Process for the preparation of spherical particles of uranium nitride and use thereof

Abstract

The application discloses a preparation method of uranium nitride spherical particles, and comprises the following steps: mixing a carbon source and a solution to prepare gel particles; the carbon source comprises diamond powder; the gel particles are pretreated and subjected to carbonthermal reduction and nitriding treatment to obtain the uranium nitride spherical particles. The preparation method can effectively control the C / U molar ratio, and the prepared uranium nitride spherical particles have the advantages of compact structure, smooth surface and high purity.

Description

Technical Field

[0001] This invention relates to the field of nitride nuclear fuel technology, specifically to a method for preparing uranium nitride spherical particles and their application. Background Technology

[0002] Uranium nitride (UN) possesses properties such as a high melting point, high uranium density, high thermal conductivity, good compatibility, and easy recyclability, making it a promising candidate to replace uranium dioxide (UO2) in future advanced micro-nuclear reactors. Uranium nitride-coated fuel (UN-TRISO) particles not only exhibit high thermal conductivity and good radiation stability but also effectively prevent the release of fission products, making them suitable for advanced micro-reactors such as gas-cooled microreactors.

[0003] Currently, the common technical route for preparing uranium nitride spherical particles is a combination of gelation and carbothermal reduction nitridation. Gelation is the shaping process, including internal and external gelation. Carbothermal reduction nitridation is the synthesis route. However, in existing technologies, the gel solution used in the internal gelation process is temperature-sensitive, requiring preparation and storage in an environment of 0–4°C, which places high demands on equipment and processes, hindering large-scale production.

[0004] In the carbothermal reduction nitridation route, the stoichiometric ratio of carbon to UO3 required for UN preparation is mostly 2.5. When using the internal gelation process, a ratio of 2.65 is commonly used to ensure sufficient carbon source. In an inert gas environment, the organic matter (raw material) in the formulation will decompose to generate carbon during heat treatment, further increasing the uncertainty of the C / U molar ratio in the particles. Existing research shows that precise control of the C / U molar ratio is a crucial factor in the preparation of high-purity UN using the carbothermal reduction nitridation method. Furthermore, in studies on the preparation of spherical uranium nitride particles using external gelation combined with carbothermal reduction nitridation technology, the carbon-containing uranium gel particles may crack during heat treatment in an inert gas environment due to the high organic matter content.

[0005] To remove organic matter as completely as possible, it is currently necessary to increase the heat treatment temperature in air or extend the pretreatment time. However, excessively high heat treatment temperatures in air can cause oxidation of the carbon source within the particles, leading to insufficient subsequent carbothermic reduction reactions and impure product phases. Increasing the amount of carbon source to ensure sufficient carbon source for subsequent reactions, on the other hand, results in a higher concentration of carbon impurities in the product. Furthermore, the density of uranium nitride spherical particles prepared by the above methods needs further improvement.

[0006] Therefore, there is an urgent need for a method to prepare uranium nitride spherical particles that can effectively control the C / U molar ratio, thereby further improving the purity, compactness and other properties of uranium nitride spherical particles. Summary of the Invention

[0007] The present invention aims to address at least one of the technical problems existing in the prior art to a certain extent. To this end, the present invention provides a method for preparing uranium nitride spherical particles. This method can effectively control the C / U molar ratio, resulting in uranium nitride spherical particles with a dense structure, smooth surface, and excellent performance.

[0008] Therefore, in a first aspect, the present invention provides a method for preparing uranium nitride spherical particles, comprising the following steps:

[0009] Gel particles were prepared by mixing a carbon source and a solution; the carbon source included diamond powder.

[0010] The gel particles were pretreated and then subjected to carbothermic reduction nitridation to obtain spherical uranium nitride particles.

[0011] Therefore, the preparation method of the present invention can effectively control the C / U molar ratio, and the prepared uranium nitride spherical particles have a dense structure, high purity, and excellent overall performance.

[0012] In some embodiments, the diamond powder satisfies at least one of the following:

[0013] (1) The average particle size of diamond powder is 0.1–10 μm;

[0014] (2) The specific surface area of ​​diamond powder is 15-30 m². 2 / g.

[0015] In some embodiments, the C / U molar ratio of the gel particles is 2.4 to 2.6.

[0016] In some embodiments, the pretreatment is performed in an air atmosphere; the pretreatment satisfies at least one of the following:

[0017] (A) The heating rate for pretreatment is 0.5–2 °C / min;

[0018] (B) The pretreatment temperature is 360–560℃;

[0019] (C) The pretreatment time is 3 to 7 hours.

[0020] In some embodiments, the preparation method of gel particles includes an internal gelation process or an external gelation process, preferably an external gelation process; in the preparation method of the external gelation process, the solution includes at least one of the following: uranyl nitrate solution, urea, ammonium nitrate, tetrahydrofurfuryl alcohol, and polyvinyl alcohol solution.

[0021] In some embodiments, the solution further includes a dispersant; the dispersant satisfies at least one of the following:

[0022] (a) The dispersant includes at least one of ammonium citrate, polypropylene pyrrolidone, polyethyleneimine, ammonium polyacrylate and tetramethylammonium hydroxide, preferably polyethyleneimine or ammonium polyacrylate;

[0023] (b) The amount of dispersant added is 0.07 to 0.09% of the mass of the carbon source.

[0024] In some embodiments, the carbothermic reduction nitriding treatment step includes:

[0025] The uranium nitride spherical particles are obtained by roasting, carbonization, and nitriding; the carbothermic reduction nitriding treatment satisfies at least one of the following:

[0026] (i) The calcination process is carried out in a protective atmosphere; the protective atmosphere includes argon and / or helium; the calcination process includes: heating at a rate of 0.5 °C / min and holding at 200 °C, 400 °C and 500 °C for 1 h respectively;

[0027] (ii) The carbonization process is carried out in a protective atmosphere; the protective atmosphere includes argon and / or helium; the carbonization process includes: heating to 600°C at 0.5°C / min, then heating to 1400°C at 5°C / min, and then heating to 1500°C at 0.5°C / min.

[0028] (iii) Nitriding is carried out in nitrogen gas; nitriding includes holding at 1500-2000℃ for 3-7 hours.

[0029] In some embodiments, after the carbothermic reduction nitriding treatment, a heat preservation treatment is further included; the heating rate of the heat preservation treatment is 5℃ / min, the temperature is 1750~2000℃, and the heat preservation time is 4~6h.

[0030] In a second aspect, the present invention provides spherical uranium nitride particles, comprising spherical uranium nitride particles prepared by the method of the first aspect. Therefore, the spherical uranium nitride particles of the present invention have high purity, dense structure, and excellent performance.

[0031] In a third aspect of the invention, the invention proposes the use of uranium nitride spherical particles obtained by the preparation method of the first aspect, or the uranium nitride spherical particles of the second aspect, in nuclear fuel or nuclear materials.

[0032] Compared with the prior art, the beneficial technical effects achieved by the present invention are as follows:

[0033] The carbon source of this invention uses diamond powder to prepare uranium nitride spherical particles, which can obtain uranium nitride spherical particles with dense structure and good performance at a higher pretreatment temperature and a shorter processing time. Furthermore, the C / U molar ratio is accurately controlled during the carbothermic reduction nitridation process to obtain uranium nitride spherical particles with high purity.

[0034] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0035] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0036] Figure 1 The diagram shows the dispersion effect of gel particles using different dispersants in this invention.

[0037] Figure 2 The images show the microstructure of uranium nitride spherical particles after pretreatment at different temperatures for 5 hours in Comparative Example 1 of the present invention; wherein (a) and (a') are treated at 300℃, (b) and (b') are treated at 350℃, (c) and (c') are treated at 400℃, (d) and (d') are treated at 450℃, and (e) and (e') are treated at 500℃.

[0038] Figure 3 These are optical photographs of uranium nitride spherical particles after pretreatment with different carbon sources in Comparative Example 1 and Example 5 of the present invention; wherein, (a) is the uranium nitride spherical particle of Comparative Example 1, and (b) is the uranium nitride spherical particle of Example 5.

[0039] Figure 4 Optical photographs of uranium nitride spherical particles prepared in Examples 2 to 4 of the present invention; wherein, (a) is a uranium nitride spherical particle of Example 2, (b) is a uranium nitride spherical particle of Example 3, and (c) is a uranium nitride spherical particle of Example 4;

[0040] Figure 5 The XRD patterns of uranium nitride spherical particles prepared in Examples 2 to 4 of the present invention are shown; wherein, 1500℃ corresponds to Example 2, 1750℃ corresponds to Example 3, and 2000℃ corresponds to Example 4.

[0041] Figure 6 Optical photographs of uranium nitride spherical particles prepared with different C / U molar ratios in Comparative Example 2 of the present invention; wherein, (a) is a C / U molar ratio of 2.1, (b) is a C / U molar ratio of 2.3, (c) is a C / U molar ratio of 2.5, (d) is a C / U molar ratio of 2.7, and (e) is a C / U molar ratio of 2.9;

[0042] Figure 7 A micrograph of the spherical uranium nitride particles prepared in Comparative Example 3 of the present invention;

[0043] Figure 8Microscopic images of uranium nitride spherical particles prepared in Examples 2 to 4 of the present invention; wherein, (a) and (d) are uranium nitride spherical particles of Example 2, (b) and (e) are uranium nitride spherical particles of Example 3, and (c) and (f) are uranium nitride spherical particles of Example 4. Detailed Implementation

[0044] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0045] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. Furthermore, in the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0046] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0047] In this document, the terms “comprising” or “including” are open-ended expressions, meaning that they include the contents specified in this invention, but do not exclude other aspects.

[0048] In a first aspect of the present invention, a method for preparing uranium nitride spherical particles is provided, comprising the following steps:

[0049] Gel particles were prepared by mixing a carbon source and a solution; the carbon source included diamond powder.

[0050] The gel particles were pretreated and then subjected to carbothermic reduction nitridation to obtain spherical uranium nitride particles.

[0051] In this invention, since the thermal stability of diamond powder is generally higher than that of amorphous carbon, using diamond powder as a carbon source can effectively increase the pretreatment temperature of the gel particles without causing oxidation. During the pretreatment stage, carbon- and oxygen-containing organic matter in the gel particles undergoes oxidative decomposition and release, being completely eliminated as much as possible. This effectively prevents the formation of residual carbon during the subsequent carbothermic reduction nitriding process, ensuring that almost all carbon in the carbothermic reduction nitriding process comes from the carbon source. This allows for better control of the C / U molar ratio in the uranium nitride spherical particles, preventing particle cracking during subsequent processing and ensuring the purity of the final product. Furthermore, the inventors have found that using diamond powder as a carbon source to prepare uranium nitride spherical particles can significantly increase their density, with an apparent density reaching 11.45 g / cm³. 3 The apparent density of uranium nitride spherical particles prepared using amorphous carbon powder as a carbon source was 9.15 g / cm³. 3 Therefore, the preparation method of the present invention can effectively control the C / U molar ratio, and obtain uranium nitride spherical particles with high purity, dense structure and excellent overall performance.

[0052] In some embodiments of the present invention, the diamond powder satisfies at least one of the following:

[0053] (1) The average particle size of diamond powder is 0.1–10 μm;

[0054] (2) The specific surface area of ​​diamond powder is 15-30 m². 2 / g.

[0055] As an example, the average particle size of diamond powder is 0.1μm, 0.5μm, 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, etc.

[0056] As an example, the specific surface area of ​​diamond powder is 15m². 2 / g、17m 2 / g、19m 2 / g、21m 2 / g、23m 2 / g、25m 2 / g、27m 2 / g、29m 2 / g、30m 2 / g etc.

[0057] In some embodiments of the present invention, the C / U molar ratio of the gel particles is 2.4 to 2.6, preferably 2.6.

[0058] In the preparation of uranium nitride spherical particles, accurately controlling the C / U molar ratio is crucial for obtaining high-purity UN. Therefore, the C / U molar ratio of the gel particles of this invention is 2.4 to 2.6, preferably 2.6. This ensures that the subsequent carbothermic reduction reaction proceeds fully while reducing the carbon impurity content in the uranium nitride spherical particles, thereby obtaining high-purity uranium nitride spherical particles.

[0059] For example, the C / U molar ratios are 2.4, 2.42, 2.44, 2.46, 2.48, 2.50, 2.52, 2.54, 2.56, 2.58, 2.6, etc.

[0060] In some embodiments of the present invention, the preparation method of gel particles includes an internal gelation process or an external gelation process, preferably an external gelation process; in the preparation method of the external gelation process, the solution includes at least one of the following: uranyl nitrate solution, urea, ammonium nitrate, tetrahydrofurfuryl alcohol, and polyvinyl alcohol solution.

[0061] In some embodiments of the present invention, the pretreatment is performed in an air atmosphere; the pretreatment satisfies at least one of the following:

[0062] (A) The heating rate of the pretreatment is 0.5 to 2 °C / min, preferably 1 °C / min;

[0063] (B) The pretreatment temperature is 360–560°C, preferably 400–450°C;

[0064] (C) The pretreatment time is 3 to 7 hours, preferably 5 hours.

[0065] In this invention, the gel particles are heat-treated at 360-560°C for 3-7 hours in an air atmosphere, which can oxidize and decompose the organic matter in the solution and release it, prevent the organic matter from generating residual carbon in the subsequent carbothermic reduction nitridation process, which would make it difficult to control the C / U molar ratio, and at the same time avoid the doping of carbon impurities into the uranium nitride spherical particles.

[0066] When the gel particles are prepared using an internal gelation process, a portion of the urea in the solution reacts with uranyl ions (UO2). 2+In addition to complexation, some of the urea and urea-formaldehyde resin react with hexamethylenetetramine (HMTA) to form urea-formaldehyde resin. After sol-gel coagulation, organic matter such as urea and urea-formaldehyde resin remains inside the gel particles, which cannot be completely removed by washing processes. To ensure the integrity of the particles during heat treatment, the heating rate must be sufficiently slow under inert gas protection. In the preparation process of external gelation, the presence of polyvinyl alcohol (PVA) makes spherical particles prone to cracking during heat treatment in an inert gas environment. The decomposition behavior of PVA under different atmospheres is the main factor affecting the integrity and cracking of UO3·C particles. Under an inert atmosphere, PVA pyrolysis releases a large amount of gas, and the residual carbon produced causes channel blockage, preventing timely gas discharge, thus making UO3·C particles prone to cracking. Under an air atmosphere, PVA undergoes oxidative decomposition, leaving less carbon residue, and in-situ decomposition can also create gas channels, making UO3·C particles less prone to cracking. Therefore, pretreating carbon-containing uranium gel particles in an air atmosphere at a certain temperature can effectively prevent cracking and ensure particle integrity.

[0067] As an example, the pretreatment heating rates are 0.5℃ / min, 0.8℃ / min, 1.0℃ / min, 1.2℃ / min, 1.5℃ / min, 1.7℃ / min, 2℃ / min, etc.

[0068] As an example, the pretreatment temperatures are 360℃, 380℃, 400℃, 420℃, 440℃, 460℃, 480℃, 500℃, 520℃, 540℃, 560℃, etc.

[0069] As an example, the preprocessing time is 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, etc.

[0070] Therefore, the preparation method of the present invention can effectively control the C / U molar ratio and obtain spherical uranium nitride particles with high purity and good performance.

[0071] In some embodiments of the present invention, the solution further includes a dispersant; the dispersant satisfies at least one of the following:

[0072] (a) The dispersant includes at least one of ammonium citrate, polypropylene pyrrolidone, polyethyleneimine, ammonium polyacrylate and tetramethylammonium hydroxide, preferably polyethyleneimine or ammonium polyacrylate;

[0073] (b) The amount of dispersant added is 0.07 to 0.09% of the mass of the carbon source.

[0074] The uranyl nitrate used in the sol-gel process for preparing uranium nitrate is acidic, with a pH typically around 2. After the carbon source is added, severe agglomeration prevents the formation of a stable suspension. Powder stabilization mechanisms typically include electrostatic stabilization, steric hindrance stabilization, electrostatic-steric hindrance stabilization, exhaustion stabilization, and half-vacancy stabilization. The inventors conducted dispersion experiments using five dispersants: ammonium citrate, polypropylene pyrrolidone, polyethyleneimine, ammonium polyacrylate, and tetramethylammonium hydroxide (the suspensions were prepared and observed after 0.5 hours) to improve the dispersibility of the carbon source powder in acidic solutions. Among these, polyethyleneimine and ammonium polyacrylate showed better dispersion effects in acidic solutions with a pH of 2. Figure 1 As shown.

[0075] In some embodiments of the present invention, after the gel particles are prepared, the process further includes washing, drying, and heat treatment; the heat treatment includes drying the gel particles at 60-80°C for 12 hours.

[0076] In some embodiments of the present invention, the carbothermic reduction nitriding treatment step includes:

[0077] The uranium nitride spherical particles are obtained by roasting, carbonization, and nitriding; the carbothermic reduction nitriding treatment satisfies at least one of the following:

[0078] (i) The calcination process is carried out in a protective atmosphere; the protective atmosphere includes argon and / or helium; the calcination process includes: heating at a rate of 0.5 °C / min and holding at 200 °C, 400 °C and 500 °C for 1 h respectively;

[0079] (ii) The carbonization process is carried out in a protective atmosphere; the protective atmosphere includes argon and / or helium; the carbonization process includes: heating to 600°C at 0.5°C / min, then heating to 1400°C at 5°C / min, and then heating to 1500°C at 0.5°C / min.

[0080] (iii) The nitriding treatment is carried out in nitrogen gas; the nitriding treatment includes: holding at 1500-2000℃ for 3-7 hours, preferably at 1500℃ for 5 hours.

[0081] In this invention, after carbonization, nitriding can be performed at the same temperature and with a different nitrogen atmosphere to avoid excessively rapid reaction due to increased temperature, which could lead to uneven particle composition and structure and cracking.

[0082] In some embodiments of the present invention, after the nitriding treatment is completed, a protective atmosphere is switched and the temperature is reduced to room temperature at a cooling rate of 10°C / min to obtain spherical uranium nitride particles.

[0083] In some embodiments of the present invention, after the carbothermic reduction nitriding treatment, a heat preservation treatment is further included; the heating rate of the heat preservation treatment is 5°C / min, the temperature is 1750-2000°C, and the heat preservation time is 4-6 hours. The heat preservation treatment is mainly used for particle densification. The role of the nitrogen atmosphere at this time is to prevent the solid solution of carbon elements, so as to ensure the purity of uranium nitride, that is, to reduce the carbon impurity content.

[0084] In a second aspect of the present invention, a spherical uranium nitride particle is provided, comprising the uranium nitride spherical particle prepared by the method of the first aspect. Therefore, the uranium nitride spherical particle of the present invention has high purity, dense structure, and excellent performance.

[0085] In a third aspect of the present invention, the present invention proposes the application of uranium nitride spherical particles obtained by the preparation method of the first aspect, or the application of uranium nitride spherical particles of the second aspect in nuclear fuel or nuclear materials.

[0086] Those skilled in the art will understand that the features and advantages described above for spherical uranium nitride particles also apply to this application, and will not be repeated here.

[0087] The present invention will be explained below with reference to embodiments. Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be considered as limiting the scope of the invention. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0088] Example 1: Preparation of carbon-containing uranium gel particles by external gelation process

[0089] Urea was added to a 2.38 mol / L uranyl nitrate solution (ADUN), with a urea to U molar ratio of 2.35. After thorough mixing, the solution was placed in a water bath and heated to 85°C for 2 hours. Then, ammonium nitrate (0.432 molar ratio to U) was added, along with polyethyleneimine (PEI, 0.09% of the diamond powder) as a dispersant. The mixture was stirred until homogeneous, forming a final solution. Then, a solution with a specific surface area of ​​17.8 m² was obtained. 2A small, continuous amount of diamond powder (C / U molar ratio of 2.6) with an average particle size of 0.22 μm was added to the mixture while stirring and simultaneously sonicating for at least 20 minutes to ensure thorough dispersion of the carbon powder. The prepared carbon-uranium colloid solution was added to a dispersion container, with the flow rate controlled at 8 mL / min using a high-precision valve. The colloid solution was extruded through a nozzle (0.60 mm inner diameter) and jetted into equal-volume segments under the action of a vibrator (100 Hz excitation frequency). These segments then formed dispersed spherical droplets under surface tension. During dispersion, a laser holographic monitoring system was used to assist in measuring the size and out-of-roundness of the droplets. The droplets passed through an air zone (10 cm high) and entered an ammonia zone (10 cm high). At this point, the substances on the droplet surface reacted with the ammonia gas to form a gel layer. The spherical particles of the surface gel continued to fall, colliding with the ammonia water until they were submerged, and continued to react with the ammonia water. After a thorough aging reaction for 12 hours, gel particles were obtained. The fully aged gel particles were washed three times with deionized water and dried in an oven at 60°C for 12 hours to obtain carbon-containing uranium gel particles.

[0090] Example 2: Preparation of spherical uranium nitride particles

[0091] Carbon-containing uranium gel particles were obtained according to the preparation method of Example 1, and then subjected to pretreatment and carbothermic reduction nitridation treatment, as follows:

[0092] Pretreatment: In an air atmosphere, heat to 400℃ at a heating rate of 1℃ / min and hold for 5 hours, then remove from the furnace at room temperature.

[0093] Calcination treatment: In an argon atmosphere, the temperature was increased at a rate of 0.5℃ / min and held at 200℃, 400℃ and 500℃ for 1 hour respectively.

[0094] Carbonization treatment: In an argon atmosphere, the temperature is increased to 600℃ at a rate of 0.5℃ / min, then increased to 1400℃ at a rate of 5℃ / min, and then increased to 1500℃ at a rate of 0.5℃ / min.

[0095] Nitriding treatment: The mixture was held at 1500℃ for 5 hours in a nitrogen atmosphere; finally, it was cooled to room temperature at a rate of 10℃ / min in an argon atmosphere to obtain spherical uranium nitride particles, such as... Figure 4 As shown in (a), the XRD pattern of the spherical uranium nitride particles is as follows: Figure 5 As shown.

[0096] Example 3: Preparation of spherical uranium nitride particles

[0097] Carbon-containing uranium gel particles were obtained according to the preparation method in Example 1, and then pretreated and subjected to carbothermal reduction nitridation treatment, as follows:

[0098] Pretreatment: In an air atmosphere, heat to 400℃ at a heating rate of 1℃ / min and hold for 5 hours, then remove from the furnace at room temperature.

[0099] Calcination treatment: In an argon atmosphere, the temperature was increased at a rate of 0.5℃ / min and held at 200℃, 400℃ and 500℃ for 1 hour respectively.

[0100] Carbonization treatment: In an argon atmosphere, the temperature is increased to 600℃ at a rate of 0.5℃ / min, then increased to 1400℃ at a rate of 5℃ / min, and then increased to 1500℃ at a rate of 0.5℃ / min.

[0101] Nitriding treatment: The mixture was held at 1500℃ for 5 hours in a nitrogen atmosphere; then heated to 1750℃ at a rate of 5℃ / min and held for 5 hours; finally, it was cooled to room temperature at a rate of 10℃ / min in an argon atmosphere to obtain spherical uranium nitride particles, such as... Figure 4 As shown in (b), the XRD pattern of the spherical uranium nitride particles is as follows: Figure 5 As shown.

[0102] Example 4: Preparation of spherical uranium nitride particles

[0103] Carbon-containing uranium gel particles were obtained according to the preparation method in Example 1, and then pretreated and subjected to carbothermal reduction nitridation treatment, as follows:

[0104] Pretreatment: In an air atmosphere, heat to 400℃ at a heating rate of 1℃ / min and hold for 5 hours, then remove from the furnace at room temperature.

[0105] Calcination treatment: In an argon atmosphere, the temperature was increased at a rate of 0.5℃ / min and held at 200℃, 400℃ and 500℃ for 1 hour respectively.

[0106] Carbonization treatment: In an argon atmosphere, the temperature is increased to 600℃ at a rate of 0.5℃ / min, then increased to 1400℃ at a rate of 5℃ / min, and then increased to 1500℃ at a rate of 0.5℃ / min.

[0107] Nitriding treatment: The mixture was held at 1500℃ for 5 hours in a nitrogen atmosphere; then heated to 2000℃ at a rate of 5℃ / min and held for 5 hours; finally, it was cooled to room temperature at a rate of 10℃ / min in an argon atmosphere to obtain spherical uranium nitride particles, such as... Figure 4 As shown in (c), the XRD pattern of the spherical uranium nitride particles is as follows: Figure 5 As shown.

[0108] Example 5: Preparation of spherical uranium nitride particles

[0109] Carbon-containing uranium gel particles were obtained according to the preparation method of Example 1, except that the C / U molar ratio in Example 5 was 2.4. Further pretreatment and carbothermic reduction nitridation were then performed, as follows:

[0110] Pretreatment: In an air atmosphere, heat to 450℃ at a heating rate of 1℃ / min and hold for 5 hours, then remove from the furnace at room temperature.

[0111] Calcination treatment: In an argon atmosphere, the temperature was increased at a rate of 0.5℃ / min and held at 200℃, 400℃ and 500℃ for 1 hour respectively.

[0112] Carbonization treatment: In an argon atmosphere, the temperature is increased to 600℃ at a rate of 0.5℃ / min, then increased to 1400℃ at a rate of 5℃ / min, and then increased to 1500℃ at a rate of 0.5℃ / min.

[0113] Nitriding treatment: In a nitrogen atmosphere, the temperature was held at 1500℃ for 5 hours; then the temperature was increased to 2000℃ at a heating rate of 5℃ / min and held for 5 hours; finally, in an argon atmosphere, the temperature was reduced to room temperature at a cooling rate of 10℃ / min to obtain spherical uranium nitride particles.

[0114] Comparative Example 1: Preparation of spherical uranium nitride particles using amorphous carbon powder as the carbon source at different pretreatment temperatures

[0115] Uranium nitride spherical particles were prepared according to the method of Example 2, except that the carbon source in Comparative Example 1 was TPX-1408 amorphous carbon powder, the C / U molar ratio was 2.5, and the pretreatment temperatures in air atmosphere were 300℃, 350℃, 400℃, 450℃, and 500℃, respectively. Internal images of the uranium nitride spherical particles obtained after pretreatment at different temperatures for 5 hours are shown below. Figure 2 As shown.

[0116] Depend on Figure 2 It can be seen that, from the overall morphology of the particles, the carbon source is uniformly distributed inside the particles, but agglomeration is obvious (size approximately 10–20 μm), at 300℃ ( Figure 2 a, Figure 2 a'), 350℃ Figure 2 b、 Figure 2 b') After treatment, the internal carbon particles are darker in color, at 400℃ ( Figure 2 c. Figure 2 c') The internal carbon particles after treatment are in an intermediate color, appearing grayish-white, such as Figure 2 Arrow c' indicates the gaps between the carbon particles and the matrix. 450℃ ( Figure 2 d、 Figure 2 d') After treatment, a clear separation occurs between the internal carbon particles and the matrix (e.g. Figure 2(Indicated by arrow d'), the color is the same as the matrix, and pores (approximately 20 μm) are present. 500℃ ( Figure 2 e Figure 2 e') The internal carbon particles after treatment are severely depleted (e.g. Figure 2 (As indicated by arrow e') the pore size is larger than that at 400℃. This indicates that when using amorphous toner as the carbon source, the air pretreatment temperature should not exceed 350℃.

[0117] Figure 3 Uranium nitride spherical particles pretreated at 350°C for 5 hours in an air atmosphere using TPX-1408 amorphous carbon powder as the carbon source in Comparative Example 1 ( Figure 3 a) Uranium nitride spherical particles obtained in Example 5 by pretreatment at 450°C for 5 hours using diamond powder as the carbon source. Figure 3 Comparison of optical photographs (b). Figure 3 It can be seen that the rough surface of the particles in (a) usually originates from the non-dense structure; while the surface of the particles in (b) is smooth, intact and without cracks.

[0118] This demonstrates that the uranium nitride spherical particles prepared by the present invention using diamond powder as a carbon source have a dense, intact structure, high purity, and excellent performance.

[0119] Comparative Example 2: Preparation of spherical uranium nitride particles using amorphous carbon powder as the carbon source at different C / U molar ratios

[0120] Uranium nitride spherical particles were prepared according to the method of Example 2, except that the carbon source in Comparative Example 2 was TPX-1408 amorphous carbon powder, and the C / U molar ratios were 2.1, 2.3, 2.5, 2.7, and 2.9, respectively. Optical photographs of the uranium nitride spherical particles prepared under different C / U molar ratios are shown below. Figure 6 As shown, where, Figure 6 a to Figure 6 The C / U molar ratios of e are 2.1, 2.3, 2.5, 2.7, and 2.9, respectively.

[0121] Depend on Figure 6 It can be seen that the surface of uranium nitride spherical particles obtained with amorphous carbon powder as carbon source is relatively rough at different C / U molar ratios.

[0122] Depend on Figure 4 and Figure 6 The comparison shows that the uranium nitride spherical particles prepared by using diamond powder as a carbon source and external gelation combined with carbothermal reduction nitridation method in Examples 2 to 4 have uniform size and smooth surface.

[0123] Comparative Example 3: Preparation of spherical uranium nitride particles using amorphous carbon powder as a carbon source

[0124] Uranium nitride spherical particles were prepared according to the methods of Examples 2 to 4, the difference being that the diamond powder in Examples 2 to 4 was replaced with TPX-1408 amorphous carbon powder. A microstructure photograph of the uranium nitride spherical particles prepared in Comparative Example 3 is shown below. Figure 7 As shown.

[0125] Figure 8 The images show the microstructures of uranium nitride spherical particles prepared in Examples 2 to 4, where (a) and (d) are the microstructures of the uranium nitride spherical particles of Example 2, (b) and (e) are the microstructures of the uranium nitride spherical particles of Example 3, and (c) and (f) are the microstructures of the uranium nitride spherical particles of Example 4.

[0126] Depend on Figure 7 and Figure 8 The comparison shows that, due to the use of amorphous toner as the carbon source in Comparative Example 3, therefore... Figure 7 The uranium nitride spherical particles contain voids of varying sizes within their internal structure; and Figure 8 The uranium nitride spherical particles exhibit a more dense and uniform microstructure. This indicates that using diamond powder as a carbon source can yield higher quality and denser uranium nitride spherical particles at higher pretreatment temperatures.

[0127] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0128] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for preparing uranium nitride spherical particles, characterized in that, Includes the following steps: Carbon-containing uranium gel particles are prepared by mixing a carbon source and a solution; the preparation method of the carbon-containing uranium gel particles includes an internal gelation process or an external gelation process, and the carbon source includes diamond powder. The carbon-containing uranium gel particles were pretreated and then subjected to carbothermic reduction nitridation to obtain spherical uranium nitride particles. The pretreatment is carried out in an air atmosphere; the pretreatment satisfies the following conditions: (A) The heating rate of the pretreatment is 0.5~2℃ / min; (B) The pretreatment temperature is 360~560℃; (C) The pretreatment time is 3 to 7 hours.

2. The method according to claim 1, characterized in that, The diamond powder satisfies at least one of the following: (1) The average particle size of the diamond powder is 0.1~10μm; (2) The specific surface area of ​​the diamond powder is 15~30m². 2 / g.

3. The method according to claim 1 or 2, characterized in that, The C / U molar ratio of the carbon-containing uranium gel particles is 2.4~2.

6.

4. The method according to any one of claims 1 to 3, characterized in that, In the preparation method of the external gel process, the solution includes: uranyl nitrate solution, urea, and ammonium nitrate.

5. The method according to any one of claims 1 to 4, characterized in that, The solution further includes a dispersant; the dispersant satisfies at least one of the following: (a) The dispersant comprises at least one of ammonium citrate, polypropylene pyrrolidone, polyethyleneimine, ammonium polyacrylate, and tetramethylammonium hydroxide; (b) The amount of the dispersant added is 0.07 to 0.09% of the mass of the carbon source.

6. The method according to any one of claims 1 to 5, characterized in that, The carbothermic reduction nitriding treatment step includes: The uranium nitride spherical particles are obtained by roasting, carbonization, and nitriding; the carbothermic reduction nitriding treatment satisfies at least one of the following: (i) The calcination process is carried out in a protective atmosphere; the protective atmosphere includes argon and / or helium; the calcination process includes: holding at 200℃, 400℃ and 500℃ for 1 h at a heating rate of 0.5℃ / min; (ii) The carbonization process is carried out in a protective atmosphere; the protective atmosphere includes argon and / or helium; the carbonization process includes: heating to 600°C at 0.5°C / min, heating to 1400°C at 5°C / min, and then heating to 1500°C at 0.5°C / min. (iii) The nitriding treatment is carried out in nitrogen gas; the nitriding treatment includes: holding at 1500~2000℃ for 3~7 h.

7. The method according to any one of claims 1 to 6, characterized in that, Following the carbothermic reduction nitriding treatment, a heat preservation treatment is also included; the heating rate of the heat preservation treatment is 5℃ / min, the temperature is 1750~2000℃, and the heat preservation time is 4~6 h.

8. A spherical uranium nitride particle, characterized in that, Uranium nitride spherical particles prepared by the method according to any one of claims 1 to 7.

9. Uranium nitride spherical particles obtained by the preparation method according to any one of claims 1 to 7, or the use of uranium nitride spherical particles according to claim 8 in nuclear fuel or nuclear materials.

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