Gypsum (CaSO4 center dot 2H(2)O) dehydration kinetics were investigated through energy dispersive X-ray diffraction (EDXD), under reduced pressure (100 Pa), in the temperature range 313-353 K. The process follows the JMAK (Johnson-Mehl-Avrami Kinetic) model. The fitting procedure of the Arrhenius expression provides an activation barrier of 18(2) kcal/mol. Under these experimental conditions, dehydration proceeds via a single-step conversion path gypsum --> gamma-anhydrite. Separate experiments of bassanite (CaSO4 center dot 0.5H(2)O) dehydration, carried out at similar conditions, indicate, as expected, a faster process gamma-anhydrite being the final product. According to the structural relationships between bassanite and gamma-anhydrite, dehydration should occur via the escape of water molecules along the axis of the channel (c axis) following a one-dimensional behaviour. Therefore, no Avrami model (which implies nucleation and growth of a new phase) can be applied.

Carbone, M., Ballirano, P., Caminiti, R. (2008). Kinetics of gypsum dehydration at reduced pressure: an energy dispersive X-ray diffraction study, 20(4), 621-627 [10.1127/0935-1221/2008/0020-1826].

Kinetics of gypsum dehydration at reduced pressure: an energy dispersive X-ray diffraction study

CARBONE, MARILENA;
2008-01-01

Abstract

Gypsum (CaSO4 center dot 2H(2)O) dehydration kinetics were investigated through energy dispersive X-ray diffraction (EDXD), under reduced pressure (100 Pa), in the temperature range 313-353 K. The process follows the JMAK (Johnson-Mehl-Avrami Kinetic) model. The fitting procedure of the Arrhenius expression provides an activation barrier of 18(2) kcal/mol. Under these experimental conditions, dehydration proceeds via a single-step conversion path gypsum --> gamma-anhydrite. Separate experiments of bassanite (CaSO4 center dot 0.5H(2)O) dehydration, carried out at similar conditions, indicate, as expected, a faster process gamma-anhydrite being the final product. According to the structural relationships between bassanite and gamma-anhydrite, dehydration should occur via the escape of water molecules along the axis of the channel (c axis) following a one-dimensional behaviour. Therefore, no Avrami model (which implies nucleation and growth of a new phase) can be applied.
2008
Pubblicato
Rilevanza internazionale
Articolo
Sì, ma tipo non specificato
Settore CHIM/03 - CHIMICA GENERALE E INORGANICA
Settore CHIM/02 - CHIMICA FISICA
English
Con Impact Factor ISI
gypsum; dehydration kinetics; bassanite; gamma-anhydrite
Carbone, M., Ballirano, P., Caminiti, R. (2008). Kinetics of gypsum dehydration at reduced pressure: an energy dispersive X-ray diffraction study, 20(4), 621-627 [10.1127/0935-1221/2008/0020-1826].
Carbone, M; Ballirano, P; Caminiti, R
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2108/26180
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