JPH06317553A - Reference electrode for concrete burying - Google Patents

Abstract

PURPOSE:To obtain a reference electrode which can be manufactured without much labor and which is electrochemically stable for a long time under alkali surroundings by a method wherein a silver particle and a silver oxide particle which are at a specific particle size are mixed in a specific ratio so as to form an electrode for a half-cell reference electrode. CONSTITUTION:A mixed layer in which a silver particle and a silver oxide particle at an average particle size of 1mm or lower are mixed in the ratio of (2:5) to (15:1) in terms of a weight ratio is used as an electrode 3 for a half- cell reference electrode. When the mixture weight ratio of the silver particle and the silver oxide particle is outside this range, a fault that the impedance of the electrode in a low-frequency region is raised or that the stability of a potential is worsened is caused. In addition, even when the average particle size exceeds 1mm, the same phenomenon is caused. Potassium nitrate at 0 to 10wt.% in order to reduce the potential difference between liquids caused in a concrete liquid-junction part and to prevent a drop in the Faraday impedance, acetylene black at 0 to 2wt.% in order to stabilize the water retentivity of an electrode part, and a calcium hydroxide powder at 0 to 10wt.% are mixed with the electrode 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reference electrode for burying concrete, which is installed inside a relevant environment and stably measures the electrode potential of metal.

[0002]

Corrosion of reinforcing bars in concrete structures has become a major social problem. Accurate corrosion monitoring is necessary to prevent this and take appropriate measures. Since the corrosion mechanism of rebar is an electrochemical phenomenon, the electrochemical method has recently been mainly used as a monitoring method.

By the way, in the electrochemical measurement, the existence of a reference electrode is indispensable, and a reference electrode having a stable electrode potential is necessary for highly accurate measurement. However, there is a safe and stable reference electrode that can be embedded in a solid phase environment such as concrete,
It's hard to say at this point.

As a reference electrode in electrochemical measurement, a saturated calomel electrode or a silver chloride electrode is used as an electrode which can obtain the most potential stability, but recently, from the viewpoint of pollution, the use of a silver chloride electrode is increasing. is doing.

Regarding the structure and manufacturing method of the silver chloride electrode, as disclosed in Japanese Patent Laid-Open No. 172751/1993,
A mixture of silver oxide and silver chloride is pressure-molded, 190-455
A method has been proposed in which silver is precipitated by thermally decomposing silver oxide at a temperature of ° C to prepare a mixed sintered body of silver powder and silver chloride.

However, these electrodes use chloride as an internal solution, which is not desirable as a reference electrode installed inside concrete where salt damage is a problem.
In addition, since the concrete electrode is in an alkaline environment, the reference electrode that uses a neutral salt as an internal solution not only lacks long-term stability, but also creates a liquid-potential difference at the liquid junction, which causes instability of the electrode potential. ing. The problem of the liquid-potential difference at the liquid junction is difficult to erase even when the internal solution is changed to alkaline, and is an important problem for stabilizing the electrode potential in an alkaline environment.

[0007] Further, since it is an industrial electrode, a method of directly burying a carbon electrode or zinc is adopted in the United States and the like, but there is a problem that the electrode potential depends on the environment and is not stable. .

In the field of electrochemistry, a mercury / mercury oxide electrode is recognized as the most reliable electrode as a reference electrode in an alkaline environment, but it is inevitable from a pollution standpoint as a practical electrode. I don't get.

The above-mentioned conventional reference electrode for burying concrete is a chloride aqueous solution type reference electrode used in a neutral environment, and in other cases, the electrochemical reaction has one electrode potential. It is an electrode of a simple metal that is not determined by. In the former, it is originally used for an aqueous solution system, and it has long-term water retention of internal solution, chloride outflow,
There is a problem in the occurrence of a potential difference between liquids at the liquid junction.

In the latter case, the measured electrode potential is the corrosion potential, and the potential fluctuates due to the influence of the oxidation-reduction characteristics on the environment side, so that the stability of the electrode potential cannot be obtained.

In connection with the silver / silver oxide electrode of the present invention described below, JP-A-3-172751 discloses a composition for forming a silver / silver compound electrode comprising silver oxide and a silver compound other than silver oxide. However, the function of silver oxide shown here is that which acts as a feed material of silver powder in forming an electrode composed of silver and one silver compound (mainly silver chloride), Silver oxide does not exist in the finally formed electrode system, and the oxide itself is a substance that does not participate in determining the electrode potential at all. This is completely different in function from the silver oxide contained in the electrode structure of the present invention.

[0012]

DISCLOSURE OF THE INVENTION The present invention solves these problems of the prior art, is easy to manufacture, and is used for concrete embedding which has electrochemically definable long-term stability in an alkaline environment. It is intended to provide a reference electrode.

[0013]

To achieve this object, the present invention has the following configuration. That is,
In the present invention, the average particle diameter of 1 mm is used for the electrode of the half-cell reference electrode.
Silver particles of φ or less and silver oxide particles in a weight ratio of 2: 5 to 15:
A reference electrode for burying concrete is characterized by using a mixed layer mixed at a ratio of 1.

The present invention will be described below with reference to the drawings.
FIG. 1A is a schematic sectional view showing an example of the reference electrode of the present invention, and FIG. 1B is a schematic sectional view showing another example of the reference electrode of the present invention. In the figure, 1 is a filler, 2 is a silver plate or silver wire, 3 is an electrode, 3'is an electrode solidified with gypsum, 4 is a gelled calcium hydroxide saturated solution containing a water-absorbing polymer, and 5 is porous. Each material is shown.

In FIG. 1 (a), silver particles and silver oxide particles having an average particle size of 1 mmφ or less and silver oxide particles are in a weight ratio of 2: 5 to 15: 1, preferably on the surface of a silver plate or silver wire 2 for external extraction. An electrode (silver particle / silver oxide particle mixed layer) 3 mixed at a ratio of 2: 5 to 9: 1 is spread over the entire cross section of the electrode case. If the mixing weight ratio of the silver particles and the silver oxide particles deviates from the above range, the impedance of the electrode in the low frequency range (0.1 Hz or less) increases, and the potential stability deteriorates. Also, the average particle size of silver particles is 1 mmφ
Even if it exceeds, a similar phenomenon occurs, which is not preferable.

This electrode (silver particle / silver oxide particle mixed layer) 3
In addition, 0 to 10% by weight of potassium nitrate, preferably 2-1
0% by weight, acetylene black 0 to 2% by weight, preferably 0.002 to 2% by weight, calcium hydroxide powder 0-1
0% by weight, preferably 2-10% by weight, are mixed. An irrelevant electrolyte, potassium nitrate, is mixed in order to reduce the potential difference between the liquids generated in the liquid junction of concrete and to prevent the Faraday impedance of the silver electrode from decreasing. In addition, acetylene black is mixed to make the electrode part water-retaining. Further, the calcium hydroxide powder is mixed to keep the pH stable.

A gel-like calcium hydroxide solution 4 containing a water-absorbing polymer resin is filled in the lower portion of the silver particle / silver oxide particle mixed layer 3. Examples of the water-absorbent polymer resin used here include polyethylene oxide modified product (R-30F manufactured by Sumitomo Chemical Co., Ltd.) and the like. The high viscosity gel calcium hydroxide solution is used here because the calcium hydroxide aqueous solution has a small pH difference from the concrete. The lower portion of the water-absorbent polymer resin-containing gel-like calcium hydroxide solution 4 is sealed with a porous material such as wood stopper, cork stopper, gypsum and mortar.

In FIG. 1B, instead of the silver particle / silver oxide particle mixed layer 3 and the water-absorbing polymer resin-containing gel calcium hydroxide solution 4 of FIG. 1A, silver particles / silver oxide particles are used. The above mixture was mixed, and this was mixed with gypsum dissolved in a calcium hydroxide solution to form a solidified or pasted electrode 3 ', which was filled in the entire container having the silver plate for external extraction or the silver wire 2. Then, the porous material 5 as described above
It is sealed with.

As described above, according to the present invention, a silver / silver oxide electrode, which has a small influence on pollution, is selected from the electrode system exhibiting a stable redox potential in an alkaline environment, and the electrode container is replaced without changing the sensor container. In order to increase the exchange current density,
By using powder particles and placing the mixture in the entire container, a larger electrode surface area is secured, the apparent exchange current density is increased, and the electrode potential is stabilized.

[0020]

The redox potential (E) of silver / silver oxide shows a pH-dependent electrode potential as shown by the following equation. E = 1.173-0.0591 pH (V, SHE)

In order to show this electrode potential stably, it goes without saying that the pH is constant, but the exchange current density of the electrode reaction should be increased, and further, in a solid phase environment such as concrete. In the use of, the important issue is how to retain water inside the electrode.

In the present invention, the stability of pH is maintained by using a saturated solution of calcium hydroxide, and the increase in exchange current density is dealt with by providing a layer in which silver particles and silver oxide particles are mixed. I was able to. In other words, the exchange current per unit area is the same as that of a silver plate in terms of silver particles alone, but by making the electrodes finer,
It became possible to secure a larger electrode area than a normal plate electrode in a limited space, and the apparent exchange current density could be greatly increased.

The water retention property inside the electrode is improved by mixing acetylene black in the silver particle / silver oxide particle mixed layer. Furthermore, the mixing of the irrelevant electrolyte potassium nitrate results not only in reducing the liquid-potential difference at the electrode-concrete interface, but also in increasing the exchange current density of the silver / silver oxide electrode.

[0024]

EXAMPLES The present invention will be specifically described below based on examples.

Example 1 The influence of the mixing ratio of silver particles and silver oxide particles in a saturated calcium hydroxide aqueous solution was evaluated. The evaluation method was to prepare a silver particle / silver oxide particle mixed layer adjusted to various mixing ratios to 10 mm.
The sample was placed on a platinum plate of φ, the electrode potential was measured, and the absolute value (R _p ) of the impedance at 0.01 Hz was obtained by the AC impedance method, and mutual comparison was performed. The results are shown in Table 1.
Shown in. The average particle size of the silver particles is 200 mesh.
Is.

[0026]

[Table 1]

As is clear from the results in Table 1, the effect of the weight ratio on the electrode potential was not recognized, but 0.01
The absolute value of impedance at Hz decreases as the silver particle / silver oxide particle weight ratio increases. This indicates an increase in exchange current density, and it is considered that a mixing ratio of 2/5 or more of silver particles / silver oxide particles is desirable for a practical electrode.

Example 2 In order to evaluate the influence of the silver particle size on the electrode potential and the exchange current density of the silver particle / silver oxide particle electrode, silver particles having various sizes were sieved and the size of the silver particles was changed. 10 different silver particles / silver oxide particles mixed layers (mixing ratio 9: 1)
It was placed on a platinum plate of mmφ, and the electrode potential was measured and the absolute value of impedance (R _p ) at 0.01 Hz was measured by the AC impedance method. The results are shown in Table 2.

[0029]

[Table 2]

As is clear from the results shown in Table 2, the impedance increases as the silver particle diameter increases, so in order to maintain a large exchange current density, at least the average particle diameter of the silver particles is 1 mmφ or less. It turned out to be important.

Example 3 Various silver particle / silver oxide particle electrodes shown in FIG. 1 (a) in FIG. 2 and various silver particle / silver oxide particle electrode shown in FIG. 1 (b) in concrete. The results of the potential stability test are shown in comparison with the reference electrode (No. 1) that does not consider water retention.

2 to 3, each No. Indicates the following configuration. No. 1: (silver particle / silver oxide particle electrode) / porous material No. 2: (silver particle / silver oxide particle electrode) / water-absorbing polymer-containing gelled calcium hydroxide saturated solution / porous material No. 3: (silver particles / silver oxide particles electrode) + potassium nitrate / gelled calcium hydroxide saturated solution containing water-absorbing polymer /
Porous material No. 4: (silver particle / silver oxide particle electrode) + acetylene black + potassium nitrate / gelled calcium hydroxide saturated solution containing water-absorbing polymer / porous material No. 5: (silver particle / silver oxide particle electrode) + gypsum / porous material No. 6: (silver particle / silver oxide particle electrode) + potassium nitrate + gypsum / porous material No. 7: (silver particle / silver oxide particle electrode) + acetylene black + potassium nitrate + gypsum / porous material

From the results shown in FIGS. 2 and 3, the reference electrode (No. 1), which does not take water retention into consideration, has a potential oscillation which is considered to be caused by instability of water with the passage of days, and the potential is stabilized for a long period of time. I found that there was a problem with sex.

On the other hand, No. In the reference electrodes 2 to 7, although there are some variations in the electrode potential between the electrodes,
In practice, it showed a stable potential with no problem.
Among them, the reference electrodes (No. 3 to 4, 6 to 7) to which acetylene black or potassium nitrate was added showed more stable electrode performance.

Example 4 The effect of adding potassium nitrate on the frequency characteristics of the AC impedance of the silver particle / silver oxide particle electrode is shown in FIG. In the figure, A is an (Ag + Ag ₂ O) electrode, and A
g: Ag ₂ O is 9: 1 (weight ratio). Further, B is (Ag + Ag ₂ O) + potassium nitrate electrode, and Ag:
Ag ₂ O is 9: 1 (weight ratio).

It can be seen from FIG. 4 that the mixing of potassium nitrate lowers the impedance in the low frequency region, and thus the mixing of potassium nitrate is effective for increasing the exchange current density of the silver particle / silver oxide particle electrode.

Example 5 Using the silver particle / silver oxide particle electrode shown in FIG. 1 (a),
The difference in the electrode potential measured through the mortar junction was evaluated for the case where the electrode configuration contained potassium nitrate and the case where it did not. Note that Ag: Ag ₂ O is 9: 1 (weight ratio).

[0038]

[Table 3]

As shown in Table 3, it was found that the mixture of potassium nitrate alleviates the potential difference between the liquids generated at both ends of the liquid junction.

[0040]

As described above, according to the present invention, the instability of the electrode potential under the alkaline solid-phase environment of the conventional reference electrode is improved by the powder electrode of silver particles / silver oxide particles and the water retention technique. As a result, a more stable potential can be obtained for a long time. As a result, it becomes possible to perform highly accurate electrochemical measurement in a concrete environment, and it is possible to easily and accurately monitor the corrosion protection of reinforcing bars.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing an example of a reference electrode for embedding concrete in the present invention.

FIG. 2 is a graph showing the relationship between the electrode potential of a reference electrode and the elapsed days.

FIG. 3 is a graph showing the relationship between the electrode potential of a reference electrode and the elapsed days.

FIG. 4 is a graph showing the relationship between the impedance of the reference electrode and the frequency.

[Explanation of symbols]

1: Filler, 2: Silver plate or silver wire, 3: Electrode, 3 ': Electrode solidified or pasted with gypsum, 4: Saturated gel calcium hydroxide solution containing water-absorbing polymer, 5: Porous material .

Claims (4)

[Claims] 1. An average particle diameter of 1 m is applied to the electrode of the half-cell reference electrode.
Silver particles of mφ or less and silver oxide particles in a weight ratio of 2: 5 to 1
A reference electrode for burying concrete, comprising a mixed layer mixed in a ratio of 5: 1. 2. The mixed layer is provided around the silver plate or the silver wire so as to be spread over the entire cross section of the container, and the lower part thereof is filled with a gelled calcium hydroxide saturated solution containing a water-absorbing polymer. Reference electrode for burying concrete. 3. A silver plate or a silver wire, wherein the mixed layer is solidified or pasted with gypsum dissolved in a saturated solution of calcium hydroxide, and is spread around the silver plate or the silver wire over the entire cross section of the container. Item 1. A concrete burying reference electrode according to item 1. 4. The concrete burying method according to claim 1, 2 or 3, wherein 0 to 10% by weight of potassium nitrate, 0 to 2% by weight of acetylene black, and 0 to 10% by weight of calcium hydroxide powder are mixed in the mixed layer. Reference electrode.