US2600352A

US2600352A - Bright zinc electroplating

Info

Publication number: US2600352A
Application number: US137483A
Authority: US
Inventors: Christian J Wernlund
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 1950-01-07
Filing date: 1950-01-07
Publication date: 1952-06-10
Anticipated expiration: 1969-06-10

Description

Patented June 10, 1952 UNITED STATES TENT OFFICE signor fto I. an Pont de Nemours & Company, Wilmington, DeL, a corporation of Delaware N Drawing. Application January 7,1950, Serial No. 137,483

4 Claims. 1

This invention relates to the electrodeposition of zinc, and more particularly to a method for electroplating bright zinc from a 'zinc cyanide solution.

Zinc electroplated onto steel or other base metal from a zinc cyanide electrolyte without the use of addition agents generally has an undesirable dark grey appearance. Bright Zinc deposits can be obtained by adding to the electroplating bath various know'n'addition agents but generally in such cases, the bright deposit is covered by a thin brownish film'which has to be removed by a subsequent operation consisting of dipping the electroplated article into a dilute solution of an oxidizing agent. Acetone and certain other ketones have been proposed as addition agents for zinc plating. These have not proved to excel other known brighteners and also require the bright dipping after treatment.

An object of the present invention is to provide an improved method for electroplating bright zinc onto steel and other base metals. A further object is to electrodeposit bright zinc which is free from the usual brownish film or other discoloration and which does not have to be treated after electroplating in order to obtain a filmfree, bright, smooth surface. Still other objects will be apparent from the following description of the invention.

The above objects may be attained in accordance with the present invention by electroplating zinc from a zinc cyanide solution which contains a small amount of an alkali metal stannate together with a small amount of one ormore of certain ketones. The ketones suitable for practicing the invention are methyl gamma-hydroxypropyl ketone, methyl n-propyl ketone, methyl ethyl ketone, acetone, diacetone alcohol, acetyl acetone, mesityl oxide, cyclopropyl methyl ketone and cyclohexanone. Of these, the preferred ketone is methyl gamma-hydroxypropyl ketone. The other ketones mentioned above are efiective brighteners only when used in conjunction with an alkali metal stannate. In the absence of the stannate they have only a comparatively slight brightening effect on the-electroplated zinc and form the usual film which must be removed by bright dipping. On the other hand, the methyl gamma-hydroxypropyl ketone gives excellent results when used alone, producing a clear, bright electrodeposit which is filmfree and needs no after treatment. The best results have been obtained by using methyl gamma-hydroxypropyl ketone in conjunction with an alkali metal stannate, which-produces electrodepos'its of great brilliancy.

In place of the above ketones, I may use their cyanhydrins, as'the cyanhydrins readilyhydrolize in the aqueous plating bath to set free the "ketones therein. Thus, one method of adding a ketone to the electroplating bath is to add its cyanhydrin, which immediately-forms the-ketone in situ. 7

The invention is illustrated by the following examples:

Example '1 Aqueous zinc cya'nidelectroplating solutions were prepared having the following "compositions:

Zn(CN) 2 ag./l. NaCN 5060'g./1. NaOI-I g./l. NazS 0 5'g;/l. Na2SnO3.3HzO -1;5g./1.

In a series of electroplating operations utilizing electrolytes of the above composition, with the further addition in each case of a ketone as indicated in the table below, sheet steel electrodes were electroplated with zinc atcurrent densities of 2 to amps/sq. ft. and at a bath temperature of 25 to 30 C.

Each ketone was tested at several concentrations, an indicated in the'above table under Ketone concentration. Within the ketone concentration ranges shown, excellent bright 'zinc deposits of high brilliancy were obtained "withinl-the current density rangesas indicatedin the table. All the deposits were -free'from film and required no after treatment of any kind.

Example 2 Zinc was electrodeposited from an electrolyte like that of Example '1," except that it contained no sodium stannate. With the'f'platin'g conditions of Example 11 this stannate" free bath ias operated in separate trials with the addition of difierent ketones, as shown below:

Ketone Kewne Concentration Acetone SccJl. Acetyl Acetone 10 cc./l.

In each case the resulting electrodeposit was coated with a brown film. On dipping in a dilute nitric acid solution, the film was removed producing a bright plate, but less bright than that obtained with these ketones in Example 1.

Example 3 Zinc was electroplated onto steel crank hole covers from the aqueous electrolyte given below using gamma-hydroxypropyl methyl ketone without sodium stannate addition:

Cathode current densities varied from 10 to 30 amps/sq. ft. The solution temperature was 25 0. Bright zinc deposits which required no bright dipping were secured at current densities of 18 to 30 amps/sq. ft.

Example 4 The following ketones were tested by the procedure of Example 1 and produced the results tabulated below:

Ketone Concentration Results Ketone Methyl Isobutyl Kc 5, l and 15 g.il. Dark colored deposit.

tone

Hydroquinone 4, 8 and 12 g./l Dull deposit. Di-tetrahydrofuryl gjl Brown film at 30 amps./ Pentauone. sq. ft. and dull plate at 1-20 amps/sq. it. Methyl vinyl ketone.- 4-8 cc./l Bright plate at first,

but ketone polymerizes making solution inoperable.

In practicing the invention to obtain the desired bright zinc deposits the alkali metal stannate and ketone are added to the electroplating bath from time to time as required, to maintain therein an alkali metal stannate concentration equivalent to 1 to 2.5 grams per liter of sodium stannate and a dissolved ketone concentration of approximately 3 to 26 grams per liter. When the methyl gamma-hydroxypropyl ketone is used, either with or without stannate addition, its concentration in the plating bath preferably is maintained at 5 to 15 grams per liter. In concentrations below 1 gram per liter the effect of the stannate is relatively small; and in order to obtain a film-free bright deposit, the stannate concentration should equal at least 1 gram per liter. At concentrations above 2.5 grams per liter, the stannate causes the formation of a dull plate, destroying the brightening eifect of the ketone. At concentrations within the range of 1 to 2.5 grams per liter, the stannate enhances the brightening effect of the ketone and prevents film formation.

A concentration of at least about 3 grams per liter of the ketone is required to obtain a commercially acceptable bright plate, although smaller amounts have more or less brightening effect. While amounts larger than 26 grams per liter may be used with good results (it the ketone is sumciently soluble), generally the results are no better than at 3 to 26 grams per liter. As the ketone must go into solution to function as a brightener, I prefer a ketone concentration not exceeding the solubility limit. The solubilities of the ketones used herein vary considerably. Thus, acetone is soluble throughout the range of 3 to 26 grams per liter, while other ketones such as methyl gamma-hydroxypropyl ketone is not- However, adding the ketone in amount in excess of its solubility in the plating bath does no harm within the limits of 3 to 26 grams per liter.

7 While generally it is preferred to use sodium stannate as addition agent in practicing the invention, potassium stannate and other alkali metal stannates may be used with equally good results at the same molar concentration.

In practicing the present invention it is preferable to utilize as electrolyte a zinc alkali metal cyanide solution such as that illustrated by the above examples which contains free cyanide and added alkali metal hydroxide. Also the best results are secured if the bath is purified as required by the addition of sodium sulphide or other alkali metal sulphide, zinc dust, or the like, which serves to precipitate out any heavy metal impurities which may be introduced into the bath from the zinc anodes or from the zinc cyanide. The invention, however, is not restricted to these preferred solutions but may be carried out with any solution of a zinc alkali metal cyanide.

The electroplating conditions such as bath temperature, current density, filtration of electrolyte, choice and location of anodes, and the like may be those conventionally employed in cyanide zinc electroplating operations. The herein described invention permits the production of excellent bright zinc electrodeposits over a wide range of current densities, e. g., from 2 to amps/sq. ft. and higher.

I claim:

1. The process which comprises electroplating zinc from an aqueous zinc cyanide solution which contains about 60 grams per liter of zinc cyanide and an alkali metal stannate in amount equivalent to 1 to 2.5 grams per liter of sodium stannate and to which has been added about 3 to 26 grams per liter of a ketone selected from the group consisting of acetone, methyl ethyl ketone, methyl n-propyl ketone. gamma-hydroxypropyl methyl ketone, acetyl acetone, diacetone alcohol, mesityl oxide and cyclopropyl methyl ketone.

2. The process which comprises electroplating zinc from an aqueous zinc cyanide solution which contains about 60 grams per liter of zinc cyanide and 1 to 2.5 grams per liter of sodium stannate and to which has been added about 3 to 26 grams per liter of a ketone selected from the group consisting of acetone, methyl ethyl ketone, methyl n-propyl ketone, gamma-hydroxypropyl methyl ketone, acetyl acetone, diacetone alcohol, mesityl oxide and cyclopropyl methyl ketone.

3. The process which comprises electroplating zinc from an aqueous zinc cyanide solution which contains about 60 grams per liter of zinc cyanide and 1 to 2.5 grams per liter of sodium stannate and to which has been added about 3 to 26 grams per liter of acetone.

4. The process which comprises electroplating zinc from an aqueous zinc cyanide solution which contains about 60 grams per liter of zinc cyanide and 1 to 2.5 grams per liter of sodium 5 stannate and to which has been added about 5 Number to 15 grams per liter of gamma-hydroxypropyl 1,904,732 methyl ketone. 1,905,105 CHRISTIAN J. WERNLUND. 2,109,887

REFERENCES CITED 0 The following references are of record in the gggg file of thls patent. 548:009

UNITED STATES PATENTS 10 Number Name Date 736,565 Szirmay Aug. 18, 1903 Name v Date Haneisen et a1. Apr. 18, 1933 Kersten Apr. 25, 1933 Mattacotti Mar. 1, 1938 FOREIGN PATENTS Country Date Great Britain Oct. '7, 1937 Great Britain Sept. 21, 1942

Claims

1. THE PROCESS WHICH COMPRISES ELECTROPLATING ZINC FROM AN AQUEOUS ZINC CYANIDE SOLUTION WHICH COMTAINS ABOUT 60 GRAMS PER LITER OF ZINC CYANIDE AND AN ALKALI METAL STANNATE IN AMOUNT EQUIVALENT TO 1 TO 2.5 GRAMS PER LITER OF SODIUM STANNATE AND TO WHICH HAS BEEN ADDED ABOUT 3 TO 26 GRAMS PER LITER OF A KETONE SELECTED FROM THE GROUP CONSISTING OF ACETONE, METHYL ETHYL KETONE, METHYL N-PROPYL KETONE, GAMMA-HYDROXYPROPYL METHYL KETONE, ACETYL ACETONE, DIACETONE ALCOHOL, MESITYL OXIDE AND CYCLOPROPYL METHYL KETONE.