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

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 kinds such as visible light. These bright aluminum surfaces may be produced either by etching for the production of diffusely reflecting surfaces or by mechanical bufflng 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.
• hydrofluoric acid modifies the normal electrochemical action of the sulfuric acid on the aluminum surface by decreasing its oxide coatforming properties and imparting to the electrolyte the property of removing impurities present of removing impurities is apparently due to an increase in the solvent action of the electrolyte.
• This solvent action is, however, so uniform under the influence of the applied electric current that even when a polished specular aluminum reflecting surface is treated, according to the invention, as anode in a sulfuric acid electrolyte containing a small amount of hydrofluoric acid, the surface is cleaned and brightened with an increase in the reflection factor depending upon the amount of impurities and dirt removed from the surface, and at the same time the specular characteristics of the surface are not materially modified.
• Hydrofluosilicic acid and other fluorine compounds which yield hydrofluoric acid when in solution with sulfuric acid such as the fluoride salts, may be substituted for hydrofluoric acid in equivalent amounts for the purposes of this invention;
• the minimum effective amount of hydrofluoric acid necessary to impart to the sulfuric acid electrolytes the desired properties varies somewhat. Very small amounts of hydrofluoric acid in the in some degree. In general, however, it is considered desirable to have present in the electrolyte not less than 0.2 per cent of HF by weight. With increased amounts 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.
• electrolytes containing about 5 to 35 per cent sulfuric acid it is generally not desirable however, to use electrolytes containing about 5 to 35 per cent sulfuric acid, and very good results are obtainable with electrolytes containing 25 per cent by weight sulfuric acid.
• the temperature of the electrolyte be somewhat above room temperature
• This electrolytic brightening treatment may be carried out either with direct or alternating current.
• the current density used will vary with the exact composition of the electrolyte and the temperature of operation. The current density should be sufficient to prevent any direct chemical attack of the electrolyte on the aluminum surface and this current density should not be substantially exceeded. With greater current densities the modifying effect of the hydrofluoric acid on the oxide coat-forming properties of the sulfuric acid is lessened. In general higher current densities are required for operation at the higher temperatures. When using direct current with electrolytes containing 1 to per cent sulfuric acid and 0.2 to 1.5 per cent hydrofluoric acid at temperatures of about 30 to 70 C., satisfactory results are obtainable with current densities in the range of about 10 to 100 amperes per square foot of anode surface. When using alternating current, somewhat higher current densities are used than are required with direct current for corresponding electrolytes at corresponding temperatures.
• 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 dirt and grease such as may be present thereon as a 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 reflecting 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 for this purpose. The amount .of reduction in reflectivity caused by oxide coatticularly when the step of treating in hot water.
• a very light polishing 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.
• An aluminum article having a high purity aluminum surface was buffed to produce a specular reflecting surface which had a reflection factor of 75.5 per cent.
• the article was then made the anode in an electrolytic cell containing an electrolyte formed by the addition of 2 per cent of commercial hydrofluoric acid containing 48 per cent HF to a solution of sulfuric acid containing 25 per cent by weight H2304.
• a direct current, at a current density of about 92 amperes per square foot was employed at a potential of about 8 volts for 10 minutes, the electrolyte being maintained at a temperature of about 60 C.
• the reflecting surface, after this treatment. had a reflection factor of 87.0 .per cent.
• the article was then anodically oxidized in a 12 per cent sulfuric acid solution at a temperature of 24 C., using a current density of about 12 amperes per square foot anda potential of 16 volts for about 10 minutes.
• the oxide-coated reflecting surface thus obtained wastreated 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 84.5 per cent.
• the article could be handled without permanent marking or staining and could be readily washed or wiped without depreciation of its reflecting power.
• Another similar article having a high purity buffed aluminum surface which had a reflection factor of 75.2 per cent was made an electrode in an electrolytic cell, the electrolyte of which was formed by the addition, of 2 per cent of commercial hydrofluoric acid, containing 48 per cent HF, to a 25 per cent solution of sulfuric acid.
• An alternating current having a current density of about 80 amperes per square foot was employed at a potential of about 10 volts for 20 minutes,
• aluminum alloy reflecting surfaces when treated according to the invention in sulfuric acid-hydrofluoric acid electrolyte 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 clear, transparent film comprising removing dirt and impurities from said surface by subjecting said surface to an electrolytic treatment in a solution containing 1 to 60 per cent sulfuric acid by weight and hydrofluoric acid.
• a method of brightening aluminum surfaces and simultaneously producing thereon a transparent film comprising removing dirt and impurities from said surface by treating said surface anodically in an electrolyte containing 1 to 60 per cent sulfuric acid by weight and hydrofluoric acid.
• a method of brightening aluminum surfaces and simultaneously producing thereon a clear, transparent film comprising removing dirt and impurities from said surface by subjecting said surface to an electrolytic treatment in an electrolyte containing 1 to 60 per cent by weight of sulfuric acid and 0.2 to 1.5 per cent by weight of BF.
• a method of brightening aluminum surfaces and simultaneously producing thereon a transparent film comprising removing dirt and impurities from said surface by treating said surface anodically in an electrolyte containing 1 to 60 per cent by weight of sulfuric acid 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 electrolytically treating the aluminum article in an electrolyte containing 1 to 60 per cent sulfuric acid by weight 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 electrolytically treating the aluminum in an electrolyte containing 1 to 60 per cent sulfuric acid by weight and hydrofluoric acid and thereafter producing on said surface, by anodic oxidation, 9.
• a method of producing an aluminum article having a durable, bright surface comprising ancdically treating the aluminum article in an electrolyte containing 1 to 60 per cent sulfuric acid and 0.2 to 1.5 per cent HF by weight and thereafter producing on said surface a clear, transparent, impermeable 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 to 60 per cent sulfuric acid by weight and hydrofluoric acid and thereafter producing on said surface, by anodic oxidation in sulfuric acid, a clear, transparent coating consisting substantially of aluminum oxide.
• a method of producing an aluminum article having a durable, bright surface comprising electrolytically treating the aluminum article in an electrolyte containing 1 to 60 per cent sulfuric acid by weight 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 an aluminum article having a durable, bright surface comprising electrolytically treating the aluminum article in an electrolyte containing 1 to 60 per cent sulfuric acid by weight and 0.2 to 1.5 per cent HF by weight, 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 water at to C.
• a method of producing a specular, highly reflecting surface on aluminum comprising removing dirt and impurities from a polished a1uminum reflecting surface by treating said surface electrolytically in a solution containing 1 to 60 per cent sulfuric acid by weight and 0.2 to 1.5 per cent HF by weight at a current density sufflcient to substantially prevent direct chemical attach of the electrolyte on the aluminum surface.
• a method of producing a durable, specular, reflecting surface on aluminum comprising removing dirt and impurities from a polished aluminum reflecting surface by treating said surface electrolytically in a solution containing 1 to 60 per cent sulfuric acid by weight and 0.2 to 1.5 per cent HF by weight at a current density sufficient to substantially prevent direct chemical attack of the electrolyte on the aluminum surface, and thereafter anodically oxidizing the clean, bright surface obtained.
• a method of producing a durable, specular, reflecting surface on aluminum comprising removing dirt and impurities from a polished aluminum reflecting surface by treating said surface electrolytically in asolution containing 1 to 60 per cent sulfuric acid by weight and 0.2 to 1.5 per cent HF by weight at a current density sufficient to substantially prevent direct chemical attack of the electrolyte on the aluminum surface, thereafter anodically oxidizing the clean, bright surface obtained, and treating the oxide-coated surfaces with water at 80 to 100 C.
• a method of producing an aluminum article having a durable, bright surface comprising electrolytically treating the aluminum article in an electrolyte containing 1 to 60 per cent sulfuric acid by weight and 0.2 to 1.5 per cent HF by weight, and thereafter producing on said surface a clear, transparent, impermeable coati 15.
• a method of producing an aluminum article having a durable, bright surface comprising electrolytically treating the aluminum article in an electrolyte containing 1 to 60 per cent sulfuric acid by weight and 0.2 to 1.5 per cent HF by weight, and thereafter producing on said surface, by anodic oxidation, a clear, transparent coating consisting substantially of aluminum oxide.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Application Of Or Painting With Fluid Materials (AREA)
• ing And Chemical Polishing (AREA)

Priority Applications (5)

Applications Claiming Priority (1)

Publications (1)

Family

ID=24855243

Family Applications (1)

Country Status (5)

Cited By (17)

• 0
  • BE BE407434D patent/BE407434A/xx unknown
• 1934
  • 1934-02-10 US US710723A patent/US2040618A/en not_active Expired - Lifetime
  • 1934-04-05 GB GB10341/34A patent/GB436154A/en not_active Expired
  • 1934-05-25 FR FR778018D patent/FR778018A/fr not_active Expired
• 1935
  • 1935-01-29 DE DEA75162D patent/DE646736C/de not_active Expired

Also Published As

Similar Documents