US3672971A - Bright-zinc plating bath - Google Patents

Bright-zinc plating bath Download PDF

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Publication number
US3672971A
US3672971A US53038A US3672971DA US3672971A US 3672971 A US3672971 A US 3672971A US 53038 A US53038 A US 53038A US 3672971D A US3672971D A US 3672971DA US 3672971 A US3672971 A US 3672971A
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Prior art keywords
zinc
bright
bath
reaction mixture
baths
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Expired - Lifetime
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US53038A
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English (en)
Inventor
Gerd Senge
Rolf Sieburg
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Riedel and Co
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Riedel and Co
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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
    • C25D3/22—Electroplating: Baths therefor from solutions of zinc

Definitions

  • a bright-zinc plating bath in which the primary brightening agent consists of a reaction mixture of polyamines, salts of the metals of Groups V and VI of the Periodic Table and sulfur-releasing organic compounds.
  • the sulfursplitting compounds are preferably aliphatic aromatic and heterocyclic compounds containing sulfur and include mercaptane, thiocompounds and the like.
  • Our present invention relates to a bright-zinc electrobathing bath, a method of making such a bath, and an electrogalvanizing method for producing a bright-zinc coating and the product made by the latter method; more particularly, the invention relates to a bright-zinc electrogalvanizing system which eliminates many of the disadvantages of earlier electrogalvanizing methods, including toxicity of the bath, the difliculty in processing the waste liquors, and the poor plating efficiency of those baths which are free from the other disadvantages.
  • the cyanide-containing zinc bath has the further disadvantage that the presence of cyanide salts renders the bath highly toxic and makes it difficult to so treat the bath liquor as to enable its convenient disposal. Aside from the handling problems arising with the use of highly acidic zinc-plating baths, such baths are found to have poor throwing power and to give poor coatings in many instances.
  • alkaline cyanide-free electrogalvanizing baths generally include significant quantities of complexing agents or complex formers which are water pollutants of no small degree as well.
  • disposal of the waste electrolyte is a major problem.
  • Such conventional brighteners include gelatine and aldehydes (e.g. benzaldehyde, vanillin, heliotropin or piperonal and anisaldehyde or anisic aldehyde), compounds generally salts) of metals of Groups VI and VII of the periodic system, especially chromium, molybdenum, tungsten and manganese, and generally compounds of the eighth Group of the Periodic Table, namely, iron, cobalt and nickel.
  • the disadvantage of this system is that the gelatine and aldehydes are unstable in a strongly alkaline medium and sutfer alkali-hydrolysis, therefore rendering the system practically transparent for commercial operations.
  • complex formers or complexing agents such as triethanolamine, polyethylenamine, ethylenediaminetetraacetate, triisopropanolamine, dimethylamine, polyamines (such as diethylenetriamine, triethylenetetramine and pentaethylene) and hexamethylenetetramine.
  • Complexing agents of this type have the advantage that they stabilize the stability of the electrolyte although they often give rise to the problem of treatment of the waste electrolyte. This is all the more significant when it is recognized that zinc and other toxic heavy metals may be solubilized as a result of the presence of the complex formers and remain in the electrolyte as the latter is treated as a waste efiluent.
  • the principal object of the present invention to provide a bright-zinc electroplating or electrogalvanizing bath which is free from the difliculties of disposal, is nontoxic, and can produce bright-zinc coatings over a relatively wide current-density range at high efficiency and with good throwing power.
  • Another object of this invention is to provide an improved bright-zinc electrogalvanizing bath which avoids the difficulties hitherto encountered with conventional baths and yet is able to produce an excellent bright-zinc plating or coating in a highly stable manner with high efliciency.
  • Still another object of our invention is the provision of an improved method of making a bright-zinc electroplating bath which permits highly efficient zinc plating of a bright or shiny coating with high throwing power and current density and without the toxic difliculties encountered with some of the earlier baths proposed for bright-zinc electrogalvanizing.
  • Another object of our invention is found in a plating body in which the above methods and improved plating systems are employed.
  • the invention also has as its object the provision of an improved brightening composition or brightening agent for bright-zinc electrogalvanizing baths.
  • an aqueous alkali cyanidefree bright-zinc electrogalvanizing or electroplating bath which includes as a brightening system, agent or composition a combination of at least three components and, preferably, a reaction mixture thereof, the three components being a polyamine (of the type mentioned earlier and hitherto used as a component of brightening agents for zinc electroplates baths), a salt soluble in the alkali medium of at least one of the metals of Groups V and VI of the Periodic Table and preferably a vanadate or a molybdate, and a sulfur-splitting organic compound, i.e. an organic compound containing sulfur from which the sulfur is readily released.
  • reaction mixture When reference is made herein to a reaction mixture, it is to be understood that we have found that a mixture of the three components appears to undergo a chemical reaction of the complex-forming or like type. In other words, chemical bonds are created when the three components are combined, which bonds are not found in the three components individually. It has been discovered that it is advantageous to combine the three components prior to their introduction into the bath to obtain maximum benefit from the interaction observed above, although the effect of the brightening system is noticeable to a lesser extent when the three components are introduced individually into the electroplating electrolyte.
  • Reference to the Periodic Table is intended to mean the chart of the periodic arrangement of the elements contained on pages 445 and 446 of the Handbook of Chemistry and Physics, 41 edition, 1959-1960 or the periodic chart of the elements contained on pages 448 and 449 of this publication.
  • the groups to which the metals should belong are Groups V-B and VI-B. More specifically, the applicable metals are vanadium, chromium, niobium, molybdenum, tantalum and tungsten, although preference is given to vanadium and molybdenum, as discussed above.
  • the sulfur-splitting compounds most suitable for the purposes of the present invention are those which react most readily with the other components of the reaction mixture, as defined above. These compounds include mercaptans and thio-compounds and are generally describable as the aliphatic, aromatic, aromatic-heterocyclic compounds readily yielding sulfur.
  • the compounds which have been used, in combination or individually, include mercaptothiazoline, mercaptopyridine (C H NSH) thioureas and derivatives thereof, dithiocarbamic acids and salts and derivatives thereof, thioacetamide and thiocarbanilide (diphenylthiourea)
  • the reaction mixture is reacted at a temperature of about 20 C.
  • the second stage of the reaction or the after reaction is effected at a temperature of 70 C., i.e. at the temperature of the hot water which is introduced into the reaction mixture or 4 vice versa.
  • the temperature of the reaction mixture is slowly cooled to a temperature of about 20 C.
  • the reaction mixture is cooled progressively to the temperature of 20 C. in the presence of formaldehyde or sodium hydroxide.
  • the reaction mixture is present in the electrolyte or plating bath in an amount ranging between 0.01 to 10 parts by weight per parts by weight of the remainder of the bath, although these limits are not critical and it is possible merely to add the reaction mixture in the cyanide-free alkaline plating bath until the desired quality of brightplating is obtained.
  • the ratios of the three components may range widely and, for example, the polyamine may be present in an amount (by weight) ranging between 1 and 20 times that of the sulphur-containing compound, while the sulphur-containing compounds may be present in an amount (by weight) ranging between 0.5 and 20 times that of the metal salt.
  • An important advantage of the electrolyte of the present invention is the low proportion of complex formers therein and, consequently, the ease with which the waste liquor can be treated or disposed of.
  • a dilution of 1:100 yields a complexed-zinc concentration which is relatively low, i.e. below 3 mg. per liter.
  • compositions of the zinc electroplating bath bright plating of zinc was carried out in each case at a temperature of 10 to 30 C., at intervals of 2 C., at current densities of 0.5 to 4 amperes per/dm. for a treatment time of 10 to 20 minutes.
  • the treatment times were varied at two-minute increments and the current density tests were taken with 0.5 ampere per/dm. increments.
  • the composition yielded a bright zinc coat upon a metallic substrate electrogalvanized in the bath.
  • Example I Grams/liter Zinc chloride 50.0 Sodium hydroxide 230.0 Tetraethylenepentamine 2.0 Ammonium molybdate 0.1 Sodium dimethyldithiocarbamate 0.1 Heliotropin or heliotropin-bisulphite 1.0 Water Balance
  • Example II Grams/liter Zinc oxide 30.0 Sodium hydroxide 200.0 Pentaethylenehexamine 4.0 Thiourea 0.2 Mercaptothiazoline 1.0 Sodium diethyldithiocarbamate 0.1 Ammonium molybdate 0.28 35% aqueous solution of formaldehyde 0.4 Vanillin 1.0 Water Balance
  • Example III Grams/liter Crystalline zinc sulphate 130.0 Sodium hydroxide 250.0 Tetraethylenepentamine 2.0 Thiourea 1.0 Triethylenetetramine 1.5 Thioacetamide 1.0 Ammonium vanadate 0.5 Formaldehyde (35% aqueous solution) 0.5 Piperonal 0.4 Vanillin 0.4
  • Example IV Grams/liter Zinc oxide 30.0 Sodium hydroxide 180.0 Triethylenetetramine 2.0 Ammonium molybdate 0.2 4-mercaptopyridine 0.5 Formaldehyde (35% aqueous solution) 0.5 Piperonal 0.4 Vanillin 0.4
  • the current-efliciency curve of electrogalvanic metallic substrates with bright zinc produced from the baths of Examples LIV, above appproximates the curves obtained with bright zinc coating from cyanide baths, without however the toxicity associated therewith.
  • This high advantageous currentefliciency characteristic is not, however, obtained when the substances of the reaction mixture are supplied to the electrolyte individually, i.e. without a preliminary reaction. Whereas the prereacted mixture provides an extremely bright coating, the use of the same quantities of the individual components yields a bright coating which is less brilliant, is striated and is flakey.
  • the reaction mixture can be employed together with conventional brighteners as enumerated above. While, as pointed out, the mechanism time which the active species of the reaction mixture is formed is not fully clear, it has been found that deviations from the proportions given above and reaction steps under markedly different conditions do not yield the active species or a reaction mixture which is optimally elfective in the formation of bright zinc coatings.
  • the polyamine, the sulphur-containing organic compounds and the metal salts are reacted at about room temperature, i.e. 20 C. by being brought together for a period of a few minutes and intimately mixed. Thereafter, about 20 ml. of water at 70 C.
  • reaction mixture second stage reaction
  • formaldehyde and caustic soda is added (about 5 grams for the amounts indicated of the reaction mixture).
  • the formaldehyde appears to be an accelerator while the caustic soda functions as a stabilizer.
  • the electroplating bath is formed by dissolving the zinc salt and the sodium hydroxide in water and adding the reaction mixture to make up the specified compositions. Thereafter, any customary brighteners, if any, may be supplied.
  • a method of making an electrolyte for the brightzinc plating of a substrate comprising the steps of interreacting at least one organic polyamine selected from the group which consists of diethylenetriamine, triethylenetetraamine, pentaethylenehexamine, hexamethylenetetramine, and ethylenediamine; at least one aliphatic, aromatic or aromatic-heterocyclic sulphur-containing compound selected from the group which consists of mercaptothiazolines, mercaptopyridines, thioureas, dithiocarbamic acids and salts thereof, thioacetamides and thiocarbanilids; and at least one vanadate or molybdate salt and incorporating the resulting reaction mixture into an alkaline electrolyte containing zinc.
  • organic polyamine selected from the group which consists of diethylenetriamine, triethylenetetraamine, pentaethylenehexamine, hexamethylenetetramine, and ethylenediamine
  • reaction mixture is subjected to an initial reaction step at a temperature of about 20 C., is thereafter treated with water at a temperature of about 70 C. in a second reaction stage and is cooled to a temperature of about 20 C. slowly.
  • a method of brighbzinc electroplating a substrate comprising the step of electrodepositing zinc from the electrolyte prepared as defined in claim 1 at a current density of 0.5 to 4 amperes per dm. at a temperature of 10 to 30 C. for a period of 10 to 20 minutes.

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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)
  • Removal Of Specific Substances (AREA)
  • Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
US53038A 1969-07-15 1970-07-07 Bright-zinc plating bath Expired - Lifetime US3672971A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
DE19691935821 DE1935821B2 (de) 1969-07-15 1969-07-15 Verfahren zur herstellung eines glanzzusatzes fuer alkalische cyanidfreie zinkbaeder

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DE (1) DE1935821B2 (fr)
FR (2) FR2030619A5 (fr)
GB (1) GB1321648A (fr)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3871974A (en) * 1973-09-24 1975-03-18 Richardson Chemical Co Alkaline bright zinc plating
US3886054A (en) * 1973-09-24 1975-05-27 Richardson Chemical Co Alkaline bright zinc plating
US3960677A (en) * 1974-09-27 1976-06-01 The Harshaw Chemical Company Acid zinc electroplating
US5618634A (en) * 1993-06-23 1997-04-08 Sumitomo Metal Industries, Ltd. Composite zinc- or zinc alloy-electroplated metal sheet and method for the production thereof
WO2005021836A2 (fr) 2003-09-02 2005-03-10 Olin Corporation Composition de traitement antiternissure exempte de chrome et favorisant l'adhesion

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3841982A (en) * 1972-04-17 1974-10-15 Oxy Metal Finishing Corp Method to improve the brightness of zinc from an alkaline zincate electrodeposition bath

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3871974A (en) * 1973-09-24 1975-03-18 Richardson Chemical Co Alkaline bright zinc plating
US3886054A (en) * 1973-09-24 1975-05-27 Richardson Chemical Co Alkaline bright zinc plating
US3960677A (en) * 1974-09-27 1976-06-01 The Harshaw Chemical Company Acid zinc electroplating
US5618634A (en) * 1993-06-23 1997-04-08 Sumitomo Metal Industries, Ltd. Composite zinc- or zinc alloy-electroplated metal sheet and method for the production thereof
WO2005021836A2 (fr) 2003-09-02 2005-03-10 Olin Corporation Composition de traitement antiternissure exempte de chrome et favorisant l'adhesion
EP1709215A2 (fr) * 2003-09-02 2006-10-11 Olin Corporation Composition de traitement antiternissure exempte de chrome et favorisant l'adhesion
EP1709215A4 (fr) * 2003-09-02 2008-08-27 Gbc Metals Llc Composition de traitement antiternissure exempte de chrome et favorisant l'adhesion

Also Published As

Publication number Publication date
FR2049184B1 (fr) 1974-08-09
FR2049184A1 (fr) 1971-03-26
GB1321648A (en) 1973-06-27
FR2030619A5 (fr) 1970-11-13
DE1935821A1 (de) 1971-02-04
DE1935821B2 (de) 1972-03-16

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