US2899368A - Methods of sealing anodic aluminium - Google Patents
Methods of sealing anodic aluminium Download PDFInfo
- Publication number
- US2899368A US2899368A US2899368DA US2899368A US 2899368 A US2899368 A US 2899368A US 2899368D A US2899368D A US 2899368DA US 2899368 A US2899368 A US 2899368A
- Authority
- US
- United States
- Prior art keywords
- sealing
- aluminium
- bath
- solution
- methods
- 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.)
- Expired - Lifetime
Links
- 238000007789 sealing Methods 0.000 title claims description 40
- 239000004411 aluminium Substances 0.000 title claims description 16
- 229910052782 aluminium Inorganic materials 0.000 title claims description 16
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminum Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 title claims description 16
- PNEYBMLMFCGWSK-UHFFFAOYSA-N al2o3 Chemical compound [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 claims description 48
- 239000000243 solution Substances 0.000 claims description 26
- TVXXNOYZHKPKGW-UHFFFAOYSA-N Sodium molybdate Chemical compound [Na+].[Na+].[O-][Mo]([O-])(=O)=O TVXXNOYZHKPKGW-UHFFFAOYSA-N 0.000 claims description 18
- 239000011684 sodium molybdate Substances 0.000 claims description 18
- 235000015393 sodium molybdate Nutrition 0.000 claims description 18
- 229910001884 aluminium oxide Inorganic materials 0.000 claims description 16
- QGAVSDVURUSLQK-UHFFFAOYSA-N Ammonium heptamolybdate Chemical compound N.N.N.N.N.N.O.O.O.O.O.O.O.O.O.O.O.O.O.O.O.O.O.O.O.O.O.O.O.O.[Mo].[Mo].[Mo].[Mo].[Mo].[Mo].[Mo] QGAVSDVURUSLQK-UHFFFAOYSA-N 0.000 claims description 6
- 239000000956 alloy Substances 0.000 claims description 6
- 229910045601 alloy Inorganic materials 0.000 claims description 6
- NUYGZETUIUXJCO-UHFFFAOYSA-N dipotassium;dioxido(dioxo)molybdenum Chemical compound [K+].[K+].[O-][Mo]([O-])(=O)=O NUYGZETUIUXJCO-UHFFFAOYSA-N 0.000 claims description 6
- 239000007864 aqueous solution Substances 0.000 claims description 4
- 239000011248 coating agent Substances 0.000 description 22
- 238000000576 coating method Methods 0.000 description 22
- 229910052751 metal Inorganic materials 0.000 description 18
- 239000002184 metal Substances 0.000 description 18
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 10
- KMUONIBRACKNSN-UHFFFAOYSA-N Potassium dichromate Chemical compound [K+].[K+].[O-][Cr](=O)(=O)O[Cr]([O-])(=O)=O KMUONIBRACKNSN-UHFFFAOYSA-N 0.000 description 8
- 238000009835 boiling Methods 0.000 description 8
- VLAPMBHFAWRUQP-UHFFFAOYSA-L Molybdic acid Chemical compound O[Mo](O)(=O)=O VLAPMBHFAWRUQP-UHFFFAOYSA-L 0.000 description 6
- 238000005260 corrosion Methods 0.000 description 6
- 150000003839 salts Chemical class 0.000 description 6
- 239000011780 sodium chloride Substances 0.000 description 6
- HEMHJVSKTPXQMS-UHFFFAOYSA-M sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 6
- 229910015621 MoO Inorganic materials 0.000 description 4
- 240000007817 Olea europaea Species 0.000 description 4
- 229940069002 Potassium Dichromate Drugs 0.000 description 4
- 229910052783 alkali metal Inorganic materials 0.000 description 4
- 239000002585 base Substances 0.000 description 4
- 238000007654 immersion Methods 0.000 description 4
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 2
- -1 alkali metal molybdate Chemical class 0.000 description 2
- 150000001340 alkali metals Chemical class 0.000 description 2
- 150000003863 ammonium salts Chemical class 0.000 description 2
- ZCDOYSPFYFSLEW-UHFFFAOYSA-N chromate(2-) Chemical compound [O-][Cr]([O-])(=O)=O ZCDOYSPFYFSLEW-UHFFFAOYSA-N 0.000 description 2
- 238000004040 coloring Methods 0.000 description 2
- 230000000052 comparative effect Effects 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 230000035515 penetration Effects 0.000 description 2
- 238000009877 rendering Methods 0.000 description 2
- 230000000717 retained Effects 0.000 description 2
- 239000000565 sealant Substances 0.000 description 2
- 239000007921 spray Substances 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- 239000001117 sulphuric acid Substances 0.000 description 2
- 235000011149 sulphuric acid Nutrition 0.000 description 2
- 230000004580 weight loss Effects 0.000 description 2
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
- C25D11/24—Chemical after-treatment
- C25D11/246—Chemical after-treatment for sealing layers
Definitions
- the present invention relates to a method of sealing anodic aluminium oxide coatings formed on aluminium or aluminium-base alloys.
- a very simple treatment which is satisfactory for most ordinary purposes is to immerse the coated metal in boiling water for a period of about 30 minutes. This treatment is not, however, sufiicient to seal the coating in an entirely satisfactory manner where the coated metal is later to be exposed to external atmospheric conditions.
- the preferred range of concentration of the salt in the sealing bath is 0.1-5 (preferably about 2%) held at a pH value between 5.8 and 8.0, preferably 6.5-7.0.
- the pH value of the bath may be adjusted to the desired value by adding molybdic acid or sodium hydroxide.
- K MoO solutions potassium molybdate
- sodium molybdate sodium molybdate is preferred by reason of its lower cost.
- ammonium paramolybdate may also be employed with satisfactory results.
- mixtures of two or more of these salts may be employed in the sealing bath. Again for commercial reasons a bath containing 2% sodium molybdate is preferred to a stronger bath, since it gives equally good results.
- the coated metal to be sealed is preferably immersed in the bath for 5-30 minutes whilst the temperature of the bath is held approximately at boiling point; the necessary time for sealing will increase with the depth of the anodic coating.
- a method of sealing anodically formed aluminium oxide coatings comprises immersing the metal on which the coating is formed in a bath containing a solution of an alkali metal or ammonium salt of molybdic acid held at a temperature above 90 C.
- a method of sealing anodically formed aluminium oxide coatings on a metal selected from the group consisting of aluminium and aluminium-base alloys comprising immersing the coated metal in a bath containing an aqueous solution of at least one of the group consisting of sodium molybdate, potassium molybdate and ammonium paramolybdate, the said solution being held at a pH value within the range 5.8-8.0 and a temperature above C.
Description
METHODS OF SEALING ANODIC ALUMINIUM OXIDE COATINGS Roy C. Sp'ooner, Kingston, Ontario, Canada, assignor to Aluminium Laboratories Limited, Montreal, Quebec, Canada, a corporation of Canada No Drawing. Application July 29, 1957 Serial No. 674,562
Claims priority, application Great Britain July 30, 1956 Claims. (Cl. 204-35) The present invention relates to a method of sealing anodic aluminium oxide coatings formed on aluminium or aluminium-base alloys.
It is common practice to apply a sealing treatment to such anodic aluminium oxide coatings for the purpose of rendering the coating less porous and less permeable to penetration by substances which can corrode the underlying aluminium.
A very simple treatment which is satisfactory for most ordinary purposes is to immerse the coated metal in boiling water for a period of about 30 minutes. This treatment is not, however, sufiicient to seal the coating in an entirely satisfactory manner where the coated metal is later to be exposed to external atmospheric conditions. Where it is desired to render an anodic aluminium oxide coating particularly corrosion-resistant, it is already known to seal the coating by treatment in a solution containing chromates; for example, by immersion for 30 ice is due to the presence in the sealing bath of the molybdate ion M00 and this is said to be stable in solutions having a pH value of 6.5 and over, but it has been found in practice that satisfactory results are obtained with the pH value of the sealing bath held between 5.8 and 8.
Using sodium molybdate (N-a MoO :2H O), it is found that the preferred range of concentration of the salt in the sealing bath is 0.1-5 (preferably about 2%) held at a pH value between 5.8 and 8.0, preferably 6.5-7.0. The pH value of the bath may be adjusted to the desired value by adding molybdic acid or sodium hydroxide.
Similar results may be obtained using potassium molybdate (K MoO solutions, but sodium molybdate is preferred by reason of its lower cost. The commercially available ammonium paramolybdate may also be employed with satisfactory results. Also mixtures of two or more of these salts may be employed in the sealing bath. Again for commercial reasons a bath containing 2% sodium molybdate is preferred to a stronger bath, since it gives equally good results.
The coated metal to be sealed is preferably immersed in the bath for 5-30 minutes whilst the temperature of the bath is held approximately at boiling point; the necessary time for sealing will increase with the depth of the anodic coating.
The results of one comparative test carried out on aluminium panels all anodised under the same conditions and then sealed in sealing baths containing water alone, a 2% sodium molybdate solution and a 5% potassium dichromate solution, are given below.
Water sealing Sodium molybdate (2O g./1.) Potassiurggiclilrgimate Sealing time to an 30, Sealing em 98- 98-100 98-100. Sealant pH 6.1. 6.7.. Colour sealed panel Light grey Light grey Pronounced olive green. Weight loss during 6 hrs. immersion in 7Q 11 38.
cold sulphuric acid (mgJdmJ). Cathodic current value (ma/(1m 2 2 Intermittent acidified salt spray 110 days exposure.
1.4 2.1. Very slight pitting attack. Very slight pitting attack.
minutes in a 5% solution of potassium dichromate at 98-100 C.
This treatment greatly increases the corrosion and weathering resistances of the anodically coated metal, but unfortunately the treatment imparts an olive green shade to the anodic coating, which makes the metal thus treated less acceptable for purposes, such as curtain walling, than it would be if it retained the ordinary grey colour of Water-sealed anodised aluminium.
It is an object of the present invention to provide a new method of sealing an anodic aluminium oxide coating to render it appreciably more resistant to corrosion and weathering than could be achieved by a water sealing treatment, Whilst at the same time avoiding the undesirable colouring of the anodic coating which arises when the coating is sealed in a chromate solution.
According to the present invention a method of sealing anodically formed aluminium oxide coatings comprises immersing the metal on which the coating is formed in a bath containing a solution of an alkali metal or ammonium salt of molybdic acid held at a temperature above 90 C.
The sealing treatment of anodic coatings with an alkali metal molybdate leaves the coatings with a final light grey colour similar to that achieved when an anodic coating is sealed in boiling water.
It is believed that the improved effectiveness of sealing I claim:
1. A method of sealing anodically formed aluminium oxide coatings on a metal selected from the group consisting of aluminium and aluminium-base alloys comprising immersing the coated metal in a bath containing an aqueous solution of at least one of the group consisting of sodium molybdate, potassium molybdate and ammonium paramolybdate, the said solution being held at a pH value within the range 5.8-8.0 and a temperature above C.
2. The method of claim 1, wherein the pH value is held within the range '6.5-7.0.
3. The method of claim 1, wherein the bath solution contains 0.1-5% sodium molybdate.
4. The method of claim 3, wherein the bath solution contains about 2% sodium molybdate.
5. The method of claim 1, wherein the bath solution is held substantially at boiling point and the coated metal is immersed therein for 5-30 minutes.
References Cited in the file of this patent UNITED STATES PATENTS 2,313,755 Loose Mar. 16, 1943 2,448,513 Brennan Sept. 7, 1948 2,574,225 Ringk et a1. Nov. 6, 1951 2,723,952 Evangelides Nov. 15, 1955
Claims (1)
1. A METHOD OF SEALING ANODICALLY FORMED ALUMINIUM OXIDE COATINGS ON A METAL SELECTED FROM THE GROUP CONSISTING OF ALUMINIUM AND ALUMINIUM-BASE ALLOYS COMPRISING IMMERSING THE COATED METAL IN A BATH CONTAINING AN AQUEOUS SOLUTION OF AT LEAST ONE OF THE GROUP CONSISTING OF SODIUM MOLYBDATE, POTASSIUM MOLYBDATE AND AMMONIUM PARAMOLYBDATE, THE SAID SOLUTION BEING HELD AT A PH VALUE WITHIN THE RANGE 5.8-8.0 AND A TEMPERATURE ABOVE 90*C.
Publications (1)
| Publication Number | Publication Date |
|---|---|
| US2899368A true US2899368A (en) | 1959-08-11 |
Family
ID=3448168
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| US2899368D Expired - Lifetime US2899368A (en) | Methods of sealing anodic aluminium |
Country Status (1)
| Country | Link |
|---|---|
| US (1) | US2899368A (en) |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3272665A (en) * | 1963-04-24 | 1966-09-13 | Reynolds Metals Co | Molybdate coatings on aluminum and aluminum base alloys |
| US3275441A (en) * | 1963-03-07 | 1966-09-27 | Technilith Inc | Printing plate and method of making same |
| US4230539A (en) * | 1979-07-09 | 1980-10-28 | Fujikura Cable Works, Ltd. | Method for surface treatment of anodic oxide film |
| US4504325A (en) * | 1982-03-19 | 1985-03-12 | The Boeing Company | Method for sealing an aluminum oxide film |
Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2313755A (en) * | 1938-12-02 | 1943-03-16 | Dow Chemical Co | Method of producing protective coatings upon magnesium and its alloys |
| US2448513A (en) * | 1942-11-26 | 1948-09-07 | Brennan | Electrostatic condenser plate |
| US2574225A (en) * | 1948-07-28 | 1951-11-06 | Benzol Products Company | Process for rendering metal surfaces antiseptic and products therefrom |
| US2723952A (en) * | 1952-11-03 | 1955-11-15 | Harry A Evangelides | Method of electrolytically coating magnesium and electrolyte therefor |
-
0
- US US2899368D patent/US2899368A/en not_active Expired - Lifetime
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2313755A (en) * | 1938-12-02 | 1943-03-16 | Dow Chemical Co | Method of producing protective coatings upon magnesium and its alloys |
| US2448513A (en) * | 1942-11-26 | 1948-09-07 | Brennan | Electrostatic condenser plate |
| US2574225A (en) * | 1948-07-28 | 1951-11-06 | Benzol Products Company | Process for rendering metal surfaces antiseptic and products therefrom |
| US2723952A (en) * | 1952-11-03 | 1955-11-15 | Harry A Evangelides | Method of electrolytically coating magnesium and electrolyte therefor |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3275441A (en) * | 1963-03-07 | 1966-09-27 | Technilith Inc | Printing plate and method of making same |
| US3272665A (en) * | 1963-04-24 | 1966-09-13 | Reynolds Metals Co | Molybdate coatings on aluminum and aluminum base alloys |
| US4230539A (en) * | 1979-07-09 | 1980-10-28 | Fujikura Cable Works, Ltd. | Method for surface treatment of anodic oxide film |
| US4504325A (en) * | 1982-03-19 | 1985-03-12 | The Boeing Company | Method for sealing an aluminum oxide film |
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