EP3222757A1 - Method and device for loosening zinc - Google Patents

Abstract

The present invention relates to a process for dissolving zinc or a zinc alloy in an aqueous alkaline solution. In accordance with at least one embodiment, metallic zinc or a zinc alloy is brought into electrically conductive contact with an iron layer and immersed with it in whole or in part in an aqueous, alkaline solution. The iron layer consists of an iron material thermally sprayed onto a substrate. Furthermore, the invention relates to a method for galvanic coating with zinc or a zinc alloy and a device for dissolving zinc or a zinc alloy.

Description

The present invention relates to a method of dissolving zinc or a zinc alloy in an aqueous alkaline solution, a zinc or zinc alloy electroplating method using this method of dissolving zinc or a zinc alloy, and a zinc dissolving apparatus or a zinc alloy.

In the galvanic deposition of zinc from alkaline, cyanide-free zinc baths in the active baths usually insoluble anodes are used. In order to control the zinc content of the electrolyte, it is usually passed through a separate zinc dissolving compartment (a so-called zinc dissolving compartment) in which larger amounts of zinc are held. The problem is that zinc dissolves only very slowly in an alkaline electrolyte, since the hydrogen evolution is inhibited on the zinc surface by a high overpotential.

The prior art attempts to solve this problem by bringing zinc into direct contact or electrically conductive contact with a material having a lower hydrogen overvoltage so as to increase the dissolution rate of the zinc (zinc dissolvers). For reasons of cost, usually steel release baskets are filled with zinc pellets or zinc balls and immersed in the alkaline electrolyte. In addition to the anodic oxidation of zinc, a cathodic reduction of protons to hydrogen takes place on the steel baskets. The reaction equations may be formulated, for example, as follows:

(1) Zn (0) → Zn (II) + 2 e ^-

(2) 2 H ⁺ + 2 e ^- → H ₂ or 2 H ₂ O + 2 e ^- → H ₂ + 2 OH ^-

In addition to a sufficient flooding, which should serve to avoid anode passivation, it has been shown to be advantageous if the catalytic surface is increased. For example, steel can be oxidized for use. Usually sufficient oxidation is achieved by acid dewatering and subsequent removal of the steel from a few days to the atmosphere or by thermal processes ( R. Ludwig, R. Holland: Zinc Generator Tanks for the Alkaline Cyanide-Free Zinc Plater, Metal Finishing, 1998, Vol. 6, pp. 106-112 ).

However, these conventional methods have some disadvantages. For example, fluctuations in zinc dissolution rates can lead to recurrent irregularities and bottlenecks in the supply of dissolved zinc. In addition, the solubility rate decreases with increasing concentration of zinc in the solution. In addition, the dissolution rate in these conventional methods is usually highly dependent on the temperature. As a rule, the zinc dissolution rate decreases when the temperature is lowered. In the case of alkaline, cyanide-free zinc baths, care should be taken to ensure an operating temperature of the active baths of 20 to 35 ° C (cf. DE 10 2004 038 650 A1 ). Furthermore, the alkaline zinc baths used for galvanic processes also contain additives, in particular organic additives, which have a negative effect on the zinc dissolution rates in comparison to pure potash or sodium hydroxide solution.

Overall, therefore, a cathode that is active over a long period of time and resistant to external influences would be desirable, with which a high zinc dissolution rate can also be achieved in real alkaline zinc baths and no negative influence on the functioning of these zinc baths is observed.

• In der Patentschrift US 5,302,260 werden Beschichtungen aus Raney-Nickel und Raney-Kobalt als geeignet und ausreichend inert beschrieben, um Zink oder Zinkbeschichtungen im alkalischen Milieu zu lösen. Die verwendeten Materialen sollen sich durch eine sehr hohe spezifische Oberfläche und eine niedrige Wasserstoff-Überspannung auszeichnen.

In the prior art, there are some approaches to solve this problem:

• In the patent US 5,302,260 For example, coatings of Raney nickel and Raney cobalt are described as being suitable and sufficiently inert to dissolve zinc or zinc coatings in an alkaline environment. The materials used should be characterized by a very high specific surface and a low hydrogen overvoltage.

In the published patent application DE 197 11 717 A1 describes a nickel and / or cobalt-based material that is brought into direct contact with a base metal, in particular zinc, which should lead to a faster dissolution of the base metals.

In DE 10 2004 038 650 A1 Another possibility is described which should accelerate the dissolution of zinc in sodium or potassium hydroxide solution. It is added to the liquor more iron sulfide, as it is soluble. In direct contact with zinc, hydrogen is developed on the iron sulfide. Compared to the use of iron powder, the dezincification times of hot-dip galvanized steel sheets can be shortened.

The above-described methods are not used industrially for reasons of cost, inadequate bath compatibility, too low zinc dissolution rates, inadequate robustness, or even for ecological and regulatory considerations, in order to bring zinc into solution for electroplating.

It is therefore an object of the present invention to provide an improved process for dissolving metallic zinc or a zinc alloy which reduces or overcomes needs arising from the prior art processes. It is especially a task of the present invention to provide a low cost, ecologically acceptable, robust high zinc dissolving process. Another object is to provide a zinc or zinc alloy plating method using the zinc or zinc alloy dissolution method, and a zinc or zinc alloy dissolution apparatus.

The above objects are achieved by the method of dissolving zinc or a zinc alloy, the method of electroplating zinc or a zinc alloy, and the device for dissolving zinc or a zinc alloy according to the independent claims. Dependent claims indicate further advantageous embodiments.

One aspect of the invention relates to a method of dissolving zinc or a zinc alloy. According to this method, metallic zinc, ie zinc (0), or a zinc alloy is brought into electrically conductive contact with an iron layer and immersed with it in whole or in part in an aqueous, alkaline solution. The iron layer consists of an iron material thermally sprayed onto a substrate. This iron layer is also referred to below as "thermally sprayed iron layer".

In the process, therefore, metallic zinc (ie zero oxidation state zinc) is dissolved and is then present in the solution as Zn (II), for example as zincate. If necessary, zinc (0) can also be dissolved out of an alloy so that residues of the alloy remain and not the entire alloy is dissolved. Such a variant is counted according to the invention for "dissolving" a zinc alloy.

For dissolution, the zinc or zinc alloy (anode) is brought into electrically conductive contact with the thermally sprayed iron layer (cathode). It can be an immediate or indirect spatial contact between zinc or zinc alloy and the iron layer. Direct physical contact occurs when the thermally sprayed iron layer is directly adjacent to the zinc or zinc alloy. An example of this would be a releasing basket coated with the iron layer, for example a steel basket filled with zinc or zinc alloy, for example in the form of pellets, granules or spheres.

An indirect spatial contact is present when the thermally sprayed iron layer is not directly adjacent to the zinc or the zinc alloy, that is spaced apart. Such a spacing can be realized for example by means of a spacer, for example a washer. It is also possible to hang the zinc or zinc alloy and the substrate with the thermally sprayed iron layer separately from each other in the bath. The electrically conductive contact between the iron layer and zinc or zinc alloy can then take place via a metallic conductor, for example a metal pin, a metal screw or a cable, which electrically conductively connects the iron layer to the zinc or zinc alloy.

In order to bring zinc into solution, the zinc or the zinc alloy and the iron layer must be completely or partially immersed in the aqueous, alkaline solution. Consequently, zinc or zinc alloy and the thermally sprayed iron layer respectively form surfaces which come into direct contact with the aqueous alkaline solution.

Surprisingly, it has been found that the process enables high zinc dissolution rates which are significantly higher than those of conventional processes in which an untreated steel or iron sheet or a rusted steel sheet is used as the cathode. In addition, high levels of zinc dissolution can occur over a long period of time and even at high zinc concentrations in the aqueous alkaline solution be enabled. Thus, the erfindungsmäße method allows to provide within a relatively short time a larger amount of dissolved zinc and dissolved zinc in high concentrations. This allows the zinc concentration to be more easily and reliably controlled, for example, in zinc baths used in galvanic processes. Furthermore, it is possible by the method according to the invention to keep smaller volumes of zinc solution in stock or to use smaller zinc solution compartments, since zinc can be brought into solution quickly and in higher concentration if required.

In terms of cost-effectiveness, in addition to the increased process reliability, advantages are also obtained with regard to the system technology, since in general a more compact design or less solution can be used. Likewise, dissolution times or Entzinkungszeiten can be shortened. A limitation of galvanic processes by the dissolution of the zinc is thus overcome or at least significantly mitigated. Furthermore, the iron layer can be produced easily and inexpensively by means of thermal spraying. Of course, good economic efficiency also results in ecological advantages, such as lower material usage and lower energy consumption.

The inventors have further found that the above method of dissolving zinc or a zinc alloy is very robust. It shows only a small dependence on the temperature and can be operated at all common for galvanic coating with zinc temperatures. Furthermore, the process is insensitive to the common additives used in zinc baths for electroplating. Organic additives can be readily used. The method is therefore particularly suitable for providing dissolved zinc for galvanic processes.

According to a further embodiment, the aqueous, alkaline solution is cyanide-free. It is preferably an alkaline, cyanide-free zinc bath or a zinc electrolyte, which is suitable for the electrodeposition of zinc or zinc alloys. The zinc bath may contain one or more typical additives for alkaline zinc baths, such as brighteners, surfactants, polymers, carbonates, silicates, and chelating agents.

The method for dissolving zinc or a zinc alloy can thus be combined with a process for electroplating with zinc or a zinc alloy.

Another field of application of the process for dissolving zinc or a zinc alloy is the dezincing of scrap metal containing zinc or zinc alloy (e.g., scrap metal). The scrap contains at least on the surface of metallic zinc or a zinc alloy. Examples of zinc or zinc alloy-containing scrap metal are metal having a coating of electrodeposited zinc or electrodeposited zinc alloy, hot-dip galvanized metal and zinc flake-coated metal.

The aqueous alkaline solution may contain a hydroxide, for example, an alkali metal hydroxide and / or an alkaline earth metal hydroxide. Preference is given to sodium hydroxide and / or potassium hydroxide. The pH of the aqueous alkaline solution is usually 10 or more, preferably 12 or more, more preferably 13 or more.

The zinc to be dissolved or the zinc alloy to be dissolved can basically be present in any desired form, for example in the form of a sheet, a coating on a support, as ingots or in the case of a dissolving basket as pellets, granules, spheres or the like. For the process, metallic zinc, a zinc alloy or combinations used of it. A zinc alloy preferably contains at least 50% by weight of zinc, more preferably at least 75% by weight of zinc, more preferably at least 95% by weight of zinc, for example 98.0 to 99.9% by weight.

As stated above, the iron layer is a thermally sprayed iron layer. That is, it was obtained by a thermal spraying method on the substrate or is obtainable by such a method. The production by means of thermal spraying is easy to carry out and associated with less effort than, for example, the production of Raney catalysts, so that there are also economic advantages over the latter.

The thermally sprayed iron layer contains iron (0) and at least one or more iron (III) oxygen compounds. Iron (III) oxygen compounds can be detected, for example, in an XPS analysis of a thermally sprayed iron layer. The iron (III) oxygen compounds are formed by thermal spraying of the iron material, that is by reaction of iron with oxygen.

The iron (III) oxygen compounds include at least one compound selected from an iron (III) oxide, an iron (III) oxide hydroxide, a ferric hydroxide and combinations thereof. It can be assumed that hydroxide compounds, for example on the surface of the thermally sprayed iron layer, can also be formed in the presence of the aqueous, alkaline solution. After thermal spraying and before use in the aqueous alkaline solution, the sprayed iron layer contains in particular at least one iron (III) oxygen compound selected from iron (III) oxide (Fe ₂ O ₃ ), iron (III) oxide hydroxide ( FeOOH) or a combination thereof.

The iron material used for thermal spraying usually contains metallic iron and / or an iron alloy. Suitable iron alloys are, in particular, those which contain at least one transition metal other than iron and / or carbon. A suitable iron alloy may also consist of iron and the at least one transition metal and / or carbon. In the iron alloys, the transition metal is selected, for example, from manganese, nickel, copper, molybdenum, zirconium, and combinations thereof.

The iron material used for the thermal spraying may contain, for example, at least 60% by weight of iron. The content of iron refers to both iron in the form of metallic iron, iron alloys described above, and other iron compounds. It thus indicates the total iron content based on the total weight of the iron material used for thermal spraying.

The inventors have found that a high iron content in the iron material results in particularly high zinc dissolution rates. Preferably, the iron material used for thermal spraying therefore contains at least 80% by weight of iron, more preferably at least 90% by weight and even more preferably at least 95% by weight of iron, based on the total weight of the iron material.

The iron material used is preferably metallic iron or a steel which, in addition to iron for example, contains small amounts (<5% by weight, in particular <2% by weight) of carbon and transition metal. As a result, particularly favorable, environmentally friendly thermally sprayed iron layers can be produced, with which high zinc dissolution rates are made possible.

The iron material is preferably used in a form suitable for thermal spraying, for example as a powder or wire.

Usually, during the thermal spraying, heated, on, off or molten spray particles are accelerated and thrown onto the substrate. As a result, a good connection to the substrate and a crack-resistant iron layer is formed. In this case, an oxidation, presumably also takes place on the surface of the particles, whereby one or more iron (III) oxygen compounds are formed.

Due to the process, a relatively rough surface is usually produced during thermal spraying. According to a preferred embodiment, the iron layer has a roughness Ra of at least 4 μm, preferably 5 to 50 μm, more preferably 6 to 40 μm. Here, Ra indicates the arithmetic mean roughness value according to DIN EN ISO 4287: 2010.

The roughness of the thermally sprayed iron layer need not result in a very high specific surface area. In some examples, significantly lower specific surface values were found for a thermally sprayed iron layer than for a rusted steel sheet. Since significantly higher zinc dissolution rates were nevertheless observed with a thermally sprayed iron layer, it can be assumed that the specific surface of the thermally sprayed iron layer has only a slight influence on the zinc dissolution rates.

The thermally sprayed iron layer has a comparatively positive potential. Thus, the thermally sprayed layer may comprise iron in 1 M sodium hydroxide solution has a redox potential of more than +0.6 V, when a hydrogen electrode (for example, a hydro-Flex ^® -Wasserstoffelektrode Fa. Gaskatel) is used as reference electrode.

According to a preferred embodiment, the iron layer has an average thickness of 10 μm to 1000 μm, preferably 30 μm to 600 μm and particularly preferably 50 μm to 400 μm. A certain layer thickness is helpful for the strength of the iron layer. If the layer thickness is chosen too large, this in turn may lead to the iron layer flaking off. The average thickness of the iron layer is determined by scanning electron microscopy on a transverse section of the iron layer.

In principle, the substrate may be a metal, a semiconductor or a nonmetal. Of course, those materials are used which are suitable for the thermal spraying of the iron material, so in particular have a sufficient temperature stability. Preferably, a substrate made of metal, in particular steel, is used. It may for example be in the form of a sheet, preferably in the form of a perforated plate, or in the form of a basket. The substrate is preferably not of a thermally sprayed iron material. The substrate primarily serves to produce a flat iron layer by thermal spraying. The iron layer is supported by the substrate.

Between substrate and the iron layer, a primer may be arranged. This may for example be based on bronze, nickel or a nickel-titanium alloy or consist entirely of it. By using a primer, the adhesion of the thermally sprayed layer to the substrate is further improved. A primer is preferably applied flatly directly to the substrate before the iron material is thermally sprayed on. The primer may be produced by the same thermal spraying method as the iron layer, for example flame spraying or arc spraying. Usually, the primer is produced with a thickness of up to 50 microns. If a primer is used, the iron material is usually sprayed directly on the primer thermally.

If no primer is used, the iron material is typically thermally sprayed directly onto the substrate.

The iron layer according to one of the embodiments described above can be thermally sprayed onto the substrate (with or without a primer) by means of conventional methods. For example, to produce the iron layer, the iron material according to one of the embodiments described above may be thermally sprayed onto the substrate by one of the following methods: arc wire spraying, thermo spray powder spraying, flame spraying, high velocity flame spraying, plasma spraying, autogenous rod spraying, Autogenous wire spraying, laser spraying, cold gas spraying, detonation spraying and PTWA spraying. These methods are known per se to the person skilled in the art. The iron layer can be produced in particular by means of flame spraying or arc spraying. Flame spraying is particularly suitable for the use of a pulverulent iron material. In the case of a wire-shaped iron material, in particular arc spraying is suitable.

Arc spraying is characterized by a high application rate and low energy consumption. Furthermore, there is a comparatively low substrate heating, so that there is great variability in the substrate used. The thermally sprayed iron layer is therefore preferably produced by means of arc spraying, in particular when working on an industrial scale.

As mentioned above, the zinc or zinc alloy is brought into electrically conductive contact with the iron layer. This can be done via the Substrate happen when this is electrically conductive and in contact with the zinc or the zinc alloy. Another possibility is to provide a dissolving basket with a thermally sprayed iron layer and to fill the zinc or the zinc alloy in these.

Regardless of the material of the substrate, the iron layer may also be brought into electrical contact with the zinc or zinc alloy via a metallic conductor. Such a conductor may be, for example, a metal rod or a metal screw, for example made of steel, copper or another metal, which is not attacked by the aqueous alkaline solution, or the like. For this purpose, the substrate with the iron layer and the zinc. or the zinc alloy in parallel, for example, via a spacer such as a washer separated from each other to be arranged. The metallic conductor can then be guided perpendicular thereto by substrate and iron layer and zinc or zinc alloy to produce the electrically conductive contact. Optionally, the metallic conductor may also pass through the spacer. Another possibility is to make the electrically conductive contact via a cable that connects zinc or zinc alloy with the iron layer or a metallic substrate.

As already explained above, the substrate with the thermally sprayed iron layer and the zinc or zinc alloy can be spaced apart from one another. For this purpose, a spacer, for example a washer, can be used. There may also be a separate suspension of zinc or zinc alloy and substrate with iron layer. The electrically conductive contact can take place via one or more metallic conductors, for example as described in the preceding paragraph. The spacing can thus be designed so that the contact surface with the aqueous, alkaline solution of the substrate with the Iron layer and the zinc or zinc alloy is relatively large.

The process for dissolving zinc or a zinc alloy is very robust. It can be carried out successfully over a wide temperature range. The aqueous alkaline solution may, for example, have a temperature of 10 to 90 ° C, preferably 15 to 75 ° C, particularly preferably 20 to 60 ° C. The process can be readily operated at temperatures typical of galvanic zinc baths, especially in the range of 10 to 60 ° C, preferably 15 to 50 ° C and more preferably 20 to 40 ° C. At such temperatures, the additives commonly used in zinc baths are stable. If this need not be taken into account, for example, if the dezincification of scrap metal only a simple caustic solution is used, then higher temperatures can be used.

Preferably, the aqueous, alkaline solution is mixed during the process. This can be done, for example, by stirring, circulation or (partial) replacement of the aqueous, alkaline solution.

To control the zinc dissolution rates, the immersion depth can be varied into the aqueous, alkaline solution. To interrupt or terminate the dissolution process, zinc or zinc alloy and substrate having the thermally sprayed iron layer can be easily taken out of the aqueous alkaline solution, or the aqueous alkaline solution is drained.

The method for dissolving zinc or a zinc alloy can be easily carried out on an industrial scale.

1. (A) das galvanische Abscheiden von Zink oder einer Zinklegierung aus einer wässrigen, alkalischen Lösung, die gelöstes Zink und gegebenenfalls andere gelöste Metalle enthält, auf einem Bauteil oder einem anderen elektrisch leitenden Körper, um das Bauteil oder den elektrisch leitenden Körper mit Zink oder einer Zinklegierung zu beschichten, und
2. (B) das Durchführen eines Verfahrens zum Auflösen von Zink oder einer Zinklegierung gemäß einer der oben beschriebenen Ausführungsformen, um gelöstes Zink für den Schritt (A) bereitzustellen.

Another aspect of the invention relates to a process for electroplating zinc or a zinc alloy. This method includes:

1. (A) the galvanic deposition of zinc or a zinc alloy from an aqueous alkaline solution containing dissolved zinc and optionally other dissolved metals, on a component or other electrically conductive body to the component or the electrically conductive body with zinc or a To coat zinc alloy, and
2. (B) performing a method of dissolving zinc or a zinc alloy according to any of the above-described embodiments to provide dissolved zinc for the step (A).

The process coats a component or other electrically conductive body with zinc or a zinc alloy. The deposited zinc alloy may differ from the zinc alloy used for dissolution. The method of electrodeposition benefits from the above-described advantages of the method of dissolving zinc or a zinc alloy.

The steps (A) and (B) are preferably performed spatially separated from each other. For example, step (B) may be performed in a separate compartment. The zinc-containing aqueous alkaline solution may then be supplied as needed to the zinc bath used for coating to supply dissolved zinc, which is consumed in electroplating.

The steps (A) and (B) can thus be carried out at the same time or else offset in time.

The galvanic coating with zinc or a zinc alloy from a zinc-containing, aqueous, alkaline solution, in particular a cyanide-free zinc bath, is known per se to a person skilled in the art.

• eine Anordnung mit einer Zinkanode, einer Eisenschicht als Kathode, die in elektrisch leitenden Kontakt mit der Zinkanode steht, wobei
  • die Zinkanode metallisches Zink oder eine Zinklegierung umfasst oder daraus besteht,
  • die Eisenschicht aus einem auf ein Substrat thermisch aufgespritzten Eisenmaterial besteht, und
  • die Vorrichtung einen Behälter umfasst, der zur Aufnahme einer wässrigen, alkalischen Lösung, in die die Anordnung ganz oder teilweise eintauchen kann, geeignet ist.

Another aspect of the invention relates to an apparatus for dissolving zinc or a zinc alloy. This device comprises:

• an arrangement with a zinc anode, an iron layer as a cathode, which is in electrically conductive contact with the zinc anode, wherein
  • the zinc anode comprises or consists of metallic zinc or a zinc alloy;
  • the iron layer consists of an iron material thermally sprayed onto a substrate, and
  • the device comprises a container which is suitable for receiving an aqueous, alkaline solution into which the arrangement can completely or partially submerge.

The container, for example a tub, is thus large enough in terms of dimensions that the arrangement fits in whole or in part.

This arrangement or the device is suitable for dissolving zinc or a zinc alloy. To operate the device, an aqueous, alkaline solution, preferably an alkaline, cyanide-free zinc bath, is then filled into the container and the assembly wholly or partially immersed therein. The container preferably contains an opening for filling and a closable outlet in order to drain the aqueous alkaline solution.

Furthermore, the device preferably comprises means with which the depth of immersion of the arrangement into the aqueous, alkaline solution can be controlled during operation of the device. Preferably, the arrangement can then be removed completely from the aqueous alkaline solution to interrupt the dissolution process. The control can be effected, for example, by the arrangement being suspended at different heights. To control the Method, the aqueous alkaline solution can also be partially or completely drained.

According to another embodiment, the device comprises means for mixing the aqueous alkaline solution during the dissolution process. The device can, for example, comprise means for stirring, circulating or for a (partial) replacement of the aqueous, alkaline solution.

The device may also include means to regulate the temperature in the aqueous alkaline solution.

• Zusätzlich oder stattdessen entspricht das Substrat einem Substrat gemäß einer der oben beschriebenen Ausführungsformen. Es kann beispielsweise aus Metall, bevorzugt aus Stahl, sein. Es kann beispielsweise als Blech, Lochblech oder Korb geformt sein.
• Zusätzlich oder stattdessen kann zwischen Substrat und Eisenschicht ein Haftgrund, bevorzugt auf Basis von Bronze, Nickel oder einer Nickel-Titan-Legierung, angeordnet sein.

According to a further embodiment of the device, the iron layer corresponds to an iron layer according to one or more of the embodiments described above.

• Additionally or instead, the substrate corresponds to a substrate according to one of the embodiments described above. It may for example be made of metal, preferably of steel. It can be shaped, for example, as a sheet metal, perforated plate or basket.
• In addition or instead, a primer, preferably based on bronze, nickel or a nickel-titanium alloy, can be arranged between the substrate and the iron layer.

The device can be combined with a galvanic bath.

In the following, the invention will be explained in more detail with reference to figures and examples, without thereby limiting the invention defined in the claims invention.

Fig. 1

an einem Querschliff einer thermisch gespritzten Eisenschicht gemäß einer Ausführungsform der Erfindung aufgenommene XPS-Spektren;

Fig. 2

REM-Aufnahmen der Oberfläche dieser thermisch gespritzten Eisenschicht bei 500-facher Vergrößerung sowie bei 100-facher Vergrößerung; und

Fig. 3

ein dazugehöriges EDX-Spektrum;

Fig. 4

an einem Querschliff einer thermisch gespritzten Eisenschicht auf einem Stahlsubstrat mit einem Nickel/Titan-Haftgrund gemachte REM-Aufnahmen bei 100-facher Vergrößerung und 500-facher Vergrößerung; und

Fig. 5

dazugehörige EDX-Spektren;

Fig. 6

eine Langzeitstromdichtemessung von Beispiel 1 und Vergleichsbeispiel 1; und

Fig. 7

eine schematische Darstellung einer in den Beispielen 2 bis 10 und Vergleichsbeispielen 2 bis 8 verwendeten Anordnung zur Messung der Zinklöserate.

Show it

Fig. 1

XPS spectra recorded on a transverse section of a thermally sprayed iron layer according to an embodiment of the invention;

Fig. 2

SEM images of the surface of this thermally sprayed iron layer at 500x magnification and at 100x magnification; and

Fig. 3

an associated EDX spectrum;

Fig. 4

SEM images taken at a cross section of a thermal sprayed iron layer on a steel substrate with a nickel / titanium primer at 100x magnification and 500x magnification; and

Fig. 5

associated EDX spectra;

Fig. 6

a long term current density measurement of Example 1 and Comparative Example 1; and

Fig. 7

a schematic representation of an arrangement used in Examples 2 to 10 and Comparative Examples 2 to 8 for the measurement of zinc solubles.

In order to further characterize the composition and structure of a thermally sprayed iron layer in accordance with an embodiment of the invention, the in Fig. 1 recorded XPS spectra of a thermally sprayed iron layer. For this thermally sprayed iron layer was analogously to Example 4, a steel sheet without primer coated by arc spraying. As the iron material, an iron arc wire was used. The average layer thickness was about 200 μm.

On a transverse section of the thermally sprayed iron layer, three XPS spectra (Fe2p and Ols) were recorded within the coating, which in Fig. 1A and Fig. 1B are shown. It was near the substrate ("substrates") (13), below the surface ("oxide layer") (11) and measured centrally in the coating ("Interface") (12).

In addition to iron (0), iron (III) compounds were mainly detected in all measurements. In particular, the iron (III) oxygen compounds FeOOH and Fe ₂ O ₃ could be detected. It is noticeable that more iron (III) oxygen compounds were found on the surface of the thermally sprayed iron layer than in the interior of the layer.

The XPS analysis was performed on an XPS Quantum 2000 system equipped with a 180 ° hemispheric analyzer and a 16 channel detector. The spectra were recorded by a focused, monochromatic X-ray source (Al-Kα, 1486.68 eV) with a beam diameter of 50 μm and a power of 12 W. The pressure in the analysis chamber was about 5 × 10 ^-7 Pa. The instrument was operated in FAT mode of the analyzer with a 45 ° electron take-off angle to the surface normal. The samples were neutralized using an electron gun (cold cathode 1.2 eV) and a low energy Ar ion beam (10 eV). Previously, a sputter cleaning was performed using an Ar ion beam with an energy of 2 kV, rastered over the area of 3 x 3 mm.

Fig. 2A and Fig. 2B show SEM images of the surface of the above-described thermally sprayed iron layer Fig. 1 at a 500 times ( Fig. 2A ) and at a 100x magnification ( Fig. 2B ). These images clearly show a rough surface structure formed by the particles spun during thermal spraying.

At the in Fig. 2B An EDX measurement was carried out with the section marked "10" (acceleration voltage EHT = 15 kV, detector = SE, WD = 8.5 mm). The corresponding spectrum is in Fig. 3 shown. According to this EDX survey measurement, the surface generated by thermal spraying of iron wire mainly consists of the elements iron in the form of Fe (0) and Fe (III) and oxygen. Furthermore, a small amount of carbon was found. The inventors suspect that this is the carbon from the used iron arc wire or adsorbed carbon from the air.

FIGS. 4A and 4B show SEM images at 100x magnification ( Fig. 4A ) and at 500X magnification of a cross section of a thermal sprayed iron layer according to another embodiment of the invention.

For the in FIGS. 4A and 4B As shown embodiment, a steel sheet (5) was first provided with a primer made of nickel-titanium alloy. The primer was applied by arc spraying. Subsequently, an iron arc wire was applied as iron material by arc spraying as a thermal spraying method. The average layer thickness of the thermally sprayed iron layer was about 250 to 300 microns. The preparation was carried out analogously to Example 5.

In FIG. 4B For example, a part of the primer with "6", grain edges of spin iron particles with "7" and "8" and a spot inside such a grain are marked with "9". In each case an EDX measurement was carried out at these locations. The corresponding spectra are in the Figs. 5A to 5D in this order. In the lower part of Fig. 4B the steel substrate (5) can be seen.

As in Fig. 5A shown in the primer at the point "6" especially nickel (0), nickel (II) and some iron and titanium detected.

Iron (0) and iron (III) oxygen compounds were detected at the grain boundaries of spin-coated iron particles, marked "7" and "8" respectively, which is reflected in the Fig. 5B and 5C you can see. In the interior of a grain, at the location "9", mainly iron was found ( Fig. 5D ). Apparently, the iron particles spun on thermal spraying were oxidized, especially at the surface.

The roughness of an uncoated strip steel sheet, a rusted steel sheet and two thermally sprayed iron layers according to the invention were measured analogously to DIN EN ISO 4287: 2010. Instead of the palpation procedure, measurements were taken with a confocal microscope (μsurf explorer from NanoFocus AG) and then evaluated in accordance with DIN EN ISO 4287: 2010. The thermally sprayed iron layers according to the invention were produced with an iron powder (Example 2) or an iron wire (Example 4) as iron material. Table 1 sample Average Average Average Ra [μm] Rt [μm] Rz [μm] Uncoated steel sheet (Comparative Example 1) 0.2 2.1 1.5 Rusted steel sheet (Comparative Example 8) 0.9 19.8 11.3 Iron layer (iron powder, example 2) 7.1 71.0 43.5 Iron layer (iron wire, example 4) 22.6 180.0 121.0

As already mentioned above, in the thermally sprayed iron layers according to the invention, a robust, rough surface structure was found. These showed about 7 times or 23 times the roughness Ra of the rusted steel sheet.

However, the increased roughness of the thermally sprayed iron layer was only partially reflected in a large specific surface area. In the iron layer produced by thermal spraying with an iron wire as an iron material on a steel sheet, a value of 0.0141 m ² / g was determined for the specific surface area. In comparison, the atmospheric rusted steel sheet gave a significantly higher value of 0.2171 m ² / g. Surprisingly, it was found that a rusted steel sheet gave a low zinc dissolution rate despite the approximately 15 times higher specific surface area (see Table 4). In the uncoated band steel sheet, no determination of the specific surface area was possible. The measured values are summarized in Table 2.

The specific surface area denotes a BET specific surface measured in accordance with DIN ISO 9277 (krypton at 77 K). Table 2 sample Specific surface area [m ² / g] Uncoated steel sheet (Comparative Example 1) not definable Rusted steel sheet (Comparative Example 8) 0.2171 ± 0.0021 Iron layer (iron wire, example 4) 0.0141 ± 0.0001

Furthermore, the redox potential was measured in 1 M sodium hydroxide solution. As a reference electrode, a hydrogen electrode served (Hydroflex ^® -Wasserstoffelektrode the company. Gaskatel). In Table 4, the measured values that were set after 1 hour are indicated. Table 3 sample Redox Potential [V] Uncoated steel sheet (Comparative Example 1) + 0.529 Iron layer (iron powder) (Comparative Example 8) + 0.770 Iron layer (iron wire, example 4) + 0,761

As shown in Table 3, there were only insignificant differences in the redox potential between the thermal sprayed coatings of iron wire and iron powder as the iron material. Overall, the potentials compared to the uncoated steel sheet were significantly more positive.

Example 1 and Comparative Example 1

Preparation of the cathodes:

example 1

A steel sheet (A = 0.175 dm ² ) was degreased, blasted with glass beads (diameter 150 to 250 microns) and then freed of adhering residues with compressed air. The steel sheet was then thermally sprayed 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 3000 to 4000 ° C at the burner head) melted and with compressed air (6 bar) as sputtering gas blasted onto the steel sheet. By pivoting the beam at a distance of 15 to 18 cm, a uniform, about 300 microns thick thermally sprayed iron layer was produced. This coated steel sheet was used as a cathode for the long-term measurement of current density described below.

Comparative Example 1

A steel sheet (A = 0.175 dm ² ) was degreased.

• Die katalytische Wirkung der Kathode auf die Zinklöserate bzw. die entsprechende Wasserstoffentwicklung beim Auflösen von Zink oder einer Zinklegierung spiegelt sich in der Stromdichte wider, die in einem elektrischen Leiter, der Zinkanode und die Kathode miteinander verbindet, fließt. In Fig. 6 ist eine Langzeitmessung dieser Stromdichte gezeigt (x-Achse: Zeit t in Sekunden, y-Achse: Stromdichte in A/dm²). Dabei diente jeweils eine Zink-Elektrode (A = 0,35 dm²) als Anode, die über einen Kupfer-Leiter mit der Kathode aus Beispiel 1 bzw. aus Vergleichsbeispiel 1 verbunden wurde. Zum Befestigen dienten Krokodilklemmen. Anode und die Kathode waren jeweils parallel in einem Abstand von 3,5 cm angeordnet.

Experimental procedure:

• The catalytic effect of the cathode on the zinc dissolution rates or the corresponding evolution of hydrogen in the dissolution of zinc or a zinc alloy is reflected in the current density flowing in an electrical conductor connecting the zinc anode and the cathode. In Fig. 6 a long-term measurement of this current density is shown (x-axis: time t in seconds, y-axis: current density in A / dm ² ). In each case, a zinc electrode (A = 0.35 dm ² ) was used as the anode, which was connected via a copper conductor to the cathode of Example 1 or of Comparative Example 1. Crocodile clips were used for attaching. Anode and the cathode were each arranged in parallel at a distance of 3.5 cm.

The measurements were each carried out in 3 M NaOH (350 mL) at 25 ° C., stirring at 100 revolutions per minute (rpm) using a magnetic stir bar. The current flow measured in the conductor was recorded over 15 hours (see Fig. 6 ).

Compared to a bare steel sheet as a cathode (Comparative Example 1, curve (2)), the cathode according to the invention with a thermally sprayed iron layer (Example 1, curve (1)) gave a significantly higher current flow. This means that a correspondingly higher zinc dissolution rate than in Comparative Example 1 was achieved. After 1 hour, the current flow in Example 1 was higher by a factor of 13.5 than in Comparative Example 1 (see Fig. 6 ). During the flow of electricity in Comparative Example 1 presumably then dropped sharply due to the higher zinc concentration, it remains relatively constant in Example 1 at a high level. After 15 hours, at the end of the measurement, the current flow is a flow of current of 1.048 A / dm ² over 0,025 A / dm ² was in Example 1 with the inventive iron layer by a factor of 40 higher than in Comparative Example 1. It was measured.

Examples 2 to 10 and Comparative Examples 2 to 8

Preparation of the cathodes:

Example 2

A steel perforated plate (Rv 8-10, A = 1.1 cm ² ) was degreased, blasted with glass beads (diameter 150 to 250 microns) and then freed of adhering residues with compressed air. The steel perforated plate was preheated with a welding torch to approx. 300 ° C and then thermally sprayed by means of flame spraying. In this case, an iron powder (-325 mesh, 97% from Sigma-Aldrich) was fed to the flame, which was operated with an acetylene-oxygen mixture (burner flame temperature was about 2000 ° C), and by compressed air (maximum 3 bar ) from a distance of 15 to 20 cm sprayed onto the steel perforated plate. With a pivoting movement (about 50 to 100 mm / s) was coated until a uniform, about 300 microns thick thermally sprayed iron layer has been produced.

Example 3

A steel perforated plate (Rv 8-10, A = 1.1 cm ² ) was degreased, blasted with glass beads (diameter 150 to 250 microns) and then freed of adhering residues with compressed air. Then a primer made of bronze (CuSn ₈ ) as a primer by flame spraying under the same conditions as the subsequently applied thermally sprayed Iron layer applied with a thickness of about 10 to 40 microns. Subsequently, the steel perforated plate with primer was preheated to about 300 ° C. with a welding torch and then, in analogy to example 2, a uniform, approximately 300 μm thick thermally sprayed iron layer was produced by means of flame spraying.

Example 4

A steel perforated plate (Rv 8-10, A = 1.1 cm ² ) was pretreated analogously to Example 1 and then a uniform, about 300 microns thick thermally sprayed iron layer using an iron wire (iron arc wire with 0.7 wt.% Mn, 0.07 wt% C and the balance Fe, diameter 1.6 mm).

Example 5

A steel perforated plate (Rv 8-10, A = 1.1 cm ² ) was degreased, blasted with glass beads (diameter 150 to 250 microns) and then freed of adhering residues with compressed air. Then a primer made of bronze (CuSn ₈ ) was applied as a primer by means of arc spraying under the same conditions as the subsequently applied thermally sprayed iron layer with a thickness of about 10 to 40 microns. Thereafter, a uniform, approximately 300 μm thick, thermally sprayed iron layer was produced analogously to Example 1 using an iron wire (iron arc wire with 0.7% by weight of Mn, 0.07% by weight of C and the remainder Fe, diameter 1.6 mm).

Examples 6 to 10

A steel perforated plate (Rv 8-10, A = 1.1 cm ² ) was pretreated analogously to Example 1 and then a uniform, about 300 microns thick thermally sprayed iron layer using a wire made of an iron alloy (diameter 1.6 mm) produced ,

• Beispiel 6: Eisen-Nickel-Legierung mit 90 Gew.% Fe und 10 Gew.% Ni.
• Beispiel 7: Eisen-Kupfer-Legierung mit 90 Gew.% Fe und 10 Gew.% Cu.
• Beispiel 8: Eisen-Molybdän-Legierung mit 90 Gew.% Fe und 10 Gew.% Mo.
• Beispiel 9: Eisen-Zirkonium-Legierung mit 90 Gew.% Fe und 10 Gew.% Zr.
• Beispiel 10: Eisen-Kupfer-Zirkonium-Legierung mit 70 Gew.% Fe, 25 Gew.% Cu und 5 Gew.% Zr.

In this case, the wire used for the arc spraying had the following composition:

• Example 6: Iron-nickel alloy with 90 wt.% Fe and 10 wt.% Ni.
• Example 7: Iron-copper alloy with 90 wt.% Fe and 10 wt.% Cu.
• Example 8: Iron-molybdenum alloy with 90% by weight of Fe and 10% by weight of Mo.
• Example 9: Iron-zirconium alloy with 90 wt.% Fe and 10 wt.% Zr.
• Example 10: Iron-copper-zirconium alloy with 70 wt.% Fe, 25 wt.% Cu and 5 wt.% Zr.

Comparative Examples 2 to 6

A steel perforated plate (Rv 8-10, A = 1.1 cm ² ) was pretreated analogously to Example 1 and then a uniform, about 300 micron thick layer using a wire (diameter 1.6 mm) thermally sprayed analogously to Example 1 ,

• Vergleichsbeispiel 2: Nickel-Legierung mit 95 Gew.% Ni und 5 Gew.% Al/Ti.
• Vergleichsbeispiel 3: Kupfer.
• Vergleichsbeispiel 4: Molybdän.
• Vergleichsbeispiel 5: Zirkoniumoxid.
• Vergleichsbeispiel 6: Chromoxid.

In this case, the wire used for the arc spraying had the following composition:

• Comparative Example 2: Nickel alloy with 95 wt.% Ni and 5 wt.% Al / Ti.
• Comparative Example 3: Copper.
• Comparative Example 4: Molybdenum.
• Comparative Example 5: zirconium oxide.
• Comparative Example 6: Chromium oxide.

Comparative Example 7

A steel perforated sheet (Rv 8-10; A = 1.1 cm ²⁾ was degreased, blasted with glass beads (diameter 150 to 250 microns) and then freed from adhering residues with compressed air. Comparative Example 8

A steel perforated plate (Rv 8-10, A = 1.1 cm ² ) was degreased. Subsequently, it was decanted in 5% aqueous HCl solution and stored for 4 days at room temperature in the atmosphere over this solution, so that an atmospheric rusted steel sheet was obtained.

Experimental procedure:

As in Fig. 7 In a 5 liter beaker (21), an aqueous, alkaline, cyanide-free zinc bath (5 L) (20) was used in each case as the electrolyte at 25 ° C. by means of a magnetic stir bar (22) and an in Fig. 7 Magnetic stirrer, not shown, mixed at 1000 rpm. The zinc bath contained in each case 8 g / L Zn (II), 120 g / L NaOH, 40 g / L Na ₂ CO ₃ and 20 mL / L ZINCASLOT 81 (a basic additive for the novel preparation of an electrolyte from Dr.-Ing Schlotter GmbH & Co. KG). The zinc bath thus corresponds to a typical zinc bath used in electroplating.

In each case, a zinc anode (19.8 × 5 × 1 cm with A = 2.48 cm ² ) (15) with a steel screw (17) and associated nut (18) made of steel at the respective cathode was used to produce the electrically conductive contact (16) fixed in parallel and immersed in a hook (23) made of polypropylene (PP) entirely in the electrolyte. By means of a washer (19), the distance between the zinc anode and the respective cathode was set to 1.6 mm.

In each case, the amount of dissolved zinc was determined after 5 hours in the electrolyte. The results are summarized in Table 4. Table 4 sample coating comment Dissolved zinc after 5 h [g] Example 2 iron powder No primer 30.5 Example 3 iron powder Primer: bronze 31.9 Example 4 iron wire No primer 30.6 Example 5 iron wire Primer: bronze 28.8 Example 6 Iron-nickel alloy Fe / Ni = 90/10% by weight 19.6 Example 7 Iron-copper alloy Fe / Cu = 90/10% by weight 19.5 Example 8 Iron-molybdenum alloy Fe / Mo = 90/10 wt.% 22.8 Example 9 Iron-zirconium alloy Fe / Zr = 90/10% by weight 20.1 Example 10 Iron-copper-zirconium alloy Fe / Cu / Zr = 70/25/5 wt.% 18.6 Comparative Example 2 Nickel alloy 95 wt.% Ni, 5 wt.% Al / Ti 6.6 Comparative Example 3 copper - 3.8 Comparative Example 4 molybdenum - 6.3 Comparative Example 5 zirconia - 4.3 Comparative Example 6 chromium - 5.7 Comparative Example 7 uncoated - 1.6 Comparative Example 8 uncoated Atmospherically rusted 8.7

Examples 2 to 10 show that dissolution of zinc by the process of the present invention gives significantly higher zinc dissolution rates than using a conventional steel sheet or a rusted steel sheet. As compared with rusted steel (Comparative Example 8), an increase of up to 350% was observed. With respect to uncoated steel (Comparative Example 7), even increases by a factor of 20 could be observed.

The use of steel sheets with a thermally sprayed layer of an iron material according to the invention as a cathode (Examples 2 to 10) resulted in significantly higher zinc dissolvers than the use of cathodes with thermally sprayed coatings of other materials, regardless of whether metal (Comparative Examples 2 to 4) or an oxide is used for thermal spraying (Comparative Examples 5 and 6).

The thermal sprayed coatings of metallic iron as the iron material (Examples 2 to 5) gave better zinc dissolvers in these experiments than the thermally sprayed coatings made of iron alloys (Examples 6 to 10).

Irrespective of the different roughness (see Table 1), thermally sprayed iron layers of iron wire and iron powder as iron material gave comparable zinc dissolution rates. As already mentioned above, the catalytic activity is considerably higher than in the case of the rusted steel sheet (Comparative Example 8), which has a higher specific surface than the examples according to the invention (see Table 2).

In Examples 2 to 10, a real zinc bath, as used in galvanic zinc coating, was used as the alkaline aqueous solution. These examples impressively prove that the process according to the invention is robust because it tolerates organic additives, for example, and is particularly suitable for providing dissolved zinc for galvanic processes.

With the cathodes from Example 3 and Comparative Example 8, the catalytic effect on the dezincification of zinc-containing scrap metal (scrap) was further investigated.

• In eine Petrischale (1000 mL) mit wässriger NaOH-Lösung (500 mL) wurde die jeweilige Kathode aus Beispiel 3 bzw. Vergleichsbeispiel 8 gelegt. Darauf wurde in direkten Kontakt über die Grundfläche der Kathode ein zu entzinkender Testkörper mittig positioniert. Die Testkörper hatten jeweils die Maße 30 mm x 40 mm x 6 mm und waren mit einer ca. 30 µm dicken galvanisch abgeschiedenen Zinkschicht verzinkt (Testkörper 1) oder mit einer ca. 100 µm dicken Zinkschicht feuerverzinkt (Testkörper 2). Bei den Experimenten wurde die Temperatur (T) und die Konzentration der Natronlauge ([NaOH]) variiert und der Abtrag der Zinkbeschichtung pro Zeiteinheit (Kontaktzeit t) ausgewogen. Die Ergebnisse sind in Tabelle 5 zusammengefasst.

Tabelle 5 Testkörper Kathode T [NaOH] t Abtrag Zn 1 Beispiel 3 25°C 120 g/L 60 min 0,98 g 1 Vergleichsbeispiel 8 25°C 120 g/L 60 min 0,55 g 1 Beispiel 3 40°C 120 g/L 15 min 0,52 g 1 Vergleichsbeispiel 8 40°C 120 g/L 15 min 0,25 g 2 Beispiel 3 25°C 120 g/L 15 min 0,35 g 2 Vergleichsbeispiel 8 25°C 120 g/l 60 min 0,13 g 2 Beispiel 3 25°C 200 g/L 15 min 0,49 g 2 Vergleichsbeispiel 8 25°C 200 g/L 60 min 0,27 g Experimental procedure:

• In a Petri dish (1000 mL) with aqueous NaOH solution (500 mL), the respective cathode of Example 3 and Comparative Example 8 was placed. Then, in direct contact over the base of the cathode, a test piece to be dezincified was centered. The test specimens each had the dimensions 30 mm × 40 mm × 6 mm and were galvanized with a zinc coating deposited approximately 30 μm thick (test body 1) or hot-dip galvanized with a zinc layer approximately 100 μm thick (test specimen 2). In the experiments, the temperature (T) and the concentration of the sodium hydroxide solution ([NaOH]) were varied and the removal of the zinc coating per unit time (contact time t) was balanced. The results are summarized in Table 5.

Table 5 test body cathode T [NaOH] t Removal Zn 1 Example 3 25 ° C 120 g / L 60 min 0.98 g 1 Comparative Example 8 25 ° C 120 g / L 60 min 0.55 g 1 Example 3 40 ° C 120 g / L 15 minutes 0.52 g 1 Comparative Example 8 40 ° C 120 g / L 15 minutes 0.25 g 2 Example 3 25 ° C 120 g / L 15 minutes 0.35 g 2 Comparative Example 8 25 ° C 120 g / l 60 min 0.13 g 2 Example 3 25 ° C 200g / L 15 minutes 0.49 g 2 Comparative Example 8 25 ° C 200g / L 60 min 0.27 g

The dezincing carried out by the process according to the invention, which uses an iron layer produced by thermal spraying on a substrate as the cathode, shows significantly higher zinc removals under comparable conditions. That is, more zinc per unit time can be removed from the test body.

The results in Table 5 show that the process according to the invention is suitable for the dissolution of both electrodeposited zinc and more robust hot-dip galvanizing.

Claims (16)

Process for dissolving zinc or a zinc alloy, in which
metallic zinc or a zinc alloy is brought into electrically conductive contact with an iron layer and is immersed with this wholly or partly in an aqueous alkaline solution, wherein the iron layer consists of a thermally sprayed onto a substrate iron material. A method of dissolving zinc or a zinc alloy according to claim 1, wherein the aqueous alkaline solution is an alkaline, cyanide-free zinc bath. A method of dissolving zinc or a zinc alloy according to claim 1, wherein scrap metal containing zinc or zinc alloy is used for dissolving zinc or a zinc alloy. A method of dissolving zinc or a zinc alloy according to any one of claims 1 to 3, wherein the iron layer comprises iron (0) and one or more iron (III) oxygen compounds. A method of dissolving zinc or a zinc alloy according to claim 4, wherein the iron (III) oxygen compound comprises at least one compound selected from a ferric oxide, an iron (III) oxide hydroxide, an iron (III) Hydroxide and combinations thereof. A method of dissolving zinc or a zinc alloy according to any one of claims 1 to 5, wherein the iron material used for thermal spraying comprises metallic iron and / or an iron alloy. A method of dissolving zinc or a zinc alloy according to claim 6, wherein the iron alloy is one of iron various transition metal, preferably selected from manganese, nickel, copper, molybdenum, zirconium, and combinations thereof, and / or carbon. A method of dissolving zinc or a zinc alloy according to claim 6 or 7, wherein the iron material used for thermal spraying at least 60 wt.% Iron, preferably at least 80 wt.% Iron, more preferably at least 90 wt.% Iron, particularly preferably at least 95 wt % Iron, based on the total weight of the iron material. A method for dissolving zinc or a zinc alloy according to any one of claims 1 to 8, wherein the iron layer has a roughness Ra of at least 4 microns, where Ra is the arithmetic mean roughness according to DIN EN ISO 4287: 2010. A method of dissolving zinc or a zinc alloy according to any one of claims 1 to 9, wherein the iron layer has an average thickness of 10 μm to 1000 μm as determined by scanning electron microscopy (SEM) on a transverse section of the iron layer. A method of dissolving zinc or a zinc alloy according to any one of claims 1 to 10, wherein the substrate is of metal, preferably of steel. A method of dissolving zinc or a zinc alloy according to any one of claims 1 to 11, wherein between substrate and iron layer, a primer, preferably based on bronze, nickel or a nickel-titanium alloy, is arranged. A method of dissolving zinc or a zinc alloy according to any one of claims 1 to 12, wherein, to produce the iron layer, the iron material is thermally sprayed onto the substrate by one of the following methods: Arc wire spraying, Thermo spray powder spraying, Flame spraying, high velocity flame spraying, plasma spraying, oxy-fuel spraying, oxy-fuel wire spraying, laser spraying, cold gas spraying, detonation spraying and PTWA spraying. A process for electroplating zinc or a zinc alloy comprising: (A) the galvanic deposition of zinc or a zinc alloy from an aqueous alkaline solution containing dissolved zinc and optionally other dissolved metals, on a component or other electrically conductive body to the component or the electrically conductive body with zinc or a To coat zinc alloy, and (B) performing a method of dissolving zinc or a zinc alloy according to any one of claims 1 to 13 to provide dissolved zinc for the step (A). An apparatus for dissolving zinc or a zinc alloy comprising an assembly having a zinc anode, an iron layer as a cathode in electrical contact with the zinc anode, wherein the zinc anode comprises metallic zinc or a zinc alloy, - The iron layer consists of a thermally sprayed onto a substrate iron material, and - The device comprises a container which is suitable for receiving an aqueous alkaline solution into which the arrangement can be immersed in whole or in part. A device for dissolving zinc or a zinc alloy according to claim 15, wherein the iron layer is an iron layer as defined in any one of claims 4 to 10, and / or the substrate is made of metal, preferably of steel, and / or - An adhesive base, preferably based on bronze, nickel or a nickel-titanium alloy, is disposed between the substrate and the iron layer.

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