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
  • C25D11/14—Producing integrally coloured layers
• • 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
  • C25D11/06—Anodisation of aluminium or alloys based thereon characterised by the electrolytes used

Definitions

• Anodic .oXide coating of aluminum which involves the use of an aqueous electrolyte in which the aluminum is made anode, is a useful technique widely used to provide an aluminum surface or a portion thereof with an oxide coating serving one or more useful functions such as protective, decorative, adsorptive or the like.
• the requirements of such a process may be widely variant in object from one aluminum product to another.
• a clear or substantially colorless coating may be desired.
• a protective coating with no emphasis on appearance may be desired.
• a coating substantially colorless as produced but receptive to a dye or pigment for decorative purposes may be desired.
• a coating having some lightfast color or tint as produced may be desired.
• the processor who produces such anodic coatings has need for a process and electrolyte suited to such multi-purpose employment, in the sense that the same can advantageously be used for one or more of these purposes, that present no real problem of voltage rise beyond the capacity of equipment when operated at substantial current density, and that are capable of being operated over a relatively wide range of temperature.
• the present invention provides an anodizing process and an electrolyte therefor which meet these conditions to a substantial degree.
• the process of this invention employs an electrolyte containing succinic acid, a non-acid hydrogen of which is substituted with the group SO H.
• succinic acid a non-acid hydrogen of which is substituted with the group SO H.
• Such a compound has been described in the literature, of. Beilstein, volume 4, page 25; Beilstein, 2nd Supplement, volume 4, pages 537-538; and Chemical Abstracts, volume 21, page 3351.
• the electrolyte of the invention also contain sulfuric acid and water. The amount of sulfuric acid and the proportioning of the sulfuric acid content to the substituted succinic acid content are, as hereinafter explained, desirably governed by specific purposes for which particular anodic coatings are intended.
• the sulfuric acid content in a given electrolyte may be adjusted, for example, either by addition of sulfuric acid or removal of sulfuric acid, in the latter case by employment of a sulfate precipitant such as barium hydroxide or other precipitant, preferably one the use of which does not introduce into the electrolyte soluble metal which might be detrimental to the operation, as hereinafter noted.
• a sulfate precipitant such as barium hydroxide or other precipitant
• the electrolyte of the invention is essentially substituted succinic acid, sulfuric acid, and water.
• the substituted succinic acid content of the electrolyte may be introduced directly by the use of the substituted succini acid. If a salt of'the substituted succinic acid is used, e.g., a sodium neutralized substituted succinic acid compound, the same should be ion-exchanged to make available in the solution the desired free substituted succinic acid content.
• the amount of the substituted succinic acid to be used may range from a practical coating forming minimum, such as so called grays and blacks.
• the sulfuric acid content of the electrolyte may be introduced directly by the use of sulfuric acid, but a water soluble sulfate donor such as a metal, ammonium, or organic sulfate or bisulfate may be used to introduce the sulfuric acid content if desired.
• a water soluble sulfate donor such as a metal, ammonium, or organic sulfate or bisulfate
• the sulfuric acid content may be regarded as provided by the sulfate donor and some of the acid hydrogen from the substituted succinic acid present, the effective amount of free substituted succinic acid in such cases thereby being reduced somewhat, unless restored by ion-exchange in accordance with usual ion-exchcange practices.
• amount of sulfuric acid to be used may range from a prac-' tical coating forming minimum, such as about /2 gram per liter, to any higher amount desired in the aqueous electrolyte. Generally, in the practice of the invention, amounts greater than about 250 grams per liter do not appear to afford special advantage. A convenient operating range for some purposes may be a range above about 15 and up to about 200 grams per liter, while for other purposes a relatively low range such as about 2 to about 12.5 grams per liter is preferred. Adjustment of the sulfuric acid content may be made as hereinbefore described, i.e., by addition of sulfuric acid or precipitation of insoluble sulfate.
• tints or colors readily obtained are usually in a range of yellows and browns (which might be termed by an observer as light to dark bronzes), and the Herein these terms as to tint or color convey no more than an approximation since the exact characterization of a tint or color is, as to any given observer, a matter of language and degree of emphasis.
• the intensity of the tints or colors will generally depend upon the anodizing time, i.e., the coating thickness (which is normally a function of anodizing time), the particular composition of the electrolyte, and the particular composition of the aluminum and its prior fabrication and thermal history.
• Every aluminum composition or alloy has some limitation as to the tint shade or color of anodic coating which can readily be produced on it by the practice of this invention.
• aluminum of what is currently termed commercial purity will not readily produce in the indicated coating thicknesses, tints or shades beyond yellows or golds to browns (or bronzes), but alloys of commercial purity aluminum with small amounts of manganese, or magnesium silicide,
• electrolytes such as those of the following compositions may be used:
• Electrolyte 2 may be considered as a representative example for the indicated purpose, but within the range of electrolyte indicated by these examples, such range being but indicative, commercially pure articles of aluminum may be made anode therein and provided with substantially colorless anodic oxide coatings.
• the electrolyte may be maintained at about 75 F., and the anodizing current density may be maintained at 36 amperes per square foot, for example. In minutes a coating about 0.5 mil thick will be formed; with longer periods of anodizing, thicker coatings may be produced.
• electrolytes of the composition range indicated generally produce coatings with approximately the same lack of color or shade of color that is obtained in coatings of corresponding thickness produced by conventional anodizing practices in percent sulfuric acid electrolytes.
• sulfuric acid content of the electrolyte is preferably adjusted and maintained at a level above about 15 grams per liter.
• electrolytes of a composition range such as is generally indicated by the following compositions:
• composition (g./l.balance water)
• Example Electrolyte Substituted Suceinic Acid Sulfuric Acid It is desirable for such a purpose that the amount of sulfuric acid present in the electrolyte should be at least about /2 gram per liter, preferably about 2 to about 12.5 grams per liter, and that the weight ratio of sulfuric acid to the substituted succinic acid be no more than about 1 to 8. For example, if the substituted succinic acid c0ntent is 100 grams per liter or more, the sulfuric acid content preferably is no more than about 12.5 grams per liter.
• Electrolyte C may be considered as a preferred example, but with any of the above electrolytes various aluminum compositions and alloys, pure or impure, may be made anode therein and provided with uniform coatings that are tinted or exhibit color.
• the electrolyte may be maintained at about 75 F., and the anodizing current may be maintained at 24 amperes per square foot. Under such As an ex-- conditions the initial anodizing voltage with Electrolyte C, for example, will be about 35 volts, rising as the coat ing builds up in thickness.
• a commercial aluminum alloy containing 1.25 percent manganese acquires a dark gray coating in 30 minutes under similar conditions.
• electrolyte temperatures at or near room temperature may be employed, but in the process of this invention there is a considerable latitude or permissibility of temperature of operation. Lower temperatures such as 40 F. or higher temperatures such as 100 F. are tolerable. Temperatures in the range between about 60 and about F. will usually be found desirable in most commercial operations.
• the current density may be maintained at a lower value such as about 12 amperes per square foot or even lower, or at a higher value such as about 64 amperes per square foot or even higher.
• a constant current density may be preferred, but changing current density may also be used.
• practices employing a constant initial current density and thereafter a constant terminal voltage allowing the current density to decay may be employed.
• the color or shade of color of an anodic oxide coating produced in accordance with the invention usually depends on the coating thickness, all other things being equal.
• the anodizing time will therefore be chosen with reference to the thickness and/ or color desired.
• Decorative coatings for indoor use may be made in thicknesses on the order of 0.1 mil, while protective coatings will usually be at least 0.4 mil in thickness to meet current northern hemispheric specifications, and on the order of 0.7 mil or more in thickness for outdoor service in temperate climate.
• the coatings produced in accordance with the invention are adsorptive and thus may be sealed if desired. They may also be supplementally dyed or pigmented so as to color the same or modify the color as produced.
• the reduction in conductivity and other eifects upon operating characteristics of the electrolyte accompanying dissolution of aluminum therein indicate that the effective free substituted succinic acid content of the electrolyte may be considered as less than the total substituted succinate present by about 20 times the weight of dissolved aluminum.
• the aluminum articles treated in accordance with the invention may be made of aluminum alone, or may be aluminum coated or clad products, or any other products presenting aluminum surfaces for anodizing.
• An electrolyte for anodizing aluminum consisting essentially of at least about 35 grams per liter of succinic acid, a nonacid hydrogen of which is substituted with the group SO H,
• the weight ratio of the sulfuric acid to the substituted succinic acid being no more than about 1 to 8.
• An electrolyte as set forth in claim 1 which contains not more than about 2.5 grams per liter of dissolved aluminum.
• a process for anodizing aluminum comprising making an aluminum article anode in an electrolyte consisting essentially of at least about 5 grams per liter of succinic acid, a non-acid hydrogen of which 6 is substituted with the group -SO H, at least about /2 gram per liter of sulfuric acid, and
• a process for anodizing aluminum comprising making an aluminum article anode in an electrolyte consisting essentially of at least about 35 grams per liter of succinic acid, a non-acid hydrogen of which is substituted with the group -SO H, about 2 to about 12.5 grams per liter of sulfuric acid, and water,
• the weight ratio of the sulfuric acid to the substituted succinic acid being no more than about 1 to 8, while the electrolyte is maintained at a temperature between about and about F.
• the current density is maintained between about 12 and and about 64 amperes per square foot

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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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Publications (1)

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Cited By (4)

Citations (7)

• 1964
  • 1964-06-02 US US372088A patent/US3280013A/en not_active Expired - Lifetime
• 1965
  • 1965-05-27 GB GB25006/65A patent/GB1092698A/en not_active Expired
  • 1965-06-01 DE DE1621028A patent/DE1621028C3/de not_active Expired
  • 1965-06-02 CH CH767565A patent/CH471235A/de not_active IP Right Cessation
  • 1965-06-02 SE SE7206/65A patent/SE302875B/xx unknown

Patent Citations (9)

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