EP2184384A1 - Galvanic bath and method for deposition of zinc-containing layers - Google Patents

Abstract

Zinc electroplating apparatus with a catholyte compartment (6) containing an acidic catholyte and a substrate (2) to be plated and an anolyte compartment (5) containing a neutral or acidic zinc-containing anolyte and a consumable zinc anode (4), the compartments being separated by a cation-permeable membrane (3), comprises a device that is in hydraulic communication with the anolyte compartment and exchanges any foreign metal ions in the anolyte for zinc ions or protons. An independent claim is also included for a zinc electroplating process using apparatus as above, where the anolyte is withdrawn from its compartment and passed through a device in which any foreign metal ions are exchanged for zinc ions or protons.

Description

The present invention relates to a galvanic bath and a method for the deposition of zinc-containing layers on substrate surfaces. In particular, the present invention relates to a galvanic bath and a method for the deposition of zinciferous layers from an acidic deposition electrolyte.

The deposition of zinciferous layers on substrate surfaces has been widely used in many fields of technology. Zinc-containing layers are characterized in particular by their high corrosion resistance. Due to the appearance of the resulting zinc coatings, zinc layers or zinc-containing layers are used less in the field of decorative coatings than in the field of functional coatings. Thus, for example, it is common to coat small parts such as screws, nuts, washers, prefabricated structural elements such as angle plates or connecting plates and the like in large numbers. In many cases, the small parts are immersed in so-called drum baskets in appropriate Abscheidebäder and it is created between the Abscheidekorb and an anode a Abscheidestrom.

Often, another metal is deposited in addition to zinc, whereby the obtained properties of the deposited zinc-containing layer can be influenced. In particular, the appearance, the corrosion resistance and the mechanical properties of the deposited layers can be influenced by appropriate alloying depositions. So it is for example from the DE 103 06 823 A1 known to deposit zinc-manganese alloys. In the DE 101 46 559 describes the galvanic deposition of zinc-nickel alloys.

From the DE 195 38 419 A1 It is known to mitabzuscheiden iron, cobalt and nickel as alloying metals in addition to zinc.

A problem with the electrodeposition of zinc-containing layers on substrate surfaces of acidic zinc-containing electrolytes is that the use of dissolving zinc anodes leads to the formation of deposits on the anode surface, which passivate them and adversely affect the production cycle. By these deposits and the effectiveness of the electrodeposition can be reduced.

This, also known as cementation effects to avoid is one of the objects of the present invention. Moreover, it is the object of the present invention to generally improve the methods known from the prior art for the deposition of zinc-containing layers on substrate surfaces.

This object is achieved by a galvanic bath for depositing a zinc-containing layer on a substrate surface, comprising a first cell space, which receives an acidic deposition electrolyte, and a second cell space, which receives a neutral or acidic anolyte, wherein the first cell space of the second Cell space is separated by a cation-permeable membrane and wherein in the anolyte receiving cell space a dissolving zinc anode is arranged, which is characterized in that the anolyte receiving cell space is in hydraulic communication with a device which contains any in the anolyte Exchange foreign metal ions for zinc ions and / or protons.

With regard to the method, the object is achieved by a method for electrodeposition of a zinc-containing layer on a substrate surface, wherein the substrate to be coated is brought into contact with an acidic, at least zinc ion-containing deposition electrolyte in a galvanic bath and between the substrate and at least one An anode current is applied, which is suitable to induce the deposition of a zinc-containing layer on the substrate surface, wherein the galvanic bath is divided into at least two cells and the cells separated from one another by a membrane permeable to cations, wherein one cell receives the acidic deposition electrolyte and the second cell a neutral or acid zinc ion-containing anolyte and wherein a dissolving zinc anode is disposed in the cell receiving the anolyte, which is characterized in that the acid anolyte is at least partially removed from the cell space receiving it and passed through a device in which any foreign metal ions are exchanged for zinc ions and / or protons.

Surprisingly, it has been found that the subdivision of a galvanic bath into a separation electrolyte receiving space and anolyte space, which are separated from each other by a cation exchange membrane, is capable of overcoming the problems known from the prior art, provided at least a partial flow of the anolyte is derived and passed through a device in which any foreign metal ions are exchanged for zinc ions and / or protons.

According to the invention, the device in which any foreign metal ions contained in the anolyte are exchanged can be, for example, a precipitation compartment or a cation exchanger. In the case of the precipitation compartment, for example, the pH of the anolyte will be increased to a value at which the foreign metal ions possibly contained in the anolyte precipitate out as hydroxides. The resulting precipitate can be separated off by means of sedimentation, filtration, centrifugation or the like, and the anolyte, depleted of any foreign metal ions, can then be returned to the cell space accommodating the anode. Before recycling, the pH is adjusted to a corresponding acidic pH by addition of an acid. As a result, foreign metal ions are finally exchanged for protons.

In a preferred embodiment of the invention, the device in which any foreign metal ions contained in the anolyte are exchanged for other cations is a cation exchanger which, for example, has a suitable cation exchange resin. In this case, the foreign metal ions can advantageously be exchanged for other cations without the addition of anions in the anolyte. In this case, the foreign metal ions can preferably be exchanged for protons or zinc ions.

In the galvanic bath of the present invention, the cation-permeable membrane serves to retain a majority of the foreign metal ions contained in the deposition electrolyte, such as ions of the group consisting of nickel, cobalt, manganese or iron, although the membrane is essentially for these ions is also permeable. Without being bound by this theory, the Applicant assumes that the voltage gradient of about 1 volt across the membrane is a barrier which is difficult to overcome for the foreign metal ions contained in the deposition electrolyte. The foreign metal ions which nevertheless migrate into the anolyte are intercepted via the device to be provided according to the invention for exchanging the foreign metal ions and are preferably exchanged for zinc ions and / or protons. In this case, the device serves not only to catch any foreign metal ions which may be present in the anolyte, but also to maintain a certain zinc ion level in the anolyte.

In one embodiment of the galvanic bath according to the invention, the anolyte has, in addition to zinc ions, an acid and / or alkali metal ions. Suitable acids in the anolyte may be, for example, boric acid, acetic acid, citric acid, tartaric acid, aminoacetic acid, methanesulfonic acid, hydrochloric acid, sulfuric acid and the like. Suitable sources of zinc ions in the anolyte may be soluble zinc compounds such as zinc chloride, zinc sulfate or organic zinc compounds such as zinc methanesulfonate. Suitable sources of alkali ions may be, for example, alkali salts such as sodium fluoride, sodium chloride, sodium bromide, lithium chloride, lithium fluoride, potassium chloride, potassium fluoride, potassium bromide and the like.

Suitable membranes for separating the cell spaces are according to the invention cation exchange membranes which are permeable to 2-valent cations, such as perfluorinated membrane. Furthermore, microporous membranes such as dialysis membranes are suitable for use in the galvanic bath according to the invention.

In the embodiment of the invention, in which in addition to zinc other metals such as nickel, cobalt, manganese or iron are deposited, is in the acid Dependent electrolytes receiving cell space to provide another anode, which preferably consists of the mitabzuscheidenden metal.

In a particular embodiment of the invention, both this second anode and the zinc anode accommodated in the cell space accommodating the anolyte can be electrically connected to the substrate via a single rectifier. The adjustment of the deposition ratio between zinc and the further metal to be deposited is carried out according to the invention by varying the anolyte composition. In particular, in this case, the variation of the alkali metal concentration is decisive, since this has a significant influence on the conductivity of the anolyte and thus on its electrical resistance. As a result, it is advantageously possible to dispense with further rectifiers, which leads to a significant cost reduction with regard to the structural design.

In a further embodiment of the invention, a plurality of separate cell spaces for receiving the anolyte may be provided in the galvanic bath, which are each equipped with a zinc anode. The individual Anolyte dreams are hydraulically connected to each other, so that an exchange of the anolyte between the individual Anolyträumen is possible. In a further development of this embodiment, the anolyte is withdrawn in a first anolyte space, fed to the device for exchanging any foreign metal ions contained in the anolyte, and returned from the latter to the anolyte space removed from the first anolyte space. As a result, it is advantageous to provide only a single device for exchanging the foreign metal ions.

In the device to be provided according to the invention for exchanging any foreign metal ions, it is possible to provide an ion exchange resin for exchanging the foreign metal ions for zinc ions and / or protons. Suitable cation exchangers are, for example, weakly acidic, macroporous resins with chelating lminodiacetic acid groups which selectively bind heavy metal cations. When selecting the ion exchange resin, it must be ensured that it has sufficient selectivity for the exchange of divalent cations and is essentially neutral towards monovalent cations. The cation exchange resins are usually conditioned and loaded with zinc ions by means of a zinc ion-containing solution, such as, for example, a zinc chloride solution. When flowing through the anolyte by the cation exchange device then possibly containing in the anolyte Foreign metal ions are taken up by the cation exchange resin and exchanged for zinc ions. In this way, on the one hand, the contamination of the anolyte with foreign metal ions sustainably avoided, on the other hand, the cation exchange device acts as a kind of zinc ion buffer, whereby the zinc ion level in the anolyte can be maintained at a desired level.

Fig. 1

zeigt die schematische Darstellung eines erfindungsgemäßen galvanischen Bades,

Fig. 2

zeigt die schematische Darstellung eines erfindungsgemäßen galvanischen Bades in einer weiteren Ausgestaltung zur Abscheidung von Zink-Mangan-Schichten.

In a further embodiment of the invention, it may be provided to carry out the replacement of any foreign metal ions contained in the anolyte against zinc ions and / or protons already in the cell space receiving the anolyte. For this purpose, it can be provided, for example, to provide a filled with a corresponding ion exchange resin liquid-permeable bag or hollow body in the anolyte-receiving cell space. This can advantageously be dispensed with facilities such as pumps or the like for the promotion of the anolyte.

Fig. 1

shows the schematic representation of a galvanic bath according to the invention,

Fig. 2

shows the schematic representation of a galvanic bath according to the invention in a further embodiment for the deposition of zinc-manganese layers.

Fig. 1 shows an embodiment of a galvanic bath 1 according to the invention, in which a substrate 2 to be coated is arranged, wherein the galvanic bath 1 is divided by means of a cation exchange membrane 3 into a cell space 5 and a cell space 6, wherein the cell space 5 is a neutral or acidic anolyte and the Cell space 6 receives the deposition electrolyte. In the cell space 5, a dissolving zinc anode 4 is arranged. In the case of co-deposition of other metals such as nickel, cobalt, manganese or iron, a second anode 7 is provided in the cell space 6, which consists of the mitabzuscheidenden metal and is preferably also designed to dissolve. The anode 4, and in the case of the co-deposition of other metals and the anode 7, are electrically connected via rectifier 8 to the substrate 2. By applying a suitable separation stream, metal ions are now deposited on the substrate 2 from the deposition electrolyte. To the extent that zinc ions have been deposited, zinc ions dissolve from the zinc electrode 4 and diffuse out of the cell space 5 through the cation exchange membrane 3 into the cell space 6. This results in a constant level of zinc in the cell space 6. At the cation exchange membrane 3 is formed 1 volts, whereby further foreign metal ions contained in the deposition electrolyte, such as nickel, cobalt, manganese or iron ions, are substantially prevented from passing through the cation exchange membrane 3 into the cell space 5. However, since a passage of these foreign metal ions through the cation exchange membrane 3 can not be completely avoided and, in particular when the deposition voltage is switched off, no potential gradient is applied to the cation exchange membrane 3 which impedes passage of the foreign metal ions, certain foreign metal concentrations in the cell space 5 are to be expected. In order to avoid the cementation effects on the anode 4 caused by these foreign metal ions, the anolyte contained in the cell space 5 is at least partially removed from the cell space 5 by means of suitable conveying devices such as a pump 11 and passed through a cation exchanger 9 before being returned to the cell space 5 becomes. The cation exchange device 9 is filled with a cation exchange resin 10 which has been charged with zinc ions in an upstream conditioning step. The foreign ions contained in the anolyte are now absorbed in the cation exchange device 9 on the cation exchange resin 10 and exchanged for zinc ions.

Fig. 2 shows an embodiment of the galvanic bath 1 according to the invention, in which in addition to the cell space 6, a second cell space 12 is separated by a cation exchange membrane 13 from the cell space 5. Cell space 12 in this case takes on a further anolyte, such as a manganese-containing anolyte and a foreign metal anode 7, which may be formed, for example, recorded in a titanium basket Elektrolytmangan. The anolyte in cell space 12 has a manganese ion source such as manganese (II) sulfate and is by means of suitable acids such. As sulfuric acid, adjusted to a pH <2. By applying a voltage between the anodes 4 and 7 and the substrate 2, manganese ions are released through the cation exchange membrane 13 to the deposition electrolyte under current flow.

The invention will be explained below with reference to exemplary embodiments, without, however, limiting the invention to these exemplary embodiments.

Example 1: Deposition of a zinc-nickel layer

In a galvanic bath according to the invention, as in Fig. 1 is reproduced in the cell space 6, a deposition electrolyte is presented which 40-100 g / l zinc chloride,

60-130 g / l nickel chloride hexahydrate, 140-220 g / l potassium chloride, 10-30 g / l boric acid, 25 g / l sodium acetate trihydrate, 30 g / l aminoacetic acid, 2-12 g / l sodium saccharin,

0.025-0.20 g / l benzalacetone, 0.006-0.01 g / l orthochlorobenzaldehyde, 0.8-1.2 g / l octanol ethoxylate, and 2.5-3.2 g / l potassium salt of the sulfopropylated polyalkoxylated naphthol. The pH of the electrolyte composition described herein is between 5 and 6.

In the cell space 5, an anolyte containing 120 g / l of zinc chloride, 215 g / l of potassium chloride and 20 g / l of boric acid is charged. The concentration of the anolyte-containing components can be varied in a range between 80 g / l and 500 g / l for zinc chloride, 150 g / l to 300 g / l for potassium chloride and 15 g / l to 25 g / l for boric acid , whereby the deposition ratio between zinc and nickel on the substrate surface can be influenced.

In the cell space 5 a dissolving zinc anode is arranged, whereas in the cell space 6 a dissolving nickel anode is arranged. As a substrate to be coated screws are filled in a galvanizing drum, wherein the cathodic contacting takes place via centrally arranged contact pins. At a temperature of the deposition electrolyte of 25 ° C to 50 ° C and a pH of pH 5 to pH 6 for the deposition electrolyte is at a cathodic current density of 0.1 to 1.5 A / dm ^2, a zinc nickel layer with a Deposition speed deposited to about 0.4 microns per minute on the screws serving as a substrate.

Example 2: Deposition of a zinc-nickel layer

In a galvanic bath according to the invention, as in Fig. 1 is reproduced in the cell space 6, a deposition electrolyte is presented, which 40-100 g / l zinc chloride, 60-130 g / l nickel chloride hexahydrate, 140-220 g / l potassium chloride, 10-30 g / l boric acid, 25 g / l sodium acetate trihydrate, 30 g / l aminoacetic acid, 2-12 g / l sodium saccharin, 0.025-0.20 g / l benzalacetone, 0.006-0.01 g / l orthochlorobenzaldehyde, 0.8-1.2 g / l octanol ethoxylate and 2.5-3.2 g / l potassium salt of the sulfopropylated polyalkoxylated naphthol. The pH of the electrolyte composition described herein is between 5 and 6.

In the cell space 5, an anolyte containing 120 g / l of zinc chloride, 215 g / l of potassium chloride and 20 g / l of boric acid is charged. The concentration of the anolyte-containing components can be varied in a range between 80 g / l and 500 g / l for zinc chloride, 150 g / l to 300 g / l for potassium chloride and 15 g / l to 25 g / l for boric acid , whereby the deposition ratio between zinc and nickel on the substrate surface can be influenced.

In the cell space 5, dissolving zinc pellets are arranged in an anode basket made of titanium, whereas in the cell space 6 a dissolving nickel anode is arranged. As the substrate to be coated castings are attached to largely insulated racks, wherein the cathodic contacting takes place via the metallic tips of the frame. At a temperature of the deposition electrolyte of 25 ° C to 50 ° C and a pH of pH 5 to pH 6 for the deposition electrolyte is at a cathodic current density of 0.1 to 4 A / dm ^2, a zinc nickel layer with a deposition rate to deposited at 1 micron per minute on the casting used as a substrate.

Example 3: Deposition of a zinc-cobalt layer

In a galvanic bath according to the invention, as in Fig. 1 is reproduced in the cell space 6, a deposition electrolyte is presented which 60-70 g / l zinc chloride, 100 - 130 g / l cobalt chloride hexahydrate, 190 - 220 g / l potassium chloride, 15 - 20 g / l boric acid, 25 g / l sodium acetate trihydrate, 30 g / l aminoacetic acid, 2-12 g / l sodium saccharin, 0.025-0.20 g / l benzalacetone, 0.006-0.01 g / l orthochlorobenzaldehyde and 2.5-3.2 g / l potassium salt of the sulfopropylated polyalkoxylated Naphtols contains. The pH of the electrolyte composition described herein is between 5 and 6.

In the cell space 5 is an anolyte, which consists of 250 g / l zinc chloride. The concentration of the zinc chloride contained in the anolyte can vary in a range between 80 g / l and 500 g / l zinc chloride. In the cell space 5, dissolving zinc pellets are arranged in a titanium anode basket, whereas in the cell space 6 a dissolving cobalt anode is arranged. As a substrate to be coated screws are filled in a galvanizing drum, wherein the cathodic contact via contact pins. At a temperature of the deposition electrolyte of 25 ° C to 50 ° C and a pH of pH 5.3 to pH 5.6 for the deposition electrolyte is at a cathodic current density of 0.2 to 4 A / dm ^2, a zinc Cobalt layer deposited with a deposition rate of up to about 1 micron per minute on the serving as a substrate screws.

Example 4: Deposition of a bright zinc coating

In a galvanic bath according to the invention, as in Fig. 1 is reproduced, in the cell space 6, a deposition electrolyte is presented, which 40-90 g / l zinc chloride, 180 - 230 g / l potassium chloride, 20 - 30 g / l boric acid, 0.025 - 0.20 g / l benzalacetone, 0 , 8-1.2 g / l octanol ethoxylate and 2.5-3.2 g / l potassium salt of the sulfopropylated polyalkoxylated naphtol. The pH of the electrolyte composition described herein is between 5 and 6.

In the cell space 5 is an anolyte which consists of 250 g / l zinc chloride and 220 g / l potassium chloride. The concentration of the zinc chloride contained in the anolyte can vary in a range between 80 g / l and 500 g / l zinc chloride. Potassium chloride can be used in a concentration of 10 to 300 g / l. In the cell space 5, dissolving zinc pellets are arranged in a titanium anode basket. As a substrate to be coated screws are filled in a galvanizing drum, wherein the cathodic contact via contact pins. At a temperature of the deposition electrolyte of 25 ° C to 50 ° C and a pH of pH 5.3 to pH 5.6 for the deposition electrolyte is at a cathodic current density of 0.1 to 2 A / dm ^2, a zinc layer deposited at a deposition rate of up to about 0.5 microns per minute on the serving as a substrate screws.

Example 5: Deposition of a zinc-manganese layer

In a galvanic bath according to the invention, as in Fig. 2 is reproduced in the cell space 6, a deposition electrolyte is presented, which 40-62 g / l divalent zinc, 80-110 g / l of divalent manganese, 190-220 g / l of a conductive salt, 30 -100 g / l of a Buffer, 10 -15 g / l of a wetting agent, 0.1-0.6 g / l of a defoamer, 0-10 g / l of an antioxidant and 0-1 g / l of a brightener.

In the cell space 5 is an anolyte which consists of 250 g / l zinc chloride and 220 g / l potassium chloride. The concentration of the zinc chloride contained in the anolyte can vary in a range between 80 g / l and 500 g / l zinc chloride. Potassium chloride can be used in a concentration of 10 to 300 g / l. In the cell space 5, a dissolving zinc plate is arranged.

In the third cell space 12, which has no connection to the cation exchange device 12 and which is separated from the cell space 6 by a cation exchange membrane 13, an anolyte containing 150 g / l of manganese (II) sulfate and 30 g / l of sulfuric acid is contained , The concentration of the manganese (II) sulfate contained in this anolyte can vary within a range between 50 g / l to 250 g / l manganese (II) sulfate. The initially used amount of sulfuric acid of 30 g / l is supplemented during operation so that the pH remains below pH 2. As an electric feeder, broken electrolyte manganese is used in a titanium anode basket.

As a substrate to be coated screws are filled in a galvanizing drum, wherein the cathodic contact via contact pins. At a temperature of the deposition electrolyte of 25 ° C to 50 ° C and a pH of pH 5 to pH 6 for the deposition electrolyte at a cathodic current density of 0.2 to 2 A / dm ^2, a zinc layer with a deposition rate to About 0.5 microns per minute deposited on serving as a substrate screws.

LIST OF REFERENCE NUMBERS

1

galvanic bath

2

substratum

3

Cation exchange membrane

4

Zinc anode

5

Cell space for anolyte

6

Cell space for separation electrolyte

7

Foreign metal anode

8th

rectifier

9

cation-exchange

10

cation

11

pump

12

another cell space

13

another cation exchange membrane

Claims (13)

A galvanic bath for depositing a zinc-containing layer on a substrate surface, comprising a first cell space receiving an acidic deposition electrolyte, and a second cell space receiving a neutral or acidic zinc ion-containing anolyte, the first cell space being separated from the second cell space by one for cations permeable membrane is separated and in which the anolyte receiving cell space is arranged a dissolving zinc anode, characterized in that the anolyte receiving cell space is in hydraulic communication with a device which any foreign metal ions containing anolyte in the zinc ions and / or protons exchanges. Galvanic bath according to claim 1, wherein the anolyte in addition to zinc ions, an acid and / or alkali ions. A galvanic bath according to claim 2, wherein the anolyte comprises between 80 and 500 g / l zinc chloride. A galvanic bath according to claim 2, wherein the anolyte comprises between 150 g / l to 300 g / l of an alkali halide. A galvanic bath according to any one of claims 2 to 3, wherein the anolyte comprises between 10 g / l and 30 g / l of an acid. A galvanic bath according to any one of the preceding claims, wherein the precipitating electrolyte comprises, in addition to zinc ions, at least one metal of the group consisting of nickel, cobalt, manganese and iron. A galvanic bath according to any one of the preceding claims wherein the cation permeable membrane is a cation exchange membrane or a microporous membrane. Galvanic bath according to one of the preceding claims, wherein the means for the exchange of any foreign metal ions contained in the anolyte against zinc ions and / or protons is a precipitating compartment or an ion exchange device. Galvanic bath according to one of the preceding claims, wherein the galvanic bath has a plurality of zinc ion-containing anolyte receiving cell spaces, which are each separated from the separating the electrolyte accommodating cell space by a cation-permeable membrane, wherein the anolyte receiving individual cell spaces in hydraulic communication with each other stand. Galvanic bath according to one of the preceding claims, wherein the galvanic bath has at least one further cell space, which is also separated from the deposition-electrolyte bath by a cation exchange membrane and anions of anolyte having zinc with metal on the substrate surface and a dissolving one Anode from the mitabzuscheidenden metal receives. A method of electrodepositing a zinc-containing layer on a substrate surface, wherein the substrate to be coated is contacted in a plating bath with an acidic at least zinc ion-containing deposition electrolyte and a current is applied between the substrate and at least one anode which is suitable to induce the deposition of a zinc-containing layer on the substrate surface, wherein the galvanic bath is divided into at least two cells and the cells are separated from each other by a cation-permeable membrane, one cell separating the acidic to neutral deposition electrolyte and the second cell receiving neutral or acidic anolyte and wherein a dissolving zinc anode is arranged in the cell receiving the anolyte, characterized in that the neutral or acid anolyte is at least partially removed from the cell space receiving it and passed through a device, in which any foreign metal ions are exchanged for zinc ions and / or protons. A method according to claim 11, wherein in addition to the zinc anode there is provided a further dissolving anode serving as a source of zinc serves together on the substrate surface to be deposited metals and which is arranged in the deposition cell electrolyte accommodating the cell space. A method according to claim 12, wherein the two anodes are electrically contacted with the substrate via a common rectifier and the deposition ratio of the metals to be deposited on the composition of the anolyte, in particular its concentration of alkali metal ions, is influenced.

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