US2714088A - Electrodeposited coatings - Google Patents

Description

July 26, 1955 w p, KARASH 2,714,088

ELECTRODEPOSITED COATINGS Filed Jan. 8, 1952 I3 CHROMIUM -.Zeaazaszzaeaaezazzezze. NICKEL I2 MONY LEAD WALTER P. KARASH INVENTOR.

2,17%,088 Patented July 26, 1955 ELECTRODEPOSITED COATINGS Walter P. Karash, Cleveland, Ohio, assignor to The Harshaw Chemical Company, Cleveland, Ohio, a corporation of Ohio Application January 8, 1952, Serial No. 265,450

15 Claims. (Cl. 204-36) This invention relates to the production of protective inch or more, or chromium over nickel applied over a thin coating of copper. These nickel coatings, when applied to a suficient thickness and buffed, or when applied from a solution containing a brightening addition agent, are quite satisfactory for chromium plating.

Nickel, however, is expensive and sometimes difficult to 7 obtain. A need therefore exists for a protective and decorative coating having substantially the protective and decorative effect of nickel but which can be produced at a lower cost and from materials which are less expensive and less difiicult to obtain.

Various metals havebeen considered as replacements for nickel, but difficulties have always been encountered. Among the other metals which have been considered, lead is attractive from the standpoint of cost, but is too soft for most uses, and is difiicult to buff to a bright finish. Antimony also has been seriously considered, since it is harder than lead, affords good protection against corrosion, and is readily buffed. Like nickel, antimony will tarnish if exposed, and must therefore be protected. It was an obvious procedure to try protecting an antimony deposit by applying a chromium deposit thereover in accordance with the practice in nickel plating, chromium over nickel over steel being a very common type of coating for automobile trim, plumbing fixtures and many other uses. When, however, it was attempted to electro- I deposit chromium on a bright (image reflecting) antimony surface it was found that the resulting chromium deposit was not bright.

I have now discovered that a bright, adherent, chromium deposit can be applied over a bright antimony surface by interposing between such antimony surface and the chromium a very thin nickel (or equivalent) deposit. Such nickel deposit may be exceedingly thin, for example as thin as 0.000002 of an inch. The nickel deposit may be produced in any of various nickel plating solutions such as the Watts bath which ordinarily contains nickel sulfate, nickel chloride and boric acid but no brightening addition agent and which ordinarily produces a gray deposit. Deposits from the gray nickel solution on a bright antimony surface are bright enough for my purposes up to a thickness of 0.00003 of an inch. The deposit may also be produced in a solution which does contain one or more brightening addition agents, but these are not desirable unless the thickness of the nickel (or equivalent) exceeds about 0.00003 of an inch. If the nickel (or equivalent) is deposited from a so-called bright plating solution or is lightly buffed to remove any slight grayness the thickness may be as much as 0.0001 of an inch. A heavier deposit of nickel, for example such as normally used for automobile decoration, that is, a deposit in the order of 0.001 of an inch in thickness, is not satisfactory. Such deposits exhibit poor adherence, even tend to flake off after the chromium deposit is applied. If produced in a so-called bright nickel solution, which always results in harder and more brittle deposits, the adherence diliiculties, the tendency to flake oif after chromium plating, would be increased for a thick layer such as ordinarily used in nickel plating, although remaining imperceptible in the case of very thin layers. Accordingly I prefer to use gray nickel in the thickness range from 0.000002 to 0.00003 of an inch.

Ordinarily, the bright antimony surface will have been produced by bufling and then thoroughly cleaningan electrodeposit of antimony, the production of which as an adherent coating on steel is known to the art. For example, Bloom (U. S. Patent No. 2,389,131) describes a method of etching the steel and plating on the resulting surface from an antimony trifiuoride bath containing a monovalent fluoride and operating at a pH somewhat below 6.0. By the use of suitable addition agents bright (as plated) deposits of antimony can be obtained. The older literature describes the use of the antimony trifiuoride bath with sodium or potassium fluoride, also antimony trifluoride with sulfuric acid, sometimes SbF3 with free HF. (See Metal Cleaning and Finishing, vol 7, page 339.) Tartrate, citrate, and oxalate antimony plating solutions are also described in the literature. The particular plating solutions by means of which the antimony and other deposits are produced do not, per se, form any part of the present invention, the foregoing being cited merely to indicate that antimony plating solutions and processes are available and form a part of the knowledge of the operator skilled in the art. Lead, nickel, chromium, etc. plating also are well established arts.

It the primary object is to form a protective and decorative coating on steel or any of numerous other metals and alloys a very excellent procedure is to apply first an electrodeposit of lead, tin, silver or alloys thereof which are easily applied to steel, zinc base die castings, copper, copper plated die casting, brass, lead base and pewter castings, etc. Adherent antimony deposits are easily applied to unbuifed lead, tin or silver, or lead, tin or silver alloy electrodeposits in the form of adherent coatings which can be readily buffed to a high lustre. On the buffed antimony, there may be then applied a very thin coating of nickel or cobalt or, less desirably, zinc, copper, white brass or iron. Over the resulting thin deposit there is applied an electrodeposited coating of chromium, suitably of a thickness of the order of 0.00001 of an inch, which will not be dull, as in the case where it is plated directly on polished antimony, and which will not cause a separation of the thin nickel (or the like) deposit from the antimony, as when relatively heavy deposits of nickel are applied on the antimony and followed by chromium.

So far as I am aware, no one has heretofore realized that chromium could be applied as a brilliant, strongly adherent coating over bright antimony by interposing a thin coating of nickel, cobalt or the like. It is perhaps surprising that the chromium deposit would not turn out bright when applied over highly polished antimony, but that has been found to be what happens; and while it would be expected from nickel plating practice that a bright chromium deposit could be applied on a bright nickel surface, it is surprising that an ultrathin layer of nickel would result in overcoming the tendency of chromium to plate dull over polished antimony and at the same time retain excellent adhesion in the case of thin layers only of nickel, cobalt or the like.

In the accompanying drawing, the figure is a schematic with usual polishing compounds.

representation of a multiple-layer deposit according to the invention, wherein the thicknesses are greatly exaggerated, and wherein the bufifing step is indicated by a schematic representation of a buffing-wheel applied on the surface which is buffed.

In the drawing, the numeral indicates the base metal to be coated, which, as indicated, may be steel or zinc base die casting metal, copper, brass, pewter, etc. Electrodeposited on the base metal is the optional layer 11 of lead which, it is to be understood, may be omitted if suit able care is taken to apply a strongly adherent coating of antimony on the base metal, or which may be replaced by tin or silver. The antimony deposit 12 must be strongly adherent, and should be of a thickness great enough that, upon being buffed, there is no danger of cutting through and exposing the underlying layer. The antimony deposit normally may be of a thickness of about 0.0003 of an inch, and preferably is of a thickness of the order of 0.0005 to 0.002 of an inch. A thickness from 0.00075 to 0.0015 of an inch should prove adequate for any reasonable amount of bufling. The antimony deposit is buffed to a bright finish, as indicated by the schematic indication of a bufiing-wheel 13 in contact with its surface, and thereafter there is applied the ultrathin coating 14 of nickel or cobalt (less desirably copper, zinc, iron or white' brass). This coating may be of a thickness from 0.000002 to 0.0001 of an inch, but preferably is from 0.000002 to 0.00003 ofan inch in thickness. The chromium deposit 15 is applied over the ultrathin coating 14 of nickel, cobalt V or the like.

It should be emphasized that even though Bloom and others, especially Mathers, Trans. Am. Electrochem. Soc. 31, 289 (1917), found solutions to the problem of forming satisfactory electrodeposits of antimony, and the further fact that antimony is cheaper than nickel, the use of antimony for protective coating of metals has not become widespread. While antimony deposits are brittle, they do on buffing form good, bright, corrosion resistant coatings which, however, soon tarnish in air to an extent that their brightness is not restored by polishing Attempts to apply chromium over buffed antimony were highly successful as to adherence, but the brightness was lost. For example, 0.001" of antimony was applied on steel from an aqueous solution containing 250 grams per liter of SbFs and 200 grams perliter NHiF at a pH of 4.5, temperature 130 F. and cathode current density of amperes per square foot. The resulting deposit was bufied to a high lustre and chromium was applied to a thickness of 0.00001" from an aqueous solution containing 250 grams per liter of CrOa and 2.5 grams per liter of sulfate ion, operated at a temperature of 113 F. and a cathode current density of 150 amperes per square foot (initially about 280 amperes per square foot for starting). The resulting deposit was firmly adherent but cloudy. The experiment was re- 7:

peated with the exception that after buffing the antimony deposit there were applied to each of four buffed antimony electrodeposits respectively nickel deposits of thicknesses approximately 0.000002, 0.00002, 0.0001 and 0.001 from, in each case, an aqueous solution containing 240 g./l. of NiSO4.6H2O, 40 g./l. of NiCl2.6I-I2O and 40 g./l. of H3BO3. Chromium was then applied as before. In each of the first two instances the deposit was firmly adherent and fully bright. In the case of the deposit 0.0001 thick, it was firmly adherent after chromium plating but not fully bright. Adding brightening addition agents to the solution resulted in a fully bright, firmly adherent deposit after chromium plating at a thickness of 0.0001" of'nickel. (The brightening addition agent may be any commercially obtainable brightener, e. g., 2 g./l. naphthalene disulfonic acid and 0.002 g./l. fuchsin.) In the case of the deposit 0.001" thick, the deposit was bright but not firmly adherent, tending to flake off easily. Cobalt in similar thicknesses was found to be the full equivalent of nickel except for its higher cost. Iron,

copper, zinc and white brass in similar thicknesses gave fairly comparable results but proved more difficult to control.

Plating solutions suitable for the electrodeposition of antimony, lead, nickel, cobalt, zinc, iron, copper and white brass are as follows:

(1) SbF g./l 250 NHiF g./l 200 pH 4.5 Temperature F 130 (2) SbF3(NH4)2SO4 g./l 400 pH 4.0 Temperature F 130 (3) Pb(BF4)2 oz./gal 33.5 HBF4 oz./gal 10.7 H3BO3 oz./gal 3.0

Glue oZ./gal .03-.06

1 pH 4.0 Temperature F 120 (4) NiSO4.6H2O g./l 250 NiClz.6H2O g./l H3303 g./l 35 pH 4.0 Temperature F 120 (5) NiSO4.6HzO g./l 100 NiCl2.6H2O g./l l5 H3BO3 g./l 30 0 pH 3 0 Temperature Room The antimony surface must be well cleaned before nickel is applied.

35 (6) C0Cl2.6H2O g./l 100 NH4F.HF g./l 20 pH 3.0 Temperature F 130 40 (7) Zn(CN)2 g/l NaCN g./l 42 NaOH g./l 79 NazS g./l 0.75 Temperature F 80 (8) FeSO4.7I-Iz0 g./l 200 NaBF4 g./l 40 pH 3.0 Temperature F (9) CuCN g./l 120 Free cyanide g./l 3.75

Water Remainder pH 10.5 Temperature F '3 (l0) Zn(CN)2 g./l 60 Cu(CN) g./l 14 NaOH g./l 60 NaCN g./l 52 Na2SO3 g./l 0.48

= Temperature F 90 Having thus described my invention, what I claim is:

l. A process of producing a bright, electrodeposited coating wherein chromium is applied subsequent to antimony comprising electrodepositing on a bright antimony metal surface a film of a metal of the class consisting of nickel, cobalt. zinc, iron, white brass and copper of a thickness from 0.000002 to 0.0001 of an inch and electrodepositing a layer of chromium over said film, said bright antimony metal surface being the surface of an elec tin-deposit of antimony on and firmly adherent to a metallic base.

2. A process comprising electrodepositing on a bright tony metal surface a film of a metal of the class cong of nickel, cobalt, zinc, iron, white brass and copper of a thickness from 0.000002 to 0.0001 of an inch and electrodepositing a layer of chromium over said film, said bright antimony metal surface being the surface of an electrodeposit of antimony on and firmly adherent to a metallic base of the class consisting of lead, tin, and silver.

3. A process comprising electrodepositing on a bright antimony metal surface a film of a metal of the class consisting of nickel, cobalt, zinc, iron, white brass and copper of a thickness from 0000002 to 0.0001 of an inch and electrodepositing a layer of chromium over said film, said bright antimony metal surface being the surface of an electrodeposit of antimony on and firmly adherent to a metallic base of the class consisting of lead, tin, and silver applied on steel.

4. A process of producing a bright, electrodeposited coating wherein chromium is applied subsequent to antimony comprising electrodepositing on a bright antimony metal surface a film of nickel of a thickness from 0.000002 to 0.0001 of an inch and electrodepositing a layer of chromium over said film, said bright antimony metal surface being the surface of an electrodeposit of antimony on and firmly adherent to a metallic base.

5. A process of producing a bright, electrodeposited coating wherein chromium is applied subsequent to antimony comprising electrodepositing on a bright antimony metal surface a film of cobalt of a thickness from 0.000002 to 0.0001 of an inch and electrodepositing a layer of chromium over said film, said bright antimony metal surface being the surface of an electrodeposit of antimony on and firmly adherent to a metallic base.

6. A process comprising electrodepositing on a metal base a layer of antimony metal having a bright surface, electrodepositing on said bright antimony metal surface a film of a metal of the class consisting of nickel, cobalt, zinc, iron, white brass and copper of a thickness from 0.000002 to 0.00003 of an inch and electrodepositing a layer of chromium over said film, said bright antimony metal surface being the surface of an electrodeposit of antimony on and firmly adherent to a metallic base.

7. A process comprising electrodepositing on a metal base a layer of antimony metal having a bright surface, electrodepositing on said bright antimony metal surface a film of nickel of a thickness from 0.000002 to 0.00003 of an inch and electrodepositing a layer of chromium over said film.

8. A process comprising electrodepositing on a metal base a layer of antimony metal having a bright surface, electrodepositing on said bright antimony metal surface a film of cobalt of a thickness from 0.000002 to 0.00003 of an inch and electrodepositing a layer of chromium over said film.

9. A process comprising the steps of electrodepositing on a metallic base a layer of antimony metal, bufiing said layer of antimony metal to produce a bright surface thereon, electrodepositing on the resulting buffed surface a film of nickel of a thickness from 0.000002 to 0.00003 of an inch, and then electrodepositing a layer of chromium over said film.

10. A process according to claim 9 wherein said layer of antimony is electrodeposited on an electrodeposited layer of a metal of the class consisting of lead, tin and silver on a base metal.

11. A process comprising the steps of electrodepositing on a metallic base a layer of antimony metal, bufiing said layer of antimony metal to produce a bright surface thereon, electrodepositing on the resulting buffed surface a film of nickel of a thickness from 0.000002 to 0.0001 of an inch, and then electrodepositing a layer of chromium over said film.

12. A process according to claim 11 wherein said layer of antimony is electrodeposited on an electrodeposited layer of a metal of the class consisting of lead, tin and silver on a base metal.

13. A process comprising the steps of electrodepositing on a metallic base a layer of antimony metal, buffing said layer of antimony metal to produce a bright surface thereon, electrodepositing on the resulting bulfed surface a film of cobalt of a thickness from 0.000002 to 0.00003 of an inch, and then electrodepositing a layer of chromium over said film.

14. A process according to claim 13 wherein said layer of antimony is electrodeposited on an electrodeposited layer of a metal of the class consisting of lead, tin and silver on a base metal.

15. A process comprising the steps of electrodepositing on a metallic base a layer of antimony metal, bufiing said layer of antimony metal to produce a bright surface thereon, electrodepositing on the resulting bufied surface a film of cobalt of a thickness from 0.000002 to 0.0001 of an inch, and then electrodepositing a layer of chromium over said film.

References Cited in the file of this patent UNITED STATES PATENTS 1,061,674 Hoyt May 13, 1913 1,087,561 Tebbetts Feb. 17, 1914 1,738,748 Wirshing et al. Dec. 10, 1929 1,792,082 Fink et al Feb. 10, 1931 1,836,598 Humphries Dec. 15, 1931 2,093,428 Ford et al Sept. 21, 1937 2,637,686 McKay May 5, 1953 2,658,266 Du Rose et al Nov. 10, 1953

Claims (1)

1. A PROCESS OF PRODUCING A BRIGHT, ELECTRODEPOSITED COATING WHEREIN CHROMIUM IS APPLIED SUBSEQUENT TO ANTIMONY COMPRISING ELECTRODEPOSITING ON A BRIGHT ANTIMONY METAL SURFACE A FILM OF A METAL OF THE CLASS CONSISTING OF NICKEL, COBALT, ZINC, IRON, WHITE BRASS AND COPPER OF A THICKNESS FROM 0.000002 TO 0.0001 OF AN INCH AND ELECTRODEPOSITING A LAYER OF CHROMIUM OVER SAID FILM, SAID BRIGHT ANTIMONY METAL SURFACE BEING THE SURFACE OF AN ELECTRODEPOSIT OF ANTIMONY ON AND FIRMLY ADHERENT TO A METALLIC BASE.

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