Polyacrylamide gel electrolyte, method for producing the same, and use

Abstract

This invention provides a polyacrylamide gel electrolyte for use in a portable three-electrode corrosion sensor for monitoring metal corrosion in the atmosphere, and a method for manufacturing the same. [Solution] The polyacrylamide gel electrolyte 5 is obtained by radical polymerization of acrylamide monomer, initiator, crosslinking agent, and glycerin under aqueous phase conditions and oxygen-free conditions. The polyacrylamide gel electrolyte obtained in this way exhibits excellent moisturizing properties due to the presence of glycerin, and can be stored stably at room temperature and used effectively, making it suitable for long-term monitoring of the corrosion status of metal materials.

Description

Technical Field

[0005] , ,

[0001] The present invention relates to polyacrylamide gel electrolyte, its manufacturing method and application, and belongs to the field of metal corrosion monitoring.

Background Art

[0002] Electrochemical test techniques are widely applied in corrosion research. However, these techniques have some special difficulties in corrosion research in the field of cultural buildings. In general tests, artificial materials are prepared to mimic the original components of metals, and research is carried out using conventional laboratory techniques. However, since these components formed over a long time on the buildings to which they belong cannot be completely reproduced repeatedly, the information they provide also has limitations. How to non-destructively monitor corrosion information has become the focus of research.

[0003] Conventional liquid electrolytes are likely to evaporate or leak during long-term use, so the monitoring data becomes unstable and inaccurate.

[0004] In the field of atmospheric corrosion monitoring, using polymer electrolytes instead of conventional liquid electrolytes has become a common and effective method. Such an alternative can effectively avoid the risk of liquid leakage or evaporation, which is particularly important in the design and application of portable corrosion sensors. In the monitoring field, there are still some problems to be solved. First, in order to ensure the accuracy of long-term monitoring, it is still necessary to further optimize the stability and conductivity of existing polymer electrolytes under different environmental conditions. Second, how to improve the sensitivity and response speed of the sensor to capture minute corrosion changes is also the focus of current research.

Summary of the Invention

Problems to be Solved by the Invention

[0005] Regarding the objectives of the invention, the first objective of the present invention is to provide a polyacrylamide gel electrolyte; the second objective of the present invention is to provide a method for producing the polyacrylamide gel electrolyte; the third objective of the present invention is to provide an application of the polyacrylamide gel electrolyte in the manufacture of a portable three-electrode corrosion sensor; and the fourth objective of the present invention is to provide a portable three-electrode corrosion sensor using the polyacrylamide gel electrolyte, thereby eliminating the associated difficulties faced when conducting in-situ tests using liquid electrolytes, particularly in the field of atmospheric corrosion monitoring. [Means for solving the problem]

[0006] Regarding the technical solution, the polyacrylamide gel electrolyte according to the present invention is obtained by using acrylamide monomer, initiator, crosslinking agent and glycerin as raw materials, dissolving the acrylamide monomer under aqueous phase conditions, adding the initiator and crosslinking agent, and initiating radical polymerization of acrylamide by the initiator under oxygen-free conditions.

[0007] Furthermore, the initiator is ammonium persulfate or potassium persulfate.

[0008] Furthermore, the crosslinking agent is methylenebisacrylamide.

[0009] Furthermore, the aqueous phase is either a sodium sulfate solution or a simulated rainwater solution, with the concentration of the sodium sulfate solution being 0.002 to 1 mol / L, and the concentration of the total solute in the simulated rainwater solution being 0.0005 to 0.05 mol / L.

[0010] Furthermore, the simulated rainwater solution contains calcium sulfate, ammonium sulfate, ammonium chloride, and sodium nitrate.

[0011] Furthermore, the concentration of acrylamide monomer in the aqueous phase is 10-50%, the amount of initiator used is 4-6% of the monomer mass, and the amount of crosslinking agent used is 0.01-0.5% of the monomer mass.

[0012] The method for producing a polyacrylamide gel electrolyte according to the present invention is: The process includes the steps of dissolving acrylamide in an aqueous phase, adding an initiator, a crosslinking agent, glycerin, and a sodium sulfate solution, stirring uniformly, introducing an inert gas, bubbling for 10-20 minutes, standing at 60-100°C for 30-60 minutes, and cooling to room temperature to obtain a polyacrylamide gel electrolyte.

[0013] Application of the present invention in the manufacture of a portable three-electrode corrosion type sensor using a polyacrylamide gel electrolyte.

[0014] The present invention further includes a portable three-electrode corrosion sensor using a polyacrylamide gel electrolyte according to the present invention, including an outer mold, wherein the outer mold is filled with the polyacrylamide gel electrolyte according to the present invention, a counter electrode and a reference electrode are inserted into the polyacrylamide gel electrolyte according to the present invention, and a working electrode is provided at the bottom of the polyacrylamide gel electrolyte according to the present invention.

[0015] Furthermore, the outer mold is manufactured from epoxy resin and a hardening agent, the reference electrode is a silver / silver chloride electrode, a silver wire electrode, or a silver wire plated silver electrode, the electrode is a carbon rod or carbon plate, and the working electrode is a stainless steel plate.

[0016] Furthermore, the reference electrode and the counter electrode are positioned parallel to each other, and the bottom end of the reference electrode is 2 to 6 mm away from the top surface of the working electrode.

[0017] Furthermore, the outer mold was created by mixing epoxy resin and a hardener, pouring the mixture into a silica gel mold, and letting it stand for 24 to 48 hours.

[0018] Furthermore, the working electrode needs to be pre-treated, and the pre-treatment step includes sequentially ultrasonicating the working electrode for 20-40 minutes each in acetone, ethanol, and deionized water until it is thoroughly cleaned, drying the treated working electrode at 40-60°C for 1-2 hours, and sequentially polishing the dried working electrode using 280#, 800#, and 1200# sandpaper.

[0019] The present invention further includes applications of the polyacrylamide gel electrolyte according to the present invention or the portable three-electrode corrosion sensor according to the present invention in atmospheric corrosion monitoring.

[0020] The polyacrylamide gel electrolyte used in this invention can non-destructively monitor metals, evaluate their corrosion status in real time, thereby providing a scientific basis for the maintenance and protection of metal materials, extending their service life, and reducing potential safety risks. The addition of glycerin not only improves the moisture retention performance of the electrolyte but also enhances the timeliness of monitoring, allowing the electrolyte to operate stably under long-term environmental conditions. Such improvements not only enhance the reliability and durability of sensors using polyacrylamide gel electrolytes, but also enable the electrolyte to continuously and effectively monitor the corrosion status of metal materials in practical applications, providing a more effective solution for real-time monitoring of atmospheric corrosion of metal materials, offering reliable data support for implementing corrosion prevention measures, further ensuring the safety and durability of metal structures, and providing a scientific basis for formulating relevant corrosion prevention measures. [Effects of the Invention]

[0021] In terms of beneficial effects, the present invention has the following significant advantages compared to the prior art.

[0022] (1) The polyacrylamide gel electrolyte according to the present invention has good stability and is easy to manufacture, and has the following advantages in particular: (I) Regarding the stability of the electrolyte, the acrylamide gel electrolyte can be stored for a certain period of time, is suitable for multiple tests, and improves the flexibility and efficiency of experiments. (II) By adding glycerin, the moisture retention performance of the gel electrolyte is improved, and the electrolyte can maintain a stable state under various environmental conditions, thereby enabling long-term monitoring. Such improvements improve the reliability and durability of the sensor.

[0023] (2) The advantages of the portable three - electrode corrosion sensor provided by the present invention are that it can realize non - destructive testing and facilitate corrosion monitoring in different environments. The specific advantages include the following. (I) The sensor is designed to be portable, facilitating rapid detection on - site and reducing damage to samples. (II) Regarding good reproducibility, the sensor has good stability. Even if the same sample is repeatedly tested three times continuously, the difference in results is not large, indicating its highly reliable measurement ability. (III) The position layout of the electrodes in the gel electrolyte is optimized. By using a carbon plate as the counter electrode, it contributes to the uniform distribution of the electric field between the electrodes, thereby reducing interference and improving the accuracy of measurement.

Brief Description of the Drawings

[0024] ​​​​​​​​​​​​​​​​​​​​Figure 7 shows the stable electrochemical impedance spectrum of the portable three-electrode corrosion sensor using polyacrylamide gel electrolyte, which was manufactured in Example 6. [Figure 8] Figure 8 is a comparative diagram of the electrochemical impedance spectra and TAFEL of three-electrode corrosion type sensors using seven groups of agar gel electrolytes, manufactured in Comparative Example 1. [Figure 9] Figure 9 shows the results of a 2-day stability test for the optimal ratio in Comparative Example 1. [Figure 10] Figure 10 shows the electrochemical impedance spectra of a portable three-electrode corrosion sensor using a polyacrylamide gel electrolyte and a three-electrode corrosion sensor using an agar gel electrolyte in Example 7, for the corrosion status of different metal blocks within 24 hours. [Figure 11] Figure 11 shows the corrosion rate of different metal ingots within 24 hours using the coupon method in Example 7. [Modes for carrying out the invention]

[0025] The technical solutions of the present invention will be further described below with reference to the drawings.

[0026] Example 1 As shown in Figure 1, the portable three-electrode corrosion sensor using a polyacrylamide gel electrolyte according to the present invention includes an outer mold 1, the outer mold 1 is filled with the polyacrylamide gel electrolyte 5 according to the present invention, and a counter electrode 2 and a reference electrode 3 are inserted into the polyacrylamide gel electrolyte 5 according to the present invention. An active electrode 4 is provided at the bottom of the polyacrylamide gel electrolyte 5 according to the present invention.

[0027] Reference electrode 3 and electrode 2 are positioned parallel to each other, with a distance of 2 cm between reference electrode 3 and electrode 2, and a distance of 2-6 mm between reference electrode 3 and electrode 4. The distance between counter electrode 2 and electrode 4 is longer than the distance between reference electrode 3 and electrode 4 (approximately 1 mm longer). Outer mold 1 was prepared by mixing 25 mL of epoxy resin adhesive E44 (Dongguan Elice New Materials Co., Ltd.) and 25 mL of epoxy hardener 650 (Dongguan Elice New Materials Co., Ltd.), pouring the mixture into a two-layer cylindrical silica gel mold with an inner diameter of 4 cm, an outer diameter of 5 cm, a height of 6 cm, and a layer thickness of 5 mm, and letting it stand for 30 hours. Reference electrode 3 is a silver / silver chloride electrode, electrode 2 is a carbon rod, and working electrode 4 is a stainless steel plate with dimensions of 5 cm × 5 cm × 0.2 cm in length × width × thickness. The pretreatment process for the working electrode 4 involves sequentially ultrasonically treating it for 30 minutes each in acetone, ethanol, and deionized water until it is thoroughly cleaned. Next, the cleaned working electrode 4 is sequentially polished using 280#, 800#, and 1200# sandpaper. Finally, the treated working electrode 4 is dried in a 60°C oven for 2 hours to obtain the working electrode 4.

[0028] Example 2: Preparation of portable three-electrode corrosion type sensors using the polyacrylamide electrolyte described in Example 1 at different sodium sulfate concentrations.

[0029] (1) Preparation of polyacrylamide gel electrolyte with a sodium sulfate concentration of 0.002 mol / L First, 2.84 mg of sodium sulfate was weighed and dissolved in 10 mL of water to obtain a sodium sulfate solution. Then, 2 g of acrylamide, 0.1 g of ammonium persulfate, and 2.5 mg of methylenebisacrylamide were weighed and dissolved in the sodium sulfate solution. The mixed solution was deoxygenated for 10 minutes using nitrogen gas, and then heated at 60°C for 30 minutes to polymerize. The mixture was then poured into a cylindrical silica gel mold with a diameter of 40 mm and a height of 40 mm, and cooled to obtain a polyacrylamide gel electrolyte.

[0030] (2) The polyacrylamide obtained in step (1) was poured into a mold 1 in which silver / silver chloride as the counter electrode 2 and reference electrode 3 were inserted, and then the mold 1 with the gel electrolyte was placed on the working electrode 4 to form a portable three-electrode corrosion type sensor. The distance between the reference electrode 3 and electrode 4 was 4 mm, and the distance between the counter electrode 2 and electrode 4 was 5 mm.

[0031] Using the above process, four groups of portable three-electrode corrosion sensors were fabricated using polyacrylamide gel electrolytes at sodium sulfate concentrations of 0.02 mol / L, 0.2 mol / L, 0.5 mol / L, and 1 mol / L, respectively.

[0032] Electrochemical performance tests were conducted on three-electrode corrosion type sensors using five groups of polyacrylamide gel electrolytes in this example, and their effects on the working electrodes were studied. The test results are shown in Figure 2. Figure 2 is a comparative diagram of the electrochemical impedance spectra and Tafel diagrams of five groups of polyacrylamide gel electrolytes with different sodium sulfate content, manufactured in Example 2. Figure A is the electrochemical impedance spectrum, and Figure B is the Tafel diagram. As can be seen from Figure 2A, the capacitive reactance arc gradually decreases as the sodium sulfate content increases, and the range of change in the capacitive reactance arc becomes smaller when the sodium sulfate concentration changes between 0.2 mol / L and 1 mol / L. This indicates that the effect of the electrolyte tends to stabilize within this concentration range. As a result of comprehensive consideration, 0.5 mol / L of sodium sulfate was selected as the optimal electrolyte concentration. At this concentration, good conductivity is ensured, while avoiding the adverse effects that may result from excessive concentration, thereby providing a more reliable electrochemical environment for subsequent corrosion monitoring.

[0033] Example 3: Preparation of polyacrylamide gel electrolyte at different glycerin concentrations The manufacturing process is the same as in Example 1, but the difference is that the concentration of glycerin is changed, specifically as follows.

[0034] (1) Preparation of polyacrylamide gel electrolyte with a glycerin content of 30% w / w First, 0.710 g of sodium sulfate was weighed and dissolved in 10 mL of water to obtain a 0.5 mol / L sodium sulfate solution. Then, 2 g of acrylamide, 0.1 g of ammonium persulfate, and 2.5 mg of methylenebisacrylamide were weighed and dissolved in the sodium sulfate solution to obtain a homogeneous mixed solution. 30% w / w glycerin was added to the mixed solution, and the solution was deoxygenated for 10 mins using nitrogen gas. The mixture was then heated at 60°C for 30 mins to polymerize, and the mixture was poured into a cylindrical silica gel mold with a diameter of 40 mm and a height of 40 mm. The mixture was then cooled to obtain a polyacrylamide gel electrolyte.

[0035] (2) The polyacrylamide obtained in step (1) was poured into a mold 1 in which a counter electrode 2 and silver / silver chloride as a reference electrode 3 were inserted, and then the mold 1 with the gel electrolyte was placed on the working electrode 4 to form a portable three-electrode corrosion type sensor.

[0036] Using the above process, four groups of portable three-electrode corrosion sensors were manufactured using polyacrylamide gel electrolytes with glycerin content of 0% W / W, 10% W / W, 20% W / W, and 40% W / W, respectively.

[0037] Electrochemical performance tests were conducted on the five groups of polyacrylamide gel electrolytes used in this example, and the test results are shown in Figure 3. Figure 3 is a comparative diagram of the electrochemical impedance spectra and Tafel diagrams of the five groups of polyacrylamide gel electrolytes used in Example 3. A is the electrochemical impedance spectrum of polyacrylamide gel electrolytes with different glycerin content, and B is the Tafel diagram of polyacrylamide gel electrolytes with different glycerin content. By analyzing the data in Figure 3, it can be observed that all the curve characteristics with different glycerin concentrations show a similar trend, indicating that the characteristics of the electrode reaction do not change significantly depending on the amount of glycerin added, thus supporting the effectiveness of performing electrochemical tests using such gel electrolytes.

[0038] Further analysis of the EIS and Tafel test results revealed that as the glycerin content gradually increased, the corrosive effect of the gel electrolyte on the working electrode gradually decreased, and the sensor performance also improved. This indicates that an appropriate amount of glycerin can effectively improve the stability and corrosion resistance of the electrolyte. However, when the glycerin content exceeds 40%, the electrolyte exhibits high softening properties and viscosity, making it unsuitable for experimentation. Therefore, based on the electrochemical test results and the state of the electrolyte during actual use, it is appropriate to select a gel electrolyte with a glycerin content of 30% to 40% for testing.

[0039] Figure 4 shows the results of the effective service life test of portable three-electrode corrosion-type sensors using five groups of polyacrylamide gel electrolytes manufactured in Example 3. A is a statistical graph of impedance tests at different time points for electrolytes without added glycerin, B is a statistical graph of impedance tests at different time points for electrolytes with 10% added glycerin, C is a statistical graph of impedance tests at different time points for electrolytes with 20% added glycerin, D is a statistical graph of impedance tests at different time points for electrolytes with 30% added glycerin, and E is a statistical graph of impedance tests at different time points for electrolytes with 40% added glycerin. As can be seen from Figure 4, as the glycerin content increases to 30%, the effective service life of the corrosion-type sensors using polyacrylamide gel electrolytes also extends accordingly. Figure 4E is a statistical graph of the impedance test over 30 days for the sensor with 40% added glycerin. During the first 11 days of the test period, the test results of the sensor were stable and did not change, indicating that the corrosion status could be effectively monitored during this period. Over time, the electrolyte's moisturizing effect gradually decreased, potentially triggering a phase change. Furthermore, conductivity improved, impedance decreased, and the corrosive effect on stainless steel gradually increased.

[0040] Based on the above, the sensor can effectively monitor corrosion conditions for up to 11 days. This result further validates the important role of glycerin in improving the long-term monitoring capability of polyacrylamide gel electrolytes and provides a solid foundation for its application in atmospheric corrosion monitoring.

[0041] Example 4: Manufacturing of a three-electrode corrosion sensor using gel with different electrodes. The basic steps for manufacturing the corrosion-type sensor using polyacrylamide gel are the same as in Example 3, except that the glycerin concentration is set to 40% W / W in this example. The difference is that the counter electrode 2 used is a carbon plate, and the reference electrode 3 uses a silver / silver chloride electrode, a silver wire electrode, and a silver chloride-plated silver wire electrode, respectively, thereby manufacturing three groups of portable three-electrode corrosion-type sensors using polyacrylamide gel.

[0042] Electrochemical tests were performed on these three groups of three-electrode corrosion-type sensors, and the results are shown in Figure 5. Figure 5 shows a comparison of the electrochemical impedance spectra of the three groups of corrosion-type sensors manufactured in Example 4. As can be seen from Figure 5, the curve characteristics of these three types of reference electrodes are basically identical, and it was shown that changing reference electrode 3 does not significantly affect the corrosion test results. This finding provides more possibilities for the flexible application of the sensor, allowing for the selection of an appropriate reference electrode under different experimental conditions without affecting the accuracy of the test.

[0043] Based on the results of this embodiment, the reliability and applicability of the polyacrylamide gel-based corrosion sensor are further verified, laying the foundation for future research and applications.

[0044] Example 5: Effect of gel on a three-electrode corrosion type sensor at various distances between the reference electrode and the working electrode. The basic steps for manufacturing the corrosion-type sensor using polyacrylamide gel are the same as in Example 4, except that the glycerin concentration is set to 40% W / W. The counter electrode 2 used is a carbon plate, and the difference is that the reference electrode 3 is a silver / silver chloride electrode. Combined with practical applications, three groups of portable three-electrode corrosion-type sensors using polyacrylamide gel were manufactured by selecting the distance between the reference electrode 3 and the working electrode 4 to 2 mm, 4 mm, and 6 mm, respectively. Electrochemical tests were performed on these three groups of three-electrode corrosion-type sensors, and the results are shown in Figure 6. Figure 6 shows a comparison of the electrochemical impedance spectra of the three groups of corrosion-type sensors manufactured in Example 5. Figure A is the Nyquist figure, and Figure B is the Bode figure. As can be seen from Figure 6A, the curve characteristics of these three types of reference electrodes are basically identical, and the fact that the curve characteristics of the three types of reference electrodes are basically identical indicates that the electrode spacing has little effect on the overall characteristics of the electrochemical reaction. The increase in impedance in the low-frequency region of the Bode plot in Figure 6 indicates a gradual increase in the electrolyte's resistance, demonstrating that the electrolyte's conductivity is affected by distance. Combined with actual tests, the distance between different reference electrodes has little effect on the characteristic curve of the electrochemical reaction, but the electrolyte's resistance is certainly affected. Therefore, considering actual tests, selecting a distance of 4 mm between the reference electrode and the working electrode effectively ensures the validity and reproducibility of the experiment.

[0045] Example 6: Effects of gels prepared with various salt solutions on trielectrode corrosion type sensors The basic steps for manufacturing the corrosion-type sensor using polyacrylamide gel are the same as in Example 2, the only difference being that a simulated rainwater aqueous solution is used as the aqueous phase when manufacturing the polyacrylamide gel electrolyte, and the total solute concentration in the simulated rainwater aqueous solution is 0.00073 mol / L, specifically as follows.

[0046] (1) Preparation of simulated rainwater electrolyte First, 14.43 mg of calcium sulfate dihydrate (CaSO4·2H2O), 15.04 mg of ammonium sulfate [(NH4)2SO4], 19.15 mg of ammonium chloride [(NH4)Cl], and 15.13 mg of sodium nitrate (NaNO3) were weighed and dissolved in 1000 mL of distilled water. This mixed solution was used as a liquid electrolyte, and the pH was adjusted to 6.5 with a 1 mol / L sodium hydroxide solution to obtain a simulated rainwater electrolyte.

[0047] (2) Manufacturing of a three-electrode corrosion type sensor using polyacrylamide gel electrolyte First, 2 g of acrylamide, 0.1 g of ammonium persulfate, and 2.5 mg of methylenebisacrylamide were weighed and dissolved in 20 mL of simulated rainwater electrolyte to obtain a homogeneous mixed solution. 40% w / w glycerin was added to the mixed solution, and the solution was deoxygenated for 10 minutes using nitrogen gas. The mixture was then heated at 60°C for 30 minutes to polymerize, and the mixture was poured into a cylindrical silica gel mold with a diameter of 40 mm and a height of 40 mm. The mixture was then cooled to obtain a polyacrylamide gel electrolyte.

[0048] (3) The polyacrylamide obtained in step (2) was poured into a mold 1 in which silver / silver chloride as the counter electrode 2 and reference electrode 3 were inserted, and then the mold 1 with the gel electrolyte was placed on the working electrode 4 to form a portable three-electrode corrosion type sensor. The distance between the reference electrode 3 and electrode 4 was 4 mm, and the distance between the counter electrode 2 and electrode 4 was 5 mm.

[0049] The system and its stability were verified by performing electrochemical tests on the three-electrode corrosion type sensor. Figure 7 shows three consecutive EIS measurements on the same sample. The results demonstrated good overall measurement stability.

[0050] Comparative Example 1: Agar Gel Electrolyte (1) Preparation of simulated rainwater electrolyte First, 14.43 mg of calcium sulfate dihydrate (CaSO4·2H2O), 15.04 mg of ammonium sulfate [(NH4)2SO4], 19.15 mg of ammonium chloride [(NH4)Cl], and 15.13 mg of sodium nitrate (NaNO3) were weighed and dissolved in 1000 mL of distilled water. This mixed solution was used as the liquid electrolyte, and the pH was adjusted to 6.5 with a 1 mol / L sodium hydroxide solution to obtain a liquid electrolyte.

[0051] (2) Manufacturing of a three-electrode corrosion type sensor using agar gel electrolyte Agar powder at a concentration of 2% w / w was added to 40 mL of electrolyte, stirred at room temperature for 30 minutes, then the solution was left in an oil bath at 110°C for 30 minutes, cooled at room temperature for a certain period of time, and then the electrolyte was poured into mold 1 filled with a carbon rod as counter electrode 2 and silver / silver chloride as reference electrode 3. The solution was then cooled until solidification was obtained to obtain a three-electrode corrosion type sensor. The structure of the three-electrode corrosion type sensor is the same as in Example 1, but the difference is that the electrolyte is different.

[0052] Using the above process, six groups of three-electrode corrosion type sensors were obtained using agar gel electrolytes with agar content of 3% W / W, 4% W / W, 5% W / W, 6% W / W, 8% W / W, and 10% W / W, respectively.

[0053] As shown in Figure 8, electrochemical performance tests were conducted on the seven groups of corrosion-type sensors using agar gel electrolytes developed in this example. Figure 8 is a comparison of the electrochemical impedance spectra and TAFELs of the seven groups of three-electrode corrosion-type sensors using agar gel electrolytes manufactured in Comparative Example 1, where A is the electrochemical impedance spectrum of the corrosion-type sensors using gel electrolytes with different agar content, and B is the corresponding TAFEL diagram. As shown in Figure 8, the curve characteristics for all agar concentrations are similar, indicating that the electrode reaction does not change significantly even when the agar content is increased, thus supporting the use of such gel electrolytes for electrochemical testing. From the EIS and TAFEL test diagrams, it was found that when the agar content is 4% W / W, the gel electrolyte has the least effect on the corrosion of the working electrode, and from the above, it was found that the corrosion-type sensor using agar gel manufactured at this concentration has optimal performance.

[0054] As shown in Figure 9, timeliness tests were conducted on a corrosion-type sensor with an agar content of 4% W / W, and it was shown that the electrochemical impedance spectrum test results became inconsistent after 24 hours. This suggests that the performance of the agar gel electrolyte changes over time, potentially affecting the stability and accuracy of the sensor.

[0055] Example 7: Practical application of a corrosion-type sensor using polyacrylamide gel The corrosion status of different metal ingots within 24 hours was detected using the polyacrylamide gel corrosion sensor produced in Example 6 and the agar gel corrosion sensor produced in Comparative Example 1. Specifically, the results are as follows:

[0056] 316L stainless steel plates, 201 stainless steel plates, and Q235 steel plates, each measuring 5 cm in length, 5 cm in width, and 0.2 cm in thickness, were used as working electrodes. Each was sequentially ultrasonically treated for 30 minutes in acetone, ethanol, and deionized water until thoroughly cleaned. The cleaned working electrodes were then sequentially polished using 280#, 800#, and 1200# sandpaper, and dried in preparation for use. The treated 316L stainless steel, 201 stainless steel, and Q235 steel plates were placed in a constant temperature and humidity test chamber and eroded for 1 hour, 4 hours, 8 hours, and 24 hours under conditions of 15°C and 100% humidity. After placing the corrosion-type sensors using polyacrylamide gel prepared in Example 6 and the corrosion-type sensors using agar gel prepared in Comparative Example 1 onto the steel plate samples, they were connected to an electrochemical workstation, and the tests could be initiated. Electrochemical impedance spectrum tests were performed on 316L stainless steel sheets, 201 stainless steel sheets, and Q235 steel sheets within 1 to 24 hours to assess their corrosion status, and the results are shown in Figure 10.

[0057] Figure 10 shows the electrochemical impedance spectra of portable three-electrode corrosion sensors using polyacrylamide gel electrolyte and three-electrode corrosion sensors using agar gel electrolyte in Example 7, for the corrosion status of different metal ingots within 24 hours. A is the electrochemical impedance spectrum of the polyacrylamide gel corrosion sensor for 316L stainless steel, B is the electrochemical impedance spectrum of the polyacrylamide gel corrosion sensor for 201 stainless steel, C is the electrochemical impedance spectrum of the polyacrylamide gel corrosion sensor for Q235 steel, and D is the electrochemical impedance spectrum of the agar gel corrosion sensor. Figure 10 shows the impedance test diagram of the sensor against 316L stainless steel, E is the impedance test diagram of the agar gel corrosion-type sensor against 201 stainless steel, F is the impedance test diagram of the agar gel corrosion-type sensor against Q235 steel, G is the electrochemical impedance spectrum of the polyacrylamide gel corrosion-type sensor for a 24-hour corrosion comparison of 316L stainless steel, 201 stainless steel, and Q235 steel, and H is the electrochemical impedance spectrum of the agar gel corrosion-type sensor for a 24-hour corrosion comparison of 316L stainless steel, 201 stainless steel, and Q235 steel. As can be seen from Figures A, B, and C, a significant impedance change is shown, and the polyacrylamide gel sensor can clearly reflect the corrosion status of different materials at different time points. This demonstrates that the polyacrylamide gel sensor has high sensitivity to metal corrosion and can effectively capture electrochemical changes during the corrosion process. The test results of the corrosion-type sensor using agar gel (Figure 10, D, E, F) showed a weak electrochemical response, making it difficult to distinguish between differences in corrosion at different time points. Therefore, when evaluating the corrosion status of metals in a short period of time, the results of polyacrylamide gel are clearer.

[0058] As can be seen from the analysis of G and H in Figure 10, at the same time, both the polyacrylamide gel and the agar gel showed low Q235 impedance, while the 316L showed high impedance, indicating that the 316L has better corrosion resistance. This further validates the superiority of the polyacrylamide gel sensor in metal corrosion evaluation.

[0059] The Coupon method is commonly used to determine the corrosion status of a sample. The specific procedure is as follows: 316L stainless steel, 201 stainless steel, and Q235 steel are sequentially ultrasonicated for 30 minutes each in acetone, ethanol, and deionized water until thoroughly cleaned. The cleaned working electrodes are then sequentially polished using 280#, 800#, and 1200# sandpaper, and then dried to prepare for use. The treated 316L stainless steel, 201 stainless steel, and Q235 steel are placed in a constant temperature and humidity test chamber and corroded under conditions of 15°C and 100% humidity. The corrosion status of the sample within 24 hours is determined by the mass difference, and the results are shown in Figure 11.

[0060] Figure 11 shows the corrosion rates of different metal ingots within 24 hours using the coupon method in Example 7. A is a sample before corrosion, from left to right being 316L stainless steel, 201 stainless steel, and Q235 steel, respectively. B is a sample after 24 hours of corrosion, from left to right being 316L stainless steel, 201 stainless steel, and Q235 steel, respectively. C shows the mass loss of 316L stainless steel, D shows the mass loss of 201 stainless steel, and E shows the mass loss of Q235 steel. A comparison of A and B in Figure 11 reveals that observing the changes in the samples with the naked eye was not sufficient to accurately determine the corrosion status, especially when there were no significant signs of corrosion on the surface. The mass loss data (C, D, and E in Figure 11) allowed for a more objective evaluation of the degree of corrosion of each material. As can be seen from Figure 11, Q235 steel showed the largest mass loss and therefore the highest corrosion rate, but 316L stainless steel exhibited good corrosion resistance.

[0061] While the Coupon method is an effective corrosion assessment method, its complex operation and long waiting time make it unsuitable for situations requiring rapid assessment. Compared to the Coupon method, the polyacrylamide gel electrolyte sensor of the present invention offers a more efficient detection method. By directly performing electrochemical tests, electrochemical impedance spectral data can be rapidly acquired, and the corrosion resistance performance of different metals can be compared. Experimental results demonstrate that the gel sensor results are consistent with those of the Coupon method, indicating its accuracy and reliability.

[0062] Based on the above, gel-based corrosion sensors are easier and faster to operate, can effectively reduce experimental waiting times, and are applicable when it is necessary to quickly evaluate metal corrosion performance. Therefore, gel electrolyte sensors are a corrosion detection method worth promoting.

Claims

1. A polyacrylamide gel electrolyte, characterized in that it is obtained by using acrylamide monomer, an initiator, a crosslinking agent, and glycerin as raw materials, dissolving the acrylamide monomer under aqueous phase conditions, adding the initiator and crosslinking agent, and initiating radical polymerization of acrylamide by the initiator under oxygen-free conditions.

2. The polyacrylamide gel electrolyte according to claim 1, characterized in that the initiator is ammonium persulfate or potassium persulfate, the crosslinking agent is methylenebisacrylamide, the concentration of acrylamide monomer in the aqueous phase is 10 to 50%, the amount of initiator used is 4 to 6% of the monomer mass, and the amount of crosslinking agent used is 0.01 to 0.5% of the monomer mass.

3. The polyacrylamide gel electrolyte according to claim 1, characterized in that the aqueous phase is a sodium sulfate solution or a simulated rain aqueous solution, the concentration of the sodium sulfate solution is 0.002 to 1 mol / L, and the concentration of the total solute in the simulated rain aqueous solution is 0.0005 to 0.05 mol / L.

4. A method for producing a polyacrylamide gel electrolyte according to any one of claims 1 to 3, comprising the steps of dissolving acrylamide in an aqueous phase, adding an initiator, a crosslinking agent, glycerin and sodium sulfate solution and stirring uniformly, then introducing an inert gas and bubbling for 10 to 20 mins, standing at 60 to 100°C for 30 to 60 mins, and cooling to room temperature to obtain a polyacrylamide gel electrolyte.

5. Application in the manufacture of a portable three-electrode corrosion type sensor using the polyacrylamide gel electrolyte according to any one of claims 1 to 3.

6. A portable three-electrode corrosion sensor comprising an outer mold (1) and a polyacrylamide gel electrolyte according to any one of claims 1 to 3, wherein the outer mold (1) is filled with the polyacrylamide gel electrolyte (5) according to any one of claims 1 to 3, a counter electrode (2) and a reference electrode (3) are inserted into the polyacrylamide gel electrolyte (5) according to any one of claims 1 to 3, and a working electrode (4) is provided at the bottom of the polyacrylamide gel electrolyte (5) according to any one of claims 1 to 3.

7. The portable three-electrode corrosion sensor according to claim 6, characterized in that the outer mold (1) is manufactured from epoxy resin and a hardening agent, the reference electrode (3) is a silver / silver chloride electrode, a silver wire electrode, or a silver wire plated silver electrode, the electrode (2) is a carbon rod or carbon plate, and the working electrode (4) is a stainless steel plate.

8. The portable three-electrode corrosion sensor according to claim 6, characterized in that the reference electrode (3) and the counter electrode (2) are provided in parallel, and the bottom end of the reference electrode (3) is 2 to 6 mm away from the upper surface of the working electrode (4).

9. The outer mold (1) is prepared by mixing epoxy resin and a hardener, pouring the mixture into a silica gel mold, and letting it stand for 24 to 48 hours. The working electrode (4) needs to be pre-treated, and the pre-treatment step includes sequentially ultrasonically treating the working electrode (4) for 20 to 40 minutes each with acetone, ethanol, and deionized water until it is thoroughly cleaned, sequentially polishing the cleaned working electrode (4) using 280#, 800#, and 1200# sandpaper, and drying the polished working electrode (4) at 40 to 60°C for 1 to 2 hours, as described in claim 6.

10. Application of the polyacrylamide gel electrolyte according to any one of claims 1 to 3 in atmospheric corrosion monitoring.

11. Application of the portable three-electrode corrosion sensor described in claim 6 to atmospheric corrosion monitoring.

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