CA1078776A - Baths for electrodeposition of ternary alloys - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

Bright, tarnish resistant and color stable ternary alloys of about 40-90% of tin, about 10-50 % cobalt and about 1-28% of a third metal of Periodic Group IIIA or VIB.
Typical third metals are zinc or antimony. The alloys are electrodeposited from aqueous acidic baths at a temperature of about 50-85°C. and current density of about 5-45 A/ft2.

Description

.
$his invention relates to a new and improved ternary alloys, to aqueous electrolytic baths from which the alloys are deposited, and to a process for forming the alloys. . ~ -This application is a divisional of Canadian patent ;~ -:
application, serial number 225,793, filed April 29, 1975. ~-Various alloys have been developed in efforts to duplicate the superior color of chromium and alloys containing substantial amounts of chromium, while also providing the corrosion resistance and tarnish resistance required when the alloy is to be used as a protective coating. Accordingly, the prior art teaches the addition of brightening agents to plating baths for the electro-deposition of tin-nickel binary . alloys as in U.S. Patent 3,141,836 - Seyb et al, or the careful control of plating conditions, also in the deposition of nickel-tin binary alloys, such as the highly acidic baths in U.S. Patent

2,926,124 - ~aylor et al. In another approach cobalt-tin binary alloys have been studied with respect to close similarities in corrosion resistance to nicXel-tin alloys. Clarke et al, An ElectrodepoQited.Bright Tin-Cobalt Intermeffallic Compound, I
CoSn", Transactions of the Institute of Metal Finishing, 1972, ~l;
Volume 50.
Despite the usefulness of such alloys from the st~nd-point of tarnish and corrosion resistance, those of~.such alloys which initially exhibited brightness similar to that of chromium did not maintain the good color. Moreover, results in obtaining hardness, brightness, tarnish resistance and color stability have not been consistent. Such properties tend to be overly sensitive to specific process conditions and therefore are difficult to re-produce on a commercial scale.
Accordingly, an object of the invention is to provide a new and improved alloy which not only provides a chromium-like brightness and tarnish resistance, but also provides color ,. . -1-: ~

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stability and hardness superior to that found in any of the alloying metals individually.
Still another object of the invention is to provide new and improved electrolytic plating baths which are easily for~
mulated and from which ternary alloys can be efficiently deposited on a wide variety of sub~trates to give coatings which are hard, bright, tarnish resistant and which have good color stability. -Another object is to provide a new and improved process whereby tin, cobald and a third metal are electrolytically co-deposited to form a hard, bright coating which is stable andhighly resistant to tarnishing.
These and other objects, features and advantages of the invention will be apparent from the description which follows.
In accordance with one aspect of the present invention, there i9 provided a acidic, aqueous bath for the formation of a bright, tarnish resistant and color stable coating, containing a tin compound providing stannous ions, a cobalt compound pro-viding cobaltous ions and a third compound providing ions of a third metal ~aid third metal being antimony or a metal other than alwminum ~l~c~od from Periodic Group IIB, IIIA or VIB, ~aid ions being present in amounts sufficient to electrodeposit from said bath at pH of about 1-3, a current density of about 5 - 45 A/ft.2 and bath temperature of about 50 - 85C., a ternary alloy -consisting essentially of about 40 - 90 wt. % tin, about 10 - 50 -~
wt. % cobalt and about 1 - 28 wt. % of said third metal.
In accordance with a further aspect of the present invention, there is provided a new and improved ternary alloy consisting essentially of about 40 - 90 wt. % tin, about 10 - 50 wt. % cobalt and about 1 ~ 28 wt. % of a third metal selected -from antimony, zinc or a metal other than aluminum selected from Periodic Group IIIA or VIB. Preferred third metals include zinc, indium and chromium. The thlrd metals may be present in the ~ -2~

:10'787~76 alloy singly or in admixtures of two or more. The plating baths ~;
of the invention are aqueous and highly acidic, and Contain com-; ~, .
..:.

-2a-~ ~0787~6 pound~ providing stannous ions, cobaltous ions and ions of the third metal or metal~ to be deposited. The ternary alloy~ are efficiently co-deposited from the bath~ at a temperature of about S0 - 85C. and cuxrent density o about 5-45 A/ft.2. In addition to the tarni-~h resistance expected in alloys containing tin and cobalt, the alloys exhibit a hardness, chromium-like brightness and color stability which make them useful as coatings on a wide variety of substrates.
In a further aspect of the invention there is provided a process for forming a substrate a bright, tarni~h resistant and color stable coating of an alloy consisting of about 40 - 90 wt%
tin, about 10 - 50 wt. % cobalt and about 1 to 28 wt. % of at least one third metal selected from either antimony, zinc or a me-tal other than aluminum of Periodic Group IIIA or VIB, which com-pri~es electroplating said alloy from an acidic, aqueous bath at a pH of about ~-3, a current density o~ about 5-45 A/ft.2 and a bath temperature of about 50 - 85C, said bath containing about 20 -100 g/l of a tin compound providing stannous ions, about 20-400 g/l of a cobalt compound providing cobaltous ions, and about 5-175 g/l of at least one third compound providing ions of said i third metal.
The ternary alloys of the invention are electrodeposited from highly acidic, aqueous baths of pH of about 1-3. A mineral acid is utilized for this purpose, such as a hydro-halide or a sulfur acid. Preferred acids are hydrochloric and fluoboric acids since such acids provided anions in common with anions of pre-ferred compounds of the metals to be deposited, and thus promote stability of the baths and good control of electrodeposition there-from.
The metals to be deposited are present in the baths as ionic compounds, the anions of the compounds and other conditions being chosen such that the compounds are substantially completely soluble in the aqueous medium. Accordingly, the compounds may be

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present as halides, sulfates, or otherwise but preferably the compounds will have anions common to the anions of the acid utilized to provide the high acidity. Since hydrochloric and fluoboric acids are the preferred acids, the preferred metal compounds will be the chlorides and fluoborates of the metals.
The metal compounds may be di~persed and dissolved in the aqueous medium in any suitable manner with heating and ; ~ -agitation, as needed. Sequence of admixture is not critical although the usual precautions with highly acidic solutions should be exercised. However, dispersion and electroplating are each benefited by somewhat elevated temperature of the bath, of the order of about 50-85C.
As chlorides the following ranges of concentrations of the metal compounds in the baths are effective~
cobalt chloride - about 20-400 g./l.
stannous chloride - about 10-100 g./l.
zinc chloride - about 10-175 g./l.
To the baths containing the foregoing concentrations of metal compounds may be added hydrochloric acid (37% solution) at a concentration of about 40-150 mls./l., ammonium hydroxide (28%
solution) in the range of about 10-50 mls./l. and ammonium bi-.
fluoride, about 20-400 g./l., to provide the requisite acidity and bath stability.
When the tin compound is a fluoborate, it is preferred to use fluoboric acid in place of hydrochloric acid. The concentra-tions of these and other ingredients in the bath may then range as follows:
cobalt chloride - about 100-300 g./l.
stannous fluoborate (50/0 solution) - about 25-75 mls./l.
fluoboric acid - about 75-225 g./l.
ammonium hydroxide (28% solution) - about 25-150 mls./l.
zinc chloride - about 10-135 g./l.
indium chloride as a substitute for zinc chloride

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preferably is utilized at a concentration of about 5 - 35 g./l.
and chromium chloride as a substitute for either of the foregoing compounds is effective at a concentration of about 5 ~ 55 g./l.
Other conditions of electrodeposition, including the cell form of electrolytic arrangement and type of substrate to be coated, control of concentration and rejuvenation of the baths, are well known in the art and do not require further description.
For example, the well known Hull cell may be utilized. The current density preferred for efficient electrodeposition is about S -45 A/ft 2 Generally, the percentage of each metal in the ternary alloy will vary in direct proportion to the concentration of each metal in the plating bath. To a lesser extent the percentage of each metal in the alloy will also vary in accordance with electro-plating conditions such as temperature, current density and pH.
It is believed that the new alloy exists as Sn2(Co, X) or (Sn, X) ~Co, X) where X is the third metal.
While the resultant ternary alloys are analogous to tin-nlokel and tin-cobalt with respect to tarnish resistance, the alloys exhibit not only chromium-like ~rightness but also con-sistently good color and color stability. Moreover, while the ternary alloys resist corrosion essentially to the same extent as chromium, they have a higher resistance than chromium to strong alkali under a superimposed anodic potential, that is, whereas chromium will dissolve if made anodic in a caustic solution, the ternary alloys of the invention are not affected. The alloys of the invention therefore are more resistanttO chloride attack than chromium and will resist salt spray and salt water contact better than chromium.
The plating baths may contain auxiliary reagents for various purposes in accordance with the understanding in the art.
Among such auxiliary reagents are ammonium chloride, gluconic acid, thiourea, fluorides such as ammonium bifluoride, sodium~fluoride and potassium titanium fluoride, and various

-5-- 10'78776 surfactants and the like such as al~yl aryl sodium sulfonate.
Such reagents generally are useful in minor amounts, for example, about 0.01 to about 10 grams per liter of plating bath, to obtain their known benefits.
The ternary alloys may be co-deposited electrolytically upon a wide variety of substrates, including metals such as steel , brass and zinc, as well as ceramics and plastics, in accordance with techniques wèll known in the art for coating sùch substrates.
0 The following examples of aqueous plating bath for- , mulations and conditions of electrodeposition are intended as further illustration of the inventio~ but are not necessarily limiting of the scope of the invention except as set forth in the ;
claims. All parts and percentages in these exampleq as well as in the foregoing specification are by weight unless otherwi~e indicated In each example the ternary alloy deposited has an approximate composition: tin, 40 - 90%, cobalt, 10 - 50/O third metal, 1 - 28%.
Example 1 Composition of aqueous bath o Cobalt Chloride 20-400 g./l.
Stannous Chloride 10-100 ~./1.
Ammonium Bifluoride 20-400 g./l.
Hydrochloric Acid (37%) 40-150 mls./l.
Ammonium Hydroxide (28%) 10-50 mls./l.
Zinc Chloride 15-175 g./l.
.
Platinq Conditions-Temperature 60-80 C.
Current density 10-30 A/ft.
pH of bath 1-3

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10'78~776 Exam~le ?
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Composition of aqueous bath Cobalt Chloride 20-400 g./l.
Stannous Chloride 10-100 g./l.
Ammonium Bifluoride 20-400 g./l.
Hydrochloric Acid (37%) 40-lS0 mls./l.
Ammonium Hydroxide (28%) 10-50 mls./l.
Indium Chloride 5-35 g./l.
Plating Conditions:
Temperature 60-80 C.
Current density 10-30 A/ft.
pH of bath 1-3 Example 3 Composit~ion of aqueous bath Cobalt Chloride 20-400 g.~l.
Stannous Chloride 10-100 g./l.
Ammonium Bifluoride 20-400 g./l. t Hydrochloric Acid (37%) 40-150 mls./l.
Ammonium Hydroxide (28%) 10-50 mls./l.
Chromium Chloride 5-55 g./l.
Platinq'Conditions:
Temperature 60-80 C.
Current density 10-30 A/ft.
pH of bath 1-3 .. . . .

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Example 4 ..... .. . .......................................... .
Composition of aqueous bath Cobalt Chloride 100-300 g./l.
Stannous Fluoborate (50%) 25-75 mls./l.
Fluoboric Acid 75-225 g./l.
Ammonium Hydroxide (28%) 25-150 mls./l. .
Zinc Chloride 10-135 g./l. ..
Platina Conditions: :
Temperature 50-85 C.
. Current density 5-45 A/ft.2 :
pH 1-3 Example S
Composit~on of aqueous bath Cobalt Chloride 100-300 g./l.
Stannous Fluoborate (50/0) 2S-75 mls./l.
Fluoboric Acid 75-225 g./l.
Ammonium Hydroxide (28%) 25-150 mls./'l.
Chromium Chloride 10-75 g./l.
Platin~ Condition~:
- Temperature 50-85 C.
Current density 5-45 A/ft.2 pH 1-3 .
Example 6 Com~osition of aqueous bath : ' Cobalt Chloride 100-300 g./l.
Stannous Fluoborate (50X) 25-75 mls./l.
Fluoboric Acid 75-225 g./l.
Ammonium Hydroxide (28%) 25-150 mls./l. .
Indium Chloride 5-35 g./l.

Platinq Conditions:
., ~.
Temperature 50-85C.
Current density 5-45 A/ft.2 pH 1-3 -8- .~:
~ .

Claims (11)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:-

1. An acidic, aqueous bath for the formation of a bright, tarnish resistant and color stable coating, containing a tin compound providing stannous ions, a cobalt compound providing cobaltous ions and a third compound providing ions of a third metal said third metal being antimony or a metal other than aluminum selected from Periodic Group IIB, IIIA or VIB, said ions being present in amounts sufficient to electrodeposit from said bath at pH of about 1-3, a current density of about 5 - 45 A/ft.2 and bath temperature of about 50 - 85°C., a ternary alloy consisting essentially of about 40 - 90 wt. % tin, about 10 - 50 wt. % cobalt and about 1 - 28 wt. % of said third metal.

2. A bath as in claim 1, wherein said third metal is zinc, cadmium, indium, antimony or chromium.

3. A bath as in claim 1, wherein said third metal is zinc, indium or chromium.

4. A bath as in claim 1, wherein said tin compound is stannous chloride or stannous fluoborate, said cobalt compound is cobalt chloride, and said third compound is zinc chloride, indium chloride or chromium chloride.

5. A bath as in claim 4, wherein the concentrations of said compounds in said bath are:

6. A bath as in claim 4, also containing ammonium bi-fluoride, hydrochloric acid and ammonium hydroxide, and the con-centrations of the ingredients of said bath are:

7. A bath as in claim 4, also containing ammonium bi-fluoride, hydrochloric acid and ammonium hydroxide, and the concentrations of the ingredients of said bath are:

8. A bath as in claim 4, also containing ammonium bi-fluoride, hydrochloric acid and ammonium hydroxide, and the concentrations of the ingredients of said bath are;

9. A bath as in claim 1, also containing fluoboric acid and ammonium hydroxide, and the concentrations of the ingredients of said bath are:

10. A bath as in claim 1, also containing fluoboric acid and ammonium hydroxide, and the concentrations of the ingredients of said bath are:

11. A bath as in claim 1, also containing fluoboric acid and ammonium hydroxide, and the concentrations of the ingredients of said bath are: