Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
  • C23C18/16—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by reduction or substitution, e.g. electroless plating
  • C23C18/48—Coating with alloys
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
  • C23C18/16—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by reduction or substitution, e.g. electroless plating
  • C23C18/31—Coating with 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
  • C25D3/56—Electroplating: Baths therefor from solutions of alloys
• • 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
  • C25D3/60—Electroplating: Baths therefor from solutions of alloys containing more than 50% by weight of tin
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
  • C25D5/34—Pretreatment of metallic surfaces to be electroplated
  • C25D5/42—Pretreatment of metallic surfaces to be electroplated of light metals
  • C25D5/44—Aluminium
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S205/00—Electrolysis: processes, compositions used therein, and methods of preparing the compositions
  • Y10S205/916—Sequential electrolytic and nonelectrolytic, or nonelectrolytic and electrolytic coating from the same bath

Definitions

• Aluminum which is abundant, economical, and has favorable physical and electrical properties, is used in large quantities. Its use in certain fields has been limited by its surface characteristics. Aluminum surfaces oxidize to form a tight adherent refractory film which interferes with surface-to-surface contact. Aluminum surfaces cannot be joined by soldering.
• the invention also contemplates providing a bath useful without change for both immersion plating and electroplating tin on aluminum.
• the invention also contemplates a continuous method of plating aluminum wire and sheet.
• stannnatecyanide bath having the following preferred composition: CuCNabout l1 g./l. (grams per liter), free KON- about 26 g./l., KOH-about 7.5 g./l., and K Sn(OH) about 120 g./l., at a temperature of about 50 C., an adherent tin layer is chemically deposited on the aluminum surface in about to 30 seconds.
• the aluminum may be retained in the immersion bath for as long as 2 to 3 minutes at which time further deposition practically ceases.
• a deposit of about 0.00025 cm. is built up, dependent somewhat upon the temperature and specific bath utilized.
• Thick immersion deposits of this type are somewhat porous but have sufiicient continuity and stability to (i) protect the aluminum surface from oxidation; (ii) provide a surface suitable for making sliding contact; and (iii) provide an aluminum article with sufficient conductivity at the surface during its service life to enable the part to be used as an electric conductor, e.g., for screw or friction type electric contacts.
• adhesion of these immersion deposits is markedly improved by reflowing the deposit at an elevated temperature.
• An important feature of this process is the successful immersion tin coating formed on the aluminum surface in the stannate-cyanide solution.
• a dark flash deposit takes place within about 1 to 3 seconds and continues for about 2 seconds, followed amost instantaneously by a white deposition.
• the stannate-cyanide 3,1080% Patented Oct. 22, 1963 solution is transparent and fairly clear, the initial dark flash followed by the deposition of a white metal is easily observed. This initial flash is believed to be an extremely thin layer of copper.
• the subsequent white deposit is tin. Analyses of thick immersion deposits (2 to 3 minutes immersion) have shown them to have a tin content greater than 99%.
• the immersion deposit which is believed to contain a small amount of copper in the tin alloy is referred to herein as an immersion tin deposit.
• the undercoat should be one obtained by immersion for not more than about 30 or 40 seconds.
• a sound and adherent tin-copper alloy plate may be electrodeposited on aluminum surfaced with a thin immersion tin deposit prepared by immersing the aluminum in a bath of the type specified herein for between approximately 5 and not more than 40 seconds, and preferably not more than 15 seconds.
• the electrodeposition of the tin-copper alloy is preferably carried out in a bath of the same composition as that useful for the immersion dip.
• the immersion dip and the subsequent electrodeposition may be carried out in the same tank or in separate tanks.
• Aluminum surfaced With this tin-copper alloy is suitable for many purposes.
• the alloys plated from baths also useful for the immersion dip contain between 40% and 60% of tin, the remainder copper.
• Aluminum surfaced as aforesaid is also useful as a basis metal for one or more subse-- quent electrodeposits to provide decorative and/or utilitarian finishes. Without further finishing it is useful for a Wide variety of applications, including tin plated wire, tin coated sheet, fabrication of cans, electrical applications, sliding and other bearing-type applications, etc.
• tin-copper alloy be electrodeposited on the thin immersion deposit before electrodepositing the desired metal.
• Various metals, including bronze, tin-nickel, copper, and chromium have been successfully electrodeposited using a tin copper electrodeposit as the undercoat.
• the immersion bath specified hereinbefore is a composition which has been found particularly suitable for both immersion and electroplating.
• Adherent immersion tin deposits may be obtained from aqueous baths of the type:
• the aqueous baths contained sufiicient additional KCN to complex the copper [Cu(CN)
• the solution contains about 3 mols of Chi for each mol of Cu+, in addition to the free cyanide. This method of specifying the solution composition is common for cyanide copper solutions and is used herein.
• Baths prepared from the salts hereinbefore specified are preferred. It is possible to obtain adherent immersion tin deposits from baths in which the sodium salts replace in part the potassium salts. For a given bath composition more adherent deposits are obtianed from the allpotassium bath. Deposits become progressively less adherent as sodium replaces potassium. Baths containing less than about 20% potassium ions (80% sodium ions) result in deposits having somewhat inferior adhesion characteristics. When replacing some of the potassium salts by the equivalent sodium salts, the weight of the salts must be modified to conform with the relative atomic weights of sodium and potassium.
• Potassium st-annate is known to be normally solid as disclosed on pages 472 and 473, item No. 11, of Handbook of Chemistry and Physics, 30th edition, Chemical Rubber Publishing Co., 1947. Potassium copper cyanide and potassium cyanide are also known to be normally solids (ibid., pages 466 and 467, items Nos. 9 and 11).
• a composition containing the aforenoted three compounds is utilized in the solid form; it is added to the aqueous solution where it is dissolved to provide a bath suitable for producing immersion tin deposits in accordance with the process of the instant invention.
• Potassium stannate comprises between 90 and 130 parts of this solid composition.
• the amount of dissolved copper in the solution is a and caustic, and with low concentration of free cyanide and stannate. Low temperatures also promote copper deposition. By proper manipulation of these factors it is possible to obtain sound deposits outside the range specified hereinbefore. It is sometimes possible to obtain immersion deposits in stannate-cyanide baths of the type specified hereinbefore with a dissolved copper content as low as about 1.5 g./l., by proper manipulation of these various factors and by the addition to the solution of such materials as tartrates, citrates, gluconatcs, and saccharates, which are known to influence the deposition of copper from bronze electroplating baths. The use of these additives also sharply lowers the maximum amount of copper in operative baths. The operative baths contain a small critical amount of dissolved copper effective to obtain adherent immersion deposits.
• the electrodeposition of tin-copper alloy is preferably carried out from baths of the same composition as those used for the immersion dip. As noted, the tin-copper alloy is electrodeposited on a thin immersion tin deposit. The electrodeposition is carried out between 32 C. and 65 C.; preferably between 48 C. and 55 C. Current densities conventional for copper-tin alloy plating are suitable. These generally vary from 1 amp/sq. dm. to 15 amp/sq. dm. for conventional batch plating and may be as high as 150 amp/sq. dm., or higher, for continuous wire and strip plating. The tin-copper alloy may be electrodeposited to any desired thickness. Its appearance is best at a thickness of 0.0025 to 0.00025 cm.
• the elcctrodeposited coating be at least 0.001 cm. thick if it is to serve as the undercoat for electrorleposition of other metals deposited from highly caustic solutions, or if it is to be used in applications requiring soldering to produce joints with good physical properties.
• the deposit may be brightened by the addition of a lead-containing brightener to the plating solution.
• a multi-layered deposit with alternate tin and tin-copper layers is obtained by interruption of the current during electrodeposition using a bath specified herein.
• a commercially pure sheet aluminum, 1100 (2S) alloy was used for comparative purposes. Before im- 0 mersion in the specified solution it was cleaned by dipping in a caustic solution containing 30 g./l. of trisodium phosphate and 22 g./l. of caustic soda, between C. and C. It was then rinsed in cold water, dipped in a concentrated nitric acid solution and again rinsed. The solutions tested and the conditions specified in the following table resulted in sound adherent deposits. All the electrodeposits were made on thin immersion deposits.
• Aluminum wire was surfaced with the tin-copper electrodeposit from the same bath used to obtain the immersion tin undercoat. An extremely high current density was used. This process is particularly suitable to the electro-coating of wire and sheet in continuous high speed 1111118.
• a process for producing an immersion tin coating on aluminum comprising immersing cleaned aluminum in an aqueous solution containing about 23 g./l. to 59 g./l. of Sn' 15 g./l. to 38 g./l. of free alkali metal cyanide, 3 g./l. to 12 g./1. of alkali metal hydroxide, at least 20% of said alkali metal in the solution being potassium and the remainder sodium, and sufiicient Cu+ selected from the range of 1.5 g./l. to 11.5 g./l. to form an adherent immersion tin deposit.
• a process for producing an immersion tin coating on aluminum comprising immersing cleaned aluminum in an aqueous solution, at a temperature between about 32 C. and 65 C., containing about 23 g./l. to 59 g./l. of Sn, 15 g./l. to 38 g./l. of free alkali metal cyanide, 3 g./1. to 12 g./l. of alkali metal hydroxide, at least 20% of said alkali metal in the solution being potassium and the remainder sodium, and sufficient Cu selected from the range of 3.5 g./l. to 11.5 g./l. to form an adherent immersion tin deposit.
• a process for producing an immersion tin coating on aluminum comprising immersing cleaned aluminum in an aqueous solution, at a temperature between about 48 C. and 55 C., and containing about 23 g./l. to 59 g./l. of So, 15 g./l. to 38 g./1. of free alkali metal cyanide, 3 g./l. to 12 g./l. of alkali metal hydroxide, at least 20% of said alkali metal solution being potassium and the remainder sodium, and about 3.5 g./l. to 11.5 g./l. of 011+, the ratio of copper to tin being between 1:45 and 1:65, to form an adherent immersion tin deposit.
• a process for producing an immersion tin coating on aluminum comprising immersing cleaned aluminum in an aqueous solution, at a temperature between about 32 C. and 65 C., containing about 35.6 g./l. to 51.5 g./l. of Sn, 22 g./l. to 30 g./l. of free potassium cyanide, 5 g./l. to g./1. of potassium hydroxide, and about 5.7
• a process for producing an immersion tin coating on aluminum comprising immersing cleaned aluminum in an aqueous solution, at a temperature between about 48 C. and 55 C., containing about 35.6 g./l. to 51.5 g./1. of Sn+ 22 g./l. to 30 g./l. of free alkali metal cyanide, 5 g./l. to 10 g./l. of alkali metal hydroxide, at least 20% of said alkali metal solution being potassium and the remainder sodium, and about 5.7 g./l. to 10.6 g./l. of Cu+, to form an adherent immersion deposit.
• a process for producing an immersion tin coating on aluminum comprising immersing cleaned aluminum in an aqueous solution at a temperature about 50 C., containing about g./l. of potassium stannate, 26 g./l. of free potassium cyanide, 7.5 g./l. of potassium hydroxide, and 11 g./l. of copper cyanide, to form an adherent immersion tin coating.
• a process for producing an immersion tin coating on aluminum comprising immersing cleaned aluminum in an aqueous solution, at a temperature between about 32 C. and 65 C., containing about 90 g./l. to g./l. of potassium stannate, 22 g./l. to 30 g./l. of free potassium cyanide, 5 g./1. to 10 g./l. of potassium hydroxide, and 8 g./l. to 16 g./l. of copper cyanide, to form an adherent immersion tin deposit.
• a process for producing an immersion tin coating on aluminum comprising immersing cleaned aluminum in an aqueous solution containing about 23 g./l. to 59 g./l. of Su 15 g./l. to 38 g./l. of free alkali metal cyanide, 3 g./l. to 12 g./l. of alkali metal hydroxide, said alkali metal in the solution being selected from the class consisting of potassium and sodium, and sufiicient Cu+ selected from the range of 1.5 g./l. to 11.5 g./l. to form an adherent immersion tin deposit.
• a solid composition of matter for making up an aqueous bath for producing an immersion tin deposit on aluminum comprising 90 to 130 parts of potassium stannate, and copper in the form of potassium copper cyanide, the weight ratio of copper to tin being between 1:45 and 126.5, and sufiicient potassium cyanide so that when the composition is dissolved in water containing between 3 g./1. and 12 g./l. of potassium hydroxide, the solution contains between 23 g./l. and 59 g./l. of Sn+ between 5.7 g./l. and 10.6 g./l. of Ou and between 15 g./l. and 38 g./l. of free potassium cyanide.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Electrochemistry (AREA)
• General Chemical & Material Sciences (AREA)
• Mechanical Engineering (AREA)
• Electroplating And Plating Baths Therefor (AREA)
• Coating With Molten Metal (AREA)
• Electroplating Methods And Accessories (AREA)

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Cited By (31)

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Citations (13)

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• 1959
  • 1959-07-13 US US826497A patent/US3108006A/en not_active Expired - Lifetime
• 1960
  • 1960-06-29 GB GB22796/60A patent/GB957778A/en not_active Expired
  • 1960-06-30 FR FR831675A patent/FR1434105A/fr not_active Expired
  • 1960-07-12 DE DEM45906A patent/DE1233693B/de active Pending
• 1962
  • 1962-08-27 US US219747A patent/US3193474A/en not_active Expired - Lifetime
• 1964
  • 1964-07-17 SE SE8743/64A patent/SE309522B/xx unknown

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