Thermal decomposition of Ferrian chamosite: an infrared emission spectroscopic study |
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| Authors: | J T Kloprogge R L Frost |
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| Institution: | (1) Centre for Instrumental and Developmental Chemistry, Queensland University of Technology, GPO Box 2434, Brisbane Q 4001, Australia e-mail: t.kloprogge@qut.edu.au Tel.: +61-7-3864-1220; Fax: +61-7-3864-1804, AU |
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| Abstract: | The thermal behaviour of ripidolite, an iron-rich chlorite, has been studied in situ by infrared emission spectroscopy up
to 800 °C. The more di,trioctahedral nature due to significant amounts of Fe3+ is reflected, in addition to the two bands around 3420 and 3560 cm−1, by an extra band around 3345 cm−1. This extra band is absent in pure dioctahedral chlorites without Fe3+. These bands have been assigned to (AlAl)O-OH, (SiAl)O-OH and (SiSi)O-OH stretching modes with increasing frequencies. The
bands disappear upon dehydroxylation around 650 °C. A similar behaviour is observed for the corresponding libration modes
around 716, 759 and 802 cm−1. The stretching and bending modes of the inner-OH of the octahedral sheet in the 2:1 clay-like layer are observed around
3645, 943 and 904 cm−1. Although the bands decrease in intensity, they remain present up to 800 °C as dehydroxylation of the octahedral sheet is
not yet complete at this temperature. The presence of two bending modes is explained as being due to a differentiation between
Mg-OH and Fe-OH modes. At 650 °C a new sharp band is observed around 502 cm−1 assigned to a (Fe,Mg)-O-Al bending mode caused by the formation of a spinel-like interlayer phase after dehydroxylation.
Received: 4 June 1999 / Accepted: 6 August 1999 |
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