An electrochemical method for testing metal corrosion suitable for low conductivity coolant environments

Abstract

The application discloses a metal corrosion electrochemical test method suitable for a low-conductivity coolant environment and belongs to the technical field of metal corrosion electrochemical test, and comprises the following steps: processing a to-be-tested metal into a working electrode array containing a plurality of mutually insulated microelectrodes, immersing the working electrode array, a reference electrode and an auxiliary electrode into a low-conductivity coolant, and the low-conductivity coolant is a glycol-water mixed solution or a deionized water-based coolant with a conductivity not higher than 50 microsiemens per centimeter (µS / cm). The application can effectively overcome the ohmic drop interference caused by high solution resistance in the low-conductivity coolant by processing the to-be-tested metal into the working electrode array containing the plurality of mutually insulated microelectrodes, synchronously applying an alternating excitation signal with a preset frequency to each microelectrode and adopting a dynamic current interruption method to independently perform dynamic ohmic drop compensation, so that real-time solution resistance measurement and compensation of each microelectrode are realized.

Description

Technical Field

[0001] This invention relates to the field of electrochemical testing technology for metal corrosion, and more specifically, to an electrochemical testing method for metal corrosion suitable for low-conductivity coolant environments. Background Technology

[0002] In the field of electrochemical testing for metal corrosion, low-conductivity coolants (such as ethylene glycol-water mixtures and deionized water-based coolants) are widely used in automotive engine cooling systems, new energy battery thermal management systems, and precision instrument temperature control equipment. Because the conductivity of these coolants is typically no higher than 50 microsiemens per centimeter (µS / cm), their ion concentration is extremely low, and their solution resistance often reaches tens of kiloohms or even higher. In traditional electrochemical testing methods (such as potentiostatic polarization, electrochemical impedance spectroscopy, and electrochemical noise), high solution resistance leads to a significant ohmic drop, causing the actual potential applied to the metal electrode surface to deviate significantly from the set value. The polarization current signal becomes extremely weak and easily drowned out by background noise. Furthermore, metal corrosion in coolant environments often manifests as localized corrosion (such as pitting and crevice corrosion) rather than uniform corrosion. Traditional methods typically use a single, large-area working electrode, and the measured current signal is the average current across the entire electrode surface. This fails to distinguish between uniform and localized corrosion, and cannot pinpoint the specific location of pitting corrosion, resulting in a severely distorted assessment of actual corrosion risk.

[0003] However, existing electrochemical testing techniques have the following significant drawbacks in low-conductivity coolant environments: First, they lack effective compensation methods for high ohmic drops. Traditional methods either do not compensate or use simple fixed resistor compensation, which cannot adapt to the dynamic drift of coolant conductivity with temperature and operating time, leading to severe distortion in polarization current measurements and complete masking or significant underestimation of localized corrosion events. Second, traditional single-electrode methods cannot identify and locate the specific location of pitting corrosion initiation, only providing a global average corrosion rate. However, localized pitting corrosion in actual coolant systems often occurs in tiny areas with corrosion rates far exceeding the average rate. The average rate cannot reflect the true corrosion risk and may even lead to false negatives. Third, existing microelectrode array technologies are mostly applied to high-conductivity aqueous solutions, and are less suitable for low-conductivity coolant environments. In liquid, independent dynamic ohmic drop compensation between microelectrodes is difficult to achieve, and each microelectrode cannot obtain accurate real-time solution resistance measurement and compensation, resulting in a significant decrease in test accuracy. Fourth, when using electrochemical noise for pitting corrosion discrimination, existing technologies usually only analyze the amplitude or power spectral density of the noise, lacking statistical discrimination indicators (such as the joint criteria of kurtosis coefficient and skewness coefficient) for current waveform characteristics under low conductivity environments, making it difficult to accurately distinguish between pitting corrosion initiation and uniform corrosion or background interference. Fifth, when existing microelectrode arrays are tested in low conductivity coolants, the microelectrodes in the array edge region experience different current distributions than the central region due to the edge effect of the electric field, resulting in a systematic deviation in the pitting corrosion discrimination results of the edge microelectrodes. Existing technologies lack effective correction methods for the edge effect, further reducing the accuracy of pitting corrosion location.

[0004] Based on this, the present invention designs an electrochemical testing method for metal corrosion suitable for low conductivity coolant environments to solve the above problems. Summary of the Invention

[0005] The purpose of this invention is to provide an electrochemical testing method for metal corrosion suitable for low-conductivity coolant environments, in order to solve the problems mentioned in the background art.

[0006] An electrochemical testing method for metal corrosion suitable for low-conductivity coolant environments includes the following steps:

[0007] S1. The metal to be tested is processed into a working electrode array containing multiple mutually insulated microelectrodes. The working electrode array, reference electrode and auxiliary electrode are immersed in a low conductivity coolant. The low conductivity coolant is an ethylene glycol-water mixture or a deionized water-based coolant with a conductivity of no more than 50 microsiemens per centimeter (µS / cm).

[0008] S2. Apply a preset frequency AC excitation signal to each microelectrode synchronously through a multi-channel electrochemical workstation, measure the real-time solution resistance between each microelectrode and the auxiliary electrode, and use the dynamic current interruption method to perform independent dynamic ohmic drop compensation for each microelectrode channel. Under the compensation state, continuously and synchronously acquire the current noise signal and potential noise signal of each microelectrode.

[0009] S3. Analyze the current noise spectrum and potential noise spectrum of each microelectrode, extract the kurtosis coefficient and skewness coefficient of the current waveform. When the kurtosis coefficient is greater than 3.0 and the skewness coefficient is positive, it is determined that pitting corrosion has occurred at the corresponding microelectrode position. The number of microelectrodes that have pitted corrosion is counted, and the corrosion current of each pitted microelectrode is determined. Based on this, the local corrosion rate is calculated and output.

[0010] The preset threshold range for the kurtosis coefficient is 3.0–5.0, with specific values ​​adjusted according to the type of metal material: ≥3.5 for aluminum alloys, ≥4.0 for pure copper, and ≥3.0 for carbon steel. The skewness coefficient is positive, i.e., greater than 0. This threshold was obtained through statistical analysis of numerous electrochemical noise experiments under low conductivity environments and is statistically significant (p<0.01).

[0011] Preferably, the dynamic current interruption method in step S2 specifically involves: periodically interrupting the polarization current with a preset short period, measuring the potential drop at the moment of interruption, and calculating the real-time solution resistance based on the ratio of the potential drop to the current before the interruption. Then, based on the real-time solution resistance, the compensation coefficient is dynamically adjusted using a positive feedback mechanism. and will compensate voltage Superimposed on the set potential of the potentiostat Above, among which The current polarization current, This is a dimensionless proportionality constant, ranging from 0 to 1. The higher the solution resistance, the greater the proportionality. The larger the value, the better.

[0012] Compensation coefficient With solution resistance The relationship is a piecewise linear function: when hour, ;when hour, ;when hour, This relationship can be adjusted according to the actual system response characteristics.

[0013] The positive feedback method is specifically implemented using a proportional-integral (PI) control algorithm:

[0014]

[0015] in , , The target solution resistance is set to 10kΩ. When it rises, Rapidly increasing, forming a positive feedback regulation. Preferably, after determining the microelectrode where pitting corrosion has occurred in step S3, the method for calculating the local corrosion rate is as follows: the microelectrode where pitting corrosion has occurred is electrochemically isolated from the working electrode array and used as a new working electrode. An independent auxiliary counter electrode with a known area is introduced, forming a two-electrode test circuit only with the pitting microelectrode. A constant small-amplitude anodic overpotential is applied to the isolated pitting microelectrode, with a value of +20mV to +100mV relative to the open circuit potential, driving only the metal dissolution reaction within the pitting pit. The steady-state current measured at this time is the true corrosion current of the pitting microelectrode. The local corrosion rate is calculated based on the true corrosion current and the geometric area of ​​the pitting microelectrode.

[0016] A small overpotential refers to an anodic overpotential that does not exceed 100 mV relative to the open circuit potential, preferably in the range of +30 mV to +60 mV. This range can effectively drive the metal dissolution reaction within the pitting corrosion pit while avoiding the initiation of new pitting corrosion or alteration of the local chemical environment.

[0017] Preferably, in step S1, the arrangement of the working electrode array is as follows: a ring of dummy electrodes is set around the array. These dummy electrodes have the same geometric dimensions and materials as the microelectrodes in the working electrode array, but the dummy electrodes do not participate in the acquisition of current noise signals and pitting detection. The spacing between each microelectrode and the dummy electrode is equal to the spacing between adjacent working microelectrodes. When calculating the kurtosis coefficient and skewness coefficient of each working microelectrode, a position weighting factor is introduced. The position weight factor is dynamically obtained through an edge effect self-calibration procedure. The position weight factor of the working microelectrode located at the edge of the array is lower than that of the working microelectrode located at the center of the array, so as to correct the interference of the edge effect on the pitting corrosion determination.

[0018] Location weight factor

[0019] in For the first The response amplitude of a microelectrode under AC excitation This represents the average response amplitude of the microelectrodes in the central region of the array. This factor is recalculated every 30 minutes to track changes in conductivity.

[0020] Preferably, in step S2, the dynamic current interruption method and noise acquisition are performed in a time-division manner: within a test cycle, the current interruption function is turned off in the first time period, and the current noise signal and potential noise signal of each microelectrode are continuously acquired for pitting corrosion initiation discrimination in step S3. In the second time period, the dynamic current interruption method is turned on for ohmic drop compensation, and polarization signals are acquired for corrosion rate calculation. The first time period and the second time period are switched alternately, and the switching frequency is not less than 0.1 Hz. The duration of the first time period is not less than 1 second to ensure that a sufficiently long noise sequence is acquired for spectral analysis.

[0021] Preferably, in step S3, the calculation of the local corrosion rate is further performed in the following manner: the microelectrodes that have pitted are not electrochemically isolated, but the microelectrodes that have not pitted in the working electrode array are used as distributed auxiliary counter electrodes. Specifically, when one or more microelectrodes are determined to have pitted, the potential of the pitted microelectrode is controlled relative to the reference electrode at a preset anodic overpotential value. At the same time, all microelectrodes that have not pitted are short-circuited and used as auxiliary counter electrodes. At this time, the anodic dissolution current on the pitted microelectrode and the cathodic reduction current on the non-pitted microelectrode are naturally separated. The steady-state current measured on the pitted microelectrode is the true corrosion current of the pitted microelectrode. The local corrosion rate is calculated based on the true corrosion current and the geometric area of ​​the pitted microelectrode. There is no need to introduce an independent auxiliary counter electrode or interrupt the in-situ continuous monitoring.

[0022] Preferably, the method for setting up the dummy electrodes and determining the weighting factors further includes: the number of dummy electrodes is at least two rings, arranged ring by ring from the inside out, the innermost ring of dummy electrodes is adjacent to the working microelectrode array, and the width of the outermost ring of dummy electrodes is not less than 20% of the overall width of the working microelectrode array. Before the test begins, an edge effect self-calibration procedure is executed: the same weak AC test signal is applied to all microelectrodes in the working microelectrode array, the response amplitude of each microelectrode is measured, and an edge attenuation curve of the response amplitude changing with the position of the microelectrode is plotted. Based on the measured slope of the attenuation curve, the position weighting factor of each ring of working microelectrodes is dynamically calculated, instead of using a preset fixed weighting factor. During the test, the self-calibration procedure is repeated every preset time interval to track the edge effect drift caused by the change in the conductivity of the coolant.

[0023] Preferably, when the dynamic current interruption method and noise acquisition are executed in a time-division manner, the switching between the first time period and the second time period is not periodic, but dynamically triggered by the pitting corrosion discrimination result: In the default state, the system continuously runs in the first time period, continuously acquires noise signals and performs real-time pitting corrosion initiation discrimination. When the pitting corrosion initiation discrimination result is negative, it does not enter the second time period; when the pitting corrosion initiation discrimination result is positive, it immediately triggers the switch to the second time period, performs quantitative measurement of corrosion rate under ohmic drop compensation on the identified pitting corrosion microelectrodes, and after the measurement is completed, the system automatically switches back to the first time period. At the same time, in the second time period, the potential signals of each microelectrode are still continuously acquired at a reduced sampling frequency to monitor whether new pitting corrosion events occur in this time period. If abnormal potential fluctuations are detected, the second time period is interrupted and the system immediately switches back to the first time period.

[0024] Preferably, when using the unpitted microelectrode as a distributed auxiliary counter electrode, a cathode carrying capacity monitoring and dynamic compensation mechanism is further introduced: the mixed potential of the unpitted microelectrode shorted as the counter electrode is monitored in real time, and the drift of the mixed potential relative to the initial value is calculated and recorded as the cathode potential drift. When the absolute value of the cathode potential drift exceeds a preset threshold, it is determined that the cathode carrying capacity is insufficient. At this time, the auxiliary compensation mode is activated: the test is paused, a small amount of high conductivity electrolyte is briefly injected into the coolant or short-term forced convection is performed to restore the dissolved oxygen concentration on the surface of the unpitted microelectrode. After the mixed potential drifts back to near the initial value, the test continues. At the same time, the cathode potential drift is subtracted from the anodic overpotential setting of the pitting microelectrode in real time to compensate for the potential drift of the distributed electrodes, ensuring that the actual anodic overpotential borne by the pitting microelectrode remains constant. When the number of pitted microelectrodes exceeds 30% of the total number of array microelectrodes, the short-circuit grouping of the remaining unpitted microelectrodes in the array is automatically switched from a single group to multiple groups for alternating use. Each group of short-circuited unpitted microelectrodes works for no more than 60 seconds before rotating to the next group, in order to avoid the accumulation of cathode reaction products or depletion of reactants in any group.

[0025] Compared with the prior art, the advantages of this invention are:

[0026] 1. This invention processes the metal under test into a working electrode array containing multiple mutually insulated microelectrodes, and synchronously applies an AC excitation signal of a preset frequency to each microelectrode. It also uses a dynamic current interruption method for independent dynamic ohmic drop compensation, which can effectively overcome the ohmic drop interference caused by high solution resistance in low conductivity coolant (conductivity not higher than 50 micro-Siemens per centimeter (µS / cm)) and realize real-time solution resistance measurement and compensation for each microelectrode.

[0027] 2. This invention analyzes the current noise spectrum and potential noise spectrum of each microelectrode, extracts the kurtosis coefficient and skewness coefficient of the current waveform, and sets the kurtosis coefficient greater than a preset threshold and the skewness coefficient as a positive criterion for pitting corrosion initiation. It can accurately identify the location of the microelectrode where pitting corrosion occurs and count the number of pitting microelectrodes, thereby achieving high sensitivity and high specificity in identifying the initiation of local corrosion of metals in low conductivity coolant, overcoming the defect of traditional methods that cannot locate the pitting corrosion location.

[0028] 3. This invention electrochemically isolates the pitting microelectrode after pitting occurs and introduces an independent auxiliary counter electrode to form a dual-electrode test circuit. A constant small-amplitude anodic overpotential is applied to measure the steady-state current as the true corrosion current, which can quantitatively calculate the local corrosion rate at each pitting location. This solves the problem that the local corrosion rate cannot be obtained due to the current averaging effect in low conductivity environments.

[0029] 4. This invention, by setting at least one ring of pseudo-electrodes around the working electrode array and introducing a position weighting factor (the weighting factor of the edge microelectrodes is lower than that of the center microelectrodes) when calculating the kurtosis coefficient and skewness coefficient, can effectively correct the interference of edge effects on pitting corrosion judgment, improve the accuracy of pitting corrosion judgment of microelectrodes in the edge region of the array, and avoid misjudgment or missed judgment caused by uneven distribution of edge electric field.

[0030] 5. This invention executes the dynamic current interruption method and noise acquisition in a time-division manner (the first time period is used to acquire noise for pitting corrosion identification, and the second time period is used to enable dynamic compensation for corrosion rate calculation), and sets the two to switch alternately. This ensures that a sufficiently long noise sequence is available for spectral analysis, while also achieving accurate corrosion rate measurement under ohmic drop compensation. It avoids mutual interference between the two functions and improves the reliability of the test and the quality of the data. Attached Figure Description

[0031] Figure 1 This is a flowchart of an electrochemical testing method for metal corrosion suitable for low-conductivity coolant environments, as proposed in this invention. Detailed Implementation

[0032] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] Example

[0034] In the following examples, the local corrosion rate (Unit: mm / year) Calculated according to Faraday's law using the following general formula:

[0035]

[0036] in, : The measured steady-state current (A); : Molar mass of the metal (g / mol); : Number of electrons in the reaction; Faraday constant (96485 C / mol); Metal density (g / cm³); : Geometric area (cm²) of pitting microelectrode.

[0037] The parameter values ​​for different metallic materials are as follows:

[0038] Aluminum alloy (6061): =26.98, =3, =2.70;

[0039] Pure copper: =63.55, =2, =8.96.

[0040] If the above materials are used in any embodiment, they are directly substituted into the formula for calculation, and will not be explained again.

[0041] Example 1 (Basic Scheme: Pitting Corrosion Detection + Independent Counter Electrode Measurement)

[0042] I. Fabrication of Microelectrode Arrays

[0043] Step 1: Substrate Preparation

[0044] Select a 6061 aluminum alloy sheet with dimensions of 20 mm in length, 20 mm in width, and 1 mm in thickness. Grind it sequentially with 400, 800, 1200, and 2000 grit metallographic sandpaper, then polish it to a mirror finish with 3-micron and 1-micron diamond polishing paste. Afterward, ultrasonically clean it in deionized water for 10 minutes, then ultrasonically clean it in anhydrous ethanol for 10 minutes, and finally dry it with nitrogen gas.

[0045] Step 2: Mask Creation

[0046] A 10x10 square grid mask pattern was formed on the metal surface using laser etching technology. Each microelectrode has a diameter of 200 micrometers, and the center-to-center spacing between adjacent microelectrodes is 500 micrometers, forming a total of 100 microelectrodes. Non-microelectrode areas were protected by photoresist.

[0047] Step 3: Insulation Treatment

[0048] A 1.5-micrometer-thick silicon nitride insulating layer was deposited on the metal surface using plasma-enhanced chemical vapor deposition (PECVD). Then, reactive ion etching (RIE) was used to selectively remove the insulating layer directly above each microelectrode, exposing a circular metal working area. The areas between the microelectrodes remained insulated throughout.

[0049] Step 4: Independent electrical connection

[0050] Conductive silver paste was applied to the back of each microelectrode, and insulated copper wires with a diameter of 0.1 mm and a length of 15 cm were soldered on them. All wires converged to a 100-channel micro-socket. All solder joints and wire roots were sealed with epoxy resin to ensure that only the working surface of the microelectrode was exposed to the environment.

[0051] Step 5: Array Packaging

[0052] The microelectrode array was embedded in a polyetheretherketone (PEEK) frame with the test side facing upwards, and the back side and wire interfaces were completely sealed with epoxy resin. After encapsulation, the array was ultrasonically cleaned for 5 minutes each with deionized water and a 1:1 volume ratio of ethylene glycol to water.

[0053] II. Test Setup

[0054] The packaged working electrode array, saturated calomel reference electrode, and platinum mesh auxiliary electrode (2 square centimeters in area) were simultaneously immersed in 1 liter of low-conductivity coolant. The coolant was a 1:1 volume ratio of ethylene glycol to water with a conductivity not exceeding 50 microsiemens per centimeter (µS / cm), and the initial measured conductivity was 32 microsiemens per centimeter (µS / cm). The working electrode array was placed horizontally with the test surface facing upwards, and the tip of the reference electrode was close to the center of the array, approximately 2 millimeters away.

[0055] III. Test Steps

[0056] Step 1: Synchronous Excitation, Dynamic Compensation, and Noise Acquisition

[0057] Using a 100-channel electrochemical workstation, a sinusoidal AC signal with a frequency of 10 Hz and an amplitude of 10 mV (relative to open circuit potential) was simultaneously applied to all microelectrodes for 1 second, and the initial solution resistance between each microelectrode and the auxiliary electrode was measured.

[0058] The dynamic current interruption method is enabled: the interruption frequency is 5 kHz, and each interruption lasts for 30 microseconds. The solution resistance of each microelectrode is calculated in real time, and the dynamic compensation coefficient is initially set to 80%. When the solution resistance is greater than 10 kΩ, the compensation coefficient increases according to the rule that the higher the solution resistance, the larger the compensation coefficient, but it does not exceed 99%.

[0059] The test employs a time-division multiplexing method: the system defaults to the first time period (noise acquisition segment), lasting 2 seconds with a sampling frequency of 2 kHz, during which no current interruption occurs. Current and potential noise signals from all 100 microelectrodes are continuously acquired. Upon detecting a positive signal of pitting corrosion initiation, the system switches to the second time period (ohm compensation segment) within 10 milliseconds, lasting 1 second. During this segment, dynamic current interruption is activated for ohm drop compensation, and polarization signals are acquired for subsequent calculations.

[0060] Step 2: Pitting Identification

[0061] Statistical analysis was performed on the current noise sequence collected in the first time period (2 seconds, 2000 data points per second, totaling 4000 data points), and the kurtosis coefficient and skewness coefficient of the current waveform of each microelectrode were calculated. The discrimination threshold was set as follows: when the kurtosis coefficient is greater than 3.5 and the skewness coefficient is greater than 0.5, pitting corrosion initiation is determined to have occurred at the location of the microelectrode.

[0062] In this embodiment, microelectrode No. 28 and microelectrode No. 57 simultaneously meet the above two conditions, therefore it is determined that pitting corrosion has occurred at these two locations.

[0063] Step 3: Corrosion rate determination (independent counter electrode method)

[0064] Microelectrodes 28 and 57 were electrochemically isolated from the array, i.e., their electrical connections with other microelectrodes were disconnected. A separate platinum microelectrode with a diameter of 200 micrometers and an area of ​​3.14 x 10⁻⁴ square centimeters was introduced as an auxiliary counter electrode, forming a two-electrode test circuit only with the pitting corrosion microelectrode to be tested.

[0065] A constant anodic overpotential of 50 mV relative to the open circuit potential was applied to each pitting microelectrode for 60 seconds. The average steady-state current between the 50th and 60th seconds was recorded. 0.82 μA was measured at microelectrode 28 and 1.13 μA at microelectrode 57.

[0066] Corrosion current density and localized corrosion rate were calculated using Faraday's law. The corrosion current density of microelectrode #28 was 2.61 × 10⁻³ amperes per square centimeter, translating to a localized corrosion rate of 0.0328 mm / year. The corrosion current density of microelectrode #57 was 3.60 × 10⁻³ amperes per square centimeter, with a localized corrosion rate of 0.0452 mm / year. The average localized corrosion rate at the two pitting sites was 0.0390 mm / year.

[0067] IV. Results Output

[0068] Output test report: Pitting corrosion initiation occurred at microelectrode positions 28 and 57, with local corrosion rates of 0.0328 mm / year and 0.0452 mm / year, respectively, and an average local corrosion rate of 0.0390 mm / year.

[0069] Example 2 (Improved solution: Distributed counter electrode + edge effect correction + dynamic trigger switching)

[0070] I. Fabrication of Microelectrode Array (Adding Dummy Electrodes)

[0071] It is basically the same as Example 1, with the following differences:

[0072] The array configuration was changed to an 8-row by 8-column working microelectrode array, with a total of 64 microelectrodes. Each microelectrode has a diameter of 300 micrometers, and the center-to-center spacing between adjacent microelectrodes is 600 micrometers.

[0073] Adding dummy electrodes: Two rings of dummy electrodes are arranged around the array. The first ring of dummy electrodes is adjacent to the outermost working microelectrode. The width of the second ring of dummy electrodes is 20% of the overall width of the working array. In this embodiment, the overall width of the working array is approximately 4.8 mm, therefore the width of the second ring of dummy electrodes is 1.0 mm. The dummy electrodes and the working microelectrodes use the same material, the same geometry, and the same insulation treatment, but the dummy electrodes do not participate in the acquisition of current noise signals or pitting detection. After encapsulation, the dummy electrodes are exposed to the coolant but not connected to the electrochemical workstation.

[0074] II. Edge Effect Self-calibration

[0075] Perform a self-calibration procedure before starting the test:

[0076] A sinusoidal AC signal with a frequency of 10 Hz and an amplitude of 10 mV was applied to all 64 working microelectrodes. The response current amplitude of each microelectrode was measured. The average response amplitude of the 16 microelectrodes in the central region (4 rows by 4 columns) was calculated and measured to be 1.23 μA. The edge attenuation coefficient of each microelectrode was calculated, which is the response amplitude of that microelectrode divided by the average response amplitude of the central region. Then, the position weighting factor of each microelectrode was calculated, which is equal to the square of the edge attenuation coefficient. During the test, a self-calibration procedure was automatically repeated every 30 minutes to track edge effect drift caused by changes in coolant conductivity.

[0077] III. Dynamic Trigger Switching

[0078] The system defaults to operating in the first time period (noise acquisition segment), continuously acquiring noise signals and calculating the kurtosis and skewness coefficients of each microelectrode in real time. The trigger condition is set as follows: when the kurtosis coefficient of a microelectrode is greater than 3.2 and the skewness coefficient is greater than 0.4, a switch to the second time period is immediately triggered. During the second time period, the potential signals of each microelectrode are continuously acquired at a sampling frequency of 200 data points per second to monitor for new pitting events. If a potential fluctuation exceeding ±5 millivolts is detected, the second time period is immediately interrupted and the system switches back to the first time period. After the measurement is completed, the system automatically switches back to the first time period.

[0079] The dynamism of dynamic ohm sag compensation is reflected in the following three aspects:

[0080] Real-time measurement: The interrupt frequency can be dynamically adjusted according to the noise level within the range of 1kHz to 20kHz;

[0081] Adaptive compensation coefficient: based on Adjustment based on PI control law ;

[0082] Time-sharing switching: Dynamically switch between the noise acquisition segment and the compensation measurement segment based on the pitting detection results.

[0083] When a potential fluctuation exceeding ±5mV is detected, the interrupt frequency is automatically increased to above 10kHz to quickly track changes in solution resistance.

[0084] IV. Corrosion Rate Determination (Distributed Counter Electrode Method)

[0085] This embodiment does not introduce a separate auxiliary counter electrode, but instead adopts a distributed counter electrode method:

[0086] Once pitting corrosion was detected on microelectrode #12, its potential was controlled relative to the saturated calomel reference electrode at an anodic overpotential of +50 mV. Simultaneously, all the remaining 63 non-pitted microelectrodes were short-circuited and used as a single distributed auxiliary counter electrode. At this point, the anodic dissolution current on the pitted microelectrode naturally separated from the cathodic reduction current on the non-pitted microelectrodes. The steady-state current on microelectrode #12 was measured for 60 seconds, and the average value for the last 10 seconds was 1.05 μA.

[0087] The geometric area of ​​the pitting microelectrode is 7.07 x 10⁻⁴ square centimeters. The corrosion current density is 1.49 x 10⁻³ amperes per square centimeter, which translates to a local corrosion rate of 0.0187 millimeters per year.

[0088] V. Monitoring of Cathode Load Capacity

[0089] The mixed potential of 63 unpitted microelectrodes, shorted as counter electrodes, was monitored in real time. The initial mixed potential was -0.21 V (relative to a saturated calomel reference electrode). After 120 minutes of testing, the mixed potential drifted to -0.218 V, a drift of -8 mV, exceeding the preset threshold of 5 mV.

[0090] At this point, the auxiliary compensation mode is activated: the test is paused, 0.1 ml of a 0.01 mol / L potassium chloride solution is injected into the coolant, and the micro stirrer is turned on to stir at 100 rpm for 30 seconds. The mixing potential returns to -0.212 volts, and the test continues.

[0091] Simultaneously, corrections are made to the anodic overpotential setting of the pitting microelectrode. Since the cathode potential has drifted 8 millivolts in the negative direction, the setting potential needs to be adjusted to 58 millivolts to maintain a constant positive 50 millivolts for the actual anodic overpotential experienced by the pitting microelectrode.

[0092] In this embodiment, the number of pitting microelectrodes did not exceed 30% of the total number of array microelectrodes, so the grouping and rotation mechanism was not triggered.

[0093] Example 3 (High conductivity drift environment + multiple pitting events + automatic grouping and rotation)

[0094] I. Fabrication of Microelectrode Arrays

[0095] Similar to Example 2, this method uses 64 working microelectrodes arranged in 8 rows by 8 columns, plus two rings of dummy electrodes. However, the metal to be tested is replaced with pure copper (99.99% purity). Each microelectrode has a diameter of 500 micrometers, and the center-to-center distance between adjacent microelectrodes is 1 millimeter. The coolant is a deionized water-based coolant with an initial conductivity of 8 microsiemens per centimeter (µS / cm). During the test, the coolant conductivity is allowed to gradually rise to a maximum of 55 microsiemens per centimeter (µS / cm) due to carbon dioxide absorption and impurity dissolution, slightly exceeding the limits of this invention, to verify the applicability of the method under conditions of fluctuating conductivity.

[0096] II. Test Parameter Adjustment

[0097] The first time period lasts 3 seconds with a sampling frequency of 5 kHz. The second time period lasts 0.8 seconds with a current interruption frequency of 10 kHz. The pitting detection threshold is adjusted to: kurtosis greater than 4.0 and skewness greater than 0.6 (because the electrochemical noise characteristics of copper are different from those of aluminum). The self-calibration interval is adjusted to 15 minutes.

[0098] III. Multiple pitting events

[0099] When the test ran for 45 minutes, five microelectrodes (No. 8, No. 15, No. 32, No. 44, and No. 51) simultaneously met the pitting corrosion detection criteria. By the 90-minute mark, the cumulative number of microelectrodes that had pitted had reached 22, exceeding 30% of the total number of 64 microelectrodes in the array.

[0100] Automatic grouping and rotation: At this point, there are 42 remaining microelectrodes that have not yet pitted. The system automatically divides them into 3 groups of 14 microelectrodes each. The first group operates for 45 seconds, then switches to the second group for 45 seconds, and then switches to the third group for 45 seconds, and so on in a cyclical rotation. While each group is operating, the other two groups are disconnected or grounded and do not participate in the current loop. During the rotation process, the anodic overpotential of the pitting microelectrodes is always controlled at +40 mV (relative to the saturated calomel reference electrode), and cathode potential drift compensation is continuously performed.

[0101] IV. Corrosion Rate Measurement

[0102] The steady-state current of each pitting microelectrode was measured using a distributed counter electrode method. For pure copper, the corrosion current density was multiplied by 11.57 according to Faraday's law to obtain the local corrosion rate in millimeters per year.

[0103] The measurement results are as follows: Microelectrode No. 8 has a steady-state current of 2.45 μA, a corrosion current density of 1.25 × 10⁻³ amperes per square centimeter, and a local corrosion rate of 0.0145 mm / year; Microelectrode No. 15 has a steady-state current of 2.89 μA, a corrosion current density of 1.47 × 10⁻³ amperes per square centimeter, and a local corrosion rate of 0.0170 mm / year; Microelectrode No. 32 has a steady-state current of 2.11 μA and a corrosion current density of 1.08 μA / year. The localized corrosion rate of the five pitting microelectrodes is 0.0125 mm / year (1.54 × 10⁻³ amperes per square centimeter). Microelectrode #44 has a steady-state current of 3.02 μA and a corrosion current density of 1.14 × 10⁻³ amperes per square centimeter, resulting in a localized corrosion rate of 0.0178 mm / year. Microelectrode #51 has a steady-state current of 2.23 μA and a corrosion current density of 1.14 × 10⁻³ amperes per square centimeter, leading to a localized corrosion rate of 0.0132 mm / year. The average localized corrosion rate of the five pitting microelectrodes is 0.0150 mm / year.

[0104] V. Verification of Edge Effect Correction

[0105] During self-calibration at the 45-minute mark, edge decay curves were plotted showing the response amplitude as a function of microelectrode position. Without calibration, the average response amplitude of the edge microelectrodes (i.e., those in the first row, eighth row, first column, and eighth column) was only 68% of the average response amplitude of the microelectrodes in the central region. After applying a position weighting factor, the effective weight of the edge microelectrodes decreased to 46%, successfully suppressing false positive pitting detections that might be caused by edge effects. In this embodiment, none of the edge microelectrodes triggered pitting. However, without calibration, the edge microelectrodes might have been misjudged as having pitting due to abnormal responses caused by edge effects.

[0106] Comparative Example 1 (without dynamic ohmic drop compensation, traditional constant potential method)

[0107] I. Preparation Method

[0108] Completely identical to Example 1. A 10-row by 10-column microelectrode array was fabricated using 6061 aluminum alloy, with each microelectrode having a diameter of 200 micrometers and an adjacent spacing of 500 micrometers. Surface grinding, polishing, insulation treatment, independent leads, and packaging were all consistent with Example 1.

[0109] II. Testing Methods (Differences)

[0110] This comparative example does not perform the dynamic current interruption method and dynamic ohmic drop compensation in step S2 of the present invention. Specifically:

[0111] A constant polarization potential of -0.8 volts (relative to a saturated calomel reference electrode) is applied to simulate test conditions under cathodic protection or corrosion potential, without any form of ohmic drop compensation. Current and potential noise signals for each microelectrode are not collected, and kurtosis and skewness coefficients are not used for pitting corrosion detection. The total current of all 100 microelectrodes is directly measured, and then the total current is divided by the total geometric area of ​​all microelectrodes to obtain the average corrosion current density.

[0112] III. Test Results

[0113] The coolant has an initial conductivity of 32 microsiemens per centimeter (µS / cm) and a solution resistance that fluctuates between 20 kilohms and 50 kilohms. Without ohmic drop compensation, the ohmic drop (i.e., current multiplied by solution resistance) can be as high as several millivolts to tens of millivolts, causing the actual potential applied to the electrodes to deviate significantly from the set potential value.

[0114] The measured total current was 0.35 microamps. The total geometric area of ​​all microelectrodes was 100 times the area of ​​each microelectrode (each microelectrode area is 3.14 times 10⁻⁴ square centimeters), which is 0.0314 square centimeters. Therefore, the calculated average corrosion current density was 0.35 microamps divided by 0.0314 square centimeters, which equals 1.11 times 10⁻⁵ amperes per square centimeter, or 11.1 microamps per square centimeter.

[0115] This value is about five orders of magnitude different from the pitting current density measured in Example 1 (2.61 times 10 to the power of negative 3 amperes per square centimeter, i.e. 2610 microamps per square centimeter), meaning that the pitting current density in Example 1 is about 235,000 times the average current density of this comparative example.

[0116] Furthermore, this comparative example cannot identify the specific location of pitting corrosion, cannot obtain any local corrosion rate information, and can only provide a severely distorted average corrosion rate.

[0117] IV. Conclusion

[0118] In coolants with low conductivity, without dynamic ohmic drop compensation, the traditional potentiostatic method results in a severely low polarization current due to the high ohmic drop, making it impossible to detect localized corrosion events, and the average corrosion rate is severely underestimated.

[0119] Comparative Example 2 (No microelectrode array + single working electrode + no pitting detection)

[0120] I. Preparation Method

[0121] This comparative example does not use a microelectrode array. Only a single large-area working electrode is fabricated, made of the same 6061 aluminum alloy, with an area of ​​1 square centimeter. The surface is subjected to the same step-by-step grinding, polishing, and cleaning process as in Example 1. No insulating separation treatment is applied to the electrode surface, and no dummy electrodes are used. The reference electrode and auxiliary electrode are the same as in Example 1.

[0122] II. Testing Methods

[0123] A conventional three-electrode testing system was used, connected to a single-channel electrochemical workstation. The same polarization procedure as in Example 1 was applied, i.e., an anodic overpotential of +50 mV relative to the open-circuit potential. However, current interruption compensation was not performed in this comparative example because the single-channel electrochemical workstation cannot simultaneously achieve independent compensation for multiple microelectrodes. The total current noise signal of the entire working electrode was acquired, and the kurtosis and skewness coefficients of the entire working electrode current waveform were calculated; at this point, only one data sequence was available.

[0124] III. Test Results

[0125] The measured total steady-state current was 1.8 microamps. The working electrode area was 1 square centimeter, therefore the average corrosion current density was 1.8 microamps per square centimeter, or 1.8 x 10^-6 amperes per square centimeter.

[0126] Statistical analysis of the current noise sequence of the entire working electrode yielded a kurtosis coefficient of 2.1 and a skewness coefficient of 0.2. Neither of these values ​​exceeds the discrimination threshold set by this invention (kurtosis coefficient greater than 3.5 and skewness coefficient greater than 0.5). Therefore, according to the discrimination criteria of this invention, pitting corrosion initiation cannot be determined.

[0127] However, after the test, observation of the electrode surface using a scanning electron microscope revealed multiple micron-sized pitting corrosion. This indicates that localized corrosion did indeed occur on the electrode during the actual test, but the test method used in this comparative example missed the pitting corrosion event.

[0128] Furthermore, this comparative example cannot obtain the independent corrosion rate of each pitting location, but can only obtain a total average current that masks local information.

[0129] IV. Conclusion

[0130] A single large-area working electrode cannot distinguish between localized and uniform corrosion. In low-conductivity coolants, due to high ohmic drop and current averaging effects, the weak current signal generated by pitting events is masked by the background current on the large-area electrode, leading to serious false negatives. This indicates that microelectrode arrays are a necessary condition for the detection of localized corrosion in low-conductivity coolant environments.

[0131] Summary of technical effects

[0132] By comparing the above three embodiments with the two comparative examples, the following conclusions can be drawn, as shown in the table below:

[0133] Should dynamic ohm sag compensation be used? yes yes yes no no Whether to use a microelectrode array Yes (100) Yes (64 + dummy electrodes) Yes (64 + dummy electrodes) Yes (100) No (single large electrode) Is it possible to determine the initiation of pitting corrosion? able able able no No (false negative) Is it possible to pinpoint the location of pitting corrosion? Yes (No. 28, No. 57) Yes (No. 12) Yes (numbers 8, 15, 32, 44, 51, etc., 22 in total) no no Methods for measuring local corrosion rate Independent counter electrode method Distributed counter electrode method Distributed counter electrode method + group rotation Local velocity cannot be measured Local velocity cannot be measured Should edge effect correction be performed? no Yes (weighting factor) Yes (self-calibration) no not applicable Should cathode load capacity monitoring be performed? Not involved Yes (drift compensation) Yes (group rotation) Not involved Not involved Multi-pitting event handling capability Can handle 2 pitting corrosions Can handle 1 pitting corrosion It can handle 22 pitting corrosions (more than 30% of the total). Unrecognized Unrecognized Can localized corrosion be effectively detected in low-conductivity coolants? able able able cannot cannot

[0134] Based on the analysis in the table above:

[0135] Example 1 (Basic Solution): The basic technical solution of this invention can successfully identify the specific location of pitting corrosion initiation in low-conductivity coolants and quantitatively calculate the local corrosion rate at each pitting location. Microelectrodes No. 28 and No. 57 were accurately identified, with local corrosion rates of 0.0328 mm / year and 0.0452 mm / year, respectively.

[0136] Example 2 (Improved Scheme): Based on Example 1, the addition of a dummy electrode, edge effect self-calibration, dynamic trigger switching, and a distributed counter electrode method can further correct the interference of edge effects on pitting corrosion detection, reduce unnecessary ohmic compensation time, and achieve in-situ continuous monitoring without the need for an independent auxiliary electrode. Microelectrode No. 12 was accurately identified, with a local corrosion rate of 0.0187 mm / year.

[0137] Example 3 (Extreme Condition Scheme): Under extreme conditions such as multiple pitting events (simultaneous or sequential pitting of 22 microelectrodes), coolant conductivity drift even slightly exceeding the limit (up to 55 micro-Siemens per centimeter (µS / cm)), and the number of pitting microelectrodes exceeding 30% of the total array, requiring automatic grouping and rotation, the present invention can still operate stably and accurately output the local corrosion rate of each pitting location. The average local corrosion rate of the five representative pitting microelectrodes is 0.0150 mm / year.

[0138] Comparative Example 1 (without dynamic ohmic drop compensation): Without dynamic ohmic drop compensation, the polarization current is severely low due to the high ohmic drop in the traditional potentiostatic method. The measured average corrosion current density is only about 1 / 235,000 of the corrosion current density at the pitting corrosion site in Example 1. The measurement results are severely distorted and local corrosion cannot be detected at all.

[0139] Comparative Example 2 (without microelectrode array): When a single large-area working electrode is used instead of a microelectrode array, the weak current signal generated by the pitting event is masked by the background current on the large-area electrode. The kurtosis coefficient (2.1) and skewness coefficient (0.2) do not reach the discrimination threshold, resulting in false negatives. However, scanning electron microscopy confirms that pitting has actually occurred.

[0140] Overall Conclusion

[0141] In summary, the technical solution proposed in this invention can effectively and accurately detect the initiation of localized corrosion in metals and quantitatively calculate the localized corrosion rate in a low-conductivity coolant environment. It overcomes the technical obstacles of traditional electrochemical methods under conditions such as high ohmic drop, edge effect, and insufficient cathode load capacity, and has significant technical progress and practicality.

[0142] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. An electrochemical testing method for metal corrosion suitable for low-conductivity coolant environments, characterized in that, Includes the following steps: S1. The metal to be tested is processed into a working electrode array containing multiple mutually insulated microelectrodes. The working electrode array, reference electrode and auxiliary electrode are immersed in a low conductivity coolant. The low conductivity coolant is an ethylene glycol-water mixture or a deionized water-based coolant with a conductivity of no more than 50 microsiemens per centimeter (µS / cm). S2. Apply a preset frequency AC excitation signal to each microelectrode synchronously through a multi-channel electrochemical workstation, measure the real-time solution resistance between each microelectrode and the auxiliary electrode, and use the dynamic current interruption method to perform independent dynamic ohmic drop compensation for each microelectrode channel. Under the compensation state, continuously and synchronously acquire the current noise signal and potential noise signal of each microelectrode. S3. Analyze the current noise spectrum and potential noise spectrum of each microelectrode, extract the kurtosis coefficient and skewness coefficient of the current waveform. When the kurtosis coefficient is greater than 3.0 and the skewness coefficient is positive, it is determined that pitting corrosion has occurred at the corresponding microelectrode position. The number of microelectrodes that have pitted corrosion is counted, and the corrosion current of each pitted microelectrode is determined. Based on this, the local corrosion rate is calculated and output.

2. The electrochemical testing method for metal corrosion in a low-conductivity coolant environment according to claim 1, characterized in that, The dynamic current interruption method in step S2 specifically involves periodically interrupting the polarization current with a preset short period, measuring the potential drop at the moment of interruption, and calculating the real-time solution resistance based on the ratio of this potential drop to the current before the interruption. Then, based on the real-time solution resistance, the compensation coefficient is dynamically adjusted using a positive feedback mechanism. and will compensate voltage Superimposed on the set potential of the potentiostat Above, among which The current polarization current, This is a dimensionless proportionality constant, ranging from 0 to 1. The higher the solution resistance, the greater the proportionality. The larger the value, the better.

3. The electrochemical testing method for metal corrosion in a low-conductivity coolant environment according to claim 1, characterized in that, After identifying the pitting microelectrode in step S3, the method for calculating the local corrosion rate is as follows: the pitting microelectrode is electrochemically isolated from the working electrode array and used as a new working electrode. An independent auxiliary counter electrode with a known area is introduced to form a two-electrode test circuit with the pitting microelectrode. A constant small-amplitude anodic overpotential is applied to the isolated pitting microelectrode, with a value of +20mV to +100mV relative to the open circuit potential, which drives the metal dissolution reaction in the pitting pit. The steady-state current measured at this time is the true corrosion current of the pitting microelectrode. The local corrosion rate is calculated based on the true corrosion current and the geometric area of ​​the pitting microelectrode.

4. The electrochemical testing method for metal corrosion suitable for low-conductivity coolant environments according to claim 1, characterized in that, In step S1, the working electrode array is arranged as follows: a ring of dummy electrodes is set around the array. The dummy electrodes have the same geometric dimensions and materials as the microelectrodes in the working electrode array, but the dummy electrodes do not participate in the acquisition of current noise signals and pitting discrimination. The distance between each microelectrode and the dummy electrode is equal to the distance between adjacent working microelectrodes. When calculating the kurtosis and skewness coefficients of each working microelectrode, a position weighting factor is introduced. The weighting factor is dynamically obtained through an edge effect self-calibration procedure. The weighting factor of the working microelectrode located at the edge of the array is lower than that of the working microelectrode located at the center of the array, in order to correct the interference of the edge effect on the pitting corrosion determination.

5. The electrochemical testing method for metal corrosion suitable for low-conductivity coolant environments according to claim 2, characterized in that, In step S2, the dynamic current interruption method and noise acquisition are performed in a time-division manner: within a test cycle, the current interruption function is turned off in the first time period, and the current noise signal and potential noise signal of each microelectrode are continuously acquired for pitting corrosion initiation discrimination in step S3. In the second time period, the dynamic current interruption method is turned on for ohmic drop compensation, and polarization signals are acquired for corrosion rate calculation. The first time period and the second time period are switched alternately, and the switching frequency is not less than 0.1 Hz. The duration of the first time period is not less than 1 second to ensure that a sufficiently long noise sequence is acquired for spectral analysis.

6. The electrochemical testing method for metal corrosion suitable for low-conductivity coolant environments according to claim 3, characterized in that, In step S3, the following method is further adopted when calculating the local corrosion rate: the microelectrode that has pitted is not electrochemically isolated, but the microelectrode that has not pitted in the working electrode array is used as a distributed auxiliary counter electrode. Specifically, when one or more microelectrodes are determined to have pitted, the potential of the pitted microelectrode is controlled relative to the reference electrode at a preset anodic overpotential value. At the same time, all microelectrodes that have not pitted are short-circuited and used as auxiliary counter electrodes. At this time, the anodic dissolution current on the pitted microelectrode and the cathodic reduction current on the non-pitted microelectrode are naturally separated. The steady-state current measured on the pitted microelectrode is the true corrosion current of the pitted microelectrode. The local corrosion rate is calculated based on the true corrosion current and the geometric area of ​​the pitted microelectrode. There is no need to introduce an independent auxiliary counter electrode, nor is there a need to interrupt the in-situ continuous monitoring.

7. The electrochemical testing method for metal corrosion suitable for low-conductivity coolant environments according to claim 4, characterized in that, The method for setting up the dummy electrodes and determining the weighting factors further includes: the number of dummy electrodes is at least two rings, arranged ring by ring from the inside out, the innermost ring of dummy electrodes is adjacent to the working microelectrode array, and the width of the outermost ring of dummy electrodes is not less than 20% of the overall width of the working microelectrode array. Before the test begins, an edge effect self-calibration procedure is executed: the same weak AC test signal is applied to all microelectrodes in the working microelectrode array, the response amplitude of each microelectrode is measured, and an edge attenuation curve of the response amplitude changing with the position of the microelectrode is plotted. Based on the measured slope of the attenuation curve, the position weighting factor of each ring of working microelectrodes is dynamically calculated, instead of using a preset fixed weighting factor. During the test, the self-calibration procedure is repeated every preset time interval to track the edge effect drift caused by the change in the conductivity of the coolant.

8. The electrochemical testing method for metal corrosion in a low-conductivity coolant environment according to claim 5, characterized in that, When the dynamic current interruption method and noise acquisition are executed in a time-division manner, the switching between the first and second time periods is not periodic, but dynamically triggered by the pitting corrosion discrimination result: In the default state, the system continuously runs in the first time period, continuously acquiring noise signals and performing real-time pitting corrosion initiation discrimination. When the pitting corrosion initiation discrimination result is negative, it does not enter the second time period; when the pitting corrosion initiation discrimination result is positive, it immediately triggers the switch to the second time period, performs quantitative measurement of corrosion rate under ohmic drop compensation on the identified pitting corrosion microelectrodes, and after the measurement is completed, the system automatically switches back to the first time period. At the same time, in the second time period, the potential signals of each microelectrode are still continuously acquired at a reduced sampling frequency to monitor whether new pitting corrosion events occur in this time period. If abnormal potential fluctuations are detected, the second time period is interrupted and the system immediately switches back to the first time period.

9. The electrochemical testing method for metal corrosion in a low-conductivity coolant environment according to claim 6, characterized in that, When using unpitted microelectrodes as distributed auxiliary counter electrodes, a cathode carrying capacity monitoring and dynamic compensation mechanism is further introduced: The mixed potential of the unpitted microelectrodes short-circuited as counter electrodes is monitored in real time, and the drift of this mixed potential relative to the initial value is calculated and recorded as the cathode potential drift. When the absolute value of the cathode potential drift exceeds a preset threshold, the cathode carrying capacity is determined to be insufficient. At this time, the auxiliary compensation mode is activated: the test is paused, a small amount of high-conductivity electrolyte is briefly injected into the coolant or short-term forced convection is performed to restore the dissolved oxygen concentration on the surface of the unpitted microelectrodes, thus... After the mixed potential drifts back to near the initial value, the test continues. At the same time, the cathode potential drift is subtracted from the anodic overpotential setting of the pitting microelectrode in real time to compensate for the potential drift of the distributed electrodes, ensuring that the actual anodic overpotential borne by the pitting microelectrode remains constant. When the number of pitted microelectrodes exceeds 30% of the total number of array microelectrodes, the short-circuit grouping of the remaining non-pitted microelectrodes in the array is automatically switched from a single group to multiple groups for alternating use. Each group of short-circuited non-pitted microelectrodes works for no more than 60 seconds before being rotated to the next group to avoid the accumulation of cathode reaction products or depletion of reactants in any group.

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