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
  • C23C22/05—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 using aqueous solutions
  • C23C22/06—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 using aqueous solutions using aqueous acidic solutions with pH less than 6
  • C23C22/40—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 using aqueous solutions using aqueous acidic solutions with pH less than 6 containing molybdates, tungstates or vanadates
  • C23C22/44—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 using aqueous solutions using aqueous acidic solutions with pH less than 6 containing molybdates, tungstates or vanadates containing also fluorides or complex fluorides

Definitions

• This invention relates to a treatment for aluminum and aluminum containing alloys and has as a principal aim provision of .a corrosion-resistant coating of good appearance which has improved wet hardness and non-smearing characteristics. In addition, the formation of the coating is substantially accelerated.
• Another principal aim of this invention is the provision of coating solutions of greatly improved stability.
• chromate con version coatings can be obtained by using baths which include' tungstic acid and/or water solublesalts of tungstic acid, notably alkali metal salts in conjunction with one or more cations from the group-consisting of beryllium, magnesium, calcium, strontium and barium; the pH of the bath-being maintained within the range of about 1.3 to 2.2.
• Coatings as formed in the treating bath are built up to a greater thickness without sloughing-off or becoming powdery or non-adherent. It has been observed that the coatings while still wet'have a much greater reance, to wiping or smearing than has heretofore been encountered. However, serious limitations are encountered with regard to stability and workability of treating solutions as described above.
• tungstic acid tends to precipitate from solution on standing for a period of several days to several weeks, so thatth e concentration of tungstate ion remaining in solution is nil or so low as to be ineffective.
• the tungstate salts of the cations referred to above tend to be of limited solubility, especially the tungstates of barium and magnesium. Therefore, when these cations are used in conjunction with soluble tungstates, they cause the precipitation of tungstate from solution, so that the tungstate ion concentration remaining in solutionis essentially nil or sufliciently low as to reduce its effectiveness drastically.
• coating solutions containing soluble tungstate salts whose stability may be improved by the incorporation of phosphate or arsenate compounds are those containing also a chromic compound yielding a chromic ion (CH and a fluo compound yielding a fluoride ion (F*) in solution.
• the chromic ion may be provided by chromic acid or water-soluble salts thereof and the fluoride ion may be provided by simple fluorides such as alkali metal fluorides and bifluorides, or complex fluorides such as fluosilicates and fluoborates.
• Preferred compounds for providing the fluoride ion include fluosilicic acid and salts thereof and particularly certain alkali metal salts thereof.
• the above described coating solutions may also contain ferricyanic or ferrocyanic acid, water-soluble salts thereof and mixtures of the same.
• the chromic acid and salts thereof are utilized in a range of concentrations equivalent to from 0.5 to 50 grams of CrO per liter of solution.
• the fluo compound may be employed in amounts equivalent to from 0.05 to 5 grams hydrofluoric acid, from 0.075 to 8 grams fiuosilicic acid and from 3.3 to 33 grams fiuoboric acid per liter of solution.
• the concentration of ferricyanic or ferrocyanic acid or salts thereof can vary from that equivalent to 0.1 to 50 grams of potassium ferricyanide per liter of solution.
• the soluble tungstate may be present in amounts equivalent to 0.035 to 7 grams of W per liter of solution.
• the amounts of phosphates or arsenates used depend on the tungstate concentration and the ratios, as set forth heretofore, are from 1:10 to 1:150 of phosphates calculated as P 0 or arsenates calculated as AS205 to the tungstate calculated as W0 In using any of the above coating baths, objects of aluminum and alloys thereof are immersed therein under the operating conditions discussed hereinafter.
• aqueous solution was employed and the panels were immersed in the same by dipping, However, the aqueous bath or solution could be sprayed or brushed or otherwise applied to the alumi num containing article to be protected.
• additions of about 1.0 ml./l. of nitric acid are used to offset rising of the pH of the treating solution.
• sodium tungstate because of its commercial availability, other soluble salts may be utilized, notably potassium tungstate, and, in fact, any of the water-soluble salts of tungstic acid.
• solution temperature is not critical. Temperatures within the range of 60 to 120 F. are found to be satisfactory but normal room temperatures, generally in the range of 70 to 90 F., are preferred for convenience.
• Treatment time may vary from as low as 5 seconds to as high as minutes, depending on concentration and pH of the solution, and thickness of coating desired. For most immersion applications a treatment time between 1 and 6 minutes is preferred for convenience.
• a coating solution was prepared having the following composition:
• test panel of 2024-T3 was immersed for two minutes at at temperature of 75 F.
• the solution reacted faster than without Na WO and K PO present and produced a uniform golden brown coating, having superior resistance to wiping while wet.
• EXAMPLE 2 Ingredient: Amount in g./l. CF03 5 NaHF2 0.5 K Fe CN 6 1 N32WO4 1 K PO 0.03 pH 1.6
• test panel of 2024T3 was treated as in Example 1.
• a uniform medium brown coating was formed having superior resistance to wiping while wet.
• Example 3 The procedure of Example 2 was repeated using 0.02 g./l. of Na HPO in place of the K PO with comparable results.
• a six minute treatment at F. of a 2024-T3 test panel resulted in a uniform light golden brown coating of superior wet hardness (resistance to wiping while wet).
• a 'six minute treatment at 80 F. of a 2024-T3 test panel produced a uniform medium brown coating of superior wet hardness.
• the treated panel showed no corrosion after 500 hours exposure to 5% salt spray.
• a uniform golden yellow coating of superior wet hardness' was produced on a 2024-T3 test panel immersed for three minutes in the above solution at 80 F.
• EXAMPLE 7 Ingredient: Amount in g./l.- CF03 5 .0 Na SiF 8.4 K Fe(CN) 5.0 Na WO 0.5 K3PO4 pH 1.6
• a 2024-T3 test panel treated as in Example 6 resulted in the formation of a uniform golden brown coating of superior wet hardness.
• Example 8 The procedure of Example 6 was repeated using 0.09 gram per liter of AS205 in place of the K PO with comparable results.
• Example 9 The procedure of Example 7 was repeated using 0.09 gram per liter of AS205 in place of the K PO with comparable results.
• solutions of the foregoing examples may be prepared from suitable dry powdered mixtures of the respective ingredients. It may be found advantageous, from the standpoint of stability of the powdered mixture, to prepare this in two separate parts.
• a typical 2-part powdered mixture may be made up as follows:.
• a preferred working mixture is prepared as follows:
• a typical 2 part liquid concentrate may be made up as shown in the following table:
• a typical working solution may be prepared as follows:
• composition of claim 1 wherein the watersoluble fluorine containing compound is selected from the group consisting of hydrofluoric acid, fluoboric acid, fluosilicic acid, the water-soluble salts of said acids and mixtures of any of these acids and salts.
• composition of claim 1 including a cyanic acid selected from the group consisting of ferricyanic acid, ferrocyanic acid, water-soluble salts thereof and mixtures of said acids and salts present in amounts of 0.1 to 50 grams per liter calculated as potassium ferricyanide.
• a cyanic acid selected from the group consisting of ferricyanic acid, ferrocyanic acid, water-soluble salts thereof and mixtures of said acids and salts present in amounts of 0.1 to 50 grams per liter calculated as potassium ferricyanide.
• a hexavalent chromium compound selected from the group consisting of chromic acid and water-soluble salts thereof present in amounts of 0.5 to 50 grams calculated as CrO per liter of said solution
• the aqueous solution of claim 4 wherein the watersoluble fluorine containing compound is selected from the group consisting of hydrofluoric acid, fluoboric :acid, fiuosilicic acid, the water-soluble salts of said acids and mixtures of any of these acids and salts.
• composition of claim 4 including a cyanic acid selected from the group consisting of ferri-cyanic acid, ferrocyanic acid, water-soluble salts thereof and mixtures of said acids and salts present in amounts of 0.1 to 50 grams per liter calculated as potassium ferricyanide.
• a cyanic acid selected from the group consisting of ferri-cyanic acid, ferrocyanic acid, water-soluble salts thereof and mixtures of said acids and salts present in amounts of 0.1 to 50 grams per liter calculated as potassium ferricyanide.
• a method of imparting a corrosion-resistant coating to aluminum and alloys thereof which comprises subjecting the latter to an aqueous acidic solution comprising water, a hexavalent chromium compound selected from the group consisting of chromic acid and water-soluble salts thereof present in amounts of 0.5 to 50 grams calculated as CrO per liter of said solution, a water-soluble fluorine containing compound yielding free fluoride ions in said solution present in amounts equivalent to 0.05 to 5 grams of hydrofluoric acid per liter of solution, a watersoluble tungstate present in amounts of 0.05 to 10 grams calculated as W0 per liter of solution and a phosphate selected from the group consisting of phosphoric acid and water-soluble salts thereof calculated as P 0 present in a ratio of from 1:10 to 1:150 to sand tungstate calculated as W0 9.
• water soluble fluorine containing compound is selected from the group consisting of hydrofluoric acid, fluoboric acid, fluosilicic acid, the water-soluble salts of said acids and mixtures of any of these acids and salts.
• a cyanic acid selected from the group consisting of ferricyanic acid, ferrocyanic acid, water-soluble salts thereof and mixtures of said acids and salts present in amounts of 0.1 to 50 grams per liter calculated as potassium ferricyanide.
• a method according to claim 8 wherein the temperature of the solution is between about 60 and 120 F.
• a method of imparting stability to an aqueous solution containing a water-soluble tungstate salt which comprises adding to said solution a phosphate selected from the group consisting of phosphoric acid and watersoluble salts thereof calculated as P 0 and present in a ratio of from 1:10 to 1:150 to said tungstate calculated as W0 References Cited UNITED STATES PATENTS 2,796,371 6/1957 Ostrander et a1 1486.2 2,868,679 1/ 1959 Pimbley 148-6.27 X 2,936,254 5/1960 Newhard et a1. 1486.27

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• Chemical Kinetics & Catalysis (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Chemical Treatment Of Metals (AREA)

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Citations (4)

• 0
  • NL NL128122D patent/NL128122C/xx active
• 1964
  • 1964-12-29 US US422041A patent/US3410707A/en not_active Expired - Lifetime
• 1965
  • 1965-12-21 NL NL6516677A patent/NL6516677A/xx unknown
  • 1965-12-22 GB GB54319/65A patent/GB1128369A/en not_active Expired
  • 1965-12-22 DE DE19651521672 patent/DE1521672A1/de active Pending

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