Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25F—PROCESSES FOR THE ELECTROLYTIC REMOVAL OF MATERIALS FROM OBJECTS; APPARATUS THEREFOR
  • C25F1/00—Electrolytic cleaning, degreasing, pickling or descaling
• • 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
• • 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
  • Y10S205/917—Treatment of workpiece between coating steps

Definitions

• This invention relates to a process for driving out occlusions of gases like hydrogen from the surface layers of work-pieces in an electrolytic manner to increase the resistance to corrosion of such layers.
• the most important field of application of the process is the pretreatment of metals to be coated for subsequent electroplating so as to impart to the work a surface quality adapted for placing thereon metallic deposits of any kind and producing durable coatings of high corrosion resistance.
• Electrolytic refining orcleaning processes in which the metal objects to be treated are used either as cathode or as anode in an electrolytic bath are in particular widely employed.
• anodic treatment is especially effective and, above all, applicable Where it is necessary to neutralize, as for subsequent electroplating, the hydrogen found in the surface layers of a work, which enters the metal, or is not oxidized, during cathodic cleaning as well as for instance during pickling in an acid solution.
• the invention avoids the drawbacks of the hitherto known anodic treating methods and provides a process which insures complete liberation of the surface of a. work not only from all oxide films but also from the carbides, etc., embedded in the body of the metal, as well as full oxidation of the hydrogen contained in the pores of the metal.
• the invention is based on the knowledge that the process of the dissolution of the metal and of the reoxidation thereof does not occur immediately after.
• current is applied to the bath containing the workserving as anode, but sets in, depending on the nature of the alkaline or neutral, though not acid, bath, that is an aqueous bath whose DH is at least 7, awcertain time after the current has begun to act.
• the gas reactions on the other hand, i. e. the oxidation of the hydrogen and the conversion of the carbides, etc., whose presence directly at the surface of a work subsequently to be coated is highly detrimental and absolutely prevents for instance the production of deposits free from pores in electroplating commence as soon as the current begins to act.
• the invention proposes to operate the bath in which the work, previously preferably cathodically treated to effect decreasin and removalof the surface oxide films, is used as anode by currentimpulses occurring at intervals the duration of which and of the impulses is adapted to thepeculiar nature of the metal and of the electrolyte in such manner thatthe reactions leading to the formation of an oxidic deposit of the metal on the work do not set in as yet.
• each current action diifers therefore and, depending on circumstances, may last up to seconds, though it is much shorter as a rule and may amount to less than one second.
• the actions of the current are continued until it is apparent that all oxidizable constituents, besides the metal treated, are completely oxidized at the surface. This can be well observed with the naked eye. For example, during the first current impulses islandsand band-like regions appear on a test piece, which are irregularly distributed over the entire surface and on which a particularly strong gas development can be noticed. After a certain number of impulses these at first clearly contrasting regions disappear, and the gas development proceeds uniformly over the entire area. At this moment no oxidizable constituents are present any more.
• the new process is preferably carried out with the aid of a switch connected in the circuit for automatically cutting off and interrupting the current for adjustable periods.
• electroplating 3 produces a metal layer of highest quality, which is not only completely free from pores and pitting, but which is distinguished also by an extraordinary adhesiveness to the basic metal.
• the layer produced is, moreover, much more non-corrodible than a layer obtained in the usual manner.
• the sheets were subjected to the usual corrosion test by boiling in distilled water, that is, they were boiled for four minutes and then allowed to stand four hours in their boiling water. The subsequent count of rusty places yielded 1,486 points.
• a second series of 20 sheets was treated in the same manner with the difference, however, that during the anodic treatment the current was applied only for one second whereupon the current supply was interrupted for another second.
• the sheets remained in the anodic bath for 30 seconds, but only current impulses lasting one second each were applied, so that the total current action amounted to 15 seconds.
• the application and effect of the new process have been described above with a View to employin it as a pretreating process for subsequent electroplating.
• the range of uses of the new process is. however, not limited hereto, but is far more general.
• the new process can be advantageously applied in all cases where occlusions of gas, particularly hydrogen, have to be driven out of the surface layers of work-pieces. It may serve for instance for after-treating already produced metal coatings to considerably increase their resistance to corrosion, or for giving intermediate treatment when electroplating several superposed metal layers of the same or different kind, as for instance for dehydrating a nickel layer prior to final chrome-plating.
• a process for cleaning comprising driving out of occluded gases and removal of oxide films and surface embedded impurities including carbides from the exterior layers of metals consisting in using the metal to be cleaned as an anode in an aqueous bath where the pH is at least '7, operating this bath with current impulses whose duration varies from one second to sixty seconds according to the metal to be cleaned and is sufficiently long to oxidize impurities in and on the metal surface and to remove occluded gases but is stopped before oxidation and solution of any metal of the surface takes place, repeating these anodic impulses a sufiicient number of times to bring about a gas development which is uniform over the entire surface area and depositing an additional metal layer by electro-plating.

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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 Methods And Accessories (AREA)

Applications Claiming Priority (2)

Publications (1)

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ID=25763644

Family Applications (1)

Country Status (5)

Cited By (5)

Families Citing this family (3)

Citations (4)

• 1940
  • 1940-04-27 DE DEB190570D patent/DE715515C/de not_active Expired
  • 1940-10-22 NL NL99295A patent/NL58143C/xx active
  • 1940-11-28 CH CH223783D patent/CH223783A/de unknown
• 1941
  • 1941-01-30 FR FR869641D patent/FR869641A/fr not_active Expired
  • 1941-04-25 US US390374A patent/US2421863A/en not_active Expired - Lifetime

Patent Citations (4)

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