Crystallization experiments on amorphous magnesium silicate. I. Estimation of the activation energy of enstatite crystallization

Abstract

In order to clarify the crystallization process of silicates in circumstellar environments around young and evolved stars, we performed a laboratory simulation of the crystallization of silicate materials by use of synthetic samples in the MgO-SiO2 system with an Mg/Si ratio of 1.07. The starting amorphous material was synthesized by a sol-gel method. The samples were heated at 1023-1073 K in an electric furnace in the atmosphere. The crystallization process of enstatite (MgSiO3) shows nucleation delay in the early stage of the infrared spectral evolution. We quantitatively evaluated the time constant of the enstatite crystallization, and determined the activation energy to be 1.12 × 105 K. The activation energy is much affected by the temperature dependence of nucleation. This large value indicates the kinetic inhibition of crystallization in cold circumstellar regions. © 2009. The American Astronomical Society. All rights reserved.