Carbonation of wollastonite(001) competing hydration: microscopic insights from ion spectroscopy and density functional theory.

In this paper, we report about the influence of the chemical potential of water on the carbonation reaction of wollastonite (CaSiO3) as a model surface of cement and concrete. Total energy calculations based on density functional theory combined with kinetic barrier predictions based on nudge elastic band method show that the exposure of the water-free wollastonite surface to CO2 results in a barrier-less carbonation. CO2 reacts with the surface oxygen and forms carbonate (CO3(2-)) complexes together with a major reconstruction of the surface. The reaction comes to a standstill after one carbonate monolayer has been formed. In case one water monolayer is covering the wollastonite surface, the carbonation is no more barrier-less, yet ending in a localized monolayer. Covered with multilayers of water, the thermodynamic ground state of the wollastonite completely changes due to a metal-proton exchange reaction (also called early stage hydration) and Ca(2+) ions are partially removed from solid phase into the H2O/wollastonite interface. Mobile Ca(2+) reacts again with CO2 and forms carbonate complexes, ending in a delocalized layer. By means of high-resolution time-of-flight secondary-ion mass spectrometry images, we confirm that hydration can lead to a partially delocalization of Ca(2+) ions on wollastonite surfaces. Finally, we evaluate the impact of our model surface results by the meaning of low-energy ion-scattering spectroscopy combined with careful discussion about the competing reactions of carbonation vs hydration.

[1]  A. Funk,et al.  DFT Study on the Effect of Water on the Carbonation of Portlandite , 2013 .

[2]  G. Kresse,et al.  Ab initio molecular dynamics for liquid metals. , 1993 .

[3]  Kresse,et al.  Efficient iterative schemes for ab initio total-energy calculations using a plane-wave basis set. , 1996, Physical review. B, Condensed matter.

[4]  François Renard,et al.  In situ kinetic measurements of gas–solid carbonation of Ca(OH)2 by using an infrared microscope coupled to a reaction cell , 2010 .

[5]  J. Yarwood,et al.  Structural Features of C–S–H(I) and Its Carbonation in Air—A Raman Spectroscopic Study. Part II: Carbonated Phases , 2007 .

[6]  K. Burke,et al.  Generalized Gradient Approximation Made Simple [Phys. Rev. Lett. 77, 3865 (1996)] , 1997 .

[7]  E. Oelkers,et al.  The surface chemistry of multi-oxide silicates , 2009 .

[8]  G. Grundmeier,et al.  Toward a microscopic understanding of the calcium–silicate–hydrates/water interface , 2014 .

[9]  A. Nonat,et al.  Formation of the C-S-H Layer during early hydration of tricalcium silicate grains with different sizes. , 2006, The journal of physical chemistry. B.

[10]  E. Lesniewska,et al.  Study of C-S-H growth on C3S surface during its early hydration , 2005 .

[11]  G. Henkelman,et al.  Improved tangent estimate in the nudged elastic band method for finding minimum energy paths and saddle points , 2000 .

[12]  Blöchl,et al.  Improved tetrahedron method for Brillouin-zone integrations. , 1994, Physical review. B, Condensed matter.

[13]  K. Volgmann,et al.  The adsorption of CO2 and CO on Ca and CaO films studied with MIES, UPS and XPS , 2009 .

[14]  J. Grossman,et al.  Understanding and Controlling the Reactivity of the Calcium Silicate phases from First Principles , 2012 .

[15]  G. Kresse,et al.  From ultrasoft pseudopotentials to the projector augmented-wave method , 1999 .

[16]  G. Henkelman,et al.  A climbing image nudged elastic band method for finding saddle points and minimum energy paths , 2000 .

[17]  J. Banfield,et al.  Leaching and reconstruction at the surfaces of dissolving chain-silicate minerals , 1993, Nature.

[18]  W. Schmidt,et al.  Formation of Hydroxyl Groups at Calcium-Silicate-Hydrate (C-S-H): Coexistence of Ca–OH and Si–OH on Wollastonite(001) , 2014 .

[19]  Burke,et al.  Generalized Gradient Approximation Made Simple. , 1996, Physical review letters.