A dense nano-transition metal carbide high-entropy ceramic and its preparation method

Abstract

This invention belongs to the field of ceramic technology. It discloses a dense nano-transition metal carbide high-entropy ceramic and its preparation method. First, a transition metal salt and a carbon source are mixed and stirred in an organic solvent at 50-70°C to obtain a wet gel of a high-entropy carbide precursor. The wet gel is dried to obtain a dry gel of the high-entropy carbide precursor. The dry gel is ground into powder and then subjected to thermal pyrolysis under a protective atmosphere. The pyrolyzed powder is then subjected to spark plasma sintering at 1900-2000°C to obtain the dense nano-transition metal carbide high-entropy ceramic. The high-entropy carbide ceramic prepared by this invention has a density greater than 95%, uniform composition, and a grain size of 70-80 nm, meeting the requirements for density, purity, and grain size of high-entropy carbide ceramics.

Description

Technical Field

[0001] This invention belongs to the field of ceramic technology, and relates to the preparation of nano-carbide ceramics, and particularly to a dense nano-transition metal carbide high-entropy ceramic and its preparation method. Background Technology

[0002] Single-component transition metal (IVB–VB group) carbide ceramics are a class of ceramic materials with melting points greater than 3000℃, capable of long-term use in high-temperature environments, and possessing excellent ablation resistance, high-temperature mechanical properties, and thermal shock resistance. They have wide applications in the aerospace field, such as hypersonic vehicles, rocket propulsion systems, and reentry vehicles. In recent years, the method of improving the intrinsic properties of materials through high entropy has attracted widespread attention. High-entropy carbide ceramics are solid solutions composed of five or more IVB, VB, and VIB group transition metal carbides, exhibiting strong covalent bonds, chemical disorder, and four major effects (high-entropy effect, hysteresis diffusion effect, lattice distortion effect, and cocktail effect). Compared to single-component carbide ceramics, high-entropy carbide ceramics possess a variety of superior properties, including high hardness, high elastic modulus, excellent mechanical properties, good oxidation resistance, good thermal stability, and adjustable thermal conductivity. Furthermore, high-entropy materials offer vast potential for compositional design and performance control, bringing unlimited challenges and possibilities to the development of new materials and meeting the needs of extreme (high temperature, high pressure, corrosion, irradiation, stress) environments such as aviation, aerospace, marine, and nuclear energy.

[0003] Patent application CN 110104648 A discloses a high-entropy carbide nanopowder and its preparation method. The nanopowder is prepared via a sol-gel reaction between a transition metal salt and an organic carbon source, resulting in ceramic nanopowder with a particle size of 100–200 nm. Patent application CN 115772034 A discloses a high-entropy carbide ceramic precursor, high-entropy carbide ceramic, and its preparation method. The high-entropy carbide ceramic precursor obtained by this method is in a liquid state, which is easy to store, but the grain size of the final ceramic is distributed between 100-200 nm. Patent application CN 116514553 A discloses a composite carbide ceramic powder material, its preparation method, and its application. The high-entropy carbide powder prepared by the sol-gel method has uniformly distributed components, resulting in high-entropy powder with a submicron (-350 nm) size. In summary, the reported preparation of high-entropy carbide powders currently available all have particle sizes greater than 100 nm. Due to the presence of numerous covalent bonds in carbide ceramics and high-entropy carbides, they are difficult to sinter, and the sintering of nanoscale high-entropy carbide ceramics remains a blank. Summary of the Invention

[0004] The purpose of this invention is to address the aforementioned problems in the prior art by providing a dense nano-transition metal carbide high-entropy ceramic and its preparation method, which can precisely control the ceramic grain size while regulating the uniformity of the high-entropy ceramic composition.

[0005] The sol-gel method, unlike traditional powder metallurgy, involves high-temperature pyrolysis and sintering of high-entropy carbide precursors to obtain nano-ceramic powders. This method achieves uniform molecular size composition, produces nano-sized powders, and lowers the synthesis temperature. Spark plasma sintering (SPS) is a rapid sintering process for preparing bulk materials using field-assisted sintering. It controls ceramic grain size while promoting solid solution formation in high-entropy ceramics and rapidly densifying them.

[0006] In view of this, this application proposes a method for preparing dense nano-transition metal carbide high-entropy ceramics using sol-gel precursors, comprising the following steps:

[0007] (1) The transition metal salt and carbon source are mixed and stirred in an organic solvent at 50-70℃ to obtain a high-entropy carbide precursor wet gel; the transition metal salt and carbon source are measured in a molar ratio of (1.2-1):(1-5) of transition metal to carbon.

[0008] (2) The high-entropy carbide precursor wet gel is dried to obtain high-entropy carbide precursor dry gel.

[0009] (3) The obtained high-entropy carbide precursor dry gel was ground into powder and then pyrolyzed under a protective atmosphere.

[0010] (4) The pyrolyzed powder was subjected to discharge plasma sintering at 1900-2000℃ to obtain dense nano-transition metal carbide high-entropy ceramics.

[0011] In step (1) above, the transition metal salt includes at least one transition metal chloride; the transition metal (IVB–VB group) is selected from Ti, Nb, Ta, Cr, Mo, Zr, W, V or Hf; in the sol-gel preparation of nanopowders, the transition metal salt preferably includes three or more transition metal chlorides, and the carbon source is at least one of furfuryl alcohol, starch, glucose, etc. The organic solvent is ethanol. The transition metal salt and carbon source are mixed and stirred in the organic solvent for 1-2 hours to obtain a high-entropy carbide precursor wet gel.

[0012] In step (2) above, the high-entropy carbide precursor wet gel is dried at 100-170℃ to obtain high-entropy carbide precursor dry gel, and the heat preservation time is 12-18h.

[0013] In step (3) above, the high-entropy carbide precursor dry gel is ground to a powder particle size range of 200-400 mesh. The pyrolysis temperature of the high-entropy carbide precursor dry gel can be determined based on infrared spectroscopy and thermogravimetric analysis. Studies have shown that the pyrolysis temperature of the high-entropy carbide precursor dry gel is 1000-1600℃, and the holding time at the pyrolysis temperature is 1-2h. The pyrolysis temperature program is as follows: heating or cooling at a rate of 3-5℃ / min, divided into 2-3 temperature gradients, holding each temperature range for 30-90min. When the temperature reaches 1000-1600℃, continue holding for 1-2h, and then cool down to room temperature. The protective atmosphere used is argon or nitrogen. The pyrolysis yield is 30-55%.

[0014] In step (4) above, the pyrolyzed powder is first ball-milled and then subjected to spark plasma sintering; the ball milling speed is 80-120 rpm and the time is 10-14 h. Spark plasma sintering is performed at a temperature ≤5×10⁻⁶ rpm. -2 Under a vacuum of 40 MPa, the heating or cooling rate is 50-100℃ / min, divided into 2-3 temperature gradients. After reaching the set maximum temperature, the temperature is held for 10-25 min. The discharge plasma sintering pressure is 40-65 MPa.

[0015] The dense nano-transition metal carbide high-entropy ceramics prepared by the above method have a grain size of 70-80 nm, a porosity of 0-5% (excluding the end value of 0), and a density greater than 95%.

[0016] Compared with the prior art, the transition metal carbide high-entropy ceramics and their preparation method provided by the present invention have the following beneficial effects:

[0017] (1) This invention uses the sol-gel precursor method to prepare high-entropy carbide ceramics. The sol-gel method prepares carbide precursors, which are then subjected to high-temperature pyrolysis to achieve carbothermic reduction reaction, thereby obtaining nanoscale high-entropy carbides. Therefore, adjusting the dry gel pyrolysis process can improve the density, composition control, and uniformity of high-entropy carbide ceramics.

[0018] (2) The present invention uses spark plasma sintering, which has the advantages of high heating rate, low sintering temperature and short sintering time. It can suppress the growth of ceramic grains and sinter quickly while making high-entropy carbide ceramics dense.

[0019] (3) The preparation method provided by the present invention enables the high-entropy carbide ceramics to have a density greater than 95% (95.09%–99.86% in the examples), uniform composition, and grain size of 70-80 nm, which can meet the requirements of high-entropy carbide ceramics for density, purity and grain size.

[0020] (4) The method for preparing high-entropy transition metal carbide ceramics provided by the present invention is simple to operate, has a short production cycle, and is widely applicable. Attached Figure Description

[0021] Figure 1 This is a process flow diagram of the transition metal carbide high-entropy ceramic of the present invention;

[0022] Figure 2 Optimize the high-temperature pyrolysis curve for the tubular furnace; where (a) corresponds to the pyrolysis curve at 1000℃ and (b) corresponds to the pyrolysis curve at 1600℃.

[0023] Figure 3 SPS sintering regime curve;

[0024] Figure 4 The results are as follows: (a) is the thermogravimetric analysis curve of the dry gel of the sol-gel precursor prepared in Example 5, and (b) is the infrared spectrum of the pyrolysis products prepared in Examples 4, 5 and 6.

[0025] Figure 5 XRD patterns of dense nano-transition metal carbide high-entropy ceramics prepared in Examples 2-5;

[0026] Figure 6 This is a high-resolution TEM and elemental energy dispersive spectroscopy analysis for Example 4. Detailed Implementation

[0027] The principles and features of the present invention are described below. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0028] The following embodiments of the present invention employ a method for preparing high-entropy transition metal carbide ceramics, such as... Figure 1 As shown, it includes the following steps:

[0029] (1) The transition metal chloride powder and the carbon source are mixed and stirred in ethanol at 50-70℃ to obtain a high-entropy carbide precursor wet gel; the transition metal salt and the carbon source are measured according to the molar ratio of transition metal to carbon as (1.2-1):(1-5); the stirring time is 1-2h.

[0030] (2) The wet gel of the high-entropy carbide precursor was dried to obtain the dry gel of the high-entropy carbide precursor; the drying temperature was 100-170℃ and the holding time was 12-18h.

[0031] (3) The obtained high-entropy carbide precursor dry gel is ground into powder (final particle size range is 200-400 mesh), and then pyrolyzed under a protective atmosphere; the pyrolysis temperature is 1000-1600℃, the pyrolysis temperature holding time is 1-2h, and the protective atmosphere used is argon or nitrogen; the pyrolysis temperature program is as follows: the pyrolysis temperature program is to increase or decrease the temperature at 3-5℃ / min, divided into 2-3 gradient increases, each temperature segment is held for 30-90min, when the temperature is increased to 1000-1600℃, continue to hold for 1-2h, and then decrease to room temperature;

[0032] (4) The pyrolysis powder was subjected to spark plasma sintering at 1900–2000℃ to obtain high-entropy transition metal carbide ceramics. The specific operation was as follows: the pyrolysis powder was first ball-milled, and then spark plasma sintered; the ball milling speed was 80–120 rpm, and the time was 10–14 h; the spark plasma sintering temperature was ≤5×10⁻⁶. -2 Under a vacuum of 40 MPa, the heating or cooling rate is 50-100℃ / min, divided into 2-3 temperature gradients. After reaching the set maximum temperature, the temperature is held for 10-25 min. The discharge plasma sintering pressure is 40-65 MPa.

[0033] The pyrolysis temperature can be optimized by thermogravimetric analysis (TG) / differential scanning calorimetry (DSC) and free-float infrared spectroscopy (FTIR) on the wet gel of the high-entropy carbide precursor obtained in step (1) or the dry gel of the high-entropy carbide precursor obtained in step (2).

[0034] Example 1

[0035] The transition metal salt used in this embodiment is TiCl4, the carbon source is furfuryl alcohol (C5H6O2), and the molar ratio of TiCl4 to furfuryl alcohol is 6:1.

[0036] The preparation method of transition metal carbide high-entropy ceramics provided in this embodiment includes the following steps:

[0037] (1) Add 151.38g TiCl4 to 70g ethanol solution and stir until homogeneous; then add 13g furfuryl alcohol to the resulting mixture and stir at 60℃ for 1h to obtain a high-entropy carbide precursor wet gel.

[0038] (2) The obtained high-entropy carbide precursor wet gel was placed in an oven and dried at 120℃ for 12h to obtain high-entropy carbide precursor dry gel.

[0039] (3) The obtained high-entropy carbide precursor dry gel was ground into a powder with a particle size range of 200-400 mesh, and then placed in a tube furnace for pyrolysis at 1000℃ for 1 hour under an argon protective atmosphere. The pyrolysis temperature program was as follows: first, the temperature was increased to 350℃ at 3℃ / min and held for 60 min; then, the temperature was increased to 600℃ at 3℃ / min and held for 60 min; then, the temperature was increased to 1000℃ at 5℃ / min and held for 60 min; and then, the temperature was decreased to room temperature at 5℃ / min. Figure 2 As shown in (a).

[0040] (4) The pyrolysis powder was placed in a ball mill and ball-milled at 90 rpm for 12 hours; then it was placed in a mold and sintered in a spark plasma sintering furnace at a temperature of ≤5×10⁻⁶. -2 Nanoscale TiC ceramics were obtained by spark plasma sintering under a vacuum of 40 MPa and a pressure of 40 MPa, following specific heating and cooling programs. The heating program was as follows: temperature increased from room temperature to 1500℃ at a rate of 100℃ / min, then increased to 1900℃ at a rate of 80℃ / min, then increased to 2000℃ at a rate of 50℃ / min, and held for 10 min. The cooling program was as follows: temperature decreased from 2000℃ to 1900℃ at a rate of 50℃ / min, then decreased to 1500℃ at a rate of 80℃ / min, then decreased to room temperature at a rate of 100℃ / min. Figure 3 As shown.

[0041] Example 2

[0042] The transition metal salts used in this embodiment are TiCl4, NbCl5, and TaCl5, and the carbon source is furfuryl alcohol (C5H6O2). The molar ratio of TiCl4, NbCl5, and TaCl5 is 1:1:1; the molar ratio of all transition metal chlorides to furfuryl alcohol is 6:1.

[0043] The preparation method of transition metal carbide high-entropy ceramics provided in this embodiment includes the following steps:

[0044] (1) Add 36.04g TiCl4, 51.34g NbCl5 and 68.05g TaCl5 to 70g ethanol solution and stir until homogeneous; then add 9.34g furfuryl alcohol to the resulting mixture and stir at 60℃ for 1h to obtain a high-entropy carbide precursor wet gel.

[0045] (2) The obtained high-entropy carbide precursor wet gel was placed in an oven and dried at 120℃ for 12h to obtain high-entropy carbide precursor dry gel.

[0046] (3) The obtained high-entropy carbide precursor dry gel was ground into a powder with a particle size range of 200-400 mesh, and then placed in a tube furnace for pyrolysis at 1000℃ for 1 hour under an argon protective atmosphere. The pyrolysis temperature program was as follows: first, the temperature was increased to 350℃ at 3℃ / min and held for 60 min; then, the temperature was increased to 600℃ at 3℃ / min and held for 60 min; then, the temperature was increased to 1000℃ at 5℃ / min and held for 60 min; and then, the temperature was decreased to room temperature at 5℃ / min. Figure 2 As shown in (a);

[0047] (4) The pyrolysis powder was placed in a ball mill and ball-milled at 90 rpm for 12 hours; then it was placed in a mold and sintered in a spark plasma sintering furnace at a temperature of ≤5×10⁻⁶. -2 Nanoscale (TiNbTa)C ceramics were obtained by spark plasma sintering under a vacuum of 40 MPa and a cooling program, following specific heating and cooling procedures. The heating program was as follows: heating from room temperature to 1500℃ at a rate of 100℃ / min, then to 1900℃ at a rate of 80℃ / min, then to 2000℃ at a rate of 50℃ / min, and holding at that temperature for 10 min. The cooling program was as follows: cooling from 2000℃ to 1900℃ at a rate of 50℃ / min, then to 1500℃ at a rate of 80℃ / min, and then back to room temperature at a rate of 100℃ / min. Figure 3 As shown.

[0048] Example 3

[0049] The transition metal salts used in this embodiment are TiCl4, NbCl5, and TaCl5, and the carbon source is furfuryl alcohol (C5H6O2). The molar ratio of TiCl4, NbCl5, and TaCl5 is 1:1:1; the molar ratio of all transition metal chlorides to furfuryl alcohol is 6:1.

[0050] The preparation method of transition metal carbide high-entropy ceramics provided in this embodiment includes the following steps:

[0051] (1) Add 36.04g TiCl4, 51.34g NbCl5 and 68.05g TaCl5 to 70g ethanol solution and stir until homogeneous; then add 9.34g furfuryl alcohol to the resulting mixture and stir at 60℃ for 1h to obtain a high-entropy carbide precursor wet gel.

[0052] (2) The obtained high-entropy carbide precursor wet gel was placed in an oven and dried at 120℃ for 12h to obtain high-entropy carbide precursor dry gel.

[0053] (3) The obtained high-entropy carbide precursor dry gel was ground into a powder with a particle size range of 200-400 mesh, and then placed in a tube furnace for pyrolysis at 1600℃ for 1 hour under an argon protective atmosphere. The pyrolysis temperature program was as follows: first, the temperature was increased to 350℃ at 3℃ / min and held for 60 min; then, the temperature was increased to 600℃ at 3℃ / min and held for 60 min; then, the temperature was increased to 1000℃ at 5℃ / min and held for 60 min; then, the temperature was increased to 1600℃ at 5℃ / min and held for 60 min; and then, the temperature was decreased to room temperature at 5℃ / min. Figure 2 As shown in (b);

[0054] (4) The pyrolysis powder was placed in a ball mill and ball-milled at 90 rpm for 12 hours; then it was placed in a mold and sintered in a spark plasma sintering furnace at a temperature of ≤5×10⁻⁶. -2 Nanoscale (TiNbTa)C ceramics were obtained by spark plasma sintering under a vacuum of 40 MPa and a cooling program, following specific heating and cooling procedures. The heating program was as follows: heating from room temperature to 1500℃ at a rate of 100℃ / min, then to 1900℃ at a rate of 80℃ / min, then to 2000℃ at a rate of 50℃ / min, and holding at that temperature for 10 min. The cooling program was as follows: cooling from 2000℃ to 1900℃ at a rate of 50℃ / min, then to 1500℃ at a rate of 80℃ / min, and then back to room temperature at a rate of 100℃ / min. Figure 3 As shown.

[0055] Example 4

[0056] The transition metal salts used in this embodiment are TiCl4, NbCl5, TaCl5, CrCl3, and MoCl5, and the carbon source is furfuryl alcohol. The molar ratio of TiCl4, NbCl5, TaCl5, CrCl3, and MoCl5 is 1:1:1:1:1; the molar ratio of all transition metal chlorides to furfuryl alcohol is 6:1.

[0057] The preparation method of transition metal carbide high-entropy ceramics provided in this embodiment includes the following steps:

[0058] (1) 22.76g TiCl4, 32.42g NbCl5, 42.98g TaCl5, 19g CrCl3, and 32.78g MoCl5 were added to 70g ethanol solution and stirred until homogeneous; then 9.72g furfuryl alcohol (C5H6O2) was added to the resulting mixture and stirred at 60℃ for 1h to obtain a high-entropy carbide precursor wet gel;

[0059] (2) The obtained high-entropy carbide precursor wet gel was placed in an oven and dried at 120℃ for 12h to obtain high-entropy carbide precursor dry gel.

[0060] (3) The obtained high-entropy carbide precursor dry gel was ground into a powder with a particle size range of 200-400 mesh, and then placed in a tube furnace for pyrolysis at 1000℃ for 1 hour under an argon protective atmosphere. The pyrolysis temperature program was as follows: first, the temperature was increased to 350℃ at 3℃ / min and held for 60 min; then, the temperature was increased to 600℃ at 3℃ / min and held for 60 min; then, the temperature was increased to 1000℃ at 5℃ / min and held for 60 min; and then, the temperature was decreased to room temperature at 5℃ / min. Figure 2 As shown in (a);

[0061] (4) The pyrolysis powder was placed in a ball mill and ball-milled at 90 rpm for 12 hours; then it was placed in a mold and sintered in a spark plasma sintering furnace at a temperature of ≤5×10⁻⁶. -2 Nanoscale (TiNbTaCrMo)C ceramics were obtained by spark plasma sintering under a vacuum of 40 MPa and a cooling program, following specific heating and cooling procedures. The heating program was as follows: heating from room temperature to 1500℃ at a rate of 100℃ / min, then to 1900℃ at a rate of 80℃ / min, then to 2000℃ at a rate of 50℃ / min, and holding for 10 min. The cooling program was as follows: cooling from 2000℃ to 1900℃ at a rate of 50℃ / min, then to 1500℃ at a rate of 80℃ / min, and then back to room temperature at a rate of 100℃ / min. Figure 3 As shown.

[0062] Example 5

[0063] The transition metal salts used in this embodiment are TiCl4, NbCl5, TaCl5, CrCl3, and MoCl5, and the carbon source is furfuryl alcohol. The molar ratio of TiCl4, NbCl5, TaCl5, CrCl3, and MoCl5 is 1:1:1:1:1; the molar ratio of all transition metal chlorides to furfuryl alcohol is 1:1.

[0064] The preparation method of transition metal carbide high-entropy ceramics provided in this embodiment includes the following steps:

[0065] (1) Add 3.6g TiCl4, 5.13g NbCl5, 6.8g TaCl5, 3g CrCl3 and 5.19g MoCl5 to 70g ethanol solution and stir until homogeneous; then add 9.52g furfuryl alcohol (C5H6O2) to the resulting mixture and stir at 60℃ for 1h to obtain a high-entropy carbide precursor wet gel.

[0066] (2) The obtained high-entropy carbide precursor wet gel was placed in an oven and dried at 120℃ for 12h to obtain high-entropy carbide precursor dry gel.

[0067] (3) The obtained high-entropy carbide precursor dry gel was ground into a powder with a particle size range of 200-400 mesh, and then placed in a tube furnace for pyrolysis at 1600℃ for 1 hour under an argon protective atmosphere. The pyrolysis temperature program was as follows: first, the temperature was increased to 350℃ at 3℃ / min and held for 60 min; then, the temperature was increased to 600℃ at 3℃ / min and held for 60 min; then, the temperature was increased to 1000℃ at 5℃ / min and held for 60 min; then, the temperature was increased to 1600℃ at 5℃ / min and held for 60 min; and then, the temperature was decreased to room temperature at 5℃ / min. Figure 2 As shown in (b);

[0068] (4) The pyrolysis powder was placed in a ball mill and ball-milled at 90 rpm for 12 hours; then it was placed in a mold and sintered in a spark plasma sintering furnace at a temperature of ≤5×10⁻⁶. -2 Nanoscale (TiNbTaCrMo)C ceramics were obtained by spark plasma sintering under a vacuum of 40 MPa and a cooling program, following specific heating and cooling procedures. The heating program was as follows: heating from room temperature to 1500℃ at a rate of 100℃ / min, then to 1900℃ at a rate of 80℃ / min, then to 2000℃ at a rate of 50℃ / min, and holding for 10 min. The cooling program was as follows: cooling from 2000℃ to 1900℃ at a rate of 50℃ / min, then to 1500℃ at a rate of 80℃ / min, and then back to room temperature at a rate of 100℃ / min. Figure 3 As shown.

[0069] Example 6

[0070] The transition metal salts used in this embodiment are TiCl4, NbCl5, TaCl5, CrCl3, and MoCl5, and the carbon source is furfuryl alcohol. The molar ratio of TiCl4, NbCl5, TaCl5, CrCl3, and MoCl5 is 1:1:1:1:1; the molar ratio of all transition metal chlorides to furfuryl alcohol is 1:1.

[0071] The preparation method of transition metal carbide high-entropy ceramics provided in this embodiment includes the following steps:

[0072] (1) Add 5.12g TiCl4, 7.29g NbCl5, 9.67g TaCl5, 4.28g CrCl3, and 7.38g MoCl5 to 70g ethanol solution and stir until homogeneous; then add 13.32g furfuryl alcohol (C5H6O2) to the resulting mixture and stir at 60℃ for 1h to obtain a high-entropy carbide precursor wet gel;

[0073] (2) The obtained high-entropy carbide precursor wet gel was placed in an oven and dried at 120℃ for 12h to obtain high-entropy carbide precursor dry gel.

[0074] (3) The obtained high-entropy carbide precursor dry gel was ground into powder with a particle size range of 200-400 mesh, and then placed in a tube furnace and pyrolyzed at 1500℃ for 1h under an argon protective atmosphere. The pyrolysis temperature program was as follows: first, the temperature was increased to 350℃ at 3℃ / min and held for 60min, then increased to 600℃ at 3℃ / min and held for 60min, then increased to 1000℃ at 5℃ / min and held for 60min, then increased to 1500℃ at 5℃ / min and held for 60min, and then decreased to room temperature at 5℃ / min.

[0075] (4) The pyrolysis powder was placed in a ball mill and ball-milled at 90 rpm for 12 hours; then it was placed in a mold and sintered in a spark plasma sintering furnace at a temperature of ≤5×10⁻⁶. -2 Nanoscale (TiNbTaCrMo)C ceramics were obtained by spark plasma sintering under a vacuum of 40 MPa and a cooling program, following specific heating and cooling procedures. The heating program was as follows: heating from room temperature to 1500℃ at a rate of 100℃ / min, then to 1900℃ at a rate of 80℃ / min, then to 2000℃ at a rate of 50℃ / min, and holding for 10 min. The cooling program was as follows: cooling from 2000℃ to 1900℃ at a rate of 50℃ / min, then to 1500℃ at a rate of 80℃ / min, and then back to room temperature at a rate of 100℃ / min. Figure 3 As shown.

[0076] Example 7

[0077] The transition metal salts used in this embodiment are TiCl4, NbCl5, TaCl5, CrCl3, and MoCl5, and the carbon source is glucose. The molar ratio of TiCl4, NbCl5, TaCl5, CrCl3, and MoCl5 is 1:1:1:1:1; the molar ratio of all transition metal chlorides to glucose is 6:1.

[0078] The preparation method of transition metal carbide high-entropy ceramics provided in this embodiment includes the following steps:

[0079] (1) Add 13.66g TiCl4, 19.45g NbCl5, 25.79g TaCl5, 11.4g CrCl3, and 19.67g MoCl5 to 70g ethanol solution and stir until homogeneous; then add 11g glucose (C6H) to the resulting mixture. 12 O6), and stirred at 50℃ for 2h to obtain a high-entropy carbide precursor wet gel;

[0080] (2) The obtained high-entropy carbide precursor wet gel was placed in an oven and dried at 100℃ for 18h to obtain high-entropy carbide precursor dry gel.

[0081] (3) The obtained high-entropy carbide precursor dry gel was ground into powder with a particle size range of 200-400 mesh, and then placed in a tube furnace and pyrolyzed at 1000℃ for 1h under an argon protective atmosphere. The pyrolysis temperature program was as follows: first, the temperature was increased to 300℃ at 3℃ / min and held for 60min, then increased to 600℃ at 5℃ / min and held for 60min, then increased to 1000℃ at 5℃ / min and held for 60min, and then decreased to room temperature at 5℃ / min.

[0082] (4) The pyrolysis powder was placed in a ball mill and ball-milled at 80 rpm for 14 hours; then it was placed in a mold and sintered in a spark plasma sintering furnace at a temperature of ≤5×10⁻⁶. -2 Nanoscale (TiNbTaCrMo)C ceramics were obtained by spark plasma sintering under a vacuum of 40 MPa and a pressure of 40 MPa, following a heating and cooling program. The heating program was as follows: heating from room temperature to 1500℃ at a rate of 100℃ / min, then heating to 1900℃ at a rate of 80℃ / min, and holding at that temperature for 25 min. The cooling program was as follows: cooling to 1500℃ at a rate of 80℃ / min, then cooling to room temperature at a rate of 100℃ / min.

[0083] Example 8

[0084] The transition metal salts used in this embodiment are TiCl4, NbCl5, TaCl5, CrCl3, and MoCl5, with furfuryl alcohol as the carbon source. The molar ratio of TiCl4, NbCl5, TaCl5, CrCl3, and MoCl5 is 1:1:1:1:1; the molar ratio of all transition metal chlorides to furfuryl alcohol is 1:1.

[0085] The preparation method of transition metal carbide high-entropy ceramics provided in this embodiment includes the following steps:

[0086] (1) Add 3.6g TiCl4, 5.13g NbCl5, 6.8g TaCl5, 3g CrCl3 and 5.19g MoCl5 to 70g ethanol solution and stir until homogeneous; then add 9.52g furfuryl alcohol to the resulting mixture and stir at 70℃ for 1h to obtain a high-entropy carbide precursor wet gel.

[0087] (2) The obtained high-entropy carbide precursor wet gel was placed in an oven and dried at 170℃ for 12h to obtain high-entropy carbide precursor dry gel.

[0088] (3) The obtained high-entropy carbide precursor dry gel was ground into a powder with a particle size range of 200-400 mesh, and then placed in a tube furnace for pyrolysis at 1600℃ for 1 hour under an argon protective atmosphere. The pyrolysis temperature program was as follows: first, the temperature was increased to 350℃ at 3℃ / min and held for 60 min; then, the temperature was increased to 600℃ at 3℃ / min and held for 60 min; then, the temperature was increased to 1000℃ at 5℃ / min and held for 60 min; then, the temperature was increased to 1600℃ at 5℃ / min and held for 60 min; and then, the temperature was decreased to room temperature at 5℃ / min. Figure 2 As shown in (b);

[0089] (4) The pyrolysis powder was placed in a ball mill and ball-milled at 120 rpm for 10 h; then it was placed in a mold and sintered in a spark plasma sintering furnace at a temperature of ≤5×10⁻⁶. -2 Nanoscale (TiNbTaCrMo)C ceramics were obtained by spark plasma sintering under a vacuum of 65 MPa and a cooling program, following specific heating and cooling procedures. The heating program was as follows: heating from room temperature to 1500℃ at a rate of 100℃ / min, then to 1900℃ at a rate of 80℃ / min, then to 2000℃ at a rate of 50℃ / min, and holding at that temperature for 10 min. The cooling program was as follows: cooling from 2000℃ to 1900℃ at a rate of 50℃ / min, then to 1500℃ at a rate of 80℃ / min, and then back to room temperature at a rate of 100℃ / min. Figure 3 As shown.

[0090] Study on pyrolysis process

[0091] Thermogravimetric analysis (TG) and differential scanning calorimetry (DSC) were performed on the high-entropy carbide precursor dry gel prepared in step (2) of Example 5. The results are as follows: Figure 4 As shown in (a). The pyrolysis products prepared in step (3) of Examples 4, 5, and 6 were subjected to infrared spectroscopy analysis, and the results are as follows. Figure 4 As shown in (b). Through Figure 4 Analysis shows that the high-entropy carbide precursor dry gel underwent chemical bonding fracture during high-temperature pyrolysis. Based on the mass before and after pyrolysis, the pyrolysis yield was approximately 45-55%.

[0092] Structure and property characterization of prepared transition metal carbide high-entropy ceramics

[0093] The high-entropy carbides prepared in Examples 2, 3, 4, and 5 were subjected to XRD analysis, and the results are as follows: Figure 5 As shown, from Figure 5 It can be seen that the high-angle main crystalline phase of the dense nano-transition metal carbide high-entropy ceramic prepared by the method provided in this invention is NbC.

[0094] High-resolution TEM tests were performed on the transition metal carbide high-entropy ceramic prepared in Example 4. The test results are as follows: Figure 6 As shown in the figure, the elements are evenly distributed and the grain size ranges from 70 to 80 nm.

[0095] The high-entropy carbide ceramics obtained in Examples 1-4 above were subjected to relative density and porosity tests. The specific results are shown in Table 1.

[0096] Table 1 Performance parameters of Examples 1-4

[0097]

[0098] Note: Relative density refers to the ratio of the actual density to the theoretical density of high-entropy transition metal carbide ceramics.

[0099] As shown in Table 1, the high-quality transition metal carbide high-entropy ceramics prepared in Examples 1 to 4 were mainly due to the high temperature and high pressure used in the SPS sintering process, which suppressed atomic diffusion and grain coarsening, promoted single-phase carbide solid solution, and made the prepared high-entropy carbide ceramics dense. The density of the high-entropy carbide ceramic targets prepared in Examples 1 to 4 was 95.09%–99.86%. The tube furnace pyrolysis precursor process ensured complete in-situ reaction in the high-entropy carbide precursor powder, while rapid sintering suppressed grain growth and controlled the grain size within the range of 70-80 nm.

[0100] Therefore, the high-entropy carbide ceramics prepared by this invention have high density and nanoscale grain size, making them widely applicable in radiation resistance and thermal protection fields. The method described in this application is simple to operate, has a short production cycle, and is widely applicable.

[0101] In summary, the preparation method of transition metal carbide high-entropy ceramics provided by this invention significantly affects the grain size and final compositional uniformity of the high-entropy carbide ceramics due to the holding temperature of the high-temperature pyrolysis precursor. Spark plasma sintering, as a field-assisted sintering process, offers advantages such as uniform heating, high heating rate, low sintering temperature, short sintering time, controllable microstructure, and high production efficiency. Therefore, the embodiments of this invention can achieve rapid sintering, reduce energy consumption, and produce high-entropy carbide ceramics with a density of 95.09%–99.86%, uniform composition, and an adjustable grain size range of ≥70 nm.

[0102] The above are merely preferred embodiments of this application and are not intended to limit this application. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of this application without inventive effort, and any modifications, equivalent substitutions, improvements, etc., made based on the concept of this application should fall within the scope of protection of the appended claims. Therefore, any technical solution that can be obtained based on the concept of this application through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A method for preparing dense nano-transition metal carbide high-entropy ceramics, characterized in that, Includes the following steps: (1) The transition metal salt and carbon source are mixed and stirred in an organic solvent at 50-70℃ to obtain a high-entropy carbide precursor wet gel. The transition metal salt and carbon source are measured in a transition metal to carbon molar ratio of (1.2-1):(1-5); the transition metal salt includes at least five transition metal chlorides, the transition metal is selected from Ti, Nb, Ta, Cr, Mo, Zr, W, V or Hf, and the carbon source is at least one of furfuryl alcohol and glucose; (2) The high-entropy carbide precursor wet gel is dried to obtain high-entropy carbide precursor dry gel. (3) The obtained high-entropy carbide precursor dry gel was ground into powder and then pyrolyzed at 1000℃ for 1-2 hours under a protective atmosphere. (4) The pyrolyzed powder was subjected to spark plasma sintering at 1900~2000℃ to obtain dense nano-transition metal carbide high-entropy ceramics; the specific operation was as follows: the pyrolyzed powder was first ball-milled, and then spark plasma sintered; the ball milling speed was 80-120 rpm, and the time was 10-14 h; the spark plasma sintering temperature was ≤5×10 -2 Under a vacuum of 40 MPa, the heating or cooling rate is 50-100℃ / min, divided into 2-3 gradient heating or cooling, and held at the set maximum temperature for 10-25 min; the discharge plasma sintering pressure is 40-65 MPa.

2. The method for preparing dense nano-transition metal carbide high-entropy ceramics according to claim 1, characterized in that, The organic solvent is ethanol.

3. The method for preparing dense nano-transition metal carbide high-entropy ceramics according to claim 1, characterized in that, In step (2), the high-entropy carbide precursor wet gel is dried at 100-170℃ to obtain high-entropy carbide precursor dry gel, and the heat preservation time is 12-18h.

4. The method for preparing dense nano-transition metal carbide high-entropy ceramics according to claim 1, characterized in that, In step (3), the protective atmosphere used is argon or nitrogen.

5. A dense nano-transition metal carbide high-entropy ceramic prepared by the method according to any one of claims 1 to 4, having a grain size of 70-80 nm, a porosity of 0-5% excluding the end value of 0, and a density greater than 95%.

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