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
  • C23C22/34—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 fluorides or complex fluorides
• • 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
  • C23C2222/00—Aspects relating to chemical surface treatment of metallic material by reaction of the surface with a reactive medium
  • C23C2222/10—Use of solutions containing trivalent chromium but free of hexavalent chromium

Definitions

• the invention relates to a method for producing an acidic chromium-containing and fluoride-containing passivation bath for zinc or cadmium surfaces.
• an acidic chromium-containing passivation bath for zinc or cadmium surfaces is known from US Pat. No. 4,263,059 and DE-OS 30 38 699, which, in addition to a "blue solution" of trivalent chromium and an acid, such as formic, acetic or propionic acid or nitric, sulfuric, hydrochloric and hydrofluoric acid contains a fluoride with a "green solution" of hexavalent chromium, for example Chromium trioxide, alkali metal chromate and dichromate and a reducing agent such as an aldehyde or alcohol or an alkali metal sulfite, bisulfite, metabisulfite, iodide, hydrogen peroxide, sulfur dioxide or an iron (II) salt is formed.
• a fluoride with a "green solution” of hexavalent chromium for example Chromium trioxide, alkali metal chromate and dichromate and a reducing
• surfaces made of zinc, zinc alloys, galvanically or hot-dip galvanized on zinc or iron or steel layers or cadmium surfaces are made more corrosion-resistant, which is indicated by a coloration that ranges from blue to black and yellow to olive and is also used for decorative purposes.
• a passivation for example, the so-called blue passivation, ie Generation of a light blue, very thin passivation layer with a good decorative appearance, formation of zinc corrosion products also called "white rust", greatly delayed.
• the salt spray test according to DIN 50021 provides a measure of the corrosion protection of these chromates.
• a zinc-coated and passivated part is exposed to a 5% sodium chloride mist at 40 ° C and 100% humidity. The time required to oxidize 5 - 10% of the surface to white rust is then given.
• the corrosion protection according to DIN 50021 should be 20 to 24 hours.
• Chromium (III) fluorine complexes of chromium (III) are known, the formation of which is accelerated by zinc, but there is no evidence of the blue passivation of zinc or galvanized in this investigation of equilibrium constants Iron surfaces, on where there is no chrome metal deposition, but a polymeric compound with divalent chromium is deposited.
• the object of the invention is to avoid the disadvantages mentioned by creating an acidic, chromium-containing passivation bath which contains only chromium (III) compounds, but no oxidizing agents and no strong complexing agents, which has a long service life, produces and permits colorable passivations, organic polymers to better adsorb onto the generated passivation layer and not become unusable due to iron dissolved in the bath.
• This object is achieved according to the invention by a process for producing an acidic, chromium (III) -containing and fluoride-containing passivation bath for surfaces made of zinc, zinc alloys and cadmium by mixing 20 to 200 g / l of a soluble chromium (III) compound 20 to 600 g / l of a soluble nitrate (total nitrate) 5 to 100 g / l of a fluoride and an acid dissolved, which is characterized in that hydrochloric or sapric acid is added up to a pH of 1.8 to 2.2, that an anion from the group selected from nitrate, sulfate, phosphate, chloride, Bromide, fluoride, and iodide is added that the soluble nitrate is added at a concentration in g / l that is greater than the chromium (III) concentration, that the mixture is either heated to 60 ° C or with a catalyst above 15 ° C is treated and that
• the bath in the presence of iron, is characterized by the fact that it additionally contains an acidic ion exchanger loaded with Cr3 ein and / or an agent for the insolubilization of Fe3+ ions in an amount of 0.1 to 100 g / l.
• the bath is particularly quick to act if it has been heated to at least 60 ° C or treated with a analyzer above 15 ° C. _This treatment is advantageously carried out with the bath concentrate before dilution to the application concentration.
• Passivation baths preferred according to the invention contain the following amounts in a concentrate which is usually used in a concentration of 2 to 20% by weight in water: 20-200 g / l chromium (III) compound, e.g. as chromium chloride or chromium nitrate, 20 - 600 g / l soluble nitrate, such as sodium, potassium or ammonium nitrate, 5 - 100 g / l fluoride, e.g. sodium, potassium, ammonium fluoride Hydrochloric or nitric acid up to a pH of 1.8 to 2.2.
• a concentrate which is usually used in a concentration of 2 to 20% by weight in water: 20-200 g / l chromium (III) compound, e.g. as chromium chloride or chromium nitrate, 20 - 600 g / l soluble nitrate, such as sodium, potassium or ammonium nitrate, 5 - 100
• Passivation baths made from this concentrate show corrosion protection values of a blue passivation according to DIN 50021 from 44 to 50 h, the layers can be colored and good organic polymers are applied to the layers.
• a concentrate of the following composition was produced: 50 g / l chromium (III) chloride 125 g / l sodium nitrate 50 g / l sodium fluoride
• the concentrate was also heated to 65 ° C. It contained complexes of the formula
• the bath was mixed with water in a weight ratio of 1:10 and adjusted to pH 2.0 with nitric acid. With this bath, hot-dip galvanized iron bars of 2 cm in diameter and 20 cm in length were blue passivated. After 3 seconds, the rods were removed from the bath and checked for corrosion behavior in accordance with DIN 50021. The corrosion protection value was 48 hours.
• the durability of the bath was extended by a factor of 10 by adding 50 g / l of acetylacetone.
• a bath was out 60 g / l Cr (NO3) 3.9H2O 100 g / l NaNO3 40 g / l NaF NHO3 ad pH 2.1 and without heating, but prepared by treating with granular activated carbon in a porous bag for 10 minutes and, after mixing with water in a weight ratio of 1:12, used for the same experiment. It contained complexes of the formula The same corrosion protection value was obtained.
• the following results were obtained in a comparison test on normal blue chromating (commercially available): with Cr VI (commercially available): 15 mg Cr / m2 zinc; 24 h corrosion protection Cr III (according to the invention: 30 mg Cr / m2 zinc; 48 h corrosion protection.
• the shelf life of the bath was extended by a factor of 5 by adding 20 g / l salicylic acid.
• Example 1 A bath according to Example 1 with a strongly acidic ion exchanger, which had been loaded with a 3 M chromium (III) nitrate solution, was used in a bath with 1.0 g / l Fe3+ content. The same bath without ion exchanger was used for comparison.
• the bath with the ion exchanger showed a perfect blue passivation, while the comparison bath was unusable after a short time.
• the addition of 10 g / l fumaric acid increases the life of the bath by a factor of 5.

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• Chemical & Material Sciences (AREA)
• Metallurgy (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• General Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Chemical Treatment Of Metals (AREA)
• Chemically Coating (AREA)
• Preventing Corrosion Or Incrustation Of Metals (AREA)
• Electroplating And Plating Baths Therefor (AREA)
• Cleaning And De-Greasing Of Metallic Materials By Chemical Methods (AREA)
• Glass Compositions (AREA)

Priority Applications (2)

Applications Claiming Priority (2)

Publications (3)

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ID=6351774

Family Applications (1)

Country Status (5)

Cited By (12)

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• 1988
  • 1988-04-12 DE DE3812076A patent/DE3812076A1/de active Granted
• 1989
  • 1989-04-10 DD DD89327449A patent/DD280557A5/de not_active IP Right Cessation
  • 1989-04-10 YU YU00716/89A patent/YU71689A/xx unknown
  • 1989-04-11 AT AT89106447T patent/ATE97700T1/de not_active IP Right Cessation
  • 1989-04-11 EP EP89106447A patent/EP0337411B1/fr not_active Expired - Lifetime
  • 1989-04-11 DE DE89106447T patent/DE58906227D1/de not_active Expired - Fee Related

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