Investigation of the role of alkali cation in early stage of oligomerization in silicate fluids: a molecular dynamics study

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Investigation of the role of alkali cation in early stage of oligomerization in silicate fluids: a molecular dynamics

study

Amaury Coste, Olivier Diat, Arnaud Poulesquen, Jean-François Dufrêche, Magali Duvail

To cite this version:

Amaury Coste, Olivier Diat, Arnaud Poulesquen, Jean-François Dufrêche, Magali Duvail. Investiga-tion of the role of alkali caInvestiga-tion in early stage of oligomerizaInvestiga-tion in silicate fluids: a molecular dynamics study. 7th EuCheMS Chemistry Congress, Aug 2018, Liverpool, United Kingdom. �hal-02142629�

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220 240 260 280 300

Number of Si inside the aggregate

0 50 100 150 200 count MD profile Gaussian fit Lorentzian fit µ=257 σ = 8.2 5 6 7 8 9 10 11 12 13 10-3 10-2 10-1 10-0 Insolubility Domain SiO₂ (amorph) Monomeric solution

H₄SiO₄ H₃SiO₄- H₂SiO₄2-

Olig ome ric so lutio n mo l kg -1 Si pH

Investigation of the role of alkali cation in early stage of

oligomerization in silicate fluids: a molecular dynamics

study

amaury.coste @cea.fr

Context

This work was made possible thanks to the financial support of the ANR DYNAMISTE (ANR-15-CE07-0013-01) and high performance computing facilities of TGCC/CCRT and the computing center of CEA Marcoule.

Amaury Coste

a

_{, Olivier Diat}

a

_{, Arnaud Poulesquen}

b

_{, Jean-François Dufrêche}

a

_{and Magali Duvail}

a

a_{Institute for Separation Chemistry in Marcoule (ICSM), UMR 5257 CEA – Université Montpellier - CNRS - ENSCM, BP 17171, F-30207 Bagnols-sur-Cèze}

b_{CEA, Nuclear Energy Division, Research DE2D (SEAD, LCBC) BP 17171, F-30207 Bagnols-sur-Cèze}

§

Solutions of activation (= alkali media) of alumino-silicate are environmentally friendly and considered as green chemistry (used for ground stabilization, painting….)

§

The formulation is complex since the parameters are various and numerous

Conclusions and Outlooks

§

Understanding the ion-ion interactions for the oligomerization process where the nature and concentration of alkali drives the final properties of the gel [1]

§

Molecular dynamics is a useful tool to fill the gap between theoretical and experimental studies

§

Molecular dynamics allows the calculation of the structural and dynamical properties of the solutes in solution

§

Effect of water, alkali and hydroxide are explicitly taking into account

[1] L. Provis et al., Ind. Eng. Chem. Res. 2005, 44, 8899

[2] C. T. Knight and S. D. Kinrade, Silicon in Agriculture, Elsevier,

2001, vol. 8, chap. 4

[3] D.A. Case et al., Computat. Chem., 2005, 26, 1668 [4] A. Coste et al., J. Chem. Phys., submitted (2018)

Ground stabilization on building site (Wöllner GmbH&Co.KG)

§  Structure of the solution depends on the oligomer composition and nature:

-  Spontaneous aggregation of dimers in solution: aggregates composed of silicates and Na+

-  Dimers Si₂O₃(OH)₄2- interact strongly with Na+

-  Monomers SiO(OH)₃-: small aggregates, and destabilize the aggregation (entropic effect)

§  Similar behaviours of Na+: “buffer media” with the hydroxide anions

§  MD simulations of “real” solutions:

-  Different [Si]/[Na+] ratios with respect to NMR experiments

-  Influence of the alkali nature on the aggregation

n Si(OH)₄+ n OH- _{= SiO(OH)} 3- SiO₂(OH)₂2- Si₂O₂(OH)₅ Si₂O₃(OH)₄2- Si₃O₅(OH)₅3- Si₄O₈(OH)₄4- etc…

Method

§  Molecular dynamics simulations using explicit

polarization with AMBER14 [3]

Classical Molecular Dynamics (MD)

SiO(OH)₃- _Si 2O2(OH)5- Si2O3(OH)4 2-anionic fragment neutral fragment §  Development of a polarizable silicate force

field for describing all the silicate oligomers by assembling neutral and anionic fragment (10 types of atom)

§  MD simulations focused on 3 species:

§  Calculation of I(q) from radial distribution functions

§  Theoretical I(q) directly comparable to experimental one

§  Efficient method for describing alkali media [4] è study

of silicate oligomers in such media 1 10

q (Å-1) 0 1×104 2×104 3×104 4×104 5×104 6×104 7×104 I(q) + offset MD Experiments 9.66 mol L-1 5.0 mol L-1 3.0 mol L-1 1.0 mol L-1 0.5 mol L-1 pure water

X ray scattering intensity from MD simulation

I(q) =

X

↵

X

f

_↵

(q)f (q)

p

N

_↵

N S

_↵

(q)

S

_↵

(q) =

_↵

+ p⇢

_↵

⇢ FT

_3D

(g

_↵

(r)

1)

Concentrated aqueous solutions of NaOH 0.01 0.1 1 10 Q / Å-1 0 1 2 3 4 5 6 7 I(Q)/I 0 SiO(OH)₃ -Si₂O₂(OH)₅ -Si₂O₃(OH)₄ 2-mixture of dimers mixture of all

box size cut-off

SAXS WAXS SiO(OH)₃- Si₂O₂(OH)₅- Si₂O₃(OH)₄ 2-mixture of dimers mixture of dimers and monomers

Silicate in NaOH concentrated media

§  Same structure for Q > 1 Å-1

§  Rise for Q < 0.4 Å-1

(aggregation)

§  Presence of monomers

decreases the I(Q) at small angles

Mixtures of oligomers

300 Na+ 75 Si₂O₂(OH)₅- 75 Si₂O₃(OH)₄2- 75 OH- 300 Na+ 37 Si₂O₂(OH)₅- 37 Si₂O₃(OH)₄2- 152 SiO(OH)₃- 37 OH- Mixture of dimers and monomers

Scattering intensities from MD

300 Na+ 150 Si₂O₂(OH)₅- 150 OH- 300 Na+ 150 Si₂O₃(OH)₄2- 300 Na+ 300 SiO(OH)₃- 65 Å

Pure oligomer solutions

_[Si]/[Na+_{] = 1}

§  Monomers: “homogeneous” media

§  Dimers: spontaneous aggregation

0 4 8 12 16 20 24 28 32 60 50 40 30 20 10 2 40 10 1 time (ns) N umb er o f Si in si de the ag gre ga te

Evolution of the silicate oligomers without considering the main aggregate Percentage 0 5 10 15 20 25 30 35 40 60 50 40 30 20 10 2 40 10 1 time (ns) N umb er o f Si in si de the ag gre ga te Percentage §  [Na+]_freeconstant

§  Provide a “buffer media”

Mixture of dimers 0 5 10 15 20 25 30 35 40 time / ns 0 20 40 60 80 100 Percentage 0 10 20 30 40 50 time / ns 0 20 40 60 80 100 Percentage

Si inside the main aggregate Na+ free 0 10 20 30 40 50 time / ns 0 20 40 60 80 100 Percentage

Si inside the main aggregate Na+ free

Stability diagram for soluble silicates at 298 K [2]

Acknowledgements