This paper relates the in situ X-ray diffraction and FTIR high-T study of pitiglianoite from Monte Cavalluccio (Campagnano, Rome, Italy), with composition Na4.7K2.6Ca0.1Si6.1Al5.9O24(SO4)0.8 Æ 2H2O. Upon heating, the cell parameters increased in the range 25–226 C, following paths which were best fitted by the equations a = 1 · 106T2 + 4 · 104T + 12.821 and c = 6 · 107T2 + 2 · 104T + 5.264, for a and c, respectively. In the range 226–403 C, there was a strong decrease of both a and c, while for T > 403 C there was a new expansion of the structure. The FTIR data showed a major loss of both H2O and CO2 in the range 200–400 C. The structure of pitiglianoite at room-T, before the heating run, was characterised by columns of base-sharing undecahedral cages, containing chains of alternating Na cations and H2O molecules, and by large channels containing sulphate groups as well as Na and K ions. Structure refinement at 457 C showed that all water was released from the cages and that significant extra-framework K (1.4 apfu) migrated from the large channel into the cages, throughout the hexagonal tetrahedral rings. A corresponding amount of Na cations migrated from the cages into the channels; a rotation of the sulphate groups, due to the presence of Na instead of K between two sulphate groups was also observed. Refinement at room-T after the experiment showed that the thermally-induced changes were substantially irreversible. The re-hydration of pitiglianoite was prevented by the Na () K cation exchange within the pores due to the thermal treatment.
|Autori:||BONACCORSI E; DELLA VENTURA G; BELLATRECCIA F; MERLINO S|
|Titolo:||The thermal behaviour and dehydration of pitiglianoite, a mineral of the cancrinite-group|
|Anno del prodotto:||2007|
|Digital Object Identifier (DOI):||10.1016/j.micromeso.2006.09.040|
|Appare nelle tipologie:||1.1 Articolo in rivista|