Dissolution of Portlandite in Pure Water: Part 1 Molecular Dynamics (MD) Approach.

Khondakar Salah Uddin,Mohammadreza Izadifar,Neven Ukrainczyk,Bernhard Middendorf,Eduardus Koenders

doi:10.3390/ma15041404

Khondakar Salah Uddin, Mohammadreza Izadifar + Show 3 more

Open Access

https://doi.org/10.3390/ma15041404

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Journal: Materials	Publication Date: Feb 14, 2022
Citations: 11	License type: CC BY 4.0

Affiliation: Technical University of Darmstadt, University of Kassel

Abstract

The current contribution proposes a multi-scale bridging modeling approach for the dissolution of crystals to connect the atomistic scale to the (sub-) micro-scale. This is demonstrated in the example of dissolution of portlandite, as a relatively simple benchmarking example for cementitious materials. Moreover, dissolution kinetics is also important for other industrial processes, e.g., acid gas absorption and pH control. In this work, the biased molecular dynamics (metadynamics) coupled with reactive force field is employed to calculate the reaction path as a free energy surface of calcium dissolution at 298 K in water from the different crystal facets of portlandite. It is also explained why the reactivity of the (010), (100), and (10) crystal facet is higher compared to the (001) facet. In addition, the influence of neighboring Ca crystal sites arrangements on the atomistic dissolution rates is explained as necessary scenarios for the upscaling. The calculated rate constants of all atomistic reaction scenarios provided an input catalog ready to be used in an upscaling kinetic Monte Carlo (KMC) approach.

Highlights

The crystal dissolution kinetics are of wide industrial importance, upscaling of fundamental atomistic modeling approaches still presents a major scientific challenge
In order to understand the interaction between bulk water and Portlandite facet, the dynamics of the system have been followed for 600 picoseconds at 298 K and standard ambient pressure (101.325 kPa)
The primary objective of this research was to achieve a deeper understanding of the dissolution mechanism of portlandite; different crystal faces were considered

Summary

Introduction

The crystal dissolution (and precipitation) kinetics are of wide industrial importance, upscaling of fundamental atomistic modeling approaches still presents a major scientific challenge. The dissolution (and precipitation) of minerals phases is governed by complex physico-chemical processes starting at the atomistic scale, where the individual crystal building units (atoms or molecules) at the solid–liquid interface are dissolved and transported into the bulk solution. Molecular dynamics (MD) computations provide a powerful way for revealing how the atomistic processes of basic building units of the crystals affect the dissolution kinetics. The dissolution of portlandite (CH, Ca(OH)2 ), was selected as a relatively simple crystal representative for the dissolution/precipitation process of other more complex cementitious phases (e.g., cement clinker phases) in general. Portlandite is a key by-product of cement hydration in the amount of approximately 27% in volume, which protects the steel reinforcement from corrosion by maintaining a higher pH value [1]

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