Nano tantalum carbide ceramic powder and preparation method thereof

Abstract

The invention discloses nano tantalum carbide ceramic powder and a preparation method thereof, and belongs to the technical field of advanced ceramic preparation. The method comprises the following steps: carrying out alcoholysis reaction on a tantalum source and n-butyl alcohol under a protective atmosphere to obtain tantalum alkoxide; adding a complexing agent and alkali metal halide into the tantalum alkoxide, and mixing to obtain precursor gel; and finally, performing pyrolytic reaction after the precursor gel is prepared into powder, and cleaning and removing impurities. Alkali metal halide is introduced into a metal organic precursor system, low-temperature controllable synthesis of nano tantalum carbide is realized by utilizing the molecular-level dispersion characteristic of the precursor and the dispersion promoting effect of the alkali metal halide, and meanwhile, high purity and particle size uniformity of the product are ensured; the problems of high energy consumption, low efficiency, poor performance and the like in the existing TaC powder preparation process are solved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of advanced ceramic preparation technology, and relates to a nano-powder of tantalum carbide ceramic and a preparation method thereof, in particular to a conversion method for preparing a nano-TaC ceramic powder by regulating and controlling a metal-organic precursor containing an alkali metal salt prepared by a sol-gel method and pyrolyzing the precursor. BACKGROUND

[0002] Tantalum carbide (TaC) ceramic is an important transition metal carbide coating material, with a melting point as high as 3880℃, ultra-high hardness, excellent Young's modulus, and good thermal and electrical conductivity. It also exhibits outstanding wear resistance, corrosion resistance and catalytic activity in extreme environments, and is widely used in high-speed cutting tools, aircraft engine blades, nuclear reactor cladding, electronic heat dissipation substrates and fuel cell catalyst carriers, etc. The demand in aerospace and precision manufacturing is continuously growing.

[0003] At present, the preparation methods of TaC powder mainly include carbothermal reduction method, metal thermal reduction method, chemical vapor deposition method, physical vapor deposition method and sol-gel method. Among them, carbothermal reduction method and chemical vapor deposition method are the mainstream choices due to their high technical maturity, but both have significant technical bottlenecks: the carbothermal reduction method is a method of using carbon as a reducing agent to reduce the metal in the metal oxide at high temperature, and at the same time, the corresponding carbide is generated by combining with carbon. The traditional carbothermal reduction method for preparing tantalum carbide is to reduce Ta2O5 with carbon, and the reaction process is as follows:

[0004] Ta2O5(s) + 7C (s) → 2TaC (s) + 5CO (g) (1);

[0005] However, carbothermal reduction method is essentially a high-temperature solid-phase reaction, which requires heating the reaction system to 1500-2000℃. The extremely high temperature results in high energy consumption per unit product, and puts high requirements on the high-temperature resistance and heat preservation performance of the reaction furnace, leading to significant increase in equipment investment and operating cost. In addition, the long-term high-temperature environment easily causes excessive grain growth and abnormal agglomeration, resulting in the prepared TaC powder generally being in micron level (usually 5-50 μm), wide particle size distribution and poor uniformity, making it difficult to obtain ultra-fine or nano-sized powder, which limits its application in high-precision and high-performance fields. In addition, the long high-temperature heat preservation period also greatly reduces the production efficiency, making it difficult to meet the high-efficiency production demand of modern manufacturing industry.

[0006] Chemical vapor deposition method (CVD) also has obvious limitations. It requires high-purity tantalum halide, methane and other gaseous raw materials, and the reaction process needs to be carried out in a closed high-pressure environment, which requires high equipment sealing performance and corrosion resistance, resulting in high equipment investment cost. At the same time, the deposition rate is slow, which is difficult to meet the demand of large-scale industrial production.

[0007] To solve the above problems, researchers have made improvements through various ways. For example, Chinese patent CN110746190A discloses a low-temperature rapid preparation method of tantalum carbide ceramic, which provides carbon source and tantalum source simultaneously in the reaction process. The single-source precursor prepared has good uniformity and high reactivity. However, when using single-source precursor to prepare tantalum carbide powder, although the reaction temperature is lower than that of the traditional carbothermic reduction method, the overall reaction temperature is still relatively high, resulting in high energy consumption. At the same time, during the pyrolysis process, as the pyrolysis temperature increases, the particle size of TaC particles will increase significantly, resulting in a product grain size of only micron level.

[0008] For example, Chinese patent CN101723367A discloses a preparation method of nano-tantalum carbide powder, which adds nano-sized activated carbon powder into the liquid precursor, which can act as both carbon source and nucleating agent for tantalum oxide, so that the tantalum oxide and the subsequently formed tantalum pentoxide and tantalum carbide can maintain nano size and the reaction temperature can be reduced. However, this method has obvious defects: on the one hand, the particle size control of tantalum carbide is highly dependent on the size range of activated carbon, which greatly limits the selection of raw material sources; on the other hand, nano-activated carbon itself has poor dispersibility and is easy to agglomerate, resulting in agglomeration of tantalum carbide powder during sintering.

[0009] Therefore, developing a preparation process that can reduce the reaction temperature by adjusting the composition of the precursor, ensure that the particle size distribution and grain size distribution of the product are both nano-scale, high-purity and non-agglomerated, has become the focus of current research. SUMMARY

[0010] In view of the problems of high preparation temperature, uneven particle size of the prepared tantalum carbide powder, large grain size, low purity and easy agglomeration in the existing preparation methods of tantalum carbide powder, the first object of the present application is to provide a preparation method of nano-tantalum carbide ceramic powder, which introduces alkali halide into the metal organic precursor system, utilizes the molecular dispersion characteristics of the precursor and the dispersion-promoting effect of the alkali halide, realizes the low-temperature controllable synthesis of nano-tantalum carbide, and ensures the high purity, particle size uniformity and grain uniformity of the product.

[0011] The second object of the present application is to provide a nano-tantalum carbide ceramic powder with narrow particle size distribution and good dispersibility.

[0012] In order to achieve the above technical purposes, the present application provides a preparation method of nano-tantalum carbide ceramic powder, comprising the following steps:

[0013] S1 subjecting a tantalum source to alcoholysis reaction with n-butanol under a protective atmosphere to obtain a tantalum alkoxide;

[0014] S2 adding complexing agent and alkali metal halide into tantalum alkoxide, mixing to obtain precursor gel;

[0015] S3 after the precursor gel is powdered, pyrolysis reaction and impurity removal are carried out, and then the method ends.

[0016] The key of the technical scheme of the present application is that alkali metal halide is introduced into the metal organic precursor system, so that nano-sized high-purity and non-agglomerated tantalum carbide powder can be synthesized at low temperature. Specifically, the alkali metal halide can react with the transition metal precursor to generate non-volatile liquid alkali metal salt, and these liquid intermediates can fuse with each other, reduce the nucleation density and promote the growth of the powder; at the same time, the alkali metal halide can also act as a catalyst to reduce the reaction energy barrier and increase the surface reaction rate; more importantly, the reaction of the alkali metal halide with the precursor can also form high-activity volatile metal oxyhalides with a lower evaporation temperature, which can act as a dispersion medium in the pyrolysis process, further reduce the activation energy and hinder the formation of sintering necks between particles, and promote the uniformity of the particle size.

[0017] The unique mechanism of the alkali metal halide in the system of the present application is that, as an ionic compound, the alkali metal halide does not need external intermediate triggering, and the halide ion directly forms an unstable coordination intermediate with the Ta ion in the tantalum source by virtue of strong nucleophilicity, thereby reducing the Ta-O bond breaking energy; the alkali metal ion can polarize the C-H bond of n-butanol, promote the activation and migration of the C atom, and thus essentially reduce the reaction energy barrier of the Ta-C bond. Thus, the generation temperature of TaC can be reduced from the traditional 1500-2000℃ to 1300-1500℃, which significantly reduces the energy consumption and inhibits grain coarsening. In the precursor stage, the ionic characteristics of the alkali metal halide salt can also produce ion-hydrogen bond synergies with the complexing groups of the complexing agent and the hydroxyl groups of n-butanol, inhibit the hydrolysis of Ta ions, achieve the molecular-level uniform distribution of Ta and C elements, and avoid phase separation and composition segregation. In the pyrolysis process, the liquid phase formed by the alkali metal halide has low viscosity and moderate volatility, can uniformly wrap the TaC grains to inhibit sintering, and can avoid residual through gradual volatilization, so that the particle size is stable at the nanoscale; and these liquid phases can also be wrapped on the surface of the grains to inhibit the excessive growth of the grains and also play a role in refining the grains. In addition, the alkali metal halide has large solubility, and the un-volatilized part can be completely removed through simple water washing without heavy metal residues, which ensures the high purity and green environmental protection characteristics of the product, so that it can be directly used in high-end application scenarios such as electronic packaging and catalytic carriers.

[0018] Compared with the carbon source commonly used in the prior art, the n-butanol selected by the present application has the properties of carbon source and organic solvent. It has a longer carbon chain and a higher carbon content, can provide more active carbon atoms, and thus can avoid the generation of Ta2O5 residues or Ta2C intermediate phases due to insufficient carbon source. In the precursor formation stage, the n-butanol has moderate polarity, is easy to form a stable mixed solvent system with the tantalum source and the alkali metal halide, and realizes the molecular-level uniform dispersion of Ta, C and alkali metal ions. At the same time, the long carbon chain of the n-butanol is more easily polarized and activated under the catalysis of the alkali metal halide, and the generated active carbon atoms can react with Ta 5+ efficiently combined. In the pyrolysis process, the n-butanol can slowly decompose, gradually release the carbon source and react with Ta 5+ , avoid incomplete carbonization caused by rapid escape of the carbon source, and the active carbon atoms generated by decomposition of the long carbon chain are more reactive and are not easy to form free carbon impurities, thereby further ensuring the purity of the obtained tantalum carbide ceramic powder.

[0019] As a preferred scheme, the tantalum source is selected from at least one of the group consisting of tantalum pentachloride, potassium heptafluorotantalate and ethanoltantalum. Further preferably, the tantalum source is tantalum pentachloride. It has been found that when the tantalum source is the tantalum pentachloride selected by the present application, the halogen atoms can combine with H to generate volatile halides in the process of reacting with the n-butanol to form tantalum alcoholates, thereby avoiding the influence of impurity atoms on the purity of the tantalum carbide powder.

[0020] As a preferred scheme, the alkali metal halide is selected from at least one of the group consisting of potassium bromide, potassium chloride, potassium iodide, sodium chloride, sodium bromide and sodium iodide. Further preferably, the alkali metal halide is at least one of potassium bromide and potassium chloride.

[0021] As a preferred scheme, the complexing agent comprises acetylacetone.

[0022] As a preferred scheme, the conditions of the alcoholysis reaction are as follows: 1: (8~10) of the tantalum source and the alcohol solvent, the temperature is 45~50℃, and the time is 30~60min.

[0023] As a preferred scheme, the molar ratio of the complexing agent to the alkali metal halide is (1.8~3.5):(1~1.5).

[0024] As a preferred scheme, the molar ratio of the alkali metal halide to the tantalum source is (0.8~1.5):1.

[0025] In the present application, the complexing agent can coordinate with the tantalum alkoxide compound to form a stable complex, inhibiting the hydrolysis of tantalum ions to improve the uniformity of the precursor composition. The amount of added alkali metal halide needs to be controlled within the range of the present application. If the amount is too small, the roles of the catalyst and liquid phase former cannot be fully played, resulting in insufficient decrease in the Ta-O bond breaking energy, reduced C atom activation and migration efficiency, and difficulty in effectively reducing the reaction energy barrier, so that the TaC generation temperature cannot be significantly lowered, which is not conducive to the inhibition and uniformity control of nanocrystalline grains. At the same time, insufficient coordination of halide ions with Ta ions will weaken their inhibitory ability on the hydrolysis of Ta ions, which is not conducive to the molecular-level uniform distribution of Ta and C in the precursor, and is easy to cause phase separation or composition segregation in the subsequent pyrolysis process. If the amount of added alkali metal halide is too large, the excess low-viscosity liquid phase excessively wraps the crystal nucleus, which instead inhibits the moderate growth and fusion of TaC grains, affecting the integrity of the crystallization process.

[0026] As a preferred scheme, in S2, the temperature of the mixing is 70-80℃, and the reaction time is 4-6h. Within the temperature range and time range of the present application, the components can be molecularly mixed and coordinated in the solvent, so as to obtain a precursor gel with uniform composition.

[0027] As a preferred scheme, in S3, the precursor gel is dried in a vacuum environment at 70-80℃ to obtain a porous precursor gel, and then powdering is performed. In the present application, the vacuum environment can accelerate the volatilization rate of water and dispersant, while avoiding oxidation of raw materials during the drying process. If the drying temperature is too high, the carbon source will decompose too early, and if the temperature is too low, the drying efficiency will be significantly reduced. At the same time, the dried xerogel needs to be crushed and ground to be free of obvious lumps, and then sieved to obtain a dry gel powder with uniform particle size.

[0028] As a preferred scheme, in a protective atmosphere, first increase the temperature to 700-750℃ at a rate of 10℃ / min, keep the temperature for 10-20min, then increase the temperature to 1300-1500℃ at a rate of 5-10℃ / min, keep the temperature for 1-5h, then reduce the temperature to 800-900℃ and cool to room temperature with the furnace. In the present application, the powder can be prevented from being oxidized at high temperature in a protective atmosphere. Then, through low-temperature short-time holding, the metal-organic precursor is pyrolyzed to generate intermediates containing Ta-O and Ta-C bonds, and the alkali metal salt is melted and reacts with the oxygen-containing intermediates to form a non-volatile liquid alkali metal salt. At this stage, a large amount of TaC crystal phase has not yet been formed. Then, through high-temperature long-time holding, the amorphous carbon reacts with the Ta-O bond through carbothermal reduction to gradually deoxidize and generate TaC crystal nuclei and grow. The liquid alkali metal salt acts as a fluxing agent to promote the reaction and inhibit the abnormal growth of the crystal grains. Finally, by reducing the temperature to 800-900℃, the TaC crystal lattice is arranged regularly, and the residual alkali metal salt is solidified and distributed in the grain boundaries, which plays a pinning effect on the microstructure.

[0029] As a preferred scheme, the cleaning and impurity removal is first water washing and then acid washing. The application utilizes the water solubility of alkali metal halide, and most of the residual alkali metal halide can be removed by water washing, and then a small amount of metal oxide impurities can be effectively dissolved by acid washing, further improving the purity of the product.

[0030] Further, vacuum drying treatment is carried out after cleaning and impurity removal.

[0031] The application also provides a nano-particle tantalum carbide ceramic powder obtained by the above preparation method. The nano-particle tantalum carbide ceramic powder prepared by the application has narrow particle size distribution, good dispersibility, high purity, and spherical particle morphology.

[0032] As a preferred scheme, the particle size is 150-560 nm, the grain size is 100-400 nm, and the TaC phase content is greater than or equal to 98 wt%. The particle size in the application refers to the overall size of the nano-particle tantalum carbide ceramic powder product after cleaning and impurity removal, and the particle size is determined by the particle dispersibility; the grain size is the crystallographic size of the single crystal region inside the particle. Further, the particle size range of D50 of the nano-particle tantalum carbide ceramic powder of the application is 300-475 nm.

[0033] Compared with the prior art, the application has the following beneficial effects

[0034] (1) The application significantly reduces the synthesis temperature of the TaC powder by introducing alkali metal halide, shortens the reaction time compared with the traditional process, and improves the energy utilization efficiency. At the same time, the alkali metal halide in the system can also act as a catalyst to reduce the reaction energy barrier and improve the surface reaction rate; more importantly, the reaction of the alkali metal halide with the precursor can also form a high-activity volatile metal halide oxide with a lower evaporation temperature, which acts as a dispersion medium in the pyrolysis process, further reduces the activation energy and hinders the formation of sintering necks between particles, promotes the uniformity of particle size, and effectively avoids the occurrence of agglomeration.

[0035] (2) The application uses n-butanol to replace the existing carbon source and introduces alkali metal halide in the precursor stage, thereby ensuring the molecular-level dispersion of tantalum and carbon elements in the precursor stage. The alkali metal halide and the precursor form a non-volatile liquid alkali metal salt, which forms a liquid medium in the pyrolysis process to effectively inhibit particle agglomeration, and finally stabilizes the product particle size in a relatively narrow range, effectively controls the grain size, and realizes the preparation of nano-powder with narrow particle size distribution and good dispersibility, which is suitable for the preparation of high-performance ceramic materials, and the comprehensive performance is significantly better than that of the products prepared by the traditional method.

[0036] (3) The process flow of the application is simple, the raw material cost is low, and the compatibility with the traditional carbon thermal reduction method is strong. No large-scale modification is needed for the existing production equipment, and the application is convenient for industrialization and popularization.

[0037] (4) The preparation method of the present application synchronously realizes that the particle size and the grain size of the prepared nano-powder of tantalum carbide are both nanoscale, which can ensure better high-temperature stability, better creep resistance and higher density of the nano-powder of tantalum carbide in the application process. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 SEM and EDS images of the dry gel powder prepared in Example 1 are shown in the figure. Among them, (a)-(c) are SEM images of different positions of the dry gel powder, (d) is a sample morphology image of the position for EDS analysis of the dry gel powder, and (e)-(i) are element distribution images of Ta, C, K, Br and O, respectively.

[0039] Figure 2 EDS quantitative analysis results of the dry gel powder prepared in Example 1 are shown in the figure.

[0040] Figure 3 XRD pattern of the nano-powder of tantalum carbide coarse product prepared in Example 1 is shown in the figure.

[0041] Figure 4 SEM image of the nano-powder of tantalum carbide coarse product prepared in Example 1 is shown in the figure, wherein (b) is a local enlarged view of (a).

[0042] Figure 5 Grain distribution histogram of the nano-powder of tantalum carbide coarse product prepared in Example 1 is shown in the figure.

[0043] Figure 6 XRD pattern of the nano-powder of tantalum carbide coarse product prepared in Example 3 is shown in the figure.

[0044] Figure 7 SEM image of the nano-powder of tantalum carbide coarse product prepared in Example 3 is shown in the figure, wherein (b) is a local enlarged view of (a).

[0045] Figure 8 XRD pattern of the nano-powder of tantalum carbide coarse product prepared in Example 4 is shown in the figure.

[0046] Figure 9 SEM image of the nano-powder of tantalum carbide coarse product prepared in Example 4 is shown in the figure, wherein (b) is a local enlarged view of (a).

[0047] Figure 10 SEM and EDS images of the dry gel powder prepared in Comparative Example 1 are shown in the figure. Among them, (a)-(c) are SEM images of different positions of the dry gel powder, (d) is a sample morphology image of the position for EDS analysis of the dry gel powder, and (e)-(g) are element distribution images of Ta, C, K, Br and O, respectively.

[0048] Figure 11 XRD pattern of the nano-particle ceramic powder crude product prepared for Comparative Example 1.

[0049] Figure 12 SEM image of the nano-particle ceramic powder crude product prepared for Comparative Example 1, wherein (b) is a partial enlarged view of (a).

[0050] Figure 13 XRD pattern of the nano-particle ceramic powder crude product prepared for Comparative Example 2.

[0051] Figure 14 SEM image of the nano-particle ceramic powder crude product prepared for Comparative Example 2; wherein (b) is a partial enlarged view of (a).

[0052] Figure 15 Particle size distribution graph of the nano-particle ceramic powder crude products prepared for Comparative Example 1 and Comparative Example 2. DETAILED DESCRIPTION

[0053] The present application will be further described in conjunction with specific examples. It is to be understood that the examples described below are only a part of the examples, and all other examples obtained by those skilled in the art without making creative efforts are still within the scope of the present application.

[0054] Unless otherwise specified, the various raw materials, reagents, instruments and equipment used in the present application can be purchased from the market or prepared by existing methods.

[0055] The alkali metal salt used in the examples and comparative examples of the present application is potassium bromide or potassium chloride, and other alkali metal salts can also be used in the method of the present application.

[0056] Example 1

[0057] A method for preparing a nano-particle ceramic powder, prepared by the following steps:

[0058] S1, 0.05 mol of pentachloride and 0.4 mol of n-butanol were weighed according to the molar ratio of pentachloride to n-butanol of 1:8, and the pentachloride was slowly dissolved in n-butanol under an Ar gas protection atmosphere. The mixture was placed in a constant temperature water bath at 50℃ and stirred for 30 min to generate a light yellow transparent tantalum alcohol salt solution.

[0059] S2, 0.15 mol of acetylacetone and 0.05 mol of potassium bromide (particle size 0.5 μm) were weighed and sequentially added to the entire tantalum alcohol salt solution obtained in S1, and then the temperature was raised to 80℃ and stirred for 5 h to obtain a brownish red viscous precursor gel.

[0060] S3 The precursor wet gel is transferred into a vacuum drying oven and dried at a temperature of 80℃ and a vacuum degree of ≤10Pa for 20h to obtain a black porous dry gel. The dry gel is then crushed, ground, and sieved to obtain dry gel powder.

[0061] S4 The dry gel powder is loaded into a graphite crucible and placed in a tube furnace. Ar gas is continuously introduced at a flow rate of 1L / min to prevent high-temperature oxidation. At the same time, the temperature is raised to 700℃ at a rate of 10℃ / min, and then held for 10min. The temperature is then raised to 1300℃ at a rate of 5℃ / min, and held for 5h. The temperature is then lowered to 900℃, and the furnace is cooled to room temperature to obtain a crude nano-tantalum carbide ceramic powder product.

[0062] S5 The crude nano-tantalum carbide ceramic powder product cooled to room temperature is removed, and washed with 40℃ deionized water for 4 times, with an ultrasonic power of 150W and a time of 25min each time. Then, the product is washed with 8wt% dilute hydrochloric acid at 50℃ for 45min. After washing, the product is vacuum dried at 80℃ for 12h, and sieved through a 1500 mesh standard sieve to obtain a high-purity nano-tantalum carbide ceramic powder.

[0063] Figure 1 The SEM and EDS images of the dry gel powder prepared in this example are shown. The SEM image shows that the uniformity of the precursor powder is good. The EDS surface scanning analysis and Figure 2 EDS element mapping show that the distribution of Ta and O elements is uniform and the content is similar, and the distribution of C element is more, with a small amount of K and Br elements.

[0064] Figure 3 The XRD pattern of the crude nano-tantalum carbide ceramic powder product prepared in this example is shown. The strong TaC phase peak indicates that the crystallinity of tantalum carbide is good, and most of the precursor has been converted to tantalum carbide.

[0065] Figure 4 The SEM image of the crude nano-tantalum carbide ceramic powder product prepared in this example is shown. The SEM analysis shows that the microstructure presents partial inhomogeneity. Figure 4 (a) in Figure 1 is the tantalum carbide powder after complete reaction. The SEM and XRD analysis show that the TaC powder is successfully synthesized by pyrolysis at 1300℃ in this example, and the dispersion is good. Under high magnification, a large number of primary particles with nano-particle size are observed, and these single particles show a tendency to evolve into spherical shape.

[0066] Figure 5The grain size distribution histogram of the crude nano-particle TaC ceramic powder prepared in this example is shown in the figure. The histogram corresponds to the actual frequency of different grain size intervals, and the curve is the distribution fitting curve. The distribution conforms to the normal distribution law. The statistical interval of the grain size covers 100-500 nm, more than 80% of the grains are concentrated in the range of 250-350 nm, and the frequency peak value near 300 nm accounts for nearly 35%, indicating that the size of most grains in the sample is close to the average level.

[0067] In the high-purity nano-TaC ceramic powder finally prepared in this example, the content of TaC phase is 99.2wt%, the particle size range is 150-500 nm (D50=300 nm), and the grain size is 100-400 nm (80% concentrated in 250-350 nm).

[0068] Example 2

[0069] A method for preparing a nano-particle TaC ceramic powder is prepared by the following steps:

[0070] S1, according to the molar ratio of tantalum pentachloride to n-butanol = 1:9, 0.04 mol of tantalum pentachloride and 0.36 mol of n-butanol are weighed, and the tantalum pentachloride is slowly dissolved in n-butanol under Ar gas protection atmosphere. It is placed in a constant temperature water bath at 50℃ and stirred for 40 min to generate a light yellow transparent tantalum alcoholate solution.

[0071] S2, 0.12 mol of acetylacetone and 0.048 mol of potassium chloride (particle size 0.8 μm) are weighed and added into the whole tantalum alcoholate solution obtained in S1, and then heated to 80℃ and stirred for 4h to obtain a brown red viscous precursor gel.

[0072] The remaining steps and conditions are the same as in Example 1.

[0073] In the high-purity nano-TaC ceramic powder finally prepared in this example, the content of TaC phase is 98.8wt%, the particle size range is 220-420 nm (D50=320 nm), and the grain size is 150 nm-300 nm.

[0074] Example 3

[0075] The difference between this example and Example 1 is that S4 is replaced by: the dry gel powder is loaded into a graphite crucible and placed in a tube furnace. Ar gas is continuously introduced at a flow rate of 1 L / min to prevent high-temperature oxidation. At the same time, the temperature is raised to 700℃ at a rate of 10℃ / min, and the temperature is kept for 10 min. Then the temperature is raised to 1400℃ at a rate of 5℃ / min, and the temperature is kept for 1h. Then the temperature is lowered to 900℃ and finally cooled to room temperature with the furnace to obtain the crude nano-particle TaC ceramic powder. The remaining steps and conditions are consistent with Example 1.

[0076] Figure 6 The XRD pattern of the nano-tantalum carbide ceramic powder crude product prepared in this example is shown in Figure 4. It can be seen that most of the precursor powder is reduced to tantalum carbide powder, and only a small amount of tantalum oxide is not converted. Figure 6

[0077] Figure 7 The SEM image of the nano-tantalum carbide ceramic powder crude product prepared in this example is shown in Figure 5. The micro-morphology is shown to be composed of nano-level primary particles, and the single particles have an approximately equiaxed morphology with initial spheroidization characteristics. Compared with Example 1, a small amount of adjacent particles form sintering necks, and the particle size of the single particles is slightly larger than that in Example 1. In the high-purity nano-TaC ceramic powder finally prepared in this example, the content of the TaC phase is 98.5wt%, the particle size range is 260~420nm (D50=350nm), and the grain size is 140~390nm. Figure 4

[0078] Example 4

[0079] The difference between this example and Example 1 is only that S4 is replaced by: the xerogel powder is loaded into a graphite crucible and placed in a tube furnace, and Ar gas is continuously passed at a flow rate of 1L / min to prevent high-temperature oxidation. At the same time, the temperature is increased to 700℃ at a rate of 10℃ / min, and then held for 10min, and then increased to 1500℃ at a rate of 5℃ / min, and then held for 1h, and then cooled to 900℃, and finally cooled to room temperature with the furnace to obtain a nano-tantalum carbide ceramic powder crude product. The remaining steps and conditions are consistent with Example 1.

[0080] Figure 8 The XRD pattern of the nano-tantalum carbide ceramic powder crude product prepared in this example is shown in Figure 4. It can be seen that most of the precursor powder is reduced to tantalum carbide powder, and only a small amount of tantalum oxide is not converted.

[0081] Figure 9 The SEM image of the nano-tantalum carbide ceramic powder crude product prepared in this example is shown in Figure 5. The micro-morphology is shown to be composed of nano-level primary particles, and the single particles have an approximately equiaxed morphology with initial spheroidization characteristics. Compared with Example 1, a small amount of adjacent particles form sintering necks, and the particle size of the single particles is slightly larger than that in Example 1. In the high-purity nano-TaC ceramic powder finally prepared in this example, the content of the TaC phase is 98.5wt%, the particle size range is 260~420nm (D50=350nm), and the grain size is 140~390nm.

[0082] In the high-purity nano-TaC ceramic powder finally prepared in this example, the content of the TaC phase is 98.6wt%, the particle size range is 300~450nm (D50=400nm), and the grain size is 160~310nm.

[0083] Example 5

[0084] ​​The embodiment differs from embodiment 1 only in that the alkali metal halide is replaced by an equimolar amount of NaCl, and the remaining steps and conditions are consistent, to obtain a high-purity nano-powder of tantalum carbide ceramic, the particle size of the obtained powder is in the range of 290-500 nm (D50=370 nm), the grain size is 120-350 nm, and the TaC phase is greater than or equal to 98wt%.

[0085] Embodiment 6

[0086] A method for preparing a nano-powder of tantalum carbide ceramic is prepared by the following steps:

[0087] S1, according to the molar ratio of tantalum pentachloride to n-butanol of 1:9, 0.04 mol of tantalum pentachloride and 0.36 mol of n-butanol are weighed, and the tantalum pentachloride is slowly dissolved in n-butanol under an Ar gas protection atmosphere, and placed in a constant temperature water bath at 50°C for stirring reaction for 40 min, to generate a light yellow transparent tantalum alcoholate solution.

[0088] S2, 0.06 mol of acetylacetone and 0.032 mol of potassium chloride (particle size 0.8 μm) are weighed and added to the whole tantalum alcoholate solution obtained in S1, and then heated to 80°C for stirring reaction for 4 h, to obtain a brown-red viscous precursor gel.

[0089] The remaining steps and conditions are the same as in embodiment 1.

[0090] In the high-purity nano-TaC ceramic powder finally prepared in this embodiment, the particle size of the obtained powder is in the range of 340-560 nm (D50=430 nm), the grain size is 110-330 nm, and the TaC phase is 98.2wt%.

[0091] Embodiment 7

[0092] A method for preparing a nano-powder of tantalum carbide ceramic is prepared by the following steps:

[0093] S1, according to the molar ratio of tantalum pentachloride to n-butanol of 1:9, 0.04 mol of tantalum pentachloride and 0.36 mol of n-butanol are weighed, and the tantalum pentachloride is slowly dissolved in n-butanol under an Ar gas protection atmosphere, and placed in a constant temperature water bath at 50°C for stirring reaction for 30 min, to generate a light yellow transparent tantalum alcoholate solution.

[0094] S2, 0.06 mol of acetylacetone and 0.032 mol of potassium chloride (particle size 0.8 μm) are weighed and added to the whole tantalum alcoholate solution obtained in S1, and then heated to 80°C for stirring reaction for 4 h, to obtain a brown-red viscous precursor gel.

[0095] The remaining steps and conditions are the same as in embodiment 1.

[0096] The high-purity nanometer TaC ceramic powder prepared in the embodiment has a particle size range of 310-540 nm (D50=475 nm), a grain size of 130-360 nm, and a TaC phase content of 98.7 wt%.

[0097] Comparative Example 1

[0098] The difference between the comparative example and Example 1 is that no alkali metal halide potassium bromide is added in the preparation of the precursor, and the rest of the steps and conditions are consistent. The powder after washing and drying is sieved through a 1000-mesh standard sieve to prepare a TaC ceramic powder.

[0099] Figure 10 The SEM and EDS spectra of the dry gel particles prepared in the comparative example show that the dry gel particles are in a large block shape. Through EDS surface scanning analysis, the Ta and O elements are uniformly distributed on the surface of the particles.

[0100] Figure 11 The XRD spectrum of the nanometer TaC ceramic powder coarse product prepared in the comparative example shows that the peak of the Ta2O5 phase is relatively strong, and the peak of the TaC phase is relatively weak, indicating that most of the precursors have not reacted.

[0101] Figure 12 The SEM image of the nanometer TaC ceramic powder coarse product prepared in the comparative example shows that the microstructure presents a high degree of heterogeneity. The completely reacted areas and the unreacted original powder particles are interwoven and mixedly distributed.

[0102] The TaC ceramic powder prepared in the comparative example has a particle size range of 0.1 μm-100 μm, a grain size of 100 nm-10 μm, and a TaC phase content of 94.5 wt%.

[0103] Comparative Example 2

[0104] The difference between the comparative example and Comparative Example 1 is that the pyrolysis reaction procedure is replaced by: continuously passing Ar gas with a flow rate of 1 L / min to prevent high-temperature oxidation. At the same time, the temperature is increased to 700℃ at a rate of 10℃ / min, and the temperature is kept for 10 min. Then the temperature is increased to 1400℃ at a rate of 5℃ / min, and the temperature is kept for 1 h. Then the temperature is decreased to 900℃, and finally the furnace is cooled to room temperature. The rest of the steps and conditions are consistent.

[0105] Figure 13 The XRD spectrum of the nanometer TaC ceramic powder coarse product prepared in the comparative example shows that there is a relatively strong TaC peak, but there are more unreacted Ta2O5 phases, and the reaction process is relatively slow.

[0106] Figure 14The SEM image of the nano-tantalum carbide ceramic powder crude product prepared for the present comparative example, the SEM morphology analysis of the pyrolysis sample shows that the microstructure exhibits significant heterogeneity, and the fully reacted regions and the initial powder particles that have not undergone reaction show interpenetrating and mixed distribution.

[0107] Figure 15 The particle size distribution curve of the nano-tantalum carbide ceramic powder crude product prepared for Comparative Example 1 and the present comparative example, as can be seen from the figure, the particle size distribution curve of Comparative Example 1 under the process of pyrolysis at 1300°C for 5h, the bulk density is relatively low, and there is only a slight peak near 1μm, but the particle size distribution is more dispersed. The particle size distribution curve of Comparative Example 2 under the process of pyrolysis at 1400°C for 1h, the TaC powder particle size is mainly concentrated around 10μm, and the volume fraction of large particles is high. Both processes cannot achieve the preparation of nano-sized tantalum carbide with uniform particle size without adding alkali metal halide.

[0108] In the TaC ceramic powder prepared in the present comparative example, the particle size range is 1μm~100μm, the grain size is 500nm~20μm, and the content of TaC phase is 94.7wt%.

[0109] Comparative Example 3

[0110] The present comparative example and Example 1 differ only in that n-butanol is replaced by an equal molar amount of ethanol, and the remaining steps and conditions are consistent.

[0111] In the TaC ceramic powder prepared in the present comparative example, the particle size range is 500nm~1μm, the grain size is 300nm~600nm, and the content of TaC phase is only 92.8wt%.

[0112] Comparative Example 4

[0113] The present comparative example and Example 1 differ in that the pyrolysis reaction procedure is replaced by: continuously passing Ar gas with a flow rate of 1L / min to prevent high-temperature oxidation. At the same time, the temperature is increased to 700°C at a rate of 10°C / min, and the temperature is maintained for 10min. Then the temperature is increased to 1700°C at a rate of 5°C / min, and the temperature is maintained for 1h. Then the temperature is decreased to 900°C, and finally the furnace is cooled to room temperature. The remaining steps and conditions are consistent.

[0114] The results show that the obtained nano-tantalum carbide ceramic powder has a particle size range of 1~3μm, a grain size of 500~650nm, and a TaC phase content of 90.2wt%. Compared with Example 1, the particle size and grain size of the product increase significantly, and the purity decreases slightly.

[0115] Comparative Example 5

[0116] The present comparative example differs from example 1 only in that potassium bromide is replaced by an equimolar amount of potassium oxide, the remaining steps and conditions being identical.

[0117] The results show that the obtained nano-particle ceramic powder of tantalum carbide has a particle size range of 1.5-4 μm, a grain size of 0.8-1 μm, and a content of TaC phase of 90.6 wt%.

Claims

1. A method for preparing nano-tantalum carbide ceramic powder, characterized in that: Includes the following steps: S1 involves reacting a tantalum source with n-butanol under a protective atmosphere to produce a tantalum alkoxide. S2 Add the complexing agent and alkali metal halide to tantalum alkoxide and mix to obtain the precursor gel; The precursor gel described in S3 is obtained by pyrolysis reaction and cleaning to remove impurities after being powdered.

2. The method for preparing nano-tantalum carbide ceramic powder according to claim 1, characterized in that: The tantalum source is selected from at least one of tantalum pentachloride, potassium heptafluorotantalate, and tantalum ethoxide. The alkali metal halide is selected from at least one of potassium bromide, potassium chloride, potassium iodide, sodium chloride, sodium bromide, and sodium iodide; the complexing agent includes acetylacetone.

3. The method for preparing nano-tantalum carbide ceramic powder according to claim 1 or 2, characterized in that: The conditions for the alcoholysis reaction are as follows: the molar ratio of tantalum source to alcohol solvent is 1:(8~10), the temperature is 45~50℃, and the time is 30~60min.

4. The method for preparing nano-tantalum carbide ceramic powder according to claim 3, characterized in that: The molar ratio of the complexing agent to the alkali metal halide is (1.8~3.5):(1~1.5). The molar ratio of the alkali metal halide to the tantalum source is (0.8~1.5):

1.

5. The method for preparing nano-tantalum carbide ceramic powder according to claim 4, characterized in that: In S2, the mixing temperature is 70~80℃ and the reaction time is 4~6h.

6. The method for preparing nano-tantalum carbide ceramic powder according to claim 1, characterized in that: In S3, the precursor gel is dried in a vacuum environment at 70~80℃ to obtain a porous precursor gel, which is then powdered.

7. The method for preparing nano-tantalum carbide ceramic powder according to claim 6, characterized in that: The conditions for the pyrolysis reaction are as follows: under a protective atmosphere, the temperature is first raised to 700~750℃ at a heating rate of 10℃ / min and held for 10~20min, then raised to 1300~1500℃ at a heating rate of 5~10℃ / min and held for 1~5h, and then cooled to 800~900℃ and cooled to room temperature with the furnace.

8. A method for preparing nano-tantalum carbide ceramic powder according to claim 1 or 7, characterized in that: The cleaning and impurity removal process involves first washing with water and then acid washing.

9. A nano-tantalum carbide ceramic powder, characterized in that: It is obtained by the preparation method according to any one of claims 1 to 8.

10. The nano-tantalum carbide ceramic powder according to claim 9, characterized in that: The particle size is 150~560nm, the grain size is 100~400nm, and the TaC phase content is greater than or equal to 98wt%.

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