Aluminosilicate colloidal gels : from the early age to the crystallization of zeolite
Résumé
Aluminosilicate hydrogels are often considered as precursors for the crystallisation of zeolites carried
out under hydrothermal conditions. The preparation of mechanically homogeneous aluminosilicate
gels allows the study of these materials in another way, especially by bulk rheology, and through the
observation of the aging dynamics until the precipitation of crystalline zeolites. The first part of this
study deals with the establishment of ternary diagrams, in order to identify the suitable chemical
formulation for the preparation of a homogeneous gel. Recently, we have shown that these gels can be
considered as fractal weak colloidal gels, exhibiting both glassy and gel-like characteristics according
to the probed length and time scales [Keshavarz et al., PNAS, 2021, 118 (15), e2022339118]. By
monitoring the evolution in the viscoelastic modulus during the gelation reaction, combined with
measurements of the frequency dependence of the mature gels and by yielding the gel under large
deformation, we first propose an empirical law considering the partial order of reaction on each
chemical elements, to predict the gelation time according to the chemical formulation. Secondly, the
scaling behavior of the elastic properties of this colloidal gel shows that a strong link behavior, [Shih
et.al., PRA, 1990, 4 (42), 4772], is initially observed and then moves towards a weak link regime,
especially by modifying the sodium concentration. The long term aging results in a shrinkage of the
gel, concomitant to the coming out of interstitial liquid at the surface due to syneresis mechanism.
Zeolites precipitate through crystallisation by a particle attachment mechanism, when thermodynamic
equilibrium is reached. The stoichiometry of the precipitated zeolites is not only consistent with the
remaining species concentration in the supernatant but surprisingly, it is also very close to the partial
order of reaction of the chemical elements involved in the determination of the critical gel point.
This indicates a strong correlation between the morphology and the texture of the amorphous gel
network at early age and those of the final solid precipitated crystals.
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Origine | Fichiers produits par l'(les) auteur(s) |
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