The effect of SiO2/Al2O3 and TiO2/SiO2 ratios on the viscosity of the TiO2–MnO–SiO2–Al2O3 welding flux system was studied using the rotational spindle method. The viscosity was measured at the fully liquid region of the melt from 1773 K to the break temperature at approximately 1623 K. Higher TiO2/SiO2 ratio resulted in lower viscosity in the temperature range of interest. The SiO2 dominant slag system showed higher viscosity values than the Al2O3 dominant slag in the present TiO2 based system until a SiO2/Al2O3 ratio of 1.61. Fourier transform infrared (FTIR) results revealed the [SiO4]4–-tetrahedral symmetric stretching vibrations and the [AlO4]5–-tetrahedral asymmetric stretching vibration became weaker with higher TiO2/SiO2, which was also apparent with the increase in the extended basicity ((TiO2+MnO)/(SiO2+Al2O3)). The Al–O–Si bending vibration and [SiO4]4–-tetrahedral symmetric stretching vibrations were also pronounced with higher SiO2/Al2O3 ratio. From the X-ray photoelectron spectroscopy (XPS) results, the bridged oxygen (O0) slightly decreased with higher TiO2/SiO2 and increased with higher SiO2/Al2O3.
