ELECTROPLATING BATH CONTAINING TRIVALENT CHROMIUM AND PROCESS FOR DEPOSITING CHROMIUM

Abstract

The present invention refers to an electroplating bath for depositing chromium which comprises at least one trivalent chromium salt, at least one complexing agent, at least one halogen salt and optionally further additives. Moreover, the invention refers to a process for depositing chromium on a substrate using the mentioned electroplating bath.

Claims

1-15. (canceled)

16. An electroplating bath for depositing chromium or chromium alloys comprising: (a) 50 to 400 g/L (0.164 M to 1.314 M) of at least one trivalent chromium salt, (b) 100 to 400 g/L (2.17 M to 8.68 M) of at least one complexing agent, (c) 1 to 50 g/l (0.0085 M to 0.425 M) of at least one halogen salt, and (d) 0 to 10 g/L of additives, wherein the electroplating bath has a pH from 4 to 7 and is substantially free of divalent sulphur compounds and boric acid, its salts and/or derivatives and wherein the molar ratio of the complexing agent to the trivalent chromium salt is from 8:1 to 15:1.

17. The electroplating bath of claim 16, wherein the trivalent chromium salt is selected from the group consisting of chromium(III)sulphate, in acidic or alkaline form, chromium(III)chloride, chromium(III) acetate, chromium(III) hydroxy acetate, chromium(III) formate, chromium(III) hydroxy formate, chromium(III) carbonate, chromium(III) methanesulfonate, potassium chromium(III) sulphate, and mixtures thereof.

18. The electroplating bath of claim 16, wherein the trivalent chromium salt is present in an amount of 100 to 300 g/L (0.328 M to 0.984 M).

19. The electroplating bath of claim 16, wherein the trivalent chromium salt is present in an amount of 120 to 160 g/L (0.3936 M to 0.5248 M).

20. The electroplating bath of claim 16, wherein the anion of the trivalent chromium salt is the anion of a volatile or electrochemically consumable acid.

21. The electroplating bath of claim 16, wherein the electroplating bath comprises an alloy former selected from the group consisting of vanadium, manganese, iron, cobalt, nickel, molybdenum, tungsten, and mixtures thereof.

22. The electroplating bath of claim 16, wherein the electroplating bath further comprises carbon, oxygen, and nitrogen provided from organic components or ammonia in the electroplating bath.

23. The electroplating bath of claim 16, wherein the complexing agent is selected from the group consisting of carboxylic acids and carboxylate salts.

24. The electroplating bath of claim 16, wherein the complexing agent is present in an amount of 100 to 300 g/L (2.17 M to 6.61 M) and/or the molar ratio of the complexing agent to the trivalent chromium salt is from 10:1 to 13:1.

25. The electroplating bath of claim 16, wherein the halogen salt is selected from the group consisting of bromide, chloride, iodide, and fluoride salts, and/or wherein the halogen salt is present in an amount of 5 to 50 g/L.

26. The electroplating bath of claim 16, wherein the electroplating bath further comprises fluorides as at least one further complexing agent and/or as at least one further halogen salt.

27. The electroplating bath of claim 16, wherein the additives are selected from the group consisting of brighteners and wetting agents.

28. The electroplating bath of claim 16, wherein the electroplating bath is substantially free of chloride ions and/or substantially free of aluminium ions.

29. A process for depositing chromium on a substrate including the following steps: providing an electroplating bath of claim 16, immersing a substrate in the electroplating bath, and applying an electrical current to deposit the trivalent chromium on the substrate.

30. The process of claim 29, wherein the electroplating bath is separated from the anode by a membrane, defining an anolyte and a catholyte.

31. The process of claim 30, wherein the anolyte comprises chromium (III) sulphate.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0047] The present invention is further illustrated by the following Figures and Examples. However, the present invention is not limited to these specific embodiments.

[0048] FIG. 1 shows a schematic illustration of the anodic setup according to one embodiment of the present invention.

[0049] FIG. 2 shows a diagram illustrating the development of the sulphate concentration for different electroplating systems

DETAILED DESCRIPTION OF THE INVENTION

[0050] The inventive embodiment 1 illustrated in FIG. 1 uses an anolyte 7 that can serve as a reservoir of Cr(III) ions. A solution of a trivalent chromium salt such as chromium sulphate or any other chromium salt comprising 10-50 g/L of trivalent chromium and 30-140 g/L of sulfate anions or other anions is used as a component of the anolyte 7 in the FIG. 1. The ion exchange membrane 3 may be included in or bound to a carrier 2 and will preferably be selected as a cation exchange membrane like Nafion N424 mentioned above. The catholyte 5 is composed of the trivalent chrome electrolyte of the invention as described in the following Example 2. The anode 6 is made of graphite material. A sample part to be plated is placed as cathode 4. The replenishment of chromium salt in the form of chromium(III) sulphate is carried out in the anolyte.

[0051] In FIG. 2, the diagram demonstrates the time-dependence of the sulphate concentration in different electroplating systems. While the sulphate concentration for the electroplating system based on a bath with Cr(III) sulphate and without a membrane rapidly increases, the concentrations for the first embodiment according to the present invention using a temporary anion and for the second embodiment according to the present invention using a membrane separation stay substantially constant for the measurement period.

[0052] In Table 1 shows the compositions of the electroplating baths of the inventive Examples 1-4 and of a reference example based on Cr(VI) together with the operation parameters for each electroplating bath.

TABLE-US-00001 TABLE 1 Reference Example Example Example Example Example 1 2 3 4 CrO.sub.3 300 g/L H.sub.2SO.sub.4 3.5 g/L Organic 50 mL/L Catalyst Chromium 140 g/l 140 g/l 140 g/l 140 g/l Sulphate basic (0.46M) (0.46M) (0.46M) (0.46M) Formic Acid 250 g/L 250 g/L 250 g/L 250 g/L (5.43M) (5.43M) (5.43M) (5.43M) NH.sub.3 90 g/L 90 g/L 90 g/L 90 g/L (5.3M) (5.3M) (5.3M) (5.3M) KBr 10 g/L 10 g/L 10 g/L 10 g/L (0.085M) (0.085M) (0.085M) (0.085M) PEG 400 0.5 g/L 0.5 g/L 0.5 g/L 0.5 g/L Quaternary 1 g/L 1 g/L 1 g/L 1 g/L ammonium compound Operating parameters Temperature 50 C. 35-45 C. 35-45 C. 35-45 C. 35-45 C. Current 50A/dm2 50A/dm2 50A/dm2 density DC DC PRC pH 5-5.5 5-5.5 5-5.5 5-5.5 Cathodic duty 96% 96% 96% cycle Frequency 6.5 Hz 6.5 Hz 6.5 Hz Magnetic 300 C. - 500 C. - induction 2 sec 2sec DC: Direct current PRC: Pulse Reverse Current

[0053] The resulting properties of the deposits obtained from the electroplating baths in table 1 are shown in table 2.

TABLE-US-00002 TABLE 2 Reference Example Example Example Example example 1 2 3 4 Thickness (m) 130 m 130 m 130 m 130 m 130 m Hardness (HV) 1000-1200 750-800 800-900 1100-1200 1900-2100 Adherence by Chisel- Excellent Poor Good Excellent Excellent ling UNI EN ISO 2819 Cathodic efficiency 25-30% 12-15% 12-15% 12-15% 12-15% on Cr(III) on Cr(III) on Cr(III) on Cr(III) Crystallinity Crystalline Amorphous Amorphous Crystalline Crystalline Chemical composition Cr >99 Cr = 92.5-95% w Cr = 92.5-95% w Cr = 92.5-95% w Cr = 92.5-95% w (by XPS) C = 2-3% w C = 2-3% w C = 2-3% w C = 2-3% w O = 3-4% w O = 3-4% w O = 3-4% w O = 3-4% w N = 0.1-0.5% w N = 0.1-0.5% w N = 0.1-0.5% w N = 0.1-0.5% w