Configurational Contribution to the Thermodynamic Driving Force for Crystallization

Abstract

Determining the thermodynamic driving force of crystallization, ΔG, is difficult without precise knowledge of temperature-dependent heat capacity data for the crystal of interest and the corresponding supercooled liquid. The heat capacity of each of these phases, however, is often challenging to obtain experimentally for the necessary temperature range. This difficulty has prompted several approximations including the Turnbull, Hoffman, and Gutzow–Dobreva approaches. Each of these approximations are based on a simplifying assumption relating to the nature of the liquid–crystal heat capacity difference. Here we consider the heat capacity as a sum of vibrational and configurational contributions, where only the configurational contribution is relevant when studying crystallization processes. We apply this approach for ten glass-forming borate and silicate liquids, and analyze the role that vibrations play in ΔG with experimentally derived heat capacity data for lithium diborate. Configurational models were compared to other approximations for ΔG. This work finds that ΔG can be estimated from configurational thermodynamics alone with knowledge of the fragility index, glass transition temperature, and the liquidus temperature. This work then presents a method for approximating the driving force for any compositions.