Activities in the system cryolite-alumina

Abstract

Reasons are outlined for thinking that accepted values for the activity of Al 2 O 3 in solution in cryolite are in error, and a new analysis is made of literature cryoscopic data. A general treatment is given for the effect of incongruent melting caused by the nonstoichiometry of solid cryolite. The effect is substantial, and accurate calculations require a knowledge of the effect of the solute on the activity of NaF in the solution, since that controls the composition of the solid separating. The results in the case of alumina as solute show that the slope of the log (activity) vs log (concentration) plot is about 3 in dilute solution and 1.5 in concentrated solution, corresponding to species containing 1 and 2 atoms of oxygen, respectively. Any calculations employing the earlier relation ϰ (wt pct a Al O 2 3 Al 2 O 3 ) 2.77 , which was based on electrochemical measurements of activity, need to be redone.

Solubility of some transition metal oxides in cryolite-alumina melts: Part I. Solubility of FeO, FeAl2O4, NiO, and NiAl2O4

“…was much slower to reach saturation, probably because of Figure 4 shows a log-log plot of the solubilities as a the use of tablets instead of powder, and 5 hours stirring function of the alumina activity, which is taken from the time was necessary. A sample of 3 to 6 g was withdrawn equation proposed by Dewing and Thonstad [22] for the binary from the melt by sucking it up into a quartz tube immersed cryolite-alumina system: 5 to 10 mm into the solution. The liquid was quenched on N Al 2 O 3 ϭ 0.0772a 1/3 Al 2 O 3 ϩ 0.159a 2/3…”

Entropic Heat Effects in Aluminum Electrolysis Cells with Inert Anodes

“…For the system [10] (a) for sodium fluoride as a function of the NaF/ AlF 3 molar ratio (r), (b) for aluminum fluoride as a function of r, (c) for (AlF 3 -3NaF) as a function of r, (d) for alumina as a function of the alumina concentration at different r. Na 3 AlF 6 -Al 2 O 3 , there is very good agreement between Solheim and Sterten [10] and Dewing and Thonstad. [14] Generally, the mentioned activity models show the same trends, and all models are based on Hong and Kleppa's set of experimental enthalpies of mixing in the system NaF-AlF 3 .…”

“…[14] through [16] with the data shown in Figure 1, and the result is shown in Figure 2. As can be observed, there is a moderate heating of the cathode, about 0.2 to 0.4 V depending on the NaF/AlF 3 ratio, but almost independent of the alumina concentration.…”

Prédiction de l'efficacité de courant du procédé Hall-Héroult /

“…Elle correspond à la sommation du potentiel à l'équilibre ainsi que des diverses surtensions. Des expérimentations effectuées par Dewing et Thonstad [9], publiées en 1999, ont permis de démontrer que l'exposant de l'équation de Rolin devrait être de 1.5 plutôt que de 2.77. Les diverses surtensions, incluent dans la force contre-électromotrice, ne seront pas traitées dans cette section, mais seront l'objet des pages qui suivent.…”