Thermodynamic study of the CaSO4-H20 solid-gas transformations: How much water does calcined gypsum contain?

Autor: Preturlan, João, Vieille, Laetitia, Quiligotti, Sara, Favergeon, Loïc
Přispěvatelé: École des Mines de Saint-Étienne (Mines Saint-Étienne MSE), Institut Mines-Télécom [Paris] (IMT), Université de Lyon, Centre National de la Recherche Scientifique (CNRS), Laboratoire Georges Friedel (LGF-ENSMSE), Université de Lyon-Centre National de la Recherche Scientifique (CNRS)-École des Mines de Saint-Étienne (Mines Saint-Étienne MSE), Institut Mines-Télécom [Paris] (IMT)-Institut Mines-Télécom [Paris] (IMT), Centre Sciences des Processus Industriels et Naturels (SPIN-ENSMSE), Département Procédés de Transformations des Solides et Instrumentation (PTSI-ENSMSE), Institut Mines-Télécom [Paris] (IMT)-Institut Mines-Télécom [Paris] (IMT)-École des Mines de Saint-Étienne (Mines Saint-Étienne MSE), Saint-Gobain Recherche (SGR), SAINT-GOBAIN, Central and Eastern European Committee for Thermal Analysis & Calorimetry (CEEC-TAC)TCAR)., Transilvania University of Brasov (UniTBv), National Institute for Laser, Plasma and Radiation Physics (INFLPR), Institute of Physical Chemistry 'Ilie G. Murgulescu' of the Romanian Academy (ICF), Commission for Thermal Analysis and Calorimetry of the Romanian Academy (CATCAR)., Andrei Rotaru, Crian Popescu, Saint-Gobain Recherche, Lillouch, Fatima
Jazyk: angličtina
Rok vydání: 2018
Předmět:
Zdroj: ESTAC12-12th European Symposium on Thermal Analysis and Calorimetry
Andrei Rotaru; Crian Popescu. ESTAC12-12th European Symposium on Thermal Analysis and Calorimetry, Aug 2018, Brasov, Romania. Central and Eastern European Committee for Thermal Analysis and calorimetry (CEEC-TAC)-Academica Greifswald, Book of abstracts-12th European Symposium on Thermal Analysis and Calorimetry (ESTAC12), pp.205 / PS1.021, 2018
Popis: Poster Session 1 : Materials, Chemicals, Thin films & Nanomaterials, Thermal Processing and Applications - ISBN 978-3-940237-50-7; International audience; Gypsum is the mineralogical used term to describe materials that are mainly constituted of calcium sulfate dihydrate (CaSO4.2H20). The calcination of gypsum, i.e. the dehydration of gypsum under solid-gas conditions, is of great technological importance because it represents the main industrial process for the production of plaster, the inorganic material with the largest production in the world. Plaster, in turn, is mainly constituted of calcium sulfate hemihydrate (CaSO4.0.5H20). In spite of the significance of these materials for this and other scientific fields, some important aspects of the chemical system CaSO4- H20 are still unknown. In particular, the water content within the gypsum calcination products is only partially described in the literature.This absence of a complete understanding of this system despite its importance and the fact Chat these materials have been used since antiquity can be attributed to several phenomena Chat contribute to its complexity. First of ail, the literature acknowledges the existence of several calcium sulfate polymorphs. For instance, the dehydration of gypsum can lead to different calcium sulfate hydrates of the form CaSO4•εH2O, where ε can be 0.625, 0.5, or 0, depending on the temperature (T) and water vapor partial pressure (P) under which the reaction takes place. Moreover, these compounds can also present zones of divariance, i.e., domains where the overall water content of these hydrates can change continuously with T and P. The fine knowledge of the stability domain of each species throughout successive thermal transformations of the CaSO4.2H20 is still debatable. In this context, the objective of the present work is to determine the stability conditions and domains for the CaS04.2H20 dehydration products. Furthermore, the nature of the divariant behavior is also investigated. Thermogravimetric analysis under isotherm and isobaric conditions using different protocols with temperature ranges of 30°C to 250°C and water vapor partial pressure ranges of 5 hPa to 60 hPa was performed. The results allowed the determination of two zones of divariance and one univariant domain. The variations of the measured water contents in contrast with the stoichiometry of each polymorph were interpreted with models adapted for each zone. Finally, a phase diagram P-T is proposed based on the stability domain of each phase, and values of change in enthalpy and entropy of reaction were obtained for each transformation and compared with previously published values.
Databáze: OpenAIRE
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