USE OF A COMPOSITION FOR INHIBITION OF CORROSION OF METALS OR METAL ALLOYS AND METHOD FOR INHIBITION OF CORROSION OF METALS OR METAL ALLOYS

Abstract

The present invention relates to the use of a corrosion inhibition composition for protection of metals and/or metallic surfaces from corrosion and a method for inhibition of corrosion of metallic surfaces using the corrosion inhibition composition.

Claims

1-9. (canceled)

10. A method for inhibition of corrosion of a metal and/or metallic surface comprising: a) providing a corrosion inhibition composition comprising at least one zinc carboxylate and calcium gluconate, wherein the mass ratio of the at least one zinc carboxylate and the calcium gluconate is in the range of 1:10 to 1:600, and b) adding the corrosion inhibition composition to a liquid medium, wherein the metal and/or metallic surface is exposed to the liquid medium or will be exposed to the liquid medium.

11. The method according to claim 10, wherein the concentration of the corrosion inhibition composition in the liquid medium is in the range of 0.01% to 20% (w/w).

12. The method according to claim 10, wherein the carboxylate anion in the zinc carboxylate is selected from the group comprising gluconate, bisglycinate, glycinate, citrate, acetate, ascorbate, DL-hydrogenaspartate, L-hydrogenaspartate, malate and mixtures of these.

13. The method according to claim 10, wherein the corrosion inhibition composition additionally comprises at least one magnesium carboxylate.

14. The method according to one of the claim 10, wherein the corrosion inhibition composition additionally comprises a chelating agent.

15. The method according to claim 10, wherein the metal and/or the metallic surface is selected from the group consisting of cast iron, copper, aluminum, cast aluminum, steel, mild steel, zinc, magnesium, cast magnesium, tin, solder, titanium, brass and combinations thereof.

16. The method according to claim 11, wherein the carboxylate anion in the zinc carboxylate is selected from the group comprising gluconate, bisglycinate, glycinate, citrate, acetate, ascorbate, DL-hydrogenaspartate, L-hydrogenaspartate, malate and mixtures of these.

17. The method according to claim 11, wherein the corrosion inhibition composition additionally comprises at least one magnesium carboxylate.

18. The method according to claim 12, wherein the corrosion inhibition composition additionally comprises at least one magnesium carboxylate.

19. The method according to claim 11, wherein the corrosion inhibition composition additionally comprises a chelating agent.

20. The method according to claim 12, wherein the corrosion inhibition composition additionally comprises a chelating agent.

21. The method according to claim 13, wherein the corrosion inhibition composition additionally comprises a chelating agent.

22. The method according to claim 11, wherein the metal and/or the metallic surface is selected from the group consisting of cast iron, copper, aluminum, cast aluminum, steel, mild steel, zinc, magnesium, cast magnesium, tin, solder, titanium, brass and combinations thereof.

23. The method according to claim 12, wherein the metal and/or the metallic surface is selected from the group consisting of cast iron, copper, aluminum, cast aluminum, steel, mild steel, zinc, magnesium, cast magnesium, tin, solder, titanium, brass and combinations thereof.

24. The method according to claim 13, wherein the metal and/or the metallic surface is selected from the group consisting of cast iron, copper, aluminum, cast aluminum, steel, mild steel, zinc, magnesium, cast magnesium, tin, solder, titanium, brass and combinations thereof.

25. The method according to claim 16, wherein: the corrosion inhibition composition additionally comprises at least one magnesium carboxylate; the corrosion inhibition composition additionally comprises a chelating agent; and the metal and/or the metallic surface is selected from the group consisting of cast iron, copper, aluminum, cast aluminum, steel, mild steel, zinc, magnesium, cast magnesium, tin, solder, titanium, brass and combinations thereof.

26. The method according to claim 10, wherein said method protects the metal and/or metallic surface from corrosion in liquids comprising water.

27. The method according to claim 10, wherein the liquid medium comprises water, at least one organic solvent, or a mixture thereof.

28. The method according to claim 10, wherein said adding the corrosion inhibition composition to the liquid medium forms a liquid formulation having a concentration of the corrosion inhibition composition in the range of 0.01% to 50% (w/w) of the total liquid formulation.

29. The method according to claim 10, wherein the corrosion inhibition composition is a solid formulation comprising at least one further component selected from a carrier material, complexing agent, softener and surfactant.

Description

[0042] FIG. 1 a)-e) depicts corrosion current densities (i.sub.corr) in artificial tap water (see ASTM D1384-05) containing either i) no additive or ii) 5% (w/w) calcium gluconate additive (the additive consisting of 5% (w/w) Ca-GDL and 95% (w/w) water) or iii) 5% (w/w) calcium gluconate and zinc acetate additive (the additive consisting of 5% (w/w) Ca-GDL, 0.08% (w/w) zinc acetate and 94.92% (w/w) water) or iv) 5% (w/w) additive A (the additive consisting of 4% (w/w) calcium gluconate, 1% (w/w) magnesium gluconate, 0.08% (w/w) zinc acetate and 94.92% (w/w) water) for a) mild steel, b) cast iron, c) zinc, d) aluminum and e) copper.

[0043] In a first aspect the present invention provides an environmentally friendly corrosion inhibition composition for inhibition of corrosion of metals and/or metallic surfaces comprising at least one zinc carboxylate and calcium gluconate, wherein the mass ratio of the at least one zinc carboxylate and the calcium gluconate is in the range of 1:10 to 1:600.

[0044] In preferred embodiments, all or at least one of the carboxylates are water-soluble and/or emulsifiable.

[0045] As mentioned above, zinc salts are known to act as cathodic corrosion inhibitors for certain metals only, e.g. only for mild steel. Furthermore, salts of carboxylic acids are known additives for the protection of metals from corrosion.

[0046] However, only certain concentrations lead to a desired effect and only specific metals can be protected. In some cases, aqueous solutions of the metal salts alone even show a higher corrosion rate on specific metals than pure water.

[0047] Surprisingly, metal salts of carboxylic acids show an increased corrosion inhibition efficiency for not only steel, but for a broad variety of metals or metal alloys concurrently, when mixed in a combination according to the invention.

[0048] According to the invention, the corrosion inhibition composition for metallic surfaces comprises at least one zinc carboxylate and calcium gluconate.

[0049] In terms of the invention, “at least one zinc carboxylate” means that the carboxylate anion of the zinc carboxylate may be of one structural kind or it might be a mixture of two or more different structural kinds of carboxylate anions.

[0050] In the following “carboxylate anion” includes one or more kinds of carboxylate anions.

[0051] In preferred embodiments, all or at least one of the carboxylates are water-soluble and/or emulsifiable.

[0052] In certain embodiments, the carboxylate anions of the zinc carboxylate are selected from the group comprising gluconate, bisglycinate, glycinate, citrate, acetate, ascorbate, DL-hydrogenaspartate, L-hydrogenaspartate, malate and mixtures of these. In certain embodiments, the zinc carboxylate is zinc gluconate.

[0053] In certain embodiments, the carboxylates are water-soluble and/or water-emulsifiable.

[0054] In terms of the invention, “water-soluble” means that the carboxylate can be dissolved in water or aqueous solutions at acidic, neutral or basic pH value without precipitation, providing a clear solution.

[0055] In terms of the invention “water-emulsifiable” carboxylate means, that the salt can be kept in water or aqueous solutions at acidic, neutral or basic pH value by adding an emulsifying agent, without precipitation, providing a clear solution.

[0056] As stated in the prior art, a synergistic effect of Zn.sup.2+ ions of organic and/or inorganic sources on other metal salts, such as sodium gluconate, can be observed for a mass ratio of Zn.sup.2+ ions/sodium gluconate in a very narrow range of mass ratio.

[0057] At higher mass ratios, the inhibition efficiency might even drop again.

[0058] Surprisingly, the range of possible concentrations of calcium gluconate within the liquid medium surrounding the metallic surface, increases, when combined with a zinc carboxylate.

[0059] According to the invention, the mass ratio of the at least one zinc carboxylate and the calcium gluconate is in the range of 1:10 to 1:600, preferably in the range of 1:50 to 1:100.

[0060] Surprisingly, a corrosion inhibition composition according to the present invention with said mass ratio shows constantly good results in corrosion inhibition for a broad variety of metals.

[0061] Surprisingly, the corrosion inhibition composition according to the invention allows a symbiosis of zinc carboxylates and calcium gluconate in an advantageous manner: [0062] a) On the one hand, zinc carboxylates, that are not soluble in water, will be kept in solution by an emulsifying effect of the calcium gluconate, at neutral and even at basic pH values. [0063] b) On the other hand, the corrosion inhibiting effect of a carboxylate in aqueous solution, which is used to protect only very specific metal surfaces, can now be applied to a large variety of metal surfaces concurrently. Even a concurrent protection of aluminum and cast iron is given.

[0064] Magnesium carboxylates may enhance the advantageous effects.

[0065] In certain embodiments, the corrosion inhibition composition according to the invention additionally comprises at least one magnesium carboxylate.

[0066] In certain embodiments, the carboxylate anions of the magnesium carboxylate are selected from the group comprising gluconate, bisglycinate, glycinate, citrate, acetate, ascorbate, DL-hydrogenaspartate, L-hydrogenaspartate, malate and mixtures of these.

[0067] In embodiments, the corrosion inhibition composition for metallic surfaces consists of at least one zinc carboxylate, calcium gluconate and optionally at least one magnesium carboxylate, wherein the mass ratio of the at least one zinc carboxylate and the calcium gluconate is in the range of 1:10 to 1:600.

[0068] In certain embodiments, the corrosion inhibition composition according to the invention comprises additionally a chelating agent. In terms of the invention, “chelating agents” are chemical compounds that react with metal ions to form a stable, water-soluble complex. They are also known as chelants, chelators or sequestering agents.

[0069] In certain embodiments, chelating agents have a ring-like centre, which forms at least two bonds with the metal ion allowing it to be excreted. Chelating agents are known in the art. In certain embodiments, the chelating agent is selected from metal salts.

[0070] To avoid turbid solutions of the corrosion inhibition composition a chelating agent can be added. Surprisingly, the addition of a chelating agent to the composition not only provides clear aqueous solutions of the composition. In some cases, the corrosion inhibition efficiency of the composition even increases.

[0071] In certain embodiments, the mass ratio of the at least one zinc carboxylate to the sum of calcium gluconate plus the chelating agent, preferably to the sum of all, magnesium and calcium carboxylates plus the chelating agent, is in the range of 1:5 to 1:200, preferably in the range of 1:10 to 1:100, more preferably in the range of 1:20 to 1:100.

[0072] In certain embodiments, the chelating agent is different from the zinc carboxylate and calcium gluconate, or, in certain embodiments, different from the at least one zinc carboxylate and from calcium gluconate and from the at least one magnesium carboxylate in the corrosion inhibition composition according to the invention.

[0073] In further embodiments, the chelating agent is selected from amino acids or metal gluconates.

[0074] In the documents depicting the state of the art, the inhibition of corrosion using zinc salts or other metal salts showed satisfying results for a limited number of metals only. Furthermore, most environmentally friendly corrosion inhibitors used in the state of the art effectuate ionization of copper in presence of other metal salts in aqueous solution. Advantageously, ionization of copper is prevented, when using the corrosion inhibition composition according to the invention and in addition to it, a high protection of other metallic surfaces is provided.

[0075] Surprisingly, the corrosion inhibition composition according to the invention shows high corrosion inhibition efficiency for a wide range of metals and/or metallic surfaces concurrently.

[0076] In accordance to the invention, the term “metallic surface” comprises surfaces of metals and/or metal alloys, as well as of any other metal and/or metal alloy containing material.

[0077] In certain embodiments, the metal in the metallic surface is selected from the group comprising cast iron, copper, aluminum, cast aluminum, steel, mild steel, zinc, magnesium, cast magnesium, tin, solder, titanium, brass and combinations thereof.

[0078] Additionally, the present invention comprises a method for inhibition of corrosion of metals and/or metallic surfaces comprising the steps [0079] a) Providing a corrosion inhibition composition comprising [0080] at least one zinc carboxylate and [0081] calcium gluconate, [0082] wherein the mass ratio of the at least one zinc carboxylate and the calcium gluconate is in the range of 1:10 to 1:600, and [0083] b) Addition of the corrosion inhibition composition to a liquid medium, wherein the metal and/or metallic surface is exposed to the liquid medium or will be exposed to the liquid medium.

[0084] In a first step, a corrosion inhibition composition is provided. According to the invention the composition comprises [0085] at least one zinc carboxylate and [0086] calcium gluconate.

[0087] According to the invention, the mass ratio of the at least one zinc carboxylate and the calcium gluconate is in the range of 1:10 to 1:600, preferably in the range of 1:50 to 1:100.

[0088] A further explanation can be found in the paragraph describing the corrosion inhibition composition according to the invention.

[0089] In certain embodiments of the invention, the composition additionally comprises at least one magnesium carboxylate. Further embodiments of the corrosion inhibition composition can be found in the respective paragraph above.

[0090] According to the invention, in a second step b) the corrosion inhibition composition is added to the liquid medium, wherein the metal and/or metallic surface is exposed to or contacted with the liquid medium or will be exposed to or contacted with the liquid medium.

[0091] In certain embodiments, the corrosion inhibition composition is part of a superordinate composition added to the liquid medium for various purposes, e.g. cleaning purposes or paint/coating purposes.

[0092] In certain embodiments, the liquid medium is an aqueous medium.

[0093] In certain embodiments, the liquid medium comprises a water-soluble organic and/or inorganic solvent.

[0094] In further embodiments, the liquid medium comprises water and an organic and/or inorganic solvent and at least one surface tension modifying additive selected from emulsifiers, surfactants and/or detergents. In embodiments, the liquid medium is a water/oil emulsion or an oil/water emulsion.

[0095] Advantageously, the corrosion inhibition composition according to the invention can be added to aqueous liquid media and organic and/or inorganic solvents containing emulsions. It can also be part of a solid composition, which can be added to a liquid medium for various purposes. More advantageously, the corrosion inhibition composition according to the invention is highly compatible with amines or alkaline formulations, which are often used in standard corrosion inhibition compositions.

[0096] This offers a broad field of application for the composition according to the invention. Examples for potential applications are: [0097] Hydraulic fluids (HF-A; HF-C), [0098] House-hold and/or institutional cleaners, [0099] Dishwashing tablets/powder/liquid, [0100] Chelating agent for aqueous systems, [0101] Paint and/or coating (liquid and/or powder coating), [0102] Deicing fluid for airfield runways, [0103] Deicing fluid aircrafts, [0104] Deicing fluids for roads and/or parking areas, [0105] Corrosion additive package for deicing fluids, [0106] Aluminum drawing and rolling process, [0107] Aluminum and magnesium tapping processes, [0108] Copper drawing and rolling processes, [0109] Lubricants, [0110] Automotive coolants, [0111] Metal working fluids, [0112] Coolant fluids for (sea-) containers and display cabinets in supermarkets, [0113] Solar fluids, [0114] Heating systems, [0115] Heat transfer fluids, [0116] Off-shore drilling fluids, [0117] Temporary corrosion inhibitor for copper, brass, ferrous, aluminum magnesium, [0118] Cast iron production, [0119] Cast aluminum production and [0120] Cast magnesium production.

[0121] In certain embodiments, the liquid medium, the metal will be exposed to, comprises amines or alkaline formulations.

[0122] In certain embodiments, the liquid medium and the corrosion inhibition composition or the superordinate composition are mixed thoroughly before exposing the metal and/or metallic surface to the liquid medium.

[0123] The concentration of additives in the metal contacting liquid medium often plays an important role for the efficiency of corrosion inhibition. Too low concentrations may not have a sufficient effect on corrosion inhibition, whereas other studies show that concentrations excelling a certain value can lead to decreased inhibition effects.

[0124] As stated in the prior art, each metal or metal alloy often requires a defined corrosion inhibitor composition with defined dosages of each ingredient and defined concentrations of additives to achieve sufficient inhibition efficiency. Additionally, prior art corrosion inhibitors often exhibit sufficient efficiency at very low concentrations in the metal contacting medium, e.g. water. This aspect strongly generates the problem of over-dosage, since smaller volumes or amounts of metal surrounding media (e.g. 10 to 20 liters of water in a dishwasher) require very little amounts of additives. Advantageously, the current invention allows a high variability in the total concentration of additives in the liquid medium the metallic surface is or will be exposed to.

[0125] In certain embodiments, the concentration of the corrosion inhibition composition in the liquid medium, with or without a superordinate composition, is in the range of 0.01% to 20% (w/w), more preferably in the range of 0.05% to 15% (w/w), most preferably in the range of 0.1% to 10% (w/w); to achieve sufficient corrosion inhibition to a large variety of metallic surfaces.

[0126] Corrosion inhibition compositions according to the invention were tested at different concentrations and different mass ratios of organic and/or inorganic zinc salts and metal salts for protection of surfaces of copper, aluminum, mild steel, zinc and cast iron and investigated optically. All metallic surfaces showed no corrosion but preserved their metallic gloss.

[0127] To evaluate the performance of additive formulations electrochemical measurements were conducted to obtain corrosion current densities (i.sub.corr) in artificial tap water (see ASTM D1384-05) with and without corrosion inhibition compositions according to the invention. Specimen from different metals are immersed in the specific electrolytes for 1 hour. After that period, the specimen was continuously polarized with 1 mV/s from cathodic to anodic direction based on the open circuit potential. From the resulting current density-potential-plot i.sub.corr was determined by using Tafel extrapolation of the cathodic and anodic branch of the curve (see ASTM G3-14 (Reapproved 2019): Standard Practice for Conventions Applicable to Electrochemical Measurements in Corrosion Testing). The higher i.sub.corr, the higher the corrosion rate or the metal loss.

[0128] For an evaluation of the protection capabilities of an additive or inhibitor, the inhibition efficiency (IE) was calculated using formula 1

IE[%]=100*(i.sub.corr1−i.sub.corr2)/i.sub.corr1  (1),

wherein i.sub.corr1 is the corrosion current density of the specific sample in the non-inhibited electrolyte and i.sub.corr2 the corrosion current density of the specific sample in the inhibited electrolyte.

[0129] Surprisingly, all investigated compositions showed increased corrosion inhibition efficiency to a broad variety of metals or metallic surfaces respectively, such as aluminum, mild steel, zinc, copper or even cast iron.

[0130] Advantageously, this effect opens the possibility for a wide range of applications such as addition of the corrosion inhibition composition to coolants, cleaning systems, deicing systems and/or lubrication solvents to prevent corrosion of the metal and/or metallic surfaces, surrounded by a liquid medium.

[0131] In embodiments, the corrosion inhibition composition is a liquid formulation further comprising a liquid medium selected from water and/or an organic and/or inorganic solvent or a mixture thereof.

[0132] In certain embodiments, the concentration of the corrosion inhibition composition in the liquid medium is in the range of 0.01% to 50% (w/w), preferably in the range of 0.05% to 50% (w/w), more preferred in the range of 0.05% to 20% (w/w), regarding the total mass of the liquid formulation.

[0133] In embodiments, the liquid medium comprises water and at least one water-soluble organic solvent.

[0134] In certain embodiments, the liquid medium comprises water and at least one organic solvent and at least one surface tension modifying additive such as emulsifiers, surfactants and/or detergents.

[0135] Advantageously, the liquid formulation can be added to a wide range of liquid media to protect metals and/or metallic surfaces from corrosion at different temperatures and different concentrations.

[0136] In further embodiments, the corrosion inhibition composition is a solid formulation further comprising at least one further component, wherein the at least one further component is selected from carrier materials, complexing agents, such as magnesium gluconate; softener and surfactants.

[0137] In certain embodiments, the solid formulation is selected from powder, suspension, grouted powder and particles. In embodiments, the concentration of the corrosion inhibition composition in the solid formulation is in the range of 0.05% to 99% (w/w), preferably in the range of 0.05% to 50% (w/w), more preferred in the range of 0.05% to 20% (w/w), regarding the total mass of the solid formulation.

[0138] According to the invention, the corrosion inhibition composition is used for the protection of metals and/or metallic surfaces from corrosion.

[0139] In embodiments, the corrosion inhibition composition is used for the protection of metals and/or metallic surfaces from corrosion in liquids comprising water, e.g. in an aqueous medium.

[0140] In embodiments, the corrosion inhibition composition is used for protection of metals and/or metallic surfaces from corrosion in [0141] Hydraulic fluids (HF-A; HF-C), [0142] House-hold and/or institutional cleaners, [0143] Dishwashing tablets/powder/liquid, [0144] Chelating agent for aqueous systems, [0145] Paint and/or coating (liquid and/or powder coating), [0146] Deicing fluid for airfield runways, [0147] Deicing fluid for aircrafts, [0148] Deicing fluids for roads and/or parking areas, [0149] Corrosion additive package for deicing fluids, [0150] Aluminum drawing and rolling processes, [0151] Aluminum and magnesium tapping processes, [0152] Copper drawing and rolling processes, [0153] Lubricants, [0154] Automotive coolants, [0155] Metal working fluids, [0156] Coolant fluids for (sea-) containers and display cabinets in supermarkets, [0157] Solar fluids, [0158] Heating systems, [0159] Heat transfer fluids, [0160] Off-shore drilling fluids [0161] Temporary corrosion inhibitor for copper, brass, ferrous, aluminum magnesium, [0162] Cast iron production, [0163] Cast aluminum production and/or [0164] Cast magnesium production.

[0165] In embodiments, the corrosion inhibition composition is used for protection of metals and/or metallic surfaces from corrosion in fluids containing amines or alkaline formulations.

[0166] In certain embodiments, the corrosion inhibition composition is added to the liquid, the metallic surface is or will be exposed to, in an amount that the concentration of the corrosion inhibition composition in the liquid is in the range of 0.01% to 20% (w/w), more preferably in the range of 0.05% to 15% (w/w), most preferably in the range of 0.1% to 10% (w/w).

[0167] In further embodiments, the recently described embodiments can be combined.

FIGURES AND EXAMPLES

[0168] The present invention will now be further explained by the following non-limiting figures and examples.

[0169] FIG. 1 shows corrosion current densities (i.sub.corr) in artificial tap water (see ASTM D1384-05) containing either i) no additive or ii) 5% (w/w) calcium gluconate additive (the additive consisting of 5% (w/w) Ca-GDL and 95% (w/w) water) or iii) 5% (w/w) calcium gluconate and zinc acetate additive (the additive consisting of 5% (w/w) Ca-GDL, 0.08% (w/w) zinc acetate and 94.92% (w/w) water) or iv) 5% (w/w) additive A (the additive consisting of 4% (w/w) calcium gluconate, 1% (w/w) magnesium gluconate, 0.08% (w/w) zinc acetate and 94.92% (w/w) water) for a) mild steel, b) cast iron, c) zinc, d) aluminum and e) copper.

EXAMPLES

[0170] Investigations on corrosion inhibition efficiency have been provided using the metal coupons according to Tab. 1.

TABLE-US-00001 TABLE 1 Specification and densities of metal coupons (UNS: Unified Numbering System for metals and/or alloys. It specifies exactly the composition of the metal in question). UNS code Trade name Density (g/cm.sup.3) G10100 C1010 Mild Steel 7.87 C11000 CDA 110 ETP Copper 8.89 A91100 Al 1100 Aluminum 2.71 Z15001 Zinc 7.13 F12801 Grey Cast Iron Type G-2 CL40 6.97

[0171] Electrochemical Measurements

[0172] General Procedure

[0173] Electrochemical measurements are conducted to obtain corrosion current densities (i.sub.corr) in artificial tap water [see ASTM D1384-05] with and without corrosion inhibition compositions. Specimen of different metals are immersed in the specific electrolytes for 1 hour. After that period, the specimen is continuously polarized with 1 mV/s from cathodic to anodic direction based on the open circuit potential. From the resulting current density-potential-plot i.sub.corr is determined by using Tafel extrapolation of the cathodic and anodic branch of the curve (see ASTM G3-14). The higher i.sub.corr, the higher the corrosion rate or the metal loss.

[0174] For an evaluation of the protection capabilities of an additive or inhibitor, the inhibition efficiency (IE) is calculated using formula 1

IE[%]=100*(i.sub.corr1−i.sub.corr2)/i.sub.corr1  (1),

wherein i.sub.corr1 is the corrosion current density of the specific sample in the non-inhibited electrolyte and i.sub.corr2 the corrosion current density of the specific sample in the inhibited electrolyte.

[0175] Electrolyte

[0176] For testing of one specific composition, the relevant composition or formulation is mixed together with the corrosive water (tap water) before the experiment to obtain a specific concentration. For each test, 200 ml of fresh solution is made and used.

[0177] Specimen

[0178] The tested metallic samples are commercially obtained coupons of mild steel (C1010), cast iron (GCL40), zinc, copper and aluminum (AL1100) (also see Tab. 1). Before the test, each specimen is ground with abrasive paper grit 600, rinsed and dried in air. The actual value of the exposed surface area in the corrosion tests is 3 cm.sup.2 and is used to calculate current densities from measured currents.

[0179] Electrochemical Equipment

[0180] For the performance testing, electrochemical equipment is used consisting of a glass vessel for the electrolyte, a counter electrode made of a platinum mesh and a KCl-saturated Ag/AgCl reference electrode with an electrode potential of E=197 mV vs. standard hydrogen electrode (SHE). For conducting the polarization measurements, the potentiostat “Reference 1000” (Gamry) and the software “Gamry Frameworks” is used. For evaluation of the corrosion current density by Tafel extrapolation the software “Gamry Echem Analyst” is used.

[0181] Investigation of corrosion efficiency of Ca-GDL [0182] a) Ca-GDL=(D,L)-calcium gluconate, analytical grade, Sigma Aldrich, [0183] b) Mg-CDL=(D,L)-magnesium gluconate, analytical grade, Sigma Aldrich, [0184] c) Zn-acetate=zinc acetate, analytical grade, Sigma Aldrich.

[0185] Comparative experiments are performed with all metal samples in a corrosive electrolyte for 1 h in [0186] i) Artificial tap water without additive, [0187] ii) Solution consisting of 95% (w/w) artificial tap water and 5% (w/w) Ca-GDL additive (the additive consisting of 5% (w/w) Ca-GDL and 95% (w/w) water) [0188] iii) Solution consisting of 95% (w/w) artificial tap water and 5% (w/w) Ca-GDL and zinc acetate additive (the additive consisting of 5% (w/w) Ca-GDL, 0.08% (w/w) zinc acetate and 94.92% (w/w) water) [0189] iv) Solution of 99.5% (w/w) artificial tap water and 5% (w/w) additive composition (formulation: 0.08% (w/w) Zn acetate, 1.0% (w/w) Mg-GDL, 4.0% (w/w) Ca-GDL).

[0190] The resulting current density-potential-plots are shown in FIG. 1 (a)-(e). The resulting values for corrosion inhibition efficiency are shown in Tab. 2.

TABLE-US-00002 TABLE 2 Corrosion current densities and inhibition efficiencies. Experiment Mild steel Cast iron Zinc Aluminum copper (i) i.sub.corr [μA/cm.sup.2] 43 55.7 15.4 1.4 1.9 no additive (ii) icorr [μA/cm.sup.2] 0.3 23.8 8.8 4.1 1.4 with Ca-GDL additive IE [%] 99.3 57.3 42.9 −192.9.9 26.3 (iii) i.sub.corr [μA/cm.sup.2] 0.4 2.6 0.9 0.4 0.4 with additive A IE [%] 99.1 95.3 94.2 71.4 78.9 (iv) i.sub.corr [μA/cm.sup.2] 0.3 9.7 0.7 0.3 0.6 with additive A IE [%] 99.3 82.6 95.5 78.6 68.4

[0191] The tab water (experiment (i)) shows high corrosion rates. Partial corrosion inhibition can be achieved by adding Ca-GDL (experiment (ii)), still zinc, copper and aluminum show strong corrosion. Only the corrosion inhibition composition according to the invention (experiment (iii) and (iv)) provides high corrosion inhibition efficiency for all investigated metals at the same time.

TABLE-US-00003 TABLE 3 Corrosion current densities and inhibition efficiencies of the metal samples in the corrosive electrolyte iv) for 1 h and 8 weeks. Experiment Mild steel Cast iron Zinc Aluminum copper 1 h i.sub.corr [μA/cm.sup.2] 0.3 9.7 0.7 0.3 0.6 with additive A IE [%] 99.3 82.6 95.5 78.6 68.4 8 weeks i.sub.corr [μA/cm.sup.2] 0.4 3.9 2.1 0.12 0.6 with additive A IE [%] 99.1 93.0 86.4 91.4 68.4

[0192] The corrosion inhibition composition according to the invention (experiment (iv)) provides even after 8 weeks a high corrosion inhibition efficiency for all investigated metals (see Tab. 3).