Method for cathodic corrosion protection of chromium surfaces

1. A method for cathodic corrosion protection of a chromium surface, the method comprising in this order the steps of

(i) providing a substrate having a chromium surface and at least one intermediate layer between the substrate and the chromium surface selected from the group consisting of nickel, nickel alloys, copper and copper alloys,

(ii) contacting said substrate with an aqueous solution comprising at least one compound containing phosphorous according to formulae II. and V.:

wherein R is selected from the group consisting of H, unsubstituted C 1 -C 20 -alkyl, linear or branched, unsubstituted C 1 -C 6 -alkaryl, linear or branched, and unsubstituted aryl, R2 and R3 can be equal or different and are independently selected from the group consisting of H, NH 4 + , Li + , Na + , K + , unsubstituted C 1 -C 20 -alkyl, linear or branched, unsubstituted C 1 -C 6 -alkaryl, linear or branched, and unsubstituted aryl, and wherein n is an integer ranging from 1 to 15, and

at least one additive which increases the solubility of the at least one compound containing phosphorus, wherein the at least one additive which increases the solubility of the at least one compound containing phosphorous is a polyether compound;

while passing an electrical current through said substrate, at least one anode and the aqueous solution wherein said substrate serves as cathode

and thereby forming a corrosion protection layer on the chromium surface.

2. The method for cathodic corrosion protection according to claim 1 wherein the at least one compound containing phosphorous is selected from compounds according to formulae II. and V. wherein R is selected from the group consisting of n-octyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, n-tridecyl, n-tetradecyl, n-pentadecyl, n-hexadecyl, n-heptadecyl, n-octadecyl, unsubstituted branched C 8 to C 18 alkyl residues, and wherein R2 and R3 are H or a suitable counter ion independently selected from Li + , Na + , K + and NH 4 + .

3. The method for cathodic corrosion protection according to claim 1 wherein the at least one compound containing phosphorous is selected from compounds according to formula II. wherein R of the compound containing phosphorous is selected from the group consisting of n-octyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, n-tridecyl, n-tetradecyl, n-pentadecyl, n-hexadecyl, n-heptadecyl, n-octadecyl, and wherein R2 and R3 are H or a suitable counter ion independently selected from Li + , Na + , K + and NH 4 + .

4. The method for cathodic corrosion protection according to claim 1 wherein the concentration of the at least one compound containing phosphorous in the aqueous solution ranges from 0.0001 to 0.5 mol/l.

5. The method for cathodic corrosion protection according to claim 1 wherein the electrical current passed through the substrate ranges from 0.005 to 5 A/dm 2 .

6. The method for cathodic corrosion protection according to claim 1 wherein the aqueous solution is held during step (ii) at a temperature in the range of 20 to 80° C.

7. The method for cathodic corrosion protection according to claim 1 wherein the substrate is contacted in step (ii) with the aqueous solution for 10 to 900 s.

8. The method for cathodic corrosion protection according to claim 1 wherein the at least one anode is made from a material selected from the group consisting of stainless steel, platinum or platinized titanium.

9. The method for cathodic corrosion protection according to claim 1 wherein the at least one additive which increases the solubility of the at least one compound containing phosphorous is selected from compounds represented by formula VII.

wherein m, n, o and p are integers ranging from 0 to 200 and are the same or different and m+n+o+p is at least 2, and wherein R4 and R10 are the same or different and are selected independently from the group consisting of H, a suitable counter ion like Li + , Na + , K + and NH 4 + , C 1 -C 20 -alkyl, substituted or unsubstituted, linear or branched, C 1 -C 6 -alkaryl, linear or branched, allyl, aryl, sulfate, phosphate, halide and sulfonate and wherein each of the R5, R6, R8 and R9 groups may be the same or different and are selected independently from the group consisting of H, C 1 -C 6 -alkyl, linear or branched, substituted or unsubstituted and wherein R7 is selected from the group consisting of C 1 -C 12 -alkylene, linear or branched, substituted or unsubstituted, arylene 1,2-, 1,3- and 1,4-substituted, naphthylene, 1,3-, 1,4- 1,5- 1,6- and 1,8-substituted, higher annulated arylene, cylcloalkylene, —O—(CH 2 (CH 2 ) n OR4, wherein R4 has the meaning defined above, and moieties represented by formula VIII.

wherein in formula VIII, the substitution independently is 1,2-, 1,3- or 1,4 for each ring and wherein q and r are the same or different and range independently from 0 to 10 and R11 and R12 are selected independently from the group consisting of H and C 1 -C 6 -alkyl, linear or branched.

10. The method for cathodic corrosion protection according to claim 1 wherein the at least one additive which increases the solubility of the at least one compound containing phosphorous is one or more compound selected from compounds according to the following formulae XI., XII., and XIII.

and wherein n ranges from 1 to 20,

and wherein n ranges from 1 to 20,

wherein n ranges from 1 to 20.

11. The method for cathodic corrosion protection according to claim 1 wherein the concentration of the at least one additive which increases the solubility of the at least one compound containing phosphorous ranges from 0.0001 to 0.1 mol/l.

12. The method for cathodic corrosion protection according to claim 1 wherein the aqueous solution further comprises a co-solvent selected from the group consisting of alcohols, alkyl ethers of glycols, ketones, esters and ethers.

13. The method for cathodic corrosion protection according to claim 12 wherein the concentration of the co-solvent ranges from 0.0001 to 40 wt.-%.