EP3481976B1 - Method for the galvanic deposition of zinc and zinc alloy layers from an alkaline coating bath with reduced degradation of organic bath additives - Google Patents

Description

Technical field

The present invention relates to a process for the galvanic deposition of zinc-nickel coatings from an alkaline coating bath with zinc-nickel electrolytes and organic bath additives, comprising amine-containing complexing agents. Furthermore, the invention relates to the use of materials as anode for the galvanic deposition of a zinc nickel coating from an alkaline coating bath with zinc nickel electrolytes and organic bath additives, comprising amine-containing complexing agents, and a corresponding galvanic device for the deposition of zinc nickel electrolytes.

Technical background

Alkaline zinc and zinc alloy baths are typically not operated with soluble zinc anodes. In the case of soluble zinc anodes, the zinc is electrochemically oxidized to Zn (II) during anodic operation. The Zn (II) ions formed enter into the soluble zincate complex, Zn [(OH) ₄ ] ^2- , with the surrounding hydroxide ions. In addition to the electrochemical dissolution, zinc is oxidized to Zn (II) by the alkaline environment with the formation of hydrogen. This means that the zinc anode additionally chemically dissolves due to the above-mentioned redox reaction, which leads to an uncontrolled increase in the Zn (II) concentration in the zinc alloy electrolyte.

On the one hand, this means a reduction in process reliability, and on the other hand, the need to carry out further analyzes to determine the additionally dissolved zinc content in order to be able to correctly set the concentration ratio in the zinc alloy electrolyte.

Therefore, alkaline zinc and zinc alloy baths are usually operated with insoluble anodes, and zinc is often dissolved in a separate zinc dissolving tank to form Zn (II) and metered into the bath.

Materials that are electrically conductive and chemically inert at least to bases are therefore used as the anode material. These include metals such as nickel, iron, stainless steel, cobalt or alloys of the metals mentioned. Another possibility, for example to use the favorable properties of nickel as an anode material, but on the other hand to save costs, is to use galvanically nickel-plated steel anodes (bright nickel-plated steel anodes) with nickel coatings of e.g. 30 µm layer thickness. The main reaction is the oxidative formation of oxygen at the insoluble anode.

When operating alkaline coating baths for the galvanic deposition of a zinc or zinc alloy coating, organic bath additives such as complexing agents, brightening agents and wetting agents are usually used in addition to the zinc or zinc alloy electrolyte.

In practice, it cannot be avoided that the development of oxygen not only occurs selectively on the surface of the insoluble anode. In some cases there is also an unwanted anodic oxidation of the organic bath additives. This means that due to this decomposition, the concentration ratio of bath additive to zinc or zinc alloy electrolytes in the alkaline coating bath is no longer true, which is why additives have to be added. As a result, the process costs are inevitably increased.

The anodic oxidation of the organic bath additives can also form undesired by-products such as oxalates, carbonates, etc., which can have a disruptive effect in the galvanic coating process.

In alkaline zinc and zinc alloy baths, where amine-containing complexing agents are used, an increased formation of cyanides can also be observed due to the undesirable anodic oxidation of the amine-containing additives.

Amine-containing complexing agents are used in coating baths for the galvanic deposition of a zinc-nickel alloy coating. The nickel is used in the form of Ni (II), which in an alkaline environment forms a poorly soluble nickel hydroxide complex with the surrounding hydroxide ions. Alkaline zinc nickel electrolytes must therefore contain special complexing agents with which Ni (II) forms a complex more preferably than with the hydroxide ions in order to be able to dissolve the nickel in the form of Ni (II). Amine compounds such as triethanolamine, ethylenediamine, diethylenetetramine or homologous compounds of ethylenediamine, such as e.g. Diethylene triamine, tetraethylene pentamine, etc. used.

When operating such coating baths to deposit a zinc-nickel alloy coating with amine-containing complexing agents, values of up to 1000 mg / l cyanide can be established in the practice electrolyte until a balance of new formation and drag-out is reached. The formation of cyanides is disadvantageous for several reasons.

When disposing of alkaline zinc and zinc alloy baths, as well as the rinsing wastewater, which Operation, certain limit values must be observed and monitored. A frequently requested limit for the exposure to cyanides in waste water is 1 mg / l. Due to national or regional legislation, the permitted limit values for the cyanide loads in wastewater can still be below this value. The cyanides formed must therefore be detoxified at great expense. In practice, this is done by oxidation, for example with sodium hypochlorite, hydrogen peroxide, sodium peroxodisulfate, potassium peroxomonosulfate or similar compounds. In addition to the cyanide, the electrolyte that is carried out also contains other oxidizable substances, which is why much more oxidizing agent is used for complete oxidation than can be theoretically determined from the cyanide content.

Apart from the aspect mentioned above, an increased cyanide formation furthermore leads to the problem that undesired complexes can be formed with the bath additives.

From a technical point of view, the cyanide content is very disadvantageous when using a zinc nickel electrolyte, since nickel forms the stable tetracyanonickelate complex, Ni [(CN) ₄ ] ^2- with the cyanide ions formed, which means that the nickel bound in this complex is no longer used for the deposition Available. Since it is not possible to differentiate between the nickel complexed by the cyanide and the complexed by the amines in the current electrolyte analysis, the increase in the cyanide content in the electrolyte means a reduction in process reliability.

The deposition of zinc-nickel alloy coatings with a proportion of 10-16% by weight of nickel provides very good corrosion protection on components made of iron materials and is therefore of great importance for technical corrosion protection. For the coating of components, Strongly alkaline electrolytes are used for the deposition of zinc-nickel alloy coatings, in particular for accessories for automobile production, in order to ensure a uniform layer thickness distribution even on complex three-dimensional geometries of the components to be coated. To achieve a predetermined corrosion resistance, a minimum layer thickness on the component must be maintained, which is usually 5 - 10 µm.

In order to be able to maintain the required alloy composition of 10-16 wt.% Nickel over the entire current density range, the nickel concentration has to be adjusted in the course of operation according to the cyanide concentration in the electrolyte, since the part of nickel complexed by cyanide is not available for deposition stands. With the increase in the cyanide content in the electrolyte, the nickel content must be adjusted accordingly in order to be able to keep the nickel content in the layer constant. In order to maintain the required alloy composition, unscheduled additions of nickel salts to the electrolyte must be made. Suitable supplementary solutions are nickel salts, which have a high water solubility. Nickel sulfate solutions are preferably used in combination with various amine compounds.

The effects of a cyanide concentration of 350 mg / l in a commercial zinc-nickel alloy bath (zinc-nickel alloy bath SLOTOLOY ZN 80, from Schlötter) are shown in Table 1 in the examples below. [Table 1] electrolyte Current density (A / dm ² ) Current efficiency (%) Alloy composition (wt.% Ni) New batch SLOTOLOY ZN 80 6.5 g / l Zn; 0.6 g / l Ni 2nd 50 14.3 0.5 86 13.2 New batch SLOTOLOY ZN 80 6.5 g / l Zn; 0.6 g / l Ni, 350 mg / l CN ^- (660 mg / l NaCN) 2nd 73 8.1 0.5 83 8.9 New batch SLOTOLOY ZN 80 6.5 g / l Zn; 0.6 g / l Ni, 350 mg / l CN ^- (660 mg / l NaCN) + 0.6 g / l Ni 2nd 49 13.9 0.5 80 14.6

The above experiments show that a deliberate addition of 350 mg / l cyanide to a newly prepared zinc nickel alloy bath SLOTOLOY ZN 80 reduces the nickel incorporation rate from 14.3% by weight to 8.1% by weight at a deposition current density of 2 A / dm ² . In order to bring the alloy composition back into the specified range of 10-16% by weight, an addition of 0.6 g / l of nickel is necessary. This means a doubling of the nickel content in the electrolyte compared to the new batch.

The accumulation of cyanide in a zinc-nickel alloy electrolyte can also have a negative effect on the optical appearance of the deposition. Milky-veiled deposition can occur in the high current density range. This can be corrected in part by higher dosing of brighteners. However, this measure is associated with an increased consumption of brighteners and thus additional costs for the deposition.

If the cyanide concentration in a zinc-nickel alloy electrolyte reaches values of approx. 1000 mg / l, it may also be necessary for the electrolyte to be partially renewed, which in turn increases process costs. In addition, large amounts of old electrolytes are generated in such partial bathroom renewals, which have to be disposed of in a complex manner.

literature

• In EP 1 344 850 B1 wird ein Verfahren beansprucht, bei dem der Kathodenraum und der Anodenraum durch eine Ionenaustauschermembran abgetrennt werden. Dadurch wird verhindert, dass die Komplexbildner aus dem Kathodenraum an die Anode gelangen können. Eine Cyanid-Bildung wird dadurch verhindert. Als Anode wird eine platinierte Titananode eingesetzt. Der Anolyt ist sauer und enthält Schwefelsäure, Phosphorsäure, Methansulfonsäure, Amidosulfonsäure und/oder Phosphonsäure.
• Ein ähnliches Verfahren wird in EP 1 292 724 B1 beschrieben. Hier werden ebenfalls Kathoden- und Anodenraum durch eine Ionenaustauschermembran abgetrennt. Als Anolyt wird eine Natrium- oder Kaliumhydroxidlösung eingesetzt. Als Anode wird ein Metall oder ein Metallüberzug aus der Gruppe, die aus Nickel, Kobalt, Eisen, Chrom oder Legierungen davon besteht, ausgewählt.
• Bei beiden Verfahren wird die Bildung von Cyaniden reduziert. Nachteilig ist bei beiden Verfahren, dass durch den Einbau der Ionenaustauschermembranen sehr hohe Investitionskosten entstehen. Zusätzlich muss noch eine Vorrichtung für eine getrennte Kreislaufführung des Anolyten installiert werden. Der Einbau von Ionenaustauschermembranen ist bei Verfahren zur Zinknickelabscheidung außerdem nicht generell realisierbar. Zur Erhöhung der Produktivität und somit zur Senkung der Beschichtungskosten werden oftmals Hilfsanoden eingesetzt, um bei dichter Behängung der Gestelle die Schichtdickenverteilung zu optimieren. Aus technischen Gründen ist es hier nicht möglich, diese Hilfsanoden durch Ionenaustauschermembranen abzutrennen. Eine Cyanid-Bildung kann bei dieser Anwendung daher nicht vollständig vermieden werden.
• EP 1 702 090 B1 beansprucht ein Verfahren, welches die Abtrennung des Kathoden- und Anodenraumes durch ein offenporiges Material vorsieht. Der Separator besteht aus Polytetrafluorethylen oder Polyolefin, wie Polypropylen oder Polyethylen. Die Porendurchmesser weisen eine Abmessung zwischen 10 nm und 50 µm auf. Im Unterschied zum Einsatz von Ionenaustauschermembranen, wo der Ladungstransport durch die Membran durch den Austausch von Kationen oder Anionen erfolgt, kann er bei Einsatz von offenporigen Separatoren nur durch den Elektrolyttransport durch den Separator erfolgen. Eine vollständige Abtrennung des Katholyten vom Anolyten ist nicht möglich. Es kann daher auch nicht vollständig verhindert werden, dass Amine an die Anode gelangen und dort oxidiert werden. Eine Cyanid-Bildung ist bei diesem Verfahren deshalb nicht vollständig auszuschließen.
• Nachteilig ist bei diesem Verfahren außerdem, dass bei Einsatz von Separatoren mit sehr kleinem Porendurchmesser (z.B. 10 nm) der Elektrolytaustausch und somit der Stromtransport sehr stark behindert ist, was zu einer Überspannung führt. Obwohl die Überspannung anspruchsgemäß weniger als 5 Volt betragen soll, wäre eine Badspannung mit höchstens 5 Volt Überspannung, verglichen mit einem Verfahren, welches ohne Abtrennung von Kathoden- und Anodenraum arbeitet, dennoch nahezu verdoppelt. Dadurch ist ein wesentlich höherer Energieverbrauch bei der Abscheidung der Zinknickelschichten gegeben. Die bis zu 5 Volt höhere Badspannung bewirkt außerdem eine starke Erwärmung des Elektrolyten. Da zur Abscheidung einer konstanten Legierungszusammensetzung die Elektrolyttemperatur im Bereich von +/- 2°C konstant gehalten werden soll, muss bei Anlegen einer höheren Badspannung der Elektrolyt durch erheblichen Aufwand gekühlt werden. Zwar ist beschrieben, dass der Separator auch einen Porendurchmesser von 50 µm betragen kann, was die Bildung von Überspannung möglicherweise verhindert, jedoch erlaubt der relativ große Porendurchmesser wiederum einen nahezu ungehinderten Elektrolytaustausch zwischen Kathoden- und Anodenraum und kann somit die Bildung von Cyaniden nicht verhindern.
• Ein ähnliches Konzept wird in der EP 1 717 353 B1 beschrieben. Der Anoden- und Kathodenraum wird dort durch eine Filtrationsmembran abgetrennt. Die Größe der Poren der Filtrationsmembran liegt im Bereich von 0,1 bis 300 nm. Ein gewisser Übertritt von Elektrolyt aus dem Kathoden- in den Anodenraum wird dabei bewusst in Kauf genommen.
• Bei Verwendung bestimmter organischer Glanzbildner arbeiten Zinknickelelektrolyte nicht zufriedenstellend, wenn Membranverfahren entsprechend EP 1 344 850 oder EP 1 292 724 verwendet werden. Diese Glanzbildner benötigen offensichtlich eine anodische Aktivierung, um ihre volle Wirkung zu erzeugen. Diese Reaktion ist bei Einsatz von Filtrationsmembranen, wie in EP 1 717 353 beschrieben, gewährleistet. Allerdings bedingt das auch, dass die Bildung von Cyaniden nicht vollständig vermieden werden kann. Der Tabelle 4 der EP 1 717 353 kann entnommen werden, dass bei Einsatz der Filtrationsmembranen bei einer Badbelastung von 50 Ah/l eine Neubildung von 63 mg/l Cyanid erfolgt. Ohne Einsatz von Filtrationsmembranen erfolgt unter sonst gleichen Bedingungen eine Neubildung von 647 mg/l Cyanid. Der Einsatz der Filtrationsmembranen kann die Neubildung von Cyanid somit um ca. 90% verringern, aber nicht vollständig verhindern.
• Alle vorstehend genannten Membranverfahren haben zudem den Nachteil, dass sie einen erheblichen Platzbedarf in einem Badbehälter eines Zinknickelelektrolyten haben. Ein nachträglicher Einbau in eine bestehende Anlage ist daher aus Platzgründen meistens nicht möglich.
• Ferner wird in DE 103 45 594 A1 eine Zelle zur anodischen Oxidation von Cyaniden in wässrigen Lösungen, umfassend eine Festbettanode sowie eine Kathode beschrieben, die dadurch gekennzeichnet ist, dass das Partikelbett der Anode aus Partikeln aus Mangan oder den Oxiden des Titans oder Mischungen dieser Partikel besteht. In der Offenlegungsschrift ist beschrieben, dass dieses Verfahren zur Reduzierung von Cyanometallat-Komplexen in Abwässern geeignet ist. Demnach ist es bei der Behandlung der in DE 103 45 594 A1 beschriebenen Cyanid-haltigen wässrigen Lösungen das Ziel, bereits vorhandene Cyanide und Cyanometallat-Komplexe aus dem Abwasser zu entfernen. Dies steht im Gegensatz zu der Aufgabe der vorliegenden Erfindung, bei der überhaupt erst die Entstehung von Cyaniden verhindert werden soll.

There are several starting points in the prior art for solving the problem described above:

• In EP 1 344 850 B1 A method is claimed in which the cathode compartment and the anode compartment are separated by an ion exchange membrane. This prevents the complexing agents from reaching the anode from the cathode compartment. This prevents cyanide formation. A platinized titanium anode is used as the anode. The anolyte is acidic and contains sulfuric acid, phosphoric acid, methanesulfonic acid, amidosulfonic acid and / or phosphonic acid.
• A similar process is described in EP 1 292 724 B1 described. Here, too, the cathode and anode compartments are separated by an ion exchange membrane. A sodium or potassium hydroxide solution is used as the anolyte. A metal or a metal coating from the group consisting of nickel, cobalt, iron, chromium or alloys thereof is selected as the anode.
• Both processes reduce the formation of cyanides. A disadvantage of both methods is that very high investment costs arise due to the installation of the ion exchange membranes. In addition, a device for separate circulation of the anolyte must be installed. The installation of ion exchange membranes is also generally not feasible with zinc nickel deposition processes. Auxiliary anodes are often used to increase productivity and thus to reduce coating costs used to optimize the layer thickness distribution when the frames are dense. For technical reasons, it is not possible to separate these auxiliary anodes by ion exchange membranes. Cyanide formation cannot therefore be completely avoided in this application.
• EP 1 702 090 B1 claims a method which provides for the separation of the cathode and anode space by an open-pore material. The separator is made of polytetrafluoroethylene or polyolefin, such as polypropylene or polyethylene. The pore diameter is between 10 nm and 50 µm. In contrast to the use of ion exchange membranes, where the charge is transported through the membrane by the exchange of cations or anions, when using open-pore separators it can only be carried out by the electrolyte transport through the separator. A complete separation of the catholyte from the anolyte is not possible. It cannot therefore be completely prevented that amines get to the anode and are oxidized there. Cyanide formation cannot therefore be completely ruled out in this process.
• Another disadvantage of this method is that when separators with a very small pore diameter (for example 10 nm) are used, the electrolyte exchange and thus the current transport are very severely hampered, which leads to an overvoltage. Although the overvoltage is supposed to be less than 5 volts, a bath voltage with at most 5 volts overvoltage would still be almost doubled compared to a method that works without separating the cathode and anode compartments. This results in a significantly higher energy consumption when depositing the zinc-nickel layers. The bath voltage, which is up to 5 volts higher, also causes the electrolyte to become very hot. Since the electrolyte temperature is in the range for the deposition of a constant alloy composition should be kept constant of +/- 2 ° C, the electrolyte must be cooled with considerable effort when applying a higher bath voltage. Although it is described that the separator can also have a pore diameter of 50 μm, which may prevent the formation of overvoltage, the relatively large pore diameter in turn allows an almost unhindered electrolyte exchange between the cathode and anode space and therefore cannot prevent the formation of cyanides.
• A similar concept is used in the EP 1 717 353 B1 described. The anode and cathode compartments are separated there by a filtration membrane. The size of the pores of the filtration membrane is in the range of 0.1 to 300 nm. A certain transfer of electrolyte from the cathode to the anode space is consciously accepted.
• When using certain organic brighteners, zinc nickel electrolytes do not work satisfactorily if membrane processes are used accordingly EP 1 344 850 or EP 1 292 724 be used. These brighteners obviously need anodic activation to be fully effective. This reaction is when using filtration membranes, as in EP 1 717 353 described, guaranteed. However, this also means that the formation of cyanides cannot be completely avoided. Table 4 of the EP 1 717 353 it can be seen that when the filtration membranes are used with a bath load of 50 Ah / l, a new formation of 63 mg / l cyanide occurs. Without the use of filtration membranes, 647 mg / l cyanide is formed under otherwise identical conditions. The use of filtration membranes can therefore reduce the formation of new cyanide by approx. 90%, but not completely prevent it.
• All of the membrane processes mentioned above also have the disadvantage that they require a considerable amount of space in a bath container of a zinc nickel electrolyte. On Subsequent installation in an existing system is therefore usually not possible due to space constraints.
• Furthermore, in DE 103 45 594 A1 describes a cell for the anodic oxidation of cyanides in aqueous solutions, comprising a fixed bed anode and a cathode, which is characterized in that the particle bed of the anode consists of particles of manganese or the oxides of titanium or mixtures of these particles. The published specification describes that this method is suitable for reducing cyanometalate complexes in waste water. Accordingly, it is in the treatment of the in DE 103 45 594 A1 described cyanide-containing aqueous solutions the goal of removing existing cyanides and cyanometalate complexes from the wastewater. This is in contrast to the object of the present invention, in which the formation of cyanides is to be prevented in the first place.

Task

The object of the present invention is to provide a process for the galvanic deposition of zinc nickel coatings from an alkaline coating bath with zinc nickel electrolytes and organic bath additives, which method has a reduced anodic oxidation and a concomitant reduced degradation of the organic bath additives which comprise amine-containing complexing agents , as well as a reduced formation of unwanted degradation products, such as cyanides. The method according to the invention should make it possible to be integrated into existing alkaline zinc nickel baths without additional effort and should allow the methods to be operated much more economically.

Solution of the task and detailed description

1. 1) aus metallischem Mangan oder einer Mangan-haltigen Legierung hergestellt ist, wobei die Mangan-haltige Legierung mindestens 5 Gew.% Mangan enthält, oder
2. 2) aus einem elektrisch leitfähigen Träger und einer darauf aufgebrachten metallisches Mangan und/oder Manganoxid enthaltenden Beschichtung hergestellt ist, wobei die metallisches Mangan und/oder Manganoxid enthaltende Beschichtung mindestens 5 Gew.% Mangan, bezogen auf die Gesamtmenge an Mangan, die sich aus metallischem Mangan und Manganoxid ergibt, enthält, oder
3. 3) aus einem Verbundmaterial hergestellt ist, das metallisches Mangan und/oder Manganoxid und ein elektrisch leitfähiges Material umfasst, wobei das Verbundmaterial mindestens 5 Gew.% Mangan, bezogen auf die Gesamtmenge, die sich aus metallischem Mangan und Manganoxid ergibt, enthält.

The object defined above is achieved by the provision of a method for the galvanic deposition of zinc nickel coatings from an alkaline coating bath with zinc nickel electrolytes and organic bath additives, which comprise amine-containing complexing agents, in which a metallic manganese and / or manganese oxide which is insoluble in the bath is present as anode Electrode is used, the

1. 1) is made from metallic manganese or a manganese-containing alloy, the manganese-containing alloy containing at least 5% by weight of manganese, or
2. 2) is produced from an electrically conductive carrier and a coating containing metallic manganese and / or manganese oxide applied thereon, the coating containing metallic manganese and / or manganese oxide containing at least 5% by weight of manganese, based on the total amount of manganese which results from metallic Manganese and manganese oxide gives, contains, or
3. 3) is made from a composite material comprising metallic manganese and / or manganese oxide and an electrically conductive material, the composite material containing at least 5% by weight of manganese, based on the total amount resulting from metallic manganese and manganese oxide.

Surprisingly, it was found that the use of insoluble electrodes containing metallic manganese and / or manganese oxide, as described above, has a very positive effect on reducing the degradation of organic bath additives which comprise amine-containing complexing agents. This is particularly advantageous since, in the course of the lower degradation of the amine compounds, a significant reduction in the cyanide concentration also occurs at the same time.

Spectroscopic investigations have shown that the decisive component for the reduced degradation of the organic bath additives, as well as the reduced formation of cyanides, is manganese oxide. However, metallic manganese can also be used, since manganese oxides, often in the form of a brown-black film, are formed in situ during operation as an anode in the alkaline zinc and zinc alloy electrolyte. The manganese oxides formed can exist in different oxidation states.

The above-mentioned embodiments of the electrode containing metallic manganese and / or manganese oxide are explained in more detail below.

Full electrodes

In the method according to the invention, electrodes which are made of metallic manganese or an alloy containing manganese and which are suitable for use as an insoluble anode in an alkaline zinc and zinc alloy bath are suitable. The manganese-containing alloy is preferably selected from a manganese-containing steel alloy or a manganese-containing nickel alloy. In the process according to the invention, the use of a steel alloy containing manganese is particularly preferred. The proportion of alloy in the manganese-containing alloy has a manganese content of at least 5% by weight of manganese, preferably 10-90% by weight of manganese, particularly preferably 50-90% by weight of manganese. Commercially available steel electrodes have e.g. a manganese content of 12% by weight manganese (X120Mn12 with the material number: 1.3401) or 50% by weight manganese (fried iron).

Coated carrier electrodes

In addition to the above-mentioned full electrodes, which are made of metallic manganese or an alloy containing manganese, electrodes made of an electrically conductive carrier material, which is suitable for use as an insoluble anode in an alkaline zinc and zinc alloy bath, with a coating containing metallic manganese and / or manganese oxide are also suitable. The carrier material is preferably selected from steel, titanium, nickel or graphite. In the process according to the invention, the use of steel as a carrier material is particularly preferred. The coating containing metallic manganese and / or manganese oxide has a manganese content of at least 5% by weight of manganese, preferably 10-100% by weight of manganese, particularly preferably 50-100% by weight of manganese, and particularly preferably 80-100% by weight. Manganese, based on the total amount of manganese resulting from metallic manganese and manganese oxide.

It is not important how the coating containing metallic manganese and / or manganese oxide is applied to the surface of the carrier as long as it is adherent. The metallic manganese and / or manganese oxide-containing coating may therefore, by several methods, including by thermal spraying, cladding, or chemical vapor deposition such as physical vapor deposition (PVD of Engl. Physical vapor deposition) may be applied to the carrier. The layer thickness of the coating containing metallic manganese and / or manganese oxide is not decisive here and can vary depending on the process
range from a few nanometers (eg using a PVD process) to several millimeters (eg using a thermal spray process).

Thermal spraying

As already stated above, the coating containing metallic manganese and / or manganese oxide can be applied to the carrier by thermal spraying. The Manganese-containing coating material used for thermal spraying can consist both of metallic manganese and of a mixture which contains iron and / or nickel in addition to metallic manganese.

The manganese-containing coating material used for thermal spraying preferably has a manganese content of 80% by weight of manganese or more, preferably 90% by weight of manganese or more, particularly preferably 100% by weight of manganese.

The manganese-containing coating material is preferably used in a form suitable for thermal spraying, for example as a powder or wire.

Usually, during thermal spraying, heated, melted or melted spray particles inside or outside a spray gun are accelerated using atomizing gas (e.g. compressed air or inert gas such as nitrogen and argon) and flung onto the surface of the substrate to be coated. This forms a good connection to the carrier surface and an adherent metallic manganese and / or manganese oxide layer, mainly by mechanical clamping.

Additional measures can be taken to achieve particularly good layer adhesion on the surface of the carrier. For example, the substrate to be coated can be roughened by means of corundum blasting (blasting material is zirconium corundum) before the thermal spraying process. Another possibility is to arrange an additional adhesive base between the carrier and the coating containing metallic manganese and / or manganese oxide. The primer may consist of nickel, for example. The use of an adhesive base further improves the adhesion of the thermally sprayed layer on the carrier. An adhesive primer is preferably applied directly to the surface of the substrate before the manganese-containing coating material is thermally applied is sprayed on. The primer can be produced using the same thermal spraying method as the coating containing metallic manganese and / or manganese oxide, for example flame spraying or arc spraying. The primer is usually created with a layer thickness of 50 - 100 µm. If an adhesive base is used, the manganese-containing coating material is generally sprayed directly onto the adhesive base.

If no primer is used, the manganese-containing coating material is generally sprayed directly onto the substrate to be coated.

The manganese-containing coating material can be thermally sprayed onto the carrier by means of conventional spraying processes. These include: arc wire spraying, thermo-spray powder spraying, flame spraying, high-speed flame spraying, plasma spraying, autogenous rod spraying, autogenous wire spraying, laser beam spraying, cold gas spraying, detonation spraying and PTWA (plasma transferred wire arc) spraying. These methods are known per se to the person skilled in the art. The manganese-containing coating material can be applied to the carrier in particular by means of flame spraying or arc spraying. Flame spraying is particularly suitable for the use of a powdered manganese-containing coating material.

Powder flame spraying distinguishes between self-flowing and self-adhesive powders. The self-flowing powders usually require additional thermal treatment, which significantly increases the adhesion of the spray layer to the carrier. The thermal aftertreatment is usually carried out with acetylene-oxygen burners. Due to the thermal aftertreatment, the spray layer is both gas and liquid tight, which is why the manganese-containing coating material is preferably applied to the carrier by means of powder flame spraying.

From a technical point of view, layer thicknesses of 50 µm to several millimeters can be applied to the carrier by means of the above-mentioned processes.

Furthermore, thermal spraying can be carried out both in an air atmosphere and in an inert gas atmosphere. This can usually be regulated by the type of atomizing gas. If an inert gas, such as nitrogen or argon, is used as the atomizing gas, oxidation of the manganese-containing coating material is largely prevented. For example, a manganese layer made of metallic manganese or a manganese alloy can be applied to the carrier. In the process according to the invention, manganese oxides, which represent the active surface, would then form in the course of the galvanic deposition process on the carrier anode with the metallic manganese or manganese alloy layer applied thereon. Alternatively, these can be applied to the carrier in advance. This has the advantage that the active surface does not have to form only during the galvanic deposition process, so that a positive effect, ie suppression of the anodic oxidation of the organic bath additives, becomes visible after a short time. Due to the use of compressed air, for example, the high temperatures from the manganese-containing coating material used result in oxidation products which solidify on the surface of the covering with the melt and thus form an adherent film. The manganese-containing coating material sprayed under an air atmosphere then contains manganese oxides as well as metallic manganese and optionally iron and / or nickel as well as optionally iron oxides and / or nickel oxides or combinations thereof as a layer applied to the carrier.

Cladding

In addition to the thermal spraying process, the coating containing metallic manganese and / or manganese oxide can also be applied by cladding, also called welding plating. The manganese-containing coating material used for cladding can consist both of metallic manganese and of a mixture that contains iron and / or nickel in addition to metallic manganese.

The manganese-containing coating material preferably has a manganese content of 80% by weight of manganese or more, preferably 90% by weight of manganese or more, particularly preferably 100% by weight of manganese.

The manganese-containing coating material is preferably used in a form suitable for cladding, for example as a powder, wire, rod, tape, paste or cored wire.

During build-up welding, both the coating material and a thin surface layer of the support to be coated are usually melted by suitable energy sources and metallurgically connected to one another. The diffusion and mixing of the coating material with the carrier material creates a non-stick and non-porous layer. Deposition welding essentially differs from thermal spraying in that the surface of the carrier is melted during build-up welding.

The manganese-containing coating material can be applied to the carrier by means of conventional build-up welding processes. Suitable energy sources for this include: arc, flame, Joule heat, plasma beam, laser beam and electron beam. These energy sources are known per se to the person skilled in the art.

From a technical point of view, relatively high layer thicknesses of 1 mm and more can be applied to the carrier by means of the above-mentioned processes. For this purpose, the energy source is guided over the carrier in oscillating movements, as a result of which the manganese-containing coating material is then applied in individual layers.

Furthermore, similar to thermal spraying, cladding can also be carried out under an air atmosphere as well as under an inert gas atmosphere such as nitrogen or argon. For example, a manganese layer made of metallic manganese or a manganese alloy can be applied to the carrier under an inert gas atmosphere. In an air atmosphere, the high temperatures form oxidation products from the manganese-containing coating material used. The layer formed in an air atmosphere then contains, in addition to metallic manganese and optionally iron and / or nickel, also manganese oxides, and optionally iron oxides and / or nickel oxides or combinations thereof.

Vapor deposition

Furthermore, the coating containing metallic manganese and / or manganese oxide can also be applied to the carrier by gas phase deposition, such as physical gas phase deposition (PVD).

The manganese-containing coating material used for physical vapor deposition is usually metallic manganese, but other manganese-containing solids, such as manganese oxide, which are suitable for this process can also be used.

The manganese-containing coating material can be applied to the carrier by means of conventional vapor deposition processes. The processes of physical Deposition from the gas phase include the processes: evaporation, such as thermal evaporation, electron beam evaporation, laser beam evaporation and arc evaporation, sputtering, and ion plating, as well as reactive variants of these processes.

In the PVD process, the manganese-containing coating material is usually atomized by bombardment with laser beams, magnetically deflected ions, electrons or by arc discharge (e.g. during sputtering) or brought into the gas phase (e.g. during evaporation) in order to subsequently form a solid containing manganese to be deposited on the surface of the substrate to be coated.

So that the gaseous manganese-containing coating material also reaches the support to be coated, the process must be carried out under reduced pressure of approximately 10 ^-4-10 Pa.

From a technical point of view, layer thicknesses of 100 nm - 2 mm can be applied to the carrier using the PVD method.

Composite anodes

In addition to the manganese-containing full electrodes and carrier electrodes coated with metallic manganese and / or manganese oxide, electrodes which consist of a composite material comprising metallic manganese and / or manganese oxide and a conductive material can also be used. For example, carbon, preferably graphite, can be used as the conductive material.

The composite material containing metallic manganese and / or manganese oxide has a manganese content of at least 5% by weight of manganese, preferably at least 10% by weight of manganese, particularly preferably at least 50% by weight of manganese, based on the total amount of manganese resulting from metallic manganese and manganese oxide.

The method of manufacturing such a manganese-containing composite electrode is not particularly limited. Common processes such as sintering or pressing with a binder are therefore suitable. Furthermore, the manganese-containing composite electrode can also be produced by incorporating metallic manganese or manganese oxide in foam metal. These methods are known per se to the person skilled in the art.

Zinc nickel baths

In the process according to the invention for the electrodeposition of a zinc nickel coating from an alkaline electrolyte, the zinc nickel baths are not particularly limited, provided that they are alkaline and contain organic bath additives which comprise amine-containing complexing agents.

The zinc nickel bath is used for the deposition of a zinc nickel coating from an alkaline zinc nickel electrolyte on a substrate connected as a cathode. In the new batch, this typically contains a zinc ion concentration in the range from 5 to 15 g / l, preferably 6 to 10 g / l calculated as zinc, and a nickel ion concentration in the range from 0.5 to 3 g / l, preferably 0.6 to 1, 5 g / l, calculated as nickel. The zinc and nickel compounds used for the production of the zinc nickel electrolyte are not particularly limited. For example, nickel sulfate, nickel chloride, nickel sulfamate or nickel methane sulfonate can be used. The use of nickel sulfate is particularly preferred.

The alkaline zinc nickel baths also contain organic bath additives such as complexing agents, brightening agents, wetting agents, etc.

When using zinc-nickel electrolytes, the addition of complexing agents is inevitable, since the nickel is not amphoteric and therefore does not dissolve in the alkaline electrolyte. Alkaline zinc nickel electrolytes therefore contain special complexing agents for nickel. The complexing agents are not particularly limited, and any known complexing agents comprising amine-containing complexing agents can be used. Amine compounds such as triethanolamine, ethylenediamine, tetrahydroxopropylethylenediamine (Lutron Q 75), diethylenetetramine or homologous compounds of ethylenediamine, such as e.g. Diethylene triamine, tetraethylene pentamine, etc. used. The complexing agent and / or mixtures of these complexing agents is / are usually used in a concentration in the range of 5-100 g / l, preferably 10-70 g / l, more preferably 15-60 g / l.

In addition, brighteners are usually used in zinc nickel baths. These are not particularly limited, and any known brightener can be used. Aromatic or heteroaromatic compounds, such as benzylpyridinium carboxylate or pyridinium-N-propane-3-sulfonic acid (PPS), are preferably used as brighteners.

Furthermore, the electrolyte used in the method according to the invention is basic. For example, but not limited, sodium hydroxide and / or potassium hydroxide can be used to adjust the pH. Sodium hydroxide is particularly preferred. The pH of the aqueous, alkaline solution is usually 10 or more, preferably 12 or more, particularly preferably 13 or more. A zinc nickel bath therefore usually contains 80 - 160 g / l sodium hydroxide. This corresponds to an approximately 2-4 molar solution.

Cathodes or substrates to be coated

The substrate connected as a cathode is not particularly limited, and any known materials suitable for use as a cathode in an electroplating process for depositing a zinc nickel coating from an alkaline electrolyte can be used. In the process according to the invention, for example, substrates made of steel, hardened steel, forged casting or zinc die casting can be used as the cathode.

1. 1) von metallischem Mangan oder einer Mangan-haltigen Legierung, wobei die Mangan-haltige Legierung mindestens 5 Gew.% Mangan enthält, oder
2. 2) von einem elektrisch leitfähigen Träger und einer darauf aufgebrachten metallisches Mangan und/oder Manganoxid enthaltenden Beschichtung, wobei die metallisches Mangan und/oder Manganoxid enthaltende Beschichtung mindestens 5 Gew.% Mangan, bezogen auf die Gesamtmenge an Mangan, die sich aus metallischem Mangan und Manganoxid ergibt, enthält, oder
3. 3) von einem Verbundmaterial, das metallisches Mangan und/oder Manganoxid und ein elektrisch leitfähiges Material umfasst, wobei das Verbundmaterial mindestens 5 Gew.% Mangan, bezogen auf die Gesamtmenge, die sich aus metallischem Mangan und Manganoxid ergibt, enthält,

als Anode zur galvanischen Abscheidung von Zinknickelüberzügen aus einem alkalischen Beschichtungsbad mit Zinknickelelektrolyten und organischen Badzusätzen, umfassend Amin-haltige Komplexbildner.In addition to the methods described above, the invention further relates to the use

1. 1) metallic manganese or a manganese-containing alloy, the manganese-containing alloy containing at least 5% by weight of manganese, or
2. 2) of an electrically conductive carrier and a coating containing metallic manganese and / or manganese oxide applied thereon, wherein the coating containing metallic manganese and / or manganese oxide contains at least 5% by weight of manganese, based on the total amount of manganese which consists of metallic manganese and Manganese oxide gives, contains, or
3. 3) a composite material comprising metallic manganese and / or manganese oxide and an electrically conductive material, the composite material containing at least 5% by weight of manganese, based on the total amount resulting from metallic manganese and manganese oxide,

as an anode for the galvanic deposition of zinc-nickel coatings from an alkaline coating bath with zinc-nickel electrolytes and organic bath additives, comprising amine-containing complexing agents.

Furthermore, a galvanic device for the deposition of zinc nickel coatings from an alkaline coating bath with zinc nickel electrolytes and organic bath additives is provided, which as anode contains an insoluble electrode containing metallic manganese and / or manganese oxide, as described above, and an alkaline coating bath with zinc nickel electrolytes and organic bath additives. comprising amine-containing complexing agents.

The device according to the invention does not require that the anode and cathode compartments are separated from one another by membranes and / or separators.

The invention is explained in more detail below with the aid of examples.

Examples Test example 1.1

Stress tests were carried out with the alkaline zinc nickel electrolyte SLOTOLOY ZN 80 (Schlötter) using different anode materials. The deposition behavior was analyzed over a longer period of time with a constant cathodic and anodic current density. Depending on the amount of electricity passed through, the zinc nickel electrolyte was selected with regard to the degradation products which form at the anode, e.g. Cyanide. An analysis of the organic complexing agents and brighteners was also carried out.

Test conditions:

The basic bath mix (2 liters of SLOTOLOY ZN 80) had the following composition: Zn: 7.5 g / l as ZnO Ni: 0.6 g / l as NiSO ₄ x 6 H ₂ O NaOH: 120 g / l SLOTOLOY ZN 81: 40 ml / l (complexing agent mixture) SLOTOLOY ZN 82: 75 ml / l (complexing agent mixture) SLOTOLOY ZN 87: 2.5 ml / l (basic gloss additive) SLOTOLOY ZN 83: 2.5 ml / l (basic gloss additive) SLOTOLOY ZN 86: 1.0 ml / l (top gloss agent)

The above-mentioned basic bath batch contains: 10.0 g / l DETA (diethylene triamine), 9.4 g / l TEA (85% by weight triethanolamine), 40.0 g / l Lutron Q 75 (BASF; 75% by weight tetrahydroxopropylethylene diamine) and 370 mg / l PPS (1- (3-sulfopropyl) pyridinium betaine).

The bath temperature was set at 35 ° C. The stirring motion during the current efficiency sheet coating was 250 to 300 rpm. In contrast, the stirring movement during the loading sheet coating was 0 rpm. The current densities at the anode and at the cathode were kept constant. The cathodic current density was I _k = 2.5 A / dm ² , the anodic current density was I _a = 15 A / dm ² .

• Kathodenmaterial: Stahlblech aus Kaltbandstahl gemäß DIN EN 10139/10140 (Qualität: DC03 LC MA RL)
• Anodenmaterialien:
  • Vergleichsanode 1: Stahl mit der Werkstoffnummer 1.0330, bzw. DC 01 (Zusammensetzung: C 0,12%; Mn 0,6%; P 0,045%; S 0,045%); kommerziell erhältlich
  • Vergleichsanode 2: Glanzvernickelter Stahl; Stahl (Werkstoffnummer 1.0330) mit einer Schichtauflage von 30 µm Glanznickel (beschichtet mit SLOTONIK 20 Elektrolyt der Fa. Schlötter);
• Herstellung: Siehe hierzu J. N. Unruh, Tabellenbuch Galvanotechnik, 7. Auflage, EUGEN G. LEUZE Verlag, Bad Saulgau, S.515 )
  • Vergleichsanode 3: Stahl (Werkstoffnummer 1.0330) mit einer durch thermisches Spritzen darauf aufgebrachten Eisenoxidschicht (im Folgenden als "Fe-Oxidanode" definiert); Herstellung: Ein 2 mm dickes Stahlblech (Werkstoffnummer 1.0330) wurde entfettet, mit Glasperlen (Durchmesser 150 bis 250 µm) gestrahlt und anschließend mit Druckluft von anhaftenden Resten befreit. Das Stahlblech wurde dann zur Verbesserung des Haftgrundes mittels Lichtbogenspritzen zunächst mit Nickel thermisch bespritzt. Dabei wurde ein Nickeldraht im Lichtbogen (Temperatur am Brennerkopf 3000 bis 4000°C) abgeschmolzen und mit Druckluft (6 bar) als Zerstäubergas in einem Abstand von 15 bis 18 cm auf das Stahlblech aufgespritzt. Anschließend wurde die Eisenoxidschicht ebenfalls durch Lichtbogenspritzen aufgebracht. Dabei wurde ein Eisendraht (sogenannter Eisen-Lichtbogendraht mit 0,7 Gew.% Mn, 0,07 Gew.% C und dem Rest Fe; Durchmesser 1,6 mm) im Lichtbogen (Temperatur am Brennerkopf 3000 bis 4000°C) abgeschmolzen und mit Druckluft (6 bar) als Zerstäubergas in einem Abstand von 15 bis 18 cm auf das Stahlblech aufgespritzt. Durch schwenkende Bewegungen wurde so lange beschichtet, bis eine gleichmäßige, ca. 300 µm dicke thermisch gespritzte Eisenoxidschicht erzeugt worden ist.
  • Erfindungsgemäße Anode 1: Stahl (Werkstoffnummer 1.0330) mit einer durch thermisches Spritzen darauf aufgebrachten Manganoxidschicht (im Folgenden als "Mn-Oxidanode" definiert);
• Herstellung: Ein 2 mm dickes Stahlblech (Werkstoffnummer 1.0330) wurde entfettet, mit Korundstrahlen (Strahlgut ist hierbei Zirkonkorund) aufgeraut und anschließend mit Druckluft von anhaftenden Resten befreit. Das Stahlblech wurde dann zur Verbesserung des Haftgrundes mittels Lichtbogenspritzen zunächst mit Nickel thermisch bespritzt. Dabei wurde ein Nickeldraht im Lichtbogen (Temperatur am Brennerkopf 3000 bis 4000°C) abgeschmolzen und mit Druckluft (6 bar) als Zerstäubergas in einem Abstand von 15 bis 18 cm auf das Stahlblech aufgespritzt. Anschließend wurde die Manganoxidschicht mittels Pulver-Flammspritzen thermisch aufgespritzt. Dabei wurde metallisches Manganpulver (-325 mesh, ≥99%ig von Sigma Aldrich) in einer Acetylen-Sauerstoff-Flamme (Temperatur der Brennerflamme betrug 3160°C) geschmolzen und mit Druckluft (maximal 3 bar) als Zerstäubergas in einem Abstand von 15 bis 20 cm auf das Stahlblech aufgespritzt. Durch schwenkende Bewegungen wurde so lange beschichtet, bis eine gleichmäßige, ca. 250 µm dicke thermisch gespritzte Manganoxidschicht erzeugt worden ist.

The following anode and cathode materials were used:

• Cathode material: Cold-rolled steel sheet in accordance with DIN EN 10139/10140 (quality: DC03 LC MA RL)
• Anode materials:
  • Comparative anode 1: steel with the material number 1.0330 or DC 01 (composition: C 0.12%; Mn 0.6%; P 0.045%; S 0.045%); commercially available
  • Comparative anode 2: bright nickel-plated steel; Steel (material number 1.0330) with a layer of 30 µm bright nickel (coated with SLOTONIK 20 electrolyte from Schlötter);
• Manufacturing: See here JN Unruh, table book electroplating, 7th edition, EUGEN G. LEUZE Verlag, Bad Saulgau, p.515 )
  • Comparative anode 3: steel (material number 1.0330) with an iron oxide layer applied to it by thermal spraying (hereinafter defined as "Fe oxide anode"); Production: A 2 mm thick steel sheet (material number 1.0330) was degreased, blasted with glass beads (diameter 150 to 250 µm) and then freed of adhering residues with compressed air. The steel sheet was then first thermally sprayed with nickel by means of arc spraying in order to improve the adhesive base. A nickel wire was melted in the arc (temperature at the burner head 3000 to 4000 ° C) and sprayed onto the steel sheet at a distance of 15 to 18 cm using compressed air (6 bar) as atomizing gas. The iron oxide layer was then also applied by arc spraying. An iron wire (so-called iron arc wire with 0.7% by weight Mn, 0.07% by weight C and the rest Fe; diameter 1.6 mm) was melted in the arc (temperature at the torch head 3000 to 4000 ° C) and sprayed onto the steel sheet with compressed air (6 bar) as atomizing gas at a distance of 15 to 18 cm. Coating movements were carried out until a uniform, approximately 300 µm thick, thermally sprayed iron oxide layer was produced.
  • Anode 1 according to the invention: steel (material number 1.0330) with a manganese oxide layer applied to it by thermal spraying (hereinafter defined as “Mn oxide anode”);
• Production: A 2 mm thick steel sheet (material number 1.0330) was degreased, roughened with corundum blasting (blasting material is zirconium corundum) and then freed of adhering residues with compressed air. The steel sheet was then first thermally sprayed with nickel by means of arc spraying in order to improve the adhesive base. A nickel wire was melted in the arc (temperature at the burner head 3000 to 4000 ° C) and sprayed onto the steel sheet at a distance of 15 to 18 cm using compressed air (6 bar) as atomizing gas. The manganese oxide layer was then thermally sprayed on using powder flame spraying. Metallic manganese powder (-325 mesh, ≥99% from Sigma Aldrich) was melted in an acetylene-oxygen flame (temperature of the burner flame was 3160 ° C) and with compressed air (maximum 3 bar) as atomizing gas at a distance of 15 to Sprayed 20 cm onto the steel sheet. The coating was carried out by swiveling movements until a uniform, approximately 250 μm thick, thermally sprayed manganese oxide layer was produced.

• SLOTOLOY ZN 86: 1 ml (entspricht einer Zugabemenge von 1 l/10kAh)
• SLOTOLOY ZN 83: 0,3 ml (entspricht einer Zugabemenge von 0,3 l/10kAh)

Nach einer durchgesetzten Strommenge von jeweils 2,5 Ah/l wurde die auf dem Abscheidungsblech (Kathode) vorhandene abgeschiedene Zinknickellegierungsmenge durch Auswaage ermittelt. Die durch die Abscheidung im Zinknickelelektrolyten fehlende Gesamtmetallmenge wurde auf 85 Gew. % Zink und 15 Gew. % Nickel umgerechnet (beispielsweise sind für eine abgeschiedene Gesamtmetallmenge von 1,0 g Zinknickellegierungsschicht 850 mg Zink und 150 mg Nickel zudosiert worden).After a current of 5 Ah / l had been passed through, the following brighteners or fine-grain additives were added to the zinc nickel electrolyte:

• SLOTOLOY ZN 86: 1 ml (corresponds to an addition of 1 l / 10kAh)
• SLOTOLOY ZN 83: 0.3 ml (corresponds to an addition of 0.3 l / 10kAh)

After a current of 2.5 Ah / l had been passed through, the amount of zinc-nickel alloy deposited on the deposition plate (cathode) was determined by weighing. The total amount of metal missing due to the deposition in the zinc-nickel electrolyte was converted to 85% by weight of zinc and 15% by weight of nickel (for example, 850 mg of zinc and 150 mg of nickel were added for a total amount of metal deposited from 1.0 g of zinc-nickel alloy layer).

The zinc used in the electrolyte was added as zinc oxide, the used nickel was supplemented with the nickel-containing liquid concentrate SLOTOLOY ZN 85. In SLOTOLOY ZN 85 contains nickel sulfate, as well as the amines triethanolamine, diethylene triamine and Lutron Q 75 (1 ml SLOTOLOY ZN 85 contains 63 mg nickel).

The NaOH content was determined after 10 Ah / l by acid-base titration and adjusted to 120 g / l in each case.

Execution of the experiment and results:

The amount of cyanide formed was determined in each case after a current of 50 Ah / l and 100 Ah / l had been passed through. The results of the analytical determination depending on the bath load are shown in Table 2. [Table 2] anode Anode material Cyanide content (mg / l) after 50 Ah / l exposure Cyanide content (mg / l) after 100 Ah / l exposure Comparative anode 1 Steel anode 116 224 Comparative anode 2 bright nickel-plated steel anode 130 234 Comparative anode 3 Fe oxide anode 195 288 Anode 1 according to the invention Mn oxide anode 75 106

The cyanide was determined using the cuvette test LCK 319 for easily releasable cyanides from Dr. Lange (today Hach company). Easily released cyanides are converted into gaseous HCN by a reaction and transferred through a membrane into an indicator cuvette. The color change of the indicator is then evaluated photometrically.

As shown in Table 2, the least amount of cyanide was formed using the Mn oxide anode according to the invention. Even after an enforced amount of electricity of 100 Ah / l, the cyanide content was using the Mn oxide anode according to the invention is only half as high compared to the comparison anodes 1 to 3.

Furthermore, the amount of complexing agents still present was determined after a current of 50 Ah / l and 100 Ah / l had been passed through. The results of the analytical determination as a function of the bath load are summarized in Table 3. [Table 3] anode Anode material After 50 Ah / l load After 100 Ah / l load DETA (g / l) TEA (85% by weight) (g / l) Lutron Q 75 (g / l) DETA (g / l) TEA (85% by weight) (g / l) Lutron Q 75 (g / l) Comparative anode 1 Steel anode 7.8 9.0 41.0 7.3 9.8 45.3 Comparative anode 2 bright nickel-plated steel anode 8.0 9.1 42.1 7.0 9.4 46.9 Comparative anode 3 Fe oxide anode 7.8 8.8 41.6 6.8 8.0 43.7 Invention anode 1 Mn oxide anode 10.2 9.9 41.1 10.2 10.8 43.2

As shown in Table 3, significantly less amines (DETA and TEA) were consumed using the Mn oxide anode according to the invention. Even after a current of 100 Ah / l had been passed through, the consumption of DETA and TEA using the Mn oxide anode according to the invention was significantly lower compared to the comparison anodes 1 to 3.

Test example 1.2 Test conditions:

Test example 1.2 was carried out under the same conditions as described in test example 1.1.

Execution of the experiment and results:

A straight cold-rolled steel sheet (DIN EN 10139/10140; quality: DC03 LC MA RL) with a sheet surface of 1 dm ^2, which was connected as the cathode, was coated with a zinc nickel electrolyte using the comparative anodes 1 to 3 and the Mn oxide anode according to the invention. The current yield and the proportion of nickel alloys in the initial state and after a current flow of 100 Ah / l were determined at cathodic current densities of 0.25, 2.5 and 4 A / dm ² .

The result of the determination of the current yield and the proportion of nickel alloy as a function of the bath load is shown in Tables 4 to 7. [Table 4] Comparative anode 1 // steel anode burden 0.25 A / dm ² 2.5 A / dm ² 4.0 A / dm ² Ni [%] Sa [%] Ni [%] Sa [%] Ni [%] Sa [%] 0 Ah / l 12.2 87.2 15.4 33.7 15.6 26.7 100 Ah / l 12.8 61.9 14.0 33.8 14.6 27.2 Comparative anode 2 // bright nickel-plated steel anode Load 0.25 A / dm ² 2.5 A / dm ² 4.0 A / dm ² Ni [%] Sa [%] Ni [%] Sa [%] Ni [%] Sa [%] 0 Ah / l 11.8 84.0 15.3 32.6 15.6 26.1 100 Ah / l 12.8 55.7 14.4 32.6 14.3 25.5 Comparative anode 3 // Fe oxide anode burden 0.25 A / dm ² 2.5 A / dm ² 4.0 A / dm ² Ni [%] Sa [%] Ni [%] Sa [%] Ni [%] Sa [%] 0 Ah / l 12.1 89.3 15.4 34.1 15.3 26.8 100 Ah / l 11.8 69.2 14.0 40.5 14.3 31.1 Anode 1 // Mn oxide anode according to the invention burden 0.25 A / dm ² 2.5 A / dm ² 4.0 A / dm ² Ni [%] Sa [%] Ni [%] Sa [%] Ni [%] Sa [%] 0 Ah / l 11.7 89.7 15.1 32.4 15.4 26.5 100 Ah / l 12.9 63.4 15.0 37.5 15.3 28.6

Table 7 shows that with approximately the same nickel alloy content, depending on the cathodic current density applied, after 100 Ah / l loading, a 3 to 8% higher current yield could be achieved by using the Mn oxide anode according to the invention, compared to the comparison anode usually used as a standard anode 2 (bright nickel-plated steel; see table 5).

By using the Mn oxide anode according to the invention, the specified layer thickness on components can thus be achieved in practice in a shorter time. This leads to a significant reduction in process costs.

Test example 1.3 Test conditions:

Test example 1.3 was carried out under the same conditions as described in test example 1.1.

After 100 Ah / l loading, the deposition of the zinc nickel electrolyte was checked using a Hull cell test according to DIN 50957. The electrolyte temperature was set at 35 ° C. A 250 ml Hull cell was used. Cold-rolled steel DIN EN 10139/10140 (quality: DC03 LC MA RL) was used as the cathode sheet. The cell current was 2 A, the coating time was 15 minutes.

Test results:

The result of the Hull cell coating to determine the appearance and the alloy distribution depending on the bath load is shown in Schemes 1 and 2.

Scheme 1 shows the result of the test sheets, which were coated in a bath and were operated with comparison anodes 1 to 3. Scheme 2 shows the result of the test sheet which was coated in a bath which was operated with the Mn oxide anode according to the invention.

The Hull cell sheet, which was operated with the Mn oxide anode according to the invention (see Scheme 2), shows after 100 Ah / l a semi-glossy to glossy appearance which is uniform over the entire current density range, which is a measure of the still present and undamaged bath additives.

The Hull cell sheets made of the zinc-nickel electrolytes of the comparison anodes 1 to 3 only show a semi-glossy to shiny appearance in the range <2 A / dm ² (corresponds to a distance of 4 cm from the right sheet edge to the right sheet edge). The rest of the sheet metal range is from satin to matt.

It can be seen from test examples 1.1 to 1.3 that the use of the Mn oxide anode according to the invention has a positive effect on the consumption of organic bath additives. It has been shown that the amine-containing complexing agents, in particular DETA and TEA, are consumed significantly less, which leads to a reduction in process costs. A significantly reduced formation of cyanides can also be observed. In addition, after 100 Ah / l, using the Mn oxide anode according to the invention, depending on the current density, a 3 to 8% higher current yield than with the comparison anode 2 can be achieved, which in turn significantly reduces process costs. In addition to the aspects mentioned above, using the Mn oxide anode according to the invention there is no deterioration in gloss formation even after 100 Ah / l loading, compared to the use of comparison anodes 1 to 3.

Test example 2

Stress tests were carried out with the alkaline zinc nickel electrolyte SLOTOLOY ZN 210 (Schlötter) using different anode materials. The deposition behavior was analyzed over a longer period of time with a constant cathodic and anodic current density. Depending on the amount of electricity passed through, the zinc nickel electrolyte was examined with regard to the decomposition products, such as cyanide, which form on the anode. An analysis of the organic complexing agents and brighteners was also carried out.

Test conditions:

The basic bath mix (2 liters SLOTOLOY ZN 210) had the following composition: Zn: 7.5 g / l as ZnO Ni: 1.0 g / l as NiSO ₄ x 6 H ₂ O NaOH: 120 g / l SLOTOLOY ZN 211: 100 ml / l (complexing agent mixture) SLOTOLOY ZN 212: 30 ml / l (complexing agent mixture) SLOTOLOY ZN 215: 14 ml / l (nickel solution) SLOTOLOY ZN 213: 5 ml / l (basic gloss additive) SLOTOLOY ZN 216: 0.2 ml / l (top gloss agent)

The above-mentioned basic bath batch contains: 22.4 g / l TEPA (tetraethylene pentamine), 10.2 g / l TEA (85% by weight) and 5.4 g / l Lutron Q 75 (BASF; 75% by weight tetrahydroxopropylethylene diamine) and 75 mg / l PPS (1- (3-sulfopropyl) pyridinium betaine).

The bath temperature was set at 28 ° C. The stirring movement during the loading sheet coating was 0 rpm. The current densities at the anode and at the cathode were kept constant. The cathodic current density was I _k = 2.0 A / dm ² , the anodic current density was I _a = 12.5 A / dm ² .

• Kathodenmaterial: Stahlblech aus Kaltbandstahl gemäß DIN EN 10139/10140 (Qualität: DC03 LC MA RL)
• Anodenmaterialien:
  • Vergleichsanode 2: Glanzvernickelter Stahl; Stahl (Werkstoffnummer 1.0330) mit einer Schichtauflage von 30 µm Glanznickel (beschichtet mit SLOTONIK 20 Elektrolyt der Fa. Schlötter);
• Herstellung: Siehe hierzu J. N. Unruh, Tabellenbuch Galvanotechnik, 7. Auflage, EUGEN G. LEUZE Verlag, Bad Saulgau, S.515 )
  Erfindungsgemäße Anode 2: Stahl mit der Werkstoffnummer 1.3401 bzw. X120Mn12 (Zusammensetzung: C 1,2%; Mn 12,5%; Si 0,4%; P 0,1%; S 0,04%); kommerziell erhältlich (im Folgenden als "Manganlegierungsanode" definiert)

Nach einer durchgesetzten Strommenge von jeweils 2,5 Ah/l wurden nachfolgend aufgeführte Glanzbildner bzw. Feinkornzusätze dem Zinknickelelektrolyten zudosiert:

• SLOTOLOY ZN 214: 0,25 ml (entspricht einer Zugabemenge von 1 l/10kAh)
• SLOTOLOY ZN 216: 0,1 ml (entspricht einer Zugabemenge von 0,4 l/10kAh)

Nach einer durchgesetzten Strommenge von jeweils 2,5 Ah/l wurde die auf dem Abscheidungsblech (Kathode) vorhandene abgeschiedene Zinknickellegierungsmenge durch Auswaage ermittelt. Die durch die Abscheidung im Zinknickelelektrolyten fehlende Gesamtmetallmenge wurde auf 85 Gew. % Zink und 15 Gew. % Nickel umgerechnet (beispielsweise sind für eine abgeschiedene Gesamtmetallmenge von 1,0 g Zinknickellegierungsschicht 850 mg Zink und 150 mg Nickel zudosiert worden).The following anode and cathode materials were used:

• Cathode material: Cold-rolled steel sheet in accordance with DIN EN 10139/10140 (quality: DC03 LC MA RL)
• Anode materials:
  • Comparative anode 2: bright nickel-plated steel; Steel (material number 1.0330) with a layer of 30 µm bright nickel (coated with SLOTONIK 20 electrolyte from Schlötter);
• Manufacturing: See on this JN Unruh, table book electroplating, 7th edition, EUGEN G. LEUZE Verlag, Bad Saulgau, p.515 )
  Anode 2 according to the invention: steel with the material number 1.3401 or X120Mn12 (composition: C 1.2%; Mn 12.5%; Si 0.4%; P 0.1%; S 0.04%); commercially available (hereinafter referred to as "manganese alloy anode")

After a current of 2.5 Ah / l had been passed through, the following brighteners or fine-grain additives were added to the zinc nickel electrolyte:

• SLOTOLOY ZN 214: 0.25 ml (corresponds to an addition of 1 l / 10kAh)
• SLOTOLOY ZN 216: 0.1 ml (corresponds to an addition of 0.4 l / 10kAh)

After a current of 2.5 Ah / l had been passed through, the amount of zinc-nickel alloy deposited on the deposition plate (cathode) was determined by weighing. The total amount of metal missing due to the deposition in the zinc-nickel electrolyte was converted to 85% by weight of zinc and 15% by weight of nickel (for example, 850 mg of zinc and 150 mg of nickel were added for a total amount of metal deposited from 1.0 g of zinc-nickel alloy layer).

The nickel used in the electrolyte was supplemented with the nickel-containing liquid concentrate SLOTOLOY ZN 215. The SLOTOLOY ZN 215 contains nickel sulfate, as well as the amines triethanolamine, tetraethylene pentamine and Lutron Q 75 (1 ml SLOTOLOY ZN 215 contains 70 mg nickel).

The NaOH content was determined after 10 Ah / l by acid-base titration and adjusted to 120 g / l in each case.

In order to keep the zinc content in the zinc-nickel electrolyte as constant as possible during the entire coating period, zinc pellets were introduced into the electrolyte without current. Zinc dissolution occurs due to the alkalinity of the electrolyte. The zinc content was also regularly analyzed analytically using titration in the laboratory.

Execution of the experiment and results:

The amount of cyanide formed was determined after a current of 50 Ah / l had passed through.
The results of the analytical determination depending on the bath load are shown in Table 8. [Table 8] anode Anode material Cyanide content (mg / l) after 50 Ah / l exposure Comparative anode 2 bright nickel-plated steel anode 98 Anode 2 according to the invention Manganese alloy anode 37

The cyanide was determined using the cuvette test LCK 319 for easily releasable cyanides from Dr. Lange (today Hach company). Easily released cyanides are converted into gaseous HCN by a reaction and transferred through a membrane into an indicator cuvette. The color change of the indicator is then evaluated photometrically.

As shown in Table 8, the use of the manganese alloy anode according to the invention resulted in a significantly lower cyanide formation than in the comparison anode 2 (bright nickel-plated steel).

Furthermore, the amount of additives still present was determined after a current of 50 Ah / l had been passed through. The results of the analytical determination of the organic bath additives, ie amine-containing complexing agents, such as TEPA and TEA, and gloss agents, such as PPS, as a function of the bath load, are shown in Table 9. [Table 9] anode Anode material After 50 Ah / l load TEPA (g / l) TEA (85% by weight) (g / l) Lutron Q 75 (g / l) PPS (mg / l) Comparative anode 2 bright nickel-plated steel anode 25.8 13.6 6.1 111 Anode 2 according to the invention Manganese alloy anode 29.6 15.6 6.2 148

As shown in Table 9, significantly less amines (TEPA and TEA) and PPS were consumed using the manganese alloy anode according to the invention than using the comparison anode 2. These substances were consequently less strongly oxidized on the manganese alloy anode according to the invention.

Test example 3

The manganese alloy anode according to the invention was also compared with the comparison anode 2 made of high-gloss nickel-plated steel in the technical center. For this purpose, a newly prepared SLOTOLOY ZN 80 (from Schlötter) electrolyte was operated for about 6 months with four standard anodes made of bright nickel-plated steel (comparison anode 2), a cyanide content in the zinc nickel electrolyte of 372 mg / l being achieved. After 6 months, the standard anodes made of bright nickel-plated steel were replaced by manganese alloy anodes according to the invention exchanged. The zinc nickel electrolyte was then subjected to a further 4 months under the same conditions.

Test conditions:

The basic bath mix (200 liters SLOTOLOY ZN 80) had the following composition: Zn: 7.5 g / l as ZnO Ni: 0.6 g / l as NiSO ₄ x 6 H ₂ O NaOH: 110 g / l SLOTOLOY ZN 81: 40 ml / l (complexing agent mixture) SLOTOLOY ZN 82: 75 ml / l (complexing agent mixture) SLOTOLOY ZN 87: 2.5 ml / l (basic gloss additive) SLOTOLOY ZN 83: 2.5 ml / l (basic gloss additive) SLOTOLOY ZN 86: 1.0 ml / l (top gloss agent)

The above-mentioned basic bath batch contains: 10.0 g / l DETA (diethylene triamine), 9.4 g / l TEA (85% by weight triethanolamine), 40.0 g / l Lutron Q 75 (BASF; 75% by weight tetrahydroxopropylethylene diamine) and 370 mg / l PPS (1- (3-sulfopropyl) pyridinium betaine).

The bath volume was 200 liters. The bath temperature was set at 33 ° C. The current densities at the anode and at the cathode were kept constant. The cathodic current density was I _k = 2.5 A / dm ² , the anodic current density was I _a = 25 A / dm ² . The monthly bath load was 25,000 Ah.

• Kathodenmaterial: Stahlblech aus Kaltbandstahl gemäß DIN EN 10139/10140 (Qualität: DC03 LC MA RL)
• Anodenmaterialien:
  Vergleichsanode 2: Glanzvernickelter Stahl; Stahl (Werkstoffnummer 1.0330) mit einer Schichtauflage von 30 µm Glanznickel (beschichtet mit SLOTONIK 20 Elektrolyt der Fa. Schlötter);
• Herstellung: Siehe hierzu J. N. Unruh, Tabellenbuch Galvanotechnik, 7. Auflage, EUGEN G. LEUZE Verlag, Bad Saulgau, S.515 )
• Erfindungsgemäße Anode 2: Stahl mit der Werkstoffnummer 1.3401 bzw. X120Mn12 (Zusammensetzung: C 1,2%; Mn 12,5%; Si 0,4%; P 0,1%; S 0,04%); kommerziell erhältlich (im Folgenden als "Manganlegierungsanode" definiert)

Die Belastung im Technikum erfolgte unter Praxisbedingungen, d.h. dass die Badzusätze, Metalle und die Natronlauge kontinuierlich nachdosiert wurden.The following anode and cathode materials were used:

• Cathode material: Cold-rolled steel sheet in accordance with DIN EN 10139/10140 (quality: DC03 LC MA RL)
• Anode materials:
  Comparative anode 2: bright nickel-plated steel; Steel (material number 1.0330) with a layer of 30 µm bright nickel (coated with SLOTONIK 20 electrolyte from Schlötter);
• Manufacturing: See here JN Unruh, table book electroplating, 7th edition, EUGEN G. LEUZE Verlag, Bad Saulgau, p.515 )
• Anode 2 according to the invention: steel with the material number 1.3401 or X120Mn12 (composition: C 1.2%; Mn 12.5%; Si 0.4%; P 0.1%; S 0.04%); commercially available (hereinafter referred to as "manganese alloy anode")

The load in the technical center was carried out under practical conditions, ie the bath additives, metals and the sodium hydroxide solution were continuously replenished.

• Beim Betrieb mit glanzvernickelten Stahlanoden (Vergleichsanode 2):
  • SLOTOLOY ZN 86: 100 ml (entspricht einer Zugabemenge von 1 l/10kAh)
  • SLOTOLOY ZN 83: 60 ml (entspricht einer Zugabemenge von 0,6 l/10kAh)
• Beim Betrieb mit erfindungsgemäßen Manganlegierungsanoden (erfindungsgemäße Anode 2):
  • SLOTOLOY ZN 86: 60 ml (entspricht einer Zugabemenge von 0,6 l/10kAh)
  • SLOTOLOY ZN 83: 60 ml (entspricht einer Zugabemenge von 0,6 l/10kAh)

Die Dosiermenge an Zusatz SLOTOLOY ZN 86 wurde hier bewusst reduziert, da der Zusatzabbau an den erfindungsgemäßen Manganlegierungsanoden geringer ist.The following dosing amounts of brighteners or fine-grain additives were added to the zinc nickel electrolyte after a current of 5 Ah / l had been passed through:

• When operating with bright nickel-plated steel anodes (comparison anode 2):
  • SLOTOLOY ZN 86: 100 ml (corresponds to an addition of 1 l / 10kAh)
  • SLOTOLOY ZN 83: 60 ml (corresponds to an addition of 0.6 l / 10kAh)
• When operating with manganese alloy anodes according to the invention (anode 2 according to the invention):
  • SLOTOLOY ZN 86: 60 ml (corresponds to an addition of 0.6 l / 10kAh)
  • SLOTOLOY ZN 83: 60 ml (corresponds to an addition of 0.6 l / 10kAh)

The amount of SLOTOLOY ZN 86 added was deliberately reduced here, since the additional degradation at the manganese alloy anodes according to the invention is less.

The nickel used in the electrolyte was supplemented with the nickel-containing liquid concentrate SLOTOLOY ZN 85. The SLOTOLOY ZN 85 contains nickel sulfate, as well as the amines triethanolamine, diethylene triamine and Lutron Q 75 (1 ml SLOTOLOY ZN 85 contains 63 mg nickel). The necessary amount of nickel was determined using suitable analysis methods (e.g. ICP, AAS).

In order to keep the zinc content in the zinc-nickel electrolyte as constant as possible during the entire coating period, zinc pellets were introduced into the electrolyte without current. Zinc dissolution occurs due to the alkalinity of the electrolyte. The zinc content was also regularly analyzed analytically using titration in the laboratory.

In order to keep the sodium hydroxide content in the electrolyte as constant as possible during the entire coating period, the sodium hydroxide content was analyzed analytically regularly (after 5 Ah / l load) by means of titration in the laboratory and supplemented accordingly.

Excess carbonate was also removed. It is known to the person skilled in the art that the carbonate content in the bath increases with prolonged operation of the electrolyte. In order to be able to keep this constant at a value of less than 60 g / l sodium carbonate, the carbonate was removed at regular intervals using so-called freezers.

Under practical conditions, the electrolyte is diluted to a certain extent due to carry-over losses and the necessary freezing out of carbonate.

Execution of the experiment and results:

The newly prepared SLOTOLOY ZN 80 electrolyte, which was operated with four standard anodes made of bright nickel-plated steel (comparison anode 2), had a cyanide content of 372 mg / l after about 6 months. After this time, the standard anodes made of bright nickel-plated steel were replaced by manganese alloy anodes according to the invention (defined as "start" in Table 10). The zinc nickel electrolyte was then subjected to a further 4 months under the same conditions. The influence of the manganese alloy anodes according to the invention on the cyanide content and the organic bath additives was examined at intervals of one month each.

The results of the analytical determination of cyanide and the organic bath additives as a function of the bath load are shown in Table 10. [Table 10] date Cyanide (mg / l) Zinc (g / l) Nickel (g / l) NaOH (g / l) DETA (g / l) TEA (85 wt.) (G / l) Lutron Q 75 (g / l) SLOTO -LOY ZN 86 (ml / 1) PPS (mg / l) begin 372 6.5 1.1 107 6.5 9.7 18.1 1.5 555 after 1 month 206 6.9 0.9 109 9.3 11.7 20.2 1.3 481 after 2 months 92 6.5 0.94 108 11 14.9 14.9 1.5 555 after 3 months 18th 6.7 1.0 102 11.8 18.1 12.8 1.2 444 after 4 months 23 7.5 1.1 101 12.8 21.4 14.9 1.4 518

The cyanide was determined using the cuvette test LCK 319 for easily releasable cyanides from Dr. Lange (today Hach company). Easily released cyanides are converted into gaseous HCN by a reaction and transferred through a membrane into an indicator cuvette. The color change of the indicator is then evaluated photometrically.

It can be seen from Table 10 that with the manganese alloy anodes according to the invention, the cyanide content in the electrolyte drops significantly within the test period (4 months).

During operation with the manganese alloy anodes according to the invention, the degree of gloss of the deposited layer increased as the cyanide content decreased.

Under the premise of maintaining a constant gloss level of the deposited galvanic layer over the entire course of the test, the metering of fine-grain and gloss additives, such as PPS, could be significantly reduced, since less fine-grain and gloss additives were used. Therefore, the addition SLOTOLOY ZN 86, which contains PPS, could be reduced from an addition amount of 100 ml during operation with comparison anodes 2 to 60 ml by using the manganese alloy anodes according to the invention.

Furthermore, it can be seen that the amines DETA and TEA are used less using the manganese alloy anodes according to the invention than in the comparison anodes 2.

These are two arguments which speak for a reduced additive degradation through the use of the manganese alloy anode according to the invention. A not inconsiderable cost advantage in terms of process costs can thus be achieved through the reduced consumption of organic components can be realized.

Test example 4

Stress tests were carried out with the alkaline zinc nickel electrolyte SLOTOLOY ZN 80 (Schlötter) using different anode materials. The deposition behavior was analyzed over a longer period of time with a constant cathodic and anodic current density. Depending on the amount of electricity passed through, the zinc nickel electrolyte was selected with regard to the degradation products which form at the anode, e.g. Cyanide. An analysis of the organic complexing agents and brighteners was also carried out.

Test conditions:

The basic bath mix (2 liters of SLOTOLOY ZN 80) had the following composition: Zn: 7.5 g / l as ZnO Ni: 0.6 g / l as NiSO ₄ x 6 H ₂ O NaOH: 120 g / l SLOTOLOY ZN 81: 40 ml / l (complexing agent mixture) SLOTOLOY ZN 82: 75 ml / l (complexing agent mixture) SLOTOLOY ZN 87: 2.5 ml / l (basic gloss additive) SLOTOLOY ZN 83: 2.5 ml / l (basic gloss additive) SLOTOLOY ZN 86: 1.0 ml / l (top gloss agent)

The above-mentioned basic bath batch contains: 10.0 g / l DETA (diethylene triamine), 9.4 g / l TEA (85% by weight triethanolamine), 40.0 g / l Lutron Q 75 (BASF; 75% by weight tetrahydroxopropylethylene diamine) and 370 mg / l PPS (1- (3-sulfopropyl) pyridinium betaine).

The bath temperature was set at 35 ° C. The stirring motion during the current efficiency coating was 250 to 300 rpm. In contrast, the stirring movement during the loading sheet coating was 0 rpm. The current densities at the anode and at the cathode were kept constant. The cathodic current density was I _k = 2.5 A / dm ² , the anodic current density was I _a = 15 A / dm ² .

• Kathodenmaterial: Stahlblech aus Kaltbandstahl gemäß DIN EN 10139/10140 (Qualität: DC03 LC MA RL)
• Anodenmaterialien:
  Vergleichsanode 2: Glanzvernickelter Stahl; Stahl (Werkstoffnummer 1.0330) mit einer Schichtauflage von 30 µm Glanznickel (beschichtet mit SLOTONIK 20 Elektrolyt der Fa. Schlötter);
• Herstellung: Siehe hierzu J. N. Unruh, Tabellenbuch Galvanotechnik, 7. Auflage, EUGEN G. LEUZE Verlag, Bad Saulgau, S.515 )
  Erfindungsgemäße Anode 3: Stahl (Werkstoffnummer 1.0330) mit einer durch thermisches Spritzen darauf aufgebrachten Mangan-Eisen-Oxidschicht (im Folgenden als "Mn-Fe-Oxidanode" definiert);
• Herstellung: Ein 2 mm dickes Stahlblech (Werkstoffnummer 1.0330) wurde entfettet, mit Korundstrahlen (Strahlgut ist hierbei Zirkonkorund) aufgeraut und anschließend mit Druckluft von anhaftenden Resten befreit. Das Stahlblech wurde dann zur Verbesserung des Haftgrundes mittels Lichtbogenspritzen zunächst mit Nickel thermisch bespritzt. Dabei wurde ein Nickeldraht im Lichtbogen (Temperatur am Brennerkopf 3000 bis 4000°C) abgeschmolzen und mit Druckluft (6 bar) als Zerstäubergas in einem Abstand von 15 bis 18 cm auf das Stahlblech aufgespritzt. Anschließend wurde die Mangan-Eisen-Oxidschicht mittels Pulver-Flammspritzen thermisch aufgespritzt. Als Beschichtungsmaterial wurde eine Mischung aus 90 Gew.% metallischem Manganpulver (-325 mesh, ≥99%ig von Sigma Aldrich) und 10 Gew.% metallischem Eisenpulver (-325 mesh, 97%ig von Sigma Aldrich) verwendet. Es wurde dabei darauf geachtet, dass die beiden Pulver vor dem thermischen Spritzvorgang homogen miteinander vermischt wurden. Anschließend wurde die metallische Mangan-Eisen-Mischung in einer Acetylen-Sauerstoff-Flamme (Temperatur der Brennerflamme betrug 3160°C) geschmolzen und mit Druckluft (maximal 3 bar) als Zerstäubergas in einem Abstand von 15 bis 20 cm auf das Stahlblech aufgespritzt. Durch schwenkende Bewegungen wurde so lange beschichtet, bis eine gleichmäßige, ca. 250 µm dicke thermisch gespritzte Mangan-Eisen-Oxidschicht erzeugt worden ist.
  Erfindungsgemäße Anode 4: Stahl (Werkstoffnummer 1.0330) mit einer durch thermisches Spritzen darauf aufgebrachten Mangan-Nickel-Oxidschicht (im Folgenden als "Mn-Ni-Oxidanode" definiert);
• Herstellung: Ein 2 mm dickes Stahlblech (Werkstoffnummer 1.0330) wurde entfettet, mit Korundstrahlen (Strahlgut ist hierbei Zirkonkorund) aufgeraut und anschließend mit Druckluft von anhaftenden Resten befreit. Das Stahlblech wurde dann zur Verbesserung des Haftgrundes mittels Lichtbogenspritzen zunächst mit Nickel thermisch bespritzt. Dabei wurde ein Nickeldraht im Lichtbogen (Temperatur am Brennerkopf 3000 bis 4000°C) abgeschmolzen und mit Druckluft (6 bar) als Zerstäubergas in einem Abstand von 15 bis 18 cm auf das Stahlblech aufgespritzt. Anschließend wurde die Mangan-Nickel-Oxidschicht mittels Pulver-Flammspritzen thermisch aufgespritzt. Als Beschichtungsmaterial wurde eine Mischung aus 80 Gew.% metallischem Manganpulver (-325 mesh, ≥99%ig von Sigma Aldrich) und 20 Gew.% metallischem Nickelpulver (-325 mesh, ≥99%ig von Alfa Aesar) verwendet. Es wurde dabei darauf geachtet, dass die beiden Pulver vor dem thermischen Spritzvorgang homogen miteinander vermischt wurden. Anschließend wurde die metallische Mangan-Nickel-Mischung in einer Acetylen-Sauerstoff-Flamme (Temperatur der Brennerflamme betrug 3160°C) geschmolzen und mit Druckluft (maximal 3 bar) als Zerstäubergas in einem Abstand von 15 bis 20 cm auf das Stahlblech aufgespritzt. Durch schwenkende Bewegungen wurde so lange beschichtet, bis eine gleichmäßige, ca. 250 µm dicke thermisch gespritzte Mangan-Nickel-Oxidschicht erzeugt worden ist.

The following anode and cathode materials were used:

• Cathode material: Cold-rolled steel sheet in accordance with DIN EN 10139/10140 (quality: DC03 LC MA RL)
• Anode materials:
  Comparative anode 2: bright nickel-plated steel; Steel (material number 1.0330) with a layer of 30 µm bright nickel (coated with SLOTONIK 20 electrolyte from Schlötter);
• Manufacturing: See here JN Unruh, table book electroplating, 7th edition, EUGEN G. LEUZE Verlag, Bad Saulgau, p.515 )
  Anode 3 according to the invention: steel (material number 1.0330) with a manganese-iron oxide layer applied to it by thermal spraying (hereinafter defined as "Mn-Fe oxide anode");
• Production: A 2 mm thick steel sheet (material number 1.0330) was degreased, roughened with corundum blasting (blasting material is zirconium corundum) and then freed of adhering residues with compressed air. The steel sheet was then first thermally sprayed with nickel by means of arc spraying in order to improve the adhesive base. A nickel wire was melted in the arc (temperature at the burner head 3000 to 4000 ° C) and sprayed onto the steel sheet at a distance of 15 to 18 cm using compressed air (6 bar) as atomizing gas. The manganese-iron oxide layer was then thermally sprayed on using powder flame spraying. A was used as the coating material Mixture of 90% by weight of metallic manganese powder (-325 mesh, ≥99% from Sigma Aldrich) and 10% by weight of metallic iron powder (-325 mesh, 97% from Sigma Aldrich) was used. Care was taken to ensure that the two powders were homogeneously mixed with one another before the thermal spraying process. The metallic manganese-iron mixture was then melted in an acetylene-oxygen flame (temperature of the burner flame was 3160 ° C.) and sprayed onto the steel sheet at a distance of 15 to 20 cm using compressed air (maximum 3 bar) as atomizing gas. The coating was carried out by swiveling movements until a uniform, approximately 250 μm thick, thermally sprayed manganese-iron oxide layer was produced.
  Anode 4 according to the invention: steel (material number 1.0330) with a manganese-nickel oxide layer applied to it by thermal spraying (hereinafter defined as "Mn-Ni oxide anode");
• Production: A 2 mm thick steel sheet (material number 1.0330) was degreased, roughened with corundum blasting (blasting material is zirconium corundum) and then freed of adhering residues with compressed air. The steel sheet was then first thermally sprayed with nickel by means of arc spraying in order to improve the adhesive base. A nickel wire was melted in the arc (temperature at the burner head 3000 to 4000 ° C) and sprayed onto the steel sheet at a distance of 15 to 18 cm using compressed air (6 bar) as atomizing gas. The manganese-nickel oxide layer was then thermally sprayed on using powder flame spraying. A mixture of 80% by weight of metallic manganese powder (-325 mesh, ≥99% from Sigma Aldrich) and 20% by weight of metallic nickel powder (-325 mesh, ≥99% from Alfa Aesar) was used as the coating material. Care was taken to ensure that the two powders were homogeneously mixed with one another before the thermal spraying process. The metallic manganese-nickel mixture was then heated in an acetylene-oxygen flame (temperature of Burner flame was 3160 ° C) melted and sprayed with compressed air (maximum 3 bar) as atomizing gas at a distance of 15 to 20 cm on the steel sheet. The coating was carried out by swiveling movements until a uniform, approximately 250 μm thick, thermally sprayed manganese-nickel oxide layer was produced.

• SLOTOLOY ZN 86: 1 ml (entspricht einer Zugabemenge von 1 l/10kAh)
• SLOTOLOY ZN 83: 0,3 ml (entspricht einer Zugabemenge von 0,3 l/10kAh)

Nach einer durchgesetzten Strommenge von jeweils 2,5 Ah/l wurde die auf dem Abscheidungsblech (Kathode) vorhandene abgeschiedene Zinknickellegierungsmenge durch Auswaage ermittelt. Die durch die Abscheidung im Zinknickelelektrolyten fehlende Gesamtmetallmenge wurde auf 85 Gew. % Zink und 15 Gew. % Nickel umgerechnet (beispielsweise sind für eine abgeschiedene Gesamtmetallmenge von 1,0 g Zinknickellegierungsschicht 850 mg Zink und 150 mg Nickel zudosiert worden). Das im Elektrolyten verbrauchte Zink wurde als Zinkoxid zugegeben, das verbrauchte Nickel wurde über das nickelhaltige Flüssigkonzentrat SLOTOLOY ZN 85 ergänzt. In SLOTOLOY ZN 85 sind Nickelsulfat, sowie die Amine Triethanolamin, Diethylentriamin und Lutron Q 75 enthalten (1 ml SLOTOLOY ZN 85 enthält 63 mg Nickel).After a current of 5 Ah / l had been passed through, the following brighteners or fine-grain additives were added to the zinc nickel electrolyte:

• SLOTOLOY ZN 86: 1 ml (corresponds to an addition of 1 l / 10kAh)
• SLOTOLOY ZN 83: 0.3 ml (corresponds to an addition of 0.3 l / 10kAh)

After a current of 2.5 Ah / l had been passed through, the amount of zinc-nickel alloy deposited on the deposition plate (cathode) was determined by weighing. The total amount of metal missing due to the deposition in the zinc-nickel electrolyte was converted to 85% by weight of zinc and 15% by weight of nickel (for example, 850 mg of zinc and 150 mg of nickel were added for a total amount of metal deposited from 1.0 g of zinc-nickel alloy layer). The zinc used in the electrolyte was added as zinc oxide, the used nickel was supplemented with the nickel-containing liquid concentrate SLOTOLOY ZN 85. SLOTOLOY ZN 85 contains nickel sulfate, as well as the amines triethanolamine, diethylene triamine and Lutron Q 75 (1 ml SLOTOLOY ZN 85 contains 63 mg nickel).

The NaOH content was determined after 10 Ah / l by acid-base titration and adjusted to 120 g / l in each case.

Execution of the experiment and results:

The amount of cyanide formed was determined after a current of 50 Ah / l had passed through.
The results of the analytical determination as a function of the bath load are shown in Table 11. [Table 11] anode Anode material Cyanide content (mg / l) after 50 Ah / l exposure Comparative anode 2 bright nickel-plated steel anode 130 Anode 3 according to the invention Mn-Fe oxide anode 42 Anode 4 according to the invention Mn-Ni oxide anode 75

The cyanide was determined using the cuvette test LCK 319 for easily releasable cyanides from Dr. Lange (today Hach company). Easily released cyanides are converted into gaseous HCN by a reaction and transferred through a membrane into an indicator cuvette. The color change of the indicator is then evaluated photometrically.

As shown in Table 11, the use of anodes 3 and 4 according to the invention resulted in significantly less cyanide formation than in comparison anode 2 (bright nickel-plated steel).

Furthermore, the amount of additives still present was determined after a current of 50 Ah / l had been passed through. The results of the analytical determination of the organic bath additives, ie amine-containing complexing agents, such as DETA and TEA and Lutron Q 75, as a function of the bath load are shown in Table 12. [Table 12] anode Anode material After 50 Ah / l load DETA (g / l) TEA (85% by weight) (g / l) Lutron Q 75 (g / l) Comparative anode 2 bright nickel-plated steel anode 8.0 9.1 42.1 Anode 3 according to the invention Mn-Fe oxide anode 10.0 9.8 41.7 Anode 4 according to the invention Mn-Ni oxide anode 9.8 9.7 41.5

As shown in Table 12, significantly less amines (DETA and TEA) were consumed using the anodes 3 and 4 according to the invention than using the comparison anode 2. These substances were consequently less strongly oxidized on the anodes 3 and 4 according to the invention and therefore have to be used to a lesser extent Measurements are added. This offers a not inconsiderable cost advantage in terms of process costs.

Claims (12)

1. Method for the galvanic deposition of zinc-nickel layers from an alkaline coating bath containing zinc-nickel electrolytes and organic bath additives, which method uses, as the anode, an electrode that is insoluble in the bath and that contains metal manganese and/or manganese oxide, wherein the organic bath additives comprise amine-containing complexing agents, and wherein the electrode

   1) is produced from metal manganese or a manganese-containing alloy, wherein the manganese-containing alloy contains at least 5 wt.% manganese, or

   2) is produced from an electrically conductive substrate and a coating applied thereto and containing metal manganese and/or manganese oxide, wherein the coating containing manganese and/or manganese oxide contains at least 5 wt.% manganese, based on the total amount of manganese that is obtained from metal manganese and manganese oxide, or

   3) is produced from a composite material that comprises metal manganese and/or manganese oxide and an electrically conductive material, wherein the composite material contains at least 5 wt.% manganese, based on the total amount that is obtained from metal manganese and manganese oxide.
2. Method according to claim 1, wherein the manganese-containing alloy is selected from a manganese-containing steel alloy or a manganese-containing nickel alloy.
3. Method according to any of claims 1 and 2, wherein the manganese-containing alloy contains 10-90 wt.% manganese, particularly preferably 50-90 wt.% manganese.
4. Method according to claim 1, wherein the electrically conductive substrate is selected from steel, titanium, nickel or graphite.
5. Method according to any of claims 1 and 4, wherein the coating containing metal manganese and/or manganese oxide is applied to the substrate by means of thermal spraying of metal manganese or a mixture of metal manganese and iron and/or nickel.
6. Method according to any of claims 1 and 4, wherein the coating containing metal manganese and/or manganese oxide is applied to the substrate by means of deposition welding of metal manganese or a mixture of metal manganese and iron and/or nickel.
7. Method according to any of claims 1 and 4, wherein the coating containing metal manganese and/or manganese oxide is applied to the substrate by means of vapour deposition.
8. Method according to any of claims 1 and 4 to 7, wherein the coating containing metal manganese and/or manganese oxide contains 10-100 wt.% manganese, particularly preferably 50-100 wt.% manganese, and most preferably 80-100 wt.% manganese, based on the total amount of manganese that is obtained from metal manganese and manganese oxide.
9. Method according to claim 1, wherein the electrically conductive material of the composite material is carbon, preferably graphite.
10. Method according to any of claims 1 and 9, wherein the composite material contains at least 10 wt.% manganese, particularly preferably at least 50 wt.% manganese.
11. Use of metal manganese or a manganese-containing alloy, such as that defined in any of claims 1 to 3, or an electrically conductive substrate having a coating applied thereto and containing metal manganese and/or manganese oxide, such as that defined in any of claims 1 and 4 to 8, or a composite material that comprises metal manganese and/or manganese oxide and an electrically conductive material, such as that defined in any of claims 1, 9 and 10, as the anode for the galvanic deposition of zinc-nickel layers from an alkaline coating bath containing zinc-nickel electrolytes and organic bath additives comprising amine-containing complexing agents.
12. Galvanic device for depositing zinc-nickel layers from an alkaline coating bath containing zinc-nickel electrolytes and organic bath additives, which device comprises, as the anode, an insoluble electrode containing metal manganese and/or manganese oxide, such as that defined in any of claims 1-10, and comprises an alkaline coating bath containing zinc-nickel electrolytes and organic bath additives comprising amine-containing complexing agents.