US2488246A - Process of electroplating zinc, and baths and compositions for use therein - Google Patents

Process of electroplating zinc, and baths and compositions for use therein Download PDF

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US2488246A
US2488246A US551258A US55125844A US2488246A US 2488246 A US2488246 A US 2488246A US 551258 A US551258 A US 551258A US 55125844 A US55125844 A US 55125844A US 2488246 A US2488246 A US 2488246A
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zinc
baths
bath
pyrophosphate
brightener
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US551258A
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Jesse E Stareck
Passalacqua Frank
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United Chromium Inc
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United Chromium Inc
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    • CCHEMISTRY; METALLURGY
    • C25ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25DPROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D3/00Electroplating: Baths therefor
    • C25D3/02Electroplating: Baths therefor from solutions
    • C25D3/22Electroplating: Baths therefor from solutions of zinc

Description

Patented Nov. 15, 1949 UNITED STATE PROCESS OF ELECTROPLATING zINo, AND BATHS AND COMPOSITIONS FOR USE THEREIN Jesse, E. Stareck, Birmingham, and Frank lfassalacqua, Detroit, Mich., assignors to United Chromium, Incorporated, New York, N. Y., a
corporation of Delaware No Drawing. Application August 25, 1944, Serial'No. 551,258
This invention relates to the electrodeposition of zinc, and provides improvements therein.
The invention provides a new and improved process for electrodepositing zinc,- and novel baths and compositions foruse in such process.
It is desirable and advantageous (l) to electroplate smooth zinc deposits, (2) to electroplate bright deposits of zinc, (3) to electroplate such deposits with high current efiiciency, (4) to make use of noncyanide alkaline baths which are free from cyanide fumes, (5) to make use of baths less alkaline than cyanide-zinc baths, yet of such alkalinity that iron is not soluble in the bath, (6) to have baths in which the pH remains fairly stable, (7) to have an alkaline bath with which air or mechanical agitation can be used without building up carbonates or other objectionable reaction products therein, (8) to electrodeposit zinc at greater speed than by other processes making use of alkaline baths, (9) to avoid as much as possible hydrogen embrittlement of the base metal in the process of electrodepositing the zinc, (10) to obtain brighter deposits than are obtained by processes heretofore used, (11) to electrodeposit zinc on cast iron without special preliminary'steps, (12) to have a process of electrodepositing zinc which works well in barrel plating, (13) to make use of baths which are not corrosive to equipment and which do not give off poisonous fumes; the foregoing advantages are obtained by the use of the process and baths of the present invention.
According to the present invention a bath is used which contains the complex compound potassium zinc pyrophosphate KeZn(P2O'1)2, having a controlled pH, and containing a substance which acts as a brightener and a throwing power promotor. The pyrophosphate radicals and zinc content are in the molecular ratio of 2 to 1 plus an excess of pyrophosphate radicals; with said excess the molecular weight ratio range is from 2.3 to 1 to 4.6 to 1.
Compositions of water soluble zinc and pyrophosphate compounds may be made up .for preparing baths with zinc and pyrophosphate radical contents as given above.
The bath may contain other substances which give known effects, such as wetting agents, antifeamants, buffering agents, anode depolarizers, e c.
For making up the bath, (and also thecomposition of matter) a zinc compound such as zinc sulphate or zinc chloride or zinc pyrophosphate soluble in an aqueous solution of potassium or sodium pyrophosphate, and potassium or sodium pyrophosphate, may be used. The sodium pyrophosphate is less soluble than the potassium pyrophosphate. As the commercial chemicals vary somewhat in composition, they should be .4 Claims. (01. 2 04-55) used on the basis of the ascertained pyrophosphate and zinc content.
Examples of baths can be greater or less than those given in the examples above; the concentrations given are'good working concentrations. p p
A brightener is added to the bath, and is a solution soluble carbocyclic compound having hydroxy and methoxy groups ortho to one another, specific examples of which are curcumin, phenol sulphonate condensation products of vanillin, and ortho-hydroxy meta-methoxy benzaldehyde, the last of which we have foundto be the most satisfactory to use. Vanillin is also included in the above class, its usefulness, however, appearing to beinbaths having a pH of about 9.5.. Brighteners of this type, when added to the bath, act .as very eilicient hydrogen inhibitors during plating, especially on ferrous base metals. Besides. producing a brightening action, the addition of brighteners will also markedly increase the operating current density range. Oxidation products of thebrightener, as produced by electrolysis or the addition of an oxidizing agent as for example potassium permanganate, act'as promotors of throwing power. j Thequantity of brightener used is small as regards the other bath constituents, and in the baths accordingto the examples given above, the concentration is generally maintained at onehalf .to three .gramsper liter depending on the brightener used and its solubility. The brightener'should be added to the bath in amounts to produce brightness under optimum working condition's. The. brightness of the Zinc deposit equals that or mirror-likechornium deposits with which the art is familiar. I I I The alkalinity, or pH, of the bath is maintained between 9.5 and 12.5,.with the optimum between 11.2 and 12.0. The effect of maintaining the bath in the aforesaid pH range is to eliminate roughness of the deposit and to give completecoverage, with the brightener present; high current efficiencies are also obtained. It is an important and concomitant advantage of the invention that the range of pH or alkalinity of the bath is above the pH value at which iron dis- The average current density may also vary considerably; with baths of the composition given in the above examples, current densities up to 80 amperes per square foot may be used with good results. With the aforesaid baths, current densities of to 70 amperes per square foot are optimum. The current efiiciency is nearly 100%, and the process of the. present invention, over other alkaline processes for electrodepositing zinc, has the advantage of causing much less hydrogen embrittlement. Moreover, the speed of deposition is considerably higher than with other alkaline baths heretofore in use. The throwing power is good, being better than that of acid-zinc processes, and generally better than that obtained from cyanide-zinc processes.
It is desirableto agitate the baths in operation, and this may be done either by air or mechanical means. Neither carbonates nor other objectionable reaction products accumulate by air agitation. Ii foaming occurs this can be eliminated by means of adding a suitable antifoaming agent.
' We have discovered a novel and very -advantageous antifoaming agent for use in our baths in the substance tri-octylphosphate.
Foranodes, electrolytic zinc or cast zinc of high parity is recommended. Citrate radical in the bath, in quantity of about 15 g./l., may be used-as a depolarizer.
Care should be taken to exclude metallic impurities, especially lead, hexavalent chromium, copper, cadmium and arsenic. In general, the bath shouldbe kept pure.
It is desirable to electrolyze the baths before using for plating operations, or to add a small quantity of potassium permanganate to build up or promote the throwin power of the bath.
A mode of procedure followed in the plating of steelcartridge cases is as follows:
Bath composition The steel cartridge cases were put on a rack, im-
mersed in the bath, and connected to the cathode bus-bar. Current was passed for three minutes 'ata current density of 60 amperes per square foot, at the end of which time there was obtained a uniform, smooth, mirror-bright deposit 0.0002 inch thick. The temperature of the bath was 115 F. and air agitation was used. The anodes were cast electrolytic zinc.
The baths and process of this invention can be satisfactorily used for barrel-plating.
'The zinc deposits obtained by the use of the present invention are smooth, and smooth and bright under optimum operating conditions, the brightness being like that of mirror-like chromium deposits. The deposits have a fine grained crystalline structure typical of truly bright metallic deposits.
What is claimed is:
1. An aqueous bath for electroplating zinc, con-.
sisting essentially of pyrophosphate radicals and .zinc in the molecular ratio of approximately 2.3 to-l to 4.6 to 1, and optimum amounts of approximately /2 to 3 g./l. of ortho-hydroxy meta methoxy benzaldehyde, acting as a brightener, and having a pH between 9.5.and 12.5.
2. An aqueous bath for electroplating zinc, according to claim -1, wherein the pH is between 11.2 and;12.0.
, 3. A'p'rocess of electrodepositing smooth zinc plate, which comprises passing an electric current from an outside source'from an anode to-a cathode-article immersed in an aqueous bath solution at room temperature to 140 F. and at 1 to amperes per square foot consisting essentially ol pyrophosphate radicals and zinc in the molecular ratio of approximately 2.3 to 1 to 4.6 to
1, and optimum amounts of approximately to 3 grams per liter of ortho-hydroxy meta methoxy benzaldehyde, acting as a brightener,.and having a pH between 9.5 and 12.5.
4. A composition of matter, consisting essentially of an alkali-metal pyrophosphate, zinc pyrophosphate which is soluble in a water-solw tion of the alkali-metal pyrophosphate, and ortho-hydroxy meta methoxy benzaldehyde as a brightener, the ratio of the pyrophosphate radi- .cals to the zinc in the aforesaid ingredients being in the molecular weight ratio range.2.3 tolto 4.6 to 1, and the amount of the brightener being to 3 parts brightener for 250 parts zinc and pyrophosphate radicals in the composition.
JESSE E. STARECK. FRANK PASSALACQUA.
REFERENCES CITED The following references are of record in the file .of this patent:
UNITED STATES PATENTS,
OTHER REFERENCES Ser. No. 355,522, Howaldtet al. (A. P. C.) pub, May18, 1943. Journal of American Chemical Society (18) Electrodeposition of Metals, by Langbein and Braunt, 9th edition, 1924, page 567.
Wood Chemistry, by Wise, 1944 edition, pages Transactions of the Electrochemical Society, vol. 88 (1945), page 272.
US551258A 1944-08-25 1944-08-25 Process of electroplating zinc, and baths and compositions for use therein Expired - Lifetime US2488246A (en)

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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2811484A (en) * 1956-06-20 1957-10-29 Dow Chemical Co Electrodeposition of zinc on magnesium and its alloys
US3296104A (en) * 1963-10-29 1967-01-03 Hanson Van Winkle Munning Co Electrodeposition of zinc from pyrophosphate solutions
DE1235102B (en) * 1963-01-12 1967-02-23 Schering Ag Cyanide-free galvanic bright zinc bath
US3816188A (en) * 1972-12-18 1974-06-11 Du Pont Low-fuming galvanizing fluxes
EP0171817A2 (en) * 1984-08-16 1986-02-19 Kollmorgen Corporation Composition and process for electrodepositing a Zn or Zn/Si/P coating on metal substrates

Citations (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US744170A (en) * 1899-08-26 1903-11-17 Andre Darlay Process of depositing metallic coatings on metallic objects.
US809492A (en) * 1905-09-28 1906-01-09 Alexander Classen Process for electrolytic production of lustrous metallic coatings upon metals.
US1681509A (en) * 1926-11-23 1928-08-21 Grasselli Chemical Co Cadmium plating
US1791082A (en) * 1927-04-20 1931-02-03 Bianco Giuseppe Electrolytic zinc bath
US2080479A (en) * 1935-04-04 1937-05-18 Du Pont Plating of zinc
US2250556A (en) * 1940-11-26 1941-07-29 United Chromium Inc Electrodeposition of copper and bath therefor
US2315607A (en) * 1938-03-30 1943-04-06 Du Pont Anode
US2318592A (en) * 1940-02-24 1943-05-11 Du Pont Electrodeposition
US2360135A (en) * 1944-10-10 Detergent composition and method
US2393517A (en) * 1943-08-19 1946-01-22 Indiana Steel & Wire Company Process for electroplating zinc
US2447297A (en) * 1942-01-06 1948-08-17 Wyandotte Chemicals Corp Protection of glass surfaces against alkali attack

Patent Citations (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2360135A (en) * 1944-10-10 Detergent composition and method
US744170A (en) * 1899-08-26 1903-11-17 Andre Darlay Process of depositing metallic coatings on metallic objects.
US809492A (en) * 1905-09-28 1906-01-09 Alexander Classen Process for electrolytic production of lustrous metallic coatings upon metals.
US1681509A (en) * 1926-11-23 1928-08-21 Grasselli Chemical Co Cadmium plating
US1791082A (en) * 1927-04-20 1931-02-03 Bianco Giuseppe Electrolytic zinc bath
US2080479A (en) * 1935-04-04 1937-05-18 Du Pont Plating of zinc
US2315607A (en) * 1938-03-30 1943-04-06 Du Pont Anode
US2318592A (en) * 1940-02-24 1943-05-11 Du Pont Electrodeposition
US2250556A (en) * 1940-11-26 1941-07-29 United Chromium Inc Electrodeposition of copper and bath therefor
US2447297A (en) * 1942-01-06 1948-08-17 Wyandotte Chemicals Corp Protection of glass surfaces against alkali attack
US2393517A (en) * 1943-08-19 1946-01-22 Indiana Steel & Wire Company Process for electroplating zinc

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2811484A (en) * 1956-06-20 1957-10-29 Dow Chemical Co Electrodeposition of zinc on magnesium and its alloys
DE1235102B (en) * 1963-01-12 1967-02-23 Schering Ag Cyanide-free galvanic bright zinc bath
US3296104A (en) * 1963-10-29 1967-01-03 Hanson Van Winkle Munning Co Electrodeposition of zinc from pyrophosphate solutions
DE1294134B (en) * 1963-10-29 1969-04-30 Hanson Van Winkle Munning Comp Galvanic bath and process to produce shiny zinc coatings
US3816188A (en) * 1972-12-18 1974-06-11 Du Pont Low-fuming galvanizing fluxes
EP0171817A2 (en) * 1984-08-16 1986-02-19 Kollmorgen Corporation Composition and process for electrodepositing a Zn or Zn/Si/P coating on metal substrates
EP0171817A3 (en) * 1984-08-16 1988-11-09 Kollmorgen Corporation Composition and process for electrodepositing a zn or zn/si/p coating on metal substrates

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