Reference electrode for electrochemical measurement of molten salt corrosion

Abstract

The invention belongs to the technical field of molten salt corrosion electrochemical measurement, and particularly relates to a reference electrode for molten salt corrosion electrochemical measurement. The reference electrode comprises a silver platinum alloy electrode, an electrode sleeve and electrode inner salt, the electrode inner salt is arranged in the electrode sleeve, an inner cavity of the electrode sleeve is filled with inert gas, and a sealing plug is arranged at the upper opening end of the electrode sleeve; the silver-platinum alloy electrode is immersed in the electrode inner salt, the upper end of the silver-platinum alloy electrode is connected with one end of the electrode lead, and the other end of the electrode lead penetrates through the sealing plug installed on the upper portion of the electrode sleeve. The upper portion of the electrode sleeve is in a necking shape, the sealing plug is clamped at the necking position, and the space of the sealing plug on the upper portion of the electrode sleeve is filled with high-temperature-resistant inorganic sealing materials. According to the invention, the reversible reaction kinetics of Ag / Ag + couple reaction can be obviously improved, the side reaction of the electrode is avoided, the internal resistance of the electrode and the liquid connection potential are reduced, and the sensitivity, the stability, the reproducibility and the long service life of the reference electrode in a molten salt corrosion electrochemical test are ensured.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical measurement technology of molten salt corrosion, and specifically relates to a reference electrode for electrochemical measurement of molten salt corrosion, which is particularly suitable for electrochemical testing in the study of corrosion of halide molten salts (such as chlorides and fluorides). Background Technology

[0002] Molten salt corrosion of metals is primarily an electrochemical reaction, and electrochemical measurement techniques are crucial for studying this process. Such measurements typically require a potential-stable reference electrode as a baseline. However, due to the high temperature and strong corrosiveness of molten salt systems, conventional reference electrodes often struggle to maintain a stable potential, posing significant challenges to their accuracy, long-term stability, and reproducibility. Therefore, developing highly stable reference electrodes suitable for molten salt environments has become a key aspect of molten salt corrosion research.

[0003] To overcome the performance bottleneck of molten salt reference electrodes, two key challenges need to be addressed: 1) how to improve the reversible reaction rate; and 2) how to avoid electrode side reactions. Even for Ag / Ag, which shows promise in halide molten salt systems... + For the reference electrode, the two major challenges mentioned above remain key bottlenecks. Existing Ag / Ag... + Reference electrodes commonly use silver wire as the electrode material. When the electrode reaction deviates from equilibrium, the response rate of the reference electrode is limited by the surface area of ​​the silver electrode. Reversible reaction kinetics are crucial; in addition, liquid junction potential and electrode sleeve (diaphragm) resistance are also factors affecting the reversible reaction rate; while the occurrence of electrode side reactions depends on cavity environment control and sealing. Chinese patent application CN110186968B discloses an Ag / AgF reference electrode suitable for fluoride molten salts and its preparation method, which uses a corundum tube with its sealed end ground into a thin film as the electrode sleeve. However, corundum material has poor ionic conductivity, and even with the bottom end ground into a thin film, the resulting film resistance and junction potential are still relatively large, severely limiting response sensitivity and test stability; furthermore, this reference electrode does not employ measures to control the atmosphere within the cavity, which leads to excessive residual water and oxygen within the cavity, resulting in severe electrode side reactions. Chinese patent application CN104090004A discloses a Ni / NiF2 reference electrode for fluoride molten salts and its fabrication method, which achieves ion conduction with the external molten salt system by opening holes in the electrode sleeve. However, openings can lead to significant material exchange between the internal environment of the electrode and the external environment, which can greatly degrade the stability of the reference electrode.

[0004] Chinese patent application CN119147602A discloses a single-hole Ag / Ag₂S reference electrode for chloride molten salts. This electrode is protected by filling its interior with an inert gas and sealed with a high-temperature stopcock and tape. While this significantly reduces the water and oxygen content within the cavity, the stopcock and tape materials age and may even fail under frequent high-temperature and temperature-alternating conditions, making it difficult to maintain the long-term airtightness of the electrode cavity. Chinese patent application CN104297311B discloses a silver / silver chloride reference electrode and its fabrication method. This electrode uses borosilicate glass as the electrode shell and is sealed by flame sintering. Although this method can ensure the airtightness of the reference electrode, the borosilicate glass decomposes and releases volatile substances such as boron oxides and basic oxides during the sintering and melting process. These substances, when sealed in the electrode shell, will change the composition of the salt inside the electrode and trigger electrode side reactions, affecting the reliability of the reference electrode. In addition, borosilicate glass as an electrode salt bridge also has the problem of excessively low ionic conductivity, and it can react with molten halides, resulting in poor stability. Summary of the Invention

[0005] This invention aims to develop a reference electrode for molten salt corrosion electrochemical measurement, achieving high sensitivity, high stability, and long lifetime for Ag / Ag. + The reference electrode is specifically designed for the electrochemical corrosion measurement of halide molten salt systems, providing a reliable electrochemical testing benchmark for molten salt corrosion research.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] A reference electrode for molten salt corrosion electrochemical measurement includes a silver-platinum alloy electrode, an electrode sleeve, and an inner electrode salt. The inner electrode salt is contained within the electrode sleeve, and the inner cavity of the electrode sleeve is filled with an inert gas. A sealing plug is installed at the upper open end of the electrode sleeve. The chemical composition of the silver-platinum alloy electrode, by mass percentage, is: platinum content 0.1-10%, with the balance being silver. The silver-platinum alloy electrode is immersed in the inner electrode salt. One end of an electrode lead is connected to the upper end of the silver-platinum alloy electrode, and the other end of the electrode lead passes through the sealing plug installed at the upper part of the electrode sleeve. The upper part of the electrode sleeve is necked, and the sealing plug is secured at the neck. The space between the sealing plug and the upper part of the electrode sleeve is filled with a high-temperature resistant inorganic sealing material. The electrode sleeve is made of zirconia-based ceramic. Before encapsulation, the electrode sleeve is heat-treated in an inert gas containing hydrogen at 1000-1400℃.

[0008] The reference electrode for electrochemical measurement of molten salt corrosion has a salt composition of AgCl and other chloride matrix salts. The amount of AgCl added is 0.1-5% of the mass of the matrix salt. The matrix salt includes, but is not limited to, one or more of LiCl, KCl, NaCl, MgCl2, and CaCl2.

[0009] The reference electrode for electrochemical measurement of molten salt corrosion has a salt composition of AgF and other fluoride matrix salts. The amount of AgF added is 0.1% to 5% of the mass of the matrix salt. The matrix salt includes, but is not limited to, one or more of LiF, KF, and NaF.

[0010] The reference electrode for molten salt corrosion electrochemical measurement has a lower sealing end of the electrode sleeve that is ground into a thin film of 0.01 to 0.3 mm thickness.

[0011] The reference electrode for electrochemical measurement of molten salt corrosion is a zirconia-based ceramic coupled with yttrium oxide and calcium oxide, wherein, by molar percentage, yttrium oxide is 5-12%, calcium oxide is 1-3%, and the balance is zirconia; or, a zirconia-based ceramic coupled with yttrium oxide, calcium oxide, and cerium oxide, wherein, by molar percentage, yttrium oxide is 5-12%, calcium oxide is 1-3%, cerium oxide is 0-3%, and the balance is zirconia.

[0012] The reference electrode for molten salt corrosion electrochemical measurement has an insulating ceramic tube covering the electrode lead and its connection point with the silver-platinum alloy electrode. The upper and lower openings of the insulating ceramic tube are sealed with high-temperature resistant inorganic adhesive. The upper end of the electrode lead extends from the upper opening of the electrode sleeve and is higher than the upper opening of the electrode sleeve. The insulating ceramic tube passes through the sealing plug, and the upper end of the insulating ceramic tube is immersed in the high-temperature resistant inorganic sealing material in the upper space of the electrode sleeve.

[0013] The reference electrode for electrochemical measurement of molten salt corrosion is a silver-platinum alloy electrode in the form of a spirally wound filament or a rod with a porous surface.

[0014] The reference electrode for molten salt corrosion electrochemical measurement is a silver-platinum alloy electrode that has been pre-chlorinated to form silver chloride on its surface.

[0015] The reference electrode for molten salt corrosion electrochemical measurement is dried at 150–300°C under vacuum or inert atmosphere for 10–72 hours before the salt inside the electrode is encapsulated.

[0016] The reference electrode for molten salt corrosion electrochemical measurement, wherein the electrode sleeve undergoes heat treatment for 1–10 hours in an inert gas containing hydrogen with a hydrogen volume concentration of 1–5%, and is rapidly cooled to room temperature after heat treatment, with a cooling rate ≥1℃s in a temperature range ≥500℃. -1 .

[0017] Compared with the prior art, the beneficial effects and main design ideas of the present invention are as follows:

[0018] 1. The reference electrode exhibits high sensitivity and good reversibility. 1) A silver-platinum alloy is used instead of the conventional silver electrode material. Platinum is inert in this system, which is achieved through the interaction of Ag / Ag... +The catalytic effect of the electron couple reaction increases the Ag / Ag ratio. + The reversible reaction exchange current density allows the reference electrode to quickly reach equilibrium potential, resulting in a rapid response to minute changes on the electrode surface or changes in solution composition; 2) By filling the inner cavity of the electrode sleeve with inert gas and matching the sealing structure design and the salt drying treatment inside the electrode, the presence of water and oxygen in the cavity is minimized, and a long-term seal is achieved, thereby preventing the occurrence of electrode side reactions and ensuring that only a single Ag / Ag exists. + Reversible reaction; 3) By using spirally wound silver-platinum alloy wire or porous silver-platinum alloy rod, the specific surface area of ​​the electrode material is increased, thereby enhancing the Ag / Ag ratio. + The contribution of the redox couple reaction to the apparent electrical signal of the reference electrode.

[0019] 2. The reference electrode exhibits high stability and durability. 1) Zirconia-based ceramics with high ionic conductivity are used as the electrode sleeve (diaphragm), and the lower sealing end of the electrode sleeve is thinned to reduce internal resistance; 2) By optimizing the dopant composition, doping amount, and matching the heat treatment regime, the crystal defect structure and defect concentration of the electrode sleeve material are controlled. In particular, through heat treatment under a reducing atmosphere and rapid cooling, the anion vacancy concentration is increased, and the cation vacancy changes synchronously through the charge compensation mechanism, thereby making the diffusion coefficients of anions and cations close and further improving the ionic conductivity of the electrode sleeve, ensuring sufficiently low film resistance and liquid junction potential; 3) By innovatively introducing a necking structure in the upper middle part of the electrode sleeve, combined with a precision-locked sealing plug and high-temperature resistant sealing material filling, the interfacial stress changes caused by temperature cycling are effectively resisted, the port airtightness is maintained for a long time, and a stable closed reaction environment is constructed, thereby preventing the occurrence of side reactions.

[0020] 3. This invention selects zirconia-based ceramics with high ionic conductivity, consisting of yttrium oxide and calcium oxide coupled doped together, as the electrode sleeve material (yttrium oxide 5-12%, calcium oxide 1-3%, and the remainder zirconia by molar percentage). Before encapsulation, the ceramics undergo heat treatment at a specific temperature (heat treatment in an inert gas containing hydrogen at 1000-1400℃ for 1-10 hours), followed by rapid cooling (cooling rate ≥1℃s in a temperature range ≥500℃). -1 By controlling the crystal defect structure and defect concentration of the material, the ionic conductivity of the electrode sleeve is improved, ensuring sufficiently low film resistance and liquid junction potential.

[0021] 4. Compared with the patent published by CN110186968B (Ag / AgF reference electrode), the zirconia sleeve of this invention has an increased anion vacancy concentration after heat treatment, a similar ion diffusion coefficient, and improved conductivity compared to corundum; the inert gas filling and drying treatment completely eliminate water and oxygen, ensuring a single Ag / Ag... +The reaction. Compared with patent CN104090004A (Ni / NiF2 reference electrode), this invention is designed for halide molten salts. It achieves low internal resistance conduction through zirconium oxide sleeve thin-film formation and ionic conductivity optimization. Simultaneously, inert gas filling and a sealed structure block mass exchange, making it suitable for systems such as LiCl-KCl. Compared with patent CN119147602A (single-pore Ag / Ag2S reference electrode), this invention combines a necked structure with a high-temperature resistant inorganic sealing material. Through mechanical locking and material compatibility design, it resists temperature cycling stress, resulting in more durable airtightness. The silver-platinum alloy electrode directly enhances reaction kinetics through catalysis, without relying on coating stability. Compared with the patent published by CN104297311B (silver / silver chloride reference electrode), this invention uses zirconia-based ceramic (Y2O3 and CaO coupled doping), which significantly improves ionic conductivity after hydrogen reduction heat treatment, and the ceramic material is resistant to molten salt corrosion; the necked sealing structure combined with inert gas filling avoids impurity release and side reactions.

[0022] In summary, this invention uses a silver-platinum alloy as the electrode material, and even a trace amount of platinum can significantly improve the Ag / Ag ratio. + The exchange current density of the redox couple, and cleverly utilize Ag / Ag + The catalytic effect of the electro-coupled reaction, through this innovative material selection, breaks with conventional thinking and effectively solves the problems of insufficient sensitivity and reversibility of existing reference electrodes. This invention, through comprehensive innovation in materials, structure, and process, enables the reference electrode to possess high sensitivity, high stability, long lifespan, and good reproducibility, significantly improving the Ag / Ag ratio. + The reversible reaction kinetics of the electrode couple avoids electrode side reactions, reduces electrode internal resistance and liquid junction potential, and provides a reliable test benchmark with high sensitivity, stability, reproducibility and long life for electrochemical testing of molten salt corrosion. Attached Figure Description

[0023] Figure 1 The porous silver-platinum alloy rod Ag / Ag provided by this invention + A schematic diagram of the reference electrode. The reference electrode is labeled as follows: 1 is a porous silver-platinum alloy rod; 2 is the inner salt of the electrode; 3 is the electrode sleeve; 4 is an insulating ceramic tube; 5 is a high-temperature resistant inorganic sealing material; 6 is a connection point; 7 is the electrode lead; 8 is a sealing plug; and 9 is a necked-off electrode sleeve.

[0024] Figure 2 The spiral silver-platinum alloy wire Ag / Ag provided by this invention + A schematic diagram of the reference electrode. The reference electrode is labeled as follows: 2 is the inner salt of the electrode; 3 is the electrode sleeve; 4 is the insulating ceramic tube; 5 is the high-temperature resistant inorganic sealing material; 6 is the connection point; 7 is the electrode lead; 8 is the sealing plug; 9 is the electrode sleeve necking; 10 is the spiral silver-platinum alloy wire.

[0025] Figure 3 To test the relative potential stability of the reference electrode of this invention, the relative potential change of two reference electrodes with identical fabrication processes was measured using the open-circuit potential method in a 45wt.% LiCl-55wt.% KCl eutectic salt system. In the figure, the horizontal axis T represents time (h), and the vertical axis V represents potential (mV).

[0026] Figure 4 The electrochemical behavior of the molten salt after immersion at 550℃ for 200 h using this reference electrode was tested by voltammetry cycling in a 45wt.% LiCl-55wt.% KCl eutectic salt system. In the figure, the horizontal axis Potential represents potential (V), and the vertical axis Current represents current (A).

[0027] Figure 5 The figure shows the potentiodynamic polarization curves of the alloy during corrosion in a 45 wt.% LiCl-55 wt.% KCl eutectic salt system. In the figure, the horizontal axis I represents the logarithm of the polarization current (A), and the vertical axis E represents the electrode potential (V). Detailed Implementation

[0028] like Figure 1-Figure 2 As shown, this invention proposes a reference electrode for electrochemical measurement of molten salt corrosion. Its basic structure includes a silver-platinum alloy electrode (porous silver-platinum alloy rod 1 or spiral silver-platinum alloy wire 10), an inner salt layer 2, an electrode sleeve 3, an insulating ceramic tube 4, a high-temperature resistant inorganic sealing material 5, a connection point 6, an electrode lead 7, a sealing plug 8, and a necked-out electrode sleeve 9. The specific structure is as follows:

[0029] Electrode inner salt 2 is poured into electrode sleeve 3. Electrode lead 7, which is sealed by insulating ceramic tube 4, and porous silver-platinum alloy rod 1 or spiral silver-platinum alloy wire 10 connected to it are placed in electrode sleeve 3 and immersed in electrode inner salt 2. The lower end of insulating ceramic tube 4 is not immersed in electrode inner salt 2. Electrode sleeve 3 has a necked electrode sleeve neck 9. A sealing plug 8 is installed between the upper side of insulating ceramic tube 4 and electrode sleeve neck 9. The sealing plug 8 is stuck in the neck, so that the upper end of insulating ceramic tube 4 and electrode lead 7 pass through the sealing plug 8 and are fixed and sealed at electrode sleeve neck 9 by the sealing plug 8.

[0030] The upper end of the porous silver-platinum alloy rod 1 or the spiral silver-platinum alloy wire 10 is connected to the electrode lead 7 via connection point 6. The electrode lead 7 and the outer layer of the connection point between the electrode lead 7 and the silver-platinum alloy electrode are nested in an insulating ceramic tube 4. The lower opening of the insulating ceramic tube 4 is sealed with a high-temperature resistant inorganic sealing material 5 to ensure that the connection point 6 is sealed in the lower end of the high-temperature resistant inorganic sealing material 5. The inner cavity of the electrode sleeve 3 is filled with an inert gas. The upper opening of the insulating ceramic tube 4 and the upper opening of the electrode sleeve 3 are sealed with a high-temperature resistant inorganic sealing material 5. The lower sealing end of the electrode sleeve 3 is ground into a thin film with a thickness of 0.01 to 0.3 mm.

[0031] The porous silver-platinum alloy rod is a rod-shaped rod with a porous surface, a porosity of 30%–60%, and an average pore size of 5–50 μm. The porous structure of the porous silver-platinum alloy rod can increase the specific surface area, thereby increasing the effective reaction area of ​​the electrode and significantly increasing the Ag / Ag ratio. + The reaction sites of the redox couple are increased, thereby improving the exchange current density and shortening the potential response time. Furthermore, the spiral silver-platinum alloy wire, being spirally wound, significantly increases the effective reaction area, directly increasing the Ag / Ag ratio. + The reaction sites of the redox couple, and the periodic gaps formed by the helical structure, promote molten salt penetration and ensure Ag... + Ions are uniformly distributed on the surface of the silver-platinum alloy electrode.

[0032] In this invention, the high-temperature resistant inorganic sealing materials include, but are not limited to, silicate-based sealing materials, phosphate-based sealing materials, and flexible carbon-based sealing materials.

[0033] The present invention will be further illustrated by way of embodiments below, but the present invention is not limited to the scope of the embodiments described herein.

[0034] Example 1

[0035] The reference electrode for electrochemical measurement of molten salt corrosion was prepared using LiCl-KCl molten salt and silver chloride as the electrode internal salt, a silver-platinum alloy (platinum content of 10 wt%), molybdenum wire (electrode lead), and yttrium oxide and calcium oxide coupled-doped zirconia-based ceramic as the basic raw materials. The preparation included the following steps:

[0036] (1) Electrode sleeve treatment: Zirconia-based ceramics co-doped with yttrium oxide and calcium oxide (8% yttrium oxide and 2% calcium oxide by molar percentage) were used as electrode sleeves. The lower sealing end of the electrode sleeve was ground into a thin film with a thickness of 0.05 mm and heat-treated in an inert gas containing 3 vol% hydrogen at 1000 °C for 10 h. Then, it was rapidly cooled to room temperature (the sample was removed from the heating zone, and the cooling rate was 5 °C / s in the temperature range of ≥500 °C). -1 (When the temperature is below 500℃, allow it to cool naturally to room temperature in the original closed cavity atmosphere), clean it with an ultrasonic cleaner, then clean it with alcohol and blow it dry, and place it in an oven for later use.

[0037] (2) Salt treatment inside the electrode: Weigh 4.5g LiCl, 5.5g KCl and 0.5g AgCl, grind and mix them evenly in a mortar, transfer them to a corundum crucible, and dry them for 24h in a pit furnace with high-purity Ar gas protection (volume purity 99.999%) at a constant temperature of 200℃ for later use.

[0038] (3) Electrode preparation: The silver-platinum alloy electrode (spiral silver-platinum alloy wire) was immersed in 6 mol / L dilute nitric acid to remove the oxide layer and expose the silver surface. It was then thoroughly rinsed with deionized water and cleaned with alcohol before drying. An AgCl layer was deposited on the electrode surface using hydrochloric acid oxidation. After removing the electrode, it was immediately rinsed with plenty of deionized water and cleaned with alcohol before drying. The molybdenum wire electrode lead was connected to the silver-platinum alloy electrode using argon arc welding. The electrode was then cleaned again with deionized water and alcohol, dried, and placed in an oven for later use.

[0039] (4) Electrode encapsulation: Place the prepared electrode components into an argon-protected glove box. An insulating ceramic tube is nested around the silver-platinum alloy electrode and electrode leads. Both ends are encapsulated with a high-temperature resistant inorganic sealing material and then cured. Dry electrode salt is poured into the electrode sleeve. The encapsulated silver-platinum alloy electrode and electrode leads are placed inside the electrode sleeve, with the lower end of the insulating ceramic tube not immersed in the electrode salt. The upper end of the insulating ceramic tube is fixed to the neck of the electrode sleeve using a sealing plug. The area above the sealing plug is sealed with a high-temperature resistant inorganic sealing material and then cured.

[0040] Usage: Use two silver-platinum alloy electrodes as the working electrode and reference electrode, respectively. Vertically insert the electrodes into a pit furnace containing dry LiCl-KCl mixed molten salt at 550℃ under high-purity Ar gas protection (volume purity 99.999%). Connect the external wires of the electrodes to the corresponding electrochemical workstation. Record the potential change using the open-circuit potential method (OCP). When the potential remains stable within a certain range, it can be considered that the reference electrode diaphragm has achieved complete conductivity. Then, the alloy sample electrode can be inserted for electrochemical testing of corrosion behavior.

[0041] Example 2

[0042] The reference electrode for electrochemical measurement of the above-mentioned molten salt corrosion was prepared using LiCl-KCl molten salt and silver chloride as the electrode internal salt, a silver-platinum alloy (platinum content of 5 wt%), tungsten wire (electrode lead), and yttrium oxide and calcium oxide coupled-doped zirconia-based ceramic as the basic raw materials, including the following steps:

[0043] (1) Electrode sleeve treatment: Zirconia-based ceramics co-doped with yttrium oxide and calcium oxide (5% yttrium oxide and 1% calcium oxide by molar percentage) were used as electrode sleeves. The lower sealing end of the electrode sleeve was ground into a thin film with a thickness of 0.01 mm and heat-treated in an inert gas containing 1 vol% hydrogen at 1400 °C for 1 h, followed by rapid cooling to room temperature (the sample was removed from the heating zone, and the cooling rate was 1 °C / s in the temperature range ≥500 °C). -1 (When the temperature is below 500℃, allow it to cool naturally to room temperature in the original closed cavity atmosphere), clean it with an ultrasonic cleaner, then clean it with alcohol and blow it dry, and place it in an oven for later use.

[0044] (2) Salt treatment inside the electrode: Weigh 4.5g LiCl, 5.5g KCl and 0.1g AgCl, grind and mix them evenly in a mortar, transfer them to a corundum crucible, and dry them for 72h in a pit furnace with high-purity Ar gas protection (volume purity 99.999%) at a constant temperature of 150℃ for later use.

[0045] (3) Electrode preparation: The porous silver-platinum alloy electrode was immersed in 6 mol / L dilute nitric acid to remove the oxide layer and expose the silver surface. It was then thoroughly rinsed with deionized water and cleaned with alcohol before drying. An AgCl layer was deposited on the electrode surface using hydrochloric acid oxidation. After removing the electrode, it was immediately rinsed with plenty of deionized water and cleaned with alcohol before drying. The tungsten wire electrode lead was connected to the silver-platinum alloy electrode using argon arc welding. The electrode was then cleaned again with deionized water and alcohol, dried, and placed in an oven for later use.

[0046] (4) Electrode encapsulation: Place the prepared electrode components into an argon-protected glove box. An insulating ceramic tube is nested around the porous silver-platinum alloy electrode and electrode leads. Both ends are encapsulated with a high-temperature resistant inorganic sealing material and then cured. Dry electrode salt is poured into the electrode sleeve. The encapsulated silver-platinum alloy electrode and electrode leads are placed inside the electrode sleeve, with the lower end of the insulating ceramic tube not immersed in the electrode salt. The upper end of the insulating ceramic tube is fixed to the neck of the electrode sleeve by a sealing plug. The area above the sealing plug is sealed with a high-temperature resistant inorganic sealing material and then cured.

[0047] Usage: Use two silver-platinum alloy electrodes as the working electrode and reference electrode, respectively. Vertically insert the electrodes into a pit furnace containing dry LiCl-KCl mixed molten salt at 550℃ under high-purity Ar gas protection (volume purity 99.999%). Connect the external wires of the electrodes to the corresponding electrochemical workstation. Record the potential change using the open-circuit potential method (OCP). When the potential remains stable within a certain range, it can be considered that the reference electrode diaphragm has achieved complete conductivity. Then, the alloy sample electrode can be inserted for electrochemical testing of corrosion behavior.

[0048] Example 3

[0049] The reference electrode for electrochemical measurement of the above-mentioned molten salt corrosion was prepared using LiF-KF molten salt and silver fluoride as the electrode inner salt, silver-platinum alloy (platinum content of 1 wt%), tungsten wire (electrode lead), and yttrium oxide and calcium oxide coupled-doped zirconium oxide-based ceramic as the basic raw materials, including the following steps:

[0050] (1) Electrode sleeve treatment: Zirconia-based ceramics co-doped with yttrium oxide and calcium oxide (yttrium oxide 12%, calcium oxide 3%, cerium oxide 3% by molar percentage) were used as electrode sleeves. The lower sealing end of the electrode sleeve was ground into a 0.30 mm thick film and heat-treated in an inert gas containing 5 vol% hydrogen at 1200 °C for 10 h, followed by rapid cooling to room temperature (the sample was removed from the heating zone, and the cooling rate was 10 °C / s in the temperature range ≥500 °C). -1 (When the temperature is below 500℃, allow it to cool naturally to room temperature in the original closed cavity atmosphere), clean it with an ultrasonic cleaner, then clean it with alcohol and blow it dry, and place it in an oven for later use.

[0051] (2) Salt treatment inside the electrode: Weigh 3.2g LiF, 6.8g KF and 0.3g AgF, grind and mix them evenly in a mortar, transfer them to a corundum crucible, and dry them for 10h in a pit furnace with high-purity Ar gas protection (volume purity 99.999%) at a constant temperature of 300℃ for later use.

[0052] (3) Electrode preparation: The silver-platinum alloy electrode (spiral silver-platinum alloy wire) was immersed in 6 mol / L dilute nitric acid to remove the oxide layer and expose the silver surface. It was then thoroughly rinsed with deionized water and cleaned with alcohol before drying. An AgCl layer was deposited on the electrode surface using hydrochloric acid oxidation. After removing the electrode, it was immediately rinsed with plenty of deionized water and cleaned with alcohol before drying. The tungsten wire electrode lead was connected to the silver-platinum alloy electrode using argon arc welding. The electrode was then cleaned again with deionized water and alcohol, dried, and placed in an oven for later use.

[0053] (4) Electrode encapsulation: Place the prepared electrode components into an argon-protected glove box. An insulating ceramic tube is nested around the silver-platinum alloy electrode and electrode leads. Both ends are encapsulated with a high-temperature resistant inorganic sealing material and then cured. Dry electrode salt is poured into the electrode sleeve. The encapsulated silver-platinum alloy electrode and electrode leads are placed inside the electrode sleeve, with the lower end of the insulating ceramic tube not immersed in the electrode salt. The upper end of the insulating ceramic tube is fixed to the neck of the electrode sleeve using a sealing plug. The area above the sealing plug is sealed with a high-temperature resistant inorganic sealing material and then cured.

[0054] Usage: Use two silver-platinum alloy electrodes as the working electrode and reference electrode, respectively. Vertically insert the electrodes into a pit furnace containing dry LiF-KF mixed molten salt at 600℃ under high-purity Ar gas protection (volume purity 99.999%). Connect the external wires of the electrodes to the corresponding electrochemical workstation. Record the potential change using the open-circuit potential method (OCP). When the potential remains stable within a certain range, it can be considered that the reference electrode diaphragm has achieved complete conductivity. Then, the alloy sample electrode can be inserted for electrochemical testing of corrosion behavior.

[0055] Example of the effect:

[0056] The corundum crucible was rinsed sequentially with deionized water and alcohol, then dried. 45g of LiCl and 55g of KCl were weighed in a glove box, mixed thoroughly in a mortar, and transferred to the corundum crucible. The crucible was then placed in a pit furnace nested within the glove box. The furnace lid was sealed, a vacuum was created, and high-purity Ar gas was continuously introduced. The temperature was raised to 200℃ and held for 24 hours to remove moisture from the molten salt. Two prepared silver-platinum alloy electrodes were inserted through the electrode holes in the furnace lid, fixed above the mixed salt, and a vacuum was created. High-purity Ar gas (99.999% volume purity) was introduced.

[0057] (1) After heating the pit furnace to 550℃ and stabilizing for 2 hours, two silver-platinum alloy electrodes, fabricated using the same process as in Example 1, were inserted into the molten salt for the next electrochemical measurement. The electrochemical testing workstation was a GamryInterference 600+. Figure 3 As shown, the electrode relative potential data in LiCl-KCl eutectic molten salt are from... Figure 3 The data shows that the relative potential shift of the silver-platinum alloy specific electrode of the present invention is very small after 10 hours of use, with a maximum shift value not exceeding ±2.5mV, demonstrating good potential stability. The reference electrodes in Examples 2 and 3 also achieved the excellent technical effects of the present invention.

[0058] (2) After confirming the high stability of the reference electrode prepared in (1), it was left to stand for 190 hours (i.e., the total soaking time reached 200 hours). Then, two silver-platinum alloy reference electrodes were used to conduct voltammetric cycling tests on the electrochemical behavior of the LiCl-KCl eutectic molten salt, with a scan rate of 0.1 V / s and a range of -1.0 to 1.0 V. For example... Figure 4 As shown, the silver-platinum alloy electrode yielded good results, with no other side reactions introduced by the reference electrode.

[0059] (3) Insert an alloy sample electrode through the electrode hole in the furnace cover, fix it above the molten salt, evacuate, and introduce high-purity Ar gas (volume purity 99.999%). Insert the alloy sample electrode into the molten salt. Use the alloy sample electrode as the working electrode, and two silver-platinum alloy electrodes as the reference and counter electrodes, respectively. After 24 hours of corrosion, perform polarization curve testing. Figure 5 As shown in the figure, the potentiodynamic polarization curve of the alloy in the 45wt.%LiCl-55wt.%KCl eutectic salt system shows that the test data is good and meets the requirements of electrochemical testing.

[0060] The results show that the present invention can significantly improve the Ag / Ag ratio. + The reversible reaction kinetics of the electrode couple avoids electrode side reactions, reduces electrode internal resistance and liquid junction potential, and ensures the sensitivity, stability, reproducibility and long life of the reference electrode in molten salt corrosion electrochemical testing.

Claims

1. A reference electrode for electrochemical measurement of molten salt corrosion, characterized in that, The device comprises a silver-platinum alloy electrode, an electrode sleeve, and an inner electrode salt. The inner electrode salt is contained within the electrode sleeve, and the inner cavity of the electrode sleeve is filled with an inert gas. A sealing plug is installed at the upper open end of the electrode sleeve. The chemical composition of the silver-platinum alloy electrode, by mass percentage, is: 0.1-10% platinum content, with the balance being silver. The silver-platinum alloy electrode is immersed in the inner electrode salt. One end of the electrode lead is connected to the upper end of the silver-platinum alloy electrode, and the other end of the electrode lead passes through the sealing plug installed at the upper part of the electrode sleeve. The upper part of the electrode sleeve is necked, and the sealing plug is secured at the neck. The space between the sealing plug and the upper part of the electrode sleeve is filled with a high-temperature resistant inorganic sealing material. The electrode sleeve is made of zirconia-based ceramic. Before encapsulation, the electrode sleeve is heat-treated in an inert gas containing hydrogen at 1000-1400℃.

2. The reference electrode for molten salt corrosion electrochemical measurement according to claim 1, characterized in that, The composition of the salt inside the electrode is AgCl and other chloride matrix salts. The amount of AgCl added is 0.1% to 5% of the mass of the matrix salt. The matrix salt includes, but is not limited to, one or more of LiCl, KCl, NaCl, MgCl2, and CaCl2.

3. The reference electrode for molten salt corrosion electrochemical measurement according to claim 1, characterized in that, The composition of the electrode internal salt is AgF and other fluoride matrix salts. The amount of AgF added is 0.1% to 5% of the mass of the matrix salt. The matrix salt includes, but is not limited to, one or more of LiF, KF, and NaF.

4. The reference electrode for molten salt corrosion electrochemical measurement according to claim 1, characterized in that, The lower sealing end of the electrode sleeve is ground into a thin film with a thickness of 0.01 to 0.3 mm.

5. The reference electrode for molten salt corrosion electrochemical measurement according to claim 1, characterized in that, Zirconia-based ceramics are coupled with yttrium oxide and calcium oxide, with yttrium oxide accounting for 5-12% and calcium oxide accounting for 1-3% by molar percentage, and the balance being zirconia oxide; or, zirconia-based ceramics are coupled with yttrium oxide, calcium oxide and cerium oxide, with yttrium oxide accounting for 5-12% and calcium oxide accounting for 1-3% by molar percentage, and cerium oxide accounting for 0-3% by molar percentage, and the balance being zirconia oxide.

6. The reference electrode for molten salt corrosion electrochemical measurement according to claim 1, characterized in that, The electrode lead and its connection point with the silver-platinum alloy electrode are covered with an insulating ceramic tube. The upper and lower openings of the insulating ceramic tube are sealed with high-temperature resistant inorganic adhesive. The upper end of the electrode lead extends from the upper opening of the electrode sleeve and is higher than the upper opening of the electrode sleeve. The insulating ceramic tube passes through the sealing plug, and the upper end of the insulating ceramic tube is immersed in the high-temperature resistant inorganic sealing material in the upper space of the electrode sleeve.

7. The reference electrode for molten salt corrosion electrochemical measurement according to claim 1, characterized in that, Silver-platinum alloy electrodes are in the form of spirally wound filaments or porous rods.

8. The reference electrode for molten salt corrosion electrochemical measurement according to claim 1, characterized in that, The silver-platinum alloy electrode is pre-chlorinated, forming silver chloride on its surface.

9. The reference electrode for molten salt corrosion electrochemical measurement according to claim 1, characterized in that, Before encapsulating the internal salt of the electrode, it is dried at 150–300°C under vacuum or inert atmosphere for 10–72 hours.

10. The reference electrode for molten salt corrosion electrochemical measurement according to claim 1, characterized in that, The electrode sleeve undergoes heat treatment for 1–10 hours, using an inert gas mixture containing hydrogen at a volume concentration of 1–5%. After heat treatment, it is rapidly cooled to room temperature, with a cooling rate ≥1℃s within a temperature range ≥500℃. -1 .

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