JPS6129456B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a local susceptibility measuring device for electrochemically measuring local changes in corrosion susceptibility of a metal surface.

As an electrochemical method for measuring the local corrosion susceptibility of a metal surface, there is a method using a corrosion measuring electrode consisting of a probe electrode and a guard electrode. Its structure, as shown in FIG. 1, includes a probe electrode 1 and a guard electrode 2 that is electrically insulated from the probe electrode and surrounds it on the same plane, and is connected to a variable voltage power source 3. Further, a metal specimen 5 is placed facing the probe electrode 1 and guard electrode 2 in the electrolytic solution 4 and connected to a variable voltage power source 3. When a voltage is applied between the probe electrode 1 and the guard electrode 2 and the metal under test 5, the current flows in the electrolyte 4 like a group of streamlines 6, and the metal 5 under test is connected to the probe electrode 1. Current flows only from a portion corresponding to the area of the facing probe electrodes 1. Probe electrode 1
The current flowing through can be measured by the amplifier 8 as a voltage drop across the current detection resistor 7. Since the current flowing through the probe electrode 1 changes depending on the corrosion sensitivity of the surface of the metal under test 5, the corrosion sensitivity can be measured.

The problems with this method are that it requires an electrolytic bath 9 to hold the electrolytic solution 4, that the metal under test 5 needs to be processed into a size and shape suitable for measurement, and that it is difficult to measure a large area. It takes a lot of time. On the other hand, there is a method using a solid electrolyte that allows easy measurement over a wide area. This structure is shown in FIG. In FIG. 2, a solid electrolyte 21 is placed between the probe electrode 1, the guard electrode 2, and the metal under test 5.
By installing this, the local corrosion susceptibility of the metal under test 5 can be measured without requiring an electrolytic bath. This method does not require an electrolytic bath, so it is easy to measure a wide area at any location, but the guard electrode 2 is required, making the electrode structure complicated and difficult to use.

The purpose of the present invention is to provide a local corrosion susceptibility measurement method that can reliably supply an electrolyte to a minute portion of a metal surface without using an electrolytic bath, and can measure the corrosion susceptibility of a minute portion of a metal surface without using a guard electrode. The goal is to provide equipment.

Hereinafter, the present invention will be explained with reference to the drawings. FIG. 3 is a diagram showing the structure of the local corrosion susceptibility measuring device according to the present invention. An electrolytic solution 4 is placed in a hollow electrode holder 31, and a metal electrode 33 is immersed in this electrolytic solution 4. A contact 34 made of a porous material having a tapered portion is fixed to the lower part of the electrode holder 31 .
At this time, the structure is such that the electrolytic solution 4 does not leak out of the electrode holder 31 from any part other than the contactor 34. The tapered tip portion of this contactor 34 that is not in contact with the electrolyte 4 is brought into contact with the metal 5 to be tested. As the contactor 34, a non-conductive porous material such as Teflon, (registered trademark), ceramic, porous rubber, etc., or a water-absorbing material such as felt (hereinafter all of these will be referred to as porous materials) is used. When a voltage is applied between the metal electrode 33 and the metal 5 under test by the variable voltage power supply 3, a current flows through the metal electrode 33 only through the portion of the metal 5 under test that is in contact with the contact 34. Therefore, the smaller the area of the contact portion between the contact 34 and the metal under test 5, the more localized corrosion susceptibility can be measured. The current flowing through the metal electrode 33 can be measured by the amplifier 8. Note that gas generated from the surface of the metal electrode 33 is easily exhausted to the outside through the exhaust port 38. Furthermore, measurement sensitivity can be improved by shortening the distance between the metal electrode 33 and the metal 5 to be tested and reducing the ohmic drop.

According to the present invention, without the need for complicated equipment or complicated operations when using conventional guard electrodes,
In addition, it is possible to quickly measure local corrosion susceptibility at arbitrary positions over a wide range of the metal surface of the test object to be corroded without performing any pretreatment.

FIG. 4 shows an example of measurement results according to the present invention. This measurement is carried out using the apparatus shown in Figure 3. A contact impregnated with an electrolyte, which is a mixed solution of sulfuric acid and salt water, is brought into contact with the rust-free steel test piece over an area of 2φ. This is a measurement of the position where the inserted 2φ copper exists. In FIG. 4, the horizontal axis represents the distance from the center of the rust-free copper surface, and the vertical axis represents the current value flowing through the metal electrode 33. From Figure 4, it is seen that peak currents occur at locations where copper is present, indicating that copper is more susceptible to corrosion than rust-free steel.

FIG. 5 is a structural diagram showing another embodiment of the measurement electrode. In this case, the metal mesh electrode 35 is brought into close contact with the solid electrolyte contact 34 to reduce the ohmic drop.

Here, the measurement electrode used in the present invention has a hollow electrode holder 31 containing an electrolytic solution, and a contact 3 having a tapered part made of a porous material at the bottom thereof.
4 is attached, and the tip of this contactor 34 is brought into contact with the surface of the metal to be tested 5 during measurement. Therefore, the electrolytic solution 54 passes through the contactor 34 under pressure corresponding to the liquid level height in the electrode holder 31, and a sufficient amount is reliably supplied to the surface of the metal under test 5. Moreover, since the contactor 34 has a tapered shape, the electrolytic solution 5 is supplied to a minute area without spreading over the surface of the metal under test 5, and the local corrosion susceptibility of the surface of the metal under test 5 can be measured with high sensitivity. .

As described above, according to the present invention, an electrolytic solution is reliably supplied to a minute area on the surface of a metal to be tested without using an electrolytic bath or a guard electrode, and local corrosion susceptibility in this minute area can be measured with high sensitivity. can do.

[Brief explanation of the drawing]

1 and 2 are diagrams showing the structure of a conventional device used for measuring local corrosion susceptibility, FIG. 3 is a diagram showing an example of the structure of a local corrosion susceptibility measuring device according to the present invention, and FIG. 4 is a diagram showing the structure of a device used for measuring local corrosion susceptibility according to the present invention. FIG. 5 is a diagram showing another example of the present invention. 1... Probe electrode, 2... Guard electrode, 3...
... Variable voltage power supply, 4 ... Electrolyte, 5 ... Test object metal, 7 ... Current detection resistor, 8 ... Amplifier, 9
...Electrolytic cell, 34...Solid electrolyte contactor, 31...
... Electrode holder, 33 ... Metal electrode, 38 ... Exhaust port.

Claims (1)

[Scope of Claims] 1. A contact having a tapered part formed of a porous material, and a hollow shape that is integrally connected to a part of the contact except for the tip and contains an electrolyte therein. an electrode holder, a metal electrode provided in an electrolytic solution in the electrode holder, and a space between the metal electrode and the metal to be tested with the tip of the contactor in contact with the surface of the metal to be tested from above. A local corrosion susceptibility measuring device comprising: a power source that applies a voltage; and a measuring device that measures the current flowing through the metal electrode. 2. Local corrosion susceptibility measurement according to claim 1, characterized in that a metal mesh electrode is used as the metal electrode, and this is brought into contact with the portion of the contact facing inside the electrode holder in the electrolytic solution. Device.