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 a process for electrochemically coloring preanodized articles of aluminum or aluminum alloys by the electrolytic deposition of heavy metals or heavy metal compounds into the pores of the oxide layer.
• direct current covers any form of one-way current, such as rectified and non-filtered currents and currents that are even periodically interrupted, as in the case of the rectification of a single alternation of a single-phase current.
• an article of anodized aluminum can be colored by causing particles of metal or metal compounds to penetrate into the pores of the layer of alumina through electrolysis in an aqueous acid solution of a heavy metal salt, such as Ni, Co, Cu, Ag, Pb, Sn.
• electrolysis has generally been carried out with sinusoidal alternating current voltage.
• the layer of alumina acts as an imperfect rectifier for the electrical current, with the result that the momentary intensity of the current is not merely a function of the momentary voltage. It is governed by the previous anodization and fluctuates during the coloring electrolysis operation. The amount of electricity which travels in the direction required for deposition of the metal into the layer of alumina cannot readily be determined. It is for this reason that the production of a uniform color finish which is identical throughout a series of articles calls for extremely strict control of all the operations involved in preliminary anodization and coloring electrolysis.
• the concepts of the present invention reside in a method for coloring anodized articles of aluminum or an alloy of aluminum in which the article is mounted as the cathode in an electrolysis bath of an aqueous solution of a heavy metal sulfamate and a direct current is passed through the bath.
• the process can be applied with the electrical equipment available in a conventional anodizing plant. No difficulties are encountered in accurately measuring the amount of electricity passing through the bath. Since the penetrating power of the metal is extremely high, the surface ratio of the electrodes has hardly any bearing on the process, and satisfactory reproducibility is obtained with much more ease than in conventional baths without any need for agents intended to improve the penetrating power to be added to the bath.
• free sulfamic acid is added as and when required, and a buffer, preferably boric acid, is used to keep the pH-value constant.
• the pH-value should be between 1 and 1.5 for the cations silver, lead, tin, which necessitates the addition of sulfamic acid.
• Nickel requires a higher pH-value amounting to between 3.5 and 5.5, so that there is generally no need to add acid.
• the direct-current electrolysis in a sulfamic bath gives an excellent Faraday efiiciency so that the quantity of metal deposited and the coloring of the article are influenced hardly at all by the working conditions.
• the concentration of heavy metal sulfamate can vary within very wide limits without causing appreciable differences in the color finish obtained.
• the type and size of the anode have hardly any bearing at all and the current density can be selected within a very wide range of from 0.05 to 3 amps/dm. without involving any modifications other than the duration of the operation.
• the nickel sulfa-mate is used in concentrations of from 0.2 to 1.6 mole/ liter with a nickel counterelectrode with a surface from 0.1 to two times the surface of the article to be colored which has the advantage that it is possible successively to treat aluminum articles differing widely from one another in their size in the same bath without having to modify the anode surface.
• the counter-electrodes can be formed of metal, namely lead or tin, or of graphite.
• the preferred current density is that which corresponds to a 2 to -minute duration of the operation which simultaneously provides for fast coloring and strict control of the time, resulting in extremely good reproducibility.
• the electrolysis operation is carried out at temperatures in the vicinity of ambient temperature, and preferably at temperatures of from to C.
• discharge is used in a broad sense because the phenomenon of discharge or depolarization of the article to be treated is not exactly known. It would appear that it is similar to that which is observed in the case of an electrolytic capacitor. During the breaks in the current, there occurs an inverse flow of current whose momentary initial intensity can be extremely high, although it decreases very rapidly and finally disappears altogether. Discharge of the article to be treated makes the subsequent active period much more effective than it would be had the break in current not taken place.
• the article to be treated is advantageously discharged by short-circuiting with the anode.
• a switching system can be used for interrupting the direct electrolysis current and for short-circuiting the electrodes with a predetermined frequency and for a predetermined time.
• the duration of these cycles can either be constant or variable in time.
• the direct current is preferably applied for a time t of from about two seconds to three minutes, the period for which the current is interrupted being between t and approximately /5 t.
• the choice and the duration of the cycles and of the cyclic ratio is determined experimentally by observing the voltage or current intensity curves as a function of time.
• the operation can be carried out either with a constant D.C. voltage source or with a source of constant-intensity current.
• Ni(SO NH -4H O and 27 g./l. of boric acid 220 g./l. of nickel sulfamatc (Ni(SO NH -4H O and 27 g./l. of boric acid.
• This bath has a pH-value of 4.5 and its temperature is maintained between 20 and 25 C. It is used for coloring sheets of commercial-grade 99.5% aluminum, previously anodized to 18 microns in a sulfuric bath and with direct current in accordance with the conventional process. These plates are used as cathode while the anode consists of a nickel plate with the same surface area as the aluminum plates.
• Example 1 The test is carried out with the same plates as in Example 1 with the same nickel anode, the current densities and the durations being varied.
• Examples 1 to 3 show that the intensity of the color finish is directly related to the quantity of electric current passing through the cell. This enables the electrical conditions to be automatically regulated to obtain a predetermined color finish. Accordingly, the process is much easier to work on an industrial scale than electrolysis processes using alternating current.
• Example 2 The test is carried out with the same aluminum panels as in Example 1 and with a graphite anode.
• a golden yellow color finish is obtained after 1 minute at 1.6 amps/dm. while a deep yellow color finish is obtained after 2 minutes at 1:6 amps/dmP.
• the test is carried out with the same aluminum panels as in Example 1 and with a lead anode of the same surface area as the aluminum panels.
• a light bronze color finish is obtained after 2 minutes at 0.4 amps./dm. while a deep bronze color finish is obtained after 5 minutes with a current density increasing linearly with time from 0.2 to 0.8 amps/dmF.
• EXAMPLE 7 After a total treatment time of 6 minutes, of which 4.5 minutes represent effective time, the aluminum article has taken on a deep black color.
• the maximum voltages at the terminals measured just before the current is broken are, successively, 11.3, 10.5, 9 and 8.6 volts.
• EXAMPLE 8 An identical panel is treated in the same bath, but with a current source equipped with an automatic voltage regulator which 'fixes the voltage at 14 volts after a substantially linear increase from 0 to 14 volts over a period of 10 seconds.
• the cycle is made up of a 30 second halfcycle in which effective coloring takes place, and a 30 second half-cycle during which discharge occurs. After 8 cycles corresponding to an effective time of 4 minutes 30 seconds, out of a total period of 8 minutes 30 seconds, the article is deep black in color.
• EXAMPLE 9 A profile of Al-Mg-Si alloy which has a surface area of 50 dm. and which has been preanodized in a sulfuric bath, is treated.
• the current source is provided with an automatic regulator which fixes the intensity at 10 amperes.
• Each cycle comprises 10 seconds of progressive application of voltage, 50 seconds of electrolysis at 10 amperes and 30 seconds of discharge. After 8 cycles, having lasted a total of 11 minutes 30 seconds and corresponding to an effective duration of 8 minutes, the profile has acquired a deep black color.
• the voltages observed at the end of each of the 8 cycles, just before the current is interrupted, are, respectively, 10.5, 10.2, 8.9, 8.1, 7.6, 7.2, 6.8 and 6.5 volts.
• the color finish is obtained at a constant current density of 0.2 amps/ drn. under considerably lower voltages than the final voltages of around 32 volts obtained in continuous operation, and it is possible to obtain a black color finish which would have been substantially impossible in continuous operation.
• EXAMPLE 10 A profile identical to that used in Example 9 was treated using a constant voltage source of 14 volts. Each cycle is made up of 10 seconds of increase in voltage, 20 seconds of coloring under 14 volts and 30 seconds of discharge. Seven successive cycles were applied, given a 5 total duration of 7 minutes of which 3 minutes 30 seconds represent effective time. In each cycle, the maximum intensity is of the order of 30 amps, while the minimum intensity just before the current is broken fluctuates between 8 and 10 amperes. The profile is colored deep black.
• EXAMPLE 1 l The preceding test was repeated in an industrial 4,000 liter cell of which the nickel sulfamate bath had already been used to color more than 800 m? of aluminum articles. The test was carried out on 6 m profiles of Al- Mg-Si preanodized in a sulfuric bath. A constant voltage source equal to 14 volts was used, each cycle being made up of 10 seconds voltage application, 5.0 seconds of coloring at 14 volts and 30 seconds of discharge. 5 cycles are sufiicient to obtain a deep black color finish on the profiles.
• a process for electrochemically coloring anodized articles of aluminum or alloys of aluminum by electrolytic deposition of heavy metals or heavy metal compounds comprising mounting the article as the cathode in a bath of an aqueous solution of a heavy metal sulfamate and passing a direct current through the bath.
• aqueous solution contains nickel sulfamate in a concentration of from 0.2 to 1.6 mole/liter and boric acid as a buffer in a concentration of from 25 to 50 g./liter, the pH being in the range from 3.5 to 5.5.
• aqueous solution contains silver sulfamate in a concentration of from 0.002 to 0.01 mole/liter, boric acid in a concentration of from 25 to 50 g./ liter and sulfamic acid in a quantity sufficient to adjust the pH to between 1 and 1.5.

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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)
• Electrolytic Production Of Metals (AREA)
• Electrochemical Coating By Surface Reaction (AREA)
• Electroplating And Plating Baths Therefor (AREA)
• Insulated Metal Substrates For Printed Circuits (AREA)
• Electrical Discharge Machining, Electrochemical Machining, And Combined Machining (AREA)

Applications Claiming Priority (2)

Publications (1)

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Family Applications (1)

Country Status (16)

Cited By (5)

• 1971
  • 1971-09-10 FR FR7132743A patent/FR2152399B2/fr not_active Expired
• 1972
  • 1972-06-22 SE SE7208286-0A patent/SE380836B/xx unknown
  • 1972-06-22 LU LU65580D patent/LU65580A1/xx unknown
  • 1972-06-22 HU HUCE881A patent/HU166192B/hu unknown
  • 1972-06-22 YU YU1645/72A patent/YU35383B/xx unknown
  • 1972-06-23 CH CH947572A patent/CH549097A/fr not_active IP Right Cessation
  • 1972-06-23 US US00265653A patent/US3788956A/en not_active Expired - Lifetime
  • 1972-06-23 BE BE785351A patent/BE785351A/xx unknown
  • 1972-06-23 GB GB2955772A patent/GB1370857A/en not_active Expired
  • 1972-06-23 JP JP6313272A patent/JPS5411788B1/ja active Pending
  • 1972-06-23 AR AR242719A patent/AR193409A1/es active
  • 1972-06-23 DE DE2230868A patent/DE2230868C3/de not_active Expired
  • 1972-06-23 AU AU43819/72A patent/AU468076B2/en not_active Expired
  • 1972-06-23 CA CA145,574A patent/CA992909A/en not_active Expired
  • 1972-06-23 NL NL7208645A patent/NL7208645A/xx not_active Application Discontinuation
  • 1972-06-24 RO RO7271381A patent/RO66345A/ro unknown

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