Atomic theories of phyllosilicates: Quantum chemistry, statistical mechanics, electrostatic theory, and crystal chemistry

Bleam, William F.

doi:10.1029/92rg01823

Cited by 87 publications

(65 citation statements)

References 160 publications

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“…The present results are to be compared to the results obtained by the groups of Skipper and Sposito that were reviewed by Chang et al 16 The calculated d(001) spacing of the monolayer hydrates in these studies was close to 12 Å using a constant stress in the c-axis direction of 10 5 Pa, while the interlayer water densities are in the range of 400-500 kg/m 3 . Note that in these studies Wyoming-type montmorillonite with a lower charge ͑xϭ0.75͒ containing both tetrahedral and octahedral substitution sites were generally used.…”

Section: Resultsmentioning

confidence: 86%

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Adsorption isotherms of water in Li–, Na–, and K–montmorillonite by molecular simulation

Hensen

Tambach

Bliek

et al. 2001

The Journal of Chemical Physics

107

133

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A biased Monte Carlo method for the insertion of water in dense clay-water systems is presented. The use of this algorithm results in a considerable increase of the success rate of insertion attempts. It allows us to compute water adsorption isotherms up to high water densities, where the conventional Monte Carlo scheme fails. The isotherms were calculated by a combination of molecular dynamics and grand-canonical Monte Carlo simulation for Li-, Na-, and Kmontmorillonite at a fixed d(001) spacing of 12.0 Å. At low water pressure, the degree of clay hydration is governed by the type of counterion, Li-montmorillonite having the highest water content. Hydrogen bonding between water molecules is absent. Li ϩ and Na ϩ are small enough to be organized in two layers close to the clay mineral surfaces, whereas K ϩ is mainly located in the midplane. In both cases, the water molecules primarily reside in the midplane of the interlayer. Increasing the water pressure leads to water adsorption at higher energy sites closer to the surface, i.e., coordinating to the structural OH groups in the hexagonal cavities. A hydrogen bond network is formed in the clay interlayer. This points to water condensation and leads to a sharp increase in the clay water content.

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Section: Resultsmentioning

confidence: 86%

“…Reviews on such molecular simulations are available. 16,17 In most clay applications, the system is open with respect to water transport. An example is the measurement of water adsorption isotherms in clay minerals.…”

Section: Introductionmentioning

confidence: 99%

Adsorption isotherms of water in Li–, Na–, and K–montmorillonite by molecular simulation

Hensen

Tambach

Bliek

et al. 2001

The Journal of Chemical Physics

107

133

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“…The surfaces of kaolinite can be grouped into basal surfaces and edge surfaces (White and Zelazny, 1988;Bleam, 1993). Kaolinite has two types of basal surfaces, i.e.…”

Section: Introductionmentioning

confidence: 99%

Atomic scale structures of interfaces between kaolinite edges and water

Liu

Wang

et al. 2012

Geochimica et Cosmochimica Acta

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This paper reports the atomic scale structures of kaolinite edge surfaces in contact with water. The commonly occurring edge surfaces are investigated (i.e. (0 1 0) and (1 1 0)) by using first principles molecular dynamics (FPMD) technique. For (1 1 0)-type edge surface, there are two different surface topologies (denoted as (1 1 0)-1 and (1 1 0)-2) and they are considered separately.By using constrained FPMD technique, the free-energy changes for the leaving processes of water ligands of O-sheet Al cations have been calculated and thus, the coordination states of those Al cations are determined. The results show that for (0 1 0) and (1 1 0)-2 edges, both the 5 and 6-fold coordination states are possible whereas for (1 1 0)-1 edges, only the 6-fold states are stable. Based on the analyses of H-bonding structures at the interfaces, the surface acid/base reactive sites are illustrated. (1) T-sheet groups are "Si-OH, behaving as both proton donors and acceptors. (2) Bridging oxygen At (0 1 0) and (1 1 0)-2 edges, these sites are inaccessible from the water and thus, they are not effective reactive sites. At (1 1 0)-1 edges, the bridging oxygen atoms are proton accepting sites. (3) O-sheet groups At (0 1 0) and (1 1 0)-2 edges, for 6-fold Al cases, the active surface groups are "Al-(OH)(OH 2 ) and for the 5-fold Al cases, the active surface groups are "Al-(OH). At (1 1 0)-1 edges, the active site is "Al-OH 2 . This study provides fundamental structural properties for understanding the interface chemistry of widely occurring 1:1 type phyllosilicates.

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“…The crystal structure of 2:1-type phyllosilicates is formed by stacking "T-O-T" layers along the c-axis; these layers are composed of an octahedral sheet (O-sheet) between two tetrahedral sheets (T-sheet) (Brindley and Brown, 1980;Bleam, 1993). Because of their layered structures, the surfaces of phyllosilicates are commonly classified as basal surfaces (i.e., (0 0 1)) and edge surfaces or broken surfaces (such as (0 1 0), (1 1 0)) (White and Zelazny, 1988;Bleam, 1993). Extensive studies have detailed the structures and properties of basal surfaces.…”

Section: Introductionmentioning

confidence: 99%

Atomic-scale structures of interfaces between phyllosilicate edges and water

Liu

Meijer

et al. 2012

Geochimica et Cosmochimica Acta

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We report first-principles molecular dynamics (FPMD) studies on the structures of interfaces between phyllosilicate edges and water. Using FPMD, the substrates and solvents are simulated at the same first-principles level, and the thermal motions are sampled via molecular dynamics. Both the neutral and charged silicate frameworks are considered, and for charged cases, the octahedral (Mg for Al) and tetrahedral (Al for Si) substitutions are taken into account. For all frameworks, we focus on the commonly occurring (0 1 0)-and (1 1 0)-type edge surfaces.With constrained FPMD, we calculated the free energy of the leaving processes of coordinated water of octahedral cations; therefore, the coordination states of those edge cations are determined. For (0 1 0)-type edges, both the 5-and 6-fold coordination states of Al are stable and occur with a similar probability, whereas only the 5-fold coordination is stable for Mg cations. For (1 1 0)-type edges, only the 6-fold states of Al cations are stable. However, for Mg cations, both coordination states are stable. In the 5-fold case, the solvent water molecules form H-bonds with the bridging oxygen atoms (i.e., "MgAOASi"). The free energy results indicate that there should be a considerable number of 5-fold coordinated octahedral sites (i.e., "MgAOH/ "AlAOH) at the interfaces. The interfacial structures and acid/base groups were determined by detailed H-bonding analyses.(1) Bridging oxygen sites. For (0 1 0) edges, the bridging oxygen atoms are not effective proton-accepting sites because they are inaccessible from the solvent. For (1 1 0) edges, the oxygen atoms of neutral and octahedrally substituted frameworks (i.e., "MAOASi" for M@Al/Mg) are proton-accepting sites. For T-sheet substituted cases, the bridging oxygen site becomes a proton-donating group (i.e., "AlAOHASi") through the capture of a proton. (2) T-sheet groups. All T-sheet edge groups are "MAOH (M@Si/Al) and act as both proton donors and acceptors. (3)O-sheet groups. For (0 1 0) edges with 6-fold Al, the active surface groups include "AlA(OH)(H 2 O) and "AlA(OH) 2 , whereas for Mg cations, the edge group is "MgA(OH 2 ) 2 . For 5-fold coordination, the active groups are "AlAOH. At (1 1 0) edges, proton-donating sites include "AlAOH, "AlAOH 2 and "MgAOH 2 groups. Overall, our results reveal the significant effects of isomorphic substitutions on the interfacial structures, and the models provide a molecular-level basis for understanding relevant interfacial processes.

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Atomic theories of phyllosilicates: Quantum chemistry, statistical mechanics, electrostatic theory, and crystal chemistry

Cited by 87 publications

References 160 publications

Adsorption isotherms of water in Li–, Na–, and K–montmorillonite by molecular simulation

Adsorption isotherms of water in Li–, Na–, and K–montmorillonite by molecular simulation

Atomic scale structures of interfaces between kaolinite edges and water

Atomic-scale structures of interfaces between phyllosilicate edges and water

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