JPH0211783A - Method of monitoring contact corrosion of different metals and corrosion resistance tester - Google Patents

Abstract

PURPOSE:To rapidly decide the corrosiveness of a bi-metal can by immersing an anode sample metal and a cathode nobler than said metal into a test soln. and determining the anode polarization resistance on the surface of the sample metal by increasing or decreasing the cathode area by a specific means and by using the specific equation. CONSTITUTION:The sample electrode (anode) 3 consisting of an Al alloy material and the 1st cathode 4 consisting of an iron material are immersed into the test soln. 2 in an electrolytic cell 1 at the time of deciding the contact corrosion of the bi-metal can having a can body which consists of the iron material and a can cap which consists of the Al alloy material. The 2nd cathode 4 having the same nature as the nature of the 1st cathode 4 is simultaneously so provided as to be electrically turned on-off with the 1st cathode 4 to increase or decrease the cathode area. The displacement of galvanic current (Ig) and sample metal potential (Em) is calculated and recorded by a recorder 26 and the anode polarization resistance (Ha) on the surface of the sample metal is determined from the equation by a personal computer 27 and is displayed on an X-Y plotter 26. The corrosion resistance of the different metals to the contact corrosion is easily and rapidly decided with high accuracy in this way.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention provides a corrosion resistance measuring method and apparatus for quickly determining the corrosivity caused by contact between dissimilar metals, such as contact between A1 alloy and iron in bimetalization. Regarding.

(Prior Art) In recent years, bimetallic cans, in which the can bodies are made of iron and the can lids are made of A1 alloy, have been widely used for food and drinking cans. In such cans, there is a problem that so-called dissimilar metal contact corrosion may occur. Contact corrosion of dissimilar metals is when a metal with a base potential comes into contact with a noble metal in an aqueous solution, the base metal becomes an anode and the noble metal becomes a cathode, forming an electrochemical circuit and forming an anode. This refers to corrosion caused by corrosion.

For example, when an A-pattern alloy comes into contact with iron, A1, which has a base potential,
It becomes an alloy or an anode and corrodes. This can body or iron material,
When converting can lids to bimetallic A1 alloys, the contact corrosion resistance of A-type alloy lids depends on the A-type alloy composition, the chlorine ion (0-type) concentration of the aqueous solution that is the contents of the can, the amount of dissolved oxygen, etc. There is.

Therefore, when bimetallic products are used as food cans or drinking cans, it is necessary to conduct corrosion resistance tests under these conditions. Conventionally, the method of determining corrosion resistance has been to use a pack test using a large number of actual cans. Another method is to use the metal used for bimetalization as an electrode and measure the potential difference with respect to each reference electrode, then find out the potential difference when the two metals come into contact, and estimate the likelihood of contact corrosion.

(Problem to be solved by the invention) However, the results of the above-mentioned backtest methods 1 to 1 are not reliable;
It requires 3 to 12 months), and there is no easy way to do it. In addition, the method of measuring the potential difference of both metals with respect to reference electrodes requires individual measurement operations, and is not a good method in terms of accuracy and reliability for actual contact corrosion of both metals. Ta.

Therefore, an object of the present invention is to provide a simple and highly accurate corrosion resistance measuring method (monitor link method).

Another object of the present invention is to provide a test device that can easily measure the influence of one type of metal alloy composition, the ion concentration of a solution, etc. on corrosion resistance.

(Means for Solving the Problem) As a result of various studies to achieve the above object, the present inventor has discovered that the solution to be tested, the metal that will be the anode (for example, A
1 alloy) and the first cathode electrode are set in an electrolytic bath, and a second cathode is used separately to increase or decrease the cathode area, thereby changing the galvanic current (I g) and the displacement of the sample electrode potential (A alloy potential). When observing the polarization resistance (Ha) of the AfL alloy surface from Polarization resistance (H
We have found that a) suddenly decreases to almost 0, and based on this knowledge, we have accomplished the present invention.

That is, the present invention provides a first method comprising a sample metal to serve as an anode and a metal having a nobler natural potential than the sample metal in a test solution.
The cathode area is increased or decreased by immersing the cathode and electrically turning on and off the first cathode and second cups 1 to 1 made of the same material that were immersed at the same time, and the galvanic current (I g) and sample metal potential ( The present invention provides a dissimilar metal catalytic corrosion monitoring link method characterized in that the anode polarization resistance (Ha) of the sample metal surface is calculated from the displacement of E m ) using a formula.

Furthermore, in the present invention, an electrolytic cell containing a test solution is provided with a sample metal serving as an anode, a first cathode made of a material having a natural potential nobler than the metal, and further made of the same material as the first cathode, and an ON- A second cathode connected via a switch that can be turned off freely is provided, and the O of the second cathode is
A metal corrosion resistance test characterized by measuring changes in galvanic current (Ig) due to NOFF with a non-resistance ammeter and changes in sample potential (Em) with a voltmeter to determine anode polarization resistance (Ha). It provides equipment.

In the present invention, the electrolytic cell is usually made of glass, stainless steel, plastic, etc., but is not limited thereto.

There are no particular restrictions on the sample metal that becomes the anode to which the method of the present invention is applied; examples thereof include A1 alloy, carbon steel, stainless steel, copper alloy, and the like. The material of the first cathode is AI
When testing the corrosion resistance of A pattern alloy with bimetallic alloy can lid color, a tin plated steel plate or a tin fried steel plate will be used. It is preferable to use a saturated calomel electrode, a silver chloride electrode, or the like as the reference electrode.

The size of the cathode used in the method of the present invention is from 1:0.2 to l as the surface area ratio of the first cathode to the second cathode.
It is preferably between 1 and 0.5, and more preferably between 1 and 0.5. The surface area ratio between the anode and the first cup 1 is preferably determined with reference to the area ratio between the anode side material and the cathode side material used in the product.

If the switch opening/closing (ON-OFF) interval is too short, the measurement will be inaccurate, and if it is too long, the measurement time will become long. It is preferably about 20 to 120 minutes.

Note that the time from setting the sample electrode (anode) to starting the measurement.When measuring in the atmosphere, it is possible to measure immediately after setting, but when the sample electrode (anode) is set and the atmospheric gas is adjusted. Since it may not show the true value within 3 hours after setting the sample electrode, it is preferable to judge the anode polarization resistance Ha 3 to 4 hours after the start of measurement.

In the method of the present invention, the polarization resistance (Ha) of the anode made of the sample metal is measured as described above.When the sample metal is corrosion resistant, it shows a high polarization resistance value, or when corrosion starts, it rapidly decreases. This makes it possible to quickly determine whether the sample metal surface is in a corrosion-resistant region (non-corrosion region) or in a corroded region (pitting region). That is, by measuring Ha in the environment to be tested, it is possible to easily know the corrosion resistance of the sample electrode material by determining whether it is in the corrosion-resistant region or in the corrosion-resistant region.

Further, in the present invention, the temperature of the test solution can be controlled by placing the electrolytic cell in a constant temperature device, if necessary.

Further, in the present invention, an automatic measurement system may be installed to perform the opening/closing of the switch, the measurement of Ig and Em in conjunction with this, and the calculation display of Ha.

In this case, the automatic measurement system itself may be a known one based on a personal computer or the like. In this way, you can automate the measurement.

As mentioned above, the contact corrosion of dissimilar metals depends on the concentration of various ions in the intervening aqueous solution, the amount of dissolved oxygen in the aqueous solution, etc. According to the method of the present invention, by changing these conditions, the corrosion of dissimilar metals It is possible to test these effects by conducting a contact corrosion test.

(Example) Next, one of the measuring devices suitable for use in carrying out the method of the present invention
An example will be explained according to the drawings. Figure 1 is a cross-sectional view of the measuring device. In the figure, 1 is an electrolytic tank containing test liquid 2, 3 is a sample electrode (anode) made of sample metal, and 4 is made of a material with a higher natural potential than the sample metal. A first cathode 5 is made of the same material as the first cathode 4, and a second cathode 5 is made of the same material as the sample electrode 3.
and the first cathode 4 are electrically connected via a non-resistance ammeter Z-A, and the second cathode 5 is electrically connected via a switch SW which can be turned on and off.

6 is a reference electrode, and the voltmeter V connected to it indicates that
Measure the change in sample potential.

7 is in the gas cylinder, and from this the internal space 8 of the electrolytic cell 1
Gas (nitrogen gas, argon gas, etc.) is sent through line 9. 10 is a flow meter, and 11 is a valve.

On the other hand, 12 is a gas sealing device, and gas from the electrolytic cell is discharged through pipes 13 and 14. As shown in the figure, the electrolytic cell 1 preferably has a top-closed structure. A sealing structure 15 having electrical insulation properties is provided between the upper surface 1a and a connecting wire that electrically connects the cathode, anode, etc.

Further, the electrolytic cell of the present invention may be appropriately provided with a stirring device, a temperature control device, etc. as shown in the drawings. In the figure, 16 is a stirrer, 17 is a thermometer, 18 is a temperature controller connected to the thermometer (19L/19L), and 20 is a heater with temperature control. In this way, while stirring the test liquid 2 with the stirrer,
The temperature controller detects the measured temperature and turns on and off the temperature-controlled heater to maintain the test liquid in the electrolytic cell 1 at a predetermined temperature. A magnetic stirrer may be used as the stirring device.

Next, FIG. 2 shows a schematic diagram of an example of the measuring device of the present invention when used as an automatic measuring system. In the figure, the structure of the electrolytic cell portion is basically the same as that in FIG. 1, so only the main parts are shown.

In FIG. 2, the same parts as in FIG. 1 are indicated by the same reference numerals to avoid duplication of explanation, and in the figure, a Macnet stirrer 21 is used as the stirring device. 22 is an electromagnetic relay with a timer that turns on and off the first cathode and the second cathode, 23 is a non-resistance ammeter, and 24 is an electrometer.
A system is formed by connecting a recorder 25 for recording measurements of g and Em, and connecting this recorder to a personal computer 27 having an X-Y plotter 26 and displaying calculations of Ha.

The present invention will be explained in more detail based on examples. The following examples were carried out using the apparatus shown in FIG.

Example 1 After sufficiently degassing the oxygen in the solution with high-purity nitrogen gas, a 0.1% NaCl aqueous solution (temperature 25°C) was used as the test liquid, and a 5052A1 alloy (surface area 1crrI) was used as the sample electrode.
') was used as the first cathode using a tin plated steel plate (3crn
') as the second cathode, and a tin plated steel plate (2c r
n'), each electrode was set in the device, and the measurement was started after being left for 3 hours. The measurements were conducted under the following conditions.

■Switch opening/closing automatically at 30 minute intervals ■Measurement of Ha Measure Em and Ig at 5 minute intervals after the above opening/closing starts, calculate Ha = ΔE m /ΔIg each time, and average the calculated values for 30 minutes. was automatically recorded.

■Stopping air blowing and degassing Two hours after the start of the measurement, air blowing was started and the measurement was changed to atmospheric air.

The measurement results are 5052 under degassing conditions as shown in Figure 3.
Is the AJJ alloy in the corrosion resistant range?
a decreased, indicating that pitting corrosion occurred in the 5052AM alloy. According to past pack tests, it has been found that under these conditions, 5052A1 alloy is corrosion resistant in a degassed atmosphere, but pitting corrosion occurs in the atmosphere, and the results shown in Figure 3 are in good agreement with this knowledge. ing.

Example 2 After sufficiently degassing the oxygen in the solution with high-purity nitrogen gas, 0.03% NaCl was used as the test liquid, and then 1.0% N
A test to change to aC1 was conducted at a temperature of 258C. A 5052A4 alloy (surface area 1 crrf) was used as the sample electrode, a tin steel plate (5 crn') was used as the first cathode, and a tin steel plate (3 crn') was used as the second cathode. Each electrode was set in the device and left for another 4 hours. After degassing with N2, we waited until it stabilized and started measurement. The measurements were conducted under the following conditions.

■Automatic opening/closing of the switch at 30-minute intervals ■Measurement of Ha Measure Em and Ig at 3-minute intervals after the above opening/closing starts, calculate Ha = ΔE m /ΔIg each time, and average the calculated values for 30 minutes. was automatically recorded.

(2) Change in solution concentration by addition of NaCu Two hours after the start of the measurement, NaCl equivalent to 1% NaCl was added to the solution and uniformly stirred from the outside with a matanet stirrer.

The measurement results are as shown in Figure 4: 0.03% NaC! :L
In aqueous solution, Ha is as high as 13,000 Ωcm', and 505
The 2AsL alloy was in the corrosion resistance range, or the Ha decreased at the same time as NaC1 was added, indicating that the 5052 alloy surface had moved into the corrosion range (pitting corrosion range), indicating that pitting corrosion had occurred on the 5052A1 alloy surface. Recognize.

A pack test prior to this measurement showed that the 5052A1 alloy was corrosion resistant at 0.03% NaCl compared to the same Allj alloy and galvanic cathode, and 1% NaCl.
It is known that pitting corrosion occurs in the steel, and the results shown in Figure 4 are in good agreement with this knowledge.

Example 3 After sufficiently degassing the oxygen in the solution using high-purity nitrogen gas, a test solution of 0.03% NaCl was used as a sample electrode at a temperature of 25°C.
052 (surface area 1 crrf) was first used, then 508
2 alloy (surface area 1 cm'). Using a tin plated steel plate (5 cm) as the first cathode and a tin plated steel plate (3 cm) as the second cathode, each electrode was placed in the device, and then degassed with N2 for 2 hours and waited for it to stabilize. Measurement started. The measurements were conducted under the following conditions.

■Automatic opening/closing of the switch at 30 minute intervals ■Measurement of Ha After starting the above opening/closing, measure Em and Ig at 3 minute intervals, calculate Ha - ΔE m /ΔIg each time, and calculate the calculated value for 30 minutes. The average was recorded automatically.

■Replace the sample electrode 10 minutes after starting the measurement, change the sample electrode from 5052 alloy to 50
Converted to 82 alloy.

As shown in Figure 5, the measurement results show that the Ha of the 5052 alloy is 12,000 to 13,000 in a 0.03% NaC aqueous solution.
It can be seen that the value is as high as Ωcm', indicating that it is in the corrosion resistance range, or that Ha decreases when changing to 5082 alloy, indicating that it is in the corrosion range (pitting corrosion range). 300ppm NaC1 (0,03%NaCJ1
) In the pack test of beverage cans containing A1 can lids, 5052 alloys may have complete corrosion resistance, or 5082 alloys may cause pitting corrosion from coating defects, and the results of this test method are the results of the pack test. A good match was seen.

(Effects of the Invention) According to the method of the present invention, the corrosion resistance of dissimilar metals against contact corrosion can be easily and quickly measured with high accuracy. Furthermore, according to the measuring device of the present invention, it is possible to easily and quickly measure, specifically, the relationship between the ion concentration of the content of catalytic corrosion of dissimilar metals occurring on a bimetallic structure of an An-made can lid, dissolved butyric, etc. It is highly reliable. Moreover, the measuring device itself has a simple structure and has the advantage of being relatively inexpensive to manufacture. The method and apparatus of the present invention are particularly suitable for determining the corrosion resistance of A1 alloy of bimetallic food cans and drinking cans (cans made of steel for the body and aluminum alloy for the lid).

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing one embodiment of the corrosion resistance testing device of the present invention, and FIG. 2 is a schematic diagram of the other side of the testing device.
3 to 5 are graphs showing changes over time in anode polarization resistance (Ha) in Examples 1 to 3 of the present invention.

Claims (4)

[Claims] (1) A sample metal that will serve as an anode and a first cathode made of a metal with a higher natural potential than the metal are immersed in a test solution, and a second cathode and a first cathode made of the same material as the first cathode are immersed at the same time. By electrically turning on and off the cathode area, the galvanic current (
A dissimilar metal catalytic corrosion monitoring method that is characterized by determining the anode polarization resistance (Ha) of the sample metal surface from the displacement of the sample metal potential (Ig) and the sample metal potential (Em) using the formula ▲There are mathematical formulas, chemical formulas, tables, etc.▼. (2) A first tube consisting of a sample metal and a material having a nobler natural potential than the metal, which will serve as an anode, is placed in an electrolytic cell containing a test solution.
A cathode and a second cathode made of the same material as the first cathode and connected to the first cathode via a switch that can be turned ON and OFF are provided.
Measure the change in galvanic current (Ig) due to F with a non-resistance ammeter, and measure the change in sample potential (Em) with a voltmeter.
A metal corrosion resistance testing device characterized in that the anode polarization resistance (Ha) is determined. (3) The metal corrosion resistance testing device according to claim (2), wherein the inside of the electrolytic cell is sealed from the outside atmosphere. (4) Opening/closing the switch of the second cathode, measuring the galvanic current (Ig) and sample potential (Em) in conjunction with this, and calculating and displaying the anode polarization resistance (Ha) using an automatic measurement system. The metal corrosion resistance testing device according to claim (2), characterized in that: