EP0220557A1 - Inert composite electrode, particularly an anode for molten salt electrolysis - Google Patents

Inert composite electrode, particularly an anode for molten salt electrolysis Download PDF

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Publication number
EP0220557A1
EP0220557A1 EP86113930A EP86113930A EP0220557A1 EP 0220557 A1 EP0220557 A1 EP 0220557A1 EP 86113930 A EP86113930 A EP 86113930A EP 86113930 A EP86113930 A EP 86113930A EP 0220557 A1 EP0220557 A1 EP 0220557A1
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EP
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Prior art keywords
active elements
composite electrode
elements
plate
electrode according
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EP86113930A
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German (de)
French (fr)
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EP0220557B1 (en
Inventor
Christine Dr. Zöllner
Herbert Hahn
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C Conradty Nuernberg GmbH and Co KG
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C Conradty Nuernberg GmbH and Co KG
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Priority to AT86113930T priority Critical patent/ATE43366T1/en
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    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
    • C25C3/00—Electrolytic production, recovery or refining of metals by electrolysis of melts
    • C25C3/06—Electrolytic production, recovery or refining of metals by electrolysis of melts of aluminium
    • C25C3/08—Cell construction, e.g. bottoms, walls, cathodes
    • C25C3/12—Anodes
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
    • C25C7/00—Constructional parts, or assemblies thereof, of cells; Servicing or operating of cells
    • C25C7/02—Electrodes; Connections thereof
    • C25C7/025—Electrodes; Connections thereof used in cells for the electrolysis of melts

Definitions

  • the invention relates to an inert composite electrode, in particular anode for melt flow electrolysis, for example for the extraction of aluminum, magnesium, sodium, lithium, among other things consisting of an active part in the form of a plurality of rod-shaped active elements, in particular made of oxide ceramics, with their longitudinal axes parallel to each other and are arranged in mutually aligned groups, an electrode holder which comprises a current-conducting plate, with one main surface of which the electrode elements are in frictional contact with their end faces, and a connecting arrangement which connects the active elements in groups to one another and keeps them in contact with the plate.
  • melt flow electrolysis e.g. In aluminum production, intensive development is underway to use so-called inert anodes, which consist in particular of oxide ceramics, for the electrolysis instead of the consumable carbon anodes.
  • the inert electrodes must, on the one hand, take into account the requirements of the existing cells that are still equipped with carbon anodes. This applies in particular with regard to the power supply line and the arrangement and / or the dimensioning of the active parts of the anodes. On the other hand, of course, the requirements made of the material from which the active parts of the inert anodes are made must also be taken into account. This applies in particular with regard to the physical parameters and the manufacturing technology.
  • An inert composite electrode of the type defined in the introduction is known from DE-PS 30 03 922. This essentially consists of an active part, an electrode holder and an arrangement for connecting the two first-mentioned assemblies.
  • the active part is formed by a plurality of rod-shaped active elements. These are arranged with their longitudinal axes parallel to one another and in groups aligned with one another. The total cross section perpendicular to the longitudinal axes of the active elements corresponds approximately to the corresponding cross section of a conventional carbon anode for a melt flow electrolysis cell.
  • the individual active elements consist of an oxide ceramic material.
  • a tubular support is provided to hold the active elements and to supply current to them.
  • a further tube is arranged concentrically in the latter, the lower end of which is provided with a base plate.
  • This base plate has a central bore through which a rod-shaped current feeder is passed, the lower end of which, below the base plate, is provided with a current-conducting pressure plate. With this pressure plate, the upper end faces of the active elements are brought into mechanical and electrical contact in a non-positive manner.
  • the active elements aligned in groups with one another each have a bore in their upper section, which are also aligned with one another with respect to a group.
  • a suspension rod the ends of which rest on a support plate, is passed through the mutually aligned bores of a group.
  • This support plate and the base plate mentioned are to be clamped using screw bolts, as a result of which the upper end faces of the active elements are brought into contact with the current-carrying pressure plate. If appropriate, an electrically highly conductive intermediate layer can be introduced between the end faces of the active elements and the pressure plate.
  • This known electrode construction has several serious disadvantages.
  • the production of the bores in the head sections of the active elements requires a greater production outlay. They can only be generated when the oxide ceramic active elements are green.
  • bores, in particular with regard to the alignment of the active elements arranged in groups are subject to greater tolerances, since such tolerances already occur in the green state during the production of the active elements and further dimensional deviations are unavoidable when the active elements are sintered.
  • the bores of a group of active elements are not exactly aligned, so that some of the active elements which are arranged one below the other on a suspension rod do not come into contact with their end faces, or do not come into sufficient contact with the current-carrying plate of the electrode holder.
  • the aforementioned weakening of the cross section of the active elements of the known anode also reduces the mechanical strength of the active elements, specifically in an area in which on the one hand the respective suspension rod exerts an increased compressive stress on the material of the active elements due to its prestressing and on the other hand also the highest tensile stresses due to the Weight of the active elements occur. Because of this, the greatest mechanical stresses act precisely in the area of the weakened cross section of the active elements, so that there is an increased risk of the electrode elements breaking at the point mentioned.
  • the active elements each have a plate side Have head section, which is substantially wedge-shaped in its cross section perpendicular to the line of flight of a group and in the direction of the plate-side end face, and with each of the two opposite wedge faces of the head section of the respective active element, a tensioning element is brought into contact with a wedge face, the wedge angle of which corresponds essentially to the respective wedge surface of the head section, so that there is a dovetail connection.
  • the active part of the anode according to the invention is thus broken down into a plurality of rod-shaped active elements, as is known per se.
  • the active elements have a favorable design in terms of production technology, because the wedge-shaped head section complies with the design in ceramic technology, whereas the holes provided in the head section of the active elements of the known anode already cause a number of problems in terms of production technology, as has been explained above.
  • the active elements in the area of the wedge bracing are only subjected to pressure, which can be easily accommodated by the oxide-ceramic material due to its high compressive strength, especially since the cross section in the pressurized area of the active elements is enlarged due to the wedge shape of the head sections.
  • the tensile stresses due to the weight of the active elements can also be absorbed. Overall, this results in a mechanically very stable anode construction.
  • the wedge or dovetail bracing of the active elements by means of the clamping elements described also results in a self-adjusting effect, with the result that all of the active elements come with their end faces in intimate contact with the current-carrying plate, with bridging or due to compensation for any existing manufacturing tolerances. Due to the self-adjusting wedge tension between the active elements on the one hand and the tensioning elements or the plate on the other hand, any movements of the assemblies towards one another are compensated for due to the different thermal expansion coefficients of the materials, so that the end faces of the active elements also have intimate contact with the tensioning elements during operation of the anode and the current-carrying plate is preserved. In this way, a permanent and both electrically and mechanically optimal connection between the metallic power supply and the ceramic active elements is guaranteed.
  • the current transfer area between the current-carrying plate and the active elements is increased in the anode according to the invention in that the tensioning elements are also in electrical connection both to the plate and to the wedge surfaces of the electrode elements, so that the latter Increase the total contact area of the active elements in relation to the component to be energized accordingly. Due to the increased total contact area, the voltage drop is also reduced accordingly.
  • the current flow at this critical point is significantly improved.
  • the area utilization of the anode according to the invention is therefore very good, since the streamlines have a certain lateral wrap and the effective anode area is approximately equal to the projected anode area.
  • the anode elements consist of a material with thermistor properties
  • they are in the cold, i.e. non-conductive area of the anode elements measures taken to increase the conductivity, namely the cross-sectional enlargement in the head section of the anode elements, the special design of the material of the anode elements to increase the conductivity and the enlarged current transmission area crucial for increasing the electrical efficiency.
  • the anode arrangement according to the invention therefore has a very good electrochemical efficiency.
  • Channels between the active elements are formed between the active elements arranged in groups, at least where the tensioning elements are provided.
  • Active elements circulate the melt and the electrolyte in these channels, which effectively counteracts an otherwise possible depletion of the electrolyte.
  • these channels provide enough space for the gas discharge so that the developed gas is quickly removed. Both contribute to an increase in the electrochemical efficiency of the process carried out with the electrodes according to the invention.
  • the active elements of a group can be in line with each other in their escape line.
  • only channels are formed between the active elements where there are clamping elements between the active elements.
  • the wedge-shaped widening of the head sections of the active elements has already largely reduced the voltage drop in the cold region. Nevertheless, it may still be advisable to design the electrical conductivity of the material of the active elements higher in the area of the head section than in the rest of the area after these materials have thermistors possess properties. This is possible, for example, in that the material of the active elements in the area of the head section is a cermet, which is preferably tin oxide containing silver. The current conductivity in the critical head section of the active elements in the electrode according to the invention is thus further improved.
  • a contact layer in order to reduce the contact resistance between the current-carrying plate and the active elements even further, it can be advantageous for a contact layer to be introduced between the relevant main surface of the plate and the corresponding end faces of the active elements.
  • This can be formed by a network of highly conductive metal, in particular copper.
  • a continuous clamping element or separate clamping elements can be provided on both sides for each aligned group of active elements.
  • the tensioning element is designed for fastening two opposite active elements of two adjacent groups and for this purpose has two opposite wedge surfaces with an essentially mirror-image arrangement. This further reduces the effort in manufacturing and assembly
  • the mentioned clamping element can expediently be trapezoidal in cross section perpendicular to the line of alignment of the groups of active elements.
  • clamping elements are assigned to each active element and the length of a clamping element essentially corresponds to the length of an active element.
  • the plate is expediently cooled by water cooling, for which the plate is designed as a hollow body, within which channels for the cooling water are arranged.
  • the respective current feeder to the plate is guided through the interior of the hollow body and is electrically connected to the inside of the main surface with which the active elements are in contact.
  • the inert electrode according to the invention in particular anode for the melt flow electrolysis, essentially consists of three assemblies, namely an active part, generally designated 10, an electrode holder, generally designated 30, and an arrangement, generally designated 40, for connecting the two first-mentioned assemblies.
  • the active part consists of a plurality of rod-shaped active elements, which are generally designated 20. These are arranged with their longitudinal axes vertically aligned in the cell in the assembly position parallel to one another and in groups 11, 12, 13 etc. aligned with one another along the alignment line 25 (FIG. 3). They are essentially square or rectangular in their cross section perpendicular to their longitudinal axis. They consist of an electrically conductive and electrochemically active oxide ceramic material that can be described in more detail.
  • the active elements 20 each have a head section 21, which is widened by wedge surfaces 23 in its cross section lying perpendicular to the alignment line of a group and in the direction of the corresponding end face 22.
  • the essentially plate-shaped electrode holder 30 has a main surface 31, as seen in the electrolysis cell in the assembly position, on which the active elements 20 are mechanically and electrically kept in contact with their end surfaces 22. This is done with the aid of the connecting arrangement 40 representing tensioning elements 41. These tensioning elements are so trapezoidal in their cross section parallel to the longitudinal axis of the active elements 20 and perpendicular to the alignment line of a group that the two opposite wedge surfaces 42 with the wedge surfaces 23 lying at the same angle are two in two neighboring groups, e.g. 12, 13, opposite active elements 20 with appropriate bias are in contact.
  • the clamping elements 41 are screwed to the plate-shaped electrode holder 30 by means of screws.
  • two adjacent groups 11, 12, 13, etc. of active elements are spaced apart such that channels 50 are formed which, in the manner described, circulate the electrolyte or the melt between the lower ones, into the melt or into the electrolyte immersed sections 26 of the active elements 20 is made possible and, on the other hand, ensure rapid removal of the gas developed in the electrolysis process between the groups of active elements 20 arranged upwards.
  • the plate-shaped electrode holder 30 is designed as a hollow body, consisting of a lower horizontal plate 32, an upper plate 33 arranged parallel to the first and side walls 34 perpendicular thereto.
  • the cavity serves for the circulation of cooling water in the interior 35 of the electrode holder 30.
  • This is a cooling water Inlet pipe 36 is provided which opens into the interior 35 on the edge.
  • the cooling water circulates along spiral-shaped guide walls 37 through the interior 35 of the plate-shaped electrode holder 30 up to its central area and from there again into the peripheral area, from where the correspondingly heated cooling water is drawn off through a cooling water drain pipe 38.
  • the plate-shaped electrode holder 30 is further equipped with a plurality of current supply bolts 60, via which the electrical current is fed to the plate-shaped electrode holder 30 and is transmitted from there to the electrode elements 20.
  • a plurality of current supply bolts 60 via which the electrical current is fed to the plate-shaped electrode holder 30 and is transmitted from there to the electrode elements 20.
  • sleeves 61 are welded to the inner surface of the lower plate 33, which have an internal thread with which the lower and externally threaded section of the corresponding power supply bolt 60 is screwed.
  • protective sleeves 62 made of corrosion-resistant material.
  • a network 39 e.g. made of copper.
  • the plate-shaped electrode holder 30 and the clamping elements 41 and their clamping screws 43 are expediently made of steel. They can also consist of nickel or of steel or nickel alloys. Cover elements are provided to protect these components against corrosion.
  • the cover elements 44 arranged on the underside of the tensioning elements are secured to the tensioning elements 41, for example by means of a dovetail guide.
  • the side cover elements 45 can be screwed to the front ends of the clamping elements 41 by screws 46.
  • the active elements 20 expediently consist of doped oxide ceramic, e.g. Tin oxide, nickel ferrite or yttrium oxide.
  • the composition can be as follows: 94.1 atomic percent tin oxide 3.8 atomic% copper 2.1 atomic% antimony
  • the following dimensioning of the rod-shaped active elements has proven to be appropriate: Cross section of the upper face: 3 x 3 cm Cross section of the lower face: 2 x 2 cm Length: 25 cm Wedge angle: 20 ° Distance between two adjacent groups of electrode elements: 1.5 cm
  • the side length of the upper cross section can expediently be between approximately 2 and 6 cm.
  • the length of the active elements can be between approx. 15 cm and approx. 40 cm.
  • the aforementioned distance between two groups of active elements can be between approximately 1 cm and approximately 2 cm.
  • the wedge angle of the head section of the respective active elements can be between approximately 5 ° and approximately 25 °.
  • the described exemplary embodiment of the anode according to the invention was operated in an electrolysis test cell with the following operating data: Bath composition: cryolite 84% by weight A1F3 5% by weight A1203 10% by weight CaF2 1% by weight Temperature: 980-1000 C. Clamp voltage: 4-5 volts Current: 30 A. Current density at the anode: 2 A / cm2 Current density at the cathode: 0.14 A / cm2 Electrode distance: 3 cm Immersion depth of the anodes: 2cm

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Abstract

An inert composite electrode, such as an anode, for molten salt electrolysis consists of an active part in the form of a plurality of bar-shaped active elements, in particular of ceramic oxide, which are arranged with their longitudinal axes mutually parallel and in mutually aligned groups, an electrode holder which comprises a current-conducting plate, with one main surface of which the active elements are in firm contact with their end surfaces, and a joining arrangement which joins the active elements together in groups and holds them in contact with the plate. This composite electrode is characterized in that the active elements each have a head section adjacent to the plate which is widened in the direction of the end surfaces adjacent to the plate substantially in a wedge shape considered in cross-sections lying perpendicular to the line of alignment of a group, and in that a clamping element has a wedging surface which is brought into contact with each of the two oppositely-lying wedging surfaces of the head section of the respective active element, the wedging angle of the clamping element substantially corresponding to that of the respective wedging surface of the head section.

Description

Die Erfindung betrifft eine inerte Verbundelektrode, insbesondere Anode für die Schmelzflußelektrolyse, z.B. für die Gewinnung von Aluminium, Magnesium, Natrium, Lithium, u.a. bestehend aus einem Aktivteil in Form einer Mehrzahl von stabförmigen Aktivelemen­ten, insbesondere aus Oxidkeramik, die mit ihren Längsachsen parallel nebeneinander und in zueinander fluchtenden Gruppen angeordnet sind, einem Elektro­denhalter, der eine stromleitende Platte umfaßt, mit deren einen Hauptfläche die Elektrodenelemente mit ihren Stirnflächen kraftschlüssig in Kontakt stehen, und einer Verbindungsanordnung, die die Aktivelemente gruppenweise untereinander verbindet und mit der Platte in Kontakt hält.The invention relates to an inert composite electrode, in particular anode for melt flow electrolysis, for example for the extraction of aluminum, magnesium, sodium, lithium, among other things consisting of an active part in the form of a plurality of rod-shaped active elements, in particular made of oxide ceramics, with their longitudinal axes parallel to each other and are arranged in mutually aligned groups, an electrode holder which comprises a current-conducting plate, with one main surface of which the electrode elements are in frictional contact with their end faces, and a connecting arrangement which connects the active elements in groups to one another and keeps them in contact with the plate.

In der Schmelzflußelektrolyse, z.B. bei der Alumi­niumerzeugung, ist eine intensive Entwicklung im Gange, für die Elektrolyse anstelle der sich verzeh­renden Anoden aus Kohlenstoff sogenannte inerte Ano­den, die insbesondere aus Oxidkeramik bestehen, ein­zusetzen.In melt flow electrolysis, e.g. In aluminum production, intensive development is underway to use so-called inert anodes, which consist in particular of oxide ceramics, for the electrolysis instead of the consumable carbon anodes.

Für diese Entwicklung bilden eine Reihe von Vorteilen den Anreiz:
- Bei Herstellung und bei Betrieb der inerten Ano­den ergibt sich eine erhebliche Energieeinspa­rung.
- Zugleich wird Rohstoff eingespart. Bei der Her­stellung muß nicht auf fossilen Rohstoff Erdöl, aus dem dann Petrol, Koks und Pech gewonnen wird, zurückgegriffen werden. Beim Betrieb der inerten Anoden ergibt sich kein oder nur ein sehr gerin­ger Verbrauch an Anodenmaterial. Damit fallen des weiteren Investitionen und Betriebskosten für die Anodenfabrikation weg.
- Da der sich bei verzehrenden Anoden turnusgemäß notwendige Anodenwechsel entbehrlich wird, können die Zellen geschlossener gefahren werden. Dadurch verbessern sich die Arbeitsbedingungen.
- Die Abluft aus den Zellen enthält weder Schwefel­dioxid noch polyaromatische Kohlenwasserstoffe. Aus dem geschlossenen Abluftsystem können die Fluoride leichter zurückgewonnen werden.
- Schließlich können inerte Anoden mit höheren Stromdichten als Kohlenstoffanoden gefahren werden. Dadurch erhöht sich die Produktionskapa­zität auf weniger Fläche und/oder in weniger Zeit.There are a number of advantages to this development:
- Considerable energy savings result from the manufacture and operation of the inert anodes.
- At the same time, raw material is saved. It is not necessary to make use of fossil fuels such as petroleum, from which petroleum, coke and pitch are extracted. The operation of the inert anodes results in little or no consumption of anode material. This also eliminates investments and operating costs for anode production.
- Since the anode change, which is required as part of the rotation when the anodes are consumed, can be dispensed with, the cells can be driven more closed. This improves working conditions.
- The exhaust air from the cells contains neither sulfur dioxide nor polyaromatic hydrocarbons. The fluorides can be recovered more easily from the closed exhaust system.
- Finally, inert anodes with higher current densities than carbon anodes can be used. This increases the production capacity in less space and / or in less time.

Konstruktiv müssen die inerten Elektroden einerseits den Vorgaben der bereits vorhandenen, noch mit Koh­lenstoffanoden ausgerüsteten Zellen Rechnung tragen. Dies gilt insbesondere in bezug auf die Stromzulei­tung und die Anordnung und/oder die Dimensionierung der Aktivteile der Anoden. Andererseits müssen aber natürlich auch die Erfordernisse, die aus dem Werk­stoff, aus dem die Aktivteile der inerten Anoden bestehen, Berücksichtigung finden. Dies gilt insbe­sondere in bezug auf die physikalischen Parameter und die Herstellungstechnologie.In terms of construction, the inert electrodes must, on the one hand, take into account the requirements of the existing cells that are still equipped with carbon anodes. This applies in particular with regard to the power supply line and the arrangement and / or the dimensioning of the active parts of the anodes. On the other hand, of course, the requirements made of the material from which the active parts of the inert anodes are made must also be taken into account. This applies in particular with regard to the physical parameters and the manufacturing technology.

Eine inerte Verbundelektrode der eingangs definierten Art ist aus der DE-PS 30 03 922 bekannt. Diese be­steht im wesentlichen aus einem Aktivteil, einem Elektrodenhalter und einer Anordnung zum Verbinden der zwei erstgenannten Baugruppen.An inert composite electrode of the type defined in the introduction is known from DE-PS 30 03 922. This essentially consists of an active part, an electrode holder and an arrangement for connecting the two first-mentioned assemblies.

Der Aktivteil ist durch eine Mehrzahl von stabförmi­gen Aktivelementen gebildet. Diese sind mit ihren Längsachsen parallel nebeneinander und in zueinander fluchtenden Gruppen angeordnet. Der zu den Längsach­sen der Aktivelemente senkrechte Gesamtquerschnitt entspricht in etwa dem entsprechenden Querschnitt einer herkömmlichen Kohlenstoffanode für eine Schmelzflußelektrolysezelle. Die einzelnen Aktivele­mente bestehen aus einem oxidkeramischen Werkstoff.The active part is formed by a plurality of rod-shaped active elements. These are arranged with their longitudinal axes parallel to one another and in groups aligned with one another. The total cross section perpendicular to the longitudinal axes of the active elements corresponds approximately to the corresponding cross section of a conventional carbon anode for a melt flow electrolysis cell. The individual active elements consist of an oxide ceramic material.

Zur Halterung der Aktivelemente und zur Stromzufüh­rung zu diesen ist ein rohrförmiger Träger vorgese­hen. In diesen ist konzentrisch ein weiteres Rohr angeordnet, dessen unteres Ende mit einer Bodenplatte versehen ist. Diese Bodenplatte weist eine zentrische Bohrung auf, durch die ein stabförmiger Stromzuleiter hindurchgeführt ist, dessen unteres, unterhalb der Bodenplatte endendes Ende mit einer stromleitenden Anpreßplatte versehen ist. Mit dieser Anpreßplatte werden die oberen Stirnflächen der Aktivelemente auf kraftschlüssige Weise in mechanischen und elektri­schen Kontakt gebracht. Hierzu weisen die gruppenwei­se untereinander fluchtenden Aktivelemente in ihrem oberen Abschnitt je eine Bohrung auf, die in bezug auf eine Gruppen ebenfalls zueinander fluchten. Durch die zueinander fluchtenden Bohrungen einer Gruppe ist jeweils ein Aufhängestab hindurchgeführt, dessen Enden auf einer Auflageplatte aufliegen. Diese Aufla­geplatte und die genannte Bodenplatte sind über Schraubbolzen zu verspannen, wodurch die oberen Stirnflächen der Aktivelemente in Kontakt mit der stromführenden Anpreßplatte gebracht werden. Gegebe­nenfalls kann zwischen den Stirnflächen der Aktivele­mente und der Anpreßplatte eine elektrisch gut lei­tende Zwischenschicht eingebracht sein.A tubular support is provided to hold the active elements and to supply current to them. A further tube is arranged concentrically in the latter, the lower end of which is provided with a base plate. This base plate has a central bore through which a rod-shaped current feeder is passed, the lower end of which, below the base plate, is provided with a current-conducting pressure plate. With this pressure plate, the upper end faces of the active elements are brought into mechanical and electrical contact in a non-positive manner. For this purpose, the active elements aligned in groups with one another each have a bore in their upper section, which are also aligned with one another with respect to a group. A suspension rod, the ends of which rest on a support plate, is passed through the mutually aligned bores of a group. This support plate and the base plate mentioned are to be clamped using screw bolts, as a result of which the upper end faces of the active elements are brought into contact with the current-carrying pressure plate. If appropriate, an electrically highly conductive intermediate layer can be introduced between the end faces of the active elements and the pressure plate.

Diese bekannte Elektrodenkonstruktion weist mehrere gravierende Nachteile auf.This known electrode construction has several serious disadvantages.

Zum einen ist ihr Aufbau insgesamt relativ kompli­ziert, insbesondere in bezug auf die Aufhängestäbe, die durch die Bohrungen im Kopfabschnitt der Aktiv­elemente hindurchgeführt sind und entsprechend gela­gert und gespannt werden müssen.On the one hand, their overall structure is relatively complicated, in particular with regard to the suspension rods, which are passed through the bores in the head section of the active elements and must be appropriately stored and tensioned.

Des weiteren erfordert die Herstellung der Bohrungen in den Kopfabschnitten der Aktivelemente einen größe­ren Herstellungsaufwand. Sie sind nur im Grünzustand der oxidkeramischen Aktivelemente zu erzeugen. Des weiteren sind Bohrungen, insbesondere in bezug auf die Fluchtung der in Gruppen angeordneten Aktivele­mente, mit größeren Toleranzen behaftet, da derartige Toleranzen schon bei der Herstellung der Aktivelemen­te im Grünzustand eingehen und des weiteren beim Sintern der Aktivelemente weitere Maßabweichungen unvermeidlich sind. Dies hat zur Folge, daß die Boh­rungen einer Gruppe von Aktivelementen nicht genau fluchten, so daß einige der Aktivelemente, die an einem Aufhängestab untereinander gereiht sind, nicht oder nicht genügend mit ihren Stirnflächen in Kontakt mit der stromführenden Platte des Elektrodenhalters gelangen. Dies gilt dann umso mehr im Betrieb, wo sich die unterschiedlichen Ausdehnungskoeffizienten der Werkstoff der Aktivelemente einerseits und der stromzuführenden Platte andererseits verstärkt nega­tiv in bezug auf die Kontaktierung zwischen den Stirnflächen der Aktivelemente und der Platte auswir­ken. Dadurch ergibt sich ein erhöhter Spannungsabfall mit der Folge, daß der elektrische Wirkungsgrad sinkt.Furthermore, the production of the bores in the head sections of the active elements requires a greater production outlay. They can only be generated when the oxide ceramic active elements are green. Furthermore, bores, in particular with regard to the alignment of the active elements arranged in groups, are subject to greater tolerances, since such tolerances already occur in the green state during the production of the active elements and further dimensional deviations are unavoidable when the active elements are sintered. As a result, the bores of a group of active elements are not exactly aligned, so that some of the active elements which are arranged one below the other on a suspension rod do not come into contact with their end faces, or do not come into sufficient contact with the current-carrying plate of the electrode holder. This is all the more true in operation, where the different expansion coefficients of the material of the active elements on the one hand and the current-carrying plate on the other hand have an increasingly negative effect with regard to the contact between the end faces of the active elements and the plate. This results in an increased voltage drop, with the result that the electrical efficiency drops.

Dieser Nachteil wird noch dadurch verschärft, daß die Bohrungen die Querschnittsfläche parallel zur Längs­achse der Aktivelemente verkleinern, und zwar gerade im kalten Bereich der Aktivelemente. Dadurch werden gerade dort die Strombahnen eingeschnürt.This disadvantage is exacerbated by the fact that the bores reduce the cross-sectional area parallel to the longitudinal axis of the active elements, specifically in the cold region of the active elements. As a result, the current paths are constricted there.

Die genannte Schwächung des Querschnittes der Aktiv­elemente der bekannten Anode vermindert auch die mechanische Festigkeit der Aktivelemente, und zwar in einem Bereich, in dem einerseits der jeweilige Auf­hängestab aufgrund dessen Vorspannung einer erhöhte Druckspannung auf den Werkstoff der Aktivelemente ausübt und andererseits auch die höchsten Zugspannun­gen aufgrund des Gewichtes der Aktivelemente auftre­ten. Aufgrund dessen wirken die größten mechanischen Spannungen gerade im Bereich des geschwächten Quer­schnitts der Aktivelemente, so daß eine erhöhte Ge­fahr des Bruches der Elektrodenelemente an der ge­nannten Stelle gegeben ist.The aforementioned weakening of the cross section of the active elements of the known anode also reduces the mechanical strength of the active elements, specifically in an area in which on the one hand the respective suspension rod exerts an increased compressive stress on the material of the active elements due to its prestressing and on the other hand also the highest tensile stresses due to the Weight of the active elements occur. Because of this, the greatest mechanical stresses act precisely in the area of the weakened cross section of the active elements, so that there is an increased risk of the electrode elements breaking at the point mentioned.

Schließlich ist bei der bekannten Anodenkonstruktion kein bzw. wenig Augenmerk gerichtet auf die notwendi­ge Elektrolytbewegung im Bereich der in die Schmelze eintauchenden unteren Abschnitte der Elektrodenele­mente sowie auf die Gasabfuhr im Bereich der Elektro­denelemente.Finally, in the known anode construction, little or no attention is paid to the necessary electrolyte movement in the region of the lower sections of the electrode elements immersed in the melt and to the gas removal in the region of the electrode elements.

Es ist Aufgabe der Erfindung, eine inerte Verbund­elektrode der vorausgesetzten Art zu schaffen, bei der die oxidkeramischen Aktivelemente unter Berück­sichtigung der Werkstoff- und Herstellungstechnologie für Oxidkeramik gestaltet sind, die einen einfachen Aufbau besitzt und leicht montierbar ist sowie einen guten elektrochemischen Wirkungsgrad aufweist.It is an object of the invention to provide an inert composite electrode of the presupposed type in which the oxide ceramic active elements are designed taking into account the material and manufacturing technology for oxide ceramics, which has a simple structure and is easy to assemble and has a good electrochemical efficiency.

Diese Aufgabe wird bei einer inerten Verbundelektrode mit den eingangs genannten Merkmalen dadurch gelöst, daß die Aktivelemente jeweils plattenseitig einen Kopfabschnitt aufweisen, der in seinem senkrecht zur Fluchtlinie einer Gruppe liegenden Querschnitt und in Richtung der plattenseitigen Stirnfläche im wesentli­chen keilförmig verbreitert ist, und mit jeder der zwei gegenüberliegenden Keilflächen des Kopfab­schnitts des jeweiligen Aktivelements ein Spannele­ment mit einer Keilfläche in Anlage gebracht ist, deren Keilwinkel dem der jeweiligen Keilfäche des Kopfabschnittes im wesentlichen entspricht, so daß sich eine Schwalbenschwanz-Verbindung ergibt.This object is achieved in the case of an inert composite electrode with the features mentioned at the outset in that the active elements each have a plate side Have head section, which is substantially wedge-shaped in its cross section perpendicular to the line of flight of a group and in the direction of the plate-side end face, and with each of the two opposite wedge faces of the head section of the respective active element, a tensioning element is brought into contact with a wedge face, the wedge angle of which corresponds essentially to the respective wedge surface of the head section, so that there is a dovetail connection.

Der Aktivteil der erfindungsgemäßen Anode ist also aufgelöst in eine Mehrzahl von stabförmigen Aktivele­menten, wie dies an sich bekannt ist. Die Aktivele­mente sind herstellungstechnologisch günstig gestal­tet, weil der keilförmige Kopfabschnitt der Gestal­tung in der Keramik-Technologie entgegenkommt, wo­hingegen die im Kopfabschnitt der Aktivelemente der bekannten Anode vorgesehenen Bohrungen schon her­stellungstechnisch eine Reihe von Problemen verursa­chen, wie oben dargelegt wurde.The active part of the anode according to the invention is thus broken down into a plurality of rod-shaped active elements, as is known per se. The active elements have a favorable design in terms of production technology, because the wedge-shaped head section complies with the design in ceramic technology, whereas the holes provided in the head section of the active elements of the known anode already cause a number of problems in terms of production technology, as has been explained above.

Im montierten Zustand sind die Aktivelemente im Be­reich der Keilverspannung ausschließlich auf Druck beansprucht, was durch den oxidkeramischen Werkstoff aufgrund dessen hoher Druckfestigkeit ohne weiteres aufgenommen werden kann, zumal der Querschnitt im druckbeaufschlagten Bereich der Aktivelemente auf­grund der Keilform der Kopfabschnitte vergrößert ist. Als Folge der Querschnittsvergrößerung im Einspannbe­reich der Aktivelemente können auch die Zugspannungen aufgrund des Gewichtes der Aktivelemente gut aufge­nommen werden. Insgesamt ergibt sich also eine mecha­nisch sehr stabile Anodenkonstruktion.In the assembled state, the active elements in the area of the wedge bracing are only subjected to pressure, which can be easily accommodated by the oxide-ceramic material due to its high compressive strength, especially since the cross section in the pressurized area of the active elements is enlarged due to the wedge shape of the head sections. As a result of the increase in cross section in the clamping area of the active elements, the tensile stresses due to the weight of the active elements can also be absorbed. Overall, this results in a mechanically very stable anode construction.

Die Keil- bzw. Schwalbenschwanzverspannung der Aktiv­elemente mittels der beschriebenen Spannelemente ergibt zugleich einen selbstjustierenden Effekt mit der Folge, daß sämtliche der Aktivelemente mit ihren Stirnflächen in innigen Kontakt mit der stromführen­den Platte gelangen, und zwar unter Überbrückung bzw. aufgrund Ausgleichs eventuell bestehender Fertigungs­toleranzen. Aufgrund der selbstjustierenden Keilver­spannung zwischen den Aktivelementen einerseits und den Spannelementen bzw. der Platte andererseits werden des weiteren eventuelle Bewegungen der Bau­gruppen zueinander aufgrund der unterschiedlichen thermischen Ausdehnungskoeffizienten der Werkstoffe ausgeglichen, so daß auch im Betrieb der Anode ein inniger Kontakt der Stirnflächen der Aktivelemente mit den Spannelementen und der stromzuführenden Plat­te erhalten bleibt. Auf diese Weise ist eine dauer­hafte und sowohl elektrisch als auch mechanisch opti­male Verbindung zwischen der metallischen Stromzufüh­rung und den keramischen Aktivelementen gewährlei­stet.The wedge or dovetail bracing of the active elements by means of the clamping elements described also results in a self-adjusting effect, with the result that all of the active elements come with their end faces in intimate contact with the current-carrying plate, with bridging or due to compensation for any existing manufacturing tolerances. Due to the self-adjusting wedge tension between the active elements on the one hand and the tensioning elements or the plate on the other hand, any movements of the assemblies towards one another are compensated for due to the different thermal expansion coefficients of the materials, so that the end faces of the active elements also have intimate contact with the tensioning elements during operation of the anode and the current-carrying plate is preserved. In this way, a permanent and both electrically and mechanically optimal connection between the metallic power supply and the ceramic active elements is guaranteed.

Dadurch wird der Spannungsabfall zwischen der strom­zuleitenden Platte und den Stirnflächen der Aktivele­mente minimiert.This minimizes the voltage drop between the current-carrying plate and the end faces of the active elements.

Darüber hinaus ist bei der erfindungsgemäßen Anode die Stromübertragungsfläche zwischen der stromführen­den Platte und den Aktivelementen dadurch vergrößert, daß die Spannelemente ebenfalls in elektrischer Ver­bindung sowohl zur Platte als auch zu den Keilflächen der Elektrodenelemente stehen, so daß letztere die Gesamt-Kontaktfläche der Aktivelemente in bezug auf das stromzuführende Bauteil entsprechend vergrößern. Aufgrund der vergrößerten Gesamt-Kontaktfläche wird auch dementsprechend der Spannungsabfall verkleinert.In addition, the current transfer area between the current-carrying plate and the active elements is increased in the anode according to the invention in that the tensioning elements are also in electrical connection both to the plate and to the wedge surfaces of the electrode elements, so that the latter Increase the total contact area of the active elements in relation to the component to be energized accordingly. Due to the increased total contact area, the voltage drop is also reduced accordingly.

Aufgrund der schon angesprochenen Querschnittsvergrö­ßerung im Kopfabschnitt der Aktivelemente, d.h. gera­de im kalten Bereich derselben, ist die Stromführung an dieser kritischen Stelle entscheidend verbessert. Die Flächennutzung der erfindungsgemäßen Anode ist also sehr gut, da die Stromlinien einen gewissen seitlichen Umgriff haben und die wirksame Anodenflä­che in etwa gleich der projizierten Anodenfläche ist.Due to the already mentioned cross-sectional enlargement in the head section of the active elements, i.e. Especially in the cold area, the current flow at this critical point is significantly improved. The area utilization of the anode according to the invention is therefore very good, since the streamlines have a certain lateral wrap and the effective anode area is approximately equal to the projected anode area.

Nachdem die Anodenelemente aus einem Werkstoff mit Heißleiter-Eigenschaften bestehen, sind die im kal­ten, d.h. nicht gutleitenden Bereich der Anodenele­mente getroffenen Maßnahmen zur Erhöhung der Leitfä­higkeit, nämlich die Querschnittsvergrößerung im Kopfabschnitt der Anodenelemente, die spezielle Aus­bildung des Werkstoffes der Anodenelemente zur Erhö­hung der Leitfähigkeit und die vergrößerte Stromüber­tragungsfläche entscheidend zur Erhöhung des elektri­schen Wirkungsgrads. Insgesamt weist also die erfin­dungsgemäße Anodenanordnung einen sehr guten elek­tro-chemischen Wirkungsgrad auf.After the anode elements consist of a material with thermistor properties, they are in the cold, i.e. non-conductive area of the anode elements measures taken to increase the conductivity, namely the cross-sectional enlargement in the head section of the anode elements, the special design of the material of the anode elements to increase the conductivity and the enlarged current transmission area crucial for increasing the electrical efficiency. Overall, the anode arrangement according to the invention therefore has a very good electrochemical efficiency.

Zwischen den gruppenweise angeordneten Aktivelementen sind mindestens dort, wo die Spannelemente vorgesehen sind, Kanäle zwischen den Aktivelementen ausgebildet. Einerseits kann im Bereich der in die Schmelze bzw. in den Elektrolyt eintauchenden unteren Abschnitt der Aktivelemente in diesen Kanälen die Schmelze und der Elektrolyt zirkulieren, wodurch einer sonst möglichen Verarmung des Elektrolyts effektiv entgegengewirkt wird. Andererseits stellen diese Kanäle für die Gas­abfuhr genug Raum zur Verfügung, so daß das ent­wickelte Gas schnell abgeführt wird. Beides trägt zu einer Erhöhung des elektrochemischen Wirkungsgrads des mit den erfindungsgemäßen Elektroden durchgeführ­ten Prozesses bei.Channels between the active elements are formed between the active elements arranged in groups, at least where the tensioning elements are provided. On the one hand, in the area of the lower section immersed in the melt or in the electrolyte Active elements circulate the melt and the electrolyte in these channels, which effectively counteracts an otherwise possible depletion of the electrolyte. On the other hand, these channels provide enough space for the gas discharge so that the developed gas is quickly removed. Both contribute to an increase in the electrochemical efficiency of the process carried out with the electrodes according to the invention.

Zweckmäßige Ausbildungen der erfindungsgemäßen Ver­bundelektrode ergeben sich aus den übrigen Ansprü­chen.Appropriate designs of the composite electrode according to the invention result from the remaining claims.

So können beispielsweise die Aktivelemente einer Gruppe in deren Fluchtlinie untereinander in Anlage stehen. Es sind also nur Kanäle zwischen den Aktiv­elementen dort gebildet, wo Spannelemente zwischen den Aktivelementen liegen. Dadurch ergibt sich einer­seits ein sehr kompakter Aufbau des Aktivteils der erfindungsgemäßen Anode, andererseits ist aber auch ausreichend einer entsprechenden Bewegung der Schmel­ze und des Elektrolyts sowie der Gasabfuhr Rechnung getragen.For example, the active elements of a group can be in line with each other in their escape line. Thus, only channels are formed between the active elements where there are clamping elements between the active elements. This results on the one hand in a very compact structure of the active part of the anode according to the invention, but on the other hand sufficient consideration is also given to a corresponding movement of the melt and of the electrolyte and of the gas removal.

Zwar ist durch die keilförmige Verbreiterung der Kopfabschnitte der Aktivelemente bereits der Span­nungsabfall im kalten Bereich weitgehend reduziert. Trotzdem kann es sich noch empfehlen, die elektrische Leitfähigkeit des Werkstoffes der Aktivelemente im Bereich des Kopfabschnittes höher auszulegen als im übrigen Bereich, nachdem diese Werkstoffe Heißleiter­ eigenschaften besitzen. Dies ist z.B. dadurch mög­lich, daß der Werkstoff der Aktivelemente im Bereich des Kopfabschnittes ein Cermet ist, das vorzugsweise Silber enthaltendes Zinnoxid ist. Damit ist die Stromleitfähigkeit im kritischen Kopfabschnitt der Aktivelemente bei der erfindungsgemäßen Elektrode noch weiter verbessert.The wedge-shaped widening of the head sections of the active elements has already largely reduced the voltage drop in the cold region. Nevertheless, it may still be advisable to design the electrical conductivity of the material of the active elements higher in the area of the head section than in the rest of the area after these materials have thermistors possess properties. This is possible, for example, in that the material of the active elements in the area of the head section is a cermet, which is preferably tin oxide containing silver. The current conductivity in the critical head section of the active elements in the electrode according to the invention is thus further improved.

Um den Übergangswiderstand zwischen der stromzulei­tenden Platte und den Aktivelementen noch weiter zu verkleinern, kann es von Vorteil sein, daß zwischen der betreffenden Hauptfläche der Platte und den ent­sprechenden Stirnflächen der Aktivelemente eine Kon­taktschicht eingebracht ist. Diese kann durch ein Netz aus gut leitendem Metal, insbesondere Kupfer, gebildet sein.In order to reduce the contact resistance between the current-carrying plate and the active elements even further, it can be advantageous for a contact layer to be introduced between the relevant main surface of the plate and the corresponding end faces of the active elements. This can be formed by a network of highly conductive metal, in particular copper.

Es kann für jede fluchtende Gruppe von Aktivelementen beidseitig je ein durchgehendes Spannelement oder aber separate Spannelemente vorgesehen sein. Es ist aber auch möglich, daß das Spannelement zur Befesti­gung von zwei gegenüberliegenden Aktivelementen zweier benachbarter Gruppen ausgebildet ist und hier­zu zwei gegenüberliegende Keilflächen mit im wesent­lichen spiegelbildlicher Anordnung aufweist. Dadurch erniedrigt sich der Aufwand in der Fertigung und in der Montage weiterA continuous clamping element or separate clamping elements can be provided on both sides for each aligned group of active elements. However, it is also possible that the tensioning element is designed for fastening two opposite active elements of two adjacent groups and for this purpose has two opposite wedge surfaces with an essentially mirror-image arrangement. This further reduces the effort in manufacturing and assembly

Das angesprochene Spannelement kann zweckmäßigerweise im Querschnitt senkrecht zur Fluchtlinie der Gruppen der Aktivelemente trapezförmig ausgebildet sein.The mentioned clamping element can expediently be trapezoidal in cross section perpendicular to the line of alignment of the groups of active elements.

Des weiteren sind jedem Aktivelement je zwei separate Spannelemente zugeordnet und die Länge eines Spann­elements entspricht im wesentlichen der Länge eines Aktivelements.Furthermore, two separate clamping elements are assigned to each active element and the length of a clamping element essentially corresponds to the length of an active element.

Es ist aber auch möglich, daß für jeweils eine Gruppe von Aktivelementen je zwei durchgehende Spannelemente vorgesehen sind und die Länge eines Spannelementes der Länge einer Gruppe von Aktivelementen im wesent­lichen entspricht.However, it is also possible that two continuous tensioning elements are provided for each group of active elements and the length of a tensioning element essentially corresponds to the length of a group of active elements.

Für eine schnelle Montage und Demontage empfiehlt es sich, daß die Spannelemente mittels Schrauben an der Platte befestigt sind.For quick assembly and disassembly, it is recommended that the clamping elements are attached to the plate using screws.

Zur Vermeidung von Korrosion aufgrung der in der Zelle vorhandenen aggressiven Gase und der hohen Temperaturen ist es natürlich zweckmäßig, nicht nur die dem Zelleninneren zugekehrten Bereiche der strom­führenden Platte, sondern auch die Spannelemente einschließlich ihrer Befestigungselemente durch Ab­deckelemente aus korrosionsbeständigem Werkstoff zu schützen. Es bieten sich Keramik-Grafit-Verbundmate­rialien an, z.B. Tongrafit.To avoid corrosion due to the aggressive gases present in the cell and the high temperatures, it is of course expedient not only to protect the areas of the current-carrying plate which face the interior of the cell, but also the clamping elements, including their fastening elements, by means of cover elements made of corrosion-resistant material. Ceramic-graphite composite materials are available, e.g. Tongraphite.

Schließlich ist es von erheblichem Vorteil, die stromzuführende Platte zu kühlen. Dadurch ist es möglich, den Elektrodenhalter so dicht wie möglich an die Schmelze heranzuführen und trotzdem die Kontakt­temperatur zwischen Platte und Aktivelemente unter 250°C zu halten. Dies ist insbesondere dann erforder­lich, wenn die Anode mit höherer Strombelastung ge­ fahren wird, da bekanntlich die Temperatur der Elek­troden quadratisch mit der Strombelastung steigt. Bevorzugt sollte die Kühlung so ausgelegt sein, daß ca. 30 bis 35 % der Gesamtwärme über die Anodenoberfläche abgeführt werden. Der Vorteil des möglichst nahen Heranführens des Elektrodenhalters ist natürlich darin zu sehen, daß die Aktivelemente dadurch kurz ausgebildet werden können, wodurch einerseits teurer Werkstoff einge­spart werden kann und andererseits der Spannungsab­fall in den Aktivelementen weiter erniedrigt wird.Finally, it is of considerable advantage to cool the current supply plate. This makes it possible to bring the electrode holder as close as possible to the melt and still keep the contact temperature between the plate and active elements below 250 ° C. This is particularly necessary if the anode has a higher current load will drive, as is known, the temperature of the electrodes increases quadratically with the current load. The cooling should preferably be designed such that approximately 30 to 35% of the total heat is dissipated via the anode surface. The advantage of moving the electrode holder as close as possible is of course to be seen in the fact that the active elements can be made short as a result, which on the one hand saves expensive material and on the other hand further reduces the voltage drop in the active elements.

Zweckmäßigerweise wird die Kühlung der Platte durch eine Wasserkühlung verwirklicht, wofür die Platte als Hohlkörper ausgebildet ist, innerhalb dem Kanäle für das Kühlwasser angeordnet sind. In diesem Fall ist es schließlich zweckmäßig, daß der jeweilige Stromzulei­ter zur Platte durch das Innere des Hohlkörpers hin­durchgeführt und mit der Innenseite der Hauptfläche, mit der die Aktivelemente in Kontakt stehen, elek­trisch verbunden ist.The plate is expediently cooled by water cooling, for which the plate is designed as a hollow body, within which channels for the cooling water are arranged. In this case, it is finally expedient that the respective current feeder to the plate is guided through the interior of the hollow body and is electrically connected to the inside of the main surface with which the active elements are in contact.

Weitere Vorteile und Einzelheiten der erfindungsgemä­ßen Verbundelektrode ergeben sich anhand der Be­schreibung der Zeichnung und der Erläuterung eines speziellen Ausführungsbeispiels.Further advantages and details of the composite electrode according to the invention result from the description of the drawing and the explanation of a special exemplary embodiment.

In den Zeichnungen zeigt:

  • Fig. 1 eine perspektivische Darstellung eines Aus­führungsbeispiels der erfindungsgemäßen Verbundelek­trode,
  • Fig. 2 eine teilweise geschnittene Seitenansicht der erfindungsgemäßen Verbundelektrode, und
  • Fig. 3 die Ansicht A und den Schnitt B-B entsprechend der Fig. 2.
In the drawings:
  • 1 is a perspective view of an embodiment of the composite electrode according to the invention,
  • Fig. 2 is a partially sectioned side view of the composite electrode according to the invention, and
  • 3 shows the view A and the section BB corresponding to FIG. 2nd

Die erfindungsgemäße inerte Elektrode, insbesondere Anode für die Schmelzflußelektrolyse, besteht im wesentlichen aus drei Baugruppen, nämlich einem ins­gesamt mit 10 bezeichneten Aktivteil, einem insgesamt mit 30 bezeichneten Elektrodenhalter und einer insge­samt mit 40 bezeichneten Anordnung zum Verbinden der zwei erstgenannten Baugruppen.The inert electrode according to the invention, in particular anode for the melt flow electrolysis, essentially consists of three assemblies, namely an active part, generally designated 10, an electrode holder, generally designated 30, and an arrangement, generally designated 40, for connecting the two first-mentioned assemblies.

Der Aktivteil besteht aus einer Mehrzahl von stabför­migen Aktivelementen, die allgemein mit 20 bezeichnet sind. Diese sind mit ihren in der Montagestellung in der Zelle vertikal ausgerichteten Längsachsen pa­rallel nebeneinander und in zueinander längs der Fluchtlinie 25 (Fig. 3) fluchtenden Gruppen 11, 12, 13 usw. angeordnet. Sie sind in ihrem zu ihrer Längs­achse senkrechten Querschnitt im wesentlichen quadra­tisch bzw. rechteckförmig. Sie bestehen aus einem noch näher zu bezeichnenden, elektrisch leitenden und elektrochemisch aktiven oxidkeramischen Werkstoff. Die Aktivelemente 20 weisen jeweils einen Kopfab­schnitt 21 auf, der in seinem senkrecht zur Fluchtli­nie einer Gruppe liegenden Querschnitt und in Rich­tung der entsprechenden Stirnfläche 22 durch Keilflä­chen 23 verbreitert ist.The active part consists of a plurality of rod-shaped active elements, which are generally designated 20. These are arranged with their longitudinal axes vertically aligned in the cell in the assembly position parallel to one another and in groups 11, 12, 13 etc. aligned with one another along the alignment line 25 (FIG. 3). They are essentially square or rectangular in their cross section perpendicular to their longitudinal axis. They consist of an electrically conductive and electrochemically active oxide ceramic material that can be described in more detail. The active elements 20 each have a head section 21, which is widened by wedge surfaces 23 in its cross section lying perpendicular to the alignment line of a group and in the direction of the corresponding end face 22.

Der im wesentlichen plattenförmig ausgebildete Elek­trodenhalter 30 besitzt eine - in der Montagestellung in der Elektrolysezelle gesehen - nach unten gerich­tete Hauptfläche 31, an der die Aktivelemente 20 mit ihren Stirnflächen 22 mechanisch und elektrisch in Kontakt gehalten sind. Dies erfolgt mit Hilfe von die Verbindungsanordnung 40 darstellenden Spannelementen 41. Diese Spannele­mente sind in ihrem parallel zur Längsachse der Aktivelemente 20 und senkrecht zur Fluchtlinie einer Gruppe verlaufenden Querschnitt so trapezförmig aus­gebildet, daß die zwei gegenüberliegenden Keilflächen 42 mit den gleichwinklig liegenden Keilflächen 23 zweier in zwei benachbarten Gruppen, z.B. 12, 13, gegenüberliegenden Aktivelementen 20 mit entsprechen­der Vorspannung in Anlage stehen. Hierzu sind die Spannelemente 41 mittels Schrauben mit dem platten­förmigen Elektrodenhalter 30 verschraubt.The essentially plate-shaped electrode holder 30 has a main surface 31, as seen in the electrolysis cell in the assembly position, on which the active elements 20 are mechanically and electrically kept in contact with their end surfaces 22. This is done with the aid of the connecting arrangement 40 representing tensioning elements 41.These tensioning elements are so trapezoidal in their cross section parallel to the longitudinal axis of the active elements 20 and perpendicular to the alignment line of a group that the two opposite wedge surfaces 42 with the wedge surfaces 23 lying at the same angle are two in two neighboring groups, e.g. 12, 13, opposite active elements 20 with appropriate bias are in contact. For this purpose, the clamping elements 41 are screwed to the plate-shaped electrode holder 30 by means of screws.

Durch die Spannelemente 41 sind zwei benachbarte Gruppen 11, 12, 13 usw. von Aktivelementen so beab­standet, daß Kanäle 50 ausgebildet sind, die in be­schriebener Weise eine Zirkulation des Elektrolyts bzw. der Schmelze zwischen den unteren, in die Schmelze bzw. in den Elektrolyt eintauchenden Ab­schnitten 26 der Aktivelemente 20 ermöglicht wird und die andererseits eine rasche Abfuhr des bei dem Elek­trolyseprozeß entwickelten Gases zwischen den Gruppen angeordenten Aktivelementen 20 nach oben hin gewähr­leisten.By the clamping elements 41, two adjacent groups 11, 12, 13, etc. of active elements are spaced apart such that channels 50 are formed which, in the manner described, circulate the electrolyte or the melt between the lower ones, into the melt or into the electrolyte immersed sections 26 of the active elements 20 is made possible and, on the other hand, ensure rapid removal of the gas developed in the electrolysis process between the groups of active elements 20 arranged upwards.

Der plattenförmige Elektrodenhalter 30 ist als Hohl­körper ausgebildet, bestehend aus einer unteren hori­zontalen Platte 32, einer oberen, zur ersten parallel angeordneten Platte 33 und dazu senkrechten Seiten­wänden 34. Der Hohlraum dient zur Zirkulation von Kühlwasser im Innenraum 35 des Elektrodenhalters 30. Hierzu ist ein Kühlwasser-Zulaufrohr 36 vorgesehen, das randseitig in den Innenraum 35 mündet. Entlang spiralförmig verlaufenden Leitwänden 37 zirkuliert das Kühlwasser durch den Innenraum 35 des plattenförmigen Elektro­denhalters 30 bis zu dessen Zentrumsbereich und von dort wieder in den peripheren Bereich, von wo das entsprechend erwärmte Kühlwasser durch ein Kühlwas­serableitrohr 38 abgezogen wird.The plate-shaped electrode holder 30 is designed as a hollow body, consisting of a lower horizontal plate 32, an upper plate 33 arranged parallel to the first and side walls 34 perpendicular thereto. The cavity serves for the circulation of cooling water in the interior 35 of the electrode holder 30. This is a cooling water Inlet pipe 36 is provided which opens into the interior 35 on the edge. The cooling water circulates along spiral-shaped guide walls 37 through the interior 35 of the plate-shaped electrode holder 30 up to its central area and from there again into the peripheral area, from where the correspondingly heated cooling water is drawn off through a cooling water drain pipe 38.

Der plattenförmige Elektrodenhalter 30 ist des weite­ren mit mehreren Stromzuführungs-Bolzen 60 ausge­rüstet, über die der elektrische Strom dem platten­förmigen Elektrodenhalter 30 zugeleitet und von dort auf die Elektrodenelemente 20 übertragen wird. Zur Verbindung der Stromzuführungsbolzen 60 mit der unte­ren Platte 33 des Elektrodenhalters 30 sind an der Innenfläche der unteren Platte 33 jeweils Muffen 61 verschweißt, die ein Innengewinde besitzen, mit dem der untere und mit einem Außengewinde versehene Ab­schnitt des entsprechenden Stromzuführungsbolzens 60 verschraubt ist. Um den Stromzuführungsbolzen 60 im Bereich des Innenraums der Zelle vor Korrosion zu schützen, ist dieser mit Schutzhülsen 62 aus korro­sionsbeständigem Material umgeben.The plate-shaped electrode holder 30 is further equipped with a plurality of current supply bolts 60, via which the electrical current is fed to the plate-shaped electrode holder 30 and is transmitted from there to the electrode elements 20. To connect the power supply bolts 60 to the lower plate 33 of the electrode holder 30, sleeves 61 are welded to the inner surface of the lower plate 33, which have an internal thread with which the lower and externally threaded section of the corresponding power supply bolt 60 is screwed. In order to protect the power supply pin 60 from corrosion in the area of the interior of the cell, it is surrounded by protective sleeves 62 made of corrosion-resistant material.

Um den elektrischen Kontakt zwischen den Stirnflächen 22 der Aktivelemente 20 und der Fläche 31 des plat­tenförmigen Elektrodenhalters noch weiter zu verbes­sern, ist zwischen diesen Flächen ein Netz 39, z.B. aus Kupfer, eingebracht.In order to further improve the electrical contact between the end faces 22 of the active elements 20 and the face 31 of the plate-shaped electrode holder, a network 39, e.g. made of copper.

Der plattenförmige Elektrodenhalter 30 und die Spann­elemente 41 sowie deren Spannschrauben 43 bestehen zweckmäßigerweise aus Stahl. Sie können auch aus Nickel oder aus Stahl- bzw. Nickellegierungen beste­hen.
Zum Schutz dieser Bauteile gegen Korrosion sind Ab­deckelemente vorgesehen. Die an der Unterseite der Spannelemente angeordneten Abdeckelemente 44 sind z.B. mittels einer Schwalbenschwanzführung an den Spannelementen 41 gesichert. Die seitlichen Abdeck­elemente 45 können mit den stirnseitigen Enden der Spannelemente 41 durch Schrauben 46 verschraubt sein.The plate-shaped electrode holder 30 and the clamping elements 41 and their clamping screws 43 are expediently made of steel. They can also consist of nickel or of steel or nickel alloys.
Cover elements are provided to protect these components against corrosion. The cover elements 44 arranged on the underside of the tensioning elements are secured to the tensioning elements 41, for example by means of a dovetail guide. The side cover elements 45 can be screwed to the front ends of the clamping elements 41 by screws 46.

Die Aktivelemente 20 bestehen zweckmäßigerweise aus dotierter Oxid-Keramik, z.B. Zinnoxid, Nickelferrit oder Yttriumoxid.The active elements 20 expediently consist of doped oxide ceramic, e.g. Tin oxide, nickel ferrite or yttrium oxide.

Beispielsweise kann die Zusammensetzung wie folgt sein:
94,1 Atom-% Zinnoxid
3,8 Atom-% Kupfer
2,1 Atom-% AntimonFor example, the composition can be as follows:
94.1 atomic percent tin oxide
3.8 atomic% copper
2.1 atomic% antimony

Bei einem speziellen Ausführungsbeispiel der erfin­dungsgemäßen Anode hat sich folgende Dimensionierung der stabförmigen Aktivelemente als zweckentsprechend erwiesen:
Querschnitt der oberen Stirnfläche: 3 x 3 cm
Querschnitt der unteren Stirnfläche: 2 x 2 cm
Länge: 25 cm
Keilwinkel: 20°
Abstand zwischen zwei benachbarten Gruppen von Elektrodenelementen: 1,5 cmIn a special embodiment of the anode according to the invention, the following dimensioning of the rod-shaped active elements has proven to be appropriate:
Cross section of the upper face: 3 x 3 cm
Cross section of the lower face: 2 x 2 cm
Length: 25 cm
Wedge angle: 20 °
Distance between two adjacent groups of electrode elements: 1.5 cm

Die Seitenlänge des oberen Querschnitts kann zweckmä ßigerweise zwischen ca. 2 und 6 cm liegen. Die Länge der Aktivelemente kann zwischen ca. 15 cm und ca. 40 cm liegen. Der erwähnte Abstand zwischen zwei Gruppen von Aktivelementen kann zwischen ca. 1 cm und ca. 2 cm liegen. Der Keilwinkel des Kopfabschnittes der jeweiligen Aktivelemente kann zwischen ca. 5° und ca. 25° betragen.The side length of the upper cross section can expediently be between approximately 2 and 6 cm. The length of the active elements can be between approx. 15 cm and approx. 40 cm. The aforementioned distance between two groups of active elements can be between approximately 1 cm and approximately 2 cm. The wedge angle of the head section of the respective active elements can be between approximately 5 ° and approximately 25 °.

Das beschriebene Ausfühungsbeispiel der erfindungs­gemäßen Anode wurde in einer Elektrolysetestzelle mit folgenden Betriebsdaten betrieben:
Badzusammensetzung: Kryolith 84 Gew.-%
A1F3 5 Gew.-%
A1203 10 Gew.-%
CaF2 1 Gew.-%
Temperatur: 980-1000 C
Klemmspannung: 4-5 Volt
Stromstärke: 30 A
Stromdichte an der Anode: 2 A/cm2
Stromdichte an der Kathode:0,14 A/cm2
Elektrodenabstand: 3 cm
Tauchtiefe der Anoden: 2cmThe described exemplary embodiment of the anode according to the invention was operated in an electrolysis test cell with the following operating data:
Bath composition: cryolite 84% by weight
A1F3 5% by weight
A1203 10% by weight
CaF2 1% by weight
Temperature: 980-1000 C.
Clamp voltage: 4-5 volts
Current: 30 A.
Current density at the anode: 2 A / cm2
Current density at the cathode: 0.14 A / cm2
Electrode distance: 3 cm
Immersion depth of the anodes: 2cm

Claims (16)

1. Inerte Verbundelektrode, insbesondere Anode für die Schmelzflußelektrolyse, bestehend aus­- einem Aktivteil in Form einer Mehrzahl von stabförmigen Aktivelementen, insbesondere aus Oxidkeramik, die mit ihren Längsachsen pa­rallel nebeneinander und in zueinander fluchtenden Gruppen angeordnet sind,
- einem Elektrodenhalter, der eine stromleiten­de Platte umfaßt, mit deren einen Hauptfläche die Aktivelemente mit ihren Stirnflächen kraftschlüssig in Kontakt stehen, und
- einer Verbindungsanordnung, die die Aktivele­mente gruppenweise untereinander verbindet und mit der Platte in Kontakt hält,
dadurch gekennzeichnet, daß
- die Aktivelemente (20) jeweils plattenseitig einen Kopfabschnitt (21) aufweisen, der in seinem senkrecht zur Fluchtlinie (25) einer Gruppe (z.B. 11, 12 usw. ) liegenden Quer- schnitt und in Richtung der plattenseitigen Stirnfläche (22) im wesentlichen keilförmig (23) verbreitert ist, und
- mit jeder der zwei gegenüberliegenden Keil­flächen (23) des Kopfabschnitts (21) des jeweiligen Aktivelements (20) ein Spannele­ment (41) mit einer Keilfläche (42) in Anlage gebracht ist, deren Keilwinkel dem der jewei­ligen Keilfäche des Kopfabschnittes im we­sentlichen entspricht.1. Inert composite electrode, in particular anode for melt flow electrolysis, consisting of an active part in the form of a plurality of rod-shaped active elements, in particular made of oxide ceramic, which are arranged with their longitudinal axes parallel to one another and in groups aligned with one another,
- An electrode holder which comprises a current-conducting plate, with one main surface of which the active elements are in frictional contact with their end faces, and
a connection arrangement which connects the active elements to one another in groups and keeps them in contact with the plate,
characterized in that
- The active elements (20) each have a head section (21) on the plate side, which is essentially wedge-shaped in its cross section perpendicular to the line of alignment (25) of a group (eg 11, 12, etc.) and in the direction of the plate-side end face (22) (23) is widened, and
- With each of the two opposite wedge surfaces (23) of the head section (21) of the respective active element (20), a clamping element (41) with a wedge surface (42) is brought into contact, the wedge angle of which corresponds essentially to that of the respective wedge surface of the head section. 2. Verbundelektrode nach Anspruch 1, dadurch gekenn­zeichnet, daß die Aktivelemente (20) einer Gruppe (z.B. 11) in deren Fluchtlinie (25) untereinander in Anlage stehen.2. Composite electrode according to claim 1, characterized in that the active elements (20) of a group (e.g. 11) in their line of alignment (25) are in contact with each other. 3. Verbundelektrode nach Anspruch 1 oder 2, dadurch gekennzeichnet, daß die elektrische Leitfähigkeit des Werkstoffs der Aktivelemente (20) im Bereich des Kopfabschnitts (21) höher ist als im übrigen Bereich.3. Composite electrode according to claim 1 or 2, characterized in that the electrical conductivity of the material of the active elements (20) in the region of the head section (21) is higher than in the rest of the region. 4. Verbundelektrode nach Anspruch 3, dadurch gekenn­zeichnet, daß der Werkstoff der Aktivelemente (20) im Bereich des Kopfabschnitts (21) ein Cermet ist, das vorzugsweise Silber enthält.4. Composite electrode according to claim 3, characterized in that the material of the active elements (20) in the region of the head portion (21) is a cermet, which preferably contains silver. 5. Verbundelektrode nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß zwischen der betreffenden Hauptfläche (31) der Platte (30) und den entsprechenden Stirnflächen (22) der Aktivelemente (20) eine Kontaktschicht (39) ein­gebracht ist.5. Composite electrode according to one of the preceding claims, characterized in that a contact layer (39) is introduced between the relevant main surface (31) of the plate (30) and the corresponding end faces (22) of the active elements (20). 6. Verbundelektrode nach Anspruch 5, dadurch gekenn­zeichnet, daß die Kontaktschicht durch ein Netz (39) aus gut leitendem Metall, insbesondere Kupfer, gebildet ist.6. Composite electrode according to claim 5, characterized in that the contact layer is formed by a network (39) made of highly conductive metal, in particular copper. 7. Verbundelektrode nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß das Spann­element (41) zur Befestigung von zwei gegenüber­liegenden Aktivelementen (20) zweier benachbarter Gruppen (z.B. 11, 12) ausgebildet ist und hierzu zwei gegenüberliegende Keilflächen (42) mit im wesentlichen spiegelbildlicher Anordnung auf­weist.7. Composite electrode according to one of the preceding claims, characterized in that the clamping element (41) for fastening two opposite active elements (20) of two adjacent groups (eg 11, 12) is formed and for this purpose two opposite wedge surfaces (42) with a substantially mirror image Arrangement. 8. Verbundelektrode nach Anspruch 7, dadurch gekenn­zeichnet, daß das Spannelement (41) im Quer­schnitt senkrecht zur Fluchtlinie der Gruppen der Aktivelemente trapezförmig ist.8. Composite electrode according to claim 7, characterized in that the clamping element (41) is trapezoidal in cross section perpendicular to the line of alignment of the groups of active elements. 9. Verbundelektrode nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß jedem Aktivelement (20) je zwei separate Spannelemente (41) zugeordnet sind und die Länge eines Spann­elements (41) der Länge eines Aktivelements (20) im wesentlichen entspricht.9. Composite electrode according to one of the preceding claims, characterized in that each active element (20) is assigned two separate clamping elements (41) and the length of a clamping element (41) corresponds to the length of an active element (20) substantially. 10. Verbundelektrode nach einem der vorhergehenden Ansprüche 1 bis 8, dadurch gekennzeichnet, daß für jeweils eine Gruppe (z.B. 11) von Aktivele­menten (20) je zwei durchgehende Spannelemente (41) vorgesehen sind und die Länge eines Spann­elementes (41) der Länge einer Gruppe (z.B. 11) von Aktivelementen (20) im wesentlichen ent­spricht.10. Composite electrode according to one of the preceding claims 1 to 8, characterized in that two continuous clamping elements (41) are provided for each group (eg 11) of active elements (20) and the length of a clamping element (41) the length of a group (eg 11) of active elements (20) essentially corresponds. 11. Verbundelektrode nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß die Spann­elemente (41) mittels Schrauben (43) an der Platte (30) befestigt sind.11. Composite electrode according to one of the preceding claims, characterized in that the clamping elements (41) are fastened to the plate (30) by means of screws (43). 12. Verbundelektrode nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß die Spann­elemente (41), bevorzugt einschließlich ihrer Befestigungsmittel (43), gegen das Innere der Zelle durch Abdeckelemente (44, 45) aus kor­rosionsbeständigem Werkstoff geschützt sind.12. Composite electrode according to one of the preceding claims, characterized in that the clamping elements (41), preferably including their fastening means (43), are protected against the interior of the cell by cover elements (44, 45) made of corrosion-resistant material. 13. Verbundelektrode nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß die Platte (30) gekühlt ist.13. Composite electrode according to one of the preceding claims, characterized in that the plate (30) is cooled. 14. Verbundelektrode nach Anspruch 13, dadurch ge­kennzeichnet, daß eine Wasserkühlung vorgesehen ist.14. Composite electrode according to claim 13, characterized in that water cooling is provided. 15. Verbundelektrode nach Anspruch 14, dadurch ge­kennzeichnet, daß die Platte (30) als Hohlkörper ausgebildet ist, innerhalb dem Kanäle für das Kühlwasser angeordnet sind.15. Composite electrode according to claim 14, characterized in that the plate (30) is designed as a hollow body, are arranged within the channels for the cooling water. 16. Verbundelektrode nach einem der vorhergehenden Ansprüche 13 bis 15, dadurch gekennzeichnet, daß mindestens ein Stromzuleiter (60) zur Platte vorgesehen ist, der durch das Innere des Hohlkör­pers hindurchgeführt und mit der Innenseite der Hauptfläche (31), mit der die Elektrodenelemente (20) in Kontakt stehen, elektrisch verbunden ist.16. Composite electrode according to one of the preceding claims 13 to 15, characterized in that at least one current feeder (60) is provided for the plate, which is passed through the interior of the hollow body and with the inside of the main surface (31) with which the electrode elements (20 ) are in contact, is electrically connected.
EP86113930A 1985-10-22 1986-10-08 Inert composite electrode, particularly an anode for molten salt electrolysis Expired EP0220557B1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AT86113930T ATE43366T1 (en) 1985-10-22 1986-10-08 INERT COMPOUND ELECTRODE, IN PARTICULAR ANODE FOR MOLTEN ELECTROLYSIS.

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE19853537575 DE3537575A1 (en) 1985-10-22 1985-10-22 INERT COMPOSITE ELECTRODE, ESPECIALLY ANODE FOR MELTFLOW ELECTROLYSIS
DE3537575 1985-10-22

Publications (2)

Publication Number Publication Date
EP0220557A1 true EP0220557A1 (en) 1987-05-06
EP0220557B1 EP0220557B1 (en) 1989-05-24

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Application Number Title Priority Date Filing Date
EP86113930A Expired EP0220557B1 (en) 1985-10-22 1986-10-08 Inert composite electrode, particularly an anode for molten salt electrolysis

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US (1) US4840718A (en)
EP (1) EP0220557B1 (en)
AT (1) ATE43366T1 (en)
BR (1) BR8604998A (en)
CA (1) CA1299138C (en)
DE (2) DE3537575A1 (en)
ES (1) ES2003380A6 (en)
HU (1) HU203133B (en)
NO (1) NO168314C (en)
ZA (1) ZA867953B (en)

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FR2860247B1 (en) 2003-09-30 2005-11-11 Pechiney Aluminium DEVICE AND METHOD FOR CONNECTING INDEED ANODES FOR THE PRODUCTION OF ALUMINUM BY IGNEE ELECTROLYSIS
WO2018092103A1 (en) * 2016-11-19 2018-05-24 Jan Petrus Human Electrodes for use in the electro-extraction of metals

Citations (4)

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CH340346A (en) * 1956-01-23 1959-08-15 Aluminium Ind Ag Electrode for cathodic power supply in aluminum refining cells that work according to the three-layer process
US3607713A (en) * 1969-05-07 1971-09-21 Quaker Oats Co Anode for production of aluminum metal
EP0022921A1 (en) * 1979-07-20 1981-01-28 C. CONRADTY NÜRNBERG GmbH & Co. KG Regenerable, shape-stable electrode for use at high temperatures
DE3003922A1 (en) * 1979-12-18 1981-06-25 Schweizerische Aluminium AG, 3965 Chippis ANODE OF DIMENSIONAL STABLE OXIDE CERAMIC INDIVIDUAL ELEMENTS

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Publication number Priority date Publication date Assignee Title
US3761384A (en) * 1971-06-30 1973-09-25 Hooker Chemical Corp Anode assembly for electrolytic cells
US3984304A (en) * 1974-11-11 1976-10-05 Ppg Industries, Inc. Electrode unit
US4357226A (en) * 1979-12-18 1982-11-02 Swiss Aluminium Ltd. Anode of dimensionally stable oxide-ceramic individual elements
EP0050681B1 (en) * 1980-10-27 1985-09-11 C. CONRADTY NÜRNBERG GmbH & Co. KG Electrode for igneous electrolysis
US4462088A (en) * 1981-11-03 1984-07-24 International Business Machines Corporation Array design using a four state cell for double density

Patent Citations (4)

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Publication number Priority date Publication date Assignee Title
CH340346A (en) * 1956-01-23 1959-08-15 Aluminium Ind Ag Electrode for cathodic power supply in aluminum refining cells that work according to the three-layer process
US3607713A (en) * 1969-05-07 1971-09-21 Quaker Oats Co Anode for production of aluminum metal
EP0022921A1 (en) * 1979-07-20 1981-01-28 C. CONRADTY NÜRNBERG GmbH & Co. KG Regenerable, shape-stable electrode for use at high temperatures
DE3003922A1 (en) * 1979-12-18 1981-06-25 Schweizerische Aluminium AG, 3965 Chippis ANODE OF DIMENSIONAL STABLE OXIDE CERAMIC INDIVIDUAL ELEMENTS

Also Published As

Publication number Publication date
NO168314B (en) 1991-10-28
HU203133B (en) 1991-05-28
DE3537575A1 (en) 1987-04-23
DE3537575C2 (en) 1988-09-15
NO864210L (en) 1987-04-23
BR8604998A (en) 1987-07-14
NO864210D0 (en) 1986-10-21
ATE43366T1 (en) 1989-06-15
HUT44087A (en) 1988-01-28
NO168314C (en) 1992-02-05
US4840718A (en) 1989-06-20
DE3663537D1 (en) 1989-06-29
ZA867953B (en) 1987-06-24
CA1299138C (en) 1992-04-21
EP0220557B1 (en) 1989-05-24
ES2003380A6 (en) 1988-11-01

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