Original paper

Continuous dehydration of cavansite under dynamic conditions: an in situ synchrotron powder-diffraction study

Martucci, Annalisa; Rodeghero, Elisa; Cruciani, Giuseppe


The dehydration dynamics of cavansite, Ca(VO)(Si4O10)·4H2 O was studied by time-resolved in situ synchrotron powder diffraction between 298 and 900 K. The crystal-structure evolution was continuously monitored through twenty Rietveld structure refinements (Pnma space group) in the 298–810 K range whereupon cavansite turned amorphous without any precursor to a polymorphic phase transition to pentagonite. The results obtained from the series of time-resolved Rietveld refinements highlight the out-of-equilibrium effects that govern dehydration of cavansite powders under dynamic conditions. While confirming the general picture of cavansite dehydration, as previously reported by static single-crystal work, this dynamic study revealed an important transient phenomenon, namely the cell-volume expansion caused by framework relaxation resulting from breakdown of the hydrogen bonding network during the initial heating stages. We also documented that the channels formed by elliptical eight-membered tetrahedral rings of cavansite, when heated under the typical dynamic conditions of an industrial process, undergo a series of shortlived ''pore-mouth breathing motions'' which could be exploited for fine tuning of gas diffusion paths in possible applications of synthetic analogues of these vanadosilicates.


vanadosilicatetransient phenomenadehydration dynamicsin situ synchrotron powder diffractioncavansitemicroporous structurepore-mouth breathing motion