Insight on Tricalcium Silicate Hydration and Dissolution Mechanism from Molecular Simulations

Abstract

Hydration of mineral surfaces, a critical process for many technological applications, encompasses multiple coupled chemical reactions and topological changes, challenging both experimental characterization and computational modeling. In this work, we used reactive force field simulations to understand the surface properties, hydration, and dissolution of a model mineral, tricalcium silicate. We show that the computed static quantities, i.e., surface energies and water adsorption energies, do not provide useful insight into predict mineral hydration because they do not account for major structural changes at the interface when dynamic effects are included. Upon hydration, hydrogen atoms from dissociated water molecules penetrate into the crystal, forming a disordered calcium silicate hydrate layer that is similar for most of the surfaces despite wide-ranging static properties. Furthermore, the dynamic picture of hydration reveals the hidden role of surface topology, which can lead to unexpected water tessellation that stabilizes the surface against dissolution. KEYWORDS: dissolution, hydration, molecular dynamics, surface properties, water adsorption, calcium silicate ■ INTRODUCTIONThe hydration and dissolution of minerals is of crucial importance for a broad range of natural and synthetic phenomena: from the stability of minerals and rocks in watersheds and aquifers, 1 to hydrogen production and other heterogeneous catalytic reactions, 2,3 to the production, utilization, and ultimate degradation of building materials, 4 and to the durability of biomaterials, 5 to name only a few examples. The key properties at play during dissolution are controlled by interfacial reactions between water molecules and the solid surfaces, which can be probed experimentally via techniques such as AFM, vertical scanning interferometry (VSI), and the study of isotope exchange or solute fluxes to provide general information regarding the reaction rates or qualitative information about the formation of steps, pitches, and so on. 6 However, in many applications, much more control over the hydration and dissolution is desired, such as the ability to moderate the rate 7 or preferentially favor the dissolution of one crystal facet over other.8 To achieve such control, a deeper understanding of the molecular mechanisms governing hydration and dissolution is necessary.In this work, we use atomic-scale simulations to study the hydration of a calcium orthosilicate. We take a multistep approach, which is critical to piece together the relevant physical processes underlying hydration and dissolution. First, we analyze the surface energies and water molecule adsorption, extending beyond traditional approaches in order to obtain a more accurate picture of these properties. Next, we compare these surface properties with the results obtained from simulating a realistic hydration process over a period of 2 ns. We discuss the differences between the static and dynamic pictures and show that topological changes render the properties of the f...

Water's behaviour on Ca-rich tricalcium silicate surfaces for various degrees of hydration: A molecular dynamics investigation

“…The values computed, in the range of 1.14 to 1.55 J/m 2 (1.32 J/m 2 in average) are in good agreement with first results obtained with the same force field, and almost match for the (040) plane (1.31 ± 0.04 J/m 2 against 1324 ± 25 mJ/m 2 )[26]. Generally, they are in good agreement with other previous atomistic simulation studies[24,48]. On the same basis, the interfacial energy is computed by subtracting the energy of the C 3 S slab system E C3S and the energy…”

“…The M 3 polymorph does not exist in pure C 3 S and its stabilization is favoured by high MgO contents [42]. Despite this fact and as a first attempt to understand the features C 3 S/water interface, the 2D periodic models used here were built from the pure M 3 crystal structure [43], which has been largely used in atomistic simulations [24,26,44] (see Fig. 1).…”

“…1). Because of the Cm space group of the selected model, the only symmetric plane is (010), for which Tasker type 2 surfaces with no net dipole can be built without the need for reconstruction [24,45] . For the other planes, in order to minimize the dipole moment at the surface, the ions of the cleaved layer were equally distributed on both side of the slab.…”

“…In recent years, many scientific contributions of atomistic simulations of calcium silicate hydrate (C-S-H) [6][7][8][9][10][11][12][13][14], tobermorite [15,16], portlandite (Ca(OH) 2 ) [17][18][19][20][21] and clinker constituents [22][23][24][25][26][27][28][29] were carried out, giving rise to a force field database [30]. Although many studies are focused on the main hydration product (C-S-H), an insight on the early hydration of C 3 S was performed both with reactive [24], and classical MD [31], and is crucial to explain the mechanisms responsible for the induction period. To our knowledge, two classical force fields; namely INTERFACE FF (IFF) [32], and ClayFF [33], and the reactive force field ReaxFF [34] were already used to simulate the interface between C 3 S and water at the atomic scale.…”

“…To our knowledge, two classical force fields; namely INTERFACE FF (IFF) [32], and ClayFF [33], and the reactive force field ReaxFF [34] were already used to simulate the interface between C 3 S and water at the atomic scale. Despite its ability to capture bond breaks occurring during the hydration process such as dissociation of water, protonation of superficial anions, as well as the proton hopping phenomenon [24], the ReaxFF is limited by its computational cost and its charge equilibration M A N U S C R I P T…”