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Fresh and weathered pyrochlore studies by Fourier transform infrared spectroscopy coupled with thermal analysis

Published online by Cambridge University Press:  05 July 2018

M. Nasraoui ,
E. Bilal  and
R. Gibert
M. Nasraoui
Affiliation:
Département de Géochimie, Ecole des Mines de Saint Etienne, 158, Cours Fauriel 42023, Saint Etienne Cedex 02, France
E. Bilal
Affiliation:
Département de Géochimie, Ecole des Mines de Saint Etienne, 158, Cours Fauriel 42023, Saint Etienne Cedex 02, France
R. Gibert
Affiliation:
Département de Géochimie, Ecole des Mines de Saint Etienne, 158, Cours Fauriel 42023, Saint Etienne Cedex 02, France
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Abstract

Fresh and weathered pyrochlore from the Lueshe carbonatite complex (in the northeast of the Democratic Republic of Congo) was studied by Fourier transfom infrared (FTIR) spectroscopy and by a combination of FTIR spectroscopy and thermal analysis. The former was carried out in the spectral range 400–4000 cm−1. The spectra for fresh and weathered pyrochlores were very different. For the weathered pyrochlore, two bands were identified as OH vibration modes, one broad band with a maximum at 3413 cm−1 and another finer band at 1630 cm−1. The fresh pyrochlore does not show OH absorption bands. The presence of OH confirms the hydrated state of the weathered pyrochlore suggested by previous microanalytical work. The combination of FTIR spectroscopy and thermal analysis allows ‘real-time’ observation of gas emanations and solid-state transformations taking place during heating up to 800°C. For fresh pyrochlore, no solid transformation was detected, except a CO2 emanation from 242–576°C. For the weathered pyrochlore a dehydration was observed between 234–565°C followed by an exothermic peak in Differential Scanning Calorimetric (DSC) curve at 604°C. This exothermic peak corresponds to the formation of a Nb oxide phase. At higher temperatures the weathered pyrochlore is partly decomposed, forming a dehydrated pyrochlore and a Nb oxide phase. The combination of FTIR and thermal analysis has provided useful information on both fresh and weathered pyrochlore transformations which has clarified our understanding of the water control of the structural stability of pyrochlore minerals.

Keywords

pyrochloreweatheringIR spectroscopyheatingsolid state transformations
Type
Research Article
Information
Mineralogical Magazine , Volume 63 , Issue 4 , August 1999 , pp. 567 - 578
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1999

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Footnotes

*

Present address: Instituto Technologico e Nuclear, EN10, 2686-953, Sacavém, Portugal

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