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
  • C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
  • C23F3/00—Brightening metals by chemical means
  • C23F3/02—Light metals
  • C23F3/03—Light metals with acidic solutions

Definitions

• the present invention relates to a composition and method for glossing aluminum. More particularly, the present invention is concerned with the glossing of aluminum of relatively low purity and with the glossing of aluminum alloys containing such low-purity aluminum and generally being of the type of aluminum alloys to which gloss or luster can be imparted followed by electrolytic oxidation.
• Treating solutions have been described for the purpose of forming a glossy surface on aluminum and aluminum alloy bodies.
• these treating solutions consist of aqueous solutions containing hydrogen, ammonium, nitrate and fluoride. ions, whereby it is desired to adjust the quantative relationship between fluoride and ammonium ions so as to favor the formation of NH HF It has also been suggested to incorporate in such solutions a relatively small amount of lead ions.
• the present invention contemplates a treating solution adapted to form a glossy surface on a body of a substance belonging to the group consisting of aluminum having a purity of up to 99.95% and its alloys adapted to be lustered followed by electrolytic oxidation, the treating solution consisting of an aqueous solution containing between 6.4 and 10.2% by weight of HNO between 5.4 and 8.8% by weight of NH,,HF between 0.12 and 0.35 gram of lead ions per liter, and between 0.4 and 8.8% by weight of a hydrophilic colloid.
• a high gloss can be formed on aluminum bodies of lesser purity by treating such aluminum or glossable aluminum alloys with treating solutions which contain nitric acid, ammonium hydrofluoride, lead and a hydrophilic colloid from a group consisting of gum arabic, dextrin, agar-agar as an inhibitor, provided that the quantities and proportions of the individual constituents of the treating solution are strictly controlled and maintained within the ranges described above.
• the present invention contemplates in a method of forming a glossy surface on a body of a substance belonging to the group consisting of aluminum having a purity of up to 99.95% and of its alloys adapted to be lustered followed by electrolytic oxidation, the step of treating the surface at a temperature of between about 65 and C. for between about 40 and 60 seconds with an aqueous solution containing the equivalent of between and 160 cc. 54% nitric acid, the equivalent of between 25 and 40 cc.
• an aqueous solution which may be produced by mixing cc. of 54% nitric acid and 33 cc. of 70% hydrofluoric acid with suflicient water to form one liter of an aqueous solution of nitric acid and hydrofluoric acid; and to add to the thus formed solution 50 grams ammonium fluoride, 0.3 gram lead nitrate and 30 grams gum'arabic. In this manner, 1,060 cc. of an aqueous solution having a specific weight of 1.074 are formed.
• the treating solution according to the present invention is an aqueous solution containing between 6.4 and 10.2% by weight, preferably about 8.5% HNO between 5.4 and 8.8% by Weight, preferably about 6.8% NH HF between 0.12 and 0.35 gram per liter, preferably about 0.18 gram per liter lead ions; and between 0.4 and 8.8% by Weight of hydrophilic organic colloid, preferably about 2.6% by Weight of gum arabic.
• lead nitrate instead of lead nitrate, other water soluble lead salts, for instance, lead acetate, may be used, provided that the concentration of lead ions in the treating solution is maintained at a level corresponding to between about 0.2 and 0.6 gram lead nitrate per liter, or to between 0.12 and 0.35 gram per liter of lead ions.
• lead acetate water soluble lead salts
• viscosity-increasing hydrophilic colloids such as dextrin or agar-agar may be used.
• ammonium fluoride which is used in producing the treating solution of the present invention must be free of lead.
• the treating solution of the present invention may be formed by adding water to between 100 and cc. of 54% nitric acid and between 25 and 40 cc. 70% hydrofluoric acid so as to form one liter of solution, and to introduce into the thus formed solution between 40 and 70 grams of lead-free ammonium fluoride, between 0.2 and 0.6 gram lead nitrate (or of another water soluble lead salt containing an equivalent amount of lead), and between and 100 grams of gum arabic, dextrin, agar-agar or the like.
• Treatment of the aluminum surface of relatively low purity with the above described treating solution is carried out for a period of between about 40 and 60 seconds depending on the condition of the aluminum surface.
• the treating temperature is preferably maintained between 65 and 75 C., in case the treating solution has aged, it is preferred to carry out the treatment at somewhat higher temperatures, up to about 85 C.
• the treating solution of the present invention During use of the treating solution of the present invention. the same becomes spent more and more and slowly loses its effectiveness, if a regeneration of the solution is not carried out. It is desirable to preserve the high effectiveness of the solution for imparting to aluminum surfaces the same high degree of gloss which it was initially capable of producing.
• the gradual exhaustion of the treating solution depends primarily on the square area of aluminum surface which has been treated with a given quantity of solution, however, the surface condition of the aluminum body also affects the exhaustion of the solution.
• the treatment solution according to the present invention allows incorporation of relatively large quantities of gum arabic.
• To increase the proportion of gum arabic is desirable, however, up to now only relatively small quantities of gum arabic could be incorporated in glossing solutions due to the fact that increasing the concentration of gum arabic resulted in the formation of an uneven blue haze on the glossy surface.
• On the other hand particularly with respect to aluminum surfaces of relatively low purity, it is most desirable to increase the proportion of gum arabic in order to counteract the etching effect of the treating bath. This is now possible.
• the capacity of the treating solution according to the present invention i.e., the square area which can be treated with a given quantity of solution, is about twice as great than that of qualitatively more or less similar solutions which however are not limited to the specific quantitive relationships of the present invention.
• the close control of the lead ion content of the initial solution and of the regenerated solution according to the present invention will assure optimum lustering effect throughout the entire useful life span of the treating solution, i.e., until the solution which has been regenerated several times has been used for about 2 in. of aluminum surface per liter of solution. This again is particularly important in the glossing of aluminum which is not of highest purity.
• the examples describe the treatment in accordance with the present invention of 5 aluminum and aluminum alloy sheets of different composition and compare the results with results obtained by treating identical sheets with conventional treating solution.
• composition of the aluminum sheets was as follows:
• Example 3 A1 99.9% pure+0.5% Mg.
• Example4 A1 99.9% pure+1% Mg.
• Example 5 Al 99.99% pure.
• Treatment A was carried out in accordance with the present invention by treating the aluminum sheets after conventional de-fatting, for 40 seconds at 65 C. in a bath which was formed by making up cc. of 54% nitric acid and 33 cc. of 70% hydrofluoric acid with water so as to obtain one liter of solution and by adding to one liter of the thus formed solution 50 grams of lead-free ammonium fluoride, 0.3 gram lead nitrate and 30 grams gum arabic. The thus treated aluminum sheets were then rinsed with water, immersed for two minutes into 30% nitric acid at room temperature, again rinsed with water and then in conventional manner supplied with an anodically produced protective layer having a thickness of 5 microns.
• Treatment 13 was carried out according to the prior art, by conventionally de-fatting the aluminum sheets and thereafter treating the same for 20 seconds at 50 C. in a treatment solution which contained 16% by weight of ammonium hydrogenfiuoride, 13% by weight of nitric acid, 0.18 gram per liter of lead and 10 grams per liter of gum arabic.
• the further treatment of the aluminum sheets after removal from the treating bath, was carried out in exactly the same manner as described under The following results were obtained:
• a glossy surface on a body of a substance belonging to the group consisting of aluminum having a purity of up to 99.95% and of alloys of said aluminum adapted to be lustered followed by electrolytic oxidation the step of treating said surface at a temperature of between about 65 and 85 C. for between about 40 and 60 seconds with an aqueous solution containing the equivalent of between 100 and 160 cc. 54% nitric acid; the equivalent of between 25 and 40 cc.
• a method of regenenating partially spent treating solution according to claim 4 comprising the step of adding to said partially spent treating solution, per liter thereof: between 10 and 25 cc. 70% hydrofluoric acid,
• a method of regenerating partially spent treating solution according to claim 4, comprising the step of adding to said partially spent treating solution, per liter thereof: about 15 cc. 70% hydrofluoric acid, and about 0.08 gram of lead nitrate in the form of a concentrated aqueous solution.
• a method wherein after first treating between 0.25 and 0.30 m. of said surface per liter of said aqueous solution, between 10 and 25 cc. 70% hydrofluoric acid and a concentrated aqueous solution of a water soluble lead salt in a quantity equivalent to between 0.05 and 0.1 gram lead nitrate are added to said solution so as to regenerate the same; the thus regenerated solution then being used for treatment of an additional between 0.15 and 0.20 m. of said surface, thereby being again partially spent; and the thus again partially spent solution is again regenerated by adding said hydrofluoric acid and said soluble lead salt thereto, and whereby said additional treatment and subsequent regeneration of said solution may be repeated until a total area of about 2 m. of said surface has been treated per liter of said solution.
• a treating solution adapted to form a glossy surface on a body of a substance belonging to the group consisting of aluminum having a purity of up to 99.95 and of alloys of said aluminum adapted to be lustered followed by electrolytic oxidation, said treating'solution consisting of an aqueous solution containing between 6.4 and 10.2% weight of HNO between 5.4 and 8.8% by weight of NH.,HF between 0.12 and 0.35 gram of lead ions per liter; and between 0.4 and 8.8% by Weight of a hydrophilic colloid.
• a treating solution adapted to form a glossy surface on a body of a substance belonging to the group consisting of aluminum having a purity of up to 99.95% and of alloys of said aluminum adapted to be lustered followed by electrolytic oxidation, said treating solution consisting of an aqueous solution containing about 8.5% by weight of HNO about 6.8% by weight of NH HF,; about 0.18 gram of lead ions per liter; and about 2.6% by weight of a hydrophilic colloid.

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Citations (8)

• 1960
  • 1960-01-13 DE DEV17876A patent/DE1110982B/de active Pending
  • 1960-11-24 CH CH1316260A patent/CH423406A/de unknown
  • 1960-11-24 SE SE11351/60A patent/SE302394B/xx unknown
• 1961
  • 1961-01-12 US US82180A patent/US3155556A/en not_active Expired - Lifetime

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