Patent Publication Number: US-2018044797-A1

Title: Repair agent and repair method for plated base, as well as plated base

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to Japanese Patent Application No. 2016-159221 filed on Aug. 15, 2016, the entire disclosure of which is incorporated by reference herein. 
     BACKGROUND 
     The present disclosure relates to a repair agent and a repair method for a plated base which includes a plating layer disposed on a surface of a metal base, as well as to the plated base. 
     Zinc-plated steel sheets which are steel sheets with a zinc plating layer disposed on their surface are generally used as automobile parts. Zinc, which is included in the zinc plating layer, has a stronger tendency to ionization than iron, which is included in the steel sheets. Therefore, if the zinc plating layer suffers a scratch such that the steel sheet is exposed, the zinc plating layer offers sacrificial protection for the steel sheet as the zinc is eluted, and has the ability to form a protective film as the zinc eluted forms a film on the surface of the steel sheet exposed. Thus, the zinc plating repairs itself, and features corrosion resistance. It has been found, however, that conventional zinc plated steel sheets do not feature sufficient corrosion resistance. 
     Japanese Unexamined Patent Publication No. 2010-174273 discloses a corrosion-preventing film which is disposed on the surface of a metal body and which includes an underlayer comprised of electrically conductive microparticles and a surface comprised of electrically conductive macromolecules. De facto, however, even such a technique fails to provide sufficient corrosion resistance. 
     SUMMARY 
     The inventors of the present disclosure have come across yet another problem: in attempting to add a repair agent to a protective film, and trying to add all kinds of chemical compounds as single components, no sufficient corrosion resistance could be achieved. 
     In automotive lightweighting, steel sheets made of, e. g., high-tensile material (high-tensile steel sheets) are employed. A plated base which includes such a steel sheet having a surface covered with a plating layer is more prone to hydrogen brittleness and strength degradation caused by corrosion than a plated base including a different kind of steel sheet. This even further exacerbates the above-described problem. 
     The present disclosure attempts to provide a repair agent which features increased corrosion resistance. 
     The present disclosure relates to a repair agent for a plated base including a plating layer which is disposed on a surface of a metal base and which includes a metal with a stronger tendency to ionization than metal comprising the metal base, wherein 
     the repair agent includes a phosphoric acid compound and a phosphonic acid compound. 
     The repair agent of the present disclosure features increased corrosion resistance. More specifically, even if in an actual use environment the plated base suffers a scratch which reaches the metal base, the repair agent of the present disclosure offers such an advanced sacrificial protection and has such a remarkable ability to form a protective film that it can excellently repair itself and thus features increased corrosion resistance. 
     The repair agent of the present disclosure is particularly useful when the steel sheet is a high-tensile material (high-tensile steel sheet). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view which schematically shows an example plated base treated with a repair agent of the present disclosure. 
         FIG. 2  is a cross-sectional view which schematically shows a plated base to give an example of an embodiment in which a protective film forms on a plated base after the plated base which has been treated with the repair agent of the present disclosure has suffered a defect. 
         FIG. 3  is a cross-sectional view which schematically shows a plated base to give an example of an embodiment in which a protective film forms on a plated base after the plated base which has been treated with the repair agent of the present disclosure has suffered a defect. 
         FIG. 4  is a cross-sectional view which schematically shows a plated base to give an example of an embodiment in which the repair agent of the present disclosure is applied to a plated base which has suffered a defect, and in which a protective film forms on the plated base. 
         FIG. 5  is a block diagram which schematically shows a device for evaluating the repair agent of the present disclosure. 
         FIG. 6  shows current-potential curves of Example A1 and Comparative Examples A1, A5, A6, and A26. 
         FIG. 7  shows an SEM photograph of a surface of a working electrode after determination of cathodic current values in the scope of Example A1. 
         FIG. 8  shows an SEM photograph of a surface of a working electrode after determination of cathodic current values in the scope of Comparative Example A1. 
         FIG. 9  shows an SEM photograph of a surface of a working electrode after determination of cathodic current values in the scope of Comparative Example A18. 
         FIG. 10  shows an SEM photograph of a surface of a working electrode after determination of cathodic current values in the scope of Comparative Example A24. 
         FIG. 11  shows an SEM photograph of a surface of a working electrode after determination of cathodic current values in the scope of Comparative Example A28. 
         FIG. 12  shows an SEM photograph of a surface of a working electrode before immersion into a test fluid in the scope of Experimental Example A. 
         FIG. 13  shows results of having subjected a protective film on a surface of a working electrode after cathodic polarization to a thermogravimetric analysis (TGA) in the scope of Example A2 and Comparative Example A35. 
         FIG. 14  shows an SEM photograph of a surface of a working electrode after determination of cathodic current values in the scope of Comparative Example B4. 
         FIG. 15  shows results of having subjected a protective film formed on a surface of a working electrode after determination of cathodic current values to an X-ray diffraction analysis (XRDA) in the scope of Example B1 and Comparative Example B4. 
         FIG. 16  shows current-potential curves of Comparative Examples A1 and C1. 
     
    
    
     DETAILED DESCRIPTION 
     —Repair Agent— 
     A repair agent according to the present disclosure is intended for a plated base. When the plated base suffers a defect which reaches from a surface of a plating layer to a metal base of the plated base, the repair agent forms a protective film on an internal surface of the defect, in particular on a surface of the metal base which is exposed where the plated base has suffered the defect. Hereinafter, the present disclosure will be described in detail with reference to the drawings. Note that elements shown in the drawings are illustrated in a schematic and exemplary manner, and only serve the purpose of making the present disclosure comprehensible. Actual appearance and dimensions may vary from the drawings. Unless stated otherwise, the same reference characters and symbols refer to the same part or have the same meaning. 
     As shown in  FIG. 1 , a plated base  10  includes a metal base  1  and a plating layer  2  formed on a surface of the metal base  1 . The metal base  1  may be any kind of base including a metal. The metal base  1  usually includes iron, and may, if so desired, include carbon, silicon, manganese, phosphorus, or sulfur. The metal base comprises 1 wt % or less (in particular 0.8 wt % or less) carbon, 0.5 wt % or less (in particular 0.3 wt % or less) silicon, manganese, phosphorus, and sulfur each, and iron (remainder). 
     In the field of automobile parts, it is beneficial if the metal base  1  is a steel sheet, and even more beneficial if the metal base  1  is a so-called carbon steel sheet, particularly a high-tensile steel sheet (high-tensile material). 
     The plating layer  2  includes as main component a metal with a stronger tendency to ionization than a metal comprising the metal base  1 . Hereinafter, the metal included as the main component of the plating layer  2  and having a strong tendency to ionization is referred to as a “metal A with a strong tendency to ionization.” If the metal base  1  is a steel sheet, the metal comprising the metal base  1  is iron. As metal with a stronger tendency to ionization than iron, for example, one or more metals from a group consisting of zinc, aluminum, and magnesium may be employed. Beneficially, zinc is employed. Such a metal A with a strong tendency to ionization included in the plating layer  2  generally contributes in ionic form to a formation of a protective film, as will be described later. 
     In terms of the formation of the protective film on an exposed surface of the metal base  1 , it is beneficial if the plating layer  2  is a zinc plating layer. A zinc plating layer is a plating layer which includes zinc. Beneficially, the zinc plating layer is a zinc alloy layer. 
     All kinds of processes may be employed for forming the plating layer  2 . Possible processes include, for example, so-called wet-plating processes such as electroplating, electroless plating, and hot-dip plating, and so-called dry-plating processes such as vacuum plating (physical vapor deposition (PVD)), chemical vapor deposition (CVD), and mechanical plating. Beneficially, a dry-plating process, in particular mechanical plating, is employed. In the scope of mechanical plating, a plating layer (film) is formed by projecting composite particles onto an object (metal base  1 ) subjected to the mechanical plating. The composite particles have a core (e.g., an iron core) which has an outer shell including constituent metal particles of the plating layer.  FIG. 1  is a schematic cross-sectional view of a plated base on which the plating layer  2  has been formed by mechanical plating. In an internal portion of the plating layer  2 , constituent metal particles  21  have boundary surfaces and gaps. Alternatively, the plating layer may be formed in a different manner such that the constituent metal particles do not have the boundary surfaces and the gaps. 
     The plating layer  2  is not particularly limited in its thickness, and may be, e.g., 1 μm thick or thicker. The plating layer  2  generally has a thickness of 1 to 50 μm, and beneficially a thickness of 1 to 10 μm. 
     The repair agent of the present disclosure includes a phosphoric acid compound and a phosphonic acid compound. The repair agent is defined as an agent which forms a protective film on an exposed surface of a metal base. 
     The phosphoric acid compound is an inorganic phosphoric acid compound of phosphoric acid (H 3 PO 4 ), or a phosphate, or both. For the formation of the protective film, the phosphoric acid compound beneficially is a phosphate. The phosphate is a salt of phosphoric acid ions such as first phosphoric acid ions (H 2 PO 4 −), second phosphoric acid ions (HPO 4   2− ), or third phosphoric acid ions (PO 4   3− ), and cations. For the formation of the protective film, it is beneficial if the phosphoric acid ions are the first and second phosphoric acid ions, and even more beneficial if the phosphate ions are the first phosphoric acid ions. The cations are one or more ions selected from a group consisting of monovalent metal ions, divalent metal ions, trivalent metal ions, and ammonium ions. Beneficially, the cations are monovalent metal ions and ammonium ions. A metal comprising the monovalent metal ions may be an alkali metal (e.g., sodium, potassium, or lithium), and beneficially is sodium and potassium. A metal comprising the divalent metal ions may be an alkaline earth metal (e.g., magnesium, calcium, strontium, or barium) or manganese, and beneficially is calcium, barium, and manganese. A metal comprising the trivalent metal ions may be, e.g., chrome or aluminum, and beneficially is chrome. 
     Concrete examples of the phosphoric acid compound beneficial for the formation of the protective film include: phosphoric acid (H 3 PO 4 ), sodium dihydrogen phosphate, potassium dihydrogen phosphate, ammonium dihydrogen phosphate, calcium dihydrogen phosphate, barium dihydrogen phosphate, manganese dihydrogen phosphate, lithium dihydrogen phosphate, ammonium sodium hydrogen phosphate, diammonium hydrogen phosphate, dipotassium hydrogen phosphate, disodium hydrogen phosphate, barium hydrogen phosphate, manganese(II) hydrogen phosphate, chromium(III) phosphate, tripotassium phosphate, trisodium phosphate, and a condensed phosphoric acid compound. The condensed phosphoric acid compound may be, e.g., a compound comprised of cations and anions of tripolyphosphate, pyrophosphate, metaphosphate, or phosphorous acid. The cations are selected among alkali metal ions, alkali earth metal ions, or amphoteric metal ions (zinc ions or aluminum ions). 
     Examples of the phosphoric acid compound beneficial for the formation of the protective film include: sodium dihydrogen phosphate, potassium dihydrogen phosphate, ammonium dihydrogen phosphate, ammonium sodium hydrogen phosphate, diammonium hydrogen phosphate, dipotassium hydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, and a condensed phosphoric acid compound. Beneficial concrete examples of the condensed phosphoric acid compound include: aluminum dihydrogen tripolyphosphate, calcium tripolyphosphate, zinc tripolyphosphate, sodium tripolyphosphate, calcium metaphosphate, calcium pyrophosphate, aluminum phosphite, and zinc phosphite. 
     The phosphoric acid compound is commercially available, and thus easy to obtain. As an alternative, two or more compounds may be used as the phosphoric acid compound. 
     As long as the phosphonic acid compound includes atoms including unshared electron pairs which contribute to adhesion of the protective film to the metal base  1 , the phosphonic acid compound is not particularly limited. For example, the phosphonic acid compound may be an organic phosphonic acid compound of a nitrogen-containing phosphonic acid compound, or a salt of the nitrogen-containing phosphonic acid, or both. The organic phosphonic acid compound is a compound including an organic group and a phosphonate group. The organic group may be an alkylene group. In particular, an alkylene group with one to three carbon atoms are beneficial. The phosphonate group is represented with the formula —P(═O)(OH) 2 , and may as well have the form of a salt. The phosphonate group having the form of a salt means that hydrogen ions of the hydroxyl group of the phosphonate group are liberated, and may be replaced by, e.g., metal ions. The metal ions may be, e.g., sodium ions, potassium ions, or calcium ions. 
     As long as the nitrogen-containing phosphonic acid compound is an organic compound including nitrogen atoms and a phosphonate group, the nitrogen-containing phosphonic acid compound is not particularly limited. The nitrogen-containing phosphonic acid compound may be an amine containing a phosphonate group of, e.g., amino tris(methylene phosphonate) (ATMP) (chemical formula: N[CH 2 PO(OH) 2 ] 3 ), aminotris(ethylene phosphonate) (chemical formula: N[CH 2 CH 2 PO(OH) 2 ] 3 ), and their metallic salts. If the compound includes two or more hydroxyl groups in one molecule, in the metallic salts the hydrogen ions in a part of the hydroxyl groups may be replaced by metal ions. Alternatively, the hydrogen ions in all of the hydroxyl groups may be replaced by metal ions. 
     The phosphonic acid compound is commercially available, and thus easy to obtain. As an alternative, two or more compounds may be used as the phosphonic acid compound. 
     The phosphoric acid compound and the phosphonic acid compound are generally included in a weight ratio ranging from 10/90 to 90/10. For the formation of the protective film, the weight ratio beneficially ranges from 20/80 to 80/20, more beneficially from 40/60 to 80/20, and even more beneficially from 55/45 to 75/25. If two or more compounds are used as the phosphoric acid compound, it is beneficial if the total amount of these compounds falls within the above ranges. If two or more compounds are used as the phosphonic acid compound, it is beneficial if the total amount of these compounds falls within the above ranges. 
     Since the repair agent of the present disclosure includes a combination of the phosphoric acid compound and the phosphonic acid compound, an advantageously non-conductive and adhesive protective film can be formed on the surface of a metal base which is exposed because of a defect. As a result, it may be assumed that corrosion resistance is sufficiently improved. If a compound such as a nitrate compound, a carbonate compound, a carbonate hydrogen compound, a chromate compound, a silicate compound, a fluoride metal, or a metallic oxide is used instead of the phosphoric acid compound, or if an aromatic or aliphatic carboxylic acid, or an organic amine is used instead of the phosphonic acid compound, the protective film is not formed, or—even if the protective film is formed—the protective film declines in non-conductivity, or in adhesiveness, or in both. As a result, a sufficient corrosion resistance fails to be achieved. In the present description, non-conductivity is defined as an insulating property where volume resistivity is higher than or equal to 10 12  Ω·cm. 
     When the protective film is formed, the phosphoric acid ions in the phosphoric acid compound generate, due to a reaction (see, e.g., schematic chemical equation (I) below) with ions of the metal A with a strong tendency to ionization included in the plating layer, a non-conductive compound which serves as a main component for the structure of the film. On the other hand, while the phosphonic acid compound forms a complex together with ions of the metal A with a strong tendency to ionization (see, e.g., schematic chemical equation (II) below), unshared electron pairs of the nitrogen atoms included in the phosphonic acid compound make the phosphonic acid compound adhere to the surface of the metal base. In addition, this phosphonic acid compound complex promotes an amorphization of the film, and enhances flexibility and adhesiveness of the film with regard to the surface of the metal base. As a result, a protective film of a superb non-conductivity and adhesiveness is formed, and it may be assumed that corrosion resistance is sufficiently improved. Note that in the chemical equations below, formation of products derived from main materials involved in the formation of the protective film is expressed schematically. 
       Chemical Equation 1 
       Zn 2+ NaH 2 PO 4 →Zn 3 (PO 4 ) 2 .4H 2 O  (I)
 
       Zn 2+ +ATMP→Zn−ATMP(complex)  (II)
 
     In this description, corrosion resistance is defined as a feature which allows for resisting corrosion, in particular the ability to resist corrosion sufficiently even in the case of a defect where a metal base is exposed. The concept of corrosion resistance includes the ability of a substance to repair itself. The ability of a substance to repair itself is a behavior where the substance repairs a defect by forming a protective film on a surface of a metal base exposed due to the defect. 
     To enhance the formation of the protective film, the repair agent of the present disclosure beneficially further includes a compound including a metal with a strong tendency to ionization. Hereinafter, the metal with a strong tendency to ionization which is included in such a compound included in the repair agent is distinguished from the metal A with a strong tendency to ionization included in the plating layer, and is referred to as a “metal B with a strong tendency to ionization.” The metal B with a strong tendency to ionization also contributes in ionic form to the formation of the protective film. The metal B with a strong tendency to ionization may be chosen from the same range of metals as the metal A with a strong tendency to ionization. Beneficially, the metal B with a strong tendency to ionization is the same kind of metal as the metal A with a strong tendency to ionization. 
     As long as the metal has an ionic form in water, the metal B with a strong tendency to ionization is not particularly limited. The metal B with a strong tendency to ionization may be, e.g., zinc, iron, magnesium, cobalt, nickel, chromium, silver, zirconium, or aluminum. Among these metals, divalent to quadrivalent (beneficially divalent and quadrivalent) metals—in particular zinc, iron, nickel, and zirconium—are beneficial, and zinc is even more beneficial, for the formation of a complex in water, in particular for the formation of a complex with ATMP. As long as the metal has an ionic form in water, the compound including the metal B with a strong tendency to ionization is not particularly limited. Beneficial examples of the compound included in the metal B with a strong tendency to ionization include, for instance, zinc sulfate, iron sulfate, nickel sulfate, zirconium sulfate, zinc nitrate, aluminum sulfate, aluminum nitrate, magnesium sulfate, and magnesium nitrate. 
     The compound including the metal B with a strong tendency to ionization is beneficially included at 10 to 400 parts by weight per 100 parts by weight of a total amount of the phosphoric acid compound and the phosphonic acid compound. For the formation of the protective film, the compound is particularly beneficially included at 30 to 300 parts by weight, more beneficially at 80 to 200 parts by weight, and most beneficially at 110 to 150 parts by weight. If two or more compounds are used as the compound including the metal B with a strong tendency to ionization, it is beneficial if the total amount of these compounds falls within the above ranges. 
     —Repair Method for Plated Base (Use of Repair Agent)— 
     The present disclosure further provides a method for repairing a plated base using the repair agent described above. 
     In the scope of the repair method for a plated base, the repair agent may be already included in the plating layer, or may be applied separately as an aqueous solution. 
     If the repair agent is already included in the plated layer, for instance in the scope of a mechanical plating process, the repair agent is allowed to adhere to surfaces of the constituent metal particles in the outer shells of the composite particles projected onto the object (metal base  1 ) subjected to mechanical plating. As a result, as shown in  FIG. 2 , a repair agent  30  is present between the boundary surfaces of and in the gaps between the constituent metal particles  21  included in the plating layer  2 . However, the plating layer  2  shown in  FIG. 2 , where the repair agent  30  is indicated as black dots, is not limited to this. Alternatively, the constituent metal particles  21  may be for example present in form of a layer on the surface of the constituent metal particles  21 . In such a case the repair agent is generally included at 0.15 to 18.20 wt %, and beneficially at 0.50 to 7.70 wt %, of the total amount of the plating layer. 
     If, in this case, the plated base  10  suffers a defect  13  reaching to the metal base  1  as the one shown in  FIG. 2 , the metal with a strong tendency to ionization included in the plating layer  2 , the phosphoric acid compound, and the phosphonic acid compound are effused and migrate to the exposed surface of the metal base  1 . As a result, a protective film  14  is formed. The metal with a strong tendency to ionization which is effused onto the exposed surface of the metal base  1  may be the metal A with a strong tendency to ionization comprising the plating layer  2 . Alternatively, the metal with a strong tendency to ionization may be a mixture derived from a compound including the metal A with a strong tendency to ionization and the metal B with a strong tendency to ionization which is included in the repair agent. The effusion and migration of materials (i.e., the metal with a strong tendency to ionization, the phosphoric acid compound, and the phosphonic acid compound) comprising the protective film  14  may be accomplished by making use of moisture (e.g., rain water) adhering to the defect  13 , or by making use of moisture in the air, or by immersing the plated base  10 , which has suffered the defect  13 , in water. 
     Further, in the case where the repair agent is already included in the plating layer, for example a solution of the repair agent may be applied onto the surface of the plating layer  2  and dried such that a layer of the repair agent  30  forms on the surface of the plating layer  2 , as shown in  FIG. 3 . In this case, although not shown in  FIG. 3 , the repair agent  30  may be also present at the boundary surfaces and in the gaps between the constituent metal particles  21  as shown in  FIG. 2 . A solvent comprising the solution is not particularly limited as long as the solvent dissolves all components of the repair agent. The solvent may be water or an organic solvent medium. In such a case, the repair agent is generally included at an amount falling within the same range as in the above-mentioned case. This allows the repair agent to be present on the boundary surfaces of and in the gaps between the constituent metal particles of the plated layer. 
     If, in this case, the plated base  10  suffers a defect  13  reaching to the metal base  1  as the one shown in  FIG. 3 , the metal with a strong tendency to ionization included in the plating layer  2 , the phosphoric acid compound, and the phosphonic acid compound migrate to the exposed surface of the metal base  1 . As a result, a protective film  14  is formed. The metal with a strong tendency to ionization which migrates to the exposed surface of the metal base  1 , may be the metal A with a strong tendency to ionization comprising the plating layer  2 . Alternatively, the metal with a strong tendency to ionization may be a mixture derived from a compound including the metal A with a strong tendency to ionization and the metal B with a strong tendency to ionization which is included in the repair agent. The migration of materials (i.e., the metal with a strong tendency to ionization, the phosphoric acid compound, and the phosphonic acid compound) comprising the protective film  14  may be accomplished by making use of moisture (e.g., rain water) adhering to the defect  13 , or by making use of moisture in the air, or by immersing the plated base  10 , which has suffered the defect  13 , in water. 
     In the case where the repair agent is used separately from the plated base in the form of an aqueous solution, when the plated base suffers a defect reaching to its metal base, an aqueous solution  31  of the repair agent comes into contact with the defect  13  as shown in  FIG. 4 . As a result, the metal A with a strong tendency to ionization included in the plating layer  2  is effused onto the exposed surface of the metal base. In this case, the phosphoric acid compound and the phosphonic acid compound which are included in the repair agent dissolved in the aqueous solution, and, if desired, also the metal B with a strong tendency to ionization migrate to the exposed surface of the metal base. As a result, the metal with a strong tendency to ionization, the phosphoric acid compound and the phosphonic acid compound form a protective film on the exposed surface of the metal base. The effusion and migration of materials (i.e., the metals A and B with a strong tendency to ionization, the phosphoric acid compound, and the phosphonic acid compound) comprising the protective film  14  is accomplished by making use of the migration of these materials within the aqueous solution of the repair agent. Although the repair agent  30  is indicated as black dots dispersed in the aqueous solution  31  shown in  FIG. 4 , in general, the repair agent  30  is dissolved in the aqueous solution. 
     In  FIG. 4 , the aqueous solution  31  of the repair agent is brought into contact with the defect  13  by applying the aqueous solution  31  of the repair agent onto the defect  13 . Alternatively, however, the aqueous solution  31  of the repair agent may be brought into contact with the defect  13  by, for example, immersing the plated base which has suffered the defect in the aqueous solution of the repair agent. 
     In this case, the concentration (total concentration of all components) of the repair agent in the aqueous solution is higher than or equal to 100 ppm, in particular higher than or equal to 500 ppm. Beneficially the concentration ranges from 500 to 10000 ppm (inclusive), and even more beneficially from 800 to 10000 ppm (inclusive). Here, “ppm” is an entity indicating a proportion by weight base. 
     In the scope of the repair method for the plated base of the present disclosure, the protective film  14  is selectively formed on the exposed surface of the metal base  1 . This method is not bound to any specific theory but is employed for the following reasons: 
     (1) In an initial state the metal base  1  has a corrosion potential (negative), which is why, when the metal with a strong tendency to ionization is electrostatically pulled as cations toward the exposed surface of the metal base  1 , other constituent materials of the protective film are electrostatically pulled toward the cations. 
     (2) After having adhered to the surface of the metal base  1 , the ions which have been pulled toward the exposed surface bond together and form a film. While forming a two- or three-dimensional film, the ions are strongly absorbed into or strongly bonded to the surface of the metal base  1 , and become a strongly adhesive film. 
     The fact that the protective film  14  has been formed on the exposed surface of the metal base  1  can be easily verified by taking an SEM photograph of the surface, or by performing an X-ray diffraction analysis (XRDA) of the film on the surface. 
     In the present description, the defect  13  is a scratch so deep that it reaches from the surface of the plated base  2  to the metal base  1 . 
     EXAMPLES 
     Experimental Example A 
     Example A1 
     In a device  50  which is shown in  FIG. 5 , a carbon steel sheet (high-tensile material; 12 mm×12 mm; content proportions: 0.5 wt % carbon, 0.02 wt % silicon, 0.2 wt % manganese, 0.1 wt % phosphorus, 0.1 wt % sulfur, and iron (remainder)) has been used as a working electrode  51 , and immersed for 24 h in a test fluid  52  (35° C.) saturated with air. Then a spontaneous potential has been measured. The test fluid has been prepared by dissolving sodium dihydrogen phosphate, ATMP, and zinc sulfate, which serve as the repair agent, in a sodium chloride aqueous solution. The concentration of sodium chloride was 0.5 wt %, the concentrations of sodium dihydrogen phosphate, ATMP, and zinc sulfate were 500 ppm each. The pH level of the test fluid was adjusted to 6.2 with the aid of NaOH/HCl. A platinum electrode has been employed as a counter electrode  53 , and an Ag/AgCl electrode has been employed as a reference electrode  54 . 
     Subsequently, while keeping the working electrode  51  immersed in the test fluid  52 , the potential of the working electrode  51  has been altered using a potentiostat  55 . Simultaneously, cathodic polarization has been performed at the working electrode  51  and cathodic current values have been determined. One example of a current-potential curve obtained this way is shown in  FIG. 6 . In  FIG. 6 , the current-potential curve of Example A1 is expressed as “ATMP+NaH 2 PO 4 +ZnSO 4 .” In  FIG. 6 , a current reduction rate E has been calculated at current values of −0.8 V and −1.1 V. 
     The current reduction rate E has been calculated based on the below equation. 
         E  (%)=( I   o   −I )/ I   o ×100  Equation (1)
 
     In the above equation, I o  is current density when no repair agent has been added to the test fluid. Specifically, I o  is the current density when no repair agent has been added in the scope of Comparative Example A1 which will be described later. 
     In the equation, I is the current density when the repair agent of Example A1 is added to the test fluid. Further, I is the current density measured in this example. 
     The cathodic current value decreasing due to the addition of the repair agent means that the protective film has been formed on the exposed surface of the metal base, and indicates that the repair agent features corrosion resistance and, in particular, can repair itself. 
     Comparative Examples A1 to A34 
     In Comparative Examples A1 to A34, except for having dissolved a predetermined amount of a predetermined compound in a test fluid, the cathodic current value has been determined and the current reduction rate E has been calculated in the same manner as in Example A1. Kinds and amounts of the compounds of each of the Comparative Examples have been listed in the below table. Potentials for determining the current reduction rate have been −0.8 V and −1.1 V. In  FIG. 6 , the current-potential curve of Comparative Example A1 is indicated as “Plain,” the current-potential curve of Comparative Example A5 as “NaH 2 PO 4 ,” the current-potential curve of Comparative Example A6 as “ZnSO 4 ,” and the current-potential curve of Comparative Example A26 as “ATMP.” 
     
       
         
           
               
               
               
               
               
               
               
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                 Compar- 
                 Compar- 
                 Compar- 
                 Compar- 
                 Compar- 
                 Compar- 
                 Compar- 
                 Compar- 
                 Compar- 
               
               
                   
                   
                 ative 
                 ative 
                 ative 
                 ative 
                 ative 
                 ative 
                 ative 
                 ative 
                 ative 
               
               
                   
                 Example 
                 Example 
                 Example 
                 Example 
                 Example 
                 Example 
                 Example 
                 Example 
                 Example 
                 Example 
               
               
                   
                 A1 
                 A1 
                 A2 
                 A3 
                 A4 
                 A5 
                 A6 
                 A7 
                 A8 
                 A9 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Sodium 
                 500 ppm 
                 — 
                 — 
                 — 
                 — 
                 500 ppm 
                 — 
                 — 
                 — 
                 — 
               
               
                 Dihydrogen 
               
               
                 Phosphoric 
               
               
                 Acid 
               
               
                 Sodium 
                 — 
                 — 
                 — 
                 — 
                 500 ppm 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Nitrate 
               
               
                 Sodium 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 500 ppm 
                 — 
                 — 
               
               
                 Bicarbonate 
               
               
                 Sodium 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 500 ppm 
                 — 
               
               
                 Fluoride 
               
               
                 Colloidal 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 500 ppm 
               
               
                 Silicon 
               
               
                 Dioxide 
               
               
                 Vanadium 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Oxide 
               
               
                 Potassium 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Chromate 
               
               
                 Sodium 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Silicate 
               
               
                 ATMP 
                 500 ppm 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Sodium 
                 — 
                 — 
                 500 ppm 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Benzoate 
               
               
                 Sodium 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Oleate 
               
               
                 Ethyl Amine 
                 — 
                 — 
                 — 
                 250 ppm 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Zinc Sulfate 
                 500 ppm 
                 — 
                 — 
                 — 
                 — 
                 — 
                 500 ppm 
                 — 
                 — 
                 — 
               
               
                 E (−0.8 V) (%) 
                 81 
                 (1) 
                 7 
                 39 
                 27 
                 19 
                 0 
                 44 
                 −15 
                 46 
               
               
                 E (−1.1 V) (%) 
                 80 
                 (1) 
                 13 
                 −2 
                 −125 
                 39 
                 −34 
                 −52 
                 −55 
                 31 
               
               
                   
               
               
                 The number (1) indicates reference values. 
               
               
                 The m-dash (“—”) indicates that the respective compound has not been used. 
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
               
               
               
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 Compar- 
                 Compar- 
                 Compar- 
                 Compar- 
                 Compar- 
                 Compar- 
                 Compar- 
                 Compar- 
                 Compar- 
                 Compar- 
               
               
                   
                 ative 
                 ative 
                 ative 
                 ative 
                 ative 
                 ative 
                 ative 
                 ative 
                 ative 
                 ative 
               
               
                   
                 Example 
                 Example 
                 Example 
                 Example 
                 Example 
                 Example 
                 Example 
                 Example 
                 Example 
                 Example 
               
               
                   
                 A10 
                 A11 
                 A12 
                 A13 
                 A14 
                 A15 
                 A16 
                 A17 
                 A18 
                 A19 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Sodium 
                 — 
                 500 ppm 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 500 ppm 
                 — 
               
               
                 Dihydrogen 
               
               
                 Phosphoric 
               
               
                 Acid 
               
               
                 Sodium 
                 — 
                 — 
                 500 ppm 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Nitrate 
               
               
                 Sodium 
                 — 
                 — 
                 — 
                 — 
                 500 ppm 
                 — 
                 — 
                 1000 ppm 
                 — 
                 — 
               
               
                 Bicarbonate 
               
               
                 Sodium 
                 — 
                 — 
                 — 
                 500 ppm 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Fluoride 
               
               
                 Colloidal 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Silicon 
               
               
                 Dioxide 
               
               
                 Vanadium 
                 500 ppm 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Oxide 
               
               
                 Potassium 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Chromate 
               
               
                 Sodium 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Silicate 
               
               
                 ATMP 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Sodium 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Benzoate 
               
               
                 Sodium 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Oleate 
               
               
                 Ethyl Amine 
                 — 
                 500 ppm 
                 500 ppm 
                 500 ppm 
                 500 ppm 
                 500 ppm 
                 1000 ppm 
                 — 
                 — 
                 — 
               
               
                 Zinc Sulfate 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 500 ppm 
                 500 ppm 
               
               
                 E (−0.8 V) (%) 
                 −66 
                 30 
                 10 
                 −75 
                 11 
                 −16 
                 19 
                 30 
                 48 
                 50 
               
               
                 E (−1.1 V) (%) 
                 0 
                 29 
                 −107 
                 −68 
                 8 
                 −37 
                 −40 
                 49 
                 82 
                 62 
               
               
                   
               
               
                 The m-dash (“—”) indicates that the respective compound has not been used. 
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
               
               
               
               
               
               
             
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                   
                 Compar- 
                 Compar- 
                 Compar- 
                 Compar- 
                 Compar- 
                 Compar- 
                 Compar- 
                 Compar- 
                 Compar- 
               
               
                   
                   
                 ative 
                 ative 
                 ative 
                 ative 
                 ative 
                 ative 
                 ative 
                 ative 
                 ative 
               
               
                   
                 Example 
                 Example 
                 Example 
                 Example 
                 Example 
                 Example 
                 Example 
                 Example 
                 Example 
                 Example 
               
               
                   
                 A20 
                 A21 
                 A22 
                 A23 
                 A24 
                 A25 
                 A26 
                 A27 
                 A28 
                 A29 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Sodium 
                 — 
                 — 
                 500 ppm 
                 500 ppm 
                 500 ppm 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Dihydrogen 
               
               
                 Phosphoric 
               
               
                 Acid 
               
               
                 Sodium 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Nitrate 
               
               
                 Sodium 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Bicarbonate 
               
               
                 Sodium 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Fluoride 
               
               
                 Colloidal 
                 — 
                 — 
                 500 ppm 
                 500 ppm 
                 500 ppm 
                 — 
                 — 
                 500 ppm 
                 — 
                 — 
               
               
                 Silicon 
               
               
                 Dioxide 
               
               
                 Vanadium 
                 — 
                 — 
                 500 ppm 
                 500 ppm 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Oxide 
               
               
                 Potassium 
                 500 ppm 
                 500 ppm 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 1000 ppm 
               
               
                 Chromate 
               
               
                 Sodium 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Silicate 
               
               
                 ATMP 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 500 ppm 
                 500 ppm 
                 500 ppm 
                 — 
               
               
                 Sodium 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Benzoate 
               
               
                 Sodium 
                 — 
                 — 
                 — 
                 — 
                 — 
                 500 ppm 
                 — 
                 — 
                 — 
                 — 
               
               
                 Oleate 
               
               
                 Ethyl Amine 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Zinc Sulfate 
                 — 
                 500 ppm 
                 500 ppm 
                 — 
                 500 ppm 
                 — 
                 — 
                 — 
                 500 ppm 
                 — 
               
               
                 E (−0.8 V) (%) 
                 36 
                 61 
                 10 
                 8 
                 26 
                 −44 
                 22 
                 −21 
                 49 
                 −38 
               
               
                 E (−1.1 V) (%) 
                 10 
                 24 
                 40 
                 33 
                 74 
                 53 
                 9 
                 4 
                 76 
                 42 
               
               
                   
               
               
                 The m-dash (“—”) indicates that the respective compound has not been used. 
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
               
             
               
                   
                 TABLE 4 
               
               
                   
                   
               
               
                   
                 Comparative 
                 Comparative 
                 Comparative 
                 Comparative 
                 Comparative 
               
               
                   
                 Example 
                 Example 
                 Example 
                 Example 
                 Example 
               
               
                   
                 A30 
                 A31 
                 A32 
                 A33 
                 A34 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Sodium Dihydrogen 
                 — 
                 — 
                 500 ppm 
                 500 ppm 
                 — 
               
               
                 Phosphoric Acid 
               
               
                 Sodium Nitrate 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Sodium Bicarbonate 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Sodium Fluoride 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Colloidal Silicon Dioxide 
                 — 
                 500 ppm 
                 500 ppm 
                 500 ppm 
                 — 
               
               
                 Vanadium Oxide 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Potassium Chromate 
                 — 
                 — 
                 — 
                 — 
                 500 ppm 
               
               
                 Sodium Silicate 
                 500 ppm 
                 500 ppm 
                 500 ppm 
                 500 ppm 
                 — 
               
               
                 ATMP 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Sodium Benzoate 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Sodium Oleate 
                 — 
                 — 
                 — 
                 — 
                 500 ppm 
               
               
                 Ethyl Amine 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 Zinc Sulfate 
                 — 
                 — 
                 — 
                 500 ppm 
                 — 
               
               
                 E (−0.8 V) (%) 
                 −30 
                 −45 
                 45 
                 29 
                 62 
               
               
                 E (−1.1 V) (%) 
                 −24 
                 9 
                 62 
                 50 
                 61 
               
               
                   
               
               
                 The m-dash (“—”) indicates that the respective compound has not been used. 
               
            
           
         
       
     
     In the scope of Example A1 and Comparative Examples A1, A18, A24, and A28, SEM photographs of surfaces of working electrodes have been taken after determination of cathodic current values. The SEM photographs are shown in  FIGS. 7 to 11 . An SEM photograph of the surface of a working electrode before immersion into the test fluid is shown in  FIG. 12 . 
     Results of these examples have shown that by forming a protective film with an excellent adhesiveness on a surface of a metal base, the repair agent of the present disclosure allows for forming of a protective film with an excellent cathodic current reduction rate, i.e., a protective film excellent in reducing oxygen and hydrogen reduction reactions. 
     Example A2 
     In Example A2, apart from having set the concentration of sodium chloride in the test fluid to 3.5 wt %, cathodic polarization has been performed in the same manner as in Example A1. After cathodic polarization, the protective film on the surface of the working electrode has been subjected to thermogravimetric analysis (TGA). Analysis results are shown in  FIG. 13 . 
     Comparative Example A35 
     In Comparative Example A35, except for having set the concentration of sodium chloride in the test fluid to 3.5 wt %, cathodic polarization has been performed in the same manner as in Example A18. After cathodic polarization, the protective film on the surface of the working electrode has been subjected to thermogravimetric analysis (TGA). Analysis results are shown in  FIG. 13 . 
     Experimental Example B 
     Examples B1 to B10 and Comparative Examples B1 to B6 
     In Examples B1 to B10 and Comparative Examples B1 to B6, except for having dissolved a predetermined amount of a predetermined compound in a test fluid, the cathodic current values have been determined and the current reduction rate E has been calculated in the same manner as in Example A1. Kinds and amounts of the compounds of each of the Examples and each of the Comparative Examples have been listed in the below table. 
     The current reduction rates E have been ranked in the following manner. 
     −0.8 V 
     S: E≧85%; 
     A: E≧80%; 
     B: E≧75%; 
     C: E≧70% (unproblematic in practical use); 
     D: E&lt;70% (problematic in practical use). 
     −1.2 V 
     S: E≧91%; 
     A: E≧88%; 
     B: E≧85%; 
     C: E≧76% (unproblematic in practical use); 
     D: E&lt;70% (problematic in practical use). 
     
       
         
           
               
               
               
               
               
               
               
               
               
               
               
             
               
                   
                 TABLE 5 
               
               
                   
                   
               
               
                   
                 Example 
                 Example 
                 Example 
                 Example 
                 Example 
                 Example 
                 Example 
                 Example 
                 Example 
                 Example 
               
               
                   
                 B1 
                 B2 
                 B3 
                 B4 
                 B5 
                 B6 
                 B7 
                 B8 
                 B9 
                 B10 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Sodium 
                 30 
                 25 
                 15 
                 15 
                 20 
                 40 
                 50 
                 33.3 
                 40 
                 25 
               
               
                 Dihydrogen 
               
               
                 Phosphate 
               
               
                 (wt %) (2) 
               
               
                 ATMP (wt %) (2) 
                 15 
                 25 
                 30 
                 15 
                 40 
                 20 
                 25 
                 33.3 
                 40 
                 50 
               
               
                 Zinc Sulfate 
                 55 
                 50 
                 55 
                 70 
                 40 
                 40 
                 25 
                 33.4 
                 20 
                 25 
               
               
                 (wt %) (2) 
               
               
                 Sodium 
                 67:33 
                 50:50 
                 33:67 
                 50:50 
                 33:67 
                 67:33 
                 67:33 
                 50:50 
                 50:50 
                 33:67 
               
               
                 Dihydrogen 
               
               
                 Phosphate:ATMP 
               
               
                 Zinc 
                 122/100 
                 100/100 
                 122/100 
                 233/100 
                 67/100 
                 67/100 
                 33/100 
                 50/100 
                 25/100 
                 33/100 
               
               
                 Sulfate/(Sodium 
               
               
                 Dihydrogen 
               
               
                 Phosphate + 
               
               
                 ATMP) 
               
               
                 E (−0.8 V) (%) 
                 S 
                 A 
                 B 
                 B 
                 B 
                 C 
                 C 
                 C 
                 C 
                 C 
               
               
                 E (−1.2 V) (%) 
                 S 
                 S 
                 A 
                 B 
                 C 
                 B 
                 B 
                 B 
                 C 
                 B 
               
               
                   
               
               
                 (2) Each amount is the proportion with regard to a total amount of sodium dihydrogen phosphate, ATMP, and zinc sulfate. The total amount has been implemented as 1000 ppm. 
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
               
               
             
               
                   
                 TABLE 6 
               
               
                   
                   
               
               
                   
                 Compar- 
                 Compar- 
                 Compar- 
                 Compar- 
                 Compar- 
                 Compar- 
               
               
                   
                 ative 
                 ative 
                 ative 
                 ative 
                 ative 
                 ative 
               
               
                   
                 Example 
                 Example 
                 Example 
                 Example 
                 Example 
                 Example 
               
               
                   
                 B1 
                 B2 
                 B3 
                 B4 
                 B5 
                 B6 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Sodium 
                 100 
                 — 
                 — 
                 50 
                 — 
                 50 
               
               
                 Dihydrogen 
               
               
                 Phosphate 
               
               
                 (wt %) (2) 
               
               
                 ATMP 
                 — 
                 100 
                 — 
                 — 
                 50 
                 50 
               
               
                 (wt %) (2) 
               
               
                 Zinc Sulfate 
                 — 
                 — 
                 100 
                 50 
                 50 
                 — 
               
               
                 (wt %) (2) 
               
               
                 Sodium 
                 100:0 
                 0:100 
                 0:0 
                 50:0 
                 0:50 
                 50:50 
               
               
                 Dihydrogen 
               
               
                 Phosphate:ATMP 
               
               
                 Zinc 
                 0/100 
                 0/100 
                 100/0 
                 50/50 
                 50/50 
                 0/100 
               
               
                 Sulfate/(Sodium 
               
               
                 Dihydrogen 
               
               
                 Phosphate + 
               
               
                 ATMP) 
               
               
                 E (−0.8 V) (%) 
                 D 
                 D 
                 D 
                 D 
                 D 
                 D 
               
               
                 E (−1.2 V) (%) 
                 D 
                 D 
                 D 
                 D 
                 D 
                 D 
               
               
                   
               
               
                 (2) Each amount is the proportion with regard to a total amount of sodium dihydrogen phosphate, ATMP, and zinc sulfate. The total amount has been implemented as 1000 ppm. 
               
               
                 The m-dash (“—”) indicates that the respective compound has not been used. 
               
            
           
         
       
     
     In Comparative Example B4, an SEM photograph of a surface of a working electrode after determination of cathodic current values has been taken, and shown in  FIG. 14 . Further, in Example B1 and Comparative Example B4, the protective films formed on the surfaces of the working electrodes has been subjected to X-ray diffraction analysis (XRDA). Analysis results are shown in  FIG. 15 . Analysis results lead to the conclusion that addition of ATMP eliminates peaks of Zn 3 (PO 4 ) 2 .4H 2 O and promotes formation of amorphous structures. 
     Experimental Example C: Method for Determining Current when Measuring Current Reduction Rate E 
     Reference Example C1 
     In Reference Example C1, except for having saturated the test fluid with nitrogen instead of air, cathodic current values have been determined and a current-potential curve has been obtained in the same manner as in Comparative Example A1. In  FIG. 16 , the current-potential curve of Reference Example C1 is indicated as “N 2 ,” and the current-potential curve of Comparative Example A1 as “Air.” Since the experiment results show that oxygen reduction reactions predominantly occur at a potential around −0.8 V, and hydrogen reduction reactions predominantly occur at a potential around −1.1 V, potentials when the current reduction rate E is calculated have been determined as values close to each of these potentials.