US2866740A

US2866740A - Electrodeposition of rhodium

Info

Publication number: US2866740A
Application number: US656499A
Authority: US
Inventors: Reid Frank Herbert
Original assignee: International Nickel Co Inc
Current assignee: Huntington Alloys Corp
Priority date: 1956-05-10
Filing date: 1957-05-02
Publication date: 1958-12-30
Anticipated expiration: 1975-12-30
Also published as: CH362581A; NL217128A; FR1174957A; GB808958A; DE1085003B; NL106193C; BE557396A

Description

ttesi 2,866,740 ELECTRODEPOSITION F RHODIUM Frank Herbert Reid, Hounslow, England, assignor to The International Nickel Company, Inc., New York, N. Y., a corporation of Delaware No Drawing. Application May 2, 1957 Serial No. 656,499

Claims priority, application Great Britain May 10, 1956 9 Claims. (Cl. 204-47) thickness of a decora- 0.000005 and 0.00005 tween 0.0001 and 0.002 inch or greater.

rhodium is deposited at the cathode.

Rhodium deposits as produced from the prior art baths show a pronounced internal tensile stress, which tions, but is generally of a high order, e. g., 50 to 100 In deposits thicker than about 0.0001 inch, the stress often leads to cracking of the rhodium deposit in the as plated condition. Cracks formed in this way may be referred to as primary cracks and usually extend right through the deposit to the basis metal. They may be detected by the so-called electrographic method, in which the basis metal, which is exposed by the cracking, pattern on a suitable test paper. Cracks are of course undesirable, particularly when the eliminate this cracking tendency.

Although many attempts were made to overcome the foregoing difliculties and other disadvantages, none, as far as I am aware, was entirely successful when carried into practice commercially on an industrial scale. It has now been discovered that by the use of novel rhodium electroplating baths, substantially crack-free electrodeposits may be produced under normal commercial electroplating conditions. It is an object of the present invention to provide a novel electrochemical plating reduce or substantially eliminate cracks in rhodium electrodeposits. i Other objects and advantages will become apparent from the following description.

Generally speaking, the present inventioncontemplates the production of electrodeposits of rhodiunr through the use of an aqueous, acidic electrodeposition' bath which contains a soluble rhodium salt and at least sufficient free mineral acid to prevent hydrolysis of the selected rhodium salt and selenium inan amount equiva:

to corrosion and to alia, as the surfaces inch, and that of an industrial deposit is generally be The electro-flytes commonly used are solutions of rhodium sulphate 30 bath which enables one to memo 2,866,740 I Patented Dec. 30,1958

to provide an amount of selenate ion therein which is elfective in reducing the primary cracking tendency of the deposit. The soluble rhodium salt suflicient topro vide from about 5- to grams per liter of dissolved rhodium, for example, about 10 g. p. 1., may be selected from the group consisting of rhodium sulphate, rhodium] phosphate and rhodium fluoborate. The free acidmay be selected from the group consisting of sulphuric acid,"; phosphoric acid and fluoboric acid and maybe employed in amounts at least up to about 100 milliliterslpe liter (m. p. 1.). The necessary concentration of selenic 1 acid is supplied either by the addition of the acid itself or by the addition of a salt. which upon hydrolysis in the presence of a mineral acid will produce a satisr'aw tory effective quantity of selenic acid. 7 Of course, when adding the hydrolyzable salt, it is preferred thatthe reaction products of the hydrolysis reaction will not interfere with the electrodeposition. Accordingly, it is preferred to use a sodium or other alkali metal saltof selenic acid when a salt addition is indicated.

In carrying the invention into practice, it is preferred to provide a range between a minimum of at least 0.05

g. p. l. to a maximum of about 1 g. p. l. (or even a maximum of about 8- g. p. l.) of selenic acid in the aqueous acidic rhodium electroplating bath I prefer to add free selenic acid. Although any addition of selenicacid will reduce the cracking to some extent, I prefer always toadd at least 0.05 g. p. l. The amount necessary to ensure practical freedom from cracking under all conditions of deposition is about 0.4 g. p. l. in an electrolyte low in free mineral acid, e. g., sulphuric acid, and rather less in an electrolyte with a higher concentration of free amount of free sulphuric acid. Further sulphuric acid.

is often added to increase the content of free sulphuric acid.

While it is to be observed ontemplates the minimization of primary cracking tendtheirsame criterion,-.a' current density of aboutl where hardness of the deposit is an important charac teristic of the deposit. As was indicated hereinbefore,

to achieve optimum minimization of primary cracking tendency, the amount of selenic acid added to the electrolyte should be increased as the amount of free mineral acid is decreased. As a general rule, it is preferred to adda minimum of 0.4g. p. l. of selenic acidto the electrolyte regardless of the free mineral acid concentration.

it is to be observed that the present invention contemplates a more advantageous rhodium electrodeposition bath which contains ingredients in the following tabulated ranges of concentration in units of g. p. l.

TABLE I Ingredients Broad Desired;

Rhodium (as soluble salt)..- about 10. Free Mineral Acid about 20. selenic Acid-.... about 1. Water Balance.

Mlllillters per liter Likewise, the, operating conditions are tabulated, in Table II:

TABLE II Conditions Broad Desired Temperature, C 2070.... 50 Current Den ity, ampJdm. 05-2.... 1

It is to be observed that while the specification has disclosed that the electrodeposits produced from the aforementioned baths of the present invention are of metallic rhodium, they contain smallamounts of selenium, the,

amount thereof depending to a certain extent on the concentration of selenic acid used in the bath. For purposes. of this specification, it is intended that the terms rhodium" or electrodeposited rhodium" when used in reference to the electrodeposits include these small amounts of selenium. In view of the inclusion or codeposition of selenium with rhodium, it should be noted that when the baths disclosed herein are replenished, not only rhodium must be added thereto but also suitable additions of selenic, acid should be made.

For the purpose of giving those skilled in the art a,

better understanding of the invention, the following illustrattve examples are given:

Example I A rho'dium plating electrolyte was made by dissolving rhodium hydroxide in sulphuric acid and diluting the Example II Electrolyte composition: Rhodium '(as sulphate) gms./1iter Added sulphuric acid mls./liter 70 A deposit 0.0007 inch thick obtained from this electrolyte at temperature of 45 C. withaicurrentsdensity of 2 amp./dm. showed moderate cracking. After addition of selenic acid to give a concentration of 0.4 gm./liter, an uncracked deposit 0.0012 inch thick was obtained.

Example Ill Example IV Flat copper specimens were plated on one side only with rhodium deposits 0.0005 inch thick from the electrolytes of Example 111. The copper was then dissolved away by treatment with nitric acid. The deposit from the electrolyte that was free from selenic acid disintegrated into numerous fine flakes because of cracks in it, but the deposit from the treated electrolyte remained as a coherent foil.

The present invention is particularly applicable to the electrodeposition of rhodium on any metal which is compatible with the acid electrolytes. These metals include nickel, nickel-silver, silver, gold, platinum, palladium, copper and brass.

It is to be observed that the present invention provides a process for the production of deposits of rhodium having reduced cracking tendencies from an acid electrolyte and also provides a novel acidic electrolyte for the production of such rhodium electrodeposits.

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. An electrolyte for producing substantially crackfree rhodIum electrodeposits comprising an aqueous acidic bath containing dissolved rhodium derived from at least one compound from the group consisting of rhodium sulphate, rhodium phosphate and rhodium fiuoborate in an amount to provide from about 5 to about 20 grams per liter of rhodium, free acid in an amount sulficient to prevent hydrolysis and a compound from the group consisting of selenic acid and alkali metal salts thereof in an amount equivalent to about 0.05 to about 25 grams per liter of selenic acid.

2. An electrolyte for the production of substantially crack-free rhodium electrodeposits comprising an aqueous acid bath containing dissolved rhodium derived from at least one compound from the group consisting of rhodium sulphate, rhodium phosphate and rhodium fiuoborate in an amount to provide from about 5 to about 20 grams per liter of dissolved rhodium, an acid from the group consisting of sulphuric acid, phosphoric acid and fiuoboric acid in an amount sufficient to prevent hydrolysis of the rhodium compound but not substantially exceeding about milliliters per liter of electrolyte and a compound from the group consisting of selenic acid and alkali metal. salts thereof in an amount equivalent to about 0.05 to about 8 grams per liter of selenic acid.

3. A rhodium plating electrolyte for producing hard, substantially crack-free rhodium electrodeposits comprising an aqueous acidic bath containing dissolved rhodium derived from at least one compound from the group consisting of rhodium sulphate, rhodium phosphate and rhodium fiuoborate in an amount to provide about 10 gramsper liter of dissolved rhodium, from about 12 to about 100 milliliters per liter of sulphuric acid and about 0.05 to about 1 gram per liter of selenic acid.

4. The process for producing substantially crack-free electrodeposits of rhodium which comprises establishing an aqueous acidic electrolyte containing about 5 to about 20 grams per liter of rhodium, from about 12 to about 100 milliliters per liter of free acid selected from the group consisting of sulphuric acid, phosphoric acid and fluoboric acid, at least about 005 up to about 1 gram per liter of selenic acid, and electrolyzing said bath at a current density of about 0.5 to about 2 amperes per square decimeter and a temperature of about 50 C. to produce a rhodium electrodeposit characterized by being substantially free from cracking.

5. The process for producing substantially crack-free electrodeposits of rhodium which comprises establishing an aqueous acidic electrolyte containing about 5 to about 20 grams per liter of rhodium, from about 12 to about 100 milliliters per liter of free sulphuric acid and about 0.4 gram per liter of selenic acid, and electrolyzing said bath at a current density of about 1 ampere per square decimeter and a temperature of about 50 C. to produce a rhodium electrodeposit characterized by being substantially free from cracking.

6. A rhodium plating bath for producing substantially crack-free rhodium electrodeposits comprising an aqueous acidic electrolyte containing in solution about 5 to about 20 grams per liter of rhodium, free acid in an amount sufficient to prevent hydrolysis of said rhodium and selenate ion in an amount equivalent to a concentration of at least about 0.05 up to about 25 grams per liter of selenic acid.

7. A rhodium plating bath for producing substantially crack-free rhodium electrodeposits comprising an aqueous acidic electrolyte containing in solution rhodium derived from at least one compound from the group consisting of rhodium sulphate, rhodium phosphate and rhodium fluoborate in an amount to provide from about 5 to about 20 grams per liter of dissolved rhodium, from about 12 to about 100 milliliters per liter of free acid from the group consisting of sulphuric acid, phosphoric acid and fluoboric acid and selenate ion in an amount equivalent to about 0.05 to about 1 gram per liter of selenic acid.

8. The process for producing substantially crack-free electrodeposits of rhodium which comprises establishing an aqueous acidic electrolyte containing in solution about 5 to about 20 grams per liter of rhodium, free acid in an amount sufiicient to prevent hydrolysis of said rhodium and selenate ion in an amount equivalent to a concentration of at least about 0.05 up to about 25 grams per liter of selenic acid and electrolyzing said bath at a current density of about 0.5 to about 2 amperes per square decimeter and a temperature of about 20 C. to about C. to produce a rhodium electrodeposit characterized by being substantially free from cracking.

9. The process for producing substantially crack-free electrodeposits of rhodium which comprises establishing an aqueous acidic electrolyte containing in solution about 5 to about 20 grams per liter of rhodium, free acid selected from the group consisting of sulphuric acid, phosphoric acid and fluoboric acid in an amount suflicient to prevent hydrolysis of said rhodium but not substantially exceeding about milliliters per liter of electrolyte and a compound from the group consisting of selenic acid and alkali metal salts thereof in an amount equivalent to a concentration of at least about 0.05 up to about 8 grams per liter of selenic acid and electrolyzing said bath at a current density of about 0.5 to about 2 amperes per square decimeter and a temperature of about 20 C. to about 70 C. to produce a rhodium electrodeposit characterized by being substantially free from cracking.

References Cited in the file of this patent UNITED STATES PATENTS 2,384,501 Streicher Sept. 11, 1945 2,461,933 Smith et al. Feb. 15, 1949 2,577,365 Reid Dec. 4, 1951 FOREIGN PATENTS 440,938 Great Britain Jan. 8, 1936 OTHER REFERENCES Weisner et al.: Plating, vol. 43 (March 1956), pp.

Claims

1. AN ELECTROLYTE FOR PRODUCING SUBSTANTIALLY CRACKFREE RHODIUM ELECTRODEPOSITS COMPRISING AN AQUEOUS ACIDIC BATH CONTAINIGN DISSOLVED RHODIUM DERIVED FROM AT LEAST ONE COMPOUND FROM THE GROUP CONSISTING OF RHODIUM SULPHATE, RHODIUM PHOSPHATE AND RHODIUM FLUOBORATE IN AN AMOUNT TO PROVIDE FROM ABOUT 5 TO ABOUT 20 GRAMS PER LITER OF RHODIUM, FREE ACID IN AN AMOUNT SUFFICIENT TO PREVENT HYDROLYSIS AND A COMPOUND FROM THE GROUP CONSISTING OF SELENIC ACID AND ALKALI METAL SALTS THEREOF IN AN AMOUNT EQUIVALIENT TO ABOUT 0.05 TO ABOUT 25 GRAMS PER LITER OF SELENIC ACID.