Chromium alloy coating and a method and electrolyte for the deposition thereof
View Patent ↗The invention relates to a method for the electrolytic coating of materials, in particular metallic materials, whereby a chromium alloy is deposited from an electrolyte, comprising at least chromic acid, sulphuric acid, an isopolyanion-forming metal, a short-chain aliphatic sulphonic acid, the salts and/or halo-derivatives thereof and fluorides. According to the invention, an alloy can be deposited, which can comprise a high proportion of isopolyanion-forming metal as a result of the combined addition of the short-chain aliphatic sulphonic acid with the fluorides and is nevertheless smooth and lustrous. In comparison with the alloy coatings known in the state of the art, in particular chrome/molybdenum alloys the above is a definite advantage. Furthermore, the presence of fluorides in particular leads to the above deposited coatings having a significantly higher hardness.
1. A method for electrolytically coating a workpiece comprising depositing a chromium alloy from an electrolyte comprising chromic acid, sulfuric acid, an isopolyanion-forming metal compound wherein the isopolyanion-forming metal is selected from the group consisting of Mo, V, W, and Nb, a fluoride, and a compound selected from the group consisting of a short-chain aliphatic sulfonic acid, a salt thereof, and a halogen derivative thereof.
2. The method according to claim 1 , wherein the electrolyte has a concentration of the isopolyanion-forming metal compound of at least about 1 g/L.
3. The method according to claim 1 , wherein the electrolyte comprises chromic acid and a molybdenum compound in a weight ratio of about 2:1.
4. The method according to claim 1 Wherein the electrolyte comprises chromic acid and a vanadium compound in a weight ratio of about 5:1.
5. The method according to claim 1 wherein the electrolyte comprises chromic acid and a niobium compound in a weight ratio of about 50:1.
6. The method according to claim 1 wherein the electrolyte comprises chromic acid and a tungsten compound in a weight ratio of about 40:1.
7. The method according to claim 1 wherein the electrolyte comprises a molybdenum compound selected from the group consisting of molybdic acid and an alkali molybdate.
8. The method according to claim 7 wherein the electrolyte has a molybdic acid concentration between about 50 g/L and about 90 g/L.
9. The method according to claim 1 wherein the electrolyte comprises a vanadium compound selected from the group consisting of ammonium metavanadate, vanadic acid, and vanadium pentoxide.
10. The method according to claim 1 wherein the electrolyte comprises a niobium compound comprising niobic acid.
11. The method according to claim 1 Wherein the electrolyte comprises a tungsten compound comprising an alkali tungstenate.
12. The method according to claim 1 wherein the electrolyte has a concentration of short-chain aliphatic sulfonic acids, salts thereof, and halogen derivatives thereof of at least about 0.1 g/L.
13. The method according to claim 12 Wherein the concentration of short-chain aliphatic sulfonic acids, salts thereof, and halogen derivatives thereof is between about 0.1 g/L and about 10 g/L.
14. The method according to claim 12 wherein the concentration of short-chain aliphatic sulfonic acids, salts thereof, and halogen derivatives thereof is about 2 g/L.
15. The method according to claim 1 wherein the electrolyte has a sulfuric acid concentration between about 1 g/L and about 6 g/L.
16. The method according to claim 15 wherein the sulfuric acid concentration is about 2 g/L.
17. The method according to claim 1 wherein the electrolyte comprises chromic acid and sulfuric acid in a weight ratio of about 100:1.
18. The method according to claim 1 wherein the electrolyte has a chromic acid concentration between about 100 g/L and about 400 g/L.
19. The method according to claim 1 wherein the electrolyte has a fluoride concentration between about 30 mg/L and about 800 mg/L.
20. The method according to claim 19 Wherein the fluoride concentration is between about 30 mg/L and about 300 mg/L.
21. The method according to claim 1 wherein the chromium alloy is deposited at a current density between about 20 A/dm 2 and about 100 A/dm 2 .
22. A chromium alloy layer produced by the method according to claim 1 , the layer comprising chromium and an isopolyanion-forming metal and having a hardness of at least about 1050 HV 0.1.
23. The chromium alloy layer according to claim 22 , wherein the layer is glossy.
24. An electrolyte for electrolytic deposition of a chromium alloy, the electrolyte comprising chromic acid, sulfuric acid, an isopolyanion-forming metal compound wherein the isopolyanion-forming metal is selected from the group consisting of Mo, V, W, and Nb , a fluoride, and a compound selected from the group consisting of a short-chain aliphatic sulfonic acid, a salt thereof, and a halogen derivative thereof.
25. The electrolyte according to claim 24 wherein the isopolyanion-forming metal is in the form of an acid.
26. The electrolyte according to claim 24 wherein the electrolyte has a concentration of the isopolyanion-forming metal compound of at least about 1 g/L.
27. The electrolyte according to claim 24 wherein the electrolyte comprises chromic acid and a molybdenum compound in a weight ratio of about 2:1.
28. The electrolyte according to claim 28 Wherein the electrolyte comprises chromic acid and a vanadium compound in a weight ratio of about 5:1.
29. The electrolyte according to claim 24 Wherein the electrolyte comprises chromic acid and a niobium compound in a weight ratio of about 50:1.
30. The electrolyte according to claim 24 wherein the electrolyte comprises chromic acid and a tungsten compound in a weight ratio of about 40:1.
31. The electrolyte according to claim 24 wherein the electrolyte comprises a molybdenum compound selected from the group consisting of molybdic acid and an alkali molybdate.
32. The electrolyte according to claim 31 wherein the electrolyte has a molybdic acid concentration between about 50 g/L and about 90 g/L.
33. The electrolyte according to claim 24 wherein the electrolyte comprises a vanadium compound selected from the group consisting of ammonium metavanadate, vanadic acid, and vanadium pentoxide.
34. The electrolyte according to claim 24 wherein the electrolyte comprises a niobium compound comprising niobic acid.
35. The electrolyte according to claim 34 wherein the concentration of short-chain aliphatic sulfonic acids, salts thereof, and halogen derivatives thereof is between about 0.1 g/L and about 10 g/L.
36. The electrolyte according to claim 34 wherein the concentration of short-chain aliphatic sulfonic acids, salts thereof, and halogen derivatives thereof is about 2 g/L.
37. The electrolyte according to claim 24 wherein the electrolyte comprises a tungsten compound comprising an alkali tungstenate.
38. The electrolyte according to claim 24 wherein the electrolyte has a concentration of short-chain aliphatic sulfonic acids, salts thereof, and halogen derivatives thereof of at least about 0.1 g/L.
39. The electrolyte according to claim 24 wherein the electrolyte has a sulfuric acid concentration between about 1 g/L and about 6 g/L.
40. The electrolyte according to claim 39 wherein the sulfuric acid concentration is about 2 g/L.
41. The electrolyte according to claim 24 wherein the electrolyte comprises chromic acid and sulfuric acid in a weight ratio of about 100:1.
42. The electrolyte according to claim 24 wherein the electrolyte has a chromic acid concentration between about 100 g/L and about 400 g/L.
43. The electrolyte according to claim 24 wherein the electrolyte has a fluoride concentration between about 30 mg/L and about 800 mg/L.
44. The electrolyte according to claim 43 wherein the fluoride concentration is between about 30 mg/L and about 300 mg/L.
45. The electrolyte according to claim 24 wherein the electrolyte is capable of depositing an alloy of chromium and the isopolyanion-forming metal in an electrolytic coating process, the alloy having a hardness of at least about 1050 HV 0.1.
46. A method for electrolytically coating a workpiece comprising depositing a chromium alloy from an electrolyte comprising chromic acid in a concentration between about 100 g/L and about 400 g/L, sulfuric acid, an isopolyanion-forming metal compound, a fluoride, and a compound selected from the group consisting of a short-chain aliphatic sulfonic acid, a salt thereof, and a halogen derivative thereof.
47. An electrolyte for electrolytic deposition of a chromium alloy, the electrolyte comprising chromic acid in a concentration between about 100 g/L and about 400 g/L, sulfuric acid, an isopolyanion-forming metal compound, a fluoride, and a compound selected from the group consisting of a short-chain aliphatic sulfonic acid, a salt thereof, and a halogen derivative thereof.