Structure-Properties-Relationships in Lithiumaluminosilicate Glass Ceramics Containing High Concentrations of Nucleation Agents

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Tailored crystallization of glasses allows synthesis of a specific class of inorganic functional materials - glass-ceramics. As an example, ceramming of parent glasses based on Li2O/Al2O3/SiO2 (LAS) may lead to glass-ceramics with zero thermal expansion, the latter material is widely used in cooktop panels. A crystallization of MgO/Al2O3/SiO2 (MAS)-based glasses, on the other hand, may lead to glass-ceramics with high hardness and/or bending strength. The proposed research project is aimed to combine the useful macroscopic properties of the commercially most relevant LAS- and MAS-silicate glass-ceramics by precise control of their micro- and nanostructure. In particular, it shall be tried to gain excellent mechanical properties in LAS glass-ceramics that remain unrealized thitherto. Robust LAS glass-ceramics are very desirable, especially in combination with zero thermal expansion. To design glass-ceramics with nanoscaled crystalline phases for applications as desired, a profound understanding of the underlying nucleation and crystallization mechanisms is imperative. As such, especially a combination of contradictory properties - high hardness and zero thermal expansion - will only be realized based on a fundamental understanding of the associated processes. Comprehensive initial studies concerning MAS parent glasses with ZrO2 as nucleation agent have shown that the mechanisms which may lead to glass-ceramics with excellent mechanical properties are manifold. Besides phase changes, selective precipitation of crystalline phases with high coefficient of thermal expansion may also result in glass-ceramics of high hardness, whereas the addition of Y2O3 can stabilize the residual vitreous phase and suppress a quartz crystallization, yet still lead to glass-ceramics with excellent properties. These findings shall be deepened, and a direct comparison to nucleation- and crystallization phenomena in LAS-based glass-ceramics shall be drawn. In doing so, the planned experiments will be restricted to model glass systems with only a few components, to suppress the influence of minority components. LAS-based glasses with ZrO2 as nucleation agent only, but with defined, yet higher-than-usual nucleation agent concentration, shall be molten, cerammed and characterized in terms of physical properties and respective microstructure. Using distinct nanoanalytical methods, a comparison of the temporal evolution of crystallization in non-isochemical LAS- and MAS-based glasses shall be drawn, with a special emphasize on the early nucleation stages. Additionally, Y2O3 shall be added to chosen LAS parent glass compositions, to analyze its influence on crystal phase evolution, stabilization of the residual vitreous phase, and the mechanical properties of the resulting glass-ceramics. The planned investigations shall support a comprehensive picture of the crystallization mechanisms in silicate glass-ceramics.