JP2016205946A - Method for detecting corrosion spot of metallic material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for detecting a corrosion spot of a metallic material.SOLUTION: A corrosion spot is detected, by bringing an aqueous solution containing a tetrazolium compound with a structure expressed by the following formula (1) into contact with a metallic surface and determining that a colored spot is corrosive by using color development of the formazan dye generated by reduction of the tetrazolium compound.SELECTED DRAWING: None

Description

  The present invention relates to a method for detecting a corroded portion of a metal material, and more specifically, a metal material suitably used for detecting a corroded portion caused by a contact between different kinds of metal materials used in automobile parts, electrical equipment, electronic equipment, and aircraft parts. The present invention relates to a method for detecting a corrosion location.

  In the automobile industry, weight reduction has been achieved in order to reduce energy consumption and cost, and metals with low specific gravity are being used in metal materials.

  However, low specific gravity metals such as aluminum and magnesium alloys have a high tendency to ionize, and so to speak, they are more likely to cause different metal contact corrosion than conventional metals.

  Dissimilar metal contact corrosion is caused by contact between metals with different ionization potentials of metals, and the above-mentioned base metal is a noble metal with a low ionization tendency like copper and stainless steel that have been widely used conventionally. When an electrolyte or the like is present in contact with the base metal, it refers to a phenomenon in which a base metal serves as an anode to promote ionization (corrosion).

  Currently, various anticorrosion materials such as surface coating agents have been developed to prevent this phenomenon (see, for example, Patent Document 1).

Japanese Patent Laying-Open No. 2015-010223

  For example, as a dissimilar metal contact material having a contact portion of a dissimilar metal, there is an electric wire with a terminal in which a terminal such as a copper alloy is connected to a terminal of an electric wire using aluminum as a conductor. The electric wire with terminal is coated with an anticorrosive so as to cover the contact portion of the electric wire and the conductor. The anticorrosive is applied in a thin film state. If the coating film of the anticorrosive agent is a thin film, it is difficult to visually confirm the applied portion. For this reason, it has not been possible to easily know that the anticorrosive is covering the necessary part or peeled off.

  Therefore, at present, the development of anticorrosion materials is carried out while confirming the actual anticorrosion performance. Specifically, it is necessary to evaluate the anticorrosion performance in a corrosive environment such as salt spray or immersion.

  That is, in the evaluation of the anticorrosion performance, the evaluation piece is exposed to a corrosive environment for a certain period, and the degree of corrosion is confirmed by observing a base metal, measuring the electrical resistance of the contact surface, and the like. However, this evaluation takes time, and an accelerated test by heating is not effective.

  Further, although the degree of corrosion of the base metal can be confirmed by the above evaluation method, it is impossible to confirm the corrosion at the location of the noble metal side cathode that directly affects the dissimilar metal contact corrosion.

  Although the prevention of dissimilar metal corrosion is more effective when applied to the noble metal side than the base metal side, the noble metal cathode surface cannot be detected as described above. It was difficult to specify the necessary anticorrosion location. Therefore, the corrosion prevention process will be performed to an excessive location or an inappropriate location.

  Performing the anticorrosion treatment or the corrosion prevention treatment more than necessary or performing the treatment at an inappropriate location has a problem that the cost is high and it is difficult to guarantee the anticorrosion treatment.

  An object of the present invention is to detect a corrosion location of a metal material in a short time by a simple method, and to identify a necessary corrosion prevention location and to efficiently perform a corrosion prevention treatment. The object is to provide a method for detecting a location.

In order to solve the above problems, the method for detecting a corrosion site of a metal material according to the present invention
An aqueous solution containing a tetrazolium compound having the structure of the following (formula 1) is brought into contact with the surface of the metal, and it is determined that the colored portion is a corroded portion by utilizing the color of the formazan dye generated by the reduction of the tetrazolium compound. It is characterized by detecting a location.
In (Formula 1), R ₁ , R ₂ and R ₃ each independently has 14 or less carbon atoms, and is a group consisting of lower alkyl, aryl, substituted aryl, alkylaryl, substituted alkylaryl and heterocyclic substituted aryl And n is 1 or 2.

  In the method for detecting a corrosion location of a metal material according to the present invention, the metal material is a dissimilar metal contact material having a contact portion of a dissimilar metal, the corrosion is dissimilar metal contact corrosion, and the surface of the metal material is noble. It is preferable that the cathode region made of metal is identified as the corrosion site by utilizing the fact that the tetrazolium compound is colored with a reduced formazan dye.

  In the method for detecting a corrosion site of a metal material according to the present invention, the tetrazolium compound is preferably an electrolyte containing bound water-soluble ionic species.

  In the method for detecting a corrosion site of a metal material according to the present invention, the tetrazolium salt may be (3- (4,5-dimethyl-2-thiazolyl) -2,5-diphenyltetrazolium, (3,3 ′-(biphenyl- 4,4'-diyl) -bis (2,5-diphenyltetrazolium), (3,3 '-(3,3'-dimethoxy-4,4'-biphenylene) -bis- [2-p-nitrophenyl- 5-phenyl-2H-tetrazolium]), 3,3 ′-[3,3′-dimethoxy- (1,1′-biphenyl) -4,4′-diyl] -bis (2,5-diphenyltetrazolium), (2,2'-di-p-nitrophenyl-5,5'-distyryl-3,3 '-[3,3'-dimethoxy-4,4'-biphenylene] -tetrazolium), (3,3'- (3,3'-dimethoxy-4,4'-biphenylene) -bis- [2,5-p-nitrophenyl-2H-tetrazolium]), and (2- (4-indophenyl) -3- (4- Preferably it is one selected from the group consisting of water-soluble salts of nitrophenyl) -5-phenyltetrazolium). Arbitrariness.

  The method for detecting a corrosion site of a metal material according to the present invention includes the step of immersing the dissimilar metal contact material in an electrolyte containing the tetrazolium salt at a predetermined temperature for a predetermined time, and depositing formazan on the cathode region of the noble metal. It is preferable to detect the corrosion site by confirming the above by a predetermined method.

  In the method for detecting a corroded portion of a metal material according to the present invention, the dissimilar metal contact material is preferably an automotive wire harness component.

  The method for detecting a corrosion site of a metal material according to the present invention uses an aqueous solution containing a tetrazolium compound having a structure of (Formula 1) on the surface of a metal, and utilizes the color of formazan dye generated by reduction of the tetrazolium compound. Since the colored portion is determined to be a corroded portion and the corroded portion is detected, when performing the anticorrosion treatment (corrosion prevention treatment) of the metal material, by using the detection method of the present invention, a simple method can be used. Since the corrosion location of the metal material can be detected in a short time, it is possible to identify the necessary corrosion prevention location and efficiently perform the corrosion prevention treatment.

  Hereinafter, an embodiment of a method for detecting a corrosion site of a metal material according to the present invention will be described in detail. In a dissimilar metal contact material having a contact portion of a dissimilar metal, dissimilar metal contact corrosion occurs. As a method of confirming the corrosion location of different metal contact corrosion, it is possible to detect the cathode surface (cathode region) of a noble metal and to confirm the cathode surface visually or the like in a short time. For example, it becomes easy to develop a method for preventing contact corrosion of different metals. Therefore, the present invention focuses on the oxidation-reduction reaction that occurs on the anode or cathode surface during different metal contact corrosion.

  An oxidation reaction occurs on the anode surface, and a reduction reaction occurs on the cathode surface. Therefore, if the reduction reaction is visualized, it is possible to detect the cathode surface on the surface of the noble metal in the case of different metal contact corrosion. Therefore, the present inventors tried to use a tetrazolium salt that is used for detection and staining of dehydrogenase and the like in the biochemical field.

  This type of tetrazolium salt is water-soluble before reduction, and the aqueous solution is slightly yellow. However, as shown in (Formula 2), it is known that immediately after reduction, formazan is hardly soluble in water. Since this formazan is hardly soluble in water and has a deep purple color and has a fine crystal form, it can dye fine reduction reaction sites. Therefore, the noble metal cathode surface, which is generated when corrosion occurs, can be dyed with formazan simply by immersing the dissimilar metal contact material having a dissimilar metal contact portion in the electrolyte solution containing the tetrazolium salt.

In the present invention, an aqueous solution containing at least one tetrazolium compound represented by (Formula 1) is used as the detection solution. In (Formula 1), R ₁ , R ₂ and R ₃ each independently has 14 or less carbon atoms, and is a group consisting of lower alkyl, aryl, substituted aryl, alkylaryl, substituted alkylaryl and heterocyclic substituted aryl It is any 1 type selected from. n is 1 or 2. The tetrazolium compound can have water-soluble ionic species attached when necessary to obtain a neutral charge if desired.

  The tetrazolium compound represented by (Formula 1) is not particularly limited. For example, a commercially available tetrazolium compound can be used as it is because it is in the form of a tetrazolium salt in which a water-soluble anionic species is formed as a counter ion in order to obtain a neutral charge.

  The tetrazolium compound is preferably an electrolyte containing a tetrazolium salt having bound water-soluble ionic species. Tetrazolium salts include MTT [water-soluble salt of 3- (4,5-dimethyl-2-thiazolyl) -2,5-diphenyltetrazolium], Neo-TB (neotetrazolium blue) [3,3 '-(biphenyl-4 , 4'-diyl) -bis (2,5-diphenyltetrazolium) water-soluble salt], Nitro-TB [NTB, nitrotetrazolium blue, (3,3 '-(3,3'-dimethoxy-4,4' -Biphenylene) -bis- [2-p-nitrophenyl-5-phenyl-2H-tetrazolium])), TB [tetrazolium blue, 3,3 '-[3,3'-dimethoxy- (1, 1'-biphenyl) -4,4'-diyl] -bis (2,5-diphenyltetrazolium) water-soluble salt], SNTB [styryl nitroblue tetrazolium, (2,2'-di-p-nitrophenyl-5 , 5'-Distyryl-3,3 '-[3,3'-dimethoxy-4,4'-biphenylene] -tetrazolium) water-soluble salt], TNTB [tetranitroblue tetrazolium, (3,3'-(3 , 3'-Dimethoxy-4,4 ' -Biphenylene) -bis- [2,5-p-nitrophenyl-2H-tetrazolium]) water-soluble salt], and INT [indonitrotetrazolium, (2- (4-indophenyl) -3- (4-nitro Preferably, it is selected from the group consisting of phenyl) -5-phenyltetrazolium).

  Examples of the water-soluble ionic species of the water-soluble salt include halogen, nitrate, nitrite, carbonate, bicarbonate, sulfate, phosphonate, and transition metal oxygenates. The water-soluble ionic species is preferably halogen. The halogen is preferably selected from the group consisting of chloride, fluoride, bromide and iodide.

  The tetrazolium salt is preferably NTB, TB, TNTB or the like because of the fine crystal form of formazan produced by reduction.

The method for detecting a corrosion site according to the present invention includes the following steps (a) to (d). These steps will be described.
(A) Step of preparing a test solution (b) Step of preparing a foreign metal contact corrosion sample (c) Step of immersing the sample in the test solution (d) Step of observing a dyed portion of the sample

(A) Step of preparing test solution It is preferable that the test solution containing a tetrazolium salt for detecting the cathode surface of different metal contact corrosion has the following composition as a standard.
[Solvent] Pure water or tap water.
[Composition a] 0.01% (w / v) to 5.0% (w / v) of tetrazolium salt.
[Composition b] Electrolyte (optional) 0.0% (w / v) to 30.0% (w / v) of an aqueous solution as an electrolyte, such as NaCl and KCl.
[Other compositions] A pH adjusting agent, a viscosity adjusting agent, etc. can be added to such an extent that the function is not impaired.

  The pH of the test solution is arbitrary, but is preferably near neutral (5.5 to 8.5). (C) The temperature of the test solution in the step is arbitrary, but is preferably around 10 to 50 ° C.

(B) Step of preparing a dissimilar metal contact corrosion sample A dissimilar metal contact material in contact with a dissimilar metal used as a dissimilar metal contact corrosion sample is used. As the sample, a metal material having a structure in which a base metal and a noble metal are in contact with each other can be used as long as it can be immersed in the test solution. The dissimilar metal contact material is preferably composed of a substance that does not dissolve in water.

(C) Step of immersing sample in test solution When immersing the dissimilar metal contact corrosion sample in the test solution, the following is preferable. Remove air bubbles from the surface of the sample as much as possible. Stirring and ultrasonic irradiation are optional depending on the material form, but gentle stirring is preferred. The immersion time is arbitrary but is preferably 1 minute to 60 minutes.

(D) The process of observing the dyed part of a sample The observation method of a dyeing | staining surface takes out a sample from immersion liquid (test | inspection liquid), wash | cleans with a pure water, and observes visually. For observation, a microscope or a CCD camera can be used as appropriate. In addition, the amount of electrons received by the cathode can be quantified by the density of the coloring, and compared with other samples or other places.

  The method for detecting a corrosion site of a metal material according to the present invention is useful for evaluating the type of anticorrosive agent, the application position of the anticorrosive agent, and the like when developing an anticorrosive agent for the metal material. For example, for samples in which the types and application positions of various anticorrosives are changed, as a method for detecting a corrosion site, a cathode region in which formazan is deposited is immersed in an electrolyte containing the tetrazolium salt at a predetermined temperature for a predetermined time. By confirming this with a predetermined confirmation method, it is possible to reliably determine the corrosion location in a short time. In general, the corrosion point of the sample to which the anticorrosive agent is applied is peeled off by corrosion of the metal. According to this detection method, since the degree of peeling of the anticorrosive agent and the like can be visualized, it is possible to appropriately evaluate them.

  In the above detection method, the predetermined temperature, the predetermined time, and the predetermined confirmation method can be applied to a wide variety of samples by appropriately selecting arbitrary conditions according to the sample.

  The method for detecting a corroded portion of a metal material of the present invention can be suitably used for a wire harness component for automobiles as a metal material. Specific wire harness parts for automobiles include a terminal-attached electric wire in which an aluminum electric wire is connected to a tin-plated copper terminal fitting, a tin-plated copper conductor, and the like.

  Examples of the present invention and comparative examples are shown below. The present invention is not limited by these.

[Sample materials and manufacturers]
The test materials used in the present examples and comparative examples are shown together with the manufacturer, product name, and the like.

[Different metal contact corrosion sample pieces A to C]
(Sample piece A)
An aluminum wire having a tin-plated copper connection terminal connected to the end was used as sample piece A. The terminal portion of the sample piece A is in contact with aluminum, tin, and copper, and the respective metals are exposed. Only the end face of copper is exposed.
(Sample piece B)
An electric wire obtained by applying a colorless aluminum anticorrosive to the exposed aluminum part of the sample piece A was used as the sample piece B. The terminal portion of the sample piece B is in contact with aluminum, tin, and copper, but only aluminum is not exposed. Only the end face of copper is exposed.
(Sample piece C)
A copper wire having a tin-plated copper connection terminal connected to the end was used as the sample piece C. The terminal portion of the sample piece C is in contact with tin and copper, and the respective metals are exposed. Only the end face of copper is exposed.

[Different metal contact corrosion test solution]
A stirrer, 5 g of NaCl, and 95 mL of pure water were placed in a 200 mL beaker, placed on a magnetic stirrer, and stirred at a speed of 300 rpm at room temperature to prepare a 5% (w / v) NaCl solution. NTB (for Examples 1, 5, 6), TB (for Example 2), MTT (for Example 3), INT (for Example 4) or OPD (for Comparative Example 2) in each salt water 5 mg The mixture was stirred for 10 minutes to dissolve. Moreover, the liquid of only the salt water which does not put anything was prepared (for the comparative example 1).

  NTB is 3,3 '-(3,3'-dimethoxy-4,4'-biphenylene) -bis- [2-p-nitrophenyl-5-phenyl-2H-tetrazolium chloride (manufactured by Dojindo Laboratories) TB is 3,3 '-[3,3'-dimethoxy- (1,1'-biphenyl) -4,4'-diyl] -bis (2,5-diphenyl-2H-tetrazolium chloride) (Dojin) Chemical Laboratory), MTT is (3- (4,5-dimethyl-2-thiazolyl) -2,5-diphenyltetrazolium (manufactured by Dojin Chemical Laboratory), INT is (2- (4-Indophenyl) -3 -(4-nitrophenyl) -5-phenyltetrazolium) (manufactured by Dojindo Laboratories), OPD indicates orthophenylenediamine (manufactured by Wako Pure Chemical Industries), and OPD is commonly used in the biochemical field where color develops by oxidation. The staining reagent used.

(Example 1)
The sample piece A was placed in the test solution containing NTB so that the terminal portions were all immersed, and left for 10 minutes while stirring at 300 rpm. Thereafter, the sample piece was taken out and washed with pure water, and then the terminal portion was observed. As a result of observation, the tin plating part and the copper surface were dyed, and the aluminum conductor was not dyed at all. Both the tin-plated part and the copper surface were stained darker as they were closer to the aluminum conductor. When the dyeing degree of the tin plating part and the copper surface was compared, the copper surface was dyed darker overall.

(Example 2)
In Example 1, all was the same as Example 1 except that a test solution containing TB was used instead of NTB. When the terminal part was observed, the stained part was the same as the result of Example 1, and the aluminum conductor was not dyed at all. The tinned portion and the copper surface were stained and shaded in the same manner as in Example 1. Overall, the color tone was more reddish than the result of Example 1, but it was sufficiently visible.

Example 3
In Example 1, all was the same as Example 1 except that a test solution containing MTT was used instead of NTB. As a result of observation, the stained part was the same as the result of Example 1, and the aluminum conductor was not dyed at all. The tinned portion and the copper surface were stained in the same shade as in Examples 1 and 2, but the degree of staining was thinner than in Examples 1 and 2. As a whole, the color tone was more reddish than the result of Example 2, but was sufficiently observable visually.

Example 4
In Example 1, all were the same as Example 1 except that the test solution containing INT was used instead of NTB. As a result of observation, the stained part was the same as the result of Example 1, and the aluminum conductor was not dyed at all. The tinned portion and the copper surface were stained and shaded in the same manner as in Example 2, and the degree of staining was even thinner than that in Example 3, but was barely visible. For confirmation, when the mixture was left for an additional 5 minutes while stirring at 300 rpm, the degree of dyeing was the same as in Example 3 and was sufficiently observable visually.

(Example 5)
Example 1 was the same as Example 1 except that sample piece B was used instead of sample piece A. As a result of observation, the tin plating part was not dyed, but the copper surface of the terminal end face was dyed.

(Example 6)
Example 1 was the same as Example 1 except that sample piece C was used instead of sample piece A. As a result of observation, the tin plating part was not dyed, but the copper surface of the terminal end face was dyed. The copper wire was slightly dyed at the part close to the terminal.

(Comparative Example 1)
Example 1 was the same as Example 1 except that salt water was used instead of the test solution containing NTB. As a result of observation, the tin plating part, the copper surface, and the aluminum conductor were not stained at all.

(Comparative Example 2)
In Example 1, it was the same as Example 1 except that a test solution containing OPD was used instead of NTB. As a result of observation, the tin plating part, the copper surface, and the aluminum conductor were not stained at all.

[Evaluation of Examples and Comparative Examples]
The ionization potential of the metal contained in contact with the sample piece used this time is + 0.34V for copper, -0.14V for tin, and -1.66V for aluminum. Therefore, if the contact of these metals is exposed to the electrolyte, the higher the ionization potential (noble metal), the easier it becomes the cathode, and the lower the ionization potential (base metal), the anode becomes the ionization (corrosion). ) Is likely to occur. Considering the above items, in the sample piece A, aluminum having the lowest ionization potential corrodes as an anode, and copper and tin act as a cathode. In addition, the closer to a metal having a lower ionization potential, the more strongly acts as a cathode. That is, receiving many electrons means that the reduction reaction is fast.

  Although the results of Examples 1 to 4 have a difference in color tone due to the difference in tetrazolium salt, the above phenomenon is clearly reflected, and only the portion acting as a cathode against the contact corrosion of different metals is dyed. The intensity of dyeing also reflects the strength of the cathode.

  In Example 5, aluminum having a low ionization potential is protected, so that it does not become an anode, and different metal contact corrosion occurs only with tin and copper on the end face. In this case, since tin serves as an anode and copper serves as a cathode, the phenomenon that only copper is dyed is consistent with the above theory.

  Example 6 is the same as Example 5, and since electrons are transferred only between tin and copper, only copper is dyed. In addition, copper staining at locations far from tin, where electrons are not easily exchanged, is less in comparison to staining near tin locations.

  As described above, from the results of Examples 1 to 6, it was found that the present method can detect the cathode surface acting in the different metal contact corrosion by staining.

  On the other hand, Comparative Example 1 does not stain because it does not contain a staining reagent, and Comparative Example 2 does not stain because it contains a staining reagent but is not a reducing coloring agent. None of the cathodes could be detected.

  As described above, the method for detecting a corrosion site of a metal material using a staining method with a tetrazolium salt is a new method for visually observing a cathode reaction that could not be detected in the past in the evaluation of heterogeneous metal contact corrosion. It has become possible to easily inspect metal mixed materials.

In addition, by using the method for detecting a corrosion location of a metal material according to the present invention, the corrosion process can be detected more accurately and the development of various metal materials is facilitated, and in particular, lightweight metals such as aluminum are more widely used. Can contribute.

Claims (6)

An aqueous solution containing a tetrazolium compound having the structure of the following (formula 1) is brought into contact with the surface of the metal, and it is determined that the colored portion is a corroded portion by utilizing the color of the formazan dye generated by the reduction of the tetrazolium compound. A method for detecting a corrosion point of a metal material, characterized by detecting the point.
In (Formula 1), R ₁ , R ₂ and R ₃ each independently has 14 or less carbon atoms, and is a group consisting of lower alkyl, aryl, substituted aryl, alkylaryl, substituted alkylaryl and heterocyclic substituted aryl And n is 1 or 2.

  The metal material is a dissimilar metal contact material having a contact portion of a dissimilar metal, the corrosion is dissimilar metal contact corrosion, and a cathode region made of a noble metal on the surface of the metal material is reduced in the tetrazolium compound. The method for detecting a corrosion site of a metal material according to claim 1, wherein the corrosion site is specified by utilizing a colored site by a formazan dye.   The method for detecting a corrosion site of a metal material according to claim 1 or 2, wherein the tetrazolium compound is an electrolyte containing bound water-soluble ionic species.   The tetrazolium salt is (3- (4,5-dimethyl-2-thiazolyl) -2,5-diphenyltetrazolium, (3,3 ′-(biphenyl-4,4′-diyl) -bis (2,5- Diphenyltetrazolium), (3,3 '-(3,3'-dimethoxy-4,4'-biphenylene) -bis- [2-p-nitrophenyl-5-phenyl-2H-tetrazolium]), 3,3' -[3,3'-Dimethoxy- (1,1'-biphenyl) -4,4'-diyl] -bis (2,5-diphenyltetrazolium), (2,2'-di-p-nitrophenyl-5 , 5'-Distyryl-3,3 '-[3,3'-dimethoxy-4,4'-biphenylene] -tetrazolium), (3,3'-(3,3'-dimethoxy-4,4'-biphenylene) ) -Bis- [2,5-p-nitrophenyl-2H-tetrazolium]) and (2- (4-indophenyl) -3- (4-nitrophenyl) -5-phenyltetrazolium) water-soluble salts The metal according to any one of claims 1 to 3, wherein the metal is any one selected from the group consisting of: Method of detecting a fee of corrosion points.   Corrosion spots are detected by immersing the dissimilar metal contact material in the electrolyte containing the tetrazolium salt at a predetermined temperature for a predetermined time and confirming the cathode region of the noble metal on which formazan is deposited by a predetermined method. 5. The method for detecting a corrosion location of a metal material according to claim 3 or 4, wherein:   The method for detecting a corrosion location of a metal material according to any one of claims 2 to 5, wherein the dissimilar metal contact material is a wire harness part for an automobile.