Reference electrode and measurement method

Abstract

This reference electrode 11 is formed from a metal material of which the natural potential does not change within the time range of electrochemical measurement in the solid electrolyte 10.

Description

Reference electrode and measurement method

[0001] The present disclosure relates to a reference electrode and a measurement method.

[0002] One method for measuring material changes in solid electrolytes is electrochemical methods. For example, rebars in reinforced concrete structures resist the tensile stresses that the structure is subjected to. To maintain the safety of the structure, rebar corrosion is measured. Electrochemical measurement methods such as the half-cell potential method or polarization resistance method are applied to measure rebar corrosion.

[0003] Prior Non-Patent Document 1 discloses measuring the potential of a reinforcing bar relative to the potential of a reference electrode, or measuring by controlling the potential of the reinforcing bar relative to the potential of the reference electrode, using either the natural potential method or the polarization resistance method. A reference electrode is sometimes also called a reference electrode. Known types of reference electrodes include a copper sulfate electrode (CSE) and a silver chloride (Ag / AgCl) electrode. A reference electrode has a structure in which a metal is filled with an aqueous solution saturated with the metal ion concentration so that the natural potential of the metal used as the electrode is stabilized.

[0004] Non-Patent Document 1 discloses spraying clean water, such as tap water, onto the concrete for about 30 minutes before measurement. By keeping the concrete surface wet, electrical continuity between the rebar and the reference electrode is ensured.

[0005] Non-Patent Document 2 discloses that stainless steel forms a passive film in an aqueous solution with a pH of 0.1 to 13.1.

[0006] Non-Patent Document 3 states that the corrosion current calculated by Tafel extrapolation from polarization measurements of iron in cement is 1 to 2 × 10 -8 A / cm 2 Order (= 1 x 10 -4 A / m 2 )

[0007] Masaru Nagayama, “Theory and Practice of Nondestructive Testing of Concrete (1) Theory and Practice of Electrochemical Methods (Semi-Central Potential Method and Polarization Resistance Method)”, Concrete Engineering, Vol. 51, No. 2, pp. 194-199, 2013.2 Katsuhisa Sugimoto, “Passive Film on Stainless Steel - Current Status of Its Analysis and Theory”, Materials and Environment, 57, pp. 375-384, 2008 Kotaro Doi, Shoko Hiromoto, Eiji Akiyama, “High-Oxygen Accelerated Corrosion Test of Iron in Cement Paste and Mortar”, Journal of the Japan Institute of Metals, Vol. 82, No. 1, pp. 1-7, 2018

[0008] As disclosed in Non-Patent Document 1, in electrochemical measurements such as the half-cell potential method using a reference electrode or the polarization resistance method, it is necessary to keep the concrete surface wet to ensure electrical continuity between the reinforcing steel and the reference electrode. However, it may be difficult to apply this method to dry concrete before spraying water or to prestressed concrete, which is difficult for water to penetrate.

[0009] The present disclosure has been made in consideration of the above circumstances, and the purpose of the present disclosure is to provide a technology that can ensure electrical continuity between a reinforcing bar and a reference electrode without the need to spray water beforehand.

[0010] The reference electrode according to one embodiment of the present disclosure is formed from a metal material whose natural potential does not change within the solid electrolyte within the time range of electrochemical measurement.

[0011] In one embodiment of the measurement method of the present disclosure, a reference electrode is embedded in a solid electrolyte before the solid electrolyte hardens, and electrochemical measurements are performed using the reference electrode, and the reference electrode is formed from a metal material whose natural potential does not change within the solid electrolyte within the time range of the electrochemical measurements.

[0012] According to the present disclosure, it is possible to provide a technology that can ensure electrical continuity between a reinforcing bar and a reference electrode without spraying water in advance.

[0013] Fig. 1 is a diagram illustrating a measurement device according to the present disclosure. Fig. 2 is a graph showing the change over time in the natural potential of iron relative to the natural potential of stainless steel. Fig. 3 is a diagram illustrating a measurement method according to the present disclosure. Fig. 4 is a diagram showing the measured value of the difference between the potential of a working electrode and the potential of a reference electrode according to the present disclosure.

[0014] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In the description of the drawings, the same parts are designated by the same reference numerals and the description thereof will be omitted.

[0015] The present disclosure discloses a reference electrode 11 formed of a metal material whose natural potential does not change within the range of electrochemical measurement time within a solid electrolyte 10. The solid electrolyte 10 is a structure for which rebar corrosion is to be measured. In the present disclosure, the solid electrolyte 10 is cement, mortar, or the like.

[0016] The reference electrode 11 is embedded in the solid electrolyte 10 before the solid electrolyte 10 hardens. The measurement object is evaluated using an electrochemical method by controlling the potential of the rebar using the pre-embedded metal material as the reference electrode 11. More specifically, the measurement object is a material within the measurement object, specifically, the rebar within the solid electrolyte 10.

[0017] (Measurement Apparatus) A measurement apparatus 1 used as a specimen will be described with reference to Fig. 1. The measurement apparatus 1 is made of a solid electrolyte 10. The solid electrolyte 10 is made of cement. The cement is a material that constitutes the actual structure to be measured by the measurement apparatus 1.

[0018] In addition to the materials that constitute the original structure, the measuring device 1 also includes a reference electrode 11 for electrochemical measurements, a working electrode 12, a counter electrode 13, a resin 14 in which the working electrode 12 and the counter electrode 13 are embedded, a lead wire 15a connected to the working electrode 12, and a lead wire 15b connected to the counter electrode 13.

[0019] In the present disclosure, the reference electrode 11 is made of stainless steel. The reference electrode 11 has a structure in which the stainless steel is filled with an aqueous solution saturated with the metal ion concentration so that the natural potential of the stainless steel is stabilized. The working electrode 12 and the counter electrode 13 are made of iron. The working electrode 12 and the counter electrode 13 are embedded in resin, and the surface areas of the iron plates forming the working electrode 12 and the counter electrode 13 are defined.

[0020] In the present disclosure, the reference electrode 11 is described as being cylindrical and solid, but is not limited to this.

[0021] In Non-Patent Document 1 and other documents, the reference electrode is pressed against the surface of a test specimen that has been moistened by spraying water, etc., and measurement is performed. In some cases, the electrical resistance at the contact point is set low by inserting wet gauze between the reference electrode and the test specimen.

[0022] One possible method is to press a reference electrode against a dry specimen. However, although the specimen and reference electrode appear to be in contact over a surface area, they may in fact have small irregularities, resulting in only point contact rather than a surface area. In this case, the effective contact area is small, resulting in high electrical resistance and making measurement impossible.

[0023] Therefore, the reference electrode 11 according to the present disclosure is embedded in the solid electrolyte 10 before the solid electrolyte 10 hardens. As a result, after the solid electrolyte 10 hardens, the reference electrode 11 contacts the solid electrolyte 10 over a wide surface, thereby increasing the effective contact area between the reference electrode 11 and the solid electrolyte 10. Whether the solid electrolyte 10 is wet or dry, the reference electrode 11 and the solid electrolyte 10 are electrically connected, enabling electrochemical measurements.

[0024] In the present disclosure, the reference electrode 11 itself is embedded in the solid electrolyte 10, but this is not limiting. For example, the reference electrode 11 may be embedded so that only the tip of the reference electrode 11 is exposed to the solid electrolyte 10. Furthermore, the surface of the solid electrolyte 10 other than the tip may be covered with a predetermined material so that the reference electrode 11 does not come into contact with the solid electrolyte 10. The predetermined material may be an epoxy resin or the like. By not exposing the reference electrode 11 on the surface of the solid electrolyte 10, the stability of the natural potential of the reference electrode can be expected to be improved. This is because the contact area between the surface of the solid electrolyte 10 and the reference electrode 11 is susceptible to external environmental influences such as dryness, wetness, and the progression of neutralization, and the reference electrode 11 may react sensitively to the external environment. For example, by covering the reference electrode 11 with resin, sealing tape, an acrylic pipe (resin-sealed at both ends), or the like at the contact area between the surface of the solid electrolyte 10 and the reference electrode 11, changes in the natural potential can be prevented.

[0025] (Reference electrode) Generally, the reference electrode is independent of the object to be measured. The natural potential of the metal inside the reference electrode is stable. Therefore, by using the natural potential of the reference electrode as a reference, the electrode potential of the working electrode can be precisely controlled.

[0026] In contrast, the reference electrode 11 according to the present disclosure is embedded in the solid electrolyte 10. It has not been confirmed that the natural potential of the stainless steel that forms the reference electrode 11 is stable inside the solid electrolyte 10, so it is necessary to measure using the stainless steel as the reference electrode and confirm that accurate measurements can be made.

[0027] Furthermore, the reference electrode 11 is required to be durable because it is embedded in a structure. Specifically, the reference electrode 11 is required to have a natural potential that does not change within the time of one electrochemical measurement even if it is repeatedly dried and absorbed.

[0028] Therefore, in this disclosure, the potential difference between iron and stainless steel is measured, and after confirming that there is no change in the potential difference, a reference electrode 11 made of stainless steel is used. Figure 2 shows the change over time in the natural potential of iron relative to the natural potential of stainless steel. As shown in Figure 2, the natural potential of iron relative to the natural potential of stainless steel is stable.

[0029] The natural potentials of iron and stainless steel may change even during the short time it takes to perform electrochemical measurements. However, it is unlikely that they change in the same way, and if the potential difference is constant, it can be determined that the natural potentials of iron and stainless steel are stable. Therefore, it is believed that using stainless steel as the reference electrode 11 allows for accurate control of the potential of the working electrode 12.

[0030] The metal material forming the reference electrode 11 preferably has a protective coating formed on its surface within the solid electrolyte 10. For example, the stainless steel used for the reference electrode 11 in the present disclosure is a metal that forms a stable protective coating in the pH range that concrete can have.

[0031] Non-Patent Document 2 discloses that a passive film forms on stainless steel in aqueous solutions with a pH of 0.1 to 13.1. On the surface of stainless steel in a concrete environment, the reaction of forming a stable protective film and the reduction reaction of oxygen are in balance, so the natural potential settles at a potential where the reduction current of oxygen matches the passivation current, and the natural potential of stainless steel is thought to be a relatively stable value.

[0032] (Measurement Method) A measurement method according to the present disclosure will be described with reference to FIG.

[0033] In step S1, a material for the reference electrode 11 is selected. In the present disclosure, the metal used for the reference electrode 11 is selected based on the following conditions: the metal is formed from a metallic material whose natural potential does not change within the time range of one electrochemical measurement even after repeated drying and water absorption within the solid electrolyte 10; and a protective coating is formed on the surface within the solid electrolyte 10. In the present disclosure, the reference electrode 11 is formed from stainless steel.

[0034] In step S2, the reference electrode 11 is embedded in the solid electrolyte 10 before the solid electrolyte 10 to be measured is hardened.

[0035] Thereafter, when the measurement timing arrives in step S3, measurement is performed in step S4. In step S4, electrochemical measurement is performed using the reference electrode 11 embedded in the solid electrolyte 10. If there are multiple measurement timings, the processes of steps S3 and S4 may be repeated multiple times.

[0036] (Measurement Results) A method for evaluating the corrosion rate of rebar in solid electrolyte 10 by the polarization resistance method using reference electrode 11 according to the present disclosure will be described. Fig. 4 shows the results of polarization measurements taken within a range of ±10 mV of the natural potential of iron. The polarization resistance value of iron is the slope of the approximate value line of the measured values.

[0037] Polarization resistance is proportional to the reciprocal of the corrosion reaction rate. The corrosion current density is calculated by multiplying the polarization resistance by a constant K, which is determined by the type of metal or environmental conditions. As shown in Non-Patent Document 1, etc., the constant K is generally set to 0.026 V for steel corrosion in concrete.

[0038] In Non-Patent Document 3, the corrosion current calculated by Tafel extrapolation from polarization measurements of iron in cement is on the order of 1 to 2 x 10-8 A / cm2 (= 1 x 10-4 A / m2). On the other hand, the corrosion current obtained in this measurement was 2.76 x 10-8 A / cm2. Experimental data measured using stainless steel as the reference electrode 11 also showed that measurements equivalent to those in previous studies are possible.

[0039] In the present disclosure, the reference electrode 11 used in the electrochemical measurement method in the solid electrolyte 10 is formed of a metal material whose natural potential does not change within the measurement time range in the solid electrolyte 10. The reference electrode 11 according to the present disclosure enables electrochemical measurements even in a solid electrolyte 10 with little moisture. For example, the reference electrode 11 is embedded in a concrete structure to be measured before the concrete structure hardens. The embedded reference electrode 11 can be used to measure rebar corrosion in a dry concrete structure that has not been sprayed with water.

[0040] The present disclosure is not limited to the above-described embodiments, and various modifications are possible within the scope of the present disclosure.

[0041] REFERENCE SIGNS LIST 1 Measuring device 10 Solid electrolyte 11 Reference electrode 12 Working electrode 13 Counter electrode 14 Resin 15 Lead wire

Claims

1. A reference electrode made of a metallic material whose natural potential does not change within the time range of electrochemical measurements in a solid electrolyte.

2. The reference electrode according to claim 1, wherein a protective coating is formed on the surface of the metal material within the solid electrolyte.

3. The reference electrode of claim 1, wherein the reference electrode is embedded in the solid electrolyte before the solid electrolyte hardens.

4. A measurement method comprising: embedding a reference electrode in a solid electrolyte before the solid electrolyte hardens; performing electrochemical measurements using the reference electrode; and forming the reference electrode from a metal material whose natural potential does not change within the solid electrolyte within the time range of the electrochemical measurements.

Images