A magnesium-based controlled-release corrosion inhibitor for chloride molten salt medium, and its preparation method and application

Abstract

The present invention belongs to the technical field of material corrosion protection, and specifically relates to a magnesium-based controlled-release corrosion inhibitor for a chloride molten salt medium, and its preparation method and application. The corrosion inhibitor comprises: an inner layer, which is a magnesium-nickel alloy core; an intermediate layer, which is a metal nickel slow-release layer; and an outer layer, which is a magnesium oxide barrier layer. The preparation method comprises the following steps: S1, preparing a magnesium-nickel alloy; S2, crushing the magnesium-nickel alloy into particles; S3, electroplating a metal nickel layer on the surface of the magnesium-nickel alloy core by an electroplating method to obtain a metal nickel slow-release layer; S4, heating and oxidizing the magnesium-nickel alloy core with the metal nickel slow-release layer in an air atmosphere to obtain a magnesium oxide barrier layer. The corrosion inhibitor can not only effectively remove water and oxygen impurities in chloride salts and reduce their corrosiveness, but also avoid the problem of local destructive corrosion caused by direct contact between the liquid magnesium corrosion inhibitor and the container material, thereby greatly improving the corrosion resistance of the container material in chloride salts.

Description

Technical Field

[0001] The present invention belongs to the technical field of material corrosion protection, and in particular relates to a magnesium-based controlled-release corrosion inhibitor for a chloride molten salt medium, a preparation method thereof, and an application thereof. Background Art

[0002] Molten salts are widely used as a highly efficient heat transfer and storage medium in solar thermal power generation systems. Among them, chloride molten salts are widely considered the most promising heat storage and heat conduction material for next-generation molten salt technology due to their excellent heat capacity and thermal conductivity, low melting point, high stability, and wide operating temperature range, possessing enormous development potential. However, due to their strong water absorption, chloride salts are prone to generate highly corrosive oxidative impurities at high temperatures, which can cause severe corrosion to container materials. Therefore, the strong corrosion of chloride molten salts on container materials has become a key bottleneck restricting the development of solar thermal power generation technology.

[0003] Reducing the concentration of oxidizing impurities in chloride salts can significantly improve the corrosion resistance and service life of container materials. Common methods for purifying chloride salts include heat treatment, electrochemical reduction, and the addition of corrosion inhibitors. The addition of Mg corrosion inhibitors to chloride salts has attracted considerable attention. To achieve optimal purification, excess Mg metal is often added to remove impurities from the chloride salts. However, the operating temperature of chloride salts is typically above 700°C, while the melting point of Mg metal is approximately 650°C. This means that in a chloride salt environment, the Mg metal corrosion inhibitor exists in a liquid state. Furthermore, because the density of liquid Mg metal is lower than that of chloride salts, it floats in the molten salts and comes into direct contact with the container materials. Currently, the most commonly used container materials are Fe-Cr-Ni-based alloys, and Mg metal readily alloys with Ni. Consequently, contact between liquid Mg metal and container materials triggers liquid metal corrosion, causing severe, localized, and destructive corrosion. This corrosion is extremely severe, with the corrosion depth of the container material potentially exceeding that observed in chloride salts without the addition of corrosion inhibitors by tens of times. It can be seen that the development of a new magnesium-based corrosion inhibitor that will not cause serious liquid metal corrosion to the container material is of vital importance to promoting the development of chloride salt solar thermal power generation technology. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention provides a magnesium-based controlled-release corrosion inhibitor for chloride molten salt media, as well as its preparation method and application. This corrosion inhibitor not only effectively removes water and oxygen impurities from chloride salts, reducing their corrosiveness, but also prevents localized destructive corrosion caused by direct contact between the liquid magnesium corrosion inhibitor and the container material, significantly improving the corrosion resistance of the container material in chloride salts.

[0005] The technical solutions provided by the present invention are as follows:

[0006] A magnesium-based controlled-release corrosion inhibitor for a chloride molten salt medium, comprising:

[0007] An inner layer, which is a magnesium-nickel alloy core;

[0008] an intermediate layer, which is a metal nickel sustained-release layer;

[0009] and an outer layer, which is a magnesium oxide barrier layer.

[0010] Based on the above technical solution:

[0011] At the working temperature of chloride salt, magnesium corrosion inhibitor is liquid and fluid, and can come into direct contact with the container material. However, magnesium easily reacts with nickel in the container material to form an alloy. This reaction can cause the material to be corroded by liquid metal, leading to severe local damage. Smelting magnesium and nickel metals into a magnesium-nickel alloy with a higher melting point can ensure that magnesium can react with impurities in chloride salt and reduce the concentration of impurities, while also making the corrosion inhibitor solid at the working temperature of chloride salt, thus preventing the container material from being corroded by liquid metal. At the same time, using magnesium-nickel alloy as the core of the corrosion inhibitor can effectively reduce the concentration of magnesium in the core, making it less likely to react with nickel in the container material to form an alloy.

[0012] The nickel coating on the surface of the magnesium-nickel alloy effectively controls the rate of outward diffusion of magnesium from the core, achieving the purpose of controlled release of the magnesium corrosion inhibitor. In addition, the nickel coating can further reduce the concentration of magnesium on the surface of the corrosion inhibitor to prevent alloying reaction between magnesium and the container material. Moreover, at the molten salt operating temperature, the magnesium in the core can be maintained at a certain outward diffusion rate, thereby ensuring the reaction of magnesium with impurities.

[0013] As magnesium continues to diffuse outward, oxidation of the nickel-plated magnesium-nickel alloy can form a non-dense and insulating oxide film protective layer on the surface of the corrosion inhibitor particles, which can prevent the magnesium-nickel alloy from contacting the container material and causing galvanic corrosion, and does not affect the reaction of magnesium with molten salt impurities.

[0014] Specifically, the material of the magnesium-nickel alloy core is MgNi2, Mg2Ni or a mixture of the two.

[0015] The magnesium-nickel alloy has a high melting point and remains solid at the molten salt operating temperature, preventing liquid metal corrosion of the container material. It also reacts with impurities in the chloride salt, including but not limited to water, oxygen, HCl, or MgOHCl.

[0016] Specifically, in the magnesium-nickel alloy, the molar ratio of magnesium to nickel is (2:1) to (1:2).

[0017] Specifically, the size of the magnesium-nickel alloy core is 0.05 mm-10 mm.

[0018] Based on the above technical solution, if the core of the magnesium-nickel alloy is too small, the Mg content will be low and the consumption will be faster. If it is too large, the specific surface area of the corrosion inhibitor will be small, and its reaction activity area will be low.

[0019] Specifically, the thickness of the metal nickel sustained-release layer is 0.5-10 μm.

[0020] Based on the above technical solution, if the thickness of the metal nickel slow-release layer is too small, the magnesium in the magnesium-nickel alloy core will diffuse outward too quickly, resulting in it not being able to play a good slow-release role. If it is too large, it will make it difficult for Mg to diffuse outward.

[0021] Specifically, the thickness of the magnesium oxide barrier layer is 0.5-10 μm.

[0022] Based on the above technical solution, if the thickness of the magnesium oxide barrier layer is too small, it will not play a good barrier role, and if it is too large, it will make it difficult for Mg to diffuse outward.

[0023] The present invention also provides a method for preparing a magnesium-based controlled-release corrosion inhibitor in a chloride molten salt medium, comprising the following steps:

[0024] S1. Mixing magnesium and nickel metals in proportion, heating and melting them in an inert atmosphere to form a magnesium-nickel alloy, and cooling them to room temperature;

[0025] S2, crushing the magnesium-nickel alloy into particles to obtain a magnesium-nickel alloy core;

[0026] S3, electroplating a metal nickel layer on the surface of the magnesium-nickel alloy core by an electroplating method to obtain a metal nickel slow-release layer;

[0027] S4. The magnesium-nickel alloy core having the metal nickel slow-release layer is heated and oxidized in a gas atmosphere to obtain a magnesium oxide barrier layer.

[0028] Based on the above technical solution, each layer can be conveniently prepared in sequence from the inside to the outside.

[0029] Specifically: In step S1, the magnesium-nickel alloy is smelted at 1500-2000°C, preferably 1500-1800°C.

[0030] Further: in step S3, a carbon transition layer with a thickness of 10-50 nm is deposited on the surface of the magnesium-nickel alloy core by chemical vapor deposition in an acetylene atmosphere at 600-700°C.

[0031] Based on the above technical solution, since the mutual diffusion rate of magnesium and nickel is relatively fast, depositing a carbon transition layer between the magnesium-nickel alloy core and the metal nickel slow-release layer can further control the outward diffusion rate of magnesium.

[0032] Specifically: in step S4, oxidation is performed in an air atmosphere at 400-700° C. for 10-300 min to obtain a magnesium oxide barrier layer.

[0033] Based on the above technical solution, it can be ensured that the obtained magnesium oxide barrier layer has a suitable density.

[0034] The present invention also provides the use of a magnesium-based controlled-release corrosion inhibitor for a chloride molten salt medium as a corrosion inhibitor for a chloride molten salt medium in molten salt solar thermal power generation technology.

[0035] Specifically, the container material of the molten salt solar thermal power generation device is one of an iron-based alloy and a nickel-based alloy. Examples of iron-based alloys include 310 stainless steel, 316 stainless steel, and 321 stainless steel. Examples of nickel-based alloys include Inconel 625, Inconel 617, and Hastelloy C276.

[0036] Compared with the prior art, the present invention has the following characteristics and beneficial effects:

[0037] The corrosion inhibitor provided by the present invention can not only effectively remove water and oxygen impurities in chloride salts and reduce their corrosiveness, but also avoid the problem of local destructive corrosion caused by direct contact between the liquid Mg corrosion inhibitor and the container material, thereby significantly improving the corrosion resistance of the container material in chloride salts.

[0038] The synthesis method provided by the invention is simple, has significant effects, stable physical and chemical properties, and has no obvious influence on the heat storage performance of the chloride salt system. DETAILED DESCRIPTION

[0039] The principles and features of the present invention are described below. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0040] Unless otherwise specified, the test methods used in the examples are conventional methods; the materials and reagents used are commercially available reagents and materials unless otherwise specified.

[0041] The specific composition of chloride salt is MgCl2-NaCl-KCl (molar ratio 60:20:20).

[0042] Example 1

[0043] Mg:Ni metals were mixed in a molar ratio of 2:1, heated to 1500℃ in an inert (argon) atmosphere to melt into a magnesium-nickel alloy, and then cooled to room temperature; the magnesium-nickel alloy was crushed into 0.05 mm particles; a 0.5 μm thick metal nickel layer was then electroplated on the surface of the magnesium-nickel alloy particles by electroplating; the nickel-plated magnesium-nickel alloy particles were oxidized in an air atmosphere at 400℃ for 50 min to prepare a 2 μm thick magnesium oxide layer.

[0044] The resulting magnesium-based controlled-release corrosion inhibitor was mixed with chloride salt and then heated to 700°C under an argon atmosphere for high-temperature corrosion testing. 316 stainless steel plates were immersed in the chloride salt. After 1000 hours, the weight, corrosion products, and cross-sectional morphology of the stainless steel were analyzed to observe the corrosion. Scanning electron microscopy revealed no localized severe corrosion on the 316 stainless steel surface caused by liquid metal corrosion. The annual corrosion rate of the 316 stainless steel plates in the chloride salt containing the magnesium-based controlled-release corrosion inhibitor particles was less than 10 μm / year.

[0045] Example 2

[0046] Mg:Ni metals were mixed in a molar ratio of 1:2, heated to 1600℃ in an inert atmosphere to melt into a magnesium-nickel alloy, and then cooled to room temperature; the magnesium-nickel alloy was crushed into 0.5 mm particles; a 30 nm thick carbon transition layer was deposited on the surface of the magnesium-nickel alloy particles by chemical vapor deposition in an acetylene atmosphere at 700℃; a 0.2 μm thick metal nickel layer was then electroplated on the surface of the carbon-coated magnesium-nickel alloy particles; the nickel-plated magnesium-nickel alloy particles were oxidized in an air atmosphere at 500℃ for 10 min to prepare a 0.5 μm thick magnesium oxide layer.

[0047] The resulting magnesium-based controlled-release corrosion inhibitor was mixed with chloride salt and then heated to 700°C under an argon atmosphere for high-temperature corrosion testing. 316 stainless steel plates were immersed in the chloride salt. After 1000 hours, the weight, corrosion products, and cross-sectional morphology of the stainless steel were analyzed to observe the corrosion. Scanning electron microscopy revealed no localized severe corrosion on the 316 stainless steel surface caused by liquid metal corrosion. The annual corrosion rate of the 316 stainless steel plates in the chloride salt containing the magnesium-based controlled-release corrosion inhibitor particles was less than 10 μm / year.

[0048] Example 3

[0049] Mg:Ni metals were mixed in a molar ratio of 2:1, heated to 1500℃ in an inert atmosphere to melt into a magnesium-nickel alloy, and then cooled to room temperature; the magnesium-nickel alloy was crushed into 4 mm particles; a 1 μm thick metal nickel layer was then electroplated on the surface of the magnesium-nickel alloy particles by electroplating; the nickel-plated magnesium-nickel alloy particles were oxidized in an air atmosphere at 600℃ for 100 min to prepare a 5 μm thick magnesium oxide layer.

[0050] The resulting magnesium-based controlled-release corrosion inhibitor was mixed with chloride salt and then heated to 700°C under an argon atmosphere for high-temperature corrosion testing. 316 stainless steel plates were immersed in the chloride salt. After 1000 hours, the weight, corrosion products, and cross-sectional morphology of the stainless steel were analyzed to observe the corrosion. Scanning electron microscopy revealed no localized severe corrosion on the 316 stainless steel surface caused by liquid metal corrosion. The annual corrosion rate of the 316 stainless steel plates in the chloride salt containing the magnesium-based controlled-release corrosion inhibitor particles was less than 10 μm / year.

[0051] Example 4

[0052] Mg:Ni metals were mixed in a molar ratio of 1:2, heated to 1600°C in an inert atmosphere to melt into a magnesium-nickel alloy, and then cooled to room temperature; the magnesium-nickel alloy was crushed into 0.2 mm particles; a 0.1 μm thick metal nickel layer was then electroplated on the surface of the magnesium-nickel alloy particles by electroplating; the nickel-plated magnesium-nickel alloy particles were oxidized in an air atmosphere at 650°C for 20 minutes to prepare a 1 μm thick magnesium oxide layer.

[0053] The resulting magnesium-based controlled-release corrosion inhibitor was mixed with chloride salt and then heated to 700°C under an argon atmosphere for high-temperature corrosion testing. 316 stainless steel plates were immersed in the chloride salt. After 1000 hours, the weight, corrosion products, and cross-sectional morphology of the stainless steel were analyzed to observe the corrosion. Scanning electron microscopy revealed no localized severe corrosion on the 316 stainless steel surface caused by liquid metal corrosion. The annual corrosion rate of the 316 stainless steel plates in the chloride salt containing the magnesium-based controlled-release corrosion inhibitor particles was less than 10 μm / year.

[0054] Example 5

[0055] Referring to Example 1, the difference is that the 316 stainless steel plate is replaced with Inconel 617. The results are as follows: Scanning electron microscopy observation shows that there is no local severe corrosion phenomenon caused by liquid metal corrosion on the surface of the container, and the annual corrosion rate of Inconel 617 is less than 10 μm / year.

[0056] Comparative Example 1

[0057] High-temperature corrosion experiments were conducted by mixing excess Mg with chloride salt and heating it to 700°C under an argon atmosphere. 316 stainless steel plates were immersed in the chloride salt. After 1000 hours, the weight, corrosion products, and cross-sectional morphology of the stainless steel were analyzed to observe the corrosion. Scanning electron microscopy revealed severe localized corrosion on the surface of the 316 stainless steel caused by liquid metal corrosion. The annual corrosion rate of the 316 stainless steel plate in the chloride salt containing excess Mg was 2000 μm / year.

[0058] Comparative Example 2

[0059] A high-temperature corrosion test was conducted in which chloride salt was heated to 700°C under an argon atmosphere. A 316 stainless steel plate was immersed in the chloride salt. After 1000 hours, the weight, corrosion products, and cross-sectional morphology of the stainless steel were analyzed to observe the corrosion. The annual corrosion rate of the 316 stainless steel plate in the chloride salt without a corrosion inhibitor was 700 μm / year.

[0060] Comparative Example 3

[0061] Refer to Example 1, except that no magnesium oxide layer was prepared.

[0062] Mg:Ni metals were mixed in a molar ratio of 2:1, heated to 1500°C in an inert (argon) atmosphere to melt into a magnesium-nickel alloy, and then cooled to room temperature; the magnesium-nickel alloy was crushed into 0.05 mm particles; and a 0.5 μm thick metal nickel layer was then electroplated on the surface of the magnesium-nickel alloy particles.

[0063] The resulting corrosion inhibitor was mixed evenly with chloride salt and then heated to 700°C under an argon atmosphere for high-temperature corrosion testing. 316 stainless steel plates were immersed in the chloride salt. After 1000 hours, the weight, corrosion products, and cross-sectional morphology of the stainless steel were analyzed to observe the corrosion condition. Scanning electron microscopy revealed an annual corrosion rate of 40 μm / year for the 316 stainless steel plates in the chloride salt containing the corrosion inhibitor particles.

[0064] Comparative Example 4

[0065] Refer to Example 1, except that the magnesium oxide layer and the metal nickel layer are not prepared.

[0066] Mg:Ni metals were mixed in a molar ratio of 2:1, heated to 1500°C in an inert (argon) atmosphere to melt into a magnesium-nickel alloy, and then cooled to room temperature; the magnesium-nickel alloy was crushed into 0.05 mm particles.

[0067] The resulting corrosion inhibitor was mixed evenly with chloride salt and then heated to 700°C under an argon atmosphere for high-temperature corrosion testing. 316 stainless steel plates were immersed in the chloride salt. After 1000 hours, the weight, corrosion products, and cross-sectional morphology of the stainless steel were analyzed to observe the corrosion condition. Scanning electron microscopy revealed an annual corrosion rate of 50 μm / year for the 316 stainless steel plates in the chloride salt containing the corrosion inhibitor particles.

[0068] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A magnesium-based controlled-release corrosion inhibitor for a chloride molten salt medium, characterized in that: include: An inner layer, which is a magnesium-nickel alloy core; an intermediate layer, which is a metal nickel sustained-release layer; and an outer layer, which is a magnesium oxide barrier layer.

2. The magnesium-based controlled-release corrosion inhibitor for chloride molten salt medium according to claim 1, characterized in that: The material of the magnesium-nickel alloy core is MgNi2, Mg2Ni or a mixture of the two; In the magnesium-nickel alloy, the molar ratio of magnesium to nickel is (2:1) to (1:2); The size of the magnesium-nickel alloy core is 0.05-4 mm.

3. The magnesium-based controlled-release corrosion inhibitor for chloride molten salt medium according to claim 1, characterized in that: The thickness of the metal nickel sustained-release layer is 0.1-1 μm.

4. The magnesium-based controlled-release corrosion inhibitor for chloride molten salt medium according to claim 1, characterized in that: The thickness of the magnesium oxide barrier layer is 0.5-5 μm.

5. A method for preparing a magnesium-based controlled-release corrosion inhibitor for a chloride molten salt medium according to any one of claims 1 to 4, characterized in that: The following steps are involved: S1. Mixing magnesium and nickel metals in proportion, heating and melting them in an inert atmosphere to form a magnesium-nickel alloy, and cooling them to room temperature; S2, crushing the magnesium-nickel alloy into particles to obtain a magnesium-nickel alloy core; S3, electroplating a metal nickel layer on the surface of the magnesium-nickel alloy core by an electroplating method to obtain a metal nickel slow-release layer; S4. The magnesium-nickel alloy core having the metal nickel slow-release layer is heated and oxidized in an air atmosphere to obtain a magnesium oxide barrier layer.

6. The method for preparing a magnesium-based controlled-release corrosion inhibitor in a chloride molten salt medium according to claim 5, characterized in that: In step S1, the temperature is heated to 1500-2000° C. to be melted into a magnesium-nickel alloy.

7. The method for preparing a magnesium-based controlled-release corrosion inhibitor for a chloride molten salt medium according to claim 5, wherein: In step S3, a carbon transition layer with a thickness of 10-50 nm is deposited on the surface of the magnesium-nickel alloy core by chemical vapor deposition in an acetylene atmosphere at 600-700°C.

8. The method for preparing a magnesium-based controlled-release corrosion inhibitor in a chloride molten salt medium according to claim 5, wherein: In step S4, oxidation is carried out in an air atmosphere at 400-700° C. for 10-300 min to obtain a magnesium oxide barrier layer.

9. An application of the magnesium-based controlled-release corrosion inhibitor in a chloride molten salt medium according to any one of claims 1 to 4, characterized in that: As a corrosion inhibitor for chloride molten salt medium in molten salt solar thermal power generation.

10. The use according to claim 9, characterized in that: The container material of the molten salt solar thermal power generation device is one of iron-based alloys or nickel-based alloys.