Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Controlling current distribution within bath
Reexamination Certificate
2001-12-07
2004-09-14
King, Roy (Department: 1742)
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Controlling current distribution within bath
C205S097000, C205S099000, C205S101000, C205S103000, C205S255000, C205S269000, C205S271000
Reexamination Certificate
active
06790332
ABSTRACT:
This application claims the priority of German patent document 100 61 186.9, filed Dec. 7, 2000, the disclosure of which is expressly incorporated by reference herein.
BACKGROUND AND SUMMARY OF INVENTION
The present invention relates to a method for the galvanic deposition of nickel, cobalt, nickel alloys, or cobalt alloys in a galvanic bath, using an electrolyte containing nickel compounds or cobalt compounds, such as sulfates or sulfamates or chlorides. Such electrolytes for galvanic deposition are known, for example from the German patents DE 25 58 423 and DE 22 18 967 (U.S. Pat. No. 3,726,768); U.S. Pat. No. 2,470,775; and European Patent 0 835 335 (U.S. Pat. No. 6,036,833). For the deposition, at least one anode and at least one cathode of the bath is acted upon with periodic current pulses. Such methods with the help of current pulses are known from the state of the art, for example, from U.S. Pat. No. 2,470,775 and European Patent 0 835 335.
With such methods, nickel, cobalt, nickel alloys or cobalt alloys basically can be deposited in one galvanic bath. However, a special problem arises when the components, which are to be produced by such a deposition, should have particular mechanical properties, such as a specified strength or a specified ductility.
Such a problem arises particularly when the component that is to be produced is to be joined indissolubly later on, for example, by welding to other components. For this purpose, the ductility usually must meet certain minimum requirements, so that a welded joint can be realized between a galvanically produced nickel or cobalt layer or layer of any nickel or cobalt alloy and other components with sufficient strength and durability of the welded joint. However, if the ductility of the layer that is to be welded is too high, the strength of the corresponding layer is decreased. The corresponding layer, under some circumstances, no longer satisfies the specified requirements with regard to mechanical load-carrying capability. This is true particularly for components that are to be exposed to relatively high stresses such as to those that can occur in components of rocket engines. The thrust chambers of rocket engines, which consist essentially of components such as the injection head, combustion chamber and thrust nozzle, should be especially mentioned in this connection.
It has turned out that the methods, known from the art, cannot guarantee the necessary properties of the deposited layers of nickel or cobalt or of nickel alloys or cobalt alloys, which are an indispensable prerequisite for an indissoluble connection, especially by welding, of such a layer to other components, for example, those of an alloy based on iron or nickel.
It is therefore an object of the present invention to provide a method for the galvanic deposition of nickel, cobalt, nickel alloys, or cobalt alloys in a galvanic bath. At least one anode and at least one cathode of the bath are acted upon with periodic current pulses. Layers of nickel or cobalt or of nickel alloys or cobalt alloys can be produced, which can be connected indissolubly to other components and especially welded to other components.
This objective is accomplished according to preferred embodiments of the present invention.
In the case of a method for the galvanic deposition of nickel, cobalt, nickel alloys or cobalt alloys in a galvanic bath according to the present invention, an electrolyte is u d that contains appropriate nickel compounds or cobalt compounds, particularly sulfate or sulfamates or chloride. For the deposition, at least one anode and at least one cathode of the bath is acted upon with periodic current pulses, that is, a so-called plating method is used. Normally, a deposition body n which a layer of the appropriate material is to be deposited acts as cathode. Pursuant to the present invention, the I
A
/I
c
ratio of the anode current density I
A
to the cathode current density I
C
is selected to be greater than 1 and smaller an 1.5. The charge ratio Q
A
/Q
C
=T
A
I
A
/T
C
I
C
of the charge Q
A
, transported dun g an anode pulse of duration T
A
, to the charge Q
C
, transported during a cathode pulse of duration T
C
, is between 30% and 45%.
It has turned out that the properties, especially with regard to the strength and ductility of the layer, which are necessary for an indissoluble connection of the deposited layer to other components, can be achieved only if such a ratio is selected. According to EP 0 835 335, on the other hand, it is proposed in particular, that an I
A
/I
C
ratio be selected that is at least 1.5. This document does not go into suitable parameter ranges for achieving a layer with the aforementioned properties. Furthermore, there is no mention there of selecting a suitable Q
A
/Q
C
ratio.
In preferred embodiments, the I
A
/I
C
ratio is between 1.2 and 1.45 and particularly between 1.3 and 1.4 and the charge ratio Q
A
/Q
C
=T
A
I
A
/T
C
I
C
is between 35% and 40% For these ranges of the parameters, particularly advantageous properties of the deposited layer can be noted, especially with regard to the strength and the ductility.
In order to achieve improved and uniform deposition of the layer on a deposition body, which in the final analysis is also to the benefit of the load-carrying capability of the layer over its whole extent, provisions can be made for the deposition. At least one contoured anode is used, the contour of which is adapted to the contour of the deposition body on which the nickel, the cobalt, the nickel alloy or the cobalt alloy is to be deposited. In particular, an almost constant distance between the anode and the deposition body can be achieved over almost all of the contour of the deposition body by this matching of the anode contour. This makes a uniform deposition possible.
If several anodes are provided in the bath, a contoured anode is used for at least one of the anodes that is closest to the deposition body. The effect of contouring the anode is greater for the anodes closest to the deposition body than for anodes further removed. Anodes without contouring, which are less expensive in some cases and can be used independently of the special shape of the deposition body, can therefore be used for the anodes that are further removed. Accordingly, by this suitable combination of anodes, which have and have not been contoured, an optimum can be achieved with respect to the quality of the deposition as well as the expenditure required for this purpose.
To form the contoured anode, a contoured container, for example, may be used that is permeable to the ions of the deposited nickel or cobalt or nickel alloy or cobalt alloy and which is filled with bodies of nickel, cobalt or a nickel alloy or a cobalt alloy. Special containers for such bodies are known from German patent DE 25 58 423 in the form of titanium or plastic baskets, which are filled with nickel pellets. However, contouring of the container is not disclosed in that document.
In principle, as an alternative to such containers, a solid electrode body that has at least a coating of the nickel, cobalt, nickel alloy or cobalt alloy, which is to be deposited, or that consists even of solid nickel, cobalt, nickel alloy or cobalt alloy, can also be used as a contoured anode.
During the deposition process, it may be necessary to selectively affect the deposition, which is to take place differently for different regions of the deposition body. This affecting may take place additionally or also alternatively to the aforementioned measure of the contoured anodes. For this purpose, provisions can be made so that the deposition body is shielded partially by current restrictors at least during a portion of the total duration of the deposition. During the time in which the regions are shielded, less deposition is achieved in the shielded regions than in the unshielded regions. Layer properties, especially the thickness of the layer, but also, optionally, the mechanical properties of the layer on the deposition body can be affected locally.
In particular, the cur
Ewald Rüdiger
Filke Peter
Heckmann Michael
Keinath Wolflgang
Langel Günter
Astrium GmbH
King Roy
Leader William T.
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