Speaker: MD Alba (slides 800 Kb)
With JM Trillo and M Naranjo

Abstract: A review of the structure of the silicate minerals is performed, specially phyllosilicates, including the mica muscovite. Solid-solid transformations can be: a) Displacive, whith small changes in the cristal structure and no breaking of bonds; b) Order-disorder; and c) Reconstructive, which involve an extensive rearrangement of the crystal structure and require the breaking of chemical bons and the formation of new ones.

Reconstructive transformations can be done by different methods: ceramic, sol-gel and hydrothermal. We present experiment performed with Si MAS NMR, showing the reconstructive transformation of smectite and muscovite into lutetium disilicate. We have obtained low temperature reconstructive transformations (LTRT) by the hydrothermal method. They take place at temperatures 600 C below the lowest reported.

The activation energy and, therefore, the temperature should be the similarly high as in other reconstructive transformations, because they involve the breaking of the same strong bonds. A tentative explanation based on the expansion of the cation layer has been abandoned, as they also occur in muscovite, a nonexpandable silicate.

NLDD 2004: Nonlinear Double Day on Macroscopic Effects of Anharmonic Excitations, Sevilla, Spain, 17-18 May 2004.