Unravelling the role of titanium in glass melts: a modern systematic approach based on in-situ characterization and containerless melting

该研究项目旨在广泛调查硅酸盐熔体中钛的掺入及其对二次退火过程中玻璃结晶的影响：该研究项目将在CEMHTI研究中心实施（额外条件和材料：高级温度和辐照），TiO 2确实是商用功能玻璃和天然玻璃形成岩浆的关键成分。该金属离子在玻璃网络中显示出可变的构型，作为玻璃组合物的函数从纯四面体氧配位变化到纯八面体氧配位。它在铝硅酸盐玻璃的结晶中也起着相关的作用：它的分层倾向长期以来一直被用于玻璃陶瓷的生产，在玻璃陶瓷中，它通常被用作晶种形成剂。根据初始组成，在玻璃退火过程中可以得到多种含Ti晶相，包括TiO 2（B）、TiO 2、金红石和各种钛酸盐相。这是第一次有可能确定的外观的TiO 2（B）在散装玻璃陶瓷和研究如何深入TiO 2能够影响玻璃的结晶，从所谓的成核阶段的高温固态相变。尽管如此，对常规熔融技术和分析方法的必要坚持限制了结果对于全面理解TiO 2在玻璃结晶中的作用的整体意义。出于这些原因，本项目被设计为将以相加和逐步方式进行的广泛成分筛选，从SiO2-TiO 2二元体系开始，并朝着三种TiO 2掺杂的目标成分进行：霞石（NaAlSiO 4）、镁堇青石（Mg 2Al 4Si 5 O 18）和锌取代堇青石（Zn 2Al 4Si 5 O 18）。无容器空气动力学悬浮耦合激光加热将是必要的，以生产均匀的玻璃在选定的具有挑战性的组成。该技术可在CEMHTI，连同一些国家的最先进的原位分析方法（高温X射线衍射，拉曼光谱，电子显微镜和固态核磁共振）;他们的就业将能够直接系统的调查方式二氧化钛在二次热处理过程中参与结晶序列。主办机构和同步加速器设施之间的密切互动也将是该项目的一项资产。综合考虑，该项目的结果将揭示玻璃中钛的组成相关结构变化如何定义随后的结晶顺序，增强我们对这些过程的理解，并促进新型玻璃陶瓷材料的未来发展。

This research project is designed as a broad investigation of titanium incorporation in silicate melts and of its influence on glass crystallization during secondary annealing: it will be implemented at the CEMHTI research centre (Conditions Extrêmes et Matériaux: Haute Température et Irradiation) in Orléans, France for a total duration of 24 months.TiO2 is indeed a key component of commercially available functional glasses and of natural glass-forming magmas. This metal ion displays a variable configuration in the glass network, varying from pure tetrahedral to pure octahedral oxygen coordination as a function of glass composition. It plays also a relevant role in the crystallization of aluminosilicate glasses: its tendency towards demixing has been long exploited for the production of glass-ceramics, in which it is often employed as a seed former. According to the starting composition, a whole variety of Ti-bearing crystalline phases can be obtained during glass annealing, including TiO2(B), anatase, rutile and various titanate phases.Preliminary work was focused on the crystallization dynamics of TiO2-doped glass-ceramics belonging to the lithium-magnesium-aluminosilicate compositional system. It was possible to identify for the first time the appearance of TiO2(B) in bulk glass-ceramics and to investigate how deeply TiO2 is able to influence the crystallization of glass, from the so-defined nucleation stage up to high-temperature solid-state phase transitions. Nonetheless, the necessary adherence to conventional melting techniques and analytical methods limited the overall significance of the results for a comprehensive understanding of the role of TiO2 in glass crystallization.For these reasons, this project is designed as a broad compositional screening that will be performed additively and stepwise, starting from the SiO2-TiO2 binary system and proceeding towards three TiO2-doped target compositions: nepheline (NaAlSiO4), Mg-cordierite (Mg2Al4Si5O18) and Zn-substituted cordierite (Zn2Al4Si5O18). Containerless aerodynamic levitation coupled to laser heating will be necessary to produce homogeneous glasses at the selected challenging compositions. This technology is available at CEMHTI, together with a number of state-of-the-art in-situ analytical methods (high-temperature x-ray diffraction, Raman spectroscopy, electron microscopy and solid-state nuclear magnetic resonance); their employment will enable a direct systematic investigation of the way TiO2 takes part into the crystallization sequence during secondary heat treatments. The close interaction between the host institution and synchrotron facilities will be also an asset to the project.All things considered, the results of the project will unravel how compositionally related structural changes of titanium in the glass define the subsequent crystallization sequence, enhancing our understanding of these processes and boosting the future development of novel glass-ceramic materials.