Polyacrylamide gel electrolyte, its preparation and use

Abstract

A polyacrylamide gel electrolyte for use in a portable three-electrode corrosion sensor that monitors metal corrosion in the atmosphere, and a method for producing the same, are provided. [Solution] Polyacrylamide gel electrolyte 5 is obtained by radical polymerization of acrylamide monomer, initiator, crosslinker, and glycerin under aqueous, oxygen-free conditions. Due to the presence of glycerin, the polyacrylamide gel electrolyte thus obtained exhibits excellent moisture retention properties, can be stably stored and effectively used at room temperature, and is suitable for long-term monitoring of the corrosion status of metal materials.

Description

[Technical Field]

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

[0002] Electrochemical testing techniques are widely used in corrosion research. However, these techniques present some special challenges when it comes to corrosion research in cultural buildings. Conventional testing involves preparing artificial materials to mimic the original composition of the metal, and then conducting research using traditional laboratory techniques. However, these techniques are limited in the information they provide, as they cannot fully replicate the composition formed over time on the underlying structure. Therefore, research is focused on how to nondestructively monitor corrosion information.

[0003] Conventional liquid electrolytes are prone to evaporation and leakage during long-term use, making monitoring data unstable and inaccurate.

[0004] In the field of atmospheric corrosion monitoring, the use of polymer electrolytes instead of traditional liquid electrolytes has become a common and effective method. This alternative is particularly important in the design and application of portable corrosion sensors because it effectively avoids the risks associated with liquid leakage or evaporation. Several issues remain to be resolved in the monitoring field. First, the stability and conductivity of existing polymer electrolytes under different environmental conditions still need to be further optimized to ensure the accuracy of long-term monitoring. Second, how to improve the sensitivity and response speed of sensors to capture minute corrosion changes is also a focus of current research. Summary of the Invention [Problem to be solved by the invention]

[0005] Regarding the objects of the invention, a first object of the present invention is to provide a polyacrylamide gel electrolyte, a second object of the present invention is to provide a method for manufacturing the polyacrylamide gel electrolyte, a third object of the present invention is to provide an application of the polyacrylamide gel electrolyte in manufacturing a portable three-electrode corrosion-type sensor, and a fourth object of the present invention is to provide a portable three-electrode corrosion-type sensor using the polyacrylamide gel electrolyte, thereby eliminating the difficulties encountered when using liquid electrolytes for in-situ testing, particularly in the field of atmospheric corrosion monitoring. [Means for solving the problem]

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

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

[0008] Furthermore, the crosslinking agent is methylenebisacrylamide.

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

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

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

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

[0013] The polyacrylamide gel electrolyte of the present invention is applied to the manufacture of a portable three-electrode corrosion-type sensor.

[0014] The present invention further includes a portable three-electrode corrosion-type sensor using a polyacrylamide gel electrolyte according to the present invention, which includes an outer mold, in which the polyacrylamide gel electrolyte according to the present invention is filled, 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 made of epoxy resin and a hardener, 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 a carbon plate, and the working electrode is a stainless steel plate.

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

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

[0018] Furthermore, the working electrode needs to be pretreated. This pretreatment step involves ultrasonically treating the working electrode in acetone, ethanol, and deionized water for 20-40 min each until it is clean, drying the treated working electrode at 40-60°C for 1-2 h, and polishing the dried working electrode sequentially using 280#, 800#, and 1200# sandpaper.

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

[0020] The polyacrylamide gel electrolyte used in the present invention can nondestructively monitor metals and assess 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 electrolyte's moisturizing performance, but also improves the timeliness of monitoring, enabling the electrolyte to operate stably under long-term environmental conditions. These improvements not only improve 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 status of metal materials, providing reliable data support for the implementation of corrosion prevention measures, ensuring the safety and durability of metal structures, and providing a scientific basis for the formulation of related corrosion prevention measures. [Effects of the Invention]

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

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

[0023] (2) The portable three-electrode corrosion sensor provided by the present invention has the advantage of enabling non-destructive testing and facilitating corrosion monitoring in different environments. Specific advantages include: (I) The sensor is designed to be portable, facilitating rapid on-site detection and reducing damage to samples; (II) Good reproducibility: The sensor has good stability, and even when the same sample is tested three times in succession, the results do not vary significantly, demonstrating its reliable measurement capabilities; (III) The position layout of the electrodes in the gel electrolyte is optimized, and a carbon plate is used as the counter electrode, contributing to uniform distribution of the electric field between the electrodes, thereby reducing interference and improving measurement accuracy. [Brief explanation of the drawings]

[0024] [Figure 1] FIG. 1 is a schematic diagram showing the structure of a portable three-electrode corrosion-type sensor according to the present invention. [Figure 2] FIG. 2 is a comparative diagram of electrochemical impedance spectra and Tafel results of the portable three-electrode corrosion-type sensors using five groups of polyacrylamide gel electrolytes with different sodium sulfate contents prepared in Example 2. [Figure 3] FIG. 3 is a comparison of the electrochemical impedance spectra and Tafel results of the five groups of portable three-electrode corrosion-type sensors with polyacrylamide gel electrolytes prepared in Example 3. [Figure 4] FIG. 4 shows the results of the test on the effective use time of the five groups of portable three-electrode corrosion-type sensors using polyacrylamide gel electrolytes prepared in Example 3. [Figure 5] FIG. 5 is a comparative diagram of electrochemical impedance spectra of three groups of portable three-electrode corrosion-type sensors using polyacrylamide gel electrolyte prepared in Example 4. [Figure 6] FIG. 6 is a comparative diagram of electrochemical impedance spectra of three groups of portable three-electrode corrosion-type sensors using polyacrylamide gel electrolyte prepared in Example 5. [Figure 7]FIG. 7 shows the stable electrochemical impedance spectrum of the portable three-electrode corrosion-type sensor with polyacrylamide gel electrolyte prepared in Example 6. [Figure 8] FIG. 8 is a comparison diagram of the electrochemical impedance spectra and TAFEL of the three-electrode corrosion-type sensors using the seven agar gel electrolytes prepared in Comparative Example 1. [Figure 9] FIG. 9 shows the results of a stability test for the optimum ratio in Comparative Example 1 over two consecutive days. [Figure 10] FIG. 10 shows electrochemical impedance spectra of the portable three-electrode corrosion-type sensor with polyacrylamide gel electrolyte and the three-electrode corrosion-type sensor with agar gel electrolyte in Example 7 for corrosion status of different metal blocks within 24 hours. [Figure 11] FIG. 11 is a diagram showing the corrosion rates of different metal blocks within 24 hours using the coupon method in Example 7. DETAILED DESCRIPTION OF THE INVENTION

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

[0026] Example 1 1, the portable three-electrode corrosion-type sensor using a polyacrylamide gel electrolyte according to the present invention includes an outer mold 1, which is filled with a polyacrylamide gel electrolyte 5 according to the present invention, and which has inserted therein a counter electrode 2 and a reference electrode 3. A working 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 arranged parallel to each other. The distance between reference electrode 3 and electrode 2 is 2 cm, and the distance between reference electrode 3 and electrode 4 is 2-6 mm. The distance between counter electrode 2 and electrode 4 is longer (approximately 1 mm) than the distance between reference electrode 3 and electrode 4. Mold 1 was prepared by mixing 25 mL of epoxy resin adhesive E44 (Dongguan Ilik New Materials Co., Ltd.) and 25 mL of epoxy hardener 650 (Dongguan Ilik New Materials Co., Ltd.). The mixture was poured 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 thickness of 5 mm and allowed to stand for 30 h. Reference electrode 3 was a silver / silver chloride electrode, electrode 2 was a carbon rod, and working electrode 4 was a stainless steel plate measuring 5 cm x 5 cm x 0.2 cm in length, width, and thickness. Specifically, the pretreatment process of the working electrode 4 involves ultrasonically treating the working electrode 4 in acetone, ethanol, and deionized water for 30 minutes each until it is thoroughly cleaned. The cleaned working electrode 4 is then polished using 280#, 800#, and 1200# sandpaper in turn. Finally, the treated working electrode 4 is dried in an oven at 60°C for 2 hours to obtain the working electrode 4.

[0028] Example 2: Fabrication of a portable three-electrode corrosion-type sensor with polyacrylamide electrolyte as 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 using nitrogen gas for 10 minutes, and then heated at 60°C for 30 minutes to polymerize. The mixture was 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 with a counter electrode 2 and a silver / silver chloride as a reference electrode 3 inserted, and then the mold 1 with the gel electrolyte was placed on a 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-type sensors with polyacrylamide gel electrolytes were fabricated with 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 the five three-electrode corrosion sensors using polyacrylamide gel electrolytes in this example to investigate their effects on the working electrode. The test results are shown in Figure 2. Figure 2 compares the electrochemical impedance spectra and Tafel plots of the five portable three-electrode corrosion sensors using polyacrylamide gel electrolytes with different sodium sulfate contents, as prepared in Example 2. Figure A shows the electrochemical impedance spectra, and Figure B shows the Tafel plot. As can be seen from Figure 2A, the capacitive reactance arc gradually decreases with increasing sodium sulfate content. The change in the capacitive reactance arc narrows when the sodium sulfate concentration is between 0.2 mol / L and 1 mol / L. This indicates that the electrolyte effect tends to be stable within this concentration range. After comprehensive consideration, 0.5 mol / L of sodium sulfate was selected as the optimal electrolyte concentration. This concentration ensures good conductivity while avoiding the potential adverse effects of excessive concentrations, thereby providing a more reliable electrochemical environment for subsequent corrosion monitoring.

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

[0034] (1) Preparation of polyacrylamide gel electrolyte with 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 mixture. Glycerin with a concentration of 30% w / w was added to the mixture, and the mixture was deoxygenated using nitrogen gas for 10 minutes. It was then heated to 60°C for 30 minutes to polymerize, 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.

[0035] (2) The polyacrylamide obtained in step (1) was poured into a mold 1 with a counter electrode 2 and a silver / silver chloride as a reference electrode 3 inserted, and then the mold 1 with 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-type sensors with polyacrylamide gel electrolytes were fabricated with glycerin contents of 0% W / W, 10% W / W, 20% W / W, and 40% W / W, respectively.

[0037] Electrochemical performance tests were conducted on the five polyacrylamide gel electrolyte three-electrode corrosion-type sensors used in this example, and the test results are shown in Figure 3. Figure 3 shows a comparison of the electrochemical impedance spectra and Tafel plots for the five portable polyacrylamide gel electrolyte three-electrode corrosion-type sensors prepared in Example 3. A shows the electrochemical impedance spectra of polyacrylamide gel electrolytes with different glycerin contents, and B shows the Tafel plots for polyacrylamide gel electrolytes with different glycerin contents. Analysis of the data in Figure 3 reveals that the curve characteristics for all of the different glycerin concentrations all show similar trends, indicating that the amount of glycerin added does not significantly affect the electrode reaction characteristics, supporting the validity of electrochemical tests using such gel electrolytes.

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

[0039] FIG. 4 shows the results of the useful life test of five portable three-electrode corrosion-type sensors using polyacrylamide gel electrolytes prepared in Example 3. A is a statistical graph of impedance tests at different times for electrolytes without added glycerin; B is a statistical graph of impedance tests at different times for electrolytes with 10% added glycerin; C is a statistical graph of impedance tests at different times for electrolytes with 20% added glycerin; D is a statistical graph of impedance tests at different times for electrolytes with 30% added glycerin; and E is a statistical graph of impedance tests at different times for electrolytes with 40% added glycerin. As can be seen from FIG. 4, as the glycerin content increases to 30%, the useful life of the corrosion-type sensors using polyacrylamide gel electrolytes correspondingly increases. FIG. 4E is a statistical graph of the 30-day impedance test of the sensor with 40% added glycerin. During the first 11 days of the test, the sensor test results remained stable and unchanged, demonstrating that corrosion could be effectively monitored during this period. Over time, the moisturizing effect of the electrolyte gradually decreased, which may cause a phase change, leading to an increase in conductivity and a decrease in impedance, and the corrosion effect on stainless steel also gradually increased.

[0040] In conclusion, the sensor can effectively monitor the corrosion status for up to 11 days, which further verifies the important role of glycerin in improving the long-term monitoring capability of polyacrylamide gel electrolyte and provides a solid foundation for its application in atmospheric corrosion monitoring.

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

[0042] Electrochemical tests were conducted 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 fabricated in Example 4. As can be seen from Figure 5, the curve characteristics of these three types of reference electrodes are essentially the same, indicating that replacing reference electrode 3 does not significantly affect the corrosion test results. This finding provides more possibilities for flexible sensor application, allowing for the selection of an appropriate reference electrode under different experimental conditions without affecting the accuracy of the test.

[0043] From the above, the results of this example further verify the reliability and applicability of the corrosion-type sensor using polyacrylamide gel, and lay the foundation for future research and applications.

[0044] Example 5: Effect of different distances between the reference and working electrodes on a three-electrode corrosion-type sensor with gel The basic steps for fabricating a polyacrylamide gel-based corrosion sensor were the same as in Example 4, except that the glycerin concentration in this example was set to 40% w / w. The counter electrode 2 used was a carbon plate, with the difference being that the reference electrode 3 was a silver / silver chloride electrode. In consideration of practical applications, three groups of portable polyacrylamide gel-based three-electrode corrosion sensors were fabricated by selecting the distance between the reference electrode 3 and the working electrode 4 as 2 mm, 4 mm, and 6 mm, respectively. Electrochemical tests were performed on these three groups of three-electrode corrosion 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 sensors fabricated in Example 5. Figure A is a Nyquist plot, and Figure B is a Bode plot. As can be seen from Figure 6A, the curve characteristics of these three types of reference electrodes are essentially identical, indicating that the electrode spacing has little effect on the overall characteristics of the electrochemical reaction. The rise in impedance in the low-frequency region of the Bode diagram in Figure 6 indicates a gradual increase in electrolyte resistance, which indicates that electrolyte conductivity is affected by distance. Combined with actual testing, different reference electrode distances have little effect on the electrochemical reaction characteristic curve, but do affect electrolyte resistance. Therefore, considering actual testing, selecting a distance of 4 mm between the reference electrode and working electrode can effectively ensure the validity and reproducibility of the experiment.

[0045] Example 6: Effect of gels prepared with various salt solutions on three-electrode corrosion-type sensors The basic steps for fabricating a corrosion-type sensor using polyacrylamide gel are the same as those in Example 2, except that a simulated rainwater solution is used as the aqueous phase when fabricating the polyacrylamide gel electrolyte, and the concentration of the total solutes in the simulated rainwater solution is 0.00073 mol / L. Specifically, the steps are 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 1 mol / L sodium hydroxide solution to obtain a simulated rainwater electrolyte.

[0047] (2) Fabrication 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 mixture. 40% w / w glycerin was added to the mixture, and the mixture was deoxygenated using nitrogen gas for 10 minutes. It was then heated to 60°C for 30 minutes to polymerize, 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.

[0048] (3) The polyacrylamide obtained in step (2) was poured into a mold 1 with a counter electrode 2 and a silver / silver chloride as a reference electrode 3 inserted, and then the mold 1 with the gel electrolyte was placed on a 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, and three consecutive EIS measurements on the same sample are shown in Figure 7. The results showed 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 a liquid electrolyte, and the pH was adjusted to 6.5 with 1 mol / L sodium hydroxide solution to obtain a liquid electrolyte.

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

[0052] Using the above process, six groups of three-electrode corrosion-type sensors with agar gel electrolyte were obtained, each with an 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 agar gel electrolyte corrosion sensors used in this example. Figure 8 compares the electrochemical impedance spectra and TAFEL plots of the seven agar gel electrolyte three-electrode corrosion sensors fabricated in Comparative Example 1. A shows the electrochemical impedance spectra of the corrosion sensors fabricated with gel electrolytes containing different agar contents, and B shows the corresponding TAFEL plots. As shown in Figure 8, the curve characteristics for all agar concentrations are similar, indicating that the electrode response does not change significantly with increasing agar content, supporting the use of such gel electrolytes for electrochemical tests. The EIS and TAFEL plots indicate that the gel electrolyte has minimal effect on the corrosion of the working electrode when the agar content is 4% w / w. This indicates that the agar gel corrosion sensors fabricated with this concentration exhibit optimal performance.

[0054] As shown in Figure 9, a time-dependent test was performed on a corrosion-type sensor with an agar content of 4% W / W, and the electrochemical impedance spectrum test results showed no consistency after 24 hours. This indicates that the performance of the agar gel electrolyte changes over time, which may affect the stability and accuracy of the sensor.

[0055] Example 7: Practical application of a corrosion-type sensor using polyacrylamide gel The corrosion-type sensor using the polyacrylamide gel prepared in Example 6 and the corrosion-type sensor using the agar gel prepared in Comparative Example 1 were used to detect the corrosion status of different metal blocks within 24 hours. The details are as follows.

[0056] 316L stainless steel plates, 201 stainless steel plates, and Q235 steel plates, each measuring 5 cm long, 5 cm wide, and 0.2 cm thick, were used as working electrodes. They were ultrasonically treated in acetone, ethanol, and deionized water for 30 minutes each until thoroughly cleaned. The cleaned working electrodes were then polished with 280#, 800#, and 1200# sandpaper, respectively, and then dried for further use. The treated 316L stainless steel, 201 stainless steel, and Q235 steel plates were placed in a constant temperature and humidity test box and subjected to corrosion for 1 hour, 4 hours, 8 hours, and 24 hours at a temperature of 15°C and a humidity of 100°C. The polyacrylamide gel corrosion-type sensor prepared in Example 6 and the agar gel corrosion-type sensor prepared in Comparative Example 1 were placed on the steel plate samples and connected to an electrochemical workstation, allowing the test to begin. Electrochemical impedance spectroscopy tests were carried out on the corrosion conditions of 316L stainless steel plate, 201 stainless steel plate, and Q235 steel plate within 1 to 24 hours, and the results are shown in Figure 10.

[0057] FIG. 10 shows electrochemical impedance spectra of the portable three-electrode corrosion-type sensor with polyacrylamide gel electrolyte and the three-electrode corrosion-type sensor with agar gel electrolyte in Example 7 for corrosion conditions of different metal blocks within 24 hours. A is the electrochemical impedance spectrum of the corrosion-type sensor with polyacrylamide gel for 316L stainless steel, B is the electrochemical impedance spectrum of the corrosion-type sensor with polyacrylamide gel for 201 stainless steel, C is the electrochemical impedance spectrum of the corrosion-type sensor with polyacrylamide gel for Q235 steel, and D is the electrochemical impedance spectrum of the corrosion-type sensor with agar gel. Figure 10 shows the impedance test results of the polyacrylamide gel sensor on 316L stainless steel; Figure 10 shows the impedance test results of the agar gel sensor on 201 stainless steel; Figure 10 shows the impedance test results of the agar gel sensor on Q235 steel; Figure 10 shows the electrochemical impedance spectra of the polyacrylamide gel sensor on 316L stainless steel, 201 stainless steel, and Q235 steel after 24 hours of corrosion; Figure 10 shows the electrochemical impedance spectra of the agar gel sensor on 316L stainless steel, 201 stainless steel, and Q235 steel after 24 hours of corrosion. As can be seen from Figure 10, A, B, and C, significant impedance changes were observed, enabling the polyacrylamide gel sensor to clearly reflect the corrosion status of different materials at different times. This demonstrates the polyacrylamide gel sensor's high sensitivity to metal corrosion and its ability to effectively capture electrochemical changes during the corrosion process. The test results for the agar gel corrosion sensor (Figure 10D, E, and F) showed a weak electrochemical response, making it difficult to distinguish differences in corrosion at different time points. Therefore, the results for the polyacrylamide gel are clearer when evaluating the corrosion status of metals over a short period of time.

[0058] As can be seen from the analyses in Figure 10G and H, at the same time, the impedance of both the polyacrylamide gel and the agar gel was low for Q235, while the impedance of 316L was high, indicating that 316L had better corrosion resistance. This further verifies the superiority of the polyacrylamide gel sensor in evaluating metal corrosion.

[0059] The coupon method is commonly used to assess the corrosion status of samples. The specific procedure is as follows: 316L stainless steel, 201 stainless steel, and Q235 steel were ultrasonically treated in acetone, ethanol, and deionized water for 30 minutes each until thoroughly cleaned. The cleaned working electrode was then polished with 280#, 800#, and 1200# sandpaper, respectively, and then dried for use. The treated 316L stainless steel, 201 stainless steel, and Q235 steel were placed in a constant temperature and humidity test box and subjected to corrosion at a temperature of 15°C and a humidity of 100°C. The corrosion status of the samples was assessed within 24 hours by mass difference, and the results are shown in Figure 11.

[0060] Figure 11 shows the corrosion rate of different metal blocks within 24 hours using the coupon method in Example 7. A shows a sample before corrosion, from left to right, for 316L stainless steel, 201 stainless steel, and Q235 steel. B shows a sample after 24 hours of corrosion, from left to right, for 316L stainless steel, 201 stainless steel, and Q235 steel. 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. Comparing Figures 11A and 11B reveals that observing changes in samples with the naked eye is not an accurate way to assess the corrosion status, especially when there are no significant signs of corrosion on the surface. The mass loss data (Figures 11C, D, and E) allow for a more objective assessment of the corrosion level of each material. As can be seen from Figure 11, Q235 steel exhibits the greatest mass loss and a high corrosion rate, but 316L stainless steel exhibits better corrosion resistance.

[0061] The coupon method is an effective corrosion evaluation method, but its complicated operation and long waiting time make it inapplicable when rapid evaluation is required. Compared to the coupon method, the polyacrylamide gel electrolyte sensor of the present invention provides a more efficient detection method. By directly conducting electrochemical tests, electrochemical impedance spectrum data can be quickly obtained and the corrosion resistance performance of different metals can be compared. Experimental results show that the gel sensor results are consistent with those of the coupon method, demonstrating its accuracy and reliability.

[0062] In conclusion, gel-based corrosion sensors are simpler and faster to operate, effectively reducing waiting time for experiments and making them suitable for applications requiring rapid evaluation of metal corrosion performance. Therefore, gel electrolyte sensors are a corrosion detection method worthy of widespread adoption.

Claims

1. A polyacrylamide gel electrolyte is obtained by using an acrylamide monomer, an initiator, a crosslinking agent, and glycerin as raw materials, dissolving the acrylamide monomer under aqueous phase conditions, adding the initiator and the crosslinking agent, and initiating radical polymerization of acrylamide by the initiator under oxygen-free conditions; the aqueous phase is a sodium sulfate solution or a simulated rainwater solution, the concentration of the sodium sulfate solution is 0.002 to 1 mol / L, and the concentration of all solutes in the simulated rainwater solution is 0.0005 to 0.05 mol / L; The polyacrylamide gel electrolyte is characterized in that the simulated rainwater solution contains calcium sulfate, ammonium sulfate, ammonium chloride, and sodium nitrate.

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

3. 3. A method for producing a polyacrylamide gel electrolyte according to claim 1, comprising the steps of dissolving acrylamide in an aqueous phase, adding an initiator, a crosslinker, glycerin, and a sodium sulfate solution, stirring the mixture uniformly, introducing an inert gas and bubbling for 10 to 20 minutes, leaving the mixture at 60 to 100°C for 30 to 60 minutes, and cooling to room temperature to obtain a polyacrylamide gel electrolyte.

4. 3. Use of the polyacrylamide gel electrolyte according to claim 1 or 2 in the manufacture of a portable three-electrode corrosion-type sensor.

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

6. 6. The portable three-electrode corrosion-type sensor according to claim 5, wherein the outer mold (1) is made of epoxy resin and a hardener, the reference electrode (3) is a silver / silver chloride electrode, a silver wire electrode, or a silver electrode plated with silver wire, the electrode (2) is a carbon rod or carbon plate, and the working electrode (4) is a stainless steel plate.

7. 6. The portable three-electrode corrosion sensor according to claim 5, wherein the reference electrode (3) and the counter electrode (2) are arranged in parallel, and the bottom ends of the reference electrodes (3) are both spaced 2 to 6 mm from the top surface of the working electrode (4).

8. 3. Use of the polyacrylamide gel electrolyte according to claim 1 or 2 in atmospheric corrosion monitoring.

9. Use of the portable three-electrode corrosion-type sensor according to claim 5 in atmospheric corrosion monitoring.

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