Ernest W. Dewing

Gaseous complexes formed between trichlorides (A1C13 and FeC13) and dichlorides

It has been found that in general the volatility of dichlorides is much enhanced in the presence of gaseous A1C13 and FeCl3, and the existence of the complexes MA12C18, MAl3Cl11, and MFe2Cl8 is postulated. ΔHT, ΔST, andT for MCl2(s) + 2AlCl3(g) = MAl2Cl8(g) are CaCl2: −17.8 kcal, −25.7 cal K−1 at 900 °K; CoCl2: −15.2, −19.4 at 750°K; MgCl2: −13.8, −17.9 at 800°K; MnCl2: −15.8, −20.9 at 750°K; NiCl2: −16.3, −24.2 at 750°K. For MCl2(s) + 3AlCl3(g) = MAl3Cl11(g) − CaCl2: −30.0, −40.5 at 900°K; CoCl2: −36.6, −47.4 at 700°K; MgCl2: −42.6, −55.4 at 750°K; MnCl2: −33.3, −42.0 at 750°K. For MCl2(s) + 2FeCl3(g) = MFe2Cl8(g) − CdCl2: −19.4, −20.9 at 700°K: CoCl2: −16.5, −17.2 at 800°K, MnCl2: −19.1, −21.2 at 750°K; NiCl2: −19.7, −24.4 at 800°K. Enhanced volatility was also found for ZnCl2, PbCl2, and CuCl, but since the condensed phase was liquid of unknown composition no calculations could be made. Owing to the interplay of the above equilibria with the dimerization equilibria for A1C13 and FeCl3 the effective vapor pressures of the dichlorides in the presence of the trichlorides pass through maxima in the region 600° to 700°C.

Thermodynamics of the system NaF-AIF3: Part VI. revision

Literature data are reviewed to derive enthalpies and entropies of Na3AlF6 and NaF, and they are combined with electrochemical and equilibrium data to yield free energies of formation of Na3AlF6 from the constituent fluorides. Liquidus data and measurements of the Na content of Al in equilibrium with the melts then enable the calculation of the free energy of formation, enthalpy, and entropy of all mixtures liquid at 1293 K. In stoichiometric Na3AlF6 at 1293 K, aNaF =0.37 and aAlF3 = 4.9 × 10−4. The activity coefficient of Na in dilute solution in Al is given byRT ln γNa = (40 967 + 9.480 T) J. At 1293 K the partial pressure of NaAlF4 is given by pNaA1F4/bar = 27aNaF . aAif3- A heavier species— suggested to be NaAl3F10—is present in the vapor above AlF3-rich melts.

Loss of current efficiency in aluminum electrolysis cells

Consideration of the mechanism of loss of current efficiency (CE) leads to a form of equation which is simple, likely to give reasonable extrapolation beyond the range where experimental data are available, and convenient for responding to practical questions. With coefficients generated from plant experiments (performed by others), the equation is log (pct loss of efficiency) = 0.0095 (superheat) -−0.019 (pct A1F2) − 0.060 (pct LiF) + const where superheat is the difference (in °C) between cell temperature and the pseudo-binary eutectic temperature with A12O3, and pct A1F3 is excess A1F3. The coefficient for CaF2 is zero. The constant is characteristic of the cell design. The question of reconciling the values of the coefficients with literature data on the solubility of Al in cryolite melts and current theories of loss of efficiency is discussed.

The chemistry of solutions of CeO2 in cryolite melts

The solubility of CeO2 in cryolite has been investigated as a function of oxygen pressure, alumina content of the melt, and A1F3 content of the melt. Additional information comes from cryoscopic measurements, cyclic voltammetric studies, and thermodynamic calculations. The conclusions are that (a) cerium in solution is exclusively Ce(III), (b) the dominant species are CeOF and CeF3, the latter probably complexed as Na2CeF5, (c) control of oxygen pressure is of importance in measuring the solubility of the oxide of any metal that has more than one oxidation state, but (d) there may be serious kinetic difficulties in equilibrating gas and molten salt.

Thermodynamics of the system NaCl-AlCl3

AbstractHeat capacities of melts were measured in the range 400 to 1100 K and 0.48 < NAlCl3 < 0.62, the results being expressed by Cp = 40.96 – 0.0295T + 2.01 × 10−5T2 J K−1 g·atom−1i.e., AlCl3 contains 4 atoms, and so forth). This equation was used in interpreting literature vapor pressure data. Measurements were made of the emf of the concentration cell % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaacbaqcaaUaa8% xqaiaa-XeakmaaeeaajqgaGeqaaOWaa0baaSqaaiaa-feacaWFSbGa% a83qaiaa-XgadaWgaaadbaGaaG4maaqabaaaleaacaWFobGaa8xqai% aa-neacaWFSbGaaiikaiaa-nhacaWFHbGaa8hDaiaacMcaaaaajqga% GeGaay5bSdGcdaabbaqcKbaibeaakmaaDaaaleaacaGGOaGaa8Ntai% aa-fgadaahaaadbeqaaiabgUcaRaaaliaacMcaaeaacaWFqbGaa8xE% aiaa-jhacaWFLbGaa8hEaaaaaKazaasacaGLhWoakmaaeeaajqgaGe% qaaOWaa0baaSqaaiaa-feacaWFSbGaa83qaiaa-XgadaWgaaadbaGa% aG4maaqabaaaleaacaWFobGaa8xqaiaa-neacaWFSbGaaiikaiaa-n% hacaWFHbGaa8hDaiaacMcaaaaajqgaGeGaay5bSdGcdaabbaqcKbai% beaakmaaDaaaleaacaWFbbGaa8hBaiaa-neacaWFSbWaaSbaaWqaai% aaiodaaeqaaaWcbaGaa8Ntaiaa-feacaWFdbGaa8hBaaaaaKazaasa% caGLhWoakmaaeeaajqgaadqaaiaa-feacaWFmbaacaGLhWoajaaOca% WFGaaaaa!71A5!

Activities in the system LiF−NaF−AlF3

AL\left| {_{AlCl_3 }^{NACl(sat)} } \right.\left| {_{(Na^ + )}^{Pyrex} } \right.\left| {_{AlCl_3 }^{NACl(sat)} } \right.\left| {_{AlCl_3 }^{NACl} } \right.\left| {AL} \right.

The interfacial tension between aluminum and cryolite melts saturated with alumina

at temperatures 473 to 623 K, and the results were correlated with the vapor pressure data to yield activities of NaCl and AlCl3. Measurements with a sodium electrode confirmed the accepted values for the free energy of formation of A1C13 within about 1.5 kJ mol−1. The activities were used to analyze the phase diagram. Direct measurement of the eutectic temperature with a concentration-cell technique (which avoids supercooling) gave 386 K; the eutectic composition is 60.0 mol pct A1C13. The standard entropy of NaAlCl4(s) is S298.15° = 199.1 J K−1 mol−1. The free energy for NaAlCl4(l) = NaAlCl4(g) is ΔG° = 82740 −63.66T J mol−1 at around 950 K.

The rate of formation of intermetallic layers between aluminum and steel below 660°C

This paper assembles literature data, mainly vapor pressures and concentration-cell electromotive forces (emfs), from which the variation of activity of NaF and A1F3 when a third substance is added to Na3AlF6 can be deduced. The necessary theory is derived. Where there is more than one source of information on a given substance, the agreement is poor, showing imprecision in the experimental data. Substances are characterized by ∂ In aAlF3/∂N3, whereN3 is the molar fraction of the additive, and a value of -1 is neutral, since it corresponds to a dilution effect. Positive values show acids; A1F3 itself has a value of +27.9, while NaF has a value of -27.9. BeF2 and MgF2 are strong acids with values of +11, CaF2 is a weak acid with a value of +2, and LiF, SrF2, BaF2, and 1/3(A12O3) are weak bases with values of -2 to -3.