDGT/Csol of 0.9–1.1. In situ determination of DRP speciation was also carried out at different sites across Lake Chaohu. Overall, this study contributed to a better constructing of liquid Binding Phase DGT for the measurement of DRP in waters, facilitating the widespread application of the UiO-66 DGT as a routine monitoring technique and for large-scale environmental analysis.
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micro nanostructured porous zno as a new dgt Binding Phase for selective measurement of cu ii in water
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2018Co-Authors: Shengwen Liu, Weiping Cai, Guozhong Wang, Huijun Zhao, Xianbiao Wang, Jared G Panther, Fazhi XieAbstract:Abstract Micro/nanostructured porous ZnO was first utilized as a new Binding Phase in DGT (diffusive gradients in thin film) devices for selective measurement of Cu(II) in water, on the basis of its selective adsorption performance. In this case, the accumulated heavy metal ions onto the Binding Phase could be easily determined by a simple complete acid-dissolution elution process without the complicated elution experiments including measurement of elution efficiency. The selective adsorption performance of the micro/nanostructured porous ZnO towards Cu(II) was evaluated in single- and ternary-component metal solutions [Cu(II), Ni(II) and Cd(II) ions]. It was found that the adsorption amount and adsorption rate of Cu(II) ions onto the porous ZnO were the highest by comparing with that of Ni(II) and Cd(II) ions, exhibiting strong adsorption and good selectivity toward Cu(II) ions. The adsorption of heavy metal ions on the ZnO can be well described by Pseudo-second-order model, implying chemical bonding related interaction between the porous ZnO and heavy metal ions. Importantly, the ZnO was utilized as Binding Phase of DGT device for heavy metal ions measurement, the diffusion coefficient of Cu(II) in the diffusive gel was calculated to be 6.13 × 10−6 cm2 s−1, implying such ZnO could be a new potential Binding Phase towards trace Cu(II) ions detection.
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determination of mercury in aquatic systems by dgt device using thiol modified carbon nanoparticle suspension as the liquid Binding Phase
New Journal of Chemistry, 2017Co-Authors: Guozhong Wang, Huijun Zhao, Yunxia Zhang, Mingguang KongAbstract:A diffusive gradients in thin films technique (DGT) device using thiol-modified carbon nanoparticle (SH-CNP) suspension as the liquid Binding Phase and cellulose acetate membrane as the diffusive layer was evaluated for determination of Hg2+ in water. Laboratory DGT validation experiments gave linear mass uptake over time (R2 ≥ 0.99) for Hg2+ in solutions of different concentrations. The effect of pH, ionic strength and potential interfering ions on Hg2+ Binding with DGT devices was investigated. The results showed that the gathering amount of SH-CNPs-DGT for Hg2+ reached the maximum when the pH of solution was close to neutral and the ionic strength of solution and co-existing potential interfering ions such as Cd2+, Cr3+, Cu2+ and Pb2+ had no significant effect on gathering of SH-CNPs-DGT for Hg2+. Finally, validation of the SH-CNPs-DGT devices was undertaken for Hg2+ in spiked local water systems (Dongpu Reservoir and Nanfei River). For in situ measurements in Nanfei River water, the average labile Hg concentrations were 0.091 ± 0.009, 0.053 ± 0.003, and 0.071 ± 0.006 μg L−1 for three, six and seven days, respectively, which were lower than the value obtained by using ICP-MS, as DGT only measures ionic mercury and labile mercury species but direct measurement measures total mercury including inert organic species and large colloids.
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a nanoparticulate liquid Binding Phase based dgt device for aquatic arsenic measurement
Talanta, 2016Co-Authors: Shengwen Liu, Nannan Qin, Jieyao Song, Ya Zhang, Weiping Cai, Haimin Zhang, Guozhong Wang, Huijun ZhaoAbstract:A nanomaterials-based DGT device constructed with commercial dialysis membrane as diffusive layer and nanoparticulate Fe3O4 aqueous suspension as Binding Phase is developed and validated for in situ aquatic arsenic measurement. The Fe3O4NPs Binding Phase is capable of quantitatively accumulated both As(III) and As(V) species. As(III) and As(V) species coexist in the vast majority of environmental water samples. The large difference in diffusion coefficients of As(III) (DAs(III)=3.05×10(-7)cm(2)s(-1)) and As(V) (DAs(V)=1.63×10(-7)cm(2)s(-1)) makes the accurate DGT determination of total arsenic concentration of samples containing both species difficult. An effective diffusion coefficient (DAs¯=DAs(III)[1/(1+x)]+DAs(V)[x/(1+x)],where,x=As(V)/As(III)) approach is therefore proposed and validated for accurate DGT determination of total arsenic when As(III) and As(V) coexist. The experimental results demonstrate that for samples having As(V)/As(III) ratios between 0.1 and 0.9, the DGT determined total arsenic concentrations using DAs¯are within ±93-99% of that determined by ICP-MS. The general principle demonstrated in this work opens up a new avenue of utilizing functional nanomaterials as DGT Binding Phase, paving a way for developing new generation nanomaterials-based DGT devices that can be readily produced in massive numbers at low costs, facilitating the widespread use of DGT for large-scale environmental assessment and other applications.
Poirier Jacques - One of the best experts on this subject based on the ideXlab platform.
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Contribution à l'étude de la corrosion des réfractaires à base de SiC dans les cuves d'électrolyse de l'aluminium
2009Co-Authors: El Bakkali Abdellatif, Bessada Catherine, Poirier JacquesAbstract:L aluminium est fabriqué en Phase liquide à 1000C dans une cuve à électrolyse par réduction de l alumine dissoute dans un bain fluoré contenant essentiellement de la cryolithe Na3AlF6. Les parois latérales des cuves d électrolyse sont revêtues par des briques réfractaires, dites dalles de bordure , à base de SiC lié par Si3N4. Ces dalles, qui déterminent en grande partie la durée de vie de la cuve d électrolyse, sont soumises à la corrosion par le bain, l aluminium liquide et les gaz fluorés dégagés. Afin de contribuer à une meilleure connaissance des mécanismes de corrosion de ces dalles, l étude des échantillons post-mortem prélevés des cuves industrielles a été effectuée. La mise au point d un dispositif de simulation de corrosion en laboratoire a permis de suivre l évolution du matériau en fonction de la composition de l agent de corrosion. Ces études ont permis de mettre en évidence la forte réactivité de la Phase liante de la dalle dans tous les zones de la cuve. Le rôle majeur de sodium, qui provient du bloc cathodique et la pâte de brasque, comme accélérateur de la corrosion de la dalle a été confirmé. La corrélation entre l oxydation et la corrosion a été démontrée. La dissolution de SiO2 dans le bain fluoré a été étudiée par RMN haute température in situ et par RMN MAS à température ambiante sur les échantillons solidifiés. Nous avons montré la formation de Phases aluminosilicatées (albite et néphéline) qui ont une solubilité non négligeable dans la cryolithe.Aluminum is produced in liquid Phase at 1000 C in an electrolysis cell by reduction of alumina dissolved in a bath containing essentially cryolite Na3AlF6. The sidewalls of the electrolysis cells are lined with refractory bricks, called edge slabs , based on Si3N4 bonded SiC. These slabs, which largely determine the lifetime of the electrolysis cell, are submitted to corrosion by the bath, the liquid aluminum and fluoride gas released. To contribute to a better understanding of the corrosion mechanisms of these slabs, the study of postmortem samples from industrial cells has been completed. A specific furnace for corrosion measurements in molten fluorides has been developed in order to characterize the evolution of the refractory with the composition of the corrosion agent. These studies highlight the high reactivity of the Binding Phase of the slab in all parts of the cell. The role of sodium, which comes from the cathode block and the ramming paste, and acts as an accelerator of corrosion has been confirmed. The correlation between oxidation and corrosion has been demonstrated. The dissolution of SiO2 in the cryolitic bath has been studied in situ by NMR at high-temperature and by NMR MAS on solidified samples at room temperature. We have shown the formation of aluminosilicate Phases (albite and nepheline) which have a significant solubility in cryolite.ORLEANS-SCD-Bib. electronique (452349901) / SudocSudocFranceF
Mathieu Bauchy - One of the best experts on this subject based on the ideXlab platform.
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new insights into the mechanism governing the elasticity of calcium silicate hydrate gels exposed to high temperature a molecular dynamics study
Cement and Concrete Research, 2021Co-Authors: Yao Zhang, Qi Zhou, Mathieu BauchyAbstract:Abstract When exposed to fire, the integrity of cement-based materials is governed by thermally-induced changes in the mechanical properties of their Binding Phase, i.e., the calcium–silicate–hydrate (C–S–H) gel. However, the effect of temperature on the structure, density, and mechanical properties of C–S–H remains only partially known. Here, based on reactive molecular dynamics simulations, we reveal the nature of thermally-induced damage in C–S–H gels. In general, we show that, at the atomic scale, exposure to high temperature results in partial dehydration, volumetric shrinkage, disordering, and stiffening in the C–S–H grains. However, we show that the thermal response of C–S–H strongly depends on its chemical composition, wherein C–S–H systems associated with lower Ca/Si molar ratios are able to undergo higher temperatures before amorphization. Based on these results, we demonstrate that the stiffness of C–S–H gels (i.e., including porosity—as probed by nanoindentation) is governed by a competition between the stiffening of the grains and the decrease in packing density—wherein the latter eventually become predominant.
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effects of high temperature on the mechanical behavior of calcium silicate hydrate under uniaxial tension and compression
International Journal of Damage Mechanics, 2021Co-Authors: Yao Zhang, Qing Chen, Mathieu BauchyAbstract:When subjected to high temperatures, cement-based materials can dehydrate, which, in turn, affects the mechanical property of the main Binding Phase (calcium silicate hydrate) at the atomic scale. ...
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chemical composition of calcium silicate hydrate gels competition between kinetics and thermodynamics
Physical Review Materials, 2019Co-Authors: Qi Zhou, Zhe Wang, Gaurav Sant, Joseph V Ryan, Mathieu BauchyAbstract:Although concrete is the world's most widely used manufactured material, basic questions persist regarding the nature of its Binding Phase, namely, the calcium-silicate-hydrate (C-S-H) gel. Here, based on reactive molecular dynamics simulations, we address the following fundamental question: Is the chemical composition of C-S-H controlled by the kinetics or thermodynamics of its precipitation? As a major outcome of this study, we demonstrate that the average stoichiometry of the C-S-H gel forming upon the hydration of ordinary portland cement (i.e., Ca/Si = 1.75) is determined by the composition of the C-S-H Phase presenting the fastest precipitation kinetics, rather than the highest thermodynamic stability.
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topological control on the structural relaxation of atomic networks under stress
Physical Review Letters, 2017Co-Authors: Mathieu Bauchy, Mengyi Wang, Yingtian Yu, Bu Wang, N Anoop M Krishnan, Enrico Masoero, Roland J M PellenqAbstract:Upon loading, atomic networks can feature delayed irreversible relaxation. However, the effect of composition and structure on relaxation remains poorly understood. Herein, relying on accelerated molecular dynamics simulations and topological constraint theory, we investigate the relationship between atomic topology and stress-induced structural relaxation, by taking the example of creep deformations in calcium silicate hydrates (C─S─H), the Binding Phase of concrete. Under constant shear stress, C─S─H is found to feature delayed logarithmic shear deformations. We demonstrate that the propensity for relaxation is minimum for isostatic atomic networks, which are characterized by the simultaneous absence of floppy internal modes of relaxation and eigenstress. This suggests that topological nanoengineering could lead to the discovery of nonaging materials.
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fracture toughness of calcium silicate hydrate from molecular dynamics simulations
Journal of Non-crystalline Solids, 2015Co-Authors: Mathieu Bauchy, Roland J M Pellenq, Franzjosef Ulm, M Abdolhosseini J Qomi, Hadrien Laubie, Christian G HooverAbstract:Abstract Concrete is the most widely manufactured material in the world. Its Binding Phase, calcium–silicate–hydrate (C–S–H), is responsible for its mechanical properties and has an atomic structure fairly similar to that of usual calcium silicate glasses, which makes it appealing to study this material with tools and theories traditionally used for non-crystalline solids. Here, following this idea, we use molecular dynamics simulations to evaluate the fracture toughness of C–S–H, inaccessible experimentally. This allows us to discuss the brittleness of the material at the atomic scale. We show that, at this scale, C–S–H breaks in a ductile way, which prevents one from using methods based on linear elastic fracture mechanics. Knowledge of the fracture properties of C–S–H at the atomic scale opens the way for an upscaling approach to the design of tougher cement paste, which would allow for the design of slender environment-friendly infrastructures, requiring less material.