The role of fluoride additives in the densification of ceramics - How does it work?

Abstract: Fluoride sintering additives are frequently utilized for the densification of various ceramics, but the current comprehension of the mechanism by which they affect densification is lacking behind empirical experience. A prominent example is LiF, which is commonly used in the preparation of transparent ceramics (MgAl2O4, Y2O3, YAG, MgO). It is generally accepted that LiF melt allows the rearrangement of particles, enhances densification and later in the process escapes from the system due to its high vapor pressure, so ideally no secondary phase is present in the final product. However, the second - and the most essential - step of enhanced densification is a source of scientific dispute. It is not clear if oxygen vacancies are responsible for this enhancement and if so, under what circumstances are they created. The present work tries to shed more light on fluoride additives and how they work throughout the whole process of preparation. The results suggest that the mutual dissolution of sintering additive and the base ceramic is the key aspect. Acknowledgements: This work was supported from the grant of Specific university research - grant No. A1_FCHT_2022_002