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).2H(2)O. Upon heating, the cell parameters increased in the range 25-226 degrees C, following paths which were best fitted by the equations a = -1 x 10(-6)T(2) + 4 x 10(-4)T + 12.821 and c = -6 x 10(-7)T(2) + 2 x 10(-4)T + 5.264, for a and c, respectively. In the range 226-403 degrees C, there was a strong decrease of both a and e, while for T > 403 degrees C there was a new expansion of the structure. The FTIR data showed a major loss of both H2O and CO, in the range 200-400 degrees 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 degrees 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 double left right arrow K cation exchange within the pores due to the thermal treatment.
Bonaccorsi, E., DELLA VENTURA, G., Bellatreccia, F., Merlino, S. (2007). The thermal behaviour and dehydration of pitiglianoite, a mineral of the cancrinite group. MICROPOROUS AND MESOPOROUS MATERIALS, 99, 225-235 [10.1016/j.micromeso.2006.09.040].
The thermal behaviour and dehydration of pitiglianoite, a mineral of the cancrinite group
DELLA VENTURA, Giancarlo;BELLATRECCIA, FABIO;
2007-01-01
Abstract
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).2H(2)O. Upon heating, the cell parameters increased in the range 25-226 degrees C, following paths which were best fitted by the equations a = -1 x 10(-6)T(2) + 4 x 10(-4)T + 12.821 and c = -6 x 10(-7)T(2) + 2 x 10(-4)T + 5.264, for a and c, respectively. In the range 226-403 degrees C, there was a strong decrease of both a and e, while for T > 403 degrees C there was a new expansion of the structure. The FTIR data showed a major loss of both H2O and CO, in the range 200-400 degrees 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 degrees 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 double left right arrow K cation exchange within the pores due to the thermal treatment.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
