JPH04502786A - Protection of lead-containing anodes during chrome electroplating - Google Patents

Abstract

The present invention provides a process for electroplating chromium using lead anodes while achieving the advantages of using methanesulfonic acid without suffering the excessive anode-corrosion characteristics associated with that acid. Accordingly, chromium is electrodeposited from a bath containing chromic acid, sulfate and an alkylpolysulfonic acid containing from one to about three carbon atoms. The invention also provides a plating process for chromium electrodeposition, a plating bath for use in the inventive process, and a replenishment composition for existing plating baths.

Description

[Detailed description of the invention] Protection of lead-containing anodes during chromium electroplating Background of the invention Reference to related applications This application was filed on November 6, 1989 by the applicant. is a continuation-in-part of currently pending U.S. Patent Application No. 431,963. .

FIELD OF THE INVENTION The present invention relates to a method for protecting powder anodes from corrosion during metal electroplating processes. It is in the technical field. In particular, the present invention uses lead or gold powder anodes to Electroplating of chromium under conditions that produce highly efficient shiny chrome electrodeposit The present invention provides methods and compositions for conducting cathode low current density etching. ting is substantially reduced compared to existing high efficiency catalyst systems.

The present invention further provides for reducing anodic corrosion while eliminating depleted or active ingredients. Provides a composition for supplementation of.

Description of the prior art: Species of short-chain alkyl sulfonic acids in chromium electroplating Several advantages have been described for both decorative and functional plating systems. Chetushi United States patent granted to Chessin and assigned to the same applicant as this case. No. 3,745,097 creates a shiny iridescent chrome surface on plated articles. Alkyl sulfonic acids or halo A decorative electroplating bath containing an alkyl sulfonic acid is disclosed. U.S. Patent No. 4,58 No. 8,481, Chasin et al. However, functional chromium electricity using alkyl sulfonic acids that do not contain carboxylic acids Discloses a plating method that does not result in cathodic low current density etching. It results in hard, adherent chromium electrodeposits produced at elevated temperatures and with high efficiency.

However, the chromium plating bath taught by U.S. Pat. produced the high efficiency plating described in the disclosure therein, but on the other hand, the anode This created severe problems with scale build-up on top and etching and corrosion of the anode. . The disclosure of this U.S. Pat. No. 4,588,481 is that methane-sulfonic acid (MSA) ), ethane-sulfonic acid (ESA), methanedisulfonic acid (MDSA), and 1.Specific analysis of various sulfonic acids, including 2-ethanedisulfonic acid (EDSA) listed. Generally, for economic reasons, MSA is limited to scale accumulation and anode Numerous industrial applications against chrome plating that have appeared on the market It was a reagent that was considered particularly useful in practical applications.

As mentioned above, the chrome plating process using MSA has become established in industry. and functional plating using lead or conventional lead alloy anodes when utilized. A failure occurred in Anode following publication of U.S. Patent No. 4,588,481 Research into corrosion issues has shown that MSA in plating baths is generally less than conventional after long-term operation. resulting in excessive corrosion of the anode compared to the corrosion observed in the plating process. It turned out that

[Conventional plating process] or "conventional bath" means that the essential ingredients are It is also carried out using a plating bath comprising chromic acid and sulfate ions as In this case, the sulfate ion is generally sulfuric acid or sodium sulfate. provided by soluble sulfate, but these are not the limiting source and the requirement is All that is required is that it be provided. Functional cloning using a bath containing MSA Repeated use of lead anodes in electroplating may cause the anodes to anodes in similar conventional baths. It was discovered that it had to be replaced much sooner. In this specification, the use The term “lead anode J” refers to lead, tin, or antimony used alone or in combination with other metals. It is also possible to define anodes for plating baths formed from lead alloys containing lead in various proportions. It is intended that Such materials are well known to those skilled in the art and therefore It does not constitute a part of the present invention in that sense.

In US Pat. No. 4,786,378 by the inventor, reducing anodic corrosion In trials, baths using MSA were exposed to bismuth, arsenic, or antimony ions. introduced inside. Later, the use of sulfonic acids in the electroplating process was described In U.S. Pat. No. 4,810.337, the inventor describes the use of MSA In addition, one countermeasure for the anodic corrosion problem described herein has been disclosed. That patent smell Therefore, the present inventor has discovered that thick scale adhesion can be prevented in the plating process using MSA. scale accumulation and accompanying corrosion observed. A relatively high voltage is applied between both electrodes prior to the plating process to reduce Ta.

Another attempted solution to this problem is through bath compositions containing MSA. For example, on July 2, 1986, In West German patent application No. 3,625.187A filed on the 5th, approximately 9% by weight up to about 1% by weight of palladium, with small amounts of tin and/or Anodes consisting of lead with or without selenium were tested at 55°C and 30°C. Cathode current density within the range of ~32 A/dm" (a, s, d,) and 25 ~ Functional electrochromic electrolysis carried out using anodic current densities of 30 a, s, d. This product has been reported to show "good results" when used in plating. The authors also believe that impurities associated with MSA are at least partially responsible for this problem. Study the effect of MSA purity on anodic corrosion, assuming that did. As recognized in connection with Table II below, this may not be the case. discovered.

These publications and experimental studies are at least partially related to the anodic scaling during plating. It shows the magnitude of the effects of corrosion and corrosion, as well as various strategies for solving them. but However, until the knowledge that formed the basis of the present invention was reached, researchers in the chrome plating industry had Alkyl polysulfonic acids used as plating catalysts may improve plating efficiency. I didn't realize that it would reduce anodic corrosion at the same time.

MSA and ESA are commonly used in plating baths for functional chrome plating processes. It is recognized as a useful additive. However, as discussed above, Related literature describes the use of lead anodes in plating baths containing MSA (industrial standard). showed severe anodic corrosion problems when chromium was functionally electroplated for long periods of time.

Without giving too much attention to it, I would like to suggest a specific means to an economical solution to this problem. Nothing is suggested or disclosed.

Summary of the invention The present invention substantially reduces or eliminates excessive corrosion of the anode by plating bath after long-term use. Using a lead anode under conditions of high efficiency and no etching on the base metal cathode. A method and composition for functional electroplating of chromium from a silver plating bath are provided. Main departure The method involves adding a cathode and a lead anode to a gold substrate in sufficient quantity to obtain a useful electrodeposit of chromium. romic acid and sulfate ions, and a small number of (both one type of alkyl polysulfonic acids, halogenated alkyl polysulfonic acids or salts thereof. in contact with a plating bath containing a substantial amount of soil, and at a cathode efficiency of at least 20%. , at a current density of at least about 30 a, s, d, and a plating temperature of about 45 to 70 °C. for a sufficient period of time to obtain the desired functional chromium electrodeposit, but at a minimum low current density. Virtually no monosulfonic acid, which is prone to corrosion, can only cause etching. Including electrodepositing chromium in its absence. As used herein: The term "in the substantial absence of corrosive monosulfonic acids" refers to One or more monosulfonic acids or salts are added to the bath or are generated in situ. However, the anodic corrosion exceeds the levels encountered in conventional plating baths. used to mean that it contains an insufficient amount of water.

Description of preferred embodiments Preferred embodiments of the invention include substantially free of corrosive amounts of monosulfonic acid. A high-efficiency plating bath with no etching on the base metal cathode using a lead anode in the presence of This composition ensures that chromium is electroplated. chromate and sulfate ions in sufficient amounts to obtain the desired electrodeposit of 1 to approximately 3 At least one alkyl polysulfonic acid, halogenated atom, having a number of carbon atoms Contains rukyl polysulfonic acid or its salt. The method of the present invention uses a base metal cathode and a lead metal cathode. the anode with sufficient amounts of chromate and sulfate ions to obtain useful deposits of chromium. , at least one alkyl polysulfonic acid having from 1 to approximately 3 carbon atoms; Contact with a plating bath consisting essentially of rogogenated alkyl polysulfonic acid or its salt and at a cathode efficiency of at least 20%, from about 11 to about 230 a, s, d, and at a plating temperature of about 45 to about 70°C. Involves electrodepositing chromium for a sufficient period of time to obtain a dense and adherent chromium electrodeposit. do.

In an attempt to reduce anodic corrosion in the chrome plating process, Surprisingly, the species consisting in chromium electroplating baths for use with lead anodes Substitution of a substantial amount of MSA by alkyl polysulfonic acid increases plating efficiency or chromatography. It was found that the amount of anodic corrosion can be dramatically reduced without sacrificing adhesiveness. . That is, the use of alkyl polysulfonic acid or its salt according to the present invention is useful. ROM-plated articles, i.e., whose properties were obtained in the use of high-efficiency baths of the prior art. This makes it possible to manufacture articles with similar properties.

An advantage of the present invention is that in a plating bath, an alkyl having from 1 to approximately 3 carbon atoms Polysulfonic acids, halogenated alkyl polysulfonic acids and such acids and halogenated The group consisting of salts of genic acids (these acids and salts also contain from 1 to approximately 3 carbon atoms) This is achieved by using at least one substance selected from the following. halogenated acid is , fluorine, chlorine, bromine and iodine combined with carbon atoms. Fluorine and salt Elementary substituted derivatives are preferred. Typical acids and salts include MDSA, mono- and di- Chloro-methane disulfonic acid, 1,1-ethane disulfonic acid and monochloro Examples include 1,2-dichloroethanedisulfonic acid and salts thereof. however There shall be no precipitation of chromium or sulfate components resulting from the addition of the salt. stomach. Preferred cations are selected from alkali metals. sodium and potassium Salts are particularly preferred. The alkyl polysulfonic acid or salt in the present invention has the following formula: Has: R, -[C, -(So□OH), ].

It's X Here, a and b independently range from O to 2, n ranges from 1 to 3, and m and y independently range from 1 to 3, provided that the total number of sulfone groups in the molecule is 2 or more, X is halogen or oxygen, and R is unsubstituted lower alkyl or Substituted lower alkyl, in which case the substituent in R is halogen or oxygen. and hydrogen is any carbon or oxygen not occupied even when hydrogen is not present. position, that is, any position that satisfies the unfilled valence of carbon or oxygen. occupies a place. Those skilled in the art will appreciate that the salts of the present invention may include metal salts such as sodium, potassium, etc. Let us recognize that it can be formed by substitution of a labile hydrogen of a sulfonic group by the genus .

As presented in the above formula, the alkyl polysulfonic acid of the present invention is bonded to a carbon atom. one carbon atom consists of three A sulfonic acid group can be attached thereto.

In the practice of the present invention, polysulfonic acid or its salt is used in a functional chromium plating bath. in substantially catalytic amounts. Within the scope and spirit of the invention, and Depending on the plating conditions, this amount ranges from about 0.25 to about 40 grams per liter (g/liter). l), preferably about 1 to 12 g/l of alkyl polysulfonic acid, halogenated atom It was determined to be lucyl polysulfonic acid or its salt. A particularly preferable amount is 2 to It is in the range of 8g/l. In a preferred embodiment, the alkyl polysulfonic acid is M It is DSA.

As used herein, "excessive corrosion J" refers to The amount of corrosion appreciably exceeds the corrosion observed in the conventional process. "Long Period J use results in no discernible corrosion of the lead anode in conventional systems. This is the amount of usage that results in

The present invention further provides a lead anode, a base metal cathode, and a lead anode in a sufficient amount to provide efficient functional electrodeposition. of chromate and sulfate ions and having from 1 to approximately 3 carbon atoms, at least One type of alkyl polysulfonic acid, halogenated alkyl polysulfonic acid or and a plating bath consisting essentially of salt. , the inventive bath minimizes cathodic low current density etching in the absence of monosulfonic acids. It is possible to produce a shiny and adherent chromium electrodeposit while maintaining the chromium electrodeposit. [ "Efficient functional electrodeposition" is, for example, at a cathode efficiency of at least 20% and about 30 a, s, d and at about 55°C. "Corrosion" of added bath substances ``Suppression amount'' means that the conventional type This is the amount that gives improved plating efficiency over the plating bath.

The present invention is useful for producing highly efficient, shiny, and adherent chromium electrodeposits. Moreover, the functionality virtually avoids the excessive anodic corrosion inherent in industrial baths containing MSA. The present invention provides a chromium electroplating bath in which a chromium electroplating bath is provided in a sufficient amount to obtain efficient functional electrodeposition. , chromic acid and sulfate, and at least one species having approximately 3 carbon atoms from ■ alkyl polysulfonic acids, halogenated alkyl polysulfonic acids or salts thereof. and is substantially free of monosulfonic acids. What we use here and The term "substantially free", when used for monosulfonic acids, refers to produced from chromate and sulfate ions in sufficient quantities to obtain useful ROM electrodeposits. Detectable corrosion rates higher than those found in high quality conventional plating baths selected to mean a concentration of monosulfonic acid low enough to not result in be done.

The functional chromium electroplating bath of the present invention contains chromic acid, sulfate ions, and at least Also, one kind of alkyl polysulfonic acid, halogenated alkyl polysulfonic acid or the like. The salt and the real soil are acidified. The useful amount of romic acid is about 100 to about 450 g/l. , the preferred range is about 200 to about 300 g/l. Sulfate ion is about 1 to about 5 g/l, preferably in an amount ranging from about 1.5 to about 3.5 g/l .

Electroplating baths affect process efficiency in a negative manner.

May contain other seed components that do not substantially adversely affect chrome adhesion or gloss. Yes, such additives may improve bath handling properties, such as fume suppressants, brighteners, etc. Contains vine to improve.

Functional electroplating processes are typically performed in one plating process at temperatures above 40°C. be done. In a preferred embodiment, the current density is at a plating temperature of about 45 to about 70°C. in the range of about 50 to about 100 a, s, d. Approximately 11 to approximately 230a , s, d, are suitable in the method of the invention, among them about 50 to 1 O Densities of Oa, s, d are preferred. Plating efficiencies of at least 20% are easily achieved and values of about 22% to about 28% are typical under the most preferred conditions described. Ru.

The functional chromium electroplating system of the present invention uses a lead anode and a It includes a cathode, which is a workpiece, and a ROM electroplating bath as described above. representative Cathode articles include crankshafts, piston rings, and the like. Already written down As mentioned above, typical anode materials include substantially pure lead, but more commonly tin, Combination of antimony, tellurium and various other elements singly or in combination It is a lead-containing alloy. In the example expression here, such as rPb-7%SnJ The term refers to tin-- which is primarily lead and has about 7% tin by weight as the alloying metal. It is a lead alloy composition. In such compositions, trace amounts of other seed elements may also be present. Vine.

The utility of the present invention is illustrated by the following example, which is illustrative and not intended to be limiting. Show.

Example 1 Pre-weighted in several different chromium plating baths as described below. An accelerated anodic corrosion test was carried out using a weighed Pb-7%Sn anode: ( a) Conventional chromium plating bath (100:1 chromate to sulfate ion ratio); (b) similar baths containing chromic acid, sulfate and MSA; (c) alternative to MSA; A bath according to the invention containing MDSA as a typical disulfonic acid.

Long-term bath use plating at 60 °C for 30 min at an anodic current density of 0.5 a, s, d. , followed by a non-plating state for 30 minutes. This process takes about 8 The bath was allowed to cool for an hour and the power was turned off overnight while the bath was allowed to cool. these stages for several weeks repeated over a period of Take out the anode halfway, dry it, weigh it, and wash it after bathing. was reinserted. The results are presented in Table 1.

Table I Anode weight loss (g) Electroplating bath 600A-Hr 605A-Hr used in the method of the present invention In a bath (c) containing MDSA as presented here for The level of the conventional chromium plating bath (a) remains virtually unchanged, and on the other hand, the plating has improved. Bath (b) using MSA as the medium resulted in corrosion at a significantly higher rate. Ru. In bath (b) there is evidence of significant interfacial erosion at the anode, while the In the conventional bath (a) and the bath of the present invention (c), the appearance of the anode depends on the plating process. virtually unaffected. The quality of the electrodeposit obtained using the bath of the present invention was The plating method can be achieved using either a commercially available plating bath or a bath containing MSA. at least as good as the original, and in some cases somewhat harder. stomach.

Example 2 In a second type of accelerated test, the concentration of chromic acid was intentionally low and the MSA Alternatively, the direct current under measurement in a bath solution maintained high in MDSA concentration −7% Sn anode. % of current that formed soluble products (leading to corrosion) % of current) to measure the actual anode loss and calculate that value using Faraday's law. It was determined by dividing the weight loss by the specified weight loss. This calculation is all about weight loss is assumed to result from the corrosion reaction Pb-Pb(II). The results are shown in Table II. to be presented.

From consideration of the above table, it can be seen that the one of Chetsushin et al. in U.S. Pat. No. 4,588,481 It will be observed that the teaching of a sulfur to oxygen ratio of /3 was in fact too broad.

Both ethane and propane sulfonic acids are suitable plating catalysts such as Chassin. is well within the limits disclosed by It also promotes corrosion at an undesirable level.

These results also indicate that the corrosion of the anode in the presence of MDSA is the same as in conventional baths. On the other hand, we demonstrate that the presence of MSA results in substantially increased anodic corrosion.

The invention further has utility as a replenishment composition for existing plating operations.

That is, sufficient amount of chromic acid to replenish the amount consumed by plating and at least 1 Species alkyl polysulfonic acids, halogenated alkyl polysulfonic acids or salts thereof Existing equipment is operated using prior art baths. Functionality to improve plating efficiency with reduction in anodic corrosion even when Useful as an additive to chrome plating equipment.

Specifically, the utility according to the present invention is from about 1 to 1 kg CrO3 unit of the supplemental composition. chromic acid in an amount of about 40 g, preferably about 2 to about 25 g/kg. , at least one alkyl polysulfonic acid, halogenated alkyl polysulfone Found in replenishment compositions for chrome plating baths containing acids or salts thereof. This composition The substance can be either a solid mixture or a solution. Those skilled in the art understand that chromium is an oxide, Chromium-containing substances that may exist as acids or salts and the amount of chromium present Regardless of its exact properties, it can be conveniently calculated and expressed as CrO3. Let's recognize it.

Modifications and improvements to the preferred forms of the invention disclosed and described herein are based on this principle. and could be done by one of ordinary skill in the art after understanding the teachings. Therefore, it is registered based on this application. The scope of patent rights to be claimed should be limited only to the specific examples of the invention presented herein. and should be limited only by the scope of the advances in technology achieved by this invention. .

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Claims (48)

[Claims] 1. Substrate using a lead anode in the virtual absence of monosulfonic acids that cause corrosion Electroplating of chromium on metal cathodes from a highly efficient, non-etching plating bath A method for obtaining a desired electrodeposit of chromium by combining the base metal cathode and the lead anode. a small amount of chromate and sulfate ions having from 1 to approximately 3 carbon atoms. At least one alkyl polysulfonic acid, halogenated alkyl polysulfonic acid, or or a salt thereof, and at least 20% of the cathode Efficiency of at least about 30a. s. d. at a current density of and about 45 Sufficient to obtain glossy, adherent chromium electrodeposit at plating temperatures of ~70°C A chromium electroplating method comprising electrodepositing chromium for a period of time. 2. A method according to claim 1, wherein the plating temperature is in the range of about 50 to about 60°C. 3. The cathode efficiency is in the range of about 22 to about 28% and the current density is in the range of about 45 to about 9 0a. s. d. A method according to claim 1, wherein the method is within the scope of claim 1. 4. A claim in which the amount of chromic acid in the plating bath is in the range of about 100 to about 450 g/l Method according to section 1. 5. The method according to claim 4, wherein the amount of chromic acid is in the range of about 200 to about 300 g/l. Law. 6. Alkyl polysulfonic acid or salt is methanedisulfonic acid, mono- and di- Chloroethane 1,2-disulfonic acid, 1,1-ethanedisulfonic acid and mono- and dichloromethane disulfonic acid and its salts. Method according to 1. 7. Alkyl disulfonic acid or salt is added to the bath in an amount ranging from about 0.5 to about 20 g/l. A method according to claim 6 residing in. 8. 8. A method according to claim 7, wherein the amount ranges from about 1 to about 12 g/l. 9. A method according to claim 8, wherein the amount ranges from about 2 to about 8 g/l. 10. The method according to claim 6, wherein the alkyl polysulfonic acid is methanedisulfonic acid. . 11. 10. The methanedisulfonic acid is present in an amount ranging from about 2 to about 8 g/l. How to follow. 12. A method according to claim 1, wherein the amount of sulphate ranges from about 1 to about 5 g/l. 13. 13. The method according to claim 12, wherein the amount of sulphate is in the range of about 1.5 to about 3.5 g/l. Law. 14. When the current density is about 15 to 100 a. s. d. The method according to claim 1, which is within the scope of . 15. Lead anode, base metal cathode, and virtually no corrosive monosulfonic acids Sufficient amounts of chromic acid and sulfate to obtain efficient functional electrodeposition in the presence of the formula ▲ , chemical formulas, tables, etc.▼ (Here, a and b independently range from 0 to 2, and n range from 1 to 3, m and y independently range from 1 to 3, provided that the total number of sulfone groups in the molecule is 2 or more, X is halogen or oxygen, and R is unsubstituted lower alkyl or is substituted lower alkyl, in which case the substituent in R is halogen or oxygen. Yes, and hydrogen is a carbon or occupy the position of intention. ) or at least one alkyl polysulfonic acid having A plating bath consisting essentially of salt that produces a shiny, adherent chromium electrodeposit. A chrome plating method that uses a chromium plating bath. 16. A claim in which the amount of chromic acid in the plating bath ranges from about 100 to about 450 g/l. Method according to section 15. 17. According to claim 16, the amount of chromic acid ranges from about 200 to about 300 g/l. Method. 18. The alkyl polysulfonic acid or salt is methanedisulfonic acid, mono- or Dichloromethane disulfonic acid, 1,1-ethane disulfonic acid, mono- or dichloromethane disulfonic acid A material selected from the group consisting of loloethanedisulfonic acid and its alkali metal salts. A method according to claim 15. 19. the alkyl polysulfonic acid or salt in an amount ranging from about 0.5 to about 20 g/l; 19. A method according to claim 18, wherein the method is present in a bath. 20. 20. A method according to claim 19, wherein the amount ranges from about 1 to about 12 g/l. 21. 21. A method according to claim 20, wherein the amount ranges from about 2 to about 8 g/l. 22. The person according to claim 18, wherein the alkyl polysulfonic acid is methanedisulfonic acid. Law. 23. 23. A method according to claim 22, wherein the amount ranges from about 2 to about 8 g/l. 24. 16. A method according to claim 15, wherein the amount of sulphate ranges from about 1 to about 5 g/l. 25. 25. A method according to claim 24, wherein the amount of sulphate ranges from about 1.5 to about 3.5 g/l. Law. 26. Approximately 30-100a. s. d. according to claim 15, having a current density in the range of Method. 27. A chromium electroplating bath that can reduce corrosion for use with lead anodes. to obtain chromium electrodeposit in the substantial absence of corrosive monosulfonic acids. a sufficient amount of chromate and sulfate ions and a small number of carbon atoms having from 1 to approximately 3 carbon atoms. At least one type of polysulfonic acid, halogenated alkyl polysulfonic acid or salt thereof and produces a shiny, adherent chromium electrodeposit. Chromium electroplating bath. 28. According to claim 27, the amount of chromic acid ranges from about 100 to about 450 g/l. bath. 29. According to claim 28, the amount of chromic acid ranges from about 200 to about 300 g/l. bath. 30. The alkyl polysulfonic acid or salt is methanedisulfonic acid, mono- or Dichloromethane disulfonic acid, 1,1-ethane disulfonic acid, mono- or dichloromethane disulfonic acid A material selected from the group consisting of loloethanedisulfonic acid and its alkali metal salts. A bath according to claim 27. 31. the alkyl polysulfonic acid or salt in an amount ranging from about 0.5 to about 20 g/l; 31. A bath according to claim 30 present in a bath. 32. 32. A bath according to claim 31, wherein the amount ranges from about 1 to about 12 g/l. 33. 33. A bath according to claim 32, wherein the amount ranges from about 2 to about 8 g/l. 34. A bath according to claim 30, wherein the alkyl polysulfonic acid is methanedisulfonic acid. . 35. 35. A bath according to claim 34, wherein the acid is present in the bath in an amount ranging from about 2 to about 8 g/l. 36. 28. A bath according to claim 27, wherein the amount of sulphate ranges from about 1 to about 5 g/l. 37. 37. A bath according to claim 36, wherein the amount of sulphate ranges from about 1.5 to about 3.5 g/l. . 38. When the current density is about 30 to about 100 a. s. d. According to claim 27, which is within the scope of bath. 39. Chromatography using lead anodes in the virtual absence of corrosive monosulfonic acids. A replenishing composition used in a chromic plating bath comprising chromic acid and 1 to about 3 chromic acid. At least one alkyl polysulfonic acid, halogenated atom, having a number of carbon atoms It consists essentially of lucyl polysulfonic acid or its salt, and has a glossy, close-fitting finish. A replenishment composition capable of replenishing a plating bath to produce chromium deposits. 40. Alkyl polysulfonic acid ranges from about 1 to about 40 g per kg CrO3 40. A composition according to claim 39. 41. Alkyl polysulfonic acid ranges from about 2 to about 25 g per kg of Cr03 40. A composition according to claim 39. 42. The alkyl polysulfonic acid or salt is methanedisulfonic acid, mono- or dichloromethanedisulfonic acid, 1,1-ethanedisulfonic acid and mono- or selected from the group consisting of dichloromethane disulfonic acid and its alkali metal salts; 40. A composition according to claim 39. 43. A solid composition according to claim 39. 44. A liquid composition according to claim 39. 45. The alkyl polysulfonic acid is present as a liquid and CrO3 is as a solid. A composition according to present claim 39. 46. A set according to claim 39, wherein the alkyl polysulfonic acid is methanedisulfonic acid. A product. 47. A set according to claim 39, wherein the alkyl polysulfonic acid is ethanedisulfonic acid. A product. 48. According to claim 39, the chromium plating bath is a highly efficient etching-free bath. composition.