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.

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>

The Impact of Adjuvants on Herbicide Antagonism

1989 ◽  
Vol 3 (2) ◽  
pp. 227-231 ◽  
Author(s):  
Donald Penner
Keyword(s):  
Ammonium Sulfate ◽  
Plant Species ◽  
Environmental Conditions ◽  
Alkaline Earth ◽  
Postemergence Herbicides ◽  
The Impact ◽  
Alkaline Earth Cations

Adjuvants are used to improve spray delivery, to increase spray retention on weed foliage, and to enhance foliar penetration by postemergence herbicides for increased herbicide efficacy. Numerous factors govern adjuvant efficacy, including the specific herbicide, plant species, and environmental conditions. Adding superior surfactants as adjuvants to a sethoxydim tank mix with Na-bentazon may overcome the Na-bentazon antagonsim of sethoxydim activity by facilitating increased sethoxydim absorption and by masking the antagonism similar to increasing the sethoxydim rate. Herbicides such as Na-bentazon contribute alkaline or alkaline earth cations that can form salts of a weakly acidic herbicide such as sethoxydim that are not absorbed readily by the plant. Adding abundant ammonium from ammonium sulfate or other sources may prevent and/or may overcome this antagonism.

Others' participation rate influences an individual's charitable behavior: Others' similarity as a moderator

2017 ◽  
Vol 45 (10) ◽  
pp. 1607-1618 ◽  
Author(s):  
Seung Yun Lee ◽  
Sunho Jung ◽  
Sangdo Oh ◽  
Seong Hoon Park
Keyword(s):  
Undergraduate Students ◽  
Participation Rate ◽  
High Rate ◽  
Charitable Behavior ◽  
High Participation ◽  
Negative Effect ◽  
The Impact ◽  
And Diffusion ◽  
High Participation Rate ◽  
Diffusion Of Responsibility

We proposed that a moderator, others' similarity, would determine the impact of high participation rates of others on an individual's charitable behavior, and aimed to show that this moderator would work through the diffusion of responsibility motive. Participants (N = 152 undergraduate students) completed measures of charitable behavior and diffusion of responsibility, after being assigned to 1 of 2 conditions where a set percentage of other students (manipulated as either similar undergraduate students or dissimilar graduate students) were stated to have already donated to a charitable campaign (high contribution condition = 70% participation, low contribution condition = 30% participation). Our results showed that the high participation rate of others increased an individual's charitable behavior when the others in question were similar to that individual, but not when the others were dissimilar. In addition, the high rate of participation by others increased the diffusion of responsibility motive when the others in question were dissimilar to that individual, leading to a negative effect on that individual's charitable behavior.

scholarly journals Cellulose Nanofibrils/Xyloglucan Bio-Based Aerogels with Shape Recovery

Gels ◽  
2021 ◽  
Vol 7 (1) ◽  
pp. 5
Author(s):  
Samuel Mandin ◽  
Samuel Moreau ◽  
Malika Talantikite ◽  
Bruno Novalès ◽  
Jean-Eudes Maigret ◽  
...  
Keyword(s):  
Water Absorption ◽  
Shape Recovery ◽  
Cellulose Nanofibrils ◽  
High Water ◽  
Absorption Capacity ◽  
Absorption Properties ◽  
High Affinity ◽  
High Water Absorption ◽  
Freezing Procedure ◽  
The Impact

Bio-based aerogels containing cellulose nanofibrils (CNFs) are promising materials due to the inherent physical properties of CNF. The high affinity of cellulose to plant hemicelluloses (xyloglucan, xylan, pectin) is also an opportunity to develop biomaterials with new properties. Here, we prepared aerogels from gelled dispersions of CNFs and xyloglucan (XG) at different ratios by using a freeze-casting procedure in unidirectional (UD) and non-directional (ND) manners. As showed by rheology analysis, CNF and CNF/XG dispersions behave as true gels. We investigated the impact of the freezing procedure and the gel’s composition on the microstructure and the water absorption properties. The introduction of XG greatly affects the microstructure of the aerogel from lamellar to cellular morphology. Bio-based aerogels showed high water absorption capacity with shape recovery after compression. The relation between morphology and aerogel compositions is discussed.

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