Addition product, production and use thereof as corrosion inhibitor

Abstract

The invention relates to an addition product that can be produced from hexafluorosilicic acid, hexafluorotitanic acid, and/or hexafluorozirconic acid by an acid-base reaction with one or several organic bases and a method for production and use thereof. The addition products according to the invention guarantee a rapid and lasting inhibition of corrosion processes; they are in particular suitable for inhibiting the corrosion of light metals.

Description

TECHNICAL FIELD

[0001] The invention relates to an addition product, its production from one or several organic bases and one or several of the acids hexafluorosilicic acid, hexafluorotitanic acid, and hexafluorozirconic acid, and its use as corrosion inhibitor, in particular for the protection of light metals.

PRIOR ART

[0002] For the corrosion protection of light metals or light metal alloys, conversion baths with the corrosion inhibitors hexafluorosilicic acid, hexafluorotitanic acid, and hexafluorozirconic acid are used. The light metals are treated by immersing them in the acid bath for a given time. A conversion layer forms hereby that protects the treated metal from corrosion. For prior art, reference is made here to WO 9967029 by way of example.

[0003] Such methods have the disadvantage that it is very laborious to carry out the process. Various cleaning and rinsing baths precede and follow the actual treatment in the acid bath. However, it is primarily disadvantageous that the conversion layer contains only a small content of the ions with inhibiting effect. Because of this, the duration of the protective effect is limited.

[0004] The protective effect can be lengthened by the metal to be protected having a coating, e.g., a lacquer or adhesive, that represents a reservoir for the ions with inhibiting effect. If the coating is damaged, the inhibitor can be dissolved from the coating by arriving water and transported to the damaged point, in order to have an inhibiting effect there. As inhibitors, anti-corrosive pigments such as zinc phosphate or barium metaborate are customarily added for this purpose. Metal salts of hexafluorosilicic acid, hexafluorotitanic acid, and hexafluorozirconic acid can likewise be incorporated into polymers in the form of pigments.

[0005] However, the above-named salts have the disadvantage that their solubility in water is not very high and their suitability for a rapid protection of a damaged point in the metal is therefore low. In addition, the efficacy potential of these salts is lower than that of the particularly effective chromates.

[0006] Chromates are known as particularly effective inhibitors. Because of this, it is possible to use even relatively sparingly soluble chromates as inhibitors. Chromates used particularly frequently are zinc chromate, barium chromate, and strontium chromate, as well as mixtures of these compounds.

[0007] However, due to the high toxicity of chromium compounds (hexavalent chromium is carcinogenic and mutagenic) it is necessary to replace them by less toxic substitutes.

STATEMENT OF THE INVENTION

[0008] It is the object of the present invention to overcome the disadvantages of the prior art and to make available corrosion inhibitors that guarantee a rapid and lasting inhibition of corrosion processes.

[0009] The object according to the invention is attained by the addition product according to claim 1,. the method for its production according to claim 9, its use according to claims 10 through 17, and the component according to claim 18. Dependent claims disclose advantageous developments.

[0010] The addition products according to the invention can be produced from hexafluorosilicic acid, hexafluorotitanic acid, and/or hexafluorozirconic acid by an acid-base reaction with one or several organic bases.

[0011] Salts with the anions hexafluorosilicate, hexafluorotitanate, and/or hexafluorozirconate and cations from the protonated organic bases are obtained by these means. An organic base in the sense of this invention is generally understood to mean organic compounds that when reacted with inorganic acids such as in particular hexafluorosilicic acid, hexafluorotitanic acid, or hexafluorozirconic acid, yield salts or salt-type compounds. The following can be given as a general reaction equation:

m*B+n*H2EF6→(BH+)2n(EF62−)n+(m−2n)*B

[0012] where E=Si and/or Ti and/or Zr;

[0013] B designates the organic base; if the organic base carries more than one basic group, the basic group is understood to mean B;

[0014] m and n are integers, whereby m≧2n; for non-polymer compounds in particular, m=2n.

[0015] According to the invention, an organic base is preferably understood to mean organic nitrogen-containing compounds. Furthermore, due to improved handling, it is particularly preferred that these are understood to mean non-cyclic bases with a molecular weight greater than 105 g*mol−1, and cyclic bases with a molecular weight greater than 70 g*mol−1.

[0016] Compared with metal salts of hexafluorosilicic acid, hexafluorotitanic acid, or hexafluorozirconic acid, the addition products according to the invention offer the advantage that they inhibit not only the anodic partial reaction but also, due to the organic constituent of the addition product according to the invention, the cathodic partial reaction of a corrosion process and thus result in an increased corrosion inhibition. It is mostly contaminants or more noble light metal alloy constituents that act as the cathode hereby; the anodic partial reaction takes place at the non-noble points of the alloy, mostly phases with a high proportion of the light metals. The starting point of the corrosion is as a rule a point at which damage to the coating of the light metal or the light metal alloy has taken place.

[0017] Compared with metal salts of hexafluorosilicic acid, hexafluorotitanic acid, or hexafluorozirconic acid, the addition products according to the invention also offer the advantage that they are more readily soluble in aqueous media. Because of this, the anion SiF62−, TiF62−, or ZrF62− needed for the anodic inhibition are made available more rapidly and can be dissolved from the coating more rapidly by arriving water and be transported to the damaged point in order to have an inhibiting effect there. Moreover, the addition products according to the invention have the advantage that they do not represent carcinogens such as hexavalent chromate compounds or toxic heavy metal compounds such as barium salts.

[0018] Surprisingly, it was found that in contrast to the free acids, the addition products according to the invention can be incorporated into polymers and can therefore be used for the production of protective layers with an inhibiting effect. As polymers, the basic constituents of lacquers, adhesives, primers, paints, or embedding compounds are to be named in particular hereby. The addition to a polymer has the advantage that a reservoir of the corrosion inhibitor is made available that prevents the corrosion under the polymer when corrosive media diffuse in or at damage points. Epoxy resins, urethanes, acrylates, alkyd resins, or polyvinyl acetate and its copolymers are named as polymers by way of example. However, the inhibitors according to the invention not only can be incorporated into polymers but like hexafluorosilicic acid, hexafluorotitanic acid, or hexafluorozirconic acid, also can be used in conversion baths and other liquids for the treatment of light metal surfaces.

[0019] Preferred organic bases for the production of the addition products according to the invention are heterocyclic nitrogen compounds.

[0020] Polymer and non-polymer heterocyclic nitrogen compounds form stable complexes with heavy metals. Through the complex formation, the cathodic partial reaction of the corrosion process is blocked. To produce the corrosion inhibitors according to the invention, heterocyclic nitrogen compounds are therefore preferred that are good complex-formers with metals. Heterocycles that form stable complexes with contaminants or nobler alloy constituents such as copper, which is frequently present in light metal alloys, are particularly advantageous.

[0021] For the production of particularly strongly inhibiting addition products, organic bases are used that feature at least two heteroatoms (such as N, O, S) in one or two heterocyclic rings. Preferred organic bases are heterocyclic nitrogen compounds such as, e.g., substituted and unsubstituted 1,2,4-triazoles, 1H-benzotriazoles, benzothiazoles, benzimidazoles, benzoxazoles, 2,2′-biquinolines, nitrones, 2,5-dimercapto-1,3,4-thiadiazoles, and 2,9-dimethylphenanthrolines.

[0022] Particularly preferred heterocyclic nitrogen compounds with a particularly strongly inhibiting effect are, e.g., 1H-benzotriazole, 5-methylbenzotriazole, 5-carboxybenzotriazole, benzothiazole, 2-alkyl benzothiazole, 2-mercaptobenzothiazole, 2-mercaptobenzothiazolesuccinic acid, benzimidazole, 2-alkylbenzimidazole, 2-(5-aminopentyl)benzimidazole, benzoxazole, and 2-mercaptobenzoxazole. Heterocycles with alkyl side-groups reduce the water solubility and thus improve the long-term effect of the corrosion inhibitor.

[0023] Particularly preferred organic bases are also compounds such as substituted and unsubstituted phthalocyanines, chlorines, and porphyrins. Due to the formation of very stable complexes with a large number of metals and thus the strong corrosion inhibiting effect, these compounds are particularly suitable for the production of the addition products according to the invention.

[0024] In a preferred form, the organic base for the production of the addition products according to the invention is a polymer with one or several basic groups. A basic group is understood in particular. hereby to mean the above-mentioned heterocyclic compounds, but quite generally also polymers with short side-chains such as, for example, polyvinylamine.

[0025] The addition products according to the invention are also understood to mean those produced from polymer bases whose basic groups are only partially protonated. Copolymers can also be used as polymers. For example, derivatives of the corresponding monomer organic bases that feature a vinyl group can be polymerized together with a comonomer in order to obtain suitable polymers. By the selection of the comonomer, for example the solubility in water or the compatibility with constituents of a polymer matrix into which the addition product is to be incorporated, can be influenced. Thus, for instance, the water solubility can be reduced by raising the proportion of the alkyl side-groups of the polymer and thus the long-term effect can be improved during use as a corrosion inhibitor; by using vinylimidazole monomers, the water solubility can be raised and a good short-term effect achieved.

[0026] Polymers are also used advantageously when in addition to corrosion-inhibiting properties it is also desired that a proton buffer permanently fixed in the polymer be present. This buffer binds acid formed. during the corrosion. A strong buffer effect is achieved by using addition products. in which not all basic groups are protonated.

[0027] Surprisingly, it was found that an additional adhesion-promoting effect can be achieved by polymers and copolymers. Through this additional adhesion-promoting effect a better adhesion to a substrate is achieved of a polymer matrix into which the addition product according to the invention was incorporated or of the protective layer with an inhibiting effect produced therefrom. In general, polymer-based addition products according to the invention offer a lasting protection of surfaces against corrosion.

[0028] In a particular embodiment, the addition products according to the invention are used together with metal salts with the anions SiF62−, TiF62−, and/or ZrF62− and/or additionally phosphates, borates, vanadates, molybdates, wolframates, and/or phosphonates.

[0029] With these previously known corrosion-inhibiting metal salts with the anions SiF62−, TiF62−, and/or ZrF62− and/or conventional anti-corrosive pigments based on phosphates, borates, vanadates, molybdates, wolframates, and phosphonates, it is preferred that the metal be selected from the group comprising potassium, sodium, zinc, barium, strontium, calcium, magnesium, manganese, cobalt, nickel, tin, zirconium, aluminum, and the rare earth metals. Barium, strontium, and calcium, and, depending on the application case, also zinc, are particularly suitable hereby.

[0030] The use of the addition products according to the invention in combination with previously known corrosion inhibitors or anti-corrosive pigments is preferred in particular when a synergistic effect results in the specific application case. This is, e.g., the case when the cathodic partial reaction of the corrosion process is already adequately inhibited by a small amount of the addition product according to the invention, but this amount is not sufficient for the inhibition of the anodic partial reaction. In such a case according to the invention a previously known inhibitor that is capable of inhibiting the anodic partial reaction is used in addition.

[0031] Furthermore the combination with previously known corrosion inhibitors offers the advantage that mixtures of various inhibitors can be produced that feature a broad range of application. By means of addition products according to the invention with a high water solubility, and previously known corrosion inhibitors or addition products according to the invention with a moderate solubility in water, mixtures are obtained that feature both a rapid anti-corrosive effect (primary effect) and a long-term effect (secondary effect).

[0032] The addition products according to the invention are suitable in particular for use as corrosion inhibitors.

[0033] The corrosion-inhibiting effect of the addition products according to the invention is proved, e.g., by dissolving the addition products in water together with a corrosive substance and allowing the resulting solution to act on the metals to be protected. In order to achieve an adequate differentiation, the content of the corrosive substance is selected to be higher than that of the inhibitor.

[0034] For use as corrosion inhibitors, the addition products according to the invention are advantageously incorporated into one or several polymers. Such compositions are used to produce protective layers with an inhibiting effect. In particular, polymers are understood hereby to mean lacquers, adhesives, primers, embedding compounds, sealants, paints, and/or anti-corrosive primers. The addition to a polymer has the advantage that a reservoir of the corrosion inhibitor is made available that prevents the corrosion under the polymer when corrosive media diffuse in or at damage points. Epoxy resins, urethanes, acrylates, alkyd resins, or polyvinyl acetate and its copolymers are named as polymers by way of example. The corrosion-inhibiting addition products can also be used quite generally in protective layers of any kind.

[0035] Furthermore, the addition products according to the invention are used advantageously in conversion baths. However, they can be used quite generally in aqueous solutions for the treatment of light metal surfaces.

[0036] They have the advantage hereby that in addition to the inhibiting of the anodic partial reaction of the corrosion by means of the SiF62−, TiF62−, or ZrF62−, an inhibiting of the cathodic partial reaction can take place by means of the organic bases of the conversion layer. When used in a chemical bath, the inhibitors according to the invention can also be produced as intermediates by placing the corresponding components in the bath.

[0037] The addition products according to the invention are preferably used for the corrosion protection of components made of aluminum, magnesium, zinc, and/or alloys of these elements and in particular for the corrosion protection of components made of copper-containing light metal alloys. The following are mentioned as alloys by way of example: the aluminum alloys AA2024, AC120, and the magnesium alloys AM50. Due to their high strength, the copper-containing aluminum alloys are frequently used in aircraft construction. The corrosion protection of components for aircraft construction is therefore a preferred field of application of the inhibitors according to the invention. The corrosion inhibitors according to the invention can be used here both in treatment liquids for the components and in lacquers, primers, adhesives, sealants, or embedding compounds.

[0038] A further preferred field of application of the corrosion inhibitors according to the invention is the corrosion protection of components exposed to weathering. These include in particular components for motor vehicle construction.

[0039] Components are also claimed that feature a light metal and/or a light metal alloy as well as corrosion-inhibiting constituents, whereby the latter comprise one or several bases, preferably bases described above in more detail, that inhibit the cathodic partial reaction of corrosion processes on this component. Components that have been adhered with a composition containing a corrosion inhibitor are not claimed.

EXAMPLES OF USE

[0040] Without restriction of the generality, the corrosion inhibitors according to the invention are explained in more detail below on the basis of examples of use.

Example 1

[0041] Synthesis of 1H-benzotriazole Hexafluorosilicate

[0042] 100.1 g of 1H-benzotriazole is added under stirring over the course of half an hour to 242 g of a 25% aqueous solution of hexafluorosilicic acid. The first portions dissolve and become clear. In the later stage of the reaction, the resulting reaction product partly precipitates again already. After addition of the 1H-benzotriazole is complete, 300 mL of 96% ethanol is added and the mixture is stirred for two hours. The resulting precipitate is filtered off in a Büchner funnel and the filter cake is dried under vacuum at 50° C. until constant weight is achieved. In order to obtain further product, the filtrate is concentrated to half and the precipitate is treated in the same. way as the main amount of the product. The dried product is ground in the ball mill and is screened with a 30 &mgr;m screen.

Example 2

[0043] Synthesis of 1H-benzotriazole Hexafluorotitanate

[0044] The synthesis is carried out as described in Example 1, with 115 g of a 60% hexafluorotitanic acid being used instead of the hexafluorosilicic acid.

Example 3

[0045] Synthesis of 1H-benzotriazole Hexafluorozirconate

[0046] The synthesis is carried out as described in Example 1, with 193 g of a 45% hexafluorozirconic acid being used instead of the hexafluorosilicic acid.

Example 4

[0047] Testing of the Corrosion-Inhibiting Properties

[0048] The corrosion-inhibiting properties are tested in comparison with the conventional inhibitors sodium chromate, barium metaborate, and yttrium vanadate. For comparison, the corrosive effect of a sodium chloride solution not provided with an inhibitor is determined.

[0049] The corrosion-inhibiting properties are tested using the cataplasm test. The metal sample is first degreased with methyl ethyl ketone, polished with 100-grain abrasive paper, and cleaned once again with methyl ethyl ketone. The sample is wrapped in cotton wool and saturated with the test solution. This prepared sample is stored in a tightly sealed vessel for 1344 hours ( 8 weeks) at 60° C. The test solution is made of 1% by wt sodium chloride as a corrosive substance and 0.1% by wt of the respective corrosion inhibitor in demineralized water. Aluminum AA2024 (size 20×80×1 mm), aluminum AC120 (size 25×100×1 mm), and magnesium AM50 (size 25×100×3 mm) were used as samples.

[0050] In addition to examples of the corrosion inhibitors according to the invention, commercially available corrosion inhibitors and a solution without corrosion inhibitor were tested as comparative examples. The samples are evaluated based on the corroded area and the number of pits formed. The results are shown in the following Table: 1 Magnesium Aluminum Aluminum Inhibitor Example AM50 AA2024 AC120 None Comparative 90% 100%, 90%, >10 pits 1 pit, efflo- rescences Sodium chromate Comparative 15%  40%, 10% 1 pit* 1 H-benzotriazole According to 20%  30%, 10% hexafluorosilicate the invention 1 pit* 1 H-benzotriazole According to 60%  40%, 20% hexafluorotitanate the invention 2 pits* 1 H-benzotriazole According to 60%  30%, 20% hexafluorozirconate the invention 3 pits* Barium metaborate Comparative 50% 100%, 40%, 10 pits efflo- rescences Yttrium vanadate Comparative 60% 100%, 80%, >10 pits efflo- rescences *The pits are situated only at the cut edge/plate edge

[0051] The results show that the inhibitors according to the invention are as good as the chromate, and develop a greater efficacy than the other commercially available corrosion inhibitors.

Claims

1. Addition product that can be produced from hexafluorosilicic acid and/or hexafluorotitanic acid and/or hexafluorozirconic acid by an acid-base reaction with one or several organic bases.

2. Addition product according to claim 1, characterized in that the organic base is a heterocyclic compound.

3. Addition product according to claim 2, characterized in that the organic base is selected from the group comprising 1,2,4-triazole, 1H-benzotriazole, benzothiazole, benzimidazole, benzoxazole, 2,2′-biquinoline, nitrone, 2,5-dimercapto-1,3,4-thiadiazole, and 2,9-dimethylphenanthroline, as well as derivatives of these parent substances.

4. Addition product according to claim 3, characterized in that the organic base is selected from the group comprising 1H-benzotriazole, 5-methylbenzotriazole, 5-carboxybenzotriazole, benzothiazole, 2-alkylbenzothiazole, 2-mercaptobenzothiazole, 2-mercaptobenzothiazolesuccinic acid, benzimidazole, 2-alkylbenzimidazole, 2-(5-aminopentyl)benzimidazole,. benzoxazole, and 2-mercaptobenzoxazole.

5. Addition product according to claim 2, characterized in that the organic base is selected from the group comprising phthalocyanine, chlorine, and porphyrin, as well as derivatives of these parent substances.

6. Addition product according to claims 1 through 5, characterized in that the organic base is a polymer with one or several basic groups.

7. Composition containing one or several addition products according to one or several of claims 1 through 6 as well as one or several metal salts with the anions SiF62−, TiF62−, and/or ZrF62−.

8. Composition containing one or several addition products according to one or several of claims 1 through 6 as well as phosphates, borates, vanadates, molybdates, wolframates, and/or phosphonates.

9. Method for the production of the addition product according to claims 1 through 6, characterized in that hexafluorosilicic acid and/or hexafluorotitanic acid and/or hexafluorozirconic acid as well as one or several organic bases undergo an acid-base reaction.

10. Use of an addition product according to claims 1 through 6 as a corrosion inhibitor.

11. Use according to claim 10, characterized in that the. addition product is incorporated into one or several polymers.

12. Use according to claim 10 in conversion baths.

13. Use according to claim 11, characterized in that the polymer is a lacquer, an adhesive, a primer, an embedding compound, a sealant, a paint, and/or an anti-corrosive primer.

14. Use according to claims 10 through 13 for the protection of components made of copper-containing light metal alloys.

15. Use according to claims 10 through 14 for the protection of components made of aluminum, magnesium, zinc, and/or alloys of these elements.

16. Use according to claim 15 in aircraft construction.

17. Use according to claims 10 through 16 for the protection of components that are exposed to weathering.

18. Component comprising a light metal and/or a light metal alloy as well as corrosion-inhibiting constituents, characterized in that the corrosion-inhibiting constituents comprise one or several bases, in particular according to claims 2 through 6, that inhibit the cathodic partial reaction of corrosion processes on this component, whereby components that have been adhered with a composition containing a corrosion inhibitor are not claimed.