Relationship between aqueous chemistry and composition, structure, and solubility of sodium aluminosilicate hydrates

Inorganic polymer binders (IPBs) are synthesized by the activation of aluminosilicate precursors with an alkaline solution such as sodium hydroxide. This paper studies the relationship between the composition, structure, and solubility of sodium aluminosilicate hydrates (N-A-S-(H)), the primary binding phase in IPBs. It was found that changing the aqueous Si/Al ratio had little effect on N-A-S-(H) Si/Al ratio, but small changes in the aqueous Si/Na ratio led to substantial changes in N-A-S-(H) Si/Al ratio. Early N-A-S-(H) products were found to be X-ray amorphous, but a rapid transition to the crystalline phase faujasite occurred after several weeks of aging. The transition of the solid amorphous phase to faujasite was accompanied by a rapid drop in aqueous Si(IV) and Al(III) concentrations. Solubility products were determined, temporally, for the N-A-S-(H) before and after the transition to faujasite and represent new contributions to the literature, particularly for the amorphous state. The results presented here provide fundamental insights that are needed for the development of kinetic and thermodynamic models that can establish phase balances and evolutions of IPBs across a range of precursor compositions and synthesis conditions.