JP2018004283A - Reference electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reference electrode excellent in potential reproducibility and capable of stably obtaining potential for a long period, and moreover, capable of simply manufacturing and handling with a relatively simple structure.SOLUTION: A reference electrode 1 is embedded in concrete and used for measuring potential of a metal in the concrete. The reference electrode 1 includes: an electrode main body 2 configured of at least a top surface layer portion 21 containing a noble metal oxide; and a cement molded product 3 contacting the electrode main body 2 around the electrode main body 2 and arranged to carry out liquid conjunction to the surrounding concrete of the reference electrode 1 when used. The cement molded product 3 contains calcium hydroxide and water retaining material. The water retaining material is one or more kinds selected from a group consisting of pearlite, bentonite and magnesium nitrate.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an embedded reference electrode that can be used in a potential measurement method for monitoring corrosion of a metal embedded in concrete, for example, a reinforcing bar of a reinforced concrete structure.

  Steel materials such as iron pipes and reinforcing bars arranged in concrete structures are originally protected from corrosion by forming a passive film on the surface. However, in environments where a large amount of chloride ions are present, such as coastal areas and areas where anti-freezing agents are frequently used, the passive film is partially destroyed by contact with chloride ions in steel. There is a case. In addition, concrete is essentially alkaline due to the main component of cement, but the neutralization of the concrete due to the intrusion of carbon dioxide from the outside, and the passive film of steel that is in contact with this May be partially destroyed. Thus, iron in the steel material is eluted as iron ions from the portion where the passive film in the steel material is destroyed, and promotes corrosion (oxidation) of the steel material. In addition, due to partial corrosion of the steel material, a potential difference is generated between the corroded region (anode portion) and the non-corroded region (cathode portion) of the steel material, and electrons are passed through the steel material from the anode portion to the cathode portion. As a result, a corrosion current is generated, and the corrosion of the steel material in the anode portion further proceeds. Such corrosion of the steel material reduces the strength of the steel material itself, and in the concrete structure, the expansion of the volume of the corroded part may cause the concrete structure to crack and cause the concrete to peel off. It has become a social problem.

  As a method for preventing such corrosion of steel materials, for example, an anti-corrosion method in which an anode is installed in a concrete structure, and an electric current (anti-corrosion current) is supplied from the anode to the steel material in the concrete structure through the concrete. It has been known. In the anticorrosion method, by supplying a corrosion-proof current to the steel material, the potential difference generated between the anode part and the cathode part is eliminated, the potential of the steel material is maintained at a potential at which the corrosion reaction stops, and the corrosion current is reduced. This is a method for preventing the occurrence. In the anticorrosion method, in order to obtain an effective anticorrosion effect, a method of measuring and managing the potential of the steel material to be protected is generally used. In this potential measurement method, a verification electrode (also referred to as a reference electrode or a reference electrode) is installed in the vicinity of a steel material in a concrete structure, and a potential difference from the steel material is measured with the verification electrode.

  Conventionally, as the verification electrode, an embedded type verification electrode embedded in concrete and used is often used. For example, Patent Document 1 discloses a reference electrode in which the surface of a thin-line titanium wire is covered with a noble metal selected from the group consisting of iridium, ruthenium, hafnium, and rhodium. Yes. The potential of the reference electrode described in Patent Document 1 is determined by the oxidation-reduction potential of the noble metal oxide if the pH is constant, and the oxidation-reduction potential can be obtained by a calculation formula (Nernst equation). When directly buried in an object, the pH fluctuates due to fluctuations in the moisture content around the electrode and the chloride ion concentration, which poses a problem in long-term potential stability. In addition, when the anticorrosion is applied, a part of the anticorrosion current flows into and out of the reference electrode (causes interference), and the potential of the reference electrode fluctuates. Therefore, the measured potential of the obtained steel material is not accurate. There is a problem.

  Patent Document 2 discloses an embedded collation including a conductive metal support whose surface is coated with a metal oxide or a metal oxide mixture, and a solid electrolyte made of cementitious mortar containing the conductive metal support. An electrode is described. The reference electrode described in Patent Document 2 has a problem that the potential varies with time due to the fact that the solid electrolyte does not contain a substance having a pH buffering ability or a water retention material.

  The inventors of the present invention have previously proposed an improved technique for an embedded collation electrode including a conductor and an electrode portion disposed around the conductor (Patent Documents 3 and 4). Since the reference electrode described in Patent Document 3 contains silver particles and silver oxide particles in the electrode portion, the apparent exchange current density of the electrode reaction is greatly increased as compared with the conventional product, and the potential stability is increased. Has improved. In addition, since the reference electrode described in Patent Document 4 contains manganese dioxide and acetylene black in the electrode portion, the apparent exchange current density of the electrode reaction is significantly increased as compared with the conventional product. Because the electrode part can retain a relatively large amount of water even in a solid phase environment such as concrete, the stability of the potential is greatly improved, and the potential does not easily change over a long period of use. Has features. However, higher levels of potential reproducibility and potential stability of the reference electrode have been demanded in recent years, and there is room for further improvement. Further, even if the reference electrode satisfies these characteristics, if the structure is complicated or large, it causes a problem in terms of manufacturing cost and handling.

JP 2001-13100 A JP-A-5-10915 JP-A-6-317553 Japanese Patent Application Laid-Open No. 2015-40707

  An object of the present invention is to provide a reference electrode that is excellent in potential reproducibility, can obtain a stable potential for a long period of time, and can be easily manufactured and handled with a relatively simple configuration.

  The present invention is a reference electrode embedded in concrete and used for measuring the potential of a metal in the concrete, wherein at least a surface layer portion includes a noble metal oxide, A cement molded body that is in contact with the electrode body around the electrode body and arranged in liquid junction with the concrete around the reference electrode when in use, the cement molded body comprising calcium hydroxide and a water retaining material; The water retaining material is a reference electrode that is at least one selected from the group consisting of pearlite, bentonite, and magnesium nitrate.

  According to the present invention, even in an alkaline environment having some pH fluctuation, an anticorrosion application, and a low moisture condition, the potential reproducibility is excellent and a stable potential can be obtained for a long period of time. A reference electrode that can be easily manufactured and handled with a simple configuration is provided. The reference electrode of the present invention is particularly useful for measuring the electrode potential of a reinforcing bar in a reinforced concrete structure.

FIG. 1 is a schematic longitudinal sectional view (a sectional view in the axial direction of a verification electrode) of one embodiment of the verification electrode of the present invention. FIG. 2 is a graph comparing the relationship between the potential of the iridium oxide-coated electrode (electrode body) and the surrounding pH based on theoretical values and measured values. FIG. 3 is a graph in which measured values of potentials of iridium oxide-coated electrodes (electrode bodies) in concrete are plotted on normal probability paper. FIG. 4 is a graph showing potential changes with time in the saturated calcium hydroxide aqueous solution and in the cement molded body, more specifically, as a result of the potential stability evaluation test of the electrode body according to the present invention. FIG. 5 is an explanatory diagram of an evaluation test method for reference electrodes in Examples and Comparative Examples. FIG. 6 is a graph showing the evaluation results of the verification electrodes of the examples and comparative examples according to the evaluation test method shown in FIG. 5, more specifically, the change over time of the electrode potential of the verification electrodes in concrete.

  Hereinafter, a reference electrode of the present invention will be described based on a preferred embodiment with reference to the drawings. FIG. 1 shows a verification electrode 1 which is an embodiment of the verification electrode of the present invention. The reference electrode 1 is embedded in concrete and used to measure the potential of the metal in the concrete. The reference electrode 1 is arranged around the electrode body 2 and in contact with the electrode body 2. The cement molded body 3 and the housing body 4 for housing the electrode body 2 and the cement molded body 3 are provided.

  The container 4 forms the outer shape of the verification electrode 1 and has a hollow cylindrical shape or tube shape as shown in FIG. 1, and both ends in the axial direction, that is, the longitudinal direction X are open. The container 4 is divided into an upper part 4a and a lower part 4b by a separator 5 arranged in the hollow part, and the electrode body 2 and the cement molded body 3 are accommodated in the hollow part of the lower part 4b. The hollow portion of the upper portion 4a of the container 4 is filled with a filler 6 such as epoxy resin or silicon resin, and the opening on the upper portion 4a side is sealed with a plug 7 made of resin or the like. As the material of the container 4, any material that can be used as a container in this type of reference electrode can be used without particular limitation. For example, vinyl chloride, polystyrene, polyethylene, polypropylene, acrylic, PTFE (tetrafluoroethylene resin) ), Resins such as PVDF (vinylidene fluoride resin), PEEK (polyether-ether-ketone resin), and ceramics.

  When the verification electrode 1 is used, the cement molded body 3 is arranged so as to be electrically connected to concrete (not shown) around the verification electrode 1 via a liquid junction, that is, an electrolytic solution. That is, the opening on the lower portion 4b side of the container 4 is closed by the cement molded body 3, and the cement molded body 3 is exposed at the opening, so that the lower electrode 4b side of the reference electrode 1 having such a configuration is exposed. Is embedded in concrete according to a conventional method, the cement molded body 3 is in contact with the concrete around the reference electrode 1 at the opening on the lower portion 4b side while in contact with the electrode body 2 in the housing 4. become. Here, in the concrete around the cement molded body 3 and the reference electrode 1, there are a large number of voids called pore voids, and moisture called a pore solution exists in the voids. Since the pore solution is usually an electrolytic solution containing an electrolyte such as calcium hydroxide, which is the main component of cement or concrete, when the reference electrode 1 is used, the cement molded body 3 is connected to this through the electrolytic solution inside. Liquid junction with contacting concrete.

  As shown in FIG. 1, a conductive wire 8 is connected to the electrode body 2. One end of the conducting wire 8 is connected to the electrode body 2 in the filler 6 and the other end is connected to a measuring device (not shown), and the plug 7 that closes the opening on the upper portion 4a side of the container 4 is connected to the plug 7 It penetrates in the height direction and extends to the outside. In this way, the electrode body 2 and the measuring device are electrically connected via the conductor 8, and as described above, the cement molded body 3 arranged so as to come into contact with the electrode body 2 is provided around the reference electrode 1. By being in liquid junction with the concrete, the potential of the metal in the concrete on which the verification electrode 1 is installed can be measured by the measuring device.

  The electrode body 2 has a mesh shape and has a plurality of apertures 2H that penetrate the electrode body 2 in the thickness direction. In the present invention, the shape of the electrode main body is not particularly limited, and may be, for example, a rod shape or a plate shape extending in the longitudinal direction X of the verification electrode 1, but in order to improve the electrical performance of the verification electrode, It is preferable to increase the contact area with the cement molded body 3 as much as possible, and from this viewpoint, a mesh shape as shown in FIG. 1 can be exemplified as a preferable shape of the electrode body. The dimensions and the like of each part of the mesh electrode body 2 can be arbitrarily set.

  As shown in FIG. 1 in an enlarged manner, the surface layer portion 21 of the electrode body 2 is configured to include a noble metal oxide. That is, the electrode body 2 includes a network-like base material 20 and a surface layer portion 21 that covers the surface of the base material 20, and the surface layer portion 21 contains a noble metal oxide. That is, in the verification electrode 1, the surface layer portion 21 of the electrode body 2 and the cement molded body 3 are in contact with each other. The base material 20 is desirably excellent in corrosion resistance from the viewpoint of extending the life of the electrode body 2, and from this viewpoint, the material of the base material 20 is preferably titanium, tantalum or niobium. In the present invention, it is sufficient that at least the surface layer portion of the electrode body includes a noble metal oxide, and the entire electrode body may be a noble metal oxide.

  Examples of the noble metal oxide used for the surface layer portion 21 of the electrode body 2 include iridium oxide, ruthenium oxide, and palladium oxide, and these can be used alone or in combination of two or more. Since these noble metal oxides have a high exchange current density in the oxidation-reduction reaction (electrode reaction), even if a minute current flows, the potential of the reference electrode does not fluctuate and a stable potential can be measured.

  One characteristic configuration of the reference electrode 1 is that the cement molded body 3 containing the electrode body 2 containing such a noble metal oxide contains calcium hydroxide and a water retention material. That is, the reference electrode 1 uses the oxidation-reduction potential obtained between the noble metal oxide contained in the surface layer 21 of the electrode body 2 and the noble metal constituting it as a reference. Is provided with a cement molded body 3 containing calcium hydroxide and a water retention material, thereby realizing a system that suppresses fluctuations in the pH value and moisture content around the electrode body 2, and its redox potential. As a reference, the electric potential of the steel material embedded in the concrete around the reference electrode 1 is measured. Such an oxidation-reduction potential in the reference electrode 1 can be said to be a purely reversible potential electrochemically, so that the potential of the electrode body 2 becomes stable for a long period of time, and the potential reproducibility is improved. That is, by arranging the cement molded body 3 containing calcium hydroxide and a water retaining material so as to be in contact with the electrode body 2 around the electrode body 2, the pH value and water content inside the reference electrode 1 are stabilized. Therefore, it is possible to accurately measure the potential of the steel material and the anode for cathodic protection that are embedded in the concrete, and it becomes possible to easily monitor the corrosion protection of the steel material and to maintain and manage the cathodic protection.

Hereinafter, the reason why the inventors have come up with such a characteristic configuration of the verification electrode 1 will be described.
An electrode (hereinafter also referred to as a specific electrode) having a metal titanium base material and a coating containing a noble metal oxide on its surface (hereinafter also referred to as a specific electrode) is widely used as an insoluble metal electrode for electrolysis in an electrolysis process in the field of electrolysis industry. It is also used as a pH electrode. For this reason, the inventors estimated that the potential of the specific electrode depends on the pH value of the environment and is determined by the redox potential of the noble metal oxide and the noble metal constituting the noble metal oxide.

Therefore, in order to confirm the above estimation, the present inventors prepared an electrode in which the surface of metal titanium was coated with iridium oxide (IrO ₂ ) as the specific electrode, and the iridium oxide-coated electrode was used as an electrolyte solution having a pH of 1 to 13. It was immersed and the potential of the electrode during the immersion was measured. In FIG. 2, the measured value of the potential is shown together with the theoretical value. The theoretical value of this potential is the redox potential of iridium oxide derived from the redox reaction represented by the following formula (1) using the Nernst equation represented by the following formula (2). As shown in FIG. 2, the measured value and the theoretical value show almost the same values at each pH value, whereby the potential of the iridium oxide-coated electrode depends on the redox potential of iridium oxide existing on the surface layer portion of the electrode. You can see that it is determined. Based on this, the present inventors estimated that the iridium oxide-coated electrode, that is, the specific electrode exhibits a substantially constant potential in an environment where the pH value is relatively stable, for example, in concrete.

  Therefore, in order to confirm the above estimation, the present inventors actually embedded an iridium oxide-coated electrode in concrete and measured the potential with reference to a saturated silver chloride reference electrode (Silver Silver-Chloride Electrode). FIG. 3 shows a graph in which measured values of the potential are plotted on normal probability paper. If the points plotted on the normal probability paper (measured values of potential) are aligned, a normal distribution is determined. The average value of the actually measured values was close to the oxidation-reduction potential of iridium oxide in the vicinity of pH 12.5. However, as shown in FIG.

  From the above results, the present inventors have determined that the potential of the steel material in the concrete is not changed in the specific electrode in which the surface of the base material made of metal titanium, such as an iridium oxide-coated electrode, is coated with a layer containing a noble metal oxide. It was concluded that it was difficult to use as a reference electrode for measurement. Therefore, as a result of repeated studies, the present inventors considered that the cause of the variation in potential as shown in FIG. 3 is related to the variation in pH value and moisture content at the interface between the specific electrode and the concrete. As a result, a cement molded body is arranged around the specific electrode so as to be in contact with the specific electrode, calcium hydroxide as a pH buffering agent and a water retention material for maintaining a stable moisture content in the cement molded body. As a result, it was found that the variation in pH value and water content at the interface between the electrode and concrete, which caused the variation in potential, was reduced, and the potential reproducibility and potential stability were improved. The present invention has been made based on such knowledge.

  The cement molded body 3 is a cured product of a cement composition containing cement, a water retention material, calcium hydroxide, and water. Usually, a curing period is secured until the cement composition is hardened to become a cement molded body 3. The cement composition may further comprise fine aggregates such as river sand, mountain sand, land sand, sea sand, crushed sand, quartz sand or mixtures thereof. The cement molded body 3 is easy to manufacture because it can be obtained simply by preparing a cement composition and curing it, and the cement composition, which is an intermediate product, has fluidity. Operations such as pouring into the body 4 can be performed relatively easily, and workability is excellent. Moreover, the cement molded body 3 is excellent in shape retention, and after the cement composition is hardened and becomes a cement molded body 3 having a predetermined shape, the predetermined shape is easily maintained. Therefore, the verification electrode 1 using the cement molded body 3 having such advantages has an advantage that it can be easily manufactured and handled with a relatively simple configuration.

  The cement used for the production of the cement molded body 3 includes various portland cements such as normal, medium heat, and sulfate resistant; various mixed cements obtained by mixing these portland cements with blast furnace slag, fly ash or silica (blast furnace cement, fly ash). In the present invention, one of these can be used alone or two or more can be used in combination. However, early strength / super early strength Portland cement and alumina cement generate a large amount of heat due to heat of hydration, so it is preferable to avoid using them in the present invention. Moreover, as a preferable example of the fine aggregate that can be contained in the cement molded body 3, a fine aggregate having a content of 85% by mass or more passing through all sieves having a mesh opening of 2 mm can be given.

  Calcium hydroxide contained in the cement molded body 3 is a main component of the pore solution existing in the cement molded body 3 and has a very strong buffering capacity. The saturated calcium hydroxide aqueous solution has a pH value comparable to that of the concrete in which the verification electrode 1 is embedded. Therefore, the cement molded body 3 containing calcium hydroxide stabilizes the pH value around the electrode body 2 over a long period of time.

  The content of calcium hydroxide in the cement molded body 3 is preferably 2 to 8% by mass with respect to the mass of cement in the cement molded body 3. If the content of calcium hydroxide in the cement molded body 3 is too small, the amount of calcium hydroxide aqueous solution in the cement molded body 3 is too small. Therefore, the pH of the cement molded body 3 after the reference electrode 1 is embedded in concrete. The value may fluctuate greatly, and if the content of calcium hydroxide is too large, the unhydrated calcium hydroxide in the cement molded body 3 is gradually dissolved in water, so that the cement molded body 3 collapses. May be easier.

  The water retaining material contained in the cement molded body 3 is preferably at least one selected from the group consisting of pearlite, bentonite and magnesium nitrate. By containing such a water retaining material in the cement molded body 3, the water retention of the cement molded body 3 is improved, and the verification electrode 1 incorporating the same has superior potential stability compared to the conventional verification electrode. It will be a thing.

Perlite is an artificial foam produced by heat-treating obsidian, pearlite, pine stone, diatomaceous earth, or the like at a high temperature. Among these pearlite raw materials, pearlite, pine stone, and diatomaceous earth are particularly preferable because of their excellent water retention.
There are two types of bentonite, calcium type and sodium type, which can be used in the present invention, but sodium type bentonite having higher water absorption and swelling than calcium type is advantageous. This sodium-type bentonite is bentonite in which alkali metals such as sodium ions and potassium ions are adsorbed between layers of montmorillonite sheet-like crystals.
Since magnesium nitrate has deliquescence, even with a relatively small amount, the water retention of the cement molded body 3 can be sufficiently increased, and moisture can be retained inside the verification electrode 1 for a long period of time.

  The content of the water retaining material in the cement molded body 3 is preferably 5 to 20 with respect to the mass of the cement in the cement molded body 3 from the viewpoint of further improving the water retention and shape retention of the cement molded body 3. % By mass.

  As mentioned above, although this invention was demonstrated based on the preferable embodiment, this invention is not restrict | limited to the said embodiment. For example, the outer shape of the collation electrode of the present invention is not limited to a tubular shape like the collation electrode 1 shown in FIG. 1, and an arbitrary shape can be selected. Further, in the reference electrode 1, the filler 6 and the cement molded body 3 are separated by the separator 5, but the separator 6 is not installed and the filler 6 and the cement molded body 3 are in contact with each other. good. Further, for example, in the container 4, the portion filled with the cement molded body 3 (lower portion 4 b) may be configured to be detachable with respect to the portion filled with the filler 6 (upper portion 4 a). As a result, the maintainability of the verification electrode is improved, and the maintenance work of the electrode body 2 and the cement molded body 3 is facilitated.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the scope of the present invention is not limited to such examples.

[Test Example 1]
The potential stability evaluation test of the electrode body in the reference electrode was performed. The electrode body to be tested is an “electrode body in which the surface layer portion includes a noble metal oxide”, specifically, an electrode body A in which the surface of metal titanium is coated with iridium oxide, and metal titanium. An electrode body B whose surface was coated with ruthenium oxide was prepared according to the following (preparation of electrode body).
First, a mercury / mercury oxide reference electrode (Hg / HgO / satCa (OH) ₂ electrode) in which the electrode bodies A and B to be evaluated have a saturated calcium hydroxide as an internal solution for obtaining a relative potential with the electrode bodies A and B. ) And a saturated calcium hydroxide aqueous solution for 25 days, and the potential was appropriately measured during the immersion period. The saturated calcium hydroxide aqueous solution used here was prepared by dissolving calcium hydroxide (Yoshizawa Lime Industry Co., Ltd., special slaked lime, density 2.34 g / cm ³ ) in water (tap water from Ageo City, Saitama Prefecture). The water temperature was 20 ° C. This saturated calcium hydroxide aqueous solution simulates pore void water in concrete.
Thereafter, the electrode bodies A and B taken out from the saturated calcium hydroxide aqueous solution are embedded in a cement molded body together with a mercury / mercury oxide reference electrode for obtaining a relative potential with the electrode bodies A and B for a predetermined period. Continuous measurement was performed with a data logger. The cement molded body used here was produced according to the following (production of a cement molded body).

(Production of electrode body)
Electrode body A (iridium oxide-coated electrode) was produced by the following procedure. That is, after a solution prepared by dissolving iridium chloroidic acid in n-butanol was applied to a 13 mm × 30 mm titanium mesh material spot-welded at one end with a titanium wire with a brush, the mesh material was baked to produce electrode body A. Got.
The production method of the electrode body B (ruthenium oxide-coated electrode) is the same as the production method of the electrode body A except that ruthenium chloride is used instead of iridium chloride in the production method of the electrode body A. .

(Preparation of cement molding)
100 parts by weight of cement, 5 parts by weight of calcium hydroxide, 10 parts by weight of pearlite (water retaining material) and 28 parts by weight of fine aggregate are mixed with a mixer, and 60 parts by weight of water is added to the resulting mixture and kneaded to obtain a cement composition. I got a thing. This cement composition was cured for a predetermined time and cured to obtain a target cement molded body. Details of the materials used are as follows.
Cement: Normal portland cement manufactured by Tokuyama Corporation, specific gravity 3.16
・ Calcium hydroxide: manufactured by Yoshizawa Lime Industry Co., Ltd., special slaked lime, density 2.34 g / cm ³
Perlite: Mitsui Metal Mining Co., Ltd., Mitsui Perlite A, density 0.055 g / cm ³
-Fine aggregate: Land sand from Kakegawa, Shizuoka Prefecture, specific gravity 2.59
・ Water: tap water from Ageo City, Saitama Prefecture

FIG. 4 shows the results of Test Example 1. All measured values are values converted into values based on saturated silver chloride electrodes. In FIG. 4, the test period indicated by the symbol I corresponds to the immersion period of the electrode bodies A and B in the saturated calcium hydroxide aqueous solution, and the test period indicated by the symbol II is in the cement molded body of the electrode bodies A and B. Equivalent to the period of burial.
In the test period I, an aqueous solution having a stable pH value exists around the electrode bodies A and B. Therefore, the potentials of the electrode bodies A and B are as shown in FIG. It approximated the oxidation-reduction potential of pH 12.5 to 12.7 in the noble metal oxide (iridium oxide, ruthenium oxide) contained in the surface layer portion, and was stable over the entire period (25 days) of the test period I.
Further, in the process of transition from the test period I to the test period II, the electrode bodies A and B were slightly lower in potential, but in the test period II, the potentials of the electrode bodies A and B were noble metals as shown in FIG. It was close to the oxidation-reduction potential at pH 12.7 in the oxide and was stable. The stability of the potentials of the electrode bodies A and B during the test period II is as a result of containing calcium hydroxide and pearlite (water retaining material) in the cement molded body arranged around the electrode bodies A and B. , It is assumed that the pH value and water content around B can be maintained within an appropriate range over a long period of time.

[Examples 1 to 5 and Comparative Example 1]
An embedded type verification electrode having the same configuration as that of the verification electrode 1 shown in FIG. 1 was produced. As the electrode body 2, the electrode body A (iridium oxide-coated electrode) prepared in Test Example 1 was used.
Specifically, first, a separator 5 is provided in a hollow portion of a hollow tubular container 4 made of a hard polyvinyl chloride resin tube, and then a titanium wire connected to the electrode body A is inserted into the separator 5. The titanium wire and the conductive wire 8 were connected at the hollow portion of the upper portion 4a.
Next, after filling the opening 4 on the side of the upper part 4a of the container 4 with an epoxy resin as the filler 6, a plastic stopper 7 was installed in the opening to seal the opening.
Next, a cement composition having the composition shown in Table 1 below is poured from the opening on the lower part 4b side of the container 4 to fill the entire hollow part of the lower part 4b, and then the cement composition in the hollow part is set to 1 at room temperature. It was cured and cured to obtain a cement molded body 3. As a material of this cement composition, in addition to the material used in the above (preparation of cement molded body), bentonite (TB-250 manufactured by Tachibana Material Co., Ltd., apparent specific gravity 0.68) as a water retaining material is further used. used. The opening on the lower 4b side of the container 4 is completely closed by the cement molded body 3, and the outer surface of the cement molded body 3 closing the opening is the end face of the opening on the lower 4b side of the container 4 It was one. In this way, the intended embedded reference electrode was produced.

[Test Example 2]
About the reference electrode of each Example and a comparative example, the time-dependent change of the electric potential in concrete was measured with the following method. Specifically, as shown in FIG. 5, a concrete specimen 90 (length 800 mm × width 400 mm × height 200 mm) in which reinforcing bars 91 having a diameter of 9 mm are embedded in a lattice shape is produced. On the upper surface, using an electric drill, seven reference electrode installation holes having a diameter of 26 mm and a depth of 50 mm were formed in a row at intervals of about 100 mm. Of the installation holes formed in this way, the other six installation holes excluding the installation hole located in the center are provided with the verification electrode to be tested indicated by reference numeral 10 in FIG. 5, and the installation holes located in the center. In order to secure a liquid junction with the concrete, a mercury mercury oxide reference electrode 11 for determining the relative potential of the reference electrode 10 is filled from above the gel after filling a gel of a saturated calcium hydroxide aqueous solution. Plugged in and installed. The electrolyte inside the reference electrode 11 is a solid electrolyte made of a gelled saturated calcium hydroxide aqueous solution. And while connecting the conducting wire 10L extended from the collation electrode 10 to the plus terminal of the measuring device (high resistance voltmeter) 12 arrange | positioned outside the concrete test body 90, conducting wire 11L extended from the reference electrode 11 is connected. Connected to the minus terminal of the measuring instrument 12, and in that state, the change with time of the potential of the reference electrode 10 was measured according to a conventional method.

  FIG. 6 shows the results of Test Example 2. As shown in FIG. 6, the potential of the reference electrode of Comparative Example 1 fluctuated and became noble over time, whereas the potentials of the reference electrodes of Examples 1 to 5 were all stable in the concrete for a long time. It can be seen that the cement molded bodies of the reference electrodes of Examples 1 to 5 maintained appropriate pH values and moisture amounts. The potential in FIG. 6 is a value converted to a saturated silver chloride reference electrode (Silver Silver-Chloride Electrode).

DESCRIPTION OF SYMBOLS 1 Reference electrode 2 Electrode main body 20 Base material 21 Surface layer part 3 Cement molded object 4 Container 4a Upper part of the container 4b Lower part of the container 5 Separator 6 Filler 7 Plug 8 Conductor

Claims (2)

A reference electrode embedded in concrete and used to measure the potential of a metal in the concrete,
An electrode body having at least a surface layer portion containing a noble metal oxide; and
A cement molded body arranged around the electrode body so as to come into contact with the concrete around the reference electrode and in use when in contact with the electrode body;
The cement molded body includes calcium hydroxide and a water retention material, and the water retention material is at least one selected from the group consisting of pearlite, bentonite, and magnesium nitrate.   The reference electrode according to claim 1, wherein the noble metal oxide is at least one selected from the group consisting of iridium oxide, ruthenium oxide, and palladium oxide.