Doping as a Way To Protect Silicate Chains in Calcium Silicate Hydrates

Dupuis, Romain; Dolado, Jorge S.; Surga, Jose; Ayuela, Andrés

doi:10.1021/acssuschemeng.8b03488

Cited by 26 publications

(21 citation statements)

References 46 publications

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“…More generally, in silicates, different arrangements can be found depending on the chemistry. For instance, in calcium silicate hydrates gels that can be found in cement, the Ca/ Si ratio and the hydration ratio, or Al/Si ratio, are drastically changing the structural and mechanical properties of the gels [42][43][44]. A decondensation of silicate chains by the NaOH solution could reduce the energy barriers necessary to go from one structure to the other.…”

Section: Discussion Decondensationmentioning

confidence: 99%

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Time resolved alkali silicate decondensation by sodium hydroxide solution

et al. 2020

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Silica is by far the chemical compound the most widespread and used around the world: as a raw product in the buildings and roads industry, as concrete, or as a processed product in the manufacture of glass, ceramics or zeolites. In alkali silicate solutions-often used to synthesize those materials-a complex interplay of decondensation and condensation processes leads to the restructuring of silicate clusters at the atomic scale on a short time-scale. We were able to deconvolute these effects by combining time resolved small angle x-ray scattering, nuclear magnetic resonance, and parallel tempering simulations. We investigated the impact of a dilution by pure water or by a sodium hydroxide solution on the speciation and size of the dissolved silicates in solution. Herein, we show that the silicate clusters are not affected by dilution, suggesting that sodium cations protect the silicate clusters from hydrolysis. Decondensation is triggered by hydroxide ions that weaken and break Si-O bonds. Alongside the decondensation, the evolution of the computed protonation state of the silica species indicates a change in the interaction potential. Our results pave the way towards the investigation at the atomic scale of more complex systems implying alkali silicate solutions in condensation process by the addition of calcium or aluminum to synthesize aluminosilicate binders, hydrogels or zeolites.

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Section: Discussion Decondensationmentioning

confidence: 99%

“…The formation of oligomers is a slow process compared to times reachable by MD due to the energy barrier to form Si-O bonds [44,65]. We have used a recent accelerated simulation method which is based on the parallel tempering method (PT, also called replica exchange) [11,27].…”

Section: Brief-parallel Temperingmentioning

confidence: 99%

Time resolved alkali silicate decondensation by sodium hydroxide solution

et al. 2020

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“…Another important issue regarding the use of Portland cement as encapsulating material is that metal ions have been shown to retard the hydration process that yields calcium silicate hydrate (C-S-H) [21]. Regarding the mechanical properties at macroscopic scale, the addition of doping ions to PC has been suggested to alter the bonding strength of the silicate chains of the formed C-S-H, leading to significant reduction of the compressive strength [22].…”

Section: Introductionmentioning

confidence: 99%

Immobilization of (Aqueous) Cations in Low pH M-S-H Cement

et al. 2021

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Incorporation of heavy metal ions in cement hydrates is of great interest for the storage and immobilization of toxic, hazardous, and radioactive wastes using cementitious matrix. Magnesium silicate hydrate (M-S-H) is a low pH alternative cementitious binder to commonly used Portland cement. Low pH cements have been considered as promising matrix for municipal and nuclear waste immobilization in the last decades. It is however crucial to assure that the incorporation of secondary ions is not detrimental for the formation of the hydration products. Herein, we investigate the early stages of formation of M-S-H from electrolyte solutions in presence of a wide range of metal cations (LiI, BaII, CsI, CrIII, FeIII, CoII, NiII, CuI, ZnII, PbII, AlIII). The final solid products obtained after 24 h have been characterized via powder X-ray diffraction (PXRD), attenuated total reflectance-Fourier transformed infrared spectroscopy (FTIR-ATR), elemental analysis via energy-dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HR-TEM). In all the experiments, the main precipitated phase after 24 h was confirmed to be M-S-H with a ratio (total metal/Si) close to one. The obtained M-S-H products showed strong immobilization capacity for the secondary metal cations and can incorporate up to 30% of the total metal content at the early stages of M-S-H formation without significantly delaying the nucleation of the M-S-H. It has been observed that presence of Cr, Co, and Fe in the solution is prolonging the growth period of M-S-H. This is related to a higher average secondary metal/total metal ratio in the precipitated material. Secondary phases that co-precipitate in some of the experiments (Fe, Pb, Ni, and Zn) were also effectively trapped within in the M-S-H matrix. Barium was the only element in which the formation of a secondary carbonate phase isolated from the M-S-H precipitates was detected.

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“…In recent years, the increasingly sophisticated atomistic simulation technology has been gradually applied to the field of complex cement chemistry, − which is supposed to revitalize cement chemistry with insights into the correlation between material properties and electronic structures. For instance, Dharmawardhana et al − demonstrated the contributions of different interatomic bonding structures to the mechanical properties of cement minerals as well as the cement hydrates.…”

Section: Introductionmentioning

confidence: 99%

Predicting Hydration Reactivity of Cu-Doped Clinker Crystals by Capturing Electronic Structure Modification

Tao

Zhang

et al. 2019

ACS Sustainable Chem. Eng.

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Chemical doping is a promising scheme for sustainable development of green and economical cement manufacturing related to global energy and environmental concerns. Understanding and controlling doping effect on reactive cement components is the prerequisite. This study aims to propose effective theoretical methods to reveal the correlation between hydration reactivity of doped clinker crystals and their electronic structures. Four dominant Portland cement clinker phases with copper doping are comparatively investigated by the state-of-the-art ab initio calculation. It finds that Cu ions doped in silicate and aluminate phases shift the nucleophilic reactive sites from Ca-centered regions to defect sites by decreasing the effective charges of Ca ions, which accounts for the hydration retardation of these phases. Exceptionally, the reactive sites in ferrite phase are scarcely changed by Cu doping due to the intense band-edge localization of Fe 3d state, which implies the relatively lesser influence on hydration reactivity. The corresponding experiments of the ion release rate of clinker phases during early hydration process as captured by the conductivity meter and inductively coupled plasma-optical emission spectrum strongly support our computational results. Our theoretical calculations provide a powerful method to predict the early hydration reactivity of clinker minerals and enrich the understanding of early hydration characteristics and its variations.

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Doping as a Way To Protect Silicate Chains in Calcium Silicate Hydrates

Cited by 26 publications

References 46 publications

Time resolved alkali silicate decondensation by sodium hydroxide solution

Time resolved alkali silicate decondensation by sodium hydroxide solution

Immobilization of (Aqueous) Cations in Low pH M-S-H Cement

Predicting Hydration Reactivity of Cu-Doped Clinker Crystals by Capturing Electronic Structure Modification

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