Crystallisation of alumosilicates in glass-ceramics: interface processes and diffusion of the main constituents

微晶玻璃是一种功能材料，适用于当前关键技术的不同领域。它们的效率是基于独特的热，光学和机械性能的相互作用，这可以通过使用srilanite，烧绿石和tohdite结构的成核剂（NA）催化铝硅酸盐固溶体的结晶来定制。这里的瓶颈是显着缺乏基本的理解的速度决定界面和扩散过程的异质成核与后续的经验驱动的材料开发。一方面，界面控制的外延机制的迹象被报道，而另一方面，直接接近NA晶体的Al梯度被证明。（分别为稀有稳定同位素/西姆斯和GIXRD和HT-GIXR），使用标记的主要元素的NA涂层母体玻璃（O-，Si-，Al-，Li-，K-，Sr-示踪剂），首次允许同时测定NA/铝硅酸盐界面处的化学和结构梯度以及具有纳米分辨率（西姆斯）的机械应力，一整套动力学数据，包括玻璃中主要元素的自扩散、晶体生长过程中通过液/固界面的扩散以及NA界面处的成核速率和垂直于NA界面的生长速率。特别是，通过选择不同的NA涂层，即铝贫：srilankite-ss和富铝：烧绿石-和tohdite-ss，特别强调的是铝的作用和铝型材在界面处的形成。这将是可能的洞察铝硅酸盐晶体在玻璃陶瓷，这将用于数值模拟的过程中的非均质成核机制。计算结果将有助于改善铝硅酸盐玻璃陶瓷的微观结构和宏观性能之间的相关性的预测。

Alumosilicate glass-ceramics are functional materials native to different areas of present key technologies. Their efficiency is based on the interplay of unique thermal, optical and mechanical properties, which can be tailored by catalyzing the crystallization of alumosilicate solid solutions using nucleation agents (NA) of srilankite, pyrochlor and tohdite structures. Here the bottleneck is the significant lack of fundamental understanding of the rate determining interface and diffusion processes of heterogeneous nucleation with the follow-up of an empirically driven materials development. On one side indications of an interface controlled epitaxial mechanism were reported while on the other side an Al-gradient in the direct proximity of NA crystals was evidenced.Based on isothermal experiments (rare stable isotopes/SIMS and GIXRD and HT-GIXR, respectively) using NA coated parent glasses of labelled major elements (O-, Si-, Al-, Li-, K-, Sr-tracer), which for the first time allow a simultaneous determination of chemical and structural gradients as well as mechanical stresses with nano-metric resolution (SIMS) at the NA/alumosilicate interface, a complete set of kinetic data, including self-diffusion of major elements in the glass, diffusion through the liquid/solid interface during crystal growth as well as nucleation rates at the NA interface and growth rates perpendicular to the NA interface will be generated. In particular, via selection of different NA-coatings, i.e. Al-poor: srilankite-ss and Al-rich: pyrochlor- and tohdite-ss, special emphasis will be on the role of aluminium and the formation of Al profiles at the interface. It will be possible to gain insights into the heterogeneous nucleation mechanism of alumosilicate crystals in glass-ceramics, which will be utilized for numerical modelling of the processes. Results of the calculation will help to improve predictions of correlation between microstructure and macroscopic properties of alumosilicate glass-ceramics.