US2040617A - Method of producing bright surfaces on aluminum - Google Patents
Method of producing bright surfaces on aluminum Download PDFInfo
- Publication number
- US2040617A US2040617A US710722A US71072234A US2040617A US 2040617 A US2040617 A US 2040617A US 710722 A US710722 A US 710722A US 71072234 A US71072234 A US 71072234A US 2040617 A US2040617 A US 2040617A
- Authority
- US
- United States
- Prior art keywords
- aluminum
- per cent
- electrolyte
- producing
- hydrofluoric acid
- 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
Classifications
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25F—PROCESSES FOR THE ELECTROLYTIC REMOVAL OF MATERIALS FROM OBJECTS; APPARATUS THEREFOR
- C25F3/00—Electrolytic etching or polishing
- C25F3/16—Polishing
- C25F3/18—Polishing of light metals
- C25F3/20—Polishing of light metals of aluminium
-
- 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
- C25D11/08—Anodisation of aluminium or alloys based thereon characterised by the electrolytes used containing inorganic acids
Definitions
- This invention relates to bright aluminum surfaces, and it is particularly concerned with a method for the treatment of aluminum articles to produce thereon permanent bright surfaces of high reflectivity.
- Bright aluminum surfaces have found extensive application for decorative purposes, and particularly for the reflection of radiant energy of various sorts, such as for light reflection. These bright aluminum surfaces may be produced either by etching for the production of diffusely reflecting surfaces, or by mechanical bufling or polishing to produce specular surfaces. This invention is concerned primarily with a method of increasing and preserving the brightness of such aluminum surfaces, and particularly their light reflecting power.
- the normal oxidizing action of such electrolytes upon aluminum made anodetherein may be modifled to produce a combined brightening and coating action, and that'by anodically treating an aluminum article in an electrolyte containing 5 chromic acid and hydrofluoric acid such impurities and foreign matter as may be present on the aluminum surface may be removed and a thin, substantially transparent and colorless protective film simultaneously produced on the surface. 10
- anodically treating an aluminum article in an electrolyte containing 5 chromic acid and hydrofluoric acid such impurities and foreign matter as may be present on the aluminum surface may be removed and a thin, substantially transparent and colorless protective film simultaneously produced on the surface. 10
- a more durable reflecting surface generally having an increased reflection factor.
- the bright coated aluminum reflecting surface so obtained may be further treated to increase its durability by anodic 15 oxidation without seriously impairing its reflection factor.
- Other forms of protective coatings such as clear lacquer or varnish coatings, may also be applied to the bright, durable reflecting surface by the method of
- hydrofluoric acid modifies the normal electrochemical action of the chromic acid solution on the aluminum surface by decreasing its oxide coatforming properties and imparting to the electrolyte the properties of removing impurities present in and on the aluminum surface. This property of removing impurities is apparently due to an increase in the solvent action of the electro-- lyte.
- the minimum effective amount of hydrofluoric acid necessary to impart to the chromic acid electrolytes the desired properties varies somewhat. Very small amounts of hydrofluoric acid 50 in the chromic acid solution will impart the desired properties in some degree. In general, however, it is considered desirable to have present in the electrolyte not less than about 0.2 per cent of HF by weight. With increased amount of hydrofluoric acid present, the possibility of direct chemical attack on the aluminum surface by the electrolyte is increased, and it is necessary to increase the current density of the applied electric current to prevent this direct chemical attack which tends to produce irregularities in the reflecting surface.
- the temperature of the electrolyte be somewhat above room temperature, and temperatures between about 30 and 70 have proved most satisfactory. With operation of the bath at these temperatures, satisfactory results are generally obtained by a treatment of 5 to 30 minutes. In most cases it is preferred to treat at a temperature of 50 C. for about 10 minutes.
- the current density used will vary with the exact composition of the electrolyte and the temperature of operation.
- the current density should be suflicient to prevent any direct chemical attack of the electrolyte on the aluminum surface, and this current density should not be substantially exceeded.
- the modifying effect of the hydrofluoric acid on the oxide coat-forming properties of the chromic acid islessened.
- higher current densities are required for operation at the higher temperatures.
- direct current with electrolytes containing 1 per cent to 25 per cent chromic acid and 0.2 per cent to 1.5 per cent hydrofluoric acid at temperatures of about 30 to 70 0., satisfactory results are obtainable with current densities in the range of about 20 to 140 amperes per square foot of anode surface. With the lower current densities it is generally desirable to increase the time of treatment.
- preliminarily treat the aluminum surface Prior to the treatment of an aluminum reflecting surface according to this invention it is sometimes desirable, in order to obtain the best results, to preliminarily treat the aluminum surface to remove superficial grease and dirt such as may be present thereon as the result of a previous polishing operation. Any convenient method of preliminary cleaning may be employed, preferably by washing the surface with a solvent which does not objectionably attack the metal and which does not require such rubbing of a polished surface as may tend to injure its appearance.
- the reflecting surface may be anodically' oxidized to form thereon a comparatively dense oxide coating which is substantially transparent.
- oxide coating as used herein and in the appended claims is meant such coatings concurrently so designated in the art which consist in substantial part of aluminum oxide. It is desirable that the oxide coatings produced be substantially colorless, clear and transparent, in order that the reflectivity of the brightened aluminum surface will be reduced as little as possible. While any electrolyte capable of producing such coatings may be used, it has been found. that sulfuric acid and oxalic acid solutions are particularly suitable i'or this purpose.
- the amount of reduction in face may be subjected to treatment in water at to C. to make the coating impervious.
- a very light polishing operation with a mildly abrasive material such as magnesia, silver polish or a mildly abrasive soap powder, may be desirable to remove any superficial deposit which may have been formed on the oxide-coated reflecting surface by reason of any of the previous operations.
- An aluminum article having a high purity aluminum surface was buffed to produce a specular reflecting surface which had a reflection factor of 74.9 per cent.
- the article was then made the anode in an electrolytic cell containing an electrolyte formed by the addition of 1.0 per cent of hydrofluoric acid containing 48.0 per cent HF to a solution of chromic acid containing 10.0 per cent by weight of CXOs.
- a direct current at a current density of about 46 to 52 amperes per square foot was employed at a potential of about 16 to 22 volts for 10 minutes, the electrolyte being maintained at a temperature of about 49 to 58 C.
- the reflecting surface, after this treatment, had a reflection factor of 87.2 per cent.
- the article was then anodically oxidized in a 7.0 per cent sulfuric acid solution at a temperature of about 25 (3., using a current density of about 12.0 amperes per square foot and a potential of 20 to 22 volts for 10 minutes.
- the oxide-coated reflecting surface thus obtained was treated with pure boiling water for about 10 minutes and was polished with a mildly abrasive soap powder.
- the reflection factor of the protected reflecting surface thus obtained was about 85.3 per cent.
- the article could be handled without permanent marking and staining and could be readily washed or wiped without deterioration of its reflecting power.
- aluminum alloy reflecting surfaces when treated according to the invention in chromic acid-hydrofluoric acid electrolytes and subsequently anodically oxidized, do not have as high reflection factors as are obtainable by the same treatment on a high purity aluminum surface.
- the method herein described is applicable to many aluminum base alloys with advantage, and the term aluminum as used throughout this specification is to be understood to include both aluminum and aluminum base alloys.
- a method of brightening aluminum surfaces and simultaneously producing thereon a transparent, colorless fllm comprising removing impurities and dirt from said surface by treating said surface anodically in an electrolyte containing chromic acid and hydrofluoric acid.
- a method of brightening aluminum surfaces and simultaneously producing thereon a transparent, colorless film comprising removing impurities and dirt from said surface by treating said surface anodically in an electrolyte containing 1.0 to 25.0 per cent by weight of CrOa and 0.2 to 1.5 per cent by weight of HF.
- a method of producing an aluminum article having a durable, bright surface comprising anodically treating the aluminum article in an electrolyte containing chromic acid and hydrofluoric acid, and thereafter producing on said surface a clear, transparent, impermeable coating.
- a method of producing an aluminum article having a durable, bright surface comprising anodically treating the aluminum article in an electrolyte containing chromic acid and hydrofluoric acid, and thereafter producing on said surface, by anodic oxidation, a clear, transparent coating consisting substantially of aluminum oxide.
- a method of producing an aluminum article having a durable, bright surface comprising anodically treating the aluminum article in an electrolyte containing chromic acid and hydrofluoric acid, and thereafter producing on said surface, by anodic oxidation, a clear, transparent coating consisting substantially of .aluminum oxide and impermeabilizing the oxide-coated surface by treating with hot water.
- a method of producing a specular, highly reflecting surface on aluminum comprising removing impurities and dirt from a polished aluminum reflecting surface by treating said surface anodically in a solution of chromic acid and hydrofluoric acid at a current density sufflcient to substantially prevent direct chemical attack of the electrolyte on the aluminum surface.
- a method of producing a durable, specular, reflecting surface on aluminum comprising treating a polished aluminum reflecting surface anodically in a solution of chromic acid and hydrofluoric acid, and thereafter anodically oxidizing the clean bright surface obtained.
- a method of producing a durable, specular, reflecting surface on aluminum comprising treating a polished aluminum reflecting surface anodically in a solution of chromic acid and hydrofluoric acid, and thereafter anodically oxidizing the clean bright surface obtained and treating the mode-coated surface with water at to C.
- a method of producing an aluminum article having a durable, bright surface comprising anodically treating the aluminum article in an electrolyte containing 1.0 to 25.0 per cent by weight of CrO: and 0.2 to 1.5 per cent by weight of HF, and thereafter producing on said surface a clear, transparent, impermeable coating.
- a method of producing an aluminum article having a durable, bright surface comprising anodically treating the aluminum article in an electrolyte containing 1.0 to 25.0 per cent by weight of CrO: and 0.2 to 1.5 per cent by weight of HF, and thereafter producing on said surface. by anodic oxidation, a clear, transparent coating consisting substantially of aluminum oxide.
- a method of producing an aluminum article having a durable, bright surface comprising anodically treating the aluminum article in an electrolyte containing 1.0 to 25.0 per cent by weight of CrOa and 0.2 to 1.5 per cent by weight
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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)
- Inorganic Chemistry (AREA)
- Chemical Treatment Of Metals (AREA)
- Application Of Or Painting With Fluid Materials (AREA)
- Laminated Bodies (AREA)
Priority Applications (7)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
NL42124D NL42124C (de) | 1934-02-10 | ||
BE407433D BE407433A (de) | 1934-02-10 | ||
NL41932D NL41932C (de) | 1934-02-10 | ||
US710722A US2040617A (en) | 1934-02-10 | 1934-02-10 | Method of producing bright surfaces on aluminum |
GB10340/34A GB436481A (en) | 1934-02-10 | 1934-04-05 | Improvements in or relating to the production of bright aluminium surfaces |
FR778019D FR778019A (fr) | 1934-02-10 | 1934-05-25 | Perfectionnements à la fabrication de surfaces brillantes d'aluminium |
DEA75161D DE635322C (de) | 1934-02-10 | 1935-01-29 | Verfahren zur Erhoehung der Reflexion glaenzender Aluminiumoberflaechen |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US710722A US2040617A (en) | 1934-02-10 | 1934-02-10 | Method of producing bright surfaces on aluminum |
Publications (1)
Publication Number | Publication Date |
---|---|
US2040617A true US2040617A (en) | 1936-05-12 |
Family
ID=24855239
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US710722A Expired - Lifetime US2040617A (en) | 1934-02-10 | 1934-02-10 | Method of producing bright surfaces on aluminum |
Country Status (6)
Country | Link |
---|---|
US (1) | US2040617A (de) |
BE (1) | BE407433A (de) |
DE (1) | DE635322C (de) |
FR (1) | FR778019A (de) |
GB (1) | GB436481A (de) |
NL (2) | NL42124C (de) |
Cited By (7)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US2550544A (en) * | 1947-11-14 | 1951-04-24 | Battelle Development Corp | Method of anodically polishing aluminum |
US2682503A (en) * | 1950-07-19 | 1954-06-29 | Kaiser Aluminium Chem Corp | Method and material for electrolytically brightening aluminum surfaces |
US2682502A (en) * | 1950-07-19 | 1954-06-29 | Kaiser Aluminium Chem Corp | Method and material for electrolytically brightening aluminum surfaces |
US3372008A (en) * | 1961-05-29 | 1968-03-05 | Philips Corp | Metal reflector and method of manufacturing such reflectors |
US3400057A (en) * | 1964-06-03 | 1968-09-03 | Reynolds Metals Co | Alloy and finishing system |
US3494839A (en) * | 1967-01-23 | 1970-02-10 | Amchem Prod | Method of sealing chromic acid anodized aluminum surfaces |
US5009756A (en) * | 1989-05-26 | 1991-04-23 | Gebr. Happich Gmbh | Chemical method of avoiding a rainbow effect caused by the layer of oxide produced upon the brightening of parts of aluminum or aluminum alloys |
-
0
- NL NL41932D patent/NL41932C/xx active
- BE BE407433D patent/BE407433A/xx unknown
- NL NL42124D patent/NL42124C/xx active
-
1934
- 1934-02-10 US US710722A patent/US2040617A/en not_active Expired - Lifetime
- 1934-04-05 GB GB10340/34A patent/GB436481A/en not_active Expired
- 1934-05-25 FR FR778019D patent/FR778019A/fr not_active Expired
-
1935
- 1935-01-29 DE DEA75161D patent/DE635322C/de not_active Expired
Cited By (7)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US2550544A (en) * | 1947-11-14 | 1951-04-24 | Battelle Development Corp | Method of anodically polishing aluminum |
US2682503A (en) * | 1950-07-19 | 1954-06-29 | Kaiser Aluminium Chem Corp | Method and material for electrolytically brightening aluminum surfaces |
US2682502A (en) * | 1950-07-19 | 1954-06-29 | Kaiser Aluminium Chem Corp | Method and material for electrolytically brightening aluminum surfaces |
US3372008A (en) * | 1961-05-29 | 1968-03-05 | Philips Corp | Metal reflector and method of manufacturing such reflectors |
US3400057A (en) * | 1964-06-03 | 1968-09-03 | Reynolds Metals Co | Alloy and finishing system |
US3494839A (en) * | 1967-01-23 | 1970-02-10 | Amchem Prod | Method of sealing chromic acid anodized aluminum surfaces |
US5009756A (en) * | 1989-05-26 | 1991-04-23 | Gebr. Happich Gmbh | Chemical method of avoiding a rainbow effect caused by the layer of oxide produced upon the brightening of parts of aluminum or aluminum alloys |
Also Published As
Publication number | Publication date |
---|---|
DE635322C (de) | 1936-09-17 |
GB436481A (en) | 1935-10-07 |
FR778019A (fr) | 1935-03-07 |
BE407433A (de) | |
NL42124C (de) | |
NL41932C (de) |
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