Carbon-doped gel ball taking hydro-thermally treated organic sugar as carbon source and preparation method of carbon-doped gel ball

Abstract

The invention relates to the technical field of gel materials for nuclear fuels, and particularly discloses a carbon-doped gel ball with hydro-thermally treated organic sugar as a carbon source and a preparation method of the carbon-doped gel ball aiming at the problem that carbon is easy to lose in the subsequent production and processing process when the organic sugar is used as the carbon source in the existing gel ball for the nuclear fuels. Comprising the following steps: taking an organic sugar aqueous solution, carrying out hydrothermal treatment, carrying out solid-liquid separation, taking a solid phase, washing and drying to obtain a carbon source; taking the acid-deficient uranyl nitrate solution, sequentially adding a carbon source, urea and urotropine step by step, mixing and standing to obtain sol; dispersing the sol into heated silicone oil, carrying out aging treatment, and then washing with kerosene, absolute ethyl alcohol and an absolute ethyl alcohol-ammonia water mixed solution in sequence to obtain the carbon-doped gel balls. According to the method, organic sugar is subjected to hydro-thermal treatment, the hydrophilic property of the organic sugar is improved, the carbon yield is increased, a carbon source which has the nanoscale particle size and is easily dispersed in a water phase is obtained, and then the carbon-doped gel balls which are free of carbon loss and uniform in carbon distribution can be prepared.

Description

Technical Field

[0001] This invention relates to the field of gel materials for nuclear fuel, and more specifically, to a carbon-doped gel ball using hydrothermally treated organic sugar as a carbon source and its preparation method. Background Technology

[0002] In tri-structural isotropic (TRISO) coated fuels, UO2 is traditionally used as the fuel core. However, due to the low thermal conductivity of UO2, microsphere materials such as UC or UN, which have advantages such as high thermal conductivity and high density, have been proposed for use as fuel cores to improve the overall thermal conductivity of the fuel. Sol-gel technology is commonly used to prepare these fuel microspheres. The internal gel technology in the sol-gel process has advantages such as good sphericity, uniform size, and easy uniform incorporation of other components, and is therefore widely used as a method for preparing uranium-containing fuel microspheres.

[0003] Carbon-doped gel spheres are a key intermediate in the preparation of UC or UN microspheres using internal gelation technology. The key to successfully preparing high-density UC or UN microspheres lies in ensuring uniform carbon dispersion and accurate C / U ratios during the reduction reaction. Currently, carbon black and organic sugars can be used as carbon sources in the preparation of carbon-doped gel spheres. For example, patent CN119430935A provides a method for preparing high-purity uranium carbide microspheres using a microfluidic-assisted internal gelation process. However, in existing technologies, if solid carbon black is used as the carbon source, the larger carbon particles will leave pores on the microsphere surface after the carbothermic reduction reaction, which is detrimental to improving microsphere density. If organic sugars such as sucrose and fructose are used as the carbon source, the water solubility of organic sugars will cause the gel spheres to be washed out during subsequent washing, preventing the carbothermic reduction reaction from proceeding fully and resulting in ineffective removal of oxygen.

[0004] Based on the above situation, there is an urgent need for a carbon-doped gel sphere preparation process that can better improve the carbon doping effect in order to meet the overall production and use requirements of nuclear fuel microspheres. Summary of the Invention

[0005] The purpose of this invention is to solve the problem that in existing nuclear fuel gel spheres, where organic sugars are used as a carbon source, carbon is easily lost during subsequent production and processing.

[0006] This invention is achieved through the following technical solution: This invention provides a method for preparing carbon-doped gel spheres using hydrothermally treated organic sugars as a carbon source, comprising the following steps: S1 Preparation of carbon source: Take an aqueous solution of organic sugar, perform hydrothermal treatment, then separate the solid and liquid phases, take the solid phase, wash and dry it to obtain the carbon source; S2 Preparation of Sol: Take an acid-deficient uranyl nitrate solution, add carbon source, urea and hexamethylenetetramine in sequence, mix and let stand to obtain a sol; S3 Dispersion Aging Treatment: The sol was dispersed in heated silicone oil and then impregnated and aged to form gel spheres; S4 Post-processing: The gel spheres prepared in step S3 were washed sequentially with kerosene, anhydrous ethanol, and anhydrous ethanol-concentrated ammonia solution to obtain the carbon-doped gel spheres.

[0007] Preferably, in step S1, the hydrothermal treatment temperature is 100-300℃ and the hydrothermal treatment time is 10-15h.

[0008] Preferably, in step S2, the molar ratio of carbon source to metallic uranium is 0.5-4.0, the molar ratio of urea to metallic uranium is 0.8-2.0, and the molar ratio of hexamethylenetetramine to metallic uranium is 0.8-2.0.

[0009] Preferably, the specific steps for preparing the sol are as follows: 2.1 First, cool the acid-deficient uranyl nitrate solution to 4°C or below, then add a carbon source and mix by ultrasonic vibration to obtain the first mixture; 2.2 Add urea to the first mixture in batches, mix, and obtain the second mixture; 2.3 Add hexamethylenetetramine to the second mixture in small batches, mix, and let stand at low temperature to obtain the third mixture.

[0010] Preferably, the concentration of uranyl ions in the third mixture is 1.5-2.7 mol / L.

[0011] Preferably, the pH value of the sol is 3.0-6.0.

[0012] Preferably, in step S3, the silicone oil is first heated to 50-100°C, then the sol is dispersed in the silicone oil, and the silicone oil is immersed in the silicone oil at 50-100°C for 0.1-3 hours for aging treatment.

[0013] Preferably, in step S4, the kerosene washing time is ≥10 min, the anhydrous ethanol washing time is ≥10 min, and the anhydrous ethanol-ammonia water mixed solution washing time is ≥60 min.

[0014] Preferably, the ammonia concentration is 3-8 mol / L.

[0015] The technical solution of the present invention has the following beneficial effects: This invention first employs a hydrothermal method to treat organic sugars, improving their hydrophilic properties and increasing carbon yield to obtain a carbon source with nanoscale particle size that is easily dispersed in an aqueous phase. The carbon-doped gel spheres are then washed without causing carbon loss, effectively solving problems such as carbon agglomeration and inaccurate C / U ratios. Furthermore, carbon-doped gel spheres with uniform carbon dispersion and good sphericity are prepared using a combination of pinhole dispersion and internal gelation technology. This gel sphere preparation process effectively removes the dispersion medium and NO3. - Ultimately, carbon-doped gel spheres with no carbon loss and uniform carbon distribution were obtained. Attached Figure Description

[0016] Figure 1 The image shows a SEM image (10.0 kx magnification) of glucose after hydrothermal treatment in Example 1. Figure 2 This is a graph showing the pH changes of different mixtures in Example 2. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, they are performed according to conventional conditions or conditions recommended by the manufacturer; where the manufacturers of the instruments, equipment, reagents, or raw materials used are not specified, they are all conventional products that can be purchased commercially.

[0018] This invention provides a carbon-doped gel sphere using hydrothermally treated organic sugar as a carbon source, and its preparation method includes the following steps: (1) Take 0.5-1 mol / L organic sugar aqueous solution, place it in a reaction vessel lined with polytetrafluoroethylene, and perform hydrothermal treatment at 100-300℃ for 10-15 h. After solid-liquid separation, take the solid phase, wash it with deionized water and ethanol, and then place it in an oven at 40-100℃ to dry it to obtain the carbon source.

[0019] (2) The carbon source is mixed with urea, hexamethylenetetramine and acid-deficient uranyl nitrate solution at low temperature to obtain a sol.

[0020] The specific mixing and preparation process of this sol is as follows: 2.1 The acid-deficient uranyl nitrate solution was cooled at low temperature and mixed with the hydrothermally treated carbon source by ultrasonic oscillation. The molar ratio of the added carbon source to the concentration of metallic uranium was 0.5-4.0 to obtain the first mixture. 2.2 Add urea to the first mixture in batches, with the molar ratio of urea to metallic uranium concentration being 0.8-2.0, in order to obtain the second mixture; During this process, urea undergoes hydrolysis under acidic conditions, causing an increase in the pH value of the sol solution. At low temperatures, urea forms a complex with uranyl ions (as shown in reaction ① below), preventing the hydrolysis and condensation reaction of uranyl ions (as shown in reaction ② below), thus increasing the stability of the sol. UO2 2+ + CO(NH2)2→ [UO2·CO(NH2)2] 2+ ①; [UO2(OH)] + + [UO2(OH)] + → [(UO2)2(OH)2] 2+ ②; 2.3 Add hexamethylenetetramine to the second mixture in small batches, with the molar ratio of hexamethylenetetramine to metallic uranium concentration being 0.8-2.0, to obtain a third mixture. Control the concentration of uranyl ions in the third mixture to be 1.5-2.7 mol / L. Cool the third mixture at low temperature and let it stand to obtain a sol for dispersing and preparing gel spheres, with a pH value of 3.0-6.0. In this process, hexamethylenetetramine is mainly added as a gelling agent. Hexamethylenetetramine decomposes at high temperatures to produce ammonium ions (as shown in reaction ③ below), which causes the pH value of the sol solution to rise and promotes the precipitation reaction of uranyl ions (as shown in reaction ④ below). For example, the formaldehyde produced in reaction ③ will also react with urea to produce urea-formaldehyde resin. Urea-formaldehyde resin, as an organic framework, can improve the mechanical strength of the gel spheres. (CH2)6N4·H + + 3H + + 6H2O → 4NH4 + +6HCHO③; [(UO2)2(OH)2] 2+ + 2NH4 + + 4OH - → (NH4)2U2O7+ 3H2O④.

[0021] (3) Disperse the sol in hot silicone oil at 50-100℃. Using hot silicone oil can improve the gel reaction efficiency and form spherical gel balls. Then, age the gel balls in silicone oil, that is, immerse them in silicone oil at 50-100℃ for 0.1-3h. This can improve the strength of the gel balls and prevent them from breaking during subsequent washing. Then, wash them in sequence with kerosene, anhydrous ethanol, and anhydrous ethanol-concentrated ammonia solution. The washing time of kerosene is ≥10min, the washing time of anhydrous ethanol is ≥10min, and the washing time of anhydrous ethanol-concentrated ammonia solution is ≥60min. The concentration of ammonia is 3-8mol / L. The above washing method can avoid the loss of carbon source and obtain carbon-doped gel balls.

[0022] This invention uses hydrothermally treated organic sugar as a carbon source, which ensures that the carbon is stable and uniformly dispersed in the sol and subsequent gel spheres. Then, carbon-doped gel spheres are prepared by pinhole dispersion combined with internal gelation technology. Internal gelation technology refers to the precipitation reaction between the hydrolysis products of uranyl ions and the ammonium produced by the thermal decomposition of hexamethylenetetramine. At the same time, hexamethylenetetramine also decomposes to release formaldehyde, which reacts with urea to form urea-formaldehyde resin, which can improve the mechanical strength of the gel spheres.

[0023] Example 1 First, a 0.7 mol / L glucose aqueous solution was prepared, and a hydrothermal reaction was carried out at 200℃ for 12 h. After the reaction, solid-liquid separation was performed, and the separated solid phase was washed with deionized water and ethanol, respectively. The solid phase was then dried in an oven at 80℃ for 12 h to obtain spherical nanoscale carbon source, the morphology of which is as follows: Figure 1 As shown.

[0024] The carbon content of the nano carbon source was found to be 61% using a carbon-sulfur analyzer, while the carbon content of the original glucose was only 40%. The carbon content of the carbon source can be increased by the method of this invention, which effectively increases the solid content in the gel spheres.

[0025] Example 2 Take a 2.4 mol / L acid-deficient uranyl nitrate solution, cool it to below 4°C, and then add the nano-carbon source prepared in Example 1 according to a carbon element to metallic uranium molar ratio of 2.0. Mix the mixture and sonicate for 10 min to form a first mixture. At a temperature of about 4°C, add urea to the first mixture in multiple batches according to a urea to metallic uranium molar ratio of 1.4, mix the mixture, and let it stand for 5 min to form a second mixture. At a temperature of about 4°C, add hexamethylenetetramine to the second mixture in batches according to a hexamethylenetetramine molar ratio of 1.4, mix the mixture, and form a third mixture, which is the sol.

[0026] According to the inventor's tests, the pH of the first mixture, the second mixture, and the third mixture, as well as the pH change during stable storage for 3 hours, were determined by... Figure 2 It can be seen that at low temperatures, the addition of this nano-carbon source does not cause any change in the chemical properties of the sol.

[0027] Example 3 The sol prepared in Example 2 was first placed at a temperature of about 4°C and allowed to stand for 30 minutes. Then, a needle dispersion device based on internal gelation technology was used to disperse the sol into hot silicone oil at 80°C to form gel spheres. The gel spheres were then placed in hot silicone oil at 80°C for 0.5 hours for aging treatment to form gel spheres with high mechanical strength.

[0028] Example 4 The gel balls obtained in Example 3 were washed with kerosene for 10 min, then with anhydrous ethanol for 10 min, and finally with a mixed solution of 5 mol / L concentrated ammonia and anhydrous ethanol for 60 min to remove surface impurities and obtain carbon-doped gel ball products.

[0029] Comparative Example 1 The difference between this comparative example and Example 4 is that glucose was first added directly to the sol to form gel spheres for aging. After washing with kerosene, the spheres were subjected to hydrothermal treatment at 200°C in ethanol. Other processes were the same as in Examples 3 and 4. As can be seen from reaction equation ③ above, ammonium ions are generated during the gelation reaction, resulting in a small amount of ammonium nitrate in the gel spheres. However, in this comparative example, the direct hydrothermal treatment causes a large amount of heat to be generated after the ammonium nitrate decomposes, which may cause the gel spheres to break.

[0030] According to the method in Example 1 of this invention, the carbon source is subjected to hydrothermal treatment at the beginning. In the washing process of the gel balls in Example 4, the ammonium nitrate inside the gel balls will dissolve in the washing solution, and the gel balls will not break during the subsequent calcination process.

[0031] Comparative Example 2 The difference between this comparative example and Example 4 is that the gel balls obtained in Example 3 were washed with kerosene for 10 minutes, then with anhydrous ethanol for 10 minutes, and then with 0.5 mol / L dilute ammonia solution for 60 minutes to obtain the carbon-doped gel ball product.

[0032] The carbon content of the carbon-doped gel spheres in Example 4 and Comparative Example 2 was tested using a carbon-sulfur analyzer. The carbon content of the carbon-doped gel spheres in Example 4 was 8.2%, while the carbon content of the carbon-doped gel spheres in Comparative Example 2 was only 6.1%. Compared with Example 4, Comparative Example 2 shows carbon loss from the carbon-doped gel spheres, which is not conducive to the subsequent preparation of UC or UN.

[0033] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing carbon-doped gel spheres using hydrothermally treated organic sugars as a carbon source, characterized in that, Includes the following steps: S1 Preparation of carbon source: Take an aqueous solution of organic sugar, perform hydrothermal treatment, then separate the solid and liquid phases, take the solid phase, wash and dry it to obtain the carbon source; S2 Preparation of Sol: Take an acid-deficient uranyl nitrate solution, add carbon source, urea and hexamethylenetetramine in sequence, mix and let stand to obtain a sol; S3 Dispersion Aging Treatment: The sol was dispersed in heated silicone oil and then impregnated and aged to form gel spheres; S4 Post-processing: The gel spheres prepared in step S3 were washed sequentially with kerosene, anhydrous ethanol, and anhydrous ethanol-concentrated ammonia solution to obtain the carbon-doped gel spheres.

2. The method for preparing carbon-doped gel spheres using hydrothermally treated organic sugars as a carbon source according to claim 1, characterized in that, In step S1, the hydrothermal treatment temperature is 100-300℃ and the hydrothermal treatment time is 10-15h.

3. The method for preparing carbon-doped gel spheres using hydrothermally treated organic sugars as a carbon source according to claim 1, characterized in that, In step S2, the molar ratio of carbon source to metallic uranium is 0.5-4.0, the molar ratio of urea to metallic uranium is 0.8-2.0, and the molar ratio of hexamethylenetetramine to metallic uranium is 0.8-2.

0.

4. The method for preparing carbon-doped gel spheres using hydrothermally treated organic sugars as a carbon source according to claim 3, characterized in that, The specific steps for preparing the sol are as follows: 2.1 First, cool the acid-deficient uranyl nitrate solution to 4°C or below, then add a carbon source and mix by ultrasonic vibration to obtain the first mixture; 2.2 Add urea to the first mixture in batches, mix, and obtain the second mixture; 2.3 Add hexamethylenetetramine to the second mixture in small batches, mix, and let stand at low temperature to obtain the third mixture.

5. The method for preparing carbon-doped gel spheres using hydrothermally treated organic sugars as a carbon source according to claim 4, characterized in that, The concentration of uranyl ions in the third mixture is 1.5-2.7 mol / L.

6. The method for preparing carbon-doped gel spheres using hydrothermally treated organic sugars as a carbon source according to claim 4, characterized in that, The pH value of the sol is 3.0-6.

0.

7. The method for preparing carbon-doped gel spheres using hydrothermally treated organic sugars as a carbon source according to claim 1, characterized in that, In step S3, the silicone oil is first heated to 50-100℃, then the sol is dispersed in the silicone oil, and the silicone oil is immersed in the silicone oil at 50-100℃ for 0.1-3 hours for aging treatment.

8. The method for preparing carbon-doped gel spheres using hydrothermally treated organic sugars as a carbon source according to claim 1, characterized in that, In step S4, the kerosene washing time is ≥10 min, the anhydrous ethanol washing time is ≥10 min, and the anhydrous ethanol-ammonia water mixed solution washing time is ≥60 min.

9. The method for preparing carbon-doped gel spheres using hydrothermally treated organic sugars as a carbon source according to claim 8, characterized in that, The concentration of ammonia water is 3-8 mol / L.

10. A carbon-doped gel ball prepared by the preparation method according to any one of claims 1 to 9, using hydrothermally treated organic sugar as a carbon source.

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