Stochastic approach to heterogeneous crystal nucleation in silicate glasses

该项目旨在通过研究动态和等温条件下单次成核事件的平均时间，平均滞后时间，成核速率和位点活性，加深对硅酸盐玻璃非均相成核的理解。特别提出了开始和结束于单个玻璃体积的液相温度以上的反复冷热循环的量热实验。为了说明成核的随机性质，每次实验将进行大约300次循环。设计了不同系列的实验，从改变成核点的几何形状、数量以及接触材料的类型来探索成核点的性质。数值计算及其结果与实验数据的比较旨在改进对潜在非均相成核机制的理论描述，从而有助于对其结晶动力学进行更可靠的预测。在实际方面，实验数据将提供与以前的一次性冷却实验相比的统计确定性，并将允许构建温度-时间转换（TTT）和连续冷却-转换（CCT）图。这些结晶动力学的表示，例如可以推断出临界冷却速率，与工业实践最相关，因为非均相成核是控制玻璃陶瓷制造结晶的主要机制。

The project aims at creating a deeper understanding of the heterogeneous nucleation in silicate glasses by studying the mean lag time, nucleation rates and site activities from the time average of single nucleation events under dynamic and isothermal conditions. In particular, calorimetric experiments of repeated cooling-heating cycles which start and end above liquidus temperature of an individual glass volume are proposed. To account for the stochastic nature of nucleation ca. 300 cycles will be conducted in each experiment. Different series of experiments are designed to explore the nature of the nucleation sites from changing their geometry and number of as well as the type of contact material. Numerical calculations and the comparison of their results with experimental data are intended to improve the theoretical description of underlying heterogeneous nucleation mechanisms which will help to make predictions on their crystallization kinetics more reliable. On the practical side the experimental data will provide statistical certainty in contrast to previous one-time cooling experiments and will allow to construct temperature-time-transformation (TTT) and continous-cooling-transformation (CCT) diagrams. These representations of the crystallization kinetics from which for example critical cooling rates can be deduced are most relevant to industrial practice since heterogeneous nucleation is the dominating mechanism to control crystallization in glass-ceramic manufacturing.