High-temperature wettability and structure of the TiO₂–MnO–SiO₂–Al₂O₃ welding flux system

The effect of TiO₂/SiO₂ and SiO₂/Al₂O₃ ratio on the wettability of the TiO₂–MnO–SiO₂–Al₂O₃ quaternary welding flux system was studied using the sessile drop method by measuring the contact angle at the liquid/solid interface. The contact angle was measured at 1773 K to determine the relationship between wettability and flux structure, which is affected by the flux composition. The surface and interfacial tensions of the TiO–MnO–SiO₂–Al₂O₃ flux system were calculated using Boni's equation and Young's equation, respectively, based on the measured contact angle. The adhesion energy, which corresponds to the energy required to separate the flux from a substrate, was calculated using Dupre's equation. The interfacial tension between the liquid flux and Pt-10Rh decreased and the surface tension increased with higher TiO₂ and Al₂O₃. The results of the Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS) analyses of as-quenched fluxes from 1773 K also support the structural relationship with the wettability. It was found that both O⁻ (non-bridged oxygen) and O^{2 −} (free oxygen) affect the interfacial tension between the flux and the substrate.