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Influence of structural Al and Si vacancies on the interaction of kaolinite basal surfaces with alkali cations: A molecular dynamics study.

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Title: Influence of structural Al and Si vacancies on the interaction of kaolinite basal surfaces with alkali cations: A molecular dynamics study.
Authors: Naderi Khorshidi, Zeinab1, Tan, Xiaoli1, Liu, Qi1, Choi, Phillip1 phillip.choi@ualberta.ca
Source: Computational Materials Science. Dec2017, Vol. 140, p267-274. 8p.
Subjects: Vacancy-dislocation interactions, Kaolinite, Surface analysis, Aluminum spectra, Silicon spectra, Point defects
Abstract: Point defects, particularly vacancies, exist abundantly in the structure of a variety of clay minerals (e.g., kaolinite). Such defects significantly alter the physical/chemical characteristics of the minerals. Dissolution of kaolinite in an alkali medium is a critical step in the geopolymerization process and it determines the properties of the final product. In this work, a series of molecular dynamics (MD) simulations were carried out in the isothermal-isobaric (NPT) ensemble at 298 K and 1 atm to study the influence of structural vacancies (Al and Si vacancies in particular) on the interaction/dissolution of the two basal surfaces of kaolinite (partially deprotonated octahedral and tetrahedral surfaces) exposed to alkali media. Two different alkali media were used. One contained sodium cation (Na + ) only while the other potassium cation (K + ) and their concentrations were 3 M and 5 M. The MD results showed that regardless of the type of cation and cation concentration, Al vacancies on the octahedral surface promoted the dissolution of Al into the solution compared to the surface without Al vacancies. However, there existed a vacancy concentration (2 Al vacancies per 576 Al atoms) at which the dissolution amount was the maximum and above which the dissolution decreased with increasing Al vacancy concentration. The presence of Si vacancies in the tetrahedral surface did not show significant effect on the dissociation of Si. Radial distribution function (RDF) analyses indicated that the degree of crystallinity of the octahedral surface decreased as the number of Al vacancies increased but this was not the case for the tetrahedral surface. [ABSTRACT FROM AUTHOR]
Copyright of Computational Materials Science is the property of Elsevier B.V. and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
Database: Engineering Source
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DbLabel: Engineering Source
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  Data: Influence of structural Al and Si vacancies on the interaction of kaolinite basal surfaces with alkali cations: A molecular dynamics study.
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  Data: <searchLink fieldCode="AR" term="%22Naderi+Khorshidi%2C+Zeinab%22">Naderi Khorshidi, Zeinab</searchLink><relatesTo>1</relatesTo><br /><searchLink fieldCode="AR" term="%22Tan%2C+Xiaoli%22">Tan, Xiaoli</searchLink><relatesTo>1</relatesTo><br /><searchLink fieldCode="AR" term="%22Liu%2C+Qi%22">Liu, Qi</searchLink><relatesTo>1</relatesTo><br /><searchLink fieldCode="AR" term="%22Choi%2C+Phillip%22">Choi, Phillip</searchLink><relatesTo>1</relatesTo><i> phillip.choi@ualberta.ca</i>
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  Data: <searchLink fieldCode="JN" term="%22Computational+Materials+Science%22">Computational Materials Science</searchLink>. Dec2017, Vol. 140, p267-274. 8p.
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  Data: <searchLink fieldCode="DE" term="%22Vacancy-dislocation+interactions%22">Vacancy-dislocation interactions</searchLink><br /><searchLink fieldCode="DE" term="%22Kaolinite%22">Kaolinite</searchLink><br /><searchLink fieldCode="DE" term="%22Surface+analysis%22">Surface analysis</searchLink><br /><searchLink fieldCode="DE" term="%22Aluminum+spectra%22">Aluminum spectra</searchLink><br /><searchLink fieldCode="DE" term="%22Silicon+spectra%22">Silicon spectra</searchLink><br /><searchLink fieldCode="DE" term="%22Point+defects%22">Point defects</searchLink>
– Name: Abstract
  Label: Abstract
  Group: Ab
  Data: Point defects, particularly vacancies, exist abundantly in the structure of a variety of clay minerals (e.g., kaolinite). Such defects significantly alter the physical/chemical characteristics of the minerals. Dissolution of kaolinite in an alkali medium is a critical step in the geopolymerization process and it determines the properties of the final product. In this work, a series of molecular dynamics (MD) simulations were carried out in the isothermal-isobaric (NPT) ensemble at 298 K and 1 atm to study the influence of structural vacancies (Al and Si vacancies in particular) on the interaction/dissolution of the two basal surfaces of kaolinite (partially deprotonated octahedral and tetrahedral surfaces) exposed to alkali media. Two different alkali media were used. One contained sodium cation (Na + ) only while the other potassium cation (K + ) and their concentrations were 3 M and 5 M. The MD results showed that regardless of the type of cation and cation concentration, Al vacancies on the octahedral surface promoted the dissolution of Al into the solution compared to the surface without Al vacancies. However, there existed a vacancy concentration (2 Al vacancies per 576 Al atoms) at which the dissolution amount was the maximum and above which the dissolution decreased with increasing Al vacancy concentration. The presence of Si vacancies in the tetrahedral surface did not show significant effect on the dissociation of Si. Radial distribution function (RDF) analyses indicated that the degree of crystallinity of the octahedral surface decreased as the number of Al vacancies increased but this was not the case for the tetrahedral surface. [ABSTRACT FROM AUTHOR]
– Name: AbstractSuppliedCopyright
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  Data: <i>Copyright of Computational Materials Science is the property of Elsevier B.V. and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.</i> (Copyright applies to all Abstracts.)
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        Value: 10.1016/j.commatsci.2017.09.004
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      – Code: eng
        Text: English
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        PageCount: 8
        StartPage: 267
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      – SubjectFull: Vacancy-dislocation interactions
        Type: general
      – SubjectFull: Kaolinite
        Type: general
      – SubjectFull: Surface analysis
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      – SubjectFull: Aluminum spectra
        Type: general
      – SubjectFull: Silicon spectra
        Type: general
      – SubjectFull: Point defects
        Type: general
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      – TitleFull: Influence of structural Al and Si vacancies on the interaction of kaolinite basal surfaces with alkali cations: A molecular dynamics study.
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            NameFull: Naderi Khorshidi, Zeinab
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            NameFull: Tan, Xiaoli
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            NameFull: Liu, Qi
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            – D: 01
              M: 12
              Text: Dec2017
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              Y: 2017
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