Sverre Rolseth

Liquidus temperatures for primary crystallization of cryolite in molten salt systems of interest for aluminum electrolysis

AbstractTemperatures for primary crystallization of Na3AlF6 in multicomponent electrolyte systems of interest for the aluminum electrolysis process were determined by thermal analysis. The results are presented as binary and quasibinary diagrams and discussed in view of the literature data. An empirical equation describing liquidus temperatures for primary crystallization of Na3AlF6 was derived:

Electrodeposition of Iron from Molten Mixed Chloride/Fluoride Electrolytes

\begin{gathered} t/(^\circ C) = 1011 + 0.50[AlF_3 ] - 0.13[AIF_3 ] - \frac{{3.45[CaF_2 ]}}{{1 + 0.0173[CaF_2 ]}} \hfill \\ + 0.124[CaF_2 ] \cdot [AlF_3 ] - 0.00542([CaF_2 ] \cdot [AlF_3 ])^{1.5} \hfill \\ - \frac{{7.93[Al_2 O_3 ]}}{{1 + 0.0936[Al_2 O_3 ] - 0.0017[Al_2 O_3 ]^2 - 0.0023[AlF_3 ] \cdot [Al_2 O_3 ]}} \hfill \\ - \frac{{8.90[LiF]}}{{1 + 0.0047[LiF] + 0.0010[AlF3]^2 }} - 3.95[MgF_2 ] - 3.95 \hfill \\ \end{gathered}

Liquidus Temperature and Alumina Solubility in the System Na3AlF6-AlF3-LiF-CaF2-MgF2

wheret is the temperature in degree Celsius and the square brackets denote the weight percent of components in the system Na3AlF6-AlF3-CaF2-Al2O3-LiF-MgF2-KF. The composition limitations are [AlF3] ≈ [CaF2] ≈ [LiF] < 20 wt pct, [MgF2] ≈ [KF] < 5 wt pct, and [A12O3] up to saturation.

Design and performance of a laboratory cell for determination of current efficiency in the electrowinning of aluminium

The corrosion rates of inert anodes based on tin oxide and nickel ferrite cermet materials were studied as a function of some operating parameters. To reach a better understanding of the corrosion mechanism, the behavior of the anodes was observed under some specific conditions, such as in pure cryolite, at high current densities, at different potentials, and at varying cathode surface areas. It was confirmed that low alumina concentrations led to catastrophic corrosion of the anodes and that high current densities and high as well as low NaF/AlF3 molar ratios were also detrimental. The corrosion rate of tin oxide based anodes showed a minimum (so-called “normal corrosion”) at anodic potentials of 2.2 to 2.4 V with respect to aluminum. The normal corrosion is due to chemical dissolution of the anode material and reduction of the corrosion products into the cathode metal. The corrosion rate increased with increasing cathode surface area. At potentials higher than ∼2.5 V, the anodes showed catastrophic corrosion. Catastrophic corrosion can be ascribed to decomposition of the anode material by depletion of alumina at the anode surface provoked by low bulk concentration of alumina and/or high current density.

Low Voltage PFC Emission from Aluminium Cells

The electrochemical behavior of dissolved Fe2O3 and the electrodeposition of iron in molten CaCl2-CaF2 (80-20 mol %) and other mixed chloride/fluoride electrolytes was studied at 827 °C and 890 °C by cyclic voltammetry, chronoamperometry and galvanostatic electrolysis, and deposits were characterized by XRD and SEM. Pure iron was obtained in these melts at current efficiencies greater than 90 %. High cathodic current densities (~0.5 A cm -2 ) were achieved by using a rotating cathode. The work is related to studies of the possible development of new processes for the production of iron and steel with large reductions of CO2 emissions.

Field Study of the Anodic Overvoltage in Prebaked Anode Cells

Abstract Oxygen-evolving, non-consumable anodes are being developed for use in industrial aluminum production. Ceramic-type electrodes dissolve slowly into the electrolyte, a process governed by mass transport conditions. For achievable anode life, factors determining mass transfer rates at the cathode are generally more important than those at the anode. This is discussed by means of model calculations and using experimental results. The roles of incomplete alloying of anode constituents with the aluminum upon reduction at the cathode and of metal dissolution from the cathode are also treated.

A Laboratory Study of Electrochemical Removal of Noble Elements from Secondary Aluminium

The liquidus temperature for primary crystallization of cryolite in the system Na3AlF6-AlF3-LiF-CaF2-MgF2 was determined by thermal analysis. The data were fitted to an empirical equation, valid from 1011 °C to approximately 800 °C. The alumina solubility was determined from the weight loss of a rotating sintercorundum disc. The investigated temperature range was 850–1050 °C, and the data were fitted to an empirical expression. The data are also presented in the form of quasi-binary phase diagrams.

Thermal effects by anode changing in prebake reduction cells

A new and improved laboratory cell has been specifically designed for determination of current efficiency (CE) as a function of isolated variable parameters in the Hall-Heroult aluminium electrolysis process. The anode is designed to give enhanced and reproducible bubble induced electrolyte convection, while the wettable cathode gives a well defined cathode area, and thus a uniform cathodic current density. Results are given of CE and cathode polarization as functions of cathodic current density, and of CE as a function of interpolar distance. Experiments show reproducible and high values of CE, and low and consistent values of cathode polarization. The CE does not vary for interpolar distances between 10 and 40 mm in the present cell. The cell is well suited for experimental determination of CE as function of electrolyte composition, including impurity concentrations, temperature and current density.