US3387987A

US3387987A - Bath and process for producing platinum metal immersion deposits

Info

Publication number: US3387987A
Application number: US451643A
Authority: US
Inventors: Johnson Ronald William
Original assignee: International Nickel Co Inc
Current assignee: Huntington Alloys Corp
Priority date: 1964-04-28
Filing date: 1965-04-28
Publication date: 1968-06-11
Anticipated expiration: 1985-06-11
Also published as: GB1030545A; NL6505189A; CH440905A

Description

3,337387 BATH AND PROCESS FUR iPRQDUClNG PLATI- NUM METAL EMMERSEGN DEPUSHS Ronald Wiiiiarn .lohnson, Harrow, Middlesex, England, assigrror to The international Nickel Company, ind, New York, NFL, a corporation of Delaware No Drawing. Filed Apr. 23, 1965, Ser. No. 451,543 Claims priority, appiication Great Britain, Apr. 28, 19 .64, 17,579/64 11 Claims. (Ci. 117-71) ABSTRACT UP THE DESCLGSURE Directed to a process for producing an immersion deposit of a metal from the group consisting of palladium, platinum, rhodium and ruthenium upon a metal substrate wherein the plating bath contains about 1 to about 10 grams per liter of one of the aforementioned platinum group metals, about 64 to about 96 grams per liter of hydrochloric acid, about 0.1 to about 2.5 grams per liter of copper, and up to about 5 grams per liter of ferrous iron. The resulting deposits are particularly useful in producing soldcrable coatings.

The present invention is directed to the immersion plating of platinum metals and, more particularly, to an improved immersion plating bath and process for producing immersion deposits of platinum metals upon nickel and nickel alloy substrates.

It is known that coatings consisting wholly or partly of platinum metals can be formed on metals and alloys by immersion in acid aqueous solutions of salts of palladium, platinum, rhodium and ruthenium. Copper and copper alloys are readily coated in this way but on other metals it is difficult to obtain consistent results or, in some cases, any coating at all. These difiiculties are particularly great when the metal or alloy to be coated contains residual deoxidizing elements added during melting and they are believed to be due to the formation of oxide layers on the surface. For example, it is dllTlClllt to form adherent coatings on nickel and on nickel-iron alloys and very diiiicult if these alloys contain traces of calcium, silicon or magnesium, which are often incorporated in such alloys as deoxidants.

I have now found that adherent coatings of a metal from the group consisting of palladium, platinum, rhodiurn and ruthenium can be produced by employing a special immersion coating bath.

It is an object of the present invention to provide an improvement in the production of platinum metal immersion plates upon substrates made of nickel and of nickel-iron alloys.

It is another object of the invention to provide a special immersion plating bath particularly adapted for the production of coatings made of platinum, palladium, rhodiurn and ruthenium on nickel and on nickel-iron alloys.

It is a further advantage of the invention to provide a process whereby immersion coatings of palladium, platinum, rhodium and ruthenium can be produced on nickel and on nickel alloy substrates.

Other objects and advantages of the invention will become apparent from. the following description.

Generally speaking, I have now surprisingly found that the formation of adherent coatings is facilitated by the presence of cupric or cuprous copper or ferrous iron in aqueous acid platinum metal immersion coating solutions. Iron alone is less effective than copper or copper plus iron and, advantageously, the solutions contain at States Patent c lC least about 0.1 or about 0.2 gram per liter (g.p.l.) copper with or without iron. Very satisfactory results are obtained with l g.p.l. copper or with a mixture of 0.5 g.p.l. copper and 0.5 g.p.l. iron and the solutions preferably contain from 0.5 to 2.5 g.p.l. copper. There is no advantage in increasing the copper content above 2.5 g.p.l., though larger amounts, e.g., up to 5 g.p.l., may be present if desired. The iron content preferably does not exceed 2.5 g.p.l. but some improvement in adhesion is obtained at iron contents up to 5 g.p.l.

The metal coatings are formed by chemical replacement of the basis metal and the acidity of the solution must be such that the replacement reaction will proceed to the desired extent. Hence, if more than a very thin coating is required, the acidity must be high enough to insure that more of the basis metal is attacked and dissolved than is replaced by the coating metal so that a porous coating results through which attack on the surface can continue. If the acidity is too low, a nonadherent deposit will be obtained or a thin, nonporous coating will be formed and the reaction will then cease, while if the acidity is too high, an adherent coating will not be formed. Advantageously, the free acid corresponds to the salt of the platinum metal in the solution. For palladium, platinum and rhodium, I prefer to use solutions of the chloride in hydrochloric acid while for ruthenium the solution preferably consists of ammonium nitroso ruthenium chloride or ruthenium sulfamate in hydrochloric acid.

The concentration of the platinum metal in the solution is suitably from 1 to g.p.l. and the concentration of hydrochloric acid from 200 to 300 milliliters per liter of concentrated (32% by weight per unit volume) acid, i.e., about 64 to 96 g.p.l. of HCl. My preferred solutions contain 5 g.p.l. of platinum metal and 250 milliliters per liter of concentrated hydrochloric acid (80 grams per liter of HCl).

The solutions of the invention are particularly useful for coating nickel and nickel alloys, e.g., nickel-iron alloys containing up to about 65% iron and the balance essentially nickel, to produce soldcrable coatings thereon. Nickeliron alloys, particularly the alloy containing 50% nickel and 50% iron, are used as electric conductors for sealing through glass in electrical and electronic apparatus, and in switching apparatus such as reed switches, but have the disadvantage that they are not easy to solder. It is known that their solderability can be improved by coating them with palladium or other metals and, according to a further feature of the present invention, I make use of my solutions to coat the alloys by immersion. I find, for example, that by the use of my preferred palladium solution, good adherent coatings are obtained which can reliably be tinned by an automatic dipping process.

The comparative results set out in the table below illustrate the advantages of the present solutions.

Specimens were cut from a strip of 56% nickel-5 0% iron alloy made by air melting and containing residual deoxidants (including magnesium) and were cleaned by dipplug in acetone and then in a hot detergent solution, rinsing with water, immersion for one minute in concentrated hydrochloric acid at room temperature and again rinsing with water. They were then immersed for five minutes in an aqueous solution maintained at C. to C. and containing 5 g.p.l. of palladium (added as sodium tetrachloropalladate), 250 milliliters per liter of 32% by weight per unit volume hydrochloric acid and the indicated amounts of copper and iron, added as cupric and ferrous chlorides, respectively. The coated specimens were immersed in boiling water for 10 minutes to clean the pores of the coating, dried, and then tested for solderability by o dipping them in a proprietary flux and then immersing them in pure molten tin at 260 C. for two seconds. The appearance and adhesion of the coatings and an assessment of their solderability are recorded in the following The invention is useful for the production of plated contact tips in electrical switching and the like and in instances where difficulty in soldering of the alloy employed in such applications, for example, nickel-iron alloys, has

table. 5 been encountered.

Solution Cu, Fe, Adhesion Appearance Solderability No. g.p.l. g.p.l.

0 0 Very poor 0.1 0 Moderate Dull Good when adherent. 0.5 0 Good Shghtly dull Goo 0 0.5 Dull, darkish-.- Good when adherent. 0.5 0.5 Bright Good. 1.0 0 .do Do. 0 1.0 Dull, darkish..- Good when adherent. 2.5 0 d Brig t Good. 5. 0 0 do -1 Slightly dulL-.- D0. 0 6.0 Poor Dark Solution No. 6 also produced a bright, adherent deposit on commercially pure nickel whereas Solution No. 1 failed to produce an adherent deposit on another specimen of the nickel. In another test, a solution similar to Solution No. 6 containing 1 gram per liter of copper added as cuprous chloride (Cu Cl gave a substantially identical result in the immersion plating of a 50% nickel-50% iron alloy.

In contrast to the favorable effects of additions of cupric or cuprous copper and ferrous iron, the addition to Solution No. 1 of cobalt, manganese, ferric iron, chromium or lead, each in an amount of l g.p.l., brought about no improvement in the coating.

Besides nickel and the aforementioned nickel-iron a1- loys, other metals and alloys that can be coated include nickel-chromium alloys and nickel-cobalt-chromium alloys, both with and without titanium or aluminum or both. Thus, alloys containing up to about 25% chromium, up to about 25% cobalt, up to about 65% iron, up to about 10% of aluminum and titanium, with the balance essentially nickel, can be coated in accordance with the invention. Adherent deposits are not formed on mild steel or 18% chromium-8% nickel stainless steel. Nickel-chromium and nickel-chromium-cobalt alloys on which Solution No. 1 failed to form an adherent deposit, when used as described above, are an alloy containing chromium 20% and titanium 0.4% with the balance nickel and impurities; and an alloy containing chromium 20%, cobalt 18%, titanium 2.4% and aluminum 1.4% with the balance nickel and impurities. On the other hand, Solution No. 6 gave bright adherent coatings on each of these.

To illustrate the application of the invention to solutions of other meals, specimens of the 50% nickel-50% iron alloy and of commercially pure nickel similar to those used in the previous tests were immersed for 5 minutes at 65 C. in an aqueous solution containing 5 g.p.l. of platinum and 250 milliliters per liter of concentrated hydrochloric acid. No adherent deposit was formed. Addition of 1 g.p.l. of copper to the solution resulted in the formation of an adherent, solderable deposit on the nickel and the nickel-iron alloy. Adherent solderable deposits were also obtained On specimens of this alloy by the use of solutions containing 5 g.p.l. of rhodium and 250 mil liliters per liter of concentrated hydrochloric acid (5 minutes immersion at room temperature) and solutions containing 5 g.p.l. of ruthenium (added as ammonium nitroso ruthenium chloride) and 250 milliliters per liter of concentrated hydrochloric acid (5 minutes immersion at 65 C.).

The coatings formed by means of the invention using copper-containing solutions contain substantial amounts of copper in addition to the platinum metal. The coatings are quite thin, for example, the coatings produced on a 50% iron-50% nickel alloy by immersion for 5 minutes at 20 C. to C. using Solution No. 6 were estimated to be about 0.13 micron in thickness. The corrosion resistance of the coatings, which tend to be porous, can be improved by sealing with gold applied by immersion plating or by forming a water insoluble substance in the pores.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and appended claims.

I claim:

1. The process for producing a solder coating on articles made of nickel and nickel-iron alloys which comprises immersing said article in an acid aqueous immersion plating bath containing about 1 to about 10 grams per liter of platinum, about 64 to about 96 grams per liter of hydrochloric acid, about 0.2 to about 2.5 grams per liter of copper, and up to about 5 grams per liter of ferrous iron to form upon the immersed surface of said article an adherent platinum coating, drying the platinumcoated article and immersing the platinum-coated portion thereof in a bath of molten tin solder to form upon said platinum-coated portion an adherent coating of tin solder.

2. The process for producing a solder coating on articles made of nickel and nickel-iron alloys which comprises immersing said article in an acid aqueous immersion plating bath containing about 1 to about 10 grams per liter of palladium, about 64 to about 96 grams per liter of hydrochloric acid, about 0.2 to about 2.5 grams per liter of copper, and up to about 5 grams per liter of ferrous iron to form upon the immersed surface of said article an adherent palladium coating, drying the palladium-coated article and immersing the palladium-coated portion thereof in a bath of molten tin solder to form upon said palladium-coated portion an adherent coating of tin solder.

3. The process for producing an immersion plated deposit of a platinum metal upon a metal substrate made of a metal containing up to about 25 chromium, up to about 25% cobalt, up to about 65 iron, up to about 10% of metal from the group consisting of aluminum and titanium, with the balance essentially nickel, which comprises immersing said article in an acid aqueous immersion plating bath containing about 1 to about 10 grams per liter of a metal from the group consisting of platinum, palladium, rhodium and ruthenium, about 64 to about 96 grams per liter of hydrochloric acid, about 0.1 to about 2.5 grams per liter of copper and up to about 5 grams per liter of ferrous iron to form upon the immersed surface of said article an adherent platinum metal coating.

4. The process according to claim 3 wherein the copper content of the immersion plating bath is about 1 gram per liter.

5. A metal immersion plating bath comprising about 1 to about 10 grams per liter of a metal from, the group consisting of platinum, palladium, rhodium and ruthenium, about 64 to about 96 grams per liter of hydrochloric acid, about 0.1 to about 2.5 grams per liter of copper, up to about 5 grams per liter of ferrous iron and the balance essentially water.

6. A metal immersion plating bath according to claim 5 wherein the metal is palladium.

7. A metal immersion plating bath according to claim 5 wherein the metal is platinum.

8. A metal immersion plating bath according to claim 5 wherein the metal is rhodium.

9. A metal immersion platingbath according to claim 5 wherein the metal is ruthenium.

10. A metal immersion plating bath according to claim 5 wherein the copper content is about 0.2 to about 2.5 grams per liter.

11. A metal immersion plating bath according to claim 5 wherein the copper content is about 1 gram per liter.

References Cited UNITED STATES PATENTS Harris 11713O XR Certa et al 11713O XR Robinson 117-130 XR Knapp et a1 1l7130 XR ALFRED L. LEAVITT, Primary Examiner.

10 W. F. CYRON, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent N0 3 387 987 June 11 1968 Ronald William Johnson It is certified that error a patent and that said Letter shown below:

ppears in the above identified 5 Patent are hereby corrected as In the heading to the printed specification, line 8,

"Apr 28 1964 should read Apr 20 1965 Column 1 line 61 "and" should read or Column 3 l ine 48 "meals" should read metals Signed and sealed thi s 28th day of Octobe r l 969 (SEAL) Attest:

Edward M. Fletcher, Jr. kttesting Officer Commissioner of Patents WILLIAM E. SCHUYLER, JR.