Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D3/00—Electroplating: Baths therefor
  • C25D3/02—Electroplating: Baths therefor from solutions
  • C25D3/50—Electroplating: Baths therefor from solutions of platinum group metals

Definitions

• 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.
• the present invention contemplates 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:
• 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 acid may 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
• 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.
• 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
• 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.
• 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.
• 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.
• Rhodium (as soluble salt)..- about 10. Free Mineral Acid about 20. selenic Acid-.... about 1. Water Balance.
• the electrodeposits produced from the aforementioned baths of the present invention are of metallic rhodium, they contain smallamounts of selenium, the,
• rhodium or electrodeposited rhodium when used in reference to the electrodeposits include these small amounts of selenium.
• rhodium or electrodeposited rhodium when used in reference to the electrodeposits include these small amounts of selenium.
• 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.
• 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.
• metals include nickel, nickel-silver, silver, gold, platinum, palladium, copper and brass.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Electroplating And Plating Baths Therefor (AREA)

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Cited By (4)

Citations (4)

• 0
  • BE BE557396D patent/BE557396A/xx unknown
  • NL NL217128D patent/NL217128A/xx unknown
  • NL NL106193D patent/NL106193C/xx active
• 1956
  • 1956-05-10 GB GB14604/56A patent/GB808958A/en not_active Expired
• 1957
  • 1957-05-02 US US656499A patent/US2866740A/en not_active Expired - Lifetime
  • 1957-05-07 CH CH4580057A patent/CH362581A/fr unknown
  • 1957-05-09 DE DEM34128A patent/DE1085003B/de active Pending
  • 1957-05-10 FR FR1174957D patent/FR1174957A/fr not_active Expired

Patent Citations (4)

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