US3770600A - Process for coloring the surface of aluminum workpieces by anodization - Google Patents

Process for coloring the surface of aluminum workpieces by anodization Download PDF

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Publication number
US3770600A
US3770600A US00079242A US3770600DA US3770600A US 3770600 A US3770600 A US 3770600A US 00079242 A US00079242 A US 00079242A US 3770600D A US3770600D A US 3770600DA US 3770600 A US3770600 A US 3770600A
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United States
Prior art keywords
acid
percent
anodization
aluminum
weight
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Expired - Lifetime
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US00079242A
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English (en)
Inventor
W Sautter
A Gilak
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Vereinigte Aluminium Werke AG
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Vereinigte Aluminium Werke AG
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    • 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
    • C25D11/005—Apparatus specially adapted for electrolytic conversion coating
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D17/00—Constructional parts, or assemblies thereof, of cells for electrolytic coating
    • C25D17/002—Cell separation, e.g. membranes, diaphragms

Definitions

  • ABSTRACT This invention relates to the coloring of the surface of aluminum workpieces by anodization process wherein the anolyte consists principally of maleic acid with a small proportion of sulfuric acid for conductivity, and the catholyte consists of an organic acid of good conductivity or a mixture of organic acid to which a small quantity of sulfuric acid is added to conductivity.
  • the anolyte and the catholyte are separated by a porous, ion-permeable diaphragm.
  • Colored oxide layers of aluminum can be prepared in a variety of known electrolytes consisting of aqueous solutions of sulfonic acids such as sulfosalicylic acid and sulfophthalic acid, or of dicarboxylic acids with small additions of sulfuric acid.
  • sulfonic acids such as sulfosalicylic acid and sulfophthalic acid
  • dicarboxylic acids with small additions of sulfuric acid.
  • Maleic acid is a member of the last group and is frequently used as the electrolyte with additions of oxalic and sulfuric acids because of its low cost and the uniformity of the obtainable colors at relatively low voltages. The colors range from light brown to dark gray and to black.
  • a specific disadvantage of using the unsaturated maleic acid as a major component of the electrolyte results from the fact that the hydrogen given off at the cathode reduces maleic acid to succinic acid.
  • This material has a low solubility and consequently it crystallizes out at the opening of the necessary compressed air circulator and on the equally necessary cooling coils.
  • the bath after throughput of to din of aluminum surface per liter of solution must be regenerated, this being carried out by cooling the entire bath or at least a substantial portion thereof to 10 to C in contrast with the usual operating temperature' which is 20 to 30C and removal of the crystallized out succinic acid.
  • the original concentration of the electrolyte must be maintained by addition of suitable quantities of maleic acid.
  • the formation of succinic acid from maleic acid can be avoided by separating the cathode space and the anode space. This is carried out, preferably, by enclosing the cathode in a boxed-shaped or tube-shaped enclosure, the wall of which consists of a fine-pored, ion-permeable material and which contains an electrolyte with a solute consisting of an organic acid with good electrical conductivity, or a mixture of an organic acid with a small quantity of sulfuric acid.
  • a suitable container for the cathode is a mixture based on fine aluminum silicates fired at high temperature where the pore diameters are in the neighborhood of 1 micron. At a wall thickness between preferably A; and 2/5 inch, such a container has adequate mechanical strength and at the same time a low electrical resistance.
  • the surface area of the container or the surface areas of a battery of parallel-connected containers is so regulated that a current density of about 3 A/dm is not exceeded.
  • the concentration of the electrolyte within the cathode container should preferably be so high that at worst only a small quantity of maleic acid can diffuse thereinto.
  • Suitable mixtures of electrolyte are for example, 3 to 8 wt. percent of oxalic acid and 0.2 to 1 weight percent sulfuric acid.
  • Another suitable combination is 5 to 30 wt. percent citric acid or sulfosalicylic acid with an addition of sulfuric acid in the same quantity.
  • Such electrolyte compositions have additional numerous advantages such as the fact that in the event of damage to the container, no essential change in the properties of the electrolyte in the anode chamber occurs.
  • the composition of the anolyte may be, for example, 20 weight percent of maleic acid, 1 weight percent of oxalic acid and 0.4 weight percent of sulfuric acid with the remainder being water.
  • a further advantage of the process according to the present invention lies in the fact that the aluminum which goes into solution as a result of the anodic oxidation, which according to the present state of the art is removed by ion exchange, in this case collects in the cathode container without any hindrance to the anodic oxidation process. The lifetime of such a bath is thereby enhanced.
  • FIGURE shows schematically the arrangement of an anodization cell according to the present invention.
  • the anode l which is the object to be supplied with a colored coating is placed in a vessel and is separated from a cathode 2 by means of a diaphragm 4.
  • the numeral 3 indicates the aqueous electrolyte which, for example, may consist of 20 weight percent of maleic acid, 1 weight percent of oxalic acid, and 0.4 weight percent of sulfuric acid with the remainder being water.
  • the electrolyte within the diaphragm is indicated by the numeral 5.
  • the cathode 2 is shown to be perforated as indicated at 6; the objective is to permit hydrogen to enter into the inside of the cathode and to escape at the top.
  • the following examples illustrate the advantages accruing from the operation according to the present invention.
  • the first example illustrates the results obtained when operating according to the prior art.
  • EXAMPLE I Anodization of an extruded shape consisting of AIM- gSi 0.5 composition was carried outin a solution consisting of 20 weight percent maleic acid, I weight percent oxalic acid, and 0.4 weight percent of sulfuric acid. The anodization was continued until a dark brown color resulted.
  • the cathode sheet was made of aluminum which was placed in direct contact with the electrolyte. It was found to be necessary to regenerate the solution after a throughput of about 6 dmll of bath content.
  • EXAMPLE 2 A cathode of the same type as used in Example 1 was placed in a separate container containing an electrolyte consisting of 20 weight percent citric acid, 0.4 weight percent of sulfuric acid; the anode was placed in a composition similar to that of Example 1. After a throughput of 100 dm ll of bath contents, only a small quantity of succinic acid has been formed; this amount was completely harmless with respect to continuation of the anodization process. In the cathode space, after the same period of time, the solution contained 8 percent of dissolved succinic acid, and percent of succinic acid had crystallized out. This formation of succinic acid was a result of the inward diffusion of maleic acid. This quantity of transformed maleic acid had no efi'ect whatsoever on the further color-anodization process.
  • a further effect was the increase of the aluminum content in the cathode space; this amounts to about 40 percent of the aluminum which had gone into the solution during the color anodization process.
  • the quantity of aluminum to be removed by ion exchange was greatly decreased.
  • renewal of the small quantity of solution contained in the cathode space made it possible to proceed with the color anodization as before.
  • the voltage required for operation was increased only by about 4 volts as a result of the presence of the cathode container.
  • a process for coloring the surface of an aluminum workpiece by anodization which comprises passing an electric current between the aluminum workpiece immersed as anode in an aqueous anodizing anolyte consisting essentially of maleic acid containing a minor proportion of sulfuric acid or oxalic acid or both, and a conductive cathode immersed in an aqueous catholyte which comprises an electrically conductive organic acid other than maleic acid or a mixture of the said organic acid together with a minor proportion of sulfuric acid, the said anolyte and catholyte being separated from each other by a porous ion-permeable diaphragm.
  • anolyte comprises approximately 20 percent by weight of maleic acid, approximately 1 percent by weight of oxalic acid, and approximately 0.4 percent by weight of oxalic acid.

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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)
  • Cell Electrode Carriers And Collectors (AREA)
  • Printing Plates And Materials Therefor (AREA)
  • ing And Chemical Polishing (AREA)
  • Hybrid Cells (AREA)
  • Electrochemical Coating By Surface Reaction (AREA)
  • Cosmetics (AREA)
  • Cleaning And De-Greasing Of Metallic Materials By Chemical Methods (AREA)
  • Joining Of Corner Units Of Frames Or Wings (AREA)
  • Compounds Of Alkaline-Earth Elements, Aluminum Or Rare-Earth Metals (AREA)
US00079242A 1969-10-08 1970-10-08 Process for coloring the surface of aluminum workpieces by anodization Expired - Lifetime US3770600A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
DE1950716A DE1950716C3 (de) 1969-10-08 1969-10-08 Verfahren und Vorrichtung zur Farbanodisierung von Aluminiumwerkstoffen

Publications (1)

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US3770600A true US3770600A (en) 1973-11-06

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US00079242A Expired - Lifetime US3770600A (en) 1969-10-08 1970-10-08 Process for coloring the surface of aluminum workpieces by anodization

Country Status (14)

Country Link
US (1) US3770600A (cs)
JP (1) JPS5010696B1 (cs)
AT (1) AT292409B (cs)
BE (1) BE754994A (cs)
CA (1) CA947230A (cs)
CH (1) CH541628A (cs)
DE (1) DE1950716C3 (cs)
FR (1) FR2064187B1 (cs)
GB (2) GB1319659A (cs)
LU (1) LU61309A1 (cs)
NL (1) NL7014669A (cs)
NO (1) NO126868B (cs)
SE (1) SE367441B (cs)
ZA (1) ZA706579B (cs)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5367196A (en) * 1992-09-17 1994-11-22 Olin Corporation Molded plastic semiconductor package including an aluminum alloy heat spreader
US5608267A (en) * 1992-09-17 1997-03-04 Olin Corporation Molded plastic semiconductor package including heat spreader

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3634213A (en) * 1967-07-20 1972-01-11 Reynolds Metals Co Use of cationic permselective membranes in anodizing

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR1430561A (fr) * 1965-03-03 1966-03-04 Vaw Ver Aluminium Werke Ag Procédé pour l'obtention de couches d'oxyde colorées sur des pièces en aluminium ou alliages d'aluminium
NL6912194A (cs) * 1968-08-14 1970-02-17

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3634213A (en) * 1967-07-20 1972-01-11 Reynolds Metals Co Use of cationic permselective membranes in anodizing

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5367196A (en) * 1992-09-17 1994-11-22 Olin Corporation Molded plastic semiconductor package including an aluminum alloy heat spreader
US5608267A (en) * 1992-09-17 1997-03-04 Olin Corporation Molded plastic semiconductor package including heat spreader

Also Published As

Publication number Publication date
AT292409B (de) 1971-08-25
FR2064187A1 (cs) 1971-07-16
GB1319658A (en) 1973-06-06
LU61309A1 (cs) 1970-09-10
BE754994A (fr) 1971-02-01
FR2064187B1 (cs) 1975-01-10
GB1319659A (en) 1973-06-06
CA947230A (en) 1974-05-14
DE1950716C3 (de) 1979-05-23
SE367441B (cs) 1974-05-27
NO126868B (cs) 1973-04-02
NL7014669A (cs) 1971-04-14
CH541628A (de) 1973-09-15
JPS5010696B1 (cs) 1975-04-23
DE1950716A1 (de) 1971-04-22
DE1950716B2 (de) 1978-09-28
ZA706579B (en) 1971-05-27

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