scholarly journals Cs Retention and Diffusion in C-S-H at Different Ca/Si Ratios

2018 ◽  
Author(s):  
Eduardo Duque-Redondo ◽  
Kazuo Yamada ◽  
Iñigo López-Arbeloa ◽  
Hegoi Manzano
Keyword(s):  
Diffusion Coefficients ◽  
Alkaline Earth ◽  
Diffusion Processes ◽  
Hydration Product ◽  
Cement Matrix ◽  
Water Molecules ◽  
Average Diffusion ◽  
Dynamics Simulations ◽  
And Diffusion

<div>Cement and concrete have been widely used as a barrier to isolate many types of contaminants, including radioactive waste, in repository sites. Nevertheless, the intrusion of groundwater in those nuclear repositories may release those contaminants by leaching mechanisms. Because of this, the retention and diffusion processes in cement matrix require to be analyzed in depth. The adsorption in cement and C‐S-H gel, its main hydration product, is influenced by factors as the pH, the composition or the alkali and alkaline earth content. In this work, molecular dynamics simulations were employed to study the role of Ca/Si ratio of the C‐S‐H in the capacity to retain Cs and diffusivity of these ions in gel pores. For that purpose, we built four different C‐S‐H models with Ca/Si ratios from 1.1 to 2.0. The results indicate better cationic retention at low Ca/Si ratios due to the interaction of the cations with the bridging silicate tetrahedrons. However, the average diffusion coefficients of the cations decrease at higher Ca/Si ratios because the high ionic constraint in the nanopore that induces a longrange ordering of the water molecules.</div>

scholarly journals Cs Retention and Diffusion in C-S-H at Different Ca/Si Ratios

2018 ◽  
Author(s):  
Eduardo Duque-Redondo ◽  
Kazuo Yamada ◽  
Iñigo López-Arbeloa ◽  
Hegoi Manzano
Keyword(s):  
Diffusion Coefficients ◽  
Alkaline Earth ◽  
Diffusion Processes ◽  
Hydration Product ◽  
Cement Matrix ◽  
Water Molecules ◽  
Average Diffusion ◽  
Dynamics Simulations ◽  
And Diffusion

<div>Cement and concrete have been widely used as a barrier to isolate many types of contaminants, including radioactive waste, in repository sites. Nevertheless, the intrusion of groundwater in those nuclear repositories may release those contaminants by leaching mechanisms. Because of this, the retention and diffusion processes in cement matrix require to be analyzed in depth. The adsorption in cement and C‐S-H gel, its main hydration product, is influenced by factors as the pH, the composition or the alkali and alkaline earth content. In this work, molecular dynamics simulations were employed to study the role of Ca/Si ratio of the C‐S‐H in the capacity to retain Cs and diffusivity of these ions in gel pores. For that purpose, we built four different C‐S‐H models with Ca/Si ratios from 1.1 to 2.0. The results indicate better cationic retention at low Ca/Si ratios due to the interaction of the cations with the bridging silicate tetrahedrons. However, the average diffusion coefficients of the cations decrease at higher Ca/Si ratios because the high ionic constraint in the nanopore that induces a longrange ordering of the water molecules.</div>

Adsorption and Diffusion of Na+, Cs+ and Ca+2 Ions in C-S-H and C-a-S-H Nanopores

2018 ◽  
Author(s):  
Eduardo Duque-Redondo ◽  
Kazuo Yamada ◽  
Iñigo Lopez Arbeloa ◽  
Hegoi Manzano
Keyword(s):  
Alkaline Earth ◽  
Hydration Product ◽  
Cementitious Materials ◽  
Constant Concentration ◽  
High Affinity ◽  
Strong Competition ◽  
Dynamics Simulations ◽  
The Impact ◽  
And Diffusion ◽  
Alkaline Earth Cations

Cementitious materials act as a diffusion barrier, immobilizing liquid and solid<br>radioactive waste and preventing their release into the biosphere. The retention capability of hydrated<br>cement paste and its main hydration product, C-S-H gel, has been extensively explored experimentally<br>for many alkali and alkaline earth cations. Nevertheless, the retention mechanisms of these cations at<br>the molecular scale are still unclear. In this paper, we have employed molecular dynamics simulations<br>to study the capacity of C-S-H to retain Cs, Ca and Na, analyzing the number of high-affinity sites on<br>the surface, the type of sorption for each cation and the diffusivity of these ions. We have also explored<br>the impact of aluminum incorporation in C-S-H at a constant concentration of the ions in the gel pore.<br>We found strong competition for surface sorption sites, with notable differences in the retention of the<br>cations under study and a remarkable enhance of the adsorption in C-A-S-H with respect to C-S-H.

Adsorption and Diffusion of Na+, Cs+ and Ca+2 Ions in C-S-H and C-a-S-H Nanopores

2018 ◽  
Author(s):  
Eduardo Duque-Redondo ◽  
Kazuo Yamada ◽  
Iñigo Lopez Arbeloa ◽  
Hegoi Manzano
Keyword(s):  
Alkaline Earth ◽  
Hydration Product ◽  
Cementitious Materials ◽  
Constant Concentration ◽  
High Affinity ◽  
Strong Competition ◽  
Dynamics Simulations ◽  
The Impact ◽  
And Diffusion ◽  
Alkaline Earth Cations

Cementitious materials act as a diffusion barrier, immobilizing liquid and solid<br>radioactive waste and preventing their release into the biosphere. The retention capability of hydrated<br>cement paste and its main hydration product, C-S-H gel, has been extensively explored experimentally<br>for many alkali and alkaline earth cations. Nevertheless, the retention mechanisms of these cations at<br>the molecular scale are still unclear. In this paper, we have employed molecular dynamics simulations<br>to study the capacity of C-S-H to retain Cs, Ca and Na, analyzing the number of high-affinity sites on<br>the surface, the type of sorption for each cation and the diffusivity of these ions. We have also explored<br>the impact of aluminum incorporation in C-S-H at a constant concentration of the ions in the gel pore.<br>We found strong competition for surface sorption sites, with notable differences in the retention of the<br>cations under study and a remarkable enhance of the adsorption in C-A-S-H with respect to C-S-H.

Effect of cluster-gradient architecture of nanostructured topocomposites on features of tribointeraction with heterophased material

2020 ◽  
pp. 130-135
Author(s):  
D.N. Korotaev ◽  
K.N. Poleshchenko ◽  
E.N. Eremin ◽  
E.E. Tarasov
Keyword(s):  
Wear Resistance ◽  
Titanium Alloy ◽  
Energy Dissipation ◽  
Phase Structure ◽  
Diffusion Processes ◽  
Structural Phase ◽  
High Wear Resistance ◽  
Wear Characteristics ◽  
And Diffusion

The wear resistance and wear characteristics of cluster-gradient architecture (CGA) nanostructured topocomposites are studied. The specifics of tribocontact interaction under microcutting conditions is considered. The reasons for retention of high wear resistance of this class of nanostructured topocomposites are studied. The mechanisms of energy dissipation from the tribocontact zone, due to the nanogeometry and the structural-phase structure of CGA topocomposites are analyzed. The role of triboactivated deformation and diffusion processes in providing increased wear resistance of carbide-based topocomposites is shown. They are tested under the conditions of blade processing of heat-resistant titanium alloy.

scholarly journals In situ X-ray tomography densification of firn: The role of mechanics and diffusion processes

2019 ◽  
Vol 167 ◽  
pp. 210-220 ◽  
Author(s):  
Alexis Burr ◽  
Pierre Lhuissier ◽  
Christophe L. Martin ◽  
Armelle Philip
Keyword(s):  
Diffusion Processes ◽  
X Ray ◽  
And Diffusion

Estimation for discretely observed diffusions using transform functions

2004 ◽  
Vol 41 (A) ◽  
pp. 99-118 ◽  
Author(s):  
Leah Kelly ◽  
Eckhard Platen ◽  
Michael Sørensen
Keyword(s):  
Asymptotic Normality ◽  
Diffusion Coefficients ◽  
Diffusion Processes ◽  
Estimation Technique ◽  
Consistency And Asymptotic Normality ◽  
And Diffusion ◽  
Explicit Estimators

This paper introduces a new estimation technique for discretely observed diffusion processes. Transform functions are applied to transform the data to obtain good and easily calculated estimators of both the drift and diffusion coefficients. Consistency and asymptotic normality of the resulting estimators is investigated. Power transforms are used to estimate the parameters of affine diffusions, for which explicit estimators are obtained.

Rheological Properties of Water Films Nanoconfined in Parallel Au Plates by Molecular Dynamics Simulations

2007 ◽  
Vol 121-123 ◽  
pp. 1109-1114
Author(s):  
M.L. Liao ◽  
Shin Pon Ju ◽  
Jenn Sen Lin ◽  
Y.S. Lin
Keyword(s):  
Molecular Dynamics ◽  
Shear Rate ◽  
Molecular Dynamics Simulations ◽  
Rheological Properties ◽  
Shear Viscosity ◽  
Water Film ◽  
Water Molecules ◽  
Water Films ◽  
Dynamics Simulations ◽  
And Diffusion

Rheological properties of water films nanoconfined in two parallel Au plates are investigated with the aid of molecular dynamics simulations. The density distribution, velocity profile, and diffusion coefficients of the water film in a Couette flow are studied. Shear viscosity and its dependence on the shear rate of the water film are also examined in the present research. It is found that the density of the water molecules near the plates is much higher than that in the other regions. This indicates that many water molecules are adsorbed by the plates and adsorbed layers are formed in the vicinity of the plates. The diffusion of the whole film increases dramatically as the shear rate becomes greater than 1010 s-1. The shear viscosity decreases as the shear rate increases, especially for the water film with a small thickness, which indicates the shear-thinning behavior for viscosity of the nanoconfined film. Moreover, an increase in shear viscosity with a decrease in the film thickness can also be found in the present study.

scholarly journals Intriguing Role of Water in Plant Hormone Perception

2021 ◽  
Author(s):  
Chuankai Zhao ◽  
Diego Eduardo Kleiman ◽  
Diwakar Shukla
Keyword(s):  
Free Energy ◽  
Plant Growth ◽  
Binding Site ◽  
Plant Hormones ◽  
Plant Hormone ◽  
Water Molecules ◽  
Water Displacement ◽  
Dynamics Simulations ◽  
Free Energy Of Binding

Plant hormones are small molecules that regulate plant growth, development, and responses to biotic and abiotic stresses. Plant hormones are specifically recognized by the binding site of their receptors. In this work, we investigated the role of water displacement and reorganization at the binding site of plant receptors on the binding of eight classes of phytohormones (auxin, jasmonate, gibberellin, strigolactone, brassinosteroid, cytokinin, salicylic acid, and abscisic acid) using extensive molecular dynamics simulations and inhomogeneous solvation theory. Our findings demonstrated that displacement of water molecules by phytohormones contributes to free energy of binding via entropy gain and is associated with free energy barriers. Also, our results have shown that displacement of unfavorable water molecules in the binding site can be exploited in rational agrochemical design. Overall, this study uncov- ers the role of water molecules in plant hormone perception, which creates new avenues for agrochemical design to target plant growth and development.

In Situ X-Ray Tomography Densification of Firn: Decoupling the Role of Mechanics and Diffusion Processes

2018 ◽  
Author(s):  
Alexis Burr ◽  
Pierre Lhuissier ◽  
Christophe L. Martin ◽  
Armelle Philip
Keyword(s):  
Diffusion Processes ◽  
X Ray ◽  
And Diffusion

Diffusion Barrier Reliability with Respect to the Role of Tin Stoichiometry Between Al Metallization and Si Substrate

1996 ◽  
Vol 441 ◽  
Author(s):  
Han-Yu Tseng ◽  
Aris Christou ◽  
Dan Young ◽  
Ted Tessner ◽  
Jon Orloff
Keyword(s):  
Diffusion Barrier ◽  
Diffusion Processes ◽  
Depth Profiling ◽  
X Ray Diffraction ◽  
Tin Films ◽  
Al Metallization ◽  
High Degree ◽  
Tin Diffusion Barrier ◽  
And Diffusion

AbstractIn this study, the relation between interdiffusion in Al/ TiN thin film couples and diffusion barrier stability has been investigated. The TiN diffusion barrier was deposited by reactive sputtering in an Ar-N2 gas mixture. The stoichiometry of TiN was achieved by varying the nitrogen-to-argon ratio in the sputtering gas. Interdiffiusion occurred after annealing for 30 minutes at 475°C and 575°C. Diffusion processes and interfacial reactions with respect to TiN stoichiometry were investigated via Auger Electron Spectroscopy (AES) depth profiling and X-ray diffraction (XRD). The barrier reliability with respect to the stoichiometry changes was established; nitrogen-deficient TiN films result in a high degree of interdiffiusion and decomposition at annealing temperatures of 475°C and 575°C. AI3Ti and AlN intermetallic compounds were formed at the interfaces. The sheet resistance of Al films was measured by four-point probe method. Resistance increases for all the annealed films were due to interdiffusion between Al and TiN. The degree of interdiffusion was analyzed by using AES and XRD.

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