JPH0333007Y2 - - Google Patents

Description

[Detailed explanation of the idea]

The present invention relates to a gel electrode cell for electrical measurement that measures the AC impedance and DC resistance of a metal plate coated with a film. In painted parts that are painted for the purpose of preventing metal corrosion, it is necessary to judge the quality of the paint film before appearance defects occur. The following three events serve as a guideline for such judgment. (1) It is said that a coating whose DC resistance decreases to 10 ⁶ Ω-cm ² or less in a short period of time will develop defects in the coating within a short period of time. (2) Paint films with a high water absorption rate generally have a significant drop in DC resistance, and the corrosion resistance of the paint film is also poor. The water absorption rate of this coating film can be determined by the following formula (1) by measuring the capacitance of the coating film, but unlike DC resistance, there is no clear guideline. Moisture (%) = 100log (C _o /C _p )/log80...(1) Here, C _p is the initial coating film capacitance, and C _o
indicates the capacitance of the coating film after n hours of immersion. (3) It is said that if the tan δ of the paint film exceeds 0.2, defects will occur in the paint film within a short period of time. Here, this tanδ is called AC loss, and is a characteristic value that can be calculated from the AC resistance, capacitance, and measurement frequency ω of the coating film, and is often used to evaluate the characteristics of insulation materials, etc. It is a numerical value, and the smaller the value, the better the insulation ability. In this way, the quality of the coating film on the painted member (test object) is determined by its electrical properties. For this reason, conventionally the following method was used to judge the quality of the coating film. (b) Immerse the test object with a lead wire attached in an electrolyte aqueous solution, and place an electrode (counter electrode) made of stainless steel, platinum, etc. with a lead wire attached in the same aqueous solution, and connect a measuring device between both lead wires. A method for measuring the DC resistance and capacitance of a test object. (b) Add a thickener such as acetylcellulose to the electrolyte solution to make a conductive paste. This paste is applied to the surface of the subject to form an electrolyte layer, and an aluminum foil is pasted on top of this to form a counter electrode. Then, lead wires are connected to the underlying metal surface of the test object and the aluminum foil (counter electrode), and a measuring device is provided between these lead wires to measure the direct current resistance and electric capacitance of the test object. (c) A felt or sponge impregnated with an aqueous electrolyte solution is interposed between the subject and a metal plate (counter electrode) such as aluminum foil. Then, lead wires are connected to the base metal surface of the test object and the counter electrode, respectively, and a measuring device is provided between these lead wires to measure the direct current resistance and electric capacitance of the test object. However, the conventional measurement techniques described above have various drawbacks as shown below. That is, the measurement technique (a) has drawbacks such as difficulty in measuring large objects, and inability to eliminate the effects of edges and end faces, making accurate measurements impossible. In the measurement technique (b) above, the paste is applied to each specimen, which makes the work complicated, and securing an accurate measurement area is impaired due to the paste protruding.
The disadvantages include that the paste must be removed after measurement, making the work complicated, that aluminum foil has low strength and is difficult to reuse, and that a large number of electrodes are required. Furthermore, the above measurement technique (c) has the disadvantage that it is difficult to control the amount of electrolyte aqueous solution impregnated into the felt, etc., making it usually impractical. The present invention was developed in view of the above circumstances, and it is possible to measure the direct current resistance and It is an object of the present invention to provide a gel electrode cell for electrical measurements with an extremely simple structure that allows capacitance to be measured simply and in a short time. That is, the present invention includes a single-sealed cylindrical container made of an insulating material, an electrode made of a corrosion-resistant material disposed inside the container, and a flat solidified container filled with the container so as to enclose the electrode. It has a shape in which the end portion slightly protrudes from the open end of the container, and
A gel electrode cell for electrical measurements, comprising an aqueous electrolyte gel containing at least an acrylamide monomer, N,N'-methylenebisacrylamide, N,N,N',N'-tetramethylethylenediamine, and ammonium persulfate. It is. Hereinafter, one embodiment of the present invention will be described in detail with reference to FIG. Reference numeral 1 in the figure indicates a container made of an insulating material such as plastic or ceramic and having a cylindrical shape with one side sealed or a rectangular cylindrical container with one side sealed. In other words, this container 1 has a structure in which, for example, the bottom side is open and the top wall 2 is closed, and a hole 3 is opened in the center of the top wall 2 for pulling out the terminal wire described later. . A flat electrode 4 is disposed within the container 1 . The electrode 4 is made of a metal such as stainless steel or nickel, or a material such as carbon, which has corrosion resistance against electrolyte aqueous solutions such as salts. Further, a terminal wire 5 is connected to the upper surface of the electrode 4, and the terminal wire 5 is led out through the hole 3 in the upper wall 2 of the container 1. Note that the space between the hole 3 in the upper wall 2 and the terminal wire 5 is sealed with an adhesive 6. The container 1 is filled with an electrolyte aqueous gel 7 so as to surround the electrode 4, and the solidified flat end of the gel 7 is slightly (for example, 0.1 mm) away from the open end of the container 1. ) protruding protrusion 8
A gel electrode cell C is constituted by forming. As shown in FIG. 2, the protrusion 8 of the aqueous gel 7 in the gel electrode cell C shown in FIG. A measuring device 11 is provided between the lead wires L ₁ and L ₂ drawn out from the base metal 9 of the specimen S and the DC resistance of the coating 10 of the specimen S shown below, and the same coating. 10
Measure the AC impedance of (i) Measuring the DC resistance of the film It is customary to measure the DC resistance of the film 10 of the subject S by a method generally called Bacon's method. FIG. 3 schematically shows a circuit for measuring DC resistance according to FIG. 2, and the voltage E ₀ when the switch SW is opened can be expressed by the following equation (2). E ₀ =E×R _V /R _C +R _G +R _B +R _V …(2) [However, in the formula, E is the standard voltage, R _C is the DC resistance of the film, R _G is the DC resistance of the gel 7, R _B represents the internal resistance of the standard voltage, and R _V represents the internal resistance of the voltmeter V. ] Furthermore, the voltage E _S when the switch SW is short-circuited can be expressed by the following equation (3). E _S =E×1/1/R _S +1/R _B +R _V /R _C +R _G +
1/1/R _S +1/R _B +R _V ×R _V /R _B +R _V ...(3) [However, R _S in the formula indicates the short-circuit DC resistance. ] Here, consider the case where R _V ≫R _C ≧R _S. However, it is assumed that R _C ≧R _S ≫R _G ≧R _B or R _C ≧R _S ≫R _B ≧R _G already holds true. Then, the above equations (2) and (3) can be approximated as shown in the following equations (4) and (5). E ₀ =E …(4) E _S =E×R _S /R _C +R _S …(5) Therefore, the DC resistance R _C of the film to be measured is determined by the following formula:
It can be obtained using (6). R _C = R _S (E _O /E _S −1) …(6) (ii) Measuring the AC impedance of the film An impedance bridge is used to measure the capacitance and tanδ of the film, and a 1 kHz power supply is used. A sine wave is usually used. Figure 4 schematically shows the circuit used to measure AC impedance according to Figure 2, and the electrical capacitance C _T and AC resistance R _T in the same circuit are expressed by the following equations (7) and (8). be able to. C _T = 1/1/C _f + 1/C _C ′...(7) R _T =R _f +R _G +R _C ′...(8) [However, C _f in the formula is the electric capacity of the electrode 4 interface,
C _C ′ is the capacitance of the film, R _f is the AC resistance at the interface of the electrode 4, R _g is the AC resistance of the aqueous gel 7, and R _C ′ is the AC resistance of the film] By the way, the electrode 4 in the above formula (7) Interface capacitance C _f
Comparing the film capacitance C _C ′, C _f is mF,
Since C _C ′ is on the order of nF and C _f ≫C _C ′, it can be approximated as shown in the following equation (9). C _T =C _C ′ …(9) Also, the above formula (8) is usually R _C ′≫R _f ≧R _G or R _C ′≫
Since R _G ≧R _f , it can be approximated as shown in the following equation (10). R _T =R _C ′...(10) Therefore, by using the above C _T and R _T ,
The capacitance and AC resistance of the film can be determined, and from this the water content of the film can be calculated. Further, tan δ can be determined using the following equation (11). tanδ=1/(ωR _T C _T ) …(11) [However, ω=2πf (f is 1kHz)] Therefore, the gel electrode cell for electrical measurement of the present invention has the following effects. play. Since a gel electrode cell is installed relative to the subject, a constant measurement area can always be ensured, which in turn makes it possible to accurately measure DC resistance and AC impedance. Since the electrolyte is fixed as a gel, measurements can be made in less than 1/10 the time compared to conventional methods. Since the electrolyte is fixed as a gel, it is portable and can be easily measured outdoors. Next, a specific gel electrode cell of the present invention and experiments using the gel electrode cell will be described in detail below. Example 1 First, add 300g of primary potassium chloride to 1 part of distilled water.
The mixture was added and dissolved while heating to 40° C. After completely dissolving, 50 g of acrylamide monomer was added and dissolved with stirring. Next, add N, N'-
After adding 1 g of methylenebisacrylamide (crosslinking material) together with 0.5 ml of N,N,N',N'-tetramethylethylenediamine (polymerization initiator), the mixture was thoroughly stirred and dissolved until no residue remained. Furthermore, 1 ml of a 1% aqueous solution of ammonium persulfate was added, and the prepared solution was immediately poured into a polyethylene single-sealed cylindrical tube, on which an electrode 4 made of a mesh mesh made of stainless steel and a terminal wire 5 made of a stainless steel 0.5 mm diameter wire were provided in advance. The container 1 was filled from the open end of the container 1. At this time, a cylindrical part was formed at the open end of the container 1 with a 1 mm wide vinyl tape, and the prepared liquid was poured into that part. Thereafter, when the prepared solution solidified into a gel-like state, the vinyl tape was peeled off to produce the gel electrode cell shown in FIG. 1, in which the protrusion 8 of the gel 7 was 1 mm. However, when we measured the electrical characteristics of the test object's film using the gel electrode cell of Experimental Example 1, we found the following results:

[Table] As shown in Table 1 above, the gel electrode cell of the present invention can selectively measure the coating film at a representative part (center) of the subject, so a stable measuring body can be obtained. On the other hand, in the method of immersing the specimen in an electrolyte aqueous solution (comparative example), an error in the electrical capacity caused by the edges of the specimen is added to the measured value by about 5 to 15%, making stable measurement difficult. becomes. In addition, the gel electrode cell of the present invention was able to withstand more than 400 uses because the gel had sufficient strength. Example 2 The amount of potassium chloride added to the gel preparation solution was 50%.
The gel electrode cell shown in FIG. 1 was manufactured in the same manner as in Experimental Example 1 using the same composition as in Experimental Example 1 except that the amount of the acrylamide monomer added was 25g. Therefore, using this gel electrode cell, Experimental Example 1
When the electrical properties of a similar test object were measured, the results shown in Table 2 were obtained.

[Table] As is clear from Table 2 above, stable measured values similar to those in Experimental Example 1 were obtained. Furthermore, the durability of the gel electrode cell was more than 400 times. Reference example: First, add primary potassium chloride to 1 part distilled water at 400°C.
It was added and dissolved while heating to a certain degree, and after completely dissolving, the temperature was raised to 90°C. After the temperature of the liquid rose to 90°C, 20 g of agar was gradually added and dissolved while checking the dissolution state. Immediately after dissolution, the prepared solution was placed in advance on the electrode 4 made of a stainless steel mesh net and the stainless steel mesh.
The mixture was poured into the container 1 from the open end of a glass single-sealed cylindrical container 1 provided with a terminal wire 5 made of a 0.5 mmφ wire. At this time, the open end of container 1 has 0.5
A mm-wide vinyl tape was provided in a cylindrical shape, and the prepared solution was poured into this area. After this, when the prepared solution solidifies into a gel, peel off the vinyl tape and remove the gel 7.
A gel electrode cell as shown in FIG. 1 was manufactured in which the protrusion 8 was 0.5 mm. When the gel electrode cell of this reference example was used to measure the electrical characteristics of the same test object as in Example 1, the results were shown in Table 3 below.

[Table] As is clear from Table 3 above, similar to Experimental Example 1, stable measured values were obtained. However, because the gel strength was not as strong as acrylamide gel, the durability of the gel electrode cell was reduced to about 30 times. As detailed above, according to the present invention, the DC resistance and electric capacity (AC impedance) of various coatings applied to the surface of a metal plate can be easily and accurately measured in a short time, and the superiority or inferiority of the coating can be accurately determined. Therefore, it is possible to provide a gel electrode cell for electrical measurement that can be used for electrical measurements and has a simple structure.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a gel electrode cell showing an embodiment of the present invention, FIG. 2 is a schematic diagram showing how the gel electrode cell measures the electrical characteristics of a subject, and FIG. FIG. 4 is a diagram showing a schematic circuit when measuring the DC resistance of the film, and FIG. 4 is a diagram showing a schematic circuit when measuring the capacitance of the film in FIG. DESCRIPTION OF SYMBOLS 1... Container, 4... Electrode, 7... Electrolyte aqueous gel, 8... Protrusion, 9... Base metal, 10...
Film, 11... Measuring device, C... Gel electrode cell, S
...Subject.

Claims (1)

[Scope of utility model registration request] A single-sealed cylindrical container made of an insulating material, an electrode made of a corrosion-resistant material disposed inside the container, and a flat end portion filled with and solidified so as to enclose the electrode in the container. an aqueous electrolyte gel having a shape slightly protruding from the open end of the gel and containing at least an acrylamide monomer, N,N'-methylenebisacrylamide, N,N,N',N'-tetramethylethylenediamine, and ammonium persulfate. A gel electrode cell for electrical measurement, characterized by comprising: