A method for preparing high-purity uranium carbide microspheres using a microfluidic-assisted internal gel process

Abstract

The application discloses a method for preparing high-purity uranium carbide microspheres by a microfluidic assisted internal gelation process. The method comprises the following steps: designing a uranium gel solution component containing carbon black, obtaining a uranium gel solution which is stable at room temperature for a long time and rapidly gels at high temperature; taking the uranium gel solution as a dispersed phase of microfluidic, preparing gel microspheres with uniform size by a microfluidic assisted internal gelation process; and maintaining the pore structure in the gel microspheres by washing and soaking with propylene glycol methyl ether, so as to obtain gel microspheres without cracking. The gel microspheres without cracking are subjected to a carbothermic reduction reaction under an optimized sintering system, so as to prepare UC nuclear fuel microspheres with uniform size, good sphericity and high phase purity, and the method is expected to promote the development of ultra-high temperature gas cooled reactor nuclear fuel.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of nuclear fuel preparation, and particularly relates to a method for preparing high-purity uranium carbide microspheres by a microfluidic-assisted internal gelation process. BACKGROUND

[0002] The fourth generation of nuclear power technology, i.e. the ultra-high temperature gas cooled reactor, needs uranium carbide (UC) nuclear fuel microspheres with high thermal conductivity and high uranium density. The internal gelation process can avoid direct handling of radioactive powders, ensure the safety of experimenters, and uniformly dope carbon black to reduce the temperature and time of the carbon thermal reduction reaction, and is the mainstream method for preparing UC microspheres. However, the uranium gel solution containing carbon black has poor room temperature stability, the size of the gel microspheres is uneven, and the phase purity of the UC microspheres is low in the internal gelation process for preparing UC nuclear fuel microspheres, so it is difficult to prepare pure-phase UC microspheres, and the final product often contains unreacted UO2, UC2 or carbon black. Therefore, it is urgent to optimize the internal gelation process to prepare uniform-size and pure-phase UC microspheres. SUMMARY

[0003] The present application aims to at least partially solve one of the technical problems in the related art.

[0004] To this end, an embodiment of the present application provides a method for preparing high-purity uranium carbide microspheres by a microfluidic-assisted internal gelation process. The present application solves the technical problems of poor room temperature stability of the uranium gel solution containing carbon black, uneven size of the gel microspheres, and low phase purity of the UC microspheres, and prepares uniform-size and high-purity UC microspheres.

[0005] The present application provides a method for preparing high-purity uranium carbide microspheres by a microfluidic-assisted internal gelation process, comprising the following steps:

[0006] (a) preparing a uranium gel solution;

[0007] (b) preparing monodisperse gel microspheres by a microfluidic device with the uranium gel solution as a dispersed phase;

[0008] (c) the gel microspheres are sequentially aged, washed, and dried to obtain dry microspheres;

[0009] (d) sintering the dry microspheres to obtain high-purity phase microspheres.

[0010] In some embodiments, the preparation of the uranium gel solution is mixing a HMUR solution containing carbon black with a uranyl nitrate solution with a volume ratio of 1.2-1.4 to obtain a uranium gel solution containing carbon black, wherein the concentration of the uranyl nitrate solution is 2.6-2.8 mol / L, the under-acid degree n(NO3 -U) is 1.8-1.9, the HMUR solution containing carbon black is obtained by dispersing carbon black into a HMUR solution, the HMUR solution is a mixed solution of hexamethyl tetramine and urea, the concentration of the hexamethyl tetramine is 2.5-2.8 mol / L, and the concentration of the urea is 3.5-5 mol / L.

[0011] In some embodiments, n(Urea / UO2 2+ ) is 2-2.3, n(HMTA / UO2 2 + ) is 1.10-1.30, and n(C / UO2 2+ ) is 1-5.

[0012] In some embodiments, the uranium gel solution containing carbon black is stable at room temperature for more than 85 min and forms gel microspheres within 6-7 s at 70-90 DEG C.

[0013] In some embodiments, the dispersing of carbon black into the HMUR solution is performed under the conditions of ultrasonic power of 100-200 W, ultrasonic time of 60-180 min and dispersant.

[0014] In some embodiments, in the step (b), the dimethyl silicone oil is used as a continuous phase, the continuous phase extrudes or shears the dispersed phase in the microfluidic device to obtain monodisperse sol droplets, and the sol droplets fall into the dimethyl silicone oil at 70-90 DEG C to solidify into monodisperse gel microspheres.

[0015] In some embodiments, in the step (c), the gel microspheres are aged by being placed in the dimethyl silicone oil at 70-90 DEG C for 1-5 min.

[0016] In some embodiments, in the step (c), the gel microspheres are washed by being sequentially washed with vinyl chloride, 0.5-1 mol / L ammonia water and propylene glycol methyl ether for 4-6 times, and each washing time is 20-30 min.

[0017] In some embodiments, in the step (c), the gel microspheres are dried by being immersed in propylene glycol methyl ether and dried in a far infrared drying oven at 60-80 DEG C for 12-36 h.

[0018] In some embodiments, the sintering of the dry microspheres in step (d) is carried out under an argon atmosphere, the dry microspheres are first heated to 200-240 DEG C at a rate of 0.5-2 DEG C / min, and then kept at this temperature for 200-360 min; then heated to 460-480 DEG C at a rate of 0.5-2 DEG C / min for 30-60 min; then heated to 1000-1100 DEG C at a rate of 3-5 DEG C / min, and kept at this temperature for 60-200 min to convert UO3 into UO2; then heated to 1500-1550 DEG C at a rate of 3-5 DEG C / min, and kept at this temperature for 200-360 min to convert UO2 into UC; and finally heated to 1700-1750 DEG C at a rate of 3-5 DEG C / min, and kept at this temperature for 200-400 min to completely densify the UC phase.

[0019] Compared with the prior art, the present application has the following advantages:

[0020] The present application introduces microfluidics to assist the internal gelation process, and solves the technical problems of poor room temperature stability of the uranium gel solution containing carbon black, uneven size of the gel microspheres, and low phase purity of the UC microspheres by combining with the carbothermal reduction reaction, and the UC nuclear fuel microspheres prepared by the present application are expected to promote the development of the nuclear fuel for ultra-high temperature gas cooled reactors.

[0021] The present application obtains a uranium gel solution which is stable at room temperature for a long time and rapidly gels at high temperature by designing the components of the uranium gel solution containing carbon black; the size-uniform gel microspheres are prepared by the microfluidics-assisted internal gelation process using the uranium gel solution as the dispersed phase; the gel microspheres without cracking are obtained by washing and soaking the gel microspheres with propylene glycol methyl ether to maintain the pore structure in the gel microspheres; and the size-uniform, spherical and high-phase-purity UC nuclear fuel microspheres are prepared by the carbothermal reduction reaction of the gel microspheres without cracking under an optimized sintering system. BRIEF DESCRIPTION OF DRAWINGS

[0022] The above and / or additional aspects and advantages of the present application will become apparent and be readily understood from the following description, taken in conjunction with the following drawings, in which:

[0023] Figure 1 The flow chart of the method for preparing high-purity uranium carbide microspheres by the microfluidics-assisted internal gelation process of the present application;

[0024] Figure 2 The structural schematic diagram of the microfluidic device for preparing monodisperse gel microspheres of the present application;

[0025] Figure 3 The morphology diagram of the dry microspheres prepared in Example 1 of the present application;

[0026] Figure 4 The overall morphology diagram of the ceramic microspheres prepared in Example 1 of the present application;

[0027] Figure 5This is the element distribution diagram of the cross section of the ceramic microspheres prepared in Example 1 of the present invention;

[0028] Figure 6 This is the XRD pattern of ceramic microspheres prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0029] The following describes embodiments of the present invention in detail, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and are not to be construed as limiting the present invention.

[0030] The following describes a method for preparing high-purity uranium carbide microspheres using a microfluidic-assisted internal gel process according to an embodiment of the present invention with reference to the accompanying drawings.

[0031] like Figure 1 As shown, the method for preparing high-purity uranium carbide microspheres by microfluidic-assisted internal gel process of the present invention comprises the following steps:

[0032] (a) preparing uranium colloid;

[0033] (b) Using uranium colloid as the dispersed phase, monodisperse gel microspheres were prepared using a microfluidic device;

[0034] (c) aging, washing, and drying the gel microspheres to obtain dry microspheres;

[0035] (d) Sintering and drying the microspheres to obtain high-purity microspheres.

[0036] In step (a), the uranium colloid solution is prepared by mixing the HMUR solution containing carbon black with the uranyl nitrate solution in a volume ratio of 1.2 to 1.4 to obtain the uranium colloid solution containing carbon black.

[0037] The concentration of uranyl nitrate solution is 2.6-2.8 mol / L, and the acidity is n(NO3 - / U) is 1.8 to 1.9. The HMUR solution containing carbon black is obtained by dispersing carbon black into the HMUR solution. The HMUR solution is a mixed solution of hexamethylenetetramine and urea. The concentration of hexamethylenetetramine is 2.5 to 2.8 mol / L and the concentration of urea is 3.5 to 5 mol / L. 2+ ) is 2~2.3, n(HMTA / UO2 2+ ) is 1.10~1.30, n(C / UO2 2+ ) is 1 to 5.

[0038] Based on a large number of experimental studies, it was found that the stability of uranium colloid containing carbon black is related to the lack of acidity and urea content. The present invention obtains a uranium colloid that is stable for a long time at room temperature and quickly gels at high temperature by regulating the components of the uranium colloid containing carbon black.

[0039] The uranium colloid containing carbon black obtained by the invention is stable at room temperature for more than 85 minutes and quickly forms gel microspheres within 6 to 7 seconds at 70 to 90 degrees Celsius, thus meeting the requirement that the uranium colloid is stable for a long time at room temperature.

[0040] The specific process for dispersing carbon black into the HMUR solution is to disperse the carbon black into the HMUR solution under ultrasonic conditions of 100-200W, 60-180min, and a dispersant, to obtain an HMUR solution with a uniform dispersion of nano-scale carbon black. The dispersant is 1-10wt% of Digo 760W dispersant. It is understood that other suitable dispersants may also be used.

[0041] In step (b), monodispersed gel microspheres are prepared by using a microfluidic device using uranium colloid as the dispersed phase, specifically as follows: Figure 2 As shown, the microfluidic device is a coaxial capillary microfluidic device. An aqueous uranyl nitrate solution and an HMUR solution containing carbon black are mixed in a magnetic bead micromixer to form a uranium colloid solution that is stable for a long time at room temperature. The uranium colloid solution is used as the dispersed phase of the microfluidic device, and dimethyl silicone oil is used as the continuous phase of the microfluidic device. The continuous phase is squeezed or sheared in the microfluidic device to obtain monodisperse sol droplets, and the monodisperse sol droplets fall into dimethyl silicone oil at 70°C to 90°C and quickly solidify into monodisperse gel microspheres.

[0042] In step (c), the gel microspheres are aged by placing them in dimethyl silicone oil at 70° C. to 90° C. for 1 to 5 minutes, thereby obtaining gel microspheres with no uranium segregation; the gel microspheres are washed by sequentially using vinyl chloride, 0.5 to 1 mol / L ammonia water, and propylene glycol methyl ether for 4 to 6 times, with each washing time being 20 to 30 minutes; and the gel microspheres are dried by soaking the washed gel microspheres in propylene glycol methyl ether and drying them in a far-infrared drying oven at 60° C. to 80° C. for 12 to 36 hours, thereby obtaining dry microspheres without cracks and rich in gel pore structure.

[0043] The sintering of the dried microspheres to obtain high-purity phase microspheres in step (d) is specifically as follows: under an argon atmosphere, the dried microspheres are first heated to 200°C to 240°C at a rate of 0.5 to 2°C / min and kept warm for 200 to 360 minutes; then heated to 460 to 480°C at a rate of 0.5 to 2°C / min for 30 to 60 minutes; then heated to 1000°C to 1100°C at a rate of 3 to 5°C / min and kept warm for 60 to 200 minutes to convert UO3 into UO2; then heated to 1500°C to 1550°C at a rate of 3 to 5°C / min and kept warm for 200 to 360 minutes to convert UO2 into UC; finally, heated to 1700°C to 1750°C at a rate of 3 to 5°C / min and kept warm for 200 to 400 minutes to fully densify the UC phase.

[0044] The UC microspheres prepared by the method of the present invention have uniform size, good sphericity and a UC phase purity of up to 90-95wt%.

[0045] The method of the present invention is applicable to most carbide materials prepared by sol-gel process. Adaptation of the method of the present invention can be used to prepare zirconium carbide, aluminum carbide, tungsten carbide, uranium carbon oxy (UCO) and other materials.

[0046] In addition, the present invention can not only be used to prepare carbide ceramic microspheres, but also can be used to prepare non-oxide microspheres, such as nitride microspheres, silicide microspheres, etc., by adding carbon source, nitrogen source or silicon source to the inner gel glue.

[0047] Example 1

[0048] 0.81g of carbon black was dispersed into 12.25mL of HMUR solution (a mixture of hexamethylenetetramine and urea) at an ultrasonic power of 180W for 60min and 6wt% of Digo 760W dispersant. The HMUR solution was a mixture of hexamethylenetetramine (2.64mol / L) and urea (4.4mol / L).

[0049] 10mL of 2.7mol / L, low acidity n(NO3 - Uranium nitrate solution with n(Urea / UO2)=1.85 was mixed with 12.25mL HMUR solution containing carbon black to obtain a uranium gel containing carbon black that was stable at room temperature for 85min and solidified at 80℃ for 7s. 2+ ) is maintained at 2, n(HMTA / UO2 2+ ) is maintained at 1.20, n(C / UO2 2+ ) remains at 2.5.

[0050] Using uranium colloid as the dispersed phase and dimethyl silicone oil as the continuous phase, monodisperse gel microspheres were prepared by a coaxial capillary microfluidic device. The gel microspheres were aged in dimethyl silicone oil at 80°C for 2 minutes, and then immediately taken out for a trichloroethylene-ammonia water-propylene glycol methyl ether combined washing process. Specifically, the gel microspheres were first washed with trichloroethylene 4 times, each time for 25 minutes, and then washed with 0.5 mol / L ammonia water 4 times, each time for 25 minutes, and finally washed with propylene glycol methyl ether 4 times, each time for 25 minutes. The washed gel microspheres were placed in propylene glycol methyl ether and soaked, and then sent to a far-infrared oven at 60°C for drying for 30 hours to obtain dry microspheres without cracks, such as Figure 3 shown.

[0051] The dried microspheres were heated to 200°C at 0.5°C / min under an argon atmosphere and kept at 200°C for 360 minutes; then the temperature was increased to 460°C at 0.5°C / min and kept at 460°C for 30 minutes; then the gel microspheres were heated to 1000°C at 3°C / min and kept at 1000°C for 120 minutes to convert UO3 into UO2; then the temperature was increased to 1500°C at 3°C / min and kept at 1500°C for 240 minutes to convert UO2 into UC; finally, the temperature was increased to 1700°C at 3°C / min and kept at 1700°C for 300 minutes to completely densify the UC phase and obtain high-purity UC ceramic microspheres, such as Figure 4 shown.

[0052] The cross section of UC ceramic microspheres is scanned by energy spectrum line, such as Figure 5 As shown in the figure, it can be seen that carbon and uranium are evenly distributed, and there is no obvious segregation of uranium. Figure 6 As shown, it can be seen that 92.9 wt % of the ceramic microspheres prepared in the present invention are UC phase.

[0053] Example 2

[0054] 0.99g of carbon black was dispersed into 13mL of HMUR solution under ultrasonic conditions of 180W for 120min and 6wt% of Digo 760W dispersant. The HMUR solution is a mixture of hexamethylenetetramine (2.7mol / L) and urea (4.5mol / L).

[0055] 10mL of 2.75mol / L, less acidic n(NO3 - Uranium nitrate solution with n(Urea / UO2)=1.88 was mixed with 13 mL of HMUR solution containing carbon black to obtain a uranium gel containing carbon black that was stable at room temperature for 90 min and solidified at 90°C for 6 s. 2+) was maintained at 2.13, n(HMTA / UO2 2+ ) is maintained at 1.28, n(C / UO2 2+ ) remains at 3.

[0056] Monodisperse gel microspheres were prepared using a coaxial capillary microfluidic device with uranium colloid as the dispersed phase and dimethyl silicone oil as the continuous phase. The gel microspheres were aged in dimethyl silicone oil at 90°C for 1 minute and then immediately removed for a combined washing process using trichloroethylene, ammonia, and propylene glycol methyl ether. Specifically, the gel microspheres were first washed with trichloroethylene six times for 20 minutes each, then with 1 mol / L ammonia six times for 20 minutes each, and finally with propylene glycol methyl ether six times for 20 minutes each. The washed gel microspheres were then immersed in propylene glycol methyl ether and dried in a far-infrared oven at 80°C for 15 hours to obtain crack-free dry microspheres.

[0057] The dried microspheres were heated to 240°C at a rate of 0.5°C / min under an argon atmosphere and kept at 240°C for 250 min; then the temperature was increased to 480°C at a rate of 0.5°C / min and kept at 480°C for 40 min; then the gel microspheres were heated to 1100°C at a rate of 3°C / min and kept at 1100°C for 120 min to convert UO3 into UO2; then the temperature was increased to 1550°C at a rate of 3°C / min and kept at 1500°C for 240 min to convert UO2 into UC; finally, the temperature was increased to 1750°C at a rate of 3°C / min and kept at 1750°C for 300 min to obtain high-purity UC microspheres.

[0058] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic expressions of the above terms may be directed to different embodiments or examples. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, unless they are mutually inconsistent.

[0059] Furthermore, 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 the technical features being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "plurality" means at least two, such as two, three, etc., unless otherwise specifically defined.

[0060] While embodiments of the application have been shown and described, it is to be understood that the embodiments described are merely divergences of the principles and application of the present application and that numerous modifications, changes, substitutions, and alterations can be made thereto without departing from the spirit and scope of the present application, which is defined by the following claims and their equivalents.

Claims

1. A method for preparing high-purity uranium carbide microspheres using a microfluidic-assisted internal gel process, characterized in that: The following steps are involved: (a) Preparation of uranium colloid; (b) using the uranium colloid as a dispersed phase, preparing monodisperse gel microspheres through a microfluidic device; (c) aging, washing, and drying the gel microspheres to obtain dry microspheres; (d) sintering the dried microspheres to obtain high-purity microspheres, The uranium colloid solution is prepared by mixing the HMUR solution containing carbon black with the uranyl nitrate solution in a volume ratio of 1.2 to 1.4 to obtain the uranium colloid solution containing carbon black, wherein the concentration of the uranyl nitrate solution is 2.6 to 2.8 mol / L and the acidity is n(NO3 - / U) is 1.8~1.9, the HMUR solution containing carbon black is obtained by dispersing carbon black into the HMUR solution, the HMUR solution is a mixed solution of hexamethylenetetramine (HMTA) and urea (Urea), the concentration of the hexamethylenetetramine is 2.5~2.8 mol / L, the concentration of urea is 3.5~5 mol / L, and the n(Urea / UO2) in the uranium colloid containing carbon black is 1.8~1.9, the HMUR solution containing carbon black is obtained by dispersing carbon black into the HMUR solution, the HMUR solution is a mixed solution of hexamethylenetetramine (HMTA) and urea (Urea), the concentration of the hexamethylenetetramine is 2.5~2.8 mol / L, and the concentration of urea is 3.5~5 mol / L. 2+ ) is 2~2.3, n(HMTA / UO2 2 + ) is 1.10~1.30, n(C / UO2 2+ ) is 1~5.

2. The method according to claim 1, wherein The uranium colloid containing carbon black is stable at room temperature for more than 85 minutes and forms gel microspheres within 6 to 7 seconds at 70 to 90 degrees Celsius.

3. The method according to claim 1, wherein The dispersing of carbon black into the HMUR solution is to disperse the carbon black into the HMUR solution under the conditions of ultrasonic power of 100-200W, ultrasonic time of 60-180min, and dispersant.

4. The method according to claim 1, wherein In the step (b), dimethyl silicone oil is used as the continuous phase, and the continuous phase squeezes or shears the dispersed phase in the microfluidic device to obtain monodisperse sol droplets. The sol droplets fall into dimethyl silicone oil at 70° C. to 90° C. and solidify into monodisperse gel microspheres.

5. The method according to claim 1, wherein In the step (c), the gel microspheres are aged by placing them in dimethyl silicone oil at 70° C. to 90° C. for 1 to 5 minutes.

6. The method according to claim 1, wherein In the step (c), the gel microspheres are washed 4 to 6 times using vinyl chloride, 0.5 to 1 mol / L ammonia water, and propylene glycol methyl ether in sequence, with each washing time being 20 to 30 minutes.

7. The method according to claim 1, wherein In the step (c), the gel microspheres are dried by soaking the washed gel microspheres in propylene glycol methyl ether and drying them in a far-infrared drying oven at 60° C. to 80° C. for 12 to 36 hours while soaking.

8. The method according to claim 1, wherein In the step (d), the dried microspheres are sintered in an argon atmosphere, firstly heating the dried microspheres to 200°C-240°C at a rate of 0.5-2°C / min and holding the temperature for 200-360 minutes; then heating the dried microspheres to 460-480°C at a rate of 0.5-2°C / min and holding the temperature for 30-60 minutes; then heating the dried microspheres to 1000°C-1100°C at a rate of 3-5°C / min and holding the temperature for 60-200 minutes to convert UO3 into UO2; then heating the dried microspheres to 1500°C-1550°C at a rate of 3-5°C / min and holding the temperature for 200-360 minutes to convert UO2 into UC; finally heating the dried microspheres to 1700°C-1750°C at a rate of 3-5°C / min and holding the temperature for 200-400 minutes to completely densify the UC phase.

Images