TG AND DSC INVESTIGATION OF THE DEHYDRATION OF THE EXTRA LARGE-PORE ALUMINOPHOSPHATE MOLECULAR-SIEVE VPI-5 AND RELATED MATERIALS

The dehydration of a series of VPI-5 and H3 samples, synthesized under various conditions, as well as the solid state transformation of VPI- 5 to AlPO4-8 have been investigated using combined TG-DTG-DSC and high -resolution solid state P-31-NMR. The TG curves show a quasi-continuou s release of water, the total loss being characteristic for each sampl e. Complete dehydration is achieved when the samples are heated from 2 0-degrees-C to about 150-degrees-C at various heating rates. Besides t he main dehydration effect several weak endothermic peaks are observed . These generally non-reproducible modulated peaks, recorded at high h eating rates, are presumably due to the interactions of the water mole cules leaving the channels of VPI-5 with the randomly positioned fragm ents stemming from the destruction of the water triple helix assemblag e. The non-isothermal kinetic parameters of the dehydration have been evaluated from the TG and DTG curves recorded at low heating rates.