Amorphization and post-amorphous phases of NaA Zeolite at high P–T conditions

Abstract

Hydrated NaA (hyd-NaA) and dehydrated NaA (deh-NaA) zeolites were studied at high P–T conditions (up to 4.5 GPa and 400 ^°C) by ex situ X-ray powder diffraction and in situ impedance spectroscopy. At compression of both synthetic zeolites in 1000-ton cubic press, the amorphization was observed in a wide pressure range at room T. At heating to 200–250 ^°C and compression to 2–3 GPa, a complete amorphous material was obtained from deh-NaA. After amorphization at high P–T, hyd-NaA zeolite transforms to new crystalline phases: carnegieite and nepheline. These amorphous-to-crystalline transformations in a low pressure range suggest the correlation of short-scale order parameters in both materials. The presence of water in hyd-NaA essentially changes the phase diagram. Phase transformations in zeolites may be studied by in situ impedance spectroscopy. Unusual ionic AC conductivity of hyd-NaA, characterized by high value and the Cole–Cole plot with broken line without any semicircle, was observed. The pressure range of high-conducting state increases with temperature and may be broader the measured interval of 0.8–4.5 GPa at 400 ^°C.

Keywords:

• Amorphization
• Pressure
• Zeolite
• NaA
• Carnegieite
• Nepheline

Acknowledgements

We thank RFBR (05-05-64657, 04-05-64550), Presidium RAS Programme (P-9-3), CRDF-RMSE (NO-008-X1), Integration project SB RAS 03-43, NSERC and the Centre for Chemical Physics of UWO (Canada) for support and V.V. Brazhkin and B.A. Fursenko for discussion.