Wetting in the ThO ₂/Me (Me 5 Ce, Al, U) systems: An example of the liquid phase properties role in reactive wetting

In this study, the wettability properties and chemical reactions in ThO ₂ (̃90 % dense)/Me (Me = Ce, Al, U) were measured. Sessile drop experiments were carried out at 1000, 1150, and 1250 °C for 60 min and the final apparent contact angles measured were 22° ± 2°, 45° ± 2°, and 135° ± 3°, respectively. Chemical reaction at the interface was detected only in the case of ThO ₂/Al, where a thick (100-200 μm) C ⁴ structure layer containing α-Al ₂O ₃ and Th-rich Al metallic phases were found. In this study, correlation between the thermodynamic properties of the binary Me-Th melts, chemical reaction at the interfaces, and spreading behavior was demonstrated. The Th-Al liquid solution has a negative departure from ideality and the chemical reaction at the ThO ₂/Al interface was massive. The Th-U liquid solution displays a positive departure from ideality and the chemical reaction at the ThO ₂/U interface was negligible. Th-Ce liquid solution displays a close to ideal behavior with a small positive departure from ideality, which promoted spreading without significant Th dissolution in the Ce melt and no detectable formation of new oxides at the interface. It is proposed that the mild chemical reaction in the ThO ₂/Ce system is ideal for pressure-free infiltration processes. The dominance of the liquid solution properties concerning wettability behavior and chemical reaction at the interface was demonstrated using thermodynamic evaluation.