Classifications

• • 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
  • C25D3/56—Electroplating: Baths therefor from solutions of alloys
• • 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
  • C25D3/10—Electroplating: Baths therefor from solutions of chromium characterised by the organic bath constituents used
• • 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
  • C25D3/56—Electroplating: Baths therefor from solutions of alloys
  • C25D3/62—Electroplating: Baths therefor from solutions of alloys containing more than 50% by weight of gold

Definitions

• This invention relates to improvements in the electrodeposition of chromium from aqueous acidic hcxavalent chromium baths and more particularly concerns new exceedingly stable additives for such baths which are capable of substantially reducing the formation of spray and mist during electrolysis.
• the electrodeposition of chromium from aqueous acidic hexavalent chromium solutions takes place, as iswell known, with the evolution of relatively large quantities of hydrogen at the cathode and of oxygen and ozone at the insoluble anodes.
• the undesirable spray and mist; of chromic acid results from the violent bursting of the multitudinous gas bubbles of high surface energy which are released by the electrolysis.
• the spray and mist resulting from this bubble bursting is of considerable volume because of the high current densities used in the plating, the low efficiency of chromium deposition and the use of insoluble anodes.
• the principal object of the invention to provide a stable additive for an acidic hexavalent chromium bath which greatly minimizes the formation of spray and mist during electrolysis of such baths with insoluble or highly polarized anodes.
• Another important object of this invention is to provide improved acidic, hexavalent chromium baths and a method for chromium plating which substantially eliminates the necessity for the use of expensive ventilating procedures currently employed.
• the fluorocarbon sulfonic compounds of this invention are usable in aqueous acidic hexavalent chromium plating baths of conventional composition and have been found to lower the surface tension of such solutions to incredibly lQW values and cause the formation of small, as opposed to large bubbles of electrolytically evolved gases. (Toncurrently, the compounds of this invention apparently impart sufficient surface viscosity to the bubbles which, in combination with their low surface energy, prevents. heir violent. collapse at the surface of the bath.
• the fluorocarbon sulfonic compounds of this invention can b har ct zed by h r u a h re naf e de nated Formula I where Rn represents a saturated fluorocarbon chain including straight, branched and cyclic fluorocarbon chains of 4 to 18 carbon atoms, and X is a cation.
• the cation X may represent hydrogen or may be a metallic ion from the groups including the alkali metals, alkaline earth metals, rare earth metals and heavy metals, such as NI-Li, Mg, Zn, Ca, Cr, Al, Ni, Cu, Ce, etc.
• CF3(CF2)3CF1SO3H 01-2 Perfluoro n-lauryl sulfonic acid cF (CF2) uGF2SO3H .01-2 Perfluoro cyclohexane sulfonic acid CuFuSO3H 0. 2-12 Perfluoro (4-methyl cyclohexane) sulfonic acid C7F1zSOaH 0. 2-12 Perfiuoro (Z-methyl cyclohexane) sulfonic acid C1F13SO;H 0. 2-12 Perfluoro cyclohexane methyl alphasulfonic acid C1FiaS 03H 0.
• the fluorocarbon sulfonic compounds of this invention can be further characterized by having a chain of fluorinated carbon atoms joined to the sulfur atom in the molecule and containing not less than 4 and not more than 18 carbon atoms per sulfonic group.
• Compounds containing more than about 18 carbon atoms per sulfonic groups are insufliciently soluble in the bath to produce the desired result unless the temperature of the bath is increased to a point above that generally used commercially. It will be understood that the proportions set forth in Table I represent only optimum concentrations and that concentrations up to saturation may be used with good results.
• the new soluble fluorocarbon sulfonic compounds of Table I show an unexpected degree of surface activity in For example, the incorporation of a small quantity of about .2 gram to 1 gram per liter of the relatively simple perfluoro 4-mcthyl cyclohexane sulfonic acid greatly minimizes and substantially prevents the formation of fine spray and mist, permanently in the absence of drag-out, from a chromic acid electroplating bath operating at room temperature.
• an ordinary non-fluorinated aliphatic sulfonic acid having a carbon chain containing at least 8 carbon atoms or an aromatic sulfonic acid having at-least an 8 carbon alkyl chain attached to the benzene ring is fairly stable when merely dissolved in acidic hexavalent chromium plating baths, such materials are rapidly and completely oxidized when the plating solution is eleetrolyzed using insoluble anodes, such as lead, lead-tin, lead-antimony or In less than four hours of elecalters the usual ratio of chromic acid anhydride (CrOs) amass;
• the chromium is applied over an underlayer of nickel.
• the fluorocarbon sulfonic compounds of this invention tend to render the underlying nickel plate less sensitive to passivation by contact with the chromic acid solution before current is applied.
• Such mild cathodic gassing is accomplished by using voltages below the plating voltage for a short period of time.
• One suitable condition for such gassing is a potential of 2 to 3 volts maintained for about 5-30 seconds.
• the incorporation of the fluorocarbon compounds of this invention in conventional hexavalent chromium plating baths has also been found to enable the plating of thicker bright chromium deposits over a bright surface before dulling of the chromium plate sets in.
• the thicker chromium plate increases the corrosion protection by decreasing the porosity of chromium plate.
• steel that is plated with 1-1.3 mils of bright nickel and overlaid with .05 to .08 mil of chromium provides greatly superior corrosion protection in industrial atmos pheres than is afforded when the overlayer of chromium has a thickness of only about .02 mil.
• trivalent chromium which is formed by reduction of hexavalent chromium at the cathode, tends to maintain itself at a higher level (for example, 1-3 grams per liter) in the chromium plating bath than when no fluorocarbon sulfonic compound is present, and furthermore there is a definite increase in cathode efficiency.
• a fluorocarbon carboxylic acid for example, the compounds, perfluorocaproic acid and perfluorocaprylic acid CF3(CFz)aCOOI-I or their salts
• chromic acid baths used for the electrodeposition of chromium for example, baths containing the ratio of 100:1 of CrOs to S04
• there results a darkish or much more dull chromium deposit that is, there is a marked decrease in brightness of the deposit which can be overcome only by the use of an unusual ratio of CrOa to S04, for example, 50:1 instead of the usual 100:1.
• the compounds of Table I are exhausted from the bath only by drag-out in the film which remains on the articles being plated as the articles are removed from the bath. While the amount of drag-out can be minimized by the use of drag-out tanks or ion exchangers, the fluorocarbon sulfonic compounds of this invention containing 3-8 carbon atoms produce a suprisingly low amount of drag-out. Baths have been run for months with only negligible loss from drag-out of the compounds of Table I such as perfluoro 4-methyl cyclohexane sulfonic acid.
• the shorter chain fluorocarbon sulfonic compounds of Table I that is those containing 8 or less carbon atoms when used in concentrations of, for example, 0.5 gram/ liter up to saturation, produce rapidly collapsing foams during electrolysis while concurrently lowering the surface tension of the baths to values as low as 20-30 dynes/cm.
• the shorter chain compounds produce on the surface of the bath, either no visible foam blanket or a comparatively thin one during continuous electrodeposition, the quantity of foam blanket and its thickness being dependent upon the particular compound employed, its concentration, the current concentration used, the ratio of surface to volume of the bath, and the temperature of the bath.
• a thin blanket of foam is much safer because excessively thick blankets being filled with hydrogen and oxygen are subject to explosion. Because of their tendency to quickly collapse and form thin foam blankets, the perfluoro n-hexyl sultonic compounds, perfluoro 2- or 4-metl1yl cyclohexane sulfonic compounds, perfluoro 2- or 4-ethyl cyclohexane sulfonic compounds or perfluoro dimethyl cyclohexane sulfonic compounds are preferred and are especially preferred for hexavalent chromium baths which are operated at room temperature.
• the compounds containing 8 or less carbon atoms in the chain are somewhat less effective in preventing the formation of spray and mist during electrolysis than at room temperatures. It is thought that these shorter chain compounds cause a smaller decrease in the surface tension, and also the surface viscosity and orientation of the molecules in the surface film of the bubbles is decreased at the higher bath temperatures which allows more rapid collapse of the bubbles without causing a build-up of even a very thin blanket of foam. With baths operating at temperatures above room temperature, the longer chain fluorocarbon sulfonic compounds of this invention are preferred.
• the foam becomes more stable evidently due to more pronounced orientation of the longer chains and a thicker foam blanket results on the surface of the bath. Where the foam blanket becomes too thick, it has been found that the foam can be collapsed almost instantly by passing vapors of ammonia over the bath.
• the foams which are created by the compounds of this invention are unique inasmuch as foams resulting from the use of ordinary non-fluorinated wetting agents in hexavalent chromium baths are not collapsed by ammonia vapor.
• Example III 400 grams/liter CrOs 2-3 grams/ liter S04 ion 1.5 grams/liter I-IzSiFs 0.1-1 gram/liter perfiuoro (mixed isomers of) isopropylcyclohexane sulfonic acids Temperature20 C.-60 C.
• Example IV 400 grams/ liter CrOs 2-3 grams/ liter S04 ion 1-2 grams/liter CaFz .01-.3 gram/liter perfluoro n-decyl sulfonic acid Temperature, 20 C.-60 C.
• Example V 100 grams/liter CrOs 120-220 grams/liter NazCrzOw or KzCrzOw S04 ion at 2-4 grams/liter or catalyst equivalent in F,
• Example VI 300-400 grams/ liter CrOa 3 grams/ liter S04 anion 0.5-2 grams/ liter perfluoro 4-methyl cyclohexane sulfonic acid 5-15 grams/ liter zinc dichromate, zinc oxide, or zinc carbonate Temperature 20 C.-50 C.
• Example VII 300 grams/liter CrOs 2 grams/ liter S04 0.2-2 grams/liter perfluoro 4-ethyl cyclohexane sulfonic acid 5-15 grams per liter of copper dichromate, or carbonate Temperatures 20 C.-50 C.
• zinc ions, copper ions and mixtures of zinc and copper ions may be employed in concentrations of about 5 to 20 grams per liter, and when such concentrations are employed the stability of the foam is increased.
• a method of electrodepositing chromium wherein the formation of spray and mist is substantially decreased which comprises electrolyzing an aqueous acidic hexavalent chromium solution containing at least about .01 gram/liter of a saturated flouorcarbon sulfonic compound, said compound having 4-18 carbon atoms to each sulfonic group.
• a method of electrodepositing chromium wherein the formation of spray and mist is substantially decreased which comprises electrolyzing an aqueous acidic hexavalent chromium solution containing at least about .01 gram/liter of a compound having the formula RFS03X where RF represents a saturated fluorocarbon chain of 4-18 carbon atoms, and X is a cation.
• a method of electrodepositing chromium over nickel which comprises the steps of incorporating in an aqueous acidic hexavalent chromium bath at least about .01 gram/liter of a saturated perfluorocarbon sulfonic compound having 4-18 carbon atoms to each sulfonic group, immersing a nickel coated article in the bath, cathodically gassing said article by applying a voltage to the bath less than that normally applied for plating, and thereafter electroplating chromium from said bath.
• a method of electrodepositing chromium over nickel which comprises the steps of adding to an aqueous acidic hexavalent chromium solution at least about .01 gram/liter of a compound having the formula RFS03X Where RF represents a saturated fluorocarbon chain of 4-18 carbon atoms, and X is a cation, immersing a nickel coated article in the bath, cathodically gassing said article by applying a voltage to the bath less than that normally applied for plating, and thereafter electroplating chromium from said bath.
• a method of electrodepositing chromium wherein the formation of spray and mist is substantially decreased comprising the steps of electrolyzing an aqueous acidic hexavalent chromium solution containing at least about .01 gram/ liter of a saturated perfluorocarbon sulfonic compound having 4 to 18 carbon atoms to each sulfonic group, and regulating the thickness of the foam blanket which is formed by passing ammonia vapors over the said foam blanket.
• a bath for the electrodeposition of chromium comprising an aqueous acidic hexavalent chromium solution containing a saturated perfluorocarbon sulfonic compound in sufl'icient amount to substantially decrease formation of spray and mist, said compound having 418 carbon atoms to each sulfonic group.
• a bath for the electrodeposition of chromium comprising an aqueous acidic hexavalent chromium solution containing at least about 0.01 gram/liter of a compound having the formula RFSO3X Where RF represents a saturated fluorocarbon chain of 4-18 carbon atoms, and X is a cation.
• a bath for the electrodeposition of chromium comprising an aqueous acidic hexavalent chromium solution containing at least about 0.1 gram per liter of perfluoro cthyl cyclohexane sulfonic acid.
• a bath for the clectrodeposition of chromium comprising an aqueous acidic hexavalent chromium solution containing at least about .2 gram/ liter of perfluoromethyl. cyclohexane sulfonic acid.
• a bath for the electrodeposition of chromium comprising an aqueous acidic hexavalent chromium solution containing at least about 0.05 gram/liter of perfluoro noctyl sulfonic acid.
• a bath for the electrodeposition of chromium comprising an aqueous acidic hexavalent chromium solution containing at least about .01 gram/liter of perfluoro ndccyl sulfonic acid.
• a bath for the electrodeposition of chromium comprising an aqueous acidic hexavalent chromium solution containing at least about .2 gram/liter of perfluoro 2- methyl cyclohexane sulfonic acid.
• a bath for the electrodeposition of chromium comprising an aqueous acidic hexavalent chromium solution containing at least about .1 gram/liter of a perfluoro dimethyl cyclohexane sulfonic acid.
• a bath for the electrodeposition of chromium which comprises an aqueous solution of chromic acid containing a catalyst selected from the group consisting of the sulfate ion, the fluoride ion and the fluorosilicate ion and at least about .01 gram/ liter of a compound having the formula RFSO3X where RF represents a saturated fluorocarbon chain of 418 carbon atoms, and X is a cation, and about 5 to 20 grams per liter of a metallic ion selected from the group consisting of zinc, copper and mixtures thereof.
• a catalyst selected from the group consisting of the sulfate ion, the fluoride ion and the fluorosilicate ion and at least about .01 gram/ liter of a compound having the formula RFSO3X where RF represents a saturated fluorocarbon chain of 418 carbon atoms, and X is a cation, and about 5 to 20 grams per liter of a metallic

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
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• Organic Chemistry (AREA)
• Electroplating And Plating Baths Therefor (AREA)
• Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)

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Cited By (21)

Citations (2)

• 1953
  • 1953-01-29 US US334081A patent/US2750334A/en not_active Expired - Lifetime
  • 1953-12-21 GB GB35530/53A patent/GB758025A/en not_active Expired
  • 1953-12-23 NL NL183877A patent/NL90359C/xx active
  • 1953-12-24 CH CH326572D patent/CH326572A/de unknown
  • 1953-12-29 DE DEU2549A patent/DE937210C/de not_active Expired
  • 1953-12-30 FR FR1094669D patent/FR1094669A/fr not_active Expired
• 1954
  • 1954-01-06 BE BE525524D patent/BE525524A/xx unknown

Patent Citations (2)

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