Structural and Viscous Insight into Impact of MoO3 on Molten Slags

In high-temperature experiments, the widely used molybdenum products may contaminate molten slags, affecting the properties of samples and thus the experimental accuracies. However, this impact has received little attention. Therefore, we have first undertaken detailed studies on the structure and viscosity of MoO3-containing molten slags, with a special focus on the characteristics of Mo, Si, and Al using molecular dynamic simulation and experimental measurements. It was found that the Mo ions in the molten slags were mainly hexavalent and in a four-fold coordinated state (MoO4), with the ability to polymerize Si-related frameworks and weaken bonds of the Al complexes. The decreasing degree of polymerization for the whole melt networks occurred because the introduced MoO4 tetrahedra existed as isolated islands that provided additional non-bridging oxygens. As a reflection of the microscopic structure, viscosities of molten slags at high temperatures gradually decreased, and viscous flow activation energy decreased from 218.47 to 167.79 kJ mol(-1) as MoO3 content increased from 0 to 5.7 pct. Furthermore, a universal approach to correct systematic error caused by Mo products in property tests was proposed. It was suggested to control the MoO3 content within 0.55 wt pct when the allowable viscosity error did not exceed 5 pct.

Automated summary

The research revealed that Mo ions in molten slags containing MoO3 are mainly hexavalent and in a four-coordinated state, significantly affecting the aggregation of Si-related frameworks and weakening bonds in Al complexes. As the MoO3 content increases, the polymerization of the entire slag network decreases, resulting in a gradual decrease in viscosity of molten slags at high temperatures.