Process, formulation and use of the formulation for simultaneous decoating and passivation of stainless steel surfaces

Abstract

Process for the simultaneous decoating and passivation of stainless steel surfaces, comprising the following process steps: a) Providing an aqueous decoating and passivating formulation containing i. Hydroxyethyl-amino-di(methylenephosphonic acid) (HEMPA) and at least one other aminoalkylenephosphonic acid ii. an oxidizing agent, wherein the aqueous formulation has a concentration of HEMPA between 1 and 15% by mass and a concentration of the oxidizing agent between 1 and 10% by mass, b) contacting and treating the object to be decoated and passivated with this formulation at a temperature of 10-80°C, in a pH range of 0.5 - 7 for at least one hour, c) Removing the formulation from and rinsing the decoated and passivated article, whereby a repellent organic aminoalkylenephosphonic acid layer forms on the stainless steel surface.

Description

[0001] The invention relates to a method for the simultaneous decoating and passivating of stainless steel objects as well as a ready-to-use aqueous decoating and passivating formulation and its use for decoating and passivating stainless steel surfaces.

[0002] The chemical metallization (e.g. with nickel, copper, tin, and their alloys) of metallic bodies (e.g. screws, engine cylinders) and plastic parts serves to improve corrosion protection, enhance mechanical strength, and develop adhesion for further coating of these base bodies. For chemical metallization with the respective metal (e.g. with nickel, copper, tin, and their alloys), these bodies are placed on racks and immersed in the respective bath (e.g. with nickel, copper, or tin). To prevent embrittlement or deformation, the respective metal bath is not used in plastic tubs due to the typical high operating temperatures of 85-95 °C, but stored in corrosion-resistant stainless steel tubs (in accordance with DIN EN 2516) and, if necessary, used with movement.In electroplating, chemical nickel plating is a currentless process for the chemical metallization (nickel plating) of non-metallic and metallic base materials.

[0003] The metal is deposited on the bodies to be coated, which are placed on the racks, but also on the racks and on the surface of the stainless steel tank itself. The racks and tank surfaces contaminated in this way must be cleaned on a regular basis to prevent further deposition of metal ions (nickel, copper, tin) on the already existing nuclei and thus extend the service life of the chemical metal electrolyte (e.g. nickel, copper, tin and their alloys) as well as the service life of the electroplating process. The service life of the electrolyte is to be understood as an extension of the service life of the electrolyte. The service life of the stainless steel racks and the stainless steel tank describes the interval between cleaning cycles, which becomes necessary due to the unintentional coating of the same when using the plating electrolyte.Passivating the surfaces extends the interval between cleaning cycles and thus increases service life. If the stainless steel surface is not cleaned, dissolved metal ions from the chemical metal electrolyte quickly deposit on the rack and tank surfaces. This depletes the electrolyte of metal and quickly becomes unusable, which in turn makes the process uneconomical.

[0004] According to DIN EN 2516, demetallization and passivation of the metallized tank surface are achieved with approximately 20–50% nitric acid at 20–30 °C for 30–60 minutes. Further passivation processes for ferritic and martensitic chromium steels, as well as austenitic precipitation-hardened steels, are also described in DIN EN 2516. In these processes, sodium dichromate is used in addition to nitric acid.

[0005] During the treatment of the stainless steel tank, nitrous gases are formed when using nitric acid solutions, which is why an extraction system and subsequent air purification are mandatory according to the German Federal Immission Control Act (BlmSchG) and the German Technical Instructions on Air Quality Control (TA Luft) 2002. The passivation process requires a residence time of 6 hours for the nitric acid solutions in the stainless steel tank. Disposal of the used decoating and passivation solution is usually not carried out at the site of generation, but rather externally using separate chemical-physical processes, which results in increased costs for safety measures, transport, and treatment.

[0006] The passivation of stainless steel surfaces with citric acid-containing solutions is also known from the state of the art. For this purpose, the stainless steel surface to be passivated must first be freed of metallic deposits. This is achieved using a stripper, e.g., an amine-based stripper. After demetallization, the amine-containing stripper solution is drained off, followed by repeated rinsing with water and dosing of the citric acid-based passivation solution in a separate process step. However, in practice, disposal of the citric acid solution used during treatment via the local sewage system is often not possible; instead, the used solution must be disposed of as hazardous waste, which increases operating costs and complicates economical operation.

[0007] On special stainless steel surfaces, the formation of passivation layers can be optimized by adding various substances to the nitric acid system. Examples are listed below: 1. Passivation investigations of heat-resistant austenitic steels with nitric acid or nitric acid dichromate. 2. Cleaning and passivation investigations of stainless steel surfaces in pulp drying plants. Pre-cleaning is performed mechanically, followed by chemical cleaning with nitric acid / hydrofluoric acid. The passivation treatment is performed by adding a nitric acid solution containing barium sulfate. It is primarily used on austenitic steels (V4A) [Freire et al.; Papel Journal 2001, 62(4), 98-102].

[0008] DE 101 51 180 B4 discloses a method and a solution for stripping metallic objects with nickel anti-corrosion coatings. In the presence of an aqueous solution of peroxide-containing oxidizing agents (e.g., persulfates) and special compounds containing phosphonic acid groups, nickel is oxidatively dissolved and complexed from objects coated with nickel. The proposed stripping agent is intended to enable rapid stripping of surfaces coated with nickel without attacking or removing the underlying metal. The advantage of the proposed solution can thus be seen in the high selectivity of the stripping solution for nickel. Passivation of the treated surfaces is not achieved with the described stripping process. Furthermore, DE 101 51 180 B4 discloses that the process involves attacking the iron surface.

[0009] EP 2 147 131 B1 discloses a three-step process for the thermochemical passivation of stainless steel, which initially involves a chemical treatment with an aqueous solution of a complexing agent for iron and an oxidizing agent. Hydroxycarboxylic acid, organic nitrosulfonic acids, and diphosphonic acid of the general structure R''[-PO(OH)2]2 are mentioned as complexing agents. Oxidizing agents include peroxo compounds, nitrates, or iodates, the latter two of which require complex and costly disposal (e.g., by incineration). After the wet-chemical treatment, the treated stainless steel workpieces are rinsed in a further step. In a third step, heat treatment takes place in an oxygen-containing atmosphere at a temperature of at least 80°C.Heat treatment in an oxygen-containing atmosphere, followed by chemical pretreatment, is intended to improve the resistance of the treated stainless steel surfaces to the formation of thermally induced oxide layers. However, stainless steels already exhibiting such oxide layers must be cleaned separately before applying the process described in EP 2 147 131 B1. EP 2 147 131 B1 does not provide a method for decoating stainless steel.

[0010] WO 94 / 07803 A1 discloses the use of a combination of phosphonic acid, at least one oxidizing agent, and at least one short-chain carboxylic acid, for example, ascorbic acid, for removing magnetite deposits in water-bearing systems. The total amount of phosphonic acid and oxidizing agent is 1 to 10 wt.% based on the total amount of the solution, and the weight ratio of phosphonic acid to oxidizing agent is 5:1 to 1:10. The substrate surfaces are brought into contact with this system. Magnetite deposits are removed within a short time.

[0011] DE 10 2007 010 538 A1 discloses a process for the thermochemical passivation of stainless steel. The stainless steel surface is treated with an aqueous solution containing complexing agents and oxidizing agents, followed by treatment at elevated temperatures in an oxygen-containing atmosphere. The resulting stainless steel surfaces exhibit a homogeneous passive layer with increased chemical resistance.

[0012] US 2011 / 0008645 A1 discloses a process for passivating steel surfaces with an aqueous solution that differs from traditional phosphate coatings. It contains, among other things, phosphates, Ti / Zn, and complexing agents.

[0013] A process for producing solutions containing stabilized peroxide is disclosed in DD 1 44 073 A1. By adding aminoalkylidenephosphonic acid compounds, aqueous solutions can be rendered hydrolysis-stable and non-hygroscopic. The surface tension of the aqueous system is reduced, and the builder effect is improved. This can be used advantageously, particularly for bleaching and cleaning agents.

[0014] US 4 666 528 A discloses a process for removing iron and copper-containing deposits on metallic surfaces by contacting the deposit with a composition containing a mixture of aminopolycarboxylic acid or its amino or alkali salts and a phosphonic acid or its salts, wherein the molar ratio between aminopolycarboxylic acid and phosphonic acid is 1:9 to 39:1.

[0015] It is therefore an object of the invention to provide a method and a ready-to-use decoating and passivating formulation with which demetallization or decoating and passivation of stainless steel surfaces can be carried out simultaneously within one process step.

[0016] The aim is therefore to achieve passivation of the stainless steel surface within the decoating time using one and the same ready-to-use aqueous decoating and passivation formulation and thus to optimize the process.

[0017] According to the invention, the object is achieved by an electroless process for the simultaneous decoating and passivation of stainless steel surfaces, which comprises the following process steps: a) Providing a ready-to-use aqueous decoating and passivating formulation containing i. Hydroxyethyl-amino-di(methylenephosphonic acid) (HEMPA) and at least one other aminoalkylenephosphonic acid, and ii. an oxidizing agent, wherein the aqueous formulation has a concentration of HEMPA between 1 and 15% by mass and a concentration of the oxidizing agent between 1 and 10% by mass, b) Contacting and treating the object to be decoated and passivated with this formulation at a temperature of 10 - 80 °C, in a pH range of 0.5 - 7, c) removing the formulation from and rinsing the decoated and passivated article, whereby a passivating organic aminoalkylenephosphonic acid layer is formed on the stainless steel surface by contacting and treating it with the aqueous formulation.

[0018] It has now been shown that by the inventive combined use of HEMPA and at least one other aminoalkylenephosphonic acid, in particular ATMP, the decoating and passivation of stainless steel surfaces can be carried out simultaneously within one process step.

[0019] The method according to the invention therefore has the decisive advantage that the decoating and passivation of stainless steel surfaces take place simultaneously in one step within the so-called decoating time.

[0020] The method according to the invention has the advantage that the interval between two cleaning cycles is extended and thus the service life of the stainless steel surfaces is increased.

[0021] According to the invention, the name of the aminoalkylenephosphonic acid HEMPA refers to the hydroxyethyl-amino-di(methylenephosphonic acid) and its intramolecular condensation product, since, in contrast to other known aminoalkylenephosphonic acids, HEMPA is present in aqueous solution according to formula (1) as open-chain HEMPA (hydroxyethyl-aminodi(methylenephosphonic acid) and its cyclic intramolecular condensation product (4-(phosphonomethyl)-2-hydroxy-2-oxo-1,4,2-oxazaphosphorinane).

[0022] The equilibrium of the open-chain HEMPA to the cyclic intramolecular condensation product is established in aqueous solution in such a way that both aminoalkylenephosphonic acids form a 1:1 ratio.

[0023] In electroplating, decoating (i.e. demetallizing, stripping) refers to the removal of deposited metal or metal layers (nickel, copper, tin) from metal base bodies (components, components, frame and tank surfaces).

[0024] Aminoalkylenephosphonic acids exhibit a high selectivity for the removal of deposited metal or metal layers (nickel, copper, tin), especially nickel.

[0025] Advantageously, the use of aminoalkylenephosphonic acids in combination with a peroxide (H2O2) as an oxidizing agent only attacks the nickel layer on a stainless steel surface, complexes the nickel and removes it.

[0026] Selectivity here means that the metal deposited on the stainless steel surface is removed to the greatest extent possible, while the underlying stainless steel surface is not eroded or corroded. The formation of an aminoalkylene phosphonate layer thus advantageously prevents extensive erosion of the stainless steel surface, especially the iron, and also prevents pitting corrosion.

[0027] Preferably, the aminoalkylenephosphonic acid complexes the metal ions that go into solution during decoating and thus prevents the premature decomposition of the oxidizing agent, in particular the peroxides, by free (i.e. uncomplexed) metal ions.

[0028] Potentiodynamic measurements of the anodic and cathodic reactions showed that the adsorption and passivation behavior of HEMPA dissolved in water on stainless steel surfaces differs completely from the behavior of other organic, especially open-chain aminoalkylenephosphonic acids.

[0029] It has now been surprisingly discovered that the cyclic intramolecular condensation product of aminoalkylenephosphonic acid (HEMPA) particularly preferentially produces passivating coating layers (organic aminoalkylenephosphonate layers) on metal surfaces, especially stainless steel surfaces, which prevent recoating with metals (e.g., nickel, copper, tin). The adsorption of the cyclic intramolecular condensation product, which exclusively contains a freely movable methylenephosphonic acid group, on a metal surface has proven to be thermodynamically particularly favorable. In contrast to the cyclic intramolecular condensation product, it was found that the open-chain HEMPA, which bears two methylenephosphonic acid groups and one hydroxyethylene group, is impaired in its ability to adsorb to metal surfaces.

[0030] In this case, passivation does not mean the reduction of corrosion rates, but rather the delay of re-coating by metals (nickel, copper, tin) on the stainless steel surface through chemical modification. By definition, passivation in the field of corrosion protection is the oxygen-induced formation of a protective layer consisting of metal oxides and metal hydroxides, which prevents further corrosive attack (further erosion of the underlying stainless steel surface). Thus, in the field of corrosion protection, passivation is understood to mean anodic inhibition of metal dissolution (i.e., the anodic reaction of metal to metal ions is suppressed), whereby the conversion of oxygen on the metal or stainless steel surfaces is essential. For the enhanced formation of such a passive layer, anodic inhibitors, such as Cr2O7, are used. 2- , NO2 -, MoO4 2- -ions added.

[0031] In contrast to the above, “passivation” in the sense of the present invention means exclusively the formation of an iron aminoalkylenephosphonate layer, i.e. an organic aminoalkylenephosphonic acid layer that repels the adsorption of crystallization nuclei and is formed in particular by HEMPA on the stainless steel surface.

[0032] It was also surprising that HEMPA, after adsorption on a metal surface, provides an extended passive region (i.e., the region between the passivation potential and the region of oxidative metal dissolution) of over 400 mV.

[0033] The extended passive range of at least 400 mV demonstrates the effectiveness of the aminoalkylene phosphonate layer formed on the stainless steel surface against charge and / or mass transfer (i.e., no metal ions, protons, or hydroxide ions pass through). This advantageously prevents unwanted adsorption of crystal nuclei and subsequent crystal growth of metals (nickel, copper, tin).

[0034] In a preferred embodiment of the method according to the invention, the passive range is at least 400 mV. Advantageously, the stainless steel surface is thus particularly resistant to the further formation of an undesirable metal oxide or metal hydroxide layer, which allows for subsequent recoating.

[0035] Another advantageous option for disposal of aminoalkylenephosphonic acid after use is precipitation with milk of lime (Ca(OH)2) and iron salts (e.g., FeCl3), whereby the aminoalkylenephosphonic acid is removed as a precipitate adsorbed on iron hydroxide. This preferably eliminates the need for complex and costly disposal.

[0036] Surprisingly, it has also been shown that the inventive combination of HEMPA with hydrogen peroxide eliminates the need for any further complex thermal post-treatment in an oxygen-containing atmosphere at a temperature of at least 80°C. Particularly advantageous is the elimination of superficial oxidative attack (i.e., corrosion) on the stainless steel surface of the object to be passivated.

[0037] The method according to the invention thus offers the particular advantage that, when passivation of stainless steel surfaces, in particular bulky stainless steel components, is desired, dismantling of the latter is not necessary.

[0038] A bulky stainless steel component within the meaning of the present invention is an object that, due to its shape and / or size, takes up a disproportionate amount of space in a space that is too small for it, or that, due to its use or weight, is immobile and / or unwieldy, making it impossible to transport or move. In electroplating, bulky stainless steel components include, for example, trays or racks used to line up the elements to be coated.

[0039] According to a preferred embodiment of the method according to the invention, the contacting and treatment of the object to be decoated and passivated with the formulation according to the invention takes place at a temperature below 60°C, in particular in the range between 10-60°C, most preferably at a temperature between 30 and 60°C. This advantageously eliminates the need for an extraction system for treating the exhaust air, which is required for higher temperatures according to the Federal Immission Control Act (BImSchG) and the Technical Instructions on Air Quality Control (TA Luft) 2002.

[0040] A cleaning cycle includes the decoating and passivation of frame and tank surfaces.

[0041] Ideally, passivation occurs simultaneously with decoating within the decoating time. The decoating time is the necessary residence time required by the decoating and passivation solution to remove the deposited metal nuclei or metal layers from the stainless steel surface. The decoating time depends on many factors, such as the type of deposited metal layer and its thickness. If the decoating time is not sufficient to induce passivation of the stainless steel surface, the surfaces to be passivated remain in the application formulation. This additional residence time is referred to as the passivation time.

[0042] According to the invention, the use concentration is understood to mean the concentration of the individual components in a ready-to-use aqueous decoating and passivating formulation in which demetallization or decoating and passivation of stainless steel surfaces can be carried out simultaneously within one process step without any significant corrosive attack on the treated stainless steel surfaces.

[0043] The values ​​in mass percent (m%) are derived from the mass fraction w of the respective component in the solution and are calculated as one hundred times this value (m% = 100*w). The mass fraction of the respective component is determined as the proportion of the mass of this component to the mass of the total solution after mixing, i.e., the masses of all components dissolved in the solvent plus the mass of the solvent itself.

[0044] The mass fraction of a component in solution can be determined by various methods known to those skilled in the art, for example, by gravimetric methods, complexometric titration, or acid-base titration. At the same time, the mixing ratios of the starting materials can be determined depending on their respective concentrations.

[0045] The oxidizing agent is preferably oxygen-based and water-soluble. In combination with the low pH value (pH 0.5-7), oxidizing agents can oxidize metals, converting them into metal ions. Aminoalkylenephosphonic acids belong to the group of organic phosphonic acids and, analogous to aminocarboxylates, are capable of forming so-called chelate complexes with dissolved metal ions. This so-called chelation effect allows metals (e.g., nickel, copper, tin) deposited on rack and tank surfaces to be removed in the form of a soluble metal ion complex.

[0046] In a preferred embodiment of the process according to the invention, the aqueous formulation contains at least one further aminoalkylenephosphonic acid selected from amino-tris(methylenephosphonic acid) (ATMP), ethylenediamine-tetra(methylenephosphonic acid) (EDTMP), diethylenetriamine-penta(methylenephosphonic acid) (DTPMP), hydroxyethane-diphosphonic acid (HEDP) and / or hexamethylenediamine-tetra(methylenephosphonic acid) (HDTMP) with a use concentration of 1 to 10 mass percent, wherein the ratio of the mass percent of HEMPA to the total mass percent of the further aminoalkylenephosphonic acids is between 1:9 to 9:1.

[0047] According to the invention, HEMPA is present in the aqueous solution at a concentration of 1 to 15 wt% and an oxidizing agent at a concentration of 1 to 10 wt%. Also preferred are HEMPA at a concentration of 2 to 14 wt% and at least one further aminoalkylenephosphonic acid selected from ATMP, EDTMP, DTPMP, HEDP, and / or HDTMP at a concentration of 1 to 10 wt%, particularly preferably 3 to 9 wt%, and hydrogen peroxide or another oxidizing agent at a concentration of 1 to 10 wt%.

[0048] According to the invention, a ready-to-use aqueous stripping and passivation formulation contains HEMPA at a concentration of 1-15 wt%. Such an application formulation also preferably contains HEMPA at a concentration of 2 to 14 wt%, and preferably 3 to 6 wt%, and at least one further aminoalkylenephosphonic acid selected from ATMP, EDTMP, DTPMP, HEDP, or HDTMP with a mass fraction of 1 to 40 wt%, preferably 2 to 17 wt%, and particularly preferably 3 to 9 wt%.

[0049] The mass percentages of ATMP, EDTMP, DTPMP, HEDP, and / or HDTMP refer to the proportion of an additional organic phosphonic acid in the sum of the masses of all components of the aqueous solution, including the solvent. If more than one additional organic phosphonic acid is present in the aqueous solution, the mass percentages refer to the sum of the proportions of the additional organic phosphonic acids in the total solution.

[0050] Preferably, higher HEMPA concentrations of 6 wt% are used, which preferably act on the stainless steel surfaces for a longer time, preferably between 1 and 16 hours. The decoating time required to remove the coating from the stainless steel surfaces, i.e., to remove the metal previously deposited on this surface, can vary depending on the coating thickness and composition. The longer the decoating and passivation solution is allowed to act beyond the decoating time—during the passivation time—the better the passivation of the stainless steel surface will generally be.

[0051] By combining HEMPA with another organic phosphonic acid, decoating and passivating the objects to be treated can be achieved even with low additive concentrations and short exposure times. Solutions containing more than 3 wt% HEMPA and more than 3 wt% ATMP, EDTMP, DTPMP, HEDP, and / or HDTMP can advantageously achieve passivation of the stainless steel surfaces within the decoating time. Thus, the object to be decoated undergoes decoating and passivation simultaneously.

[0052] If the aqueous solution contains less than 3 wt% HEMPA and additionally less than 3 wt% ATMP, EDTMP, DTPMP, HEDP, and / or HDTMP, the object to be decoated is also advantageously decoated and passivated. However, passivation requires a passivation time that exceeds the decoating time, during which the decoating and passivation solution acts on the stainless steel surface to be decoated and passivated. This means that the object to be decoated must remain in the decoating and passivation bath after decoating to achieve sufficient passivation. However, the time required for passivation is shorter than when using HEMPA alone.

[0053] By combining HEMPA with another organic phosphonic acid, the HEMPA concentration used can be reduced while still achieving sufficient passivation with little or no passivation time. This advantageously prevents the corrosive attack on the treated stainless steel surfaces occasionally observed at high HEMPA concentrations (over 10 wt%).

[0054] The holding or passivation time required at these low concentrations increases with decreasing concentrations of HEMPA and, if present, other organic phosphonic acids selected from ATMP, EDTMP, DTPMP, HEDP, and / or HDTMP. The required passivation time also depends on the ratio between the mass fraction of HEMPA and the sum of the mass fractions of other organic phosphonic acids, with the preferred ratio allowing passivation with no or a short passivation time being between 1:9 and 9:1, and particularly preferably 1:3 to 3:1. If there is an excess of ATMP or one of the phosphonic acids DTPMP, EDTMP, HEDP, or HDTMP in the mixture, the required passivation time increases. In the case of an excess of HEMPA, passivation is achieved, but corrosive attack on the treated stainless steel surfaces can occur.

[0055] The decoating time can be reduced (i.e., the decoating speed can be increased) by adding another aminoalkylenephosphonic acid, such as ATMP. Aminoalkylenephosphonic acids cause excellent complexation of the Ni formed. 2+ -ions, which thus no longer conform to the electrochemical equilibrium (Ni ←→Ni 2+ + 2 e - ) are available. Aminoalkylenephosphonic acids thus prevent the corrosive attack of the oxidizing agent (e.g., H2O2) on the stainless steel surface.

[0056] According to a particularly preferred embodiment of the process according to the invention, the aqueous formulation comprises as organic phosphonic acids exclusively ATMP and HEMPA in a ratio of the mass percentage of HEMPA to ATMP in the range from 3:1 to 1:3.

[0057] Surprisingly, the necessary holding or passivation time can be significantly reduced by a suitable combination of organic phosphonic acids, in particular the suitable combination of HEMPA and ATMP, EDTMP, DTPMP, HEDP, and / or HDTMP, whose mass proportions are coordinated. Particularly advantageously, a suitable, coordinated mixture of these starting materials can even completely eliminate the holding or passivation time, since the decoating and passivation occur simultaneously within the decoating time.

[0058] By balancing the mass fraction of HEMPA to the sum of the mass fractions of other organic phosphonic acids, the use of high concentrations of the individual components of the aqueous solution can be avoided. This is advantageous both from an ecological perspective, as the pollution of the rinse and wastewater is reduced, and from an economic perspective, as the service life of the racks and tanks used in the chemical coating process is extended and only small amounts of chemicals are used and consumed in the formulation.

[0059] According to a preferred embodiment of the process according to the invention, peroxides are preferably used as oxidizing agents. Particular preference is given to using hydrogen peroxide, which is generally used as a commercially available aqueous solution of hydrogen peroxide at a concentration of 35 wt%. Also preferred are peroxoacids such as Caro's acid and / or persulfates such as peroxomono- and peroxodisulfates and / or percarboxylic acids such as peracetic acid.

[0060] In a particularly preferred embodiment of the process according to the invention, hydrogen peroxide is used exclusively as the oxidizing agent.

[0061] In a preferred embodiment, the oxidizing agent is added to a provided aqueous formulation containing at least one organic phosphonic acid immediately before contact with the object to be decoated.

[0062] The aqueous formulation according to the invention is preferably prepared for use from a concentrate in a tank batch. The tank batch is introduced as a concentrate into the stainless steel tank, which normally contains the electrolyte for chemical coating and into which the parts to be coated are immersed, and is then made up to the bath concentration (tank batch) with water. Typically, the aqueous solutions of the phosphonic acids are first prepared in this tank, and then, after heating this initial batch, the oxidizing agent is added. The correct mass proportions are set beforehand by selecting the volumes of the starting materials based on their concentrations or active contents, as is obvious to those skilled in the art. If the solution is initially available as a concentrate, it is simply diluted with water to the application concentration.The preparation of the concentrate from the specified mass ratios is familiar to the expert. If the application solution is available in a ready-to-use concentration (so-called bath concentration), it is poured into the bath without further dilution and the oxidizing agent is added.

[0063] The object to be decoated and passivated is then contacted and treated with the aqueous formulation prepared in this way. This treatment is preferably carried out by immersing the object in the bath solution. To minimize the accumulation of dissolved metal particles or metallic ions near the surface of the object to be decoated, the formulation is continuously stirred or otherwise agitated. Spraying the aqueous solution onto the object to be decoated or allowing the solution to flow over or around it is also preferred. A highly viscous gel can also be produced from the aqueous solution and applied over a long period of time to the surfaces to be decoated.

[0064] According to the invention, the object to be stripped and passivated is contacted and treated with the solution at an elevated temperature between 10 and 80°C, preferably at a temperature between 30 and 60°C. This temperature promotes the stripping effect mediated by the oxidizing agent and contributes to a high stripping speed. Furthermore, the inventive treatment of the object to be stripped takes place in an acidic environment at a pH between 0.5 and 7, preferably at a pH between 1 and 3. The acidic environment, which is a prerequisite for the dissolution of the metal layer to be removed, can be created by the phosphonic acids themselves. If the salts of the phosphonic acids are used or if a basic environment prevails due to other ingredients, the pH can be adjusted by adding other substances.

[0065] Surprisingly, it has been shown that with a ratio of the mass percentage of HEMPA to the total mass percentage of the other aminoalkylenephosphonic acids according to the invention, simultaneous stripping and passivation of stainless steel objects with metallic coatings made of nickel, copper, and tin, as well as their alloys, is possible. This is achieved with an aqueous solution based on various organic phosphonic acids.

[0066] The process according to the invention finds particular application in electroplating, particularly in chemical metallization, for stripping the tanks containing the chemical electrolyte. The additional effect of passivation advantageously and surprisingly increases the service life of these tanks, the service life of the racks supporting the parts to be coated, and the service life of the electrolyte used for the chemical coating itself. This allows for significantly more economical operation of chemical coating lines.

[0067] Furthermore, it is advantageous to only fill the stainless steel tank with the decoating and passivating solution. After the required treatment time of the stainless steel surface, the used solution is fed into the company's in-house wastewater treatment system and processed in just a few steps, allowing further discharge into the local sewage system.

[0068] The invention further relates to a ready-to-use aqueous decoating and passivation formulation comprising a component A comprising HEMPA and at least one further aminoalkylenephosphonic acid, and a component B comprising an oxidizing agent, wherein component A contains HEMPA at a concentration of 1 to 53 percent by mass, wherein component A and component B are mixed before use.

[0069] The ready-to-use aqueous decoating and passivating formulation can advantageously be used as an aqueous solution for decoating and passivating metal, in particular stainless steel, surfaces in the process according to the invention.

[0070] According to a preferred embodiment of the invention, component A preferably contains, in addition to HEMPA, at least one such further organic phosphonic acid selected from ATMP, EDTMP, DTPMP, HEDP and / or HDTMP with a respective concentration of 1 to 40 m%, preferably 2 to 17 m%.

[0071] Furthermore, in a preferred embodiment of the invention, the ready-to-use decoating and passivating formulation according to the invention advantageously contains HEMPA and at least one further phosphonic acid selected from ATMP, EDTMP, DTPMP, HEDP, and / or HDTMP in a mass ratio of 1:9 to 9:1, preferably 1:3 to 3:1. The left side of the ratio represents the mass fraction of HEMPA, and the right side represents the total mass fractions of the other phosphonic acids present in the formulation, selected from ATMP, EDTMP, DTPMP, HEDP, and / or HDTMP. The mass ratios refer to the ratios of the mass fractions of the opposing components to one another.

[0072] According to a particularly preferred embodiment of the present invention, the ready-to-use decoating and passivating formulation according to the invention comprises as organic phosphonic acids exclusively HEMPA and ATMP in a mass ratio in the range of 3:1 to 1:3.

[0073] The decisive factor for the effectiveness of the decoating and passivating formulation according to the invention in decoating and passivating stainless steel surfaces is, above all, the ratio of the phosphonic acids to each other. Surprisingly, it has been shown that with a preferred HEMPA:ATMP mass ratio in the range of 3:1 to 1:3, decoating can be achieved without simultaneous corrosive attack associated with passivation. The absolute proportions of the individual components vary depending on whether the formulation is an aqueous formulation suitable for decoating or a concentrated formulation intended for transport.

[0074] According to the invention, a component A or concentrate produced for transport contains, among other things, HEMPA at a concentration of 1 to 53 wt%, preferably 5 to 30 wt%, and particularly preferably 10 to 15 wt%. Such a concentrate also preferably contains HEMPA at a concentration of 5 to 30 wt%, more preferably 10 to 15 wt%, and at least one further organic phosphonic acid selected from ATMP, EDTMP, DTPMP, HEDP, or HDTMP with a mass fraction of 1 to 40 wt%, preferably 5 to 30 wt%, and more preferably 10 to 15 wt%.

[0075] A ready-to-use aqueous stripping and passivation formulation preferably contains HEMPA at a concentration of 1-15 wt%. Such a stripping and passivation formulation also preferably contains HEMPA at a concentration of 2 to 14 wt%, and preferably 3 to 6 wt%, and at least one further organic phosphonic acid selected from ATMP, EDTMP, DTPMP, HEDP, or HDTMP with a mass fraction of 1 to 40 wt%, preferably 2 to 17 wt%, and particularly preferably 3 to 9 wt%.

[0076] According to a preferred embodiment of the invention, component B of the aqueous stripping and passivation formulation according to the invention contains hydrogen peroxide and / or other peroxides, persulfates, and / or peroxy acids as the oxidizing agent. After mixing component A and component B, the ready-to-use aqueous stripping and passivation formulation contains the oxidizing agent at a concentration of 1 to 10 wt% and preferably 1 to 6 wt%.

[0077] However, it is also conceivable that an oxidizing agent has already been added to a formulation concentrated for transport. In the formulation concentrated for transport, the oxidizing agent is preferably present at a concentration of up to 20 wt%.

[0078] A problem, however, is that many of the oxidizing agents in question do not have a long-term stability comparable to that of the acid components. For this reason, the oxidizing agent, particularly preferably hydrogen peroxide, is generally only added to the acid components of component A immediately before use. This is not a problem because hydrogen peroxide is a substance frequently used in the coatings industry and is therefore available at many potential locations for the process according to the invention. Furthermore, after a certain period of use of the formulation or bath solution for stripping and passivation, it may be necessary to readjust the oxidizing agent content of the formulation or bath solution to the values ​​stated above. In this way, the usability of the formulation or bath solution can advantageously be maintained until its maximum loading of metal ions is reached.

[0079] The present invention further relates to the use of an aqueous solution (which is preferably a concentrate) comprising HEMPA and at least one further aminoalkylenephosphonic acid for producing a ready-to-use aqueous decoating and passivating formulation for decoating and passivating stainless steel surfaces, wherein the aqueous solution contains HEMPA at a concentration of 1 to 53 mass percent.

[0080] To produce a ready-to-use aqueous decoating and passivating formulation, the aqueous solution according to the invention is preferably diluted to a use concentration of 1 to 15 mass percent HEMPA and an oxidizing agent is added.

[0081] The dilution of the aqueous solution according to the invention is preferably carried out with water or another aqueous solution. The use of component A according to the invention is further preferably characterized in that the aqueous solution contains at least one further aminoalkylenephosphonic acid selected from ATMP, EDTMP, DTPMP, HEDP, and / or HDTMP in a concentration of 1 to 40 percent by mass.

[0082] For the decoating and passivation of stainless steel surfaces, it is particularly preferred to use component A according to the invention which contains HEMPA and at least one further phosphonic acid, wherein the at least one further phosphonic acid is selected from ATMP, EDTMP, DTPMP, HEDP and / or HDTMP in a ratio of 1:9 to 9:1, preferably 1:3 to 3:1. Furthermore, it is preferred to use an aqueous decoating and passivating formulation which additionally contains an oxidizing agent, preferably a persulfate such as peroxodisulfate and / or a percarboxylic acid such as peracetic acid and / or a peroxoacid such as Caro's acid and particularly preferably hydrogen peroxide.

[0083] A component A according to the invention is used which contains HEMPA at 1 to 53 wt%. Also preferred is a formulation which contains HEMPA at a concentration of 2 to 14 wt% and at least one further phosphonic acid selected from ATMP, EDTMP, DTPMP, HEDP, HDTMP at 1 to 40 wt%, preferably 2 to 17 wt%. Also preferred is an aqueous formulation which contains HEMPA at a concentration of 3 to 6 wt% and at least one further organic phosphonic acid selected from ATMP, EDTMP, DTPMP, HEDP, and / or HDTMP at a concentration of 2 to 17 wt%, and particularly preferably 3 to 9 wt%.

[0084] Also preferred is an aqueous decoating and passivation formulation containing an oxidizing agent, which constitutes a mass fraction of the ready-to-use formulation or bath solution of 1 to 10 wt%, preferably 1 to 6 wt%. Particularly preferred is a bath solution that is first diluted to the specific application from a phosphonic acid-containing concentrate and then admixed with an oxidizing agent.

[0085] The present invention also relates to the use of an aqueous passivation formulation for the passivation of stainless steel surfaces, containing HEMPA with a concentration of 1 to 15 mass percent and at least one further aminoalkylenephosphonic acid, which are used in combination with an oxidizing agent, preferably hydrogen peroxide, wherein the use concentration of the oxidizing agent is between 1 to 10 mass percent.

[0086] The invention is explained in more detail using the following examples: To demonstrate the decoating and passivation of stainless steel surfaces using the process according to the invention, stainless steel coupons measuring 55x25x1 mm (A1.4571) were used. The pretreatment of the stainless steel coupons in all of the example tests was described as follows.

[0087] In preparation for the following tests, the stainless steel coupons were electroless nickel-plated (chemical plating) to simulate the process of nickel stripping from stainless steel tanks and racks in the laboratory. Before plating, the stainless steel coupons were degreased with alkali and pre-nickel-plated with an approximately 2 µm thick nickel strike layer. They were then treated in an electroless nickel electrolyte, in which approximately 10 µm of electroless nickel with 9% phosphorus in the deposited layer was deposited on the surface.

[0088] The pretreated coupons were degreased with ethanol before the stripping and passivation tests, weighed and then added to the stripping or passivation formulation, which was kept at a temperature of 55°C and kept in motion.

[0089] Complete decoating of a medium-phosphorus nickel layer with a layer thickness of 10 µm was achieved after 180 min.

[0090] When subjected to an additional passivation time, the test specimen was exposed to the stripping or passivation solution for a further 16 hours.

[0091] To verify the recoating, the stripped and passivated stainless steel coupon was removed from the stripping or passivation bath after the residence time, rinsed with water, weighed, and transferred to a chemical nickel electrolyte at 88°C with continuous stirring. The chemical nickel electrolyte exhibits a metal turnover of 3, has a phosphorus content of 7.5-10% in the deposited layer, and is also lead and cadmium-free. After a residence time of 5 hours in the chemical nickel electrolyte, the coupon was removed, rinsed with water, dried, and weighed.

[0092] The mass concentrations given in the examples below refer to the active acid content of phosphonic acid contained in the product used. Example 1

[0093] The decoating or passivation solution used was prepared with the following concentrations in mass percent: o 3.2 m% ATMP o 3.0 m% HEMPA o 3.9 m% hydrogen peroxide solution (35%) o ad 100 m% water.

[0094] This aqueous stripping and passivation formulation was prepared from 16 g of a commercially available industrial ATMP grade in acidic dosage form (Cublen AP5), characterized by an ATMP content of 41% determined by complexometric titration and a total acid content of 50% (calculated as ATMP), 11 g of a commercially available industrial HEMPA grade in acidic dosage form (Cublen R60), characterized by a total concentration of 57.5% of the two HEMPA forms (calculated as hydroxyethylaminobis(methylenephosphonic acid)), 22 g of a commercially available 35% hydrogen peroxide solution (H2O2) and 159 g of water.

[0095] For a non-passivated specimen, recoating would be expected within the first two hours in the electroless nickel electrolyte. However, due to its passivation, the test specimen treated as described here showed no recoating within the 5-hour exposure time in the plating electrolyte, despite not undergoing any additional passivation time. Example 2

[0096] The decoating or passivation solution used was prepared with the following concentrations in mass percent: o 3.7 m% HEDP o 3.5 m% HEMPA o 3.9 m% hydrogen peroxide solution (35%) o ad 100 m% water.

[0097] This aqueous stripping and passivation formulation was prepared from 13 g of a commercial industrial HEDP grade in acidic dosage form (Cublen K60), characterized by a HEDP content of 60%, 12 g of a commercial industrial HEMPA grade in acidic dosage form (Cublen R60) as described in Example 1, 22 g of a commercial 35% hydrogen peroxide solution (H2O2) and 157 g of water.

[0098] For a non-passivated specimen, recoating would be expected within the first two hours in the electroless nickel electrolyte. However, due to its passivation, the test specimen treated as described here did not show any recoating, despite not undergoing an additional passivation period within the 5-hour exposure time in the plating electrolyte. Example 3

[0099] The aqueous decoating or passivation solution used was prepared with the following concentrations in mass percent: o 2.7 m% ATMP o 2.6 m% HEMPA o 3.9 m% hydrogen peroxide (35%) o ad 100 m% water

[0100] This formulation was prepared from 14 g of a commercial industrial grade ATMP in acidic dosage form (Cublen AP5) as previously described, 9 g of a commercial industrial grade HEMPA in acidic dosage form (Cublen R60) as previously described, 22 g of a commercial 35% hydrogen peroxide solution (H2O2) and 163 g of water.

[0101] After one hour of treatment in the electroless nickel electrolyte, the stainless steel surface was coated with a nickel-phosphorus layer. The layer thickness was 4.4 µm of electroless nickel after one hour of treatment in the electrolyte.

[0102] The test specimen treated as described here showed no passivation effect due to its treatment in the bath solution with the specified concentration and no additional passivation time. Example 4

[0103] The aqueous decoating or passivation solution used was prepared with the following concentrations in mass percent: o 2.7 m% ATMP o 2.6 m% HEMPA o 3.9 m% hydrogen peroxide solution (35%) o ad 100 m% water

[0104] This formulation was prepared from 14 g of a commercial industrial grade ATMP acid dosage form (Cublen AP5) as previously described, 9 g of a commercial industrial grade HEMPA acid dosage form (Cublen R60) as previously described, 22 g of a commercial 35% hydrogen peroxide solution (H2O2) and 163 g of water.

[0105] After the 180-minute stripping time, the coupon remained in the stripping or passivation solution for another 16 hours. Only then were the coupons removed, rinsed with water, and weighed.

[0106] Based on Example 3, recoating would be expected within the first two hours. However, the test specimen treated as described here showed a passivation effect due to its treatment in the stripping and passivation solution at the specified concentrations and an exposure time of 16 hours.

[0107] At a higher concentration of the stripping or passivation formulation, additional exposure or passivation time would not be necessary to achieve a passivation effect. At the lower concentrations used, no passivation occurs without additional exposure or passivation time. However, passivation is achieved within an exposure or passivation time of 16 hours. Comparative Example 5 / Solution 1 and Practical Example 5 / Solution 2

[0108] The decoating or passivation solution used was prepared with the following concentrations in mass percent and can be found in Table 1: Table 1 Solution 1 Solution 2 HEMPA: 7.5 wt% ATMP: 3.2 m% & HEMPA: 3.0 m% H2O2: 3.9 m% H2O2: 3.9 m% Water: ad 100 m% Water: ad 100 m%

[0109] This stripping and passivation formulation was prepared from A g of a commercially available industrial ATMP grade in acidic dosage form (Cublen AP5) as previously described, B g of a commercially available industrial HEMPA grade in acidic dosage form (Cublen R60) as previously described, C g of a commercially available 35% hydrogen peroxide solution (H2O2), and D g of water. The masses of the solutions used are shown in Table 2. Table 2 Solution 1 Solution 2 A - 16,0 g B 25,0 g 11,0 g C 22,0 g 22,0 g D 146,0 g 159,0 g

[0110] Two tests were terminated after the decoating time with the parameters listed in Table 2 (decoating process without additional passivation time - 180 min), and the coupons were placed in the electroless nickel bath. In two further tests with analogous parameters as described in Table 2, the test specimens remained in the decoating or passivation solution not only for the required decoating time but also for an additional 16 h (passivation time) in the bath solution and were then added to the electroless nickel electrolyte.

[0111] The results obtained are shown in Table 3 below. Table 3 Exposure time t=0 Exposure time t=16h Solution 1 (HEMPA) No passivation; coating started after 0.5 h Passivation was carried out; no coating after 5 h Solution 2 (ATMP & HEMPA) Passivation was carried out; no coating after 5 h Passivation was carried out; no coating after 5 h

[0112] When HEMPA is applied individually, passivation of the stainless steel surface only occurs after a given exposure time. If this time is not met, no passivation occurs. In the presence of a second organic phosphonic acid, such as ATMP, passivation of the stainless steel surface occurs even without an exposure time. Example 6

[0113] The decoating and passivation solutions used were prepared with the following concentrations in mass percent and can be found in Table 4: Table 4 Solution 3 Solution 4 Solution 5 HEMPA: 6.9 m% HEMPA: 1.7 m% HEMPA: 3.4 m% & ATMP: 1.2 m% & ATMP: 4.7 m% ATMP: 3.5 m% H2O2:3.9 m% H2O2: 3.9 m% H2O2: 3.9 m% Water: ad 100 m% Water: ad 100 m% Water: ad 100 m%

[0114] These solutions were prepared from A g of a commercially available industrial ATMP grade in acidic dosage form (Cublen AP5) as previously described, B g of a commercially available industrial HEMPA grade in acidic dosage form (Cublen R60) as previously described, C g of a commercially available 35% hydrogen peroxide solution (H2O2), and D g of water. The masses of the solutions used are shown in Table 5. Table 5 Solution 3 Solution 4 Solution 5 A 6 g 24 g 18 g B 25 g 6 g 12 g C 22 g 22 g 22 g D 157 g 157 g 157 g

[0115] All three formulations with different ratios of ATMP and HEMPA were investigated regarding stripping behavior, corrosion phenomena and passivation effect.

[0116] The results obtained are shown in Table 6 below. Table 6 HEMPA ATMP Ratio HEMPA : ATMP Decoating corrosion Passivation Solution 3 6,9 m% 1,2 m% 1 : 0,2 after 2.5 hours Corrosion points Yes Solution 5 3,4 m% 3,5 m% 1 : 1,0 after 2.5 hours no Yes Solution 4 1,7 m% 4,7 m% 1 : 2,8 after 2.5 hours no no

[0117] This results in a preference for the stripping or passivation formulation with a HEMPA to ATMP ratio of 1:1. A formulation with a ratio of 1:0.2 also exhibited a passivation effect, but small corrosion spots formed on the surface of the coupon during the stripping process. When using more ATMP (HEMPA:ATMP ratio of 1:2.8), no corrosion was detectable, but also no passivation effect. This demonstrates that the stripping and passivation formulations must have precisely adjusted concentration values ​​for the application. Example 7 - Comparison of different aminoalkylenephosphonic acids

[0118] The formation of an organic aminoalkylenephosphonic acid layer that is resistant to the adsorption of crystallization nuclei can be determined by determining the passivation potential.

[0119] To determine the passivation potential according to DIN EN 13496:1999-06, the specimens are immersed in the corresponding test solution (0.1 mol / L Na2SO4, 0.1 wt% of the corresponding aminoalkylenephosphonic acid in distilled water) and left there for the duration of the potentiodynamic measurement. V2A stainless steel (type 1.4301) was used as the specimen. The pH of the test solution was adjusted to pH 2.0. The bath is conveniently operated at a temperature of 20 ± 0.2°C. The determination of the potential [in mV] and the anodic current [in mA / cm 2 ] was carried out under aeration in air at a potential sweep rate of 1 mV / s using a standard calomel electrode, platinum counter electrode on a potentiostat PS6 (Sensortechnik Meinsberg GmbH, Germany).

[0120] HEMPA, HEDP, ATMP, EDTMP, DTPMP, HDTMP and sodium sulfate (blank sample) were used as aminoalkylenephosphonic acids, with HEMPA being present in the form of open-chain HEMPA and cyclic HEMPA in a ratio of 1:1.

[0121] Potentiodynamic measurement of the anodic and cathodic reaction shows (according to Fig. 1) that the adsorption and passivation behavior of HEMPA dissolved in water on stainless steel surfaces (S235JRG2) differs completely from the behavior of other organic phosphonic acids.

[0122] Out of Fig. 1 are two maxima of the current intensity for HEMPA [in mA / cm 2 ] for the potential values ​​[in mV] at -189 mV and +1119 mV.

[0123] Here, adsorbed molecules of the cyclic intramolecular condensation product of HEMPA show an anodic transformation (i.e., saponification) into the open-chain form at a potential of -189 mV, which subsequently remains adsorbed on the stainless steel surface.

[0124] The current density-potential curves (according to Fig. 1) reflect the reaction of HEMPA compared to the phosphonic acids HEDP, ATMP, EDTMP, DTPMP, and HDTMP on the electrode. For this purpose, the stainless steel electrode was polarized between -800 and +1700 mV. Below -300 mV, only cathodic currents appear, which are measured on the H +-reduction. Between -300 mV and +200 mV, only HEMPA exhibits a high anodic current (maximum at -189 mV), which indicates the conversion of adsorbed cyclic HEMPA molecules into the open-chain form through saponification. As a result, the long-chain molecules occupy more area on the steel surface and densify the passive layer. Iron dissolution in the presence of HEMPA begins at +750 mV, but is stopped at the passivation potential (Flade potential) of +1119 mV. The anodic current decreases drastically, only to rise again at +1472 mV. In this range, the open-chain and adsorbed iron aminoalkylenephosphonate layer formed from the cyclic form of HEMPA prevents further iron dissolution – it passivates.

[0125] Above +1119 mV, the passivation potential, there is a sharp drop in the anodic current to 0.2 mA / cm 2This only rises again at +1472 mV. HEMPA provides an extended passive range of over 400 mV. In contrast, the aqueous solutions of the phosphonic acids hydroxyethane diphosphonic acid (HEDP), amino-tris(methylenephosphonic acid) (ATMP), ethylenediamine tetra(methylenephosphonic acid) (EDTMP), diethylenetriamine penta(methylenephosphonic acid) (DTPMP), hexamethylenediamine tetra(methylenephosphonic acid) (HDTMP), and sodium sulfate solution (blank sample) show hardly any passivation or adsorption effects.

[0126] The measurements also showed that it was not possible to deposit a nickel layer from an electroless nickel bath on a stainless steel surface (S235JRG2) treated with HEMPA. However, a nickel layer could be deposited on stainless steel surfaces in the presence of the other organic phosphonic acids mentioned above.

Claims

[1] Process for the simultaneous decoating and passivation of stainless steel surfaces, comprising the following process steps: a) Providing an aqueous decoating and passivating formulation containing i. Hydroxyethyl-amino-di(methylenephosphonic acid) (HEMPA) and at least one other aminoalkylenephosphonic acid ii. an oxidizing agent, wherein the aqueous formulation has a concentration of HEMPA between 1 and 15% by mass and a concentration of the oxidizing agent between 1 and 10% by mass, b) contacting and treating the object to be decoated and passivated with this formulation at a temperature of 10-80°C, in a pH range of 0.5 - 7 for at least one hour, c) Removing the formulation from and rinsing the decoated and passivated article, whereby a repellent organic aminoalkylenephosphonic acid layer forms on the stainless steel surface. [2] Method according to claim 1, characterized by that the further aminoalkylenephosphonic acid is selected from amino-tris(methylenephosphonic acid) (ATMP), ethylenediamine-tetra(methylenephosphonic acid) (EDTMP), diethylenetriaminepenta(methylenephosphonic acid) (DTPMP), hydroxyethane-diphosphonic acid (HEDP) and / or hexamethylenediamine-tetra(methylenephosphonic acid) (HDTMP) with a use concentration of 1 to 10 mass percent, wherein the ratio of the mass percent of HEMPA to the total mass percent of the further aminoalkylenephosphonic acids is between 1:9 and 9:

1. [3] Method according to one of claims 1 and 2, characterized by that hydrogen peroxide and / or other peroxides, persulfates and / or peroxoacids are used as oxidizing agents. [4] Aqueous decoating and passivating formulation containing a) a component A comprising HEMPA and at least one further aminoalkylenephosphonic acid, b) and a component B containing an oxidizing agent, characterized by , that component A contains HEMPA at a concentration of 1 to 53% by mass. [5] Aqueous decoating and passivating formulation according to claim 4, characterized by that in component A the further aminoalkylenephosphonic acid is selected from ATMP, EDTMP, DTPMP, HEDP and / or HDTMP in a concentration of 1 to 40 mass percent. [6] Aqueous decoating and passivating formulation according to claim 4 or 5, characterized by that component A contains HEMPA and at least one further aminoalkylenephosphonic acid selected from ATMP, EDTMP, DTPMP, HEDP and / or HDTMP in a ratio of 1:9 to 9:

1. [7] Aqueous decoating and passivating formulation according to one of claims 4 to 6, characterized by that component B contains hydrogen peroxide and / or other peroxides, persulfates and / or peroxoacids as oxidizing agents. [8] Use of an aqueous solution comprising HEMPA and at least one further aminoalkylenephosphonic acid for producing a ready-to-use aqueous decoating and passivation formulation, wherein the aqueous solution contains HEMPA at a concentration of 1 to 53 mass percent. [9] Use according to claim 8, characterized by that to produce a ready-to-use aqueous decoating and passivation formulation, the aqueous solution is diluted to a concentration of 1 to 15 mass percent HEMPA and an oxidizing agent is added. [10] Use according to claims 8 and 9, characterized bythat the further aminoalkylenephosphonic acid of the aqueous solution is selected from ATMP, EDTMP, DTPMP, HEDP and / or HDTMP in a concentration of 1 to 40 mass percent. [11] Use of an aqueous passivation formulation for the passivation of stainless steel surfaces, containing HEMPA with a concentration of 1 to 15 mass percent and at least one further aminoalkylenephosphonic acid, which are used in combination with an oxidizing agent, wherein the use concentration of the oxidizing agent is between 1 to 10 mass percent.

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