阅读说明：本技术 通过监测点蚀研究金属应力腐蚀动态过程的方法与装置 (Method and device for researching metal stress corrosion dynamic process by monitoring pitting corrosion ) 是由 朱永艳 于 2019-11-01 设计创作，主要内容包括：通过监测点蚀研究金属应力腐蚀动态过程的装置,包括工作电极A、参比电极、辅助电极、工作电极B、三维控位仪、电化学分析仪和电解池。工作电极A为发生应力腐蚀的被拉伸薄片金属试样。本发明能够对发生应力腐蚀的金属表面进行连续面扫描,实时原位监测金属/电解质界面微区点蚀的动态变化；本发明将SECM的水平面扫描方式改为垂直面扫描方式,大大减少了腐蚀产物在金属表面的沉积,所得氧化电流值更能确切地反映金属表面的微区电化学信息、更能真实地呈现金属表面点蚀发展变化时的动态过程。(The device for researching the metal stress corrosion dynamic process by monitoring the pitting corrosion comprises a working electrode A, a reference electrode, an auxiliary electrode, a working electrode B, a three-dimensional position control instrument, an electrochemical analyzer and an electrolytic cell. The working electrode a is a stretched sheet metal specimen in which stress corrosion occurs. The invention can carry out continuous surface scanning on the metal surface which is subjected to stress corrosion, and monitor the dynamic change of the metal/electrolyte interface micro-area pitting in real time in situ; the invention changes the horizontal scanning mode of the SECM into the vertical scanning mode, greatly reduces the deposition of corrosion products on the metal surface, and the obtained oxidation current value can reflect the micro-area electrochemical information of the metal surface more exactly and can present the dynamic process of the metal surface when the pitting development changes more truly.)

1. The device for researching the metal stress corrosion dynamic process in real time by monitoring the pitting corrosion is characterized by comprising a working electrode A, a reference electrode, an auxiliary electrode, a working electrode B, a three-dimensional potential control instrument, an electrochemical analyzer and an electrolytic cell, wherein the working electrode A, the reference electrode, the auxiliary electrode, the working electrode B and the three-dimensional potential control instrument are respectively connected with the electrochemical analyzer;

the three-dimensional position control instrument is positioned on one side of the electrolytic cell, the working electrode A, the reference electrode, the auxiliary electrode and the working electrode B are arranged above the electrolytic cell, the working electrode A is positioned in the middle, the working electrode B and the reference electrode are respectively arranged on two sides of the working electrode A, the upper part of the working electrode B is fixed on the three-dimensional position control instrument, the auxiliary electrode is adjacent to the reference electrode, and the reference electrode is positioned between the working electrode A and the auxiliary electrode;

the working electrode A is a stretched sheet metal sample which generates stress corrosion, two ends of the sheet metal vertically penetrate through the top surface and the bottom surface of the electrolytic cell and are fixed on the top surface and the bottom surface of the electrolytic cell through sealing pieces, and two ends of the sheet metal are provided with small holes for connecting with a clamp of a stretching machine;

the reference electrode comprises a saturated calomel electrode, a reference tube and a luggin capillary tube, the saturated calomel electrode is positioned in the reference tube, the reference tube is fixed on the electrolytic cell, the lower end of the reference tube is connected with the upper end of the luggin capillary tube, and the lower end of the luggin capillary tube extends to the middle of the working electrode A and keeps a certain distance with the working electrode A;

the working electrode B comprises an L-shaped bent pipe and an ultramicroelectrode, the ultramicroelectrode is positioned in the L-shaped bent pipe, the lower end of the L-shaped bent pipe is a sharp mouth, the upper end of the L-shaped bent pipe penetrates through the top surface of the electrolytic cell and then is fixed on a three-dimensional position control instrument, and the L-shaped bent pipe can move in a plane parallel to the sheet metal under the drive of the three-dimensional position control instrument.

2. The apparatus for real-time research on dynamic process of metal stress corrosion by monitoring pitting corrosion according to claim 1, wherein the three-dimensional position control instrument is an SECM three-dimensional positioner and the scanning mode is vertical plane scanning.

3. The apparatus for real-time study of metal stress corrosion dynamic process by monitoring pitting corrosion according to claim 1, wherein the electrochemical analyzer is a CHI 900B electrochemical analyzer.

4. The apparatus according to claim 1, wherein the ultramicroelectrode is a Pt probe with d ═ 25 μm.

5. The apparatus for real-time research on metal stress corrosion dynamic process by monitoring pitting corrosion according to claim 4, wherein the distance of the Pt probe from the thin sheet metal is 30 μm.

6. The apparatus for real-time study of metal stress corrosion dynamic process by monitoring pitting corrosion according to claim 1, wherein the distance from the thin sheet metal to the lower end of the robust gold capillary is 2 mm.

7. The apparatus for real-time study of metal stress corrosion dynamic process by monitoring pitting corrosion according to claim 1, wherein the thickness of the thin sheet metal is 2mm, the middle part of the thin sheet metal is a 10mm x 10mm working surface, and the part of the thin sheet metal other than the upper working surface is sealed with 705 silicone rubber.

8. The method for researching the dynamic process of metal stress corrosion in real time by monitoring the pitting corrosion is characterized by comprising the following steps of:

s1: assembling the device for researching the dynamic process of metal stress corrosion in real time by monitoring pitting corrosion according to claim 1, connecting the clamp of the stretcher to the small holes at the two ends of the sheet metal sample, and starting the electrochemical analyzer to obtain current data on each electrode;

s2: applying tensile stress to the sheet metal sample, and applying anodic polarization potential to the sheet metal sample under the combined action of the tensile stress and the electrolyte solution to enable the sheet metal sample to generate stress corrosion; in the process of stress corrosion, applying an anodic polarization potential to the working electrode B to enable the working electrode B to generate an oxidation reaction; two groups of current data obtained by the electrochemical analyzer are respectively an anodic polarization current value generated by the thin sheet metal sample under the polarization potential and an oxidation current value generated by the working electrode B under the anodic polarization potential; the oxidation current value on the working electrode B corresponds to the current generated by oxidation reaction, and the dynamic change of the oxidation current value is the dynamic change of the concentration of oxidized ions in the working area;

s3: and starting the three-dimensional position control instrument to drive the working electrode B to perform vertical plane scanning, wherein in the plane scanning range, the area with rapidly increased current is a pitting corrosion generation development area, and the development stage and the development trend of pitting corrosion are judged according to the numerical value and the dynamic change of the oxidation current.

9. The method for real-time study of the dynamic process of metal stress corrosion by monitoring pitting corrosion according to claim 8, wherein the anodic polarization potential is 0.70V.

10. The method for real-time study of the dynamic process of metal stress corrosion by monitoring pitting corrosion according to claim 8, wherein the oxidation reaction is Fe²⁺Is oxidized into Fe³⁺The reaction of (1).

Technical Field

The invention relates to a metal stress corrosion detection technology, in particular to a method and a device for researching a metal stress corrosion dynamic process in real time by monitoring pitting corrosion.

Background

Stress Corrosion Cracking (SCC) of metal is a common local Corrosion and one of the most harmful Corrosion forms. When the metal is subjected to stress corrosion, obvious uniform corrosion does not occur, and even corrosion products are few and are difficult to find only by naked eyes. Therefore, stress corrosion tends to occur suddenly without any sign, and is a catastrophic corrosion. Because the inducement and influencing factors of the stress corrosion are very complicated and a real-time in-situ research method is lacked, so far, many problems about the stress corrosion are not clear, and no effective method for predicting and monitoring the stress corrosion exists.

Pitting Corrosion (Pitting Corrosion), also called Pitting Corrosion and Pitting Corrosion, means that after a certain period of time, most of the surface of a metal material is not corroded or is slightly corroded, but in certain micro-areas of the surface, Corrosion holes appear, and the Corrosion holes continuously develop in the depth direction along with the passage of time to form Pitting Corrosion pits. The pitting corrosion forms a structure of a large cathode and a small anode in geometric form, so that the dissolution rate of the anode of the corrosion hole is quite high, and the corrosion perforation damage of the metal material can be caused quickly. In addition, pitting can accelerate other types of localized corrosion, such as intergranular corrosion, stress corrosion, and corrosion fatigue.

In corrosive media containing aggressive ions, pitting can exacerbate stress corrosion, and most of the time pitting is the source of stress corrosion. Lie rock^[1]The research of the people finds that the stress corrosion of the austenitic stainless steel pipeline in the atmosphere containing the chloride ions can be divided into two stages, namely, firstly, a passive film on the surface of the metal is damaged to generate pitting corrosion, and then, a sensitive point at the bottom of an etching pit is used as a crack source to expand into the stress corrosion. Therefore, the generation and development conditions of the pitting corrosion on the surface of the metal sample in the stress corrosion process are researched, then the relation between the pitting corrosion and the stress corrosion is discussed, the dynamic process of the stress corrosion can be researched, the generation and development mechanism of the stress corrosion is further discussed, and the stress corrosion is effectively predicted and monitored.

The traditional method for researching the metal stress corrosion mechanism and influencing factors mainly comprises a tensile experiment, a fast and slow potentiodynamic polarization scanning technology and an ex-situ surface physical technology. The tensile test can be divided into constant load, constant deformation, slow strain rate tensile and the like according to the loading mode. The greater the difference in anodic current density between the polarisation curves obtained by the fast and slow scans (1000 mV/min and 20mV/min respectively), the greater the tendency for stress corrosion to occur. The ex-situ surface physical technique mainly adopts a Scanning Electron Microscope (SEM) and an Energy Dispersive Spectrometer (EDS) to observe the fracture morphology and analyze the components of corrosion products at the fracture. The traditional methods generally used at home and abroad can only obtain the integral stress-strain information and electrochemical information of corroded metal within a certain period of time or obtain the appearance of ex-situ fractures and corrosion product information, and have certain limitations. Therefore, it is necessary to develop new ideas and methods to study stress corrosion so as to obtain real-time in-situ dynamic information in the metal stress corrosion process, and further discuss the mechanism and influencing factors of stress corrosion.

The research on the dynamic change of the metal surface pitting in the stress corrosion process can obtain more electrochemical information and interface dynamic information in the stress corrosion process, and further can deeply discuss the stress corrosion mechanism and its influence factors^[2]. For example, the composition and the change of the electrode surface film can be estimated according to the dynamic change of the pitting corrosion, the generation and development process of the stress corrosion can be discussed, the development stage of the stress corrosion can be judged, the influence factors of the stress corrosion can be deeply researched, the effect of the protective measures can be judged, and the like.

The traditional electrochemical methods (such as potentiodynamic polarization technology and electrochemical impedance spectroscopy) and ex-situ surface physical technologies (such as SEM and EDS) for researching the pitting corrosion cannot be used for monitoring the dynamic change of the pitting corrosion in situ in real time, and cannot be used for continuously monitoring the dynamic process of the pitting corrosion or predicting the occurrence, development and stage of the stress corrosion in situ in real time and continuously monitoring the dynamic process of the stress corrosion.

The references relevant to the present application are as follows:

[1] effects of Limonite, Skuwa, Lianhua, Cl-on the transformation behavior from pitting to stress corrosion [ J ], corrosion and protection, 2012,33(11): 955-.

[2] Zhang Xinyan, study of the influence of corrosion pits on stress concentration and corrosion fatigue life of round bar members [ D ], Gansu: university of lunzhou marble, 2013.

[3] Yuan, SECM study of the pitting process of X70 carbon steel [ D ], Jiangsu: university of Jiangsu Shi, 2011.

[4] Liu Rui, based on SECM and ultramicroelectrode technology research iron-based metal anode dissolution process [ D ], Jiangsu: university of Jiangsu, 2018.

Disclosure of Invention

The invention aims to modify a Scanning electrochemical microscope (SECM), changes conventional horizontal Scanning into vertical Scanning, and can monitor the pitting development condition of metal in situ in real time. Thereby continuously monitoring the dynamic process of pitting corrosion on the metal surface in which stress corrosion occurs.

Specifically, the invention provides a device for researching a metal stress corrosion dynamic process in real time by monitoring pitting corrosion, which comprises a working electrode A, a reference electrode, an auxiliary electrode, a working electrode B, a three-dimensional potential control instrument, an electrochemical analyzer and an electrolytic cell, wherein the working electrode A, the reference electrode, the auxiliary electrode, the working electrode B and the three-dimensional potential control instrument are respectively connected with the electrochemical analyzer;

the three-dimensional position control instrument is positioned on one side of the electrolytic cell, the working electrode A, the reference electrode, the auxiliary electrode and the working electrode B are arranged above the electrolytic cell, the working electrode A is positioned in the middle, the working electrode B and the reference electrode are respectively arranged on two sides of the working electrode A, the upper part of the working electrode B is fixed on the three-dimensional position control instrument, the auxiliary electrode is adjacent to the reference electrode, and the reference electrode is positioned between the working electrode A and the auxiliary electrode;

the working electrode A is a stretched sheet metal sample which generates stress corrosion, two ends of the sheet metal vertically penetrate through the top surface and the bottom surface of the electrolytic cell and are fixed on the top surface and the bottom surface of the electrolytic cell through sealing pieces, and two ends of the sheet metal are provided with small holes for connecting with a clamp of a stretching machine;

the reference electrode comprises a saturated calomel electrode, a reference tube and a luggin capillary tube, the saturated calomel electrode is positioned in the reference tube, the reference tube is fixed on the electrolytic cell, the lower end of the reference tube is connected with the upper end of the luggin capillary tube, and the lower end of the luggin capillary tube extends to the middle of the working electrode A and keeps a certain distance with the working electrode A;

the working electrode B comprises an L-shaped bent pipe and an ultramicroelectrode, the ultramicroelectrode is positioned in the L-shaped bent pipe, the lower end of the L-shaped bent pipe is a sharp mouth, the upper end of the L-shaped bent pipe penetrates through the top surface of the electrolytic cell and then is fixed on a three-dimensional position control instrument, and the L-shaped bent pipe can move in a plane parallel to the sheet metal under the drive of the three-dimensional position control instrument.

Furthermore, the three-dimensional position control instrument is an SECM three-dimensional positioner, and the scanning mode is vertical plane scanning.

Further, the electrochemical analyzer is a CHI 900B electrochemical analyzer.

Further, the super-micro electrode is a Pt probe with d being 25 μm.

Further, the distance between the Pt probe and the sheet metal is 30 μm.

Furthermore, an electrode in the reference electrode is a saturated calomel electrode, and the distance between the lower end of the luggin capillary and the sheet metal is 2 mm.

Further, the thickness of the sheet metal was 2mm, the middle portion of the sheet metal was a 10mm × 10mm work surface, and the portion other than the upper work surface of the sheet metal was sealed with 705 silicone rubber.

The invention also provides a method for researching the dynamic process of metal stress corrosion in real time by monitoring the pitting corrosion, which comprises the following steps:

s1: assembling the device for researching the dynamic process of metal stress corrosion in real time by monitoring the pitting corrosion, connecting a clamp of a stretcher to small holes at two ends of a sheet metal sample, and starting an electrochemical analyzer to obtain current data on each electrode;

s2: applying tensile stress to the sheet metal sample, and applying anodic polarization potential to the sheet metal sample under the combined action of the tensile stress and the electrolyte solution to enable the sheet metal sample to generate stress corrosion; in the process of stress corrosion, applying an anodic polarization potential to the working electrode B to enable the working electrode B to generate an oxidation reaction; two groups of current data obtained by the electrochemical analyzer are respectively an anodic polarization current value generated by the thin sheet metal sample under the polarization potential and an oxidation current value generated by the working electrode B under the anodic polarization potential; the oxidation current value on the working electrode B corresponds to the current generated by oxidation reaction, and the dynamic change of the oxidation current value is the dynamic change of the concentration of oxidized ions in the working area;

s3: and starting the three-dimensional position control instrument to drive the working electrode B to perform vertical plane scanning, wherein in the plane scanning range, the area with rapidly increased current is a pitting corrosion generation development area, and the development stage and the development trend of pitting corrosion are judged according to the numerical value and the dynamic change of the oxidation current.

Further, the anodic polarization potential is 0.70V.

Further, the oxidation reaction is Fe²⁺Is oxidized into Fe³⁺The reaction of (1).

Compared with the prior art, the invention has the beneficial effects that:

(1) the device can realize continuous surface scanning on the metal surface subjected to stress corrosion and monitor the dynamic change of the metal/electrolyte interface micro-area pitting in situ in real time;

(2) the invention changes the horizontal scanning mode of the SECM into the vertical scanning mode, greatly reduces the deposition of corrosion products on the metal surface, and the obtained oxidation current value can more exactly reflect the micro-area electrochemical information of the metal surface and more truly present the dynamic process when the pitting corrosion on the metal surface develops and changes;

(3) the device has the advantages of simple manufacture, easily obtained raw materials, good stability, quick response, high accuracy, good reproducibility, low cost and the like, and is simple and convenient in operation method, easy to use and wide in application range.

Drawings

FIG. 1 is a schematic structural diagram of an apparatus for real-time study of dynamic process of metal stress corrosion by monitoring pitting corrosion according to an embodiment of the present invention;

FIG. 2 is a schematic structural diagram of a working electrode B according to an embodiment of the present invention;

FIG. 3 is a schematic structural diagram of a working electrode A according to an embodiment of the present invention;

in the above fig. 1-3, 1-working electrode a, 101-rubber plug, 102-pinhole, 103-working surface, 2-reference electrode, 3-auxiliary electrode, 4-working electrode B, 401-L-bend, 402-Pt probe, 5 three-dimensional position control instrument, 6-electrochemical analyzer, 7-electrolytic cell.

The specific implementation mode is as follows:

the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.