Εξειδίκευση τύπου :	Άρθρο σε επιστημονικό περιοδικό
Τίτλος:	Structural characterization of reduced-charge montmorillonites. Evidence based on FTIR spectroscopy, thermal behavior, and layer-charge systematics
Δημιουργός/Συγγραφέας:	Skoubris E.N. [EL] Χρυσικός, Γεώργιος Δ.[EN] Chryssikos, Georgios D. Christidis G.E. [EL] Γκιώνης, Βασίλης[EN] Gionis, Vassilis
Ημερομηνία:	2013
Γλώσσα:	Αγγλικά
ISSN:	0009-8604
DOI:	10.1346/CCMN.2013.0610207
Περίληψη:	In the present study, the gradual layer-charge reduction of two Li-saturated smectites, SAz-1 from Arizona, USA, and FEO-G from Troodos, Cyprus, with octahedral charge of 0.54 electrons per half unit cell (e/huc) and 0.39 e/huc, respectively, was monitored by X-ray diffraction of K-saturated, ethylene glycol-solvated samples, by thermogravimetry-differential thermogravimetry, and by mid- and near-Fourier transform infrared spectroscopy after heating at 80-300°C. With increasing heating temperature, the layer charge and cation exchange capacity (CEC) of both smectites decreased gradually due to Li fixation. At temperatures >200°C, ~25% residual CEC was observed, suggesting incomplete Li fixation due to kinetic constraints. Dehydration of the original Li-smectites occurred in two steps, one peaking at ~100°C and another at 175-180°C. The latter decreased upon progressive Li fixation and vanished from smectites treated above ~125°C. Dehydroxylation occurred at 635-640°C in both smectites and was not affected by Li fixation. The second derivative analysis of the infrared spectra showed that Li fixation was manifested in both smectites by the growth of two new sharp OH-stretching fundamentals at ~3640 and 3670 cm-1 and their overtones at ~7115 and 7170 cm-1. The new bands constitute pairs of fixed energy and relative intensity which grow simultaneously at the expense of the broad OH-stretching and overtone features of the original smectites. Based on this result, Li fixation is suggested to be accompanied by the simultaneous formation of two distinct trioctahedral-like structural OH species, which is compatible with Li+ occupying trans-octahedral vacancies in both smectites.
Τίτλος πηγής δημοσίευσης:	Clays and Clay Minerals
Τόμος/Κεφάλαιο:	61
Τεύχος:	2
Σελίδες:	83-97
Θεματική Κατηγορία:	[EL] Φυσική και θεωρητική χημεία[EN] Physical and theoretical chemistry [EL] Φασματοσκοπία[EN] Spectroscopy
Λέξεις-Κλειδιά:	Attenuated total reflectance spectroscopy Hofmann-Klemen effect Layer charge Li fixation Near infrared spectroscopy Residual cation exchange capacity Smectite Trans-vacant
Αξιολόγηση από ομότιμους (peer reviewed):	Ναι
Εμφανίζεται στις συλλογές:	Ινστιτούτο Θεωρητικής και Φυσικής Χημείας (ΙΘΦΧ) - Επιστημονικό έργο