EP0050681A1 - Electrode for igneous electrolysis - Google Patents

Abstract

Electrode for fused melt electrolysis comprising a top portion (5) of metal or metal alloy where appropriate including a cooling device (2,3) and the top portion (5) is protected at least partially by an insulating coating (4) of high-temperature resistance, and at least one bottom portion (6) of active material. The electrodes can be used more particularly for the electrolytic production of metals such as aluminium, magnesium, alkaline metals or compounds thereof and are characterized by very advantageous energy consumption combined with high operational reliability.

Description

The invention relates to an electrode for melt flow electrolysis, in particular for the electrolytic production of metals such as aluminum, magnesium, sodium, lithium or of compounds.

In the electrolytic production of aluminum, magnesium, alkali metals and compounds etc. on a technical scale, carbon electrodes made of hard coal or graphite are still predominantly used. Although the electrodes are mainly used to conduct electricity, they are often involved in the electrode reactions themselves. The actual electrode consumption is therefore considerably higher than the theoretical wear rate, which can be attributed to the susceptibility to oxidation of the carbon electrodes under electrolysis conditions. The theoretical wear rate for aluminum melt flow electrolysis is 334 kg carbon / t aluminum, while actually a carbon wear of approx. 450 kg carbon / t aluminum occurs.

Similar problems arise for electrodes for the production of magnesium, sodium, lithium and cerium mixed metals. Side reactions of an oxidative nature on the electrode part immersed in the molten salt as well as combustion by atmospheric oxygen on the part protruding from the melt wear the electrodes unevenly and prematurely. Added to this is the destructive effect of the graphite intercalation compounds formed from electrolyte components or their secondary products. Attempts have already been made to convert carbon electrodes into a suitable material by impregnation, subsequent thermochemical treatment and conversion into carbon-silicon carbide composites.

Convert electrode material. However, these attempts have not yet led to any significant improvement in the practice of melt flow electrolysis.

The disadvantages of carbon electrodes described above as well as the rising costs for graphite and hard coal have initiated developments for dimensionally stable electrodes. It is hoped that this will not only replace the petrochemical raw material petroleum coke, the consumption of which for melt flow electrolysis in Germany alone is approx. 500,000 t / year, but also to save energy.

For this purpose, a number of ceramic materials, e.g. according to GB-PS 1 152 124 (stabilized zirconium oxide), US-PS 4 057 480 (essentially tin oxide), DE-OS 27 57 898 (essentially silicon carbide valve metal boride carbon), the South American patent application 77/1931 (yttrium oxide with surface layers made of electrocatalysts) or according to DE-OS 24 46 314 (ceramic base material coated with spinel compounds). Finally, on the proposal of using non-oxidizable composite materials, high chemical. Purity according to European patent application 80103126.1 by the applicant, filed on June 4, 1930.

A disadvantage of the use of electrodes which are formed from ceramic materials is - even after adding conductivity-increasing components - their often only moderate to medium electrical conductivity. This is only acceptable in processes where the electrode dimensions are small and the current path is short.

However, this primarily applies only to electrolysis in aqueous media, while the electrodes for melt flow electrolysis, e.g. of aluminum, have considerable dimensions. The electrodes for aluminum production can be dimensioned up to 2250 x 950 x 750 mm, while typical graphite electrodes for magnesium production are 1700 x 200 x 100 or Ø 400 x 2200 nm depending on the process type. The production of such solid blocks from the ceramic materials mentioned is expensive and results in considerable difficulties with regard to resistance to temperature changes and electrical internal resistance. In recent times, however, the efforts of the power-consuming industries have focused particularly on reducing the specific energy consumption, which is why ceramic solid electrodes have also so far not been used in practice.

The invention has for its object to provide a new type of electrode for melt flow electrolysis, in which the disadvantages of the prior art described above are reduced. In particular, an electrode that works safely with extremely low current / voltage losses is to be created, although the spectrum of active materials known to date and which will also be used in the future can be used in the same way. This type of electrode should preferably be used as an anode.

This object is achieved by the provision of an electrode of the type mentioned at the beginning, which is characterized by an upper section made of metal (alloy), which optionally includes a cooling device, the upper section being at least partially protected by a high-temperature-resistant, insulating coating, and at least a lower section of active material. As a cooling medium e.g. Liquids such as water or gases e.g. Serve air.

Such electrodes have already been proposed for use in the production of electrical steel in electric furnaces in which an arc is emitted from the tip of the electrode. Due to the existence of the arc and its possibility of migration, the resulting extreme temperatures in the vicinity of the arc, but also due to the atmosphere in the electric steel furnace and the type of electrode operation, there are such serious deviations from the melt flow electrolysis that it is possible to use such types of electrodes for the implementation was not considered by melt flow electrolysis. With regard to such a prior art, reference is made only by way of example to GB-PS 1 223 162, DE-AS 24 30 817 or European laid-open specification 79302809.3. These documents describe the electrodes there with regard to the specific requirements of the arc electrode and the efforts made to meet the specific requirements of the electrical steel production process.

A molded part which can be detachably attached is advantageously provided as the insulating coating in the electrode according to the invention. In the context of the application, the term “insulating” is to be understood as meaning an material which is inert and shielding from the electrolysis medium and which may also be electrically insulating. For most applications of the electrode or anode according to the invention, it is particularly advantageous if at least the area of the molded part that can come into contact with the electrolyte and the resulting products shields the metal shaft and possibly other metallic parts, in particular the nipple, in a gas-tight and liquid-tight manner . _4th

The high temperature resistant, insulating molded part can be a single pipe. But it can also be beneficial comprise a series of pipe sections, segments, half-shells or the like, which surround the lower region of the upper section of the electrode into the region of the screw nipple, possibly beyond.

The material of the insulating molded part can e.g. made of high temperature resistant ceramic, but also e.g. Represent graphite that has an insulating coating on it. Such insulating, high-temperature resistant ceramic or other materials are known.

The use of a detachable molded part, in particular in the form of a series of pipe sections, segments or half-shells, achieves a number of advantages which are still to be discussed.

According to a preferred embodiment of the electrode according to the invention, the insulating molded part is arranged between a lower partial area of the upper section made of metal and the lower, consuming section such that the outer edges of the molded part running in the direction of the electrode axis and those of the outer area of the upper section made of metal are essentially flush with each other.

In the electrode according to the invention there are no restrictions with regard to the counter bearing on which the molded part is carried. This can be a counterpart, also made of insulating material that can be subjected to high temperatures, the screw nipple itself, possibly even a part of the active part itself, or a combination thereof. In general, however, the insulating molded part will not rest on the active part alone, provided that this is a consumable material, but will be at least partially carried by a non-"consumable", heat-resistant material.

The position of the molded part can of course be controlled in a suitable form during the manufacture of the electrode. In a preferred form of the electrode according to the invention, the insulating molded part can, however, also during operation of the electrode without having to lead the electrode out of the electrolysis furnace, through bores provided in the upper section through pins, threaded screws, etc. onto the counter bearing, e.g. by the additional provision of springs. Regardless of the provision of bores and threaded screws or the like, it can also be advantageous to place the insulating molded part in such a way that it slides or loosely with respect to the metal shaft, in such a way that in the event of failure of a partial segment or the individual tube breaking off, e.g. due to mechanical damage, the remaining intact sub-segments or the individual tube itself can slip or are movable in the direction of the electrode longitudinal axis.

Depending on the application of the electrode, it is possible to place the insulating molded part on holders, which can preferably be attached to the metal of the inner cooling unit. However, this is primarily taken into account in such applications of the electrodes, where the free mobility or the "moving up" of intact (insulating or electrically conductive) individual segments is not important in the event of damage to a segment lying below.

In the context of the invention it is also possible that the insulating molded part does not encompass the entire area of the metal shaft to be protected, but instead in an area where less stress can be expected, instead of the further molded part, an insulating, highly fire-resistant injection molding compound is anchored, is used. Such insulating molding compounds are known per se, which can be fastened with holding pieces that are soldered on, for example.

Amorphous carbon, graphite, ceramic conductors or a composite of inorganic fibers with an electrochemically active material can be listed as examples of active materials which are connected to the upper section by one or more screw nipples or, if appropriate, threads. In this context, reference is made in particular to the applicant's European patent application 80103126.1 ', where particularly preferred composites composed of inorganic fibers with an electrochemically active material are listed. The description of the active materials in this regard, as well as their arrangement, is to be regarded as fully introduced into the present application by express reference to this European patent application. It is explained in detail there that the active material can be formed from a number of rods, plates, tubes or the like, which are connected or separated from one another. However, the arrangements of rods, plates or tubes listed there should not be subject to any restrictions with regard to the ceramic or other active materials that can be used in the present invention. In other words, the active substances or composites described in the European patent application given should be considered in the context of the present invention. The structural arrangements of the active parts described above can be connected in the electrode according to the present invention to the upper, metallic section - be it through nipples, threads or the like. 4th

It is also possible that the lower section consists of active material in several units, which are held by one or more nipple connections, the The units can be arranged side by side and / or one below the other. Thus, in particular with regard to consumable active substances, for example graphite, intermediate pieces made of such material are considered, to which a unit that then completely consumes can in turn be screwed. As a result, the last active unit can be completely used up without the nipple connection, with which the metallic upper section is connected, being exposed to a hazard.

In cases where the top section is not exposed to excessively high temperatures, the provision of a cooling device may be unnecessary.

The electrode according to the invention has a number of advantages: the extremely low current and voltage losses on the way to the active part of the electrode are to be emphasized. As a result, considerable energy savings can be achieved compared to conventional solid blocks, whether made of carbon, graphite or ceramic material. Furthermore, the side burn-off is minimized, since it is no longer the entire electrode but only its active part that is exposed to the aggressive electrolysis medium and the reaction gases and vapors that develop in the process. Finally, the electrode can be used in a variety of ways, since its construction allows the use of a spectrum of active materials that can be used in the field of melt flow electrolysis.

The insulating molded part can also be easily inserted in a targeted position during manufacture. Through the use of an insulating, external solid part mechanical strength can be improved. By dividing the insulating outer zone into segments, it is not necessary to replace the entire electrode in the event of faults or damage, since the damage can be remedied quickly and economically by introducing the corresponding section. Due to the loose placement of the insulating molded part, as far as it is made up of several sections, in the event of a mechanical or other destruction, the underlying protective segments result in an "automatic" sliding of the upper segments, which may be additionally secured by springs is. The electrode is therefore still able to work even if damage has already occurred, since the most vulnerable lower electrode area, which is closest to the working zone of the electrode, is "automatically" protected by the sliding of intact elements.

Although the insulating molded part or the insulating coating, if it consists of a series of individual segments or half-shells, can have a certain amount of play due to the type of axial and internal support, the tongue and groove system provides complete and comprehensive protection, for example the sensitive metal area of the electrode. If there is still damage to the lower area of the "protective shield" of the electrode, it can still work as long as it is necessary to replace the consumable part made of, for example, graphite. When the electrode is removed, the corresponding replacement of the damaged individual segment, etc. can then easily be carried out. •

• Fig. 1 einen Längsschnitt durch eine erfindungsgemässe Elektrode;
• Fig. 2 einen Längsschnitt durch eine erfindungsgemässe Elektrode, bei der der durch Isolierungen geschützte Bereich nicht vollständig sowie der anschliessende Verbrauchsteil nicht gezeigt sind;
• Fig. 3 Querschnitte durch den oberen Abschnitt sowie 4 aus Metall bzw. dessen Teilbereich geringeren Durchmessers;
• Fig. 5 eine Unteransicht des Aktivteiles der Elektrode.

Particularly preferred electrode constructions of the invention, which are to be used in particular as anodes, are shown below in FIGS. 1 to 5. Electrodes and anodes in particular are shown in which the upper section made of conductive metal has an upper part of larger diameter and a lower part of smaller diameter. The part of smaller diameter is then at least partially covered by the insulating molded part. This arrangement is within the scope of the Invention particularly preferred, although the invention is neither limited to this nor to the particularly advantageous embodiments according to the figures below. In the figures, the same parts are identified with the same reference numbers. Show it:

• 1 shows a longitudinal section through an electrode according to the invention;
• 2 shows a longitudinal section through an electrode according to the invention, in which the area protected by insulation and the subsequent consumable part are not shown completely;
• 3 shows cross sections through the upper section and 4 made of metal or its partial area of smaller diameter;
• Fig. 5 is a bottom view of the active part of the electrode.

In the electrode according to FIG. 1, the cooling medium, for example water, air or inert gas, is introduced through the feed channel 2 and returned through the return channel 3. This occurs Cooling medium also into a chamber within the screw nipple 1, which is formed, for example, from cast iron, nickel or a temperature-resistant, corrosion-resistant metal alloy. The upper section 5 made of metal consists of an upper area of larger diameter and a lower-lying area of smaller diameter, which is drawn into the screw nipple 1, which is the connection to the lower section o made of, for example, consumable material, such as graphite or ceramic active material , forms. The insulating molded part 4 is supported by a counter bearing 7, for example made of high-temperature-resistant, insulating ceramic. In the upper region, the insulating molded part 4 is delimited by the upper edge of the region of larger diameter of the metal shaft.

In the electrode shown in FIG. 1, the insulating molded part 4 is divided into segments which are slidable in the direction of the electrode axis when a (lower) segment breaks out. Alternatively, they can also be held by hook elements 14.

In addition to the cooling bores 15, additional bores 8 can be provided, through which the inserted pins 9 via the spring 10 ensure a good fit of the insulating molded part 4.

From Fig. 2 as well as Fig. 4, the use of half-shells in the composite or of rings, e.g. made of graphite coated with an insulating coating.

The lower section 6 made of consumable or durable material is divided into a series of individual rods 20 which are bound by the nipple 1.

The preferred lateral power supply takes place via jaws 18, advantageously made of graphite, which are fastened, not shown, to holders, preferably on the metal shaft. In Fig. 1 the alternative possibility of attaching the jaws 18 to the power supply rail itself is shown.

Gas purging channels, which are not shown in the figures, can be provided between the insulating layer 4 and the upper section 5. The gas flushing can damage the insulating ceramic, e.g. about a corresponding pressure drop, can be easily determined. In addition, a certain cooling effect is possible. In addition, it is within the scope of the invention - which is also not shown in the figures - that the upper section 5 and / or the nipple connection 1 or its outer surfaces can be coated with a high-temperature-resistant coating. Depending on the dimensions of the at least partially overlying, high-temperature-resistant, insulating coating 4, the high-temperature-resistant coating can be designed to be electrically conductive or also insulating. In the case of an insulating design, this results in a second protective line, which can take action if the outer insulating coating 4 breaks. If the latter does not have to be expected depending on the operating conditions, the coating can also consist of a high-temperature-resistant, conductive material, in which case the material has the effect of a "heat shield" or "inert shield" to protect the underlying metal.

Claims (17)

1. Electrode for the melt flow electrolysis, in particular for the electrolytic production of metals such as Al, Mg, _N a, Li or of compounds, characterized by (a) an upper section (5) made of metal (alloy), which optionally includes a cooling device (2, 3), (b) the upper section (5) being at least partially protected by a high-temperature-resistant, insulating coating (4), and (c) at least one lower section (6) made of active material. 2. Electrode according to claim 1, characterized in that a molded part (4), which can be detachably attached, is provided as the insulating coating. 3. Electrode according to claim 1, characterized in that the molded part (4) comprises a single tube, a series of tube sections, segments or half-shells which cover the lower region of the upper section (5) up to or up to the vicinity of the screw nipple (1 ) surround. 4. Electrode according to claim 1 or 2, characterized in that the molded part (4) and the outer edges of the upper section (5) are arranged substantially flush with each other. 5. Electrode according to claims 1 to 3, characterized in that the molded part (4) between an incision in the metal of the upper section (5) and an approximately in the area of the screw nipple (1) arranged counter bearing (7), the screw nipple (1 ), the active part or a combination of these. 6. Electrode according to claims 1 to 3, characterized in that the shaped part is held on the counter bearing (7) by pins or threaded screws (9), preferably resiliently, in bores (8) of the metal part. 7. Electrode according to claims 1 to 5, characterized in that the inner metal part (12) is coated with a dense, heavy-duty, optionally conductive coating, preferably made of ceramic. 8. Electrode according to claims 1 to 7, characterized in that the insulating molded part (4) consists of high-temperature-resistant ceramic or graphite tube coated with an insulating coating. 9. Electrode according to claims 1 to 8, characterized in that the insulating molded part (4) is placed on holders (14) which are preferably attached to the metal shaft. 1 ₀ . Electrode according to Claims 1 to 9, characterized in that the insulating molded part (4) in the upper region of the metal part is partially replaced by insulating, highly fire-resistant injection molding compound which is anchored with holding pieces. 11. An electrode according to claims 1 to 10, characterized in that the insulating molding (4) is mounted such that upon failure of a part segment or damage of the individual tube the remaining intact part segments or the individual tube ^g themselves in direction of the electrode longitudinal axis to the Beanspruchun szone movable are. 12. Electrode according to claims 1 to 11, characterized in that the connection of the upper section (5) made of metal with the lower section (6) made of active material is provided via a thread. 13. Electrode according to claims 1 to 12, characterized in that the connection is provided by a screw nipple (1). 14. Electrode according to claims 1 to 13, characterized in that the lower section (6) is formed from active material from a number of rods, plates or tubes (20) which are connected or separated from one another. 15. Electrode according to claims 1 to 14, characterized in that the lower section (6) consists of several units (20) which are held by one or more nipple connections (1), the arrangement of the units (20) next to each other and / or interrogated. 16. Electrode according to claims 1 to 15, characterized in that the active material is amorphous carbon, graphite, a ceramic conductor, or a compound of inorganic fibers with an electrochemically active material. 17. Electrode according to claims 1 to 16, characterized in that the molded part (4) is placed gas and liquid-tight at least in the area that can come into contact with the electrolyte and the resulting products.

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