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Alicja Michalik-Zym, Małgorzata Zimowska, Krzysztof Bahranowski and Ewa Serwicka

Layered Sodium Disilicates as Precursors of Mesoporous Silicas. Part I: Optimisation of the Synthesis Procedure of δ-Na2Si2O5 and α-Na2Si2O5

Optimization of the synthetic procedures described in literature aimed at preparing pure δ-Na2Si2O5 has been carried out. The results show that a substantial shortening of the calcination time of amorphous silicate precursor is required, in order to minimize the appearance of the thermodynamically stable α-Na2Si2O5. The use of commercial water glass solution rather than freshly synthesized silica/NaOH slurry is the preferred source of the starting amorphous silicate. Optimized preparative routes for synthesis of single-phase δ-Na2Si2O5 and α-Na2Si2O5 have been described.

Open access

Alicja Michalik-Zym, Małgorzata Zimowska, Elżbieta Bielańska, Krzysztof Bahranowski and Ewa Serwicka

Layered Sodium Disilicates as Precursors of Mesoporous Silicas. Part II: Hydration of δ-Na2Si2O5 and α-Na2Si2O5

Reaction of δ-Na2Si2O5 and α-Na2Si2O5 with water at ambient conditions has been studied. The first substrate produced kanemite, the other a crystalline solid, assumed to be the layered hydrated α phase of yet unknown structure. Important differences have been observed in the kinetics of δ-Na2Si2O5 and α-Na2Si2O5 reactions with water, the phase transformation of the latter being distinctly slower. The observed different rates of hydration were associated with the different structural properties of the disilicates investigated. Hydrated δ-Na2Si2O5 and α-Na2Si2O5 possess, respectively, the platy and the needle-like morphology. Hydrated α-Na2Si2O5 contains less interlayer water, which is considered the reason for basal spacing being lower than that of kanemite. The interlayer water trapped between the layers of hydrated α-Na2Si2O5 is more strongly bound than that in kanemite.