Aluminium Pechiney

Aluminum Pechiney

Yves Bertaud

Michel Leroy

Gerard Picard

Bernard Jean Gurtner

Francoise Seon

Joseph Cohen

Maurice Keinborg

Philippe Varin

Evelyne Prat

Bernard Tremillon

The invention concerns a process and apparatus for electrochemical measurement of the concentration of oxide ions dissolved in a bath based on molten halides. The process is based on impedance measurement at a low current and a low overvoltage, between an indicator electrode, a reference electrode and a counter electrodes. The real value Z.sub.r of the impedance is determined for two frequencies, a low frequency Zr(B) (such as 15-25 Hz) and a high frequency Zr(H) (such as 10-100 kHz); the inverse of the concentration of oxide ions is a linear function of the difference between Zr(B) and Zr(H). This method has a high level of accuracy in the low ranges of concentration of oxide ions.

Process for electrochemical measurement of the concentration of oxide

The invention concerns a process for the electrolytic preparation of a mother alloy of iron and neodymium by the reduction of a mixture comprising at least one reactive oxygen-bearing compound of neodymium in a bath of molten halides with at least one metallic cathode, preferably of iron, and a carbon anode. In accordance with the invention, the bath is primarily formed by a mixture of molten fluorides whose decomposition potential is close to that of NdF.sub.3 or more negative, such as for example NdF.sub.3, MgF.sub.2, ScF.sub.3, CeF.sub.3, LaF.sub.3, BaF.sub.2, CaF.sub.2 and SrF.sub.2, and permitting solubilization of the oxides by a complexing effect, the solute to be reduced is formed by a mixture of salts primarily containing a reactive oxygen-bearing compound of neodymium which is very rapidly soluble in the molten electrolyte. The working temperature is in a range of from 640.degree. to 1030.degree. C., the anodic current density is from 0.1 to 1.5 A/cm.sup.2, and the cathodic current density is between 2 and 30 A/cm.sup.2.

Process for the preparation of mother alloys of iron and neodymium by

A process for the production of aluminum by the electrolysis of anhydrous aluminum chloride produced by the carbochlorination of alumina in a molten salt bath containing at least one alkali metal and/or alkaline-earth metal halide, comprising carrying out the carbochlorination of the alumina and electrolysis of the aluminum chloride in a continuous production loop using the molten salt bath emanating from carbochlorination as the electrolysis bath and the molten salt bath emanating from electrolysis as the carbochlorination bath.

Process for the continuous production of aluminum by the

Selective chlorination method for mixtures of metallic oxides of natural

The invention concerns floating cathode elements which are intended for the electrolytic production of aluminum using the Hall-Heroult process in an electrolysis tank comprising a molten cryolite-base bath, between a carbon anode, and a cathodic layer of molten aluminum, said elements comprising at least one active cathode element (30) formed of electrically conductive refractory material such as titanium diboride and supported by an intermediate support (31) which is inert with respect to the liquid aluminum and the electrolyte, the mean relative density of the assembly of the acitve cathode element and the inert intermediate support being lower than the relative density of the liquid aluminum under the normal conditions of operation of the electrolysis tank. They may also and preferably be provided with anchoring and abutment means (32) for limiting the amplitude of movements thereof in a vertical direction, and guide means for limiting the amplitude of movements thereof in directions other than a vertical direction.

Floating cathode elements based on electrically conductive refractory

A subcathodic shield for use with Hall-Heroult electrolysis cells. The shield, which is located below the carbonaceous blocks which make up the cathode, and above the cell housing, comprises at least one continuous steel sheet at least 5 mm thick extending substantially over the total area between the base of the cathode and the base of the housing, and which has at least one deformable zone for absorbing thermal stresses caused by differences in temperatures between the shield section situated below the central area of the cathode and the shield section situated below the peripheral areas of the cathode.

Sub-cathodic shield with deformable zones for Hall-Heroult electrolysis

A cell for producing a metal by electrolysis of an anhydrous metal halide in a bath of molten salts comprises an external jacket of substantially parallelipipedal shape, having cooling means, ports for the input and output of liquid and gaseous fluids and means for supplying electricity, the lower end of the jacket includes a receptacle zone to collect the metal produced; a plurality of stacked electrodes in the central portion of the cell, each stack comprising, in a vertical direction and in descending order, a current supply electrode, intermediate multipolar members and a current output electrode, defining regular interpolar spaces; and a gas collecting zone in the top portion. The cell is characterized in that the multipolar members are assembled in a vertical stack, and the interpolar spaces are substantially vertical. The cell is particularly well adapted for the production of aluminum by electrolysis of the corresponding chloride.

Growing community of inventors

St. Jean de Maurienne, France

Yves Bertaud