Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D21/00—Processes for servicing or operating cells for electrolytic coating
  • C25D21/12—Process control or regulation
  • C25D21/14—Controlled addition of electrolyte components
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D3/00—Electroplating: Baths therefor
  • C25D3/02—Electroplating: Baths therefor from solutions
  • C25D3/04—Electroplating: Baths therefor from solutions of chromium

Definitions

• This invention is in the field of protecting lead anodes from corrosion during metal-electroplating processes. More particularly, this invention provides a process and composition for electroplating chromium, using lead or lead-containing anodes under conditions which produce adherent, bright chromium deposits at high efficiencies, where cathodic low-current-density etching i r substantially reduced in comparison with existing high-efficiency catalyst systems. The invention further provides a composition for the replenishment of exhausted or depleted plating baths while diminishing anode corrosion. Description of the Prior Art. Several advantages of certain short-chain alkylsulfonic acids in chromium electroplating have been described for both decorative and functional systems. U.S. Patent No.
• Chessin discloses decorative electroplating baths containing alkylsulfonic or haloalkylsulfonic acids in combination with certain carboxylic acids to produce bright, iridescent chromium surfaces on the articles plated.
• Chessin et al. further disclose functional chromium electroplating processes which use baths containing alkylsulfonic acids having a ratio of sulfur to carbon of 1/3 or greater, but free of carboxylic acids; the processes result in hard, adherent chromium deposits produced at elevated temperatures and high efficiencies without cathodic low-current-density etching.
• MSA has become the agent of choice in a number of commercial embodiments for chromium plating which have appeared in the marketplace, even though severe scale buildup and anodic corrosion are encountered.
• MSA has become the agent of choice in a number of commercial embodiments for chromium plating which have appeared in the marketplace, even though severe scale buildup and anodic corrosion are encountered.
• MSA has become the agent of choice in a number of commercial embodiments for chromium plating which have appeared in the marketplace, even though severe scale buildup and anodic corrosion are encountered.
• MSA in the plating baths generally causes the excessive corrosion of those anodes after extended operation, relative to the corrosion observed in conventional plating processes.
• Conventional plating processes or “conventional baths” are herein defined as those which are conducted with a plating bath consisting of chromic acid and sulfate ion as the essential ingredients, the sulfate ion generally being provided by sulfuric acid or sodium sulfate, although those are not limiting sources, the requirement being solely that a soluble sulfate be provided. It has been found that as a lead anode is used repeatedly in functional chromium electroplating with baths containing MSA, the anode disintegrates at a faster rate than in conventional baths, and it must therefore be replaced much sooner than the anode in an anal- ogous conventional bath.
• lead anode is intended to define plating-bath anodes formed of lead or lead alloys commonly containing varying percentages of tin or antimony, either alone or in combination with other metals. Such materials are well known to those skilled in the art, and as such form no part of this invention.
• I introduced bismuth, arsenic or antimony ion into the bath with MSA in an attempt to reduce anode corrosion.
• MSA and ESA have been generically identified as useful additives in plating baths for functional chromium-plating processes.
• the relevant references have indicated the problem of severe anodic corrosion when chromium is functionally electroplated for an extended period of time with lead anodes in plating baths containing MSA, the industry standard.
• those references fail to suggest or disclose any particular means for an economical solution to the problem without sacrificing cost or process efficiency, or the other advantages obtained using baths containing MSA.
• the present invention provides a process of and composition for functionally electroplating chromium from a high-efficiency, etch-free plating bath onto a basis-metal cathode with a lead anode under conditions which substantially reduce or eliminate excessive corrosion of the anode by the plating bath after extended use, which process comprises contacting the basis-metal cathode and the lead anode with a plating bath consisting essentially of chromic acid and sulfate in amounts sufficient to obtain a useful deposit of chromium, and at least one alkylpolysulfonic acid, halogenated alkylpolysulfonic acid, or salt thereof, which acid or salt contains from one to about three carbon atoms, and electrodepositing chromium at a cathode efficiency of at least 20% at a current density of about 30 a.s.d.
• the term "substantial absence of a corrosion-producing monosulfonic acid” is used to mean the inclusion in the plating bath of amounts of one or more monosulfonic acids or salts, whether added to the bath or formed in situ, which acids or salts are insufficient to cause anode corrosion greater than that encountered in conventional plating baths.
• the preferred embodiment of the present invention is the composition for securing chromium electroplated from an etch-free, high-efficiency, plating bath onto a basis-metal cathode with a lead anode in the substantial absence of corrosion- causing amounts of monosulfonic acids, which composition comprises chromic acid and sulfate ion in amounts sufficient to obtain the desired deposit of chromium, and at least one alkylpolysulfonic acid, halogenated alkylpolysulfonic acid, or salt thereof, which acid or salt contains from one to about three carbon atoms.
• the process of this invention comprises contacting a basis-metal cathode and a lead anode with a plating bath consisting essentially of chromic acid and sulfate ion in amounts sufficient to obtain a useful deposit of chromium, and at least one alkylpolysulfonic acid, halogenated alkylpolysulfonic acid, or salt thereof, which aci or salt contains from one to about three carbon atoms, and electrodepositin chromium at a cathode efficiency of at least 20%, at a current density of fro about 11 to about 230 a.s.d., and at a plating temperature of about 45 to abou 70°C for a time sufficient to obtain a bright, adherent chromium deposit.
• a plating bath consisting essentially of chromic acid and sulfate ion in amounts sufficient to obtain a useful deposit of chromium, and at least one alkylpolysulfonic acid, halogenated
• the benefits of the present invention may be realized by the use in the plating bath of at least one material selected from the group consisting of alkylpolysulfonic acids containing from one to about three carbon atoms, halogenated _dkylpolys_dfonic acids, and salts of such acids and halogenated acids, which acids or salts contain from one to about three carbon atoms.
• Halogenated acids are those containing fluorine, chlorine, bromine or iodine bound to a carbon atom; fluorine- and chlorine-substituted derivatives are preferred.
• acids and salts include MDSA, mono- and dichloro-methanedisulfonic acid, 1,1-ethanedisulfonic acid, and monochloro- or 1,2-dichloroethanedisulfonic acid and their salts, provided that there is no precipitation of chromium or sulfate moieties caused by the addition of the salt.
• Preferred cations are chosen from alkali metals. Particularly preferred are sodium and potassium salts.
• the alkylpolysulfonic acids or salts of the present invention have the formula
• I X radiation where a and b are independently from 0 to 2, n is from 1 to 3, m and y are independently from 1 to 3, provided that the total number of sulfonic groups in the molecule is not less than 2, X is halogen or oxygen, R is unsubstituted lower alkyl or substituted lower alkyl, where the substituents on R are halogen or oxygen, and where hydrogen occupies any positions otherwise unaccounted for, i.e., to satisfy unfilled valences of carbon or oxygen.
• the salts of this invention can be formed by the replacement of the labile hudrogen of the sulfonic group by a metal, such as, e.g., sodium, potassium, or the like.
• the alkylpolysulfonic acids of this invention contain at least two sulfonic acid groups connected to carbon, and any one carbon atom can have up to three sulfonic acids groups attached thereto.
• the polysulfonic acids or salts thereof are incorporated into a functional chromium-plating bath in substantially catalytic amounts.
• that amount has been determined to be from about 0.25 to about 40 grams per liter (g/1), and preferably from about 1 to about 12 g/1, of an alkylpolysulfonic acid, halogenated alkylpoly-sulfonic acid or salt thereof. Particularly preferred amounts range from about 2 to about 8 g/1.
• the alkylpolysulfonic acid is MDSA.
• Excessive corrosion is that amount of corrosion perceptibly in excess of the corrosion observed in conventional plating processes.
• Extended use is the amount of use of a lead anode in a conventional system which leads to detectable corrosion of that anode.
• the present invention further provides a functional chromium- plating system comprising a lead anode, a basis-metal cathode and a plating bath consisting essentially of chromic acid and sulfate ion, and at least one alkylpolysulfonic acid, halogenated alkylpolysulfonic acid, or a salt thereof, which acid or salt contains from one to about three carbon atoms, in amounts sufficient to obtain efficient functional electrodeposition, the bath being capable of producing bright, adherent chromium deposits while maintaining minimal cathodic low-current-density etching in the substantial absence of monosulfonic acids.
• Electrodeposition occurs, for example, at cathode efficiencies of at least 20% at 30 a.s.d. and 55°C.
• a "corrosion-inhibiting amount" of added bath material is that amount which provides enhanced plating efficiency over conventional plating baths while avoiding electrolytic or chemical attack at an electrode.
• the present invention provides a functional chromium electroplating bath which is useful to produce bright, adherent chromium deposits at high efficiencies, but which substantially avoids the excessive anode corrosion which is characteristic of industrial baths containing MSA the inventive bath consisting essentially of chromic acid and sulfate in amounts sufficient to obtain efficient functional electrodeposition, and at least one alkylpolysulfonic acid, halogenated alkylpolysulfonic acid, or a salt thereof, which acid or salt contains from one to about three carbon atoms, and is substantially free of monosulfonic acids.
• the term "substantially free”, when applied to monosulfonic acids, is chosen to mean a concentration of monosulfonic acid low enough not to cause a detectable rate of corrosion higher than that experienced in a conventional plating bath consisting essentially of chromic acid and sulfate ion, in amounts sufficient to obtain a useful deposit of chromium.
• the functional chromium electroplating baths of this invention consist essentially of chromic acid, sulfate ion and at least one alkylpolysulfonic acid, halogenated alkylpolysulfonic acid or salt thereof.
• Useful chromic acid amounts range from about 100 to about 450 g/1, preferred ranges being from about 200 to about 300 g/1.
• Sulfate ion is incorporated in amounts ranging from about 1 to about 5 g/1, and preferably ranging from about 1.5 to about 3.5 g/1.
• the electroplating baths may include other ingredients which do not substantially affect process efficiency, chromium adherence or brightness in a negative manner. Such additives may be incorp-orated to improve handling of the baths, such as, e.g., fume suppressants, brightening agents and the like.
• the functional electroplating process is carried out at plating temperatures typically exceeding 40°C.
• current density is from about 50 to about 100 a.s.d. at a plating temperature of from about 45 to about 70°C.
• Current den-sities of from about 11 to about 230 a.s.d. are suitable in the process of this invention, while densities of from about 50 to about 100 a.s.d. are preferred.
• Plating efficiencies of at least 20% are easily achieved, with values of from about 22 to about 28% being typical under the described most-preferred conditions.
• the functional electroplating system of the present invention includes a lead anode, a cathode generally comprising a work-piece for plating, and the chromium electroplating bath as described above.
• Typical cathode items include crankshafts, piston rings and the like.
• typical anode materials include substantially pure lead, but are more generally alloys containing lead in combination with tin, antimony, tellurium and a variety of other metals, either singly or in combination.
• Pb-7%Sn is a tin-lead composition being primarily lead, and having about 7% tin by weight as the alloying metal. In such compositions, there may further be minor amounts of other materials present.
• Example 1 Accelerated anode-corrosion tests were conducted using previously weighed Pb-7%Sn anodes in several different chromium-plating baths as described here:
• Extended bath usage was simulated by plating at 60°C at an anode current density of 0.5 a.s.d. for 30 minutes, followed by 30 minutes of non-plating. This process was conducted for abo eight hours and the power turned off overnight, during which time the bath was allowed to cool. These steps were repeated for a period of several weeks; the anodes were occasionally removed, dried, weighed and then re-inserted into the bath. The results are given in Table I.
• bath (c) containing MDSA as set forth herein for use in the process of this invention, anode corrosion remains substantially at the level of a conventional chromium-plating bath (a), whereas bath (b), with MSA as the plating-improvement medium, leads to corrosion at a substantially higher rate.
• bath (b) there was evidence of serious interfacial attack on the anode
• inventive bath (c) the appearance of the anode was substantially unaffected by the plating process.
• the quality of the deposit obtained with the inventive bath was at least as good as, and possibly somewhat harder than, the plating achieved with either the conventional commercial plating bath or that containing MSA.
• the present invention has further utility as a replenishment composition for existing operations.
• a composition consisting essentially of chromic acid in amounts sufficient to replenish what has been consumed in plating, and at least one alkylpolysulfonic acid, halogenated alkylpolysulfonic acid, or salt thereof is useful for addition to a functional chromium-plating installation to improve plating efficiency with concomitant decrease in anode corrosion, even where the existing installation is operating with baths of the prior art.
• a replenishment composition for a chromium-plating bath having chromic acid and at least one alkylpolysulfonic acid, halogenated alkylpolysulfonic acid or salt thereof in amounts from about 1 to about 40 g per kilogram (kg) of Cr0 3 , and preferably from about 2 to about 25 g per kg, of replenishment composition.
• This composition can be either a solid mixture or a solution.
• the chromium can be present as the oxide, the acid or a salt, and that the amount of chromium is calculated and expressed for convenience as

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• 1990
  • 1990-11-06 AT AT90917257T patent/ATE150100T1/de not_active IP Right Cessation
  • 1990-11-06 DE DE69030176T patent/DE69030176T2/de not_active Expired - Lifetime
  • 1990-11-06 BR BR909006995A patent/BR9006995A/pt not_active IP Right Cessation
  • 1990-11-06 EP EP90917257A patent/EP0452471B1/de not_active Expired - Lifetime
  • 1990-11-06 SG SG1996008067A patent/SG52702A1/en unknown
  • 1990-11-06 CA CA002054201A patent/CA2054201C/en not_active Expired - Lifetime
  • 1990-11-06 AU AU67569/90A patent/AU638512B2/en not_active Expired
  • 1990-11-06 WO PCT/US1990/006422 patent/WO1991006693A1/en active IP Right Grant
  • 1990-11-06 JP JP3500497A patent/JPH04502786A/ja active Pending

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