Dehydration and phase transformation in sepiolite

Abstract

Radial distribution analysis of X-ray intensities diffracted by sepiolite samples untreated and treated at different temperatures up to 1000°C have been carried out. Interatomic distances, coordination numbers, mean square displacements and the interatomic coupling constants for different atom pairs have been calculated from the radial distribution curves. The results show that the disorder takes place in the octahedral layer which finally collapses above 600°C with the elimination of hydroxyl groups leading finally to the formation of the amorphous phase at 800°C, characterized by coordination number four of Mg. The variation of lattice parameters including volume reveals that the dehydration is accompanied by contraction of the cell dimensions at each stage of dehydration till the amorphous phase is fully developed around 800°C. It is also seen that there is a similarity between the starting material and the new crystalline product formed at 1000°C. The entire dehydration process and thermal transformation have been interpreted in terms of these data.