Kinetics and mechanisms of crystal growth and diffusion in a glass-forming liquid

Abstract

Extensive data on the viscosity, covering 15 orders of magnitude, and crystal growth rate, covering seven orders of magnitude, of liquid diopside (CaO.MgO.2SiO(2)) were collected in a wide range of undercoolings from 1.10T(g) to 0.99T(m) (T(g) is the glass transition temperature and T(m) the melting point). The raw growth rate data were corrected for the increased interfacial temperature produced by the heat released during crystallization. A detailed analysis confirms that growth mediated by screw dislocations reasonably explain the experimental data in these wide ranges of temperatures and growth rates. Effective diffusion coefficients were calculated from crystal growth rates and from viscosity, and were then compared with measured self-diffusion coefficients of silicon and oxygen in diopside melt. The results show that oxygen and silicon control the diffusion dynamics involved in crystal growth and viscous flow. This study not only unveils the transport mechanism in this complex liquid, but also validates the use of viscosity (through the Stokes-Einstein or the Eyring equations) to account for the kinetic term of the crystal growth expression in a wide range of temperatures.