CA1060376A - Electrolytic colouring of anodised aluminum - Google Patents
Electrolytic colouring of anodised aluminumInfo
- Publication number
- CA1060376A CA1060376A CA251,112A CA251112A CA1060376A CA 1060376 A CA1060376 A CA 1060376A CA 251112 A CA251112 A CA 251112A CA 1060376 A CA1060376 A CA 1060376A
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- CA
- Canada
- Prior art keywords
- acid
- aluminum
- phosphoric acid
- based electrolyte
- anodised aluminum
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Abstract
A B S T R A C T
In the process of electrocolouring aluminum by passage of alternating current between anodised aluminum and a counter-electrode while immersed in a bath containing a salt of one or more of the group nickel, cobalt, tin, the range of colours obtainable by the process is extended by subjecting aluminum, which has been anodised under conventional D.C. conditions while immersed in a sulfuric acid-based electrolyte, to an electrolytic treatment in a phosphoric acid based electrolyte before the electrocolouring operation.
In the process of electrocolouring aluminum by passage of alternating current between anodised aluminum and a counter-electrode while immersed in a bath containing a salt of one or more of the group nickel, cobalt, tin, the range of colours obtainable by the process is extended by subjecting aluminum, which has been anodised under conventional D.C. conditions while immersed in a sulfuric acid-based electrolyte, to an electrolytic treatment in a phosphoric acid based electrolyte before the electrocolouring operation.
Description
~ he present invention relates to the production ~f coloured anodic oxide films on aluminum (includin~ aluminum alloys) .
~ he colouring of anodic oxide films b~ electrolytic deposition of inorganic particles has become well kno~m.
One of the earliest descriptions of a process of this type i~ in Ger~an Patent No. 741,75~. ~he process as first put into commercial operation is described in United States Patent ~o. 3,382,160 and British Patent No. 1,022,927. Since those patents descriptions of very many different variants and impxovements in the process have appeared in the patent litexature~
In the electrocolouring process inorganic particles are deposited in the pores of an anodic aluminum oxide film (formed by application of D.C. in a sulfuric acid bath) by the passage of electric current, usually alternating current, between an anodised aluminum surface and a counterelectrode, whilst i~mersed in an acidic bath of an appropriate metal salt. The most co~only employed electrolytes are salts of nickel, cobalt, tin and copper. The counterelectrode i~
usually ~raphite or stainless steel, althou~h nickel, tin ~nd copper electrodes are also e~ployed when the bath contains the salt of the corresponding metal.
~he nature of the deposited particles has been the subject of much speculation and it is still uncertain whether the particles.are in the form of metal or metallic oxide (or a combination of both).
AJ~
~ 2-7f~
Usin~, for esample~ a nickel sulfato electrolyto the colour~ obtained range from golden bron~- throu~h dark bronza to black with increaso in treatment time and applied voltago. It would be an obvious advanta~e to be able to provide a widor ran~o of coloura than $s available at pr-sent.
Although ~any difforent ~alt solutions havo boen propo~od for uao in the olectrocolourin~ of aluminum, it is found in practico that th- bost oolour ~tability ia achieved with batha containing nickol~ cobalt or tin salts or ~ome-times mistures of thes- ~alta.
In curront co~ercial practico direct-current anodis-ing in a aulfuric acid-based electrolyte has almost totally replaced all othor anodi-~in~ proceJsos for the production of thick, cl-ar~ porous-type anodic oxide coatings~ such as are omployod a~ protoctive coating~ on aluminum curtain wall panels and window fra~o~, which are exposed to the wcather.
In gonoral, anodising voltagos employed for sulfuric acid-ba~ed electrolytos range fro~ 12 to 22 voltQ dopending upon tho stron~th and t~perature of tho acid. Co~ventional ~ulfuric acid-ba~ed electrolytes include mixtures of sulfuric acid with othor acids~ such as oxalic acid and sulfa~ic acid, in which tbo anodising charact~ristic~ are broadly determined by tbo sulfuric acid content.
In the process of the present inventio~ the anodi^
oxide film is produced by a conventional sulfuric acid process of the type discussed above to produce a film of t~pical thickness, for exa~ple in the range of at least 1 micron to 25 ~icrons or more. The thus anodized aluminum is subjected to a further electrolytic treatment, which forms the special feature of the present invention, before being el~ctrocoloured in a metal salt bath containing salts of one or more of the metals nickel, cobalt and tin, by passage of alternatin~ current between the anodized alu~inum and a counter-electrode, which is usùally graphite or stainless steel, but may be nickel or tin where the salts of thes~
metals form the predominating component of the electro-colourin~ bath.
lt has long been recognized that the structure of an anodic oxide film is dependent upon the acid in which the anodizing operation is perfor~ed. Thus it is well recognized that anodization in sulfuric acid, oxalic acid, boric acid, chromic acid or phosphoric acid lead to the production of anodic oxide fil~s which possess differences in barrier layer thick~ess, pore diameter and density and also differences i~
the rectif~ing characteristics of the film.
The present invention is concerned with the discovery ~, that the colour of the fil~ resulting fro~ electrocolouring is diff~rent when anodization has been performed in a phos-phoric ~cid electro yte or in an electrolyte of which phos-phoric acid is the ~ajor co~ponent as compared with the , 1()~0~7~;
colou~ obtained ~:hen anadization has been performed in a conventional sul-furic acid electrolyte. Since it is di~ficult and indeed nearly impossible to produce an anodic film of adequate thickness by anodization in phosphoric acid, the present invention relies on first forming a porous anodic oxide film of at least 1 micron thickness by direct current anodizing aluminum in a sulfuric acid based electrolyte. The anodization of this film is then continued under direct current conditions in a phosphoric acid based elec-trolyte, such as orthophosphoric acid or pyrophosphoric acid, and finally the anodized aluminunl is electrocoloured by subjecting it to passage of alternating current between itself and a counter electrode while immersed in a bath containing a salt of one or more of the group consisting of nickel, cobalt and tin. The metal salt is preferably a sulfate.
The aqueous phosphoric acid-based electrolyte in the second stage may contain a proportion of other acids, such as oxalic acid, sulfosalicylic acid, sulfamic acid, chromic acid, tartaric acid, citric acid or gluconic acid or even a minor proportion of sulfuric acid.
The anodic oxidation treatment in a phosphoric acid-based electro-lyte may be performed at a selected voltage in the range of 20-50 volts and preferably at a temperature in the range of 20-35C. The electrolyte may ~0 contain 50-150 gms/litre phosphoric acid, more preferably 80-120 gms/litre.
The film produced by this two-stage anodizing procedure may acquire colours in the range of gray through bronze to black by the de-position of microparticles in the pores of the anodic oxide film by the alternating current electrocolouring process in an electrolyte containing a salt of one or more ~;
~0~03'76 of tho metals Ni~ C0, Sn. In a typical operation the abo~e quoted rango of ¢olours is obtained by ~ariation of the treat-ment time within the ran~e of 20 soconds to 30 ~inuteJ.
Tho in~ention is illustrated by the followin~ Examples.
~SX~IPLE 1 Aluminum wa- first anodi-ed under con~entional condition- by the application of diroct current at 17-lô ~olts to produco un anodic oxido film haYing a thicknos~ of 15 microns. Thi# was ~ubjoct-d to further electrolytic tr-atmont und-r D.C. oondition# for further formation of fllm in ~ bath containing phosphoric acid (80 9/l) and sulfuric acid (10 9/1) for 2 minutos. Aftor rinsing the aluminum was treatod under alternatin~ current conditionJ
in a bath containing ni~kel sulfato, 6H2o (28 9/l)~ ammoniu0 citrato (20 9/l) and boric aoid (20 9/l) at pH 5.0 for the timo and under the current donsity conditions described below in order to obtain aluminum with various colours. The counter-olectrodos wore graphito.
Current Den~ity Timo Colour 1) 0.13 A~d~a(15 V) 30 sec. ~old
~ he colouring of anodic oxide films b~ electrolytic deposition of inorganic particles has become well kno~m.
One of the earliest descriptions of a process of this type i~ in Ger~an Patent No. 741,75~. ~he process as first put into commercial operation is described in United States Patent ~o. 3,382,160 and British Patent No. 1,022,927. Since those patents descriptions of very many different variants and impxovements in the process have appeared in the patent litexature~
In the electrocolouring process inorganic particles are deposited in the pores of an anodic aluminum oxide film (formed by application of D.C. in a sulfuric acid bath) by the passage of electric current, usually alternating current, between an anodised aluminum surface and a counterelectrode, whilst i~mersed in an acidic bath of an appropriate metal salt. The most co~only employed electrolytes are salts of nickel, cobalt, tin and copper. The counterelectrode i~
usually ~raphite or stainless steel, althou~h nickel, tin ~nd copper electrodes are also e~ployed when the bath contains the salt of the corresponding metal.
~he nature of the deposited particles has been the subject of much speculation and it is still uncertain whether the particles.are in the form of metal or metallic oxide (or a combination of both).
AJ~
~ 2-7f~
Usin~, for esample~ a nickel sulfato electrolyto the colour~ obtained range from golden bron~- throu~h dark bronza to black with increaso in treatment time and applied voltago. It would be an obvious advanta~e to be able to provide a widor ran~o of coloura than $s available at pr-sent.
Although ~any difforent ~alt solutions havo boen propo~od for uao in the olectrocolourin~ of aluminum, it is found in practico that th- bost oolour ~tability ia achieved with batha containing nickol~ cobalt or tin salts or ~ome-times mistures of thes- ~alta.
In curront co~ercial practico direct-current anodis-ing in a aulfuric acid-based electrolyte has almost totally replaced all othor anodi-~in~ proceJsos for the production of thick, cl-ar~ porous-type anodic oxide coatings~ such as are omployod a~ protoctive coating~ on aluminum curtain wall panels and window fra~o~, which are exposed to the wcather.
In gonoral, anodising voltagos employed for sulfuric acid-ba~ed electrolytos range fro~ 12 to 22 voltQ dopending upon tho stron~th and t~perature of tho acid. Co~ventional ~ulfuric acid-ba~ed electrolytes include mixtures of sulfuric acid with othor acids~ such as oxalic acid and sulfa~ic acid, in which tbo anodising charact~ristic~ are broadly determined by tbo sulfuric acid content.
In the process of the present inventio~ the anodi^
oxide film is produced by a conventional sulfuric acid process of the type discussed above to produce a film of t~pical thickness, for exa~ple in the range of at least 1 micron to 25 ~icrons or more. The thus anodized aluminum is subjected to a further electrolytic treatment, which forms the special feature of the present invention, before being el~ctrocoloured in a metal salt bath containing salts of one or more of the metals nickel, cobalt and tin, by passage of alternatin~ current between the anodized alu~inum and a counter-electrode, which is usùally graphite or stainless steel, but may be nickel or tin where the salts of thes~
metals form the predominating component of the electro-colourin~ bath.
lt has long been recognized that the structure of an anodic oxide film is dependent upon the acid in which the anodizing operation is perfor~ed. Thus it is well recognized that anodization in sulfuric acid, oxalic acid, boric acid, chromic acid or phosphoric acid lead to the production of anodic oxide fil~s which possess differences in barrier layer thick~ess, pore diameter and density and also differences i~
the rectif~ing characteristics of the film.
The present invention is concerned with the discovery ~, that the colour of the fil~ resulting fro~ electrocolouring is diff~rent when anodization has been performed in a phos-phoric ~cid electro yte or in an electrolyte of which phos-phoric acid is the ~ajor co~ponent as compared with the , 1()~0~7~;
colou~ obtained ~:hen anadization has been performed in a conventional sul-furic acid electrolyte. Since it is di~ficult and indeed nearly impossible to produce an anodic film of adequate thickness by anodization in phosphoric acid, the present invention relies on first forming a porous anodic oxide film of at least 1 micron thickness by direct current anodizing aluminum in a sulfuric acid based electrolyte. The anodization of this film is then continued under direct current conditions in a phosphoric acid based elec-trolyte, such as orthophosphoric acid or pyrophosphoric acid, and finally the anodized aluminunl is electrocoloured by subjecting it to passage of alternating current between itself and a counter electrode while immersed in a bath containing a salt of one or more of the group consisting of nickel, cobalt and tin. The metal salt is preferably a sulfate.
The aqueous phosphoric acid-based electrolyte in the second stage may contain a proportion of other acids, such as oxalic acid, sulfosalicylic acid, sulfamic acid, chromic acid, tartaric acid, citric acid or gluconic acid or even a minor proportion of sulfuric acid.
The anodic oxidation treatment in a phosphoric acid-based electro-lyte may be performed at a selected voltage in the range of 20-50 volts and preferably at a temperature in the range of 20-35C. The electrolyte may ~0 contain 50-150 gms/litre phosphoric acid, more preferably 80-120 gms/litre.
The film produced by this two-stage anodizing procedure may acquire colours in the range of gray through bronze to black by the de-position of microparticles in the pores of the anodic oxide film by the alternating current electrocolouring process in an electrolyte containing a salt of one or more ~;
~0~03'76 of tho metals Ni~ C0, Sn. In a typical operation the abo~e quoted rango of ¢olours is obtained by ~ariation of the treat-ment time within the ran~e of 20 soconds to 30 ~inuteJ.
Tho in~ention is illustrated by the followin~ Examples.
~SX~IPLE 1 Aluminum wa- first anodi-ed under con~entional condition- by the application of diroct current at 17-lô ~olts to produco un anodic oxido film haYing a thicknos~ of 15 microns. Thi# was ~ubjoct-d to further electrolytic tr-atmont und-r D.C. oondition# for further formation of fllm in ~ bath containing phosphoric acid (80 9/l) and sulfuric acid (10 9/1) for 2 minutos. Aftor rinsing the aluminum was treatod under alternatin~ current conditionJ
in a bath containing ni~kel sulfato, 6H2o (28 9/l)~ ammoniu0 citrato (20 9/l) and boric aoid (20 9/l) at pH 5.0 for the timo and under the current donsity conditions described below in order to obtain aluminum with various colours. The counter-olectrodos wore graphito.
Current Den~ity Timo Colour 1) 0.13 A~d~a(15 V) 30 sec. ~old
2) 0.13 A~d~ (15 V) 1 min. 30 ~ec. blue
3) 0.25 A/dma(17 V) 4 min. bronze
4) 0.3 A~dm2(17.5 V) 6 min. bronze
5) 0.3 A/dm (lô V) 12 min. black After ~asbing~ the colour anodised aluminum was subjoctod to a conYentional sealing treatment.
` EXA~E 2 l(H~V3 7~
Aluminum, anodized in sulfuric acid as in Example 1, was subjected to further anodizing treatment in an electro-lytic bath containing phosphoric acid (100 g/l) and sulfa~ic ~
5 acid (50 ~l) at 25 volts D.C. for 3 minutes. After rinsing, the aluminum was treated under alternating current co~ditions in an electrolyte containin~ cobalt sulfate (25 g/l), tin (II) sulfate (4 g/l), ammonium tartarate (20 ~l) and boric acid ~20 g~l) at pH 7.5 for the time and under the current density `
conditions described below. ~he counter-electrodes were stainless steel sheets.
Current Densit~ ime Colour `
1) 0.11 A/dm2 (15 V)45 sec. -blue 2) 0.18 A/dm2 (16 V)4 mi~. light bronze 3) 0.23 A/dm2 (16.5 V) 5 min. dark brow~
4) 0.28 A/dm2 (17 V)10 min. blac~
` After washing the colour anodized aluminum was subjected ` to a conventional sealing treatment.
I;E
Aluminum, anodized in sulfuric acid as in Exa~ple 1, was subjected to further anodizing treatment i~ an electro-lytic bath containin~ pyrophosphoric acid ~120 g/l)j and ~ . ~
i~ oxalic acid (20 ~l) fox 3 minutes. After washing, said aluminum was treated with an alternatin~ current in an electro-lyte containin~ nickel sulfate (25 g/l), sulfosalicylic acid (2~ ~1) and a~monium sulfate (10 ~/l) at p~ 7.5 for the time and un~er the current density conditions described below.
.
-~ lO~ 7~
~he counter-electrodes were spaced nickel rod~.
~ ~ime Colour 1) 0.13 A/dm2 (15 V) 20 sec. gold 2) 0.2 A/dm2 (15 V) 1 min. 15 sec. greyish blue 3) 0.28 A/dm2 (17.5 V) 4 min. - bronze 4) 0.~2 A/dm2 (18 V) 12 min. black After washing, the colour anodized aluminum was ~ub~ected to a conventional sealing treatment.
~ s described in detail in the foregoing sections and in examples, anodized films formed on the surface of aluminum in a sulfuric acid bath were improved further in their character for deposition of particles in electrocolouring by the treatment with phosphoric acid. Aluminum with blue and greyish blue colours (which cannot be obtained by the conventional method) and also light bronze to black can be obtained from the ~ame (i.e. single) electrolytic bath.
Other baths that may be employed for performing the colourin~ stage may contain nickel sulfate and tin (II) sulfate in relative proportions of about 2:1, together with tartaric acid in an amount of 15-30 g/l. Optionally the bath ma~ contain an ammonium salt, such as a~monium sulfate, and in some instances it may be desirable to add a magnesium salt, particularly magnesium sulfate.
` EXA~E 2 l(H~V3 7~
Aluminum, anodized in sulfuric acid as in Example 1, was subjected to further anodizing treatment in an electro-lytic bath containing phosphoric acid (100 g/l) and sulfa~ic ~
5 acid (50 ~l) at 25 volts D.C. for 3 minutes. After rinsing, the aluminum was treated under alternating current co~ditions in an electrolyte containin~ cobalt sulfate (25 g/l), tin (II) sulfate (4 g/l), ammonium tartarate (20 ~l) and boric acid ~20 g~l) at pH 7.5 for the time and under the current density `
conditions described below. ~he counter-electrodes were stainless steel sheets.
Current Densit~ ime Colour `
1) 0.11 A/dm2 (15 V)45 sec. -blue 2) 0.18 A/dm2 (16 V)4 mi~. light bronze 3) 0.23 A/dm2 (16.5 V) 5 min. dark brow~
4) 0.28 A/dm2 (17 V)10 min. blac~
` After washing the colour anodized aluminum was subjected ` to a conventional sealing treatment.
I;E
Aluminum, anodized in sulfuric acid as in Exa~ple 1, was subjected to further anodizing treatment i~ an electro-lytic bath containin~ pyrophosphoric acid ~120 g/l)j and ~ . ~
i~ oxalic acid (20 ~l) fox 3 minutes. After washing, said aluminum was treated with an alternatin~ current in an electro-lyte containin~ nickel sulfate (25 g/l), sulfosalicylic acid (2~ ~1) and a~monium sulfate (10 ~/l) at p~ 7.5 for the time and un~er the current density conditions described below.
.
-~ lO~ 7~
~he counter-electrodes were spaced nickel rod~.
~ ~ime Colour 1) 0.13 A/dm2 (15 V) 20 sec. gold 2) 0.2 A/dm2 (15 V) 1 min. 15 sec. greyish blue 3) 0.28 A/dm2 (17.5 V) 4 min. - bronze 4) 0.~2 A/dm2 (18 V) 12 min. black After washing, the colour anodized aluminum was ~ub~ected to a conventional sealing treatment.
~ s described in detail in the foregoing sections and in examples, anodized films formed on the surface of aluminum in a sulfuric acid bath were improved further in their character for deposition of particles in electrocolouring by the treatment with phosphoric acid. Aluminum with blue and greyish blue colours (which cannot be obtained by the conventional method) and also light bronze to black can be obtained from the ~ame (i.e. single) electrolytic bath.
Other baths that may be employed for performing the colourin~ stage may contain nickel sulfate and tin (II) sulfate in relative proportions of about 2:1, together with tartaric acid in an amount of 15-30 g/l. Optionally the bath ma~ contain an ammonium salt, such as a~monium sulfate, and in some instances it may be desirable to add a magnesium salt, particularly magnesium sulfate.
Claims (6)
1. A process for the production of a coloured anodised aluminum article which comprises forming a porous anodic oxide film of at least 1 micron thickness on aluminum by direct current anodising in a sulfuric acid-based electro-lyte, continuing the anodisation of the anodised aluminum under direct current conditions in a phosphoric acid-based electrolyte and finally subjecting the anodised aluminum to passage of alternating current between itself and a counter-electrode while immersed in a bath containing a salt of at least one metal selected from the group comprising nickel, cobalt and tin.
2. A process as claimed in claim 1 in which the phosphoric acid-based electrolyte contains 50-150 gms/litre phosphoric acid.
3. A process as claimed in claim 1 comprising subject-ing the anodised aluminum to alternating current for a period of 20 secs. to 12 minutes.
4. A process as claimed in claim 2 in which the phosphoric acid-based electrolyte contains at least one additional acid selected from the group comprising oxalic acid, chromic acid, sulfosalicylic acid, sulfamic acid, tartaric acid, citric acid, gluconic acid and sulfuric acid.
5. A process as claimed in claim 2 comprising subjecting the sulfuric acid-anodised aluminum to direct current treatment in the phosphoric acid-based electrolyte at a voltage of 20-50 volts.
6. A process as claimed in claim 5 further comprising maintaining the phosphoric acid-based electrolyte at a temperature in the range of 20-35°C.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
CA251,112A CA1060376A (en) | 1976-04-27 | 1976-04-27 | Electrolytic colouring of anodised aluminum |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
CA251,112A CA1060376A (en) | 1976-04-27 | 1976-04-27 | Electrolytic colouring of anodised aluminum |
Publications (1)
Publication Number | Publication Date |
---|---|
CA1060376A true CA1060376A (en) | 1979-08-14 |
Family
ID=4105790
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
CA251,112A Expired CA1060376A (en) | 1976-04-27 | 1976-04-27 | Electrolytic colouring of anodised aluminum |
Country Status (1)
Country | Link |
---|---|
CA (1) | CA1060376A (en) |
-
1976
- 1976-04-27 CA CA251,112A patent/CA1060376A/en not_active Expired
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