JP2018136133A - Micro working electrode for highly precise local electrochemical measurement, method for producing micro working electrode for highly precise local electrochemical measurement, and method for releasing insulating coating layer of micro working electrode for highly precise local electrochemical measurement - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a micro working electrode for highly precise local electrochemical measurement for analysis of local electrochemical phenomenon, the analysis required in highly precise electrochemical measurement of an origin of micro corrosion, a point of initiation of plating reaction, a process of formation of a micro defect, and so on of metallic materials, to provide a method for producing the same easily and with high precision, and to provide a method for easily releasing an insulating coating layer of the micro working electrode for the highly precise local electrochemical measurement.SOLUTION: A micro working electrode for highly precise local electrochemical measurement comprises: a working electrode surface 2 whose area is 0.01 mmor less; and an insulating coating layer 1 around a periphery of the working electrode surface 2, the insulating coating layer being composed of a hydrophobic organic compound to which a contact angle of a water droplet is larger than 70 degrees. The organic compound is one of ethyl methyl ketoxime, styrene-butadiene, nitrile, and so on or a mixture of two or more thereof. The micro working electrode further comprises a hydrophilic organic compound layer 3 which is on a surface of the insulating coating layer 1 in a form in which to surround the periphery of the working electrode surface 2.SELECTED DRAWING: Figure 1

Description

The present invention relates to a micro-working electrode for high-precision local electrochemical measurement having a working electrode surface area of 0.01 mm ² or less, a method for producing a micro-working electrode for high-precision local electrochemical measurement, and a micro-working electrode for high-precision local electrochemical measurement. It is related with the peeling method of this insulation coating layer.

  The surface of practical materials is uneven, and in order to develop new materials with controlled electrochemical reactions such as corrosion, electroplating, chemical conversion treatment, and anodization, a small area on the material surface is selected and localized in that area. It is necessary to analyze the electrochemical characteristics with high accuracy. For example, pitting corrosion, which is one of the local corrosions of stainless steel, is an electrochemical reaction starting from sulfide inclusions such as MnS having a size of several micrometers (μm). Therefore, it is considered that very useful information regarding the improvement of the corrosion resistance of the metal material can be obtained by producing a minute working electrode surface and performing electrochemical measurement of a minute region including a single inclusion. Similarly, it is expected that important knowledge regarding the improvement of corrosion resistance of practical materials can be obtained by setting the grain boundaries and surface defects of polycrystalline metals, the inside of specific crystal grains, and the like as targets of electrochemical measurement.

  By the way, conventionally, as a technique related to a microworking electrode for local electrochemical phenomenon analysis, a technique related to fabrication of a microworking electrode surface using two or more kinds of insulators has been disclosed (for example, see Patent Document 1). That is, it is a method in which two or more kinds of insulators are combined to form a coating layer so as to surround the working electrode surface, and the working electrode surface is immersed in the electrolyte together with the outer insulating coating. In general, it is not easy to completely remove air bubbles remaining at the boundary between the micro-working electrode surface and the coating. For this reason, it is said that it is necessary to combine two or more types of insulators. In other words, when the coating on the outer periphery of the electrode surface is composed of a combination of two or more types of insulators, fine bubbles gather around one type of insulator due to the difference in surface tension between the individual insulators, causing aggregation and coarsening. This is the principle that bubbles are easily removed. However, with this method, it is easy to artificially remove bubbles, and there is a technical problem that it is impossible to eliminate bubbles completely.

  Conventionally, a micro working electrode composed of a hydrophilic organic compound has also been disclosed (see, for example, Patent Document 2). The content is that a coating layer made of a hydrophilic organic compound having a contact angle with a water droplet of 70 degrees or less is provided on the outer peripheral portion of the working electrode surface. When the coating layer is composed of a hydrophilic organic compound, it is advantageous in terms of interfacial energy that no bubbles remain on the outer periphery of the working electrode, and the bubbles are removed spontaneously.

  When forming an insulating coating layer using a hydrophilic organic compound based on this technology, from the viewpoint of accuracy and ease of coating work and safety of the working environment, nitrocellulose, acrylic resin, polyvinyl resin, Among cellulose acetate, polyamide and polyacrylonitrile, at least one kind is preferably contained in 20% or more by mass percentage. This is because these substances are said to exhibit excellent characteristics with respect to the removal of bubbles as substances constituting the coating layer when producing the micro working electrode. In addition, it is speculated that the main reason is that it has a highly polar bond structure in the molecule and easily forms hydrogen bonds with water molecules. As the substance having such chemical characteristics, nitrocellulose, acrylic resin, polyvinyl resin, cellulose acetate, polyamide, and polyacrylonitrile are preferable from the viewpoints of availability, cost, safety during storage, and the like. . Furthermore, since these substances are difficult to apply to the sample surface alone, the viscosity can be adjusted by dissolving them in methanol, ethanol, propanol, or a mixture of two or more of them. Preferred.

  However, when the insulating coating layer is formed using a hydrophilic organic compound having a contact angle with water droplets of 70 degrees or less, even if it has undergone a drying process, it causes a redox reaction as a constituent component of the insulating coating layer. There is a problem that methanol, ethanol, propanol, or two or more of them are inevitably contained. That is, when electrochemical measurement is performed on the surface of a micro working electrode in which an insulating coating layer is formed using a hydrophilic organic compound having a contact angle with water droplets of 70 degrees or less, either methanol, ethanol, propanol, or If the current value due to two or more types of oxidation-reduction reactions is measured and the current value due to the original electrochemical reaction on the working electrode surface is very small, the change in the current value due to the reaction on the electrode surface is highly accurate. It is difficult to measure in detail.

  Furthermore, in the case of a micro working electrode, the ratio of the coating layer / electrode surface boundary portion (electrode outer peripheral portion) to the electrode area is higher than that of a working electrode (usually 1 cm × 1 cm) used for normal macroelectrochemical measurement. At the boundary between the coating layer and the electrode surface, chemical species that carry charges, such as metal ions due to the dissolution reaction of the sample and chloride ions contained in the solution, are likely to concentrate, so that an environment in which the reaction occurs more easily occurs. In particular, in local electrochemical measurement, in-situ observation of the working electrode surface with a microscope or the like is often performed at the same time, so the surface of the working electrode is often placed horizontally with respect to the vertical direction. Ions have the inevitability of staying on the electrode surface. Therefore, the current density due to the electrochemical reaction is greatly different between the coating layer / electrode surface boundary portion and the electrode central portion. And this is a factor which produces a big measurement error with respect to local electrochemical measurement. However, no technique is disclosed that is effective for avoiding a current measurement error due to an increase in the outer peripheral portion of the working electrode accompanying the miniaturization of the working electrode surface. In other words, a micro working electrode for local electrochemical phenomenon analysis that is necessary for electrochemical measurement with high accuracy, such as the starting point of minute corrosion of metal materials, the starting point of plating reaction and the formation process of micro defects, The current situation is that it is not known as a simple and highly accurate manufacturing method.

  In general, an insulating coating layer made of a hydrophobic organic compound is extremely difficult to peel off when fixed to a substrate having electrical conductivity such as metal. However, the minute working electrode is required to be observed and analyzed with an apparatus using an ultrahigh vacuum such as an electron microscope or an X-ray photoelectron spectrometer after the electrochemical measurement is completed. For this purpose, in addition to maintaining the performance of the apparatus such as ultra-high vacuum, it is necessary to easily peel off the insulating coating without corroding or eroding the working electrode surface in order to ensure analysis accuracy. However, there is no known method for easily peeling an insulating coating layer made of a hydrophobic organic compound from a metal substrate or the like. In particular, a method that can be applied to a metal material with low corrosion resistance that is easily corroded by chemicals such as ordinary steel is not disclosed.

Japanese Patent No. 5136997 Japanese Patent No. 5987230

The present invention has been made in view of the above circumstances, and an object thereof is to perform electrochemical measurement with high accuracy such as a starting point of minute corrosion of a metal material, a starting point of a plating reaction, a formation process of minute defects, and the like. Micro-working electrode for high-accuracy local electrochemical measurement for analysis of local electrochemical phenomena that is necessary in the process, its simple and high-precision manufacturing method, and simple insulation coating layer of the micro-working electrode for high-precision local electrochemical measurement Providing a simple peeling method.

  The present inventor has completed various aspects of the present invention by overcoming various limitations of the prior art and solving various problems. The gist of the present invention is as follows.

The fine working electrode for high precision local electrochemical measurement according to the present invention has a working electrode surface area of 0.01 mm ² or less, and the insulating coating layer on the outer periphery of the working electrode surface has a contact angle of more than 70 degrees with water droplets. It is characterized by comprising a hydrophobic organic compound.

  The fine working electrode for high-accuracy local electrochemical measurement according to the present invention, wherein the insulating coating layer on the outer periphery of the working electrode surface is ethylmethylketoxime, styrenebutadiene, nitrile, chloroprene, methylvinyl, methylphenyl, fluorosilicone, ethylene One of propylene, fluorine, and dimethylpolysiloxane, or a mixture of two or more of them is preferable.

  The fine working electrode for high-accuracy local electrochemical measurement according to the present invention has a hydrophilic organic compound layer having a contact angle with water droplets of 70 degrees or less on the surface of the insulating coating layer. The distance between the hydrophilic organic compound layer and the outer periphery of the working electrode surface is 0.5 mm or more and 3 mm or less over the entire circumference, and the hydrophilic organic compound layer has a width of 1 mm or more. Is preferred.

  The method for producing a micro-working electrode for high-accuracy local electrochemical measurement according to the present invention is a method for producing a micro-working electrode for high-accuracy local electrochemical measurement according to the present invention, and the insulating coating layer on the outer peripheral portion of the working electrode surface In the preparation, the organic compound is diluted with an organic solvent having a wider potential window than water, the viscosity is adjusted, applied to the solid material constituting the working electrode, and then dried.

  The method for producing a micro-working electrode for high precision local electrochemical measurement according to the present invention is the organic solvent having a wider potential window than water, toluene, xylene, kerosene, cyclohexane, acetonitrile, dichloroethane, dichloromethane, diethyl ether, N, It is preferable to use any one of N-dimethylformamide, dimethyl sulfoxide, N-methyl-2-pyrrolidone, propylene carbonate, tetrahydrofuran, tetramethylsilane, or a mixture of two or more thereof.

  The method for peeling off the insulating coating layer of the micro-working electrode for high precision local electrochemical measurement according to the present invention is such that the working electrode surface is coated with toluene, xylene, diethyl ether, 1,2-butylene oxide, methanesulfonic acid, 1-bromopropane It is characterized by being immersed in any one of the above or a mixture of two or more of them.

  According to the present invention, a micro-working electrode for high-precision local electrochemical measurement that enables high-precision electrochemical measurement of a minute corrosion starting point of a metal material, a starting point of a plating reaction, a formation process of a minute defect, and the like. Can be provided. Specifically, in addition to the fine working electrode for high precision local electrochemical measurement according to the present invention, by using a counter electrode and a reference electrode, various potential potential polarization curves, electrode impedance, chronoamperometry, etc. by the three-electrode method are used. Electrochemical measurement can be performed with high accuracy. In addition, it is possible to provide a production method that can easily produce a high-precision local electrochemical measurement micro-working electrode for that purpose with high accuracy. Furthermore, the peeling method which can peel easily the insulation coating layer of the micro working electrode for a high precision local electrochemical measurement can be provided.

(A) When there is no hydrophilic organic compound layer on the surface of the insulating coating layer, and (b) the surface of the insulating coating layer, using the micro-working electrode for high precision local electrochemical measurement of the embodiment of the present invention FIG. 2 is a schematic side view of a microelectrode system for electrochemical measurement when a hydrophilic organic compound layer is present in a form surrounding the outer periphery of the working electrode surface. The action produced by applying an organic compound mainly composed of nitrocellulose dissolved in ethanol to the surface of carbon steel (S45C) of the fine working electrode for high precision local electrochemical measurement of the embodiment of the present invention electrode surface, the electrode area of 0.0009 mm ^2, 0.008 mm ^2, in the case of 0.025 mm ^2, is a graph showing the anodic polarization curves measured in borate buffer pH is 8.0 (non-degassed). (A) a micro working electrode having a coating layer coated with a hydrophilic organic compound having a contact angle with water droplets of 70 degrees or less on the surface; and (b) a hydrophobic organic with a contact angle with water droplets exceeding 70 degrees. The fine working electrode for high-precision local electrochemical measurement according to the embodiment of the present invention is provided with a coating layer in which a compound is coated on the surface with a viscosity adjusted by dissolving the compound in an organic solvent having a wider potential window than water. It is explanatory drawing which shows the mode of the spreading | diffusion of the metal ion in the working electrode surface and surface vicinity. In the fine working electrode for high precision local electrochemical measurement of the embodiment of the present invention, a hydrophilic organic compound layer having a contact angle with a water droplet of 70 degrees or less is formed on the surface of the insulating coating layer, and the outer peripheral portion of the working electrode surface FIG. The pH of the working electrode surface produced by applying a fine working electrode for high precision local electrochemical measurement of an embodiment of the present invention to platinum, which is an organic compound mainly composed of nitrocellulose dissolved in ethanol. It is a graph which shows the anodic polarization curve measured with the borate buffer (non-deaeration) whose is 8.0. The fine working electrode for high-accuracy local electrochemical measurement of the embodiment of the present invention is produced by applying an organic compound mainly composed of ethylmethylketoxime dissolved in toluene on the surface of carbon steel (S45C). 2 is an optical micrograph of the working electrode surface. The fine working electrode for high-accuracy local electrochemical measurement of the embodiment of the present invention is produced by applying an organic compound mainly composed of ethylmethylketoxime dissolved in toluene on the surface of carbon steel (S45C). Measured with a borate buffer solution (non-degassed) with a pH of 8.0 on a working electrode surface and a working electrode surface prepared by applying an organic compound mainly composed of nitrocellulose dissolved in ethanol It is a graph which shows an anodic polarization curve.

Hereinafter, embodiments for carrying out the present invention will be described.
FIG. 1 shows a schematic diagram of a microelectrode system for electrochemical measurement according to an embodiment of the present invention. However, FIG. 1 shows an example in which electrochemical measurement of a minute region and optical microscope observation of an electrode surface are performed simultaneously. The essence of the present invention is a fine working electrode for high precision local electrochemical measurement that performs electrochemical measurement of a minute region on the surface of a material, and a working electrode surface 2 having an area of 0.01 mm ² or less and an outer peripheral portion of the working electrode surface 2. , A high-accuracy local area comprising an insulating coating layer 1 whose surface is coated with a hydrophobic organic compound having a contact angle with water droplets exceeding 70 degrees and dissolved in an organic solvent whose potential window is wider than water. A micro-working electrode for electrochemical measurement and a production method thereof. 1A shows a case where the hydrophilic organic compound layer 3 is not present on the surface of the insulating coating layer 1, and FIG. 1B shows a case where the hydrophilic organic compound layer 3 is formed on the surface of the insulating coating layer 1. These are the schematic diagrams in case it exists in the form surrounding the outer peripheral part of the working electrode surface 2. FIG. The objective lens, acrylic container, potentiostat, and the like shown in FIG. 1 are not constituent elements of the present invention.

In the electrochemical measurement of a minute region in the apparatus configuration shown in FIG. 1, when targeting a specific structure or crystal grain in a steel material, the size of one phase in the metal structure is often 100 μm or less. Since it is (0.1 mm or less), the area of the working electrode surface 2 needs to be 0.01 mm ² or less. If the area is larger than this, the electrode surface includes a plurality of metal structures, and it becomes difficult to produce an electrode surface including only a specific metal structure. In the characteristic analysis of the plating starting point and the non-plated part, the starting point size is about 10 μm in diameter (about 0.01 mm). For this reason, the area of the working electrode surface 2 needs to be 0.01 mm ² or less.

FIG. 2 shows an example in which the working electrode surface 2 is produced by applying carbon steel (S45C) with an organic compound mainly composed of nitrocellulose dissolved in ethanol. This figure shows carbon steel (S45C) measured with borate buffer (non-degassed) with a pH of 8.0 when the area of the working electrode surface 2 is 0.0009 mm ² , 0.008 mm ² , and 0.025 mm ² . It is an anodic polarization curve of a ferrite structure. The potential was scanned at a moving potential at a rate of 23 mV / min in the anodic polarization direction from -0.3 V (Ag / AgCl electrode standard with the internal solution being saturated KCl, hereinafter the same standard). The current value around 0.5 V is called the passive state maintaining current density, and it can be seen that this current density increases as the electrode area becomes smaller. In this figure, a commonly used working electrode surface of 100 mm ² (1 cm ² ) was prepared, and the measured value of the passive state maintaining current density of the ferrite structure was indicated by an arrow. According to FIG. 2, when the area of the working electrode surface 2 is 0.01 mm ² or less, when the insulating coating layer 1 is formed by dissolving an organic compound mainly composed of nitrocellulose with ethanol, a passive state maintaining current is obtained. It turns out that there is a risk of overestimating the density.

By the way, in electrochemical measurement where the area of the working electrode is 0.01 mm ² or less, in order to perform electrochemical measurement with high accuracy, from the hydrophobic organic compound with a contact angle with water droplets exceeding 70 degrees, the outer peripheral part of the working electrode surface The insulating coating layer 1 must be configured. When the working electrode area is extremely small, the ratio of the coating layer / electrode surface boundary portion in the electrode area increases. Since the chemical species that carry charges such as metal ions due to the dissolution reaction of the sample and chloride ions contained in the solution are likely to concentrate at the coating layer / electrode surface boundary portion, an environment in which the reaction occurs more easily occurs. In particular, in local electrochemical measurement, in-situ observation of the working electrode surface 2 with a microscope or the like is often performed at the same time. Therefore, as shown in FIG. 1, the working electrode surface is often arranged horizontally with respect to the vertical direction. The metal ions eluted from the working electrode and the like have a necessity to stay on the electrode surface. Therefore, the current density due to the electrochemical reaction is greatly different between the coating layer / electrode surface boundary portion and the electrode central portion.

  However, although details are unknown, when the insulating coating layer 1 on the outer peripheral portion of the working electrode surface 2 is made of a hydrophobic organic compound having a contact angle with a water droplet of more than 70 degrees, the model is schematically shown in FIG. As shown, the concentration of metal ions and chloride ions eluted from the electrode surface at the coating layer / electrode surface boundary is reduced. This is considered to be a movement phenomenon of the solution based on the difference in surface tension between the aqueous solution containing ionic species and the aqueous solution not containing these ionic species. That is, in the case of the hydrophilic insulating coating layer 1 having a contact angle with water droplets of 70 degrees or less, the aqueous solution / insulating coating interface has low energy regardless of the presence or absence of metal ions eluted from the electrode surface and the concentration level. Stable in condition. On the other hand, in the case of the hydrophobic insulating coating layer 1 having a contact angle with water droplets exceeding 70 degrees, the aqueous solution / insulating coating interface is in a high energy state. It is preferable in terms of interfacial energy to contact with a solution having a low surface tension containing a large amount of metal ions eluted from the surface. For this reason, the movement of the metal ion-containing solution is triggered by the subtle convection of the aqueous solution, and the ion species that cause an error in electrochemical measurement does not accumulate at the coating layer / electrode surface boundary portion. An electrochemical reaction takes place on the electrode outer periphery under almost the same conditions.

Therefore, in electrochemical measurement where the area of the working electrode surface 2 is 0.01 mm ² or less, in order to perform electrochemical measurement with high accuracy, the insulating coating layer 1 on the outer periphery of the working electrode surface 2 is formed from a hydrophobic organic compound. Must be configured. As the degree of hydrophobicity, the contact angle with water droplets needs to exceed 70 degrees. Desirably, it is 80 degrees or more. Here, the contact angle is measured in accordance with “Test method for wettability of substrate glass surface” described in JIS R 3257 (1999).

  The present invention is not limited to the organic compound constituting the insulating coating layer 1, but from the viewpoint of accuracy and ease of coating work and safety of the working environment, ethyl methyl ketoxime, styrene butadiene, nitrile, chloroprene. , Methyl vinyl, methylphenyl, fluorosilicone, ethylene propylene, fluorine, dimethylpolysiloxane, or a mixture of two or more thereof. The reason why these substances exhibit excellent characteristics as a substance constituting the insulating coating layer 1 when producing a micro working electrode is that they do not have a highly polar bond structure in the molecule, and It is thought that the main cause is that it is difficult to form a hydrogen bond between them. Substances with such chemical properties are not limited to ethyl methyl ketoxime, styrene butadiene, nitrile, chloroprene, methyl vinyl, methyl phenyl, fluorosilicone, ethylene propylene, fluorine, dimethylpolysiloxane, but available These materials are preferred from the viewpoints of ease of use, cost, and safety during storage. These may be used alone, but may be mixed with other substances as required. In addition, when used in combination with other than ethyl methyl ketoxime, styrene butadiene, nitrile, chloroprene, methyl vinyl, methyl phenyl, fluorosilicone, ethylene propylene, fluorine, dimethylpolysiloxane, one or more of these It is preferable to contain 20% or more by mass percentage.

  Further, in order to easily bring the solution into contact with the entire working electrode surface 2 without leaving air bubbles in the vicinity of the working electrode surface, as shown in FIG. 1B and FIG. A hydrophilic organic compound layer 3 having a contact angle with water droplets of 70 degrees or less is present on the surface of the layer 1 so as to surround the outer periphery of the working electrode surface 2, and the hydrophilic organic compound layer 3 and the working electrode The distance from the outer peripheral portion of the surface 2 is 0.5 mm or more and 3 mm or less over the entire circumference, and the width of the hydrophilic organic compound layer 3 needs to be 1 mm or more. When the shortest distance between the hydrophilic organic compound layer 3 and the outer periphery of the working electrode surface 2 is less than 0.5 mm, the error in electrochemical measurement due to the elution component from the hydrophilic organic compound layer 3 is not negligible. growing. If the longest distance between the hydrophilic organic compound layer 3 and the outer periphery of the working electrode surface 2 exceeds 3 mm over the entire circumference, the effect of easily bringing the solution into contact with the entire working electrode surface 2 without leaving bubbles is not expected. If the width of the hydrophilic organic compound layer 3 is less than 1 mm, it is difficult to easily bring the solution into contact with the entire working electrode surface 2 without leaving bubbles.

By the way, in the production of the insulating coating layer 1 on the outer peripheral portion of the working electrode surface 2, the hydrophobic organic compound is diluted with an organic solvent having a wider potential window than water and the viscosity is adjusted, and the solid material constituting the working electrode It is suitable to apply to and then dry. That is, many of the hydrophobic organic compounds such as ethyl methyl ketoxime, styrene butadiene, nitrile, chloroprene, methyl vinyl, methyl phenyl, fluorosilicone, ethylene propylene, fluorine, and dimethylpolysiloxane constituting the insulating coating layer 1 have a viscosity. It is difficult to produce the working electrode surface 2 having a high area and an area of 0.01 mm ² or less at a predetermined target position on the material surface with high accuracy. Therefore, in the production of the working electrode surface 2 having an area of 0.01 mm ² or less, it is preferable to adjust the viscosity by adding an organic solvent to the hydrophobic organic compound constituting the insulating coating layer 1. At this time, if an organic solvent with a narrower potential window than water such as ethanol, methanol, isopropanol, etc. is used, it will elute into an aqueous solution (electrolyte) although it is a trace amount during electrochemical measurement, and it will not be the target oxidation. It causes a reduction reaction and makes current measurement with high accuracy difficult.

5, an organic compound mainly nitrocellulose platinum coated those dissolved in ethanol, in the case of producing a working electrode surface 2 of the area 0.008 mm ^2, borate buffer is at a pH of 8.0 ( An anodic polarization curve measured by (non-degassing) is shown. The potential was scanned at a dynamic potential from -0.3 V (Ag / AgCl electrode standard with the internal solution as saturated KCl) in the anodic polarization direction at a rate of 23 mV / min. In this case, a region where the current density does not depend on the potential appears in the vicinity of 0.8 V, but when a working electrode surface 2 of 1 cm square that is normally used is fabricated and measured, the current value at 0.8 V is 10 ^-2 A / m ² or less. Therefore, the current density at 0.8 V when prepared from 5, an organic compound mainly nitrocellulose platinum coated those dissolved in ethanol, the working electrode surface 2 of the area 0.008 mm ² is usually It can be seen that the current density when the working electrode surface of 1 cm square used is 10 times or more.

That is, when the area of the working electrode surface 2 is 0.01 mm ² or less, there is a risk of overestimating the current value when ethanol with a narrow potential window is used as the organic solvent in the production of the insulating coating layer 1. is there. This is considered to be due to the measurement of the current value due to the redox reaction of ethanol. Therefore, an organic solvent having a wider potential window than water is suitable as a diluent for the organic compound constituting the insulating coating layer 1.

  The present invention is not limited to the type and composition of the organic solvent for dilution, but from the viewpoint of workability, safety, and economy, toluene, xylene, kerosene, cyclohexane, acetonitrile, dichloroethane, dichloromethane, diethyl ether, It is preferable to use any one of N, N-dimethylformamide, dimethyl sulfoxide, N-methyl-2-pyrrolidone, propylene carbonate, tetrahydrofuran and tetramethylsilane, or a mixture of two or more thereof. Furthermore, after forming the insulating coating layer 1, it is necessary to perform sufficient drying in order to volatilize the diluting solvent.

  By the way, it may be necessary to observe and analyze the electrode surface with an electron microscope or the like after performing electrochemical measurement of a minute region on the surface of the material. In such a case, it is important that the insulating coating layer 1 can be easily peeled off. Further, in order to ensure analysis accuracy, it is necessary to easily peel off the insulating coating layer 1 without corroding or eroding the working electrode surface 2. In order to peel the insulating coating layer 1 without corroding / eroding the working electrode surface 2, a method of immersing the electrode surface in an organic solvent having a dielectric constant smaller than that of water is desirable. This is because the corrosion reaction of metal hardly occurs in an organic solvent having a dielectric constant smaller than that of water. Soak in toluene, xylene, diethyl ether, 1,2-butylene oxide, methanesulfonic acid, 1-bromopropane, or a mixture of two or more of them as such organic solvents Thus, the insulating coating layer 1 can be easily peeled off. Substances having such chemical properties are not limited to toluene, xylene, diethyl ether, 1,2-butylene oxide, methanesulfonic acid, and 1-bromopropane, but are easily available, costly, and stored. From the viewpoint of safety at times, these substances are preferable.

  Hereinafter, the present invention will be described in detail based on examples, but the present invention is not limited to the description of the examples.

An organic compound was applied to the surface of the surface-polished carbon steel (S45C) to form an insulating coating layer 1, and a fine working electrode surface (50 μm square electrode surface: area 0.0025 mm ² ) 2 was produced. In production, carbon steel is etched in advance with nital, and as shown in FIG. 6, the periphery of the pearlite structure is marked with an indentation of a Vickers hardness meter, and the working electrode surface 2 is composed only of the pearlite structure. Then, the potentiodynamic anodic polarization curve was measured at a rate of 23 mV / min with a borate buffer (non-degassed) having a pH of 8.0. Table 1 shows the contact angle between the kind of the organic compound used for the production of the insulating coating layer 1 and water droplets. As shown in Table 1, when an organic compound is ethyl methyl ketoxime, styrene butadiene, nitrile, chloroprene, methyl vinyl, methyl phenyl, fluorosilicone, ethylene propylene, fluororesin, or dimethylpolysiloxane, the contact angle with water droplets It can be seen that exceeds 70 degrees.

Tables 2 and 3 show the organic compounds and organic solvents for dilution used in the production of the insulating coating layer 1. Furthermore, in this table, a case where the contact angle with the water droplet exceeds 70 degrees is indicated as “◯” as a hydrophobicity evaluation result, and a case where the contact angle with the water droplet is 70 degrees or less is indicated by “x”. Furthermore, using these organic compounds and a diluting solvent, an insulating coating layer 1 having a micro-working electrode surface (50 μm square electrode surface: area 0.0025 mm ² ) 2 is prepared, and a borate buffer solution (pH of 8.0) In the degassing), the potentiodynamic anodic polarization curve was measured at a rate of 23 mV / min. At this time, the value of the passive state maintaining current density at a potential of 0.5 V is less than 5 times the value of the current density when a 1 cm square electrode surface is prepared on carbon steel with a pearlite structure and measured under the same conditions. In some cases, the evaluation of the accuracy of the electrochemical measurement was “」 ”, and the case where it exceeded 5 times but was 7 times or less was assigned“ ◯ ”.

  As shown in Table 2 and Table 3, ethyl methyl ketoxime, styrene butadiene, nitrile, chloroprene, methyl vinyl, methyl phenyl, fluorosilicone, ethylene propylene, fluororesin, dimethylpolysiloxane are used as the organic compound, and toluene is used as the organic solvent. , Xylene, kerosene, cyclohexane, acetonitrile, dichloroethane, dichloromethane, diethyl ether, N, N-dimethylformamide, dimethyl sulfoxide, N-methyl-2-pyrrolidone, propylene carbonate, tetrahydrofuran, tetramethylfuran, ie insulation coating It can be seen that when the contact angle between the layer 1 and the water droplet exceeds 70 degrees, electrochemical measurement can be performed with high accuracy using the micro working electrode.

  As an example, FIG. 7 shows a case where the working electrode surface 2 is made of an organic compound mainly composed of ethylmethylketoxime dissolved in toluene (Example 1 in Table 2). An anodic polarization curve in the case of preparing a working electrode surface 2 by applying an organic compound containing nitrocellulose as a main component dissolved in ethanol (Comparative Example 18 in Table 3) is shown. As is clear from FIG. 7, even in a potential region other than the potential of 0.5 V, which is the potential for evaluation, the insulating coating layer 1 made of a hydrophobic organic compound is used to form a coating layer made of a hydrophilic organic compound. Since the electric current value has fallen compared with the case where it uses, it turns out that the unintended electrochemical reaction can be suppressed effectively.

Table 4 shows an insulating coating layer 1 having a small working electrode surface (50 μm square electrode surface: area 0.0025 mm ² ) 2 using ethyl methyl ketoxime as an organic compound and toluene as an organic solvent. As shown, the outer peripheral portion of the working electrode surface 2 and the hydrophilicity when the hydrophilic organic compound layer 3 is formed on the outer peripheral portion of the insulating coating layer 1 using nitrocellulose as the organic compound and ethanol as the organic solvent. The shortest distance and the longest distance of the organic compound layer 3 and the width of the hydrophilic organic compound layer 3 are shown. Further, an insulating coating layer 1 and a hydrophilic organic compound layer 3 are produced with these dimensions, and a potentiodynamic anodic polarization curve at a rate of 23 mV / min with a borate buffer solution (non-deaerated) having a pH of 8.0. Was measured. At this time, the value of the passive state maintaining current density at a potential of 0.5 V exceeds 5 times the value of the current density when a 1 cm square electrode surface is produced on carbon steel having a pearlite structure and measured under the same conditions. The accuracy of the electrochemical measurement was evaluated by assuming that “” is 7 times or less, and “Δ” is 7 times or more.

  By the way, in the experiment using the minute working electrode surface 2, bubbles remain at the boundary portion between the outer peripheral portion of the working electrode surface 2 and the insulating coating layer 1 and cause a decrease in the accuracy of electrochemical measurement. Accordingly, the insulating coating layer 1 and the hydrophilic organic compound layer 3 having the above dimensions are prepared, and the electrode surface is immersed in a borate buffer solution (non-deaerated) having a pH of 8.0, and an optical microscope and water are used. When the surface of the electrode surface is observed using an immersion objective lens, “◯” indicates that less than 5% of the distance on the outer periphery of the electrode surface is covered with bubbles, and “△” indicates that 5% or more is covered with bubbles. The contact between the electrode surface and the solution was evaluated. As shown in Table 4, the distance between the hydrophilic organic compound layer 3 and the outer periphery of the working electrode surface 2 is 0.5 mm or more and 3 mm or less over the entire circumference, and the width of the hydrophilic organic compound layer is 1 mm. In the case of the above, it turns out that the bubble remaining can be suppressed.

  Table 5 shows the peelability of the insulating coating layer 1 when the insulating coating layer 1 mainly composed of ethylmethylketoxime is immersed in an organic solvent. “○” indicates that 80% or more of the insulating coating layer 1 peels off after 24 hours of immersion, “△” indicates that 50% or more and less than 80% peels, and “x” indicates that only 50% or less peels off. The peelability of the insulating coating layer 1 was evaluated. As shown in Table 5, when the insulating coating layer 1 is composed of an organic compound mainly composed of ethyl methyl ketoxime, the electrode surface is immersed in toluene and xylene for 24 hours. % And less than 80% peeled off. It is considered that the insulating coating layer 1 can be further peeled by being immersed for a longer time. Further, when the electrode surface was immersed in diethyl ether, 1,2-butylene oxide, methanesulfonic acid, and 1-bromopropane for 24 hours, 80% or more of the insulating coating layer 1 was peeled off. It can be seen that the insulation coating layer 1 can be peeled to such an extent that the surface observation is not hindered by being immersed in these substances.

  As described above, the micro-working electrode for high-precision local electrochemical measurement according to the embodiment of the present invention can be applied to the microelectrode surface without being affected by the reaction of the coating layer or the concentration of ions at the boundary of the coating layer / electrode surface. It can be seen that electrochemical measurement is possible.

  Examples of the use of the present invention include a micro-working electrode for high-accuracy local electrochemical measurement for local electrochemical phenomenon analysis of a material that easily causes corrosion, such as ordinary steel, a manufacturing method thereof, and a micro-electrode for high-accuracy local electrochemical measurement It can be used as a method for peeling off the insulating coating layer of the working electrode, and is extremely useful not only for academic research but also for industry.

DESCRIPTION OF SYMBOLS 1 Insulation coating layer 2 Working electrode surface 3 Hydrophilic organic compound layer

The micro-working electrode for high-accuracy local electrochemical measurement according to the present invention has a contact angle between a working electrode surface with an area of 0.01 mm ² or less , which is produced at an arbitrary position on the surface of the material to be measured, and a water droplet. And an insulating coating layer formed on the outer peripheral portion of the working electrode surface .

The fine working electrode for high-accuracy local electrochemical measurement according to the present invention, wherein the insulating coating layer on the outer periphery of the working electrode surface is ethylmethylketoxime, styrenebutadiene, nitrile, chloroprene, methylvinyl, methylphenyl, fluorosilicone, ethylene propylene, fluorocarbon resins, one type of dimethylpolysiloxane or is preferably a mixture of two or more of them.

The present invention is not limited to the organic compound constituting the insulating coating layer 1, but from the viewpoint of accuracy and ease of coating work and safety of the working environment, ethyl methyl ketoxime, styrene butadiene, nitrile, chloroprene. , methyl vinyl, methyl phenyl, fluorosilicone, ethylene propylene, fluorocarbon resins, one type of dimethylpolysiloxane, or be a mixture of two or more of them preferred. The reason why these substances exhibit excellent characteristics as a substance constituting the insulating coating layer 1 when producing a micro working electrode is that they do not have a highly polar bond structure in the molecule, and It is thought that the main cause is that it is difficult to form a hydrogen bond between them. Substances having such chemical properties, ethyl methyl ketoxime, styrene-butadiene, nitrile, chloroprene, methyl vinyl, methyl phenyl, fluorosilicone, ethylene propylene, fluorocarbon resins, but are not limited to dimethyl polysiloxane, These substances are preferable from the viewpoints of availability, cost, safety during storage, and the like. These may be used alone, but may be mixed with other substances as required. Then, when used as a mixture of ethyl methyl ketoxime, styrene-butadiene, nitrile, chloroprene, methyl vinyl, methyl phenyl, fluorosilicone, ethylene propylene, fluorocarbon resins, and other than dimethylpolysiloxane, one of these It is preferable to contain 20% or more by mass percentage.

By the way, in the production of the insulating coating layer 1 on the outer peripheral portion of the working electrode surface 2, the hydrophobic organic compound is diluted with an organic solvent having a wider potential window than water and the viscosity is adjusted, and the solid material constituting the working electrode It is suitable to apply to and then dry. That is, ethyl methyl ketoxime constituting the insulating coating layer 1, the number of styrene-butadiene, nitrile, chloroprene, methyl vinyl, methyl phenyl, fluorosilicone, ethylene propylene, fluorocarbon resins, hydrophobic organic compounds such as dimethyl polysiloxane, It is difficult to produce the working electrode surface 2 having a high viscosity and an area of 0.01 mm ² or less at a predetermined target position on the material surface with high accuracy. Therefore, in the production of the working electrode surface 2 having an area of 0.01 mm ² or less, it is preferable to adjust the viscosity by adding an organic solvent to the hydrophobic organic compound constituting the insulating coating layer 1. At this time, if an organic solvent with a narrower potential window than water such as ethanol, methanol, isopropanol, etc. is used, it will elute into an aqueous solution (electrolyte) although it is a trace amount during electrochemical measurement, and it will not be the target oxidation. It causes a reduction reaction and makes current measurement with high accuracy difficult.

Claims (6)

The area of the working electrode surface is 0.01 mm ² or less, and the insulating coating layer on the outer periphery of the working electrode surface is composed of a hydrophobic organic compound having a contact angle with water droplets exceeding 70 degrees. Micro working electrode for precision local electrochemical measurements.   The insulating coating layer on the outer periphery of the working electrode surface is any one of ethylmethylketoxime, styrenebutadiene, nitrile, chloroprene, methylvinyl, methylphenyl, fluorosilicone, ethylenepropylene, fluorine, dimethylpolysiloxane, or these The fine working electrode for high precision local electrochemical measurement according to claim 1, which is a mixture of two or more of the above.   On the surface of the insulating coating layer, a hydrophilic organic compound layer having a contact angle with water droplets of 70 degrees or less exists in a form surrounding the outer peripheral portion of the working electrode surface, and the hydrophilic organic compound layer and the action The high-precision local portion according to claim 1 or 2, wherein the distance from the outer peripheral portion of the electrode surface is 0.5 mm or more and 3 mm or less over the entire circumference, and the width of the hydrophilic organic compound layer is 1 mm or more. Micro working electrode for electrochemical measurement.   The method for producing a micro-working electrode for high precision local electrochemical measurement according to any one of claims 1 to 3, wherein the potential is higher than that of water when the insulating coating layer on the outer peripheral surface of the working electrode is produced. An organic compound diluted with an organic solvent having a wide window, applied to a solid material constituting the working electrode after adjusting the viscosity, and then dried. Manufacturing method.   As the organic solvent having a wider potential window than water, toluene, xylene, kerosene, cyclohexane, acetonitrile, dichloroethane, dichloromethane, diethyl ether, N, N-dimethylformamide, dimethyl sulfoxide, N-methyl-2-pyrrolidone, propylene carbonate, The method for producing a micro-working electrode for high precision local electrochemical measurement according to claim 4, wherein any one of tetrahydrofuran and tetramethylsilane, or a mixture of two or more thereof is used. A method for peeling off an insulating coating layer of a micro-working electrode for high precision local electrochemical measurement according to any one of claims 1 to 3, wherein the working electrode surface is coated with toluene, xylene, diethyl ether, 1, Insulation of micro working electrode for high precision local electrochemical measurement characterized by being immersed in one kind of 2-butylene oxide, methanesulfonic acid, 1-bromopropane or a mixture of two or more of them The peeling method of a coating layer.