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.