DE69930163T2 - POLYMETALATE AND HETEROPOLYMETALLATE FOR PASSIVATING COATINGS OF METALLIC SURFACES - Google Patents

Abstract

A method employing oxide film conversion coatings prepared using ferrate (VI) as the oxidizing agent is disclosed. Metal substrates or surfaces, such as aluminum, aluminum alloys or other metals, are contacted with an aqueous solution comprising ferrate (VI) anions to form a corrosion resistant conversion coating on the surface thereof. The ferrate anion concentration is preferably between about 0.0166 % and about 1.66 % by weight. The coating process is carried out by dipping, spraying, or painting at temperatures ranging from 25 DEG C to 100 DEG C for a period of time ranging from about 1 second to about 5 minutes.

Description

Territory of invention

The The present invention relates to a method of forming passivation coatings Metal substrates, such as aluminum or aluminum alloys.

background the state of the art

Dry Passivation coatings are generally formed by the surface of the metal into a firmly adhering coating (passivated) ", all or part of which is an oxidized form of the Substrate metal consists. Provide chemical passivation coatings often good corrosion resistance and strong binding affinity for coatings, like paints. The industrial application of a paint on metals generally requires the use of a chemical Passivation coating, especially if the operating conditions high performance requirements are required.

Even though Aluminum and aluminum alloys typically have good corrosion resistance due to the formation of a natural Oxide coating on the surface offer protection is limited. Aluminum alloys, the one Combination of moisture and electrolytes exposed, corrode much faster than pure aluminum, especially where Such aluminum alloys may contain copper.

It Generally, there are two types of processes for forming corrosion resistant passivation coatings on metal substrates, such as aluminum or aluminum alloy substrates. The first procedure closes anodic oxidation (anodization) where the substrate is in a chemical bath, such as a chromic acid or sulfuric acid bath, submerged and an electric current through the substrate and the chemical bath becomes. The passivation coating so on the surface of the Substrate is formed, provides improved corrosion resistance and an improved bonding surface for organic Coatings and finishes ready.

The second method of forming a corrosion resistant chemical Passivation coating creates a chemical passivation coating by subjecting the substrate to a chemical solution, such as a chromic acid solution, however without using an electric current in the process. The chemical Solution can by submerging the substrate, manual application or spray application be applied. The resulting passivation coating on the surface of the aluminum or Aluminum alloy substrate provides improved resistance across from Corrosion and improved bonding surface for organic coatings and finishes.

Passsivierungsbeschichtungen Chromate-based are widespread been used in applications where maximum corrosion protection is needed. For example, treatment of aluminum or aluminum alloy substrates results with a chromate passivation coating bath in general a preferably thick, corrosion-resistant film consisting of hydrated Cr (III) and Al (III) oxides. This reaction is through the reduction driven by high-valent Cr (VI) ions and the oxidation of the Al metal. Of the Benefits of this chromate passivation coating include hydrophobicity and self-healing properties one.

The Light weight and the high strength of aluminum and aluminum alloys make these materials especially in aerospace applications suitable. Many aluminum structural parts, including Cd-plated Aluminum, Zn-clad aluminum and Zn-Ni clad aluminum, become present using chromic acid process technology treated. Chromsäurepassivierungsfilme, as they are formed on aluminum and aluminum alloy substrates, fulfill the 168-hour Salt fog exposure corrosion resistance criterion according to ASTM method B-117, however serve they mainly as a substrate surface for coatings or paint painting adhesion. Chromsäurepassivierungsbeschichtungen are relatively thin and coatings of low weight (40-150 mg per square foot) and do not cause unfavorable reductions in the durability of the aluminum and aluminum alloy structures, on which they are applied.

The use of chromate passivation coatings for aluminum and aluminum alloy substrates, as well as other substrates, is not without its disadvantages. Researchers have increasingly found problems with chromate passivation coatings associated with their extreme toxicity and carcinogenicity. Researchers have linked exposure to chromates to a variety of human diseases, including irritation of the respiratory tract, ulcerations and perforations of the nasal septum, dermatitis, skin allergy, asthma and lung cancer. As a result of these findings, government environmental regulations have been promulgated, particularly in California, as well as in other states that have drastic restrictions the permissible levels of hexavalent chromium (Cr (IV)) compounds in effluents and emissions associated with metal finishing operations. Consequently, chemical passivation processes using hexavalent chromium compounds have become prohibitively expensive, if any, and this has led to the need for an alternative means of achieving comparable material properties without the use of chromates.

recent Efforts to Non-Chromate Passivation Coatings have made use of other oxidizing agents including cerium compounds, alkaline solutions lithium salts and manganates and molybdates, included. Researchers have the effects of cerium compounds as a corrosion inhibitor for aluminum and copper alloys, such as Al 2024-T3, in chloride-containing solutions. It it has been suggested that cerium Corrosion of this alloy by reducing the speed the cathodic reduction of oxygen due to the formation of Cer (III) -rich films about Copper-containing intermetallic compounds inhibited, the act as local cathodic sites.

One Process for the surface modification of Aluminum-based materials that dip into boiling cerium salts followed by anodic polarization in a molybdate solution been reported. Although this surface modification method good corrosion resistant Produced films caused the long-term cooking of the substrate problems when pretreating large Structures dar. The problems of long-term cooking together with such of the electrochemical post-treatment step made this process for practical Applications not attractive.

Unusual passivity of aluminum alloys has been found when the aluminum alloys are exposed to alkaline solutions of lithium salts. The observed passivity has been explained as a consequence of the formation of a polycrystalline Li ₂ [Al ₂ (OH) ₆ ] ₂ CO ₃ .3H ₂ O film on the aluminum alloy surface. This film, referred to as hydrotalcite or "talc" coating, has been reported to provide enhanced corrosion protection during exposure to aggressive environments, however, the best results were obtained when the coated samples were allowed to cure for at least one week before This extremely long cure time would undoubtedly cause problems in practical industrial applications of talc coatings Although talc coatings improve the corrosion resistance of various substrates, only alloys with low concentrations of alloying elements (Al 6061-T6 and Al 1100) did so according to the salt spray test ASTM Method B-117.

attention has also been directed to the use of manganates and molybdenum in passivation coating solutions for aluminum alloys. The Permanganate passivation coating solutions included salts, such as silicates, Borates, nitrates, halides and phosphates, a.

Isomolybdate has been shown to improve the corrosion resistance of aluminum and aluminum alloys against localized attack by shifting the breakdown potential (E _b ) in a positive direction. The following reactions are believed to be included in the formation of a molybdenum-based passivation coating on aluminum: MoO ₄ ^2- + 5H ⁺ + Al = Mo ³⁺ + ½Al ₂ O ₃ · 3H ₂ O + H ₂ O 3MoO ₄ ^2- + 6H ⁺ + 2Al = 3MoO ₂ + Al ₂ O ₃ · 3H ₂ O

The treatment converts the aluminum surface into a superficial layer containing a complex mixture of aluminum / molybdenum compounds. It has been shown that the concentration of hydrated Mo ⁴⁺ in the film at all potentials was about 2 to 3 times greater than the concentration of hexavalent Mo ⁶⁺ . It has been suggested that the corrosion resistance of these molybdate coatings was due to the molybdate (VI) -rich areas on the film surface which inhibit access of Cl ^- anions to the metal / film surface. However, in the presence of alkaline solutions, molybdenum has a slight tendency to decompose water with the evolution of hydrogen to dissolve the molybdate in the hexavalent state as the molybdate anion MoO ₄ ^2- , thus weakening the passivation coating on the metal surface. Thus, to prepare a suitable hexavalent molybdate (Mo ⁶⁺ ) passivation solution, it is necessary to operate in an alkaline region having a pH greater than 10. In molybdate-free solutions at pH 10, AlOOH, which would normally form under lower pH conditions, is not suitable and will tend to dissolve. The presence of molybdenum data in the solutions is not sufficient to limit the rapid dissolution of the Al, and thus formation of an isomolybic-based passivation coating under these conditions is not favored.

Therefore there is a need for a passivation coating solution, containing non-toxic ions, the one stable corrosion resistant passivation coating on metal surfaces, in particular aluminum and aluminum alloys.

EP 1,136,591 relates to a hydrophilic agent for metallic material. The hydrophilizing agent does not contain chromium and imparts excellent corrosion resistance and long-term hydrophilicity to an element such as a heat exchanger made of aluminum. The hydrophilizing composition comprises a hydrophilic polymer having at least one nonionic functional group selected from primary amide, secondary amide, tertiary amide, hydroxy and polyoxyalkylene groups together with a hydrophilic polymer having at least one ionic functional group selected from Sulfo, phosphonatecarboxy, primary amino, secondary amino, tertiary amino and quaternary ammonium group, together with a vanadium compound, and a compound having at least one element selected from Zr, Ti and Si.

It is desirable that the conversion coating for one perfect adhesion of an applied protective coating, such as a paint, is suitable. There is also a need for a A method of using a passivation coating solution which contains non-toxic ions, a stable corrosion-resistant passivation coating on metal surfaces, especially on aluminum and aluminum alloys.

SUMMARY THE INVENTION

According to this invention, there is provided a method of oxidizing a metal surface using a first aqueous solution containing anions selected from one or more heteropolymetalates having the general formula BM _x O _y ^n- , wherein M is a transition metal, B Heteroatom selected from P, Si, Ce, Mn, Co or mixtures thereof, x is about 1 or greater than 1, y is about 1 or greater than 1, and n- is the valency of the selected anions, and wherein aqueous solution has a pH of between about 2 and about 5.

conveniently, comprises the method includes the following step of contacting the oxidized metal surface a second aqueous solution, the Alkali metal silicate, alkali metal borate, alkali metal phosphate, magnesium hydroxide, Calcium hydroxide, barium hydroxide or mixtures thereof in a concentration between about 0.015% and about 10%.

Prefers comprises the method further comprising contacting the oxidized metal surface with a third aqueous solution, the Contains alkali metal silicate.

The Procedure can continue rinsing the surface with deionized water after oxidizing the metal surface with the first aqueous solution, still before contacting the oxidized metal surface with the second aqueous solution, and Rinse the surface with deionized water after contacting the oxidized metal surface with the second aqueous solution, still prior to contacting the oxidized metal surface with the third aqueous solution.

Prefers contains the second aqueous solution calcium hydroxide and lithium nitrate. Preferably, the transition metal is selected from Mo, V or W.

conveniently, is the concentration of anions in the first solution between about 1 and about 5 wt .-%.

Advantageously, the anions are selected from (PMo ₁₂ O ₄₀ ) ^3- , (PMo ₁₀ V ₂ O ₄₀ ) ^5- , (MnPW ₁₁ O ₃₉ ) ^5- , (PW ₁₂ O ₄₀ ) ^3- , (SiMo ₁₂ O ₄₀ ) ^4- , (SiW ₁₂ O ₄₀ ) ^4- , (Mo ₇ O ₂₄ ) ^6- , (CeMo ₁₂ O ₄₂ ) ⁸ or mixtures thereof.

conveniently, contains the first aqueous solution fluoride ions, wherein the fluoride ions are provided by a compound, which is selected from ammonium fluoride, alkali metal fluorides, fluorosilicic acid salts, Fluorine acid salts of titanium, Fluorzirkonsäuresalzen or mixtures thereof, wherein the concentration of the fluoride ions between about 0.1 and about 3.0 weight percent.

Prefers contains the first solution Oxyanions, wherein the oxyanions are selected as alkali metal permanganate, Perrhenate, metavanadate or mixtures thereof, the concentration of the Oxyanions between about 0.1 and about 3.0 wt .-% is.

advantageously, contains the solution Silications, wherein the silications by water-soluble alkali metal silicate salts be provided, the concentration of the silicates between about 0.1 and about 3.0 weight percent.

conveniently, contains the aqueous solution borate ions, wherein the borate ions are provided by water-soluble alkali metal salts wherein the concentration of borate ions is between about 0.1 and about 3.0% by weight.

advantageously, the alkali metal salts are alkali metal tetraborate.

In a preferred method the first solution Phosphate ions, wherein the phosphate ions are selected from alkali metal orthophosphate, Alkali metal metaphosphate, alkali metal pyrophosphate or mixtures the same, wherein the concentration of phosphate ions between about 0.1 and about 3.0 wt .-% is.

conveniently, contains the first solution Nitrate ions, wherein the nitrate ions are selected from alkali metal nitrates, Ammonium nitrates and mixtures thereof, wherein the concentration of the nitrate is between about 0.1 and about 1% by weight.

advantageously, the first aqueous solution has one pH between about 2 and about 5.

in the preferred method, the metal surface is selected from aluminum, aluminum alloys and mixtures thereof, the method further comprising the steps a cleaning the metal surface before contacting the metal surface with the aqueous solution and forming a boehmite layer around the metal surface to coat a process that is selected from boiling or anodizing before the contact of the metal surface with the first aqueous solution.

The present invention provides a passivation coating solution containing polymetalates and / or heteropolymetallates to oxidize the surface of various metal substrates. The polymetalates have the general formula M _x O _y ^{n -} , wherein M is selected from the group comprising Mo, V and W or mixtures thereof. The heteropolymetalates have the general formula BM _x O _y ^{n -} , where B is a heteroatom selected from P, Si, Ce, Mn or Co or mixtures thereof, and M is in turn selected from Mo, V, W or combinations the same. The concentration of the polymetalate and / or heteropolymetallate anions is preferably between about 1 and about 5% by weight. Examples of typical anions that are used include, but are not limited to, (PMo ₁₂ O ₄₀ ) ^3- , (PMo ₁₀ V ₂ O ₄₀ ) ^5- , (MnPW ₁₁ O ₃₉ ) ^5- , (PW ₁₂ O ₄₀ ) ^3- , (SiMo ₁₂ O ₄₀ ) ^4- , (SiW ₁₂ O ₄₀ ) ^4- , (Mo ₇ O ₂₄ ) ^6- , (CeMo ₁₂ O ₄₂ ) ⁸ and mixtures thereof. The present invention also provides a method of using the solution to provide corrosion resistance and adhesion to exterior coatings over the treated metal substrate.

SHORT DESCRIPTION THE DRAWINGS

In order to the above features and advantages of the present invention can be understood in detail is a more detailed description of the invention, summarized above briefly, with reference to the embodiments given in the attached Drawings are illustrated. It should be noted, however, that the appended drawings only typical embodiments of this invention, and therefore not as limiting for her Scope are to be considered since the invention is equally effective for others embodiments can stand.

1 provides graphene from Mo3d XPS spectra of (a) H ₃ PMo ₁₂ O ₄₀ xH ₂ O; (b) an argon-dried Al-2024 plate treated with passivation coating solution containing H ₃ PMo ₁₂ O ₄₀ and Na ₂ SiF ₆ , and (c) an air-dried Al-2024 plate coated with passivation coating solution containing H ₃ PMo ₁₂ O ₄₀ and Na ₂ SiF ₆ had been treated.

2 Figure 4 is a graph showing the effect of heteropolyoxylate source and temperature on salt fog survival of 2024-T3 aluminum treated as described in Example 5.

3 Figure 4 is a graph showing the effect of additives and temperature on salt fog survival of 2024-T3 aluminum treated as described in Example 6.

4 Figure 12 is a table showing the solutions and conditions used to make passivation coatings on a large number of Al-2024 plates and the salt fog survival of such coated plates.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to non-chromate passivation coating solutions for metal substrates, the selected are made of aluminum, aluminum alloys, steels (e.g., carbon steels and stainless steels) and other ferrous metals. Where the terms "aluminum" and "aluminum alloys" are used herein should they be interpreted to include any other, i. "Aluminum" includes aluminum alloys not unless the description indicates otherwise.

Non-toxic polymetalates and heteropolymetallates are inorganic, non-toxic metal-oxygen clusters which entail large reservoirs of transition metals such as Mo _x ⁶⁺ , W _x ⁶⁺ and V _x ⁵⁺ (x> 1) hold. At their highest oxidation states, these compounds are very similar to chromates in forming active, self-healing coatings. These compounds accept electrons without major changes in their structures, are highly soluble in various solvents, exhibit good adsorption on solid surfaces and are very strong oxidants. In addition, the reduced form of these compounds can be oxidized in air, providing continuously regenerated reservoirs of high valence metal states on the metal surface which introduce the beneficial "self-healing" effect given to preferred chemical passivation coatings MoO ₄ ^2- , stable only in very basic solutions, where the dissolution of aluminum is a major problem Another attractive feature of the heteropolymetalate compounds is that they readily accept heteroatoms, such as Ce, Si, P and Mn, which form a passivation coating are known useful.

One aspect of the present invention provides a passivation coating solution containing polymetalates and / or heteropolymetallates to oxidize the surface of various metal substrates. The polymetalates have the general formula M _x O _y ^{n -} , where M is selected from the group consisting of Mo, V and W. The heteropolymetallates have the general formula BM _x O _y ^{n -} , wherein B is a heteroatom selected is selected from P, Si, Ce, Mn or Co, and wherein M is again selected from Mo, V, W or combination thereof. The concentration of the polymetalate and / or heteropolymetallate anions is preferably between about 1 and about 5 weight percent. Examples of typical anions used include, but are not limited to, (PMo ₁₂ O ₄₀ ) ^3- , (PMo ₁₀ V ₂ O ₄₀ ) ^5- , (MnPW ₁₁ O ₃₉ ) ^5- , (PW ₁₂ O ₄₀ ) ^3- , (SiMo ₁₂ O ₄₀ ) ^4- , (SiW ₁₂ O ₄₀ ) ^4- , (Mo ₇ O ₂₄ ) ^6- , (CeMo ₁₂ O ₄₂ ) ⁸ and mixtures thereof.

A Another aspect of the present invention relates to a method for forming an oxide or hydrous oxide passivation coating on a metal surface. The metal surface is treated with an aqueous passivation coating solution, the Polymetalates and / or Heteropolymetallate contacted. These passivation coating solutions contain preferably between about 1 and about 5% polymetalate or heteropolymetallate anions, and preferably have a pH between about 2 and about 5 on. These solutions create chemical passivation coatings that protect against metallic Substrates that perform the salt fog standard test according to ASTM method B-117.

The chemical passivation coating solutions disclosed in the present Invention can be used also contain fluoride ions. Fluoride ions are useful for the passivation coating, as they help in building thickness of the coating on the metal surface. These Fluoride ions can obtained from a number of sources, such as ammonium metal fluorides, Alkali metal fluorides, fluorosilicic salts, fluortitic acid salts and fluorocyclo acid salts. The Concentration of the fluoride ions in the solution is preferably between about 0.1 and about 3.0 wt%.

The conversion coating can also in addition, transition metal oxides with high-valent transition metal cations such as Mn ^+7, V ^5+, Re ^7+, included. The transition metal oxides can be obtained from sources such as alkali metal permanganate, perrhenate and metavanadate. The concentration of transition metal oxides in the solution is preferably between about 0.1 and about 3.0 wt%. Pentavalent vanadium species are known to form polyvanadate anions, such as HV ₁₀ O ₂₈ ^4- , in acidic solutions. Polyvanadate anions have been used for the seal passivation of coated metal surfaces.

The Adding ionic compounds to the aqueous chemical passivation coating solution in suitable concentrations may be for the performance of the resulting Passivation coating useful be. The particular additives for improved performance depend on the chemical composition of the substrate, the chemical composition the aqueous solution and the assumed conditions of use. The concentrations of each certain additives can be from the same parameters as well as the concentrations of other additives in the solution depend.

The aqueous chemical conversion coating The present invention may also contain silicates in concentrations between about 0.1 and about 3.0 wt .-%. The silications can from water-soluble Alkali metal silicate salts are obtained.

The aqueous chemical conversion coating The present invention also provides borate ions in concentrations between about 0.1 and about 3.0 wt .-%. The borate ions can from water-soluble Alkali metal salts, for example Alkalimetalltetraborat obtained become.

The aqueous passivation chemical coating solution of the present invention may also contain phosphate ions in concentrations between about 0.1 and about 3.0 weight percent. The phosphate ions can be made from water-soluble alkali metal phosphate salts, including, but not limited to, alkali metal orthophosphate, alkali metal metaphosphate, alkali metal pyrophosphate, and mixtures thereof.

The aqueous chemical conversion coating The present invention may also include nitrate ions in concentrations between 0.1 and about 3 wt .-%. The nitrate ions can be out Alkali metal or ammonium nitrates are obtained.

The Quantities of the various ions discussed above can theoretically determined prior to the preparation of the aqueous passivation coating solution be or they can be measured analytically using methods that professionals are known in the art and can be adjusted accordingly become.

Preferably, the surface of the substrate is thoroughly cleaned and pretreated prior to contacting with the aqueous chemical passivation coating solution. The substrate surface may be cleaned by sonication in acetone or by any of several commercially available alkaline cleaning solutions to remove soil, grease or other contaminants, followed by water rinse and treatment with one of several commercially available deoxidizer solutions such as LNC deoxidizer (Oakite Products Inc., Berkeley Heights, New Jersey) to remove any residual oxidic surface coating. When the substrate is aluminum, the cleaned surface is then rinsed or immersed in boiling water or anodized to form a boehmite layer of the general formula (AlO _x (OH) _y ) prior to immersion in the aqueous chemical passivation coating solution.

The Properties of the chemical passivation coating under Use of the present invention are also dependent on the contact time of the passivation solution with the substrate, the Temperature of the passivation solution and the substrate, and the pH of the passivation solution. The contact time is typically in the range of about 1 minute to about 5 minutes. The temperature of the passivation solution is typically in the Range of about 25 ° C up to about 80 ° C lie. The pH of the passivation solution is typically between about 2 and about 5 are dependent from the composition of the passivation solution.

After this the polymetalate or heteropolymetalate passivation coating is applied, can Post-treatment steps are used to apply the passivation coating the surface of the substrate to seal and thereby the overall performance of the chemical Passivation coating to improve. A post treatment of applied chemical passivation coating can contact the oxidized substrate surface with an aqueous post-treatment solution which contains one or more connections that are selected the group comprising an alkali metal silicate, an alkali metal borate, an alkali metal phosphate, magnesium hydroxide, calcium hydroxide, barium hydroxide and combinations thereof. Preferably, the concentration is this Compounds in the post-treatment solution between about 0.015 and about 10% by weight. The contact time during which the treated Substrate immersed in the aftertreatment solution is preferably between about 1 minute and about 20 minutes. The temperature of the post-treatment solution and the substrate during the post-treatment step is preferably between about ambient or room temperature (typically about 25 ° C) and about the boiling point of the aqueous solution (typically about 100 ° C).

Of the Aftertreatment step, for example using calcium hydroxide, by reducing the concentration of carbon dioxide in water, Forming a solution by combining calcium hydroxide with the water at a reduced level Concentration of carbon dioxide and providing a contact between the metal surface and the solution carried out. The concentration of carbon dioxide in the water can by any known method can be reduced, but is preferred by Heat the water is reduced, most preferably to a temperature between 50 ° C and 100 ° C. Other Method for reducing the carbon dioxide concentration in the water shut down passing the water through an electroosmotic pump Passing the carbon dioxide through a hydrophobic membrane or Centrifuging the water. It is important that the carbon dioxide content of the water is reduced, as the amount of carbon dioxide in the Water at room temperature will give a solution that will not the desired Passivation coating generated.

Aluminum plates prepared with heteropolymetalate passivation coatings are immersed in one or more post-treatment solutions, such as alkali metal silicate and calcium hydroxide, between 80 ° C and 100 ° C for 1 minute to 20 minutes. Preferably, the treated aluminum plates were then post-treated by immersing first in an aqueous solution containing 0.09% by weight of calcium hydroxide and 0.6% by weight of lithium nitrate at 100 ° C. for 20 minutes and secondly in an aqueous solution containing 2.4 Wt .-% alkali metal silicate at 80 ° C for 5 minutes. Optional can the aqueous calcium hydroxide solution further includes manganese, molybdenum, or a combination thereof which forms stable metal oxides in the coatings and acts as corrosion inhibitors of the coatings.

The show the following examples of use of the present invention the function of the invention and disclose some of its preferred Embodiments. These examples are not intended to limit the scope of the invention on the steps described herein, since the invention may include other steps and conditions. Except where it is were aluminum plates with a degree of 1.5 Inches by 2 inches in the following examples, and all amounts are weight percentages.

example 1

This example describes the pretreatment of the aluminum plates. Prior to contacting the aluminum plates with an aqueous chemical passivation coating solution, the plates were degreased and prepared by sonication in acetone for 30 minutes. They were then cleaned with an alkaline cleaning solution (such as 4215 NCLT, available from Elf Atochem - Turco Products Division, Westminster, California) for 10 minutes at 60 ° C. The plates were then rinsed with deionized water and treated with a deoxidizer solution of 15% LNC deoxidizer (Oakite Products Inc., Berkely Heights, New Jersey) for 10 minutes at 25 ° C. The plates were then immersed in boiling water for 20 minutes and coated with a thin layer of boehmite of a general formula AlO _x (OH) _y .

Example 2

This Example describes the treatment of aluminum plates with a aqueous chemical passivation coating solution containing contains only polymetalate or heteropolymetalate compounds. Aqueous chemical coating solutions of polymetalates or heteropolymetalates with concentrations between about 1.0 and 5.0 wt% were prepared, and the like in Example 1 pretreated aluminum plates were described in the. solution for 2 to Immersed for 5 minutes at different temperatures in the range of 25 ° C to 80 ° C. The plates were then thoroughly rinsed with deionized water, in the air for Dried for 48 hours and exposed in a salt fog chamber according to ASTM method B-117 tested.

Example 3

This Example describes the treatment of the aluminum plates with passivation coating solutions, the polymetalate or heteropolymetalate compounds in combination with one or more compounds, such as phosphates, borates, silicates, Fluorides or metal oxides. Aqueous solutions of polymetallates or Heteropolymetallates with concentrations ranging from 1.0% to 5.0% and one or more additives at concentrations of 0.1% up to 3.0% were produced. The prepared as described in Example 1 Aluminum plates were different in these solutions for 2 to 5 minutes Temperatures of 25 ° C up to 80 ° C immersed. The plates were then washed thoroughly with deionized water rinsed, in the air for Dried for 48 hours and exposed in a salt fog chamber according to ASTM method B-117 tested.

Example 4

This Example describes the formation of reduced heteropolymolyb data on the substrate surfaces and a self-oxidation in air. The as described in Example 1 pretreated plates were immersed in a passivation coating solution, from 1.0% to 5.0% heteropolymolyb data and 0.1% to 3.0% fluoride containing species. The plates were coated with the passivation coating solution for 2 minutes at temperatures between 60 ° C and 80 ° C keep in touch. The yellow passivation solution (a characteristic color for the most of the heteropolymolybdates changed to dark green after 2 Minutes, and the substrate surfaces were coated with dark films.

It has been repeatedly observed that the dark coatings obtained from the treatments of Al 2024-T3 plates with passivating solutions of H ₃ PMo ₁₂ O ₄₀ and Na ₂ SiF ₆ became brighter when dried in air for extended periods of time , This was indicative of the formation of the reduced heteropolymolybdate species during the passivation process and a slow reoxidation during the final air drying process. To test this hypothesis, heteropolymolybdate coatings were prepared and handled in an argon atmosphere. This resulted in the preservation of the coating color. XPS spectra of such a coating were compared with a pure heteropolymolybdate compound (H ₃ PMo ₁₂ O ₄₀ ) as well as with XPS spectra of the same coating dried in air for 10 days (see 1 ). As can be seen, the air-dried heteromolybdate coating showed a set of Mo 3d peaks with a 3d5 / 2 binding energy (see 1C ), which is in good agreement with that of pure H ₃ PMo ₁₂ O ₄₀ (see 1A ) and is consistent with the presence of hexavalent Mo lybdänspezies. On the other hand, the Mo3d XPS spectrum of argon-dried coatings appeared to be somewhat complicated. The XPS spectrum used in 1b shows at least 2 sets of Mo3d peaks indicative of reduced molybdenum species. These results suggest that reduced heteropolymolybdates are formed during the passivation process and oxidize themselves in air to form hexavalent species which can be further used to self-heal the aluminum surface.

The Plates were then thoroughly rinsed with deionized water. While This step became a solution with a blue color (a characteristic color for the reduced Heteropolymolybdate) rinsed from the substrate surfaces. A set of plates became in a chamber under running Helium for Air dried for 12 hours. The dark coating on the plates, which left in air was turned into a very pale brown color in a few hours transformed. When the plates are dried in an inert atmosphere In contrast, the dark coating was preserved. However, if these dark coatings were exposed to air for 12 hours, The dark color disappeared in a few hours due to oxidation the reduced heteropolymolybdate.

Example 5

This example describes the post-treatment of the coated substrates to improve and preserve the performance of the chemical passivation coating. An aqueous solution of polymetalates or heteropolymetallates having concentrations in the range of 1.0 to 5.0 weight percent. The substrate plates prepared as described in Example 1 were immersed in the prepared solutions for 2 minutes at different temperatures of 50 ° C to 80 ° C. The plates were rinsed thoroughly with deionized water and then aftertreated by immersion first in an aqueous solution containing 0.09% by weight of calcium hydroxide and 0.6% by weight of lithium nitrate, at 100 ° C for 20 minutes, and secondly in an aqueous solution containing 2.4 wt .-% alkali metal silicate at 80 ° C for 5 minutes. They were finally dried in air for 48 hours and tested by exposure in a salt spray chamber according to ASTM Method B-117. The results are in 2 shown.

Example 6

This example describes the post-treatment of the coated substrates to improve and preserve the performance of the chemical passivation coating. An aqueous solution of polymetalates or heteropolymetallates having concentrations ranging from 1.0 to 5.0 weight percent and one or more additives at concentrations of 0.1 to 3.0 percent were prepared. The substrate plates prepared as described in Example 1 were immersed in the prepared solutions for 2 minutes at different temperatures of 50 ° C to 80 ° C. The plates were rinsed thoroughly with deionized water and then aftertreated by immersion first in an aqueous solution containing 0.09% by weight of calcium hydroxide and 0.6% by weight of lithium nitrate, at 100 ° C for 20 minutes, and secondly in an aqueous solution containing 2.4 wt .-% alkali metal silicate at 80 ° C for 5 minutes. They were finally dried in air for 48 hours and tested by exposure in a salt spray chamber according to ASTM Method B-117. The results are in 3 shown.

While that The foregoing refers to the preferred embodiment of the present invention Invention is directed, can other and further embodiments the invention designed without departing from the basic scope of the same and the scope thereof is determined by the following claims.

Claims (16)

A process comprising oxidizing a metal surface using a first aqueous solution containing anions selected from one or more heteropolymetalates having the general formula BM _x O _y ^n- , wherein M is a transition metal, B is a heteroatom selected from P, Si, Ce, Mn, Co or mixtures thereof, x is about 1 or greater than 1, y is about 1 or greater than 1, and n- is the valency of the selected anions, and wherein the aqueous solution has a pH between about 2 and about 5. The method of claim 1, wherein the method comprises following step of contacting the oxidized metal surface with a second aqueous solution comprising Alkali metal silicate, alkali metal borate, alkali metal phosphate, magnesium hydroxide, calcium hydroxide, Barium hydroxide or mixtures thereof in a concentration between about 0.015% and about 10%. The method of claim 2, further comprising contacting the oxidized metal surface with a third aqueous solution, the Contains alkali metal silicate. The method of claim 3, further comprising rinsing the surface with deionized water after oxidizing the metal surface with the first aqueous solution, before contacting the oxidized metal surface with the second aqueous solution, and rinsing the surface with deionized water after contacting the oxidized metal surface with the second aqueous solution, before contacting the oxidized metal surface with the third aqueous solution. A method according to claim 3 or claim 4, wherein the second aqueous solution calcium hydroxide and Contains lithium nitrate. Method according to one of the preceding claims, wherein the transition metal is selected from Mo, V or W. Method according to one of the preceding claims, wherein the concentration of anions in the first solution is between about 1 and about 5 wt .-% is. Method according to one of the preceding claims, wherein the anions are selected from (PMo ₁₂ O ₄₀ ) ^3- , (PMo ₁₀ V ₂ O ₄₀ ) ^5- , (MnPW ₁₁ O ₃₉ ) ^5- , (PW ₁₂ O ₄₀ ) ^3- , (SiMo ₁₂ O ₄₀ ) ^4- , (SiW ₁₂ O ₄₀ ) ^4- , (CeMo ₂₄ O ₄₂ ) ⁸ or mixtures thereof. Method according to one of the preceding claims, wherein the first aqueous solution fluoride ions contains wherein the fluoride ions are provided by a compound, the selected is made from ammonium fluoride, alkali metal fluorides, fluorosilicic acid salts, Fluoro titanic acid salts, Fluorzirkonsäuresalzen or mixtures thereof, wherein the concentration of the fluoride ions between about 0.1 and about 3.0 weight percent. Method according to one of the preceding claims, wherein the first solution Contains oxyanions, wherein the oxyanions are selected are made of alkali metal permanganate, perrhenate, metavanadate or Mixtures thereof, wherein the concentration of the oxyanions between about 0.1 and about 3.0 wt .-% is. Method according to one of the preceding claims, wherein the first solution Contains silicates, wherein the silications by water-soluble alkali metal silicate salts be provided, the concentration of the silicates between about 0.1 and about 3.0 weight percent. Method according to one of the preceding claims, wherein the aqueous solution contains borate ions, wherein the borate ions by water-soluble alkali metal salts be provided, the concentration of borate ions between 0.1 and about 3.0 wt .-% is. The method of claim 12, wherein the alkali metal salts Alkali metal tetraborate are. Method according to one of the preceding claims, wherein the first solution Contains phosphate ions, wherein the phosphate ions are selected are made of alkali metal orthophosphate, alkali metal metaphosphate, Alkali metal pyrophosphate or mixtures thereof, wherein the concentration of the phosphate ions is between about 0.1 and about 3.0 weight percent. Method according to one of the preceding claims, wherein the first solution Contains nitrate ions, wherein the nitrate ions are selected are made of alkali metal nitrates, ammonium nitrates or mixtures the same, wherein the concentration of nitrate is between about 0.1 and about 1% by weight. Method according to one of the preceding claims, wherein the metal surface is selected aluminum, aluminum alloys and mixtures thereof, and the method further comprising the steps of cleaning the metal surface before Contact the metal surface with the aqueous solution and forming a boehmite layer around the metal surface to coat a process that is selected from boiling or anodizing before the contact of the metal surface with the first aqueous solution.