The solubility of titanium dioxide in cryolite-alumina melts at 1300 K

Modeling of the solubilities of NiO/NiAl2O4 and FeO/FeAl2O4 in cryolite melts at 1300 K

“…As presented in the previous article, [8] the solubility of alumina in cryolite melts at 1300 K is described in terms of three oxyfluoride solutes Na 2 Al 2 OF 6 (acidic solute, called A), Na 2 Al 2 O 2 F 4 (neutral solute, called N), and Na 4 Al 2 O 2 F 6 (basic solute, called B), and two oxygen-free solutes Na 3 AlF 6 (called C) and NaAlF 4 (called E), excluding the questionable solute Na 2 AlF 5 with an asymmetric anion geometry. These equilibria are given by [1] [2] [3] [4]…”

“…For the elemental balance of oxygen, [12] where x 3 is the molar fraction alumina solubility in the cryolite melt. [8] and [9]. For the Na elemental balance, [13] For the Al elemental balance, [14] For the F elemental balance, [15] In addition to these elemental balances, the sum of molar fractions for all the solutes should be unity for each composition of cryolite melt: [16] These equations are solved simultaneously upon the introduction of experimental data for the unknown equilibrium constants K 6 and K 7 in Eqs.…”

“…They determined experimentally: (1) the solubilities of NiAl 2 O 4 and FeAl 2 O 4 in Al 2 O 3saturated cryolite melts for 1293 K over wide melt composition ranges of 2 Յ cryolite ratio r Յ 12 and 2 Յ r Յ 8, respectively (cryolite ratio r is defined as the ratio of moles NaF to moles AlF 3 ); (2) the temperature dependence of the solubility of NiAl 2 O 4 and FeAl 2 O 4 in the Al 2 O 3 -saturated "stoichiometric" cryolite melt (r ϭ 3); and (3) the solubilities of NiO/NiAl 2 O 4 and FeO/FeAl 2 O 4 in Al 2 O 3 -undersaturated "stoichiometric" cryolite melts (r ϭ 3) in dependence upon the dissolved Al 2 O 3 concentration for 1293 K. The authors [6,7] used the traditional log-log methodology to discuss the dissolution mechanisms. [7] As emphasized in a previous article, [8] the log-log method of thermodynamic modeling is only effective when indeed a single solute species is dominant over a specific range of melt composition. In the FeAl 2 O 4 case, they failed to identify the Fe-containing solute species in the melts using the log-log method.…”

The Solubility of Some Transition Metal Oxides in Cryolite-Alumina Melts: Part III. Solubility of CuO and Cu2O

“…The problem, however, is to decide what terms should entered into the regression analysis, and that information can be generated only by studying log-log plots of the dependence of the solubilities on the activity of alumina. Although Zhang and Rapp [13] have criticized the procedure, there is simply no other way to start elucidating a system as complex as the present one. Interpretation of the results at 1020°C thus proceeds in three stages.…”

“…The experimental data are too scattered and do not extend far enough for a limiting slope to be established accurately, since it seems that both species are present to a significant extent over the whole range investigated. One must instead adopt equation [13] as a working hypothesis for the mechanism of solution in the low-alumina region and see if a consistent interpretation can be found. The quantity K 1 can be written as the sum of two terms: Fig.…”