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Surface reconstruction and cleavage of phyllosilicate clay edge by density functional theory
Abstract Phyllosilicate materials (e.g., smectite) have been proposed to act as a waste barrier within long-term deep geological repositories. Aside from longevity, these clay materials must also limit the mobility of radionuclides, which is achieved through intermolecular interaction involving clay basal planes and edge surfaces. We aim to contribute to the fundamental knowledge of clay edges by investigating surface reconstruction in a dehydrated context. Using density functional theory, surface reconstruction, charge redistribution, and formation energies have been explored for pyrophyllite edges resulting from thirteen terminations. Three primary reconstruction mechanisms were identified: (1) the displacement of Al into the tetrahedral layer, (2) proton shift, and (3) sub-surface reconstruction involving sub-surface -OH or apical O and surface Si. Reduction in overall relative bond deficiency and charge redistribution to becoming more bulk-like were found to be the main driving force for reconstruction. Formation energies were also determined with dispersion correction for dehydrated and hydrated surfaces. The presence of water terminating agents reduced energetic costs by approximately one order of magnitude and the inclusion of dispersion correction resulted in indistinguishable formation energies between different hydrated surfaces. Linear regression models were also explored to predict surface formation energies based on relative bond deficiency and charge. These models were able to identify the key contributions to the surface energy; however, due to the small dataset they were not found to be predictive.
Highlights DFT calculations on dehydrated pyrophyllite edges fundamentally study surface reconstruction. Inherent pyrophyllite edge surface reconstruction occurs via three major mechanisms. Relative bond deficiency and charge distribution drive edge reconstruction in phyllosilicate clays. Machine learning model can be used to identify key contributors to surface formation. Presence of water terminating agent lowers surface formation energy by ∼1 order magnitude.
Surface reconstruction and cleavage of phyllosilicate clay edge by density functional theory
Abstract Phyllosilicate materials (e.g., smectite) have been proposed to act as a waste barrier within long-term deep geological repositories. Aside from longevity, these clay materials must also limit the mobility of radionuclides, which is achieved through intermolecular interaction involving clay basal planes and edge surfaces. We aim to contribute to the fundamental knowledge of clay edges by investigating surface reconstruction in a dehydrated context. Using density functional theory, surface reconstruction, charge redistribution, and formation energies have been explored for pyrophyllite edges resulting from thirteen terminations. Three primary reconstruction mechanisms were identified: (1) the displacement of Al into the tetrahedral layer, (2) proton shift, and (3) sub-surface reconstruction involving sub-surface -OH or apical O and surface Si. Reduction in overall relative bond deficiency and charge redistribution to becoming more bulk-like were found to be the main driving force for reconstruction. Formation energies were also determined with dispersion correction for dehydrated and hydrated surfaces. The presence of water terminating agents reduced energetic costs by approximately one order of magnitude and the inclusion of dispersion correction resulted in indistinguishable formation energies between different hydrated surfaces. Linear regression models were also explored to predict surface formation energies based on relative bond deficiency and charge. These models were able to identify the key contributions to the surface energy; however, due to the small dataset they were not found to be predictive.
Highlights DFT calculations on dehydrated pyrophyllite edges fundamentally study surface reconstruction. Inherent pyrophyllite edge surface reconstruction occurs via three major mechanisms. Relative bond deficiency and charge distribution drive edge reconstruction in phyllosilicate clays. Machine learning model can be used to identify key contributors to surface formation. Presence of water terminating agent lowers surface formation energy by ∼1 order magnitude.
Surface reconstruction and cleavage of phyllosilicate clay edge by density functional theory
Ta, An T. (author) / Ullberg, R. Seaton (author) / Phillpot, Simon R. (author)
Applied Clay Science ; 246
2023-10-17
Article (Journal)
Electronic Resource
English
METHOD FOR GRINDING A PARTICULATE PHYLLOSILICATE MATERIAL
| European Patent Office | 2015