Thermally treated soil clays as ceramic raw materials: Characterization by X-ray diffraction, photoacoustic spectroscopy and electron spin resonance

Soil clay used as ceramic raw material under heat treatment was investigated using X-ray diffraction, X-ray fluorescence, photoacoustic spectroscopy - PAS and electron spin resonance - ESR. The results indicated the presence of at least three different sites for the Fe3+ ions, one of them representative of a set of distorted cubic sites. The optical absorption spectra obtained with the photoaccustic technique showed bands associated with d-d transitions of Fe3+ ions. Mullite and hematite were detected in the 1100 degrees C heated samples. Crystalline-amorphous-crystalline transformations were detected between 110 degrees C and 1100 degrees C. The conclusion drawn from photoacoustic and magnetic resonance measurements agreed very well with that obtained by X-ray diffraction. (C) 2008 Elsevier B.V. All rights reserved.