FACT Hall-Héroult Database


The FThall Database has been developed for thermodynamic and phase equilibrium calculations involving liquid metal – cryolitic bath – Al2O3-based oxides in alumina reduction electrolysis cells, and for molten aluminum treatment with fluoride fluxes.


The FThall Database is a self-contained database for the Al-Mg-Na-Li-Ca-F-O-C system. No extra phases from other databases are needed for this 8-component system (except Al-Ca and Mg-Ca stoichiometric intermetallic phases Al4Ca, Al2Ca, Mg2Ca, etc…, and the Li-Mg-BCC and Mg-Li-HCP solid solutions). The element “C” refers to the solubility of Al4C3 in presence of dissolved metal (with Al4C3(s) and Al4O4C(s) saturations) and the solubility of CO2(g) (in the form of carbonates) in the NaF-AlF3-CaF2-Al2O3 base electrolyte.


The Gibbs energy parameters of the FThall Database have been obtained by a critical analysis and optimization of all available thermodynamic data and phase equilibrium data for the Al-Mg-Na-Li-Ca-F-O-C system. These include electromotive force (emf), calorimetry (mixing enthalpies, dissolution enthalpies, heating curves, etc…), metal-salt-gas equilibria (vapour pressures, equilibrium alkali-content of molten Al with different bath compositions), phase diagram data (liquidus, solubilities, eutectic temperatures, etc…).


In general, the simultaneous use of data from FThall and any other database may give rise to problems of compatibility.


A density model (taking into account excess volume upon mixing) and a viscosity model are available for the NaF-AlF3-CaF2-Al2O3-LiF-MgF2 electrolyte as a function of temperature and composition. Results are less satisfactory for very acidic baths (CR = molar ratio NaF / AlF3      < 1.50). In order to perform density and/or viscosity calculations for the cryolitic bath, the following procedure must be followed : in the Menu Window of Equilib, select the liquid solution FThall-BathA and check the box “include molar volumes”. (The viscosity model uses both the molar volume calculated from the density model and the quadruplet mole fractions calculated from the thermodynamic model, in addition to the viscosity model parameters.) In the Results Window, the density value (in gram/cm3) calculated from the model is displayed (in parentheses) at the 2nd line of the block corresponding to the liquid phase. A system density (in gram/cm3) that takes into account the available density data for all phases at equilibrium (liquid + 1 or more solid phases) is displayed below the integral property table. The viscosity value (in Pa.s) calculated from the model is displayed at the end of the block corresponding to the liquid phase.


Volumetric properties (density) as a function of temperature were entered for the Al, Ca, Li, Mg and Na pure liquids in the “Liqu” liquid metal solution of the FThall database. Moreover, a density model (taking into account excess volume upon mixing) is available for the Al-Mg binary liquid. Approximate density calculations may be performed for the entire Al-Ca-Li-Mg-Na liquid metal : all binary liquids other than Al-Mg are then assumed to be ideal (in terms of the volumetric properties). A viscosity model is available for the Al-Mg binary liquid. Currently, viscosity calculations (even approximate) CANNOT be performed for metallic systems other than Al-Mg. In order to perform density and/or viscosity calculations for the liquid metal, the following procedure must be followed : in the Menu Window of Equilib, select the liquid metal solution FThall-Liqu and check the box “include molar volumes”. The density value (in gram/cm3) and the viscosity value (in Pa.s) calculated from the models are displayed in the Results Window, as described before.     





The following SOLUTIONS are found in the FThall Solution Database:


Cryolitic bath                                                                          FThall - Bath

High-temperature Na3AlF6 solid solution                               FThall - CryH

Low-temperature Na3AlF6 solid solution                                FThall - CryL

Very low-temperature Li3AlF6 solid solution                         FThall - LiCB

Low-temperature Li3AlF6 solid solution                                 FThall - LiCG

High-temperature Li3AlF6 solid solution                                FThall - LiCD

Cryolithionite Na3Li3Al2F12 solid solution                              FThall - CrLt

NaF rocksalt solid solution                                                     FThall - NaF

LiF solid solution                                                                    FThall - LiF

MgF2 solid solution                                                                 FThall - MgF2

Liquid alloy                                                                             FThall - Liqu

FCC Al-rich solid solution                                                      FThall - FCC

HCP Mg-rich solid solution                                                    FThall - HCP

BCC Ca-rich or Na-rich solid solution                                   FThall - BCC

Al12Mg17 gamma solid solution                                               FThall - AlMg

MgAl2O4 spinel solid solution                                                FThall - Spin

Monoxide CaO – MgO solid solution                                                FThall - Mono



The following COMPOUNDS are found in the FThall Compound Database:


Li                          L   

C                           S   

Li2O                        S    L   

LiF                         S    L   

Na                          L   

Na2O                        S1   S2   S3   L   

Na2CO3                      S1   S2   S3   L   

NaF                         S    L    G   

(NaF)2                      G   

Mg                          S    L   

MgO                         S    L   

MgF2                        S    L   

NaMgF3                      S   

Al                          S    L   

Al4C3                       S   

Al2O3                       S1   S2   S3   S4   L   

LiAlO2                      S   

Al4O4C                      S   

AlF3                        S1   S2   L   

Li3AlF6                     S1   S2   S3  

NaAlO2                      S1   S2  

NaAl9O14                    S   

Na2Al12O19                  S   

Na3AlF6                     S1   S2  

Na5Al3F14                   S   

Na2LiAlF6                   S1   S2  

MgAl2O4                     S   

Na2MgAlF7                   S   

Na2Mg2Al3F15                S   

Ca                          S1   S2   L   

CaO                         S    L   

CaCO3                       S1   S2   L   

CaF2                        S1   S2   L   

Na2Ca(CO3)2                 S1   S2  

CaAl2O4                     S   

CaAl4O7                     S   

CaAl12O19                   S   

Ca3Al2O6                    S   

CaAlF5                      S1   S2  

Ca2AlF7                     S   

LiCaAlF6                    S   

Ca12Al14F2O32               S   

NaCaAlF6                    S1   S2   S3  

NaCaAl2F9                   S   

Na2Ca3Al2F14                S   

Na4Ca4Al7F33                S   


Note: all gaseous species (NaAlF4, Na2AlF5, AlF3, AlF, AlOF, etc..) are found in the FactPS Compound Database.


Note: the FThall database is compatible with C(graphite), CO(g), CO2(g) and other C-O species in the FactPS Compound Database.


The following limitations should be considered when using FThall:


·                     Metal dissolution in the bath - NaF-AlF3-[Na-Al]:     the model covers the whole liquid range for P < 3 atm (the Na-NaF liquid miscibility gap cannot be "closed" at high pressures). Metal dissolution outside the NaF-AlF3-Al2O3 system is approximate.


·                     Alumina dissolution in the bath - NaF-AlF3-Al2O3:   the model has good predictive capabilities for CR < 5 and CR > 1.5 and for T < 1100oC. A spurious miscibility gap appears for very high CR at NaAlO2-NaAl9O14 co-saturation.


·                     Fluoride additives:      In the oxide-free system, the model covers the whole range of composition in the LiF-NaF-MgF2-CaF2-AlF3 system but predictions in the LiF-MgF2-AlF3 system rich in AlF3 are not very good.  The error in the calculated liquidus of AlF3 may also be large in the CaF2-AlF3 system.


·                     Density and viscosity models for the NaF-AlF3-CaF2-Al2O3-LiF-MgF2 electrolyte : Results are less satisfactory for very acidic baths (CR < 1.50).