Nitrogen-oxygen atmosphere controllable high-temperature oxidation method for porous sponge zirconium

Abstract

The invention discloses a nitrogen-oxygen atmosphere controllable high-temperature oxidation method for porous sponge zirconium, and relates to the technical field of nuclear fuel circulation and materials.The method comprises the following steps that S1, unqualified porous sponge zirconium materials are loaded into a high-temperature oxidation furnace, and then inert gas is introduced into the oxidation furnace to exhaust air; s2, the furnace temperature is increased to the target oxidation temperature at the set heating rate, and meanwhile mixed gas of nitrogen and oxygen is introduced into the furnace; s3, at the target oxidation temperature, keeping constant temperature and continuously introducing the mixed gas for oxidation reaction; and S4, after oxidation is finished, heating is stopped, and inert gas continues to be introduced for protective cooling to the room temperature. According to the method provided by the invention, the catalytic effect of nitrogen in the oxidation process is utilized to promote the porous sponge zirconium to be quickly and uniformly converted into zirconium oxide which is stable in phase and adaptive to subsequent ball milling in particle size and hardness, and the oxidation conversion rate is greater than or equal to 98%.

Description

Technical Field

[0001] This invention belongs to the field of nuclear fuel cycle and materials technology, specifically relating to a method for high-temperature oxidation of substandard sponge zirconium with porous and irregular structures, and in particular a process for achieving efficient and uniform oxidation by precisely controlling a nitrogen-oxygen atmosphere. Background Technology

[0002] Nuclear-grade sponge zirconium is a key material for nuclear reactor fuel cladding. During its production, approximately 20% of the zirconium ingots are de-scaling and filtration processes, resulting in substandard products such as surface oxides and filtration residues. These substandard products are irregularly shaped, porous, and exhibit significantly different physical properties compared to qualified dense zirconium materials. Currently, these substandard products are mostly disposed of at low prices, causing substantial economic losses and a waste of strategic resources. To achieve the recycling and reuse of substandard sponge zirconium, it is necessary to first convert it into a stable intermediate product that is easily processed. Oxidation treatment is a crucial step in converting metallic zirconium into zirconium oxide (ZrO2). However, traditional single high-temperature oxidation or air oxidation methods face severe challenges when processing porous and irregular sponge zirconium: due to the porous and irregular shape of the material, the heat and oxygen transfer inside the material is uneven, which can easily lead to "outer ripening and inner stagnation" or local over-oxidation, resulting in large differences in product properties; the formation of a dense oxide layer will hinder the inward diffusion of oxygen, resulting in a slow oxidation rate, long processing cycle, and high energy consumption; the product properties are uncontrollable: the particle size, hardness, phase, etc. of the oxidation products directly affect the subsequent ball milling efficiency and chlorination effect, and traditional methods cannot guarantee the stability and uniformity of product properties.

[0003] Therefore, there is an urgent need to find an oxidation method that can efficiently and uniformly process porous sponge zirconium and seamlessly integrate with subsequent recycling processes. Summary of the Invention

[0004] In view of the deficiencies in the existing technology, the purpose of this invention is to provide a nitrogen-oxygen atmosphere controllable high-temperature oxidation method for porous sponge zirconium. Using this method, the material can be rapidly and uniformly oxidized to obtain zirconium oxide with uniform and stable physical properties, and can meet the requirements of subsequent ball milling processes.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A nitrogen-oxygen atmosphere-controlled high-temperature oxidation method for porous sponge zirconium includes the following steps:

[0007] S1. The substandard porous sponge zirconium material is loaded into a high-temperature oxidation furnace, and then inert gas is introduced into the oxidation furnace to expel air.

[0008] S2. Raise the furnace temperature to the target oxidation temperature at the set heating rate, while simultaneously introducing a mixture of nitrogen and oxygen into the furnace.

[0009] S3. At the target oxidation temperature, maintain a constant temperature and continuously introduce the mixed gas to carry out the oxidation reaction;

[0010] S4. After oxidation is complete, stop heating and continue to pass inert gas for protective cooling to room temperature.

[0011] Furthermore, in the nitrogen-oxygen atmosphere controlled high-temperature oxidation method for porous sponge zirconium described above, during the loading process in step S1, it is ensured that the material is loosely packed to facilitate atmosphere flow.

[0012] Furthermore, in the nitrogen-oxygen atmosphere controlled high-temperature oxidation method for porous sponge zirconium described above, the heating rate in step S2 ranges from 5 to 20 °C / min.

[0013] Furthermore, in the nitrogen-oxygen atmosphere controlled high-temperature oxidation method for porous sponge zirconium described above, the target oxidation temperature in step S2 is 500℃~1000℃.

[0014] Furthermore, in the nitrogen-oxygen atmosphere controlled high-temperature oxidation method for porous sponge zirconium described above, the target oxidation temperature range in step S2 is 700℃~900℃.

[0015] Furthermore, in the nitrogen-oxygen atmosphere controlled high-temperature oxidation method for porous sponge zirconium as described above, the oxygen volume concentration in the mixed gas in step S2 ranges from 0% to 100%.

[0016] Furthermore, in the nitrogen-oxygen atmosphere controlled high-temperature oxidation method for porous sponge zirconium as described above, the oxygen volume concentration in the mixed gas in step S2 ranges from 20% to 80%.

[0017] Furthermore, in the nitrogen-oxygen atmosphere controlled high-temperature oxidation method for porous sponge zirconium described above, the oxidation reaction time in step S3 is 1-8 hours.

[0018] Compared with the prior art, the nitrogen-oxygen atmosphere controllable high-temperature oxidation method for porous sponge zirconium provided by the present invention has the following beneficial effects:

[0019] This invention precisely controls the ratio of nitrogen to oxygen, utilizing the catalytic effect of nitrogen to alter oxidation kinetics, breaking down the diffusion barrier of the dense oxide layer, and achieving rapid and uniform oxidation of the material to obtain zirconium oxide with uniform and stable physical properties. The oxidation product's particle size and hardness are highly compatible with the requirements of subsequent ball milling processes, providing an ideal raw material for chlorination purification. This method fundamentally solves the uniformity and efficiency problems in the oxidation process of porous sponge zirconium, significantly improving the overall stability and economy of the non-conforming product recycling process, and providing key technical support for the green recycling and high-value utilization of nuclear-grade zirconium materials. Attached Figure Description

[0020] To further illustrate the above and other advantages and features of this application, the specific embodiments of this application will be described in more detail below with reference to the accompanying drawings. The accompanying drawings, together with the following detailed description, are included in and form a part of this specification. It should be understood that these drawings only depict typical examples of this application and should not be considered as limiting the scope of this application.

[0021] Figure 1 This is a flowchart of a nitrogen-oxygen atmosphere-controlled high-temperature oxidation method for porous sponge zirconium provided in a specific embodiment of the present invention. Detailed Implementation

[0022] Exemplary embodiments of this application will be described below with reference to the accompanying drawings. For clarity and brevity, not all features of actual implementations are described in the specification. However, it should be understood that many implementation-specific decisions must be made in the development of any such actual embodiment to achieve the developer's specific goals, such as complying with constraints related to the system and business, and these constraints may vary depending on the implementation. Furthermore, it should be understood that while development work can be very complex and time-consuming, such development work is merely a routine task for those skilled in the art who benefit from the content of this application.

[0023] It should also be noted that, in order to avoid obscuring this application with unnecessary details, only the equipment structure and / or processing steps closely related to the solution according to this application are shown in the accompanying drawings, while other details that are not closely related to this application are omitted.

[0024] The embodiments or examples disclosed below are used to implement this application. To simplify the disclosure of this application, the components and methods of specific examples are described below. Of course, they are merely examples and are not intended to limit this application.

[0025] To address the problems of poor uniformity, low efficiency, and unstable product properties in the oxidation treatment of porous and irregular sponge zirconium in existing technologies, this invention provides a high-temperature oxidation method with controllable nitrogen-oxygen atmosphere. The core of this method lies in precisely controlling the oxidation temperature and the ratio of nitrogen-oxygen mixed atmosphere, utilizing the "catalytic" effect of nitrogen under specific conditions to change the oxidation kinetics, break the diffusion barrier of the dense oxide layer, thereby achieving rapid, deep, and uniform oxidation of porous sponge zirconium, and obtaining zirconium oxide products with stable physical properties and easy subsequent processing.

[0026] The technical principle of this invention is that introducing an appropriate amount of nitrogen gas during high-temperature oxidation can significantly promote the oxidation kinetics of sponge zirconium. The mechanism is as follows: In the initial stage of oxidation, oxygen reacts with zirconium to form a dense ZrO2 layer, which hinders further internal diffusion of oxygen, leading to a decrease in the oxidation rate. However, in a nitrogen-oxygen mixed atmosphere, nitrogen molecules also react with zirconium to generate a small amount of zirconium nitride (ZrN) mesophase. ZrN is gradually oxidized to ZrO2 during subsequent oxidation. This phase transition, accompanied by volume change, induces microcracks in the dense ZrO2 layer. These microcracks provide additional rapid channels for oxygen to diffuse inward, thereby significantly accelerating the overall oxidation reaction rate and ensuring uniform and thorough oxidation even for irregular, thick-walled porous sponge zirconium. By precisely controlling the temperature and nitrogen-oxygen ratio, this "catalytic" effect can be optimized, avoiding excessive formation or insufficient oxidation of zirconium nitride, thus obtaining a zirconium oxide product with uniform properties and easy ball milling.

[0027] The processing flowchart of this method is as follows: Figure 1 As shown, the method mainly includes the following steps:

[0028] S1. Charging and Atmosphere Replacement: Unqualified porous sponge zirconium material is charged into the high-temperature oxidation furnace to ensure that the material is loosely packed and facilitates atmosphere flow; then inert gas (such as argon or nitrogen) is introduced into the furnace to purge air until the oxygen content in the furnace drops to a predetermined threshold (such as <1%).

[0029] S2. Programmed heating and atmosphere control: The furnace temperature is raised to the target oxidation temperature at a set heating rate (e.g., 5-20℃ / min), which is 500-1000℃. At the same time, a mixture of nitrogen and oxygen with a preset volume concentration is introduced into the furnace, wherein the oxygen concentration is adjustable from 0% to 100% and the nitrogen concentration is adjustable from 0% to 100%.

[0030] S3. Constant Temperature Oxidation: At the target oxidation temperature, maintain a constant temperature and continuously introduce a nitrogen-oxygen mixture in a set ratio to carry out the oxidation reaction. The oxidation time is 1-8 hours.

[0031] S4. Cooling and Discharging: After oxidation is complete, stop heating and continue to pass inert gas for protective cooling to room temperature, then remove the oxidation product.

[0032] Compared with the prior art, the beneficial effects of the present invention are reflected in:

[0033] 1) Through the "catalytic" effect of nitrogen, the diffusion limitation of the dense oxide layer is effectively broken, the oxidation rate is significantly improved, and the oxidation uniformity of porous and irregular materials is ensured.

[0034] 2) By adjusting the temperature-atmosphere-time process parameters, the phase composition, particle size distribution and hardness of the oxidation products can be precisely controlled, making them more suitable for the subsequent ball milling process requirements.

[0035] 3) This method can be implemented in a dedicated modular vertical oxidation furnace, is easy to integrate into existing non-conforming product recycling production lines, is simple to operate, and has controllable operating costs.

[0036] Example 1

[0037] The oxidation method used in this embodiment to treat substandard sponge zirconium comprises the following steps:

[0038] 1) Take 1 kg of surface oxides and filter material (unqualified sponge zirconium) generated during the production process of CNNC Crystal Ring Zirconium Industry, and loosely pack them into the alumina crucible of the laboratory tube furnace.

[0039] 2) Seal the furnace body and introduce high-purity argon gas (flow rate 2L / min) for atmosphere replacement for 30 minutes to ensure that all air in the furnace is exhausted.

[0040] 3) Raise the furnace temperature to 800℃ at a heating rate of 10℃ / min. At the same time, switch the gas source to a nitrogen-oxygen mixture, with an oxygen volume concentration of 50% and a nitrogen volume concentration of 50%, and maintain the total flow rate of the mixture at 2L / min.

[0041] 4) Oxidize at 800℃ for 4 hours while continuously introducing a mixture of 50% N2 and 50% O2.

[0042] 5) After oxidation, stop heating and switch to pure argon gas for protective cooling to room temperature (<50℃). Remove the oxidation product, which is observed to be a uniform white to light gray blocky or granular ZrO2. XRD phase analysis shows that the product is mainly monoclinic ZrO2. Samples were taken for oxidation conversion calculation; the conversion rate, determined by gravimetric method, is ≥99%.

[0043] Example 2

[0044] The oxidation method of this embodiment was used to study the effect of different nitrogen-oxygen ratios on the oxidation effect:

[0045] 1) Take several portions of the same batch of unqualified sponge zirconium, each weighing 1 kg, and load them into a high-temperature furnace.

[0046] 2) In all experiments, the oxidation temperature was uniformly set to 800℃, and the oxidation time was 4h. The ratio of nitrogen and oxygen mixture was changed to: 100% O2, 80% O2 + 20% N2, 50% O2 + 50% N2, 20% O2 + 80% N2, and 100% N2.

[0047] 3) After oxidation, the products were characterized. The results showed that oxidation was relatively complete in a 100% O2 atmosphere, but the product surface was dense, and some large pieces of material had slight under-oxidation inside; the oxidation products had the best uniformity in 80% O2 + 20% N2 and 50% O2 + 50% N2 atmospheres, and the products were loose and brittle, which was conducive to ball milling; the oxidation rate decreased slightly in a 20% O2 + 80% N2 atmosphere, but was still better than in a pure oxygen atmosphere; in a 100% N2 atmosphere, a golden yellow zirconium nitride film was formed on the sample surface, and the oxidation conversion rate was extremely low.

[0048] 4) Conclusion: At 800℃, mixing N2 and O2 at concentrations of 20%-80% can effectively promote oxidation, with 50% N2-50% O2 showing the best effect.

[0049] Example 3

[0050] The oxidation method of this embodiment was used to conduct a pilot-scale test at the 100-kilogram scale:

[0051] 1) Take 100 kg of substandard sponge zirconium and put it into the basket of a specially developed vertical modular high-temperature oxidation furnace.

[0052] 2) After the furnace body is sealed, the air is first replaced with argon. Then the temperature is increased to 900℃ at a program of 15℃ / min.

[0053] 3) After reaching the target temperature, introduce a mixed gas with a volume ratio of 40% N2-60% O2 and oxidize at a constant temperature for 5 hours.

[0054] 4) After oxidation, argon gas is introduced to cool the product to the discharge temperature. After discharge, the oxidation product consists of uniform grayish-white ZrO2 particles and small pieces. Random samples were taken for particle size distribution and hardness testing. The results showed that the product had a concentrated particle size distribution and a hardness comparable to ZrO2 obtained from calcined Zr(OH)4, meeting the feed requirements for subsequent ball milling. Based on material balance calculations, the oxidation conversion rate of this batch is ≥98.5%.

[0055] This invention provides a controlled high-temperature oxidation method for porous sponge zirconium using a nitrogen-oxygen atmosphere. By precisely controlling the ratio of nitrogen to oxygen, the oxidation kinetics are altered through the catalytic effect of nitrogen, breaking down the diffusion barrier of the dense oxide layer and achieving rapid and uniform oxidation of the material to obtain zirconium oxide with uniform and stable properties. The oxidation product exhibits particle size and hardness highly compatible with the requirements of subsequent ball milling processes, providing an ideal raw material for chlorination purification. This method fundamentally solves the problems of uniformity and efficiency in the oxidation process of porous sponge zirconium, significantly improving the overall stability and economy of the non-conforming product recycling process, and providing key technical support for the green recycling and high-value utilization of nuclear-grade zirconium materials.

[0056] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention is also intended to include these modifications and variations.

Claims

1. A method for controlled high-temperature oxidation of porous sponge zirconium in a nitrogen and oxygen atmosphere, comprising the following steps: S1. The substandard porous sponge zirconium material is loaded into a high-temperature oxidation furnace, and then inert gas is introduced into the oxidation furnace to expel air. S2. Raise the furnace temperature to the target oxidation temperature at the set heating rate, while simultaneously introducing a mixture of nitrogen and oxygen into the furnace. S3. At the target oxidation temperature, maintain a constant temperature and continuously introduce the mixed gas to carry out the oxidation reaction; S4. After oxidation is complete, stop heating and continue to pass inert gas for protective cooling to room temperature.

2. The nitrogen-oxygen atmosphere controlled high-temperature oxidation method for porous sponge zirconium according to claim 1, characterized in that, In step S1, ensure that the material is piled up loosely during loading to facilitate air circulation.

3. The nitrogen-oxygen atmosphere controlled high-temperature oxidation method for porous sponge zirconium according to claim 2, characterized in that, The heating rate in step S2 is in the range of 5-20℃ / min.

4. The nitrogen-oxygen atmosphere controlled high-temperature oxidation method for porous sponge zirconium according to claim 3, characterized in that, The target oxidation temperature in step S2 is 500℃~1000℃.

5. The nitrogen-oxygen atmosphere controlled high-temperature oxidation method for porous sponge zirconium according to claim 4, characterized in that, The target oxidation temperature range in step S2 is 700℃~900℃.

6. The method for controlled high-temperature oxidation of porous sponge zirconium in a nitrogen-oxygen atmosphere according to any one of claims 1-5, characterized in that, The oxygen volume concentration in the mixed gas in step S2 ranges from 0% to 100%.

7. The nitrogen-oxygen atmosphere controlled high-temperature oxidation method for porous sponge zirconium according to claim 6, characterized in that, The oxygen volume concentration in the mixed gas in step S2 ranges from 20% to 80%.

8. The nitrogen-oxygen atmosphere controlled high-temperature oxidation method for porous sponge zirconium according to claim 1, characterized in that, The oxidation reaction in step S3 lasts for 1-8 hours.

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