Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C22/82—After-treatment
  • C23C22/83—Chemical after-treatment
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C22/73—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals characterised by the process
• • 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
• • 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 invention relates to methods of treating oxide coatings, composed in substantial part of aluminum oxide, to alter or modify the properties and characteristics of the coatings. Particularly is the invention concerned with the treatment of oxide coatings formed on aluminum and aluminum base alloy surfaces, herein collectively referred to as aluminum surfaces.
• oxide coating By several known processes aluminum surfaces may be provided with What is generally termed an oxide coating. This coating is substantially composed of aluminum oxide. It may contain, because of the process used, other components which essentially alter its specific characteristics.
• Such oxide coatings have, as general properties, a good resistance to corrosion, a good resistance to abrasion, and an ability, in various degrees, to take organic dyes or inorganic colors to form a colored surface.
• the oxide coatings may be more or less permeable and adsorb or absorb moisture or liquids. Quite often, also, the coating forms an excellent insulation against the passage of electric current.
• the oxide coatings may be formed on aluminum surfaces by various methods.
• the aluminum may be made an anode in an electrolytic cell containing an electrolyte such as sulfuric acid, chromic acid, organic acids, acid salts, etc. When external electrical energy is impressed upon 39 the ce l an oxide coating is formed on this anode.
• the aluminum is immersed in a suitable solution, generally alkaline, and the oxide coating is formed by chemical reaction without the use of external electrical energy.
• the oxide-coated aluminum surface may then be immersed in organic dyes, or in solutions of dyes, to produce characteristic colors.
• the object of the present invention is to treat oxide coatings formed on aluminum surfaces to produce certain results, among which may be numbered: a decrease in the permeability of the oxide coating; a modification of the adsorptive 50 or absorptive capacity of the oxide coating for coloring agents; increase in corrosion resistance of the coating; increase of the ability of the colored oxide coating to retain color under the action of solvents.
• Another object of the inven- 55 tion is to treat colored oxide coatings after the coloring operation to uniformly fix said color in and on the coating.
• the invention is predicated upon the discovery that by the treatment of oxide-coated aluminum in hot or boiling solutions of certain salts the properties of the coating are considerably modified and new and advantageous properties are 15 developed.
• the solutions to which this invention refers are solutions containing a salt of a weak metallic base which salt is capable of hydrolyzing in solution to form a substantially insoluble compound of the metal in the oxide coat- 20 ing.
• the hydrogen ion concentration of the solution should be such that the hydrolysis in hot or boiling solution promotes precipitation of the metal compound and this condition is usually evidenced by the appearance of turbidity in 25 the solution.
• salts which will form such solutions are metallic acetates, such as nickel, cobalt, cadmium, zinc, barium, copper, aluminum or lead acetates, and metallic sulfates, oxalates, chlorides, nitrates, citrates, tartrates and fluorides, but there are other salts of similar chemical characteristics which will produce the desired results.
• the salt solution be one that does not materially attack or dissolve the oxide coating or the aluminum.
• Such preferred properties 01' the salt solution are, however, desirable only in certain applications of the invention, and the broad class of salt solutions herein defined are, per se, commercially useful.
• the solutions used in the practice of the invention are prepared by dissolving a salt of the class described in water and then, if necessary, adjusting the hydrogen ion concentration to the point where hydrolysis in hot or boiling solutions, i. e., in solutions heated above 40 centigrade, will promote precipitation in the oxide coating.
• the hydrolysis under these conditions, may be such that suspension of colloidal dimensions is formed in the solution and no precipitate is evident. But if, on heating, a precipitate is evident, the hydrogen ion concentration is so adjusted that a substantial amount of the metallic base is not precipitated in fiocculent form and does not settle from the solution. In solutions where, on hydrolysis, precipitation is evident, it is desirable that the hydrolys's does not substantially proceed past the point of turbidity.
• turbidity denotes not only a turbid but likewise an opalescent or cloudy solution. In the practice of my invention with preferred solutions such turbidity is customarily observed.
• the proper hydrogen ion concentration is readily predetermined by simple experiment, but it is preferred and usually advisable to use solutions having a hydrogen ion concentration, as measured at 25 centigrade, of between a pH of about 4.5 and a pH of about 7.5. When the solution has pH values widely variant from this range, the proper solution conditions are not usually obtained and, moreover, the oxidecoated aluminum will be attacked. In the case of each solution, however, the proper hydrogen ion concentration is readily and simply determined by experiment, such as by immersing several pieces of oxide-coated aluminum in solutions of varying hydrogen ion concentration and observing the results obtained thereby.
• the salt is one of a weak metallic base and a strong acid it is very desirable to add to the solution a buffer such as boric acid, borates, acetates, or other well known buffering agents, in order that the proper hydrogen ion concentration may be readily obtained and maintained, the buffering agent tending to reduce the sensitivity of the adjustment.
• a buffering agent may be desirable in the interests of maintaining the predetermined hydrogen ion concentration desired. For instance, excellent results have been obtained by adding boric acid to solutions of nickel or cobalt acetate.
• the salt solution may contain large or small amounts of a salt of the general class described. While amounts of 0.1 per cent by weight have been found eflicient, and solutions containing the salt to the maximum solubility thereof are useful, it is preferable in commercial solutions, when solubility relations permit, to use about 1 or 2 per cent of the salt in solution. From time to time the solution may have to be renewed as it becomes exhausted or inactive by use.
• the oxide-coated aluminum is immersed in the hot or boiling salt solution for a time sumcient to effect the result desired.
• the time of treatment varies with the particular coating and with the Particular effect desired. It is usually between about 2 and 30 minutes.
• the oxide coating is placed upon aluminum utensils such as trays, ice-freezing receptacles and the like. In such cases the coating is not colored since the natural oxide-coated aluminum finish is desired. Such trays and receptacles are often in cont/act with colored liquids, colloidal or otherwise, and such liquids, if adsorbed by the oxide coating, stain the coating.
• the coating is made substantially non-porous and impermeable, thus eliminating or materially decreasing the propensity of the coating to stain.
• salt solutions which do not, themselves, color the oxide coating or act as a mordant for coloring agents.
• the aluminum article may have been provided with a colored oxide coating or with a coating containing in its pores a substance such as sodium silicate, which will increase the corrosion resistance of the coating.
• a coated aluminum article may, in its use, be subject to detrimental external agencies such as moisture, general weather conditions, solvents, etc., which will tend to remove the coloring or other materials from the pores of the coating.
• the coating is made impermeable or substantially so; and, at the same time, the useful substance, coloring matter or otherwise, is more or less permanently bound in the pores of the oxide coating and protected against the action of solvents, etc.

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• Chemical & Material Sciences (AREA)
• General Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Mechanical Engineering (AREA)
• Electrochemistry (AREA)
• Chemical Treatment Of Metals (AREA)
• Chemically Coating (AREA)
• Application Of Or Painting With Fluid Materials (AREA)

Priority Applications (6)

Applications Claiming Priority (1)

Publications (1)

Family

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Family Applications (1)

Country Status (5)

Cited By (19)

Families Citing this family (3)

• 0
  • FR FR754077D patent/FR754077A/fr not_active Expired
  • NL NL64809D patent/NL64809B/xx unknown
  • NL NL38285D patent/NL38285C/xx active
• 1932
  • 1932-05-26 US US613793A patent/US2008733A/en not_active Expired - Lifetime
• 1933
  • 1933-03-20 GB GB8355/33A patent/GB413814A/en not_active Expired
  • 1933-03-28 DE DEA69089D patent/DE620793C/de not_active Expired

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