Εξειδίκευση τύπου :	Άρθρο σε επιστημονικό περιοδικό
Τίτλος:	Near-infrared investigation of folding sepiolite
Δημιουργός/Συγγραφέας:	Tsampodimou M. Bukas V.-J. Stathopoulou E.T. [EL] Γκιώνης, Βασίλης[EN] Gionis, Vassilis [EL] Χρυσικός, Γεώργιος Δ.[EN] Chryssikos, Georgios D.
Εκδότης:	Walter de Gruyter GmbH
Ημερομηνία:	2015
Γλώσσα:	Αγγλικά
ISSN:	0003-004X
DOI:	10.2138/am-2015-4988
Περίληψη:	Sepiolite is an industrially important clay mineral of the palygorskite-sepiolite group with alternating 2:1 ribbons and hydrated tunnels. Dry sepiolite, Mg8Si12O30(OH)4(OH2)4, loses half of its OH2 content upon further heating and undergoes a structural collapse known as folding. This treatment is considered essential for enhancing the absorptive properties of the clay. In this paper, the folding process is studied by near-infrared (NIR) spectroscopy, mid-infrared attenuated total reflectance (ATR), and thermogravimetric analysis (TGA). The folded state, Mg8Si12O30(OH)4(OH2)2, reveals a new spectrum of fundamental and higher-order OH2 vibrations, as well as systematically split doublets of structural and surface O-H vibrations. Detailed assignments for the stretching, combination, and overtone O-H modes are proposed on the basis of the two non-degenerate populations of Mg3OH (and SiOH) present in the folded state. It is demonstrated that NIR is of particular diagnostic value in monitoring conveniently and non-invasively the folding process, which appears as a simple transition between well-defined dry- and folded-structures. At the level of elementary sepiolite particles (laths), folding is described as a cooperative process requiring the integrity of the ribbons and the inter-ribbon linkages (moderately acid-leached sepiolite does not fold). This is opposed to the skewed and sometimes complex OH2 desorption trace observed by high-resolution TGA, which appears to indicate a multimodal distribution of laths. It is proposed that the rate-determining step for a sepiolite (also, palygorskite) lath to fold is the creation of a critical zone at mid-particle length, which is OH2-deficient and contains unstable, fivefold-coordinated Mg2+.
Τίτλος πηγής δημοσίευσης:	American Mineralogist
Τόμος/Κεφάλαιο:	100
Τεύχος:	1
Σελίδες:	195-202
Θεματική Κατηγορία:	[EL] Φυσική και θεωρητική χημεία[EN] Physical and theoretical chemistry [EL] Φασματοσκοπία[EN] Spectroscopy
Λέξεις-Κλειδιά:	Acid activation ATR Folding High-resolution TGA Near-infrared spectroscopy Palygorskite Sepiolite
Αξιολόγηση από ομότιμους (peer reviewed):	Ναι
Κάτοχος πνευματικών δικαιωμάτων:	© 2015, Walter de Gruyter GmbH. All rights reserved.
Σημειώσεις:	Funding of this work has been provided by Geohellas S.A., the project POLYNANO-KRIPIS 447963/GSRT-Greece and theApplied Spectroscopy Laboratory of TPCI-NHRF.
Εμφανίζεται στις συλλογές:	Ινστιτούτο Θεωρητικής και Φυσικής Χημείας (ΙΘΦΧ) - Επιστημονικό έργο