An in situ study of the edingtonite dehydration process from X-ray synchrotron powder diffraction
Ståhl, Kenny; Hanson, Jonathan C.
European Journal of Mineralogy Volume 10 Number 2 (1998), p. 221 - 228
published: Mar 31, 1998
manuscript accepted: Nov 27, 1997
manuscript received: Feb 7, 1997
ArtNo. ESP147051002003, Price: 29.00 €
Abstract The dehydration process of the zeolite edingtonite, Ba1.8Ca0.2Al4Si6O20·H2O, has been studied in situ by X-ray synchrotron radiation powder diffraction. 61 consecutive powder patterns were collected between 310 and 684 K, in steps of 6 K, at 5 minute intervals, and the structures were refined using the Rietveld method. At 310 K the two water sites in edingtonite, OW(l) and OW(2), are both 3/4 occupied. Between 310 and 400 K the occupancy of OW(l) drops smoothly to 1/2. At the same time as the OW(l) expulsion continues, the OW(2) occupancy starts to increase to reach a maximum of 88 % at 450 K. A simple electrostatic model is suggested to explain this behaviour. Between 450 and 600 K, OW(2) shows a regular dehydration behaviour. The remaining water is then rapidly expelled as the water contents drop below one per Ba ion. Finally, as a consequence of an unstable Ba-O coordination, the edingtonite structure breaks down between 660 and 680 K. The framework responds to the dehydration first by a chain rotation and later by an intra-chain folding. Both mechanisms can be related to the electrostatic and spatial needs of the Ba ion.