EP2492371A1 - Cobalt-free passivation solution and method for depositing cobalt-free passivation coatings on zinc and zinc alloy surfaces - Google Patents

Abstract

Cobalt-free aqueous passivating solution comprises: chromium(III) ions; vanadyl cations; nitrate ions; sulfate ions; and one or more complexing agents for chromium(III) ions comprising monocarboxylic acids, dicarboxylic acids, tricarboxylic acids, hydroxycarboxylic acids or fluoride. An independent claim is included for producing a chromium(III)-containing conversion layer on a zinc or zinc alloy layer, where the zinc or zinc alloy layer is immersed in the passivating solution.

Description

Technical area

The invention relates to a cobalt-free aqueous passivation solution for producing conversion layers on zinc and zinc alloy layers, to a process for producing a Cr (III) -containing, cobalt-free conversion layer on a zinc or zinc alloy layer, and to the use of the passivation solution for coating Zinc or zinc alloy layers.

State of the art

The galvanic coating of components made of iron or steel with zinc or zinc alloys is carried out on a large scale and has a high economic importance. The deposited layers protect the base material against corrosion and thus lead to a high increase in the value of the components. The corrosion protection of iron or steel by zinc or zinc alloys is based on the anodic protection mechanism. Zinc or zinc alloys are less electrochemical than the base material. The corrosion attack therefore begins on the coating and the base material remains protected against corrosion as long as a closed zinc or zinc alloy surface is present. The applied less noble zinc or zinc alloy layers are therefore also referred to as "sacrificial layers".

In order to delay the corrosion attack on the sacrificial layers of zinc or a zinc alloy even further and thus improve the overall corrosion protection, it is known in the art to apply an additional conversion layer to the zinc or zinc alloy layers. Here, it has been customary in the past to produce such conversion layers by treating the components in acidic, chromate-containing solutions. A disadvantage of these layers is that also hexavalent chromium compounds are incorporated therein. These are partially water-soluble and can be leached out of the layers. Because of the high toxicity of the chromium (VI) compounds, such layers pose a risk to humans and the environment. For some applications, therefore, there is already a ban on the use of Cr (VI) -containing processes (Ordinance 2000/53 / EC "End-of-Life Vehicles"; / 95 / EC "RoHS Directive") The processes based on hexavalent chromium compounds are therefore increasingly being replaced by processes based on non-toxic chromium (III) compounds. However, in order to achieve corrosion protection, such as e.g. in the standard DIN 50979 is required, it is state of the art that such passivating solutions based on trivalent chromium compounds additionally also water-soluble cobalt compounds such. Cobalt sulfate or cobalt nitrate. However, these cobalt compounds are classified under the Labeling Regulation 1272/2008 / EC as substances suspected of causing cancer in humans. There is therefore an urgent need for cobalt-free passivation processes which at least meet the requirements for corrosion resistance in accordance with DIN 50979.

US 4,126,490 describes an aqueous, Cr (VI) -free passivation solution for forming passivation layers on zinc and zinc alloy layers. The passivation solution contains a chromium (III) compound, alum and vanadate. According to the examples described there, the corrosion resistance of the passivation layers obtained with this passivation solution is at least 24 hours in the salt spray test according to ASTM B 117-54T (identical conditions as in DIN EN ISO 9227). When reworking the examples from the US 4,126,490 a beginning coating corrosion ("white rust") was already visible after 36 hours. This protective effect is significantly below the values obtained from cobalt-containing passivation solutions based on trivalent chromium compounds and is therefore considered to be unsatisfactory.

WO 2010/025442 A1 discloses a composition that is substantially free of hexavalent chromium and does not contain cobalt. The composition comprises a dry water-soluble chromium (III) compound and a dry, vanadium-based compound which is also water-soluble. As the water-soluble vanadium-based compound, metavanadate, pyrovanadate and orthovanadate are named. The user then uses the ready-to-use passivation solution with this dry mixture. The advantage should be that so the transport of the aqueous solutions can be avoided. Furthermore, the passivation solution is according to WO 2010/025442 preferably free of nitrates and other oxidizing agents. Refinements according to the teaching of WO 2010/025442 however, did not yield useful passivation layers as the layers were stained and wipeable after drying.

Furthermore, both in the reworking of the US 4,126,490 as well as those of WO 2010/025442 in that the passivation solutions were unstable and excreted chromium hydroxides after only a short lifetime. Therefore, the life of such coating solutions is limited to a few hours and, for this reason, also disadvantageous.

EP 0 907 762 A1 discloses chromium (III) -containing conversion layers on zinc or zinc alloy layers which have a corrosion protection of 100-1000 hours and a layer thickness of 100-1000 nm. It is said that the corrosion protection of such a layer can be increased by the fact that the layers contain additional components from the group of silicate, cerium, aluminum and borate and additional metal compounds, in particular 1- to 6-valent metal compounds, for example compounds of Na, Al, Ag, Co, Ni, Fe, Ga, In, lanthanides, Zr, Sc, Ti, V, Mn, Cu, Zn, Y, Nb, Mo, Hf, Ta, W, as well as numerous possible anions or polymers. However, only to Cobalt-containing passivation layers are given specific information on the composition of the passivation solution and preparation of the layer.

The object underlying the present invention is to provide a cobalt-free passivation solution with which a passivation layer can be produced on a zinc or zinc alloy layer which exhibits a resistance of more than 300 hours in the salt spray test according to DIN EN ISO 9227.

The above object is achieved by a cobalt-free passivating solution comprising Cr (III) ions, vanadyl cations, nitrate ions, sulfate ions and one or more complexing agents for Cr (III) ions selected from the group of monocarboxylic acids, dicarboxylic acids, tricarboxylic acids , Hydroxycarboxylic acids and fluoride.

As Cr (III) ions, all water-soluble Cr (III) compounds can be used. As examples there may be mentioned Cr (III) chloride (CrCl ₃ · H ₂ O), basic chromium sulfate (CrOHSO _4, for example Chromosal BD ^® from. Lanxess), Cr (III) nitrate (Cr (NO _{3) 3} · 9H ₂ O) or potassium chromium sulfate (KCr (SO ₄ ) ₂ .6H ₂ O). The Cr (III) ions are in the Passivierungslösung preferably in an amount of 0.1 - 50 g / 1, more preferably 0.5 - 5 g / l, present.

Furthermore, it is essential to the invention that vanadium is present in cationic form in the passivation solution, ie as a vanadyl cation. Examples of compounds which have vanadium in cationic form and can be used in the passivation solution of the present invention are the vanadyl trihalides VCl ₃ and VBr ₃ , vanadyl sulfate (VOSO ₄ ) and vanadyl acetylacetonate (V (acac) ₂ ). In addition, the vanadyl cation can also be used as Diacetatokomplex. The diacetate complex can be prepared, for example, by first reacting vanadyl sulfate with 5 moles of sodium acetate. It is preferred that the passivating solution of the present invention contains vanadyl sulfate and / or the vanadyl diacetate complex. In the case of vanadyl sulfate and the vanadyl diacetate complex, the vanadium is in the valence state +4, and the compounds have a covalent V = O bond. The best corrosion protection values are achieved when the weight ratio Cr / V in the passivation solution is 5/1 to 100/1. Particularly preferred is a weight ratio of Cr / V of 10/1 to 50/1. In this way, passivation layers can be produced which have a weight ratio of Cr / V of about 1/1 to 4/1 in the deposited layer.

The passivation solution according to the present invention also contains nitrate ions. Preferably, the amount of nitrate ions contained in the passivating solution is 0.75-75 g / l passivating solution, more preferably 2.25-40 g / l. The nitrate ions may be added to the passivating solution in any form. For example, the nitrate ions may be added together with the Cr (III) ions as the chromium nitrate, Cr (NO ₃ ) ₃ .9H ₂ O. It is particularly preferred to add the nitrate ions as sodium nitrate. It is also possible to combine different nitrate sources, for example, by the addition of chromium (III) nitrate, which is then simultaneously source of the Cr (III) ions, and sodium nitrate.

Further, the passivating solution according to this invention contains sulfate ions. The preferred sulfation concentration is in the range of 0.07 to 50 g / L, more preferably 0.35 to 10 g / L. It has been found to be particularly advantageous to select the sulfate concentration such that it is present in the passivating solution in half the molar amount based on Cr (III). As source of sulfate ions, all water-soluble sulfate salts can be used, provided that the counterion does not adversely affect the formation of the passivation layer. Preferably, sodium sulfate is used. Further, the sulfate ions may also be added together with the vanadyl cation as vanadyl sulfate and / or together with the chromium (III) ions as the chromium sulfate.

The passivation solution of the present invention further contains one or more complexing agents capable of complexing Cr (III) ions. The complex image is selected from the group consisting of monocarboxylic acids, dicarboxylic acids, tricarboxylic acids, hydroxycarboxylic acids and fluoride. A typical representative of a monocarboxylic acid is acetic acid. Examples of dicarboxylic acids which can be used in the passivation solution of the present application are oxalic acid, malonic acid and succinic acid. As the tricarboxylic acid, there may be mentioned, for example, citric acid and, as the hydroxy acid, the malic acid, glycolic acid and tartaric acid. Other possible hydroxycarboxylic acids are aromatic hydroxy or polyhydroxycarboxylic acids such as salicylic acid or gallic acid. The carboxylic acid can be added as a salt, for example sodium or potassium salt, or as the free acid. However, it is most preferred to use fluoride as the complexing agent. As fluoride ions, all soluble fluoride compounds can be used. Preferably used are sodium fluoride, NaF, potassium fluoride, KF, ammonium fluoride, NH ₄ F, sodium bifluoride, NaF · HF, potassium bifluoride, KF · HF, ammonium bifluoride, NH ₄ F · HF. Among them, sodium fluoride, NaF, is particularly preferable. In the case of fluoride and other monodentate chelating agents, it is preferred that the molar ratio to Cr (III) ions be 2/1, so that at least two coordination sites of the chromium atom can be occupied. In the case of more-functional complexing agents, as in the case of the di- and tricarboxylic acids, it is likewise preferable for these to be present in a doubly molar ratio to chromium, based on the functional groups of the complexing agent. The preferred maximum amount of complexing agent is achieved when the Cr (III) complex is fully coordinated with complexing ligands. That is, in the case of monovalent ligands, such as fluoride, the preferred maximum amount is the 6-fold molar amount based on Cr (III) and in the case of eg bidentate ligands (eg malonic acid) the 3-fold molar amount based on Cr (III) , For example, when sodium fluoride is used as a complexing agent, it is preferable to use an amount of 0.1 to 50 g / l, more preferably 0.5 to 10 g / l.

• 0,1 - 50 g/l Cr(III)- Ionen,
• Vanadyl-Kationen in einer Menge, dass das Gewichtsverhältnis Cr/V in einem Bereich von 5/1 bis 100/1 liegt,
• 0,75 - 75 g/l Nitrationen,
• 0,07 - 50 g/l Sulfationen und
• einen oder mehrere Komplexbildner für Cr(III)-Ionen ausgewählt aus der Gruppe der Monocarbonsäuren, Dicarbonsäuren, Tricarbonsäuren, Hydroxycarbonsäuren und Fluorid,
• wobei der Komplexbildner in einer Menge zugesetzt wird, dass mindestens zwei Koordinationsstellen des Chromatoms besetzt werden.

According to a particularly preferred embodiment of the present invention, the cobalt-free, aqueous passivation solution contains the following components:

• 0.1-50 g / l Cr (III) ions,
• Vanadyl cations in an amount such that the weight ratio Cr / V is in a range of 5/1 to 100/1,
• 0.75 - 75 g / l nitrate ions,
• 0.07 - 50 g / l sulfate ions and
• one or more complexing agents for Cr (III) ions selected from the group consisting of monocarboxylic acids, dicarboxylic acids, tricarboxylic acids, hydroxycarboxylic acids and fluoride,
• wherein the complexing agent is added in an amount to occupy at least two coordination sites of the chromium atom.

In a most preferred embodiment, in the above passivating solution, the sulfate ion concentration is selected to be in one-half molar amount based on Cr (III).

• 0,1 - 50 g/l Cr(III)- Ionen,
• Vanadyl-Kationen in einer Menge, dass das Gewichtsverhältnis Cr/V in einem Bereich von 5/1 bis 100/1 liegt,
• 0,75 - 75 g/l Nitrationen,
• Sulfationen in einer Menge, dass sie in der halben molaren Menge bezogen auf Cr(III) vorliegen, und
• Fluorid,
• wobei das molare Verhältnis von Fluorid/Cr(III) mindestens 2/1 beträgt.

According to a further preferred embodiment, the cobalt-free, aqueous passivation solution contains the following components:

• 0.1-50 g / l Cr (III) ions,
• Vanadyl cations in an amount such that the weight ratio Cr / V is in a range of 5/1 to 100/1,
• 0.75 - 75 g / l nitrate ions,
• Sulfate ions in an amount that they are present in half the molar amount based on Cr (III), and
• Fluoride,
• wherein the molar ratio of fluoride / Cr (III) is at least 2/1.

The present invention further provides a process for producing a Cr (III) -containing conversion layer on Zn or Zn alloy layers. The conversion layer is formed by dipping the Zn or Zn alloy layer in the passivation solution of the present invention. Preferably, the immersion time is in the range of 30 to 120 seconds. The passivation solution preferably has a temperature of 15 ° C to 60 ° C. In this way, conversion layers can be produced which have a thickness of about 20 to 500 nm. The longer the immersion time and the higher the temperature of the passivation solution, the thicker the layers obtained become. The conversion layers obtained are Cr (VI) -free. After immersing the Zn or Zn alloy layers in the passivation solution, the samples are taken, then usually rinsed with water and then dried, preferably at elevated temperature (eg 80 ° C, 20 minutes).

According to a particularly preferred embodiment, the layers obtained have a thickness of less than 100 nm, in particular of about 50-70 nm, and even at these low layer thicknesses, a resistance in the salt spray test according to DIN EN ISO 9227 of more than 300 hours can be achieved. Such a layer can be obtained, for example, under the process conditions described in Example 1.

Examples

Inventive Example 1

• 497 g Wasser
• 108,5 g Chrom(III)-chlorid CrCl₃*6 H₂O
• 38 g Natriumfluorid NaF
• 17 g Vanadylsulfat VOSO₄*6 H₂O
• 216 g Natriumnitrat NaNO₃
• 31 g Natriumsulfat NaSO₄

Preparation of the Passivierungskonzentrates invention

• 497 g of water
• 108.5 g of chromium (III) chloride CrCl ₃ .6H ₂ O
• 38 g sodium fluoride NaF
• 17 g of vanadyl sulfate VOSO ₄ * 6 H ₂ O
• 216 g of sodium nitrate NaNO ₃
• 31 g sodium sulfate NaSO ₄

The components are mixed in the order listed and stirred for 30 minutes at 65 ° C. After cooling to room temperature and supplementing the evaporation losses to 1000 g, the passivation concentrate is ready for use. To prepare a passivation solution, 25 ml of the passivation concentrate described above are made up to 1000 ml with water and the pH is adjusted to 1.9 with nitric acid. In a weakly acidic commercial zinc bath (zinc bath Slotanit OT 1, Dr.-Ing Max Schlötter) steel sheets are coated with about 10 μm zinc. These Test panels are passivated at 25 ° C for 60 seconds in the passivation solution. The treated panels were then rinsed with deionized water and dried in a convection oven at 80 ° C for 20 minutes. This results in slightly violet-blue iridescent passive layers.

In the salt spray test according to DIN EN ISO 9227, no zinc corrosion was observed after 360 hours of testing.

Inventive Example 2

• 171 g entionisiertes Wasser
• 108,5 g Chrom(III)-chlorid CrCl₃*6 H₂O, 50 Gew.%-ige Lösung
• 19 g Natriumfluorid

Before the passivation solution was prepared, vanadyl sulfate was first reacted with 5 times the molar amount of sodium acetate to form the vanadyl diacetate complex. To this was dissolved 4.15 g of vanadyl sulfate VOSO ₄ * 6 H ₂ O with 10.24 g of sodium acetate CH ₃ COONa * 3 H ₂ O in 80 ml of deionized water and stirred for 1 hour at room temperature. This solution was then used to prepare the following passivating concentrate.

• 171 g of deionized water
• 108.5 g of chromium (III) chloride CrCl ₃ .6H ₂ O, 50% by weight solution
• 19 g sodium fluoride

• 15,5 g Natriumsulfat, wasserfrei, Na₂SO₄ die oben beschriebene Umsetzungslösung aus Vanadylsulfat und Natriumacetat und
• 108 g Natriumnitrat, NaNO₃

zugegeben und mit entionisiertem Wasser auf 500 g aufgefüllt. Von diesem Passivierungskonzentrat wurden 200 ml mit entionisiertem Wasser zur gebrauchsfertigenThis approach is first stirred for 1 hour at 65 ° C to form the chromium fluoro complex. Then be

• 15.5 g of sodium sulfate, anhydrous, Na ₂ SO _4, the above-described reaction solution of vanadyl sulfate and sodium acetate and
• 108 g of sodium nitrate, NaNO ₃

added and made up to 500 g with deionized water. From this passivating concentrate, 200 ml of deionized water was ready for use

Passivation solution made up to 1000 ml and the pH adjusted to 1.9 with nitric acid. In a weak Acid, commercially available zinc bath (zinc bath Slotanit OT 1, Dr.-Ing Max Schlötter) steel sheets are coated with about 10 microns of zinc. These test panels are passivated at 25 ° C for a period of 120 seconds in the passivation solution. The treated panels were then rinsed with deionized water and dried in a convection oven at 80 ° C for 20 minutes. This results in yellow-violet, greenish iridescent passive layers.

In the salt spray test according to DIN EN ISO 9227, no zinc corrosion was observed after 360 hours of testing.

Comparative Example 1

• 581,5 g Wasser
• 108,5 g Chrom(III)-chlorid CrCl₃*6 H₂O
• 38 g Natriumfluorid NaF
• 25 g Cobaltsulfat COSO₄*7 H₂O
• 216 g Natriumnitrat NaNO₃
• 31 g Natriumsulfat NaSO₄

For comparison, a cobalt-containing passivation according to the prior art was used. The preparation of the passivation concentrate was carried out as described above. Instead of vanadyl sulfate, cobalt sulfate was used.

• 581.5 g of water
• 108.5 g of chromium (III) chloride CrCl ₃ .6H ₂ O
• 38 g sodium fluoride NaF
• 25 g cobalt sulphate COSO ₄ * 7 H ₂ O
• 216 g of sodium nitrate NaNO ₃
• 31 g sodium sulfate NaSO ₄

The components are mixed in the order listed and stirred for 30 minutes at 65 ° C. After cooling to room temperature and supplementing the evaporation losses to 1000 g, the passivation concentrate is ready for use. To prepare a passivation solution, 35 ml of the passivation concentrate described above are made up to 1000 ml with water and the pH is adjusted to 1.9 with nitric acid. In a weakly acidic commercial zinc bath (zinc bath Slotanit OT 1, Dr.-Ing Max Schlötter) steel sheets are coated with about 10 μm zinc. These test sheets are baked at 25 ° C for 60 seconds the passivation solution passivated. The treated panels were then rinsed with deionized water and dried in a convection oven at 80 ° C for 20 minutes. This results in slightly violet-blue iridescent passive layers.

The salt spray test in accordance with DIN EN ISO 9227 was discontinued after 96 hours of test, because a strong staining on 10-20% of the tested surface was already evident here.

Comparative Example 2

• 606,5 g Wasser
• 108,5 g Chrom(III)-chlorid*6 H₂O
• 38 g Natriumfluorid
• 216 g Natriumnitrat
• 31 g Natriumsulfat

As Comparative Example 2, a Passivierungskonzentrat was prepared which contained neither cobalt nor vanadium salts.

• 606.5 g of water
• 108.5 g of chromium (III) chloride * 6H ₂ O
• 38 g sodium fluoride
• 216 g of sodium nitrate
• 31 g sodium sulfate

The components are mixed in the order listed and stirred for 30 minutes at 65 ° C. After cooling to room temperature and supplementing the evaporation losses to 1000 g, the passivation concentrate is ready for use. To prepare a passivation solution, 35 ml of the passivation concentrate described above are made up to 1000 ml with water and the pH is adjusted to 1.9 with nitric acid. In a weakly acidic commercial zinc bath (zinc bath Slotanit OT 1, Dr.-Ing Max Schlötter) steel sheets are coated with about 10 μm zinc. These test panels are passivated at 25 ° C for 60 seconds in the passivation solution. The treated panels were then rinsed with deionized water and dried in a convection oven at 80 ° C for 20 minutes. This results in slightly violet-blue iridescent passive layers. In the salt spray test according to DIN EN ISO 9227, staining in the edge area of the test panels was already detectable after 8 hours of testing. After 136 hours of testing approximately 20% of the surface showed strong zinc corrosion.

The results of Comparative Example 2 and Comparative Example 1 show that addition of cobalt sulfate to the passivation concentrate can improve the corrosion resistance of the passivation layer. The replacement of cobalt sulfate by the vanadium compound according to the invention, however, again causes a substantial increase in the corrosion protection.

Comparative Example 3

As Comparative Example 3, Example 1, Test No. 21 was made US 4,126,490 reworked.

• 10 g/l Chromnitrat Cr(NO₃)₃*9 H₂O
• 30 g/l Kaliumaluminiumsulfat KAl(SO₄)₂
• 2,25 g/l Ammoniumvanadat NH₄VO₃
• 5,1 g/l Salzsäure (36 Gew.%)

Approach:

• 10 g / l chromium nitrate Cr (NO ₃ ) ₃ * 9 H ₂ O
• 30 g / l potassium aluminum sulfate KAl (SO ₄ ) ₂
• 2.25 g / l ammonium vanadate NH ₄ VO ₃
• 5.1 g / l hydrochloric acid (36% by weight)

The pH of the passivation solution was 1.8.

In a weakly acidic commercial zinc bath (zinc bath Slotanit OT 1, Dr. Max Schlötter) steel sheets were coated with about 10 μm zinc. These test panels were passivated at 25 ° C for a period of 10 seconds in the passivation solution. The treated panels were then rinsed with deionized water and dried in a convection oven at 80 ° C for 20 minutes. Passivation layers with blue-violet irrigation were obtained.

In the salt spray test according to DIN EN ISO 9227, clear coating corrosion (white rust) was observed after just 32 hours of testing.

Comparative Example 4

As Comparative Example 4 was a passivation solution according to the information in WO 2010/025442 A1 reworked.

38.50 g of potassium chrome alum KCr (SO ₄ ) ₂ * 12H ₂ O and 6.78 g of potassium vanadate KVO ₃ were mixed and made up to 1 liter with deionized water. The salts dissolved only slowly. Only after heating to 60 ° C and prolonged stirring a homogeneous solution was obtained. The pH was adjusted to 1.9 with 16% strength by weight hydrochloric acid. In the passivation solution prepared in this way, a freshly galvanized steel sheet (zinc bath Slotanit OT 1, Schlötter) was passivated at 25 ° C. for 60 seconds. After drying in a convection oven (80 ° C, 20 minutes), a colorless, wipeable passivation layer was obtained. In this form, passivation layers are not suitable as corrosion protection layers. A salt spray test was therefore not performed.

Inventive Example 3

Five passivating concentrates according to the invention having the same chromium salt concentration but different vanadium salt concentrations were used. Passivation solutions each containing 35 ml / l of the passivation concentrate were prepared from these concentrates and passivated freshly galvanized copper sheets (surface 1 dm ² ) at 25.degree. C. for 60 seconds each. The passivation layer of one test sheet was then removed by immersion in 16% strength by weight hydrochloric acid. This solution was dissolved in a 100 ml volumetric flask and therein the elements chromium and vanadium were determined by ICP analysis and thus the relative Proportions of chromium and vanadium in the passivation layer determined.

• 605,96 g Wasser
• 108,5 g Chrom(III)-chlorid CrC1₃*6 H2O
• 38 g Natriumfluorid NaF
• 5,4 g Vanadylsulfat VOSO₄*6 H₂O
• 216 g Natriumnitrat NaNO₃
• 31 g Natriumsulfat NaSO₄

Inventive Example 3a

• 605.96 g of water
• 108.5 g of chromium (III) chloride CrC1 ₃ * 6 H2O
• 38 g sodium fluoride NaF
• 5.4 g of vanadyl sulfate VOSO ₄ * 6H ₂ O
• 216 g of sodium nitrate NaNO ₃
• 31 g sodium sulfate NaSO ₄

This concentrate contains 1.0 g / kg vanadium and 21.2 g / kg chromium.

• 598,2 g Wasser
• 108,5 g Chrom(III)-chlorid CrCl₃*6 H₂O
• 38 g Natriumfluorid NaF
• 8,3 g Vanadylsulfat VOSO₄*6 H₂O
• 216 g Natriumnitrat NaNO₃
• 31 g Natriumsulfat NaSO₄

Inventive Example 3b

• 598.2 g of water
• 108.5 g of chromium (III) chloride CrCl ₃ .6H ₂ O
• 38 g sodium fluoride NaF
• 8.3 g vanadyl sulfate VOSO ₄ * 6 H ₂ O
• 216 g of sodium nitrate NaNO ₃
• 31 g sodium sulfate NaSO ₄

This concentrate contains 1.56 g / kg vanadium and 21.2 g / kg chromium.

• 589,5 g Wasser
• 108,5 g Chrom(III)-chlorid CrCl₃*6 H₂O
• 38 g Natriumfluorid NaF
• 17 g Vanadylsulfat VOSO₄*6 H₂O
• 216 g Natriumnitrat NaNO₃
• 31 g Natriumsulfat NaSO₄

Inventive Example 3c

• 589.5 g of water
• 108.5 g of chromium (III) chloride CrCl ₃ .6H ₂ O
• 38 g sodium fluoride NaF
• 17 g of vanadyl sulfate VOSO ₄ * 6 H ₂ O
• 216 g of sodium nitrate NaNO ₃
• 31 g sodium sulfate NaSO ₄

This concentrate contains 3.2 g / kg vanadium and 21.2 g / kg chromium.

• 604,33 g Wasser
• 108,5 g Chrom(III)-chlorid CrCl₃*6 H₂O
• 38 g Natriumfluorid NaF
• 21,7 g Vanadylsulfat VOSO₄*6 H₂O
• 216 g Natriumnitrat NaNO₃
• 31 g Natriumsulfat NaSO₄

Inventive example 3d

• 604.33 g of water
• 108.5 g of chromium (III) chloride CrCl ₃ .6H ₂ O
• 38 g sodium fluoride NaF
• 21.7 g of vanadyl sulfate VOSO ₄ * 6H ₂ O
• 216 g of sodium nitrate NaNO ₃
• 31 g sodium sulfate NaSO ₄

This concentrate contains 4.08 g / kg vanadium and 21.2 g / kg chromium.

• 581 g Wasser
• 108,5 g Chrom(III)-chlorid CrCl₃*6 H₂O
• 38 g Natriumfluorid NaF
• 25,5 g Vanadylsulfat VOSO₄*5 H₂O
• 216 g Natriumnitrat NaNO₃
• 31 g Natriumsulfat NaSO₄

Inventive example 3e

• 581 g of water
• 108.5 g of chromium (III) chloride CrCl ₃ .6H ₂ O
• 38 g sodium fluoride NaF
• 25.5 g vanadyl sulfate VOSO ₄ * 5 H ₂ O.
• 216 g of sodium nitrate NaNO ₃
• 31 g sodium sulfate NaSO ₄

This concentrate contains 4.8 g / kg vanadium and 21.2 g / kg chromium.

Inventive Example 4

A passivation test was carried out with the concentrate from experiment 3c with a batch concentration of 200 ml / l. The passivation solution contained 5.6 g / l of chromium and 412 mg / l of vanadium and thus, based on the chromium content, corresponds to a passivation solution of the type used in the cobalt-containing passivations. Galvanized sheets were passivated at pH 1.9 and 25 ° C for 120 seconds. A yellowish-green passivation layer was obtained. The ICP analysis of the detached passivation layer gave a chromium content of 1.43 mg / dm ² chromium and 1.06 mg / dm ² vanadium, thus a chromium: vanadium ratio of 1.35. In the salt spray test according to DIN EN ISO 9227, no zinc corrosion was detected after 360 hours of testing. The result is surprising in that operating temperatures of 50-60 ° C must be set in the cobalt-containing thick film passivations to deposit such yellowish-green passivation layers (layer thickness about 300 nm). Inventive example Proportion of vanadium in the solution (mg / l) Proportion of vanadium in the layer (mg / dm ² ) Proportion of chromium in the solution (mg / l) Proportion of chromium in the layer (mg / dm ² ) Ratio of chromium: vanadium 3a 46 0.17 980 0.35 2.1 3b 72 0.18 980 0.29 1.6 3c 148 0.20 980 0.30 1.5 3d 188 0.34 980 0.3 0.89 3e 222 0.28 980 0.30 1.07 4 412 1.06 5600 1.43 1.35

All the sheets from Examples 3a-3e according to the invention still showed no zinc corrosion in the salt spray test according to DIN EN ISO 9227 at 288 hours.

Claims (8)

Cobalt-free, aqueous passivation solution comprising: Cr (III) ions, - vanadyl cations, - nitrate ions, - Sulfate ions and - One or more complexing agents for Cr (III) ions selected from the group of monocarboxylic acids, dicarboxylic acids, tricarboxylic acids, hydroxycarboxylic acids and fluoride. A cobalt-free, aqueous passivating solution according to claim 1, wherein the vanadyl cations are added to the passivation solution as vanadyl sulfate or as a vanadyl diacetate complex or as a mixture thereof. A cobalt-free, aqueous passivating solution according to claim 1 or 2, comprising: 0.1-50 g / l Cr (III) ions, Vanadyl cations in an amount such that the weight ratio Cr / V is in a range of 5/1 to 100/1, - 0.75 - 75 g / l nitrate ions, - 0.07 - 50 g / l sulfate ions and one or more complexing agents for Cr (III) ions selected from the group consisting of monocarboxylic acids, dicarboxylic acids, tricarboxylic acids, hydroxycarboxylic acids and fluoride, - Wherein the complexing agent is added in an amount that at least two coordination sites of the chromium atom are occupied. A cobalt-free, aqueous passivating solution according to one or more of claims 1-3, comprising: 0.1-50 g / l Cr (III) ions, Vanadyl cations in an amount such that the weight ratio Cr / V is in a range of 5/1 to 100/1, - 0.75 - 75 g / l nitrate ions, Sulfate ions in an amount such that they are present in half the molar amount relative to Cr (III), and Fluoride, wherein the molar ratio of fluoride / Cr (III) is at least 2/1. A process for producing a Cr (III) -containing conversion layer on a zinc or zinc alloy layer, wherein the zinc or zinc alloy layer is immersed in the passivating solution according to any one of claims 1-4. The method of claim 5, wherein the duration of the immersion is 30 to 120 seconds. A method according to claim 5 or 6, wherein the passivating solution has a temperature of 15 to 60 ° C. Use of the passivating solution according to any one of claims 1-4 for coating zinc or zinc alloy layers.