Preparation method of a low-density U3O8 foam ceramic

Abstract

A preparation method of low-density U3O8 foam ceramics, which method comprises the following steps: 1) preparing a uranium oxide precursor solution; 2) immersing a foam template in the uranium oxide precursor solution prepared in step 1), and then drying in air; 3) repeating the above steps 1 to 10 times to obtain a uranium oxide foam green body; 4) performing high-temperature treatment on the uranium oxide foam green body obtained in step 3) under a low-pressure environment to obtain a uranium oxide / carbon composite foam ceramic; 5) performing high-temperature sintering on the product obtained in step 4) in an air atmosphere to obtain U3O8 foam ceramics. The present invention can obtain a low-density U3O8 foam ceramic bulk material with a complete structure, high material phase purity, a large regulation range of density and foam pore size, a maximum porosity of the material reaching ~95%, and can meet its applications in fields such as catalysis and laser fusion engineering technology.

Description

Technical Field

[0001] The present invention belongs to the technical field of preparing foamed ceramic materials, and particularly relates to a method for preparing low-density U3O8 foamed ceramics. Background Art

[0002] Uranium oxide is an important nuclear material. Among the components of various uranium oxides, U3O8 has the most stable properties. In addition to being used as nuclear fuel, U3O8 is also an important catalyst, which can be used to catalytically degrade volatile organic compounds such as benzene and methanol. At the same time, U3O8 is an n-type intrinsic material, and its semiconductor properties have received great attention. In addition, in the field of inertial confinement fusion, U3O8 is also one of the main candidate materials for the inner wall of the hohlraum. At present, the preparation, shaping and performance evaluation of uranium oxide materials are mainly reflected in dense bulk materials and thin film materials, while the research on uranium oxide foamed ceramics is less. Theoretical research shows that using low-density U3O8 foam materials as the functional lining of the hohlraum can effectively inhibit the filling of plasma on the cavity wall, reduce the spot movement speed, and improve the energy conversion efficiency. In addition, as a catalyst, the large specific surface area of U3O8 foam materials is beneficial to improving its catalytic activity. However, there are very few reports on the preparation of U3O8 foamed ceramics at present. Zhao Ran et al. used silica colloidal crystals as templates, immersed molten uranyl nitrate into the templates, and obtained U3O8 mesoporous materials after high-temperature treatment and chemical etching to remove the templates. However, the U3O8 foamed ceramics prepared by this method have low structural strength, and it is difficult to obtain complete foamed ceramic bulk materials, and there is silicon element residue at the same time. Therefore, it is still very challenging to prepare U3O8 foamed ceramics with certain shape, size and density requirements, which greatly limits the application scope of uranium oxide materials. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for preparing low-density U3O8 foamed ceramics. This method uses polymer foam or carbon foam as a template, deposits uranium oxide precursor on the template skeleton through impregnation and drying, and obtains U3O8 foamed ceramics with certain shape, size and density requirements through sintering treatment. The method of the present invention obtains a complete-structured and high-phase-purity low-density U3O8 foamed ceramic bulk material, solving the above-mentioned existing problems.

[0004] A method for preparing low-density U3O8 foamed ceramics of the present invention is carried out according to the following steps:

[0005] I. Dissolve uranium oxide precursor, structure-directing agent and organic additive in a mixed solvent of deionized water and ethanol, stir evenly and then stand for aging to obtain a uranium oxide precursor solution;

[0006] II. Place the foam template into the uranyl precursor solution prepared in Step I, and leave it standing in a low-vacuum environment to remove the residual gas inside the foam template material, and then dry it in air; wherein, the vacuum degree in the low-vacuum environment is 10 - 50 kPa, and the vacuum treatment time is 1 - 5 min;

[0007] III. Repeat Step II for 1 - 10 times to obtain a uranium oxide foam blank;

[0008] IV. Place the uranium oxide foam blank obtained in Step III into a tubular furnace, and carry out heat preservation treatment for 1 - 5 h under the conditions of a vacuum degree of 1 - 1000 Pa, a treatment temperature of 500 - 800 °C, and a heating rate of 0.2 - 2 °C / min, and then cool it to room temperature to obtain a uranium oxide / carbon composite foam ceramic;

[0009] V. Place the uranium oxide / carbon composite foam ceramic obtained in Step IV into a muffle furnace, sinter it in an air atmosphere, and then cool it to room temperature to obtain the described low-density U3O8 foam ceramic.

[0010] Furthermore, the uranyl precursor is uranyl nitrate, uranyl chloride or uranyl acetate.

[0011] Furthermore, the structure-directing agent is F127 or P123.

[0012] Furthermore, the organic additive is acetylacetone or polyethyleneimine.

[0013] Furthermore, the molar mass volume ratio of the uranyl precursor, the structure-directing agent, the organic additive and the mixed solvent is 0.01 - 0.05 mol:0.5 - 8 g:1 - 6 g:11 - 70 mL.

[0014] Furthermore, the volume ratio of the deionized water and ethanol is 1 - 10:10 - 60.

[0015] Furthermore, the drying time in Step II is 12 - 72 h.

[0016] Furthermore, the foam template in Step II is polyurethane foam, melamine foam, polystyrene foam, poly-4-methyl-1-pentene foam or carbon foam.

[0017] Furthermore, in Step IV, carry out heat preservation treatment for 1 - 5 h under the conditions of a vacuum degree of 10 - 500 Pa, a treatment temperature of 600 - 700 °C, and a heating rate of 0.2 - 1 °C / min.

[0018] Furthermore, in Step V, the sintering temperature is 600 - 1000 °C, the heating rate is 1 - 5 °C / min, and the heat preservation time is 1 - 20 h.

[0019] The present invention has the following beneficial effects:

[0020] 1. The present invention provides a method for preparing low-density U3O8 foam ceramics. The prepared U3O8 foam ceramics have a uniform structure and high structural strength, and a complete foam ceramic bulk material can be obtained. Moreover, the foam ceramics can well replicate the shape of the template, realizing the near-net forming of U3O8 foam ceramics.

[0021] 2. The present invention uses the template method to prepare U3O8 foam ceramics. The material density and foam pore size can be adjusted within a wide range according to design requirements, and the maximum porosity of the material reaches ~95%, realizing the preparation of low-density U3O8 foam ceramics.

[0022] 3. Compared with the prior art, the present invention can effectively control the content of impurity elements in U3O8 foam ceramics, and the prepared foam ceramics have high phase purity.

[0023] 4. In the present invention, the uranium oxide foam blank is pre-treated at high temperature in a low-pressure environment, which can effectively improve the structural reliability of the foam ceramics. This is because a large number of gas small molecule products are generated during the high-temperature thermal degradation of the uranium oxide precursor, which is not conducive to the stability of the foam structure. The low-pressure environment combined with a relatively low heating rate can effectively inhibit the damage of the release of gas products to the structure of the ceramic blank.

[0024] 5. The method for preparing low-density U3O8 foam ceramics provided by the present invention has a simple experimental process, convenient operation control, and does not require expensive experimental equipment. The low-density U3O8 foam ceramics prepared by the method of the present invention have great application value in the fields of catalysis, laser fusion engineering technology, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a photo of a U3O8 foam ceramic sample;

[0026] Figure 2 is an XRD pattern of a U3O8 foam ceramic sample. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the spirit of the content disclosed by the present invention will be described in detail below. After any person skilled in the art understands the embodiments of the content of the present invention, the techniques taught by the content of the present invention can be changed and modified, which does not deviate from the spirit and scope of the content of the present invention.

[0028] The illustrative embodiments of the present invention and their descriptions are used to explain the present invention, but are not used to limit the present invention.

[0029] Example 1:

[0030] A method for preparing low-density U3O8 foam ceramics is specifically realized according to the following steps:

[0031] (1) 0.02 mol of uranyl chloride, 2.0 g of structure-directing agent F127, and 3.0 g of acetylacetone were dissolved in a mixed solvent of 1.5 mL of deionized water and 30 mL of ethanol. After stirring evenly, the mixture was allowed to stand and age for 3 days to obtain a urania precursor solution.

[0032] (2) The poly-4-methyl-1-pentene foam template was placed in the urania precursor solution prepared in step (1), and the residual gas inside the foam template material was removed by standing treatment under a low vacuum environment. The vacuum treatment time was 3 min, and the vacuum degree was 20 kPa. Subsequently, it was dried in air for 72 h to obtain a urania foam green body.

[0033] (3) The urania foam green body obtained in step (2) was placed in a tube furnace and heat-treated at high temperature under a low-pressure environment. The vacuum degree was 200 Pa, the treatment temperature was 600 °C, the heating rate was 1.0 °C / min, and the holding time was 2 h. After cooling to room temperature, a urania / carbon composite foam ceramic was obtained.

[0034] (4) The urania / carbon composite foam ceramic obtained in step (3) was placed in a muffle furnace and sintered at high temperature in an air atmosphere. The sintering temperature was 600 °C, the heating rate was 2 °C / min, the holding time was 10 h, and after cooling to room temperature, the described low-density U3O8 foam ceramic was obtained.

[0035] The porosity of the poly-4-methyl-1-pentene foam template described in step two of this example was ~94%.

[0036] The macroscopic photograph of the U3O8 foam ceramic sample obtained in this example is as Figure 1 shown. The U3O8 foam ceramic bulk material has a complete and defect-free structure, and the porosity of the sample is ~90%. By using a scanning electron microscope for microstructure observation, it can be found that the material structure is uniform, and the pore size is on the order of ten micrometers. The XRD test results show that the U3O8 foam ceramic sample has a high phase purity, and there are no other phases except the characteristic peaks of U3O8. The mechanical properties of the U3O8 foam ceramic sample were tested, and its compressive strength was 0.5 MPa.

[0037] Example 2:

[0038] A preparation method of a low-density U3O8 foam ceramic is specifically realized according to the following steps:

[0039] (1) 0.025 mol of uranyl acetate, 3.0 g of structure-directing agent P123, and 2.5 g of polyethyleneimine were dissolved in a mixed solvent of 2.0 mL of deionized water and 45 mL of ethanol. After stirring evenly, the mixture was allowed to stand and age for 3 days to obtain a urania precursor solution.

[0040] (2) Place the polystyrene foam template in the urania precursor solution prepared in step (1), and statically treat it in a low-vacuum environment to remove the residual gas inside the foam template material. The vacuum treatment time is 2 min and the vacuum degree is 25 kPa. Then dry it in air, and the drying time is 24 h;

[0041] (3) Repeat step (2) twice to obtain a urania foam blank;

[0042] (4) Place the urania foam blank obtained in step (3) in a tube furnace and perform high-temperature treatment in a low-pressure environment. The vacuum degree is 100 Pa, the treatment temperature is 700 °C, the heating rate is 0.5 °C / min, the holding time is 5 h, and cool it to room temperature to obtain a urania / carbon composite foam ceramic;

[0043] (5) Place the urania / carbon composite foam ceramic obtained in step (4) in a muffle furnace and perform high-temperature sintering in an air atmosphere. The sintering temperature is 800 °C, the heating rate is 1 °C / min, the holding time is 8 h, and cool it to room temperature to obtain the described low-density U3O8 foam ceramic.

[0044] In step two of this example, the porosity of the polystyrene foam template is ~90%.

[0045] The pore size of the U3O8 foam ceramic sample obtained in this example is in the micron order of magnitude, and the XRD pattern is as Figure 2 shown. The results show that the U3O8 foam ceramic sample has high phase purity and no other phases exist except for the characteristic peaks of U3O8.

[0046] Example 3:

[0047] A preparation method of a low-density U3O8 foam ceramic is specifically realized according to the following steps:

[0048] (1) Dissolve 0.035 mol of uranyl nitrate, 6.0 g of structure-directing agent F127 and 4.0 g of acetylacetone in a mixed solvent of 8.0 mL of deionized water and 60 mL of ethanol, stir evenly and then statically age for 5 days to prepare a urania precursor solution;

[0049] (2) Place the polyurethane foam template in the urania precursor solution prepared in step (1), and statically treat it in a low-vacuum environment to remove the residual gas inside the foam template material. The vacuum treatment time is 1 min and the vacuum degree is 40 kPa. Then dry it in air, and the drying time is 24 h;

[0050] (3) Repeat step (2) five times to obtain a urania foam blank;

[0051] (4) Place the uranium oxide foam green body obtained in step (3) in a tube furnace and perform high-temperature treatment under a low-pressure environment. The vacuum degree is 1000 Pa, the treatment temperature is 700 °C, the heating rate is 2.0 °C / min, the holding time is 1 h, and cool to room temperature to obtain the uranium oxide / carbon composite foam ceramic;

[0052] (5) Place the uranium oxide / carbon composite foam ceramic obtained in step (4) in a muffle furnace and perform high-temperature sintering in an air atmosphere. The sintering temperature is 1000 °C, the heating rate is 4 °C / min, the holding time is 2 h, and cool to room temperature to obtain the low-density U3O8 foam ceramic.

[0053] In step two of this embodiment, the porosity of the polyurethane foam template is ~99%.

[0054] The porosity of the U3O8 foam ceramic sample obtained in this embodiment is ~95%, and its pore size is in the order of hundreds of micrometers.

[0055] Example 4:

[0056] A preparation method of a low-density U3O8 foam ceramic is specifically realized according to the following steps:

[0057] (1) Dissolve 0.015 mol of uranyl acetate, 1.0 g of structure-directing agent P123, and 1.5 g of acetylacetone in a mixed solvent of 5.0 mL of deionized water and 20 mL of ethanol. After stirring evenly, let it stand and age for 2 days to obtain a uranium oxide precursor solution;

[0058] (2) Place the carbon foam template in the uranium oxide precursor solution prepared in step (1), and perform static treatment in a low-vacuum environment to remove the residual gas inside the foam template material. The vacuum treatment time is 4 min, and the vacuum degree is 10 kPa; then dry in air, and the drying time is 48 h;

[0059] (3) Repeat step (2) three times to obtain a uranium oxide foam green body;

[0060] (4) Place the uranium oxide foam green body obtained in step (3) in a tube furnace and perform high-temperature treatment under a low-pressure environment. The vacuum degree is 50 Pa, the treatment temperature is 500 °C, the heating rate is 0.3 °C / min, the holding time is 3 h, and cool to room temperature to obtain the uranium oxide / carbon composite foam ceramic;

[0061] (5) Place the uranium oxide / carbon composite foam ceramic obtained in step (4) in a muffle furnace and perform high-temperature sintering in an air atmosphere. The sintering temperature is 900 °C, the heating rate is 2 °C / min, the holding time is 12 h, and cool to room temperature to obtain the low-density U3O8 foam ceramic.

[0062] In step two of this embodiment, the porosity of the carbon foam template is ~85%.

[0063] The pore size of the U3O8 foam ceramic sample obtained in this example is in the order of hundreds of nanometers, and the compressive strength of the sample is 1.2 MPa.

Claims

1. A preparation method of low-density U3O8 foam ceramics, characterized in that The method described above is carried out according to the following steps:

1. Dissolve the uranium oxide precursor, structure-directing agent and organic additive in a mixed solvent of deionized water and ethanol, stir evenly and then stand for aging to obtain a uranium oxide precursor solution; 2. Place the foam template in the uranium oxide precursor solution prepared in step 1, and stand for treatment in a low-vacuum environment to remove the residual gas inside the foam template material, and then dry in air; wherein, the vacuum degree in the low-vacuum environment is 10-50 kPa, and the vacuum treatment time is 1-5 min; 3. Repeat step 2 for 1-10 times to obtain a uranium oxide foam blank; 4. Place the uranium oxide foam blank obtained in step 3 in a tubular furnace, keep it warm for 1-5 h under the conditions of a vacuum degree of 1-1000 Pa, a treatment temperature of 500-800 °C, and a heating rate of 0.2-2 °C / min, and then cool to room temperature to obtain a uranium oxide / carbon composite foam ceramic; 5. Place the uranium oxide / carbon composite foam ceramic obtained in step 4 in a muffle furnace, sinter it in an air atmosphere, and then cool to room temperature to obtain the described low-density U3O8 foam ceramic.

2. The preparation method of a low-density U3O8 foam ceramic according to claim 1, characterized in that The uranium oxide precursor described above is uranyl nitrate, uranyl chloride or uranyl acetate.

3. The preparation method of a low-density U3O8 foam ceramic according to claim 1, characterized in that The structure-directing agent described above is F127 or P123.

4. The preparation method of a low-density U3O8 foam ceramic according to claim 1, wherein The organic additive described above is acetylacetone or polyethyleneimine.

5. A method for preparing a low-density U3O8 foam ceramic according to claim 1, 2, 3 or 4, characterized in that The molar mass volume ratio of the uranium oxide precursor, structure-directing agent, organic additive and mixed solvent is 0.01-0.05 mol: 0.5-8 g: 1-6 g: 11-70 mL.

6. The preparation method of a low-density U3O8 foam ceramic according to claim 1, characterized in that The volume ratio of the deionized water and ethanol described above is 1-10: 10-60.

7. The preparation method of a low-density U3O8 foam ceramic according to claim 1, characterized in that The drying time in step 2 is 12-72 h.

8. The preparation method of a low-density U3O8 foam ceramic according to claim 1, characterized in that The foam template described in step 2 is polyurethane foam, melamine foam, polystyrene foam, poly-4-methyl-1-pentene foam or carbon foam.

9. The preparation method of a low-density U3O8 foam ceramic according to claim 1, characterized in that In step 4, keep it warm for 1-5 h under the conditions of a vacuum degree of 10-500 Pa, a treatment temperature of 600-700 °C, and a heating rate of 0.2-1 °C / min.

10. The preparation method of a low-density U3O8 foam ceramic according to claim 1, characterized in that In step 5, the sintering temperature is 600-1000 °C, the heating rate is 1-5 °C / min, and the holding time is 1-20 h.

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