Investigation of Water and Hydroxyl Groups Associated with Coal Fly Ash by Thermal Desorption and Fourier Transform Infrared Photoacoustic Spectroscopies

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Abstract
Thermal desorption spectrometry (TDS) and Fourier transform infrared photoacoustic spectroscopy (FT-IR/PAS) have been used in combination to analyze the water and hydroxyl groups associated with four coal fly ashes. Measurements using the former technique on these ashes resulted in identification of three water desorption regions in the temperature range from 25° to 1100°C. The regions consisted of a small desorption peak at 50°, a broad band from 180° to 400°, and an intense peak from 400° to 590°. No additional water desorption was observed up to 1100°. A fourth ash gave a similar spectrum except that it lacked the intense last peak. The TDS spectra together with FT-IR/PAS spectra taken on samples exposed to pre- and post-desorption peak temperatures allowed the first TDS peak to be assigned to the desorption of physically adsorbed water, the broad band to desorption of hydrogen-bonded surface hydroxyls, and the intense last peak to the decomposition of Ca(OH)2.