A method for protecting metal materials in a high-temperature chloride molten salt corrosion environment

Abstract

The present application discloses a method for protecting metal materials in a high-temperature chloride molten salt corrosion environment, and belongs to the technical field of metal material protection. The protection method includes: electrically connecting the protected metal material to the negative electrode, electrically connecting the graphite electrode to the positive electrode, and the protected metal material and the graphite electrode are in a high-temperature chloride molten salt to form a closed loop; a first regulating mechanism is set on the circuit connecting the protected metal material to the negative electrode, and the first regulating mechanism is configured to adjust the potential value of the protected metal material in real time. A second regulating mechanism is set on the circuit connecting the graphite electrode to the positive electrode, and the second regulating mechanism is configured to adjust the potential value of the graphite electrode in real time. The present application can achieve the anti-corrosion protection effect of the protected metal material in high-temperature chloride molten salt.

Description

Technical Field

[0001] The present application relates to the technical field of metal material protection, and in particular to a method for protecting metal materials in a high-temperature chloride molten salt corrosion environment. Background Art

[0002] At present, molten salt heat storage technology is one of the powerful technologies for long-term energy storage needs. The basic principle of molten salt heat storage involves storing energy in the form of thermal energy in a high-temperature medium to convert it into electrical energy when electricity is needed. Compared with other energy storage technologies, molten salt heat storage has unique advantages such as providing thermal energy and adapting to traditional power generation technology, making it have great potential in dealing with peak load auxiliary services, system heating and energy storage.

[0003] Solar salts are widely used heat storage media in the world, and its main representative is nitrates, but the working temperature of nitrates can no longer reach the working temperature proposed by the next generation of solar thermal technology. Compared with nitrates, the upper limit of the working temperature of heat storage molten salts based on chloride molten salts has been increased by nearly 300°C. It has excellent thermophysical properties and can work in an environment above 800°C. Due to the sensible heat characteristics of molten salt heat storage, the working temperature range is equivalent to the temperature requirements of thermal power systems. The increase in working temperature not only increases the operating temperature of the entire system, but also improves the thermoelectric conversion efficiency and reduces the cost of heat storage. Compared with nitrates, the conversion efficiency is increased by 15%, and the price of MgCl2-KCl-NaCl mixed salts with abundant reserves is much lower than commercial nitrates and carbonates. Therefore, chloride molten salts are the most popular heat storage molten salts for the next generation of solar thermal technology.

[0004] However, high-temperature chloride molten salt itself is extremely corrosive and chemically active, and will corrode the metal tanks that store it. It is necessary to develop methods to protect metal materials in the corrosive environment of high-temperature chloride molten salt. Summary of the invention

[0005] The embodiments of the present application provide a method for protecting metal materials in a high-temperature chloride molten salt corrosion environment, thereby solving the problem that the high-temperature chloride molten salt itself has extremely strong corrosiveness and chemical activity and will corrode the metal material storage tanks storing it.

[0006] In order to achieve the above object, the technical solution of the embodiment of the present invention is:

[0007] The embodiment of the present invention provides a method for protecting a metal material in a high-temperature chloride molten salt corrosion environment, comprising:

[0008] The protected metal material is electrically connected to the negative electrode, and the graphite electrode is electrically connected to the positive electrode, wherein the protected metal material and the graphite electrode are in a high-temperature chloride molten salt to form a closed loop;

[0009] A first regulating mechanism is provided on the circuit connecting the protected metal material and the negative electrode, and the first regulating mechanism is configured to regulate the potential value of the protected metal material in real time.

[0010] In a possible implementation, the first adjustment mechanism includes a first variable resistor, a first potentiometer, and a first reference electrode;

[0011] The sliding end of the first variable resistor is electrically connected to the negative electrode, and the fixed end is electrically connected to the protected metal material;

[0012] One end of the first potentiometer is electrically connected between the protected metal material and the fixed end of the first variable resistor, and the other end is electrically connected to one end of the first reference electrode;

[0013] The other end of the first reference electrode is arranged in the high-temperature chloride molten salt.

[0014] In a possible implementation, the potential value of the protected metal material is adjusted in a range of -0.07V to -0.10V.

[0015] In a possible implementation, the method for protecting metal materials in a high-temperature chloride molten salt corrosion environment also includes:

[0016] A second regulating mechanism is provided on the circuit connecting the graphite electrode and the positive electrode, and the second regulating mechanism is configured to regulate the potential value of the graphite electrode in real time.

[0017] In a possible implementation, the second adjustment mechanism includes a second variable resistor, a second potentiometer, and a second reference electrode;

[0018] The sliding end of the second variable resistor is electrically connected to the positive electrode, and the fixed end is electrically connected to the graphite electrode;

[0019] One end of the second potentiometer is electrically connected between the graphite electrode and the fixed end of the second variable resistor, and the other end is electrically connected to one end of the second reference electrode;

[0020] The other end of the second reference electrode is arranged in the high-temperature chloride molten salt.

[0021] In a possible implementation, the graphite electrode potential value is adjusted in the range of -0.04V to -0.3V.

[0022] In a possible implementation, the protection temperature range of the high-temperature chloride molten salt is 700°C to 900°C.

[0023] In a possible implementation, the specific surface area of ​​the protected metal material and the graphite electrode is 3:1 to 10:1.

[0024] One or more technical solutions provided in the embodiments of the present invention have at least the following technical effects or advantages:

[0025] The embodiment of the present application provides a method for protecting metal materials in a high-temperature chloride molten salt corrosion environment. First, the protected metal material is electrically connected to the negative electrode, and the graphite electrode is electrically connected to the positive electrode. The protected metal material and the graphite electrode are in a high-temperature chloride molten salt to form a closed loop, ensuring that the current flows from the power supply through the protected metal material and the graphite electrode to form a cathodic protection potential value to achieve cathodic protection. Afterwards, a first regulating mechanism is set on the circuit where the protected metal material is connected to the negative electrode, and the first regulating mechanism is configured to adjust the potential value of the protected metal material in real time, so that the current is input to the protected metal material in a specific manner. A second regulating mechanism is set on the circuit where the graphite electrode is connected to the positive electrode, and the second regulating mechanism is configured to adjust the potential value of the graphite electrode in real time, so that the current is input to the graphite electrode in a specific manner. The graphite electrode applies a layer of electric field to the surface of the protected metal material, causing the protected metal material to lose electrons and replenish electrons at the same time, thereby achieving the purpose of preventing the protected metal material from corrosion. By adjusting the potential value of the protected metal material in real time through the first adjusting mechanism and adjusting the potential value of the graphite electrode in real time through the second adjusting mechanism, it is possible to ensure appropriate potential values ​​at the protected metal material and the graphite electrode, thereby achieving the best and more comprehensive anti-corrosion protection effect for the protected metal material in high-temperature chloride molten salt. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the accompanying drawings in the following description are some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying any creative work.

[0027] Figure 1 A diagram of a device for implementing a method for protecting metal materials in a high-temperature chloride molten salt corrosion environment provided in an embodiment of the present application;

[0028] Figure 2 A polarization curve diagram of HT700 alloy protected in chloride molten salt by using the protection method for metal materials in a high-temperature chloride molten salt corrosion environment provided in an embodiment of the present application;

[0029] Figure 3 The XRD diagram of the HT700 alloy after being protected in a chloride molten salt by using the protection method for metal materials in a high-temperature chloride molten salt corrosion environment provided in an embodiment of the present application;

[0030] Figure 4This is the SEM image of the HT700 sample without adding protective potential after corrosion in a high-temperature chloride molten salt corrosion environment;

[0031] Figure 5 This is a SEM image of the HT700 alloy after being protected in a chloride molten salt using the method for protecting a metal material in a high-temperature chloride molten salt corrosion environment provided in an embodiment of the present application.

[0032] Icons: 1-metal material; 2-graphite electrode; 3-potentiostat; 31-negative electrode; 32-positive electrode; 4-first regulating mechanism; 41-first variable resistor; 42-first potentiometer; 43-first reference electrode; 5-second regulating mechanism; 51-second variable resistor; 52-second potentiometer; 53-second reference electrode; 6-chloride molten salt. DETAILED DESCRIPTION

[0033] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] In the description of the embodiments of the present invention, it should be noted that the terms "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the embodiments of the present invention and simplifying the description, rather than indicating or implying that the devices or elements referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limitations on the present invention. The terms "first", "second", and "third" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance. In addition, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be a connection between the two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present invention can be understood according to the specific circumstances.

[0035] An embodiment of the present invention provides a method for protecting a metal material in a high-temperature chloride molten salt corrosion environment, comprising steps 1 to 3.

[0036] Step 1: The protected metal material 1 is electrically connected to the negative electrode 31, and the graphite electrode 2 is electrically connected to the positive electrode 32, and the connection is ensured to be firm and reliable, so as to ensure that the current can flow through the protected metal material 1 and the graphite electrode 2. The protected metal material 1 and the graphite electrode 2 are in a high-temperature chloride molten salt 6 to form a closed loop. The protected metal material 1 is a metal material 1 that actually needs to be protected from corrosion, and it is connected to the negative electrode 31 to realize impressed current cathodic protection. In practice, the negative electrode 31 and the positive electrode 32 can be provided by a constant potential instrument 3.

[0037] Step 2: A first regulating mechanism 4 is provided on the circuit connecting the protected metal material 1 and the negative electrode 31 . The first regulating mechanism 4 is configured to regulate the potential value of the protected metal material 1 in real time.

[0038] The graphite electrode 2 acts as an auxiliary electrode, and by applying an electric field to the surface of the protected metal material 1, the protected metal material 1 loses electrons and replenishes electrons, thereby preventing the protected metal material 1 from corrosion. The protected metal material 1 is connected to the graphite electrode 2 through the high-temperature chloride molten salt 6 (the chloride molten salt 6 is conductive, so it can be connected), and both are connected to the constant potential instrument 3 to form a complete closed loop.

[0039] The processing method of the graphite electrode 2 is as follows: the graphite is placed in anhydrous ethanol for ultrasonic cleaning for 20 minutes and then dried, a through hole is made in the middle of one end of the graphite electrode 2, an iron wire is inserted into the through hole, both ends are sealed with high-temperature resistant inorganic glue, and then placed in an oven for drying to obtain a graphite electrode 2 with good conductivity and high temperature resistance.

[0040] Among them, Figure 1 As shown, the first adjustment mechanism 4 includes a first variable resistor 41 , a first potentiometer 42 and a first reference electrode 43 .

[0041] The sliding end of the first variable resistor 41 is electrically connected to the negative electrode 31 , and the fixed end is electrically connected to the protected metal material 1 .

[0042] One end of the first potentiometer 42 is electrically connected between the protected metal material 1 and the fixed end of the first variable resistor 41, and the other end is electrically connected to one end of the first reference electrode 43. The first potentiometer 42 is used to display the cathode protection potential value of the protected metal material 1. The first variable resistor 41 is used to adjust the cathode protection potential value according to the detection data of the first potentiometer 42 to keep the potential value of the protected metal material 1 within an appropriate range to prevent the protected metal material 1 from being corroded and damaged.

[0043] The other end of the first reference electrode 43 is disposed in the high-temperature chloride molten salt 6 to measure the reference potential in real time. Specifically, the first reference electrode 43 is usually composed of an electrode with a known potential value, which is connected to the protected metal material 1. By measuring the potential difference between the protected metal material 1 and the first reference electrode 43, the potential value of the protected metal material 1 can be obtained.

[0044] The first variable resistor 41 is an electronic component, such as a sliding variable resistor, and the first variable resistor 41 can adjust the potential value of the protected metal material 1 by adjusting the resistance value. When the potential value is within the desired cathodic protection potential range, effective cathodic protection can be ensured for the protected metal material 1 to prevent corrosion and damage. By adjusting the first variable resistor 41, the cathodic protection potential can be adjusted as needed to ensure effective cathodic protection and minimize the risk of corrosion, ensure that a suitable protection current is applied to the protected metal material 1, and prevent damage to the surface of the protected metal material 1 or unnecessary side reactions caused by excessive current, thereby extending the service life of the protected metal material 1. By adjusting the resistance value of the first variable resistor 41, the distribution of current on the surface of the protected metal material 1 can be optimized to ensure that all parts can be evenly protected. The adjustment function of the first variable resistor 41 can help the closed loop maintain stable operation under different working conditions, prevent the negative impact of current fluctuations on the closed loop, and dynamically adjust the resistance value according to real-time monitoring data to cope with environmental changes or changes in the state of the closed loop.

[0045] In practice, the resistance of the first variable resistor 41 can be automatically adjusted in real time according to the potential value of the protected metal material 1 monitored by the first potentiometer 42, so as to achieve accurate control of the cathode protection potential, so that the cathode potential value is kept within an appropriate range, and the cathode protection effect is improved. In addition, the cathode protection potential can be controlled in real time to maximize the utilization efficiency of the cathode protection current and reduce energy waste. For example, the first potentiometer 42 and the first variable resistor 41 are both connected to the controller, the first potentiometer 42 transmits data to the controller, and the controller then adjusts the resistance of the first variable resistor 41 in real time according to the received data.

[0046] Cathodic protection is a method of controlling metal corrosion. The protected metal material 1 is set as a cathode, making it an electrode that is not prone to corrosion relative to the surrounding environment. In order to achieve effective cathodic protection, the potential of the protected metal material 1 needs to be adjusted to an appropriate range. The potential value adjustment range of the protected metal material 1 is -0.07V to -0.10V, so that the corrosion resistance of the protected metal material 1 is the best. If the cathode potential is more positive than -0.07V, "under-protection" may be formed, and the expected protection effect cannot be achieved. On the contrary, if the cathode potential is more negative than -0.10V, hydrogen evolution reaction is likely to occur, and excess hydrogen is likely to diffuse to defective positions in the metal. The protected metal material 1 is prone to hydrogen embrittlement, which is not conducive to the protection of the protected metal material 1.

[0047] In order to ensure the normal operation of the closed loop and effectively protect the protected metal material 1, it is necessary to adjust the potential within the range of -0.07V to -0.10V to keep the protected metal material 1 within the appropriate potential value range. This can prevent over-protection and over-corrosion, optimize electrochemical reactions, improve protection efficiency, reduce energy consumption, extend the service life of the closed loop and materials, adapt to various working conditions, provide continuous and effective metal corrosion protection, and maximize the corrosion resistance of the protected metal material 1, ensuring the reliability and long-term performance of the closed loop.

[0048] Step 3: A second regulating mechanism 5 is provided on the circuit connecting the graphite electrode 2 and the positive electrode 32 . The second regulating mechanism 5 is configured to adjust the potential value of the graphite electrode 2 in real time.

[0049] Among them, Figure 1 As shown, the second adjustment mechanism 5 includes a second variable resistor 51 , a second potentiometer 52 and a second reference electrode 53 .

[0050] The sliding end of the second variable resistor 51 is electrically connected to the positive electrode 32 , and the fixed end is electrically connected to the graphite electrode 2 .

[0051] One end of the second potentiometer 52 is electrically connected between the graphite electrode 2 and the fixed end of the second variable resistor 51, and the other end is electrically connected to one end of the second reference electrode 53. The second potentiometer 52 is used to display the anode protection potential value of the graphite electrode 2. The second variable resistor 51 is used to adjust the anode potential value according to the detection data of the second potentiometer 52 to keep the potential value of the graphite electrode 2 within an appropriate range to reach the protection potential value.

[0052] The function of the second variable resistor 51 is to change the size of the anode current, thereby adjusting the anode potential value. By adjusting the resistance of the second variable resistor 51, the size of the anode current can be controlled, and then the anode potential value can be adjusted. Adjusting the anode potential value to the protective potential value can ensure effective cathodic protection and minimize the risk of corrosion. The second variable resistor 51 can achieve precise protection of local areas, especially in complex structures or areas with severe local corrosion. By adjusting the potential, more effective protection is provided to ensure that it is in the best cathodic protection state and avoid metal over-corrosion caused by too low potential. Fine adjustment of the potential can optimize the efficiency of the electrochemical reaction so that the protective current can more effectively prevent corrosion. Under the premise of ensuring the protection effect, the energy consumption of the closed loop is reduced by adjusting the potential, and the overall energy utilization efficiency is improved. By adjusting the second variable resistor 51, different corrosion conditions and electrochemical environments can be adapted.

[0053] In practice, the resistance of the second variable resistor 51 can be automatically adjusted in real time according to the potential value of the graphite electrode 2 monitored by the second potential meter 52, so as to achieve accurate control of the anode protection potential, so that the anode potential value is kept within an appropriate range, and the anode protection effect is improved, so that a layer of electric field is applied to the metal surface, so that the protected metal loses electrons and replenishes electrons at the same time, thereby achieving the purpose of preventing alloy corrosion. In addition, the anode protection potential can be controlled in real time to maximize the utilization efficiency of the anode protection current and reduce energy waste. For example, the second potential meter 52 and the second variable resistor 51 are both connected to the controller, and the second potential meter 52 transmits data to the controller, and the controller adjusts the resistance of the second variable resistor 51 in real time according to the received data. By measuring the potential value of the graphite electrode 2, it can be determined whether the performance of the closed loop meets the requirements. If the potential deviates from the predetermined range, the closed loop may need to be adjusted to keep it within the expected range.

[0054] The first variable resistor 41 and the second variable resistor 51 work in a complementary manner. The first variable resistor 41 mainly controls the overall potential value. To adjust the large range of the potential value, a sliding variable resistor with a larger range of variation can be used. The second variable resistor 51 is used to finely adjust the potential and adjust the fine range of the potential value. A sliding variable resistor with a smaller range of variation can be used. The two work together to enable the closed loop to flexibly adapt to different environmental conditions and corrosion conditions, ensuring that the closed loop is always in the best working state. By properly adjusting the potential value, the closed loop can be prevented from overloading and excessive corrosion of the material, the failure rate can be reduced, and the reliability and durability of the closed loop can be improved. The optimized protection effect can significantly extend the service life of the protected metal, reduce maintenance and replacement costs, and achieve the best cathodic protection effect.

[0055] The other end of the second reference electrode 53 is set in the high-temperature chloride molten salt 6 to measure the reference potential in real time. The manufacturing process of the first reference electrode 43 and the second reference electrode 53 is as follows: a protective tube with one end closed and the other end open is made of a high-temperature resistant and corrosion-resistant ceramic material, and a tungsten wire or a platinum wire is inserted into the protective tube from the opening to obtain a reference electrode, and the chloride molten salt 6 can contact the tungsten wire or the platinum wire through the opening. A connecting device is then set to connect the tungsten wire or the platinum wire to an external circuit to ensure the stability and reliability of the measurement.

[0056] The first reference electrode 43 and the second reference electrode 53 are electrodes that are not prone to potential changes, and their function is to provide a reference potential. They can be shared as a reference electrode. The first reference electrode 43 and the second reference electrode 53 are respectively provided for the protected metal material 1 and the graphite electrode 2 in order to provide a stable standard potential, which are used as references for the potential measurement of the protected metal material 1 and the graphite electrode 2, respectively. Further, in order for the protection method of the embodiment of the present application to have a protective effect on the protected metal material 1 in the high-temperature chloride molten salt 6, the first reference electrode 43 and the second reference electrode 53 of the high-temperature chloride molten salt 6 are set to be tungsten wire electrodes, which have the characteristics of stable potential, high temperature resistance, corrosion resistance, high conductivity, providing reference potential, low cost and easy preparation in the high-temperature chloride molten salt 6, so as to measure and control the potential value of the working electrode.

[0057] The first potentiometer 42 and the second potentiometer 52 can use digital or analog potentiometers, and the appropriate type can be selected according to the requirements.

[0058] Furthermore, the potential value adjustment range of the graphite electrode 2 is -0.04V to -0.3V, which ensures that the metal surface is in an effective cathodic protection state, prevents excessive polarization and side reactions, improves the electrochemical reaction efficiency of the closed loop, and extends the service life of the anode and the protected metal. At the same time, it adapts to a variety of working conditions and improves the safety and reliability of the closed loop. Through precise potential adjustment, more efficient corrosion protection and longer equipment life can be achieved. The potential value adjustment range of the graphite electrode 2 can be typical but non-restrictive potential values ​​such as -0.04V, -0.07V, -0.1V, -0.15V, -0.2V, -0.25V, and -0.3V.

[0059] In practice, the protection temperature range of the high-temperature chloride molten salt 6 is 700°C to 900°C, so that the method of the embodiment of the present application can ensure that the protected metal material 1 has a good protection effect in the high-temperature chloride molten salt 6. Within this range, the conductivity of the high-temperature chloride molten salt 6 is significantly improved, which helps the impressed current to be more effectively transmitted in the chloride molten salt 6, thereby enhancing the effect of cathodic protection. High temperature also helps to reduce the polarization of the electrode, so that the impressed current can be more stably and evenly distributed on the surface of the protected metal material 1, ensuring effective electrochemical protection. The protection temperature range of the high-temperature chloride molten salt 6 can be typical but non-restrictive temperatures such as 700°C, 750°C, 800°C, 850°C, and 900°C.

[0060] Due to the microstructure of graphite, including its layered structure and surface micropores, it can provide a large specific surface area. The specific surface area of ​​graphite electrode 2 is generally 0.01m 2 / m 3 To 0.1m 2 / m 3 For the protected metal material 1 (cathode), its specific surface area depends on the size, shape and surface treatment of the metal. In general, the specific surface area of ​​metals can range from micrometers to centimeters, and the specific value depends on the metal's geometry, surface roughness, porosity, and whether specific surface treatment (such as sandblasting, plating, etc.) has been performed to increase its surface area.

[0061] When designing the closed loop of the embodiment of the present application, it is usually necessary to calculate the required specific surface area according to the size of the protected object and the expected protection current density. For example, if the protection current density is 1mA / cm2 and the thickness of the metal is 1cm, the required specific surface area is approximately 1cm 2 / cm 3 .

[0062] The ratio of the specific surface area of ​​the protected metal material 1 to the graphite electrode 2 in the embodiment of the present application is 3:1 to 10:1, which can ensure that the method of the embodiment of the present application has a good protection effect on the protected metal material 1 in the high-temperature chloride molten salt 6. In this embodiment, the specific surface area of ​​the protected metal material 1 to graphite is 3:1 to 10:1, which can significantly improve the protection effect of the protection method of the embodiment of the present application on the protected metal material 1 in the high-temperature chloride molten salt 6 environment. The specific surface area setting within this range can ensure uniform current distribution, stable electrochemical reaction, improved material durability, and long-term stable operation of the closed loop. This not only optimizes the protection effect, but also improves the cost-effectiveness and operating efficiency of the closed loop. The specific surface area of ​​the protected metal material 1 and graphite can be typical but non-restrictive specific surface areas such as 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, etc.

[0063] The protection method of the metal material 1 in the corrosion environment of the high-temperature chloride molten salt 6 provided in the embodiment of the present application is firstly to electrically connect the protected metal material 1 with the negative electrode 31, and the graphite electrode 2 with the positive electrode 32. The protected metal material 1 and the graphite electrode 2 are in the high-temperature chloride molten salt 6 to form a closed loop, ensuring that the current flows from the power supply through the protected metal material 1 and the graphite electrode 2 to form a cathode protection potential value, thereby realizing cathode protection. Afterwards, a first regulating mechanism 4 is set on the circuit connecting the protected metal material 1 with the negative electrode 31, and the first regulating mechanism 4 is configured to adjust the potential value of the protected metal material 1 in real time, so as to input the current into the protected metal material 1 in a specific manner. A second regulating mechanism 5 is set on the circuit connecting the graphite electrode 2 with the positive electrode 32, and the second regulating mechanism 5 is configured to adjust the potential value of the graphite electrode 2 in real time, so as to input the current into the graphite electrode 2 in a specific manner. The graphite electrode 2 applies a layer of electric field to the surface of the protected metal material 1, so that the protected metal material 1 loses electrons and replenishes electrons at the same time, thereby achieving the purpose of preventing the corrosion of the protected metal material 1. By adjusting the potential value of the protected metal material 1 in real time through the first adjustment mechanism 4 and adjusting the potential value of the graphite electrode 2 in real time through the second adjustment mechanism 5, it is possible to ensure appropriate potential values ​​at the protected metal material 1 and the graphite electrode 2, thereby achieving the best and more comprehensive anti-corrosion protection effect for the protected metal material 1 in the high-temperature chloride molten salt 6.

[0064] Here is provided an example of using the method for protecting a metal material in a high-temperature chloride molten salt corrosion environment according to an embodiment of the present invention to protect the metal to be protected.

[0065] In order to verify that the protection method of metal materials in a high-temperature chloride molten salt corrosion environment of the embodiment of the present application has a protective effect on the HT700 alloy material in the high-temperature chloride molten salt 6, the HT700 alloy was immersed in the high-temperature chloride molten salt 6 to accelerate the corrosion. According to the polarization curve of the HT700 alloy in the high-temperature chloride molten salt 6, an experimental group with different protection potentials was set. The experiment proved that the protection method of the embodiment of the present application has a protective effect on the HT700 alloy.

[0066] Specifically, the prepared HT700 alloy electrode (protected metal material 1), graphite electrode 2, first reference electrode 43 (using platinum wire electrode) and second reference electrode 53 (using platinum wire electrode) are placed in a graphite crucible, and chloride molten salt 6 is placed in the graphite crucible, the temperature is set to 600°C, and the electrodes are immersed in the chloride molten salt 6 for 2 hours. The power switch of DJS-292B constant potential instrument 3 is turned on, and the instrument is preheated for 30 minutes and then in a stable state, and then the constant potential instrument 3 is set to a constant potential working state.

[0067] The HT700 alloy is electrically connected to the negative electrode 31 of the DJS-292B constant potential instrument 3, the graphite electrode 2 is electrically connected to the positive electrode 32 of the DJS-292B constant potential instrument 3, and the HT700 alloy and the graphite electrode 2 are placed in the high-temperature chloride molten salt 6 to form a closed loop.

[0068] A first regulating mechanism 4 is provided on the circuit connecting the HT700 alloy and the negative electrode 31, and the first regulating mechanism 4 is configured to regulate the potential value of the HT700 alloy material in real time. The first regulating mechanism 4 comprises a first variable resistor 41, a first potentiometer 42 and a first reference electrode 43. The sliding end of the first variable resistor 41 is electrically connected to the negative electrode 31, and the fixed end is electrically connected to the HT700 alloy material. One end of the first potentiometer 42 is electrically connected between the HT700 alloy material and the fixed end of the first variable resistor 41, and the other end is electrically connected to one end of the first reference electrode 43. The other end of the first reference electrode 43 is provided in the high-temperature chloride molten salt 6.

[0069] A second regulating mechanism 5 is provided on the circuit connecting the graphite electrode 2 and the positive electrode 32, and the second regulating mechanism 5 is configured to adjust the potential value of the graphite electrode 2 in real time. The second regulating mechanism 5 includes a second variable resistor 51, a second potentiometer 52 and a second reference electrode 53. The sliding end of the second variable resistor 51 is electrically connected to the positive electrode 32, and the fixed end is electrically connected to the graphite electrode 2. One end of the second potentiometer 52 is electrically connected between the graphite electrode 2 and the fixed end of the second variable resistor 51, and the other end is electrically connected to one end of the second reference electrode 53. The other end of the second reference electrode 53 is provided in the high-temperature chloride molten salt 6.

[0070] Press the "load" key and the "reference" key of the potentiostat 3 at the same time to put the instrument into the "reference" state, the "reference" indicator light will light up, and the value displayed in the potential display bar is the reference potential of the HT700 alloy in the chloride molten salt 6 relative to the first reference electrode 43 and the second reference electrode 53, that is, the open circuit potential of the HT700 alloy (the stable open circuit potential is also the corrosion potential of the HT700 alloy in the chloride molten salt 6). The open circuit potential of the HT700 alloy in the chloride molten salt 6 is measured to be 0.152V.

[0071] Measure the open circuit potential of HT700 alloy, press the "load" key and the "electrolytic cell" key at the same time to put the instrument in the "electrolytic cell" state, and use the static method to measure the polarization curve of HT700 alloy in chloride molten salt 6. Take the open circuit potential of HT700 alloy (0.152V) as the starting point, and adjust the negative voltage by 20mV each time (0.132V after the first adjustment) until -0.608V by rotating the "DC" button. After each adjustment of the potential, record and observe the corresponding potential and current data every one minute. Finally, plot the measured potential and current data into a polarization curve, as shown in the figure below: Figure 2 shown.

[0072] according to Figure 2 As shown, under the action of the external current, the cathode potential shifts negatively, and the protection potential is generally taken in the range between two inflection points. The first inflection point is generally the minimum protection potential, such as Figure 2 The figure shows -0.068V. A voltage higher than -0.068V may result in "under-protection" and fail to achieve the expected protection effect. The second inflection point is generally the maximum protection potential, such as Figure 2 The voltage shown is -0.108V. When the potential is more negative than this, hydrogen evolution reaction is more likely to occur. Excess hydrogen is easy to diffuse to the defective position in the metal. HT700 alloy is prone to hydrogen embrittlement, which is not conducive to the protection of the metal. The protection potential is between -0.068V and -0.108V. The current gradually increases as the protection potential becomes smaller (negative). Judging from the polarization curve, the protection potential range of HT700 alloy is -0.068V to -0.108V. This is consistent with the result that the potential value adjustment range of the protected metal material 1 is -0.07V to -0.10V.

[0073] The potential value of the protected metal material 1 is adjusted to -0.068V, -0.088V, and -0.108V in three experimental groups. The XRD analysis results of the HT700 alloy in the three experimental groups are as follows: Figure 3 As shown, the three experimental groups with added protection potential are mainly composed of oxide layers, and the oxides are Al2O3, Cr2O3 and MgO respectively.

[0074] Al2O3 was detected on the surface of HT700 alloy without potential protection because the alloy itself contains Al. Figure 3 It can be seen that Cr2O3 was detected on the surface of the HT700 alloy in the three experimental groups, and the peaks of Cr2O3 detected on the samples at -0.068V and -0.108V were higher than that of the sample at -0.088V, indicating that during the corrosion process, the outward diffusion degree of the Cr element in the sample at -0.088V was low. It can be seen that the potential value adjustment range of the protected metal material 1 is -0.07V to -0.10V, which can well protect the protected metal material 1. A large amount of MgO was detected on the surface of the HT700 alloy in the three experimental groups, which was produced by the hydrolysis of MgCl2 in the chloride molten salt 6, and due to the characteristics of MgO itself, it is difficult to dissolve in the chloride molten salt 6, so it is deposited on its surface.

[0075] The SEM morphology analysis results of the HT700 alloys of the three experimental groups in the high-temperature chloride molten salt corrosion environment of the metal material protection method of the embodiment of the present application were corroded in the chloride molten salt 6 for 100 hours as shown in the following figure: Figure 5 shown.

[0076] After the treatment of the HT700 alloy samples in the three experimental groups, the surface of the HT700 alloy sample with a protection potential of -0.068V had dense corrosion products, a "spheroidization" phenomenon, and a large number of spherical particles were distributed. The surface oxide film of the sample with a protection potential of -0.088V was broken, and local damage occurred. There were a large number of dense holes distributed on the surface of the sample, but the added current still played a cathodic protection role. The surface composition of the HT700 alloy in the three experimental groups was analyzed by ESD scanning, and the results are shown in Table 1.

[0077] Table 1

[0078]

[0079] Combination Figure 5 As can be seen from Table 1, compared with the uncorroded alloy, the Cr and Fe contents on the surface of the HT700 alloy in the three experimental groups decreased after 100 hours of corrosion, indicating that the elements in the alloy diffused and some elements reacted with impurities into the molten salt. When the potential was -0.108V, a large amount of oxides appeared on the surface of the sample, and a small amount of spherical particles could be observed on the surface, and their corrosion products densely formed an oxide layer. As the protection potential was closer to -0.088V, the corrosion of the alloy was reduced. After the experiment, the Fe / Cr elements on the surface of the alloy were slightly higher than those of the other two groups of samples. Applying current to the sample did not change the corrosion mechanism of the alloy.

[0080] like Figure 5 As shown in the figure, the cross-sectional morphology of the HT700 alloy after 100 hours of corrosion in the chloride molten salt 6 under the action of an external current is also clearly divided into two layers, the outer layer is an oxide layer, the middle layer is a diffusion layer, and the inner layer is a matrix layer. The outer layer is exposed to the molten chloride molten salt 6, and the oxide formed is easily dissolved, resulting in a thin and loose oxide layer with limited protective effect. The middle layer shows that diffusion of elements such as Cr and Fe occurred during the corrosion process. As the protective potential approaches -0.088V, the thickness of the diffusion layer is significantly reduced, and the thicknesses are 62.3μm (-0.068V), 18.3μm (-0.088V), and 68.1μm (-0.108V), respectively, indicating that the external current can hinder the outward diffusion of elements in the HT700 alloy, especially Cr.

[0081] like Figure 4 As shown, the corrosion depth of the HT700 sample without adding protective potential in high-temperature chloride molten salt 6 is 87μm after 100 hours of corrosion. The surface of the HT700 alloy continuously loses electrons and suffers severe corrosion. Figure 5The corrosion layer depth and diffusion layer depth of the HT700 samples in the three experimental groups can be measured. The corrosion depth of the sample with a protective potential of -0.068V is reduced to 62.3μm. When the protective potential is -0.088V, the corrosion depth of the HT700 alloy in 100 hours decreases significantly to 18.3μm, which is only 29.3% of the sample with a protective potential of -0.068V. When the protective potential is increased to -0.108V, an obvious corrosion layer is observed on the surface of the sample, and the corrosion depth of the sample increases significantly, which is higher than that of the sample with a protective potential of -0.068V, indicating that the alloy has the best anti-corrosion effect when the protective potential is -0.088V. The corrosion of the alloys under the protection of the potential values ​​of -0.068V, -0.088V, and -0.108V is reduced.

[0082] HT700 alloy corrodes in chloride molten salt 6, and the alloy surface continuously loses electrons. When current is applied to the sample, the metal atoms lose electrons during the corrosion process, and the external current is applied to replenish the electrons to prevent the loss of alloy matrix elements. This is equivalent to applying an electric field to the metal surface. When the protection potential is -0.068V, the current applied to the alloy surface may form an "underprotected" state, and the alloy surface formation fails to achieve the expected protection effect. As the protection potential gradually decreases, the corrosion resistance of the alloy gradually improves. When the protection potential reaches -0.108V, hydrogen evolution reaction may occur on the alloy surface, and hydrogen atoms are prone to diffuse to defective positions in the metal. The defects that appear in the alloy during the corrosion process will continue to expand under the hydrogen evolution reaction, and hydrogen embrittlement is prone to occur.

[0083] The various embodiments in this specification are described in a progressive manner, and the same or similar parts between the various embodiments can be referenced to each other. Each embodiment focuses on the differences from other embodiments.

[0084] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit the present application. Although the present application has been described in detail with reference to the aforementioned embodiments, a person of ordinary skill in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some or all of the technical features thereof may be replaced by equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the present application.

Claims

1. A method for protecting metal materials in a high-temperature chloride molten salt corrosion environment, characterized in that: include: The protected metal material is electrically connected to the negative electrode, and the graphite electrode is electrically connected to the positive electrode, wherein the protected metal material and the graphite electrode are in a high-temperature chloride molten salt to form a closed loop; A first regulating mechanism is provided on the circuit connecting the protected metal material and the negative electrode, wherein the first regulating mechanism is configured to adjust the potential value of the protected metal material in real time; A second regulating mechanism is provided on the circuit connecting the graphite electrode and the positive electrode, wherein the second regulating mechanism is configured to regulate the potential value of the graphite electrode in real time; The first adjustment mechanism includes a first variable resistor, a first potentiometer and a first reference electrode; The sliding end of the first variable resistor is electrically connected to the negative electrode, and the fixed end is electrically connected to the protected metal material; One end of the first potentiometer is electrically connected between the protected metal material and the fixed end of the first variable resistor, and the other end is electrically connected to one end of the first reference electrode; The other end of the first reference electrode is disposed in a high-temperature chloride molten salt; The second adjustment mechanism includes a second variable resistor, a second potentiometer, and a second reference electrode; The sliding end of the second variable resistor is electrically connected to the positive electrode, and the fixed end is electrically connected to the graphite electrode; One end of the second potentiometer is electrically connected between the graphite electrode and the fixed end of the second variable resistor, and the other end is electrically connected to one end of the second reference electrode; The other end of the second reference electrode is disposed in a high-temperature chloride molten salt; The first reference electrode and the second reference electrode are platinum wire electrodes.

2. The method for protecting metal materials in a high-temperature chloride molten salt corrosion environment according to claim 1, characterized in that: The potential value of the protected metal material is adjusted in the range of -0.07V to -0.10V.

3. The method for protecting metal materials in a high-temperature chloride molten salt corrosion environment according to claim 1, characterized in that: The graphite electrode potential value adjustment range is -0.04V~-0.3V.

4. The method for protecting metal materials in a high-temperature chloride molten salt corrosion environment according to claim 1, characterized in that: The protection temperature range of the high-temperature chloride molten salt is 700°C to 900°C.

5. The method for protecting metal materials in a high-temperature chloride molten salt corrosion environment according to claim 1, characterized in that: The specific surface area of ​​the protected metal material and the graphite electrode is 3:1-10:1.

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