Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
  • C25D11/02—Anodisation
  • C25D11/04—Anodisation of aluminium or alloys based thereon
  • C25D11/18—After-treatment, e.g. pore-sealing
  • C25D11/20—Electrolytic after-treatment
  • C25D11/22—Electrolytic after-treatment for colouring layers

Definitions

• This invention relates to the coloring of the layer of alumina on the surface of aluminum and its alloys.
• the layer of alumina can be colored by subjecting the anodized article of aluminum or alloys of aluminum to electrolytic treatment with alternating current, using a counter-electrode of nickel, in an acid nickel salt bath. It is possible in this way to obtain bronze color finishes of the kind required for architectural purposes.
• Electrolysis times of the order of 15 minutes are required to produce dark color finishes at low current densities. It is obvious that it would be advantageous from the standpoint of economics to be able to increase the current density and shorten the electrolysis time and thus increase the productivity of the cells, and it is an object of this invention to achieve the same.
• the electrolysis is carried out in a bath of nickel salt and boric acid, using alternating current, with current densities markedly higher than those which have heretofore been considered possible.
• composition of the electrolysis bath must be modified considerably.
• chemical ingredients formulated into the composition of the bath had to be present in relatively low concentrations of the order of 25 g./ liter of NiSO .7H O, 25 g./ liter of H BO and 15 g./liter of (NH SO) it has been found, in direct contrast thereto, that it is advantageous markedly to increase the concentration of the bath and to ice buffer the solution heavily with boric acid. In this manner, it becomes possible to make use of a current density from two to three times greater for electrolysis without rupturing the layer of alumina and with marked decrease in electrolysis time.
• an electrolysis bath which enables the use of a current density within the range of 0.7 to 1.5 a./dm. is formulated to contain NiSO .7H O in an amount within the range of 50 to 150 g./liter, ammonium sulphate in an amount within the range of 25 to 35 g./.liter, optionally with a small excess of sulphuric acid or ammonia added to adjust the pH value, and boric acid in an amount within the range of 45 to 60 g./liter as bulfering agent.
• the bath can be operated at a temperature range within 20 to 35 C.
• the object of the following examples is to demonstrate the influence which the boric acid concentration has upon the rupturing of the layer of alumina in nickel sulphate baths, during an electrolysis operation carried out with 50 c./s. alternating current, a constant current density of 0.8 a./dm. for a period of 6 minutes, which is sufficient to form a dark bronze layer.
• the metal used was a plate of commercial 99.5% pure aluminum containing the usual impurities, mainly silicon and iron. After the conventional treatments of degreasing and scouring, the metal is anodized in a sulphuric acid bath, containing 20% by weight of H over a period of 30 minutes, at a temperature of 20 C., and at a current density of 1.5 a./dm. (D.C. voltage).
• the layer of alumina has a thickness of 12 microns.
• the coloring bath had the following composition:
• the pH value of the solution is adjusted to the required value for each series of tests by addition of a small quantity of a dilute solution of H 804 or NH
• the temperature of the bath was maintained at 30 C. during electrolysis.
• the cell used for the tests was a Hull cell. It is in the form of a parallelepiped, the base of which is a rectangular trapezium. The working conditions are hardly favorable to the production of uniform color finishes because the surfaces of the electrode are not parallel but instead
• the first test identified in Table II was carried out with a plate of anodized aluminum of reduced surface. After 6 minutes electrolysis, the voltage had increased to 14 volts. The operation was then continued until signs of rupturing appeared in the layer of alumina. This occurred form a dihedral angle of 50. only after 40 minutes at a final voltage of 17 volts. The first test identified in Table II was carried out with a plate of anodized aluminum of reduced surface. After 6 minutes electrolysis, the voltage had increased to 14 volts. The operation was then continued until signs of rupturing appeared in the layer of alumina. This occurred form a dihedral angle of 50. only after 40 minutes at a final voltage of 17 volts.
• the first test identified in Table II was carried out with
• Irregular color finish Dcep color finish Deep color finish. Beginning 10", end 17"-- Beginning 10", end 16 Beginning 11 end 17". 8. Numerous ruptures Incipient ruptures Deep color finish Deep color finish Beginning 10 end 17 Beginning 10", and 10 16 Numerous ruptures Numerous ruptures.
• the tests were voluntarily carried out under conditions most unfavorable to the production of a uniform color layer.
• the same bath composition was then used in industrial cells having a capacity of several cubic meters, with electrodes arranged parallel to one another.
• the results obtained fully confirmed the ability very quickly to produce dark color finishes, free from rupturing, using current densities of the order of 0.7 to 1.3 amperes per dm. on aluminum, or aluminum alloys having an alumina layer formed by previous anodization.
• NiSO -7H O nickel sulphate
• boric acid is present in an amount within the range of 45 to 60 g./liter.
• a process for coloring articles of aluminum and aluminum alloys having an alumina surface by subjecting the articles to alternating current electrolysis with a nickel counter-electrode in an electrolysis bath having the com position claimed in claim 1 at a temperature within the range of 20 to 35 C. and a current density within the range of 0.7 to 1.5 a./dm.

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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)
• Electrolytic Production Of Metals (AREA)

Applications Claiming Priority (1)

Publications (1)

Family

ID=9064781

Family Applications (1)

Country Status (13)

Cited By (4)

Families Citing this family (1)

• 1970
  • 1970-11-26 FR FR7042544A patent/FR2115061A1/fr active Granted
• 1971
  • 1971-11-18 US US00200225A patent/US3759801A/en not_active Expired - Lifetime
  • 1971-11-23 IT IT31488/71A patent/IT941246B/it active
  • 1971-11-23 GB GB5433771A patent/GB1358709A/en not_active Expired
  • 1971-11-23 CA CA128,387A patent/CA957638A/en not_active Expired
  • 1971-11-24 BE BE775766A patent/BE775766A/xx unknown
  • 1971-11-24 DE DE19712158291 patent/DE2158291A1/de active Pending
  • 1971-11-24 AU AU36116/71A patent/AU455689B2/en not_active Expired
  • 1971-11-25 LU LU64344D patent/LU64344A1/xx unknown
  • 1971-11-25 HU HU707042544A patent/HU163389B/hu unknown
  • 1971-11-25 SE SE7115121A patent/SE384385B/xx unknown
  • 1971-11-25 CH CH1715771A patent/CH535286A/fr not_active IP Right Cessation
  • 1971-11-26 NL NL7116253A patent/NL7116253A/xx unknown

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