Modeling the viscosity of liquid solutions used in aluminum alloys production

This work is a part of VLAB (A Virtual Laboratory for the aluminum industry) project aiming to develop thermodynamic and physical properties databases required by the aluminum industry. These databases can be accessed through the FactSage thermochemical software to perform multi-component thermodynamic and physical property calculations for the processes involved in the aluminum industry.;The available viscosity models in the literature are reviewed and a structural based viscosity model is presented that can predict the viscosity of multi-component systems by simultaneously employing the density and thermodynamic models. A modification is proposed to the model to better reproduce the composition dependency of the viscosity in highly short-range ordered systems.;The temperature dependency of the viscosity in this model is given by an Eyring type exponential equation. The activation energy for viscous flow of a multi-component system is given by the summation of the activation energies of the second nearest neighbor (SNN) pairs present in the melt. The composition dependency of the viscosity for a liquid mixture is thereby expressed in the viscous activation energy term through the variation of the SNN pair fractions upon mixing (the SNN pair fractions being calculated by the thermodynamic model). The activation energies for the SNN pairs are the parameters of the model given by linear functions of temperature. However for highly short-range ordered systems, the model is modified by introducing composition dependent terms in the activation energy as well as the temperature dependent terms.;The model parameters are optimized based on the reliable experimental data. A thorough literature review is performed to collect the available experimental data. The experimental viscosity measurement methods are introduced and compared to each other. The most reliable data sets are selected based on the critical review of the employed measurement methods. Due to the inconsistencies between the reported unary and binary data sets in the literature, correction functions are applied to the data and the systematically corrected binary data sets are employed for the optimizations.;The objective of this master project is to model the viscosity of liquid solutions involved in the aluminum production process namely, NaCl-KCl-MgCl ₂-CaCl₂ liquid solution and Al-Si-Zn liquid alloy. The main aim is to develop a viscosity database that can be used for the viscosity calculations of these multi-component mixtures at various compositions and temperatures.;The calculated viscosity curves by the proposed modified form of the model could well reproduce the viscosity behavior predicted by the experiments for simple binary systems: NaCl-KCl, MgCl₂-CaCl₂, NaCl-CaCl ₂ and KCl-CaCl₂ as well as the highly short-range ordered systems: NaCl-MgCl₂, KCl-MgCl₂, RbCl-MgCl ₂ and CsCl-MgCl₂. There were few experimental data in the literature for multi-component molten salt systems, however the predictions of the model for NaCl-KCl-MgCl₂-CaCl₂ system compare reasonably well with the available experimental data reported for a limited range of composition and temperature. The viscosity curves calculated by the model well reproduce the experimental data reported for the Al-Zn and Al-Si binary alloys.;In summary, the model leads to very satisfactory results for the molten chloride mixtures and liquid aluminum alloys studied in the present work. The proposed modification to the model could properly reproduce the viscosity behavior of highly short-range ordered systems as a function of composition of the melt. The optimized model parameters as well as the modified composition dependent parameters are added to the viscosity database of the molten salts and liquid alloys. Employing the mentioned database, viscosity calculations for multi-component molten salts and aluminum alloys can be performed. This viscosity database is included in the FactSage 5.6 data bases where the viscosity of multi-component molten salts and binary aluminum alloys can be calculated through the presented viscosity model by simultaneously employing the thermodynamic and density models.