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

本研究项目旨在广泛调查钛在硅酸盐熔体中的掺入及其在二次退火过程中对玻璃析晶的影响：它将在法国奥尔良的CEMHTI研究中心实施，总持续时间为24个月。二氧化钛确实是商业功能玻璃和天然玻璃形成岩浆的关键成分。这种金属离子在玻璃网络中表现出不同的构型，从纯四面体到纯八面体氧配位随着玻璃组成的变化而变化。它在铝硅酸盐玻璃的析晶过程中也扮演着重要的角色：长期以来，它的分相倾向一直被用于微晶玻璃的生产，在微晶玻璃中，它经常被用作种子形成物。根据初始组成，在玻璃退火过程中可以得到包括TiO2(B)、锐钛矿相、金红石相和各种钛酸盐相在内的各种含钛晶相。初步研究了锂镁铝硅酸盐系统掺钛微晶玻璃的析晶动力学。首次确定了块状微晶玻璃中的二氧化钛(B)的存在，并研究了从定义的晶化阶段到高温固态相变，二氧化钛对玻璃析晶的影响有多深。然而，对传统熔化技术和分析方法的必要坚持限制了结果对于全面了解二氧化钛在玻璃结晶中的作用的整体意义。出于这些原因，该项目被设计为广泛的成分筛选，将从二氧化硅-二氧化钛二元系开始，逐步进行三个掺杂二氧化钛的目标成分：霞石(NaAlSiO4)，镁堇青石(Mg2Al4Si5O18)和锌取代的堇青石(Zn2Al4Si5O18)。无容器空气动力悬浮与激光加热相结合，将是在选定的具有挑战性的成分下生产均匀玻璃所必需的。CEMHTI提供了这项技术，以及许多最先进的现场分析方法(高温X射线衍射、拉曼光谱、电子显微镜和固态核磁共振)；它们的使用将使人们能够直接系统地研究二氧化钛在二次热处理过程中参与结晶序列的方式。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。考虑到所有这些因素，该项目的结果将揭示玻璃中钛的成分相关结构变化如何定义随后的析晶序列，加深我们对这些过程的了解，并促进新型微晶玻璃材料的未来发展。

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.