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
  • C25D3/56—Electroplating: Baths therefor from solutions of alloys
  • C25D3/62—Electroplating: Baths therefor from solutions of alloys containing more than 50% by weight of gold

Definitions

• C25D 3/62; C25D 3/56 substantially 0.5 to substantially 3.0 grams of gold per [58'] Field of Search 204/43 G, 43 N, 44, I23 liter.
• the bath is operated at a temperature preferably in the range of from substantially 50C to substantially [5 6] References Cited 65C.
• This invention relates to the electrodeposition of gold-platinum alloys.
• Gold-platinum alloys have been used for many yearsas spinning jets in the viscose rayon industry where theywithstand corrosive conditions and severe mechanical conditions for long periods.
• the gold-platinum alloys are also suitable for use as crucibles for alkaline fusions.
• Electrodeposition of alloys involves; more complicated processes than the deposition of ,pure metals. Alloy deposition is much more sensitive to a variety of factors than a'single metal. Variables-must be controlled much more closelythan in a single metal deposition in o'rderto obtain deposits of uniform color, corrosion resistance, composition and appearance. The supporting electrolyte must be chosen so that the reduction potential of the metals will, be fairly close. Indeed, it is often difficult to predict the composition of an alloy from thatof the electrolyte andfrom the plating conditions. I
• gold-platinum alloy deposits of consistently excellent quality canbe obtained by electrodeposition from an aqueous electroplating bath comprising an alkali metal hexahydroxyplatinate and an alkali metal aurate.
• concentration of the alkali metal hexahydroxyplatinate should be sufficiently high numin solution within the range of from substantially 19 to substantially 22 grams per liter is preferred, with the concentration of the alkali metal aurate being adjusted in accordance with the concentration of gold desired in the finaldeposit.
• Deposits containing from substan'tially 15% to substantially 95% gold can be obtained with the baths of the present invention.
• One of thevariables requiring control in the utilizationof the baths of the present invention is the pH of the solution. It is important that the electroplating bath be'highly alkalineythe pH of the solution should be maintained above substantially 11.0. If the pH of the solution-falls below substantially llIO, the alkali metal hexahydroxyplatinate tends to form a precipitate.
• the solutions preparedby dissolving an alkali metal hexahydroxyplatinate and an alkali metal aurate have a sufficiently high pH for use in the present invention, but, if necessary, the pH of the solution can be adjusted before and/or during use by the addition of suitable amounts of water-soluble alkaline acting substances such as alkali metal'salts of weak acids, e.g., phosphoric acid, acetic acid or citric acid.
• weak acids e.g., phosphoric acid, acetic acid or citric acid.
• the plating temperature affects not only the structure and appearance-of theelectrodeposited alloys but also theirchemic'al"composition. 'Ingeneral, the preferred temperature is in the range of from substantially 50C to substantially 65C.
• an electroplating bath for the electrodeposition of goldplatinum alloys comprising an alkali metal-hexahydroxyplatinate and tion.”
• the aqueous electroplating bath comprises from substantially 15 and from substantially 0.5 to substantially 3.0, preferably from substantially 1.0 to substantially 2.0, grams per liter of gold as sodium or potassiumaurate, the pH of the solution being maintained at above substantially l 1.0, preferably above substantially ll.5.
• the operatingconditions suitable for any particular plating -application may be readily' determined by one skilled in the art.
• the average cathode current density used will depend upon the alloy desired and on the shape and size of the article to be plated. It is preferable an alkali metal aurate i'n aqueous soluto employ cathode current densities of below substantially 20 amperes/ft? preferably substantially 5 to substantially 8 amperes/ft under normal direct current plating conditions, with a deposition rate of from substantially 0.0002 to substantially 0.00025 inch/hr.
• the electrolyte solution is used with insoluble platinum or platinum clad anodes, and it is necessary to replenish the gold and platinum deposited from the electrolyte solution by addition of fresh gold and platinum compounds.
• water-soluble alkaline substances such as alkali metal salts of weak acids, e.g., potassium phosphate, potassium acetate, or potassium citrate can be added before and/or during use in sufficient quantities to maintain the pH of the solution in the required range.
• Suitable brightening agents which are well known in the art, can be added from time to time to maintain the desired physical characteristics of the alloy deposited.
• the electrolyte of the present invent-ion is operated at temperature of substantially 50C to substantially 65C.
• EXAMPLE I A 250 m1. aqueous electroplating solution was prepared containing 21 grams per liter of platinum as K Pt( OH) and 0.7 grams per liter of gold as KAuO The .pH .of the solution was above 11.5. The bath was operated at a temperature of 55C. The electrolyte was used to plate clean brass parts. The composition of the deposited alloy was 10% Au-90% Pt. The deposit was found to be smooth.
• EXAM PLE An aqueous electroplating solution was prepared as in Example 1, except that theconcentration of gold present (as KAuO was 2.8 grams per liter. The electrolyte was used to plate clean brass parts. The bath was operated at a temperature of 65C. A current of 0.2 ampere was employed. The composition of the final deposit was 30% Pt-70% Au. The deposit was found to be of excellent quality.
• EXAMPLE III A 250 ml. aqueous electroplating solution was prepared containing grams per liter of platinum as K Pt(OH and 1.55 gram per liter of gold as KAuO The pH of the solution was above 1 1.5. The bath was operated at a temperature of 53C and 0.4 ampere was used to plate a clean brass panel. The final deposit contained 37.538% Pt.
• the electroplating solutions illustrated in the above examples can also be prepared with other alkali metal hexahydroxyplatinates, particularly Na Pt(OH) and 4 with other alkali metal aurates, particularly NaAuO
• the potassium salts are preferred.
• Alloy deposits containing from substantially 15% to substantially gold can be obtained by using electroplating baths similar to those illustrated above.
• the concentration of the alkali metal hexahydroxyplatinate should be such as to provide from substantially 15 to substantially 25 grams, and preferably from substantially 19 to substantially 22 grams, of platinum per liter of solution, with the concentration of the alkali metal aurate being adjusted to provide the desired concentration of gold in the final deposit.
• concentration of the alkali metal aurate to provide from substantially 0.5 to substantially 3.0 grams of gold per liter of solution will yield goldplatinum alloy deposits within the composition range contemplated by the present invention providing a constant current density is used.
• the platinum and gold contents in the bath must be carefully controlled as well as the current density.
• An aqueous electrolyte solution for the electrodeposition of gold-platinum alloys comprising an alkali metal hexahydroxyplatinate and an alkali metal aurate and wherein the pH of the solution is above substantially ll.0.
• alkali metal hexahydroxyplatinate is selected from the group consisting of sodium hexahydroxyplatinate and potassium hexahydroxyplatinate
• alkali metal aurate is selected from the group consisting of sodium aurate and potassium aurate.
• a process for the electrodeposition of goldplatinum alloys which comprises electrolyzing an aqueous electrolyte solution as claimed in claim 1 at a.temperature between substantially 50C and substantially 65C.

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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)
• Electroplating Methods And Accessories (AREA)

Priority Applications (5)

Applications Claiming Priority (1)

Publications (2)

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ID=23770021

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Cited By (8)

Families Citing this family (5)

Citations (1)

• 1974
  • 1974-02-25 US US445740A patent/US3923612A/en not_active Expired - Lifetime
• 1975
  • 1975-01-20 GB GB231475A patent/GB1448549A/en not_active Expired
  • 1975-02-25 JP JP50022529A patent/JPS5110130A/ja active Pending
  • 1975-02-25 DE DE19752508130 patent/DE2508130A1/de active Pending
  • 1975-02-25 FR FR7505861A patent/FR2262132A1/fr not_active Withdrawn

Patent Citations (1)

Non-Patent Citations (1)

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