Muséum national d'histoire naturelle, Dpt. de Préhistoire UMR 7194, Centre de spectroscopie infrarouge CP 57, 57, rue Cuvier 75231, Paris Cedex 05, France.
Spectrochim Acta A Mol Biomol Spectrosc. 2011 Oct 15;81(1):552-9. doi: 10.1016/j.saa.2011.06.050. Epub 2011 Jun 25.
Chalcedony is a porous spatial arrangement of hydroxylated nanometre sized α-quartz (SiO(2)) crystallites. 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 reflectivity. 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.
玉髓是一种多孔的空间排列，由羟基化的纳米级α-石英（SiO2）微晶组成。由于热处理时的微结构转变，岩石的光学和机械性能得到了修饰。我们通过傅里叶变换近红外和中红外光谱，使用直接透射和反射率，研究了沉积长度快速玉髓中的这些转变。我们发现，在热处理后，化学吸附势和孔隙对 H2O 的吸收减少。我们发现，在 150°C 以上的温度下，开放孔隙中的水分会减少。在 250 到 300°C 之间，硅醇明显减少，新的桥接 Si-O-Si 进一步减少了开放孔隙的表面积，形成了一种多孔性较低的材料。分子水，由 Si-OH HO-Si→Si-O-Si+H2O 反应产生，在材料内部形成新的孤立孔隙。在 500°C 以上的温度下，样品开始内部破裂，使孤立孔隙中所含的水分得以排出。这些结果阐明了玉髓的热转变，并使我们更好地理解了热处理后的机械转变。
