JP2013185872A - Electrochemical measuring probe and coating film evaluation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrochemical measuring probe and a coating film evaluation method, which prevent leakage of an electrolytic solution on a non-flat part and allow for highly accurate measurement.SOLUTION: A counter electrode 15 and a reference electrode 16 are inserted in the inside of a probe 1 filled with an electrolytic solution 14. A tip of the probe 1, which contacts a measuring object, is provided with a sponge 13 holding the electrolytic solution 14, and side faces of the sponge 13 are exposed. The sponge 13 preferably has a 30% compression stress of 3.0 to 4.7 kPa, a pore diameter of 130 to 200 μm, and a water retention rate of 1150 to 1300%. The electrolytic solution 14 preferably contains a surface active agent and water-soluble polymer, and has a viscosity of 30 to 1000 mPa s.

Description

  The present invention relates to an electrochemical measurement probe and a coating film evaluation method used for inspecting a deterioration state of a coating film having electrical insulation properties such as a coating film provided on a structure.

In order to protect structures such as buildings and equipment installed outdoors, protective films such as paint films and oxide films are provided. These protective films are water, salt, dust, light rays, pollutants, etc. Deteriorated over time under the influence of Deterioration of the protective film, for example, defects such as peeling or cracking, may expose the structure under the protective film and cause the steel material to corrode as a result of exposure to the external environment. In order to accurately perform the maintenance of the structure, it is desirable to periodically examine the deterioration state of the protective film, for example, as necessary, and to consider repainting or repairing of the coating.
Conventionally, for example, Patent Document 1 describes an electrochemical measurement method and apparatus for grasping the anticorrosion function of a film using an alternating current impedance method in order to grasp the deterioration state of the anticorrosion film.

JP 2005-274138 A

The conventional electrochemical measurement method is based on whether or not the structure is electrically insulated by contacting the electrolytic solution to energize a certain area of the structure to be measured and measuring the electrical resistance and impedance. The performance of the protective film is evaluated.
In some cases, a coated steel sheet used for building materials, roofing materials, and the like is intended to be measured for non-flat portions such as bent portions and uneven portions, such as when bent after coating. As a result of processing such as bending, the non-flat portion is subjected to a greater load on the protective film, and the deterioration may proceed faster than the flat portion. However, in the conventional apparatus, the electrolyte solution easily leaks in the non-flat portion, and measurement is difficult.

  The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide an electrochemical measurement probe and a coating film evaluation method capable of preventing leakage of an electrolyte solution in a non-flat portion and measuring with high accuracy. To do.

In order to solve the above problems, the present invention provides a probe in which a counter electrode and a reference electrode are inserted in a probe filled with an electrolyte solution, and a sponge for holding the electrolyte solution is provided at a tip portion where the probe contacts a measurement object. Provided is an electrochemical measurement probe, characterized in that the side surface of the sponge is exposed.
The sponge preferably has a 30% compressive stress of 3.0 to 4.7 kPa, a pore diameter of 130 to 200 μm, and a water retention of 1150 to 1300%.
The electrolytic solution preferably contains a surfactant.
The electrolytic solution preferably contains a water-soluble polymer and has a viscosity of 30 to 1000 mPa · s.
In the present invention, the measurement object is a structure having a coating film on a metal surface, and the deterioration of the coating film is evaluated by measuring an alternating current impedance using the electrochemical measurement probe. A method for evaluating a coating film is provided.
It is preferable that the surface of the measurement target has a concave portion or a convex portion, and the sponge is brought into close contact with the structure by pressing and deforming the sponge against the concave portion or the convex portion.

  According to the present invention, the sponge can easily follow the non-flat portion, and the electrolyte can be prevented from leaking, thereby enabling high-precision measurement.

It is (a) assembly drawing which shows an example of the probe for electrochemical measurements of this invention, (b) Parts sectional drawing, (c) Assembly sectional drawing, and (d) End view of syringe front end side. It is a side view which shows an example of the coated steel plate which carried out the bending process. It is a schematic diagram which shows an example of the structure of an object to be measured, and an equivalent circuit. It is a graph which shows an example of a measurement result.

The present invention will be described below based on preferred embodiments with reference to the drawings.
FIG. 1 shows an example of an electrochemical measurement probe 1 according to this embodiment. The probe 1 includes a syringe 10 in which a piston 12 is inserted into a cylinder 11 serving as an outer cylinder, a sponge 13 provided at a tip portion 11a of the cylinder 11, an electrolyte solution 14 filled in the syringe 10, an electrolysis A counter electrode 15 for energizing an object to be measured through a sponge 13 and an electrolyte solution 14 sufficiently containing a liquid, and a reference electrode 16 as a reference for potential are provided. The electrodes 15 and 16 are held by the piston 12, and the electrode tip portions 15 a and 16 a are accommodated in a recess 12 b provided at the tip portion 12 a of the piston 12.

  The piston 12 is inserted from the base end portion 11b (opposite the tip end portion 11a) side of the cylinder 11, and the electrolyte solution 14 is pressed toward the sponge 13 by pushing the piston 12, and the inside of the sponge 13 and the tip end portion of the electrode are pressed. The recess 12b for accommodating 15a, 16a can be filled with the electrolyte solution 14. The electrode tip portions 15a and 16a are disposed at a position deeper than the tip portion 12a of the piston 12. Even if the piston 12 is pushed in until the tip portion 12a of the piston 12 contacts the sponge 13, the electrode tip portions 15a and 16a It does not hit the sponge 13. The cylinder 11 has a tip portion 11a having a smaller diameter than the body portion 11c, and the sponge 13 also has a tip surface 13a having a smaller diameter than the portion 13c accommodated in the body portion 11c of the cylinder 11. The sponge 13 may or may not be fixed in the cylinder 11 by adhesion or the like.

  In the probe 1 according to this embodiment, the distal end surface 13a of the sponge 13 protrudes from the distal end portion of the syringe 10 (specifically, the distal end portion 11a of the cylinder 11), and the side surface 13b of the sponge 13 is exposed. That is, the sponge 13 can be easily deformed at the tip of the probe 1. Thereby, even when the measurement target has a non-flat portion, the tip 13a of the sponge 13 is made to follow the shape of the non-flat portion by pressing and deforming the sponge 13 against the concave or convex portion of the measurement target. It can be brought into close contact with the object. The area where the sponge 13 is in contact with the surface of the measurement object is substantially equal to the area of the tip surface 13a of the sponge 13 and can be electrochemically measured under substantially the same measurement conditions regardless of the degree of deformation. .

For example, when the measurement target is a bent portion 23 of a coated steel sheet that has been bent (see FIG. 2), the height H of the bent portion 23 is smaller than the diameter of the sponge 13, but the width W of the bent portion 23 is the width of the sponge 13. May be larger than diameter. According to the probe 1 of the present embodiment, the sponge 13 is also deformed with respect to such a bent portion 23, and the tip surface 13a thereof is in a certain area range of the bent portion 23 (about the area of the tip surface 13a of the sponge 13). It is possible to adhere. The sponge 13 is preferably projected over 360 ° around the distal end surface 13a. The length L by which the tip end surface 13a of the sponge 13 protrudes may be about several times the height of the unevenness of the measurement target, and does not have to be the entire length of the sponge 13, but is, for example, 1 to 5 mm or more. It is preferable that the length protrudes from the tip of the syringe 10.
If the tip surface 13a of the sponge 13 does not protrude from the tip of the syringe 10 and the entire side surface 13b of the sponge 13 is covered by the cylinder 11 or other member, the cylinder 11 or other member Since the deformation of the sponge 13 is limited, the gap is easily opened, and it is not easy to make the tip surface 13a of the sponge 13 adhere to the non-flat portion.

  In order to suppress leakage of the electrolyte solution 14 contained in the sponge 13 when the tip surface 13a of the sponge 13 is brought into contact with the measurement target 20, the electrolyte solution 14 contains a water-soluble polymer that serves as a thickener, It is preferable to adjust to high viscosity. The viscosity of the electrolytic solution 14 is preferably, for example, 30 to 1000 mPa · s.

  In addition, when the viscosity of the electrolytic solution 14 is high, the electrolytic solution 14 is difficult to sag, but it is difficult to penetrate into a defective portion such as peeling or cracking of the coating film. It is preferable to reduce the tension. Examples of the electrolytic solution include a solution in which a salt such as an alkali metal chloride (Na, K, etc.) or a sulfate is used as an electrolyte and dissolved in a solvent such as water or a polar organic solvent. When adding a surfactant to the electrolyte, there are options such as a cationic (cationic) surfactant, an anionic (anionic) surfactant, an amphoteric surfactant, and a nonionic surfactant. Can be used.

Examples of the material of the sponge 13 include PVA (polyvinyl acetal), PU (polyurethane), and cellulose. PVA sponge is preferable because it has high hydrophilicity, causes capillary action due to fine pores, and is excellent in water absorption and water retention.
The sponge 13 preferably has moderate hardness and voids. For example, it is preferable that the 30% compression stress is 3.0 to 4.7 kPa, the pore diameter is 130 to 200 μm, and the water retention is 1150 to 1300%. If the sponge 13 is too hard, it is difficult to deform along the processed portion as shown in FIG. 2, but if it is too soft, liquid leakage due to excessive deformation occurs. From the viewpoint of adhesion (followability) to the non-flat portion, it is preferable that 30% compression stress or the like is within a predetermined upper limit and lower limit. In addition, if the size of the gap of the sponge 13 is too small, the supply of the electrolyte solution 14 to the measurement target tends to be insufficient, and if the size is too large, the electrolyte solution 14 tends to leak. In order to optimize the seepage of 14, the pore diameter, water retention rate, etc. are adjusted, and the electrolyte 13 is sufficiently contained so that the sponge 13 does not become an electrical resistance and falls within the predetermined upper and lower limits. It is preferable.
Since the probe of this embodiment does not have liquid leakage or liquid dripping, in a member provided with a narrow interval between the processing parts such as a roof plate and a steel sheet pile, not only the measurement of the processing part having a non-flat part but also the processing Even in the measurement of a flat but narrow general part (narrow part) between the parts, the measurement can be performed by applying the probe to the measurement object from below the measurement object upward or from side to side.

The 30% compression stress (kPa) is the stress when the sponge is compressed 30% in the thickness direction, and is a value obtained by dividing the load F at 30% compression by the cross-sectional area S perpendicular to the compression direction ( F / S).
The pore diameter (μm) is a measured value of an average pore diameter based on ASTM (Designation: D4404-84), and can be specifically obtained using a mercury intrusion porosimeter.
The water retention rate (%) is the mass percentage that water occupies when it is hydrated to the saturated state, and measures the mass Mdry of the sponge in the dry state and the mass Mwet when hydrated to the saturated state. Mwet−Mdry) / Mdry × 100.

Further, according to the present invention, the deterioration of the coating film is evaluated by measuring the AC impedance using the above-described electrochemical measurement probe with the structure having the coating film on the metal surface as the measurement object. Can do.
The method of electrochemical measurement is not particularly limited, and can be performed in the same manner as in the past. As shown in FIG. 3, when the measuring object 20 is a structure having a coating film 22 on the surface of a steel material 21, the surface of the coating film 22 is covered with the electrolytic solution 14 supplied from the sponge 13 of FIG. By bringing a working electrode (not shown) into contact with a portion of the steel material 21 where the metal is exposed, a current can flow between the working electrode and the counter electrode 15 from an AC power supply.
At this time, an electrostatic capacity C ₁ is generated by the electric double layer of the coating film 22 sandwiched between the electrolytic solution 14 and the steel material 21. In addition, if there is a defective portion 24 such as peeling or cracking of the coating film 22, in order for a current to flow through the defective portion 24, a bulk solution resistance R ₀ of the electrolytic solution 14 or a solution resistance R ₁ in the defective portion 24 is added. . Further, when the corroded portions 25, such as rust defect 24 is formed, it occurs the electrostatic capacitance C ₂ by reaction resistance R ₂ and the electric double layer even in metal interface. However, in such an RC parallel circuit, if the current to be supplied is a high-frequency current, charge transfer through the capacitor becomes significant, and the contribution of resistance decreases.

The impedance Z in alternating current can be expressed as a complex number by a real part Z ′ (resistance R) corresponding to the electric resistance of the direct current circuit and an imaginary part Z ″ (reactance X) generated by an inductor or a capacitor, Z = Z ′ + jZ "= R + jX. Here, j is an imaginary unit. The reciprocal of complex impedance Z is admittance Y (Y = Z ⁻¹ ), the real part of admittance Y is referred to as conductance G (the reciprocal of electrical resistance in a DC circuit), and the imaginary part of admittance Y is referred to as susceptance B. = G + jB. Further, when the complex impedance Z is expressed in a polar form, it is expressed as Z = | Z | × exp (jθ). Here, | Z | is the absolute value of Z, and θ is the deflection angle. Examples of measurement parameters in the AC impedance measurement method include Z ′, Z ″, | Z |, θ, and the like.

As the measuring device, the measurement range is 10Ω to 1000MΩ, the measurement frequency can be selected from a plurality of 1Hz, 10Hz, 100Hz, 1kHz, 10kHz, 100kHz, etc., the AC voltage is 10mV to 1000mV, the DC bias voltage is It is preferable that it is −1.50 to 0.00V, and the number of integrations is 5 cycles (5 cycles) or more. As the power source, it is preferable that a battery or a 100V power source can be used. If the weight of the measuring device is made as light as possible, it is easy to make it portable (portable), and is preferably less than 1.5 kg. It is preferable to set the measurement conditions only by using an arrow key or a numeric keypad of a general-purpose input device. In order to calibrate the apparatus, it is preferable to use a calibration plate having a predetermined resistance value such as 1 kΩ.
The configuration of the container (probe main body) filled with the electrolyte with the probe may not be a syringe, but in that case, in the present invention, a sponge for holding the electrolyte is provided at the tip of the container, and the tip of the sponge Preferably protrudes from the tip of the container.

  Hereinafter, the present invention will be specifically described with reference to examples.

(AC impedance measurement example)
Prepare a coated steel plate (pre-coated metal) as the object of measurement, flat general part with a healthy coating film, cut part of the coating film cut to a length of 1 mm using a cutter knife, bent as shown in FIG. The AC impedance was measured for three types of bent portions.
FIG. 4 shows the measurement results. The measurement parameter at this time is the absolute value | Z | of the impedance, and the average value obtained by adjusting the potential of the reference electrode to 0 V and measuring and integrating for 5 cycles (5 cycles) was used. As the electrolytic solution, an aqueous solution prepared by dissolving 1% by mass of NaCl and 0.2% by mass of a surfactant in water was used. Compared with the general part, it was confirmed that the bent part had a low impedance due to the deterioration of the coating film and showed the same tendency as the cut part.

(Selection of sponge)
When several types of sponges having different hardness and voids were tested from sponges made of polyvinyl acetal (PVA) manufactured by Aion Co., Ltd., the results shown in Table 1 were obtained. If the sponge is too hard (30% compressive stress is high), it is difficult to deform, but if it is too soft, liquid leakage due to excessive deformation occurs, and the evaluation of “deformation” is “x”. In addition, if the size of the gap of the sponge 13 is too small, the supply of the electrolyte solution 14 to the measurement object is likely to be insufficient, and if it is too large, the electrolyte solution 14 is liable to leak. × ”. In addition, when the sponge containing the electrolytic solution itself becomes an electrical resistance, an error occurs in the measurement data. Therefore, when the “electrical resistance” is evaluated, the water retention rate is 1150% or more, which is a level with no problem. It has been confirmed. In Table 1, it can be said that the thing of No1-2 or No1-3 is preferable.

Evaluation criteria for “deformation”: “X” indicates that the sponge cannot visually follow the object to be measured, or that deforms too much and causes liquid leakage.
Evaluation criteria for “bleed out”: “X” indicates that the electrolyte filling work cannot be performed with good workability.
Evaluation criteria for “electric resistance”: “x” indicates that the sponge itself has electric resistance in a state where the electrolyte is sufficiently contained.

(Concentration of water-soluble polymer)
As the electrolytic solution, an aqueous solution prepared by dissolving 2% by mass of sodium sulfate (Na ₂ SO ₄ ) and a water-soluble polymer having a concentration shown in “Water-soluble polymer” in Table 2 in water was used. The water-soluble polymer used here is commercially available carboxymethyl cellulose (CMC). In addition, surfactant is not added to electrolyte solution. The concentration of the water-soluble polymer is 0% by mass (none), 1% by mass, 3% by mass, 5% by mass, and 10% by mass. When the properties were examined, the results shown in Table 2 were obtained. When the viscosity is increased, the electrolytic solution does not sag, but the electrolytic solution is less likely to penetrate into the coating film cracks. Therefore, in Table 2, it can be said that those of No2-2 and No2-3 are preferable.

Evaluation criteria for “sag”: When a sponge containing an electrolytic solution was pressed against an object to be measured, the case where the electrolytic solution did not sag was indicated as “◯”, and the case where the electrolyte sagged was indicated as “X”.
Evaluation criteria for “penetration into coating film crack”: “◯” indicates that the electrolyte solution penetrates well into the coating film crack, “Δ” indicates that the penetration is slightly poor, and “x” indicates that the penetration is poor.

(Concentration of surfactant)
In Table 3, 2% by weight of sodium sulfate (Na ₂ SO ₄ ) and 1% by weight of water-soluble polymer (CMC) were added as the electrolyte, and a surfactant having a concentration shown in “Surfactant” in Table 3 was added. An aqueous solution was used. In Table 4, 2% by weight of sodium sulfate (Na ₂ SO ₄ ), 3% by weight of water-soluble polymer (CMC), and a surfactant having a concentration shown in “Surfactant” in Table 4 were added as an electrolytic solution. An aqueous solution was used. The surfactant used here is an anionic surfactant (Lapisol (registered trademark) A-80 manufactured by NOF Corporation, sodium dialkylsulfosuccinate). Table 3 and Table 4 differ in the concentration of the water-soluble polymer, and for each, the surfactant concentration was 0% by mass (none), 0.001% by mass, 0.01% by mass, 0.1% by mass, Measurements were made by preparing five different electrolyte solutions of 0.2% by mass.

Evaluation criteria for “penetration into coating film crack”: Same as Table 2 (concentration of water-soluble polymer).
Evaluation criteria for “bubble entrainment”: “◯” indicates that bubbles are not generated or rapidly defoamed after the electrolytic solution is prepared, and “×” indicates that many bubbles are likely to remain.

  Lowering the surface tension improves wettability and facilitates penetration into coating film cracks. However, if the addition amount of the surfactant is too large in a state where the viscosity is high, it is difficult for bubbles to escape and it becomes difficult to handle as an electrolytic solution. In Table 3, it can be said that No. 3-2 to No. 3-5 are preferable, and in Table 4, No. 4-2 to No. 4-5 are preferable.

As an example of a preferable composition of the electrolytic solution, an aqueous solution in which 2.0% by mass of sodium sulfate (Na ₂ SO ₄ ), 1.6% by mass of a water-soluble polymer (CMC), and 0.04% of a surfactant are further added. The viscosity is 100 mPa · s, and the surface tension is 26.2 mN / m.

DESCRIPTION OF SYMBOLS 1 ... Probe, 10 ... Syringe, 11 ... Cylinder, 12 ... Piston, 13 ... Sponge, 14 ... Electrolyte, 15 ... Counter electrode, 16 ... Reference electrode, 20 ... Measurement object, 21 ... Steel material, 22 ... Coating film, 23 ... bent part, 24 ... defect part, 25 ... corroded part.

Claims (6)

  A counter electrode and a reference electrode are inserted into the probe filled with the electrolyte solution, and a sponge for holding the electrolyte solution is provided at the tip where the probe contacts the measurement object, and the side surface of the sponge is exposed. An electrochemical measurement probe characterized by comprising:   2. The probe for electrochemical measurement according to claim 1, wherein the sponge has a 30% compressive stress of 3.0 to 4.7 kPa, a pore diameter of 130 to 200 μm, and a water retention of 1150 to 1300%.   The electrochemical measurement probe according to claim 1, wherein the electrolytic solution contains a surfactant.   The said electrolyte solution contains water-soluble polymer, and the viscosity is 30-1000 mPa * s, The probe for electrochemical measurements as described in any one of Claims 1-3 characterized by the above-mentioned.   The said measuring object is a structure which has a coating film on the surface of a metal, The said coating film is measured by measuring alternating current impedance using the probe for electrochemical measurements as described in any one of Claims 1-4. A coating film evaluation method characterized by evaluating deterioration of the film.   The surface of the measurement object has a concave portion or a convex portion, and the sponge is brought into close contact with the structure by pressing and deforming the sponge against the concave portion or the convex portion. Coating film evaluation method.

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