Scanning microprobe, scanning local impedance microelectrode test system and application thereof

Abstract

The invention discloses a scanning microprobe, a scanning local impedance microelectrode testing system and application thereof, and relates to the field of material surface, metal corrosion and protection. The scanning microprobe comprises a microelectrode and a microprobe body, the microelectrode comprises a glass tube and a first electrode, the diameter of the first end of the first electrode is 20-25 microns, the first electrode is located in the glass tube and is a platinum wire, and the first end of the first electrode is flush with the first end of the glass tube; the microprobe comprises a platinum-iridium alloy wire, the first end of the platinum-iridium alloy wire is a tip, the diameter of the first end is 100-200 nm, the microelectrode and the microprobe are attached in parallel, the attached positions are insulated from each other, and the first end of the platinum-iridium alloy wire exceeds the first end of the first electrode by 1-2 micrometers. By designing the structure of the scanning microprobe, the local impedance and the microcell morphology in the metal corrosion process can be accurately measured, and the scanning microprobe is suitable for researching the metal corrosion phenomenon and developing new materials.

Description

Technical Field

[0001] The present application relates to the technical field of material surface, metal corrosion and protection, and in particular to a scanning microprobe, a scanning local impedance microelectrode test system and applications thereof. Background Art

[0002] Electrochemical impedance spectroscopy (EIS) applies a small-amplitude sinusoidal potential (or current) perturbation signal to an electrochemical electrode system and measures the resulting current (or potential) response. This method provides rich information about the electrode interface structure and dynamics, and has been widely used in fields such as metal corrosion, electrochemical energy, and materials electrochemistry. However, traditional EIS lacks spatial resolution and can only measure the overall average of the sample surface, failing to distinguish microscopic structures or analyze local variations in the sample's surface impedance.

[0003] Although commercial local impedance detection instruments are currently available, they generally use a dual micro-reference probe. By measuring the potential difference between two micro-reference electrodes with a vertical height difference, the local current density is calculated, and then the local impedance is obtained based on Ohm's law. The shortcomings of this measurement method are: 1. The dual micro-reference probe can only collect current in the vertical direction. Due to the vectorial nature of the current distribution in the medium, the measured local impedance has certain errors and lacks research information for electrochemical impedance spectroscopy; 2. The dual micro-reference probe can only manually adjust the distance between the probe tip and the sample surface with the help of a microscope, and the spatial resolution is generally low; 3. It is impossible to use a three-electrode system to measure the electrochemical AC impedance spectroscopy at specific locations on the sample surface. Summary of the Invention

[0004] The main purpose of this application is to provide a scanning microprobe, a scanning local impedance microelectrode testing system and its application to solve the problem that the existing technology cannot accurately measure the local electrochemical impedance.

[0005] In order to achieve the above-mentioned purpose, according to the first aspect of the present application, a scanning microprobe is provided, which includes a microelectrode and a microprobe, wherein the microelectrode includes a glass tube and a first electrode, the diameter of the first end of the first electrode is 20 to 25 μm, the first electrode is located in the glass tube, the first electrode is a platinum wire, and the first end of the first electrode is flush with the first end of the glass tube; the microprobe includes a platinum-iridium alloy wire, the first end of the platinum-iridium alloy wire is a pointed tip, the diameter of the first end of the platinum-iridium alloy wire is 100 to 200 nm, the microelectrode and the microprobe are parallel to each other, and the bonding portion is insulated from each other, and the first end of the platinum-iridium alloy wire extends beyond the first end of the first electrode by 1 to 2 μm.

[0006] Furthermore, the first electrode is fixed in the glass tube by resin.

[0007] Furthermore, the side surfaces of the platinum-iridium alloy wire are wrapped with insulating glue.

[0008] Furthermore, the microprobe is attached to the microelectrode in parallel via an insulating adhesive.

[0009] Furthermore, the microelectrode also includes a second electrode, which is composed of a silver wire and an AgCl film covering the first end of the silver wire, and the side of the AgCl film away from the first end of the silver wire is flush with the first end of the first electrode; the glass tube is a multi-channel glass tube, and the first electrode and the second electrode are respectively located in different channels of the multi-channel glass tube.

[0010] Furthermore, the parallel distance between the first electrode and the second electrode is 10-20 μm, the microprobe is adjacent to the side of the microelectrode close to the first electrode, and the parallel distance between the platinum-iridium alloy wire and the first electrode is 10-20 μm.

[0011] Furthermore, the second end of the first electrode, the second end of the second electrode and the second end of the platinum-iridium alloy wire are respectively used for connecting wires.

[0012] Furthermore, the second end of the first electrode and the second end of the second electrode are respectively connected to the wire through conductive silver glue.

[0013] Furthermore, the second end of the platinum-iridium alloy wire is connected to the lead by soldering.

[0014] Furthermore, the scanning microprobe further comprises a sheath, and a side of the microelectrode away from the first end of the glass tube and a side of the microprobe away from the first end of the platinum-iridium alloy wire are inserted into the sheath.

[0015] In another typical embodiment of the present application, a scanning local impedance microelectrode testing system is provided, which includes an electrochemical scanning tunneling microscope testing platform, a scanning microprobe control and drive unit, a tunneling current signal and local impedance measurement unit, and a measurement signal control and processing unit; the scanning microprobe control and drive unit includes the scanning microprobe in the above-mentioned embodiment of the present application.

[0016] Furthermore, the scanning microprobe control and drive unit also includes an XYZ three-dimensional piezoelectric microscanner and a stepper motor driven XY two-dimensional mechanical scanner; the tunnel current signal and local impedance measurement unit includes a tunnel current pre-signal conversion, amplification and feedback circuit, and a local impedance pre-signal conversion and amplification circuit.

[0017] By applying the technical solution of the present application, by combining a microelectrode and a microprobe and designing the structure of the microelectrode and the microprobe, on the one hand, the microprobe can be used to detect the tunnel current, and the tunnel current is used as a pointer to accurately control the distance between the scanning microprobe and the sample to be tested, with high spatial resolution; on the other hand, it is conducive to using a three-electrode system (with the sample to be tested as the working electrode, the platinum wire as the counter electrode, and the platinum-iridium alloy wire as the reference electrode) to measure the electrochemical AC impedance spectrum of specific sites on the surface of the sample to be tested, which is suitable for analyzing localized metal corrosion and has broad application prospects in the field of metal corrosion and protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a schematic structural diagram of a scanning microprobe in one embodiment of the present application;

[0019] Figure 2 This is a schematic diagram of a three-electrode system for local impedance testing in one embodiment of the present application;

[0020] Figure 3 This is a schematic diagram of a scanning local impedance microelectrode testing system in one embodiment of the present application;

[0021] Figure 4 A two-dimensional graph showing the surface impedance modulus distribution of the sample to be tested in one embodiment of the present application;

[0022] Figure 5 A three-dimensional stereogram of the surface impedance modulus distribution of the sample to be tested in one embodiment of the present application;

[0023] Figure 6 This is a surface electrochemical potential distribution diagram of a pretreated sample in one embodiment of the present application;

[0024] Figure 7 This is the local electrochemical impedance spectroscopy of the passivation area and pitting area on the surface of the pretreated sample in one embodiment of the present application;

[0025] Figure 8 A two-dimensional graph showing the distribution of local impedance modulus values on the surface of a pretreated sample in one embodiment of the present application;

[0026] Figure 9 A three-dimensional stereogram showing the distribution of local impedance modulus values on the surface of a pretreated sample in one embodiment of the present application;

[0027] Figure 10 This is an ECSTM image of the pitting area on the surface of the pretreated sample in one embodiment of the present application.

[0028] Figure 11 A two-dimensional graph showing the distribution of local impedance modulus values on the surface of a pretreated sample in one embodiment of the present application;

[0029] Figure 12A three-dimensional stereogram showing the distribution of local impedance modulus values on the surface of a pretreated sample in one embodiment of the present application;

[0030] Figure 13 This is the local electrochemical impedance spectroscopy of the passivation area and pitting area on the surface of the pretreated sample in one embodiment of the present application;

[0031] The following reference numerals are present in the above drawings:

[0032] 1. First electrode; 2. Glass tube; 3. Platinum-iridium alloy wire; 4. Resin; 5. Second electrode; 6. Wire; 7. Conductive silver glue; 8. Metal sheath; 9. Test object; 10. Scanning microprobe; 11. XYZ three-dimensional piezoelectric microscanner; 12. Stepper motor-driven XY two-dimensional mechanical scanner; 13. Pre-signal conversion, amplification and feedback circuit for tunnel current; 14. Pre-signal conversion and amplification circuit for local impedance; 15. Test signal control and processing unit; 16. Electrochemical scanning tunneling microscope test platform. DETAILED DESCRIPTION

[0033] To make the purpose, technical solutions and advantages of the examples of the present application clearer, the technical solutions in the examples of the present application will be described clearly and completely below. Where specific conditions are not specified in the examples, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be purchased commercially.

[0034] As described in the background of this application, the existing technology has the problem of low accuracy in measuring the local impedance of metal corrosion. In order to solve the above problem, a scanning microprobe is provided in a typical embodiment of this application, and its structural diagram is shown as follows: Figure 1 As shown, it includes a microelectrode and a microprobe, wherein the microelectrode includes a first electrode 1 and a glass tube 2, the diameter of the first end of the first electrode 1 is 20 to 25 μm, the first electrode 1 is located in the glass tube 2, the first electrode 1 is a platinum wire, and the first end of the first electrode 1 is flush with the first end of the glass tube 2; the microprobe includes a platinum-iridium alloy wire 3, the first end of the platinum-iridium alloy wire 3 is a pointed end, the diameter of the first end of the platinum-iridium alloy wire 3 is 100 to 200 nm, the microelectrode and the microprobe are parallel to each other, and the bonding portion is insulated from each other, and the first end of the platinum-iridium alloy wire 3 extends beyond the first end of the first electrode 1 by 1 to 2 μm.

[0035] In this embodiment, by selecting a combination of a microelectrode and a microprobe as a scanning microprobe, on the one hand, the microprobe can be used to detect tunneling current, and then the distance between the microelectrode and the sample can be precisely controlled using the tunneling current as a pointer. On the other hand, during the detection of the sample to be tested, the sample to be tested is used as the working electrode, the first electrode 1 in the microelectrode is used as the counter electrode, and the platinum-iridium alloy wire 3 in the microprobe is used as the reference electrode. The potential change of the working electrode can be more accurately measured, thereby obtaining more accurate corrosion current data. In addition, the three-electrode system can perform more complex electrochemical experiments, such as cyclic voltammetry and potential step method, thereby providing more information on the metal corrosion mechanism, which is of great significance for the study of metal electrochemical corrosion phenomena.

[0036] Controlling the first end of the platinum-iridium alloy wire 3 to extend 1-2 μm beyond the first end of the first electrode 1 facilitates high-resolution measurement of the sample's surface microstructure. Controlling the diameters of the first end of the glass tube 2 and the first end of the first electrode 1 within the aforementioned ranges not only meets spatial resolution requirements but also maintains the stability of the scanning microprobe, resulting in highly accurate measurement results. Controlling the diameter of the first end of the platinum-iridium alloy wire within the aforementioned ranges is intended to improve spatial resolution and enable the study and analysis of corrosion phenomena in micro-regions of the sample being measured.

[0037] In some embodiments, the first end of the platinum-iridium alloy wire 3 is sharpened to a nanometer scale by a tip processing process such as electrochemical etching, mechanical shearing, etc.

[0038] In some embodiments, the outer diameter of the first end of the glass tube 2 is 50-100 μm. Controlling the outer diameter of the first end of the glass tube 2 within this range can, on the one hand, enable the scanning microprobe to have higher spatial resolution during the test process, and on the other hand, avoid the tip effect and maintain the stability of the measurement system.

[0039] In some embodiments, the first electrode 1 is fixed to the glass tube by a resin 4. Specifically, but not limited to, the resin 4 may be epoxy resin, polyimide resin, or the like. The sides of the platinum-iridium alloy wire 3 are coated with an insulating adhesive. Specifically, but not limited to, such insulating adhesive includes, but is not limited to, hot melt adhesive, polymethyl styrene, or the like. The microprobe is attached parallel to the microelectrode by an insulating adhesive. Specifically, but not limited to, such insulating adhesive includes 502 glue, hot melt adhesive, silicone, epoxy resin, or the like. These materials have excellent electrical insulation properties and good curing and bonding properties, which helps improve the structural stability of the scanning microprobe.

[0040] In some embodiments, the microelectrode further comprises a second electrode 5, which is composed of a silver wire and an AgCl film covering the first end of the silver wire, and a side of the AgCl film away from the first end of the silver wire is flush with the first end of the first electrode 1; when the second electrode 5 is included, the glass tube 2 is a multi-channel glass tube, and the first electrode 1 and the second electrode 5 are respectively located in different channels of the multi-channel glass tube.

[0041] In this embodiment, during the measurement process, the second electrode 5 serves as a reference electrode. Figure 2 The AgCl film is formed in situ on the end of the silver wire by anodic chlorination. Specifically, the end of the silver wire is chlorinated in a hydrochloric acid solution with a hydrogen chloride concentration of 0.01 mol / L for 3 hours at a constant current, and the current density is controlled at 0.5 mA / cm 2 The AgCl film is formed on the end of the silver wire. The AgCl film can be formed in situ on the first end of the silver wire by the above method. The preparation method is simple and has good stability.

[0042] Specifically, but not limiting, before forming the AgCl film, the first electrode 1 and the second electrode 3 are fixed in the glass tube 2. Then, the first end of the first electrode 1, the first end of the second electrode 5, and the first end of the glass tube 2 are ground and polished. Grinding can be performed using 5000-grit sandpaper and polishing can be performed using polishing powder and a polishing cloth. The ground and polished microelectrodes can provide more stable and accurate measurement data. Furthermore, the first electrode 1 and the second electrode 5 can be cleaned with ethanol before use to improve the cleanliness of the electrode surfaces.

[0043] Specifically, but not limiting, before use, the glass tube 2 is cleaned with a mixture of 30% H₂O₂ and 98% H₂SO₄ (the volume ratio of hydrogen peroxide to concentrated sulfuric acid in the mixture is 1:4), then rinsed with water until neutral, dried, and then stretched using a glass tube stretching apparatus to obtain a glass capillary tube having an inner diameter of 20 to 30 μm at the first end of the glass tube 2. The glass tube 2 may be a θ-shaped glass tube.

[0044] In some embodiments, the parallel distance between the first electrode 1 and the second electrode 5 is 10-20 μm, the microprobe is adjacent to the side of the microelectrode close to the first electrode 1, and the parallel distance between the platinum-iridium alloy wire 3 and the first electrode 1 is 10-20 μm.

[0045] In this embodiment, by controlling the parallel spacing between the first electrode 1 and the second electrode 5 and the parallel spacing between the platinum-iridium alloy wire 3 and the first electrode 1, it helps to reduce the ohmic drop in the electrolyte, reduce external interference, improve measurement accuracy, and help improve the detection capability of local electrochemical reactions.

[0046] In some embodiments, the second ends of the first electrode 1, the second electrode 5, and the platinum-iridium alloy wire 3 are each connected to a wire 6 to connect the scanning microprobe to the measurement device. Specifically, but not limiting of the invention, the second ends of the first electrode 1 and the second electrode 5 are each connected to the wire 6 via a conductive silver paste 7; the second end of the platinum-iridium alloy wire 3 is connected to the wire 6 via solder. The conductive silver paste 7 contains silver particles, which form a low-resistance contact between the first electrode 1, the second electrode 5, and the wire 6. After curing, the conductive silver paste 7 provides a certain degree of mechanical strength, and its operation is relatively simple.

[0047] In some embodiments, the scanning microprobe further includes a sheath 8, and the microelectrode and the microprobe are fixed on the sheath 8 to facilitate the control of the movement of the scanning microprobe and improve the overall structural stability and durability of the scanning microprobe. Specifically but not restrictively, the sheath can be a stainless steel sheath, and the side of the microelectrode away from the first end of the glass tube 2 and the side of the microprobe away from the first end of the platinum-iridium alloy wire 3 are passed through the sheath 8.

[0048] In another typical embodiment of the present application, a scanning local impedance microelectrode testing system is also provided, and its structural schematic diagram is shown as follows: Figure 3 As shown, it includes an electrochemical scanning tunneling microscope test platform (ECSTM), a scanning microprobe control and drive unit, a tunneling current signal and local impedance measurement unit, and a measurement signal control and processing unit; the scanning microprobe control and drive unit includes the scanning microprobe 10 in the above-mentioned embodiment of the present application.

[0049] The electrochemical scanning tunneling microscope test platform can obtain a nanometer-resolution morphological image of the surface of the sample to be tested. The morphological image is based on the tunneling effect in quantum mechanics and is obtained by detecting the tunneling current on the sample surface through the scanning microprobe 10. In addition, based on the electrochemical principle, the scanning microprobe 10 can detect the electric field distribution at the electrode-solution interface, thereby obtaining a potential distribution image of the local area on the surface of the test object 9. The use of the above-mentioned scanning local impedance microelectrode test system of the present application can achieve high-precision scanning measurement of micro-region sites on the metal surface. The scanning microprobe control and drive unit can accurately control the contact distance between the scanning microelectrode and the sample surface, so that while measuring the impedance, the electrochemical scanning tunneling microscope image and the micro-region corrosion potential distribution can be accurately obtained, which significantly improves the spatial resolution and provides rich information for the study of complex corrosion electrochemical systems.

[0050] In some embodiments, the scanning microprobe control and drive unit also includes an XYZ three-dimensional piezoelectric microscanner 11 and a stepper motor driven XY two-dimensional mechanical scanner 12; the tunnel current signal and local impedance measurement unit includes a tunnel current pre-signal conversion, amplification and feedback circuit 13, a local impedance pre-signal conversion and amplification circuit 14, a test signal control and processing unit 15, and an electrochemical scanning tunneling microscope test platform 16.

[0051] The tunneling current is used as an indicator of the scanning microprobe reaching the sample surface. The stepper motor drives the coarse adjustment of the XY two-dimensional mechanical scanner 12 and the fine adjustment of the XYZ three-dimensional piezoelectric microscanner 11 to control the precise distance between the tip of the scanning microprobe 10 and the test object surface.

[0052] Specifically, during the test process, the scanning microprobe 10 automatically approaches the sample surface. When the first end of the platinum-iridium alloy wire 3 approaches the surface of the test object (usually less than 1 nm), a tunnel current signal can be detected. After the tunnel current pre-signal conversion, amplification and feedback of the feedback circuit 13, the scanning microprobe 10 stops moving. At this time, the microelectrode in the scanning microprobe 10 basically reaches the sample surface; then the control and processing unit 15 of the test signal controls the scanning microprobe control and drive unit to drive the scanning microprobe 10 to lift 1 to 10 μm along the Z direction, and then drive the scanning microprobe 10 to scan in a constant height mode.

[0053] During the test, a metal sample with a mechanically polished surface is used as the working electrode (WE), the first electrode 1 in the scanning microprobe 10 is used as the counter electrode (CE), and the platinum-iridium alloy wire 3 is used as the reference electrode (RE). In the presence of a second electrode 5, the second electrode 5 is used as the reference electrode, forming a three-electrode system in the electrolyte. There are two test modes: (1) applying a small-amplitude AC potential signal perturbation of a specific frequency (10-1000 Hz) that is sensitive to corrosion to the electrode system, and detecting the two-dimensional distribution image of the electrochemical impedance of the metal sample surface by the scanning microprobe 10; (2) moving the scanning microprobe 10 to a specific location on the sample surface, applying a small-amplitude AC potential signal perturbation of a specific frequency range (0.01-10000 Hz) to the electrode system, and detecting the electrochemical impedance spectrum of the specific location on the metal sample surface; during the test, the distance between the scanning microprobe 10 and the sample surface is kept constant. In the scanning microprobe 10, the platinum-iridium alloy wire 3 not only detects tunneling current and precisely controls the distance between the scanning microprobe and the sample surface, but also enables conventional ECSTM measurements, acquiring in situ images of the sample's surface structure and topography. Furthermore, because the first electrode 1 is enclosed in a glass tube, with only the micrometer-sized area of the first end near the sample surface exposed, it can also measure micro-area potentials, acquiring images of the micro-area potential distribution on the test object's surface.

[0054] The present application is further described in detail below with reference to specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in this application.

[0055] Example 1

[0056] An embodiment of the scanning microprobe of the present application, and a method for preparing the scanning microprobe of the present embodiment are as follows:

[0057] S1, cutting platinum wire and silver wire with a diameter of 20 μm and a length of 3 cm respectively, cleaning the platinum wire and the silver wire with anhydrous ethanol, and drying them to obtain cleaned platinum wire and silver wire;

[0058] S2, clean the θ-type glass capillary with a mixture of hydrogen peroxide with a mass fraction of 30% H2O2 and concentrated sulfuric acid with a concentration of 98% H2SO4 (the volume ratio of hydrogen peroxide to concentrated sulfuric acid in the mixture is 1:4), then rinse with water until neutral, dry, and then stretch using a glass tube stretching instrument to obtain a glass capillary with an inner diameter of 20 μm at both tube tips, and a glass capillary diameter of 100 μm;

[0059] S3, place the cleaned platinum wire and silver wire into the two tubes of the glass capillary respectively, with the first ends of the platinum wire and silver wire flush with the tip of the glass capillary, and then fix them with epoxy resin. After the resin is completely cured, the tip of the glass capillary is polished on 5000-mesh sandpaper using a glass grinder, and polished with polishing powder and polishing cloth to obtain a microelectrode. The second ends of the platinum wire and silver wire are connected to the copper wire through conductive silver glue for electrical signal transmission; wherein, the parallel spacing between the platinum wire and the silver wire is 10 μm, and the parallel spacing between the platinum-iridium alloy wire and the platinum wire is 10 μm.

[0060] S4: Immerse the first end of the silver wire in the microelectrode in a hydrochloric acid solution with a HCl concentration of 0.01 mol / L and perform anodic chlorination for 3 h under constant current conditions, controlling the current density to 0.5 mA / cm 2 , a dense AgCl film is formed on the first end of the silver wire, which serves as a reference electrode;

[0061] S5, a section of platinum-iridium alloy wire with a diameter of 300 μm was cut, and a tip with a diameter of 100 nm was prepared at the first end of the platinum-iridium alloy wire by mechanical shearing. The tip was then encapsulated with hot melt adhesive, exposing only the tip and the second end to obtain a microprobe, and a copper wire was welded to the second end;

[0062] S6. Use hot melt glue to parallelly attach the microelectrode and microprobe under a microscope. The microelectrode and microprobe are insulated from each other. In addition, the tip of the platinum-iridium alloy wire is controlled to extend 2μm beyond the platinum wire. Finally, use a stainless steel sheath to fix the microelectrode and microprobe to obtain a scanning microprobe.

[0063] Example 2

[0064] An embodiment of a scanning local impedance microelectrode test system of the present application includes an electrochemical scanning tunneling microscope (ECSTM) test platform, a scanning microprobe control and drive unit, a tunneling current signal and local impedance measurement unit, and a measurement signal control and processing unit;

[0065] Among them, the electrochemical scanning tunneling microscope (ECSTM) test platform includes a scanning microprobe control and drive unit including the scanning microprobe in Example 1 of the present application, an XYZ three-dimensional piezoelectric microscanner and a stepper motor driving an XY two-dimensional mechanical scanner; the tunnel current signal and local impedance measurement unit includes a tunnel current pre-signal conversion, amplification and feedback circuit, and a local impedance pre-signal conversion and amplification circuit.

[0066] Example 3

[0067] An embodiment of the scanning microprobe of the present application is provided. The scanning microprobe of this embodiment differs from that of embodiment 1 only in that the microelectrode does not contain silver wire.

[0068] Example 4

[0069] An embodiment of the scanning local impedance microelectrode testing system of the present application is provided. The scanning local impedance microelectrode testing system of this embodiment is different from that of embodiment 2 only in that embodiment 3 is used as the scanning microprobe.

[0070] Performance testing

[0071] The performance test of the scanning local impedance microelectrode test system described in Example 2 was performed:

[0072] 304 stainless steel was processed into samples measuring 12 mm × 4 mm in diameter. The surface of the sample was polished with 400-, 800-, 1200-, 1500-, and 2000-grit sandpaper to remove the surface rust. The sample was then polished to a mirror finish with 1.0 μm and 0.3 μm alumina powder, respectively. The sample was cleaned with acetone and deionized water, respectively, and allowed to air dry for 24 hours to obtain the pretreated sample. A conductive adhesive coating was applied to the pretreated sample surface using a brush coating method to a thickness of 10 μm. The coating was scratched in the middle area with a utility knife, with a width of approximately 200 μm, to obtain the test sample.

[0073] 1. Test the local impedance distribution on the surface of the sample to be tested:

[0074] The test solution is a 0.1M NaCl solution, and the scanning range is 4 mm x 4 mm. During the scanning measurement, the tip of the platinum-iridium alloy wire moves toward the sample surface until a tunneling current is detected, stopping the needle's advance. The scanning microprobe is then raised 1 μm in the Z direction (perpendicular to the sample surface) by the test signal control and processing unit. The test solution is then added to perform a scanning measurement of the local surface impedance. A 1000 Hz, 10 mV AC signal perturbation is applied to the electrode system, and the sample surface is scanned stepwise in a constant-height mode.

[0075] Figure 4 is a two-dimensional graph of the surface local impedance modulus distribution, Figure 5 It is a three-dimensional diagram of the distribution of local impedance modulus on the surface. Figures 4-5 It can be found that there are obvious differences in the impedance modulus values of the coating defect area.

[0076] 2. Test the electrochemical potential distribution on the surface of the pretreated sample, the local electrochemical impedance spectrum of the passivation area and pitting area on the surface of the pretreated sample, the surface impedance distribution of the pretreated sample, and the ECSTM image:

[0077] (1) The pretreated sample is placed in the sample tank, and the scanning microprobe automatically approaches the surface of the pretreated sample until the tunnel current is detected and the needle is stopped. Then, the scanning microprobe is moved upward by 5 μm in the Z direction (perpendicular to the surface of the pretreated sample) through the control and processing unit of the test signal. Then, a FeCl3 solution with a mass fraction of 5% FeCl3 is added to the sample tank, and the micro-area electrochemical potential is scanned and measured in a constant height mode. The scanning area is 4 mm × 2 mm, and the electrochemical potential distribution map of the pretreated sample surface is obtained, as shown in FIG. Figure 6 As shown;

[0078] (2) Continue to position the scanning microprobe to the passivation area and pitting area through the XYZ three-dimensional piezoelectric microscanner, control the distance between the scanning microprobe and the pretreated sample to remain unchanged, and perform local electrochemical impedance tests respectively. The frequency range is 0.01 to 10000 Hz, and the local electrochemical impedance spectra of the passivation area and pitting area on the surface of the pretreated sample are obtained. The results are as follows Figure 7 shown.

[0079] (3) Continue to apply 1000Hz, 10mV AC signal disturbance to the electrode system, and control the movement of the scanning microprobe through the test signal control and processing unit to gradually scan the surface of the pretreated sample. The local impedance distribution diagram of the pretreated sample surface is shown in the figure below. Figures 8-9 As shown, Figure 8 is a two-dimensional graph of the surface local impedance modulus distribution, Figure 9The figure shows the distribution of local impedance modulus on the surface in three dimensions. As can be seen from the figure, there is a clear local peak in the impedance distribution, indicating that local corrosion is obvious on the surface. The point with the highest corrosion activity is selected and the tip of the platinum-iridium alloy wire in the scanning microprobe is moved to this position for ECSTM measurement. The results are shown in the figure. Figure 10 As shown. Figure 10 It can be seen that there are small pore corrosion pits at the corrosion active points, and corrosion products are accumulated around the pits.

[0080] The performance test of the scanning local impedance microelectrode test system described in Example 4 was performed:

[0081] The test method is consistent with that of Example 2, except that the microelectrode does not contain silver wire and a platinum-iridium alloy microprobe is used as a quasi-reference electrode.

[0082] The local impedance distribution diagram of the pretreated sample surface is as follows Figures 11-12 As shown, Figure 11 is a two-dimensional graph of the surface local impedance modulus distribution, Figure 12 The figure shows the distribution of local impedance modulus values on the surface in a three-dimensional stereogram. As can be seen from the figure, it can capture larger pitting sites with higher corrosion activity, but the sensitivity for other small pitting sites with weak activity is not as good as that of Example 1. The scanning microprobe is positioned at the passivation area and pitting area by an XYZ three-dimensional piezoelectric microscanner. The distance between the scanning microprobe and the pretreated sample is kept constant, and local electrochemical impedance tests are performed respectively. The frequency range is 0.01 to 10000 Hz, and the local electrochemical impedance spectra of the passivation area and pitting area on the surface of the pretreated sample are obtained, as shown in FIG. Figure 13 As shown. Figure 13 It can be seen that there is a significant difference in the impedance between the passivation area and the pitting area.

[0083] From the above test results, it can be seen that the scanning microprobe of this application can not only measure the local impedance distribution on the surface and the local impedance spectrum of specific points, but also measure ECSTM images and detect the distribution of electrochemical corrosion potential in surface micro-areas. It has high spatial resolution and is suitable for studying metal corrosion and protection.

[0084] The above description is merely a preferred embodiment of the present application and is not intended to limit the present application. Various modifications and variations are possible for those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present application shall be included within the scope of protection of the present application.

Claims

1. A scanning microprobe, characterized in that: The invention comprises a microelectrode and a microprobe, wherein the microelectrode comprises a first electrode (1) and a glass tube (2), wherein the diameter of the first end of the first electrode (1) is 20 to 25 μm, the first electrode (1) is located in the glass tube (2), the first electrode (1) comprises a platinum wire, and the first end of the first electrode (1) is flush with the first end of the glass tube (2); the microprobe comprises a platinum-iridium alloy wire (3), the first end of the platinum-iridium alloy wire (3) is a pointed end, the diameter of the first end of the platinum-iridium alloy wire (3) is 100 to 200 nm, the microelectrode and the microprobe are parallel to each other, and the joints are insulated from each other, and the first end of the platinum-iridium alloy wire (3) extends 1 to 2 μm beyond the first end of the first electrode (1).

2. The scanning microprobe according to claim 1, characterized in that: The first electrode (1) is fixed in the glass tube (2) via a resin (4); and / or the side surface of the platinum-iridium alloy wire (3) is wrapped with an insulating adhesive; and / or the microprobe is attached to the microelectrode in parallel via an insulating adhesive.

3. The scanning microprobe according to claim 1 or 2, characterized in that: The microelectrode further comprises a second electrode (5), the second electrode (5) being composed of a silver wire and an AgCl film covering the first end of the silver wire, wherein a side of the AgCl film away from the first end of the silver wire is flush with the first end of the first electrode; the glass tube (2) is a multi-channel glass tube, and the first electrode (1) and the second electrode (5) are respectively located in different channels of the multi-channel glass tube.

4. The scanning microprobe according to claim 3, characterized in that: The parallel distance between the first electrode (1) and the second electrode (5) is 10 to 20 μm, the microprobe is adjacent to the side of the microelectrode close to the first electrode (1), and the parallel distance between the platinum-iridium alloy wire (3) and the first electrode (1) is 10 to 20 μm.

5. The scanning microprobe according to claim 3, characterized in that: The second end of the first electrode (1), the second end of the second electrode (5), and the second end of the platinum-iridium alloy wire (3) are respectively used for connecting a wire (6).

6. The scanning microprobe according to claim 5, characterized in that: The second end of the first electrode (1) and the second end of the second electrode (5) are respectively connected to the wire (6) via a conductive silver glue (7); and / or the second end of the platinum-iridium alloy wire (3) is connected to the wire (6) via welding.

7. The scanning microprobe according to claim 1 or 2, characterized in that: The scanning microprobe further comprises a sheath (8), and a side of the microelectrode away from the first end of the glass tube (2) and a side of the microprobe away from the first end of the platinum-iridium alloy wire (3) are passed through the sheath (8).

8. A scanning local impedance microelectrode test system, characterized in that: It includes an electrochemical scanning tunneling microscope test platform, a scanning microprobe control and drive unit, a tunnel current signal and local impedance measurement unit, and a measurement signal control and processing unit; the scanning microprobe control and drive unit includes the scanning microprobe according to any one of claims 1 to 7.

9. The scanning local impedance microelectrode testing system according to claim 8, characterized in that: The scanning microprobe control and drive unit further comprises an XYZ three-dimensional piezoelectric microscanner (11) and a stepping motor driven XY two-dimensional mechanical scanner (12); the tunnel current signal and local impedance measurement unit comprises a tunnel current pre-signal conversion, amplification and feedback circuit (13) and a local impedance pre-signal conversion and amplification circuit (14).

10. Application of the scanning local impedance microelectrode testing system according to claim 8 or 9 in the field of metal corrosion and protection.

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