Device and method for testing electrochemical corrosion of metal under simulated bentonite doping effect

Abstract

A kind of metal electrochemical corrosion testing device under the simulation of bentonite doping effect, the testing device includes bentonite block compaction device, deoxygenated groundwater infiltration device, constant volume compacted bentonite electrolytic cell, fixed clamp, electrochemical workstation and weighing balance.A kind of metal electrochemical corrosion testing method under the simulation of bentonite doping effect, add deionized water to configure simulation solution;The mass of required dry bentonite and dopant is calculated, then the analytical balance is weighed respectively, and is mixed uniformly;Reference electrode is installed on the side of bentonite bearing cabin, and recess for placing counter electrode is processed at the bottom of soil block at predetermined position, to form three-electrode system;Solution volume infiltrated into compacted bentonite block is recorded regularly.The advantages of the present application are: device structure is reasonable, simple to build, operation method is simple, obtained experimental data is reliable, repeatability is good, and reliable data can be provided for evaluating the corrosion resistance of disposal container.

Description

Technical Field

[0001] This invention relates to the field of corrosion electrochemical testing, specifically to a metal electrochemical corrosion testing device and method simulating the bentonite doping effect. It is applicable to studying the corrosion behavior and evolution of candidate materials for high-level radioactive waste geological disposal containers in a simulated groundwater infiltration environment of bentonite modified with different dopants. Background Technology

[0002] While the development and utilization of nuclear energy has brought significant benefits to human society, it has also generated a large amount of radioactive waste, especially high-level radioactive waste. If such waste cannot be safely and effectively disposed of, the nuclear radiation it releases will pose a long-term and serious threat to the human living environment. Currently, the international academic community has proposed various high-level radioactive waste disposal schemes, such as deep-sea burial, ice sheet disposal, rock melting, space disposal, and deep geological disposal. Among them, deep geological disposal is widely recognized as the most feasible final solution. This scheme constructs a multi-barrier system to seal high-level radioactive waste in deep geological bodies 500 to 1000 meters below the surface, thereby achieving permanent isolation from the human living environment. The multi-barrier system consists of surrounding geological rock, buffer backfill material, metal disposal containers, and vitrified bodies. In this system, the metal disposal container, as a key engineering barrier, plays a central role in preventing the migration of radionuclides. During the disposal cycle, which can last for tens of thousands of years, the high-compacted bentonite, as a buffer material, will undergo a process of groundwater infiltration to saturation, causing the metal container to be exposed to Cl-containing substances for a long period of time. - SO4 2- and HCO3 - In complex hydrogeological environments with corrosive ions, bentonite materials face severe corrosion risks. Therefore, systematically studying the corrosion evolution mechanism of candidate materials in bentonite environments is of significant academic value and engineering guiding significance for scientifically assessing the long-term performance of disposal containers and accurately predicting their service life.

[0003] In recent years, systematic studies have been conducted worldwide on the corrosion behavior of high-level radioactive waste geological disposal container materials in simulated deep geological disposal environments. Results indicate that the dynamic evolution of environmental parameters such as groundwater ion composition, dissolved oxygen concentration, and the composition and structure of backfill materials are key factors influencing the corrosion mechanism and kinetics of disposal containers. In the initial stages of reservoir operation, as groundwater continuously infiltrates, the bentonite buffer layer undergoes a transformation from an unsaturated to a saturated state. During this process, the gradient change in bentonite moisture content significantly impacts the corrosion evolution of the metal container. Furthermore, the design of functional buffer materials is a current research focus. Existing studies have shown that doping the bentonite buffer material with substances such as quartz sand, siderite, or reduced iron powder plays a crucial role in optimizing the buffer layer's performance (e.g., thermal conductivity, redox properties, and radionuclide adsorption). However, the type and proportion of dopants in the buffer material significantly affect the permeability of the bentonite layer and the media environment on the surface of the metal disposal container, leading to changes in the electrochemical corrosion behavior at the bentonite-metal container interface and ultimately impacting the safe service life of the disposal container.

[0004] To delve into the mechanisms by which the moisture content and modified bentonite components within the compacted bentonite system influence material corrosion behavior, an experimental setup is needed to accurately reflect the corrosion behavior of the groundwater-buffer material-disposal container system during underground disposal of high-level radioactive waste. The factors influencing the corrosion behavior of metal disposal containers during actual disposal are highly complex; therefore, this setup must simultaneously simulate the natural infiltration process of groundwater and perform in-situ electrochemical testing. Based on this, obtaining reliable corrosion kinetic parameters and exploring the influence of buffer material doping effects on the electrochemical corrosion behavior of the bentonite-metal interface will have significant scientific and engineering application value for the design and safety life assessment of barrier systems in high-level radioactive waste geological disposal projects. Summary of the Invention

[0005] The problem this invention aims to solve is to provide a device and method for testing the electrochemical corrosion of metals under the simulated bentonite doping effect. This method closely simulates the environmental system of bentonite modified with dopants that has permeated groundwater in deep geological disposal of high-level radioactive waste. It enables in-situ electrochemical testing of metal corrosion during the permeation process, analyzes the electrochemical characteristics of the interface between bentonite and metal with different doping contents, and analyzes the corrosion rate, products, and corrosion mechanism of steel samples in modified bentonite with different doping contents. This method can be used to study the corrosion evolution of candidate materials for high-level radioactive waste geological disposal containers in simulated bentonite environments with different dopants.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: An electrochemical corrosion testing device for metals under the effect of bentonite doping is disclosed. The device includes a bentonite block compaction device, a deoxygenated groundwater infiltration device, a constant-volume compacted bentonite electrolytic cell, a fixing fixture, an electrochemical workstation, and a weighing balance. The specific structure is as follows: The bentonite compaction device consists of a steel frame, compaction mold sleeve, mold head, mold base, separate hydraulic jack, and hydraulic pump.

[0007] The deoxygenated groundwater infiltration device consists of a high-purity nitrogen cylinder, inlet / outlet pipelines, a sealed groundwater simulation solution storage tank, and infiltration stones. The infiltration stones are located at the bottom of the device, embedded in grooves inside the storage pipes. The groundwater storage tank is made of transparent acrylic tubing, with graduations marked on the outer wall to record the groundwater infiltration rate.

[0008] The constant-volume compacted bentonite electrolytic cell consists of a stainless steel bentonite support chamber, compacted doped bentonite blocks, and a three-electrode system. Using a bentonite compaction device, powdered bentonite-doped composite material is pressed into the high-pressure compacted stainless steel bentonite support chamber to form high-pressure compacted modified bentonite blocks of a specific density. Pre-drilled grooves for the electrodes are pre-drilled on the lower surface using an electric drill, and reference electrode holes are drilled into the bentonite at the side holes of the support chamber. The constant-volume compacted bentonite electrolytic cell is placed below the deoxygenated groundwater infiltration device, with the upper surface of the compacted bentonite blocks in close contact with the lower surface of the infiltration stone.

[0009] The reference electrode is inserted into a compacted bentonite block on the side of the stainless steel bentonite support chamber, while the counter electrode is inserted from the lower surface of the compacted bentonite block. The upper surface of the working electrode (the working surface of the electrochemical sensor) is in close contact with the lower surface of the compacted bentonite block.

[0010] The fixture consists of steel plates, bolts, and nuts. The upper and lower steel plates have holes at their four corners. Matching bolts pass through the upper and lower steel plates, and nuts are used to connect and secure them from the outside. The upper steel plate has two holes drilled for the intake / exhaust pipes; the lower steel plate has two holes drilled for the working electrode and counter electrode wires. The upper and lower steel plates are placed on top of the groundwater storage tank and at the bottom of the working electrode, respectively. Then, the four bolts are passed through the round holes at the four corners of the upper and lower steel plates, and the nuts are rotated to secure the deoxygenated groundwater infiltration device and the constant-volume compacted bentonite electrolysis cell.

[0011] The working electrode is encapsulated with epoxy resin. After the resin solidifies, holes are drilled adjacent to the metal working surface to facilitate the installation and fixation of the counter electrode. Then, the upper surface of the working electrode is brought into close contact with the lower surface of the compacted bentonite block, and the counter electrode is inserted into a pre-reserved groove in the compacted bentonite block. Simultaneously, the reference electrode is embedded into the compacted bentonite block through a hole on the side of the bentonite bearing chamber, forming a three-electrode system.

[0012] After the device is fixed in place, the gaps between the parts are sealed with PTFE tape and 704 silicone sealant. Finally, the prepared groundwater simulation solution is injected into the groundwater simulation solution storage tank, the air inlet / outlet pipes are connected, high-purity nitrogen is introduced, and the pipes are sealed after 1 hour of deoxygenation.

[0013] In the three-electrode system, the working electrode is sealed in a mold with resin, the counter electrode passes through the mold and is inserted into a pre-reserved groove below the soil block, and the reference electrode is inserted into the soil block from the side through a pre-reserved hole in the support chamber. The gap between the reference electrode pore and the support chamber is sealed with silicone. The working electrode and counter electrode wires are led out through holes in the steel plate base, and the wires connecting the three-electrode system are connected to the electrochemical workstation.

[0014] The aforementioned test device for simulating metal electrochemical corrosion under bentonite doping effect is characterized in that the bentonite compaction device consists of a steel frame, a mold head, a mold base, a separate hydraulic jack, and a hydraulic pump. When in use, the stainless steel bentonite bearing chamber is placed on the mold base. The aforementioned metal electrochemical corrosion testing device simulating bentonite doping effect is characterized in that the fixture consists of steel plates, bolts and nuts, with holes at the four corners of the upper and lower steel plates, and the matching bolts and nuts passing through the upper and lower steel plates, and being connected and fixed from the outside of the two steel plates with nuts. The aforementioned device for testing electrochemical corrosion of metals under simulated bentonite doping effect is characterized in that the electrochemical workstation is connected to a three-electrode system via a workstation chassis and electrode wires.

[0015] The aforementioned device for testing metal electrochemical corrosion under simulated bentonite doping effect is characterized in that the working electrode is a metal electrochemical sensor, the reference electrode is an Ag / AgCl reference electrode, and the counter electrode is a platinum sheet.

[0016] A method for testing the electrochemical corrosion of metals under simulated bentonite doping effects includes the following steps: (1) Based on the composition of the groundwater solution, accurately weigh the required analytical grade reagents using an analytical balance, and then add deionized water to prepare a simulated solution; (2) Filter the bentonite using a 100-mesh filter screen, place the sieved bentonite in an electric heating drying oven, and dry it at a constant temperature of 100~110℃ for 6~10 hours. Then immediately place the bentonite in a sealed bag and vacuum store it. (3) Calculate the required mass of dry bentonite and admixtures based on the dry density and volume of the pre-set high-pressure compacted bentonite block, and then weigh them separately using the analytical balance and mix them evenly. (4) Install the compaction mold sleeve on the compaction mold base, invert the bentonite bearing chamber and place it into the compaction mold sleeve of the bentonite block compaction mold, then fill it with the weighed dry bentonite-doped composite powder, and compact it using the compaction mold head to obtain high-compact modified bentonite blocks. Drill holes on the side of the bentonite bearing chamber for installing the reference electrode, and process a groove at a predetermined position on the bottom of the block for placing the counter electrode; (5) The working electrode is encapsulated with epoxy resin. After the resin solidifies, holes are drilled at adjacent positions on the metal working surface to facilitate the installation and fixation of the counter electrode. Then, the upper surface of the working electrode is brought into close contact with the lower surface of the compacted bentonite block, and the counter electrode is inserted into the reserved groove in the compacted bentonite block. At the same time, the reference electrode is embedded into the compacted bentonite block from the side hole of the bentonite bearing chamber to form a three-electrode system; (6) Place the upper and lower steel plates of the clamp on the top of the groundwater storage tank and the bottom of the working electrode respectively, and then pass the four screws through the round holes at the four corners of the upper and lower steel plates respectively. Rotate the nuts to fix the deoxygenated groundwater infiltration device and the constant volume compacted bentonite electrolysis cell. (7) The groundwater simulation solution was deoxygenated using high-purity nitrogen. The deoxygenated groundwater simulation solution was then injected into a sealed groundwater solution storage tank, and the inlet / outlet gas pipelines were closed. The wires of the three-electrode system were connected to the electrochemical workstation, and in-situ electrochemical tests were performed. At the same time, the volume of solution that infiltrated into the compacted bentonite blocks was recorded periodically.

[0017] The aforementioned method for testing the electrochemical corrosion of metals under simulated bentonite doping effects is characterized in that the composition of the simulated groundwater solution is: CaCl2, 0.5792 mg / L; MgSO4·7H2O, 0.5716 mg / L; Na2SO4, 1.5777 mg / L; NaHCO3, 0.1384 mg / L; NaNO3, 0.0372 mg / L; KCl, 0.0382 mg / L; NaCl, 1.4876 mg / L; deionized water, balance.

[0018] The method for testing the electrochemical corrosion of metals under simulated bentonite doping effects is characterized in that the dry density of the high-pressure compacted modified bentonite block is 1.60 g / cm³. 3 .

[0019] The design concept of this invention is as follows: To more realistically simulate the corrosion system formed by the coupling effect of groundwater, buffer material, and metal container material during deep geological disposal of high-level radioactive waste, and to study the corrosion evolution law in the bentonite-metal interface with doping effect, this invention designs a bentonite block compaction device, a deoxygenated groundwater infiltration device, and a constant-volume compacted bentonite electrolytic cell. By uniformly mixing the dopant with bentonite to simulate the buffer material design of a real disposal reservoir, the deoxygenated groundwater infiltration device is installed on the bentonite block to investigate the natural infiltration process of groundwater in modified bentonite. The working electrode, reference electrode, and counter electrode are integrated into a three-electrode system, connected to an external electrochemical workstation via wires to obtain kinetic parameters during the corrosion process. This enables in-situ electrochemical testing of candidate disposal container materials during the simulated infiltration process of high-pressure compacted bentonite with different dopants.

[0020] The advantages and positive effects of this invention are as follows: The experimental apparatus described in this invention has a reasonable structure, is easy to set up, simple to operate, and provides reliable and reproducible experimental data. By slowly infiltrating deoxygenated groundwater into high-pressure dopant-modified bentonite, the environmental evolution characteristics of buffer / backfill materials in deep geological disposal projects for high-level radioactive waste are simulated more realistically. Through in-situ monitoring of open-circuit potential and electrochemical impedance spectroscopy, the relationship between the infiltration process of different dopant-modified bentonite and the early corrosion behavior of candidate metal container materials is established. Using the experimental apparatus and method described in this invention, long-term corrosion performance testing of candidate materials for high-level radioactive waste geological disposal containers can be achieved in a simulated dopant-modified bentonite environment, providing reliable data for evaluating the corrosion resistance of disposal containers. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of a bentonite block compaction mold; in the diagram, 1 is the compaction mold sleeve, 2 is the compaction mold base, and 3 is the compaction mold pressure head. Figure 2 This is a schematic diagram of a high-pressure compaction bentonite bearing chamber; in the diagram, 4 is a nut, 5 is a steel plate, 6 is a bolt, 7 is a simulated solution, 8 is a working electrode, 9 is a counter electrode, 10 is an air inlet / exhaust pipe, 11 is a groundwater simulated liquid storage tank, 12 is a permeable stone, 13 is a high-pressure compaction modified bentonite block, 14 is a reference electrode, 15 is a stainless steel bentonite bearing chamber, 16 is epoxy resin, and 17 is a three-electrode system base mold. Figure 3 This is a schematic diagram of an electrochemical workstation; in the diagram, 18 represents the electrode wire, and 19 represents the electrochemical workstation chassis. Figure 4 It is a curve simulating the change of groundwater infiltration in bentonite mixed with quartz sand over time; Figure 5This is the curve showing the evolution of the open circuit potential over time in NiCu low alloy steel during the natural infiltration of modified bentonite; Figure 6 This is the electrochemical impedance modulus-frequency spectrum of NiCu low alloy steel during the natural infiltration process of modified bentonite. Detailed Implementation

[0022] In its specific implementation, this invention provides a metal electrochemical corrosion testing device simulating the bentonite doping effect. The device includes a bentonite compaction mold, a filter screen, an electrically heated drying oven, a weighing balance, a stainless steel bentonite support chamber, a deoxygenated groundwater infiltration device, a constant-volume compacted bentonite electrolytic cell, and an electrochemical workstation. The testing method is as follows: First, bentonite is filtered through a 100-mesh filter screen and dried at 105°C for 8 hours to prepare a high-pressure compacted bentonite block. After preparation, a three-electrode system is installed below the prepared bentonite block, with the metal electrochemical sensor working surface in close contact with the lower surface of the high-pressure compacted bentonite block. Platinum sheets and Ag / AgCl reference electrodes are embedded in the reserved positions on the high-pressure compacted bentonite block. After the lower structure of the constant-volume compacted bentonite electrolytic cell is assembled, the deoxygenated groundwater infiltration device above it is assembled. The structure consisting of a groundwater storage tank and infiltration stones is fixed above the bentonite block using silicone and PTFE tape. Then, a prepared groundwater simulation solution is injected into the electrolytic cell device and deoxygenated. The upper and lower steel plates of the clamp are placed on top of the groundwater storage tank and bottom of the working electrode, respectively, and the nuts are tightened to ensure that the volume of bentonite remains constant when it absorbs water and expands. The wires are connected to an electrochemical workstation for in-situ electrochemical monitoring. The volume of the permeated groundwater solution is recorded periodically. This invention realistically and accurately simulates the corrosion environment of bentonite, a buffer material for deep geological disposal of high-level radioactive waste, during the process of being wetted by a simulated groundwater solution. It is used to study the corrosion evolution behavior of metals in candidate materials for deep geological disposal containers of high-level radioactive waste, considering the bentonite doping effect.

[0023] like Figure 1 As shown, the bentonite block compaction mold consists of a mold sleeve 1, a mold base 2, and a mold head 3. A stainless steel bentonite bearing chamber 15 is placed on the mold base 2, and the mold sleeve 1 is fitted onto the mold base 2. A certain mass of bentonite is added to the mold sleeve 1, and the mold head 3 is used to make high-pressure compacted bentonite blocks 13.

[0024] like Figure 2 As shown, the bentonite-doped permeation simulation electrolysis cell device mainly consists of a deoxygenated groundwater permeation device, a constant-volume compacted bentonite electrolysis cell, and a fixing fixture: The constant-volume compacted bentonite electrolytic cell mainly consists of a bentonite support chamber, high-pressure compacted doped bentonite blocks, and a three-electrode system. The three-electrode system comprises a working electrode 8, a counter electrode 9, a reference electrode 14, a three-electrode base mold 17, and epoxy resin 16. During system construction, the working electrode 8 is sealed into the mold 17 with resin 16. Holes are drilled at adjacent positions, and the wires of the counter electrode 9 are led out from the holes and vertically embedded into the high-pressure compacted bentonite block 13. The reference electrode 14 is inserted into the high-pressure compacted bentonite block through a pre-drilled hole in the stainless steel bentonite support chamber 15. The bentonite support chamber consists of the high-pressure compacted bentonite block 13, the bentonite support chamber 15, and a clamp. A hole is left on the side of the bentonite support chamber 15 for the insertion of the reference electrode 14. The bentonite support chamber 15 is placed on the base mold 17 of the three-electrode system.

[0025] The deoxygenated groundwater infiltration device consists of a deoxygenated groundwater solution 7, an air inlet / outlet pipe 10, a groundwater simulation solution storage tank 11, and a permeable stone 12. The groundwater simulation solution storage tank 11 has volume graduations on its surface. The permeable stone 12 is placed in a groove inside the storage tank 11. This composite component is placed on a high-pressure compacted modified bentonite block 13 in 15, ensuring that the lower surface of the permeable stone 12 is in close contact with the upper surface of the bentonite block 13. The gaps between the parts are sealed with polytetrafluoroethylene tape and 704 silicone to ensure the airtightness of the device.

[0026] Two steel plates 5 are placed on the top of the underground water storage tank 11 and the bottom of the three-electrode system base 17, respectively. The upper and lower steel plates 5 have holes at the four corners. Matching bolts and screws 6 pass through the upper and lower steel plates and are connected and fixed from the outside of the two steel plates with nuts 4. The constant volume expansion of the high-pressure compacted bentonite during the wetting process is ensured by adjusting the nuts.

[0027] The three-electrode system consists of a base mold 17, a working electrode 8, a reference electrode 14, and a counter electrode 10. The working electrode 8 is vertically sealed into the base mold 17 using resin 16. Holes are punched in the resin 16 to allow the counter electrode 10 to pass through. The counter electrode 9 is embedded in a high-pressure modified bentonite block 13. The reference electrode 14 is inserted into the high-pressure modified bentonite block 13 through a side hole in the bentonite support chamber 15, contacting the upper surface of the resin 16. The wires of the working electrode 8 and the counter electrode 9 are led out through holes in the steel plate base, while the wire of the reference electrode 14 is led out from the side of the support chamber 15. The system is then connected to an electrochemical workstation.

[0028] After pouring solution 7 into the groundwater simulation solution storage tank 11, high-purity nitrogen gas was introduced into the air inlet pipe 10 for 1 hour for deoxygenation. After completion, both pipes 10 were sealed. The groundwater simulation solution 7 was allowed to naturally permeate from the top through the permeable stone 12 and through the bentonite contact surface to permeate through the high-pressure compacted bentonite block 13, simulating the permeation process of high-pressure compacted bentonite with different dopants. At the same time, the electrochemical workstation was turned on to conduct electrochemical tests.

[0029] like Figure 3 As shown, the electrochemical workstation mainly consists of an electrochemical workstation chassis 19 and electrode wires 18. One end of the electrode wires 18 is connected to the three-electrode system, and the other end of the electrode wires 18 is connected to the electrochemical workstation chassis 19. The electrochemical workstation is turned on to perform electrochemical tests.

[0030] This embodiment simulates the electrochemical test of NiCu low-alloy steel (composition also needs to be given) corrosion during high-pressure compaction bentonite infiltration containing 20% ​​quartz sand dopant. The specific experimental steps are as follows: (1) Based on the composition of the groundwater solution, accurately weigh the required analytical grade reagents using an analytical balance. The specific composition of the solution is as follows: CaCl2, 0.5792 mg / L; MgSO4·7H2O, 0.5716 mg / L; Na2SO4, 1.5777 mg / L; NaHCO3, 0.1384 mg / L; NaNO3, 0.0372 mg / L; KCl, 0.0382 mg / L; NaCl, 1.4876 mg / L. Then add deionized water to prepare simulation solution 7.

[0031] (2) Dry at 105℃ for 8 hours, then weigh bentonite and quartz sand respectively according to the ratio of 20% sand content using an analytical balance, then mix them evenly, and then immediately place the mixture in a sealed bag and vacuum store it.

[0032] (3) Based on the corrosion test conditions and the dimensions of the bentonite bearing chamber 15, it is proposed to prepare a bentonite with a diameter of 6 cm, a height of 2.5 cm, and a dry density of 1.60 g / cm³. 3 The high-pressure compaction of bentonite block 13 was used to calculate the required mass of the dried mixture as 113.1 g, and the dried bentonite mixed powder was weighed using an analytical balance.

[0033] (4) Place the bentonite bearing chamber 15 on the mold base 2, insert the sleeve 1, fill in the weighed dry dopant bentonite mixture, place the compaction mold head 3 inside the sleeve 1, and compact it using a hydraulic compaction device to obtain a high-compact modified bentonite block 13; drill holes on the side of the bentonite bearing chamber 15 for installing the reference electrode 14, and process a groove at a predetermined position at the bottom of the bentonite block 13 for placing the counter electrode 9;

[0034] (5) The working electrode 8 (NiCu low alloy steel electrochemical sensor) is encapsulated with epoxy resin. After the resin solidifies, holes are drilled at adjacent positions on the metal working surface to facilitate the installation and fixation of the counter electrode 9 (platinum sheet). Then, the upper surface of the working electrode 8 is brought into close contact with the lower surface of the compacted bentonite block 13, and the counter electrode is inserted into the reserved groove of the compacted bentonite block 13. At the same time, the reference electrode 14 is embedded into the compacted bentonite block 13 from the side hole of the bentonite bearing chamber to form a three-electrode system; (6) Place the upper and lower steel plates 5 of the clamp on the top of the groundwater storage tank 11 and the bottom of the three-electrode system mold base 17 respectively. Then, pass the four screws 6 through the round holes at the four corners of the upper and lower steel plates 5 respectively, and rotate the nuts 4 to fix the deoxygenated groundwater infiltration device and the constant volume compacted bentonite electrolysis cell.

[0035] (7) Place the groundwater simulation solution 7 in the groundwater simulation solution storage tank 11, connect the air inlet pipe and the exhaust pipe 10, fill with high-purity nitrogen, deoxygenate for 1 hour, and then seal the pipe 10. Connect the wires of the three-electrode system to the electrode wires 18 of the electrochemical workstation. After the groundwater simulation solution 7 has seeped into the compacted bentonite block, perform in-situ electrochemical testing.

[0036] (8) At the same time, the volume of the underground aqueous solution that seeps into the high-pressure compacted bentonite block 13 is recorded periodically through the scale on the surface of the underground aqueous solution storage tank 11.

[0037] like Figure 4 As shown in the curve, the infiltration rate of simulated groundwater in bentonite mixed with quartz sand changes over time. It can be seen that the infiltration rate is relatively fast in the initial stage of the experiment, leading to an increase in water content in the bentonite. As time progresses, the infiltration rate of the simulated solution tends to stabilize, and the compacted bentonite reaches a water-saturated state.

[0038] like Figure 5 As shown in the curve, the evolution of the open-circuit potential of NiCu low-alloy steel over time during the natural infiltration of modified bentonite reveals that the open-circuit potential oscillates violently in the initial stage of the experiment, indicating that the water content in the bentonite on the electrode surface is low and the electrode is in a state of incomplete conduction. As time progresses, the simulated solution continuously infiltrates into the electrode surface, and the open-circuit potential gradually stabilizes.

[0039] like Figure 6 As shown in the curves, the evolution of the electrochemical impedance modulus-frequency spectrum of NiCu low-alloy steel during the natural infiltration of modified bentonite over time reveals that the high-frequency and low-frequency impedance moduli are relatively high in the initial stage of the experiment, indicating that the dielectric resistance of the bentonite on the electrode surface is large, and the corrosion rate of NiCu steel is relatively low. With prolonged time, the water content at the NiCu steel / bentonite interface increases, the dielectric resistance decreases, and corrosion accelerates.

[0040] The results of the above embodiments show that the present invention can realistically and accurately simulate the natural infiltration process of groundwater in bentonite with different doping and modification, as well as the corrosion evolution process of metal materials in the system. It can obtain real and useful corrosion kinetic parameters and reveal the influence of the buffer material doping effect on the electrochemical corrosion behavior of the bentonite-metal interface.

[0041] The above embodiments are merely one example of the present invention, and not all examples. All other embodiments obtained by those skilled in the art based on the above embodiments without inventive effort are within the scope of protection of the present invention.

[0042] Matters not covered in this invention are common knowledge.

[0043] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A testing device and method for simulating the electrochemical corrosion of metals under the effect of bentonite doping, characterized in that, Includes bentonite block compaction device, deoxygenated groundwater infiltration device, constant volume compacted bentonite electrolytic cell, fixing fixture, electrochemical workstation and weighing balance; The bentonite compaction device consists of a steel frame, compaction mold sleeve, mold head, mold base, separate hydraulic jack, and hydraulic pump. The deoxygenated groundwater infiltration device consists of a high-purity nitrogen cylinder, an inlet / outlet pipeline, a sealed groundwater simulation liquid storage tank, and a seepage stone. The seepage stone is located at the bottom of the infiltration device and is embedded in the groove on the inner side of the tank wall. The groundwater storage tank is made of transparent plexiglass tube, and the outer wall of the tube is marked with graduations to record the groundwater infiltration rate. The constant volume compacted bentonite electrolytic cell consists of a stainless steel bentonite support chamber, compacted doped bentonite blocks, and a three-electrode system. The constant volume compacted bentonite electrolytic cell is located below the deoxygenated groundwater infiltration device, and the upper surface of the compacted bentonite blocks is in close contact with the lower surface of the infiltration stone.

2. The device and method for testing electrochemical corrosion of metals under simulated bentonite doping effect according to claim 1, characterized in that, The three-electrode system consists of a working electrode, a reference electrode, and a counter electrode; The working electrode is a metal electrochemical sensor, the reference electrode is an Ag / AgCl reference electrode with a salt bridge, and the counter electrode is a platinum sheet. The reference electrode is inserted into a compacted bentonite block on the side of the stainless steel bentonite support chamber, and the counter electrode is embedded from the lower surface of the compacted bentonite block. The upper surface of the working electrode, i.e. the working surface of the electrochemical sensor, is in close contact with the lower surface of the compacted bentonite block.

3. The device and method for testing electrochemical corrosion of metals under simulated bentonite doping effect according to claim 1, characterized in that, The fixing fixture consists of steel plates, bolts, and nuts. The upper and lower steel plates have holes at their four corners. The matching bolts pass through the upper and lower steel plates and are fixed by connecting them from the outside with nuts. The upper steel plate has two holes drilled for installing the air inlet / exhaust pipe. The lower steel plate has two holes drilled for leading out the working electrode and the counter electrode wires. The fixture is used to fix the deoxygenated groundwater infiltration device and the constant volume compacted bentonite electrolysis cell.

4. A method for testing electrochemical corrosion of metals under simulated bentonite doping effect using the apparatus described in any one of claims 1 to 3, characterized in that, Includes the following steps:

1. Based on the composition of the groundwater solution, accurately weigh the required analytical grade reagents using an analytical balance, and then add deionized water to prepare a simulated solution; 2. Filter the bentonite using a 100-mesh filter screen, place the sieved bentonite in an electric heating drying oven, and dry it at a constant temperature of 100~110℃ for 6~10 hours. Then immediately place the bentonite in a sealed bag and vacuum store it.

3. Based on the dry density and volume of the pre-set high-pressure compacted bentonite block, as well as the type and proportion of the dopant, calculate the required mass of dried bentonite and dopant, and then weigh them separately using the analytical balance and mix them evenly.

4. Install the compaction mold sleeve on the compaction mold base, invert the bentonite bearing chamber and place it into the compaction mold sleeve of the bentonite block compaction mold, then fill it with the weighed dry bentonite-doped composite powder, and compact it using the compaction mold head to obtain high-compact modified bentonite blocks; drill holes on the side of the bentonite bearing chamber for installing reference electrodes, and process grooves at predetermined positions on the bottom of the blocks for placing counter electrodes; 5. The working electrode is encapsulated with epoxy resin. After the resin solidifies, holes are drilled at adjacent positions on the metal working surface to facilitate the installation and fixation of the counter electrode. Then, the upper surface of the working electrode is brought into close contact with the lower surface of the compacted bentonite block, and the counter electrode is inserted into the reserved groove of the compacted bentonite block. At the same time, the reference electrode is embedded into the compacted bentonite block from the side hole of the bentonite bearing chamber to form a three-electrode system.

6. Place the upper and lower steel plates of the clamp on the top of the groundwater storage tank and the bottom of the working electrode, respectively. Then, pass the four screws through the round holes at the four corners of the upper and lower steel plates, and rotate the nuts to fix the deoxygenated groundwater infiltration device and the constant volume compacted bentonite electrolysis cell.

7. Use high-purity nitrogen to deoxygenate the groundwater simulation solution storage tank, then inject the deoxygenated groundwater simulation solution into a sealed groundwater solution storage tank and close the inlet / outlet gas pipelines; connect the wires of the three-electrode system to the electrochemical workstation and conduct in-situ electrochemical tests; at the same time, record the volume of solution that seeps into the compacted bentonite blocks periodically.

5. The method for testing electrochemical corrosion of metals under simulated bentonite doping effect according to claim 4, characterized in that, The simulated groundwater solution composition was as follows: CaCl2, 0.5792 mg / L; MgSO4·7H2O, 0.5716 mg / L; Na2SO4, 1.5777 mg / L; NaHCO3, 0.1384 mg / L; NaNO3, 0.0372 mg / L; KCl, 0.0382 mg / L; NaCl, 1.4876 mg / L; deionized water, balance.

6. The method for testing electrochemical corrosion of metals under simulated bentonite doping effect according to claim 5, characterized in that, The dry density of the high-pressure compacted modified bentonite blocks is 1.60 g / cm³. 3 .

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