Chabazite: Energetics of hydration, enthalpy of formation, and effect of cations on stability

Citation
Sh. Shim et al., Chabazite: Energetics of hydration, enthalpy of formation, and effect of cations on stability, AM MINERAL, 84(11-12), 1999, pp. 1870-1882
Citations number
39
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Earth Sciences
Journal title
AMERICAN MINERALOGIST
ISSN journal
0003-004X → ACNP
Volume
84
Issue
11-12
Year of publication
1999
Pages
1870 - 1882
Database
ISI
SICI code
0003-004X(199911/12)84:11-12<1870:CEOHEO>2.0.ZU;2-
Abstract
The stability of synthetic cation-exchanged zeolites having the chabazite f ramework (CHA) and their cation-water interaction were studied using high-t emperature reaction calorimetry. Four cations (K, Na, Li, and Ca) were exch anged into CHA. The enthalpies of formation were determined for all samples , and the partial molar enthalpy of hydration was measured by varying the w ater content of one Ca-CHA. The enthalpy of formation depends strongly on the exchanged cation, becomin g more exothermic in the order Ca, Li, Na, K. The integral hydration enthal py does not depend strongly on the nature of the cation, but becomes slight ly less exothermic with increasing aluminum content, For the one Ca-CHA stu died in detail, the average enthalpy of hydration is -34.6 +/- 1.2 kJ/mol r elative to liquid water A quadratic fit to the transposed temperature drop data gives Delta (h) over bar(H2O) = -52.97 (+/-4.74) + 2.94 (+/- 0.68) n ( kJ/mol), where Delta (h) over bar(H2O) is the partial molar enthalpy of hyd ration and n is the number of water molecules per 24 oxygen formula.