A method for preparing niobium carbide by flash sintering and niobium carbide

Abstract

The application belongs to the technical field of NbC material preparation, and particularly relates to a method for preparing niobium carbide through flash sintering and niobium carbide, wherein the preparation method comprises the following steps: mixing niobium-iron powder and carbon powder and performing compression molding to obtain a compact after vacuum drying; placing the compact in two pieces of carbon paper and performing flash sintering under vacuum to obtain a sintered body after cooling; crushing the sintered body into powder, and performing screening and separation to obtain niobium carbide. The application greatly shortens the preparation time of NbC by adopting the flash sintering technology, thereby reducing the production cycle, improving the production efficiency, and significantly reducing the energy consumption. The process flow is short, the operation is simple, and the reaction process is easy to control. By reducing the sintering temperature, shortening the process cycle and reducing the energy consumption, the preparation cost and carbon emission are effectively reduced while the performance of NbC is ensured, which meets the technical trend of green manufacturing and sustainable development.

Description

Technical Field

[0001] This application belongs to the field of NbC material preparation technology, specifically a method for preparing niobium carbide by flash sintering and niobium carbide. Background Technology

[0002] Niobium carbide (NbC) is a ceramic material with high hardness, high melting point, good thermal stability, and corrosion resistance. It exhibits excellent mechanical properties and wear resistance under high temperature and pressure, and is widely used in cemented carbide, cutting tools, and turbine blades, making it an important material in aerospace and other fields.

[0003] Currently, common methods for preparing NbC include high-temperature sintering (including Nb2O5 carbothermal reduction and metallic Nb carbide), chemical vapor deposition, sol-gel method, and reactive ball milling. Although these methods have achieved certain results, they still have some drawbacks and shortcomings. (1) High-temperature sintering: It usually needs to be carried out at a temperature higher than 2000℃ and the sintering time is long, resulting in high energy consumption and production costs. In addition, incomplete reactions between carbon and niobium source are easily generated during the sintering process, resulting in low product purity and large particle size of the material, which affects the performance of NbC. (2) Chemical vapor deposition: This method can prepare NbC at lower temperatures, but the operation process is complicated and the equipment cost is high. In addition, due to the difficulty in controlling gas flow, NbC often has a lot of pores, resulting in poor mechanical properties. (3) Sol-gel method: The sol-gel method is rarely used in the preparation of NbC. It is mainly used to prepare materials with small particle size. The preparation process of this method is complicated and the density and compactness of the obtained product are low, which limits its application range. (4) Reaction ball milling: This method utilizes the chemical reaction between metal or alloy powders and other elements or compounds during ball milling to prepare NbC products. It is mainly used to prepare ultrafine NbC products. Its disadvantages include long milling time, high energy consumption, easy introduction of impurities making subsequent separation and purification difficult, and the uniformity of composition is greatly affected by the milling parameters. Therefore, there is an urgent need to develop a low-carbon, short-process, and highly efficient NbC preparation method that also considers production costs.

[0004] Flash sintering is an emerging, ultrafast, controllable, and energy-efficient sintering technology that has been successfully applied in materials synthesis, waste and precious metal recycling. Flash sintering rapidly raises the temperature within a short time (≤3s), allowing materials to reach the required sintering temperature quickly, eliminating the need to maintain high temperatures for extended periods as in traditional sintering. This process, accompanied by instantaneous high current or high temperature, significantly improves sintering efficiency and reduces energy consumption, offering advantages such as high energy utilization, low-temperature sintering, rapid preparation, and improved material properties. Summary of the Invention

[0005] To address the aforementioned issues, this application provides a method for preparing niobium carbide by flash sintering and niobium carbide itself. This method utilizes flash sintering technology to prepare NbC, solving the technical problems of traditional processes such as time and energy consumption, long and complex process flow, easy introduction of impurities, large particle size, and low purity. Under flash sintering technology, NbC is synthesized efficiently and in one step, while simultaneously achieving high purity, ultrafine particle size, and low impurity content.

[0006] According to a first aspect of this application, this application provides a method for preparing niobium carbide by flash sintering, comprising the following steps: S1. Niobium iron powder and carbon powder are mixed and pressed into shape, and then vacuum dried to obtain a pressed blank. The niobium iron powder includes Nb2O5 and Fe2O3. S2. The pressed blank is placed between two pieces of carbon paper and flash sintered under vacuum. After cooling, a sintered body is obtained. S3. The sintered body is crushed and powdered, and then screened and separated to obtain the niobium carbide.

[0007] The above technical solution is based on the fundamental principle of carbothermic reduction. It uses carbon powder as a reducing agent, mixes it with niobium-iron powder, and then prepares NbC using flash sintering. Flash sintering involves applying Joule heating to both ends of the compact, heating it to over 2000℃ within ≤5 seconds. Through a solid-solid diffusion instantaneous reaction, NbC can be successfully prepared within ≤1 minute, significantly shortening the traditional sintering time of over ten hours and substantially reducing energy consumption. Niobium-iron powder contains oxides such as Nb₂O₅ and Fe₂O₃. After being mixed with carbon powder, during flash sintering, the Fe phase undergoes reduction and transformation first: the iron oxide (Fe₂O₃) is reduced to elemental iron (Fe) under high temperature and a carbothermic reducing atmosphere, forming a continuous metallic Fe matrix. Secondly, NbC grows in situ: NbC is generated in situ at the instantaneous high temperature of flash sintering and nucleates and grows on the surface of the Fe matrix, forming a sintered body with an Fe-based NbC composite structure. This sintered body contains a metallic iron matrix (gray) and NbC particles (white particles) attached to and growing on the iron matrix. The sintered body is then crushed and powdered. The NbC phase is relatively easy to detach from the iron matrix. Due to the difference in their properties, the NbC phase in the sintered body can be enriched and separated using simple physical separation methods, such as those based on hardness / brittleness, magnetism, density, and gravity. X-ray diffraction was performed on the isolated niobium carbide, and Rietveld-refined quantitative analysis was performed using GSASII software. The refined results showed good fit (R0). p =6.11%, R wp =9.58%, R exp=4.87%, GOF=1.97%), indicating that the mass fraction of NbC present is ≥95.4%. The average particle size of NbC particles is 4.0~8.0μm. As a hard reinforcing phase, it is uniformly distributed in the iron matrix, and the NbC particles are tightly bonded to the iron matrix interface. No obvious impurity phases were observed, which confirms the in-situ enrichment and growth mechanism of NbC on the Fe matrix.

[0008] Furthermore, in step S1, the mass fraction of Nb2O5 in the niobium iron powder is 54.0%~58.0%, the mass fraction of Fe2O3 is 34.0%~36.0%, and the ratio of the total mass of Nb2O5 and Fe2O3 in the niobium iron powder to the mass of the carbon powder is (3.10~3.20):1.

[0009] Furthermore, in step S2, the power output mode for the flash sintering is manual, with a current of 300~600A, a voltage ≤12V, a frequency of 20000~30000Hz, a time of 1~60s, and a vacuum degree of 10. -2 ~10 -3 Pa.

[0010] Furthermore, in step S2, the heating rate of the flash sintering is 10. 4 ~10 6 ℃ / min, temperature range: 1000~3000℃.

[0011] Furthermore, in step S2, the cooling rate is 10. 3 ~10 4 ℃ / min.

[0012] The above reaction is a strongly exothermic reaction. The ultrafast heating rate can rapidly overcome the solid-state diffusion stage and reaction energy barrier in the low-temperature region. Utilizing a transient electric field and Joule heating effect, niobium and carbon atoms diffuse and bond instantaneously. The sintering temperature is determined based on the thermodynamic stability of the NbC single-phase region in the niobium-carbon phase diagram. Compared with traditional processes, this application significantly reduces the reaction activation energy by utilizing electric field-assisted sintering, allowing it to be carried out at lower temperatures. Furthermore, due to the high grain boundary mobility of NbC within a specific temperature range, grain coalescence is highly likely. Rapid cooling can quickly "freeze" its microstructure, effectively suppressing secondary grain growth, thereby ensuring the stability of the average particle size of niobium carbide and a uniform particle size distribution.

[0013] Furthermore, in step S1, the vacuum drying time is 12~24 hours.

[0014] Furthermore, before step S1, the method further includes pre-drying the niobium iron powder and the carbon powder for a period of 12-24 hours.

[0015] Furthermore, in step S1, the pressed blank is cylindrical with a diameter of 5-20 mm, a height of 1-10 mm, and a mass of 1-5 g. The pressing pressure is 5-10 t, and the holding time is 1-10 min.

[0016] Furthermore, in step S2, the carbon paper has a length of 50~100mm, a width of 10~50mm, a height of 0.5~1mm, and a resistance of 0.5~1Ω.

[0017] Furthermore, in step S1, the carbon powder is graphite powder.

[0018] Furthermore, in step S1, the niobium iron powder and the carbon powder are mixed in an agate mortar for 30-60 minutes.

[0019] Furthermore, in step S2, the blank is placed between two parallel carbon paper sheets, such that the two carbon paper sheets completely wrap around the blank, and the carbon paper is in close contact with the blank to form a current path.

[0020] Furthermore, in step S2, the carbon paper is disposed on the surface of a rectangular electrode, and there are two pairs of electrodes, each pair of electrodes comprising a long electrode and a short electrode.

[0021] According to a second aspect of this application, this application provides niobium carbide prepared by the above-described flash sintering method, wherein the niobium carbide has a purity ≥95.4% and an average particle size of 4.0~8.0 μm.

[0022] This application proposes a method for preparing niobium carbide by flash sintering, and the niobium carbide itself produces the following beneficial effects: 1. This application uses flash sintering technology to greatly shorten the preparation time of NbC, thereby reducing the production cycle, improving production efficiency, and significantly reducing energy consumption; 2. This application can obtain NbC through simple raw material processing and flash sintering reduction, without the need for post-processing steps such as acid leaching and leaching, which greatly reduces the risk of impurities being introduced later and reducing purity. The process is short, simple to operate, and the reaction process is easy to control. 3. This application selects low-cost carbon as a reducing agent. By reducing the sintering temperature, shortening the process cycle and reducing energy consumption, the preparation cost and carbon emissions are effectively reduced while ensuring the performance of NbC, which is in line with the technological trend of green manufacturing and sustainable development. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0024] Figure 1 This is a SEM image of NbC prepared in Example 1 of this application; Figure 2 The image shows the XRD pattern of the product of Comparative Example 1 of this application; Figure 3 The XRD pattern of the product of Comparative Example 2 of this application; Figure 4 This is a SEM image of the product of Comparative Example 2 of this application.

[0025] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0026] The technical solutions in the embodiments will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0027] According to a first aspect of this application, this application provides a method for preparing niobium carbide by flash sintering, comprising the following steps: S1. Niobium iron powder and carbon powder are mixed and pressed into shape, and then vacuum dried to obtain a pressed blank. The niobium iron powder includes Nb2O5 and Fe2O3. Preferably, the niobium-iron powder is a powder raw material with Nb and Fe oxides as the main components, wherein the mass fraction of Nb2O5 is 54.0%~58.0% and the mass fraction of Fe2O3 is 34.0%~36.0% (which translates to a mass fraction of Nb of approximately 37.74%~40.54% and a mass fraction of Fe of approximately 23.78%~25.18%); the carbon powder is graphite powder. Before mixing, the niobium iron powder and carbon powder can be pre-dried for 12-24 hours. Then, they are mixed in an agate mortar for 30-60 minutes at a ratio of the total mass of Nb₂O₅ and Fe₂O₃ in the niobium iron powder to the mass of the carbon powder of (3.10-3.20):1. The resulting mixture is then pressed in a cylindrical mold at a pressure of 5-10t for 1-10 minutes. The resulting sample is then vacuum dried in a vacuum drying oven for 12-24 hours to remove residual moisture, yielding a compact with a diameter of 5-20 mm, a height of 1-10 mm, and a mass of 1-5 g. In some preferred embodiments of this application, the niobium iron powder has a particle size of 30-50 μm, which is beneficial for rapid and uniform mixing and molding; the particle size distribution span is ≤2.53, and the concentrated particle size contributes to uniform reaction; the specific surface area is ≤363.2 m². 2 The density of the graphite powder is ≥99.5% and has a density of 1.9~2.3 g / cm³, ensuring good particle contact and electrical conductivity. Simultaneously, the niobium-iron powder itself possesses excellent electrical conductivity, a crucial prerequisite for triggering and maintaining flash sintering. 3 The particle size is 10~15μm, and the specific surface area is 5000~20000m². 2 / kg.

[0028] The compact diameter is 5-20 mm and the height is 1-10 mm to maintain a suitable diameter-to-height ratio. In flash sintering, the current is mainly introduced through the compact surface and the electrode contact surface. The smaller height ensures that Joule heat energy quickly penetrates the entire compact, eliminating the temperature difference between the core and the surface, and achieving uniform sintering. Controlling the compact mass to 1-5 g is to match the instantaneous power output of the flash sintering equipment. Too little mass will cause the compact to evaporate or melt instantly upon power-on, while too much mass will prevent the heating rate from meeting the requirements of flash sintering, resulting in degradation to conventional sintering.

[0029] Carbon powder is used as a reducing agent in the above raw materials mainly because carbon (C) has thermodynamic and kinetic advantages: firstly, carbon has strong reducing properties, a strong affinity for oxygen (O), and is easily oxidized, thus making the reaction more favorable at high temperatures; secondly, carbon has a porous structure, which can generate CO / CO2 active gases in situ. In the reaction process, carbon (C) abstracts oxygen from Nb oxides, converting them into low-valence NbC. The main components of niobium-iron powder are Nb₂O₅ and Fe₂O₃, with small amounts of oxides such as MoO₃, SiO₂, and Al₂O₃, as well as other unavoidable trace impurities (the calculated total oxygen content is approximately 26.47~28.27%, which will be reduced by carbon during the subsequent flash sintering process). Nb₂O₅ is the main and only Nb oxide, and its reaction with carbon is based on the following equation: Nb₂O₅ + 7C = 2NbC + 5CO (g) To further determine the thermodynamic conditions for carbothermic reduction, the Gibbs free energy of both was calculated using HSC software and the above reaction equations. ): =789.91-0.81T, meaning theoretically, when the temperature is greater than 975℃, <0, the reaction can proceed spontaneously, producing NbC and CO simultaneously.

[0030] S2. Place the compact between two pieces of carbon paper and perform flash sintering under vacuum. After cooling, a sintered body is obtained. Preferably, the compact is placed between two parallel carbon paper sheets of identical size, ensuring the sheets completely enclose the compact to create a current path. The carbon paper has a resistance of 0.5~1Ω. The flash sintering power output mode is manual, with a current of 300~600A, voltage ≤12V, frequency of 20000~30000Hz, time of 1~60s, and vacuum level of 10. -2 ~10 -3 Pa; in addition, the heating rate of flash sintering is 10 Pa. 4 ~10 6 ℃ / min, temperature range of 1000~3000℃; cooling rate during cooling is 10 3 ~10 4 ℃ / min. In some preferred embodiments of this application, in order to completely enclose the compact, the carbon paper is 50~100mm long, 10~50mm wide, and 0.5~1mm high; the carbon paper is disposed on the surface of the rectangular electrode; corresponding to the carbon paper, there are two pairs of electrodes, each pair of electrodes including a long electrode and a short electrode used in conjunction.

[0031] The aforementioned flash sintering relies on a flash sintering apparatus, which includes a power supply system, a high-temperature heating system, and auxiliary systems. The power supply system comprises a high-frequency pulse power supply, a cooling water system, and electrical control and data acquisition devices. The high-frequency pulse power supply primarily provides an external electric field for flash sintering; it outputs voltage / current at specific frequencies and waveforms and is the core excitation device. The electric field lowers the activation energy of the material during sintering and provides a large current to generate Joule heating when the sample resistance drops sharply. Precise adjustment of key flash sintering process parameters such as voltage, current, frequency, and time is also mainly achieved through the high-frequency pulse power supply. The cooling water system provides circulating water cooling for key components such as the power supply, preventing damage due to high temperatures and ensuring stable system operation. The electrical control and data acquisition system mainly includes external ports and a computer. Through precise control of the power output, it collects and records voltage, current, and other data in real time during the flash sintering process.

[0032] The high-temperature heating system includes a sealed cavity, electrodes, carbon paper, insulating blocks, and copper wires. The sealed cavity, constructed from spliced ​​acrylic sheets, primarily provides the high-temperature environment for real-time monitoring of the sintering process. Through-holes on both sides of the cavity allow copper wires to connect the electrodes to the power supply system. The electrodes and carbon paper must be used in conjunction. The electrodes are made of pure copper and consist of two pairs, each pair including a long electrode and a short electrode. Two rectangular sheets of carbon paper are placed on the surfaces of the two pairs of electrodes for heat conduction. The sample is placed between the two sheets of carbon paper for flash sintering. Because the sample relies on the heating of the carbon paper, its temperature remains consistently lower than that of the carbon paper. The insulating blocks isolate the two pairs of electrodes to form a current loop.

[0033] The auxiliary system includes an infrared thermometer, a vacuum pump, connecting hoses, and a pressure gauge. Due to the ultra-rapid heating and cooling characteristics unique to flash sintering, traditional temperature measuring devices often struggle to provide real-time, accurate temperature measurements during the sintering process. An infrared thermometer, a non-contact temperature measurement method, offers advantages such as high sensitivity, fast response, and a wide temperature range, making it suitable for high-temperature and dynamically changing environments. During measurement, simply pointing the laser source at the sample allows for rapid temperature readings. The vacuum pump, in conjunction with the connecting hoses, removes air from the sealed cavity, maintaining a vacuum environment and preventing sample oxidation at high temperatures during flash sintering. During vacuum extraction, the pressure gauge monitors the internal vacuum level in real-time and displays it digitally to prevent insufficient or excessive vacuum.

[0034] S3. The sintered body is crushed and powdered, and then screened and separated to obtain niobium carbide; Preferably, they can be separated by simple methods such as hardness / brittleness difference separation, magnetic separation, acid washing and gravity separation.

[0035] Because metallic iron and niobium carbide differ significantly in hardness / brittleness, magnetism, chemical properties, and density, they can be efficiently separated using known physical or chemical methods to enrich high-purity niobium carbide. Specific separation methods include, but are not limited to: hardness / brittleness difference separation (based on differences in hardness and brittleness): During crushing, softer and more malleable iron particles and harder and more brittle niobium carbide particles will form different particle shapes or size distributions. Enrichment can be achieved through air classification or fine sieving, utilizing the aerodynamic behavior caused by particle shape and hardness, or differences in sieve capacity; magnetic separation (based on magnetic differences): Utilizing the magnetic properties of iron and the non-magnetic properties of niobium carbide, separation is achieved using magnetic separation equipment; acid washing (based on differences in chemical activity): Utilizing the solubility of iron in dilute acids (such as hydrochloric acid and sulfuric acid) and the chemical stability of niobium carbide, niobium carbide is obtained by dissolving the iron matrix through acid washing; gravity separation (based on density differences): Utilizing the density difference of iron (density 7.87 g / cm³), gravity separation is achieved by... 3 ) and niobium carbide (density 7.6~7.7 g / cm³) 3 Niobium carbide can be separated by density difference in airflow or liquid flow; or by electrical property difference: iron is a good conductor, while niobium carbide is a metal-ceramic material with poor conductivity. Electrostatic separation is used to separate charged particles due to their different conductivity paths in an electric field. Any of the above methods or a combination thereof can effectively separate niobium carbide. The purity of the separated niobium carbide is ≥95.4%, because in addition to the target product NbC, niobium carbide may contain some niobium-containing compounds such as NbO and Nb2C. Using the technical solution of this application, the mass fraction of the target product in the form of NbC in the obtained niobium carbide is ≥95.4%.

[0036] According to a second aspect of this application, this application provides niobium carbide prepared by the above-described flash sintering method, wherein the niobium carbide has a purity ≥95.4% and an average particle size of 4.0~8.0 μm.

[0037] The technical solution of this application will be further described below with reference to specific embodiments. The main chemical composition of the niobium iron powder used in the embodiments of this application is shown in Table 1: Table 1 Example 1 A method for preparing niobium carbide by flash sintering includes the following steps: S1. Mix niobium iron powder and graphite powder, take 2g and press into shape, and vacuum dry for 12h to obtain a pressed blank; The ratio of the total mass of Nb2O5 and Fe2O3 in the niobium iron powder to the mass of graphite powder is 3.16:1. The pressing pressure is 5t, the pressing time is 5min, the diameter of the pressed blank is 20mm, and the height is 1.5mm. S2. Place the compact between two parallel carbon paper sheets and perform flash sintering under vacuum. After cooling, a sintered body is obtained. The carbon paper measures 70mm in length, 30mm in width, and 1mm in height, with a resistance of 1Ω. The flash sintering process uses a current of 300A, a voltage of 12V, a time of 60s, a frequency of 20000Hz, and a vacuum level of 10. -3 Pa, heating rate 10 5 The temperature was monitored at ℃ / min, and the temperature of the pressed billet was 1100℃ using an infrared thermometer. The cooling rate was 10℃ / min. 4 ℃ / min; S3. The sintered body was crushed and powdered, and then screened to obtain niobium carbide. Testing showed that the purity of niobium carbide was 95.4%, the main crystalline phase was NbC, and there were no impurity peaks such as Nb2O5, NbO2, or free C. The product was pure, with an average particle size of 5.68 μm. Its SEM image is shown below. Figure 1 As shown, the particles are regularly spherical and show no obvious aggregation.

[0038] Example 2 A method for preparing niobium carbide by flash sintering includes the following steps: S1. Mix niobium iron powder and graphite powder, take 4g and press into shape, and vacuum dry for 24h to obtain a pressed blank. The ratio of the total mass of Nb2O5 and Fe2O3 in the niobium iron powder to the mass of graphite powder is 3.16:1. The pressing pressure is 10t, the pressing time is 10min, the diameter of the pressed blank is 20mm, and the height is 2.5mm. S2. Place the compact between two parallel carbon paper sheets and perform flash sintering under vacuum. After cooling, a sintered body is obtained. The carbon paper measures 80mm in length, 40mm in width, and 1mm in height, with a resistance of 1Ω. The flash sintering process uses a current of 600A, a voltage of 12V, a time of 60s, a frequency of 30000Hz, and a vacuum level of 10. -3 Pa, heating rate 10 6 The temperature was monitored at ℃ / min, and the temperature of the pressed billet was 2500℃ using an infrared thermometer. The cooling rate was 10℃ / min. 4 ℃ / min; S3. The sintered body is crushed and powdered, and then screened and separated to obtain niobium carbide. The purity of niobium carbide is 96.7%, the main crystalline phase is NbC, and there are no impurity peaks such as Nb2O5, NbO2 and free C. The product is pure, with an average particle size of 7.87μm and regular spherical shape.

[0039] Example 3 A method for preparing niobium carbide by flash sintering includes the following steps: S1. Mix niobium iron powder and graphite powder, take 1g and press into shape, and vacuum dry for 18h to obtain pressed blank; The ratio of the total mass of Nb2O5 and Fe2O3 in the niobium iron powder to the mass of graphite powder is 3.16:1. The pressing pressure is 7t, the pressing time is 7min, the diameter of the pressed blank is 10mm, and the height is 3.5mm. S2. Place the compact between two parallel carbon paper sheets and perform flash sintering under vacuum. After cooling, a sintered body is obtained. The carbon paper measures 70mm in length, 40mm in width, and 1mm in height, with a resistivity of 0.8Ω. The flash sintering process involves a current of 500A, a voltage of 12V, a time of 60s, a frequency of 25000Hz, and a vacuum level of 10. -3 Pa, heating rate is 10 6 The temperature was monitored at ℃ / min, with the compact temperature recorded at 2000℃ using an infrared thermometer, and the cooling rate was 10℃ / min. 4 ℃ / min; S3. The sintered body is crushed and powdered, and then screened and separated to obtain niobium carbide. The purity of niobium carbide is 96.1%, the main crystalline phase is NbC, and there are no impurity peaks such as Nb2O5, NbO2 and free C. The product is pure, with an average particle size of 7.12μm and regular spherical shape.

[0040] Comparative Example 1 A method for preparing niobium carbide by flash sintering includes the following steps: S1. Mix niobium iron powder and graphite powder, take 2g and press into shape, and vacuum dry for 12h to obtain pressed blank; The ratio of the total mass of Nb2O5 and Fe2O3 in the niobium iron powder to the mass of graphite powder is 3.16:1. The pressing pressure is 5t, the pressing time is 5min, the diameter of the pressed blank is 20mm, and the height is 1.5mm. S2. Place the compact between two parallel carbon paper sheets and perform flash sintering under vacuum. After cooling, a sintered body is obtained. The carbon paper measures 70mm in length, 30mm in width, and 1mm in height, with a resistance of 1Ω. The flash sintering process uses a current of 100A, a voltage of 4V, a time of 60s, a frequency of 20000Hz, and a vacuum level of 10. -3 Pa, heating rate 10 2 The temperature of the compact was monitored at ℃ / min, and the temperature of the compact was 530℃ using an infrared thermometer. The cooling rate was 10℃ / min. S3. The sintered body is crushed, powdered, and screened for separation. The resulting product is then analyzed by XRD (e.g., ...). Figure 2As shown in the figure, the main phases are unreacted niobium oxide, iron oxide, and gangue mineral phases. In addition, a large amount of carbon matrix is ​​present, and no niobium carbide diffraction peaks were detected. This indicates that under these low current conditions, the Joule heat provided by flash sintering is insufficient to bring the system to the reaction reduction temperature, and the flash sintering and carbothermic reduction reaction cannot be triggered, thus failing to prepare niobium carbide.

[0041] Comparative Example 2 A method for preparing niobium carbide by flash sintering includes the following steps: S1. Mix niobium iron powder and graphite powder, take 2g and press into shape, and vacuum dry for 12h to obtain pressed blank; The ratio of the total mass of Nb2O5 and Fe2O3 in the niobium iron powder to the mass of graphite powder is 3.16:1. The pressing pressure is 5t, the pressing time is 5min, the diameter of the pressed blank is 20mm, and the height is 1.5mm. S2. Place the compact between two parallel carbon paper sheets and perform flash sintering under vacuum. After cooling, a sintered body is obtained. The carbon paper measures 70mm in length, 30mm in width, and 1mm in height, with a resistance of 1Ω. The flash sintering process uses a current of 700A, a voltage of 15V, a time of 60s, a frequency of 20000Hz, and a vacuum level of 10. -3 Pa, heating rate 10 7 At ℃ / min, the moment the power was turned on, the billet showed a glaring bright light and violent splashing. During this period, the temperature of the billet was monitored by an infrared thermometer and instantly exceeded the instrument's range (>3000℃). Then the power was quickly cut off. After cooling, the billet was found to be severely damaged, cracked, and deformed, with obvious signs of reduced quality.

[0042] S3. The sintered body is crushed, powdered, and screened for separation. The resulting product is then analyzed by XRD (e.g., ...). Figure 3 As shown in the image, although the product contains niobium carbide, it also exhibits a large amount of free carbon and impurity phase diffraction peaks such as Nb₂C, NbO, and Fe₃C. SEM observation shows (e.g.) Figure 4 As shown in the figure, the product has an extremely uneven microstructure, containing a large number of abnormally large particles and pores formed by melting and solidification. After refined quantitative analysis by Rietveld, the purity of niobium carbide was found to be less than 70%, and the particle size distribution was wide, completely failing to meet the requirements for use as a high-performance hard material. This indicates that excessively high current leads to excessive input energy, causing localized evaporation, decomposition, and instantaneous melting of the compact, thus disrupting the uniformity and controllability of the reaction.

[0043] In flash sintering, voltage and current jointly determine the input power. When the carbon paper resistance is fixed, voltage and current are directly proportional. Excessive voltage means excessive current and power, which can lead to thermal runaway, damage, and fragmentation of the compact. Excessive instantaneous power results in an extremely rapid heating rate, with the local temperature of the compact far exceeding the stable range of niobium carbide, causing the compact to melt, evaporate, or sputter, making it impossible to maintain its basic shape. It can also trigger arc discharge, breaking down the compact or carbon paper, causing localized ablation and contaminating the final product. Furthermore, even if niobium carbide is obtained under these conditions, the instantaneous high temperature will cause drastic grain growth, resulting in the loss of its fine-grained advantage.

[0044] Compared with the comparative examples above, Examples 1-3 of this application have specific current ranges (300-600A) and heating rates (10... 4 ~10 6 Under precise raw material ratios (3.10~3.20:1) at ℃ / min, the simultaneous rapid reduction of niobium and iron oxides and the in-situ synthesis of niobium carbide were successfully achieved, yielding niobium carbide products with a purity ≥95.4%.

[0045] The above description is only a preferred embodiment of this application and does not limit the patent scope of this application. All equivalent structural transformations made using the content of this application's specification under the inventive concept of this application, or direct / indirect applications in other related technical fields, are included within the patent protection scope of this application.

Claims

1. A method for preparing niobium carbide by flash sintering, characterized in that, Includes the following steps: S1. Niobium iron powder and carbon powder are mixed and pressed into shape, and then vacuum dried to obtain a pressed blank. The niobium iron powder includes Nb2O5 and Fe2O3. The mass fraction of Nb2O5 in the niobium iron powder is 54.0%~58.0%, and the mass fraction of Fe2O3 is 34.0%~36.0%. The ratio of the total mass of Nb2O5 and Fe2O3 in the niobium iron powder to the mass of the carbon powder is (3.10~3.20):

1. S2. The pressed blank is placed between two sheets of carbon paper and flash-sintered under vacuum. After cooling, a sintered body is obtained. The flash-sintering heating rate is 10°C. 4 ~10 6 The speed is ℃ / min, the temperature is 1000~3000℃, and the flash sintering current is 300~600A; S3. The sintered body is crushed and powdered, and then screened and separated to obtain the niobium carbide.

2. The method for preparing niobium carbide by flash sintering according to claim 1, characterized in that, In step S2, the power output mode for the flash sintering is manual, voltage ≤12V, frequency 20000~30000Hz, time 1~60s, and vacuum degree 10. -2 ~10 -3 Pa.

3. The method for preparing niobium carbide by flash sintering according to claim 1, characterized in that, In step S2, the cooling rate is 10. 3 ~10 4 ℃ / min.

4. The method for preparing niobium carbide by flash sintering according to claim 1, characterized in that, In step S1, the vacuum drying time is 12-24 hours.

5. The method for preparing niobium carbide by flash sintering according to claim 1, characterized in that, Before step S1, the method further includes pre-drying the niobium iron powder and the carbon powder for 12-24 hours.

6. The method for preparing niobium carbide by flash sintering according to claim 1, characterized in that, In step S1, the pressed blank is cylindrical with a diameter of 5-20 mm, a height of 1-10 mm, and a mass of 1-5 g. The pressing pressure is 5-10 t and the holding time is 1-10 min.

7. The method for preparing niobium carbide by flash sintering according to claim 1, characterized in that, In step S2, the carbon paper has a length of 50~100mm, a width of 10~50mm, a height of 0.5~1mm, and a resistance of 0.5~1Ω.

8. A niobium carbide, characterized in that, The niobium carbide was prepared by the flash sintering method according to any one of claims 1 to 7, wherein the niobium carbide has a purity ≥ 95.4% and an average particle size of 4.0 to 8.0 μm.

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