EP0148439B1 - Activated metal anodes and process for their manufacture - Google Patents

Activated metal anodes and process for their manufacture Download PDF

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Publication number
EP0148439B1
EP0148439B1 EP84115214A EP84115214A EP0148439B1 EP 0148439 B1 EP0148439 B1 EP 0148439B1 EP 84115214 A EP84115214 A EP 84115214A EP 84115214 A EP84115214 A EP 84115214A EP 0148439 B1 EP0148439 B1 EP 0148439B1
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Prior art keywords
anode
manganese
titanium
metallic
weight
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German (de)
French (fr)
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EP0148439A3 (en
EP0148439A2 (en
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Eberhard Dr. Preisler
Heiner Dr. Debrodt
Dieter Lieberoth
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Hoechst AG
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Hoechst AG
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    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
    • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
    • C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier
    • C25B11/073—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material
    • C25B11/075—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of a single catalytic element or catalytic compound

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  • the present invention relates to activated metal anodes, preferably those which are used in electrochemical processes in which the process product is deposited in solid form on the anode, and to a process for producing these anodes.
  • Electrolytically generated manganese dioxide is deposited technically on the anode of an electrolysis cell which contains a hot sulfuric acid manganese sulfate solution as the electrolyte. After the anode has been lifted out, the coating is knocked off by mechanical impacts and processed further.
  • lead and its alloys, graphite or titanium are known to be used as anode materials.
  • each of these materials has specific advantages and disadvantages, but in recent times titanium has become increasingly interesting because titanium anodes can be reused unchanged for a long time and because the titanium emits practically no contamination of the product, as is the case with lead alloys.
  • non-activated titanium can be used as an anode because a layer of manganese dioxide is deposited on it immediately after the formation of an extremely thin passive layer.
  • This manganese dioxide is a comparatively good electron conductor, so that electrons instead of oxygen ions enter the manganese dioxide-titanium dioxide phase boundary, which can pass freely through the thin passive layer without it continuing to grow (cf. Chem. Ing. Techn. 49, 347 (1977)) .
  • the passive layer of titanium continues to grow under a manganese dioxide layer only if certain limits of the electrolysis conditions are met.
  • Critical bath conditions are current density, sulfuric acid concentration, manganese concentration and the temperature.
  • a titanium anode is the least sensitive to changes in the manganese concentration of the electrolyte, particularly sensitive to lowering the temperature. Since the three critical operating parameters interact closely with one another, no absolute limit values can be set for each individual operating parameter. It can therefore only be checked by means of ongoing comparative tests within the framework of the technically interesting conditions whether a titanium anode behaves favorably or not.
  • a titanium anode was already described in SU-PS 891 805, which has a satisfactory stability during the electrolysis at room temperature.
  • This anode consists entirely of a titanium-manganese alloy with a manganese content between 6 and 16% by weight of manganese, on the surface of which a layer of ⁇ -manganese dioxide is applied by means of multiple thermal decomposition of manganese nitrate.
  • this electrode is unsuitable for the technical production of electrolytic manganese dioxide (EMD), because a ß-Mn0 2 layer applied in this way is not sufficiently stable against the mechanical stress when knocked off.
  • titanium alloys with a manganese content of more than 16% by weight are brittle and can no longer be machined or deformed mechanically. The rollability of titanium-manganese alloys is lost even at significantly lower manganese contents.
  • the object of the present invention is to provide an anode, in particular for the electrochemical production of manganese dioxide, which does not have the disadvantages listed above, which can therefore be used repeatedly without additional measures for electrolysis under conditions in which pure titanium is passivated, the anode base being mechanically machinable and deformable, so that the anode shape can be chosen as freely as in use from pure titanium.
  • this object can be achieved by means of a metal anode which consists of a metal from the group of the so-called valve metals zirconium, niobium, tantalum or preferably titanium and which is activated on its surface with metallic manganese, the manganese content on the anode surface is more than 16% by weight, preferably 20 to 60% by weight, and decreases towards the inside of the anode to such an extent that - measured from the anode surface - the manganese content within a range which is at most 1/4 of the material thickness the anode corresponds to - preferably within a range of 100 to 300 gm - decreased to 0% by weight.
  • Another object of the present invention is a method for producing these activated anodes, which consists in applying a layer of metallic manganese to the surface of an anode base consisting of the aforementioned valve metals zirconium, niobium, tantalum or preferably titanium and the anode then treated at a temperature between 800 and 1150 ° C, preferably between 950 and 1100 ° C, 4 hours to 1/2 hour in an inert atmosphere, for example a noble gas atmosphere, or in vacuo, the longer and choose the shorter treatment times at the higher temperatures.
  • the anode base should expediently consist of technically pure titanium and can be made from both solid titanium and sintered titanium.
  • the manganese is advantageously applied to the anode base by electrolytic means.
  • the anode base consists of sintered valve metal
  • the manganese is also possible to apply the manganese to the anode base in a plasma spraying process (sputtering).
  • the absolute manganese concentrations on the anode surface and the concentration gradients in the surface area can be varied within wide limits by the method according to the invention. This can be done both by the amount of manganese applied primarily to the anode base and by the conditions of the subsequent thermal treatment. These measures are to be coordinated with one another in such a way that the manganese concentration on the anode surface is more than 16% by weight, preferably 20 to 60% by weight.
  • the end terminal voltage of the cell was registered, the manganese dioxide coating was removed and the electrode was reinserted in the bath and electrolysis resumed. The initial terminal voltage was also registered.
  • An electrode consisting of a pure titanium sheet with an area of 0.4 dm 2 immersed in the bath was used as the anode under the conditions mentioned.
  • the initial terminal voltage was 2.3 V, reached 3.0 V after 4 days, 4.0 V after 8 days and more than 10 V on the 9th day.
  • Example 2 The same titanium sheet as in Example 1 was coated on both sides by cathodic deposition from a bath containing manganese and ammonium sulfate with 1.5 g / dm 2 of manganese metal and annealed for one hour at 950 ° under an argon protective gas atmosphere.
  • the electrode thus produced was tested under the same conditions as in Example 1.
  • the initial terminal voltage was 3.0 V, after 10 days it was still 3.0 V.
  • the electrode was reinserted, with an initial terminal voltage of 2.6 V and a final voltage of 10 days again set 3.0 V.
  • the start terminal voltage was 3.0 V and the end terminal voltage was 3.3 V.
  • the amount of manganese applied was only 0.7 g / dm 2 of manganese, and the annealing was carried out for 1 hour at 950 ° C. in a high vacuum.
  • the terminal voltage was 2.8 V at the beginning and 3.3 V at the end.
  • An electrode base consisting of 8 mm sintered titanium was placed in distilled water for 24 hours and then immediately cathodically loaded with 2 g / dm 2 manganese in an electrolysis bath as in Example 2. After removing the sintered titanium electrode from this electrolysis bath, it was washed again in slowly flowing water for 24 hours and then dried at 110 ° C. The electrode was then annealed in a high vacuum at 950 ° C. for 1.5 hours and finally used for the EMD deposition. The start terminal voltage was 2.8 V, the end terminal voltage after 10 days 3.0 V. After 28 electrolysis cycles, an end terminal voltage of 3.2 V was measured.
  • a mixture of 50% by weight of zirconium powder with a grain size of less than 100 I-Lm and 50% by weight of manganese powder with a grain size of less than 60 I-Lm was pasted with a little methyl cellulose in water to a pulpy mass and leveled on sintered zirconia plates with a thickness of 6 mm. Each side received about 5.0 g per dm 2 . After drying at 90 ° C, sintering was carried out at 1100 ° C for 2 hours under an argon atmosphere.
  • Sintering achieves an intimate connection, with some of the manganese also diffusing into the interior of the sintered zircon core, thus leading to the desired distribution.
  • the electrodeposition of manganese dioxide was carried out under the same conditions as in Example 6. After 15 electrolysis cycles, there was an average current yield of 95% and cell voltages between 1.9 and 2.2 V during the electrolysis period of 10 days each.
  • the advantages of the subject matter of the invention consist primarily in the fact that the anodes can be formed on the pure, still ductile valve metal, which is not possible with alloys with higher manganese contents, which are known to be brittle and cannot be processed. Furthermore, the anodes according to the invention retain a tough, elastic core made of pure metal, as a result of which the resistance of the anodes to mechanical loads, such as bending or impact, is significantly improved in comparison to anodes which consist of solid manganese alloys.
  • Another advantage is the lower manufacturing costs compared to precious metal activated anodes.
  • the following pictures 1 and 2 show profiles of manganese concentrations in titanium sheets, viewed from the sheet surface. These profiles were determined using an electron beam microsensor.
  • Figure 1 shows the course of the manganese concentration as a function of the annealing time.
  • Figure 2 shows manganese profiles depending on the amount of manganese originally applied to the surface.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Electrodes For Compound Or Non-Metal Manufacture (AREA)
  • Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)

Description

Vorliegende Erfindung betrifft aktivierte Metallanoden, vor zugsweise solche, die in elektrochemischen Prozessen ein-gesetzt werden, bei denen das Verfahrensprodukt in fester Form auf der Anode abgeschieden wird, sowie ein Verfahren zur Herstellung dieser Anoden.The present invention relates to activated metal anodes, preferably those which are used in electrochemical processes in which the process product is deposited in solid form on the anode, and to a process for producing these anodes.

So wird z.B. elektrolytisch erzeugtes Mangandioxid (EMD) technisch auf der Anode einer Elektrolysezelle, welche eine heiße schwefelsaure Mangansulfatlösung als Elektrolyten enthält, abgeschieden. Nach Herausheben der Anode wird der Belag durch mechanische Stöße abgeschlagen und weiterverarbeitet.For example, Electrolytically generated manganese dioxide (EMD) is deposited technically on the anode of an electrolysis cell which contains a hot sulfuric acid manganese sulfate solution as the electrolyte. After the anode has been lifted out, the coating is knocked off by mechanical impacts and processed further.

Als Anodenwerkstoffe finden bekanntlich in solchen Fällen Blei und seine Legierungen, Graphit oder Titan Verwendung. Jeder dieser Werkstoffe hat spezifische Vor- und Nachteile, jedoch hat in neuerer Zeit das Titan zunehmendes Interesse gefunden, weil Titananoden über lange Zeit unverändert wiederverwendet werden können und weil vom Titan praktisch keine Verunreinigung des Produkts ausgeht, wie dies bei den Bleilegierungen der Fall ist.In such cases, lead and its alloys, graphite or titanium are known to be used as anode materials. Each of these materials has specific advantages and disadvantages, but in recent times titanium has become increasingly interesting because titanium anodes can be reused unchanged for a long time and because the titanium emits practically no contamination of the product, as is the case with lead alloys.

Wenn beispielsveise Titan in einem wäßrigen Elektrolyten als Anode eingesetzt wird, zeigt sich üblicherweise die Erscheinung der Passivierung. Es bildet sich durch anodische Oxidation eine Titandioxidschicht aus der Anodenoberfläche aus, wodurch das darunterliegende, an sich unedle Titan zwar vor weiterer Oxidation geschützt wird, doch besitzt diese Oxidschicht eine sehr schlechte Elektronenleitfähigkeit, so daß der durch die Anode fließende Strom sehr schnell abnimmt. Wenn man nun diesen Strom jedoch konstant halten will, benötigt man eine zunehmend höhere Klemmenspannung. Deswegen ist reines Titan normalerveise in elektrochemischen Verfahren nicht brauchbar und muß durch die sogenannte aktivierte Titananode ersetzt werden, was z.B. in der Chloralkalielektrolyse in Form von edelmetallhaltigen Aktivierungsschichten bereits eine weite technische Anwendung gefunden hat.For example, when titanium is used as an anode in an aqueous electrolyte, the appearance of the passivation is usually evident. Anodic oxidation forms a layer of titanium dioxide from the surface of the anode, which protects the underlying titanium, which is inherently base, from further oxidation, but this oxide layer has very poor electron conductivity, so that the current flowing through the anode decreases very quickly. However, if you want to keep this current constant, you need an increasingly higher terminal voltage. Therefore, pure titanium is usually not usable in electrochemical processes and must be replaced by the so-called activated titanium anode, which e.g. has already found wide technical application in chloralkali electrolysis in the form of activation layers containing noble metals.

Bei der Herstellung von Elektrolytmangandioxid kann jedoch nichtaktiviertes Titan als Anode ein- gesetzt werden, weil sich unmittelbar nach Ausbildung einer extrem dünnen Passivschicht eine Schicht aus Mangandioxid darauf niederschlägt. Dieses Mangandioxid ist ein verhältnismäßig guter Elektronenleiter, so daß in die Phasengrenze Mangandioxid-Titandioxid Elektronen statt Sauerstoffionen eintreten, welche ungehindert durch die dünne Passivschicht hindurchwandern können, ohne daß dieselbe weiterwächst (vgl. Chem. Ing. Techn. 49, 347 (1977)).In the production of electrolytic manganese dioxide, however, non-activated titanium can be used as an anode because a layer of manganese dioxide is deposited on it immediately after the formation of an extremely thin passive layer. This manganese dioxide is a comparatively good electron conductor, so that electrons instead of oxygen ions enter the manganese dioxide-titanium dioxide phase boundary, which can pass freely through the thin passive layer without it continuing to grow (cf. Chem. Ing. Techn. 49, 347 (1977)) .

Das Weiterwachstum der Passivschicht des Titans unter einer Mangandioxidschicht unterbleibt jedoch nur, wenn bestimmte Grenzen der Elektrolysebedingungen eingehalten werden. Kritische Badbedingungen sind Stromdichte, Schwefelsäurekonzentration, Mangankonzentration und die Temperatur. Am wenigsten empfindlich reagiert eine Titananode gegen Veränderungen in der Mangankonzentration des Elektrolyten, besonders empfindlich auf Temperaturerniedrigung. Da die drei kritischen Betriebsparameter in enger Wechselwirkung zueinanderstehen, lassen sich für jeden einzelnen Betriebsparameter keine absoluten Grenzwerte festlegen. Es kann daher nur durch laufende Vergleichsversuche im Rahmen der technisch interessanten Bedingungen geprüft werden, ob sich eine Titananode vorteilhaft verhält oder nicht.However, the passive layer of titanium continues to grow under a manganese dioxide layer only if certain limits of the electrolysis conditions are met. Critical bath conditions are current density, sulfuric acid concentration, manganese concentration and the temperature. A titanium anode is the least sensitive to changes in the manganese concentration of the electrolyte, particularly sensitive to lowering the temperature. Since the three critical operating parameters interact closely with one another, no absolute limit values can be set for each individual operating parameter. It can therefore only be checked by means of ongoing comparative tests within the framework of the technically interesting conditions whether a titanium anode behaves favorably or not.

Um die hier beschriebenen Grenzen, welche der Anwendung von Titan bei der EMD-Elektrolyse gesetzt sind, zu erweitern, wäre es naheliegend, auf Aktivierungen mit Edelmetallen zurückzugreifen, wie sie aus der Chloralkalielektrolyse bekannt sind. Die gebildeten relativ lockeren Aktivschichten sind jedoch den mechanischen Beanspruchungen beim Abschlagen der EMD-Beläge nicht gewachsen, da sich der EMD-Belag sehr innig mit der dünnen Aktivschicht verzahnt und diese mit sich herunterreißt. Desaktivierungen ganz unregelmäßiger Art sind dann die Folge.In order to expand the limits described here, which are set for the use of titanium in EMD electrolysis, it would be obvious to resort to activations with noble metals, as are known from chlor-alkali electrolysis. The relatively loose active layers formed, however, are not able to withstand the mechanical stresses when knocking off the EMD coverings, since the EMD covering interlocks very intimately with the thin active layer and tears it down with it. Deactivations of a very irregular nature are then the result.

Um diese Schwierigkeiten zu umgehen, wurde in der DE-OS 16 71 426 vorgeschlagen, eine edelmetallreiche Schicht auf der Titanoberfläche zu erzeugen, welche anschließend durch eine Diffusionsbindung, hergestellt durch eine Glühung im Hochvakuum oder unter Edelgasatmosphäre bei - 950 - 1 000 °C, gegen die mechanische Belastung unempfindlich gemacht wird. Nachteilig an dieser Methode sind die hohen Kosten für das Edelmetall.In order to avoid these difficulties, it was proposed in DE-OS 16 71 426 to produce a noble metal-rich layer on the titanium surface, which was then produced by diffusion bonding, by annealing in a high vacuum or under an inert gas atmosphere at - 950 - 1 000 ° C, is made insensitive to mechanical stress. The disadvantage of this method is the high cost of the precious metal.

In einem anderen Zusammenhang, nämlich für die Elektrolyse von verdünnten schwefelsauren Lösungen zur Wasserspaltung in Sauerstoff und Wasserstoff, wurde bereits in der SU-PS 891 805 eine Titananode beschrieben, welche eine befriedigende Stabilität während der Elektrolyse bei Raumtemperatur besitzt. Diese Anode besteht durchgehend aus einer Titan-Mangan-Legierung mit einem Mangangehalt zwischen 6 und 16 Gew% Mangan, auf deren Oberfläche eine Schicht aus ß-Mangandioxid durch mehrfache thermische Zersetzung von Mangannitrat aufgebracht wird. Diese Elektrode ist jedoch für eine technische Gewinnung von Elektrolytbraunstein (EMD) ungeeignet, denn eine so aufgebrachte ß-Mn02 Schicht ist gegen die mechanische Belastung beim Abklopfen nicht genügend stabil, sie wird mitgerissen und müßte gegebenenfalls nach jedem Elektrolysezyklus erneut hergestellt werden.In another context, namely for the electrolysis of dilute sulfuric acid solutions for water splitting in oxygen and hydrogen, a titanium anode was already described in SU-PS 891 805, which has a satisfactory stability during the electrolysis at room temperature. This anode consists entirely of a titanium-manganese alloy with a manganese content between 6 and 16% by weight of manganese, on the surface of which a layer of β-manganese dioxide is applied by means of multiple thermal decomposition of manganese nitrate. However, this electrode is unsuitable for the technical production of electrolytic manganese dioxide (EMD), because a ß-Mn0 2 layer applied in this way is not sufficiently stable against the mechanical stress when knocked off.

Ein weiterer Nachteil der genannten Elektrode besteht darin, daß Titanlegierungen mit Mangangehalten über 16 Gew % spröde sind und mechanisch nicht mehr bearbeitet oder verformt werden können. Die Walzbarkeit von Titan-Mangan-Le gierungen geht bereits bei wesentlich niedrigeren Mangangehalten verloren.Another disadvantage of the electrode mentioned is that titanium alloys with a manganese content of more than 16% by weight are brittle and can no longer be machined or deformed mechanically. The rollability of titanium-manganese alloys is lost even at significantly lower manganese contents.

Aufgabe der vorliegenden Erfindung ist es, eine Anode, insbesondere für die elektrochemische Mangandioxidherstellung, bereitzustellen, welche die oben aufgeführten Nachteile nicht besitzt, die also ohne zusätzliche Maßnahmen wiederholt zur Elektrolyse unter Bedingungen, unter denen Reintitan passiviert wird, eingesetzt werden kann, wobei die Anodenbasis mechanisch bearbeitbar und verformbar ist, so daß die Anodenform ebenso frei gewählt werden kann, wie bei Verwendung von Reintitan.The object of the present invention is to provide an anode, in particular for the electrochemical production of manganese dioxide, which does not have the disadvantages listed above, which can therefore be used repeatedly without additional measures for electrolysis under conditions in which pure titanium is passivated, the anode base being mechanically machinable and deformable, so that the anode shape can be chosen as freely as in use from pure titanium.

Überraschenderweise wurde gefunden, daß diese Aufgabe gelöst werden kann durch eine Metallanode, die aus einem Metall aus der Gruppe der sogenannten « Ventil-Metalle Zirkon, Niob, Tantal oder vorzugsweise Titan besteht und die an ihrer Oberfläche mit metallischem Mangan aktiviert ist, wobei der Mangangehalt an der Anodenoberfläche mehr als 16 Gew %, vorzugsweise 20 bis 60 Gew%, beträgt und zum Inneren der Anode hin in einem solchen Maße abnimmt, daß - gemessen von der Anodenoberfläche her - der Mangangehalt innerhalb eines Bereiches, der maximal 1/4 der Materialstärke der Anode entspricht - vorzugsweise innerhalb eines Bereiches von 100 bis 300 gm - bis auf 0 Gew% abgesunken ist.Surprisingly, it was found that this object can be achieved by means of a metal anode which consists of a metal from the group of the so-called valve metals zirconium, niobium, tantalum or preferably titanium and which is activated on its surface with metallic manganese, the manganese content on the anode surface is more than 16% by weight, preferably 20 to 60% by weight, and decreases towards the inside of the anode to such an extent that - measured from the anode surface - the manganese content within a range which is at most 1/4 of the material thickness the anode corresponds to - preferably within a range of 100 to 300 gm - decreased to 0% by weight.

Ein weiterer Gegenstand der vorliegenden Erfindung ist ein Verfahren zur Herstellung dieser aktivierten Anoden, welches darin besteht, daß man auf die Oberfläche einer aus den genannten Ventil-Metallen Zirkon, Niob, Tantal oder vorzugsweise Titan bestehenden Anodenbasis eine Schicht von metallischem Mangan aufbringt und die Anode anschließend bei einer Temperatur zwischen 800 und 1150°C, vorzugsweise zwischen 950 und 1100 °C, 4 Stunden bis 1/2 Stunde in inerter Atmosphäre, beispielsweise Edelgasatmosphäre, oder im Vakuum behandelt, wobei man bei den tieferen Temperaturen des genannten Bereichs die längeren und bei den höheren Temperaturen die kürzeren Behandlungszeiten wählt.Another object of the present invention is a method for producing these activated anodes, which consists in applying a layer of metallic manganese to the surface of an anode base consisting of the aforementioned valve metals zirconium, niobium, tantalum or preferably titanium and the anode then treated at a temperature between 800 and 1150 ° C, preferably between 950 and 1100 ° C, 4 hours to 1/2 hour in an inert atmosphere, for example a noble gas atmosphere, or in vacuo, the longer and choose the shorter treatment times at the higher temperatures.

Es empfiehlt sich, das Mangan in einer Menge von 0,5 bis 3,0 g/dm2, vorzugsweise von 1,5 bis 2,5 g/dm2, auf die Anodenoberfläche aufzubringen. Die Anodenbasis sollte zweckmäßigerweise aus technisch reinem Titan bestehen und kann sowohl aus massivem Titan als auch aus Sintertitan gefertigt sein.It is advisable to apply the manganese in an amount of 0.5 to 3.0 g / dm 2 , preferably 1.5 to 2.5 g / dm 2 , to the anode surface. The anode base should expediently consist of technically pure titanium and can be made from both solid titanium and sintered titanium.

Vorteilhafterweise wird das Mangan auf elektrolytischem Wege auf die Anodenbasis aufgebracht.The manganese is advantageously applied to the anode base by electrolytic means.

Besteht die Anodenbasis aus gesintertem Ventilmetall, so ist es auch möglich, das Mangan in Form von Metallpulver, gegebenenfalls im Gemisch mit Ventilmetallpulver, auf die Anodenoberfläche aufzubringen. Ferner besteht auch die Möglichkeit, das Mangan im Plasmaspritzverfahren (Sputtering) auf die Anodenbasis aufzubringen.If the anode base consists of sintered valve metal, it is also possible to apply the manganese to the anode surface in the form of metal powder, optionally in a mixture with valve metal powder. There is also the possibility of applying the manganese to the anode base in a plasma spraying process (sputtering).

Besonders bewährt sich die kathodische Abscheidung aus einem Mangansulfat, Ammoniumsulfat, Schwefeldioxid und eine Selenverbindung, z.B. selenige Säure enthaltenden Elektrolyten.Cathodic deposition from a manganese sulfate, ammonium sulfate, sulfur dioxide and a selenium compound, e.g. electrolytes containing selenium acid.

Die absoluten Mangankonzentrationen an der Anodenoberfläche sowie die Konzentrationsgradienten im Oberflächenbereich können durch das erfindungsgemäße Verfahren in weiten Grenzen variiert werden. Dies kann sowohl durch die primär auf die Anodenbasis aufgebrachte Manganmenge als auch durch die Bedingungen der daran anschließenden thermischen Behandlung geschehen. Diese Maßnahmen sind so aufeinander abzustimmen, dar die Mangankonzentration an der Anodenoberfläche mehr als 16 Gew %, vorzugsweise 20 bis 60 Gew %, beträgt.The absolute manganese concentrations on the anode surface and the concentration gradients in the surface area can be varied within wide limits by the method according to the invention. This can be done both by the amount of manganese applied primarily to the anode base and by the conditions of the subsequent thermal treatment. These measures are to be coordinated with one another in such a way that the manganese concentration on the anode surface is more than 16% by weight, preferably 20 to 60% by weight.

Die erfindungsgemäßen Elektroden wurden als Anoden für die elektrolytische Mangandioxidherstellung eingesetzt. Die folgenden Prüfungsbedingungen wurden gewählt :

  • Elektrolytzusammensetzung :
  • Mangan Mol/I 0,7
  • Schwefelsäure Mol/I 0,5
  • Temperatur 95 °C
  • Stromdichte 1,4 A/dm2
  • Elektrodenformat 0,4 dm2 (eintauchend)
The electrodes according to the invention were used as anodes for the electrolytic production of manganese dioxide. The following examination conditions were chosen:
  • Electrolyte composition:
  • Manganese mol / I 0.7
  • Sulfuric acid mol / I 0.5
  • Temperature 95 ° C
  • Current density 1.4 A / d m 2
  • Electrode format 0.4 dm 2 (immersed)

Nach jeweils 10 Tagen Elektrolysedauer wurde die Endklemmenspannung der Zelle registriert, der Mangandioxidbelag entfernt und die Elektrode erneut in das Bad eingesetzt und die Elektrolyse wieder aufgenommen. Die Anfangsklemmenspannung wurde ebenfalls registriert.After every 10 days of electrolysis, the end terminal voltage of the cell was registered, the manganese dioxide coating was removed and the electrode was reinserted in the bath and electrolysis resumed. The initial terminal voltage was also registered.

Beispiel 1example 1

Eine aus einem reinen Titanblech bestehende Elektrode mit einer in das Bad eintauchenden Fläche von 0,4 dm2 wurde unter den genannten Bedingungen als Anode verwendet. Die Anfangsklemmenspannung betrug 2,3 V, erreichte nach 4 Tagen 3,0 V, nach 8 Tagen 4,0 V und am 9. Tage mehr als 10 V.An electrode consisting of a pure titanium sheet with an area of 0.4 dm 2 immersed in the bath was used as the anode under the conditions mentioned. The initial terminal voltage was 2.3 V, reached 3.0 V after 4 days, 4.0 V after 8 days and more than 10 V on the 9th day.

Beispiel 2Example 2

Ein gleiches Titanblech wie von Beispiel 1 wurde beidseitig durch kathodische Abscheidung aus einem mangan- und ammoniumsulfathaltigen Bade mit 1,5 g/dm2 Manganmetall belegt und eine Stunde lang bei 950° unter einer Argon Schutzgasatmosphäre geglüht. Die so hergestellte Elektrode wurde unter gleichen Bedingungen wie in Beispiel 1 geprüft. Die Anfangsklemmenspannung lag bei 3,0 V, nach 10 Tagen lag sie immer noch bei 3,0 V. Nach Abtrennen des EMD-Belags wurde die Elektrode erneut eingesetzt, wobei sich eine Anfangsklemmenspannung von 2,6 Volt und nach 10 Tagen eine Endspannung von wiederum 3,0 V einstellte. Nach dem fünfzigsten Lauf lag die Anfangsklemmenspannung bei 3,0 V und die Endklemmenspannung bei 3,3 V.The same titanium sheet as in Example 1 was coated on both sides by cathodic deposition from a bath containing manganese and ammonium sulfate with 1.5 g / dm 2 of manganese metal and annealed for one hour at 950 ° under an argon protective gas atmosphere. The electrode thus produced was tested under the same conditions as in Example 1. The initial terminal voltage was 3.0 V, after 10 days it was still 3.0 V. After the EMD coating had been removed, the electrode was reinserted, with an initial terminal voltage of 2.6 V and a final voltage of 10 days again set 3.0 V. After the fiftieth run, the start terminal voltage was 3.0 V and the end terminal voltage was 3.3 V.

Beispiel 3Example 3

In einem weiteren Versuch wurde auf gleiche Weise wie in Beispiel 2 eine Menge von 1,25 g/dm2 Mangan aufgebracht und 2 Stunden bei 950°C unter Argon geglüht. Die Elektrolyse zeigte den gleichen Spannungsverlauf wie in Beispiel 2. Nach dem 47. Elektrolysezyklus lagen die Anfangsklemmenspannung bei 3,0 V und die Endklemmenspannung bei 3,3 V.In a further experiment, an amount of 1.25 g / dm 2 of manganese was applied in the same manner as in Example 2 and annealed at 950 ° C. under argon for 2 hours. The electrolysis showed the same voltage curve as in Example 2. After the 47th electrolysis cycle, the initial terminal voltage was 3.0 V and the final terminal voltage was 3.3 V.

Beispiel 4Example 4

In diesem Fall betrug die aufgebrachte Manganmenge nur 0,7 g/dm2 Mangan, die Glühung wurde 1 Stunde bei 950°C im Hochvakuum durchgeführt. Im 50. Elektrolysezyklus der EMD-Elektrolyse lag die Klemmenspannung am Anfang bei 2,8 V und am Ende bei 3,3 V.In this case, the amount of manganese applied was only 0.7 g / dm 2 of manganese, and the annealing was carried out for 1 hour at 950 ° C. in a high vacuum. In the 50th electrolysis cycle of EMD electrolysis, the terminal voltage was 2.8 V at the beginning and 3.3 V at the end.

Beispiel 5Example 5

Eine aus 8 mm Sintertitan bestehende Elektrodenbasis wurde 24 Stunden lang in destilliertes Wasser eingelegt und anschließend sofort in einem Elektrolysebad analog Beispiel 2 kathodisch mit 2 g/dm2 Mangan belegt. Nach Entfernen der Sintertitanelektrode aus diesem Elektrolysebad wurde sie erneut 24 h in langsam strömendem Wasser gewaschen und dann bei 110°C getrocknet. Danach wurde die Elektrode 1,5 Stunden bei 950°C im Hochvakuum geglüht und schließlich zur EMD-Abscheidung eingesetzt. Die Anfangsklemmenspannung betrug 2,8 V, die Endklemmenspannung nach 10 Tagen 3,0 V. Nach 28 Elektrolysezyklen wurde eine Endklemmenspannung von 3,2 V gemessen.An electrode base consisting of 8 mm sintered titanium was placed in distilled water for 24 hours and then immediately cathodically loaded with 2 g / dm 2 manganese in an electrolysis bath as in Example 2. After removing the sintered titanium electrode from this electrolysis bath, it was washed again in slowly flowing water for 24 hours and then dried at 110 ° C. The electrode was then annealed in a high vacuum at 950 ° C. for 1.5 hours and finally used for the EMD deposition. The start terminal voltage was 2.8 V, the end terminal voltage after 10 days 3.0 V. After 28 electrolysis cycles, an end terminal voltage of 3.2 V was measured.

Die folgenden zwei Beispiele beschreiben, wie manganaktivierte Sintermetallanoden unter Verwendung von Manganpulver hergesetellt werden können.The following two examples describe how manganese activated sintered metal anodes can be made using manganese powder.

Beispiel 6Example 6

Mehrere Sintertitanplatten von 4 mm Dicke und den Abmessungen 50 x 40 mm wurden beidseitig mit einer Suspension aus 70 Teilen Manganpulver von einer Körnung kleiner 10/µm sowie 29,8 Teilen Wasser und 0,2 Teilen Methylzellulose bestrichen. Insgesamt wurden 1,25 g Manganpulver pro dm2 Oberfläche vorder- und rückseitig aufgetragen. Danach wurde bei 90 °C über 20 Minuten im Trockenschrank getrocknet. Anschließend wurde eine Diffusionsglühung im Vakuum mit 10-7 bar über 2 Stunden bei 1050 °C durchgeführt. Nach dem Abkühlen zeigte die Oberfläche ein gleichmäßiges graues metallisches Aussehen.Several sintered titanium plates with a thickness of 4 mm and dimensions of 50 x 40 mm were coated on both sides with a suspension of 70 parts of manganese powder with a grain size of less than 10 / µm as well as 29.8 parts of water and 0.2 parts of methyl cellulose. A total of 1.25 g of manganese powder per dm 2 surface was applied on the front and back. The mixture was then dried in a drying cabinet at 90 ° C. for 20 minutes. Subsequently, a diffusion annealing in vacuum with 10- 7 bar was carried out for 2 hours at 1050 ° C. After cooling, the surface showed a uniform gray metallic appearance.

Untersuchungen mittels elektronendispersiver Mikroanalyse ergaben, daß der Mangangehalt an der Oberfläche bis zu einer Tiefe von 10 µm etwa 45 Gew% beträgt. In einer Tiefe von 10 bis 50 µm werden noch 10 bis 20 Gew% gefunden, während in einer Tiefe von 250 bis 350 µm der Mangangehalt praktisch auf Null abgesunken ist.Investigations using electron-dispersive microanalysis showed that the manganese content on the surface down to a depth of 10 μm is approximately 45% by weight. At a depth of 10 to 50 µm, 10 to 20% by weight are still found, while at a depth of 250 to 350 µm the manganese content has practically dropped to zero.

Zwei dieser Proben wurden unter den Bedingungen der Braunsteinelektrolyse eingesetzt. Bei einer Schwefelsäurekonzentration von 50 bis 55 g/l, einer Manganionenkonzentration von 35-40 g/l und einer Temperatur von (95 ± 2) °C wurde mit einer Stromdichte von 1,30 A/dm2 Mangandioxid abgeschieden. Als Gegenelektroden dienten Graphitkathoden im Abstand von 4 cm.Two of these samples were used under the conditions of brownstone electrolysis. At a sulfuric acid concentration of 50 to 55 g / l, a manganese ion concentration of 35-40 g / l and a temperature of (95 ± 2) ° C, manganese dioxide was deposited with a current density of 1.30 A / dm2. Graphite cathodes at a distance of 4 cm served as counter electrodes.

Nach einer Elektrolysedauer von jeweils 9-10 Tagen wurde der gebildete Braunstein durch Abklopfen entfernt. Über insgesamt 15 solcher Elektrolysezyklen ergab sich bei einer Zellspannung von 2,0 V zu Beginn und 2,2 V am Ende eines Zyklus eine durchschnittliche Stromausbeute von 95 %, bezogen auf den frisch geernteten Braunstein.After an electrolysis period of 9-10 days each, the manganese dioxide formed was removed by tapping. Over a total of 15 such electrolysis cycles, a cell current of 2.0 V at the beginning and 2.2 V at the end of a cycle resulted in an average current yield of 95%, based on the freshly harvested manganese dioxide.

Beispiel 7Example 7

Eine Mischung von 50 Gew% Zirkonpulver von einer Körnung kleiner als 100 I-Lm und 50 Gew% Manganpulver einer Körnung kleiner als 60 I-Lm wurde mit etwas Methylzellulose in Wasser zu einer breiigen Masse angeteigt und auf Sinterzirkonplatten von 6 mm Dicke aufgespachtelt. Jede Seite erhielt dabei etwa 5,0 g pro dm2. Nach dem Trocknen bei 90 °C wurde unter einer Argonatmosphäre 2 Stunden lang bei 1100 °C gesintert.A mixture of 50% by weight of zirconium powder with a grain size of less than 100 I-Lm and 50% by weight of manganese powder with a grain size of less than 60 I-Lm was pasted with a little methyl cellulose in water to a pulpy mass and leveled on sintered zirconia plates with a thickness of 6 mm. Each side received about 5.0 g per dm 2 . After drying at 90 ° C, sintering was carried out at 1100 ° C for 2 hours under an argon atmosphere.

Durch das Aufsintern wird eine innige Verbindung erreicht, wobei ein Teil des Mangans auch in das Innere des Sinterzirkonkerns eindiffundiert und so zu der gewünschten Verteilung führt.Sintering achieves an intimate connection, with some of the manganese also diffusing into the interior of the sintered zircon core, thus leading to the desired distribution.

Die elektrolytische Abscheidung von Mangandioxid wurde unter gleichen Bedingungen wie im Beispiel 6 durchgeführt. Nach 15 Elektrolysezyklen ergaben sich eine durchschnittliche Stromausbeute von 95 % und Zellspannungen zwischen 1,9 und 2,2 V während der Elektrolysedauer von jeweils 10 Tagen.The electrodeposition of manganese dioxide was carried out under the same conditions as in Example 6. After 15 electrolysis cycles, there was an average current yield of 95% and cell voltages between 1.9 and 2.2 V during the electrolysis period of 10 days each.

Die Vorteile des Erfindungsgegenstandes bestehen in erster Linie darin, daß die Formgebung der Anoden am reinen, noch duktilen Ventilmetall erfolgen kann, was bei Legierungen mit höheren Mangangehalten, die bekanntlich spröde und nicht bearbeitbar sind, nicht möglich ist. Ferner behalten die erfindungsgemäßen Anoden einen zähen, elastischen Kern aus reinem Metall, wodurch die Widerstandfähigkeit der Anoden gegen mechanische Belastungen, wie Verbiegen oder Schlag, im Vergleich zu Anoden, welche massiv aus Manganlegierungen - bestehen, wesentlich verbessert ist.The advantages of the subject matter of the invention consist primarily in the fact that the anodes can be formed on the pure, still ductile valve metal, which is not possible with alloys with higher manganese contents, which are known to be brittle and cannot be processed. Furthermore, the anodes according to the invention retain a tough, elastic core made of pure metal, as a result of which the resistance of the anodes to mechanical loads, such as bending or impact, is significantly improved in comparison to anodes which consist of solid manganese alloys.

Abgesehen davon liegt ein weiterer Vorteil in den geringeren Herstellkosten, verglichen mit edelmetallaktivierten Anoden.Apart from that, another advantage is the lower manufacturing costs compared to precious metal activated anodes.

In den nachfolgenden Bildern 1 und 2 sind Profile von Mangankonzentrationen in Titanblechen, betrachtet von der Blechoberfläche her, dargestellt. Diese Profile wurden mit Hilfe einer Elektronenstrahl-Mikrosonde ermittelt.The following pictures 1 and 2 show profiles of manganese concentrations in titanium sheets, viewed from the sheet surface. These profiles were determined using an electron beam microsensor.

Bild 1 zeigt den Verlauf der Mangankonzentratation in Abhängigkeit von der Glühzeit.Figure 1 shows the course of the manganese concentration as a function of the annealing time.

Bild 2 gibt Manganprofile in Abhängigkeit von der ursprünglich auf die Oberfläche aufgetragenen Manganmenge wieder.Figure 2 shows manganese profiles depending on the amount of manganese originally applied to the surface.

Claims (10)

1. An activated metallic anode, which comprises zirkonium, niobium, tantalum or titanium and is activated on its surface by means of metallic manganese, the manganese content at the anode surface being more than 16% by weight and decreasing towards the interior of the anode to an extent such that, measured from the anode surface, the manganese content has dropped to 0 % by weight within a region which corresponds to 1/4 of the material thickness of the anode.
2. An anode as claimed in claim 1, wherein the manganese content at the surface is 20 to 60 % by weight.
3. An anode as claimed in claim 1 or 2, wherein the manganese content, measured from the anode surface, has dropped to 0% by weight within a region of 100 to 300 wm.
4. A process for the production of an activated metallic anode as claimed in claims 1 to 3, wherein a coating of metallic manganese is applied to the surface of a zirkonium, niobium, tantalum or titanium anode base, and the anode is subsequently treated for 4 hours to 1/2 hour at a temperature between 800 and 1150°C in an inert atmosphere or in vacuum, the longer treatment times being selected at the lower temperatures in the range mentioned, and the shorter treatment times at the higher temperatures.
5. The process as claimed in claim 4, vherein 0.5 to 3.0 g/dm2 of metallic manganese is applied to the anode surface.
6. The process as claimed in claim 4 or 5, wherein the anode base comprises industrially pure titanium.
7. The process as claimed in any one of claims 4 to 6, wherein the anode base comprises sintered titanium.
8. The process as claimed in any one of claims 4 to 7, wherein the manganese is applied to the anode base by electrolytic means.
9. The process as claimed in claim 7, wherein the manganese is applied in the form of metallic powder, if desired mixed with titanium powder, to the anode base of sintered titanium.
10. The process as claimed in any one of claims 4 to 7, wherein the manganese is applied to the anode base by a plasma spraying method.
EP84115214A 1983-12-21 1984-12-12 Activated metal anodes and process for their manufacture Expired EP0148439B1 (en)

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DE19833346093 DE3346093A1 (en) 1983-12-21 1983-12-21 ACTIVATED METAL ANLANDS AND A METHOD FOR THE PRODUCTION THEREOF
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US4683648A (en) * 1984-12-21 1987-08-04 Allied Corporation Lead-titanium, bipolar electrode in a lead-acid battery
DE3516523A1 (en) * 1985-05-08 1986-11-13 Sigri GmbH, 8901 Meitingen ANODE FOR ELECTROCHEMICAL PROCESSES
DE4123291C2 (en) * 1991-07-13 1993-12-09 Blasberg Oberflaechentech Use of anodes for electroplating
CN101603180B (en) * 2009-06-09 2011-01-19 湖南泰阳新材料有限公司 Preparation method for coating titanium anode for the production of electrolytic manganese dioxide
CN101694001B (en) * 2009-10-10 2011-05-18 中信大锰矿业有限责任公司 Preparation method of Ti-Mn-diffusion titanium anode plate for electrolytic manganese dioxide

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SU484893A1 (en) * 1973-05-14 1975-09-25 Грузинский Ордена Трудового Красного Знамени Политехнический Институт Им.В.И.Ленина Anode material for electrolytic production of manganese dioxide
US4140617A (en) * 1976-05-25 1979-02-20 Dzhaparidze Levan N Anode for producing electrolytic manganese dioxide
DE2645414C2 (en) * 1976-10-08 1986-08-28 Hoechst Ag, 6230 Frankfurt Titanium anodes for the electrolytic production of manganese dioxide, as well as a process for the production of these anodes
DE2734162C2 (en) * 1977-07-28 1986-10-16 Institut neorganičeskoj chimii i elektrochimii Akademii Nauk Gruzinskoj SSR, Tbilisi Electrochemical process for the production of manganese dioxide
FR2460343A1 (en) * 1979-06-29 1981-01-23 Solvay CATHODE FOR THE ELECTROLYTIC PRODUCTION OF HYDROGEN
US4235697A (en) * 1979-10-29 1980-11-25 Diamond Shamrock Corporation Oxygen selective anode
US4342792A (en) * 1980-05-13 1982-08-03 The British Petroleum Company Limited Electrodes and method of preparation thereof for use in electrochemical cells
US4549943A (en) * 1984-11-01 1985-10-29 Union Carbide Corporation Suspension bath and process for production of electrolytic manganese dioxide

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