DE1172859B - Cathode tank for the production of aluminum by fused-salt electrolysis - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Boarding school KL: C22d

German class: 40 c-3/12

Number: 1 172 859

File number: A 39030 VI a / 40 c

Filing date: December 15, 1961

Opening day: June 25, 1964

The main patent 1146 259 relates to a method for lining the walls of the cathode trough one cell for the production of aluminum by fused-salt electrolysis and one after Cathode pan manufactured using this method. Lining is done by pounding out a mass 40 to 85% silicon carbide powder, 45 to 7% coke powder and 15 to 8% pitch.

It has now been found that a cathode trough is lined with according to the method mentioned Sidewalls are very well suited for cells in which the current flows through elements made of carbides and / or borides of the transition metals titanium, zirconium, Tantalum and niobium are added to the cathodically deposited, molten aluminum.

In the following, instead of the expressions »carbides and / or borides of the transition metals« for the sake of simplicity, the term "hard metal" may be used. Such power supply elements are described e.g. in Swiss patents 301030, 330 206 and 346 033.

The power supply elements made of such "hard metal" can pass through the electrolyte bath vertically from above be introduced through to the liquid cathode metal layer.

The side walls lined according to the method of the main patent are particularly useful used in such aluminum electrolysis cells in which rod-shaped power supply elements Made of "hard metal" horizontally or almost horizontally in the side walls of the cathode tray are arranged and extend with their end to the liquid cathode metal. The poor thermal conductivity the silicon carbide-containing compound allowed the wall lining to be kept thinner than it was with the usual synthetic carbon mass is possible, so that the »hard metal current supply elements, the are very expensive, can be kept shorter.

It has already been proposed, in such a case, to manufacture the side walls of the cells from silicon carbide bonded to clay or from silicon carbide bonded to nitride. Apart from the fact that the binding agent used for joining plates or blocks made of these materials is attacked by the fusible electrolyte and that the plates or blocks can usually not be so tightly connected that the fusible electrolyte does not penetrate the joints over time, Protection by a crust of solidified electrolyte is necessary, since in particular the clay-bonded silicon carbide of the liquid aluminum and of the melt-flow cathode trough for the production of
Aluminum by fused salt electrolysis

Addendum to the patent: 1,146,259

Applicant:

Swiss Aluminum A. G.,

Chippis (Switzerland)

Representative:

Dr. K. Schwarzhans and

Dipl.-Chem. Dr. phil. E. Jung, patent attorneys,

Munich 19, Romanplatz 10

Named as inventor:
Dipl.-Chem. Dr. Erhard Herrmann,
Neuhausen am Rheinfall (Switzerland)

Claimed priority:

Switzerland of January 30, 1961 (1051)

electrolytes are attacked. The thickness of the solidification crust requires a correspondingly larger one Length of the power supply elements made of "hard metal".

Side walls made of the silicon carbide-containing lining compound described in the main patent are required a protection by solidified electrolyte not, so that with the same thickness of the lining the Power supply elements made of "hard metal" can be kept shorter than in the case of a lining made of clay-bonded or nitride-bonded silicon carbide.

Further advantages result from the following versions:

According to the method of the main patent, the side walls of the cathode trough are not lined with pre-formed, cemented together ceramic plates, but with a new type of compound that is tamped in a known manner and made, as stated above, of 40 to 85% silicon carbide powder, 45 to 7% coke powder and 15 to 8 ^fl / o pitch composed.

409 627/307

The following, narrower composition is preferably used:

Silicon carbide powder .. 70 to 80 percent by weight

Coke powder 15 to 10 percent by weight

Medium hard pitch 15 to 10 percent by weight

A mixture of 75% silicon carbide, 14% coke powder and 11% Medium hard pitch proven. It is of course possible to use small amounts of other rammed earth Adding substances as long as they do not impair the result.

The silicon carbide should be present in the rammed earth described in grain sizes from 0 to 6 mm. The coke powder can be made from any type of coke and should have a grain size from 0 to 22 mm. The mixture is expediently at a temperature between 50 and 250 ° C, with any type of pitch added either in pre-liquefied form or in pieces will.

The mechanical strength achieved by the new mass after tamping is based on the mutual Effect of pitch and powdered coke. Pitch and coke powder form a kind of honeycomb structure, the silicon carbide is embedded in the cavities as a filler body.

The new tamped mass is in a reducing atmosphere against the fusible electrolyte and against liquid aluminum resistant. Their electrical conductivity is 5- to depending on the silicon carbide content 15 times smaller than that of the previously used charcoal rammed earth. The thermal conductivity is smaller by the same order of magnitude.

A major advantage of the new rammed earth is that it works in the same way as before Usual artificial coal rammed mass processed and used for the production of rammed wall linings can be.

The new rammed earth can be firmly and seamlessly with the aluminum electrolysis cells in the construction up to now connect common carbon materials. A significant advantage of making the wall lining from the ramming mass according to the specification as opposed to the structure made from preformed silicon carbide containing plates is that the entire cathode trough can be made seamless.

Also the bottom of the cell with »hard metal power supply elements to the liquid cathode metal can be made from the new, silicon carbide-containing ramming mass, if, for example, special Value is placed on the suppression of side currents (stray currents).

It should be noted that sidewalls made according to the method of the main patent, in contrast to carbon walls, not to be impregnated by the fused-salt electrolyte, which among other things leads to leads to a lower consumption of electrolytes.

When operating the cells with side walls made of the silicon carbide-containing ramming mass, it has been shown that that the upper edge of the wall lining under the action of electrolyte splashes and of Atmospheric oxygen is attacked a little under unfavorable circumstances, causing silicon oxide, the the silicon carbide particles are encased in the thinnest layer, exposed as the carbon burns away and get into the furnace flow and thereby a slight increase in the silicon content of the cathode metal can cause. This risk is eliminated by arranging a layer of conventional Charcoal rammed earth removed from the upper edge of the wall lining. This layer of conventional Artificial coal rammed earth can itself be protected by an iron sheet, which is in a suitable Way is anchored.

The drawing illustrates the invention using an exemplary embodiment. It shows schematically in Longitudinal section of an aluminum electrolysis cell 1 with a pre-baked carbon anode 2, refractory lining 8 made of firebricks, carbon floor 3, wall lining 4 made of the new, made of silicon carbide powder, Coke powder and pitch produced rammed earth with a layer 5 of ordinary synthetic coal rammed earth without the addition of carbide and rod-shaped power supply elements 6 made of "hard metal". 7 is a sheet steel lid that holds the charcoal mass 5 protects. With 9 is the liquid, cathodic aluminum layer, with 10 the melted cryolite electrolyte and 11 denotes the alumina cover.

Claims (3)

Patent claims: 1. Cathode trough of a cell for the production of aluminum by fused-salt electrolysis according to the main patent 1146 259, the side walls with a tamped mass of 40 up to 85% silicon carbide powder, 45 to 7% coke powder and 15 to 8% pitch are lined, characterized in that it is used for supplying the current to the liquid cathode metal is equipped with current-carrying elements known per se made of carbides and / or borides of the transition metals. 2. cathode trough according to claim 1, characterized in that the power supply elements arranged horizontally or almost horizontally in the side walls of the cathode trough are. 3. Cathode trough according to claims 1 and 2, characterized in that the power supply elements are rod-shaped. Considered publications:
Austrian patent specification No. 208 606:
British Patent No. 814 031. 1 sheet of drawings 409 627βΟ7 fi. 61 © Bundesdruckerei Berlin