Classifications

• • 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

Definitions

• the other group of the pickling'solutions for the preparatory treatment of the aluminum or its alloys prior to the galvanizing process include the alkaline pickling solutions of which chiefly zincate dipping solutions are being used.
• the eiiect of the latter principally consists therein, that a firmly adhering coating of zinc is deposited upon the aluminum and subsequently the desired metallic deposit upon said zinc coating in an appropriate manner, whereby a better adhesiveness of the electro-galvanic deposits is ensured than if the latter were applied directly upon the aluminum.
• the alkaline zincate dipping solution is recommended not only for nickelplating aluminum, but also for the galvanic treatment of the aluminum in alkaline or cyanide baths.
• the present application now elucidates a process, by means of which the possibility of obtaining properly adhering deposits, particularly in alkaline baths, will be rendered practically certain.
• this process the aluminum articles are, after the usual degreasing process, treated with a zincate solution or solution to which copper salts have been added.
• composition of the dipping solutions adapted for the present invention for preparatorily treating the aluminum prior to the subsequent galvanization in cyanide baths is not a matter of indifierence.
• the eificiency of the dipping solution rather depends upon its content of free caustic potash, zinc and copper. It has, as a matter of fact, been ascertained, that the indicated aim would best be attained by means of dipping solutions, the content of free alkali of which is about 3 to 15 times normal, whilst the content of zinc should correspond at least to simple normality.
• the copper content of these solutions is then to be kept within the limits of from about 1.5 to 8.0 g. of copper per liter.
• the copper is present wholly or for the greatest part in univalent form. This will be attained, if the copper is added in the form of potassium copper cyanide or other soluble cuprous salts.
• reducing agents such as sodium-sulphite and/or similarly acting substances are added to the dipping solutions.
• the articles preparatorily treated with the dipping solution can be galvanized directly in alkaline or cyanide baths. With certain alloys, par ticularly if they contain copper, and properly burnished articles, it often proves suitable to remove the deposit formed by the dipping solution, by means of oxidizing agents, such as nitric acid or acid mixtures containing nitric acid and to repeat subsequently the treatment with the cuprous zincate dipping solution. This process can, if necessary, be repeated a few times.
• alkali carbonate and/or alkaline salts of fatty acids and/or alkaline salts of inorganic'acids As fatty acids will have to be considered in this case, above all, acid with a low molecular weight, such as formic acid, acetic acid, propionic acid, etc., as inorganic acids, phosphoric acid, boric acid, etc.
• a dipping solution for the preparatory treatment of the aluminum, according to the present invention is composed, e. g. as follows:
• Example 1 To an ordinary copper bath prepared with potassium-copper-cyanide, 10 to 20 g. of pulverized boric acid are added and the copper plating process carried through in known manner.
• the galvanized articles of aluminum are, according to the present invention, after having been copper-plated, brass-plated and the like, treated for some time with weakly acid solutions.
• Aqueous solutions containing 1 to 5% of acid may be used.
• the treatment can consist in boiling the galvanized aluminum articles in a 2-5% solution of boric acid or in a solution of tartaric acid or the like.
• Process according to claim 1 characterized in that the deposit caused to appear on the aluminum on dipping, is removed by means of oxidizing agents of such character as to be capable or removing said deposit and produced anew as a result of a repeated dipping into the zincate solution.
• Process according to claim 1 characterized in that to the alkaline baths used for electroplating purposes, substances acting as acid, are added, the dissociation constant of which does not exceed the value of 110- 9.
• Process according to claim 13 characterized in that the electroplated aluminum articles are subjected to an after-treatment with a solution of an acid, the concentration thereof being such that it does not attack the electroplated articles or only inconsiderably, said after-treatment being conducted at a temperature up to and including the boiling point of said solution.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Cleaning And De-Greasing Of Metallic Materials By Chemical Methods (AREA)
• Electroplating Methods And Accessories (AREA)
• Electroplating And Plating Baths Therefor (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=25944075

Family Applications (1)

Country Status (4)

Cited By (25)

Families Citing this family (3)

• 1935
  • 1935-11-20 DE DESCH108506D patent/DE663979C/de not_active Expired
• 1936
  • 1936-11-18 US US111389D patent/US2142564A/en not_active Expired - Lifetime
  • 1936-11-19 FR FR813761D patent/FR813761A/fr not_active Expired
  • 1936-11-19 GB GB31735/36A patent/GB466949A/en not_active Expired

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