Structural stability of aluminosilicate inorganic polymers: Influence of the preparation procedure

Abstract

The stability of amorphous aluminosilicate inorganic polymer (AIP) systems with regard to the structural role of water molecules incorporated in inorganic matrix is discussed. Innovative approach to preparation of amorphous AIP systems with identical chemical composition but differing in structural and mechanical behavior is introduced. It is shown that even small changes in the manufacture dramatically affect mechanical properties and the overall structural stability of AIP systems. If the required quantity of water is admixed to the reaction mixture during the initial step of AIPs synthesis the resulting amorphous aluminosilicate matrix undergoes extensive crystallization (zeolitization). On the other hand, if the amount of water is added to the reaction mixture during the last step of the preparation procedure, the inorganic matrix exhibits long-term stability without any structural defects. To find the structural reasons of the observed behavior a combination of traditional solid state NMR (1H and 29Si MAS NMR, 29Si CP/MAS NMR, 29Si inverse-T1-filtered NMR), XRPD and TGA measurements were used. The applied experiments revealed that the structural stability of AIPs can be attributed to the tight binding of water molecules into the inorganic matrix. The structural stability of the prepared amorphous AIP systems thus seems to be affected by the extent of hydration i.e. the strength of binding water into the inorganic framework.