Influence of TiO2/SiO2 and MnO on the viscosity and structure in the TiO2–MnO–SiO2 welding flux system

The low viscosity of the TiO2–MnO–SiO2 based ternary welding flux system has been studied using the rotating spindle method to understand the influence of TiO2/SiO2 and MnO on the viscous behavior at high temperatures. Viscosity slightly decreased with increased TiO2/SiO2 and MnO due to the limited absolute amount of SiO2 content and also the depolymerization of the flux due to the supply of free oxygen (O2 −) from the basic oxides of MnO and TiO2. The flux structure, which directly affects the viscosity of the flux, was verified by using Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS). FTIR results showed that the transmittance trough depth of the NBO/Si tetrahedral structure became less pronounced with higher MnO and TiO2 due to the relative decrease in the absolute SiO2 concentration and dominant of higher basicity. The SiOTi bending vibration trough also showed a marked decrease with the additions of MnO and TiO2, which suggests that the change in viscosity for the present flux system may also be the depolymerization of the bridged oxygen in the SiOTi complex network structures. XPS analysis suggested a slight decrease in the O° and an increase in the O2 −, O− with higher TiO2 and MnO. Thus, a decrease in the viscosity of the flux with higher TiO2/SiO2 and MnO content correlated well with the FTIR and XPS analyses. The apparent activation energy for viscous flow was found to be between 40 and 105 kJ/mol.