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Thermogravimetric analysis-mass spectrometry (TGA-MS) of hydrotalcites containing CO32-, NO3-, Cl-, SO42- or ClO4-

Kloprogge, J. Theo, Krisof, Janos, & Frost, Ray L. (2001) Thermogravimetric analysis-mass spectrometry (TGA-MS) of hydrotalcites containing CO32-, NO3-, Cl-, SO42- or ClO4-. In Dominguez, E., Mas, G., & Cravero, F. (Eds.) A Clay Odyssey. Proceedings of the 12th International Clay Conference Bahai-Blanca, Argentina. July 22-28.

Abstract

Mg/Al-hydrotalcites containing NO3-, Cl-, SO42- or ClO4- were synthesised under N2 to prevent incorporation of CO32-. The presence of the anions in the hydrotalcite structure was confirmed by infrared and Raman spectroscopy. The CO3- and the NO3-hydrotalcites contained both NO3- and CO32-, while the Cl-hydrotalcite also contained some CO32-. It is known that during thermal treatment of hydrotalcites dehydroxylation and decarbonisation strongly overlap. Mass spectrometry following TGA enables one to identify both reactions. For CO3-hydrotalcite CO2 is released simultaneously with water (dehydroxylation) around 335 degrees Celsius followed by NO around 365 and 500 degrees Celsius. The stability of the NO3-hydrotalcite is different showing a major loss of CO2 and H2O (dehydroxylation) around 410 degrees Celsius with losses of NO around 345 and 450 degrees Celsius. The Cl-hydrotalcite shows a similar behaviour for the H2O loss (dehydroxylation), but Cl is lost over a range from 400 to 900 degrees Celsius and CO2 comes off in steps around 360 and 500 degrees Celsius. Completely different is the thermal behaviour of SO4- and ClO4-hydrotalcites. SO4-hydrotalcite shows a gradual weight-loss due to dehydroxylation with two minor water peaks around 260 and 375 degrees Celsius, while the sulphate remains in the structure. The sulphate is not lost until heated to 900 degrees Celsius. The ClO4-hydrotalcite shows a complex thermal behaviour with 2 steps of water loss around 375 and 440 degrees Celsius, where the second step is accompanied by the loss of O2. A possible explanation is a redox reaction between perchlorate and the cations giving metal-chlorides and O2.

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ID Code: 924
Item Type: Conference Paper
ISBN: 0444509453
Subjects: Australian and New Zealand Standard Research Classification > CHEMICAL SCIENCE (030000) > INORGANIC CHEMISTRY (030200)
Divisions: Past > QUT Faculties & Divisions > Faculty of Science and Technology
Copyright Owner: Copyright 2001 (please consult author)
Deposited On: 24 Mar 2005
Last Modified: 11 Aug 2011 01:18

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