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
  • C25D3/567—Electroplating: Baths therefor from solutions of alloys containing more than 50% by weight of platinum group metals
• • 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

• the invention relates to a process for electroplating palladium-arsenic alloys.
• Electroplated palladium and palladium alloys are used in a variety of applications including deposition of protective coatings on decorative articles such as jewelry, watches, etc., in various containers and fixtures exposed to chemically corrosive liquids and gasses and in various electrical and electronic devices as a protective coating and electrical contact coating.
• Much of the motivation for use of palladium and palladium alloys in such applications is its lower cost compared to such traditionally-used metals as gold and platinum.
• the invention is a process for electroplating a palladium-arsenic alloy in which the electroplating bath comprises a source of palladium and a source of arsenic.
• the electroplating bath comprises a source of palladium and a source of arsenic.
• palladium sources and arsenic sources may be used in the practice of the invention.
• Two convenient sources of palladium are palladium complexed with 1,3 diaminopropane and ammonia.
• Convenient sources of arsenic are As2O3 and As2O5. Concentrations of the source of palladium may vary over wide limits from about 0.00001 molar to saturation for both sources and concentrations of the source of arsenic may vary over limits from 0.01 to 0.1 molar.
• ingredients may be contained in the electroplating bath including various additives such as surfactants and brighteners and buffers to maintain the pH of the solution.
• various additives such as surfactants and brighteners and buffers to maintain the pH of the solution.
• the invention is based on the discovery that electroplating a metallic substance from an aqueous bath containing a source of palladium and a source of arsenic yields a metallic film comprising palladium and arsenic which is ductile, crack-free, extremely adherent and which retain these properties even when electroplated to considerable thickness (e.g. 10 ⁇ m or even more).
• the electroplated metallic substance is quite hard with Knoop Hardness (KHN) over 400.
• KHN Knoop Hardness
• the metallic film appears to be an alloy of palladium and arsenic and exhibits sufficient ductility and strength so as to be useful for making free standing articles such as bellows by electroforming procedures. Plating rates can be quite high (e.g.
• palladium compounds may be used as a source of palladium in the electroplating process provided the palladium compound is compatible with the plating process.
• Particularly useful are palladium complex ion compounds with ammonia as the complexing agent such as Pd(NH3)2Cl2 and the corresponding bromide and iodide.
• palladium tetra-ammine salts such as Pd(NH3)4Cl2 and the corresponding bromide and iodide.
• Other stable anions may be used such as sulfates, etc.
• palladium complexes in which the complexing agent is an organic compound such as an amine (see for example U.S. Patent 4,486,274 which is incorporated by reference).
• palladium complex hydroxides such as palladium hydroxide complexed with various organic compounds such as organic amines and polyamines and complexed with ammonia (e.g. di- ⁇ -hydroxo-bis-[cis-diamminepalladium(II)] dihydroxide.
• organic compounds such as organic amines and polyamines and complexed with ammonia
• ammonia e.g. di- ⁇ -hydroxo-bis-[cis-diamminepalladium(II)] dihydroxide.
• Various simple palladium compounds may also be used such as PdCl2 and the corresponding bromide and iodide, PdSO4Pd(NO3)2, etc.
• a wide range of concentrations of the source of palladium and source of arsenic may be used with excellent results.
• some reasonable bath conductivity should be used, generally a conductivity greater than 0.001 mho-cm.
• the concentration of the source of palladium may vary from 0.00005 M to saturation. Excellent results are obtained in the concentration range from 0.005 to 1.0M with 0.05 to 0.3 most preferred. Too low a concentration requires frequent replenishments; too high a concentration increases palladium loss due to drag out.
• excess complexing agent is often used.
• the concentration of excess complexing agent typically ranges from about 0.5 to 30 times the molar concentration of palladium. With palladium complexed with 1,3 diaminopropane, excellent results are obtained with 0.08M palladium complex and 0.7M excess complexing agent.
• arsenic Any source of arsenic may be used provided it is compatible with the electroplating process and has reasonable solubility in the bath. Typical sources of arsenic are As2O3,As2O5, KH2AsO4,K2HAsO4, K2AsO4, NaH2AsO4, Na2HAsO4,Na3AsO3K3AsO3, KAsO2,Na3AsO3, NaAsO2 and Na4As2O7. Other arsenic compounds may also be useful. For convenience, As2O3 and As2O5 are preferred. A convenient procedure for incorporating the arsenic in the bath is to make an alkali-metal salt of arsenous acid by dissolving As2O3 in concentrated potassium or sodium hydroxide solution and adding this solution to the electroplating bath.
• the concentration of arsenic in the bath may vary over large limits, typically from 0.00005 M to saturation. Excellent results are obtained in the concentration range from 0.0005, to 0.5 with best results in the concentration range from 0.01 to 0.1 M.
• the pH above 7; typically between 8 and 13.5 or even between 10 and 12.5.
• the pH is conveniently adjusted by the addition of alkali-metal hydroxide such as potassium hydroxide and sodium hydroxide.
• additional substances may be added to the electroplating bath to improve the quality of the electroplated material, control pH, increase conductivity of the bath, etc.
• a surfactant and a brightener may be added to the electroplating bath.
• Typical surfactants that are useful are aliphatic quatemary ammonium salts with from 4-35 carbon atoms. Preferred are aliphatic straight-chain trimethylammonium chlorides with chain lengths between 8 and 18 carbon atoms. More preferred are the quatemary salts with chain lengths between 11 and 13 carbon atoms (e.g.
• the concentration of the surfactant may vary over large limits. Typical concentration ranges are from 0.0002 to 0.4 molar with the range from 0.004 to 0.02 molar prefer Too low a concentration limits the desired effect (as a wetting agent to remove bubbles from the cathode, make the plating more uniform and disburse the brightener); too high a concentration sometimes causes foaming of the bath, phase separation of the surfactant or decreased effectiveness of the brightener.
• Typical brighteners useful in the practice of the invention are often sulfur-containing organic acids and their salts. Typical examples are o-benzaldehydesulfonic acid, 1-­naphthalenesulfonic acid, 2-naphthalenesulfonic acid, benzenesulfinic acid, oxy 4,4 bis(benzene)sulfinic acid, p-toluenesulfinic acid, and 3-­trifluoromethylbenzenesulfinic acid.
• Additional brightening agents useful in the practice of the invention are allyl phenyl sulfone, o-benzoic sulfamide, benzyl sulfonyl propionamide, phenylsulfonylacetamide, 3(phenylsulfonyl) propionamide, benzenesulfonamide, bis(phenylsulfonyl)methane, guanidine carbonate, sulfaguanidine and nicotinic acid.
• a buffer may also be used to control the pH of the bath and incidentally to increase the conductivity of the bath. Any buffer consistent with the desired pH and the electroplating process may be used.
• the pH is usually adjusted by the addition of acid (e.g. hydrochloric acid or phosphoric acid) or base (e.g. aqueous ammonia or potassium hydroxide).
• Conducting salts may also be added (e.g. ammonium chloride) to increase the conductivity of the electroplating bath.
• the temperature at which the electroplating process is carried out may vary over large limits, say from the freezing point of the electroplating bath to the boiling point of the bath. In some situations, temperatures close to room temperature are used for convenience but usually some elevated temperature (e.g. 35-60 deg. C) is used to increase solubility of the bath ingredients and permit higher plating rates and more uniform platings. Preferred is an electroplating temperature of about 55 degrees C.
• An aqueous electroplating bath is made up using 0.08 molar Pd(NH3)4Cl2, 0.05 molar As2O3 and 0.01 molar K2HPO4. Included in the solution are a surfactant (dodecyltrimethylammonium chloride) and a brightener (allyl phenyl sulfone) in concentrations of 0.01 molar and 0.03 molar respectively.
• the bath has a conductivity greater than 10 ⁇ 3 mho-cm. Excellent results are obtained on electroplating on a conductive surface (e.g. metallic surfaces such as copper, nickel, palladium, etc.).
• Example 2 Same as Example 1 except the concentration of the source of palladium is 0.00005M, 0.005M, 0.05M, 0.3M, 1.0M and saturation.
• Example 2 Same as Example 1 except the concentration of the source of arsenic is 0.00005M, 0.0005M, 0.01M, 0.1M, 0.5M and saturation.
• surfactants selected from aliphatic, straight-chain trimethylammonium chlorides with chain lengths from 8 to 18 carbon atoms.
• Example 1 As in Example 1 except the pH is adjusted to 6.0,7.0,7.5,8.0,83,9.0, 10.0,11.0,11.5,12.0,13.0 and 13.5.
• Edge card connectors are particularly well made in accordance with the inventive electroplating process. Bright, crack-free, ductile and adherent electrodepositions are obtained even with thicknesses of 2.5 to 5.0 ⁇ m and thicker. Other electrical contact surfaces are advantageously made in accordance with the invention particularly where relatively thick plating deposits are required (relay contacts, electrical plugs, etc.). Often, a thin gold layer is put on top of the palladium-arsenic layer to improve wear characteristics and improve electrical performance.
• the electroplating process is also advantageously used in various electroforming processes because the electrodeposits can be made thick and the electrodeposits have advantageous physical and chemical properties.
• electroforming the palladium-arsenic alloy is deposited on a mold or mandrel and the alloy subsequently separated from the mold and mandrel.
• a number of references describe the electroforming process including the chapter entitled “Electroforming” in "Electroplating" by F. A. Lowenheim, McGraw-Hill, 1978, Cha. 20.
• Various articles are advantageously made by the electroform process including phonograph record masters, stampers, embossing plates, thin-wall articles such as foils, sheets, fine-mesh screen, seamless tubing, bellows for hydrophone devices, molds and dies for rubber and plastics, etc.
• Particularly advantageous is the combination of extreme chemical stability and resistance to chemical attack together with good metallurgical properties such as hardness, ductility, flexibility, etc.

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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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• 1990
  • 1990-08-21 EP EP90309166A patent/EP0415632A1/en not_active Withdrawn
  • 1990-08-23 CA CA002023870A patent/CA2023870A1/en not_active Abandoned
  • 1990-08-28 JP JP2224573A patent/JPH0390589A/ja active Pending
  • 1990-08-28 KR KR1019900013266A patent/KR930010328B1/ko active IP Right Grant

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