JP3853250B2 - Local corrosion sensor, local corrosion detection method and local corrosion detection apparatus using the local corrosion sensor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a local corrosion sensor that detects with high sensitivity initial local corrosion occurring in a corrosion-resistant metal material, a local corrosion detection method using the local corrosion sensor, and a local corrosion detection apparatus.
[0002]
[Prior art]
Corrosion of metals and alloys having corrosion resistance takes a form in which local corrosion called pitting corrosion proceeds. In other words, pitting corrosion does not occur uniformly on the entire surface but proceeds locally, so that it is difficult to evaluate local corrosion by shape observation.
Conventionally, in order to monitor metal corrosion, a metal sample as a specimen is immersed in the solution, and the surface change is observed with a microscope or measured and evaluated by a measuring means called an AC impedance method. It was. However, in the case of metals and alloys having corrosion resistance, a form of local corrosion called pitting corrosion progresses as described above, and pitting corrosion does not occur uniformly on the entire surface, but progresses very locally. Since the progress speed is slow, it is difficult to evaluate local corrosion by shape observation, and there is a limit in finding the corrosion resistance of metals and alloys and the corrosiveness of solutions to metals and alloys at an early stage. And this is no exception in the measuring means by the alternating current impedance method, and there is a limit to the difficulty in measuring and evaluating pitting corrosion.
[0003]
Several models have been proposed for the cause of pitting corrosion. One of them is a model as shown in FIG. In other words, pitting corrosion is a corrosion phenomenon in which extremely fine holes are formed in imperfect parts of the passive film on the surface of corrosion-resistant metals and alloys such as stainless steel. It is formed. That is, in the depths of the minute holes, the oxygen necessary for the metal oxidation reaction becomes insufficient, and no passive film is formed on the metal surface, as shown in FIG.
Metal M elutes in the aqueous solution and corrosion proceeds. Electrons e generated in metal M at this time ^- Moves to the passive film on the metal surface around the pores and acts on the reduction reaction of dissolved oxygen on the surface of the passive film. In other words, a local battery is formed between the metal surface at the back of the hole and the passive film around the hole, so that the dissolution reaction of the metal in the hole proceeds.
[0004]
As described above, once a hole is formed, oxygen is not supplied to the inner part of the hole, so that a passive film is not formed and a metal dissolution reaction proceeds. In contrast, the reduction reaction of dissolved oxygen proceeds on the metal surface.
At this time, electrons are generated by an anodic reaction on the metal surface in the back of the hole, and are supplied to the cathode reaction region on the surface of the passive film around the hole and consumed.
This reaction model can be expressed by the following equation.
2M → 2M ⁺ + 2e ^- (In the hole)
1 / 2O ₂ + H ₂ O + 2e ^- → 2OH ^- (Passive film surface)
[0005]
Thus, unlike other corrosion, pitting corrosion does not attack the passive film surface around the hole, and only the metal surface deep in the hole continues to be attacked, causing the corrosion to progress deeply. It is said that there is a risk of serious accidents.
[0006]
[Problems to be solved by the invention]
From the above, it is extremely important to discover the pitting corrosion property of metals and alloys at the earliest possible stage and accurately evaluate them. Therefore, there is a demand for the practical use of a method that can quickly evaluate without taking time. . In light of the above circumstances, the present inventors have conducted extensive research to solve the above problems, and as a result, metals and alloys having corrosion resistance are passivated to an ideal state in a solution, that is, the surface of the metal. We focused on the phenomenon that almost no current flows when oxides are formed.
[0007]
In general, the current flowing through the electrode has an area dependency in which the current density decreases as the electrode area increases and the current density increases as the electrode area decreases.
In contrast to this, including the case of the pitting corrosion model as shown in FIG. 11 above, when a current flows through an electrode having a very small area, which is generally called a microelectrode, or an extremely small area, the current that is prominent there Concentration will occur [FIG. 1 (b)].
In such a model of current concentration, which is called a microelectrode, when the current is concentrated, the current density locally increases due to a change in the current distribution due to the edge effect or the curvature effect, and the area dependence of the current density is not established.
Therefore, when the entire metal surface is covered with a passive film, and the local corrosion progresses in the electrode where current does not flow on most of the electrode surface, a hole is formed, as if the current is acting like a microelectrode. It starts to flow in the hole. Therefore, in such a case, even if the area of the electrode is changed, the above-described area dependency of the current density is not observed.
On the other hand, in a non-pitting part electrode where a uniform passive film is formed and the metal surface is passivated, such local current concentration does not occur. Concentration will be observed.
[0008]
Therefore, by pairing multiple electrodes with different areas, measuring the current in combination, and observing the current concentration status, the presence or absence of local corrosion can be observed, so that the presence or absence of pitting corrosion can be determined. The present invention has been made based on this finding. That is, by finding a pair of electrodes having different apparent areas and observing the current concentration state, the knowledge that it can be used as a local corrosion sensor was obtained, and the present invention was made based on this knowledge. It is a thing.
[0009]
[Means for Solving the Problems]
That is, the present invention can evaluate the progress and extent of local corrosion and the soundness against local corrosion by taking the measures described below, that is, can provide a function as a corrosion sensor. It was something that was found. The solution is the following (1) to ( 5 ).
[0010]
( 1 ) Test material and In the local corrosion detection method in the metal material to be Test material Metal material Same metal material as A local corrosion sensor consisting of a plurality of electrodes having different areas, the largest electrode and the smallest electrode of the pair. When Area ratio The The area of the smallest electrode of the pair larger than 1 is 1 cm ² To be below Setting The local corrosion sensor is immersed in a corrosion test solution, each electrode is held at a constant potential, and the current-time linear curve is obtained by plotting the change over time in the current value of each electrode, and then this data is processed. The current value flowing through each electrode is divided by the area of each electrode to obtain the current density, and the obtained data is further processed to obtain the relationship between the current density and the common logarithm of the electrode area, plotted, and from the slope Know whether the current density is area-dependent, and whether this is causing local corrosion Inspect A method for detecting localized corrosion using a localized corrosion sensor comprising a plurality of electrodes having different areas.
(2) The local corrosion using the local corrosion sensor according to (1) above, wherein the pair as a plurality of electrodes having different areas is a local corrosion sensor consisting of at least two pairs of large and small. Detection method.
[0011]
( 3 ) Test material A local corrosion detection method using the local corrosion sensor described in the item (1) or (2), wherein a corrosion test solution having a corrosive action on the metal material is used.
(4) The local corrosion sensor according to any one of (1) to (3), wherein the corrosion test solution is a non-aqueous solution containing a lithium salt or an aqueous solution of ammonium adipate. Local corrosion detection method.
[0012]
( 5 ) In local corrosion detection method using local corrosion sensor, Test material Metal material Same metal material as When a local corrosion sensor composed of a plurality of electrodes having different areas consisting of the above is immersed in a corrosion test solution having a corrosive action on the metal material, and a constant voltage is applied and held between each electrode and the counter electrode The current flowing through each electrode is measured, each electrode area, the current value flowing through each electrode, and the change over time are input to a computer for data processing, the relationship between the voltage application elapsed time and the current density, and the current density The local corrosion detection method using the local corrosion sensor described in any one of (1) to (4), wherein the relationship between the electrode area and the common logarithmic value is displayed as a graph.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described with reference to the drawings and examples.
FIG. 1 shows in principle and schematic a current concentration model using microelectrodes.
In FIG. 1, (a) shows that a constant potential is applied to a pair of parallel electrodes of the same area consisting of a sample electrode and a counter electrode (standard electrode), and a current flows uniformly over the entire surface of both electrodes. Represents an embodiment. On the other hand, (b) shows the state of excessive current concentration when the sample electrode has a very small area. Indicated Is. In the case of FIG. 1 (a), the area of both electrodes is reduced and the current density of the electrodes is increased. However, if one electrode is made minute as shown in FIG. 1 (b), excessive current is concentrated there. The current density at this time shows a very large value as compared with the current density of the normal relationship depending on the electrode area seen in the case of FIG.
[0015]
FIG. 2 shows a principle and model of a current concentration model by pitting corrosion.
That is, FIG. 2A is an electrode model composed of a pair of parallel electrodes having the same area as in FIG. 1A, and a constant potential is applied between both electrodes. In the above model, the sample electrode has a passive film formed on the entire surface thereof, and therefore only a small detectable current flows through the sample electrode. However, if there is a part of the sample electrode where the passive film has been torn, or if local corrosion has already occurred, the current observed will be the damaged part of the film or the local corrosion part. It also includes the current concentrated in the. In other words, this observation alone cannot identify that the current based on the excessive current concentration due to local corrosion is observed, and the current corresponding to the potential flows evenly in the sample electrode. It is only observed as. This is the same even if the electrode area is changed, and the observed current is only observed as a current that uniformly flows through a given sample electrode. That is, it is impossible to determine and identify whether the sample electrode includes local corrosion or local corrosion has occurred.
[0016]
Figure 2 (a) As It represents a local corrosion model. The current flowing through the local corrosion portion in this model can be shown by the current concentration model shown in (b), and this mode can be applied as it is to the microelectrode model described in FIG. This indicates that it can be explained.
[0017]
【Example】
Hereinafter, the present invention will be specifically described based on examples. However, this is merely an aid for understanding the present invention, and is not intended to limit the present invention.
[0018]
(Preparation of sample electrode)
The sample electrode used in the examples described below was made of the same material as the sample metal subjected to the corrosion test, and was produced in the following manner.
In the examples shown below, a sensitive aluminum metal was used as a sample for the corrosion test, and the test was performed based on this. For this sample electrode, aluminum metal was used in the examples disclosed below. However, when the material to be investigated is stainless steel, for example, the same material stainless steel is used. It goes without saying that it must be a thing.
[0019]
First, aluminum PET (a 7 μm thick polyethylene terephthalate sheet laminated with a 0.1 μm thick aluminum foil) was prepared, and 43.2 mm was formed thereon by photolithography. ² , 6.0mm ² 0.7mm ² Three types of squares having different areas were patterned and etched with a corrosive solution composed of phosphoric acid + pure water (1: 1) to passivate the aluminum metal surface.
Next, a copper wire is attached as a lead to a sample made of this aluminum foil to form an electrode, which is placed on a glass plate, and the above-described patterned square aluminum foil portion is removed, and an epoxy is formed. A sample electrode was prepared by coating with resin. The mode is as shown in FIG.
[0020]
That is, FIG. 12 shows a structure in which an aluminum foil is placed on and pasted on a glass plate. The structure consists of a part patterned into a square corresponding to the sample electrode, a terminal part to which a lead wire is attached, and a connecting part connecting the sample electrode part and the terminal part, all of which are integrally formed from one piece of aluminum PET. It has been cut out. Lead wires (copper wires) for measuring current are attached to the terminal portions via silver paste, and the aluminum foil and lead wires of the terminal portions and the connecting portions are all made of epoxy resin, except for the sample electrode portions. It is sealed. In other words, the structure is such that only the sample electrode part is open to the outside, and this makes it possible to easily and reliably ensure the electrical connections, etc. necessary to carry out the corrosion current measurement on the spot. Work can be performed smoothly.
[0021]
In order to obtain a sensor that can be reused in the preparation of the sample electrode, a set of metal materials having a predetermined cross-sectional area is embedded in an appropriate sealing material, and the surface is polished to give a fresh surface. The mode of doing so is also one of the effective and practical embodiments. If this embodiment is specifically illustrated, a structure as shown in FIG. 13 is also conceivable. That is, it has a structure in which a plurality of electrode bars corresponding to sensors having a predetermined area are embedded in a sealing material. FIG. 13 shows a pair of large and small electrodes as the sensor, but it goes without saying that a pair of large, medium, and small is also included as an embodiment. With this structure, it is not necessary to prepare a sensor each time. However, by polishing the surface each time, a new sample metal can be prepared at any time and not only can be reused. The set sample electrode can always ensure a uniform area, there is no change in the measured numerical value, and the stability and reliability of the measurement are ensured.
[0022]
The sensor shown in FIG. 13 is arranged in parallel with the counter electrode according to the arrangement relationship shown in FIG. 14, the lead wire terminal attached to each measurement electrode is connected to a power source through a switch, and a constant potential is applied between both electrodes. In addition, the current value is obtained. Alternatively, a switch may be provided for each lead, and each sample electrode may be selectively used by opening and closing those switches.
[0023]
(Preparation of corrosion test solution, measurement conditions)
Next, [1] LiPF as a corrosion test solution ₆ / PC + DME, [2] LiClO _Four / PC + DME, [3] LiBF _Four / PC + DME, [4] Four different electrolyte compositions of the 5.0 wt% ammonium adipate aqueous solution are prepared, and the aluminum foil sample electrode patterned in the above three different areas in these solutions, and platinum The counter electrode was immersed, the potential between both electrodes was maintained at 5.0 V, and the leakage current flowing through the oxide film of the sample electrode was measured.
In this current measurement, there are no particular limitations on the measurement mode, procedure, measurement means, and the like employed. Needless to say, in addition to the measurement of the leakage current, it can be carried out by a current sweeping means using a potential sweep, an AC impedance method, and other various voltage application methods.
[0024]
(Example 1);
The sample electrode of the aluminum foil and the counter electrode of platinum are LiPF. ₆ The sample was immersed in an electrolytic solution [1] composed of / PC + DME and measured under the above-described measurement conditions. As a result, FIG. 3 (current density-time characteristics) was obtained. FIG. 3 shows an aluminum foil sample electrode having a large area, a medium area, and a small area as an electrolyte (LiPF). ₆ / PC + DME) (current-time characteristics) when held at a constant potential. This figure also shows that the current flow immediately after the start of measurement is unstable. Seen Thereafter, it can be seen that the current density of each sample electrode decreases as the area of the sample electrode increases, and conversely increases as the area of the sample electrode decreases. That is, it was observed from the measurement results shown in FIG. 3 that the current density depends on the electrode area. The result of plotting this with respect to the relationship between the current density and the common logarithm of the area is as shown in FIG.
[0025]
According to FIG. 4, it is clearly shown that the current density linearly decreases to the right as the electrode area increases, and it can be seen that the current density depends on the area of the sample electrode. In addition, regarding the relationship between the current density and the area of the sample electrode in this sample, no difference based on the temporal change was observed, and the same tendency was shown after 15 minutes and after 30 minutes. In any case, these trends are a monotonic gradient in which the current density depends on the area of the sample electrode, that is, the current density is large when the area is small, and the current density is linearly small when the area is large. It showed a downward trend. From now on, no abnormal tendency was observed when the current concentrated in the holes (hereinafter referred to as pits) caused by local corrosion. Therefore, at this stage, it was possible to identify that pitting corrosion did not occur. That is, the measurement results shown in FIGS. 3 and 4 show that there is no abnormal current due to the current concentration generated in the pits, and no signs of occurrence of pitting corrosion are detected, indicating that the material is sound. In fact, no pitting corrosion was observed by surface observation with a digital high scope. From the above, it was confirmed that the curves and straight lines shown in FIG. 3 and FIG. 4 showed no abnormal current due to current concentration occurring in the pits, indicating that no pitting corrosion occurred.
[0026]
The current density-time characteristic shown in FIG. 3 was measured according to the embodiment shown in FIG. That is, a constant voltage was applied by a potentiostat, the current flowing through the sample electrode was read over time, and the current density was obtained and plotted from this (potentiostat used HA151 manufactured by Hokuto Denko Co., Ltd.). Further, the relationship between the current density in FIG. 4 and the common logarithm of the area of the sample electrode is obtained by reading the final current density from the current-potential characteristics of the sample electrode of each area, and the current density with respect to the common logarithm of the area of the sample electrode. Are plotted.
In addition, each figure used in the Example shown below is measured and plotted similarly according to this Example.
[0027]
(Example 2);
Next, a sample electrode made of three types of aluminum foils having a large area, a medium area, and a small area and a counter electrode of platinum were combined with LiClO. _Four The sample was immersed in an electrolytic solution [2] made of / PC + DME, and the current flowing through the sample electrode when the distance between both electrodes was held at a constant potential was measured. As a result, FIG. 5 (current density-time characteristics) was obtained.
According to FIG. 5, the area dependence of the current density as shown in FIG. 3 observed when there is no pitting corrosion is not seen, and it can be seen that the abnormal tendency which is difficult in normal explanation is shown. .
Moreover, as a result of obtaining and plotting the relationship between the current density and the common logarithm of the area of the sample electrode from the results shown in FIG. 5, FIG. 6 was obtained. In FIG. 6, the current density shows a substantially constant value regardless of the size of the area of the sample electrode, and is observed as in the sample of Example 1, that is, when there is no pitting corrosion. It is understood that there is no gradient depending on the size of the area of the sample electrode to be detected, and that it is detected more clearly that it shows an abnormal tendency that is difficult to perform by ordinary explanation.
The sample used for the measurement was photographed with a digital high scope, and as a result of observing the metal surface, pits showing corrosion were observed (FIG. 7).
[0028]
From this result, it was verified that the measurement results shown in FIGS. 5 and 6 indicate that local corrosion has occurred in the sample electrode. That is, pits are generated due to local corrosion, and abnormal current concentration exceeding the normal range occurs there, and the current measured thereby loses its tendency to depend on the electrode area, indicating that it has collapsed. That is, it has been detected and verified that pitting corrosion has occurred.
[0029]
(Example 3);
Electrolyte [3] (LiBF _Four / PC + DME), a measurement test was performed to determine the relationship between the current density and the common logarithm of the area of the sample electrode as in Examples 1 and 2. As a result, the result shown in FIG. 8 was obtained. That is, as in Example 1, the current density showed a monotonous right-down relationship depending on the area of the sample electrode. As for the tendency, no temporal change was observed after 15 minutes and 30 minutes. That is, the measurement results shown in FIG. 8 indicate that the pitting corrosion was not detected because the area-dependent collapse caused by the abnormal concentration of current in the pits was observed when pitting corrosion occurred. It is what. This was proved to be correct from the observation of the surface with a digital high scope and the fact that no signs of corrosion were observed.
[0030]
(Example 4);
Next, the sample electrode was immersed in a 5.0 wt% ammonium adipate aqueous solution [4], and a measurement experiment for determining current density-time characteristics was performed.
The result is as shown in FIG.
According to the measurement results of FIG. 9, the area dependence generally collapses between the sample electrode with the largest area and the second largest sample electrode, and this collapse becomes noticeable from about 220 seconds after the start of the experiment. The area dependence of the current density completely collapses, and this tendency is similar to the case of the electrode having the smallest electrode area.
That is, in the sample electrode in Example 4, it was presumed that the normal area dependence was lost during the measurement and abnormal current concentration was caused, and that pitting corrosion occurred. In other words, it was predicted that abnormal current concentration occurred due to the occurrence of pitting corrosion, and that the area dependence of the current density collapsed. This prediction also coincided with the results of surface observation with a digital high scope, and it was confirmed that pits due to pitting occurred during the measurement and corrosion started.
[0031]
(Example 5);
Using the same electrolyte [4] as in Example 4, a measurement experiment was conducted to determine the relationship between the current density and the common logarithm of the area of the sample electrode after 3 minutes, and the presence or absence of pitting corrosion was detected and identified. .
The result was as shown in FIG.
The relationship between the current density and the common logarithm of the area of the sample electrode shown in FIG. 10 shows area dependence, and the area dependence collapse detected when the current is abnormally concentrated in the pits is shown there. It was not seen, indicating that no pitting corrosion occurred. In fact, no corrosion was observed as a result of surface observation with a digital high scope.
[0032]
As described above, according to the present invention, as shown in the above-mentioned disclosed embodiments, this is achieved by a very simple means, that is, by a very simple means of pairing electrodes having the same material and different areas as the test sample. Thus, a corrosion test can be performed in a short time, and the relationship between the current density of the sample to be tested and the electrode area can be specified, thereby providing a corrosion sensor capable of early detection of the presence or absence of corrosion. It was also clarified from the Examples that a corrosion sensor capable of detecting pitting corrosion that is particularly difficult to find could be provided.
[0033]
As is clear from the above embodiments, the present invention is actually corroded using the same material as that of the test sample, and the current density is obtained from the current value flowing therethrough. For each sample electrode having a different area, the current density-time characteristic, or the relationship between the current density and the common logarithm of the area of the sample electrode is obtained, thereby detecting the area dependence of the current density, It detects the presence or absence of corrosion and the degree of its state, and is based on a very simple principle. The equipment that constitutes the detection means is composed of readily available items and has been proposed in the past. Compared to this type of sensor, it is simpler, reacts more accurately, and is extremely excellent at detecting local corrosion very early. In addition, since the previous ones were not very familiar with the measurement method and were not familiar with data analysis, the present invention requires only a short time for detection and is easy to analyze. It is also excellent in that the result can be obtained immediately.
[0034]
An automatic corrosion sensor shown in FIG. 15 is considered as one embodiment of the invention as an apparatus that automatically performs the above-described measurement and detection / identification of pitting corrosion using a computer. In FIG. 15, a sample electrode having a structure as shown in FIG. 13 in which a plurality of metal rods having different predetermined cross-sectional areas are embedded in an appropriate sealing material is immersed in the corrosion test solution and immersed in the corrosion test solution. A constant voltage power source is connected between the counter electrode and the counter electrode, and a constant voltage is applied between the sample electrode and the counter electrode within one measurement time. In addition, a switch is provided on the lead terminal of each sample electrode, and the sample electrode to be measured can be selected by opening and closing the switch according to a procedure stored in advance in the computer, and the current value of each sample electrode can be selected. It has a structure that can be measured independently. The switch may be a changeover switch.
The current value flowing through the sample electrode is converted into a voltage value by a current-voltage converter, then converted into digital data by an A-D converter, input to a computer, stored in a storage device, and data processed by the computer, Displayed on the display device as current density-time characteristics, or the relationship between the current density and the common logarithm of the area of the sample electrode.
The constant voltage applied between the sample electrode and the counter electrode is also sequentially changed based on a program input in advance to the computer, and the current density-time characteristics at various voltages and the current density and the area of the sample electrode. The relationship with the common logarithm of can be obtained.
[0035]
The main advantages of the corrosion sensor of the present invention are as follows.
1) The corrosion sensor of the present invention is based on the simple principle that a test sample itself having a different area is put in a corrosion test solution and the current density is measured. If the same material as the test sample can be obtained, it is simple and inexpensive. It can be manufactured and no special equipment is required.
Moreover, the test sample used as the corrosion sensor may be a thin foil as disclosed in the examples, and only a very small area is required.
2) The measurement can be performed in a very short time compared to a determination method by a commonly performed exposure test, and the presence or absence of pitting corrosion can be determined in a short time.
3) The test specimen (metal film) used as a sensor can be combined and changed to reflect the material, structure, history, etc. of the structure to be investigated. Judgment is possible.
4) Since the measurement includes an aspect of immersing in a corrosion test solution, it is practical because it is performed based on the corrosive environment, and it is possible to evaluate more sensitively to the influence of deterioration, and high determination accuracy. I can expect.
5) The corrosion sensor of the present invention can detect and predict all local corrosions such as pit corrosion, clevis corrosion, stress corrosion, cracking corrosion fatigue, and intergranular corrosion.
6) By introducing an automatic corrosion sensor using a computer, the presence or absence of local corrosion can be immediately determined from the current density-time characteristics displayed on the display device and the relationship between the current density and the common logarithm of the area of the sample electrode. Enables a more rapid rating.
[0036]
【The invention's effect】
The present invention provides a new corrosion sensor capable of detecting local corrosion including metal corrosion, particularly pitting corrosion, which is said to be difficult to detect. The present invention provides a corrosion sensor that is simple and can accurately measure, detect, sense, and determine in a very short time, and its significance is extremely great.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a current concentration model using microelectrodes.
FIG. 2 is a schematic diagram showing a current concentration model due to pitting corrosion.
FIG. 3 (LiPF ₆ / PC + DME) Current density vs. time characteristics at 5V holding.
FIG. 4 (LiPF ₆ / PC + DME) The outline figure which shows the relationship between each current density and the common logarithm of an area 15 minutes after and 30 minutes after the aluminum foil sample electrode in 5V holding | maintenance.
FIG. 5 (LiClO _Four / PC + DME) Current density vs. time characteristics at 5V holding.
FIG. 6 (LiClO _Four / PC + DME) Schematic diagram showing the relationship between the current density after 270 seconds and the common logarithm of the area of the aluminum foil sample electrode at 5V holding.
FIG. 7 (1M LiClO _Four / PC + DME) Observation diagram showing the corrosion state of the aluminum foil sample electrode surface at 5V (digital high-scope photograph).
FIG. 8 (LiBF _Four / PC + DME) The outline figure which shows the relationship between each current density and the common logarithm of an area 15 minutes after and 30 minutes after the aluminum foil sample electrode in 5V holding | maintenance.
FIG. 9 shows current density-time characteristics at 5 V holding in an aqueous solution of ammonium adipate.
FIG. 10 is a schematic diagram showing the relationship between each current density and the common logarithm of area after 3 minutes and 5 minutes after the aluminum foil sample electrode is held at 5 V in an ammonium adipate aqueous solution.
FIG. 11 is a schematic diagram of a principle model for explaining the occurrence of pitting corrosion.
FIG. 12 is a schematic diagram showing the structure of a sensor.
FIG. 13 is a schematic diagram of a reusable sensor structure.
FIG. 14 shows an embodiment using a sensor according to the invention.
FIG. 15 is a configuration diagram of an automatic corrosion sensor using a computer.

Claims (5)

In the method for detecting local corrosion of a metal material as a test material , a local corrosion sensor comprising a pair of electrodes made of the same metal material as the metal material as the test material is paired with the largest electrode of the pair. If greater than 1 area ratio of the smallest electrode, and set such that the area of the smallest electrode of the pair is 1 cm ² or less, and immersing the該局corrosion sensor corrosion test solution, each electrode constant potential And plot the time-dependent change in the current value of each electrode to obtain a current-time linear curve, and then process this data to obtain the current density by dividing the current value flowing through each electrode by the area of each electrode. The obtained data is further processed to obtain the relationship between the current density and the common logarithm of the electrode area and plotted, and the slope indicates the presence or absence of the area dependence of the current density, which causes local corrosion. Characterized in that it detects whether it is, the local corrosion detection method using the local corrosion sensor according to a plurality of electrodes different areas. 2. The local corrosion detection method using the local corrosion sensor according to claim 1, wherein the pair as a plurality of electrodes having different areas is a local corrosion sensor including at least two pairs of large and small. The local corrosion detection method using the local corrosion sensor according to claim 1, wherein a corrosion test solution having a corrosive action on a metal material as a test material is used. The local corrosion detection method using the local corrosion sensor according to any one of claims 1 to 3, wherein the corrosion test solution is a non-aqueous solution containing a lithium salt or an ammonium adipate aqueous solution. In local corrosion detection method using the localized corrosion sensor, the local corrosion sensor configured as a counter electrode of a plurality of different areas made of a metal material of the same metal material with a test material, the corrosive action on the metallic material Measure the current flowing through each electrode when a constant voltage is applied and held between each electrode and the counter electrode, and measure the electrode area, the current value flowing through each electrode, and its change over time. 5. The data processing is performed by inputting the data into the graph, and the relationship between the voltage application elapsed time and the current density and the relationship between the current density and the common logarithm of the electrode area are displayed as a graph. A local corrosion detection method using the local corrosion sensor described in item 1.

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