The high temperature viscosity of the TiO
2-MnO-Al
2O
3-8.64ZrO
2-2.77Na
2O welding flux system was measured by the rotating spindle method to identify the relationship between the viscosity and melt structure at various compositions of TiO
2, MnO, and Al
2O
3 contents. At temperatures of 1773 K to 1748 K and fixed TiO
2/MnO ratio, the effect of Al
2O
3 on the viscosity was not significant, but slightly increased with higher Al
2O
3. At temperatures below 1748 K, the effect of Al
2O
3 was more pronounced with increments of Al
2O
3 significantly increasing the viscosity of the molten flux. Increased extended basicity ((TiO
2/+1.13MnO)/SiO
2) depolymerized the network structure, where TiO
2 and MnO works to depolymerize the present melt. Raman analysis of as-quenched oxide melts from 1773 K showed the symmetric [AlO
4]-tetrahedral stretching vibrations to increase and the asymmetric [AlO
6]-octahedral stretching vibrations to decrease with higher concentration of Al
2O
3 at various fixed TiO
2/MnO ratios suggesting polymerization of the structure with Al
2O
3 additions. The opposite trend could be observed with increasing extended basicity. XPS (x-ray photoelectron spectroscopy) results showed the bridged oxygen (O
o) to increase and the non-bridged oxygen (O
–) to decrease with Al
2O
3 additions and lower extended basicity also suggesting polymerization of the network structure in the present melt system.
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