Method for reducing corrosion of high-temperature molten salt to container through sacrificial material and container

Abstract

The invention discloses a method for relieving corrosion of high-temperature molten salt to a container through a sacrificial material and the container. The surface of a container material for molten salt is coated with a high-temperature-resistant anti-corrosion carbon-based coating with graphite as the sacrificial material. The high-temperature-resistant anti-corrosion carbon-based coating is obtained by spraying a coating suspension containing graphite on the container material. According to the invention, the carbon-based material is used as a sacrificial material to reduce the corrosion of the high-temperature molten salt to the container material, so that the problem of high-temperature molten salt corrosion on the surface of the industrial metal high-temperature metal substrate is solved, and the average annual corrosion rate of the container infiltrated in the molten salt at 565 DEG C or above for 3000 hours is less than 10 [mu] m / year.

Description

Technical Field

[0001] The present invention belongs to the technical field of high temperature resistance and corrosion resistance, and relates to a method and a container for reducing high temperature molten salt corrosion of a container by using sacrificial materials, and specifically to a method for using carbon-based materials as sacrificial materials to reduce high temperature molten salt corrosion of a container. Background Art

[0002] As traditional energy sources are becoming increasingly depleted, people are constantly exploring new energy sources for sustainable development. Solar energy is a clean and sustainable green energy source with broad development prospects. Mainstream solar power generation technologies mainly include solar photovoltaic power generation technology and solar thermal power generation technology. Among them, solar thermal power generation technology is more environmentally friendly and has advantages such as more flexible power dispatch. In solar thermal power generation technology, the high-temperature heat storage system is a very critical module. In order to improve the power generation efficiency, molten salt is often used as a heat transfer and heat storage medium, but molten salt is easy to corrode the container material at high temperatures.

[0003] There are three methods to reduce the corrosion of container materials by molten salts. The first is to improve the corrosion resistance of container materials by alloys with high nickel and / or molybdenum content; the second is to add a small amount of divalent alkaline earth metals as corrosion inhibitors in molten salts to achieve the effect of reducing corrosion; the third is to deposit a coating on the surface of the container material, which can reduce the corrosion of the container material by blocking the direct interaction between the molten salt and the container material, and on the other hand, the corrosion of the container material can be delayed by sacrificial materials. Chinese Patent Publication No. CN115679155A discloses a nickel-molybdenum-based alloy material resistant to high-temperature chloride ion molten salt corrosion, its preparation method and its application. In the process of vacuum induction melting of nickel alloys, an alloy material with excellent hot workability and high-temperature chloride ion molten salt corrosion resistance can be prepared by adding appropriate amounts of chromium, molybdenum and other elements. Stainless steel corrodes severely in high-temperature molten salts. Compared with stainless steel, nickel-based alloys show good corrosion resistance, but their high cost makes it difficult to achieve commercial application in solar thermal power stations.

[0004] Compared with modified container materials and molten salts, the coating deposited on the surface of the container material has good effect and low cost. The main components of the most commonly used coatings in the field of high temperature corrosion resistance are metals and ceramics. China Patent Publication No. CN115418592A discloses a chloride molten salt corrosion resistant coating and its preparation method. Compared with traditional hot-dip aluminum plating, the special coating obtained by hot-dip plating of Fe-Cr-B alloy with Al-Si alloy has better chloride molten salt corrosion resistance. Metal coatings have excellent adhesion, high temperature resistance and high temperature molten salt corrosion resistance, but there are defects such as high cost, long construction period and poor coating density. Although ceramic coatings have good heat resistance, corrosion resistance, wear resistance and thermal shock resistance, they are complex to construct, easy to fall off and have poor safety. In recent years, coatings with carbon-based materials as the main component have attracted more and more attention from academia and industry due to their excellent high temperature resistance, but there are problems with the coatings with carbon-based materials as the main component currently studied.

[0005] In view of the above situation, it is urgent to study a low-cost, easy-to-construct method that can reduce the corrosion of container materials by high-temperature molten salt. Summary of the invention

[0006] In view of the above-mentioned defects existing in the prior art, the purpose of the present invention is to provide a method and container for reducing the corrosion of high-temperature molten salt containers by sacrificial materials. The corrosion of high-temperature molten salt on container materials is reduced by using carbon-based materials as sacrificial materials, aiming to solve the problem of high-temperature molten salt corrosion on the surface of industrial metal high-temperature metal substrates, so that the average annual corrosion rate of the container after immersion in molten salt above 565°C for 3000 hours is less than 10μm / year.

[0007] To achieve the above object, the present invention adopts the following technical solution:

[0008] The first aspect of the present invention provides a method for reducing high-temperature molten salt corrosion of containers by using sacrificial materials, wherein the surface of the container material for molten salt is covered with a high-temperature resistant and anti-corrosion carbon-based coating with graphite as the sacrificial material; the high-temperature resistant and anti-corrosion carbon-based coating is obtained by spraying a coating suspension containing graphite on the container material.

[0009] Preferably, the mass concentration of the graphite in the coating suspension is 10-20 wt.%.

[0010] Preferably, the particle size of the graphite is 1 to 100 μm.

[0011] Preferably, the thickness of the high temperature resistant and anti-corrosion carbon-based coating is 20 to 150 μm.

[0012] Preferably, the coating suspension uses a polymer as a binder and deionized water as a solvent for dissolving the binder.

[0013] Preferably, the polymer binder is polyvinyl alcohol or polyethylene glycol.

[0014] Preferably, the coating suspension contains inorganic nanoparticles.

[0015] Preferably, the particle size of the inorganic nanoparticles is 1 to 100 nm; and / or

[0016] The inorganic nanoparticles include oxides.

[0017] Preferably, the oxide comprises silicon dioxide or aluminum oxide.

[0018] Preferably, when preparing the high temperature resistant and anti-corrosion carbon-based coating, a coating additive is added to a coating suspension containing graphite and dispersed evenly.

[0019] Preferably, the container material includes 304 stainless steel, 304L stainless steel, 316 stainless steel, 316L stainless steel, 321 stainless steel and 347 stainless steel.

[0020] Preferably, the molten salt includes chloride, carbonate, or nitrate.

[0021] The second aspect of the present invention provides a container obtained by the method of reducing high-temperature molten salt corrosion of the container by sacrificial materials as described in the first aspect of the present invention, wherein the annual corrosion rate of the container is less than 10 μm / year after 3000 hours in a molten salt environment at 565°C.

[0022] The method and container provided by the present invention for reducing high temperature molten salt corrosion of the container by sacrificial material have the following characteristics:

[0023] Beneficial effects:

[0024] 1. The present invention delays the corrosion of container materials in a high-temperature molten salt environment by modifying the coating. Compared with modified container materials, the present invention has low cost and obvious corrosion resistance at high temperatures;

[0025] 2. Compared with metal coatings and ceramic coatings, the present invention uses graphite as a sacrificial material with low cost, and the preparation process of the graphite coating is easy for industrial production;

[0026] 3. After the graphite coating is modified by high-temperature molten salt corrosion, low-cost steel can also have good corrosion resistance. It can be used as molten salt storage tank material, which reduces the cost of raw materials for molten salt storage tank materials to a certain extent. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

[0028] Figure 1 Surface and cross-sectional SEM images of an uncoated 316 stainless steel sheet after exposure to a molten salt at 565°C, wherein (a) and (b) are surface SEM images of an uncoated 316 stainless steel sheet after exposure to a molten salt at 565°C, and (c) is a cross-sectional SEM image of an uncoated 316 stainless steel sheet after exposure to a molten salt at 565°C;

[0029] Figure 2 This is the XRD pattern of the 316 stainless steel sheet without graphite coating after exposure to molten salt at 565°C;

[0030] Figure 3 Surface and cross-sectional SEM images of the 316 stainless steel plate coated with the coating in Example 1 of the present invention after being exposed to a molten salt at 565° C., wherein (a) and (b) are surface SEM images of the 316 stainless steel plate coated with the coating after being exposed to a molten salt at 565° C., and (c) is a cross-sectional SEM image of the 316 stainless steel plate coated with the coating after being exposed to a molten salt at 565° C.;

[0031] Figure 4 316 stainless steel plate with coating in Example 1 of the present invention is exposed to molten salt at 565°C. XRD pattern. DETAILED DESCRIPTION

[0032] In order to better understand the above technical solution of the present invention, the technical solution of the present invention is further described below in conjunction with embodiments.

[0033] The present invention provides a method for reducing high-temperature molten salt corrosion of containers by using sacrificial materials. The method reduces the corrosion of container materials by high-temperature molten salt by adding graphite carbon-based materials as sacrificial materials in the coating on the surface of the container. The method aims to solve the problem of high-temperature molten salt corrosion on the surface of industrial high-temperature metal substrates, and finally obtains a container coated with a high-temperature resistant and anti-corrosion carbon-based coating, and the average annual corrosion rate of the container after immersion in 565°C molten salt (such as nitrate) for 3000 hours is less than 10μm / year.

[0034] In a method for reducing high-temperature molten salt corrosion of a container by using sacrificial materials provided by the present invention, a high-temperature resistant and anti-corrosion carbon-based coating with graphite as a sacrificial material is coated on the surface of the container material for molten salt; the high-temperature resistant and anti-corrosion carbon-based coating is obtained by spraying a coating suspension containing graphite on the container material.

[0035] In a specific embodiment, the thickness of the high temperature resistant and anti-corrosion carbon-based coating on the surface of the container material is 20 to 150 μm. The thickness of the high temperature resistant and anti-corrosion carbon-based coating can be determined according to the actual use of the container, such as a high temperature molten salt storage tank, preferably 80 μm.

[0036] As the main raw material, graphite provides the corrosion inhibition effect required for high temperature resistant and corrosion resistant carbon-based coatings. The main principle is to provide a physical and chemical barrier between the molten salt and the substrate material, effectively isolating the substrate from the electrolyte. If graphite is oxidized under the application conditions, as a sacrificial material, it helps to reduce the transmission rate of molten salt oxides to the substrate, thereby forming a more compact and adherent oxide layer on the container material. The oxide layer can further protect the container material, limiting the further diffusion of the molten salt to the substrate, thereby reducing the corrosion rate. When selecting materials, graphite is dispersed in the coating suspension in powder form, wherein the particle size of the graphite is 1 to 100 μm; the mass concentration of graphite in the coating suspension is 10 to 20 wt.%.

[0037] In a specific embodiment, the coating suspension uses a polymer as a binder for the cohesion between graphite particles and adhesion to the surface of the container substrate, and the polymer includes polyvinyl alcohol (PVA) or polyethylene glycol (PEG) of various molecular weights; the coating suspension uses deionized water as a solvent for dissolving the binder.

[0038] In a specific embodiment, inorganic nanoparticles are added to the coating suspension to improve the stability of the suspension. The inorganic nanoparticles include oxides, such as silicon dioxide or aluminum oxide or any other suitable oxides. In a specific embodiment, the particle size of the inorganic nanoparticles is 1 to 100 nm.

[0039] In a specific embodiment, the coating suspension is prepared as follows: dissolving the binder in deionized water to obtain a binder aqueous solution, adding graphite and inorganic nanoparticles to the binder aqueous solution, highly homogenizing it to make it evenly dispersed, and obtaining a coating suspension.

[0040] In a specific embodiment, the preparation process of the high temperature resistant and anti-corrosion carbon-based coating is as follows: add a coating additive to a coating suspension containing graphite and disperse it evenly; then use a spray gun to spray the coating suspension on the surface of the container and dry it at room temperature. After drying, spray it again until a certain required thickness is reached.

[0041] In a specific embodiment, the container material includes, but is not limited to, 304 stainless steel, 304L stainless steel, 316 stainless steel, 316L stainless steel, 321 stainless steel, and 347 stainless steel.

[0042] The corrosion resistance of the container covered with a high temperature resistant and anti-corrosion carbon-based coating using graphite as a sacrificial material to molten salt is tested as follows:

[0043] A container with a high-temperature resistant and anti-corrosion carbon-based coating on its surface is placed in a molten salt at a certain temperature for molten salt corrosion. After a period of time, the corrosion of the container material is observed to evaluate the corrosion resistance of the container with a high-temperature resistant and anti-corrosion carbon-based coating on its surface. Among them, the molten salt includes but is not limited to chlorides, carbonates, and nitrates. The temperature of the molten salt is 400-600°C, and the corrosion time of the molten salt is 200-3000h. The method for observing the corrosion of the container material mainly includes at least one of X-ray diffraction analysis (XRD), scanning electron microscopy analysis (SEM), Raman spectroscopy analysis (Raman), X-ray energy spectrum analysis (EDS), and gravimetric analysis.

[0044] The present invention also provides a container obtained by the above-mentioned method of reducing high-temperature molten salt corrosion of the container through sacrificial materials, and the annual corrosion rate of the container after 3000 hours in a molten salt environment at 565°C is less than 10μm / year.

[0045] The method and container of the present invention for reducing high-temperature molten salt corrosion by using sacrificial materials will be further introduced below in conjunction with specific embodiments and comparative examples.

[0046] Example 1

[0047] The method of reducing high temperature molten salt corrosion of the container by using sacrificial materials in this embodiment is as follows:

[0048] a) dissolving 4.35 g of PVA in 82.65 g of deionized water to obtain a PVA aqueous solution; adding 12 g of graphite powder and 1 g of nano-SiO2 to the PVA aqueous solution, and homogenizing at high speed to make it evenly dispersed to obtain a coating suspension;

[0049] b) When preparing the high temperature resistant and anticorrosive carbon-based coating, a coating additive is added to the coating suspension and dispersed evenly, and the coating is sprayed on a 316 stainless steel plate using a spray gun spraying technique, dried at room temperature, and sprayed again after drying until the coating thickness reaches 50 μm;

[0050] c) The 316 stainless steel sheet with the coating obtained in b) was immersed in 565°C nitrate for molten salt corrosion. After 3000 hours, the corrosion of the 316 stainless steel sheet with the coating was observed by XRD, SEM, Raman, EDS, and gravimetric analysis. Combined with Table 1, it was found that the annual corrosion rate of the 316 stainless steel sheet with the coating was 6.6±0.7μm / year.

[0051] Comparative Example 1

[0052] In this comparative example, the uncoated 316 stainless steel sheet was immersed in 565°C nitrate for molten salt corrosion. After 3000 hours, the corrosion of the 316 stainless steel sheet was observed by XRD, SEM, Raman, EDS, and gravimetric analysis. It was found that the uncoated 316 stainless steel sheet had an annual corrosion rate of 15.1±0.2μm / year as shown in Table 1; Figure 1 , Figure 2 As shown in the figure, after corrosion, a thick oxide layer (large cracked porous structure with no adhesion and no protection) is formed on the stainless steel surface. Hematite, magnetite and sodium ferrite are the main corrosion products, and salt residues are left on the rust. The cracked and highly porous oxide layer formed on the surface of uncoated 316 stainless steel indicates that it has no protective properties; the expansion of the cracks causes the oxide layer and corrosion products to fall off from the alloy surface, further accelerating corrosion.

[0053] Figure 3 The results highlight the formation of a dense and well-adherent oxide layer on the coated 316 stainless steel surface; this oxide layer is tightly bonded to the alloy surface and effectively restricts the diffusion of oxides in the molten salt into the substrate. Figure 1 and Figure 3 The surface scanning electron microscope images presented in Figure 5 highlight the microstructural differences between the oxide layers formed on uncoated (porous) and coated 316 stainless steel (dense). Figure 2 and Figure 4 The main difference between the XRD analysis results in is that the diffraction peak of the spinel structure of the coated 316 stainless steel (in Example 1) has a higher relative intensity, which can be attributed to the formation of an inner FeCr2O4 spinel layer under the outer hematite layer.

[0054] Example 2

[0055] The method of reducing high temperature molten salt corrosion of the container by using sacrificial materials in this embodiment is as follows:

[0056] a) dissolving 4.35 g of PVA in 82.65 g of deionized water to obtain a PVA aqueous solution; adding 12 g of graphite powder and 1 g of nano-SiO2 to the PVA aqueous solution, and homogenizing at high speed to make it evenly dispersed to obtain a coating suspension;

[0057] b) When preparing the coating, a coating additive is added to the coating suspension and dispersed evenly, and the coating is sprayed on a 347 stainless steel plate using a spray gun spraying technique, dried at room temperature, and sprayed again after drying until the coating thickness reaches 80 μm;

[0058] c) The 347 stainless steel sheet with the coating obtained in b) was immersed in 565°C nitrate for molten salt corrosion. After 3000 hours, the corrosion of the 347 stainless steel sheet with the coating was observed by XRD, SEM, Raman, EDS, and gravimetric analysis. Combined with Table 1, it was observed that the annual corrosion rate of the 347 stainless steel sheet with the coating was 8.2±5.4μm / year, and a thin oxide layer was formed on the surface, which may be caused by coating defects / peeling; hematite and spinel were the main corrosion products.

[0059] Comparative Example 2

[0060] In this comparative example, the uncoated 347 stainless steel sheet was immersed in 565°C nitrate for molten salt corrosion. After 3000 hours, the corrosion of the 347 stainless steel sheet was observed by XRD, SEM, Raman, EDS, and gravimetric analysis. Combined with Table 1, it was found that the uncoated 347 stainless steel sheet had an annual corrosion rate of 20.7±1.6μm / year, and a thick oxide layer (large crack porous structure without adhesion and protection) was generated on the stainless steel surface after corrosion.

[0061] Combining Example 2 and Comparative Example 2, it can be seen that the nitrate corrosion resistance of the 347 stainless steel plate with a coating on the surface at 565°C (8.2±5.4μm / year) is much better than that of the 347 stainless steel plate without a coating (20.7±1.6μm / year).

[0062] Table 1 Annual corrosion rate of containers

[0063] Annual corrosion rate (μm / year) Comparative Example 1 15.1±0.2 Example 1 6.6±0.7 Comparative Example 2 20.7±1.6 Example 2 8.2±5.4

[0064] Those skilled in the art should recognize that the above embodiments are only used to illustrate the present invention, and are not intended to limit the present invention. As long as they are within the spirit of the present invention, any changes or modifications to the above embodiments will fall within the scope of the claims of the present invention.

Claims

1. A method for reducing high temperature molten salt corrosion of a container by using sacrificial materials, characterized in that: The surface of the container material for molten salt is covered with a high-temperature resistant and anti-corrosion carbon-based coating using graphite as a sacrificial material; the high-temperature resistant and anti-corrosion carbon-based coating is obtained by spraying a coating suspension containing graphite on the container material.

2. The method for reducing high temperature molten salt corrosion of a container by using sacrificial materials according to claim 1, characterized in that: The mass concentration of the graphite in the coating suspension is 10-20 wt.%.

3. The method for reducing high temperature molten salt corrosion of a container by using sacrificial materials according to claim 1, characterized in that: The particle size of the graphite is 1 to 100 μm.

4. The method of reducing high temperature molten salt corrosion of a container by using sacrificial materials according to claim 1, characterized in that: The thickness of the high temperature resistant and anti-corrosion carbon-based coating is 20 to 150 μm.

5. The method of reducing high temperature molten salt corrosion of a container by using sacrificial materials according to claim 1, characterized in that: The coating suspension uses a polymer as a binder and deionized water as a solvent for dissolving the binder.

6. The method for reducing high temperature molten salt corrosion of a container by using sacrificial materials according to claim 5, characterized in that: The polymer binder is polyvinyl alcohol or polyethylene glycol.

7. The method of reducing high temperature molten salt corrosion of a container by using sacrificial materials according to claim 1, characterized in that: The coating suspension contains inorganic nanoparticles.

8. The method for reducing high temperature molten salt corrosion of a container by using sacrificial materials according to claim 7, characterized in that: The particle size of the inorganic nanoparticles is 1 to 100 nm; and / or The inorganic nanoparticles include oxides.

9. The method for reducing high temperature molten salt corrosion of a container by using sacrificial materials according to claim 8, characterized in that: The oxide includes silicon dioxide or aluminum oxide.

10. The method for reducing high temperature molten salt corrosion of a container by using sacrificial materials according to claim 1, characterized in that: When preparing the high temperature resistant and anti-corrosion carbon-based coating, a coating additive is added to a coating suspension containing graphite and dispersed evenly.

11. The method for reducing high temperature molten salt corrosion of a container by using sacrificial materials according to claim 1, characterized in that: The container materials include 304 stainless steel, 304L stainless steel, 316 stainless steel, 316L stainless steel, 321 stainless steel and 347 stainless steel.

12. The method of reducing high temperature molten salt corrosion of a container by using sacrificial materials according to claim 1, characterized in that: The molten salt includes one or more of chlorides, carbonates, and nitrates.

13. A container, characterized in that: The method for reducing high-temperature molten salt corrosion of a container by sacrificial materials as described in claims 1 to 12 is adopted, wherein the annual corrosion rate of the container is less than 10 μm / year after 3000 hours in a molten salt environment at 565°C.

Images