Process for preparing niobium bar by high temperature sintering

Abstract

The application discloses a process for preparing a niobium strip through high-temperature sintering, and comprises the following steps: S1, mixing niobium oxide and carbon black to obtain a mixture one; S2, carbonizing the mixture one in a carbonization furnace to obtain niobium carbide; S3, mixing the niobium carbide and the niobium oxide to obtain a mixture two; S4, performing a strip pressing operation on the mixture two to obtain a green strip; and S5, placing the green strip into a vacuum sintering furnace to perform stage sintering, first keeping the temperature at 800-1200 DEG C for 3-5 hours, then increasing the temperature to 1700-1800 DEG C and keeping the temperature for 4-6 hours, and then increasing the temperature to 1900-2000 DEG C and keeping the temperature for 22-26 hours; according to the preparation process, the process flow is shortened, the preparation reaction time is shortened, the energy consumption in the production process is reduced, and the production efficiency is improved.

Description

Technical Field

[0001] This invention relates to the field of powder metallurgy technology, and more specifically to a process for preparing niobium strips by high-temperature sintering. Background Technology

[0002] Niobium, with its excellent high-temperature strength, corrosion resistance, superconductivity, and good electrical and thermal conductivity, has become an indispensable core material in high-tech fields such as aerospace, superconducting technology, high-end electronics, and precision chemicals. In recent years, domestic demand for niobium has surged, with the high-temperature alloy and superconducting markets booming. Domestic niobium bar manufacturers have long relied on traditional manufacturing processes, resulting in relatively outdated technology, long reaction cycles, high energy consumption, and high costs. This has led to low production capacity for niobium bars, making it difficult to meet the rapidly increasing demand.

[0003] Currently, the most widely used and closest to the process route of this invention in the domestic niobium bar manufacturing industry is the carbothermal reduction process. This is the standardized production method adopted by most niobium bar manufacturers in China. However, this process requires tens of hours of high-temperature sintering in a vacuum sintering furnace to complete the carbothermal reduction reaction, deeply remove interstitial impurities, and densify the billet. This results in a long reaction cycle, low production efficiency, high overall energy consumption, and high production costs. Therefore, there is an urgent need for a manufacturing process that can shorten the niobium bar manufacturing process and reduce the sintering reaction time while meeting the required quality standards.

[0004] Publication No. CN104439264B discloses a method for preparing niobium strips, which also employs a carbothermal reduction process, including the following steps: 1) carbon preparation, 2) carbonization, 3) vacuum reduction, and 4) hydrogenation. The process involves dehydrogenation, 5) molding, and 6) pre-sintering. The parameters in the sintering step are: pre-sintering temperature 1750~1950℃, pre-sintering time 75~90 hours. The reaction time of this method is too long, resulting in high production costs.

[0005] CN107297497B discloses a process for preparing niobium bars, using niobium oxide as raw material, mainly including the following steps: A. Carbonization: mixing niobium oxide and carbon black evenly; B. Carbonization: placing the mixture obtained in step A into a carbonization furnace for carbonization to obtain niobium carbide; C. Nitrogen reduction: adding a nitrogen-reducing agent to the niobium carbide and mixing evenly, wherein the nitrogen-reducing agent mainly consists of alcohol, rubber, magnesium, sodium, and a coagulant; D. Crushing: crushing the mixture obtained in step C; E. Mixing: adding niobium oxide to the crushed material and mixing evenly; F. Molding: pressing the mixture obtained in step E into a mold. Type G, Vacuum Sintering: The shaped material obtained in step F is placed in a vacuum reduction furnace for sintering to obtain the finished product. During sintering, the temperature inside the vacuum reduction furnace is first raised to 1250~1300℃ and held for 4~10 hours. Then, the temperature inside the furnace is raised to 1400~1700℃ and held for 15~25 hours. Finally, the temperature inside the furnace is raised to 1800~2000℃ and held for more than 40 hours. The sintering process of this process is too long, resulting in high energy consumption. In addition, in order to reduce the gaseous nitrogen content in the finished product, a nitrogen reduction step is added, making its production process more complicated than the conventional process route. Summary of the Invention

[0006] To solve the above-mentioned technical problems, the present invention provides a process for preparing niobium strips by high-temperature sintering.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A process for preparing niobium strips by high-temperature sintering includes the following steps: S1: Niobium oxide and carbon black are mixed at a weight ratio of 100:30~33 to obtain mixture one; S2: The mixture is placed in a carbonization furnace for carbonization to obtain niobium carbide; S3: Mix the niobium carbide and niobium oxide in a weight ratio of 100:45~55 to obtain mixture two; S4: The mixture 2 is fed into an automatic press for pressing into strips to obtain raw material strips; S5: Place the raw material strips into a vacuum sintering furnace for staged sintering. Stage 1: Hold at 800~1200℃ for 3~5 hours, then raise the temperature to 1700~1800℃ and hold for 4~6 hours, then raise the temperature to 1900~2000℃ and hold for 22~26 hours.

[0008] Furthermore, in step S1, the mixing time is 2 to 3 hours.

[0009] Furthermore, the purity of the carbon black is greater than 98%.

[0010] Furthermore, in step S1, a conical mixer is used for mixing.

[0011] Furthermore, in step S2, the carbonization temperature is set at 1800~2000℃.

[0012] Furthermore, in step S2, the material is fed into the carbonization furnace in a continuous feeding manner, and the time from feeding to discharging of each boat of material is controlled within 4 to 5 hours.

[0013] Furthermore, in step S3, the niobium carbide is ball-milled and crushed before mixing, and then passed through a 100-mesh sieve.

[0014] Furthermore, in step S3, the mixing time is 4 to 10 hours.

[0015] Furthermore, in step S4, an automatic press is used for pressing, and the pressure of the automatic press is set at 9 MPa to 12 MPa.

[0016] Furthermore, in step S5, the vacuum level inside the vacuum sintering furnace is controlled within 1~5 Pa.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: The preparation process of this invention precisely controls the reaction time and temperature through staged sintering. The impurities in the niobium strips are removed by the stage of vacuum sintering and heat preservation. Without adding additional nitrogen reduction process steps, the impurity of N is significantly reduced, and the content of other impurities also meets the quality requirements, shortening the process flow. In addition, by controlling the reaction time and temperature, the total reaction time of the sintering stage is controlled to about 34 hours, which greatly shortens the preparation reaction time, reduces energy consumption in the production process, and improves production efficiency. Attached Figure Description

[0018] Figure 1 This is a process flow diagram for preparing niobium strips by high-temperature sintering. Detailed Implementation

[0019] The technical features of the present invention can be clearly explained. The present invention will be described in detail below through specific embodiments and with reference to the accompanying drawings.

[0020] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and therefore the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0021] Furthermore, in the description of this invention, it should be understood that the terms "center," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "axial," "radial," and "circumferential," etc., indicating orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. In addition, 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 indicated technical features. Thus, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0022] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a communication connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0023] In this invention, unless otherwise expressly specified and limited, the "on" or "below" of the second feature can mean that the first feature is in direct contact with the second feature, or that the first and second features are in indirect contact through an intermediate medium. In the description of this specification, references to terms such as "an embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described can be combined in any suitable manner in one or more embodiments or examples.

[0024] Example 1 Please see Figure 1 This embodiment provides a process for preparing niobium strips by high-temperature sintering, including the following steps: S1: Niobium oxide and carbon black are mixed at a weight ratio of 100:30 to obtain mixture one.

[0025] In step S1, a cone mixer is used for mixing, and the mixing time is 2 hours.

[0026] S2: The mixture is placed in a carbonization furnace for carbonization to obtain niobium carbide.

[0027] In step S2, the material is fed into the carbonization furnace continuously, and the time from feeding to discharging of each boat of material is controlled within 4 hours. The carbonization temperature is set at 1800℃.

[0028] S3: Mix the niobium carbide and niobium oxide in a weight ratio of 100:45 to obtain mixture two.

[0029] In step S3, the niobium carbide is first ball-milled and crushed before mixing, and then passed through a 100-mesh sieve; the mixing time is 4 hours.

[0030] S4: The mixture is fed into an automatic press for strip forming to obtain raw material strips.

[0031] In step S4, an automatic press is used for pressing, and the pressure of the automatic press is set at 9 MPa.

[0032] S5: Place the raw material strips into a vacuum sintering furnace for staged sintering. Stage 1: Hold at 800℃ for 5 hours, then raise the temperature to 1700℃ and hold for 6 hours, then raise the temperature to 1900℃ and hold for 26 hours.

[0033] In step S5, the vacuum level inside the vacuum sintering furnace is controlled at 1 Pa.

[0034] After the niobium bars were removed from the furnace, the impurity content was tested, and the test data are shown in Table 1.

[0035] Table 1: Impurity test results in Example 1

[0036] Example 2 Please see Figure 1 This embodiment provides a process for preparing niobium strips by high-temperature sintering, including the following steps: S1: Niobium oxide and carbon black are mixed at a weight ratio of 100:32 to obtain mixture one.

[0037] In step S1, a cone mixer is used for mixing, and the mixing time is 3 hours.

[0038] S2: The mixture is placed in a carbonization furnace for carbonization to obtain niobium carbide.

[0039] In step S2, the material is fed into the carbonization furnace continuously, and the time from feeding to discharging of each boat of material is controlled within 5 hours. The carbonization temperature is set at 2000℃.

[0040] S3: Mix the niobium carbide and niobium oxide in a weight ratio of 100:50 to obtain mixture two.

[0041] In step S3, the niobium carbide is first ball-milled and crushed before mixing, and then passed through a 100-mesh sieve; the mixing time is 10 hours.

[0042] S4: The mixture is fed into an automatic press for strip forming to obtain raw material strips.

[0043] In step S4, an automatic press is used for pressing, and the pressure of the automatic press is set at 11 MPa.

[0044] S5: Place the raw material strips into a vacuum sintering furnace for staged sintering. Stage 1: Hold at 1000℃ for 4 hours, then raise the temperature to 1750℃ and hold for 5 hours, then raise the temperature to 1900℃ and hold for 24 hours.

[0045] In step S5, the vacuum level inside the vacuum sintering furnace is controlled at 5 Pa.

[0046] After the niobium bars were removed from the furnace, the impurity content was tested, and the test data are shown in Table 2.

[0047] Table 2: Impurity test results in Example 2

[0048] Example 3 Please see Figure 1 This embodiment provides a process for preparing niobium strips by high-temperature sintering, including the following steps: S1: Niobium oxide and carbon black are mixed at a weight ratio of 100:33 to obtain mixture one.

[0049] In step S1, a cone mixer is used for mixing, and the mixing time is 2 hours.

[0050] S2: The mixture is placed in a carbonization furnace for carbonization to obtain niobium carbide.

[0051] In step S2, the material is fed into the carbonization furnace continuously, and the time from feeding to discharging of each boat of material is controlled within 4 hours. The carbonization temperature is set at 1900℃.

[0052] S3: Mix the niobium carbide and niobium oxide in a weight ratio of 100:55 to obtain mixture two.

[0053] In step S3, the niobium carbide is first ball-milled and crushed before mixing, and then passed through a 100-mesh sieve; the mixing time is 8 hours.

[0054] S4: The mixture is fed into an automatic press for strip forming to obtain raw material strips.

[0055] In step S4, an automatic press is used for pressing, and the pressure of the automatic press is set at 10 MPa.

[0056] S5: Place the raw material strip into a vacuum sintering furnace for staged sintering. Stage 1: Hold at 1200℃ for 3 hours, then raise the temperature to 1800℃ and hold for 4 hours, then raise the temperature to 2000℃ and hold for 22 hours.

[0057] In step S5, the vacuum level inside the vacuum sintering furnace is controlled at 4 Pa.

[0058] After the niobium bars were removed from the furnace, the impurity content was tested, and the test data are shown in Table 3.

[0059] Table 3: Impurity test results in Example 3

[0060] Comparative Example 1 The experimental conditions in this embodiment follow the preparation process disclosed in Example 1 of Publication No. CN107297497B, and the steps are as follows: A. Carbon addition: Niobium oxide and carbon black are mixed evenly in a high-efficiency ball mill to obtain mixture one; wherein the weight ratio of niobium oxide to carbon black is 100:30.

[0061] B. Carbonization: The mixture obtained in step A is placed in a carbonization furnace for carbonization. The carbonization temperature is set to 1700℃ to obtain niobium carbide.

[0062] C. Nitrogen Reduction: Nitrogen reduction agent is added to niobium carbide and mixed evenly to obtain mixture two. The nitrogen reduction agent is mainly composed of alcohol, rubber, magnesium, sodium and coagulant. The mass percentage of niobium carbide, alcohol, rubber, magnesium, sodium and coagulant is 91% niobium carbide: 6% alcohol: 5‰ rubber: 5‰ magnesium: 5‰ sodium: 1% coagulant.

[0063] D. Crushing: The mixture obtained in step C is crushed to obtain crushed material.

[0064] E. Mixing: Niobium oxide is added to the pulverized material and mixed evenly to obtain mixture three. The weight ratio of the pulverized material to niobium oxide is set to 1:1.2.

[0065] F. Molding: The mixture obtained in step E is pressed into shape.

[0066] G. Vacuum sintering: The shaped material obtained in step F is placed in a vacuum reduction furnace for sintering. First, the temperature inside the vacuum reduction furnace is raised to 1250℃ and held for 10 hours. Then, the temperature inside the furnace is raised to 1400℃ and held for 25 hours. Finally, the temperature inside the furnace is raised to 1800℃ for 48 hours, so that the vacuum degree inside the furnace reaches 5 Pa, and the finished product is obtained.

[0067] The impurity content of the finished niobium strips in step G was tested, and the test data are shown in Table 4.

[0068] Table 4: Impurity test results in Comparative Example 1

[0069] To verify the technical effectiveness of the niobium bar preparation process described in this invention, niobium bars were prepared using the process schemes of Examples 1-3 of this invention. The niobium bar preparation process disclosed in Publication No. CN107297497B was used as Comparative Example 1. The chemical composition of the finished product was analyzed according to the technical requirements of the TNb2 grade in GB / T6896-2007. The analysis showed that the measured values ​​of 14 impurity elements (C, O, N, W, Fe, Ti, Cr, Al, Ta, Mo, Zr, Ni, Cu, and Si) in the niobium bars prepared in Examples 1-3 and Comparative Example 1 were all lower than those in GB / T6896-2007. In 2007, the upper limit of the TNb2 grade specifications and the purity of the niobium matrix all met the requirement of Nb≥99.5%, and the product quality fully met the standard requirements of industrial niobium strips. In Comparative Example 1, an independent denitrification process was added, and an additional denitrification mixture composed of alcohol, rubber, magnesium, sodium, and coagulant was added, resulting in a final nitrogen content of 0.013%. This invention, by precisely matching and controlling the temperature and time of staged sintering, can stably control the nitrogen content of the finished product at 0.008%~0.011% without adding an independent denitrification process or any denitrification additives, thus simplifying the process of niobium strip preparation.

[0070] In addition, a statistical comparison of the total holding time during the vacuum sintering stage was conducted, and the results are as follows: Comparative Example 1: The sintering process is divided into three heat preservation stages, with a total heat preservation time of 83 hours (1250℃×10h+1400℃×25h+1800℃×48h). Example 1: The total holding time for the three-stage sintering was 37 hours (800℃×5h+1700℃×6h+1900℃×26h), which was 55.4% shorter than the comparative example; Example 2: The total holding time for the three-stage sintering was 33 hours (1000℃×4h+1750℃×5h+1900℃×24h), which was 60.2% shorter than the comparative example; Example 3: The total holding time for the three-stage sintering was 29 hours (1200℃×3h+1800℃×4h+2000℃×22h), which was 65.1% shorter than the comparative example.

[0071] As can be seen, this invention reduces the total vacuum sintering time from 83 hours in the existing technology to 29-37 hours through three-stage precise temperature control sintering, a reduction of up to 65%. The overall energy consumption of the vacuum sintering furnace, including power consumption and labor costs, is significantly reduced, while the production capacity per unit time is greatly increased.

[0072] 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 can make other variations or modifications 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 process for preparing niobium strips by high-temperature sintering, characterized in that: Includes the following steps: S1: Niobium oxide and carbon black are mixed at a weight ratio of 100:30~33 to obtain mixture one; S2: The mixture is placed in a carbonization furnace for carbonization to obtain niobium carbide; S3: Mix the niobium carbide and niobium oxide in a weight ratio of 100:45~55 to obtain mixture two; S4: The mixture 2 is fed into an automatic press for pressing into strips to obtain raw material strips; S5: Place the raw material strips into a vacuum sintering furnace for staged sintering. Stage 1: Hold at 800~1200℃ for 3~5 hours, then raise the temperature to 1700~1800℃ and hold for 4~6 hours, then raise the temperature to 1900~2000℃ and hold for 22~26 hours.

2. The process for preparing niobium strips by high-temperature sintering according to claim 1, characterized in that: In step S1, the mixing time is 2 to 3 hours.

3. The process for preparing niobium strips by high-temperature sintering according to claim 1, characterized in that: The purity of the carbon black is greater than 98%.

4. The process for preparing niobium strips by high-temperature sintering according to claim 1, characterized in that: In step S1, a cone mixer is used for mixing.

5. The process for preparing niobium strips by high-temperature sintering according to claim 1, characterized in that: In step S2, the carbonization temperature is set at 1800~2000℃.

6. The process for preparing niobium strips by high-temperature sintering according to claim 1, characterized in that: In step S2, the material is fed into the carbonization furnace in a continuous feeding manner, and the time from feeding to discharging of each boat of material is controlled within 4 to 5 hours.

7. The process for preparing niobium strips by high-temperature sintering according to claim 1, characterized in that: In step S3, the niobium carbide is first ball-milled and crushed before mixing, and then passed through a 100-mesh sieve.

8. The process for preparing niobium strips by high-temperature sintering according to claim 1, characterized in that: In step S3, the mixing time is 4 to 10 hours.

9. The process for preparing niobium strips by high-temperature sintering according to claim 1, characterized in that: In step S4, an automatic press is used for pressing, and the pressure of the automatic press is set at 9 MPa to 12 MPa.

10. The process for preparing niobium strips by high-temperature sintering according to claim 1, characterized in that: In step S5, the vacuum level inside the vacuum sintering furnace is controlled within 1~5 Pa.

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