Method for electrolytically depositing a zinc nickel alloy layer on at least a substrate to be treated

Abstract

The present invention is related to a method for electrolytically depositing a zinc-nickel alloy layer on a substrate, wherein the method comprises an interrupting of the execution of the electrolytical deposition of a zinc-nickel alloy layer on the surface of a substrate by terminating applying the current from the external current source to each of the soluble zinc anode(s) and to each of the soluble nickel anode(s); and wherein afterwards at least one soluble zinc anode, which is remaining in the electrolysis reaction container, is electrically connected by an electrical connection element to form an electrical connection to at least one soluble nickel anode, which is remaining in the electrolysis reaction container, for at least a part of the defined period of time in which no current from the external current source is applied to each of the soluble zinc anode(s) and to each of the soluble nickel anode(s).

Claims

1. Method for electrolytically depositing a zinc-nickel alloy layer on at least a substrate to be treated, wherein the method comprises the following method steps: i. providing an electrolysis reaction container comprising at least one soluble zinc anode and at least one soluble nickel anode; ii. providing an acidic electrolyte comprising at least a zinc ion source and at least a nickel ion source; iii. filling of the electrolysis reaction container of method step (i) with the acidic electrolyte of method step (ii); iv. providing at least a substrate to be treated in said electrolysis reaction container, which has been filled with the acidic electrolyte; v. executing an electrolytical deposition of a zinc-nickel alloy layer on a surface of said substrate to be treated by applying a current from at least an external current source to each of the at least one soluble zinc anode and to each of the at least one soluble nickel anode; vi. terminating applying the current from said external current source to each of the at least one soluble zinc anode and to each of the at least one soluble nickel anode; vii. remaining of the at least one soluble zinc anode and the at least one soluble nickel anode in the electrolysis reaction container, which remains filled with the acidic electrolyte comprising at least a zinc ion source and at least a nickel ion source, without executing the electrolytical deposition of the zinc-nickel alloy layer on the surface of said substrate to be treated for a defined period of time in which no current from said external current source is applied to each of the at least one soluble zinc anode and to each of the at least one soluble nickel anode; and viii. restarting of executing of the electrolytical deposition of a further zinc-nickel alloy layer on the surface of said substrate to be treated by restarting applying the current from said external current source to each of the at least one soluble zinc anode and to each of the at least one soluble nickel anode; characterized in that method step (vii) further comprises applying an electrical connection element to form an electrical connection from said at least one soluble zinc anode, which is remaining in the electrolysis reaction container, to said at least one soluble nickel anode, which is remaining in the electrolysis reaction container, for at least a part of the defined period of time, and wherein the electrical connection element is not the electrolyte.

2. Method for electrolytically depositing a zinc-nickel alloy layer on a substrate to be treated according to claim 1 characterized in that in method step (vii) said at least one soluble zinc anode, which is remaining in the electrolysis reaction container, is electrically connected by the electrical connection element to form the electrical connection to said at least one soluble nickel anode, which is remaining in the electrolysis reaction container, for the entire defined period of time.

3. Method for electrolytically depositing a zinc-nickel alloy layer on a substrate to be treated according to claim 1 characterized in that in method step (vii) each at least one soluble zinc anode, which is remaining in the electrolysis reaction container, is electrically connected by the electrical connection element to form the electrical connection to at least one of the at least one soluble nickel anode, which is remaining in the electrolysis reaction container.

4. Method for electrolytically depositing a zinc-nickel alloy layer on a substrate to be treated according to claim 1 characterized in that in method step (vii) the defined period of time is at least 10 minutes.

5. Method for electrolytically depositing a zinc-nickel alloy layer on a substrate to be treated according to claim 1 characterized in that in method step (viii) the restarting of execution of the electrolytical deposition of a further zinc-nickel alloy layer on the surface of said substrate to be treated is done without an activation of said at least one soluble zinc anode.

6. Method for electrolytically depositing a zinc-nickel alloy layer on a substrate to be treated according to claim 1 characterized in that the method does not comprise the provision and/or utilization of any membrane in the electrolysis reaction container.

7. Method for electrolytically depositing a zinc-nickel alloy layer on a substrate to be treated according to claim 1 characterized in that the method does not comprise the provision and/or utilization of any anode bag.

8. Method for electrolytically depositing a zinc-nickel alloy layer on a substrate to be treated according to claim 1 characterized in that in method step (vii) each of the at least one soluble zinc anode remains in the electrolysis reaction container filled with the acidic electrolyte for at least a part of the defined period of time.

9. Method for electrolytically depositing a zinc-nickel alloy layer on a substrate to be treated according to claim 1 characterized in that in method step (vii) the electrical connection between said at least one soluble zinc anode, which is remaining in the electrolysis reaction container, and said at least one soluble nickel anode, which is remaining in the electrolysis reaction container, is terminated automatically, at the latest at the beginning of method step (viii), if said electrical connection is still present at that time.

10. Method for electrolytically depositing a zinc-nickel alloy layer on a substrate to be treated according to claim 1 characterized in that in method step (v) the at least one soluble zinc anode has a current density ranging from 1 to 6 ASD.

11. Method for electrolytically depositing a zinc-nickel alloy layer on a substrate to be treated according to claim 1 characterized in that the acidic electrolyte has a pH-value ranging from 4 to 6.

12. Method for electrolytically depositing a zinc-nickel alloy layer on a substrate to be treated according to claim 1 characterized in that in method step (v) the temperature of the acidic electrolyte is ranging from 20 to 55 C.

13. Method for electrolytically depositing a zinc-nickel alloy layer on a substrate to be treated according to claim 1 characterized in that zinc ion concentration in the acidic electrolyte is ranging from 10 to 100 g/l.

14. Method for electrolytically depositing a zinc-nickel alloy layer on a substrate to be treated according to claim 1 characterized in that nickel ion concentration in the acidic electrolyte is ranging from 10 to 100 g/l.

15. Method for electrolytically depositing a zinc-nickel alloy layer on a substrate to be treated according to claim 1 characterized in that the electrical connection element is an electrical cable.

16. Method for electrolytically depositing a zinc-nickel alloy layer on a substrate to be treated according to claim 1 characterized in that in method step (viii) the restarting of execution of the electrolytical deposition of a further zinc-nickel alloy layer on the surface of said substrate to be treated is done without an activation by hydrochloric acid, sulfuric acid or mixtures thereof.

17. Method for electrolytically depositing a zinc-nickel alloy layer on a substrate to be treated according to claim 1 characterized in that the acidic electrolyte has a pH-value ranging from 5.2 to 5.6.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) As used herein, the term zinc ion source in accordance with the present invention refers to any kind of chemical compound, which is suitable to provide zinc ions in the electrolyte. For this purpose, a zinc salt or a zinc complex is exemplarily suitable.

(2) As used herein, the term nickel ion source in accordance with the present invention refers to any kind of chemical compound, which is suitable to provide nickel ions in the electrolyte. For this purpose, a nickel salt or a nickel complex is exemplarily suitable.

(3) As used herein, the term terminating applying the current from said external current source in method step (vi) in accordance with the present invention refers to an action, wherein the application of current from an external current source is switched off.

(4) The term defined period of time in which no current from said external current source is applied to each of the soluble zinc anode(s) and to each of the soluble nickel anode(s) refers to a period of time in method step (vii), which is beginning subsequently to the action of terminating applying the current in method step (vi).

(5) The term filled with an acidic electrolyte in method step (vii) refers to an acidic electrolyte comprising at least a zinc ion source and at least a nickel ion source. Preferably it is the electrolyte of method step (ii).

(6) As used herein, the term remaining of at least one soluble zinc anode and at least one soluble nickel anode in the electrolysis reaction container, which remains filled with an acidic electrolyte comprising at least a zinc ion source and at least a nickel ion source in accordance with the present invention refers to a situation, wherein a customer possibly removes one or more than one soluble zinc and/or nickel anodes out of the electrolysis reaction container during the defined period of time in method step (vii). However, it is necessary that at least one soluble zinc anode and at least one soluble nickel anode still remain in the electrolyte in the electrolysis reaction container. Furthermore, the electrolyte has at least to remain up to a certain liquid level in the electrolysis reaction container in such a way that the soluble zinc and nickel anodes being in said container are still reaching at least partially, preferably completely, into the electrolyte.

(7) The electrical connection of the at least one soluble zinc anode to the at least one soluble nickel anode in method step (vii) can be exemplarily formed by an electrical cable. Conclusively, the electrical cable allows the flow of current between such a zinc anode and a nickel anode without making use of an external current source. In principle, it works like a short-circuited galvanic cell. The current, which flows now between zinc anode and nickel anode, is caused by the difference of the electrochemical potential of zinc and nickel. Thus, elemental nickel is deposited on the surface of the respective zinc anode. The amount of nickel ions, which is able to be deposited on the zinc electrode surface, is decreasing by time. This is caused by the increased covering of the former zinc surface of the zinc electrode by the deposited nickel. That means that the total thickness of the nickel deposit is limited to a certain extent, which avoids that the nickel deposit is becoming too thick.

(8) As used herein, the term electrical connection element in accordance with the present invention refers not to an electrolyte.

(9) If the method is restarting the executing of an electrolytical deposition of a zinc-nickel alloy layer on the surface of said substrate to be treated by restarting applying the current from said external current source to each of the soluble zinc anode(s) and to each of the soluble nickel anode(s), the electrical connection between the soluble zinc anode(s) and the respective soluble nickel anode(s) has to be removed again at the latest to the time of entering method step (viii). As soon as the current from the external current source is applied again in method step (viii) to the soluble zinc and nickel anodes, the nickel deposit is going immediately again in solution (in the electrolyte). There is no obstacle due to the present nickel deposit on the surface of the zinc anode for restarting the method of electrolytical deposition of a zinc-nickel alloy layer on the surface of a substrate to be treated in the acidic electrolyte.

(10) Nickel and zinc anodes can be chosen as commonly required by these known electrolytical acidic zinc-nickel deposition methods. Zinc anodes can exemplarily be a plate, a sheet, a bar, or a bar with continuous titanium core inside of the zinc anode bar.

(11) In one embodiment, in method step (vii) said at least one soluble zinc anode, which is remaining in the electrolysis reaction container, is electrically connected by an electrical connection element to form an electrical connection to said at least one soluble nickel anode, which is remaining in the electrolysis reaction container, for the entire defined period of time.

(12) This is advantageous because it minimizes the time in which further black passivating deposit can be deposited on the surface of the soluble zinc anodes.

(13) In one embodiment, in method step (vii) each soluble zinc anode, which is remaining in the electrolysis reaction container, is electrically connected by an electrical connection element to form an electrical connection to at least one soluble nickel anode, which is remaining in the electrolysis reaction container.

(14) It is of course preferred to protect all soluble zinc anodes by the nickel deposit executed in inventive method step (vii). This minimizes effort for maintenance reasons.

(15) In one embodiment, in method step (vii) the defined period of time is at least 10 minutes, preferably at least 1 hour, and more preferably at least 3 hours.

(16) The longer the defined period of time is, the more black passivating deposit is deposited on the surface of the soluble zinc anodes.

(17) In one embodiment, in method step (viii) the restarting of execution of the electrolytical deposition of a zinc-nickel alloy layer on the surface of said substrate to be treated is done without an activation of at least a soluble zinc anode, preferably without an activation by an acid, more preferably without an activation by an inorganic acid, and most preferably without an activation by hydrochloric acid, sulfuric acid or mixtures thereof.

(18) This saves maintenance effort and cost.

(19) In one embodiment, the method does not comprise the provision and/or utilization of any kind of membrane in the electrolysis reaction container.

(20) The application of such expensive technical equipment can be avoided by the inventive method claimed herein. There is no need to provide membrane anode systems comprising separated compartments inside of the electrolysis reaction container divided by membranes.

(21) In one embodiment, the method does not comprise the provision and/or utilization of any kind of anode bags.

(22) In one embodiment, in method step (vii) all soluble zinc anodes remain in the electrolysis reaction container filled with the acidic electrolyte for at least a part of the defined period of time, preferably for the entire defined period of time.

(23) This is a clear advantage of the inventive method. A customer solely still need to take the zinc anodes out of the electrolysis reaction container for general replacement due to the consumption of the anode material by the method, but no more caused by the black passivating deposit. The formation of this black passivating deposit is in literature also called sometimes cementation effect.

(24) In one embodiment, in method step (vii) the electrical connection between said at least one soluble zinc anode, which is remaining in the electrolysis reaction container, and said at least one soluble nickel anode, which is remaining in the electrolysis reaction container, is terminated automatically, preferably by a mechanical switch, at the latest at the beginning of method step (viii), if said electrical connection is still present at that time.

(25) This offers the advantage that no trained user has to be present at customer's site for disconnecting the zinc anodes from the nickel anodes before the external current source is switched on again simultaneously or subsequently. The possibility of automatic interruption of the electrical connection between the at least one soluble zinc anode and the at least one soluble nickel anode reduces further the effort at customer's site in order to adapt especially already existing plating lines with this new inventive method. The customer has solely to install in a preferred embodiment thereof an automatic mechanical switch for the electrical connection between the at least one soluble zinc anode and the at least one soluble nickel anode.

(26) In one embodiment, in method step (v) the soluble zinc anode(s) has/have an anodic current density ranging from 1 to 6 ASD, preferably from 2 to 6 ASD, and more preferably from 3 to 5 ASD.

(27) ASD is commonly used in the galvanic industry and means also here in the context of the present invention ampere per square decimeter. If the anodic current density is higher than 6 ASD, it leads to numerous disadvantageous effects, such as excessive dissolving of the zinc anodes, high heat development, bad geometric metal distribution on the surface of the substrate to be treated and bad metal throwing power.

(28) In one embodiment, the acidic electrolyte has a pH-value ranging from 4 to 6, preferably from 4.5 to 5.8, and more preferably from 5.2 to 5.6.

(29) If the pH is becoming too high, nickel hydroxides are formed, which are known as disadvantageous in this acidic electrolytical deposition methods.

(30) In one embodiment, in method step (v) the temperature of the acidic electrolyte is ranging from 20 to 55 C., preferably from 25 to 50 C., and more preferably from 30 to 45 C.

(31) In one embodiment, the zinc ion concentration in the acidic electrolyte is ranging from 10 to 100 g/l, preferably from 12 to 70 g/l, and more preferably from 17 to 38 g/l.

(32) In one embodiment, the nickel ion concentration in the acidic electrolyte is ranging from 10 to 100 g/l, preferably from 15 to 60 g/l, and more preferably from 23 to 32 g/l.

(33) In one embodiment, the electrical connection element is an electrical cable.

(34) The present invention thus addresses the problem of avoiding the formation of the black passivating deposits on the surface of soluble zinc anodes in a defined period of time in which no current from the at least one external current source is applied to each of the soluble zinc anode(s) and to each of the soluble nickel anode(s) during such an acidic electrolytical zinc-nickel deposition method.

(35) While the principles of the invention have been explained in relation to certain particular embodiments, and are provided for purposes of illustration, it is to be understood that various modifications thereof will become apparent to those skilled in the art upon reading the specification. Therefore, it is to be understood that the invention disclosed herein is intended to cover such modifications as fall within the scope of the appended claims. The scope of the invention is limited only by the scope of the appended claims.