EP3358045A1 - 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

Abstract

The present invention relates to a process for the electrodeposition of zinc and zinc alloy coatings from an alkaline coating bath with reduced degradation of organic bath additives. In this case, the anode used is an electrode which is insoluble in the bath and contains metallic manganese and / or manganese oxide, which is produced from metallic manganese or a manganese-containing alloy, the manganese-containing alloy containing at least 5% by weight of manganese, or from an electrically conductive support and a metallic manganese and / or manganese oxide-containing coating applied thereto, or made of a composite material, wherein both the metallic manganese and / or manganese oxide-containing coating and the composite material comprise at least 5 wt% manganese, based on the total amount of manganese , which results from metallic manganese and manganese oxide contains. The inventive method is particularly suitable for the galvanic deposition of Zinknickellegierungsüberzügen from alkaline zinc nickel baths, since the formation of cyanides can be suppressed very effectively.

Description

Technical area

The present invention relates to a process for the electrodeposition of zinc and zinc alloy coatings from an alkaline coating bath with zinc and zinc alloying electrolytes and organic bath additives, e.g. Complexing agents, brighteners and wetting agents. The invention further relates to the use of materials as an anode for the electrodeposition of a zinc and zinc alloy coating from an alkaline coating bath with zinc and zinc alloying electrolytes and organic bath additives, and to a corresponding galvanic apparatus for the deposition of zinc and zinc alloy coatings.

Technical background

Alkaline zinc and zinc alloy baths are typically not operated with soluble zinc anodes. In 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, the Zn [(OH) ₄ ] ^2- , with the surrounding hydroxide ions. Zinc, in addition to electrochemical dissolution, is oxidized by the alkaline environment to Zn (II) to form hydrogen. This means that the zinc anode additionally dissolves chemically by the abovementioned redox reaction, which leads to an uncontrolled increase in the Zn (II) concentration in the zinc alloy electrolyte.

This requires, on the one hand, a reduction in process reliability and, on the other hand, the necessity of having to carry out further analyzes to determine the additionally dissolved zinc content in order to be able to correctly adjust 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 added to the bath.

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

In the operation of alkaline coating baths for electrodeposition of a zinc or zinc alloy coating, organic bath additives such as complexing agents, brighteners and wetting agents are usually used in addition to the zinc or zinc alloy electrolyte.

In practice, it is unavoidable that oxygen is not only selectively generated on the surface of the insoluble anode. In part, 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 must be added to additives. The process costs are inevitably driven up in the course of this.

The anodic oxidation of the organic bath additives also undesirable by-products, such as oxalates, carbonates, etc., can be formed, which can interfere with the galvanic coating process.

Especially with alkaline zinc and zinc alloy baths, where working with amine-containing complexing agents, an increased formation of cyanides can be observed by the unwanted anodic oxidation of the amine-containing additives.

Amine-containing complexing agents are used, for example, in coating baths for the electrodeposition of a zinc nickel alloy coating. The nickel is used in the form of Ni (II), which forms a sparingly soluble nickel hydroxide complex in an alkaline medium with the surrounding hydroxide ions. Alkaline zinc nickel electrolytes must therefore contain special complexing agents with which Ni (II) is more preferably complexed than with the hydroxide ions in order to bring the nickel into solution in the form of Ni (II). Preferred are amine compounds, such as triethanolamine, ethylenediamine, diethylenetetramine or homologous compounds of ethylenediamine, e.g. Diethylenetriamine, tetraethylenepentamine, 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 of cyanide can be established in the practice electrolyte until an equilibrium of regeneration and carry-over is achieved. The formation of cyanides is disadvantageous for several reasons.

When disposing of alkaline zinc and zinc alloy baths, as well as the flushing effluents that occur during operation, certain limits must be met and monitored. A commonly required limit for cyanide contamination in wastewater is 1 mg / l. Due to national or regional legislation, the permitted limits for cyanide contamination in wastewater may still be below this level. The cyanides formed must therefore be detoxified consuming. This is done in practice by oxidation, e.g. with sodium hypochlorite, hydrogen peroxide, sodium peroxodisulfate, potassium peroxomonosulfate or similar compounds. In addition, the removed electrolyte contains other oxidizable substances in addition to the cyanide, so much more oxidizing agent is consumed for complete oxidation than theoretically could be determined from the cyanide content.

Besides the above aspect, increased cyanide formation further causes the problem that unwanted complexes with the bath additives can be formed.

From a technical point of view, the cyanide content is very disadvantageous when using a zinc nickel electrolyte, since nickel with the cyanide ions formed forms the stable tetracyanonickelate complex, Ni [(CN) _4] ^2- , as a result of which the nickel bound in this complex is no longer available for deposition Available. Since it is not possible to differentiate between the complexed by cyanide and the complexed by the amines nickel in the current electrolyte analysis, the increase of the cyanide content in the electrolyte means a reduction in process safety.

The deposition of Zinknickellegierungsüberzügen with a share of 10-16 wt.% Nickel causes a very good corrosion protection on components made of ferrous materials and has therefore a high importance for technical corrosion protection. For the coating of components, in particular of accessories for automobile production, strongly alkaline electrolytes are used for the deposition of zinc nickel alloy coatings in order to ensure a uniform layer thickness distribution even on complex three-dimensional geometries of the components to be coated. In order 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 meet the required alloy composition of 10-16 wt.% Nickel over the entire current density range, the nickel concentration must be adjusted in the course of operation according to the cyanide concentration in the electrolyte, since the complexed by cyanide nickel content is not available for deposition stands. With the increase in the cyanide content in the electrolyte, the nickel content must therefore be adjusted accordingly in order 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 supplemental solutions are nickel salts which have a high water solubility. Nickel sulfate solutions in combination with various amine compounds are preferably used for this purpose.

The effects of a cyanide concentration of 350 mg / l in a commercial Zinknickellegierungsbad (Zinknickellegierungsbad SLOTOLOY ZN 80, Messrs. Schlötter) are shown in Table 1 in the following examples. [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 2 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) 2 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 2 49 13.9 0.5 80 14.6

The above experiments demonstrate that deliberate addition of 350 mg / L cyanide to a newly prepared zinc nickel alloying bath SLOTOLOY ZN 80 reduces the nickel incorporation rate at a deposition current density of 2 A / dm ² from 14.3 wt% to 8.1 wt%. To bring the alloy composition back within the specified range of 10-16 wt%, an addition of 0.6 g / l nickel is necessary. This means over the new approach, a doubling of the nickel content in the electrolyte.

The accumulation of cyanide in a zinc nickel alloy electrolyte can also adversely affect the optical appearance of the deposit. It can come in the high current density range to a milky veiled deposition. This can be partially corrected by higher dosage of brighteners again. However, this measure is associated with an increased consumption of brighteners and thereby additional costs in the deposition.

In addition, if the cyanide concentration in a zinc nickel alloy electrolyte reaches values of about 1000 mg / l, it may be necessary to partially renew the electrolyte, which in turn reduces the process costs Height drives. In addition, fall in such partial bath renovations large amounts of waste electrolytes, which must be disposed of consuming.

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.

There are some starting points in the prior art in order to solve the problem described above:

• In EP 1 344 850 B1 a method is claimed in which the cathode space and the anode space are separated by an ion exchange membrane. This prevents the complexing agents from getting out of the cathode compartment to the anode. Cyanide formation is thereby prevented. The anode used is a platinized titanium anode. The anolyte is acidic and contains sulfuric acid, phosphoric acid, methanesulfonic acid, amidosulfonic acid and / or phosphonic acid.

A similar procedure is in EP 1 292 724 B1 described. Here also cathode and anode compartment are separated by an ion exchange membrane. As anolyte, a sodium or potassium hydroxide solution is used. As the anode, a metal or metal coating is selected from the group consisting of nickel, cobalt, iron, chromium or alloys thereof.

Both processes reduce the formation of cyanides. A disadvantage of both methods is that very high investment costs arise from the incorporation of the ion exchange membranes. In addition, a device for separate circulation of the anolyte must be installed. The incorporation of ion exchange membranes is also not generally feasible in zinc nickel deposition processes. To increase the productivity and thus to reduce the coating costs, auxiliary anodes are often used to seal the frames when the hangers are tightly sealed To optimize layer thickness distribution. For technical reasons, it is not possible here to separate these auxiliary anodes by ion exchange membranes. Therefore, cyanide formation can not be completely avoided in this application.

EP 1 702 090 B1 claims a method which provides for the separation of the cathode and anode compartments through an open cell material. The separator is made of polytetrafluoroethylene or polyolefin, such as polypropylene or polyethylene. The pore diameters have a dimension between 10 nm and 50 μm. In contrast to the use of ion exchange membranes, where the charge transport through the membrane is carried out by the exchange of cations or anions, it can be carried out with the use of open-cell separators only by the electrolyte transport through the separator. Complete separation of the catholyte from the anolyte is not possible. It can therefore not be completely prevented that amines reach the anode and are oxidized there. Cyanide formation is therefore not completely ruled out in this process.

A disadvantage of this method also that when using separators with a very small pore diameter (eg 10 nm) of the electrolyte exchange and thus the current transport is very much hindered, which leads to an overvoltage. Although the overvoltage is claimed to be less than 5 volts, a bath voltage of at most 5 volts overvoltage would still be nearly doubled compared to a process which operates without separation of the cathode and anode compartments. This results in a much higher energy consumption during the deposition of the zinc nickel layers. The up to 5 volts higher bath voltage also causes a strong heating of the electrolyte. Since the electrolyte temperature in the range of +/- 2 ° C should be kept constant for the deposition of a constant alloy composition, when applying a higher bath voltage of the electrolyte can be cooled by considerable effort. Although it is described that the separator may also have a pore diameter of 50 microns, which may prevent the formation of overvoltage, but the relatively large pore diameter again allows a virtually unhindered exchange of electrolyte between the cathode and anode space and thus can not prevent the formation of cyanides.

A similar concept will be used in the EP 1 717 353 B1 described. The anode and cathode space is 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 deliberately accepted.

When using certain organic brighteners, zinc nickel electrolytes do not work satisfactorily when membrane processes accordingly EP 1 344 850 or EP 1 292 724 be used. These brighteners obviously require anodic activation to produce their full effect. This reaction is when using filtration membranes, as in EP 1 717 353 described, guaranteed. However, this also means that the formation of cyanides can not be completely avoided. Table 4 of the EP 1 717 353 it can be seen that when the filtration membranes are used at a bath load of 50 Ah / l, a new formation of 63 mg / l of cyanide takes place. Without the use of filtration membranes, a new formation of 647 mg / l cyanide occurs under otherwise identical conditions. The use of filtration membranes can thus reduce the formation of cyanide by about 90%, but not completely prevent it.

All of the abovementioned membrane processes also have the disadvantage that they have a considerable space requirement in a bath container of a zinc-nickel electrolyte. One Subsequent installation in an existing system is therefore usually not possible due to space limitations.

Further, 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 patent application describes that this process is suitable for reducing cyanometallate complexes in wastewaters. Accordingly, it is in the treatment of in DE 103 45 594 A1 described cyanide-containing aqueous solutions aim to remove existing cyanides and cyanometalate complexes from the wastewater. This is in contrast to the object of the present invention, in which only the formation of cyanides is to be prevented.

task

The object of the present invention is to provide a process for the electrodeposition of zinc and zinc alloy coatings from an alkaline coating bath with zinc and zinc alloying electrolytes and organic bath additives, which has a reduced anodic oxidation and a concomitant reduced degradation of the organic bath additives, such as complexing agents, brighteners, wetting agents, etc., as well as a reduced formation of undesirable degradation products, such as cyanides causes. The method according to the invention should make it possible to be integrated into existing alkaline zinc and zinc alloy baths without additional effort, and to allow a significantly more economical operation of the method.

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 above-defined object is achieved by providing a method for the electrodeposition of zinc and zinc alloy coatings from an alkaline coating bath with zinc and zinc alloying electrolytes and organic bath additives, in which the anode used is a bath-insoluble, metallic manganese and / or manganese oxide-containing electrode will the

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

Surprisingly, it has been found that the use of insoluble, metallic manganese and / or manganese oxide-containing electrodes, as described above, has a very positive effect on reducing the degradation of organic bath additives, such as complexing agents, brighteners, wetting agents, etc. This is particularly advantageous in coating baths with amine-containing complexing agents, as in the course of lesser degradation of the amine compounds also At the same time a significant reduction of the cyanide concentration occurs.

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

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

full electrodes

In the process of the present invention, electrodes made of metallic manganese or a manganese-containing alloy and 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 manganese-containing steel alloy is particularly preferred. The alloy content of the manganese-containing alloy has a manganese content of at least 5% by weight of manganese, preferably 10 to 90% by weight of manganese, particularly preferably 50 to 90% by weight of manganese. Commercially available steel electrodes have, for example, a manganese content of 12% by weight of manganese (X120Mn12 with the material number: 1.3401) or 50% by weight of manganese (mirror iron).

Coated carrier electrodes

In addition to the above-mentioned solid electrodes made of metallic manganese or a manganese-containing alloy, there are also electrodes made of an electrically conductive substrate suitable for use as an insoluble anode in an alkaline zinc and zinc alloy bath with metallic manganese deposited thereon and / or manganese oxide-containing coating in question. The support material is preferably selected from steel, titanium, nickel or graphite. In the process according to the invention, the use of steel as carrier material is particularly preferred. The metallic manganese and / or manganese oxide-containing coating 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, which results from metallic manganese and manganese oxide, on.

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

Thermal spraying

As already explained 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 of both 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 manganese or more, preferably 90% by weight manganese or more, particularly preferably 100% by weight manganese.

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

Conventionally, during thermal spraying inside or outside a spray gun, heated, blown or sprayed spray particles are accelerated by means of atomizing gas (e.g., compressed air or inert gas such as nitrogen and argon) and spun onto the surface of the carrier to be coated. As a result, a good connection to the carrier surface and a firm metallic manganese and / or manganese oxide layer is formed, mainly by mechanical clamping.

In order to achieve a particularly good layer adhesion on the surface of the carrier, additional measures can be taken. Thus, for example, the carrier to be coated can be roughened by corundum blasting prior to the thermal spraying process (blasting material in this case is zirconium corundum). Another possibility is to place an additional primer between the support and the metallic manganese and / or manganese oxide-containing coating. The primer may for example consist of nickel. By using a primer, the adhesion of the thermally sprayed layer on the support is further improved. A primer is preferably applied directly on the carrier surface before the manganese-containing coating material is thermally sprayed on. The primer may be produced by the same thermal spraying method as the metallic manganese and / or manganese oxide-containing coating, for example flame spraying or arc spraying. The primer is usually produced with a layer thickness of 50-100 μm. When a primer is used, the manganese-containing coating material is usually thermally sprayed directly onto the primer.

If no primer is used, the manganese-containing coating material is usually thermally 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 methods. These include: Arc Wire Spraying, Thermo Spray Powder Spraying, Flame Spraying, High Speed Flame Spraying, Plasma Spraying, Autogenous Bar Spraying, Autogenous Wire Spraying, Laser Spraying, Cold Gas Spraying, Detonation Spraying, and Plasma Transferred Wire Arc (PTWA) 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 electric arc spraying. For the use of a powdered manganese-containing coating material is particularly suitable flame spraying.

In powder flame spraying, a distinction is made between self-fluxing and self-adhesive powders. The self-fluxing powders usually additionally require a thermal aftertreatment, whereby the adhesion of the sprayed layer on the carrier is considerably increased. The thermal aftertreatment is usually carried out with acetylene-oxygen burners. As a result of the thermal aftertreatment, the sprayed layer becomes both gas-tight and liquid-tight, for which reason 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 up to several millimeters can be applied to the carrier by means of the abovementioned method.

Furthermore, the thermal spraying can be carried out both under an air atmosphere and under an inert gas atmosphere. This can usually be regulated by the type of nebulizer gas. When using an inert gas, such as nitrogen or argon, as a sputtering gas oxidation of the manganese-containing coating material is largely prevented. Thus, for example, a manganese layer of metallic manganese or a manganese alloy can be applied to the carrier. In the process according to the invention, manganese oxides would then form in the course of the electrodeposition process on the carrier anode with the metallic manganese or manganese alloy layer applied thereon, which constitute the active surface. Alternatively, these can also be applied in advance on the carrier. This has the advantage that the active surface does not first have to form during the electrodeposition process, so that a positive effect, ie suppression of the anodic oxidation of the organic bath additives, becomes visible after a short time. By the use of eg compressed air are formed by the high temperatures of the manganese-containing coating material used oxidation products which solidify on the surface of the lining with the melt and thus form an adherent film. The manganese-containing coating material sprayed under air atmosphere then contains, in addition to metallic, a layer applied to the carrier Manganese and optionally iron and / or nickel and manganese oxides, and optionally iron oxides and / or nickel oxides or combinations thereof.

Cladding

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

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

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

Usually, during buildup welding, both the coating material and a thin surface layer of the carrier to be coated are melted by suitable energy sources and metallurgically bonded together. As a result of the diffusion and mixing of the coating material with the carrier material, an adherent and non-porous layer is produced. Overlay welding differs essentially 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 support by means of conventional build-up welding methods be applied. Suitable sources of energy include: arc, flame, Joule heat, plasma jet, 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 or more can be applied to the carrier by means of the abovementioned methods. For this purpose, the energy source is guided in pendulum movements over the carrier, whereby the manganese-containing coating material is then applied in individual layers.

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

Vapor deposition

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

The manganese-containing coating material used for the physical vapor deposition is usually metallic manganese, but others for this Process suitable manganese-containing solids, such as manganese oxide, are used.

The manganese-containing coating material may be applied to the support by conventional vapor deposition techniques. The processes of physical vapor deposition 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 methods.

Usually, in the PVD method, the manganese-containing coating material is atomized by bombardment with laser beams, magnetically deflected ions, electrons or by arc discharge (eg during sputtering) or brought into the gas phase (eg during evaporation) and subsequently as a manganese-containing solid to deposit on the surface of the carrier to be coated.

In order for the gaseous manganese-containing coating material to reach the support to be coated, the process must be carried out under reduced pressure of about 10 ^-4 - 10 Pa.

From a technical point of view, layer thicknesses of 100 nm-2 mm can be applied to the substrate by means of PVD methods.

composite anodes

In addition to the manganese-containing full electrodes and metallic manganese and / or manganese oxide coated carrier electrodes, electrodes consisting of a composite material comprising metallic manganese and / or manganese oxide and a conductive material are also suitable. As a conductive Material can be used for example carbon, preferably graphite.

The metallic manganese and / or manganese oxide-containing composite material has a manganese content of at least 5 wt.% Manganese, preferably at least 10 wt.% Manganese, more preferably at least 50 wt.% Manganese, based on the total amount of manganese, which consists of metallic Manganese and manganese oxide yields.

The manner of preparation of such a manganese-containing composite electrode is not particularly limited. Therefore, common methods such as sintering or pressing with binder are 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 and zinc alloy baths

In the method for electrodepositing a zinc and zinc alloy coating from an alkaline electrolyte according to the present invention, the zinc and zinc alloy baths are not particularly limited as long as they are alkaline and contain organic bath additives such as complexing agents, brighteners, wetting agents, etc.

A typical zinc and zinc alloy bath for the process according to the invention is, for example, an alkaline zinc nickel alloy bath. Such a zinc nickel alloying bath is used for depositing a zinc nickel alloy plating from an alkaline zinc nickel electrolyte on a cathode connected substrate. This contains in the new batch typically a zinc ion concentration in the range of 5 to 15 g / l, preferably 6 to 10 g / l calculated as zinc, and a nickel ion concentration in the range of 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. Usable are, for example, nickel sulfate, nickel chloride, nickel sulfamate or nickel methanesulfonate. Particularly preferred is the use of nickel sulfate.

Further, the alkaline zinc and zinc alloy baths contain organic bath additives such as complexing agents, brighteners, wetting agents, etc.

In particular, when using zinc nickel electrolytes, the addition of complexing agents is inevitable because 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 can be used. Preferred are amine compounds such as triethanolamine, ethylenediamine, tetrahydroxopropylethylenediamine (Lutron Q 75), diethylenetetramine, or homologous compounds of ethylenediamine, e.g. Diethylenetriamine, tetraethylenepentamine, etc., used. The complexing agent and / or mixtures of these complexing agents is / are usually used in a concentration in the range of 5 to 100 g / l, preferably 10 to 70 g / l, more preferably 15 to 60 g / l.

Additionally, brighteners are commonly used in zinc and zinc alloy baths. These are not particularly limited, and any known brighteners may be used. Aromatic or heteroaromatic compounds, such as benzylpyridiniumcarboxylate or pyridinium-N-propane-3-sulphonic acid (PPS), are preferably used as brighteners.

Furthermore, the electrolyte used in the process according to the invention is basic. To adjust the pH, for example, but not limited to, sodium hydroxide and / or potassium hydroxide can be used. Particularly preferred is sodium hydroxide. The pH of the aqueous alkaline solution is usually 10 or more, preferably 12 or more, more preferably 13 or more. Thus, a zinc nickel bath usually contains 80-160 g / l of 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 a galvanic coating process for depositing a zinc or zinc alloy coating from an alkaline electrolyte may be used. In the method according to the invention, therefore, substrates of steel, hardened steel, forged or die-cast zinc can therefore 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 Zink- und Zinklegierungsüberzügen aus einem alkalischen Beschichtungsbad mit Zink- und Zinklegierungselektrolyten und organischen Badzusätzen.In addition to the methods described above, the invention further relates to the use

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

as an anode for the electrodeposition of zinc and zinc alloy coatings from an alkaline coating bath with zinc and zinc alloy electrolytes and organic bath additives.

Furthermore, a galvanic device for depositing zinc and zinc alloy coatings from an alkaline coating bath with zinc and zinc alloying electrolytes and organic bath additives is provided which contains as the anode an insoluble, metallic manganese and / or manganese oxide-containing electrode as described above.

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.

In the following the invention will be explained in more detail by means 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. Here, 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 enforced For example, the zinc nickel electrolyte was investigated with respect to the degradation products forming at the anode, such as cyanide. In addition, an analysis of the organic complexing agents and brighteners was carried out.

Test conditions:

The base bath batch (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 (base gloss additive) SLOTOLOY ZN 83: 2.5 ml / l (base gloss additive) SLOTOLOY ZN 86: 1.0 ml / l (top gloss)

The above base bath mixture contains: 10.0 g / l DETA (diethylenetriamine), 9.4 g / l TEA (85% by weight triethanolamine), 40.0 g / l Lutron Q 75 (BASF; 75% by weight tetrahydroxopropylethylenediamine) and 370 mg / l PPS (1- (3-sulfopropyl) pyridinium betaine).

The bath temperature was adjusted to 35 ° C. The agitation during the power pulp coating was 250 to 300 rpm. By contrast, the stirring movement during the load plate 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)

The following anode or cathode materials were used:

• Cathode material: Cold rolled steel sheet steel according to 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 coating layer of 30 μm bright nickel (coated with SLOTONIK 20 electrolyte from Schlötter);
  Production: See JN balance, Tables Galvanotechnik, 7th edition, EUGEN G. LEUZE Verlag, Bad Saulgau, p.515)
• Comparative anode 3: steel (material number 1.0330) having an iron oxide layer (hereinafter defined as "Fe oxide anode") applied thereto by thermal spraying; 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 sprayed with nickel to improve the primer by arc spraying first with nickel. A nickel wire in the arc (temperature at the burner head 3000 to 4000 ° C) was melted and sprayed with compressed air (6 bar) as atomizing gas at a distance of 15 to 18 cm on the steel sheet. Subsequently, the iron oxide layer was also applied by arc spraying. In this case, an iron wire (so-called iron arc wire with 0.7 wt.% Mn, 0.07 wt.% C and the balance Fe, diameter 1.6 mm) in the arc (temperature at the burner head 3000 to 4000 ° C) melted and sprayed with compressed air (6 bar) as a sputtering gas at a distance of 15 to 18 cm on the steel sheet. By pivoting movements was coated until a uniform, about 300 microns thick thermally sprayed iron oxide layer has been produced.

Anode 1 according to the invention : steel (material number 1.0330) with a manganese oxide layer applied thereto 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 material is zirconium corundum) and then freed of adhering residues with compressed air. The steel sheet was then sprayed with nickel to improve the primer by arc spraying first with nickel. A nickel wire in the arc (temperature at the burner head 3000 to 4000 ° C) was melted and sprayed with compressed air (6 bar) as atomizing gas at a distance of 15 to 18 cm on the steel sheet. Subsequently, the manganese oxide layer was thermally sprayed by means of powder flame spraying. In this case, metallic manganese powder (-325 mesh, ≥99% from Sigma Aldrich) in an acetylene-oxygen flame (temperature of the burner flame was 3160 ° C) melted and with compressed air (maximum 3 bar) as atomizing gas at a distance of 15 to 20 cm sprayed onto the steel sheet. By pivoting movements was coated until a uniform, about 250 microns thick thermally sprayed manganese oxide layer has been generated.

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

After passing through an amount of current of 5 Ah / l, the following brighteners or fine grain additives were metered into the zinc nickel electrolyte:

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

After an enforced amount of current of each 2.5 Ah / l, the deposited zinc nickel alloy amount present on the deposition plate (cathode) was weighed by weight determined. The total amount of metal missing from 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 metered in for a total deposited metal amount of 1.0 g of zinc nickel alloy layer).

The zinc consumed in the electrolyte was added as zinc oxide, and the spent nickel was supplemented by the nickel-containing liquid concentrate SLOTOLOY ZN 85. SLOTOLOY ZN 85 contains nickel sulphate and the amines triethanolamine, diethylenetriamine and Lutron Q 75 (1 ml SLOTOLOY ZN 85 contains 63 mg nickel).

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

Experimental procedure and results:

The amount of cyanide formed was determined in each case after an amount of current of 50 Ah / l and 100 Ah / l. The results of the analytical determination as a function of the bath load are listed in Table 2. [Table 2] anode anode material Cyanide content (mg / l) after 50 Ah / l load Cyanide content (mg / l) after 100 Ah / l load 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 Inventive anode 1 Mn-oxide anode 75 106

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

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

Furthermore, the amount of complexing agents still present was determined in each case after an enforced amount of current of 50 Ah / l and 100 Ah / l. 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 according to 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 oxido anode of this invention. Even after an enforced amount of electricity of 100 Ah / l was the consumption of DETA and TEA using the Mn-Oxidanode according to the invention compared to the comparative Anodes 1 to 3 significantly lower.

Test Example 1.2 Test conditions:

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

Experimental procedure and results:

One straight cold strip steel sheet (DIN EN 10139/10140, quality: DC03 LC MA RL) connected to the cathode with 1 dm ² sheet surface 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 efficiency and the nickel alloy content in the initial state and after an enforced amount of current of 100 Ah / l at cathodic current densities of 0.25, 2.5 and 4 A / dm ^{2 were} determined.

The result of the determination of current efficiency and nickel alloy content 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 Beslastung 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 of the invention // Mn 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 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 an approximately equal nickel alloy content, depending on the applied cathodic current density, a 3 to 8% higher current efficiency could be achieved by using the Mn oxide anode according to the invention after 100 Ah / l load compared to the comparative anode commonly used as a standard anode 2 (bright nickel-plated steel, see Table 5).

As a result of the use of the Mn oxide anode according to the invention, the predefined 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 exposure, the deposition of zinc nickel electrolyte was checked by means of a Hullzellentest according to DIN 50957. The electrolyte temperature was adjusted to 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 for determining the optics and the alloy distribution as a function of the bath load is shown in Schemes 1 and 2.

Scheme 1 shows the result of the test panels coated in a bath operated with Comparative Anodes 1 to 3. Scheme 2 shows the result of the test panel which was coated in a bath operated with the Mn oxido anode of the present invention.

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

The Hullzellenbleche from the zinc nickel electrolyte of the comparative anodes 1 to 3 show only in the range <2 A / dm ² (corresponding to a distance of 4 cm from the right sheet metal edge to the right sheet metal edge) a semi-glossy to shiny appearance. The remaining sheet metal area is semi-glossy to matt.

From Test Examples 1.1 to 1.3 it can be seen 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 found that the amine-containing complexing agents, in particular DETA and TEA, are consumed significantly less, which leads to a reduction of the process costs. Furthermore, a significantly reduced formation of cyanides can be observed. In addition, after 100 Ah / l by using the Mn Oxidanode according to the invention, depending on the current density, a 3 to 8% higher current efficiency can be achieved than with the comparative anode 2, which in turn significantly reduces process costs. In addition to the above aspects, using the Mn oxide anode according to the present invention, even after 100 Ah / l load, no deterioration occurs Shining, compared with the use of comparative anodes 1 to 3.

Test Example 2

The alkaline zinc nickel electrolyte SLOTOLOY ZN 210 (Schlötter) was subjected to load tests using different anode materials. Here, the deposition behavior was analyzed over a longer period of time with a constant cathodic and anodic current density. Depending on the amount of current applied, the zinc-nickel electrolyte has been treated with respect to the degradation products forming at the anode, e.g. Cyanide, studied. In addition, an analysis of the organic complexing agents and brighteners was carried out.

Test conditions:

The base bath batch (2 liters of 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)

The above base bath mixture contains: 22.4 g / l TEPA (tetraethylene pentamine), 10.2 g / l TEA (85 wt%) and 5.4 g / l Lutron Q 75 (BASF; 75 wt% tetrahydroxopropylethylenediamine) and 75 mg / l PPS (1- (3-sulfopropyl) pyridinium betaine).

The bath temperature was adjusted to 28 ° C. The stirring during the load plate coating was 0 rpm. The current densities at the anode, as well as 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)

The following anode or cathode materials were used:

• Cathode material: Cold rolled steel sheet steel according to 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 coating layer of 30 μm bright nickel (coated with SLOTONIK 20 electrolyte from Schlötter);
  Production: See JN balance, Tables Galvanotechnik, 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")

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

After a flow rate of 2.5 Ah / l, the following brighteners or fine grain additives were added to the zinc nickel electrolyte:

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

After an enforced amount of current of each 2.5 Ah / l, the deposited zinc nickel alloy amount present on the deposition plate (cathode) was weighed by weight determined. The total amount of metal missing from 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 metered in for a total deposited metal amount of 1.0 g of zinc nickel alloy layer).

The nickel consumed in the electrolyte was supplemented by the nickel-containing liquid concentrate SLOTOLOY ZN 215. The SLOTOLOY ZN 215 contains nickel sulphate and the amines triethanolamine, tetraethylenepentamine and Lutron Q 75 (1 ml SLOTOLOY ZN 215 contains 70 mg nickel).

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

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 in a manner corresponding to zero current. This leads to zinc dissolution due to the alkalinity of the electrolyte. The zinc content was also analyzed analytically by means of titration in the laboratory.

Experimental procedure and results:

It was determined after an enforced amount of electricity of 50 Ah / l, the amount of cyanide formed.
The results of the analytical determination as a function of the bath load are listed in Table 8. [Table 8] anode anode material Cyanide content (mg / l) after 50 Ah / l load Comparative anode 2 bright nickel plated steel anode 98 Inventive anode 2 Manganese alloy anode 37

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

As shown in Table 8, using the manganese alloy anode of the present invention, significantly less cyanide formation was produced than in Comparative Anode 2 (bright nickel-plated steel).

Furthermore, after an enforced amount of electricity of 50 Ah / l, the amount of remaining additives was determined. The results of the analytical determination of the organic bath additives, ie amine-containing complexing agents, such as TEPA and TEA, and brighteners, such as PPS, depending on 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 Inventive anode 2 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 of the present invention than using Comparative Anode 2. These materials were thus less oxidized on the manganese alloy anode of the present 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 pilot plant. For this purpose, a newly prepared SLOTOLOY ZN 80 (Schlötter) electrolyte was initially operated for about 6 months with four standard anodes of high-gloss nickel-plated steel (comparative anode 2), thereby achieving a cyanide content of 372 mg / l in the zinc nickel electrolyte. After 6 months, the standard anodes of high gloss nickel-plated steel were replaced by manganese alloy anodes according to the invention. The zinc nickel electrolyte was then subjected to another 4 months under the same conditions.

Test conditions:

The base bath batch (200 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: 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 (base gloss additive) SLOTOLOY ZN 83: 2.5 ml / l (base gloss additive) SLOTOLOY ZN 86: 1.0 ml / l (top gloss)

The above base bath mixture contains: 10.0 g / l DETA (diethylenetriamine), 9.4 g / l TEA (85% by weight triethanolamine), 40.0 g / l Lutron Q 75 (BASF; 75% by weight tetrahydroxopropylethylenediamine) 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 25000 Ah.

• Kathodenmaterial: Stahlblech aus Kaltbandstahl gemäß DIN EN 10139/10140 (Qualität: DC03 LC MA RL)

The following anode or cathode materials were used:

• Cathode material: Cold rolled steel sheet steel according to 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 coating layer of 30 μm bright nickel (coated with SLOTONIK 20 electrolyte from Schlötter);
  Production: See JN balance, Tables Galvanotechnik, 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 stress in the pilot plant was carried out under practical conditions, i. that the bath additives, metals and the sodium hydroxide solution were continuously added.

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

The following metered quantities of brighteners or fine grain additives were metered into the zinc nickel electrolyte after an amount of current of 5 Ah / l had been passed through:

• For operation with bright nickel plated steel anodes (comparative anode 2):
  • SLOTOLOY ZN 86: 100 ml (corresponds to an added amount of 1 1 / 10kAh)
  • SLOTOLOY ZN 83: 60 ml (corresponds to an added amount of 0.6 1 / 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 added amount of 0.6 1 / 10kAh)
  • SLOTOLOY ZN 83: 60 ml (corresponds to an added amount of 0.6 1 / 10kAh)

The metered amount of additive SLOTOLOY ZN 86 was deliberately reduced here, since the additional degradation of the manganese alloy anodes according to the invention is lower.

The nickel consumed in the electrolyte was supplemented by the nickel-containing liquid concentrate SLOTOLOY ZN 85. in the SLOTOLOY ZN 85 are nickel sulphate and the amines are triethanolamine, diethylenetriamine and Lutron Q 75 (1 ml of SLOTOLOY ZN 85 contains 63 mg of nickel). The necessary amount of nickel was determined by means of suitable analytical methods (eg 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 in a manner corresponding to zero current. This leads to zinc dissolution due to the alkalinity of the electrolyte. The zinc content was also analyzed analytically by means of titration in the laboratory.

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

In addition, excess carbonate was removed. It is known to the person skilled in the art that the carbonate content in the bath increases during prolonged operation of the electrolyte. In order to be able to keep this constant at a value of less than 60 g / l of sodium carbonate, the carbonate was separated off by means of so-called freezer devices at regular intervals.
Under practical conditions, some dilution of the electrolyte occurs due to removal losses and the necessary freezing of carbonate.

Experimental procedure and results:

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

The results of the analytical determination of cyanide, as well as the organic bath additives as a function of the bath load are listed in Table 10. [Table 10] date Cyanide (mg / l) Zinc (g / l) Nickel (g / l) NaOH (g / l) DETA (g / l) TEA (85% by weight) (g / l) Lutron Q 75 (g / l) SLOTO-LOY ZN 86 (ml / l) 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 18 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 determination of the cyanide was carried out with the cuvette test LCK 319 for easily releasable cyanides from Dr. Ing. Lange (today Hach company). Easily releasable cyanides are converted by a reaction into gaseous HCN and transferred through a membrane into an indicator cuvette. The color change of the indicator is then evaluated photometrically.

From Table 10 it can be seen that with the manganese alloy anodes according to the invention, the cyanide content in Electrolyte within the experimental period (4 months) drops significantly.

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

Under the premise of maintaining a uniform gloss level of the deposited galvanic layer throughout the entire course of the experiment, it was therefore possible to significantly reduce the addition of fine grain and gloss additives, such as PPS, since less fine grain and brightener additive was used up. Therefore, the additive SLOTOLOY ZN 86 containing PPS could be reduced from an addition amount of 100 ml during operation with Comparative Anodes 2 to 60 ml by using the manganese alloy anodes of the present invention.

Furthermore, it can be seen that the amines DETA and TEA are consumed 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 by the use of the manganese alloy anode according to the invention. A not inconsiderable cost advantage in the process costs can thus be realized by the reduced consumption of organic components.

Test Example 4

Stress tests were carried out with the alkaline zinc nickel electrolyte SLOTOLOY ZN 80 (Schlötter) using different anode materials. Here, 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 enforced For example, the zinc nickel electrolyte was investigated with respect to the degradation products forming at the anode, such as cyanide. In addition, an analysis of the organic complexing agents and brighteners was carried out.

Test conditions:

The base bath batch (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 (base gloss additive) SLOTOLOY ZN 83: 2.5 ml / l (base gloss additive) SLOTOLOY ZN 86: 1.0 ml / l (top gloss)

The above base bath mixture contains: 10.0 g / l DETA (diethylenetriamine), 9.4 g / l TEA (85% by weight triethanolamine), 40.0 g / l Lutron Q 75 (BASF; 75% by weight tetrahydroxopropylethylenediamine) and 370 mg / l PPS (1- (3-sulfopropyl) pyridinium betaine).

The bath temperature was adjusted to 35 ° C. The agitation during the power pulp coating was 250 to 300 rpm. By contrast, the stirring movement during the load plate 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)

The following anode or cathode materials were used:

• Cathode material: Cold rolled steel sheet steel according to 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 coating layer of 30 μm bright nickel (coated with SLOTONIK 20 electrolyte from Schlötter);
Production: See JN balance, Tables Galvanotechnik, 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 thereto 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 material is zirconium corundum) and then freed of adhering residues with compressed air. The steel sheet was then sprayed with nickel to improve the primer by arc spraying first with nickel. A nickel wire in the arc (temperature at the burner head 3000 to 4000 ° C) was melted and sprayed with compressed air (6 bar) as atomizing gas at a distance of 15 to 18 cm on the steel sheet. Subsequently, the manganese-iron-oxide layer was thermally sprayed by means of powder flame spraying. The coating material used was a mixture of 90% by weight metallic manganese powder (-325 mesh, ≥99% from Sigma Aldrich) and 10% by weight metallic iron powder (-325 mesh, 97% from Sigma Aldrich). Care was taken to mix the two powders homogeneously before the thermal spraying process. Subsequently, the metallic manganese-iron mixture in an acetylene-oxygen flame (temperature of the 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. By pivoting movements was coated until a uniform, about 250 microns thick thermally sprayed manganese iron oxide layer has been produced.

Anode 4 according to the invention: steel (material number 1.0330) with a manganese-nickel-oxide layer (hereinafter defined as "Mn-Ni-oxidanode") applied thereto by thermal spraying;
Production: A 2 mm thick steel sheet (material number 1.0330) was degreased, roughened with corundum (blasting material is zirconium corundum) and then freed of adhering residues with compressed air. The steel sheet was then sprayed with nickel to improve the primer by arc spraying first with nickel. A nickel wire in the arc (temperature at the burner head 3000 to 4000 ° C) was melted and sprayed with compressed air (6 bar) as atomizing gas at a distance of 15 to 18 cm on the steel sheet. Subsequently, the manganese-nickel oxide layer was thermally sprayed by means of powder flame spraying. As the coating material, a mixture of 80 wt% metallic manganese powder (-325 mesh, ≥99% from Sigma Aldrich) and 20 wt% metallic nickel powder (-325 mesh, ≥99% from Alfa Aesar) was used. Care was taken to mix the two powders homogeneously before the thermal spraying process. Subsequently, the metallic manganese-nickel mixture in an acetylene-oxygen flame (temperature of the 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. By pivoting movements was coated until a uniform, about 250 microns thick thermally sprayed manganese-nickel oxide layer has been generated.

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

After passing through an amount of current of 5 Ah / l, the following brighteners or fine grain additives were metered into the zinc nickel electrolyte:

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

After an enforced amount of current of 2.5 Ah / l was the deposited on the deposition plate (cathode) deposited Zinknickellegierungsmenge determined by weighting. The total amount of metal missing from 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 metered in for a total deposited metal amount of 1.0 g of zinc nickel alloy layer). The zinc consumed in the electrolyte was added as zinc oxide, and the spent nickel was supplemented by the nickel-containing liquid concentrate SLOTOLOY ZN 85. SLOTOLOY ZN 85 contains nickel sulphate and the amines triethanolamine, diethylenetriamine and Lutron Q 75 (1 ml SLOTOLOY ZN 85 contains 63 mg nickel).

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

Experimental procedure and results:

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

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

As shown in Table 11, using the inventive anodes 3 and 4, a significantly lower cyanide formation than in the comparative anode 2 (bright nickel-plated steel).

Furthermore, after an enforced amount of electricity of 50 Ah / l, the amount of remaining additives was determined. 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, depending on 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 Inventive anode 4 Mn-Ni-oxide anode 9.8 9.7 41.5

As shown in Table 12, significantly fewer amines (DETA and TEA) were consumed using the anodes 3 and 4 of the present invention than using the comparative anode 2. These fabrics were thus less oxidized on the inventive anodes 3 and 4 and therefore must be less Measures are postdosed. This offers a not inconsiderable cost advantage in terms of process costs.

Claims (14)

Process for the electrodeposition of zinc and zinc alloy coatings from an alkaline coating bath with zinc and zinc alloy electrolytes and organic bath additives, which uses as the anode a bath-insoluble, metallic manganese and / or manganese oxide-containing electrode, wherein the electrode 1) is made of metallic manganese or a manganese-containing alloy, wherein the manganese-containing alloy contains at least 5 wt.% Manganese, or 2) is made of an electrically conductive carrier and a coating containing metallic manganese and / or manganese oxide thereon, wherein the manganese and / or manganese oxide-containing coating at least 5 wt.% Manganese, based on the total amount of manganese, consisting of metallic manganese and manganese oxide yields, contains, or 3) is made of a composite material comprising metallic 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 resulting from metallic manganese and manganese oxide. The method of claim 1, wherein the manganese-containing alloy is selected from a manganese-containing steel alloy or a manganese-containing nickel alloy. Process according to either of Claims 1 and 2, in which the manganese-containing alloy contains 10 to 90% by weight of manganese, more preferably 50 to 90% by weight of manganese. The method of claim 1, wherein the electrically conductive support is selected from steel, titanium, nickel or graphite. A method according to any one of claims 1 and 4, wherein the metallic manganese and / or manganese oxide-containing coating is applied to the carrier by thermal spraying of metallic manganese or a mixture of metallic manganese with iron and / or nickel. A method according to any one of claims 1 and 4, wherein the metallic manganese and / or manganese oxide-containing coating is deposited on the carrier by build-up welding of metallic manganese or a mixture of metallic manganese with iron and / or nickel. Method according to one of claims 1 and 4, wherein the metallic manganese and / or manganese oxide-containing coating is applied by vapor deposition on the carrier. Method according to one of claims 1 and 4 to 7, wherein the metallic manganese and / or manganese oxide-containing coating 10-100 wt.% Manganese, particularly preferably 50-100 wt.% Manganese, and particularly preferably 80-100 wt.% Manganese, based on the total amount of manganese resulting from metallic manganese and manganese oxide. The method of claim 1, wherein the electrically conductive material of the composite material is carbon, preferably graphite. Method according to one of claims 1 and 9, wherein the composite material contains at least 10% by weight of manganese, more preferably at least 50% by weight of manganese. A method according to any one of claims 1 to 10, wherein the zinc alloy electrolyte is a zinc nickel electrolyte. A process according to any one of claims 1 to 11, wherein the alkaline coating bath comprises organic bath additives in the form of amine-containing complexing agents. Use of metallic manganese or a manganese-containing alloy as defined in any one of claims 1 to 3, or an electrically conductive support having a metallic manganese and / or manganese oxide-containing coating thereon as defined in any of claims 1 and 4 to 8 , or a composite material comprising metallic manganese and / or manganese oxide and an electrically conductive material as defined in any one of claims 1, 9 and 10, as an anode for electrodepositing zinc and zinc alloy coatings from an alkaline coating bath with zinc and zinc alloying electrolytes and organic bath additives. A galvanic apparatus for depositing zinc and zinc alloy coatings from an alkaline plating bath comprising zinc and zinc alloy electrolytes and organic bath additives comprising as an anode an insoluble metallic manganese and / or manganese oxide-containing electrode as defined in any one of claims 1-10.