JPH07109410B2 - Portable sensor for corrosion exploration - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a reference electrode and / or a reference electrode used for measuring an electrode potential and a corrosion rate of a metal in a corrosive environment.
Or, it relates to a portable sensor for corrosion exploration that also serves as a counter electrode.

[0002]

2. Description of the Related Art Metal structures (mainly steel) in seawater, freshwater or soil are constantly exposed to corrosive environments. In order to accurately grasp the corrosion status of metals in this corrosive environment, it is an important issue to develop a corrosion diagnosis technique that is more accurate and easy to implement for engineers involved in corrosion and corrosion prevention.

As means for ascertaining the corrosion or anticorrosion status of metals, in addition to environmental surveys (temperature, pH, environmental resistance, environmental components, etc.) in which the metal is placed, various kinds of electricity represented by potential or polarization resistance are used. Chemical factors are being measured. In recent years, in particular, the estimation of the corrosion rate of metals in the environment by measuring polarization resistance has been actively carried out. Polarization resistance is at the core of today's metal corrosion diagnostics, and is an essential element in conjunction with spontaneous corrosion potential and environmental resistance measurements.

Regarding these electrochemical measuring methods,
In "Corrosion prevention technology", 28, No. 3, 1979, many articles are introduced including "Corrosion monitoring by electrical measurement (special feature)".

In a laboratory test, the measurement of these elements has a large degree of freedom, so there is no particular problem. However, in the case of a device or a structure at a practical site, the size of the device or the structure is large. Since various constraints such as structure, location, time, etc. are imposed, measurement is not easy, and there is a problem in the accuracy and failure of the measuring instrument accompanying the movement of the measuring device.

As an example for easily measuring the above-mentioned spontaneous potential, polarization resistance and environmental resistance in real time in the field, JP-A-58-208654 and JP-A-5-58654 are available.
Japanese Patent Publication No. 9-190647 introduces an apparatus for diagnosing corrosion of a metal structure in soil. In addition,
Japanese Patent No. 27384 and Japanese Patent Laid-Open No. 63-315941 introduce a method and an apparatus for measuring and diagnosing the corrosion state of the reinforcing bar of a reinforced concrete structure.

Of these, the former two cases deal with soil as a corrosive environment, while the latter two cases deal with reinforced concrete, but essentially consist of three parameters of spontaneous potential, polarization resistance and environmental resistance. The measurement method, measurement items, and estimation method are not different.

These electrochemical measurement parameters basically consist of three electrodes: a target sample electrode, a counter electrode (mainly an insoluble anode such as platinum) and a reference electrode (sweet potato electrode, silver chloride electrode, mercury oxide electrode, etc.). Utilizing this method, the electrodes are combined according to the measurement item, and the measurement is performed while moving the electrode, the measuring instrument, and the recording instrument to the measurement location.

That is, the natural potential of the sample electrode (metal body to be measured) is measured using the reference electrode, and the polarization resistance and the environmental resistance around the sample electrode are measured using the reference electrode and the counter electrode. As a measuring instrument, a commercially available three-electrode type corrosion monitor or the like can be used. In addition, a measurement data recording device, an analysis device, etc. are attached.

As for the natural potential, the voltage between the reference electrode in the sensor and the metal body to be measured is measured with a voltmeter having a high input resistance. The lower the impedance in the sensor including the reference electrode, the more the S / N ratio is increased. Highly accurate potential measurement is possible.

To measure the polarization resistance, a minute current is passed from a measuring instrument to a metal body through a sensor, the polarization of the metal body is measured, and it is determined from the voltage-current ratio. The current is a low frequency alternating current (usually 0.1 Hz). the following square wave or sine wave) or 1
A DC pulse current of 0 second to several minutes is used. The measured polarization voltage includes the environmental resistance between the reference electrode and the metal body and the IR drop due to the measurement current. Except for this, it is customary to correct the polarization resistance by superimposing a high-frequency (about 1 KHz) AC on the low-frequency AC or DC measurement current in order to obtain the correct polarization resistance, and measuring the environmental resistance by this high-frequency AC. is there.

As described above, in the measurement of the polarization resistance, the measuring instrument and the measuring cable are required to have stable frequency characteristics ranging from low frequency (direct current) to high frequency, and the impedance of the sensor is also greatly related to this.

Reinforced concrete structures used in large structures such as bridges, bridges and buildings (hereinafter,
It is not easy to carry out the corrosion survey with these measuring devices when conducting the corrosion survey of the rebar of the RC structure) because of the limitation of the installation site and the instability of the scaffold.
In particular, when the number of measurement points is wide and wide, the handling and transportation of the device associated with the movement of each electrode becomes complicated, and the labor of the measurer increases, which may affect the reliability of the measurement data. For example, if the reliability of the data is maintained even if the measurement cable is lengthened, the frequency of movement of the measuring devices can be reduced, and the burden on the measurer can be reduced.

Self-potential, which is the three parameters for corrosion diagnosis,
Indispensable for the measurement of polarization resistance and environmental resistance is a reference electrode or a cell structure sensor having a reference electrode and a counter electrode built therein.

A sensor having a cell structure incorporating a reference electrode and a counter electrode is disclosed in the above-mentioned Japanese Patent Publication No. 1-27384 and Japanese Patent Laid-Open No. 63-315941. It is an excellent means for non-destructive corrosion diagnosis of RC structures in the field, but because the cell structure with the built-in reference electrode and counter electrode makes the sensor large, it is easy to measure. It does not exceed the range of 3-electrode system measurement consisting of a counter electrode and a sample electrode.

If the reference electrode itself can also serve as the counter electrode, the device can be simplified, the impedance of the sensor can be lowered, and a long cable can be used, so that the measurement complexity can be alleviated.

Focusing on this point, the present inventors have conducted diligent research and expanded the surface area of the metal forming the reference electrode to the full extent of the case of the reference electrode. As a result, a unipolar sensor having only a reference electrode having a counter electrode function was developed and applied for a patent (Japanese Patent Application Nos. 2-3553 and 2-21498).
No. 2).

The sensor disclosed herein is a cell composed of a conventional counter electrode (mainly Pt) and a reference electrode (sweet potato electrode, silver chloride electrode, etc.) by expanding the operating surface area at least over the entire cross section of the electrode container. Compared to the two-pole type sensor, (1) gas generation due to energization is prevented, a sensor with a completely sealed structure for the field is possible, and (2) therefore, it is possible to use it upside down, all posture type measurement (3) The conventional reference electrode has a high impedance, and it was difficult to measure in a high resistance environment due to the influence of noise, but since the impedance was lowered, the measurement became easier, and (4 ) Furthermore, the effect that the restriction on the use of the long measuring cable necessary for the field measurement was relaxed was obtained.

Thus, with these sensors,
Since the conventional 3-electrode type sensor has a high impedance in the measurement system, the use of a long cable causes the measurement to be inaccurate due to the influence of stray capacitance and noise, and in addition, it has been difficult and troublesome to handle and transport. It has become possible to greatly reduce things.

In these applications, the sweet potato electrode (Hg / Hg ₂ Cl ₂ / Cl) which is widely used as a reference electrode is used.
^-), and silver chloride electrode (Ag / AgCl / Cl ^-), etc. are those using, as the case section entire surface is covered with mercury for calomel electrode, the silver chloride electrode the area of the silver case section entire And silver chloride treatment, and a mixture of silver powder and silver chloride is made into a paste with a potassium chloride solution and laminated.

In any case, the potential of the reinforcing bar of the RC structure is 10 to 20 mV without largely changing the basic structure such as the size and size of the conventionally used reference electrode.
When the current required for polarization was 1 mA or less, the reference electrode exhibited low polarizability, that is, 2 mV or less, and especially the above-mentioned Amano electrode and silver chloride electrode exhibited low polarizability of 1 mV or less.

Among the low-polarization reference electrodes, which are the main constituents of these sensors, the saturated sweet syrup electrode and the mercury oxide electrode use mercury and mercury compounds, which are unfavorable in terms of environmental pollution. Usage is increasing.

The silver chloride electrode can be easily prepared by immersing silver whose surface is chlorinated in a predetermined chloride solution. However, since the absolute amount of silver chloride coating the silver surface is small, long-term stability is ensured. Has the drawback of lacking. A high-concentration chloride solution (saturated potassium chloride) may be used as the electrode solution so that the concentration does not change, but the solubility of silver chloride in such a high-concentration solution remarkably increases, leading to early consumption. There is a drawback that it will end up.

An electrolytic method is generally adopted as a method for forming a silver chloride layer by chlorinating the surface of silver, but in order to form a sufficient amount of silver chloride layer for extending the life of the electrode. However, it takes a lot of time to prepare an electrode, and the thick film silver chloride layer has a large electrode resistance, which may act as an insulating layer and make the measurement of the electrode potential impossible. Furthermore, since strong impact and deformation during storage and use tend to cause peeling of the silver chloride layer, it is not suitable for practical use as it must be handled with care.

[0025]

SUMMARY OF THE INVENTION According to the present invention, the electrode area of the silver chloride electrode can be made larger without changing the size of the sensor container, which is easy to handle and manufacture, and also serves as a counter electrode, which has low polarizability and long-term performance. It is an object of the present invention to provide a sensor for corrosion inspection including a reference electrode having the above stability.

[0026]

As described above, the inventors of the present invention have filed prior applications (Japanese Patent Application No. 2-3553, Japanese Patent Application No. 2-21).
4989, JP-A-3-251756), an electrode in which the electrode surface area of the conventional reference electrode is spread over the entire case may be a two-electrode polarization resistance measurement sensor having both a reference electrode and a counter electrode. In addition to the above, it was shown that by adding silver powder to the electrode components, it is possible to obtain even lower polarization. The present inventors have accomplished the present invention by examining the action of this silver powder in more detail and clarifying the means for obtaining the maximum low polarization.

That is, according to the present invention, in a silver chloride-based reference electrode, (1) silver powder particles having a diameter of 1 mm or less and silver chloride powder are mixed on a surface of a silver plate or a silver wire in a weight ratio of more than 0.2 to 5.0. Spread the mixed layer over the entire cross section of the electrode case, or
Alternatively, (2) a silver powder layer having a diameter of 1 mm or less is spread over the entire cross section of the electrode case, a silver chloride powder layer is disposed below the layer, and a gel-like potassium chloride solution containing a water-absorbent polymer resin is filled under the silver chloride powder layer. Is a portable sensor for corrosion exploration.

Hereinafter, the portable sensor for corrosion detection of the present invention will be specifically described with reference to the drawings.

FIG. 1 is a partially cutaway sectional view showing an example of a portable sensor for corrosion exploration according to the present invention. In the figure, 1 is a filler, 2 is a silver plate or silver wire, 3 is a rubber stopper,
Reference numeral 4 indicates a silver powder / silver chloride powder mixed layer, 5 indicates a saturated potassium chloride solution containing a water-absorbing polymer resin, and 6 indicates a porous material such as a sponge. In the figure, on the surface of the silver plate or the silver wire 2, silver powder particles of 1 mmφ or less and silver chloride powder are mixed in a weight ratio of 0.2.
A layer (silver powder grain / silver chloride powder mixed layer) 4 mixed at a ratio of super to 5.0 is spread over the entire cross section of the electrode case.
If the weight ratio of silver powder particles to silver chloride powder is 0.2 or less or more than 5.0, good polarization characteristics cannot be obtained. Further, a gel-like potassium chloride solution 5 containing a water-absorbent polymer resin is filled in the lower part of the silver powder grain / silver chloride powder mixed layer 4.

FIG. 2 is a partially cutaway sectional view showing another example of the portable sensor for corrosion detection according to the present invention. In the figure, the same reference numerals as those in FIG.
Indicates a silver powder layer, and 8 indicates a silver chloride powder layer. In the figure, a silver powder particle layer 7 having a diameter of 1 mm or less is spread over the entire cross section of the electrode case, and a silver chloride powder layer 8 is arranged under the silver powder particle layer 7, and a water-absorbing polymer resin is further provided below the silver chloride powder layer 8. It is filled with the contained gelled potassium chloride solution 5.

The sensor of the present invention having such a structure has about 5 in consideration of easy transportation and handling in the field measurement.
It is a container (case) of 0 mmφ or less and 200 mmL or less. With this sensor, the potential is stable over a long period of time and has low polarizability (1 mV or less) in a wide current range. Further, this sensor is effective as a reference electrode for normal potential measurement which does not require a current to flow, and also as a reference electrode with improved potential stability.

[0032]

[Function] By adding silver powder particles to the constituent elements of the electrode of the silver chloride electrode type sensor, the contact area between silver and silver chloride can be remarkably increased, which facilitates the production of a reference electrode having good stability. Not only the current is RC
0.1mA usually used when measuring the polarization resistance of structures
Of course, 1 mV or less is secured even at 10 mA, and the fluctuation is small even after repeated use, so even if it shows a considerable corrosion rate in a low resistance environment such as river water or seawater, polarization will occur at a current of 10 mA or less. If the resistance measurement is completed, it can be sufficiently measured.

A two-pole type polarization resistance measuring sensor, which has been conventionally used in combination with a counter electrode (mainly platinum) and a reference electrode (reference electrode), becomes a one-pole type sensor having only a reference electrode having a counter electrode. It has been improved in performance.

By expanding the contact area using silver powder, the influence of noise is reduced even in a high resistance environment, and not only accurate measurement is possible, but also the impedance of the potential measuring system can be lowered. Therefore, even if a long measurement cable is used, the attenuation of high-frequency alternating current for environmental resistance measurement is small, so that the restriction on measurement is relaxed and the measurement accuracy is improved.

Further, since the counter electrode and the reference electrode are integrated, the electrode shape is the same as the sensor end surface, so that the current distribution in the sensor is homogenized throughout and the sensor shape can be miniaturized. Became.

Further, in the conventional silver chloride electrode, a thin layer of silver chloride was formed on the surface of silver by electrolytic treatment, but a mixed layer of silver powder particles and silver chloride powder or a silver powder particle layer and silver chloride powder layer in the present invention is used. As a result, the presence or absence of the electrolytic silver chloride layer had almost no effect on the low polarizability, and electrolytic silver chloride treatment became unnecessary.

In addition, the electrode reaction of the sensor of the present invention is
Since it is a single redox reaction that does not generate gas, it does not require a degassing device inside the sensor that is caused by energization, and it is possible to fill the inside with a solid substance. There is no void inside even when used in various postures.

[0038]

The present invention will be described below with reference to examples, but the present invention is not limited thereto.

Example 1 A sensor having the shape of FIG. 1 having an electrode inner diameter of 28 mmφ and an electrode cross-sectional area of 6.15 cm ² was prepared by varying the mixing ratio (weight ratio) of silver powder particles of 1 mm or less and silver chloride powder as follows. . The size and amount of the silver powder were kept constant, only the silver chloride powder was varied, and the size of the silver powder was substantially spherical and under a Tyler standard sieve 200 mesh (about 0.07 mm) sieve.

The electrode potential and polarization when fed a rectangular square wave constant current of 1mA and (Delta] E) was measured and the results are shown below. (1) Mixing ratio of silver powder particles: silver chloride powder 1: 5, electrode potential (mV, SCE) -46, polarization amount (ΔE, mV) 0.9
3 (2) Mixing ratio of silver powder particles: silver chloride powder 1: 2, electrode potential (mV, SCE) -46, polarization amount (ΔE, mV) 0.4
2 (3) Mixing ratio of silver powder particles: silver chloride powder 2: 1, electrode potential (mV, SCE) -46, polarization amount (ΔE, mV) 0.0
8 (4) Mixing ratio of silver powder particles: silver chloride powder 5: 1, electrode potential (mV, SCE) -46, polarization amount (ΔE, mV) 0.0
5

As shown above, as the weight ratio of silver powder particles / silver chloride powder decreases, the low polarizability deteriorates, but even with 1/2 or half the amount of silver chloride powder, the polarization amount is 1 mA. Is 0.5 mV or less . The ratio of ⅕ is practically the limit ratio, and the polarization amount remarkably increased when the ratio of silver powder particles was further decreased. The higher the proportion of silver powder particles, the greater the effect of increasing the operating area, and the low polarizability is maintained for an extremely long period of time.

On the other hand, since the electrode potential is not affected by the mixing ratio, it is assumed that the lifetime of this type of sensor is extremely long. The electrode potential of this type of electrode shows a value which is practically in agreement with the theoretical value of -45.6 mV except immediately after the production of the electrode.

Example 2 The diameter of the silver powder particles was changed as follows, and the inner diameter of the electrode was 28 m.
A sensor having a shape of FIG. 1 having mφ and an electrode cross-sectional area of 6.15 cm ² was prepared. The weight ratio of silver powder / silver chloride powder is 5 /
It was 1.

The electrode potential and polarization when fed a rectangular square wave constant current of 1mA and (Delta] E) was measured and the results are shown below. (1) Silver powder grain size 200 mesh under (about 0.
07 mm), electrode potential (mV, SCE) -46, polarization amount (ΔE, mV) 0.05 (2) Silver powder grain size 32 to 18 mesh (0.1 to 1)
mm), electrode potential (mV, SCE) -46, polarization amount (Δ
E, mV) 0.61 (3) Silver powder grain size 10 to 5 mesh (about 2 to 4 m)
m), electrode potential (mV, SCE) -46, polarization amount (Δ
E, mV) 1.25

As shown above, as the size of the silver powder particles increases, the polarization characteristics decrease, and 1 m at 1 mA.
In order to obtain a polarization value of V or less, it is necessary that the average size of the silver powder particles does not exceed 18 mesh under (about 1 mm).

Examples 3 to 4 and Comparative Examples 1 to 3 Five kinds of sensors were prepared with the following constitutions. (1) Silver plate / silver powder particles / silver chloride powder / saturated potassium chloride solution (Example 3) (2) Silver plate / (silver powder particles + silver chloride powder) / saturated potassium chloride solution (Example 4) (3) Silver plate / Silver chloride treatment / (silver powder grain + silver chloride powder) / saturated potassium chloride solution (Comparative example 1) (4) Silver plate / silver chloride treatment / saturated potassium chloride solution (Comparative example 2) (5) Saturated sweet potato electrode (Comparative example) 3)

Each of these sensors had an electrode inner diameter of 28 mmφ and an electrode cross-sectional area of 6.15 cm ² . Also,
In Example 4, the mixing ratio of the silver powder particles and the silver chloride powder was 2:
1 and 200 mesh (about 0.07 mm) silver powder particles were used. Further, in Comparative Example 1, the mixing ratio of silver chloride powder was set to 1: 5.

For these sensors, 0.1 Hz
Rectangular square wave constant current: a polarization value in (Peak-to Peak peak-peak value) both shown in FIG. 3 shows the time course of the electrode potential in FIG.

As shown in FIG. 3, the potential ΔE of Examples 3 to 4 in which silver powder particles are laminated or mixed is 1 mV even if the potential ΔE is 10 mA.
In the following, extremely low polarizability was exhibited, and the effect of repeated measurement was not recognized. Potential ΔE of Comparative Example 3
Is 1 mV or less at 1 mA, but polarization is increased at 2 mA or more, and a large difference in polarization characteristics is observed between Examples 3 and 4. However, for example R
In the corrosion diagnosis of C structure, the current is usually 0.1mA.
Therefore, it can be practically used as a sensor without any problem.

Comparative Example 1 is an example in which the ratio of silver powder particles / silver chloride powder = 1/5, which is the largest ratio of silver chloride powder, is ΔE at 1 mA and ΔE is 1 m.
Although it is V or less, a sharp increase in polarization is observed at a current of 2 mA or more as in Comparative Example 3.

Comparative Example 2 is a conventionally used silver chloride electrode, but the polarization value at 1 mA was slightly over 1 mV, showing the result of the poorest polarization characteristics. In Comparative Examples 1 and 2, a silver chloride thin layer is provided on the surface of silver by electrolytic treatment, whereas in Examples 3 and 4, a silver chloride thin layer is not provided, but the polarization value is hardly affected. Neither was observed, nor was there any difference in electrode potential. That is, it was found that the silver chloride treatment is not always a necessary condition for the sensor of the present invention.

FIG. 4 shows the stability of the electrode potential (vs. SCE) of the sensors of Examples 3-4 and Comparative Examples 1-2. It can be seen that the fluctuations are small and both are extremely stable.

In any case, as a sensor for corrosion inspection in a high resistance environment such as an RC structure, the saturated sweet-salt electrode type sensor of Comparative Example 3 as shown in FIG. 3 can be sufficiently used in practice. Is. As shown in Examples 3 to 4 of FIG. 3, the silver chloride electrode type sensor according to the present invention can measure polarization resistance with high accuracy without any problems in terms of low polarization and potential. Furthermore, the sensor according to the present invention is
It can be judged from FIG. 3 that the polarization resistance can be sufficiently used even if it is measured in a low resistance environment such as seawater if the polarization resistance can be measured at a current of 10 mA or less.

[0054]

As described above, by using silver powder particles as a constituent material of a silver chloride electrode, one electrode which has accuracy and performance equivalent to or higher than that of a saturated sweet-salt electrode type sensor and which serves as a counter electrode and a reference electrode is obtained. In-situ sensors are possible, and in particular the greatly improved low polarizability and stability of the potential facilitate the measurement of potential and polarization resistance in a wide range of environmental resistances.

By using the silver powder particles, the electrode area can be remarkably increased in a limited electrode case, and it is possible to manufacture a small and lightweight portable sensor for site, which is also stable and serves as a reference electrode and is resistant to noise. It became easier.

[Brief description of drawings]

FIG. 1 is a partially cutaway sectional view showing an example of a portable sensor for corrosion exploration according to the present invention.

FIG. 2 is a partially cutaway cross-sectional view showing another example of the portable sensor for corrosion exploration according to the present invention.

3 is a graph illustrating the polarization properties of the various pole sensors in 0.1Hz rectangular square wave constant current.

FIG. 4 is a graph showing changes with time of electrode potentials of various silver / silver chloride electrode sensors.

[Explanation of symbols]

 2 Silver plate or silver wire 4 Silver powder grain / silver chloride powder mixed layer 5 Saturated potassium chloride solution containing water-absorbing polymer resin 7 Silver powder layer 8 Silver chloride powder layer

Claims (2)

[Claims] 1. In a silver chloride-based reference electrode, a layer obtained by mixing silver powder particles of 1 mmφ or less and silver chloride powder in a weight ratio of more than 0.2 to 5.0 on the surface of a silver plate or a wire is an electrode case cross section. A portable sensor for corrosion exploration, which is spread over the whole and further filled with a gel-like potassium chloride solution containing a water-absorbent polymer resin in the lower part. 2. In a silver chloride-based reference electrode, a silver powder grain layer of 1 mmφ or less is spread over the entire surface of the electrode case on the surface of a silver plate or a silver wire, and a silver chloride powder layer is arranged under the silver powder grain layer, and further below it. A portable sensor for corrosion detection, which is filled with a gel potassium chloride solution containing a water-absorbent polymer resin.