Steel anti-corrosion composition containing microorganisms

Abstract

To provide a microorganism-containing steel anticorrosion composition that can impart high corrosion resistance by coating on steel, etc., and to provide a coated steel obtained using the same.SOLUTION: The steel anticorrosion composition contains a microorganism, a water-soluble metal compound, and, as necessary, a solvent or the like capable of dissolving the metal compound. The microorganism is a microorganism having extracellular electron transfer ability such as metal-reducing bacteria, and bacteria belonging to the genera Shewanella, Geobacter, Desulfuromonas, Rhodoferax, Sulfurospirillum, or Pseudomonas can be exemplified. The metal compound is a compound having a solubility of 0.01 g or more at 5°C, and sulfate such as nickel sulfate, aluminum sulfate, copper sulfate, tin sulfate, chromium sulfate, calcium sulfate, cobalt sulfate, and zinc sulfate can be exemplified. The solvent is a liquid that dissolves the metal compound and allows the microorganism to act, and a typical example is water.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a composition for preventing corrosion of steel materials (hereinafter referred to as a composition for preventing corrosion of steel materials), and a steel material coated with the composition for preventing corrosion of steel materials. More specifically, the present invention relates to an anticorrosive composition for enhancing the corrosion resistance of steel materials by applying it to steel materials, steel materials covered with a rust layer, and steel materials covered with an organic layer or an inorganic layer (hereinafter collectively simply referred to as steel materials), and further relates to a steel material coated with the composition for preventing corrosion of steel materials (hereinafter referred to as a coated steel material).

Background Art

[0002] Steel materials are the base materials that make up various social infrastructure structures such as bridges and iron towers, but they are easily corroded in an atmospheric corrosion environment accompanied by repeated drying and wetting. Rust (composed of iron oxides) generated due to corrosion acts as an oxidizing agent on the steel material by undertaking the cathodic reaction during the wetting process, thus accelerating the corrosion further. Usually, the dry rust in the atmospheric corrosion environment that exhibits a reddish-brown color is reduced when acting as an oxidizing agent during the wetting process and generally becomes black. However, since it is air-oxidized during the drying process, it returns to the reddish-brown rust that acts as an oxidizing agent again. Due to the repetition of such reduction and oxidation cycles with repeated drying and wetting, the rust acts as an oxidizing agent infinitely and corrodes the steel material at a high speed. Therefore, once the steel material starts to corrode, the corrosion progresses acceleratively while accompanied by the generation of rust. Thus, the corrosion of steel materials and the generation of rust are serious problems that lead to the damage or destruction of structures and the like.

[0003] On the other hand, as a general means for ensuring the corrosion resistance of steel materials, painting in which a paint is applied to the surface of the steel material is mentioned. However, since painting cannot avoid the deterioration of the paint film and paint film defects, it cannot prevent corrosion in the medium to long term. For example, even in painting means that claim high corrosion resistance such as zinc-rich paint that utilizes the sacrificial anticorrosive action of zinc powder, the period during which its effect can be exerted is limited to a relatively short period, and it is essentially impossible to prevent the start of corrosion from the deterioration of the paint film and paint film defects.

[0004] In response to such problems, Japanese Patent Application Laid-Open No. 2017-35877 discloses that corrosion resistance can be improved by applying an inorganic zinc-rich paint to a steel material and then applying a solution containing a magnesium compound to the surface of the coating film. However, even when such treatment is performed, the improvement ratio of corrosion resistance improvement is only about twice as large at most compared to the case where the treatment is not performed, and in a severe corrosion environment containing chlorides, sufficient corrosion resistance could not be imparted.

[0005] In addition, such highly corrosion-resistant coatings such as zinc-rich paints are applied to the surface of a clean steel material obtained by shot blasting or the like, and do not exhibit high corrosion resistance when applied to a steel material covered with a rust layer due to oxidation and corrosion.

[0006] As described above, when a rust layer already exists on the base, even if a coating is applied thereon, since the rust layer on the base acts as an oxidizing agent, corrosion progresses due to the presence of the rust layer, accelerating the deterioration of the coating film formed by the coating. Therefore, it is necessary to remove all the rust layers present on the surface of the steel material when applying the coating. However, in reality, it is extremely difficult to completely remove the rust layer of the steel material, and in fact, when repairing a corroded steel structure, the coating is applied with a certain amount of rust layer remaining. Therefore, shortening the life of the coating film is a major problem in order to efficiently carry out infrastructure maintenance.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0008] The present invention has been made in view of the above circumstances, and it is possible to provide a steel material anticorrosive composition that can impart high corrosion resistance to a steel material that forms a rust layer due to subsequent corrosion or already has a rust layer formed thereon by making the rust layer corrosion - resistant, and a coated steel material obtained by using the same.

Means for Solving the Problems

[0009] The steel material anticorrosive composition according to the present invention contains a microorganism having an extracellular electron transfer ability such as a metal - reducing bacterium (hereinafter simply referred to as the microorganism), and a metal compound having a certain water solubility. Further, it can contain a solvent capable of dissolving the metal compound, but even when the solvent is not contained, if the steel material anticorrosive composition is applied to the steel material and the steel material is in a corrosion environment exposed to rainfall or dew condensation, water serves as a solvent due to rainfall or dew condensation. Here, the solvent is preferably a liquid in which the microorganism can actively act, and a typical example is water. Also, the microorganism may be an iron - reducing bacterium. The metal compound may be, for example, a metal sulfate, nitrate, or oxide.

[0010] In the present invention, by acting the steel material anticorrosive composition on the steel material surface by various means such as coating or injecting it into the rust layer on the steel material surface, the rust layer formed on the steel material or the already - formed rust layer receives electrons from the microorganism and is reduced. At the same time, the metal cations generated by the dissolution of the added water - soluble metal compound, in combination with the action of the microorganism, are taken up in large amounts into the reduced rust layer, and the reduced rust layer becomes less likely to be re - oxidized by air, so a stable rust layer that is difficult to be redox - reacted is formed. As a result, the rust layer no longer acts as an oxidizing agent on the steel material and does not participate in corrosion, and the environmental barrier function of the rust layer is improved, significantly enhancing the corrosion resistance of the steel material. That is, when the steel material anticorrosive composition of the present invention is used, due to the effects of the microorganism and metal cations, a rust layer with high corrosion resistance is formed, not only enhancing the corrosion resistance of the steel material, but also when painting is applied after the steel material anticorrosive composition is acted on, if such a rust layer with high corrosion resistance exists, the lifespan of the paint film formed by painting can also be extended.

[0011] The present invention has been made based on such findings, and the gist thereof is as follows.

[0012] [1] A steel anti-corrosion composition comprising the microorganism and a metal compound having a solubility of 0.01 g or more in 100 cm of water at 5°C. 3 [2] A steel anti-corrosion composition comprising the microorganism, a metal compound having a solubility of 0.01 g or more in 100 cm of water at 5°C, and a solvent capable of dissolving the metal compound. 3 [3] The steel anti-corrosion composition according to [1] to [2] above, wherein the metal compound contains at least one metal sulfate having a solubility of 0.01 g or more in 100 cm of water at 5°C. 3 [4] The steel anti-corrosion composition according to [1] to [2] above, wherein the metal compound contains at least one selected from the group consisting of nickel sulfate, aluminum sulfate, copper sulfate, tin sulfate, chromium sulfate, calcium sulfate, cobalt sulfate, and zinc sulfate. [5] The steel anti-corrosion composition according to any one of [2] to [4] above, wherein the solvent contains at least water. [6] The steel anti-corrosion composition according to [1] to [5] above, wherein the microorganism is an iron-reducing bacterium. [7] A steel material coated with the steel anti-corrosion composition according to [1] to [6] above.

Advantages of the Invention

[0013] According to the present invention, even in a severe corrosion environment such as containing chlorides, for steel materials and the like, due to the effect of the compound of the microorganism and the metal, a rust layer with high corrosion resistance is formed, which not only enhances the corrosion resistance of the steel material, but also when painting is further applied, the service life of the paint film by painting can be extended, so that a steel material anticorrosive composition capable of imparting high corrosion resistance and a coated steel material obtained by using the same can be provided. Therefore, in the repair of steel infrastructure structures, the present invention can impart corrosion resistance to the rust layer remaining without being completely removed during the process of removing the rust layer of the corroded steel material, so that it is not necessary to completely remove the remaining rust layer during repair, and it can also play an effect in reducing the base treatment before painting, and the industrial contribution is extremely remarkable.

Brief Description of the Drawings

[0014]

Figure 1

Modes for Carrying Out the Invention

[0015] Hereinafter, preferred embodiments of the present invention will be described.

[0016] (Steel material anticorrosive composition) The steel corrosion prevention composition contains microorganisms having extracellular electron transfer ability and a water-soluble metal compound, and optionally a solvent capable of dissolving the metal compound. By applying such a steel corrosion prevention composition to part or all of the surface of the steel, it has the function of making the structure of the rust layer corrosion-resistant. The rust layer that has changed corrosion-resistant (hereinafter simply referred to as the corrosion-resistant rust layer) does not act as an oxidizing agent as described above, but rather protects the steel from corrosion. Therefore, it is effective as a pretreatment for painting and the steel corrosion prevention composition itself can also be used as a paint. In addition, the steel corrosion prevention composition can be made to act in various ways, such as holding it in a porous body such as a sponge and pressing it against the steel surface, or covering it with some kind of coating material after application, to obtain an effect.

[0017] (Microorganisms having extracellular electron transfer ability) The microorganism, which is a microorganism having extracellular electron transfer ability, plays a role in changing the structure of the rust layer into a corrosion-resistant one. Specifically, it has the role of giving electrons to and reducing the iron oxide constituting the rust layer and injecting coexisting metal cations into the rust layer. A typical example of such a microorganism is iron-reducing bacteria. The iron-reducing bacteria effective for obtaining such an action may be bacteria that give electrons to iron oxide. For example, Aeromonas, Archaeoglobus, Deferribacter, Desulfovibrio, Desulfuromonas, Ferrimonas, Geobacter, Geothrix fermentans, Geovibrio, Pelobacter, Pyrobaculum, Pyrococcus, Shewanella, Sulfurospirillum, Thermotoga, Wolinella, etc. can be exemplified. The microorganism is not limited to these exemplified bacteria. For example, it may be a mixed culture whose species cannot be specified, or it can be iron-reducing bacteria inhabiting paddy soil, etc.

[0018] In the steel corrosion preventive composition, the concentration of the microorganism exemplified by iron-reducing bacteria may be 0.1, 1.0, or 2.0 in terms of optical density (OD(600nm) value) with a light path length of 1 cm by the microorganism, excluding the background caused by light absorption by components other than the microorganism in the steel corrosion preventive composition. The lower limit of the OD(600nm) value may be 0.01, and the upper limit may be 7.0, but it is preferably 0.03 or more. Also, the upper limit is preferably 3.0 from the viewpoint of supply stability. When the concentration of the microorganism is expressed as the number of bacteria (number of individuals) per 1 cm of the steel corrosion preventive composition, it may be 1×10 3 individuals, may be 1×10 1 individuals, may be 1×10 5 individuals, may be 1×10 7 individuals, may be 1×10 11 individuals, but in order to obtain a high effect, it is preferably 1×10 1 individuals or more, more preferably 1×10 2 individuals or more, and even more preferably 1×10 4 individuals or more, and may be 1×10 5 individuals or more. Note that if the concentration of the microorganism becomes too high, the action efficiency of the microorganism decreases, so it is preferably 1×10 10 individuals or less, and may even be 1×10 9 individuals or less. In any case, even if the concentration of the microorganism in the steel corrosion preventive composition is low before application, it is considered to increase by growth after applying the steel corrosion preventive composition to the steel.

[0019] (Compound of metal) In order to obtain the effect of the present invention, it is necessary to add a water-soluble metal compound together with the microorganism exemplified by iron-reducing bacteria. The solubility of the metal compound is 100 cm of water 3It may be 0.001 g, 0.1 g, 1 g, or 10 g at 5 °C, but it is effective that it is 0.01 g or more. Non-ferrous metal cations formed by dissolving and ionizing a metal compound in a solvent such as water, in combination with the action of the microorganism exemplified by iron-reducing bacteria, are incorporated into iron oxides such as spinel-type iron oxides formed by reducing the iron oxides constituting rust, whereby a highly corrosion-resistant rust layer can be formed.

[0020] Examples of the metal compound include metal sulfates, nitrates, oxides, etc. It is effective to use at least one selected from the group consisting of nickel sulfate, aluminum sulfate, copper sulfate, tin sulfate, chromium sulfate, calcium sulfate, cobalt sulfate, and zinc sulfate as the sulfate.

[0021] The addition amount of the metal compound is not particularly limited, but it is effective that it is 0.1 to 40.0% by mass based on the mass of the steel material anti-rust composition. The lower limit may be 0.5% by mass, 1% by mass, 2% by mass, 3% by mass, or 4% by mass. The upper limit may be 35% by mass, 30% by mass, 25% by mass, or 20% by mass.

[0022] (Solvent) The solvent is preferably one that dissolves the metal compound and provides an environment in which the microorganism can actively act. Water is a typical example, but it is not limited to water as long as it satisfies those conditions. Also, even when the steel material anti-rust composition does not contain a solvent, if it is a corrosion environment in which water is supplied by rainfall, dew condensation, etc. after the steel material anti-rust composition is applied to the steel material and allowed to act, the supplied water serves as a solvent. In this case, the microorganism may be added to the steel material anti-rust composition before coating in a freeze-dried state, etc., and when water is supplied by rainfall or dew condensation after coating, it is cultured and the number of individuals increases to an appropriate concentration. The addition amount of a solvent such as water is not particularly limited, but it is effective that it is 1 to 95.0% by mass based on the mass of the anti-rust composition. The lower limit may be 3% by mass, 15% by mass, or 25% by mass. The upper limit may be 90% by mass, 80% by mass, or 70% by mass.

[0023] (Other components) The steel corrosion prevention composition may contain a medium component effective for the growth of the microorganism. The addition amount of the medium component is not particularly limited, but can be 1 to 80.0% by mass based on the mass of the anticorrosion composition. The lower limit may be 2% by mass, 3% by mass, 5% by mass, 8% by mass, or 10% by mass. The upper limit may be 70% by mass, 50% by mass, 40% by mass, 30% by mass, or 20% by mass. Also, lactic acid, citric acid, etc. that the microorganism can extract electrons from can be added.

[0024] Furthermore, in order to hold the steel corrosion prevention composition on the steel surface, it may contain a binder such as a water-soluble resin. When using a binder, it becomes easier to hold the steel corrosion prevention composition on the steel surface and the adhesion to a base material such as steel can be improved. The addition amount of the binder when using a binder is not particularly limited, but can be 3 to 80.0% by mass based on the mass of the anticorrosion composition. The lower limit may be 4% by mass, 8% by mass, or 12% by mass. The upper limit may be 70% by mass, 50% by mass, or 30% by mass.

[0025] Also, various pigments can be added. Examples of the pigments are coloring pigments, extender pigments, rust preventive pigments, and special function pigments. There is no particular limitation on the addition ratio of the pigments, but it may be 30% by mass or less, or 20% by mass or less based on the total mass of the steel corrosion prevention composition. In addition, a pH buffer or a compound showing alkalinity can be added for pH adjustment.

[0026] (Function) When a rust layer formed on a steel material or an existing rust layer is acted upon by applying a rust preventive composition for steel materials to the entire or a part of the surface of the steel material, the rust layer is reduced by the microorganism, and at the same time, metal cations generated by dissolving a water-soluble metal compound added are taken in large amounts into the reduced rust layer, and a corrosion-resistant rust layer that is difficult to be redoxed is formed. Generally, in order to reduce the rust layer, the steel material is cathodically polarized using an electrochemical polarization device. In that case, only the rust close to the metallic iron of the base material is reduced. However, since the microorganism directly gives electrons to the entire rust layer for reduction, its effect is very large, and there is no need to perform cathodic polarization and no polarization device is required. Therefore, it is not practical to perform cathodic polarization on a structure composed of steel materials having a large area such as an infrastructure steel structure because it involves the generation of a large current. However, a rust preventive composition for steel materials can be applied even to a large area. As described above, the rust layer no longer acts as an oxidizing agent and does not participate in corrosion, and at the same time, the environmental barrier function of the rust layer is improved, and the corrosion resistance of the steel material is remarkably enhanced. That is, when the rust preventive composition for steel materials of the present invention is used, due to the effects of the microorganism and metal cations, a corrosion-resistant rust layer is formed, so that not only the corrosion resistance of the steel material is enhanced, but also when painting is further applied, the life of the coating film formed by painting can be extended.

[0027] The reason why the corrosion-resistant rust layer does not act as an oxidizing agent is that the microorganism gives electrons to the iron oxide constituting the rust layer, and a large amount of metal cations are taken into the spinel-type iron oxide generated by reduction. That is, electrons are given to the iron oxide composed of Fe 3+ in the rust layer due to the effect of the microorganism, and the resulting iron oxide contains Fe 3+ and Fe 2+ in a stoichiometric atomic ratio of 2:1. Generally, such an iron oxide containing Fe 3+ and Fe 2+ easily oxidizes Fe 2+ in the air during the drying process in an atmospheric corrosion environment involving repeated wet and dry cycles, so that Fe 3+ acting as an oxidizing agent again.It returns to the rust layer composed of iron oxide consisting only of this, but compared with the case of reducing the rust layer by cathodic polarization using a polarization device or the like in the iron oxide in which the metal cation is reduced by the effect of the microorganism, a very large amount is taken in and the air oxidation of the reduced iron oxide is significantly inhibited, so that the rust layer no longer acts as an oxidizing agent. In addition, since a large amount is taken into the iron oxide in which the metal cation is reduced, the rust layer becomes dense and the environmental barrier function is also significantly improved. That is, a corrosion-resistant rust layer is formed.

Example

[0028] Hereinafter, the present invention will be described more specifically by showing examples of the present invention. However, the present invention is not limited to these examples, and various modifications can be made without departing from the technical idea of the present invention.

[0029] (Production of coated steel material) A blast steel material having dimensions of 70 mm × 150 mm × 3 mm and having components other than iron shown in Table 1 was prepared. This steel material was exposed to the atmosphere for 1 year (Kohama City, airborne salt content 1.0 mg NaCl / dm 2 / day), and after a rust layer was naturally formed on the surface, a test steel material was obtained by removing the rust that could be easily removed with a nylon brush. An ineradicable rust layer remained on this test steel material, and the color tone was reddish-brown.

[0030]

Table 1

[0031] (Preparation of steel material anticorrosive composition) As the microorganisms, freeze-dried iron-reducing bacteria Shewanella oneidensis (ATCC / American Type Culture Collection code 700550, hereinafter abbreviated as SO) and Geobacter sulfurreducens (ATCC code 51573, hereinafter abbreviated as GS) were used. SO or GS was cultured in a sterile environment by the method recommended by ATCC using ATCC Medium (18 Tryptic Soy Agar / Broth), and then colonies were isolated and transferred to #18 Broth Medium recommended by ATCC (composition: Triptone 17.0 g + Soytone 3.0 g + Dextrose 2.5 g + NaCl TIFF0007685695000002.tif10170 The centrifuged and precipitated SO or GS was collected. Next, compounds of various metals were added to distilled water TIFF0007685695000003.tif13170 to prepare solutions, and further, Triptic Soy Broth (composition: Triptone 17.0 g + Soytone 3.0 g + Dextrose 2.5 g + NaCl 5.0 g + K 2 HPO 4 2.5 g) which aids the growth of SO or GS was added to the aqueous solutions to make them 1% by mass, and the collected SO or GS was added to the resulting aqueous solutions to prepare steel corrosion prevention compositions (hereinafter, aqueous solutions of nickel sulfate (NiSO 4 ), aluminum sulfate (Al 2 (SO 4 ) 3 ), zinc sulfate (ZnSO 4 ) were used as the basic aqueous solutions, and the compositions with SO added were abbreviated as NSO, ASO, ZSO respectively, and the compositions with GS added were abbreviated as NGS, AGS, ZGS respectively, and were used for the tests.

[0032] In this case, the concentration of SO or GS was the optical density (OD(600nm) value) with a light path length of 1 cm after removing the background caused by components other than SO and GS measured before adding SO or GS. It was 2.0 when SO was added and 0.5 when GS was added. Also, after diluting each composition, a small amount was sampled, and #18 Tryptic Soy Agar Medium recommended by ATCC (composition: Triptone 17.0 g + Soytone 3.0 g + Dextrose 2.5 g + NaCl TIFF0007685695000004.tif After culturing for 9170 hours, the concentration of the microorganism in each composition calculated from the number of colonies and the dilution ratio was The number of individuals of SO showing an OD(600nm) value of 2.0 was 5×10 8 individuals / cm 3 and the number of individuals of GS showing an OD(600nm) value of 0.5 was 8×10 5 individuals / cm 3 It was.

[0033] TIFF0007685695000005.tif (abbreviated as 17170A, Z), and a composition for preventing steel corrosion without adding a metal compound when preparing the composition for preventing steel corrosion with SO (that is, a composition obtained by removing the metal compound from the composition for preventing steel corrosion) (hereinafter abbreviated as the mixed solution) were also prepared and used in the test. Furthermore, a composition for preventing steel corrosion with SO to which no aqueous solution was added was also prepared. In this case, a composition for preventing steel corrosion (hereinafter abbreviated as the solvent-free composition) was prepared by adding freeze-dried SO and zinc sulfate powder to a polyvinyl butyral resin solution (Esrec B, manufactured by Sekisui Chemical Co., Ltd., molecular weight 25,000) dissolved in a thinner.

[0034] (Application of the composition for preventing steel corrosion) On the surface of a test steel material, which is a rusty steel material with a rust layer that cannot be easily peeled off, compositions NSO, ASO, ZSO, NGS, AGS, ZGS, aqueous solutions N, A, Z, and a mixed solution were each applied to form a liquid film with a thickness of 0.5 mm, obtaining each coated steel material. At this time, acrylic dams with a height of 1 cm from the surface were provided on the entire four sides of the coated steel material so that the liquid film would not flow down. Also, to prevent drying, the surface space with the liquid film surrounded by the dams was covered with a PET film. After application, it was kept at 30 °C and left standing for 24 hours. Then, the liquid film on the surface of the coated steel material was gently washed with distilled water and dried at 30 °C and a relative humidity of 30% for 24 hours. Also, a solvent-free composition-coated steel material was prepared by applying the solvent-free composition to the test steel material so that the film thickness during drying would be 0.2 mm and drying it. For this coated steel material, water at 30 °C with 0.5 mass% of Triptic Soy Broth powder added was 5 TIFF0007685695000006.tif817030% and dried for 24 hours. Each coated steel material was assigned a test number as shown in Table 2. Note that, by the same method as the method of culturing using the above-mentioned agar plate medium, the SO concentration in the solvent-free composition after coating and drying was 1×10 2 cells / cm 3 and the concentration of zinc sulfate was 20 mass%. Also, the butyral resin coating film did not form a continuous film and, although it had the role of holding SO and zinc sulfate powder on the surface of the test steel material, it did not have the function of suppressing the permeation of water to the steel material surface.

[0035] The appearance color tone of each coated steel material after standing for 24 hours remained rusty brown for test number 1 where nothing was applied to the test steel material before the test, black for compositions NSO, ASO, ZSO, NGS, AGS, ZGS, and the solvent-free composition in test numbers 2, 3, 4, 5, 6, 7, 8, brown for aqueous solutions N, A, Z in test numbers 9, 10, 11, and black for the mixed solution in test number 12.

[0036] The appearance color tone of each coated steel material after 24-hour drying remained reddish-brown in Test No. 1 where nothing was coated on the test steel material before the test. The compositions NSO, ASO, ZSO, NGS, AGS, ZGS in Test Nos. 2, 3, 4, 5, 6, 7, 8 were black, the aqueous solutions N, A, Z in Test Nos. 9, 10, 11 were orange, and the mixture in Test No. 12 presented a reddish-brown color. That is, when nothing was coated on the test steel material before the test, there was no change in the color tone. In the case of the aqueous solutions N, A, Z, after standing for 24 hours, the reddish-brown color of the test steel material changed to a brownish color, and the rust layer seemed to be slightly reduced. However, after 24-hour drying, it was air-oxidized and became a bright orange color. In the case of the mixture, after standing for 24 hours, the reddish-brown color of the test steel material changed to black, and it was considered that the reduction of the rust layer proceeded due to the action of the microorganism. However, after 24-hour drying, it returned to a reddish-brown color and it was considered that the rust layer was air-oxidized.

[0037] On the other hand, in the case of the compositions NSO, ASO, ZSO, NGS, AGS, ZGS, the solvent-free compositions, it was considered that they changed to black due to the action of the microorganism after standing for 24 hours and the rust layer was reduced. However, even after 24-hour drying, they presented a black color and it was considered that the rust layer was not air-oxidized.

[0038] The rust of the aqueous solutions N, A, Z and the mixture that presented an orange or reddish-brown color after 24-hour drying was a rust layer composed of Fe 3+ and was considered to act as an oxidizing agent on the steel material. On the other hand, the rust layer in the case of the compositions NSO, ASO, ZSO, NGS, AGS, ZGS, the solvent-free compositions, which remained black even after 24-hour drying, was maintained in a state containing Fe 3+ and Fe 2+ and seemed to be difficult to act as an oxidizing agent.

[0039] (Corrosion Resistance Evaluation) In order to evaluate the corrosion resistance of each coated steel sheet after 24-hour drying (Test No. 1 has no coating), an atmospheric exposure test was conducted in a horizontal position for 6 months at 1-39, Ohori Ohara, Nishikyogoku Ward, Kyoto City, Kyoto Prefecture. Since the environment is inland and mild as a corrosion environment, a 1% by mass aqueous NaCl solution was sprayed onto the entire surface of each coated steel sheet for 10 seconds once a week for the purpose of accelerating the corrosion reaction. Before the test, the sides and backs of each coated steel sheet were thickly coated with anticorrosive paint and excluded from the evaluation. After the test, the average corrosion depth of the steel sheets was measured.

[0040] The above results are summarized in Table 2.

[0041]

Table 2

[0042] The following was clarified from the test results. The average corrosion depth of the test steel sheet before the test of Test No. 1 was 85.0 μm, which is a high corrosion rate. The average corrosion depth of Test No. 2 using Composition NSO was 0.2 μm, and the corrosion rate of the steel sheet was significantly reduced. The average corrosion depth of Test No. 3 using Composition ASO was 0.3 μm, and the corrosion rate of the steel sheet was also reduced. The average corrosion depth of Test No. 4 using Composition ZSO was 0.3 μm, and the corrosion rate was low. The average corrosion depth of Test No. 5 using Composition NGS was 0.4 μm, and the corrosion rate was low. The average corrosion depth of Test No. 6 using Composition AGS was 0.6 μm, and the corrosion rate of the steel sheet was reduced. The average corrosion depth of Test No. 7 using Composition ZGS was 0.6 μm, and the corrosion rate was low. The average corrosion depth of Test No. 8 using the solvent-free composition was 0.2 μm, and the corrosion rate was low. The average corrosion depth of Test No. 9 using Aqueous Solution N was 68.5 μm, and the corrosion rate was high. The average corrosion depth of Test No. 10 using Aqueous Solution A was 71.3 μm, which is a high corrosion rate. The average corrosion depth of Test No. 11 using Aqueous Solution Z was 75.9 μm, and the corrosion rate was high. The average corrosion depth of Test No. 12 using the mixed solution was 81.1 μm, and the corrosion rate was high.

[0043] That is, in the test steel material before the test (test number 1), the reduction reaction of the rust layer remaining on the surface was fast, and the steel material was oxidized early, so the corrosion rate increased. Also, when an aqueous solution of NiSO 4 , Al 2 (SO 4 ) 3 , ZnSO 4 was allowed to act (test numbers 9, 10, 11), or when SO was added without adding a metal compound (test number 12), since the appearance was orange or reddish-brown after 24 hours of drying, it is considered that the characteristics of the rust layer did not change and the corrosion rate similarly increased.

[0044] On the other hand, when the steel material anti-rust composition was used (test numbers 2, 3, 4, 5, 6, 7, 8), since a rust-preventive layer with improved environmental barrier function that was difficult to be redox-formed, the average corrosion depth became a very low value, and it is considered that the corrosion resistance of the steel material was significantly improved. This is not inconsistent with the fact that in the coated steel material using the steel material anti-rust composition, the color tone of the rust layer remained black after 24 hours of drying and almost no air oxidation of the rust layer occurred. From the above, the effect of the steel material anti-rust composition is clear.

Explanation of symbols

[0045] 10... steel material, 20... steel material anti-rust composition, 30... rust layer, 100... coated steel material, 200... coated rusted steel material.

Claims

1. A steel corrosion prevention composition comprising a microorganism having extracellular electron transfer ability and a metal compound (excluding iron compounds) having a solubility of 0.01 g or more in 100 cm of water at 5°C. ３ ​

2. A steel corrosion preventive composition comprising a microorganism having extracellular electron transfer ability, a metal compound (excluding iron compounds) having a solubility of 0.01 g or more at 5 °C in 100 cm of water ３ and a solvent capable of dissolving the metal compound. **Claim 3**: A steel corrosion preventive composition comprising a microorganism having extracellular electron transfer ability and a metal compound having a solubility of 0.01 g or more at 5°C in 100 cm3 of water, wherein the metal compound is 100 cm of water ３ contains at least one metal sulfate having a solubility of 0.01 g or more at 5°C, characterized as a steel corrosion preventive composition.

4. A steel corrosion prevention composition comprising a microorganism having extracellular electron transfer ability, a metal compound having a solubility of 0.01 g or more at 5°C in 100 cm3 of water, and a solvent capable of dissolving the metal compound, wherein the metal compound comprises at least one metal sulfate having a solubility of 0.01 g or more at 5°C in 100 cm3 of water. A steel corrosion prevention composition characterized by this.

5. The steel corrosion prevention composition according to claim 3 or 4, wherein the metal compound comprises at least one selected from the group consisting of nickel sulfate, aluminum sulfate, copper sulfate, tin sulfate, chromium sulfate, calcium sulfate, cobalt sulfate, and zinc sulfate.

6. The steel corrosion prevention composition according to any one of claims 2, 4, and 5 that cites 4, wherein the solvent contains at least water.

7. The number of the microorganisms in the steel corrosion-preventing composition is 1 × 10 ３ or more and 1 × 10 １ or less per cm of the steel corrosion-preventing composition. The steel corrosion-preventing composition according to any one of claims 1 to 6, characterized in that it is as described above. １０ ​

8. The steel corrosion prevention composition according to any one of claims 1 to 7, wherein the concentration of the metal compound in the steel corrosion prevention composition is 0.1 to 40.0% by mass.

9. The steel corrosion prevention composition according to any one of claims 1 to 8, wherein the microorganism is an iron-reducing bacterium.

10. The steel corrosion prevention composition according to claim 9, wherein the iron-reducing bacterium comprises at least one bacterium selected from the genus Shewanella, Geobacter, Desulfuromonas, Rhodopfera, Sulfurospirillum, or Pseudomonas.

11. The steel corrosion prevention composition according to claim 9, wherein the iron-reducing bacterium comprises at least one of Shewanella loihica, Shewanella oneidensis, Shewanella putrefaciens, Shewanella algae, Geobacter sulfurreducens, Geobacter metallireducens.

12. A coated steel material coated with the steel corrosion prevention composition according to any one of claims 1 to 11.

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