JP6833626B2 - Measuring device and measuring method - Google Patents

Description

The present invention relates to a technique for measuring soil moisture content and metal corrosion rate in soil.

Various metal structures are used in a state of being buried in the ground in whole or in part, as represented by infrastructure equipment such as steel pipe columns, support anchors, and pipes. Metal structures corrode due to contact with soil and deteriorate over time.

The degree of deterioration due to soil corrosion varies significantly depending on the type and properties of soil, the structure and burial conditions of metal structures, and meteorological conditions. Factors that affect soil corrosion include soil type, temperature, pH, resistivity, water content, soluble salt concentration, oxygen concentration, gases, bacterial activity, and many other factors (Non-Patent Documents 1 and 2).

Here, the soil environment is composed of three phases of soil particles, which are solid phases, and water and gas, which occupy the gaps between them. Considering that water and dissolved oxygen in water are required for the corrosion reaction, it can be said that the soil moisture content is the dominant factor of soil corrosion. Therefore, it is important to elucidate the mechanism of soil corrosion to clarify the quantitative relationship between the soil moisture content and the corrosion rate of metals existing in the soil.

As a method for measuring soil moisture content, there are a TDR (Time Domain Reflectometry) method, an ADR (Amplitude Domain Reflectometry) method, and a tensiometer method. Since the permittivity of water is much higher than that of soil particles, the permittivity of soil changes according to the amount of water. In the TDR method and the ADR method, the relationship between the dielectric constant and the moisture content is investigated in advance, and the dielectric constant is measured to convert it into the soil moisture content. Both the TDR method and the ADR method measure by burying a metal electrode rod (sensor) in the soil. The tensiometer method is a method in which a unglazed cup called a porous cup is buried in soil for measurement. When the container in the tensiometer is filled with water, the water in the container soaks into the soil and the pressure inside the container becomes negative depending on the dry state of the soil. Therefore, the soil moisture content should be calculated from the pressure at this time. Can be done.

On the other hand, a method for measuring the corrosion rate has been established in the case of metals exposed in an aqueous solution. Generally, the target metal is exposed to an aqueous solution as a sample electrode, the potential difference between the sample electrode and the reference electrode (for example, Ag / AgCl electrode) is maintained at a predetermined value, and the sample electrode and the counter electrode (sample). A method of measuring the current response flowing between the electrode and any electrode other than the reference electrode) is used. This method is called an electrochemical impedance measurement method.

When determining the corrosion rate of the sample electrode by this method, it is necessary to determine an equivalent circuit that models the corrosion reaction in an electric circuit. For example, at the interface between the metal of the sample electrode and the aqueous solution, the ions in the aqueous solution form an electric double layer, so that the sample electrode functions as a capacitance component like a capacitor on the equivalent circuit. In addition, there is resistance to a corrosion reaction in which metal atoms are eluted as cations from the metal surface of the sample electrode, and electrical resistance (resistance in the aqueous solution) received when the cations in the aqueous solution move in the aqueous solution. The former is called polarization resistance, and the latter is called solution resistance. It is known that if the corrosion reaction of a metal in a sample electrode in an aqueous solution is modeled, it can be approximated as an equivalent circuit shown in FIG. 12 (non-patented). Document 3). That is, the circuit representing the corrosion reaction of the sample electrode in the aqueous solution is approximated by a circuit in which the _{solution resistance R s} is connected in series to the parallel coupling of _{the polarization resistance R p} and the electric double layer capacitance C _dl.

Since the polarization resistance is the resistance when metal atoms are eluted as cations due to corrosion, the reciprocal of the polarization resistance is proportional to the corrosion rate. When the ionic valence of the metal is known, the current value can be calculated from the relationship between the polarization resistance and the voltage value when a predetermined voltage is applied, and this current value corresponds to the corrosion rate.

Therefore, the sample electrode, the reference electrode, and the counter electrode of the target metal are exposed to the aqueous solution, and the predetermined voltage or current is measured while measuring the voltage between the sample electrode and the reference electrode and the current flowing between the sample electrode and the counter electrode. From the electrical response when is applied, the polarization resistance can be obtained based on the equivalent circuit shown in FIG. Moreover, the corrosion rate can be obtained from the obtained polarization resistance. The case where the applied voltage or current is DC is called the DC polarization resistance method, and the case where the applied voltage or current is AC is called the AC impedance measurement method.

Morio Kadoi, 2 outsiders, "Study on Soil Corrosion of Metallic Materials (1st Report)", Corrosion Protection Technology, Vol.16, No.6, 1967, p.10-p.18 Yoshikazu Miyata, 1 outsider, "Soil Corrosion Measurement Focusing on Electrochemical Methods (Part 2)", Materials and Environment, Vol.46, 1997, p.610-p.619 Takashi Sawada, 3 outsiders, "Research on Corrosion Protection Technology for Structures and Equipment for Telecommunications", NTT Technical Journal, November 2010, p.32-p.36 Minoru Yoneda, 3 outsiders, "Real-time measurement of moisture mass transfer in a column under a constant temperature by impedance measurement method", JSCE Proceedings, Vol.11, No.579, November 1997, p.1- p.14 Takuro Matsumura, 2 outsiders, "Application of Reinforced Corrosion Inspection Method Using AC Impedance Method to Reinforced Concrete Specimens Exposed to the Coast for 7 Years", Materials, Vol.51, May 2002, p.581-p. 586

Therefore, as a method for investigating the quantitative relationship between the soil water content and the corrosion rate of metals in the soil, for example, the above-mentioned sensor for measuring the soil water content and a target for obtaining the corrosion rate are used. A method is conceivable in which the metal (sample electrode), the reference electrode, and the counter electrode are each embedded, the soil water content is measured by a sensor, and the corrosion rate is measured by using an electrochemical impedance measurement method.

However, since this method requires burying a plurality of electrodes and sensors, it is not suitable for a soil environment in which workability is significantly lower than that in an aqueous solution. In addition, since soil is composed of three phases of soil particles, water, and gas, it is not appropriate to obtain polarization resistance using a conventional equivalent circuit that considers only an aqueous solution.

The present invention has been made in view of the above circumstances, and an object of the present invention is to easily measure the soil water content and the corrosion rate of metals in soil.

In order to solve the above problems, the measuring device according to claim 1 has a voltage between a sensor unit provided with two metals of the same type insulated from each other as a metal to be corroded and an electrode for measurement, and the two metals. Alternatively, the resistance to the corrosion reaction of the metal in the soil is shown based on a predetermined equivalent circuit by using a measuring unit that applies an electric current as an AC to measure the AC impedance and the electrical response data obtained by the AC impedance measurement. and polarization resistance is calculated with a solution shows the resistance in the soil resistance, the a calculator for calculating the polarization resistance and the solution resistance of the corrosion rate and the soil moisture content of metals in the soil from each reciprocal respectively, the The two metals are covered with a housing, each has a flat exposed surface exposed from the housing, and the exposed surfaces are arranged so as to face each other at a predetermined distance. It is a feature.

In the measuring method according to claim 2 , the measuring part is buried in the soil, and a voltage or a current is applied by alternating current between two metals of the same type that are embedded in the soil and are insulated from each other and used as electrodes for measurement. The procedure for measuring the AC impedance and the polarization resistance that the calculation unit indicates the resistance to the corrosion reaction of the metal in the soil based on the predetermined equivalent circuit using the electrical response data from the AC impedance measurement. A procedure for calculating the solution resistance indicating resistance in the soil, a procedure for the calculation unit to calculate the corrosion rate of the metal in the soil and the soil water content from the inverses of the polarization resistance and the solution resistance, respectively. The two metals are covered with a housing, each has a flat exposed surface exposed from the housing, and the exposed surfaces are arranged so as to face each other at a predetermined interval. It is characterized by.

The measuring method according to claim 3 is the measuring method according to claim 2 , wherein the equivalent circuit is formed at the interface between the metal and the soil and the polarization resistance showing the resistance to the corrosion reaction of the metal in the soil. It is characterized in that it is composed of an electric double layer capacity, a solution resistance indicating resistance in soil, and a soil capacity formed in soil.

The measuring method according to claim 4 is the measuring method according to claim 3 , wherein the equivalent circuit is a series in which the solution resistance is connected in series to two parallel circuits in which the polarization resistance and the electric double layer capacitance are connected in parallel. The circuit is characterized in that the soil capacity is connected in parallel at both ends of the circuit.

According to the present invention, the soil water content and the corrosion rate of metals in the soil can be easily measured at one time. Further, it is possible to provide a measuring device and a measuring method thereof that can easily measure the soil water content and the corrosion rate of metal in the soil at one time.

It is a figure which shows the structure of the measuring apparatus. It is a figure which shows the cross section of the side surface of a sensor part, and the state of corrosion progress of metal. It is a figure which shows the cross section of the side surface of a sensor part. It is a figure which shows the cross section (a) and the lower surface (b) of the side surface of a sensor part. It is a figure which shows the cross section (a) and the lower surface (b) of the side surface of a sensor part. It is a figure which shows the cross section (a) and the lower surface (b) of the side surface of a sensor part. It is a figure which shows the side surface (a) and the cross section (b) of the upper surface of a sensor part. It is a figure which shows the measurement procedure of soil moisture content and corrosion rate. It is a figure which shows the example of the Nyquist diagram. It is a figure which shows the equivalent circuit corresponding to the structure including the corrosion reaction of metal in soil. It is a figure which shows the relationship between the reciprocal of solution resistance and soil moisture content. It is a figure which shows the equivalent circuit corresponding to the structure including the corrosion reaction of a metal in an aqueous solution.

An object of the present invention is to easily measure the soil water content and the corrosion rate of a metal in soil at one time, and to provide a measuring device for measuring the measurement and a measuring method thereof.

Therefore, in the measuring device according to the present invention, a voltage or a current is applied by alternating current between a sensor unit provided with two metals of the same type insulated from each other as a metal to be corroded and an electrode for measurement, and the two metals. Using the measuring unit that measures the AC impedance and the electrical response data from the AC impedance measurement, the polarization resistance that indicates the resistance to the corrosion reaction of the metal in the soil and the polarization resistance in the soil are based on a predetermined equivalent circuit. It is characterized by including a calculation unit for calculating a solution resistance indicating resistance and calculating the corrosion rate of the metal and the soil water content in the soil from the inverses of the polarization resistance and the solution resistance.

Further, in the measuring method according to the present invention, the measuring part is embedded in the soil, and a voltage or a current is applied by alternating current between two metals of the same type that are embedded in the soil and are insulated from each other and used as electrodes for measurement. The procedure for measuring the AC impedance and the polarization resistance that the calculation unit shows the resistance to the corrosion reaction of the metal in the soil based on the predetermined equivalent circuit using the electrical response data from the AC impedance measurement. , A procedure for calculating the solution resistance indicating resistance in the soil, and a procedure for the calculation unit to calculate the corrosion rate of the metal in the soil and the soil water content from the inverses of the polarization resistance and the solution resistance, respectively. , Is characterized by doing.

That is, according to the present invention, one sensor unit is composed of a simple structure consisting of a metal to be corroded and two metals used as electrodes for measurement, and AC impedance measurement is performed using the two metals to perform polarization resistance. And the solution resistance is calculated, and the metal corrosion rate and the soil water content in the soil are calculated from the inverses of the polarization resistance and the solution resistance, respectively. Therefore, the soil water content and the soil water content are calculated respectively. The corrosion rate of metal can be easily measured at one time.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. As shown in FIG. 1, the measuring device according to the present embodiment includes a sensor unit 1, a measuring unit 2, and a calculating unit 3.

The sensor unit 1 fixes two metals 11a and 11b of the same type, which are arranged so as to maintain electrical insulation from each other, and one surface of each of the two metals 11a and 11b in a state of being exposed to the atmosphere. A housing 12 made of resin that forms the entire sensor portion is provided.

The measuring unit 2 is electrically connected to two metals 11a and 11b of the same type included in the sensor unit 1 via individual conducting wires 4a and 4b, respectively, and is a measuring function unit that performs at least AC impedance measurement (electrochemical impedance measurement). To be equipped. The measurement function unit is composed of a circuit or a program, and is a function unit that measures impedance by applying a voltage or current between two metals 11a and 11b by alternating current.

The calculation unit 3 is connected to the measurement unit 2 via an electric cable 5, and is predetermined by using the function of recording the electrical response data of the measurement result output from the measurement unit 2 and the electrical response data. The function of calculating the polarization resistance and the solution resistance, respectively, and the function of calculating the corrosion rate of the metal in the soil and the soil water content from each inverse of the polarization resistance and the solution resistance were recorded. It has a function to display electrical response data and calculated calculation results on a monitor.

Next, the configuration and function of the sensor unit 1 will be specifically described.

As described above, the sensor unit 1 according to the present embodiment includes two metals 11a and 11b of the same type. The types of the two metals are not particularly limited, but it is preferable to use a material for which the corrosion rate in soil is to be determined. For example, general structural steel materials such as SS400, SPHC, ductile cast iron, and stainless steel are used. In the present embodiment, the two metals 11a and 11b each function as metals to be corroded.

Further, the two metals 11a and 11b of the same type included in the sensor unit 1 are arranged so as to maintain electrical insulation. This is because, in the present embodiment, the polarization resistance is measured by the AC impedance method using two electrodes. That is, in the present embodiment, the two metals 11a and 11b included in the sensor unit 1 each function as a metal to be corroded and also as an electrode for measuring AC impedance.

Here, in the sensor unit 1 according to the present embodiment, the shapes of the two metals 11a and 11b of the same type and the shapes of the portions of the two metals 11a and 11b exposed to the soil are also particularly limited. do not do. For example, the shapes of the two metals may be the same or different from each other to form a cube or a cylinder. Further, for example, the shapes of the exposed portions exposed to the soil may be flat. As shown in FIG. 2, for example, a metal plate having a certain thickness is embedded in the insulating resin of the housing 12, and the surface of the exposed portion is polished to flatten the exposed surface. Realize. If the exposed surface is flat, it becomes easy to define the exposed area of the metal, and it becomes easy to calculate the polarization resistance and the solution resistance. Further, even if the corrosion of the two metals progresses over time, a certain area is always exposed, which facilitates computational handling. Furthermore, if the exposed areas of the two metals are the same as each other, the calculation of the polarization resistance and the solution resistance becomes easier.

Further, in the sensor unit 1 according to the present embodiment, the arrangement of the exposed portions of the two metals 11a and 11b of the same type is not particularly limited. For example, as shown in FIG. 3, when the exposed portions of each other are flat, it is conceivable to arrange the exposed surfaces of each other so as to face each other at a predetermined interval. However, in this arrangement, the concentration of iron ions and iron oxides in the soil existing in the space sandwiched between the two exposed surfaces increases rapidly, and this action may affect the corrosion rate of the metal. This is because the diffusion of eluted ions and oxides in soil is not so large as in aqueous solution. In other words, if the concentration of iron ions or iron oxides eluted as the corrosion progresses in the soil existing in the space sandwiched between the two exposed surfaces, the iron elution reaction due to corrosion is restricted, which is what we originally wanted to obtain. Results different from the corrosion rate will be obtained.

Therefore, for example, as shown in FIG. 4, the exposed surfaces of the two metals 11a and 11b may be arranged so as to be on the same plane. That is, as shown in FIG. 4B, the two exposed surfaces of the metal 11a and the metal 11b are formed so as to exist in the xy plane. As a result, in the soil existing on the exposed surface, the increase in the concentration of iron ions and iron oxides due to the corrosion reaction of the metal can be kept in a state close to that when the metal is corroded in the natural environment.

Further, in the sensor unit 1 according to the present embodiment, the shape of each exposed surface of the two metals 11a and 11b of the same type is not particularly limited. For example, at least one side of the outer circumference of one exposed surface may be arranged so as to be parallel to at least one side of the outer circumference of the other exposed surface. For example, as shown in FIG. 5, there is a method of arranging the shapes of the exposed surfaces as the same rectangle. By arranging in this way, the distance between the metals (= between the electrodes) can be kept constant, and it is possible to prevent the current from locally concentrating in a region with an exposed surface during AC impedance measurement. .. When the exposed surface is rectangular, it is preferable that the length of the vertical side b is longer than that of the horizontal side a. In addition, as shown in FIG. 6, two donut-shaped metals may be concentrically connected in a shape.

Further, the two metals 11a and 11b of the same type of the sensor unit 1 according to the present embodiment function as electrodes as described above, and these two electrodes are arranged in a state of being electrically insulated from each other. There is. For example, after arranging the two metals at a predetermined interval, all but the exposed surface may be fixed with an insulating material. For example, it may be fixed with acrylic or polyethylene. Here, since the sensor unit 1 is embedded in soil, for example, as shown in FIG. 7, two metals 11a and 11b are embedded or attached to the surface of the side surface of the housing 12, and the tip portion to be embedded has a sharp plate-like structure. By doing so, workability when burying in soil can be improved. The sharp tip is for convenience when burying in soil, and it is not necessary to sharpen the ends of the two metals 11a and 11b together. However, in the present embodiment, the shape of the sensor unit 1 is not particularly limited.

Next, the function of the measuring unit 2 will be specifically described.

As described above, the measurement unit 2 according to the present embodiment includes at least a measurement function unit that measures AC impedance. The measurement function unit to be provided by the measurement unit 2 is not particularly limited, but at least, for example, an AC voltage of about ± 5 mV is applied between two metals 11a and 11b of the same type provided in the sensor unit 1, and the two are provided. It is preferable to be able to measure the response such as the current value and impedance flowing between the metals 11a and 11b (= between the electrodes). Further, the frequency width of the AC voltage is not particularly limited, but in order to measure the solution resistance and the polarization resistance, it is preferable that the frequency can be changed in a range of, for example, about 0.1 Hz to 500 kHz. Further, as described above, the sensor unit 1 and the measuring unit 2 are electrically connected to each other via the conducting wires 4a and 4b connected to the two metals 11a and 11b of the same type provided in the sensor unit 1. The electrical connection method is not particularly limited, but it is preferable to easily connect each with a lead wire.

Next, the function of the calculation unit 3 will be specifically described.

The calculation unit 3 according to the present embodiment calculates the polarization resistance and the solution resistance based on a predetermined equivalent circuit using the electrical response data of the measurement result output from the measurement unit 2, and the polarization resistance and the solution resistance. It has a function to calculate, display and record the corrosion rate and soil water content from each inverse of. The calculation unit 3 may display and record at least one or more of the polarization resistance, the solution resistance, the corrosion rate, and the soil water content. The calculation unit 3 may be any device that performs processing such as calculation, recording, and display, and can use, for example, a personal computer or a server.

Next, a method for measuring the soil moisture content and the metal corrosion rate performed by the measuring device according to the present embodiment will be described. The measurement procedure according to this embodiment is shown in FIG.

First, in step S1, the sensor unit 1 is installed in the soil. The soil may be in a natural environment or an artificially created environment, and is buried in an environment where the desired soil moisture content and metal corrosion rate can be obtained. At this time, the method of installing the sensor unit 1 should be unified for all measurements as much as possible. For example, if the exposed surface of the sensor unit 1 was installed facing downward in the direction of gravity in the previous measurement, the exposed surface of the sensor unit 1 is set in the direction of gravity even when the soil environment is changed. It is preferable to install it facing down and compare the results obtained in each measurement.

Next, in step S2, the measuring unit 2 applies a minute voltage or a minute current between two metals 11a and 11b of the same type provided in the sensor unit 1 by using the measuring function unit provided in the measuring unit 2 to perform AC impedance. Apply with alternating current. The voltage or current width to be applied is not particularly limited, but it is preferable to make the shape of the surface of the exposed surface of the two metals 11a and 11b as small as possible so as not to be changed by the influence of the measurement. For example, it may be about ± 5 mV. The measuring unit 2 measures the electrical response while changing the AC frequency of the applied minute voltage or minute current, and inputs the measured electrical response data to the calculation unit 3. The width of the AC frequency may be any range as long as the desired solution resistance and polarization resistance can be calculated, and may be changed in the range of, for example, 0.1 Hz to 500 kHz.

Next, in step S3, the calculation unit 3 sets the polarization resistance and the solution resistance based on a predetermined equivalent circuit based on the electrical response data due to the minute voltage or minute current applied from the measuring unit 2 to the sensor unit 1. Calculate the corresponding value. The electrical response data includes a voltage value, a current value, an impedance value, and the like.

Specifically, the calculation unit 3 plots the impedance value from the measurement unit 2 on a complex plane and performs curve fitting, that is, draws an impedance locus to acquire a Nyquist diagram as shown in FIG. .. The electrical response is measured while changing the AC frequency of the applied minute voltage or minute current, and the impedance change when the width of the AC frequency is changed by the above-mentioned predetermined width is used to obtain a Nyquist diagram as shown in FIG. Obtainable. The solid line curve shown in FIG. 9 is a measurement result drawn at the time of actual measurement, and the polarization resistance and the solution resistance are obtained from this curve based on a predetermined equivalent circuit.

At this time, in the present embodiment, the equivalent circuit shown in FIG. 10 is used. The equivalent circuit has two metal 11a in the soil, two and polarization resistance R _p representing respectively the resistance to corrosion reaction of 11b, the two metal 11a, two electric double each occurrence at the interface 11b and soil The multi-layer capacity C _{dl , the solution resistance R s} (= solution resistance in the soil) representing the resistance that the cations of the two metals 11a and 11b receive when moving in the soil, and the soil capacity formed in the soil. Two parallel circuits composed of C _s (= volume component in the soil) and consisting of the polarization resistance R _p and the electric double layer capacity C _dl and the solution resistance R _s in the soil are connected in series and the same. a circuit connected in parallel to the soil volume C _s across the series circuit.

The solution resistance and the polarization resistance can be calculated by interpreting the measurement result shown in FIG. 9 by the equivalent circuit shown in FIG. 10 and theoretically performing curve fitting. _{Specifically, when the equivalent circuit shown in FIG. 10 is used, the solution resistance R s} can be obtained from the width A at which the semicircle on the high frequency side (about 500 kHz) shown in FIG. 9 and the real axis intersect. _{Further, the polarization resistance R p} can be obtained from the width B where the semicircle on the low frequency side (about 0.1 Hz) and the real axis intersect. However, the width B is considered to be twice the value of _{the desired polarization resistance R p.}

At the time of curve fitting, the electric double layer capacity C _dl and the soil capacity C _s of the equivalent circuit shown in FIG. 10 may be replaced with CPE (Constant Phase Element). In addition, as a supplement, the electric double layer capacity C _dl and soil capacity C _s of the equivalent circuit shown in FIG. 10 are also included in the arc of the measurement result shown in FIG. 9 based on the electrochemical impedance measurement method. It can be calculated from the information.

Finally, in step S4 shown in FIG. 8, the calculation unit 3 simultaneously calculates information on the soil water content and the corrosion rate of the metal from the reciprocals _{of the calculated solution resistance R s} and polarization resistance R _p.

Here, it is known that the soil water content is _{proportional to the reciprocal of the solution resistance R s} (Non-Patent Document 4). However, the proportionality coefficient differs depending on the ion concentration of the soil solution and the like. Therefore, in the present embodiment, the soil moisture content is calculated by the following method. As shown in FIG. 11, when _{the reciprocal of the solution resistance R s} in the soil (= 1 / R _s ) is taken on the horizontal axis and the soil water content is taken on the vertical axis, these show a proportional relationship. _{Therefore, for example, the relationship between the soil water content and 1 / R s} is derived in advance using the soil in the environment to be measured, and the soil water content is derived from the value of the _{solution resistance R s} obtained by the measurement methods described so far. To measure. This makes it possible to easily measure the soil moisture content.

Moreover, even if not obtained in advance a relational expression soil moisture content and 1 / R _s, it is possible to estimate the soil moisture content. For example, the soil moisture content increases due to rainfall, etc., and its value is considered to have an upper limit. This is because the water in the soil fills the gaps created by the soil particles, and the pore space is the upper limit of the water content. Therefore, for example, assuming that the maximum value (1 / R _s ) when the soil water content rises sufficiently due to rainfall or the like is regarded as the upper limit of the water content, and this is taken as 100% of the water content in the gap, FIG. 11 Can be used to estimate the approximate water content. However, the water content estimated by this method is the ratio of water occupying the gap. If an accurate value of soil moisture content is required, it is preferable to calculate the porosity from the dry and wet densities of the soil.

On the other hand, the corrosion rate of metal is determined by the following method. It is known that the reciprocal of the polarization resistance R _p and the corrosion rate of the metal are in a proportional relationship (Non-Patent Document 5). The K value of the proportionality constant at this time can be obtained experimentally. Therefore, it is preferable to obtain the K value in advance based on the results of the anodic polarization and cathode polarization tests of the metal in the target soil in the laboratory and use it. By using the K value, the corrosion current density can be calculated from the reciprocal _{of the polarization resistance R p.} This corrosion current density is the corrosion rate. For example, the weight thinning rate and the volume thinning rate may be calculated from the corrosion rate.

So far, the methods for measuring soil moisture content and metal corrosion rate have been described. By repeating the measurement method a predetermined number of times at a predetermined time interval, it is possible to monitor the soil moisture content that changes with time due to rainfall or the like and the corrosion rate at that moment. The time interval and the number of repetitions are not particularly limited. It is recommended to carry out to the extent that the relationship between the desired soil moisture content and the corrosion rate can be sufficiently judged.

Based on the above, according to the present embodiment, one sensor unit 1 is configured with a simple configuration composed of two metals 11a and 11b that are a metal to be corroded and function as electrodes for measurement, and the two metals 11a, A simple method of measuring the AC impedance using 11b, calculating the polarization resistance and solution resistance, and calculating the metal corrosion rate and soil water content in the soil from the inverses of the polarization resistance and the solution resistance, respectively. Therefore, the soil water content and the corrosion rate of the metal in the soil can be easily measured at one time, and a measuring device for measuring the measurement and a measuring method thereof can be provided.

Further, according to this embodiment, an equivalent circuit including a soil capacitance C _s, specifically, two metal 11a in soil, 11b two polarization resistance R representing respectively the resistance to corrosion reaction of _{Represents p , two electric double layer capacitances C dl} existing at the interface between the two metals 11a and 11b and the soil, and the resistance that the cations of the two metals 11a and 11b receive when moving in the soil. Since an equivalent circuit composed of the solution resistance R _s and the soil volume C _s formed in the soil is used, the soil water content in the soil environment and the corrosion rate of the metal in the soil can be appropriately measured. ..

1 ... Sensor unit 11a, 11b ... Metal 12 ... Housing 2 ... Measurement unit 3 ... Calculation unit 4a, 4b ... Conduction wire 5 ... Electric cable

Claims (4)

A sensor unit that includes two metals of the same type that are insulated from each other as a metal to be corroded and as an electrode for measurement.
A measuring unit that measures AC impedance by applying a voltage or current in AC between the two metals,
Using the electrical response data from the AC impedance measurement, the polarization resistance, which indicates the resistance to the corrosion reaction of the metal in the soil, and the solution resistance, which indicates the resistance in the soil, are calculated based on a predetermined equivalent circuit. It is provided with a calculation unit for calculating the corrosion rate of the metal and the soil water content in the soil from the inverses of the polarization resistance and the solution resistance.
The two metals are
A measuring device having a flat exposed surface covered with a housing and exposed from the housing, and the exposed surfaces are arranged so as to face each other at a predetermined interval. A procedure in which a measuring unit is embedded in the soil and a voltage or current is applied in alternating current between two metals of the same type that are insulated from each other and used as a metal to be corroded and used as an electrode for measurement, and an alternating current impedance measurement is performed.
Based on a predetermined equivalent circuit, the calculation unit uses the electrical response data from the AC impedance measurement to determine the polarization resistance, which indicates the resistance to the corrosion reaction of the metal in the soil, and the solution resistance, which indicates the resistance in the soil. And the procedure to calculate
The calculation unit performs a procedure for calculating the corrosion rate of the metal and the soil water content in the soil from the reciprocals of the polarization resistance and the solution resistance, respectively.
The two metals are
A measuring method characterized in that each of the exposed surfaces is a flat surface covered with a housing and exposed from the housing, and the exposed surfaces are arranged so as to face each other at a predetermined interval. The equivalent circuit is
Polarization resistance, which indicates resistance to the corrosion reaction of the metal in soil, electric double layer capacity formed at the interface between the metal and soil, solution resistance, which indicates resistance in soil, and soil formed in soil. The measuring method according to claim 2, wherein the measuring method is composed of a capacity. The equivalent circuit is
The third aspect of claim 3, wherein the circuit is a circuit in which the soil capacitance is connected in parallel at both ends of a series circuit in which the solution resistor is connected in series to two parallel circuits in which the polarization resistor and the electric double layer capacitance are connected in parallel. Measurement method.

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