JP2019045268A - Corrosion sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent absorption of water into a dielectric, stabilize a capacitance, and as a result, grasp an accurate corrosion state. SOLUTION: This is a corrosion sensor 1 for detecting a corrosive environment of a steel material, and a detection unit made of a corrosive metal, a plurality of through holes 5 provided in the detection unit, and facing the detection unit. A material having waterproof and corrosion resistance, which is provided so as to close the counter electrode provided at the position to be formed, the dielectric 7 provided between the detection unit and the counter electrode, and the through hole 5. The waterproof portion 6 formed of the above is provided. [Selection diagram] Fig. 1

Description

  The present invention relates to a corrosion sensor that detects the corrosion environment of a steel material.

  The steel in the concrete structure forms a passive film on the surface of the steel by maintaining the alkaline environment of the concrete, and is protected from corrosion. However, for example, if a corrosion factor such as carbon dioxide in the air, sulfuric acid in a sewerage facility, or chloride ion intrudes into the concrete, this passive film is destroyed and corrosion of the steel material is caused by water and oxygen in the concrete. Start. Moreover, in the structure using steel materials, such as a steel bridge and a plant, a protective paint is used so that rust may not arise in steel materials.

  When steel materials in concrete structures are corroded, volumetric expansion of the steel materials occurs, and the expansion pressure causes cracks in the concrete, and through the cracks, corrosion of the steel materials is accelerated by the penetration of corrosion factors and the supply of water and oxygen from the outside It will progress and eventually it will lose its function as a concrete structure. In addition, when the steel material corrodes in the steel bridge, the protective coating film is lifted or peeled off due to the volume expansion of the steel material, and the antirust effect is lost.

  Therefore, before the corrosion of the steel material starts, the penetration of the corrosion factor and the corrosion start of the steel material are detected, for example, the steel sheet is protected from corrosion by preventing further penetration of the corrosion factor and water and oxygen by measures such as surface coating. It is important to plan preventive maintenance of structures. Various corrosion diagnosis methods have conventionally been proposed for this problem. For example, a method of coring to analyze corrosion factors, a method of nondestructively measuring the natural potential and polarization resistance of steel materials, a method of detecting corrosion factors by a chemical sensor or a gas sensor, and simulating iron thin wires as simulated corrosion members There is known a method of embedding in concrete and detecting corrosion when a thin wire is broken.

  Among these corrosion diagnosis methods, the method of detecting corrosion by wire breakage is (a) not damaging the concrete such as coring by embedding the sensor in advance (b) between the concrete surface and the steel material By installing several thin wires according to the depth, it is possible to monitor the time dependency of the penetration of corrosion factors from the surface and to make it easy to formulate a maintenance plan, (c) as it directly captures iron corrosion, It can detect the possibility of corrosion including water and oxygen supply conditions as well as corrosion factors, (d) detect changes in electrical resistance, so detection with extremely low power consumption is possible and suitable for long-term monitoring, There are merits, and various corrosion diagnosis methods based on detecting fine line cutting have been proposed. In addition, a corrosion sensor using an iron foil material has also been proposed in order to increase the sensitivity and design freedom.

  In addition, many conventional corrosion sensors capture the electrical resistance of the detection unit. Since iron with high conductivity does not break, resistance does not easily change, and the sensitivity of the sensor is likely to depend on the wire diameter, line width, etc., and after breaking it loses its function as a sensor. There is a proposal to detect a corrosive environment by capturing a capacitance (Patent Document 1). In this corrosion sensor, since the corrosion can be detected by the change in the area of the detection unit, it can be grasped how much the corrosion has progressed in the concrete structure.

Unexamined-Japanese-Patent No. 2017-032516

  However, when the capacitance type corrosion sensor is installed in concrete or an aqueous solution, the value of the capacitance may change. FIG. 5 is a schematic view of a conventional corrosion sensor. As shown in FIG. 5, in order to improve the sensitivity of the corrosion sensor 1 and to ensure electrical continuity even if part of the iron foil portion 3 is broken, the detection surface of the corrosion sensor 1 The through-hole 5 is provided in the iron foil portion 3 which is the same as above, but the moisture intrudes into the through-hole 5 provided in the iron foil portion 3 to charge it, and the area of the sensor detection surface is apparently increased. I will. As a result, it is conceivable that the capacitance fluctuates depending on the wet and dry conditions of the concrete.

  In addition, after installing the corrosion sensor in concrete or aqueous solution, the capacitance gradually increases with time. The increased capacitance may be about 20% of the capacitance immediately after the corrosion sensor is installed. When the material of the dielectric is a material that absorbs water, the influence of the dielectric constant that changes due to the absorption of water may deteriorate the dielectric material itself, which makes it difficult to measure a stable capacitance. Further, when a polyimide material is used, deterioration due to water absorption is known. By absorbing water, the polyimide is degraded, and as a result, the capacitance exhibits an unstable behavior. Under such circumstances, it is not possible to grasp an accurate corrosion state from the capacitance value.

  (1) In order to achieve the above object, the present invention takes the following measures. That is, the corrosion sensor according to the present invention is a corrosion sensor for detecting a corrosive environment of a steel material, and includes a detection unit formed of a metal having corrosiveness, a plurality of through holes provided in the detection unit, and the detection And a dielectric which is provided between the detection part and the counter electrode, and which is provided so as to close the through hole, and which is waterproof and corrosion resistant. And a waterproof part formed of a material.

  As described above, the corrosion sensor includes a detection unit formed of a corrosive metal, a plurality of through holes provided in the detection unit, a counter electrode provided at a position facing the detection unit, a detection unit, Since a dielectric provided between it and the counter electrode, and a waterproof part provided to close the through hole and made of a material having waterproofness and corrosion resistance, water to the dielectric is provided. It is possible to prevent the entry of moisture such as As a result, the deterioration of the dielectric and the capacitance become stable, and it becomes possible to grasp an accurate corrosion situation.

  (2) In the corrosion sensor of the present invention, the waterproof portion is formed of carbon.

  As described above, since the waterproof portion is formed of carbon, it is possible to prevent the retention of the moisture in the through hole and the infiltration of water such as water to the dielectric without corroding, and to further ensure the conduction. It becomes.

  (3) In the corrosion sensor of the present invention, the waterproof portion is formed of a resin.

  As described above, since the waterproof portion is formed of resin, it is possible to prevent the retention of water to the through hole and the infiltration of water such as water to the dielectric without corrosion.

  (4) In the corrosion sensor of the present invention, the waterproof portion is formed of a metal nobler than iron.

  As described above, since the waterproof portion is formed of a metal nobler than iron, it prevents corrosion of moisture and penetration of water and the like to the dielectric without corrosion and secures continuity. It becomes possible. Further, the corrosive environment can be detected with high sensitivity by the cathode effect.

  According to the present invention, by providing a waterproof portion formed of a material having waterproofness and corrosion resistance, retention of water in the through hole and absorption of water in the dielectric are prevented, and capacitance is stabilized. It becomes possible. As a result, it becomes possible to grasp an accurate corrosion state.

It is a top view which shows schematic structure of the corrosion sensor which concerns on this embodiment. It is sectional drawing at the time of cut | disconnecting the corrosion sensor shown in FIG. 1 by AA. It is a figure which shows the outline of the corrosion sensor which concerns on this embodiment embed | buried in mortar or concrete. It is a flowchart which shows the manufacturing method of the corrosion sensor which concerns on this embodiment. It is a top view which shows schematic structure of the conventional corrosion sensor.

[Measurement principle of corrosion sensor]
The dielectric loss tangent increases with the increase of the resistance value. In addition, the capacitance changes due to the loss of the electrode (detection unit). Also, by detecting the dielectric loss tangent, it is possible to detect initial corrosion that has occurred on the surface of the corrosion sensor. In addition, electrical characteristics such as reactance and equivalent parallel resistance also change due to corrosion. Here, it is desirable to measure the change of the dielectric loss tangent in a high frequency region of 10 kHz or more. Furthermore, it is possible to grasp the corrosion state with higher accuracy by judging the progress of the corrosion together with the decrease degree of the capacitance.

The dielectric loss tangent tan δ of the parallel plate conductor (detecting portion) has the following relationship among ω: each frequency, C: capacitance, R: series equivalent resistance.
tan δ = ω CR (1)

The electrostatic capacitance C of the parallel plate conductor (detection part) has the following relationship between the area S of the parallel plate conductor and the distance d between the parallel plate conductors.
C = Q / V = εS / d [F] (2)
Here, ε is a dielectric constant.

  The corrosion sensor according to the present embodiment uses this principle. That is, when the detection unit surface of the sensor is corroded by the corrosion factor, the electrical resistance increases. Thus, the dissipation factor rises proportionally. After that, the corrosion of the detection unit progresses, and the capacitance starts to decrease due to the decrease in the loss of the detection unit. By grasping the degree of decrease of the capacitance, it is possible to grasp the degree of decrease of the area of the detection unit, and further the degree of progress of the corrosive environment. The dielectric loss tangent will drop if the drop in capacitance outweighs the rise in resistance.

  Therefore, the rise of the dielectric loss tangent catches the initial slight corrosion initiation, and thereafter, when the decrease of the dielectric loss tangent or the decrease of the capacitance is observed, it is expected that the detection part is broken, so the corrosion is caused. It can detect that the progress of the

[Corrosion sensor configuration]
FIG. 1 is a plan view showing a schematic configuration of a corrosion sensor according to the present embodiment. FIG. 2 is a cross-sectional view of the corrosion sensor shown in FIG. 1 cut at A-A. The corrosion sensor 1 includes an iron foil portion 3 formed of a corrosive metal to be a detection surface (detection portion), a dielectric 7, a lead wire 9, and a counter electrode 10.

  The iron foil portion 3 is made of a corrosive metal, and in the case of using iron, it is manufactured by rolling and has a thickness of 3 μm or more and 0.1 mm or less. The iron foil portion 3 may be a thin film formed by vapor deposition or plating, or may be formed in a plate shape. The reason why the thickness of the iron foil portion 3 is set to 3 μm or less is that cracking is likely to occur when the sensor is handled if it is too thin, and the sensitivity of the sensor may be reduced if it is too thick. In addition, the area of the iron foil portion 3 may be small because the initial slight corrosion initiation can be detected by the dielectric loss tangent, but it is preferable that the larger one is to grasp the progress of the corrosion by electrostatic capacity. .

  The iron foil portion 3 is provided with a plurality of through holes 5. The plurality of through holes 5 provided in the iron foil portion 3 may be mesh-like or slit-like. By providing the through holes 5 in the iron foil portion 3, the iron foil portion 3 can be corroded from the interface between the iron foil portion 3 and the through holes 5. The planar shape of the through hole 5 is circular from the viewpoint of yield of formation accuracy, but is not limited to this. For example, it may be rectangular (square) or another shape. When the through hole 5 is circular, the stress generated by thermal expansion and the like is easily dispersed, and the retention of water at the corner portion does not occur, so that the formation accuracy and yield in manufacturing the through hole 5 are improved. As a result, it becomes possible to contribute to stability of quality and cost reduction.

  Each through hole 5 is provided with a waterproof portion 6 filled with a material having waterproof property and corrosion resistance so as to close each through hole. The material to be filled may be any material as long as it is waterproof and corrosion resistant, and includes epoxy resin, carbon, corrosion resistant metal and the like. For example, if it is made of a conductive material such as carbon, it is possible to secure conduction on the entire sensor surface. When carbon is used, it is more preferable to impart water repellency or waterproofness. In addition, a metal nobler than iron can be used as a material to be filled, and the corrosive environment can be detected with high sensitivity by the cathode effect. Such a structure prevents the retention of water in the through holes and the flooding of the dielectric 7. As a result, it is possible to suppress the apparent increase of the electrostatic capacity in the wet state, the moisture absorption to the dielectric 7, and the deterioration due to it, and it becomes possible to measure the stable electrostatic capacity and improve the reliability of the measurement value. It is possible to

  The dielectric 7 is preferably a dielectric having a dielectric constant of 3 or more, and the thickness thereof is 0.05 mm to 2 mm, because the size of the dielectric is largely involved in the change of the dielectric loss tangent and the capacitance. It is desirable to have a dielectric that exhibits less change with temperature. This makes it possible to improve the measurement sensitivity of the sensor. As a dielectric, a ferroelectric having a dielectric constant as large as possible is desirable, and a polyimide film having a dielectric constant of 3.3 is preferable in terms of manufacturing because it has heat resistance to soldering.

  The counter electrode 10 is preferably a metal having high corrosion resistance. It is premised that the area of the counter electrode 10 does not change in order to capture the decrease due to the corrosion of the iron foil as the electrical characteristics. The counter electrode 10 is a metal having a smaller ionization tendency than the target metal, such as gold or a noble metal typified by platinum or palladium, and having conductivity, and in the case of iron, palladium, copper, nickel, etc. Can be used. In addition to rolling, there is also a method of forming a film by sputtering, vapor deposition, plating or the like. The thickness of the counter electrode 10 does not matter. In addition, the counter electrode 10 may be a material that does not have corrosion resistance as long as it is waterproof and dustproof. When using a non-corrosion resistant material for the counter electrode 10, it can be used by completely waterproofing / dusting-proofing the periphery and the surface with a resin, an exterior material or the like, and completely insulating it from the iron foil portion.

  The lead wire 9 is connected to the iron foil portion 3. And the connection part of the lead wire 9 and the side surface of the corrosion sensor 1 are waterproofed with resin etc., in order to prevent conduction due to the intrusion of water. Further, the iron foil portion 3 may be coated with a mortar in which a corrosion factor penetrates, in order to protect it from corrosion before installation and impact at the time of putting concrete.

  FIG. 3 is a schematic view of the corrosion sensor according to the present embodiment embedded in mortar or concrete. As shown in FIG. 3, the corrosion sensor 1 is spaced from the case 13 by a rubber plate 15, and is adhered to the case by a resin 17. In order to measure the dielectric loss tangent and capacitance, the corrosion sensor 1 solders the lead wire 9 so that the iron foil portion 3 serving as the detection surface is exposed to the surface so that the connection portion of the lead wire 9 is not corroded. In addition, the case 13 is packaged by a case 13, and the inside of the case 13 is filled with a resin 21. The reason for this configuration is to prevent the corrosion of the lead wire 9 and to avoid the influence of the fluctuation of the dielectric constant due to the moisture content of the concrete filled around it. Furthermore, it also has the meaning of protecting the corrosion sensor 1 from the impact at the time of concrete filling.

[Method of manufacturing corrosion sensor]
FIG. 4 is a flowchart showing a method of manufacturing the corrosion sensor according to the present embodiment. First, the iron in the metal foil portion (iron foil portion) is rolled to produce an iron foil (step S101). The iron foil has a thickness of 3 μm or more and 0.1 mm or less. Here, the iron foil may be a thin film formed by vapor deposition or plating, or may be formed in a plate shape.

  Next, the iron foil material and the polyimide material are bonded (step S102). A waterproof part is provided to close the through hole, and a material having waterproofness and corrosion resistance is filled (step S103). Here, for example, an epoxy resin, carbon (carbon paste), a corrosion resistant metal or the like can be used. The through holes may be formed by chemical etching after bonding the iron foil portion and the polyimide, or may be formed by bonding the iron foil portion provided with the through holes in advance and the polyimide. In the case of forming an iron foil portion by film formation by vapor deposition, plating or the like, the through hole can be formed by forming a film after performing mask processing only on the through hole portion in advance.

  Next, a counter electrode plate as a counter electrode is formed (step S104). Here, for example, sputtering, metal deposition, plating, metal coating, attachment of a metal plate and metal foil, and the like can be used. Next, lead wires are connected and waterproofed (step S105), and a corrosion sensor such as case adhesion is attached (step S106).

(Example of verification)
Here, it was verified that a stable capacitance could be measured by providing a waterproof portion so as to close the through hole and filling a material having waterproofness and corrosion resistance. In this verification example, when [I] carbon paste was used as the material having waterproofness and corrosion resistance, the change in capacitance was measured when [II] epoxy resin was used. The verification [I] [II] will be described below. It is as follows.

[I] In the case of using carbon paste [1. Method of verification]
(1) Prepare a 30 × 25 mm corrosion sensor. In this verification, six corrosion sensors (No. 1 to 6) were prepared.
(2) Next, measure the capacitance C of each corrosion sensor with an LCR meter. In addition, the dimensions of each corrosion sensor are measured with a caliper, and the effective area of the iron foil portion which is a detection portion is calculated.
(3) Of the six corrosion sensors prepared, carbon paste was used as a material to be filled in the waterproof portion provided in the through hole for the three corrosion sensors (No. 2, 4, 6). In the filling method, (A) carbon paste is applied to the whole corrosion sensor, and (B) after 10 to 20 seconds, the excess carbon paste is wiped off using a rag (cloth). The work of (A) and (B) was repeated three times, and the waterproof part was filled with carbon. The three corrosion sensors (No. 2, 4, 6) in which the waterproof part was filled with carbon were dried, and the capacitance C of the three corrosion sensors (No. 2, 4, 6) was measured again.
(4) After about 3 days passed thereafter, water was dropped on the surface of the corrosion sensor (No. 1 to 6) using a dropper, and the capacitance C was measured using an LCR meter.

[2. inspection result]
Tables 1 and 2 summarize the measurement results.

  As shown in Table 1, the capacitance of the corrosion sensors (No. 2, 4, 6) coated with carbon increased (increased) by applying carbon. As shown in Table 2, the rate of increase (rate of increase) is approximately equal to the ratio of the through hole area to the detection area. The corrosion sensors (Nos. 1, 3 and 5) not coated with carbon increase the capacitance only by dropping or immersing the corrosion sensor in water. On the other hand, in the corrosion sensors (No. 2, 4, 6) coated with carbon, the capacitance hardly changed even if the corrosion sensor was dipped in or dipped in water.

  As for the corrosion sensors (Nos. 2, 4 and 6), although the capacitance increased after applying the carbon, the fluctuation of the capacitance did not occur after that. That is, by filling the waterproof portion with carbon, it is possible to prevent the entry of water into the corrosion sensor, and as a result, it is possible to prevent the deterioration of the polyimide forming the dielectric. In addition, there is no change in capacitance due to external dryness and humidity.

[II] When using epoxy resin [1. Method of verification]
(1) Prepare a 30 × 25 mm corrosion sensor. In this verification, six corrosion sensors (No. 1 to 3) were prepared.
(2) Next, measure the capacitance C of each corrosion sensor with an LCR meter. In addition, the dimensions of each corrosion sensor are measured with a caliper, and the effective area of the iron foil portion which is a detection portion is calculated.
(3) The three corrosion sensors were filled with epoxy resin as a material for filling the waterproof part provided in the through hole. In the filling method, the through holes of the corrosion sensor were filled with an epoxy resin using a bamboo basket, and then the epoxy resin was cured in a drying oven at 50 ° C. Thereafter, after the temperature of the sensor reached about 20 ° C., the capacitances of the three corrosion sensors were measured.
(4) Thereafter, water was dropped on the surface of the corrosion sensor using a dropper, and the capacitance was measured using an LCR meter.

[2. inspection result]
Tables 3 and 4 summarize the measurement results.

  As shown in Table 3, the capacitance of the resin filled corrosion sensor did not change before and after the resin filled.

  As described above, according to the present embodiment, by providing a waterproof portion formed of a material having waterproofness and corrosion resistance, the absorption of water to the dielectric is prevented, and the capacitance is stabilized. Is possible. As a result, it becomes possible to grasp an accurate corrosion state.

REFERENCE SIGNS LIST 1 corrosion sensor 3 iron foil portion 5 through hole 6 waterproof portion 7 dielectric 9 lead wire 10 counter electrode 13 case 15 rubber plate 17 resin 21 resin

Claims (4)

A corrosion sensor that detects the corrosion environment of steel,
A detection unit formed of a corrosive metal;
A plurality of through holes provided in the detection unit;
A counter electrode provided at a position facing the detection unit;
A dielectric provided between the detection unit and the counter electrode;
A corrosion sensor comprising: a waterproof portion formed to close the through hole and formed of a material having waterproofness and corrosion resistance.   The said waterproof part is formed by carbon, The corrosion sensor of Claim 1 characterized by the above-mentioned.   The said waterproof part is formed by resin, The corrosion sensor of Claim 1 characterized by the above-mentioned.   The corrosion sensor according to claim 1, wherein the waterproof portion is formed of a metal nobler than iron.

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