US3248310A - Bright plating of chromium - Google Patents

Bright plating of chromium Download PDF

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Publication number
US3248310A
US3248310A US195106A US19510662A US3248310A US 3248310 A US3248310 A US 3248310A US 195106 A US195106 A US 195106A US 19510662 A US19510662 A US 19510662A US 3248310 A US3248310 A US 3248310A
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United States
Prior art keywords
chromium
acid
bright
plating
sulfate
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Expired - Lifetime
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US195106A
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English (en)
Inventor
Glenn R Schaer
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GEN DEV CORP
GENERAL DEVELOPMENT Corp
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GEN DEV CORP
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Priority to NL292708D priority Critical patent/NL292708A/xx
Priority to BE632459D priority patent/BE632459A/xx
Application filed by GEN DEV CORP filed Critical GEN DEV CORP
Priority to US195106A priority patent/US3248310A/en
Priority to GB18053/63A priority patent/GB1037104A/en
Priority to LU43744D priority patent/LU43744A1/xx
Priority to SE5339/63A priority patent/SE305103B/xx
Priority to DE19631496797 priority patent/DE1496797B1/de
Priority to CH611963A priority patent/CH414299A/fr
Priority to FR935008A priority patent/FR1364745A/fr
Priority to AT396463A priority patent/AT253888B/de
Application granted granted Critical
Publication of US3248310A publication Critical patent/US3248310A/en
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    • 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

Definitions

  • This invention relates to chromium plating and more particularly the invention relates to a chromium plating bath composition and the method of employing such bath composition in depositing a bright chromium plate over bright nickel and other bright metal surfaces.
  • Chromium is well known as a final electroplate finish on other metals, especially because it retains a high luster and does not tarnish. Chromium itself has the capacity to resist corrosion and is therefore desirable in providing a corrosion resistant surface.
  • the copper and/or the nickel plates may he applied in dull mat appearance and be buffed to mirror-like luster before chromium plating.
  • the more usual practice is to bright finish the basis metal object and then apply bright electroplates. Practical methods are in wide commercial use and are well known in the art for electrodepositing bright copper and bright nickel with mirror-like luster needing no buffing or coloring before chromium plating.
  • the appearance after chromium plating is the brilliant mirror-like quality that the art has become accustomed to designate as a bright chromium finish.
  • the bright chrome finish is expected to retain its attractiveness as long as the life expectancy of the object so finished.
  • the bright chrome finish on zinc die casting and on steel parts showed unsightly deterioration in a short time as three months in outdoor service on automobiles
  • advances during the last five years have shown how to achieve two years and longer duration of the bright plate without objectionable deterioration of the bright chrome appearance.
  • This progress was made possible by the use of duplex nickel plate in place of only bright nickel plate and by recognizing how to make fullest use of chromium plate.
  • the present invention relates to a novel way to attain improved chromium plate.
  • the improved chromium plating technique is especially significant in the decorative plating on bright nickel of parts of complicated shape.
  • Chromium plating baths of the known art have notably poor covering power and throwing power. Also, most of the known processes deposit chromium that is porous when the thickness is less than about 0.02 mil (0.00002 inch) thick and is macro cracked when the thickness exceeds about 0.03 mil. Furthermore, the prior art chromiurn plating baths have higher current efiiciency at higher current densities. This characteristic accounts for the abnormally poor throwing power and for a limiting current density below which no chromium metal deposits. At such below minimum current densities a rainbow stain may deposit. This limiting minimum current density is much higher than the limiting minimum current density at which bright nickel will deposit in mirror-like form.
  • the plating of bright nickel on a shaped part having deep recesses as well as relief or protruding areas When the average plating current density is 50 amps per square foot, the current density in the recessed areas is on the order of 10 amps per square foot whereas in the relief areas the maximum current density will be approximately amps per square foot.
  • a primary current density between the recessed and relief areas is between 1 and 7.5.
  • the current efficiency of the nickel deposition is the same at 10 as at 75 amps per square foot, that is, about 98%. Therefore, the plate thicknesses will be in the ratio of 1 to 7.5 at the low and high current density areas respectively.
  • minimum plate thicknesses are specified. Such thicknesses are well established in the art and for duplex nickel plate the minimum plate thicknesses should be 0.8 mil. Therefore, electroplating under conditions to give 0.8 mil duplex nickel in the recess of the above mentioned shaped part applies 7.5 times as much, or 5.6 mil This is the best that can be achieved because it is decided by the primary current distribution.
  • the electroplater has means at his disposal such as shielding and special racking techniques to shift the primary current ratio to a more favorable value of 1 to 3 to 1 to 4. Then the thickness distribution of duplex nickel plate is 0.8 mil and 2.4 to 3.2 mil.
  • the plight of the plater is clearly revealed. He can provide a uniform bright duplex nickel appearance and plate distribution satisfactory for corrosion protection but he cannot achieve uniform chromium plate for equal corrosion protection all over.
  • the chromium is macro cracked at the thicker plate regions and porous at the Both conditions have been recently shown in the plating literature to significantly diminish the protective durability of the electroplate.
  • the plater can resort to techniques of bipolar electrodes, current thieves, current shields high current densities and by juggling the temperature and sulfate ratio which are costly and makeshift at best, to get better chromium distribution. Most of his gain will be at the high current density regions, with little or none at the low current density regions.
  • An objective of the invention has been to improve the covering power and throwing power in a chromium plating process.
  • Another objective of the invention has been to tend to decrease the eflieiency of the chromium plating at the edges of a part While increasing the elliciency of the deposition in the part recesses.
  • FIG. 1 illustrates the preferred and operable ranges of .trichloroacetic acid and sulfate ion
  • FIG. 2 illustrates the preferred and operable ranges of monochloroacetic acid and sulfate ion; and FIG. 3 shows a variation in plate thickness versus current density from diflferent chromium plating baths.
  • Chromium plating has since the 1920s been practiced by employing a solution containing chromic acid and sulfate ion, the ratio of chromic acid to sulfate ion by weight being maintained approximately in the range of 80/1 to 120/ 1.
  • FIG. 3 is a plot of plate thicknesses versus densities for trichloroacetic (TCA) catalyst, S catalyst and combined TCA and S0 catalysts.
  • TCA trichloroacetic
  • S catalyst S catalyst
  • combined TCA and S0 catalysts The thicknesses were measured on Hull cell panels utilizing the process described in Patent No. 2,149,344. From FIG. 3 it can be observed that increases in sulfate ion alone or trichloroacetic acid alone to a chromium plating bath tend to increase the slope of the current efiiciency curve.
  • the surprising effect is indicated by the curve of the combined TCA and sulfate ion, that is, the curve of the bath of the present invention.
  • the etficiency of the bath at very low current densities (less than 30 amps. per sq. foot) has been improved, but the As a come-- efiiciency of the bath at high current densities has been markedly decreased.
  • this is the direction in which the curve or plot of efficiency should move in order to improve the efficacy of the bath.
  • the best results are obtained when the current effieiency at high current densities is less than the efiiciency of the bath at low current densities.
  • the protruding or relief areas do not build up chromium at such a great rate whereas it is possible to deposit greater thicknesses of chromium in the recessed areas.
  • the covering power or minimum current density at which chromium can be electr'o-deposited when both TCA and sulfate are used as catalyst is about 4 amp/sq. ft.; whereas the minimum current density at which chromium can be deposited is about 20 amp./sq. ft. when only 3 g./l. sulfate is the catalyst.
  • the significance of these numbers is that the total current needed to cause plating of chromium in a recess of a shaped part will be about 7 /2 times as much for the sulfate-only-catalyst bath as for the mixed sulfate-TCA-catalyst bath.
  • the preferred range of constituents for the plating bath is as follows:
  • the presence of sulfate ion is absolutely essential. While it is possible to obtain a chromium deposit without the sulfuric acid or sulfate ion, it is not possible to obtain anything approaching a satisfactory corrosion resistant bright plate over bright nickel when sulfate ion is absent, the only catalyst being the halogenated acetic acid.
  • the sulfate ratio that is the ratio of CrO to H If the ratio is substantially in excess of 300/1, as for example 400/1 or 600/1, a number of undesirable effects are noted.
  • the covering power suffers to the extent that it is quite difiicult to plate in deep recesses. Also, it is not possible to obtain bright plates at high current densities which will occur at the projecting portions of a shaped work piece. The chromium plate will be dull or burned.
  • the relationship of the sulfuric acid content and the trichloroacetic acid content in a bath containing 300 g./l. of chromic acid is delineated approximately in the graph of FIG. 1.
  • the area defined by the lines A, B, C, D, E, and F is the operable range. Within that area, the preferred range is defined by the lines G, H, I and I. Quite satisfactory plates can be deposited on articles which normally would be extremely difficult to plate with chromium if the sulfuric acid and trichloroacetic acid catalysts are maintained in the proper relationship and in the preferred ranges as defined by the area G, H, I, J.
  • the operable range has the utility for parts which are not toodifficult to plate and, indeed, the resulting plates will have properties which are preferable to plates obtainable by the best known prior art plating baths.
  • the bath was maintained at a temperature of between 125 and 127 F. and plating current was applied between the anode and a workpiece at approximately 288 amps per square foot.
  • the workpiece had previously been plated with copper and bright nickel prior to chromium plating.
  • Current was applied for five minutes and a bright lustrous chromium was deposited on the surface of the workpiece, the thickness of the chromium being as high as 0.16 mil without any cracks appearing and with a satisfactory bright lustrous appearance.
  • the panels were plated at a bath temperature of 92 F. for five minutes at a current density of 90 a.s.f. (The current density here is lower than that normally employed. However, the instability of MIA required a substantial deviation from the usual conditions.)
  • FIG. 2 The operable range In the practice of the instant invention in electrolytic systems wherein lead anodes are employed, there is a tendency for the plating solution to corrode the anodes and to form a contaminating sludge in the plating tank. This problem can be obviated by utilizing anodes other than lead which do not react with any of the solution constituents. Alternatively, a small amount of cobaltous ion can be added to the solution, preferably in the form of cobalt sulfate, the utilization of cobaltous ion being a well known expedient to inhabit the corrosion of l ad anodes in other electrolytic systems.
  • the various salts are not normally chemically pure.
  • the chromic acid will normally contain a small amount of a sulfate salt.
  • the commercial grade of trichloroacetic acid will contain approximately 98% trichloroacetic acid and 2% dichloroacetic acid. It should therefore be understood that the examples given hereafter are approximations and that a bath prepared from the following examples will normally be analyzed and additional salts added to bring the concentrations within the preferred ranges prescribed above.
  • the sulfate ion can be added as sulfuric acid or as a salt such as chromium sulfate which, when dissolved in the solution, will act identically as if it were introduced as sulfuric acid.
  • compositions adaptable for commercial packaging and the manner in which they are added to water to provide a chromium plating bath in which the concentrations fall within the desired ranges.
  • a satisfactory plating bath can be made by dissolving from to 450 g./l. of a salt mixture containing from 2.4 to 12.9 percent trichloroacetic acid, 1 percent water for a binder, and the balance chromic acid; then when the salts are dissolved, adding sulfuric acid to the solution .to adjust the chromic acid-sulfuric acid ratio to 250:1.
  • a satisfactory plating bath can be made by dissolving 100 to 450 grams of a salt mixture containing 300 parts chromic acid and 7.5 to 45 parts trichloroacetic acid and 1.7 to 2.5 parts of chromic sulfate hydrate
  • EXAMPLE XII A satisfactory plating bath can be made by dissolving 100 to 450 grams of a salt mixture containing 300 parts chromic acid, 10 to 20 parts trichloroacetic or monochloroacetic or tribromoacetic acid. After dissolution of the mixture, sulfuric acid should be added to give a CrO :SO ratio of 250:1.
  • the sulfuric acid content is an important variable and the most sensitive in that small changes from the preferred 1.2 g./l. of the absolute amount of sulfate (as small as 0.2 g./l.) can change covering and throwing power.
  • a change of 0.2 g./l. is a 16% percent change in the sulfate, which is a significant change in the composition.
  • HALOGENATED ACETIC ACID CONTENT The content of the halogenated acetic acid is much less For example, bright plates can be made with TCA contents from 7.5 to 45 g./l. However, the best combination of covering and throwing power are obtained at 15 g./l.
  • crack-free limit is highest at the 7.5 g./l. content and lowest at the 45 g./l. content.
  • the halogenated acetic acid is consumed slowly during plating and a small amount of the halogen ion is liberated. This decomposition might be the reason for the unexpected and advantageous results of this mixture of chemicals. In this respect, the halogenated acetic acids are not true catalysts because a true catalyst is not consumed.
  • CHROMIC ACID Changing the chromic acid content has a larger effeet on covering power and the thickness limit of crackfree plate than on throwing power.
  • the optimum covering power seems to be derived from a 300 g./l. chromic acid bath. Concentrations higher than 300 g./l. will increase the crack-free limit but decrease the covering power. Concentrations lower than 300 g./l. (such as 150 g./l.) will reduce both covering power and crackfree limit. In these discussions it is assumed that the chromic acid-sulfuric acid ratio remains constant.
  • TEMPERATURE The major effect of changing temperature is on covering power and thickness limit of crack-free plate. Lower temperatures (less than 125 P.) will improve covering but greatly decrease the crack-free limit. The optimum temperature for all around performance is considered to be 125 F. If covering power is the most important factor, such as is needed for plating for color on complex shaped parts for non-corrosive environmental use, then lower temperatures such as 110 F. would be desirable.
  • composition for use in an aqueous chromium plating solution said composition consisting essentially of: 300 parts by weight CrO 4 to 45 parts by weight halogenated acetic acid, and
  • sulfate salt wherein the sulfate contributes approximately 1.2 parts by weight of the total weight of said composition.
  • composition for use in an aqueous chromium plating solution said composition consisting essentially of:
  • sulfate salt wherein the sulfate contributes approximately 1.2 parts by weight of the total weight of said composition
  • said halogenated acetic acid being selected from the group consisting of mono-, diand trifluoroacetic acid, monodiand trichloroacetic acid, mono-, diand tribromoacetic acicl1 and mixtures of any of said halogen substituted acetic aci s.
  • chromium plating an article comprising passing a current between an anode and an article forming a cathode which are immersed in an aqueous chromium plating bath consisting essentially of chromic acid, sulfuric acid, and halogenated acetic acid in which chromic acid/sulfuric acid ratio is 100/1 to 600/1 and halogenated acetic acid is 2 to 45 g./l.
  • a chromium plating bath consisting essentially of 285-315 g./l. chromic acid, 1.0 to 1.5 g./l. sulfuric acid,

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Electroplating And Plating Baths Therefor (AREA)
  • Electroplating Methods And Accessories (AREA)
US195106A 1962-05-16 1962-05-16 Bright plating of chromium Expired - Lifetime US3248310A (en)

Priority Applications (10)

Application Number Priority Date Filing Date Title
NL292708D NL292708A (zh) 1962-05-16
BE632459D BE632459A (zh) 1962-05-16
US195106A US3248310A (en) 1962-05-16 1962-05-16 Bright plating of chromium
GB18053/63A GB1037104A (en) 1962-05-16 1963-05-07 Improvements in or relating to the plating of an article with chromium
LU43744D LU43744A1 (zh) 1962-05-16 1963-05-14
SE5339/63A SE305103B (zh) 1962-05-16 1963-05-14
DE19631496797 DE1496797B1 (de) 1962-05-16 1963-05-14 Bad und verfahren zum galvanischen verchromen von metall oberflaechen
CH611963A CH414299A (fr) 1962-05-16 1963-05-15 Procédé pour le chromage électrolytique d'articles à surface métallique, composition pour la mise en oeuvre de ce procédé et article chromé par mise en oeuvre de ce procédé
FR935008A FR1364745A (fr) 1962-05-16 1963-05-16 Perfectionnements au revêtement d'un article par le chrome
AT396463A AT253888B (de) 1962-05-16 1963-05-16 Zusammensetzung zur Herstellung eines Chrom-Elektroplattierungsbades

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US195106A US3248310A (en) 1962-05-16 1962-05-16 Bright plating of chromium

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AT (1) AT253888B (zh)
BE (1) BE632459A (zh)
CH (1) CH414299A (zh)
DE (1) DE1496797B1 (zh)
GB (1) GB1037104A (zh)
LU (1) LU43744A1 (zh)
NL (1) NL292708A (zh)
SE (1) SE305103B (zh)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3414492A (en) * 1965-12-14 1968-12-03 Corillium Corp Chromium plating process
US3475294A (en) * 1964-10-08 1969-10-28 M & T Chemicals Inc Method of electroplating chromium and compositions therefor
US3505183A (en) * 1964-12-28 1970-04-07 Edgar J Seyb Jr Process and compositions for electroplating chromium
US4206019A (en) * 1978-04-07 1980-06-03 M&T Chemicals Inc. Novel low concentration decorative chromium plating baths and method
US4472249A (en) * 1981-08-24 1984-09-18 M&T Chemicals Inc. Bright chromium plating baths and process

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2279830A (en) * 1938-03-09 1942-04-14 John J Murray Metal plating bath and method of plating
US2655471A (en) * 1951-12-21 1953-10-13 Poor & Co Chromium electroplating
US2745801A (en) * 1955-03-14 1956-05-15 Harshaw Chem Corp Chromium plating

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2279830A (en) * 1938-03-09 1942-04-14 John J Murray Metal plating bath and method of plating
US2655471A (en) * 1951-12-21 1953-10-13 Poor & Co Chromium electroplating
US2745801A (en) * 1955-03-14 1956-05-15 Harshaw Chem Corp Chromium plating

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3475294A (en) * 1964-10-08 1969-10-28 M & T Chemicals Inc Method of electroplating chromium and compositions therefor
US3505183A (en) * 1964-12-28 1970-04-07 Edgar J Seyb Jr Process and compositions for electroplating chromium
US3414492A (en) * 1965-12-14 1968-12-03 Corillium Corp Chromium plating process
US4206019A (en) * 1978-04-07 1980-06-03 M&T Chemicals Inc. Novel low concentration decorative chromium plating baths and method
US4472249A (en) * 1981-08-24 1984-09-18 M&T Chemicals Inc. Bright chromium plating baths and process

Also Published As

Publication number Publication date
LU43744A1 (zh) 1963-07-15
GB1037104A (en) 1966-07-27
NL292708A (zh)
DE1496797B1 (de) 1971-03-04
BE632459A (zh)
SE305103B (zh) 1968-10-14
CH414299A (fr) 1966-05-31
AT253888B (de) 1967-04-25

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