JPH0527818B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a metal corrosion measuring device that non-destructively evaluates the corrosion resistance of metal materials.

[Technical background of the invention and its problems]

Conventionally, the corrosion status of coated metal materials has been evaluated by visual observation of the coated film surface and by measuring the tanδ of the coated film. However, in visual observation, there is a problem that the corrosion judgment criteria are often subjective, or that unless the corrosion of the metal material under the coating film has progressed considerably, no change appears on the coating film surface and judgment cannot be made. On the other hand, the method of measuring tan δ of a paint film often does not allow comparison between the measured value and the actual state of corrosion, and cannot be considered a practical evaluation technique.

For this reason, a metal corrosion measuring device employing the electrochemical measuring means shown in FIG. 1 has recently been proposed. That is, numeral 1 in the figure is an electrolytic cell whose top and bottom are open. This electrolytic cell 1 has a coating film 2 on its surface.
is placed on the coating film 2 of the object to be measured, which is made of a base metal 3 coated with. An electrolyte solution 4 such as a saline solution is contained in the electrolytic cell 1 while the electrolytic cell 1 is installed on an object to be measured. In this electrolyte solution 4, there is a surface 5 to be measured of the coating film 2 that is in contact with the electrolyte solution 4.
A counter electrode 6 for applying electrical stimulation is immersed in the electrode. This counter electrode 6 is usually made of an insoluble metal such as platinum. Further, a reference electrode 7 serving as a reference for measuring the polarization of the surface to be measured 5 is immersed in the electrolyte solution 4 . As the reference electrode 7, a saturated sweetened electrode (SCE), a silver-silver chloride electrode, a platinum electrode with black platinum, or the like is usually used. Married wires 8 and 9 are connected to the counter electrode 6 and reference electrode 7, respectively, and the other end of the lead wire 8 of the counter electrode 6 is connected to a power source (not shown). Furthermore, a lead wire 1 is attached to a part of the base metal 3 that is the object to be measured.
0 is connected by solder or the like through a cutout hole 11 in the coating film 2, and the lead wire 10 is connected to the power source.

When the metal corrosion measuring device is installed in the state shown in FIG. Between C is an equivalent circuit diagram shown in FIG. In addition, R _c and C _c in Figure 2
are the polarization resistance and double layer capacitance of the counter electrode 6, respectively, R _s is the solution resistance of the electrolyte solution 4, R _f and C _f are the absolute wire resistance and capacitance of the coating film 2 on the surface to be measured 5, respectively, R _p ,
C _d is the coating film 2 and base metal 3 corresponding to the surface to be measured 5
The reaction resistance and double layer capacitance in the corrosion reaction at the interface with the base metal 3, and R _n represents the electrical resistance of the base metal 3.

Of the various C and R mentioned above, the solution resistance R _s
is usually very small compared to the coating film resistance R _f and the reaction resistance R _p , while the electrical resistance R _n of the base metal 3 is approximately zero and can be ignored. Also,
Since the polarization measurement is performed between terminal B of the reference electrode 7 and terminal C of the lead wire 10, the polarization resistance of the counter electrode 6
R _c and double layer capacitance C _c are not involved in polarization measurements, and their contributions can be excluded in polarization analysis. When electrical stimulation is applied between the terminals A and C from a power source (not shown), the equivalent circuit that is measured between the terminals B and C and involved in polarization is simplified as shown in FIG. When Z ₁ is the impedance between terminals B and C shown in FIG. 3, Z ₁ is expressed by the following equation (1).

Z ₁ = R _f /1 + JωR _f・C _f + R _p /1 + JωR _p・C _d ...(1) Therefore, by calculating the reaction resistance R _p from the above formula (1), the coating corresponding to the surface to be measured 5 can be calculated. The corrosion reaction (corrosion state) at the interface between the film 2 and the base metal 3 can be measured.

However, in the conventional metal corrosion measuring device shown in FIG. 1, it is necessary to provide a cutout hole 11 in the coating film 2 in order to connect the lead wire 10 to the base metal 3. Since it is necessary to remove a portion of the coating film for corrosion protection, the coating film must be removed and repaired each time a measurement is made, which is extremely inefficient. Moreover, notch hole 1
If the repair in step 1 is incomplete, corrosion may occur from that location. Furthermore, the appearance of the repaired area deteriorates, which poses a major problem in structures where aesthetics are important. Furthermore, in the conventional metal corrosion measuring device shown in FIG.
In order to obtain electrical continuity between the base metal 3 and the base metal 3, it is necessary to interpose an electrolyte solution 4. However, if the surface to be measured 5 is inclined, the electrolyte solution 4 will not be able to completely cover the surface to be measured 5, the counter electrode 6, and the reference electrode 7. As a result, measurements may become impossible or inaccurate, and
There are major problems in handling, such as injection of electrolyte solution 4 at the start of measurement, prevention of leakage during measurement, and treatment of electrolyte solution 4 at the end of measurement.

[Purpose of the invention]

The present invention aims to provide a metal corrosion measuring device that can easily and non-destructively measure the corrosion status of any part of the interface between the paint film and the base metal in a structure made of a base metal coated with a paint film. be.

[Summary of the invention]

The present invention comprises a pair of electrodes having the same shape and made of conductive paste attached to two different points on a coating film on a base metal surface, and an electrical signal containing an alternating current or a plurality of frequencies at the same time between these electrodes. By making the structure equipped with a means for applying
The object of the present invention is to obtain a metal corrosion measuring device having a simple structure that can non-destructively measure the corrosion state of a structure even if the structure is inclined without providing a notch hole in the coating film.

As the conductive paste that is the electrode material, general metals and pastes can be used, such as silver paste, copper paste, aluminum paste, etc. Others, molecular weight number 1000 to number 100000
Polyvinyl alcohol, polyvinyl butyral, etc. are used as a binder, and metal powders such as silver and copper are added at 60 to 90%.
%, and a water-soluble paste prepared using water or water to which a hydrophilic solvent such as acetone is added as a solvent can be used. To form electrodes from such a paste, after wiping the coating surface, which is the surface to be measured, apply the paste to the required electrode area with a brush, or use a mask to spray the paste only on the necessary areas. A method such as spraying with a method such as If it is necessary to remove the electrode after the measurement is completed, remove the paste electrode with an organic solvent that does not dissolve the coating film. In particular, when a water-soluble paste is used, the paste electrode can be removed simply by wiping it with water, and the coating film is not damaged, so that the electrode can be formed and removed repeatedly.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to FIG.

21 and 21' in the figure are shields made of, for example, 13Cr copper for noise prevention. These shields 21, 21' are arranged at a predetermined distance from each other on the coating film 2 of the object to be measured, which is made of a base metal 3 whose surface is coated with the coating film 2.
21' is fixed on the coating film 2 by ring-shaped magnets 22, 22'. The shield 21, 2
Electrodes 23 and 23' each having a circular shape with a diameter of 20 mm and made of silver paste are mounted on the coating film 2 within 1'. This silver paste has an average molecular weight of 20000
of polyvinyl alcohol as a binder, 10%
It was prepared by mixing 70% silver powder into a methanol-water mixture as a solvent. and,
The electrodes 23, 23' are respectively connected to coated copper wires 24, 24' inserted into the shields 21, 21'. The other end of one coated copper wire 24 is connected to a test electrode terminal of a photostat (not shown), and the other end of the other coated copper wire 24' is connected to a reference electrode terminal and a counter electrode terminal. . For example, a Solartron 1250 model is used as an AC source and an impedance analyzer, and a voltage of 0.1 MHz to
The frequency of the impedance is determined by applying an AC voltage with an amplitude of 30 mV or less in a frequency range of 100 kHz.

With such a configuration, as shown in FIG.
The coated copper wires 24, 24' are connected directly to the coating film 2 of
When an alternating current is applied to terminals 3 and 23', the equivalent circuit between the respective covered copper wires 24 and 24' (between terminals A and A') becomes as shown in FIG. In addition, R _f and R _f ' in FIG. 5 are the resistances at the interface between the electrodes 23 and 23' and the coating film 2, respectively, and C _f and
C _f ' is the capacitance at the interface between the electrodes 23, 23' and the coating film 2, respectively. Moreover, R _p and R _p ′ are the electrodes 23 and 23′, respectively.
Reaction resistance such as corrosion reaction at the interface between the lower coating film 2 and the underlying metal 3, C _d and C _d ' are double layer capacitances at the interface. Rm is the electrical resistance of the base metal 3, and R _s and R _s ' are the electrical resistances of the electrodes 23 and 23' made of silver paste.

Among the various capacitances C and resistances R mentioned above, the resistance Rm of the base metal 3 can be considered to be almost zero, and the resistances R _s and R _s ′ of the silver paste electrodes 23 and 23' are also usually several Ω or less. , coating resistance R _f , R _f ′ and reaction resistance
It can be ignored compared to R _p and R _p ′. Therefore, when electrical stimulation is applied between terminals A and A', the equivalent circuit that is measured between terminals A and A' and involved in polarization is simplified as shown in FIG. Let Z ₁ be the impedance between terminals A and A' shown in FIG. 6, and Z ₁ is expressed by the following equation (2).

Z ₁ =R _f /1+JωC _f R _f +R _p /1+JωC _d R _p +R _f ′/1+JωC _f ′R _f ′+R _p ′/1+JωC _d ′R _p ′
...(2) However, J = √-1 Also, by making the two sets of electrodes 23 and 23' made of silver paste shown in Fig. 4 the same shape,
R _f = R _f ′, C _f = C _f ′, R _p = R _p ′, C _d = C _d ′,
Impedance Z is simplified as shown in the following equation (3).

Z=2R _f /1 + JωC _f R _f +2R _p /1 + JωC _d R _p ...(3) Therefore, by finding the reaction resistance R _p from the above equation (3), Corrosion reactions (corrosion conditions) at the interface between the coating film 2 and the base metal 3 corresponding to the measurement surface can be measured. Also, the same
As shown in equation (3), the reaction resistance of the corrosion reaction to be measured is twice the true reaction resistance R _p , so noise can be easily eliminated and measurement accuracy can be improved.

In fact, when a test piece with coating film 2 coated on the surface of base metal 3 was immersed in 3% saline solution for one month and then measured using the measuring device of this example, the resistance was approximately
The resistance was 130MΩcm ² and the capacitance was 350pF/cm ² . On the other hand, after removing the silver paste electrode from the test piece,
% saline solution and measured using the test piece as a working electrode, a platinum plate as a counter electrode, and a saturated calomel electrode as a reference electrode.The resistance was 70MΩcm ² and the capacitance was
The resistance was 800 pF/cm ² , and the resistance measured by the device of the present invention was half and the capacitance was doubled, confirming the validity of the present invention.

In addition to measuring the AC impedance using the metal corrosion measuring device according to the present invention, in addition to the method of analyzing the relationship between current and voltage while changing the frequency of the AC, it is also possible to measure the AC impedance using a signal containing many frequency components, such as simulated noise or pulses. A method of applying a signal and analyzing the frequency together with the response thereto, or a method of using an impedance bridge can be adopted.

〔Effect of the invention〕

As detailed above, according to the present invention, when measuring a structure such as coated steel made of a base metal coated with a coating film, it is not necessary to form a cutout hole in the coating film for leading out the lead wire, and the coating film It is possible to provide a metal corrosion measuring device that can non-destructively and easily measure the corrosion situation under a paint film from above. In addition, measurements can be performed using only electrodes made of conductive paste without using an electrolyte, which is indispensable for normal electrochemical measurements, making measurements extremely easy even when the surface to be measured is not horizontal. . Furthermore, since an electrolytic bath is not required, the actual device can be attached to an object to be measured placed in a narrow space such as a pipe, and coating evaluation can be easily performed.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing a conventional metal corrosion measuring device, Fig. 2 is an equivalent circuit diagram between terminals A and C when the device in Fig. 1 is installed on an object to be measured, and Fig. 3 is a schematic diagram showing a conventional metal corrosion measuring device. Fig. 4 is a schematic diagram of a metal corrosion measuring device showing an embodiment of the present invention, and Fig. 5 shows the device shown in Fig. 1 installed on an object to be measured. Equivalent circuit diagram between terminals A and A' when
FIG. 6 is an equivalent circuit diagram extracted from FIG. 5 that relates to potential response. 2... Paint film, 3... Base metal, 21, 21'...
...Shield, 22, 22'...Ring magnet, 2
3, 23'... Electrode made of silver paste, 24,
24'...Coated copper wire.

Claims (1)

[Claims] 1 A pair of electrodes of the same shape and made of conductive paste are attached to two different points on the coating film on the underlying metal surface, and an electrical signal containing alternating current or multiple frequencies is applied simultaneously between these electrodes. A metal corrosion measuring device characterized by comprising means.