CAA: Transient Nucleation Behavior in Li2O-2SiO2 Glasses: The Effects of Q Speciation

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9506486 Nekvasil Crystal nucleation in silicate glasses is of great importance in both geological and materials systems. Yet, many important questions still remain regarding the effects of pre-existing amorphous phase structure on the homogeneous nucleation process in silicate melts and glasses and the dynamic processes leading to new steady-state species distributions. This CAA is requested to permit the PI to begin a new research direction focused on the structural aspects of time-dependent processes relating to crystallization from molten and glassy silicates. This direction strongly complements her previous experimental and theoretical work on equilibrium thermodynamics in molten silicates. This project would serve as an introduction to NMR spectroscopy as well as nucleation studies and would be conducted during her first sabbatical leave. The proposed study focuses specifically on evaluating the kinetics of structural readjustments and its effect on induction times. MAS and static NMR experiments on glassy lithium disilicate will be coupled with nucleation studies with the specific goal of determining the kinetics of "short" range order readjustments after structural perturbation. The kinetics of Qn species rearrangements when coupled with the effects of structure on induction times will also indicate the kinetics of the readjustment of cluster distributions (i.e., "medium" range order). In addition to advancing our understanding of the effect of pre-existing structure on induction times, the data obtained should provide a means of determining whether or not a specific measured Qn species distribution at or below Tg reflects an equilibrium state. This is of immediate relevance to the interpretation of the numerous structural data of glasses in the literature and should provide a guide to the preparation of glasses for future structural studies. The award supplement will support a particularly talented female, African-American underg raduate. She will work closely with the PI and a female chemistry professor on all aspects of the project.