Viscosity Model for Oxide Melts Relevant to Coal Ash Slags Based on the Associate Species Thermodynamic Model

A viscosity model based on the associate species thermodynamic model is currently being developed for liquid melts of the Al 2 O 3 –K 2 O–Na 2 O–SiO 2 –CaO–MgO–FeO–etc. system and subsystems relevant to coal ash slags. In the present publication, we focus on the quaternary subsystem Al 2 O 3 –SiO 2 –Na 2 O–K 2 O. The model employs concentrations of the associate species obtained from the recent thermodynamic assessments of these systems. Modified Avramov and Arrhenius approaches were investigated as possible means to describe the viscosity. The original viscosity equations were modified to include the compositional and structural dependence of the viscosity. Associate species introduced in the thermodynamic model were found to provide a reasonable approximation of the melt structure that was confirmed by comparison to available spectroscopic data. A comparison of the two approaches shows their specific applicability with respect to temperature and composition dependence.