A method for producing thorium carbide
By using wet mixing and vacuum carbothermic reduction reaction, the problems of low purity and high cost in thorium carbide preparation have been solved, achieving the preparation of high-purity thorium carbide and avoiding dust pollution and equipment wear and tear.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- ADVANCED ENERGY SCIENCE & TECHNOLOGY GUANGDONG LABORATORY
- Filing Date
- 2024-04-24
- Publication Date
- 2026-05-15
AI Technical Summary
Existing methods for preparing thorium carbide suffer from problems such as low purity, lack of environmental friendliness, and high cost.
Thorium dioxide and carbon were mixed using a wet mixing process, with anhydrous ethanol as the solvent for uniform mixing. The mixture was then subjected to a carbothermic reduction reaction under vacuum or argon atmosphere, and thorium carbide powder was obtained by crushing and grinding.
It improves the purity of thorium carbide, avoids the risks of uneven mixing and dust pollution, reduces process costs, shortens reaction time, and reduces equipment wear and tear.
Smart Images
Figure CN118458774B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the preparation of nuclear fuel, and in particular to a method for preparing thorium carbide. Background Technology
[0002] With the rapid development of advanced nuclear reactors and the shortage of uranium resources, thorium energy has attracted widespread attention. In nature, thorium reserves are 3 to 4 times greater than uranium, and it is easier to mine than uranium ore. Furthermore, thorium fuel has many advantages over uranium fuel: the production of plutonium in the thorium fuel cycle is almost negligible, effectively avoiding the generation of long-lived fission products and highly toxic transuranium waste, thus preventing the enrichment and extraction of nuclear weapons-grade fuel and preventing nuclear proliferation; at the same time, natural thorium, after being bombarded by neutrons, forms 233U, which can be directly used as nuclear fuel (the specific process is: 232Th+n→233Th→233Pa→233U), while uranium needs to be highly enriched before it can be used as nuclear fuel. Therefore, thorium is more efficient than uranium; and the thermal neutron absorption cross section of thorium is three times larger than that of uranium, so the conversion efficiency of 232Th→233U is much higher than that of 238U→239Pu; in addition, thorium-based fuel can allow higher fuel pellet temperatures and deeper burn-up in the reactor, and thorium-based nuclear fuel is more adaptable to various reactor types, without requiring major changes to the fuel assemblies and structural materials of existing reactors. Therefore, thorium has broad prospects for future applications in nuclear energy.
[0003] Among common thorium compounds, thorium carbide exists in the form of NaCl face-centered cubic lattice at room temperature and pressure, offering several advantages: First, its high metal density effectively improves fuel efficiency, reduces costs, and increases the controllability of nuclear reactions; second, its high thermal conductivity (29 W / mK) enhances the heat transfer efficiency of the fuel and reduces the internal temperature gradient; third, its relatively high melting point (~2625 K) improves the fuel's high-temperature resistance and chemical stability; and fourth, it exhibits good compatibility with cladding materials. It is precisely because of these excellent physical properties that thorium carbide (ThC) is a suitable candidate reactor fuel.
[0004] To supply reactor fuel, the preparation of thorium carbide feedstock through a simple and economical process is crucial. In the 1950s, Scaife and Wylie observed no phase other than ThC2 in the reaction of thorium dioxide and graphite under a flowing argon atmosphere. Imai of the Japan Atomic Energy Research Institute used thorium dioxide and graphite as raw materials, dry-mixing and pressing them into shape, and then preparing thorium carbide through a carbothermic reduction method under an argon atmosphere. However, the above dry mixing method carries risks of uneven mixing, radioactive dust contamination, and spontaneous combustion of carbide powder. Recently, Parkison of Los Alamos National Laboratory in the United States has achieved thorium carbide formation in the intermediate stage of thorium nitride preparation via carbothermic reduction to nitridation. This is achieved by dry-mixing and pressing thorium dioxide and graphite into shape, then heating the pressed material to 1800°C at a ramp rate of 20°C / min under flowing argon atmosphere and holding it there for 20 hours. However, the above process has the following problems: prolonged high-temperature heat treatment causes significant wear and tear on production equipment; the reaction rate of powdered samples is generally higher than that of pressed and molded samples; and the carbothermic reduction rate under vacuum is higher than the reduction rate under argon atmosphere. Summary of the Invention
[0005] This invention provides a method for preparing thorium carbide, which solves the problems of low purity, environmental unfriendliness, and high cost in the preparation of thorium carbide in the prior art.
[0006] To solve the above-mentioned technical problems, the present invention provides a method for preparing thorium carbide, comprising the following steps:
[0007] Thorium dioxide and carbon are mixed to obtain a solid mixture;
[0008] The solid mixture and anhydrous ethanol were mixed at a solid-liquid ratio of 1:1.5 to obtain the precursor raw material;
[0009] Stir the precursor raw material until the anhydrous ethanol is completely evaporated, so as to further mix the precursor raw material evenly;
[0010] The stirred precursor material is placed in a vacuum or argon environment for carbothermic reduction reaction to obtain thorium carbide product.
[0011] The thorium carbide product is pulverized and ground to obtain thorium carbide powder.
[0012] In some implementations, the molar ratio of thorium dioxide to carbon is 1:3 during ingredient preparation.
[0013] In some implementations, the carbon is graphite powder with a purity of 99.999%.
[0014] In some implementations, the temperature of the carbothermic reduction reaction is greater than 1300°C.
[0015] In some implementations, the carbothermic reduction reaction lasts for 3 hours or more.
[0016] In some implementations, the container for the carbothermic reduction reaction is a graphite crucible; as an optional implementation, the crucible can also be made of tantalum; the material of the crucible should be resistant to oxidation, high temperature, and corrosion.
[0017] In some implementations, the carbothermic reduction reaction is specifically carried out by placing a graphite crucible containing thorium dioxide and carbon inside a carbonization furnace for the reaction, wherein the environment inside the carbonization furnace is 10°C during the reaction. -3 High vacuum of Pa.
[0018] In some implementations, the mixing method is to use a planetary ball mill, wherein the forward and reverse rotation speeds of the planetary ball mill are both set to 250 r / min, and the switching time between forward and reverse rotations is set to 5 min.
[0019] In some implementations, the thorium carbide product is pulverized by using a tablet press at a constant pressure of 1000-1500 MPa for 10-15 minutes. The purpose of using a tablet press to pulverize and compress the thorium carbide product is to prevent oxidation and hydrolysis of the thorium carbide. After the reaction is completed, the thorium carbide product is pulverized and compressed into tablets using a tablet press, and then manually pounded into a fine powder at the micron level using a mortar and pestle for component analysis.
[0020] In some implementations, the precursor raw material is stirred by drying it using a thermostatic magnetic stirrer, the temperature of which is set at 110°C.
[0021] The beneficial effects of this invention are:
[0022] (1) The preparation method of the present invention uses wet mixing, which not only avoids the risks of uneven mixing, radioactive dust pollution and spontaneous combustion of carbide powder, but also improves the purity of the product.
[0023] (2) The preparation method of the present invention uses powdered samples for high-temperature sintering, which improves the reaction rate and effectively shortens the reaction time;
[0024] (3) The preparation method of the present invention carries out a carbothermic reduction reaction under high vacuum, which improves the reaction rate, reduces the wear and tear on production equipment caused by high temperature heat treatment, and reduces the process cost.
[0025] (4) The thorium carbide powder obtained by the preparation method of the present invention has high purity. Attached Figure Description
[0026] Figure 1 This is a flowchart of the preparation method in this invention;
[0027] Figure 2 This is the XRD spectrum of thorium carbide (ThC) obtained in Example 2;
[0028] Figure 3 This is the XRD spectrum of thorium carbide (ThC) obtained in Example 3.
[0029] The accompanying drawings are for illustrative purposes only and should not be construed as limiting the scope of this patent. To better illustrate this embodiment, some components in the drawings may be omitted, enlarged, or reduced, and do not represent the actual dimensions of the product. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings. The same or similar reference numerals correspond to the same or similar components. The terms describing positional relationships in the drawings are for illustrative purposes only and should not be construed as limiting the scope of this patent. Detailed Implementation
[0030] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.
[0031] Example 1:
[0032] This invention provides a method for preparing thorium carbide, such as... Figure 1 As shown, it includes the following steps:
[0033] Step 1: Mixing
[0034] First, thorium dioxide and graphite powder are mixed in a suitable molar ratio, and then anhydrous ethanol is poured into the ball mill jar at a solid-liquid ratio of 1:1.5 for mixing.
[0035] Pour the well-mixed precursor raw materials into a beaker and stir with a constant temperature magnetic stirrer until the ethanol is completely evaporated to obtain a well-mixed powder.
[0036] The uniformity of material mixing is crucial and directly related to the purity of the product. Dry mixing is particularly difficult for achieving uniform mixing of solid raw materials. Solid-phase reactions generally occur between adjacent reactants, and mass migration is a limiting factor for complete reaction. If mass migration is hindered, the product composition will be non-uniform. Using anhydrous ethanol for wet mixing increases the contact area between materials, allowing for the preparation of thoroughly mixed and homogeneous raw materials.
[0037] Step 2: Sintering
[0038] Under high vacuum, the powdered material is poured into a graphite crucible and placed in a high-temperature carbonization furnace for carbothermic reduction sintering. The specific sintering temperature is set as follows: room temperature / 80min→1200℃ / 10min→1200℃ / 60min→1800℃ / 180min-1800℃ / 30min-1400℃ / -121 to obtain thorium carbide product.
[0039] Step 3: Crushing and Grinding
[0040] After the reaction is complete, the product is crushed and compressed into tablets using a tablet press, and then manually pounded into micron-sized thorium carbide (ThC) powder using a mortar and pestle.
[0041] The preparation method of this embodiment directly uses graphite powder to carbonize and reduce thorium dioxide, which is simple and easy to control. The wet mixing method avoids the risks of uneven mixing, radioactive dust pollution, and spontaneous combustion of carbide powder, while also improving the purity of the product. High-temperature sintering of powdered samples increases the reaction rate and effectively shortens the reaction time. Carbothermic reduction under high vacuum further increases the reaction rate, reduces the wear and tear on production equipment caused by high-temperature heat treatment, and lowers process costs. The thorium carbide powder obtained by this method has high purity.
[0042] Example 2:
[0043] This embodiment provides a method for preparing thorium carbide, which is implemented based on the method in Example 1.
[0044] It should be noted that,
[0045] In this embodiment, the graphite crucible is placed inside a carbonization furnace for a carbothermic reduction reaction, and the furnace environment is maintained at ~10°C during the reaction. - 3 High vacuum of Pa.
[0046] In this embodiment, to prevent residual water vapor in the mixed raw materials from oxidizing the reaction, a segmented heating method is used for carbothermic reduction sintering, raising the temperature to 1200℃ and holding it for 10 minutes to dry the material.
[0047] It should be noted in this embodiment that the crucible used in the preparation method of this embodiment is a graphite crucible. The graphite crucible participates in the carbothermic reduction reaction, which causes the amount of graphite to increase slightly based on the initial raw material molar ratio. Therefore, in the initial raw material preparation process, the amount of graphite is reduced by different amounts (20% to 0%) based on the (ThO2:C) 1:3 molar ratio for sintering to prepare thorium carbide.
[0048] The preparation method in this embodiment is as follows:
[0049] Weigh 8g of thorium dioxide and 0.98g of graphite powder. First, add the thorium dioxide and graphite powder to a zirconia ball mill jar at a molar ratio of 1:2.72 for mixing. Then, add anhydrous ethanol to the ball mill jar at a solid-liquid ratio of 1:1.5 and ball mill for 20 hours to obtain the precursor material. The forward and reverse rotation speeds of the ball mill are both set to 250 r / min, and the time interval between forward and reverse rotations is set to 5 min. Pour the uniformly mixed precursor material into a beaker and stir using a thermostatic magnetic stirrer until the ethanol is completely evaporated to obtain a thoroughly mixed powder. The temperature of the thermostatic magnetic stirrer is set to 110℃. Then, pour the powder into a cylindrical graphite crucible and place it in a high-temperature carbonization furnace for a carbothermic reduction reaction. After the above steps, thorium carbide product can be prepared.
[0050] Specifically, the furnace will be evacuated to a vacuum level of 5.7 × 10⁻⁶. -2 After Pa, the temperature is increased to 1200℃ at a rate of 15℃ / min and held for 10 min. This is to remove residual water vapor from the material to prevent oxidation. After holding, the temperature is increased to 1800℃ at a rate of 10℃ / min and held for 3 h. Then, the temperature is decreased to 1400℃ at a rate of 13℃ / min and then allowed to cool naturally to room temperature. The thorium carbide product is removed once the furnace temperature reaches room temperature.
[0051] The extracted thorium carbide product was pulverized and compressed into tablets using a tablet press at a constant pressure of 1500 MPa for 15 minutes. Then, it was manually pounded into micron-sized thorium carbide powder using an agate mortar and pestle. The obtained thorium carbide powder was characterized by XRD, and its XRD composition is shown in the figure below. Figure 2 As shown. By Figure 2 X-ray diffraction analysis of thorium carbide (ThC) showed that the main peaks were all diffraction peaks of thorium carbide, while 2θ contained a small amount of thorium dicarbide (ThC2) in the ranges of 27.12–27.48 and 30.3–30.39. No other diffraction peaks were observed. The purity of thorium carbide (ThC) was as high as 97.3%, demonstrating the effectiveness of this method.
[0052] It should be noted that in the prior art, under high-temperature thermal equilibrium conditions of 1300-1900℃, the carbothermic reduction reaction of thorium oxide and graphite in vacuum begins in a vacuum environment above 1300℃ when powdered ThO2 and C undergo carbothermic reduction.
[0053] The preparation method of this embodiment directly uses graphite powder to carbonize and reduce thorium dioxide, which is simple and easy to control. The wet mixing method avoids the risks of uneven mixing, radioactive dust pollution, and spontaneous combustion of carbide powder, while also improving the purity of the product. High-temperature sintering of powdered samples increases the reaction rate and effectively shortens the reaction time. Carbothermic reduction under high vacuum further increases the reaction rate, reduces the wear and tear on production equipment caused by high-temperature heat treatment, and lowers process costs. The thorium carbide powder obtained by this method has high purity.
[0054] Example 3:
[0055] This invention provides a method for preparing thorium carbide, which is implemented based on the method in Example 1.
[0056] It should be noted that,
[0057] In this embodiment, the graphite crucible is placed inside a carbonization furnace for a carbothermic reduction reaction, and the furnace environment is maintained at ~10°C during the reaction. - 3 High vacuum of Pa.
[0058] In this embodiment, to prevent residual water vapor in the mixed raw materials from oxidizing the reaction, a segmented heating method is used for carbothermic reduction sintering, raising the temperature to 1200℃ and holding it for 10 minutes to dry the material.
[0059] It should be noted in this embodiment that the crucible used in the preparation method of this embodiment is a graphite crucible. The graphite crucible participates in the carbothermic reduction reaction, which causes the amount of graphite to increase slightly based on the initial raw material molar ratio. Therefore, in the initial raw material preparation process, the amount of graphite is reduced by different amounts (20% to 0%) based on the (ThO2:C) 1:3 molar ratio for sintering to prepare thorium carbide.
[0060] The preparation method in this embodiment is as follows:
[0061] Weigh 8g of thorium dioxide and 1.09g of graphite powder. First, add the thorium dioxide and graphite powder to a zirconia ball mill jar at a molar ratio of 1:3 for mixing. Then, add anhydrous ethanol to the ball mill jar at a solid-liquid ratio of 1:1.5 and ball mill for 20 hours to obtain the precursor material. The forward and reverse rotation speeds of the ball mill are both set to 250 r / min, and the time interval between forward and reverse rotations is set to 5 min. Pour the uniformly mixed precursor material into a beaker and stir using a thermostatic magnetic stirrer until the ethanol is completely evaporated to obtain a thoroughly mixed powder. The temperature of the thermostatic magnetic stirrer is set to 110℃. Then, pour the powder into a cylindrical graphite crucible and place it in a high-temperature carbonization furnace for a carbothermic reduction reaction. After the above steps, thorium carbide product can be prepared.
[0062] Specifically, the furnace will be evacuated to a vacuum level of 5.7 × 10⁻⁶. -2 After Pa, the temperature is increased to 1200℃ at a rate of 15℃ / min and held for 10 min. This is to remove residual water vapor from the material to prevent oxidation. After holding, the temperature is increased to 1800℃ at a rate of 10℃ / min and held for 3 h. Then, the temperature is decreased to 1400℃ at a rate of 13℃ / min and then allowed to cool naturally to room temperature. The thorium carbide product is removed once the furnace temperature reaches room temperature.
[0063] The extracted thorium carbide product was pulverized and compressed into tablets using a tablet press at a constant pressure of 1500 MPa for 15 minutes. Then, it was manually pounded into micron-sized thorium carbide powder using an agate mortar and pestle. The obtained thorium carbide powder was characterized by XRD, and its XRD composition is shown in the figure below. Figure 3 As shown.
[0064] Depend on Figure 3 X-ray diffraction analysis of thorium carbide (ThC) showed that the main content peaks were all diffraction peaks of thorium carbide. A small amount of thorium dicarbide (ThC2) was present in the 2θ ranges of 27–27.54, 30.18–30.39, 45.93–46.38, 51.48–51.78, and 51.99–52.35. No other diffraction peaks were observed. However, the content of thorium dicarbide (ThC2) was relatively high, with a purity of 91.1%. This indicates that when the molar ratio of thorium dioxide to graphite was 1:3, the graphite crucible participated in the reduction reaction, resulting in an excess of graphite. Therefore, the prepared thorium carbide powder contained a high content of impurities (thorium dicarbide).
[0065] It should be noted that in the prior art, under high-temperature thermal equilibrium conditions of 1300-1900℃, the carbothermic reduction reaction of thorium oxide and graphite in vacuum begins in a vacuum environment above 1300℃ when powdered ThO2 and C undergo carbothermic reduction.
[0066] The preparation method of this embodiment directly uses graphite powder to carbonize and reduce thorium dioxide, which is simple and easy to control. The wet mixing method avoids the risks of uneven mixing, radioactive dust pollution, and spontaneous combustion of carbide powder, while also improving the purity of the product. High-temperature sintering of powdered samples increases the reaction rate and effectively shortens the reaction time. Carbothermic reduction under high vacuum further increases the reaction rate, reduces the wear and tear on production equipment caused by high-temperature heat treatment, and lowers process costs. The thorium carbide powder obtained by this method has high purity.
[0067] Numerous specific details are set forth in the specification provided herein. However, it will be understood that embodiments of the invention may be practiced without these specific details. Similarly, for the sake of brevity and to aid in understanding one or more aspects of the invention, in the description of exemplary embodiments of the invention above, various features of the embodiments are sometimes grouped together in a single embodiment, figure, or description thereof. The claims, which follow the detailed description, are hereby expressly incorporated into that detailed description, wherein each claim itself is a separate embodiment of the invention.
[0068] It should be noted that the above embodiments are illustrative of the invention and not restrictive, and that those skilled in the art can devise alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses should not be construed as limiting the claims.
[0069] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.
Claims
1. A method for preparing thorium carbide, characterized in that, Includes the following steps: Thorium dioxide and carbon are mixed to obtain a solid mixture; The solid mixture and anhydrous ethanol are mixed to obtain the precursor raw material; Stir the precursor raw material until the anhydrous ethanol is completely evaporated, so as to further mix the precursor raw material evenly; The stirred precursor material is placed in a vacuum or argon environment for carbothermic reduction reaction to obtain thorium carbide product. The thorium carbide product is pulverized and ground to obtain thorium carbide powder; The temperature of the carbothermic reduction reaction is greater than 1300℃; The reaction time of the carbothermic reduction reaction is greater than or equal to 3 hours; The container for the carbothermic reduction reaction is a graphite crucible.
2. The method for preparing thorium carbide according to claim 1, characterized in that: During the preparation of the ingredients, the molar ratio of thorium dioxide to carbon is 1:
3.
3. The method for preparing thorium carbide according to claim 1, characterized in that: The carbon is graphite powder.
4. The method for preparing thorium carbide according to claim 1, characterized in that, In the carbothermic reduction reaction, the specific method is as follows: the graphite crucible containing the thorium dioxide and the carbon is placed in a carbonization furnace for reaction, and the environment inside the carbonization furnace is 10°C during the reaction. -3 A high vacuum environment of Pa.
5. The method for preparing thorium carbide according to claim 1, characterized in that: The mixing method is to use a planetary ball mill, with both the forward and reverse rotation speeds of the planetary ball mill set to 250 r / min and the switching time between forward and reverse rotations set to 5 min.
6. The method for preparing thorium carbide according to claim 1, characterized in that: The thorium carbide product is pulverized by using a tablet press at a constant pressure of 1000-1500 MPa for 10-15 minutes.
7. The method for preparing thorium carbide according to claim 1, characterized in that: The precursor raw material is stirred by drying it using a constant temperature magnetic stirrer, the temperature of which is set at 110°C.