Kinetic analysis of the thermal stability of lithium silicates (Li4SiO4 and Li2SiO3)

Abstract

The kinetics describing the thermal decomposition of Li4SiO4 and Li2SiO3 have been analysed. While Li4SiO4 decomposed on Li2SiO3 by lithium sublimation, Li2SiO3 was highly stable at the temperatures studied. Li4SiO4 began to decompose between 900 and 1000 degrees C. However, at 1100 degrees C or higher temperatures, Li4SiO4 melted, and the kinetic data of its decomposition varied. The activation energy of both processes was estimated according to the Arrhenius kinetic theory. The energy values obtained were -408 and -250 kJ mol(-1) for the solid and liquid phases, respectively. At the same time, the Li4SiO4 decomposition process was described mathematically as a function of a diffusion-controlled reaction into a spherical system. The activation energy for this process was estimated to be -331 kJ mol(-1). On the other hand, Li2SiO3 was not decomposed at high temperatures, but it presented a very high preferential orientation after the heat treatments. (C) 2005 Elsevier Inc. All rights reserved.