Clays and Clay Minerals, Vol. 55, No. 1, 45–58, 2007.
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Authors
Drits, Victor A.
Mccarty, Douglas K.
Issue Date
2007
Type
Article
Language
Keywords
Periodicals , Geology , Dehydroxylation , Illite 1M , Illite 2M2 , Leucophyllite , Thermogravimetric
Alternative Title
the Nature Of Structure-bonded H2o In Illite And Leucophyllite From Dehydration And Dehydroxylation Experiments
Abstract
Thermogravimetric analysis combined with mass spectrometry was used to study H2O bound to samples of illite-1M, illite-2M2 and leucophyllite-1M. Samples were heated in a helium atmosphere at different temperatures and after heatingat each given temperature were cooled to 35ºC. Each cycle in the mass 18 spectrum of each illite sample contains a low-temperature peak at 60-80ºC, a mediumtemperature peak at 340-360ºC, and a high-temperature peak at a temperature that is very close to the maximum temperature of sample heating of a given cycle. Within each heating-cooling cycle, the sample weight at the beginning of cooling is lower than that at the end of the same cooling stage because of H2O resorption. However, the number of H2O molecules released duringeach medium-temperature heating cycle is equal to the number of H2O molecules resorbed duringthe correspondingcoolingstag es. The weight losses, under medium-temperature heating, of the illite samples are related to dehydration when H2O molecules located in K-free sites of the illite interlayers are removed. The medium-temperature peak is reproducible for each cycle because duringeach coolingstag e the illite interlayers resorb the same number of H2O molecules that were lost duringt he preceding dehydration. Two distinct features are characteristic of leucophyllite duringheati ng-cooling treatments. First, the number of H2O molecules resorbed duringcoolingis significantly greater than the number of H2O molecules lost duringdehydration. Second, the medium-temperature peaks in the spectrum appear only in the last five cycles and the maximum-peak temperature is 450-460ºC. These data indicate that the heatingcoolingtrea tments are accompanied by partial rehydroxylation. This rehydroxylation occurs duringeach coolings tage when a small number of resorbed H2O molecules are trapped in the interlayers, although most migrate into the octahedral sheet of the 2:1 layers and reform as OH groups. The crystal chemical factors responsible for the dehydration and rehydration as well as for the rehydroxylation reactions are discussed and speculation about the origin of the low- and medium-temperature H2O losses is presented.
Description
Clays and Clay Minerals, Vol. 55, No. 1, 45–58, 2007. The Nature Of Structure-bonded H2o In Illite And Leucophyllite From Dehydration And Dehydroxylation Experiments. Victor A. Drits; And Douglas K. Mccarty. DOI: 10.1346/CCMN.2007.0550104. Copyright © 2007, The Clay Minerals Society.
Citation
Clays and Clay Minerals, Vol. 55, No. 1, 45–58, 2007.
Publisher
The Clay Minerals Society
License
Copyright © 2006-2018, The Clay Minerals Society