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

• Applicant: Dr.-Ing. Alessio Zandona
• Subject Area: Glass, Ceramics and Derived Composites ; Synthesis and Properties of Functional Materials ; Thermodynamics and Kinetics as well as Properties of Phases and Microstructure of Materials
• Term: from 2020 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 448961237

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.

• DFG Programme: WBP Fellowship
• International Connection: France
• Host: Dr. Mathieu Allix