STUDIES OF THE SYNTHESIS, AND TRANSFORMATION OF MATERIALS USING IN SITU TIME-RESOLVED POWDER DIFFRACTION. J. C. Hanson, J. Aruajo, P. Norby, Brookhaven Nat. Lab., USA; A. N. Christensen, Aarhus Univ., Denmark; K. Ståhl, DTU, Lyngby, Denmark; G. Artioli, Univ. of Milan, Italy; A. Gualtieri, Univ. of Modena, Italy.

Time-resolved synchrotron powder diffraction data will be presented that have been collected in situ with position sensitive detectors in order to study the kinetics of hydrothermal syntheses¹ and phase changes².

The hydrothermal syntheses of Co and Mg substituted alumino phosphates have been found to form many different MAPO frameworks depending on the template, pH and hydrothermal conditions.

The phase transformations of KNO₃ in the range 303 to 533K have been shown to be dependent on the thermal history of the sample.

We have also found that the in-situ time-resolved data can be used for Rietveld profile refinements³. For example, the study of laumontite⁴ offers great insight on the fine details of water molecules-cation-framework oxygen atoms interaction during the thermally driven release of the water molecules from the zeolitic channels. A molecular movie showing the steps in the dehydration of laumontite is available on the WWW at http://www.chemistry.bnl.gov/x7b/x7bhome.html. In stilbite, the site distribution of the water molecules is more complex, but the study clearly shows the temperature-dependent shift of the cations towards the framework oxygens, finally leading to a first-order phase transition with change of space group symmetry, and the systematic rearrangement of

T-O-T bonds in the high-temperature phase. To our knowledge, this is the first direct experimental evidence of a zeolite framework disruption during dehydration caused by increased cation coordination to framework oxygens.

Work supported under contract AC02-76CH00016 with US DOE Div. of Chem. Sci., Office of Basic Energy Sciences, and the by the Danish Natural Science Research Council.

1. A. N. Christensen, P. Norby and J. Hanson, Acta Chem. Scand. (1996) submitted

2. A. N. Christensen, P. Norby, J.C. Hanson and S. Shimada, J. Appl. Cryst. (1996) submitted

3. K. Ståhl and J. C. Hanson, J. Appl. Cryst. (1994) 27, 543-550

4. K. Ståhl, G. Artioli and J. C. Hanson, Phys. Chem. Min.(1996) in press