A graphite treatment method for barrier to molten salt and molten metal infiltration

Abstract

The application provides a graphite processing method for blocking molten salt and molten metal infiltration, comprising the following steps: S1: providing a thermosetting resin monomer or oligomer solution, adding a small amount of catalyst to the solution to form a precursor, and immersing the precursor into graphite pores; S2: converting the precursor immersed in the graphite pores into organic nanostructures through solidification and drying; and S3: carbonizing the organic nanostructures in the graphite pores at a temperature higher than 500 DEG C to form carbon nanostructures, so that a graphite capable of blocking molten salt and molten metal infiltration is obtained. The processing method provided by the application has the advantages of simple process, difficulty in failure, and no change in the performance of the base material, compared with the traditional surface coating, resin and other impregnation methods, and has obvious advantages over other processing methods when used for processing the graphite in a molten salt core, and has little influence on the mechanical, thermal and radiation behaviors of the graphite, so that the cost caused by the reevaluation of the graphite material can be saved or reduced.

Description

Technical Field

[0001] This invention relates to the field of materials, and more specifically to a graphite treatment method for preventing the infiltration of molten salt and molten metal. Background Technology

[0002] In molten salt reactors, graphite, acting as a moderator and reflector, is crucial for the safety and economic efficiency of the reactor's operation. Because graphite is a porous material, molten salt can seep into its pores, affecting reactor safety and graphite performance. Currently, there are three main solutions: one is to develop new, highly dense nuclear graphite materials, but this method is time-consuming, costly, and faces the risk of poor irradiation performance; the second is to repeatedly impregnate existing nuclear graphite materials with resins, bitumen, molten metals, etc., to reduce the pore size. This method significantly alters the properties of graphite and also suffers from poor irradiation performance; the third is to coat the graphite surface, but due to the difference in properties between the coating and the substrate material, it is difficult to ensure that the coating does not peel off during use. Furthermore, in applications such as molten salt energy storage, it is also necessary to prevent molten salt infiltration into the graphite, but there is currently no convenient method for this.

[0003] In summary, there is an urgent need for a simple and effective method to treat graphite in order to achieve the goal of graphite blocking molten salt and molten metal. Summary of the Invention

[0004] The purpose of this invention is to provide a graphite treatment method for preventing the infiltration of molten salt and molten metal, thereby solving the problem of molten salt and molten metal infiltration in graphite in existing molten salt piles and other systems.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] A graphite treatment method for preventing the infiltration of molten salt and molten metal is provided, comprising the following steps: S1: providing a thermosetting resin monomer or oligomer solution, adding a small amount of catalyst to the solution to form a precursor, and allowing the precursor to impregnate the graphite pores; S2: converting the precursor impregnated in the graphite pores into an organic nanostructure by curing and drying; S3: carbonizing the organic nanostructure in the graphite pores at a temperature above 500°C to form a carbon nanostructure, thereby obtaining a graphite that can prevent the infiltration of molten salt and molten metal.

[0007] In step S1, the thermosetting resin includes phenolic resins, furan resins, polyimides, etc., and the solvent used to form the thermosetting resin monomer or oligomer solution includes water, ethanol, ethylene glycol, isopropanol, acetone, petroleum ether, etc., and the molar ratio of the monomer to the solvent is between 0.01 and 0.5.

[0008] Preferably, in step S1, the catalyst used is hexamethylenetetramine, an inorganic base, or a salt, and the mass ratio of the catalyst to the thermosetting resin is 0 to 0.05.

[0009] Optionally, in step S1, the method of immersing the precursor into the graphite pores includes: vacuum impregnation, pressure impregnation, or boiling under various pressures, etc.

[0010] Preferably, in step S2, the curing includes: placing graphite in a sealed container, or placing graphite in an atmosphere where solvent vapor is nearly saturated, so that the precursor changes from a liquid phase to a solid phase; the temperature of the curing process is 50 to 200°C.

[0011] In step S2, the drying includes maintaining the graphite at a temperature of 0–300°C after curing to further remove the solvent from the precursor.

[0012] Preferably, in step S3, a heating rate of 0.01 to 10 °C / min is used to make the final temperature higher than 500 °C.

[0013] Preferably, in step S3, the sample is placed in a vacuum environment or an inert atmosphere for carbonization.

[0014] In step S3, the carbon nanostructure formed may be composed of aggregated carbon nanoparticles, the size of which ranges from 1 to 100 nanometers; alternatively, the carbon nanostructure formed may also be composed of fibrous carbon, the diameter of which ranges from 1 to 100 nanometers.

[0015] According to the graphite processing method provided by the present invention, in step S1, a solution of thermosetting resin monomers or oligomers is used. After adding a small amount of catalyst, the solution is used as a precursor and immersed into the pores of graphite. The precursor, as a sol, can solidify into a gel within the pores of graphite. In step S2, the precursor solution is transformed into an organic nanostructure using suitable curing, aging, and drying techniques. The precursor sol within the graphite pores is transformed into a gel under the action of a catalyst and temperature, and then dried after aging for a certain period of time. The purpose of aging is to increase the strength of the organic gel. In step S3, the organic nanostructure is carbonized at a temperature greater than 500°C to form a carbon nanostructure. The internal structure of the graphite with improved barrier properties prepared according to the method of the present invention is as follows: Figure 1 As shown.

[0016] As described in the background section of this invention, currently disclosed methods mainly employ resins, molten salts, or metals to impregnate or coat the surface of graphite. However, graphite is prone to cracking during the high-temperature carbonization process after resin impregnation, and the impregnation of these substances significantly alters the properties of graphite, particularly its behavior under neutron conditions, making these impregnation methods unsuitable for use in nuclear reactor cores. Surface coatings also suffer from the problem of coating failure due to differences in thermal expansion coefficients and irradiation behavior during reactor service.

[0017] However, according to the method provided by the present invention, low-modulus carbon nanostructures are used to seal the pores in graphite. Due to the shape and surface properties of carbon nanostructures, they have the characteristics of being superhydrophobic to molten salts and superhydrophobic to molten metals. The present invention utilizes this characteristic to achieve the goal of preventing graphite from being impregnated by molten salts and molten metals, while improving the barrier properties of graphite to molten salts and molten metals with little or no change to the properties of graphite (especially its irradiation behavior).

[0018] The graphite processing method provided by the present invention has the following advantages over the prior art:

[0019] 1) It can effectively improve the barrier properties of graphite against molten salt and molten metal;

[0020] 2) The properties of graphite treated by the method of the present invention remain unchanged or change very little. The barrier properties of the treated graphite will not be reduced due to use. In particular, when used for graphite treatment in molten salt cores, the mechanical and thermal properties and irradiation behavior of graphite are minimally affected, which can eliminate or reduce the cost of re-evaluating graphite materials.

[0021] 3) The process is simple and the cost is low;

[0022] 4) It can not only be used to process nuclear graphite and solve the problem of nuclear graphite infiltration in molten salt reactors, but also to process graphite materials in energy storage systems, improve the barrier properties of graphite against molten salt or molten metal, and has obvious advantages over other processing methods.

[0023] In summary, according to the present invention, a graphite treatment method for preventing the infiltration of molten salt and molten metal is provided. This method is not only simple, but also improves the barrier properties of graphite against molten salt and molten metal without changing the properties of graphite. It has high economic value and good application prospects. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the internal structure of graphite with improved barrier properties prepared according to the method of the present invention. Detailed Implementation

[0025] The present invention will be further described below with reference to specific embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0026] Example 1

[0027] In this embodiment, phenol and furfural are mixed in a ratio of 1:1.5; then, 0.5% sodium carbonate (by weight of phenol) is added and dissolved in 10 times its weight of alcohol. The processed graphite component (50mm diameter, 100mm height) is placed in an impregnation vessel, and a vacuum is drawn until the vacuum reaches 1000Pa. Then, a well-dispersed precursor solution is introduced, ensuring the graphite is completely submerged. The vessel is then pressurized to 1MPa and maintained at this pressure for 1 hour before being removed. The graphite is then cured in a sealed container at 75°C for 200 hours, and then carefully dried at 150°C. Finally, it is heated to 1000°C in a nitrogen atmosphere furnace at a heating rate of 2°C / min and then cooled.

[0028] Example 2

[0029] In this embodiment, resorcinol and furfural were mixed at a ratio of 1:1.5; then, 2% (by weight of resorcinol) of hexamethylenetetramine was added and dissolved in 20 times its weight of isopropanol. The processed graphite component (50 mm in diameter and 100 mm in height) was immersed in the precursor solution, and a vacuum was applied until the liquid boiled, maintained for 20 minutes, and then removed. The graphite was then sealed in a closed container and cured at 120°C for 50 hours. After removal, it was carefully dried. Finally, it was heated to 1000°C in a nitrogen atmosphere furnace at a heating rate of 2°C / min, cooled, and then removed.

[0030] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of the invention. Various variations can be made to the above embodiments of the present invention. All simple and equivalent changes and modifications made in accordance with the claims and description of this application fall within the protection scope of the claims of this patent. All aspects not described in detail in this invention are conventional technical content.

Claims

1. A method for treating graphite to resist molten salt and molten metal infiltration, characterized by, The method comprises the following steps: S1: providing a solution of thermosetting resin monomer or oligomer, adding a small amount of catalyst to the solution to form a precursor, and immersing the precursor into the pores of graphite; the thermosetting resin comprises phenolic resin, furan resin, and polyimide; the solvent used to form the solution of thermosetting resin monomer or oligomer comprises water, ethanol, ethylene glycol, isopropyl alcohol, acetone, and petroleum ether; the mass ratio of the monomer to the solvent is between 0.01 and 0.5; the catalyst used is hexamethylenetetramine, inorganic base, or salt; the mass ratio of the catalyst to the thermosetting resin is 0-0.05; S2: converting the precursor immersed in the pores of graphite into an organic gel through solidification, and converting the organic gel into an organic nanostructure through drying; S3: carbonizing the organic nanostructure in the pores of graphite at a temperature of 500-1000 ℃ at a temperature rising rate of 0.01-10 ℃ / min to form a carbon nanostructure, thereby obtaining a graphite that can block the penetration of molten salt and molten metal; the carbon nanostructure formed is composed of carbon nanoparticles with a size ranging from 1 nm to 100 nm or fibrous carbon with a diameter ranging from 1 nm to 100 nm; the method uses a low-modulus carbon nanostructure to block the open pores in graphite, and has the characteristics of super-salt and super-molten metal resistance.

2. The graphite processing method according to claim 1, characterized by, In the step S1, the method for immersing the precursor into the pores of graphite comprises vacuum impregnation, pressure impregnation, or boiling under various pressures.

3. The graphite processing method according to claim 1, characterized by, In the step S2, the solidification comprises placing the graphite in a sealed container or placing the graphite in an atmosphere close to saturated solvent vapor to change the precursor from a liquid phase to a solid phase; the temperature of the solidification process is 50-200 ℃.

4. The graphite processing method according to claim 1, characterized by, In the step S2, the drying comprises keeping the graphite at a temperature of 0-300 ℃ after the solidification is completed to further remove the solvent in the precursor.

5. The graphite processing method according to claim 1, wherein In the step S3, the sample is placed in a vacuum environment or inert atmosphere for carbonization.

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