Radiation-resistant material, preparation method and application

Abstract

The invention provides an irradiation-resistant material as well as a preparation method and application thereof. The radiation-resistant material comprises a base body and a gradient composite coating arranged on the surface of the base body, the base body is an isostatic pressing graphite material, the gradient composite coating comprises a transition layer and a functional layer, and the transition layer is made of beta-SiC whiskers; the material of the functional layer is a SiC-Si3N4 composite layer, and the Si3N4 phase content in the functional layer is gradually increased from the position close to the transition layer to the position close to the outer side face, so that the SiC-Si3N4 gradient composite layer with continuous components is formed. The material has excellent corrosion (fused salt / helium) resistance, neutron irradiation resistance, thermal shock resistance and scouring resistance, is simple in preparation process and low in cost, is particularly suitable for reactor core complex structural parts of fourth-generation nuclear reactors such as fused salt reactors and high-temperature gas cooled reactors, and has a wide industrial application prospect.

Description

Technical Field

[0001] This invention relates to the field of nuclear energy materials technology, and in particular to radiation-resistant materials, preparation methods and applications. Background Technology

[0002] High-temperature nuclear reactors (HTGRs) are a type of advanced nuclear reactor characterized by high outlet coolant temperatures. They primarily include molten salt reactors and high-temperature gas-cooled reactors, representing a significant direction in fourth-generation nuclear power technology. HTGRs offer outstanding advantages such as high safety, high energy efficiency, and strong fuel adaptability. However, because HTGRs operate at temperatures exceeding 700°C, the core structural materials currently widely used, such as metal alloys and SiC-coated graphite materials, are insufficient to meet the requirements.

[0003] In molten salt reactors, the molten salt is primarily composed of fluoride salts. Molten fluoride ions can cause grain boundary corrosion in metallic alloys (such as Hastelloy-N) and also exhibit penetrating corrosion on traditional SiC ceramics, affecting the structural stability of the core materials and consequently compromising their isolation performance. Secondly, under high-energy neutron flux irradiation, metallic alloys are prone to swelling and embrittlement, while the radiation dose resistance of graphite materials in traditional SiC coatings is typically below 15 dPa, insufficient to meet requirements. Finally, the mismatch in thermal expansion coefficients between the graphite matrix and the SiC ceramic coating easily leads to coating cracking and peeling during thermal cycling.

[0004] For high-temperature gas-cooled reactors (such as helium-cooled reactors), traditional metal alloys and SiC-coated graphite materials also face multiple challenges, including high-temperature helium gas erosion, fission product infiltration, high-temperature oxidation, and radiation damage. The low surface hardness, poor erosion resistance, and high porosity of traditional graphite materials lead to gas infiltration, severely impacting their service life and safety. The poor resistance to infiltration corrosion and severe high-temperature oxidation of metallic materials also limit their widespread use.

[0005] Currently, the industry's technological development focus is on the bonding performance between SiC coatings and graphite materials. For example, Chinese patent application number CN202010299210.0 discloses a composite high-temperature anti-oxidation coating for graphite materials used in nuclear reactors and its preparation method. It combines the embedding method and the molten salt method to prepare a Ti3SiC2 / SiC composite high-temperature anti-oxidation coating on the surface of graphite materials used in nuclear reactors. The preparation temperature is low, the composite coating has strong anti-oxidation ability, and the bonding strength between it and the graphite matrix material is high. The resulting composite coating has a small inner and large outer grain size.

[0006] However, the aforementioned technical solutions still struggle to achieve directional growth and reinforcement of SiC whiskers. Furthermore, the presence of metallic materials can affect the coating's oxidation resistance, impermeability, and bonding stability with the graphite matrix under high-radiation environments, leading to premature failure of the coating under multi-field coupling of irradiation, heat, mechanical, and chemical fields. Therefore, a graphite-based radiation-resistant material with a high-strength SiC ceramic coating is needed. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides radiation-resistant materials, preparation methods, and applications, which solve the problem of insufficient bonding between the coating and the graphite substrate, leading to easy failure under multi-field coupling environments of irradiation, heat, force, and chemistry.

[0008] In a first aspect, the present invention proposes a radiation-resistant material, comprising a substrate and a gradient composite coating disposed on the surface of the substrate, wherein the substrate is an isostatically pressed graphite material, and the gradient composite coating comprises a transition layer and a functional layer, wherein the transition layer is disposed between the substrate and the functional layer.

[0009] The transition layer is made of β-SiC whiskers;

[0010] The functional layer is made of SiC-Si3N4 composite material. The Si3N4 phase content gradually increases from near the transition layer to near the outer surface of the functional layer, forming a SiC-Si3N4 gradient composite layer with continuous composition.

[0011] Furthermore, the density of the matrix is ​​≥1.85 g / cm³. 3 Porosity ≤ 5%.

[0012] Preferably, the β-SiC whiskers in the transition layer grow in a <1010> orientation.

[0013] Preferably, the Si3N4 phase content in the outermost region of the functional layer is 40% to 45%.

[0015] Secondly, this invention proposes a method for preparing a radiation-resistant material, comprising the following steps:

[0016] S1. Substrate pretreatment: The graphite substrate is machined, ultrasonically cleaned and dried to make the substrate surface smooth and remove impurities.

[0017] S2. Preparation of precursor solution: Under an inert atmosphere, polycarbosilane and polysilazane are dissolved in anhydrous xylene to prepare a mixed solution with a solid content of 50-60 wt%; then, nano-γ-Al2O3 powder accounting for 1.5-2.0 wt% of the total mass of the precursor solids is added to the solution and stirred for more than 12 hours to make it uniformly mixed.

[0018] S3. Solution spraying: In a dry air or nitrogen environment, the precursor solution is uniformly sprayed onto the pretreated substrate surface using an air spraying method.

[0019] S4. Crosslinking and curing: The sprayed substrate is placed in a sintering furnace and heated to 800°C at a rate of 1-2°C / min under the protection of high-purity nitrogen, and held at that temperature for 60-90 minutes to complete the crosslinking reaction of the precursor.

[0020] S5. In-situ nitriding sintering: Under a high-purity nitrogen atmosphere, the temperature is raised to 1450℃ at a rate of 3-5℃ / min and held for 120-180 minutes, then naturally cooled to room temperature.

[0021] Furthermore, step S1 also includes sandblasting roughening to increase the roughness of the substrate surface and thus increase the adhesion to the gradient composite coating.

[0022] Preferably, in step S2, the mass ratio of polycarbosilane to polysilazane is 55-65:45-35.

[0023] Preferably, in step S3, the thickness of the wet film sprayed on the substrate surface is controlled to be 200-250 μm.

[0024] Furthermore, step S5 involves in-situ sintering in the same sintering furnace used in step S4, thereby completing the sintering of the gradient composite coating in one step.

[0026] Thirdly, the present invention provides a radiation-resistant material for use in molten salt reactor fuel element positioning grids and heat exchanger liners.

[0027] It is also used as the lining of fuel balls, prism blocks, and hot gas ducts in high-temperature gas-cooled reactors, as well as the surface coating of control rod guide tubes.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. This invention forms a SiC-Si3N4 composite coating structure by sintering a mixed solution of polycarbosilane (PCS) and polysilazane (PSN) precursor. This combines the excellent high-temperature oxidation resistance and radiation swelling resistance of Si3N4 with the thermal conductivity and thermal shock resistance of SiC. Furthermore, the method of pre-spraying the precursor solution before sintering allows the precursor solution to penetrate into the graphite micropores, forming an interlocking structure, thereby significantly improving the bonding strength and preventing interfacial delamination.

[0030] 2. This invention employs a gradient heating heat treatment method, utilizing the lower pyrolysis temperature of polycarbosilane and the higher pyrolysis temperature of polysilazane. Polycarbosilane (PCS) begins to pyrolyze to generate SiC whiskers first. At this point, the SiC whiskers tend to adhere to the side where the substrate is located, thus forming an enrichment. This results in a decreasing SiC content in the gradient composite coating from the substrate surface to the outer side. Conversely, as the temperature rises, polysilazane (PSN) begins to pyrolyze to generate Si3N4, which is more abundant on the outer side of the gradient composite coating. Thus, the surface Si3N4-rich layer provides better resistance to permeation corrosion, high-temperature oxidation, and radiation swelling, while the inner SiC-rich layer provides excellent thermal conductivity and thermal shock resistance. This makes it suitable not only for the fluoride corrosion environment of molten salt reactors but also for the helium scouring and oxidation environment of high-temperature gas-cooled reactors, thus exhibiting better adaptability and suitability for various radiation-thermal-mechanical-chemical multi-field coupling environments in high-temperature nuclear reactors.

[0031] 3. The present invention also adds nano-γ-Al2O3, which reacts with carbon or silicon during high-temperature sintering to form local liquid phase micro-regions, promoting heterogeneous nucleation and directional growth of β-SiC whiskers, thereby constructing a tough transition zone between the functional layer and the substrate interface, and improving the bonding strength between the gradient composite coating and the graphite substrate. Attached Figure Description

[0032] Figure 1 This is a process flow diagram of an embodiment of the present invention. Detailed Implementation

[0033] The technical solutions of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0034] Example 1:

[0035] The radiation-resistant material in this embodiment is suitable for the positioning grid of fuel elements in molten salt reactors. The specific preparation method is as follows:

[0036] (1) Matrix pretreatment: A matrix with a density of 1.9 g / cm³ was selected. 3 Isostatic graphite with a porosity of 4% is processed into a positioning grid with an open area of ​​65%, and then subjected to sandblasting roughening and cleaning treatment.

[0037] (2) Preparation of precursor solution: In a nitrogen glove box, PCS and PSN were mixed at a mass ratio of 60:40 and dissolved in anhydrous xylene to prepare a mixed solution with a solid content of 55wt%; then nano γ-Al2O3 powder accounting for 1.8wt% of the total mass of the precursor solid was added to the solution and magnetically stirred for 12 hours.

[0038] (3) Solution spraying: Low-pressure spraying is carried out in a nitrogen glove box using air spraying method to uniformly spray the precursor solution onto the pretreated substrate surface, and the wet film thickness is controlled to be 220 μm.

[0039] (4) Curing and sintering: The coated substrate is placed in an atmosphere sintering furnace and heated to 800°C at a rate of 1.5°C / min under the protection of high-purity nitrogen. The temperature is held for 75 minutes, then heated to 1450°C at a rate of 4°C / min and held for 150 minutes. The substrate is then cooled with the furnace.

[0041] Example 2:

[0042] The radiation-resistant material in this embodiment is suitable for the lining of a molten salt reactor heat exchanger, and the specific preparation method is as follows:

[0043] (1) Matrix pretreatment: A matrix with a density of 2.1 g / cm³ was selected. 3 Isostatic graphite with a porosity of 3% was processed into tubular inner lining parts and then subjected to sandblasting roughening and cleaning treatment.

[0044] (2) Preparation of precursor solution: In a nitrogen glove box, PCS and PSN were mixed at a mass ratio of 55:45 and dissolved in anhydrous xylene to prepare a mixed solution with a solid content of 50 wt%; then nano γ-Al2O3 powder accounting for 1.5 wt% of the total mass of the precursor solid was added to the solution and magnetically stirred for 13 hours.

[0045] (3) Solution spraying: Low-pressure spraying is carried out in a nitrogen glove box using air spraying method to uniformly spray the precursor solution onto the pretreated substrate surface, and control the wet film thickness to be 200 μm.

[0046] (4) Curing and sintering: The coated substrate is placed in an atmosphere sintering furnace and heated to 800°C at a rate of 1°C / min under the protection of high-purity nitrogen. The temperature is held for 60 minutes, then heated to 1450°C at a rate of 3°C / min and held for 120 minutes. The substrate is then cooled with the furnace.

[0048] Comparative Example 1:

[0049] The application and graphite substrate of this comparative example are the same as those in Example 1. The difference is that the SiC coating is prepared by a conventional CVD process and the coating thickness is 220 μm, which is the same as in Example 1.

[0051] The parameters of Examples 1, 2 and Comparative Example 1 were tested according to the following standards:

[0052] Corrosion test: Immerse in static FLiBe molten salt at 700℃ for 6000 hours to detect the average corrosion rate.

[0053] Irradiation test: After irradiation with 30 dpa fast neutrons, the retention rate of the component's bending strength was tested.

[0054] Thermal shock test: A water-quenched thermal shock test was conducted at a temperature difference of 800℃ to calculate the number of cycles required for the coating to peel off.

[0055] The test results are shown in Table 1:

[0056]

[0057] Example 3:

[0058] The radiation-resistant material in this embodiment is suitable for the inner lining of the hot gas duct of a high-temperature gas-cooled reactor. The specific preparation method is as follows:

[0059] (1) Matrix pretreatment: A matrix with a density of 2.0 g / cm³ was selected. 3 Isostatic graphite with a porosity of 3% was processed into tubular inner lining parts and then subjected to sandblasting roughening and cleaning treatment.

[0060] (2) Preparation of precursor solution: In a nitrogen glove box, PCS and PSN were mixed at a mass ratio of 65:35 and dissolved in anhydrous xylene to prepare a mixed solution with a solid content of 60 wt%; then, nano γ-Al2O3 powder accounting for 2.0 wt% of the total mass of the precursor solid was added to the solution and magnetically stirred for 14 hours.

[0061] (3) Solution spraying: Low-pressure spraying is carried out in a nitrogen glove box using air spraying method to uniformly spray the precursor solution onto the pretreated substrate surface, and the wet film thickness is controlled to be 250 μm.

[0062] (4) Curing and sintering: The coated substrate is placed in an atmosphere sintering furnace and heated to 800°C at a rate of 2°C / min under the protection of high-purity nitrogen. The temperature is held for 90 minutes, then heated to 1450°C at a rate of 5°C / min and held for 180 minutes. The substrate is then cooled with the furnace.

[0064] Example 4:

[0065] The radiation-resistant material in this embodiment is suitable for the inner lining of fuel prism blocks in high-temperature gas-cooled reactors. The specific preparation method is as follows:

[0066] (1) Matrix pretreatment: A matrix with a density of 1.9 g / cm³ was selected. 3 Isostatic graphite with a porosity of 4% was processed into a tubular inner lining with a regular hexagonal cross section, and then subjected to sandblasting roughening and cleaning treatment.

[0067] (2) Preparation of precursor solution: In a nitrogen glove box, PCS and PSN were mixed at a mass ratio of 60:40 and dissolved in anhydrous xylene to prepare a mixed solution with a solid content of 55wt%; then nano γ-Al2O3 powder accounting for 1.8wt% of the total mass of the precursor solid was added to the solution and magnetically stirred for 12 hours.

[0068] (3) Solution spraying: Low-pressure spraying is carried out in a nitrogen glove box using air spraying method to uniformly spray the precursor solution onto the pretreated substrate surface, and the wet film thickness is controlled to be 220 μm.

[0069] (4) Curing and sintering: The coated substrate is placed in an atmosphere sintering furnace and heated to 800°C at a rate of 2°C / min under the protection of high-purity nitrogen. The temperature is held for 90 minutes, then heated to 1450°C at a rate of 5°C / min and held for 180 minutes. The substrate is then cooled with the furnace.

[0071] Comparative Example 2:

[0072] The application and graphite substrate of this comparative example are the same as those in Example 4. The difference is that the SiC coating is prepared by a conventional CVD process, and the coating thickness is 220 μm, the same as in Example 4.

[0074] The parameters of Examples 3 and 4 and Comparative Example 2 were tested according to the following standards:

[0075] Erosion resistance test: The surface coating wear was measured for 3000 hours at 800℃ and a helium flow rate of 100 m / s.

[0076] High-temperature oxidation test: Expose the product to air at 1000℃ for 500 hours and detect the weight gain due to oxidation.

[0077] Irradiation compatibility test: The swelling rate of the graphite matrix was measured after 20 dpa neutron irradiation.

[0078] The test results are shown in Table 2:

[0079]

[0080] As shown in Tables 1 and 2, for high-temperature nuclear reactors, whether molten salt reactors or high-temperature gas-cooled reactors, the test results of the radiation-resistant material of the present invention are significantly better than those of the existing CVD-SiC coating material, which fully demonstrates the technical advantages of the present invention.

[0081] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A radiation-resistant material, characterized in that, The invention includes a substrate and a gradient composite coating disposed on the surface of the substrate. The substrate is an isostatically pressed graphite material, and the gradient composite coating includes a transition layer and a functional layer, wherein the transition layer is disposed between the substrate and the functional layer. The transition layer is made of β-SiC whiskers; The functional layer is made of SiC-Si3N4 composite material. The Si3N4 phase content gradually increases from near the transition layer to near the outer surface of the functional layer, forming a SiC-Si3N4 gradient composite layer with continuous composition.

2. The radiation-resistant material as described in claim 1, characterized in that: The density of the matrix is ​​≥1.85 g / cm³. 3 Porosity ≤ 5%.

3. The radiation-resistant material as described in claim 1, characterized in that: The β-SiC whiskers in the transition layer grow in a <1010> orientation.

4. The radiation-resistant material as described in claim 1, characterized in that: The Si3N4 phase content in the outermost region of the functional layer is 40% to 45%.

5. A method for preparing the radiation-resistant material as described in claim 1, characterized in that, Includes the following steps: S1. Substrate pretreatment: The graphite substrate is machined, ultrasonically cleaned and dried to make the substrate surface smooth and remove impurities. S2. Preparation of precursor solution: Under an inert atmosphere, polycarbosilane and polysilazane are dissolved in anhydrous xylene to prepare a mixed solution with a solid content of 50-60 wt%; then, nano-γ-Al2O3 powder accounting for 1.5-2.0 wt% of the total mass of the precursor solids is added to the solution and stirred for more than 12 hours to make it uniformly mixed. S3. Solution spraying: In a dry air or nitrogen environment, the precursor solution is uniformly sprayed onto the pretreated substrate surface using an air spraying method. S4. Crosslinking and curing: The sprayed substrate is placed in a sintering furnace and heated to 800°C at a rate of 1-2°C / min under the protection of high-purity nitrogen, and held at that temperature for 60-90 minutes to complete the crosslinking reaction of the precursor. S5. In-situ nitriding sintering: Under a high-purity nitrogen atmosphere, the temperature is raised to 1450℃ at a rate of 3-5℃ / min and held for 120-180 minutes, then naturally cooled to room temperature.

6. The method for preparing the radiation-resistant material as described in claim 5, characterized in that: Step S1 also includes sandblasting roughening to increase the roughness of the substrate surface and thus increase the adhesion to the gradient composite coating.

7. The method for preparing the radiation-resistant material as described in claim 5, characterized in that: In step S2, the mass ratio of polycarbosilane to polysilazane is 55-65:45-35.

8. The method for preparing the radiation-resistant material as described in claim 5, characterized in that: In step S3, the thickness of the wet film sprayed on the substrate surface is controlled to be 200-250 μm.

9. The method for preparing the radiation-resistant material as described in claim 5, characterized in that: In step S5, in-situ sintering is carried out in the same sintering furnace used in step S4, and the sintering of the gradient composite coating is completed in one step.

10. A radiation-resistant material as described in claim 1, characterized in that: It is used in the positioning grids of fuel elements and the lining of heat exchangers in molten salt reactors; it is also used in the lining of fuel balls, prism blocks, and hot gas ducts in high-temperature gas-cooled reactors, as well as the surface coating of control rod guide tubes.

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