US1497265A - Zinc-electroplated articles - Google Patents

Description

-I he considered are the discharge potential of'hy ra n; STATESPATENT OFFICE,

THE ROESSLER AND BASS- OE OHEILICAL COMPANY, OF NEW YORK, N. Y.,' A CORPORATION OF ZINC-ELECTRQPLATED ARTICLE.

Ho Drawing. Original application filed September 16,1922, Serial No. 588,567. Divided and. this,

application filed January 19, 1928. Serial No. 618,760.

To all whom it may concern: Be it known that I, J OSEPH Haas, J r., citizen of. the United States, and resident of Muncie, in the county of Delaware and State a of Indiana, have invented certain new and useful Improvements in Zinc-Electroplated Articles, of which the following is a specifi cation. I

My invention relates in eneral to the no electroplating of zinc or its a loys upon iron Such cyanid plator stee in cyanid baths. ing baths are widely used because of their greater throwing power as compared with other-baths which have been proposed for to zinc plating.

Hitherto the commercial zinc plating of ferrous articles in cyanid baths has been subi'lect tocertain limitations. For example, it

as been considered impracticable in cyanid ac baths to zinc plate iron castings at all.

Moreover, the plating of articles ofwrought iron or Wrought steel has been attended with some difficulty in res ect to articles of irregular surface, the di culty being that those portions. of the article which are more remote from the anode receive too thin a coating. In the plating of small ferrous articles this difliculty becomes so pronounced that hitherto it has been deemed impracticable to no zinc platesuch articles by the-basket method in cyanid baths.

In investigations to determine the cause of'these dificulties, I have foundthat it is due to the relatively low discharge potential as of hydrogen upon cast iron, which causes hydrogen to be deposited rather than zinc.

- .It has also been observed in plating cast iron and steel in the 'same' bath, that more hydrogen is evolved upon] the cast iron than so .on the steel, evidencing that the discharge potential of hydrogen on cast iron isimuch 'wer than that of hydrogen on steel. This "is further evidenced in platin copper on cast iron to use less free 4.5 cyanid t anin plating. on steel, too much 4 cyanid in either case of hydrogen. Y v

In order tosuccessfully deposit zinc on cast iron in a cyanid bath,- the factors to be causing only evolution drogen; the electrode potential of the cat osited,all-three being affected ythe common practice cathode- The that if the discharge potential of hydrogen on the cathode metal'is low, or below theelectrode potential of the deposited metal, and the difference between the electrode potential of the deposited metal and thedischarge potential of. hydrogen is great hy-- If the difi'ei'ence' drogen only is deposited. is not great, both hydrogen and metal are general rule may be said to be deposited while if the discharge potential lated with copand coatings of copper or tial of hydrogen closer to'the potential of zinc in a cyanid bath without an extra electroplating bath, by, depositing-the zinc in the presence of a metal electrochemically active to'prevent corrosion. Such a metal is Y mercury-which has the efiect in a cyanid electroplating-bath of bringing the discharge potential of ydrogen sonear the potential of zinc that zinc will be deposited together with a small percentage of mercury. 1n

other words, the eflect of making the difference between the discharge potential of hydrogen and the potential of zinc so much less than the difi'erence between the discharge potential of. hydrogen on cast iron and the potential of zinc, as. to secure a good deposit .o'f'zinc on cast articles not heretofore satisfactorilycoatedwith zinc by electroplating.

Other improvements result from my invention among which/are the following:

1. The color, s'nioothnesgfineness of am structure" resistance to corrosion,; and ardness of the zinc mercury deposit are supepresence of mercury has the rim to those formerly obtained of zinc alone ,7

from c anid baths!" e current elficieney at the cathode is markedly increased; 3, The anode wastage-due to chemical corrosion is decreased .4. The zincfcoatings do ndt stain m memes in the solution or when dried out, or when subsequently handled during assembling.

As illustrations of my invention, I will now describe the same as ap lied to the zinc e plating of various types iron and steel .15 and dirty before going to the platin tank,

it should then be again cleaned pre erably b dipping in muriatic acid solution of a ut 1.09 specific gravity after whiehitis rinsed in a hot caustic'solution containing one to five per oentNaOH until ready for the lating operation. w A 'l e fitting so cleaned may then be clipped in a mercury solution containing for example: c

Mercurie chloride 4oz.

Nitric acid, sp. g 1.4 022. Water to makelgal.

The fitting is then immediately suspended at in a zinc cyanidplating solution to which has been added a small amount of a soluble mercury compound. Excellent results are obtained from a bath of the following composition: g

. Water lgal.

Zinc cyanid 74oz. Sodium cyanid 402. Sodium hydroxidr 2oz.

Mercuric oxid- 1 oz.

The solution is maintained at a tempera ture of from 40 to C. Although in this species of the process, the mercury is first coated on the cathode, the coatingis 65 of zinc and mercury even if the mercury salt is omitted from the bath as one permeates' the other. In a thick'deposit, the zinc at the outsi'de may be practically free of mercury, but such thick -coatingis not so ordinarily desired. 'The preferred voltage is from three to six volts de ending upon the quantity of work being .p ated. When the required deposit has been secured, the fittin is removed from the solution, rinsed in cofd and hot watersuccessively, and then air dried. The bath must be replenished from time to time as the several ingredients become depleted, but the amount of mercury where used in the bath must not be permitted to become excessive inasmuch as the permanence of the coating. will be impaired. Ewample 'II.-To plate lar articles of wrought iron or wrought stee such as automobile 'rims, the article instead of being sand blasted, is cleaned by pickling alternately in alkaline and acid cleanin solu- 4 tions until a chemically clean meta 1c sur-- face is exposed. 'It ma then be dipped in the mercu solution and plated as described in Exampe I. When plated, the rim is rinsed in cold and hot water, and air dried.

The deposits thus obtained are tough and of pleasing appearance and are more resistant to corrosion and abrasion than any hitherto obtained in the art. 76 Example IlI.-To plate burrs, bolts, screws, and other small articles of iron or steel, I proceed as in Example II',"except that the articles are handled throughout 1n coarse-meshed wire basketsand are plated 80 with a current of full six volts. The deposits obtained are of excellent color and durability; moreover, the plate is of uniform thickness throughout all parts of the basket. As I believe I am the first to discover a means for increasing the otential of the cathode in zinc cyamd platlng, and thereby reducing evolution of hydrogen and increasing the amount and quality of the coating, e0

, besides producing a novel coating, I do not lirdit myself to any specific way of introducing the 'mercury exce t as specifically required by the appende claims.

Within the broad scope of the invention, at I I have obtained similar results by dipping the cathode first in a solution of a'mercury salt and then plating in an ordinary cyanid bath without added mercury salt; and by plating in a cyanid bath with added mercury salt without preliminary dipping. In

the former case, the mercury becomes alloyed with the first zinc deposited but upon continuedlat'ing, the percentage of mercury. diminishes, and finall the coating may t bepraetically pure zinc. ith mercury in the bath, the coating is uniformly ,allo ed with from 1.5% to 2.0% of mercury. e most resistant and satisfactory coatings have about.2.0% of mercury; If the percenta e are is below about 0.2%, the advantages re ting from its use are small, and the use is limited. If the; percentage of mercury is' above about 5.0%, the coatings are uns'atisfactory in texture, are brittle and of little 8w utility. I do notlimit myseli to the afore said mercurycompounds as I may use any soluble mercury salt for the dip which'wi deposit metallic mercur on the cathode, and 4 any mercuric compoun which is soluble in 3' .the bath. The oxide is preferred for the liminary dip solution and in the bath I may use other solublemercury salts such as n1- trate, sulphate, etc.

This application isa division of my ap- 1p ferrous article coated with-a dense bright menace plication Ser. No. 588,567, filed September electrolytic coating comprising zinc alloyed 16, 1922, wherein is broadly claimed the with mercury. novel process of depositing mercury in'the 2. As a new article of manufacture, a presence of zinc on a ferrous cathode, the ferrous article coated with a dense bright 3 claims herein being restricted to the novel electrolytic coating comprising zinc alloyed 15 product resulting from the process therein with between 0.2% and 5.0% of mercury.

described. Signed at Perth Amboy, in the county of I claim: x Middlesex and State, of New Jersey, this 1. As a new article of manufacture, a 13th day of January, A. D. 1923.

, JOSEP