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
  • C25D11/16—Pretreatment, e.g. desmutting
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S205/00—Electrolysis: processes, compositions used therein, and methods of preparing the compositions
  • Y10S205/917—Treatment of workpiece between coating steps

Definitions

• the present invention consists in the production of brilliant reflecting surfaces on aluminum or aluminum alloys, that is to say a treatment of the said surfaces for improving the reflective power thereof.
• the aluminum may be in the form of sheets or the like, or made into the form of various articles of commerce.
• the invention has for its object a process permitting the obtainment on an aluminum surface or on the surface of any one of a great number of aluminum alloys, a surface which is highly reflective to light rays and heat rays, this being possible even in articles of complicated construction.
• the process makes unnecessary a previous mechanical or other polishing or grinding of the surface of the article.
• the present invention permits the avoidance of these inconveniences.
• the process gives a brilliant and reflective surface on objects of aluminum or aluminum alloys, by the following steps. After being well degreased, the article is immersed in a phospho-chromic acid solution which is strongly acid, then it is submitted to an anodic electrolytic treatment in an alkaline-bath containing principally the ions PO4 and AlOr. The article is again immersed in a phospho-chromic acid solution, and is finally submitted to an anodic oxidation in an acid solution (which solution may be itself old in this art). The article can be then colored or sealed if desired.
• the degreasing ' is preferably carried out electrolytically, according .to any known method,
• the article in this operation, constitutes the anode. At a tension of 8 to 12 volts, and at approximately room temperature, a treatment for one minute isusuallysuflicient. The. article is then rinsed, preferably in running water.
• the article is immersed in a strongly acid solution composed of phosphoric acid, chromic acid and water.
• phosphoric acid dominates over the chromie'acid.
• This solution preferably contains about 30% toi.35% of phosphoric acid and about 10% to about...15.% of chromic acid, both by weight.
• the pHofthe solution is in general below 1 and preferably below 0. measure the pH of such a solution.
• the duration of this treatment depends upon the temperature of the bath. It may require ..about half a minute to one minute insaid ,phospho-chromic solution, at between '50 to '100" vC. It would require minutes or inore'of treatment at about room temperature. For reasons which will be set forth hereinafter inconnection with the operation described under 4, the preferred ranges of temperatures are 80C. to 90 C. and aduration of half a minute to one minute will then give satisfactory results.
• the brightening of the surface is the result of an anodic oxidation in an alkaline solution containing. the ions phosphatePOr and aluminate A1021 These ions are of course in. combination with a metal, preferably an alkali metal suchas sodium.
• the solutions accordingly canbe-economically prepared by dissolving trisodium phosphate and sodium aluminate in water. .Also itcould be prepared by dissolving aluminumphosphatein caustic soda solution or by. any convenient means. In any case the POP ion iii-the solution, should be 2 to 20% and theAlOz ion should be.0.5% to 5%.
• the potassium compounds can be used instead of sodium compounds, if desired.
• the pH of said alkaline phosphate aluminate solution should not be lower. than about 11. and will be preferably near.12. lnsuchvhighly alkaline solutions no aluminum phosphate can be formed as this compound is no more soluble and, in presence of the alkali metal, it gives the phosphate and the aluminate of said metal, e. g. with sodium Na3PO4 and NaAlOz.
• the piece to be brightened is made the anode in an electrolytic cell containing said solution.
• the temperature of thesolution can be between 70 and 95 C., accordin to'the degree of brilliancy desired in the coating and theage of the bath.
• a bath which has been used for some time needs a temperature'higher than a fresh bath.
• the anodic oxidation can be conducted at a tension of 8 to 20 volts, current intensity 4 to amperes per square'decimeter, time 5 to 10 minutes.
• This anodic electrolytic treatment deposits a thin coating of aluminum hydroxide on the surface of the aluminum body, the aluminum of said It is somewhat difficult to :accurately.
• the piece is then preferably rinsed, e. g. in running Water.
• the phosphate-aluminate solution can be used until all of the alumina has been transformed into gelatinous condition when the bath will be discarded.
• the preceding operations give a film of pulverulent aluminum hydroxide. This film is then dissolved and the uniformity of the brilliance of the surface is controlled, by means of a solution of phosphoric and chromic acid which may be the same as that described under 2 above. Or baths of similar compositions can be used.
• the article is immersed in the solution for l to 5
• the bath is at about to C. preferably between 83 to 87 C. and that is the reason why the same temperature is preferably used in the operation under 2 above, as it makes it possible to use the same bath for both Operations 2 and l.
• the piece is then well rinsed in running water.
• Step 5 is then taken.
• the electrolyte can be a H2504 solution e. g. a 12% H2304 solution and the voltage may be for example 12 volts, the temperature being 13 C. to 22 C. Any anodic oxidation bath may be employed.
• This operation has for its object to form on the surface of the article, a perfectly transparent coating of aluminum oxide, strongly adherin to the metal and sufiiciently thick to preserve the brilliancy of the subadjacent bright aluminum, and which is resistant to atmospheric humidity.
• the anodized article can then be subjected to a coloring treatment or the article can be subjected to a sealing treatment, e. g. in boiling water.
• the organic dyes are convenient.
• I can employ an aqueous solution of alizarin, at the temperature and the concentration corresponding to the colour to be obtained.
• the invention can be illustrated and made readily understandable by the following examples, to the details of which the invention is not restricted.
• Example 1 A plain aluminum plate is, after a preliminary polishing, degreased electrolytically in a solution of 5% sodium carbonate, 5% sodium phosphate and 2% sodium silicate at room temperature,
• the aluminum plate has acquired a highly lustrous, brilliant, mirror-like surface having a reflecting power of 90 to 93% of that of silvered glass.
• Example 2 A cast piece of alloy consisting of 95% Al, 4% Cu, 1% Mg, is polished and degreased as in Example 1.
• the first phospho-chromic acid solution can contain H3PO4 and 15% HzCrO4, and is used at 83 C. Then rinse in water.
• the piece is then introduced as the anode into a solution made by dissolving 100 grams NaOH in 1 liter of water and dissolved in this, 60 grams of aluminum phosphate, the cathode being the electrolytic cell itself.
• the temperature of the electrolytic bath is 95 C.
• the cell is operated at 10 volts, 8 amperes per square decimeter, for 5 minutes. The piece is taken out and rinsed.
• Example 3 A cast piece of alloy composed of 95% Al, 4% Cu, 1% Mg, is polished and degreased as in Example 1.
• the first phospho-chromic acid solution contains H3PO4 and 10% H2CrO4 and is used at about 50 C. for one minute. Then rinse in water.
• the cast piece is highly brightened, its reflection power being almost that of silvered glass.
• an aqueous alkaline bath consisting essentially of an alkali metal phosphate selected from the group consisting of sodium phosphate and potassium phosphate and an alkali metal aluminate selected from the group consisting of sodium aluminate and potassium aluminate in an amount such that said bath contains between 2% to 10% phosphate and between 0.5% :to. %-aluminate ions at a temperature between 70 C.
• an aqueous alkaline bath consisting essentially of an alkali metal phosphate selected'from the group consisting of sodium phosphate and potassium phosphate and an alkali metal aluminate selected from the group consisting of sodium aluminate and potassium aluminate in an amount such that said bath contains between 2% and 10% phosphate ions and between 0.5% to 5% aluminate ions at a temperature between 70 C. and 95 C.
• aqueous alkaline bath consisting essentially of the washed article
• elecan alkali metal phosphate selected from the group consisting of sodium phosphate and potassium phosphate and an alkali metal aluminate selected from the group consisting of sodium aluminate and potassium aluminate in an .amount such that said bath contains between 2% to 10% phosphate ions and between 0.5% 'to 5% aluminate ions at a temperature between C. and C.
• alkali metal phosphate is selected from the group consisting of sodium phosphate and potassium phosphate and the alkali metal aluminate is selected" from the group consisting of sodium aluminate and potassium aluminate.

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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)
• Cleaning And De-Greasing Of Metallic Materials By Chemical Methods (AREA)
• Chemical Treatment Of Metals (AREA)

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Citations (6)

• 0
  • BE BE484777D patent/BE484777A/xx unknown
  • IT IT454258D patent/IT454258A/it unknown
  • NL NL71913D patent/NL71913C/xx active
• 1947
  • 1947-09-24 FR FR966790D patent/FR966790A/fr not_active Expired
• 1948
  • 1948-09-07 CH CH280488D patent/CH280488A/fr unknown
  • 1948-09-16 GB GB24344/48A patent/GB655699A/en not_active Expired
  • 1948-09-17 US US49844A patent/US2647865A/en not_active Expired - Lifetime

Patent Citations (6)

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