DE1154948B - Process for adding carbon anodes used in the electrolytic production of metals, in particular aluminum, and anode which can be supplemented for use in fused-salt electrolysis - Google Patents

Description

GERMAN

PATENT OFFICE

M29129VIa / 40c

REGISTRATION DATE: DECEMBER 22, 1955

NOTICE
THE REGISTRATION
AND ISSUE OF

ACPSLE WRITING: SEPTEMBER 26, 1963

The invention relates to the field of fused flux electrolysis and in particular the task of removing used anodes of any kind, such as non-adjustable, d. H. Fixed anodes, adjustable or pre-fired block anodes or continuous self-baking Söderberg anodes, to be added. The invention can be advantageous in furnaces and methods for Aluminum electrolysis find application that work with baths, which molten aluminum compounds contain and consuming anodes made of coal masses of various types, e.g. B. pre-fired Use anodes, Söderberg anodes or graphite anodes. All of these mainly consist of Charcoal, vulnerable types of electrodes are hereinafter simply referred to as "carbon", "carbon electrodes bzv /. Called "carbon anodes".

As is known, the electrolysis of aluminum is currently carried out in molten baths, mainly consist of cryolite or of aluminum and sodium fluorine compounds and which periodically or continuously charged with solid aluminum oxide.

The continuous direct current decomposes the oxide, the aluminum migrates to the cathode and the oxygen to the anode. The anode carbon combines with the oxygen and forms the so-called electrolysis gases, which mainly consist of CO ₂ and partly also of CO when they exit the bath.

The anode carbon (reducing carbon) used in this way must of course be supplemented by the manufacturing process to ensure continuity.

In the drawings are on the one hand - to better clarify the nature of the problem of anode replenishment or to clarify the invention in relation to the prior art - the conventional Furnace designs, on the other hand, illustrates a previously proposed furnace design, of which the Invention proceeds, and finally the anode design according to the invention.

Fig. 1 shows schematically a conventional Söderberg anode;

Fig. 2 shows schematically the known block anodes;

Fig. 3 is a new type of multi-cell furnace;

4 shows the arrangement of anodes according to the invention in a vetical section in an exemplary embodiment in a furnace of the type of multi-cell furnace of FIG. 3 in detail;

5 and 6 show horizontal sections through other embodiments of the anode arrangement according to the invention with multi-cell ovens;

Method for piecing together at the
Melt-electrolytic production of
Metals, especially aluminum,
used carbon anodes and replaceable anode for use in fused flux electrolysis

Applicant:

Montecatini, Soc. Gen. per l'Industria

Mineraria e Chimica and Guiseppe de Varda,

Milan (Italy)

Representative:

Dipl.-Ing. Dipl.-Chem. Dr. phil. Dr.techn. J. Reitstötter, Patent attorney, Munich 15, Haydnstr. 5

Claimed priority:
Italy of December 31, 1954 (No. 529 218)

Guiseppe de Varda, Milan (Italy),
has been named as the inventor '

Fig. 7 shows an application of the invention to the conventional ovens.

The primary aluminum manufacturing industry currently only works with two types of ovens, the ovens with self-baking Söderberg anodes (Fig. 1), those with metallic electrode bolts are provided, and the furnaces with prefired block anodes (Fig. 2).

In the furnace types according to FIGS. 1 and 2, the individual anode element consists of a carbon layer or a coal mass 1, which is partially immersed in the molten bath 2 and the underside of a practically horizontal surface which is only a few centimeters away from the molten Cathode metal 3 is held, which also forms an almost horizontal layer. This layer melted Aluminum is located under a molten bath layer, in which the anode is partially is immersed.

309 689/222

In the current furnaces, in the following "Hori- The anodes in the currently in operation gezontal furnaces" called, is every anode device of the common furnace and the previously used VerOfens adjustable in height, namely it will drive the addition of the anode carbon to the Kompenvon controlled by a mechanism that makes it possible to reduce the consumption of the same To raise or lower the entire anode carbon would be the reason.

such that a desired distance from the changeable Will the voltage drop in each in a furnace

borrowed level of the cathode metal is adhered to, individual block anode or in each individual, one

called the control distance. This version of the bolt corresponds to the Söderberg anode part

If necessary, the anode carbon is assumed to be practically the same, so it follows that

to stand out from the bathroom. This device becomes in io any of the included in the anode carbons

the sequence called "anode adjustable in height". Metal conductor carries an amount of electricity through

The anode carbon of the Söderberg anode, as it is in the total resistance of the concerned

Fig. 1 is shown, is determined in intimate and extensive-electrode bolt operated anode part

system contact with the electrode bolt or bolts 5.

made of metal, e.g. B. made of steel, the or the current 15 Apparently there is a voltage drop along the

the anode feeds or feeds, and is gradually and current path through the metallic conductor, a wide-

after electrolytically consumed. rer voltage drop at the contact surface between

The order of magnitude of this consumption is more common - see metal and anode carbon and a third chip type a few inches a day. The lower ends of the voltage drop along the current path through the anodes of these Electrode bolts made of metal come to the carbon on the route from the metal conductor to the one the weld pool underneath is getting closer and closer. There anode surface that is in contact with the bath comes a moment when you find the metal.

The three resistors can be viewed as a first approximation that the metal, mostly iron, is in immediate contact as connected in series,
tion comes with the bath, through which the metal 25 can be deduced from the fact that irregularities of the would be attacked, so that the aluminum produced distribution of the current at the lower base would be contaminated with it. In the case of the Söderberg furnaces carbon anode or carbon anodes can occur, the electrode bolts are pulled out as soon as they are used. This lack of uniformity of the electricity melt pool coming too close, successively distributing it out, can lead to local overheating and over- and usually fills the cavity left behind by voltages in the anode, in the bath or in the Kamit fresh Söderberg mass. Thereupon the method will lead and consequently to a reduction of the withdrawn electrode bolts when it comes to current efficiency and an increase of the specific vertically arranged electrodes, again in consumption figures. Furthermore, the time-changing hole has stuck the same hole, only at a higher distance between the lower ends of the metallic level than before, according to which the circuit with the 35 conductor (bolt) from the bath periodic fluctuations baking the mass and the slow approach of the anodic and thus the total voltage of the lower ends of the electrode studs result in the waste of the entire furnace. This melt pool also resumes. does not facilitate the good management of the furnace, which is

The anode carbon 1 is supplemented by the fact that it is also based on the value of the total voltage

fresh (so-called raw or green) electrodes 40 should. In addition, there is a need to

Mass 1 'from above is added, which is in liquid electrode bolts, which at their lower end have high tem-

State passes and so reach the already baked solid temperatures, from time to time under strong

Söderberg anode carbon covered. mechanical stresses from the Söderberg

On its slow downward migration, the anode will be torn out so as not to get too close to that

the new mass is baked very gradually, allowing the bath to come close.

the mechanical and electrical contact between When replacing the electrode bolts or when metallic electrode studs and baked mass which come into contact with the electrolytic bath becomes more and more intimate; Finally, there is a real inevitable contamination of the anode going Coking of the anode mass. As a result of coal and the bath. Indeed, herder shows it that way Coking are the lower layers of 50 put aluminum when analyzing a content Söderberg electrode (in particular the one that differs from impurities, partly due to the anodijeweils between the lower ends of the metal studs see electrode studs made of steel. and the bathroom) to sufficiently good ladders Finally, with conventional ovens it is still in of the electric current. In the case of the ovens, one should also consider that the ones with the elec- tric burners Block anodes (Fig. 2) is used up 55 trolyse progressive removal of the anode carbon Anode, which essentially consists of at least one conditional setting of the anode by means of Nachschiemetallischen Head (bolt) 6 and from the backward movement from top to bottom it forbids the carbon level 7 consists of the anode carbon, which still has the BoI anode directly above the bath through a bath zen covered, taken out of the bath and non-touching protective layer against burning replaced by a new anode 8 in order to protect the circuit 60 from the atmospheric oxygen. To resume these oxides. tion increases the consumption of anode carbon in the

The new anode is placed in the same place of the time unit, reducing the available active anodi-

Furnace, which can be seen and occupied by the old anode, especially at Söderberg-

became. The voltage drop in preburned elec- tric ovens, local overheating cause something like that

Depending on the anode current can go far, local trickling resp.

dense and, depending on the mean distance between the crumbling, cavities on the flanks of the

Metal stud ends from the weld pool, between 0.3 anode arise. This causes a decrease

and 0.9 V. of the current yield, an increase in the voltage

5 6

waste and thus an increase in the »specific« side supplementary layer of coal and a different

Power consumption (power consumption per tonne produced - permanently liquid, electrically conductive intermediate layer,

ten aluminum) as well as the »specific« interconnection of the body forming the main layer to the

need for electrolyte and anode carbon. A white flank through a layer and preferably min-

Another disadvantage of the current anodes is that their 5 at least on the roof surface by a heat-insulating

flanks immersed in the bath are clad in the usual rende layer.

Temperatures between 900 and 1000 ° C with the electrolysis of aluminum _{, initially predominantly made of CO 2} , come into contact with trolysis gases for the production of aluminum, which rise out of the bath when the bath is vertically adjustable and electrolytically and when the ins are coated Carbon anodes which can be used can be coked, carbon-bath immersed anode flanks with binders containing carbon for hydrogen via the anode surface opposite the anode surface to be supplemented with the equation

Surface of the anodic supplemental carbon layer

CO., -RC ^ -2 CO are scattered before the supplementary layer

15 is brought. The co-reacting containing hydrocarbons, tel is placed on the preheated anode surface

All these disadvantages or at least some of them applied as a binder according to the The same are made by a multi-cell furnace with no coking in operation, the narrow joint on the adjustable or fixed electrodes corrected how the points bridged without the subsequent BiI-in Fig. 3 is shown (Belgian patent 534 969); 20 to prevent the liquid layer from forming in the joint, this does not require a device to regulate the. In another variant, aluminum shavings can be used Electrode spacing, d. H. for lifting or lowering or grains over the contact surface of the anodic of electrodes, and works with rigidly arranged supplementary bodies are distributed before the same Anodes (»stationary anodes«) and inclined, from being applied, whereby the chips or grains are polarized Electrode carbons 9 existing transverse walls 25 are placed in order to absorb the voltage drop without metallic conductors. Only the ones on the stove reducers.

capping arranged electrode carbons 10, 11 A suitable molten metal, e.g. aluminum

("End electrodes") have electrode bolts. In deminium in the case of electrolysis to produce the

that of the two also stationary end electrodes of this metal can be inserted into the joint, i.e. between the

all metallic conductors 12 have introduced preferred 30 anode surfaces and the supplementary layer

wise equal distances from the electrolysis bath. Become a.

electrolytic consumption of the anode carbon takes place. The supplementary layer can evidently also take place against the anode in these furnaces, but the supplementary surface can be left ajar during the electrolysis The anode is made while leaving the old cell containing a molten electrolyte, the anode on the spot, in that at 35 art that by itself a thin liquid electrode Anode surface a plate 13 (or more lyte layers between the supplementary layer and the Pieces together forming a plate, ζ. Β strips) anode surface forms.

is applied, which consists of carbon and which when the invention is applied to electrolytic cells for the Her-surface completely covered, so that the spent position of aluminum from molten aluminum electrode in their earlier shape and size, the minium compounds that lead to the will be produced. conventional horizontal furnace with at least one

So this is a supplement to a height-adjustable, partially submerged one

consuming, but stationary anode, with anode made of electrode carbon, z. B. a prebaked

on the exposed anode surface after the previous block anode, so the (also from

Emptying the bath the supplement made 45 electrode carbon existing) a supplementary layer

will. floating on the bath, preferably a

The invention, which is based on the knowledge that have be edge-having plate with which they

in the case of the furnace types discussed here or the lower edges of the previously from the

Anode types supplement the anode with a lifted main body of the anode on the bath

multiple leaning of the supplementary charcoal from the bath scope, if the latter (i.e. the

side to the old anode, has first lowered the complete electrode) onto the plate

A process of piecing together the will until the joint between the old anode and the line

Melt electrolysis for the extraction of metals, new plate is immersed in the bath,

whose density is greater than the density of the electro- The intermediate layer also exists in this case

lytes, consumed carbon anodes 55 preferably used from previously added molten

to the object, which is characterized in that aluminum, which is formed in the by the edge

the used anode parts are periodically found in the basin.

be supplemented that a supplementary body against the According to the invention can be the replaceable layer

the anode surface, which is subject to the erosion, of the plurality of matching ones

60 pieces of carbon electrode, and each of the

between the mentioned anode surface and the mentioned pieces is a rectangular bar that extends over

imagined supplementary layer ajar and for that a whole dimension of said main layer

The presence of a liquid, electrically conductive one is sufficient and preferably on at least one edge

the joint filling layer is taken care of. White has a raised edge that is one edge of the

Furthermore, the subject matter of the invention is a main layer that can be extended.

Anode for use in the melt flow electro- The anode according to the invention can also be a

lysis, characterized by a solid, electrically sloping downward facing surface,

conductive main layer, a replaceable solid bath- The inventive method is also based on

Electrolytic cells with fixed (non-adjustable) electrodes can be used by adding a supplementary layer in the form of a coherent plate or a plurality of plates that can be joined together to form a plate Pieces (e.g. strips) are introduced into the electrolysis chamber of the cell, whether this is now electrolyte melt contains or is empty. These plates or pieces or strips are at the smallest distance placed parallel to or ajar to the anode, so that electrolyte in the joint between the opposing Areas of the anode to be supplemented and the supplementary layer remain or in the Joint can penetrate. The supplementary plate or pieces or strips can be made of inert material manufactured stops are prevented from swimming up in the bathroom.

The already mentioned claddings made of inert, highly resistant material, as already provided in the multi-cell furnace according to FIG. 3 and in the drawings with d and d _± (covering the end or intermediate electrode or bipolar electrode) or with d! and d _t ' (roof-like approach to protect the supplementable anode layer on the end anode or on the anode side of the bipolar electrode).

This method of using a liquid contact represents, applied to the ovens with stationary (non-adjustable) consuming anodes, an improvement on the method mentioned the anode supplement according to the cited method. This improvement facilitates the operation, simplifies the operations required to complete the anode and results in a reduction of the unit consumption of electricity. It also makes it possible to save on wages; so she avoids, for example the need to remove the weld pool from the cell before replenishing and again afterwards to introduce what can otherwise lead to numerous grievances.

In the case of the multi-cell ovens with stationary (non-adjustable) electrodes, such as those mentioned in the above The method can be proposed, the anodic supplementary plate or the individual Strips from which the panel is assembled can be attached in place without particular difficulties arise. In the case of aluminum electrolysis, the bath density is around um 30 to 40% greater than the density of the electrode carbons, because electrolysis baths for aluminum have a bath density of about 2, while the The density of the electrode carbon is only about 1.5. It can happen that the friction on the contact surface between the old and the new part of the anode is insufficient to generate hydrostatic buoyancy to make up for the bath. In such a case it is easy to use some kind of anchorage device to preferably made of inert material (e.g. made of pretreated magnesite) to prevent the new The anode layer floats upwards (Fig. 4).

The invention can be advantageous with appropriate modification and with the respectively required practical support measures on horizontal furnace the usual construction. In the latter case it is possible to apply the invention to already use installed ovens with little or no structural changes.

With horizontal furnace it is possible to follow the procedure peculiar type of anode addition when partially or completely lifted out of the bath Perform anode. Of course, if you don't use an anodic binder, which is applied beforehand (whereby a binder is meant that afterwards cokes in such a way that a mechanical and electrical connection between the old anode and the new supplementary layer comes), the joint between the old anode and the new layer is normally covered by the bath liquid Electrolysis cell filled. However, it has surprisingly been found that the total resistance the mentioned liquid layer and the two contact surfaces coal-bath and bath-coal is nowhere near as great as might have been assumed if only certain limits of the distances between the areas and the current densities are not exceeded.

In all applications of the invention, the electrical current goes from the old anode part to the new, without suffering such a voltage drop at the transition surfaces as in the cell in the course electrolysis occurs and is generally believed to be around 1.7V. It lays here on the contrary, there is a total resistance which corresponds to a voltage drop, which is partly electrochemical It may have its origin, but it seems to have only static effects and is significant is smaller than the decomposition voltage requirement of the bath, as better clarified in the following list will:

Total resistance (Ω / cm ² ) of the contact zone at approx. 1000 ⁰ C and corresponding voltage drop (V)

A / cm ² vertically or horizontally
0.3 I 0.5 I 0.7 1.1 to 1.6
0.55 to 0.80
1.6
0.80 1.5
1.05 Example a
Dry touch carbon plate on carbon plate
Ω / cm ² 1.9
0.57 V Example b
Coal — iCryolite melt — coal; Thickness of the intermediate layer <1 mm
Ω / cm ² V

continuation

10

A / cm ² vertical or horizontal 0.3 I 0.5 0.7

Example c
Coal - cryolite _{melt + Al 2} O ₃ + AlF ₃ -KoMe

Ω / cm ²

V

Example d
Like c; Inclination of the layers about 60 ° to the horizontal plane

Ω / cm ²

V

Example e

Coal - cryolite _{melt + Al 2} O ₃ + AlF ₃ - coal; Thickness of the liquid
Interlayer about 12 mm

Ω / cm ²

V

Example f
Coal — cryolite electrolysis bath with advanced electrolysis — coal;

Interlayer <1 mm

Ω / cm ²
V ...

1.7
0.51

1.5
0.45

1.85 0.56

1.4 0.70

1.2 0.60

1.63 0.82

lA / cm ²

0.25
0.25

1.5 A / cm ²

0.24
0.36

The numbers in the table show that when working according to the invention with anode supplement from the bath side and with the liquid contact layer the additional anodic voltage drop is much lower than due to the known voltage requirement for the decomposition of aluminum oxide, was to be expected in an appropriate electrolysis bath.

Even so, this additional voltage drop is not negligible when taken into account becomes that the total voltage drop in current industrial cells is usually between 4.5 and 6 V fluctuates, while in the individual elements of multi-cell ovens with stationary ones, it does not electrodes supplemented according to the present invention can drop below 3.5 V. These additional voltage drops can however be further reduced up to a fraction of the stated values, if you proceed as follows:

First, you can see the extent of the two contact surfaces (the old anode or the supplementary anode) enlarge by providing a suitable corrugation or corrugation such that the two surfaces fit together. For example, in a multi-cell furnace with stationary (non-adjustable) electrodes (Figs. 4 to 6) in place of a supplementary layer for each of the transversely positioned bipolar intermediate electrodes and one equipped with a sawtooth-like surface for the stationary end anode 19 Anode layer may be provided. The exchangeable plate 14 can, as schematically in FIG. 6 shown, have an enlargement of the contact surface by about 50 to 100%.

Regardless of the design proposed under point 1, the electrical contact between Supplementary anode and the anode can be improved by ensuring that in the thin layer of liquid between the two more or less adjacent contact surfaces is present, substances are present which reduce the total resistance of this layer reduce or form a better bridge for the current transfer. It has been found that this purpose z. B. pitch, pitch- or tar-like substances or substances containing hydrocarbons, which tend to coke and, scattered over the surface, weld the old anode to the new one, Prove to be particularly suitable, furthermore molten metal, preferably aluminum, approximately of the same degree of purity as that produced in the cell, or even small amounts of carbon-like Substances as a very fine powder, e.g. B. finest coal dust.

The way of working is different, depending on the addition in a multi-cell oven with non-adjustable ones Electrodes or in one of the usual ovens with horizontal layers. In the case of multi-cell ovens with stationary electrodes, the supplementary electrodes are preferably preheated Carbon plates 14 (Fig. 4) or the corresponding preheated strips 15 (Fig. 5) in inclined, almost vertical position in the individual columns or cells until their lower edge 17 (Fig. 4) lies on the layer 18 of inert material, which the electrode 19 from the chamber below 20 for the metal separates. Afterwards you can between the old anode 19 and the one from the plate 14 or several strips IS existing supplementary anode modest quantities (e.g. in the order of magnitude from 1 to 5% of the weight of the added

309 689/222

Anode) of molten aluminum or a suspension of carbon powder into the bath melt, after which the plate or the strips are leaned against the old anode in question.

The precautions to be taken here must take into account the fact that the metal is heavier and the carbon powder is lighter than the electrolyte. Therefore, in the former case, it is advisable to use the hot melted Metal from above into one already extremely

effortlessly and puts on a new supplementary anode shell in the manner already described above the bathroom.

The thickness of this shell or plate can vary within fairly wide limits. The preferred Borders are 5 to 15 cm. If the anodes are large, it may be useful not to lift them out of the bath. but a number of matching supplementary carbon strips, preferably attached to their

pour a narrow gap so that the metal long ends have raised edges, one at a time in the bath

drops more quickly and practically stops when the two anode parts come into contact. In the case of the Powdered coal it is usually preferable to add a small amount of the normal molten bath first is provided that a certain percentage of this bath melt intimately mixed carbon powder contains, and this mixture in the contact zone at a suitable temperature below a certain, is applied by a column of liquid given pressure. These supplementary panels or strips, whose thickness preferably fluctuates between 3 and 10 cm, are - as usual - consumed electrolytically. Before adding the new anode pieces, it is advisable to introduce a specially designed one and to be arranged sequentially from below against the base of the old anode.

The invention offers the following advantages: The method of anode replenishment by simply leaning against it the new anode to the old anode in multi-cell ovens with non-adjustable electrodes the significant advantage that it is no longer necessary to drain the bath from the cell before the Completion of the anode is paced. This considerably simplifies the required actions, shortens them the working hours and also reduces the heat loss as well as the risk of oxidation of the Electrode carbon that is no longer covered by the bath.

Furthermore, it is no longer necessary to

As seen in the device, the surface of the old coal can easily be coated with binding agent, which must be wiped off after the anode and skimmed off, in order to produce a perfect fusion of the previous operation with the old anode.
Remove remnants of the previous supplementary anode. The invention allows, with the currently

In the old-style ovens (Fig. 7), the standard horizontal ovens can be used with pre-fired

The anode is completely lifted out of the bath.

the, then under the anode 21 the additional coal genes, but because of practical difficulties so far

Plate 22 are introduced in such a way that they can be realized on the measure never carried out, namely

Bath floats; this plate is preferably borrowed with the anode to protect against atmospheric oxygen,

a raised edge 22 'is provided which, for. B. at least against the carbon dioxide that forms in the bathroom as well

can be at least 1 cm high, and thus forms a type 35 against electrolytic consumption except for the flat shell. On this floating plate can
one z. B. either sprinkle a very thin layer 23 of the finest coal dust or aluminum shavings
or even a small amount of an intimate mixture

bath liquid and carbon powder or melted or pre-shrunk at very high temperatures

zenes aluminum. Afterwards you lower the old anode, tertiary solid magnesium oxide or other

so that they can with the possibly corrugated supplements, which, according to more recent results from the bathroom, are not

tongue anode plate meets; one then lowers or is only attacked very little, insist,

the entire anode device continues. Thanks to the invention, the anode becomes so

The 45 permanent anode with periodically replaceable supplements

Pressure dips the supplementary panel under the bath layer or at least reaches it a lot

surface until the normal "standard distance" between long service life. Fig. 7 shows a pre-burned one

Complementary anode and cathode metal 3 restoring anode,

is posed. In summary, it can be said that it invented

The contact between the spent anode and the method according to the present invention allows for labor

new anode part is saved by the presence of or wages and the horizontal furnaces

Coal powder or a thin layer melted- Unit consumption of anode carbon and bath-

Base area also on all other areas with an external protective layer covering the roof and flanks of the coal 24 to be provided (Fig. 7). This protective layer can be quite thin and made of pre-melted

zen aluminum or small amounts of pitch improved noticeably.

As the electrolytic consumption of the anode progresses, the supplementary plate or shell becomes getting thinner. At some point it gets to the point where the ground gets riddled with holes and the thin aluminum layer in the shell

to reduce liquidity and to avoid that the aluminum produced contains iron impurities etc.

As far as the electrical power consumption (kWh) is concerned, this can be achieved by the resistance of the intermediate layer voltage drop caused between old and new anode is limited to low values d

If necessary, it flows off through the bath and becomes weaker, especially if the cathodic aluminum layer is used with low current densities and other difficulties and the various measures are achieved. Now or a little later or and precautions are taken that the invention also earlier (i.e. if the supplementary bowl characterizes the method according to the invention,
A further advantage of the invention lies in the aforementioned contact fluid between the two 65 possibility of having emptied the permanent solid layer of the three-anode parts) if the anode is lifted from layers anode in such a way The fact that the bath comes out dissolves the shell residues from the earlier electrical resistance and the tendency towards higher additions, if necessary, and the heat radiation losses become extremely low. There

the pre-burned anode is no longer subject to consumption by oxidation as before and on one small coal residue burns together (Fig. 2), it becomes possible, for. B. the contact surface of the or in the permanent carbon layer stuck metallic conductor and significantly enlarge the upper part of the Equip the anode with a heat insulating layer.

The way in which the three-layer anode described in the electrolytic cell itself Ease comes about and how this is advantageous in electrolysis cells charged with aluminum oxide thanks to the surprising behavior of the thin intermediate layer during the passage of the electrical Stromes is used because there are noticeable nuclei in the intermediate layer, even if it is liquid Electrolytic decomposition occurs and the total electrical resistance of the intermediate layer occurs with ease can be reduced to very low values, can also be used casually and beneficially transferred to other cells or to the electrolysis of other melt pools, if only the anode is electrolytic is consumed and accordingly has to be replaced periodically and operated at high temperatures will.

The advantages of the three-layer anode (from the point of view of regularity the operation, the wage savings, the lower specific consumption of electricity and anode material per ton of aluminum produced, the possibility of using the flanks of the permanent anode layer a protective layer, etc.) is particularly beneficial if the electrolysis is also in the presence chemically particularly aggressive bath components is carried out or if multi-cell ovens operated with non-adjustable electrodes.

Claims (15)

PATENT CLAIMS: 40 1. A method for piecing together in the fused-salt electrolysis for the production of metals, the density of which is greater than the density of the electrolyte, used, consuming carbon anodes, in particular for the production of aluminum, characterized in that the consumed anode parts are periodically supplemented in that a Supplementary body is leaned against the anode surface of the electrode to be supplemented, which is subject to the ablation, forming a narrow joint between the two and care is taken to ensure the presence of a liquid, electrically conductive layer that fills the joint. 2. The method according to claim 1, characterized in that a carbon-like substance or Carbon material, such as coal dust or coal powder, in the electrically conductive one located in the joint liquid layer is suspended. 3. The method according to claim 1, characterized in that on the surface to be applied of the supplementary body a carbonizable, hydrocarbon-containing material in places is applied, which as a binding agent after coking in operation, the tight joint to the relevant bodies bridged. 4. Process according to claims 1 to 3, characterized in that metal, in particular Aluminum chips or grains, distributed over the contact surface of the anodic supplementary body before it is applied to reduce the voltage drop. 5. The method according to claims 1 to 4, characterized in that a joint filler molten metal, especially aluminum, or the electrolyte itself is used. 6. The method according to claims 1 to 5 in application to vertically adjustable, in the normal Operation in the electrolysis bath immersed anodes, characterized in that for the purpose of Anstückeins the one to be leaned against the bottom surface of the anode body to be supplemented from below Supplementary body piece by piece, z. B. as matching strips is introduced. 7. The method according to claims 1 to 5 in application to vertically adjustable, in the normal Operation of anodes immersed in the electrolysis bath, characterized in that for the purpose of the Anstückeins the anode body to be supplemented on its bottom surface over the bath surface raised and the supplementary body floating underneath placed on the bath surface and thereafter the anode body is lowered onto the same. 8. The method according to claims 1 to 5 in application to electrolytic furnaces with - vertical or inclined - standing stationary electrodes, characterized in that the supplementary body introduced either as a single plate or as a matching strip at an angle to the anode surface to be supplemented and only is then based on this. 9. Supplementary anode for use in fused flux electrolysis according to claims 1 to 8, characterized by a solid, electrically conductive main layer, a replaceable solid layer on both sides Supplementary layer and a permanently liquid, electrically conductive intermediate layer, wherein the body forming the main layer is covered on the flanks by a protective layer and preferably covered at least on the roof surface by a heat-insulating layer is. 10. Anode according to claim 9 for supplement according to claim 6 or 7, characterized in that that the supplementary body or bodies have edges into which the anode surface fits can be. 11. Anode according to claim 9 for supplement according to claim 8, characterized in that the anode body to be supplemented has projections on the protective cover into which the supplementary body fitted in or by which it can be held. 12. Anode according to claims 9 to 11, characterized in that the thickness of the supplementary body or the supplementable layer is uniform. 13. Anode according to claims 9 to 12, characterized in that the liquid intermediate layer is not thicker than 2 mm. 14. Anode according to claims 9 to 13, characterized in that the opposite Areas of the main and complementary body mating bumps, z. B. corrugations or protrusions and Have depressions, preferably ribs and grooves. 15. Anode according to claim 14, characterized by a uniform thickness of the supplementary body at the points of the depressions. Considered publications: German Patent Specifications Nos. 723 448, 827 413. For this purpose 2 sheets of drawings © 309 689/222 9.63