Detailed FT near-infrared study of the behaviour of water and hydroxyl in sedimentary length-fast chalcedony, SiO 2 , upon heat treatment
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- ISIDORE Id: 10670/1.0e6b26...
- hal: hal-02949713
- doi: 10.1016/j.saa.2011.06.050
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Patrick Schmidt et al., « Detailed FT near-infrared study of the behaviour of water and hydroxyl in sedimentary length-fast chalcedony, SiO 2 , upon heat treatment », HAL SHS (Sciences de l’Homme et de la Société), ID : 10.1016/j.saa.2011.06.050
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Chalcedony is a porous spatial arrangement of hydroxylated nanometre sized ␣-quartz (SiO 2) crystal-lites. Due to micro-structural transformations upon heat treatment, the optical and mechanical properties of the rock are modified. We investigated these transformations in sedimentary length-fast chalcedony through Fourier Transform near-and mid-infrared spectroscopy using direct transmission and the reflec-tivity. Chemical adsorption potential and absorption of H 2 O by pores was studied after heat treatment. We found that water held in open porosity is reduced upon heat treatment to temperatures above 150 • C. Silanole is noticeably lost from 250 to 300 • C upwards and new bridging Si-O-Si further reduces the surface of open pores, creating a less porous material. Molecular water, resulting from the reaction Si-OH HO-Si → Si-O-Si + H 2 O creates new isolated pores within the material. At temperatures above 500 • C, the samples start internal fracturing, permitting water held in isolated pores to be evacuated. These results shed light on thermal transformations in chalcedony and allow for a better understanding of mechanical transformations after heat treatment.
