JP7024553B2 - Probe of corrosion environment measuring device and corrosion environment measuring device - Google Patents

Description

The present invention relates to a probe of a corrosive environment measuring device and a corrosive environment measuring device. More specifically, the present invention relates to a probe of a corrosive environment measuring device for measuring the salt content and the liquid film thickness of a liquid film, and a corrosive environment measuring device.

Metals are used in various mechanical products, structural parts, and the like. Metals are known to corrode when exposed to the atmosphere (hereinafter also referred to as atmospheric corrosion). When metal corrodes, various mechanical properties such as metal strength deteriorate. When the mechanical properties of metal deteriorate, the performance of products and the like also deteriorates. Here, it is known that the corrosion rate of a metal is affected by the thickness of the liquid adhering to the metal surface, the amount of salt in the liquid film, and the like. Therefore, it is important to understand the liquid film thickness and salt content, that is, the corrosive environment.

The electrochemical impedance method is known as a method for grasping the corrosive environment. The electrochemical impedance method uses two electrodes made of metal that seek a corrosive environment. An electrolyte is sandwiched between two electrodes, and an AC voltage is applied between the electrodes to obtain a frequency response between the electrodes. Then, a frequency response is obtained for AC voltages of various frequencies. Impedance (resistance) is obtained from the frequency characteristics obtained in this way. From this impedance, the electrical conductivity of the liquid film is calculated. The electrical conductivity of the liquid film is converted into the amount of salt in the liquid film. If the electrical conductivity of the liquid film is known, the liquid film thickness is calculated from the impedance.

An apparatus for measuring the amount of salt in a liquid film is disclosed, for example, in Japanese Patent Publication No. 62-088952 (Patent Document 1). The liquid film thickness measuring device is disclosed in Non-Patent Document 1, for example.

The measuring device described in Patent Document 1 includes a moisture absorbing material that absorbs and diffuses dew condensation between two electrodes. As a result, it is described in Patent Document 1 that the size of the dew condensation particles adhering on the insulating plate between the two electrodes becomes uniform and the amount of salt content can be measured accurately.

In the measuring device described in Non-Patent Document 1, a large number of electrode pairs composed of two electrodes are arranged in a grid pattern on the surface of a probe or the like at high density. As a result, it is described in Non-Patent Document 1 that the distribution of water film thickness can be measured with a small number of conductors.

Jitsukaisho 62-088952

Takahiro Arai, Masahiro Furuya, Daizo Kanai, "Development of Liquid Film Thickness Measurement Technology by High-Density Multipoint Electrode Method, Report L09008", published by Central Institute of Electric Power, June 2010, P.M. 2-11

However, although the measuring device of Patent Document 1 can measure the amount of salt in the liquid film, it cannot measure the liquid film thickness. In addition, P.I. As described in Sections 5 and 3.2, the measuring device of Non-Patent Document 1 measures the liquid film thickness using a liquid film whose composition is known in advance. In short, in the measuring devices of Patent Document 1 and Non-Patent Document 1, only one of the salt content and the liquid film thickness can be obtained by the device alone. In most cases of atmospheric corrosion, the composition of the liquid film attached to the metal is unknown. Therefore, it is difficult to grasp the liquid film thickness and the salt content of the metal exposed to the atmospheric corrosion environment by using the measuring device of Non-Patent Document 1.

An object of the present invention is to provide a corrosive environment measuring device capable of measuring the liquid film thickness adhering to a metal and the electric conductivity (salt content) of the liquid film.

The probe of the corrosion environment measuring apparatus of the present embodiment includes a first electrode and a counter electrode paired with the first electrode. The counter electrode is divided into a second electrode and a third electrode. The first electrode, the second electrode, and the third electrode are arranged side by side in one direction. The gap between the first electrode and the second electrode is smaller than the gap between the first electrode and the third electrode.

The corrosive environment measuring device for measuring the thickness and electrical conductivity of the liquid film of the present embodiment includes the above probe and an AC power source connected to the probe. The corrosion environment measuring device calculates the thickness of the liquid film based on the current flowing through the first electrode and the current flowing through the second electrode, and calculates the electric conductivity of the liquid film based on the thickness of the liquid film. do.

The corrosive environment measuring device according to the present invention can measure the liquid film thickness and the electric conductivity (salt content) of the liquid film adhering to the metal.

FIG. 1 is a schematic diagram illustrating an electrochemical impedance method. FIG. 2 is a diagram showing an equivalent circuit in the measurement of FIG. 1. FIG. 3 is a diagram showing a submerged environment. FIG. 4 is a diagram showing a thin film environment. FIG. 5 is a schematic diagram showing the calculation model used in the study. FIG. 6 is a diagram showing the cumulative distribution of the current density on the counter electrode used in the study. FIG. 7 is a perspective view showing a probe of the corrosion environment measuring device of the present embodiment. FIG. 8 is a front view of the measurement surface of the probe. FIG. 9 is a diagram schematically showing the corrosion environment measuring device of the present embodiment. FIG. 10 is a diagram showing a liquid film thickness master curve. FIG. 11 is a diagram showing an electric conductivity master curve. FIG. 12 is a diagram showing the effect of the width of the first electrode on the measurement of the corrosive environment. FIG. 13 is a diagram showing the effect of the gap between the first electrode and the second electrode on the measurement of the corrosive environment. FIG. 14 is a diagram showing the effect of the width of the second electrode on the measurement of the corrosive environment. FIG. 15 is a diagram showing the effect of the gap between the second electrode and the third electrode on the measurement of the corrosive environment. FIG. 16 is a diagram showing the effect of the width of the third electrode on the measurement of the corrosive environment.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The same or corresponding parts in the drawings are designated by the same reference numerals and the description thereof will not be repeated.

[Electrochemical impedance method]
First, the electrochemical impedance method will be described. The electrochemical impedance method is a method of measuring the impedance between two electrodes using two electrodes connected to an AC power supply. Based on the measured impedance, the liquid film thickness or salt content that affects the corrosion rate is calculated.

FIG. 1 is a schematic diagram illustrating an electrochemical impedance method. The electrode 100 and the counter electrode 101 paired with the electrode 100 are connected to the AC power supply 102, respectively. The two electrodes (electrode 100 and counter electrode 101) are made of a metal to be measured for the corrosion rate (corrosion environment). The electrode 100 and the counter electrode 101 are arranged side by side. The end faces of the electrode 100 and the counter electrode 101 are exposed from the measurement surface 107 of the probe. When atmospheric corrosion progresses, a thin liquid film 104 is present on the end faces of each of the electrode 100 and the counter electrode 101.

FIG. 2 is a diagram showing an equivalent circuit in the measurement of FIG. 1. In FIG. 2, the counter electrode 101 will be described, but the same applies to the electrode 100. The liquid film 104 has a solution resistance RS. In particular, when the thickness of the liquid film 104 is thin, the effect of the solution resistance RS on the measurement result is large. The boundary between the liquid film 104 and the counter electrode 101 can be replaced as a parallel circuit of the corrosion reaction resistance RP and the capacitor C.

When the frequency of the AC power supply is 0 (low frequency), all the AC current passes through the corrosion reaction resistance RP. Therefore, at low frequencies, the alternating current receives the solution resistance RS and the corrosion reaction resistance RP as impedances. On the other hand, when the frequency of the AC power supply is infinite (high frequency), all the AC current passes through the capacitor C. Therefore, in the case of high frequency, the alternating current receives only the solution resistance RS as resistance (impedance). Therefore, if the impedance obtained by high frequency is used, the electric conductivity (salt content) and the liquid film thickness can be obtained. However, in the prior art, it was not possible to measure both the electric conductivity and the liquid film thickness with one measuring device.

Therefore, the present inventors have considered measuring both the electric conductivity and the liquid film thickness with one measuring device. The present inventors focused on the thickness of the liquid film and the distribution of the alternating current flowing in the liquid film, and considered that the distribution of the alternating current in the liquid film differs depending on the liquid film thickness. This point will be described.

FIG. 3 is a diagram showing a submerged environment. The submerged environment means that there is a region P in which the alternating current 12 does not flow in the thickness direction of the liquid film 104. Simply put, a submerged environment means that the liquid film is thick enough. Since the liquid film thickness is sufficiently thick in a submerged environment, it is considered that the alternating current 12 flows in a wide range of the liquid film 104. Therefore, it is considered that the alternating current 12 flowing from the electrode 100 into the liquid film 104 evenly flows on the counter electrode 101 when it flows into the counter electrode 101.

FIG. 4 is a diagram showing a thin film environment. The thin film environment means that an alternating current 12 flows over the entire thickness direction of the liquid film 104. Simply put, it means that the thickness of the liquid film 104 is thin in a thin film environment. Since the liquid film thickness is thin in the thin film environment, it is considered that the alternating current 12 flowing from the electrode 100 flows to the portion of the counter electrode 101 near the electrode 100. This is because the metal constituting the counter electrode 101 has a higher electrical conductivity than the liquid film 104. That is, in a thin film environment, alternating current is concentrated and flows at the end of the counter electrode 101, so that it is considered that a potential distribution occurs on the counter electrode 101.

In short, it is considered that the potential distribution on the counter electrode 101 changes depending on the thickness of the liquid film 104. Therefore, the present inventors considered that if the potential distribution on the counter electrode 101 could be grasped, the thickness of the liquid film 104 could be obtained based on the potential distribution.

[to be considered]
To prove this, the present inventors examined the relationship between the liquid film thickness and the potential distribution on the opposite pole by numerical calculation.

FIG. 5 is a schematic diagram showing the calculation model used in the study. As a calculation model, we assumed two electrodes (electrode and counter electrode) connected to an AC power supply and brought into contact with an aqueous solution (liquid film). It was assumed that Ohm's law of the following equation (1) was established under the condition of electrical neutrality in the aqueous solution. The two electrodes are assumed to be made of steel. It was assumed that the interface between the two electrodes and the aqueous solution was electrically short-circuited. That is, it was assumed that a high frequency AC voltage was applied to the two electrodes. The calculation was done in two dimensions.
i = -σ ・ (dφ / dx) (1)
Here, i represents the current density, σ represents the electrical conductivity of the liquid film, and φ represents the potential.

The calculation conditions will be described. The dimensions of the two electrodes were the same. The dimensions of the surface of the electrode in contact with the aqueous solution were 10 mm in length and 0.5 mm in width. The distance between the two electrodes was 0.1 mm. The thickness of the aqueous solution (liquid film) was changed to various values in the range of ^10-5 to 102 ^mm . Then, at the center of the counter electrode 101 in the vertical direction, the cumulative distribution of the current density was calculated along the width direction of the counter electrode 101 from the end 105 closer to the electrode 100 to the end 106 farther from the electrode 100 (white arrows in FIG. 5). reference).

FIG. 6 is a diagram showing the cumulative distribution of the current density on the counter electrode used in the study. The horizontal axis shows the distance from the end 105 of the counter electrode 101 closer to the electrode 100, and the vertical axis shows the ratio of the cumulative value of the current density. In FIG. 6, the solid line shows the result of the liquid film thickness of 102 mm (submerged environment), the alternate long and short dash line shows the result of 10 ^mm , the alternate long and short dash line shows the result of ^10-2 mm, ^and the broken line shows the result of 10-. The result of ⁴ mm (thin film environment) is shown.

In the submerged environment (solid line), it can be seen that the distance from the end 105 of the counter electrode 101 and the cumulative value of the current density are close to a proportional relationship. That is, it was found that the potential difference on the counter electrode 101 was small in the submerged environment, and the current flowed uniformly on the counter electrode 101. On the other hand, in the thin film environment (broken line), the value of the current density at the end 105 (the value on the horizontal axis is 0) closer to the electrode 100 of the counter electrode 101 is about 0.9, and the distance from the end 105 of the counter electrode 101. However, the cumulative ratio of the current density at about 0.05 mm is 1. That is, it was found that the potential distribution was biased toward the end closer to the electrode 100 on the counter electrode 101, and the alternating current was concentrated at the end of the counter electrode 101.

From the above, it was demonstrated that in the electrochemical impedance method using alternating current, the potential distribution on the counter electrode changes when the liquid film thickness changes. It was demonstrated that the alternating current flows uniformly on the counter electrode in the submerged environment, but the alternating current concentrates on the end of the counter electrode 101 closer to the electrode 100 as it approaches the thin film environment.

Subsequently, the present inventors examined applying the above-mentioned pre-calculated findings to actual measurements by the electrochemical impedance method. Conventionally, a pair of electrodes has been used in the electrochemical impedance method, but it is practically impossible to measure the current value of only one end of one electrode (counter electrode) of the pair of electrodes. Therefore, the present inventors have conceived that one of the pair of electrodes is used as it is and the opposite electrode is divided. That is, it was conceived that the electrode of the divided counter electrode closer to the undivided electrode can be regarded as the end of the counter electrode before the division.

(1) The probe of the corrosion environment measuring apparatus of the present embodiment based on the above findings includes a first electrode and a counter electrode paired with the first electrode. The counter electrode is divided into a second electrode and a third electrode. The first electrode, the second electrode, and the third electrode are arranged side by side in one direction. The gap between the first electrode and the second electrode is smaller than the gap between the first electrode and the third electrode.

According to such a configuration, the counter electrode paired with the first electrode is physically divided into the second electrode and the third electrode, and the second electrode can play the role of the end portion of the counter electrode. Therefore, if the current flowing through the second electrode is measured, it can be regarded as measuring the current flowing through the end of the counter electrode. As a result, the degree of concentration of the alternating current flowing at the end of the counter electrode can be grasped, and the liquid film thickness can be measured. Then, by the method described later, the electric conductivity (salt content) of the liquid film can be measured based on the measured liquid film thickness.

(2) In the probe of the corrosion environment measuring apparatus of (1) above, the width of the second electrode is preferably smaller than the width of the third electrode.

If the width of the second electrode is too large, the function as the end of the counter electrode deteriorates. Therefore, the width of the second electrode is preferably smaller than the width of the third electrode.

(3) In the probe of the corrosion environment measuring device of (1) or (2) above, the second electrode is arranged between the first electrode and the third electrode, and the gap between the second electrode and the third electrode is , It is preferably smaller than the gap between the first electrode and the second electrode.

Since the second electrode and the third electrode form a counter electrode paired with the first electrode, if the second electrode and the third electrode are excessively separated from each other, the function as the counter electrode deteriorates. Therefore, the gap between the second electrode and the third electrode is preferably smaller than the gap between the first electrode and the second electrode.

(4) In the probe of the corrosion environment measuring device according to any one of (1) to (3) above, the width of the first electrode is 10 mm or less, the width of the second electrode is 10 mm or less, and the width of the third electrode. Is 10 mm or less, the gap between the first electrode and the second electrode is preferably 10 mm or less, and the gap between the second electrode and the third electrode is preferably 10 mm or less.

The probe of this embodiment is used for measuring the corrosive environment of metal. It is known that atmospheric corrosion of metal progresses remarkably when the liquid film thickness is as thin as 1 mm or less. Such a thin liquid film has a small area attached to the metal. Therefore, if the size of the probe is excessively large, it is often not suitable for measuring such a thin liquid film. Therefore, the width of each electrode and the distance between each electrode are defined as described above.

(5) The corrosive environment measuring device for measuring the thickness and electrical conductivity of the liquid film of the present embodiment includes the probe according to any one of (1) to (4) above and an AC power supply connected to the probe. .. The corrosion environment measuring device calculates the thickness of the liquid film based on the current flowing through the first electrode and the current flowing through the second electrode, and calculates the electric conductivity of the liquid film based on the thickness of the liquid film. do.

The details will be described in the measurement method of the corrosive environment, but by grasping the degree of concentration of the alternating current flowing in the second electrode (end of the counter electrode) and collating it with the master curve regarding the liquid film thickness prepared in advance, the liquid film The thickness can be measured. Then, the electric conductivity of the liquid film can be measured by collating the measured liquid film thickness with the master curve relating to the electric conductivity of the liquid film prepared in advance.

(6) It is preferable that the corrosive environment measuring device of the above (5) further includes a first ammeter for measuring the current flowing through the first electrode and a second ammeter for measuring the current flowing through the second electrode.

Specifically, an ammeter can be used to measure the degree of concentration of the alternating current flowing through the second electrode (the end of the counter electrode). From the ratio of the value measured by the first ammeter and the value measured by the second ammeter, the degree of concentration of the alternating current flowing through the second electrode can be grasped.

Hereinafter, the probe and the corrosion environment measuring device of this embodiment will be described in detail.

[probe]
FIG. 7 is a perspective view showing a probe of the corrosion environment measuring device of the present embodiment. The probe 5 of the corrosion environment measuring device of the present embodiment includes a first electrode 1 and a counter electrode 4 paired with the first electrode 1. The counter electrode 4 is divided into a second electrode 2 and a third electrode 3. The first electrode 1, the second electrode 2, and the third electrode 3 are arranged side by side in one direction.

[First electrode]
The first electrode 1 is made of a metal to be measured for a corrosive environment. The shape of the first electrode 1 is a quadrangular prism. One end surface 13 of the first electrode 1 is exposed from the measurement surface 7 of the probe 5. That is, a part of the first electrode 1 is exposed from the measurement surface 7. In addition, "exposed" means that one end surface 13 of the first electrode 1 exists on the same plane as the measurement surface 7 of the probe 5, and one end surface 13 of the first electrode 1 protrudes from the measurement surface 7. Includes both cases and cases.

[Opposite pole]
The counter electrode 4 includes a second electrode 2 and a third electrode 3. The second electrode 2 and the third electrode, that is, the counter electrode 4, are made of the same metal as the first electrode 1.

The shape of the second electrode 2 is a quadrangular prism. Similar to the first electrode 1, one end surface 14 of the second electrode 2 is exposed from the measurement surface 7 of the probe 5. The shape of the third electrode 3 is a quadrangular prism. Similar to the first electrode 1 and the second electrode 2, one end surface 15 of the third electrode 3 is exposed from the measurement surface of the probe 5.

Although the second electrode 2 and the third electrode 3 are physically separated, their role is to be an electrode (counter electrode) paired with the first electrode 1. Therefore, the second electrode 2 and the third electrode 3 are electrically connected to each other. For example, by connecting the electric wire connected to the second electrode 2 and the electric wire connected to the third electrode 3, the second electrode 2 and the third electrode 3 can be electrically connected.

FIG. 8 is a front view of the measurement surface of the probe. The first electrode 1 has a width W1. Here, the width of the first electrode means the length of each electrode in the arrangement direction. The same applies to the width W3 of the second electrode 2 and the width W5 of the third electrode 3. The second electrode 2 is arranged parallel to the first electrode 1. The second electrode 2 is arranged with a gap W2 with respect to the first electrode 1. The second electrode 2 is arranged between the first electrode 1 and the third electrode 3. The third electrode 3 is arranged parallel to the first electrode 1 and the second electrode 2. The third electrode 3 is arranged with a gap W4 with respect to the second electrode. The gap refers to the distance between the sides of the electrodes facing each other in the arrangement direction.

As described above, the second electrode 2 plays the role of the end portion of the integrated counter electrode (the counter electrode not divided into the second electrode and the third electrode) closer to the first electrode 1. Therefore, the gap W2 between the first electrode 1 and the second electrode 2 is smaller than the gap (W2 + W3 + W4) between the first electrode 1 and the third electrode 3. That is, the second electrode 2 is provided at a position closer to the first electrode 1 than the third electrode 3. As a result, the alternating current flowing through the second electrode 2 can be regarded as the alternating current flowing through the end of the integrated counter electrode.

The width of each electrode is not particularly limited, but it is preferable that the width W1 of the first electrode 1 is equal to the sum of the width of the second electrode 2 and the width of the third electrode 3 (W3 + W5). This is because the first electrode 1 and the counter electrode 4 have the same shape. Further, it is preferable that the lengths of the electrodes in the vertical direction are the same. The length in the vertical direction means the length in the direction orthogonal to the width direction at the end face of the electrode exposed from the measurement surface. Further, it is preferable that the heights of the electrodes are also the same.

[wiring]
FIG. 9 is a diagram schematically showing the corrosion environment measuring device of the present embodiment. The electric wire 19 in which the electric wire 17 connected to the second electrode 2 and the electric wire 18 connected to the third electrode 3 are bundled is connected to the terminal of the AC power supply 6. On the other hand, the electric wire 16 connected to the first electrode 1 is connected to another terminal of the AC power supply 6. As a result, by applying an AC voltage between the first electrode 1 and the counter electrode 4 (second electrode 2 and third electrode 3), the impedance between the first electrode 1 and the counter electrode 4 is measured by the electrochemical impedance method. Can be measured.

[Ammeter]
In the corrosion environment measuring apparatus of the present embodiment, the ratio of the current value flowing through the first electrode 1 and the current value flowing through the end of the counter electrode 4 (that is, the second electrode 2) is obtained, and the liquid film thickness is obtained. The current value of the first electrode 1 and the current value of the second electrode 2 can be obtained by, for example, two ammeters (first ammeter 8 and second ammeter 9).

The first ammeter 8 is provided on the electric wire 19 from the connection between the second electrode 2 and the third electrode 3 to the AC power supply 6. Since the current flowing through the electric wire 19 is equal to the current flowing through the first electrode 1, the current flowing through the first electrode 1 can be measured by the first ammeter 8. The second ammeter 9 is provided on the electric wire 17 between the second electrode 2 and the connection between the second electrode 2 and the third electrode 3. The second ammeter 9 can measure the current flowing through the second electrode 2. As will be described later, the liquid film thickness can be determined based on the measured value of the first ammeter 8 and the value of the second ammeter 9.

The arrangement of the first ammeter 8 and the second ammeter 9 is not limited to the above example. For example, the first ammeter 8 may be arranged on the electric wire 16 connecting the AC power supply 6 and the first electrode 1. Even in this case, the first ammeter 8 can measure the current flowing through the first electrode 1. Further, the second ammeter 9 may be provided on the electric wire 18 between the third electrode 3 and the connection between the second electrode 2 and the third electrode 3. Even in this case, the current flowing through the second electrode 2 can be obtained by subtracting the value of the second ammeter 9 from the value of the first ammeter 8. Further, the first current meter 8 is provided on the electric wire 18 between the third electrode 3 and the connection between the second electrode 2 and the third electrode 3, and the second current meter 9 is provided from the second electrode 2 to the second electrode. It may be provided on the electric wire 17 between 2 and the connection between the 3rd electrode 3. Even in this case, the current flowing through the first electrode 1 can be obtained by adding the values of the first ammeter 8 and the values of the second ammeter 9.

[Measuring method]
Subsequently, the method for measuring the corrosive environment of the present embodiment will be described. Specifically, the liquid film thickness and the amount of salt in the liquid film adhering to the metal are measured by using the above-mentioned corrosion environment measuring device. The amount of salt can be calculated by obtaining the electric conductivity in the liquid film. The corrosion environment measuring method includes a liquid film thickness master curve creating step, an electric conductivity master curve creating step, a liquid film thickness measuring step, and an electric conductivity measuring step.

[Liquid film thickness master curve creation process]
In order to measure the liquid film thickness, a master curve related to the liquid film thickness (hereinafter referred to as a liquid film thickness master curve) is created in advance. This liquid film thickness master curve is created using a probe having the same shape as the probe of the corrosion environment measuring device that actually measures the liquid film thickness. This is because if the size and arrangement of the electrodes change, the liquid film thickness master curve also changes.

With reference to FIG. 9, first, a liquid film having a known liquid film thickness and electrical conductivity is prepared. The measurement surface 7 of the probe 5 of the above-mentioned corrosion environment measuring device is brought into contact with a liquid film having known physical characteristics. Next, an AC voltage is applied between the first electrode 1 and the counter electrode 4 by the AC power supply 6. Then, the ratio (hereinafter, also referred to as the current ratio) between the current flowing through the first electrode 1 and the current flowing through the second electrode 2 is calculated. As a result, the current ratio at a certain known liquid film thickness can be obtained. If this is done for various liquid film thicknesses, the relationship between the current ratio and the liquid film thickness can be obtained. This relationship becomes the liquid film thickness master curve.

The liquid film thickness master curve may be obtained by actually using a probe and a liquid film having known physical properties, or may be obtained by numerical calculation. Here, as an example, an example of calculating the liquid film thickness master curve by numerical calculation will be described. The present inventors obtained the relationship between the current ratio and the liquid film thickness using the probe model used in the above-mentioned preliminary study, and drew this relationship as the liquid film thickness master curve.

FIG. 10 is a diagram showing a liquid film thickness master curve. The solid line shows the master curve in which the width W3 of the second electrode is 0.01 mm, the alternate long and short dash line shows the master curve in which the width W3 of the second electrode is 0.03 mm, and the alternate long and short dash line shows the master curve in which the width W3 of the second electrode is 0. The master curve of 07 mm is shown, and the broken line shows the master curve of the width W3 of the second electrode of 1.0 mm. The master curve of W3 = 0.01 (solid line) will be described as an example. When the liquid film thickness exceeds 1 mm, the current ratio shows a substantially constant value regardless of the liquid film thickness because the liquid film thickness is too thick. When the liquid film thickness is smaller than 0.001 mm, the liquid film thickness is too thin and the current ratio shows a substantially constant value regardless of the liquid film thickness. On the other hand, when the liquid film thickness is in the range of 0.001 to 1 mm, the current ratio changes correspondingly when the liquid film thickness changes. That is, in this range, the liquid film thickness can be measured by the corrosion environment measuring device of the present embodiment. Using the liquid film thickness master curve thus obtained, the liquid film thickness of unknown physical properties is measured.

[Liquid film thickness measurement process]
In the liquid film thickness measuring step, the measuring surface of the probe 5 of the corrosive environment measuring device is brought into contact with the liquid film whose physical properties are actually unknown. An AC voltage is applied between the first electrode 1 and the counter electrode 4. Then, the ratio (current ratio) of the current flowing through the first electrode 1 and the current flowing through the second electrode 2 is obtained. The value of this current ratio is collated with the liquid film thickness master curve shown in FIG. For example, when a probe having a width W3 of the second electrode of 0.01 mm (solid line) is used, the current ratio obtained in the liquid film thickness measurement step is 0.5. When the obtained current ratio 0.5 is collated with the liquid film thickness master curve (solid line), it can be seen that the liquid film thickness is about 0.04 mm in the liquid film thickness master curve. This value is the measured liquid film thickness of the unknown liquid film.

Here, the liquid film thickness master curve is obtained by using a liquid film having a known electric conductivity, and the problem is whether it can be applied to the measurement of the liquid film thickness of a liquid film having an unknown electric conductivity. Become. That is, even if the electric conductivity of the liquid film is different, the problem is whether the current ratio to a certain liquid film thickness shows the same value. This point will be described.

If the electric conductivity of the liquid film to be measured is different, the absolute value of the current flowing between the first electrode and the counter electrode is different. However, as described above, the current ratio is the ratio of the current flowing between the first electrode and the second electrode (the end of the counter electrode). In the measurement method of the present embodiment, since a high-frequency AC voltage is applied between the two electrodes, the interface between the electrodes and the liquid film is electrically short-circuited, and the current density on the electrode surface follows Ohm's law. Since the current densities in the liquid film and the electrodes follow Ohm's law, the potential distribution on the electrode surface is independent of the electrical conductivity. Therefore, the ratio of the current between the first electrode and the second electrode is independent of the electrical conductivity. Therefore, although the absolute value of the alternating current flowing is different, the ratio of the current flowing between the first electrode and the second electrode does not change even if the electric conductivity of the liquid film changes. Therefore, it is possible to measure the current ratio of a liquid film having an unknown electrical conductivity, collate the value with the liquid film thickness master curve, and calculate the liquid film thickness.

Either the liquid film thickness master curve creation step or the liquid film thickness measurement step may be performed first. This is because even if the current ratio is measured using an unknown liquid film first, if the current ratio is recorded, it can be collated with the liquid film thickness master curve created later.

[Electrical conductivity master curve creation process]
In order to measure the electric conductivity, a master curve related to the electric conductivity (hereinafter referred to as an electric conductivity master curve) is created in advance. This electric conductivity master curve can be performed together with the preparation of the liquid film thickness master curve described above.

In the above-mentioned liquid film thickness master curve creating step, an alternating current was applied between the first electrode 1 and the counter electrode 4 using a liquid film having known physical characteristics. This is nothing but the execution of the electrochemical impedance method. Therefore, in the process of creating the liquid film thickness master curve, the impedance between the first electrode 1 and the counter electrode 4 is also required. In the electric conductivity master curve creation process, the electric conductivity master curve is created using this impedance.

Since the current densities in the liquid film and the electrodes follow Ohm's law, the current flowing through the electrodes is determined by the electrical conductivity and the water film thickness, and is proportional to the electrical conductivity σ. Therefore, the impedance Z, which is the ratio of the applied voltage and the current, has an inversely proportional relationship with the electric conductivity σ, and the product of the impedance Z and the electric conductivity σ is determined by the liquid film thickness regardless of the electric conductivity σ. If the product of the impedance Z and the electric conductivity σ is obtained for various liquid film thicknesses, the relationship between the product of the impedance Z and the electric conductivity σ and the liquid film thickness can be obtained. This relationship becomes the electrical conductivity master curve. The present inventors created an electric conductivity master curve using the impedance Z obtained by the numerical calculation in the above-mentioned liquid film thickness master curve creating step.

FIG. 11 is a diagram showing an electric conductivity master curve. Here, as an example, the electric conductivity master curve created by using the calculation result when the width W3 of the second electrode is 0.01 mm is shown. Using this electric conductivity master curve, the electric conductivity of a liquid film whose physical characteristics are unknown is measured.

[Electrical conductivity measurement process]
In the electric conductivity measuring step, the electric conductivity is obtained by using the liquid film thickness obtained in the liquid film thickness measuring step. The liquid film thickness obtained in the liquid film thickness measuring step is collated with the electric conductivity master curve shown in FIG. For example, it is assumed that the liquid film thickness obtained in the liquid film thickness measuring step is 0.01 mm. When this liquid film thickness of 0.01 mm is collated with the electric conductivity master curve, it can be seen that the product of the impedance and the electric conductivity is about 1. Here, the impedance has already been obtained in the liquid film thickness measuring step. Therefore, the electrical conductivity is calculated by dividing the measured impedance from the product of the impedance and the electrical conductivity. As described above, since the electric conductivity correlates with the amount of salt in the liquid film, the amount of salt in the liquid film is measured from the calculated electric conductivity.

By the above method, the liquid film thickness and the electric conductivity (salt content) of the liquid film whose physical characteristics are unknown can be obtained by using the corrosive environment measuring device of the present embodiment.

[Preferable mode]
Hereinafter, a preferred embodiment of the probe of the corrosion environment measuring device of the present embodiment will be described. In the following, the effects of the width of each electrode of the probe and the gap between the electrodes on the measurement of liquid film thickness and electrical conductivity (that is, corrosive environment) were investigated by numerical calculation. Based on the survey results, a suitable mode of the width of each electrode of the probe and the gap between the electrodes was derived.

[Evaluation index]
With reference to FIG. 10, an evaluation index for the influence of the width and the gap of each electrode on the measurement of the corrosive environment will be described. The evaluation index was evaluated based on three indexes.

The first index is "sensitivity". As described above, the corrosive environment measuring apparatus of the present embodiment can measure the liquid film thickness and the electric conductivity in the range where the current ratio changes as the liquid film thickness changes. Sensitivity is an index indicating the size of the range of current ratios at which liquid film thickness and electric conductivity can be measured. If the sensitivity is high, the measurement error is likely to be reduced, and the liquid film thickness and the electric conductivity can be measured more accurately.

The second index is the "upper limit of measurable liquid film thickness". As described above, in a submerged environment, the current ratio does not change even if the liquid film thickness changes, so that the liquid film thickness and the electric conductivity cannot be measured. If the upper limit of the measurable liquid film thickness is large, the liquid film thickness and the electric conductivity of the thicker liquid film can be measured.

The third index is the "lower limit of measurable liquid film thickness". As described above, if the liquid film thickness becomes too thin, the current ratio does not change even if the liquid film thickness changes, so that the liquid film thickness and the electric conductivity cannot be measured. If the lower limit of the measurable liquid film thickness is small, the liquid film thickness and the electric conductivity of the thinner liquid film can be measured.

[Width W1 of the first electrode]
With reference to FIG. 8, the influence of the width W1 of the first electrode 1 on the measurement of the corrosive environment was investigated. The width W1 of the first electrode 1 was investigated for three patterns of 0.1, 0.5, and 1 mm. The gap W2 between the first electrode 1 and the second electrode 2 is 0.1 mm, the width W3 of the second electrode 2 is 0.1 mm, and the gap W4 between the second electrode 2 and the third electrode 3 is 0.1 mm, the third. The width W5 of the electrode 3 was fixed at 0.4 mm. Then, a liquid film thickness master curve was created for each pattern.

FIG. 12 is a diagram showing the effect of the width of the first electrode on the measurement of the corrosive environment. The solid line shows the result that the width W1 of the first electrode is 1 mm, the alternate long and short dash line shows the result that the width W1 of the first electrode is 0.5 mm, and the broken line shows the result that the width W1 of the first electrode is 0.1 mm.

From this result, it can be seen that the sensitivity should be higher when the width W1 of the first electrode is larger. It can be seen that the upper limit of the measurable liquid film thickness should be larger when the width W1 of the first electrode is larger. It can be seen that the lower limit of the measurable liquid film thickness is not affected by the width W1 of the first electrode. From this, it can be said that the width W1 of the first electrode should be large.

[Gap between the first electrode and the second electrode W2]
The effect of the gap W2 between the first electrode 1 and the second electrode 2 on the measurement of the corrosive environment was investigated. The gap W2 between the first electrode 1 and the second electrode 2 was investigated for three patterns of 0.01, 0.1, and 1 mm. The width W1 of the first electrode 1 is 0.5, the width W3 of the second electrode 2 is 0.1 mm, the gap W4 between the second electrode 2 and the third electrode 3 is 0.1 mm, and the width W5 of the third electrode 3 is. It was fixed at 0.4 mm. Then, a liquid film thickness master curve was created for each pattern.

FIG. 13 is a diagram showing the effect of the gap between the first electrode and the second electrode on the measurement of the corrosive environment. The solid line shows the result of the gap W2 of 1 mm, the alternate long and short dash line shows the result of the gap W2 of 0.1 mm, and the broken line shows the result of the gap W2 of 0.01 mm.

From this result, it can be seen that the sensitivity should be higher when the gap W2 between the first electrode and the second electrode is large. It can be seen that the upper limit of the measurable liquid film thickness is better when the gap W2 between the first electrode and the second electrode is large. It can be seen that the lower limit of the measurable liquid film thickness is not affected by the gap W2 between the first electrode and the second electrode. From this, it can be said that the larger the gap W2 between the first electrode and the second electrode is, the better.

[Width W3 of the second electrode]
The effect of the width W3 of the second electrode 2 on the measurement of the corrosive environment was investigated. The width W3 of the second electrode 2 was investigated for three patterns of 0.01, 0.1, and 1 mm. The width W1 of the first electrode 1 is 0.5 mm, the gap W2 between the first electrode 1 and the second electrode 2 is 0.1 mm, and the gap W4 between the second electrode 2 and the third electrode 3 is 0.1 mm, the third. The width W5 of the electrode 3 was fixed at 0.4 mm. Then, a liquid film thickness master curve was created for each pattern.

FIG. 14 is a diagram showing the effect of the width of the second electrode on the measurement of the corrosive environment. The solid line shows the result that the width W3 of the second electrode is 1 mm, the alternate long and short dash line shows the result that the width W3 of the second electrode is 0.1 mm, and the broken line shows the result that the width W3 of the second electrode is 0.01 mm.

From this result, it can be seen that the sensitivity should be higher when the width W3 of the second electrode is larger. It can be seen that the upper limit of the measurable liquid film thickness should be larger when the width W3 of the second electrode is larger. It can be seen that the lower limit of the measurable liquid film thickness is better when the width W3 of the second electrode is larger. From this, it can be said that the width W3 of the second electrode should be large.

In particular, when the width W3 of the second electrode is smaller than the width W5 of the third electrode (dotted chain line and broken line), the lower limit of the sensitivity and the measurable liquid film thickness is remarkably improved. This is because the second electrode 2 plays a role as an end portion of the counter electrode 4. This is because the smaller the width W3 of the second electrode, the easier it is to capture the concentration at the end of the counter electrode of the alternating current as it approaches the thin film environment.

[Gap between the second electrode and the third electrode W4]
The effect of the gap W4 between the second electrode and the third electrode on the measurement of the corrosive environment was investigated. The gap W4 between the second electrode and the third electrode was investigated for three patterns of 0.01, 0.1, and 1 mm. The width W1 of the first electrode 1 is 0.5, the gap W2 between the first electrode 1 and the second electrode 2 is 0.1 mm, the width W3 of the second electrode 2 is 0.1 mm, and the width W5 of the third electrode 3 is. It was fixed at 0.4 mm.

FIG. 15 is a diagram showing the effect of the gap between the second electrode and the third electrode on the measurement of the corrosive environment. The solid line shows the result of the gap W4 of 1 mm, the alternate long and short dash line shows the result of the gap W4 of 0.1 mm, and the broken line shows the result of the gap W4 of 0.01 mm.

From this result, it can be seen that the sensitivity should be higher when the gap W4 between the second electrode and the third electrode is large. It can be seen that the upper limit of the measurable liquid film thickness should be larger when the gap W4 between the second electrode and the third electrode is large. It can be seen that the lower limit of the measurable liquid film thickness should be smaller when the gap W4 between the second electrode and the third electrode is smaller. The corrosive environment of metal progresses remarkably in a thin liquid film having a liquid film thickness of 1 mm or less. Therefore, the lower limit is more important than the upper limit of the measurable liquid film thickness. From this, it can be said that the smaller the gap W4 between the second electrode and the third electrode is, the better.

In particular, when the gap W4 between the second electrode and the third electrode is smaller than the gap W2 between the first electrode and the second electrode (broken line), the lower limit of the sensitivity and the measurable liquid film thickness is remarkably improved. Although the second electrode 2 and the third electrode 3 are physically separated, they are electrically connected and play a role as a counter electrode to the first electrode 1. Therefore, if the second electrode 2 and the third electrode 3 are too far apart, it is considered that the function as a counter electrode to the first electrode 1 is deteriorated due to various noises.

[Width W5 of the third electrode]
The effect of the width W5 of the third electrode 3 on the measurement of the corrosive environment was investigated. The width W5 of the third electrode 3 was investigated for three patterns of 0.1, 0.4, and 1 mm. The width W1 of the first electrode 1 is 0.5 mm, the gap W2 between the first electrode 1 and the second electrode 2 is 0.1 mm, the width W3 of the second electrode 2 is 0.1 mm, and the second electrode 2 and the third electrode The gap W4 with 3 was fixed at 0.1 mm.

FIG. 16 is a diagram showing the effect of the width of the third electrode on the measurement of the corrosive environment. The solid line shows the result that the width W5 of the third electrode is 1 mm, the alternate long and short dash line shows the result that the width W5 of the third electrode is 0.4 mm, and the broken line shows the result that the width W5 of the third electrode is 0.1 mm.

From this result, it can be seen that the sensitivity should be higher when the width W5 of the third electrode is larger. It can be seen that the upper limit of the measurable liquid film thickness should be larger when the width W5 of the third electrode is larger. It can be seen that the lower limit of the measurable liquid film thickness is not affected by the width W5 of the third electrode. From this, it can be said that the width W5 of the third electrode should be large.

Furthermore, the probe of this embodiment is used for measuring the corrosive environment of metal. It is known that atmospheric corrosion of a metal progresses remarkably when the liquid film thickness attached to the metal is as thin as 1 mm or less. In such a thin liquid film, the area covering the metal surface is not so large. Therefore, if the probe is too large, the first electrode 1, the second electrode 2, and the third electrode 3 cannot come into contact with the same liquid film. Considering this, the width W1 of the first electrode, the gap W2 between the first electrode and the second electrode, the width W3 of the second electrode, the gap W4 between the second electrode and the third electrode, and the width of the third electrode. W5 is preferably 10 mm or less, respectively. As a result, the size of the probe can be reduced, which is suitable for measuring the corrosive environment of metal.

The embodiment of the present invention has been described above. However, the embodiments described above are merely examples for carrying out the present invention. Therefore, the present invention is not limited to the above-described embodiment, and the above-mentioned embodiment can be appropriately modified and carried out within a range not deviating from the gist thereof.

The corrosive environment measuring device of the present embodiment can be used, for example, for measuring the corrosive environment of a material in an atmospheric corrosion investigation test of the material. It can also be attached to a metal part of a transport device to monitor the progress of corrosion in that part. It can also be used to measure the corrosive environment of metals in places where atmospheric corrosion is likely to progress, such as piers on the sea.

1: 1st electrode 2: 2nd electrode 3: 3rd electrode 4: Counter electrode 5: Probe 6: AC power supply 7: Measurement surface 8: 1st ammeter 9: 2nd ammeter

Claims (5)

A corrosive environment measuring device that measures the thickness and electrical conductivity of a liquid film.
A probe comprising a first electrode and a counter electrode paired with the first electrode and divided into a second electrode and a third electrode, wherein the first electrode, the second electrode, and the third electrode are provided. Are arranged side by side in one direction, and the gap between the first electrode and the second electrode is smaller than the gap between the first electrode and the third electrode .
Including an AC power source connected to the probe,
The thickness of the liquid film was calculated based on the current flowing through the first electrode and the current flowing through the second electrode.
A corrosive environment measuring device that calculates the electrical conductivity of the liquid film based on the thickness of the liquid film. The corrosive environment measuring device according to claim 1 , further
A first ammeter that measures the current flowing through the first electrode,
A corrosion environment measuring device comprising a second ammeter for measuring a current flowing through the second electrode. The corrosive environment measuring device according to claim 1 or 2.
A corrosive environment measuring device in which the width of the second electrode is smaller than the width of the third electrode. The corrosive environment measuring apparatus according to any one of claims 1 to 3.
The second electrode is arranged between the first electrode and the third electrode.
A corrosion environment measuring device in which the gap between the second electrode and the third electrode is smaller than the gap between the first electrode and the second electrode. The corrosive environment measuring apparatus according to any one of claims 1 to 4.
The width of the first electrode is 10 mm or less, and the width is 10 mm or less.
The width of the second electrode is 10 mm or less, and the width of the second electrode is 10 mm or less.
The width of the third electrode is 10 mm or less, and the width of the third electrode is 10 mm or less.
The gap between the first electrode and the second electrode is 10 mm or less, and the gap is 10 mm or less.
A corrosion environment measuring device in which the gap between the second electrode and the third electrode is 10 mm or less.

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