A method for preparing ultrafine single-phase boride and high-entropy boride powder at low temperature

Abstract

This invention discloses a method for preparing ultrafine single-phase borides and high-entropy boride powders at low temperature. The method uses transition metal chlorides, nitrates, or inexpensive organometallic salts as raw materials, boric acid and sucrose / sorbitol as the boron source and carbon source, respectively, and citric acid or acetylacetone (acac) as the complexing / chelating agent. The prepared sol is dialyzed or anion exchanged using a dialysis bag with a certain molecular weight cutoff or an activated strong-base anion exchange resin to remove NO from the precursor. 3‑ Ions and Cl ‑ Anionic impurities such as ions are removed, and then the precursor powder is obtained through gelation, drying, and grinding. The precursor powder is then pressed into tablets and calcined at low temperature to obtain ultrafine single-phase boride and high-entropy boride ceramic powders. The method of this invention has the advantages of low raw material price, low powder preparation temperature, and small and uniform particle size distribution, which is conducive to mass production and has good practical application value.

Description

Technical Field

[0001] This invention belongs to the field of high-entropy diboride powder technology, specifically relating to a method for preparing ultrafine single-phase borides at low temperature. Background Technology

[0002] Transition metal diborides (TMB2, TM=Ti, Zr, Hf, etc.), as a typical class of ultra-high temperature ceramics (UHTC), have melting points exceeding 3000℃ and possess high elastic modulus, high hardness, and good oxidation resistance. They are widely considered promising high-temperature thermal protection materials and can be applied to hot-end components such as nose cones and wing leading edges of hypersonic vehicles operating in extreme environments. Compared to single-element boride ceramics, high-entropy ceramics composed of five or more elements exhibit superior properties, such as higher hardness and oxidation resistance. By utilizing the differences in oxidation initiation temperatures among different components in high-entropy boride ceramics, and through component design and control, it is hoped that the oxidation resistance range of boride ceramics can be broadened, thereby meeting the performance requirements of ultra-high temperature ceramic materials under extreme environments.

[0003] Currently, methods for preparing high-entropy diboride ceramics include spark plasma sintering (SPS), boronothermal reduction, and boron / carbothermal reduction. These methods are all solid-state methods, where diffusion often occurs at the micrometer scale, resulting in high preparation temperatures and large particle sizes. Furthermore, mechanical mixing is required before preparation, often introducing oxide impurities during ball milling and grinding. Gild et al. (Scientific Reports 2016, 6, 37946) used seven borides—ZrB2, HfB2, TaB2, TiB2, and NbB2—as raw materials. They selected five of these raw materials, mixed them using high-energy ball milling, and then prepared high-entropy diboride ceramics at 2000℃ using SPS technology. 0.2 Zr 0.2 Ta 0.2 Nb 0.2 Ti 0.2 )B2,(Hf 0.2 Zr 0.2 Ta 0.2 Mo 0.2 Ti 0.2 B2, (Hf) 0.2 Zr 0.2 Mo 0.2 Nb 0.2 Ti 0.2 Six types of high-entropy ceramics, including B2, showed significantly improved hardness and oxidation resistance compared to single-phase borides, but oxide impurities were still found and the degree of sintering densification was relatively low.

[0004] Compared to solid-phase reaction methods, liquid-phase methods have unique advantages in powder preparation. They can achieve uniform mixing of multiple components at the molecular or even atomic scale, and diffusion typically occurs at the nanoscale. Therefore, liquid-phase methods are more conducive to synthesizing finer and more uniform powders at lower temperatures. Currently, single-phase or multi-phase UHTC powders such as ZrB2, HfB2, and ZrB2 / ZrC / SiC have been successfully synthesized using liquid-phase methods such as sol-gel and precursor pyrolysis. Recently, it has also been applied to the synthesis of medium-high entropy oxides and carbides, while there are fewer reports on its application in the preparation of high-entropy diborides.

[0005] When preparing UHTC powder using the liquid-phase method, the choice of metal source can be divided into organic salts, such as zirconium propoxide (Zr(OPr)4) and hafnium acetylacetonate (Hf(O2C5H7)4). These can provide partial carbon sources and are easily cross-linked and polymerized with organic matter in the liquid phase, making them excellent raw materials for preparing UHTC precursors. However, organic alkoxides are generally expensive, especially Hf salts and Ta salts. Some organometallic alkoxides are difficult to prepare, resulting in high costs and low economic efficiency when using them as raw materials for UHTC powder preparation, making them unsuitable for mass production. In contrast, inorganic metal salts have been widely studied due to their low price and easy availability. Common inorganic salts include nitrates and chlorides such as Zr(NO3)4, ZrCl4, TaCl4, and HfCl4. However, the preparation of high-entropy borides using inorganic salts as raw materials also faces some problems. Zr(NO3)4 contains nitrogen, which reacts with boron in the system at high temperatures to form BN impurities. During the liquid-phase preparation process, some Cl ions in chloride salts are retained in the precursor, which corrodes the furnace during pyrolysis. The presence of chlorine also has a certain impact on the chemical stability of ceramics. In addition, when the precursor sol is impregnated with ultra-high temperature ceramic matrix composites, the presence of Cl ions during pyrolysis will have an erosion effect on Cf.

[0006] Therefore, it is necessary to develop a liquid-phase method using inexpensive inorganic or organic salts as raw materials to remove NO3 from sols. - Ions and Cl - The method of preparing ultrafine, high-purity boride and high-entropy diboride ceramic powders is of great significance. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention aims to provide a method for preparing ultrafine single-phase borides at micrometer scale and high purity under low temperature. This invention primarily uses transition metal chlorides, nitrates, or inexpensive organometallic salts as the metal source; boric acid and sucrose / sorbitol as the boron and carbon source, respectively; and citric acid or acetylacetone (acac) as the complexing / chelating agent. Ion dialysis is performed using osmotic pressure in a dialysis bag, or ion exchange is performed using a strongly basic anion exchange resin after activation treatment to remove NO from the precursor. 3- Ions and Cl -By eliminating anionic impurities such as ions, ultrafine diboride and high-entropy diboride ceramic powders can be prepared at low temperatures.

[0008] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0009] A method for preparing ultrafine single-phase boride powder at low temperature includes the following steps:

[0010] Sol A1 was prepared by dissolving a metal source, a boron source, a carbon source, and a dispersant in a solvent. The sol was then dialyzed or exchanged using a dialysis membrane and an activated strong-base anion exchange resin to remove anions from sol A1, resulting in sol B1. Sol B1 was then gelled and dried to obtain a dry precursor gel C1. The dry precursor gel C1 was then ground, compressed into tablets, and pyrolyzed at high temperature to obtain ultrafine single-phase diboride powder.

[0011] Traditional solid-phase methods, such as boron / carbothermic reduction, for preparing single-phase boride powders typically involve diffusion at the micrometer scale, resulting in synthesis temperatures generally exceeding 1600℃ and particle sizes on the micrometer scale and above. This method employs a liquid-phase approach for uniform mixing at the nanometer scale and utilizes strongly basic anion exchange resins or dialysis membranes to remove Cl-. - This allows boric acid to be distributed more evenly in the precursor, thus enabling the preparation of finer powders at lower pyrolysis temperatures compared to the solid-state method.

[0012] Preferably, the steps for preparing sol A1 include: first, dissolving a boron source and a metal source M containing a metal element in a solvent; after complete dissolution, adding a dispersant; then adding a carbon source and dissolving it completely; and continuing to stir for a period of time to obtain a clear sol A1; the metal source M is derived from the metal nitrate M(NO3) of that element. m Or chloride salt MCl m The value of m is determined by the valence state of the metal ion. The boron source is boric acid, and the carbon source is sucrose or sorbitol. The elemental ratios between the boron source and the carbon source and the metal M source, respectively, are B / M = 2 to 4 and C / M = 5 to 10.

[0013] More preferably, the solvent is deionized water, or a 1:1 mixture of alcohol and water.

[0014] More preferably, the dispersant is 2% polyethylene glycol.

[0015] Preferably, the preparation steps of sol B1 include: loading sol A1 into a treated dialysis bag, performing dialysis for a certain period of time using ion osmotic pressure, or adding a certain amount of activated strong basic anion exchange resin to the sol, and continuously stirring for a certain period of time to allow NO3 in the sol to dissolve. - ions or Cl - Ions are dialyzed or reacted with OH groups in the resin. - The exchange process yields sol B1.

[0016] Preferably, the molecular weight cutoff of the dialysis membrane is 300D to 100kD; the volume ratio of the strong base anion exchange resin to the volume of the sol to be exchanged is (0.25 to 2): 1; the exchange time after the strong base anion exchange resin is added is 2 to 8 hours; and the strong base anion exchange resin is a strong base anion exchange resin containing quaternary ammonium groups.

[0017] More preferably, after the sol is added to the dialysis bag, the empty volume inside the dialysis bag is 20% to 40%; the dialysis solution is changed 2 to 3 times during the dialysis process, and each dialysis lasts 2 to 4 hours.

[0018] More preferably, the dialysis bag specifications are selected based on the diameter of the anions to be removed and the diameter of the colloidal ions in the sol. The pore size of the dialysis bag is between the two, so the specifications of the dialysis bag are 300D to 100kD molecular weight cutoff. Preferably, the molecular weight of the selected dialysis membrane is 5D to 10kD.

[0019] More preferably, the strongly basic anion exchange resin includes 717 anion exchange resin. IRA-900 anion exchange resin, IRA402 anion exchange resin, etc., including but not limited to the above-mentioned anion exchange resins, and other strongly basic anion exchange resins containing quaternary ammonium groups are also included.

[0020] Preferably, the steps for preparing the dry precursor gel C1 include: slowly adding citric acid solution dropwise to sol B1, so that the metal ions and citric acid complex to form an MOC organic structure; after the addition is complete, refluxing in a water bath at 30-90°C, followed by continuous stirring and evaporation at this temperature to hydrolyze and polymerize the complex to obtain a wet gel, and finally drying to obtain the dry precursor gel C1.

[0021] More preferably, the molar ratio of metal ions to citric acid is 2:1.

[0022] More preferably, the water bath temperature is 60–80°C, and the drying temperature of the dry precursor gel C1 is 100–200°C.

[0023] Preferably, the dry precursor gel C1 is ground to obtain boride amorphous precursor powder, which is then dry-pressed and placed in a vacuum carbon tube furnace. The powder is heated to a pyrolysis temperature of 1300-1700℃ at a heating rate of 5-10℃ / min and held at that temperature to obtain ultrafine single-phase boride powder.

[0024] More preferably, the heat preservation time is 1 to 3 hours, and the pyrolysis is carried out under vacuum conditions or Ar atmosphere.

[0025] A method for preparing ultrafine high-entropy boride powder at low temperature includes the following steps:

[0026] Sol A2 was prepared by dissolving a metal source, a boron source, a carbon source, and a dispersant in a solvent. The sol was then dialyzed or exchanged using a dialysis membrane and an activated strong-base anion exchange resin to remove anions from sol A2, resulting in sol B2. Sol B2 was then gelled and dried to obtain dry precursor gel C2. The dry precursor gel C2 was then ground, compressed into tablets, and pyrolyzed at high temperature to obtain ultrafine high-entropy boride powder.

[0027] Solid-phase methods, such as boron / carbothermic reduction, for preparing high-entropy boride powders use various oxide powders as raw materials. The mixing is primarily mechanical, and due to lattice differences, the synthesis temperature is generally >1600℃. This method employs a liquid-phase approach to achieve uniform mixing of multiple principal components at the nanoscale, and uses a strongly basic anion exchange resin or dialysis membrane to remove NO3. - Cl -

[0028] The presence of anions allows boric acid to be distributed more evenly in the precursor, thus enabling the preparation of finer powders at lower pyrolysis temperatures compared to the solid-state method.

[0029] Preferably, the steps for preparing sol A2 include: dissolving a chelating agent and a metal M source containing five metal elements in a solvent at room temperature, continuously stirring to allow the chelating agent and metal ions to form a complex with an MOC structure, obtaining a clear sol; then dissolving a boron source and a carbon source in deionized water to form a clear solution, adding the solution dropwise to the above sol, and continuously stirring at room temperature until homogeneous to obtain sol A2; the metal M source is an inorganic nitrate M(NO3) of five transition metals Zr, Hf, Nb, Ta, and Ti in equimolar or non-equimolar ratios. m Chloride MCl m Or organic alkoxides, where the value of m is determined by the valence state of the metal ion; the ratios of the boron source and carbon source to the total metal elements in the metal M source, B / M, are 2–4 and C / M, respectively, are 5–8.

[0030] More preferably, the solvent is anhydrous ethanol.

[0031] More preferably, the molar ratio of Zr:Hf:Nb:Ta:Ti is 0.2:0.2:0.2:0.2:0.2.

[0032] More preferably, the chelating agent is acetylacetone, and the molar ratio of the chelating agent to the metal M source is 1.5:1.

[0033] More preferably, the boron source and carbon source can also be added after the sol-gel after filtering the resin.

[0034] Preferably, the preparation steps of sol B2 include: sol A2 is placed into a treated dialysis bag, and dialysis is performed for a certain period of time using the osmotic pressure of ions, or a certain amount of activated strong basic anion exchange resin is added to the sol, and the mixture is stirred continuously for a certain period of time to allow the NO in the sol to... 3- ions or Cl - Ions are dialyzed or reacted with OH groups in the resin. - The exchange process yields sol B2.

[0035] Preferably, the steps for preparing dry precursor gel C2 include: placing sol B2 in a three-necked flask, continuously stirring and evaporating under a gelation temperature of 30–90°C, then pouring it into a beaker and continuing to stir to obtain a wet gel, and finally placing it in a vacuum drying oven to dry and form dry precursor gel C2.

[0036] More preferably, the gelation temperature is 60–80°C, and the drying temperature of the dry precursor gel C2 is 100–200°C.

[0037] Preferably, the molecular weight cutoff of the dialysis membrane is 300D to 100kD; the volume ratio of the strong base anion exchange resin to the volume of the sol to be exchanged is (0.25 to 2): 1; the exchange time after the strong base anion exchange resin is added is 2 to 8 hours; and the strong base anion exchange resin is a strong base anion exchange resin containing quaternary ammonium groups.

[0038] More preferably, the dialysis membrane has a molecular weight cutoff of 5D to 10kD. After the sol is added to the dialysis bag, the empty volume inside the dialysis bag is 20% to 40%; the dialysis solution is changed 2 to 3 times during the dialysis process, and each dialysis session lasts 2 to 4 hours.

[0039] More preferably, the strongly basic anion exchange resin includes 717 anion exchange resin. IRA-900 anion exchange resin, IRA402 anion exchange resin, etc., including but not limited to the above-mentioned anion exchange resins, and other strongly basic anion exchange resins containing quaternary ammonium groups are also included.

[0040] Preferably, the dry precursor gel C2 is ground to obtain a high-entropy boride precursor powder, which is then dry-pressed and placed in a vacuum carbon tube furnace. The powder is heated to a pyrolysis temperature of 1300-1800℃ at a heating rate of 5-10℃ / min and held at that temperature to obtain ultrafine high-entropy boride powder.

[0041] More preferably, the heat preservation time is 1 to 3 hours, and the pyrolysis is carried out under vacuum conditions or Ar atmosphere.

[0042] The technical solution provided by this invention has the following advantages and beneficial effects:

[0043] 1. This invention employs the sol-gel method, a liquid-phase method that enables the mixing of various metal ions at the atomic or molecular scale. This allows for the preparation of fine-particle-size, high-purity single-phase diboride and high-entropy diboride powders at relatively low temperatures. The raw materials used are mainly inorganic nitrates such as Zr(NO3)4, chlorides such as ZrCl4, and inexpensive organic salts (such as tetrabutyl titanate). These are more economical and readily available compared to most organic alkoxides, thus possessing good practical applicability and facilitating large-scale preparation.

[0044] 2. Treating the initial sol with a dialysis membrane or a strongly basic anion exchange resin with a certain molecular weight cutoff significantly reduces NO3 in the sol. - Cl - The concentration of this method avoids the problems of impurities introduced by anions and furnace erosion during the preparation of single-phase diboride powder and high-entropy diboride powder. At the same time, compared with the powder prepared without any treatment, the powder obtained by this method has a finer particle size and more uniform morphology. Attached Figure Description

[0045] Figure 1 The images show the XRD patterns of ZrB2 powder before and after treatment with a strongly basic anion exchange resin in Example 1 of this invention.

[0046] Figure 2 The images show the morphology of ZrB2 powder before and after treatment with a strongly basic anion exchange resin in Example 1 of this invention.

[0047] Figure 3 This is a particle size distribution diagram of ZrB2 powder treated with a strongly basic anion exchange resin in Example 1 of the present invention.

[0048] Figure 4 The image shows the XRD patterns of HEB powder before and after treatment with a 500D dialysis bag in Example 3 of this invention.

[0049] Figure 5 These are morphological images of HEB powder before and after treatment with a 500D dialysis bag in Example 3 of the present invention.

[0050] Figure 6 The image shows the XRD patterns of HEB powder before and after treatment with a strongly basic anion exchange resin in Example 5 of this invention.

[0051] Figure 7 The images show the morphology of HEB powder before and after treatment with a strongly basic anion exchange resin in Example 5 of this invention.

[0052] Figure 8 This is a particle size distribution diagram of HEB powder treated with a strongly basic anion exchange resin in Example 5 of the present invention. Detailed Implementation

[0053] To enable those skilled in the art to better understand the technical solutions of the present invention, the preferred embodiments of the present invention are described below in conjunction with specific examples. However, these should not be construed as limiting the present invention and are merely examples.

[0054] Unless otherwise specified, the test methods or experimental methods described in the following examples are conventional methods; unless otherwise specified, the reagents and materials are obtained from conventional commercial sources or prepared by conventional methods.

[0055] Example 1:

[0056] This embodiment provides a method for preparing ultrafine single-phase ZrB2 powder at low temperature, including the following steps:

[0057] S1. Using ZrCl4 as the Zr source and boric acid and sucrose as the C sources, the raw materials were weighed according to a molar ratio of Zr:B:C = 1:3:8, i.e., 4.66g ZrCl4, 3.71g boric acid, and 4.56g sucrose. First, the boric acid and ZrCl4 were dissolved in 100mL of deionized water. After complete dissolution, 2% polyethylene glycol (PEG) was added as a dispersant, followed by the addition of sucrose. After complete dissolution, the mixture was stirred continuously for 30 minutes to obtain a clear sol.

[0058] S2. Commercially available strong-base anion exchange resin is activated, and then 50 mL of the activated anion exchange resin is added to the sol obtained in S1 while continuously stirring, so that the Cl in the sol... - Ions and OH- in the resin - The anion exchange resin was removed after 4 hours of exchange to obtain a clear sol.

[0059] S3. Slowly add 20 mL of 0.5 mol / L citric acid solution (metal ions: citric acid = 2:1) dropwise to the solution obtained in S2. After the addition is complete, continue stirring and reflux in a water bath at 60°C for 2 h. Then, continue stirring and evaporating at the same temperature for 10 h to obtain a wet gel. Subsequently, dry the wet gel in a drying oven at 110°C for 24 h to obtain a dry gel. Grind the obtained dry gel precursor to obtain ZrB2 amorphous precursor powder.

[0060] The precursor powders obtained in S4 and S3 are dry-pressed into cylindrical powder blocks, placed in a vacuum carbon tube furnace, heated to 1400℃ at a heating rate of 10℃ / min, and held for 1.5h to obtain ZrB2 powder.

[0061] Figure 1 The XRD patterns of ZrB2 powder before and after treatment with a strongly basic anion exchange resin in this embodiment are shown. As can be seen from the figure, the main crystalline phase before and after ion exchange is ZrB2 and there are no other oxide impurities, indicating that the resin does not introduce other impurities when removing anions from the sol. Figure 2 The figures show the morphology of ZrB2 powder before and after treatment with a strongly basic anion exchange resin in this embodiment. As can be seen from the figures, after resin ion exchange, Cl is removed... - The resulting powder has a significantly finer and more uniform particle size compared to the untreated powder. Figure 3 The median particle size in the particle size distribution diagram of this embodiment is 720 nm. Traditional solid-state methods, i.e., boron / carbothermic reduction, are used to prepare ZrB2, with synthesis temperatures generally exceeding 1600℃ and particle sizes in the micrometer range. Therefore, this method can prepare finer powders at a lower synthesis temperature.

[0062] Example 2:

[0063] This embodiment provides a method for preparing ultrafine single-phase HfB2 powder at low temperature, including the following steps:

[0064] S1. Using HfCl4 as the Hf source and boric acid and sucrose as the C sources, the raw materials were weighed according to the molar ratio Hf:B:C = 1:3:8, i.e., 4.91g HfCl4, 3.71g boric acid, and 4.56g sucrose. First, the boric acid and HfCl4 were dissolved in 100mL of deionized water. After complete dissolution, 2% polyethylene glycol (PEG) was added as a dispersant, followed by the addition of sucrose. After complete dissolution, the mixture was stirred continuously for 30 minutes to obtain a clear sol.

[0065] S2. Commercially available strong-base anion exchange resin is activated, and then 50 mL of the activated anion exchange resin is added to the sol obtained in S1 while continuously stirring, so that the Cl in the sol... - Ions and OH- in the resin - The anion exchange resin was removed after 4 hours of exchange to obtain a clear sol.

[0066] S3. Slowly add 20 mL of 0.5 mol / L citric acid solution (metal ions: citric acid = 2:1) dropwise to the solution obtained in S2. After the addition is complete, continue stirring and reflux in a water bath at 60°C for 2 h. Then, continue stirring and evaporating at the same temperature for 10 h to obtain a wet gel. Subsequently, dry the wet gel in a drying oven at 110°C for 24 h to obtain a dry gel. Grind the obtained dry gel precursor to obtain ZrB2 amorphous precursor powder.

[0067] The precursor powders obtained from S4 and S3 are dry-pressed into cylindrical powder blocks, placed in a vacuum carbon tube furnace, heated to 1300℃ at a heating rate of 10℃ / min and held for 1.5h to obtain HfB2 powder.

[0068] Example 3:

[0069] This embodiment provides a method for preparing high-entropy (Ti,Zr,Hf,Nb,Ta)B2 nanoparticles at low temperature, including the following steps:

[0070] S1. Weigh the raw materials according to the molar ratio Zr:Hf:Nb:Ta:Ti = 1:1:1:1:1, wherein each metal element is 0.004 mol, i.e., 1.72 g of Zr(NO3)4·5H2O powder, 1.28 g of HfCl4 powder, 1.08 g of NbCl5 powder, 1.43 g of TaCl5 powder, and 1.36 g of C. 16 H 36 O4Ti.

[0071] S2. At room temperature, weigh 3g of acetylacetone (acac) as a chelating agent and add it to 100mL of ethanol aqueous solution (ethanol and water are mixed in a 1:1 ratio). The molar ratio of acetylacetone to total metal ions (M) is 1.5:1. Then add the metal source weighed in step S1 to the solution and stir at 600r / min for 30min to form a clear sol.

[0072] S3. Subsequently, the sol from step S2 is placed into a dialysis bag with a molecular weight cutoff of 500D. Dialysis is performed in the dialysis solution for 4 hours using the osmotic pressure of the ions. After changing the dialysis solution once, dialysis is continued for another 4 hours to remove nitrate ions and chloride ions from the sol.

[0073] S4. Using boric acid and sucrose as the B source and C source respectively, weigh 4.95g of boric acid and 3.14g of sucrose in a molar ratio of M:B:C = 1:4:5.5 and add them to the sol obtained in S3. Stir continuously at room temperature for 30 minutes to mix evenly and obtain a stable sol.

[0074] S5. Pour the sol filtered in S4 into a three-necked flask, and continuously stir and reflux at 600 r / min in an 80℃ water bath for 1 hour. Then pour it into a beaker and continue stirring for 2 hours to obtain a wet gel.

[0075] S6. Place the wet gel obtained in step S5 in a vacuum drying oven at 110°C and dry it for 24 hours to form a dry gel. Grind the dry gel to obtain high-entropy boride precursor powder.

[0076] S7. The precursor powder obtained in step S6 is dry-pressed into cylindrical powder blocks and calcined at 1400℃ for 1.5h. The obtained blocks are then ground to obtain high-entropy (Ti,Zr,Hf,Nb,Ta)B2 powder.

[0077] Figure 4 The XRD patterns of HEB powder before and after treatment with a 500D dialysis bag in this embodiment are shown. As can be seen from the figure, after treatment with the dialysis bag, the main crystalline phase consists of two sets of HEB peaks, and there are no other oxide impurities. This indicates that the dialysis bag does not have any other effect on the sol in removing anions from the sol. Figure 5(a & b) show the morphology of HEB powder before and after treatment with a 500D dialysis bag in this embodiment. As can be seen from the figures, after NO3 removal... - Cl - The powder obtained after anionization has a significantly more uniform particle size compared to the untreated powder.

[0078] Example 4:

[0079] This embodiment provides a method for preparing high-entropy (Ti,Zr,Hf,Nb,Ta)B2 nanoparticles at low temperature, including the following steps:

[0080] S1. Weigh the raw materials according to the molar ratio Zr:Hf:Nb:Ta:Ti = 1:1:1:1:1, wherein each metal element is 0.004 mol, i.e., 1.72 g of Zr(NO3)4·5H2O powder, 1.28 g of HfCl4 powder, 1.08 g of NbCl5 powder, 1.43 g of TaCl5 powder, and 1.36 g of C. 16 H 36 O4Ti.

[0081] S2. At room temperature, weigh 3g of acetylacetone (acac) as a chelating agent and add it to 50mL of anhydrous ethanol. The molar ratio of acetylacetone to total metal ions (M) is 1.5:1. Then, add the metal source weighed in step S1 to the solution and stir at 600r / min for 30min to form a clear sol.

[0082] S3. Using boric acid and sucrose as the B source and C source respectively, weigh 4.95g of boric acid and 3.14g of sucrose at a molar ratio of M:B:C = 1:4:5.5 and dissolve them in 50mL of deionized water at 60℃ to form a clear solution. Gradually add this solution dropwise to the sol in step S2 at a rate of 5mL / min and stir continuously at room temperature for 30min to mix evenly to obtain a stable sol.

[0083] S4. Then, add 50 mL of anion exchange resin to the sol in step S3 and stir continuously to remove nitrate ions and chloride ions from the sol. After stirring for 4 hours, filter out the anion exchange resin.

[0084] S5. Pour the sol filtered in S4 into a three-necked flask, and continuously stir and reflux at 600 r / min in an 80℃ water bath for 1 hour. Then pour it into a beaker and continue stirring for 2 hours to obtain a wet gel.

[0085] S6. Place the wet gel obtained in step S5 in a vacuum drying oven at 110°C and dry it for 24 hours to form a dry gel. Grind the dry gel to obtain high-entropy boride precursor powder.

[0086] S7. The precursor powder obtained in step S6 is dry-pressed into cylindrical powder blocks and calcined at 1300℃ for 1.5h. The obtained blocks are then ground to obtain high-entropy (Ti,Zr,Hf,Nb,Ta)B2 powder.

[0087] Example 5:

[0088] This embodiment provides a method for preparing high-entropy (Ti,Zr,Hf,Nb,Ta)B2 nanoparticles at low temperature, including the following steps:

[0089] S1. Weigh the raw materials according to the molar ratio Zr:Hf:Nb:Ta:Ti = 1:1:1:1:1, wherein each metal element is 0.004 mol, i.e., 1.72 g of Zr(NO3)4·5H2O powder, 1.28 g of HfCl4 powder, 1.08 g of NbCl5 powder, 1.43 g of TaCl5 powder, and 1.36 g of C. 16 H 36 O4Ti.

[0090] S2. At room temperature, weigh 3g of acetylacetone (acac) as a chelating agent and add it to 100mL of ethanol aqueous solution (ethanol and water are mixed in a 1:1 ratio). The molar ratio of acetylacetone to total metal ions (M) is 1.5:1. Then add the metal source weighed in step S1 to the solution and stir at 600r / min for 30min to form a clear sol.

[0091] S3. Then, 50 mL of anion exchange resin is added to the sol in step S2 and stirred continuously to remove nitrate ions and chloride ions in the sol. After stirring for 4 hours, the anion exchange resin is filtered off.

[0092] S4. Using boric acid and sucrose as the B source and C source respectively, weigh 4.95g of boric acid and 3.14g of sucrose in a molar ratio of M:B:C = 1:4:5.5 and add them to the sol obtained in S3. Stir continuously at room temperature for 30 minutes to mix evenly and obtain a stable sol.

[0093] S5. Pour the sol filtered in S4 into a three-necked flask, and continuously stir and reflux at 600 r / min in an 80℃ water bath for 1 hour. Then pour it into a beaker and continue stirring for 2 hours to obtain a wet gel.

[0094] S6. Place the wet gel obtained in step S5 in a vacuum drying oven at 110°C and dry it for 24 hours to form a dry gel. Grind the dry gel to obtain high-entropy boride precursor powder.

[0095] S7. The precursor powder obtained in step S6 is dry-pressed into cylindrical powder blocks and calcined at 1400℃ for 1.5h. The obtained blocks are then ground to obtain high-entropy (Ti,Zr,Hf,Nb,Ta)B2 powder.

[0096] Figure 6 The XRD patterns of HEB powder before and after treatment with a strongly basic anion exchange resin in this embodiment are shown. As can be seen from the figure, the main crystalline phases before and after ion exchange are both HEB1 and HEB2 borides, with no other oxide impurities. This indicates that the resin does not introduce other impurities when removing anions from the sol. Figure 7 The figures show the morphology of HEB powder before and after treatment with a strongly basic anion exchange resin in this embodiment. As can be seen from the figures, NO3 is removed after resin ion exchange. - Cl - The powder obtained after anionization has a significantly finer and more uniform particle size compared to the untreated powder. Figure 8 The particle size distribution diagram of this embodiment shows a median particle size of 368.82 nm. Compared with the traditional solid-state method, which uses boron / carbothermic reduction to prepare HEB phase, nano-high-entropy boride powder can be prepared at a lower synthesis temperature of 1400 °C.

[0097] Example 6:

[0098] This embodiment provides a method for preparing high-entropy (Ti,Zr,Hf,Nb,Ta)B2 nanoparticles at low temperature, including the following steps:

[0099] S1. Weigh the raw materials according to the molar ratio Zr:Hf:Nb:Ta:Ti=1:1:1:1:1, wherein each metal element is 0.004mol, i.e., 0.93g of ZrCl4 powder, 1.28g of HfCl4 powder, 1.08g of NbCl5 powder, 1.43g of TaCl5 powder, and 0.77g of TiCl4 liquid.

[0100] S2. At room temperature, weigh 3g of acetylacetone (acac) as a chelating agent and add it to 50mL of anhydrous ethanol. The molar ratio of acetylacetone to total metal ions (M) is 1.5:1. Then, add the metal source weighed in step S1 to the solution and stir at 600r / min for 30min to form a clear sol.

[0101] S3. Using boric acid and sucrose as the B source and C source respectively, weigh 4.95g of boric acid and 3.14g of sucrose at a molar ratio of M:B:C = 1:4:5.5 and dissolve them in 50mL of deionized water at 60℃ to form a clear solution. Gradually add this solution dropwise to the sol in step S2 at a rate of 5mL / min and stir continuously at room temperature for 30min to mix evenly to obtain a stable sol.

[0102] S4. Then, add 50 mL of anion exchange resin to the sol in step S3 and stir continuously to remove nitrate ions and chloride ions from the sol. After stirring for 4 hours, filter out the anion exchange resin.

[0103] S5. Pour the sol filtered in S4 into a three-necked flask, and continuously stir and reflux at 600 r / min in an 80℃ water bath for 1 hour. Then pour it into a beaker and continue stirring for 2 hours to obtain a wet gel.

[0104] S6. Place the wet gel obtained in step S5 in a vacuum drying oven at 110°C and dry it for 24 hours to form a dry gel. Grind the dry gel to obtain high-entropy boride precursor powder.

[0105] S7. The precursor powder obtained in step S6 is dry-pressed into cylindrical powder blocks and calcined at 1400℃ for 1.5h. The obtained blocks are then ground to obtain high-entropy (Ti,Zr,Hf,Nb,Ta)B2 powder.

[0106] The above are merely preferred embodiments of the present invention. It should be noted that the above preferred embodiments should not be considered as limitations on the present invention, and the scope of protection of the present invention should be determined by the scope defined in the claims. For those skilled in the art, several improvements and modifications can be made without departing from the spirit and scope of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing ultrafine single-phase boride powder at low temperature, characterized in that, Includes the following steps: Sol A1 was prepared by dissolving a metal source, boron source, carbon source, and dispersant in a solvent. Sol A1 was then dialyzed or exchanged using a dialysis membrane or a strongly basic anion exchange resin after activation treatment to remove anions, yielding sol B1. Sol B1 was then gelled and dried to obtain a dry precursor gel C1. The dry precursor gel C1 was then ground, compressed into tablets, and pyrolyzed at high temperature to obtain ultrafine single-phase diboride powder. The metal source was a metal M source containing one metal element, derived from the metal nitrate M(NO3) of that element. m Or chloride salt MCl m The value of m is determined by the valence state of the metal ion.

2. The method for preparing ultrafine single-phase boride powder at low temperature according to claim 1, characterized in that, The steps for preparing sol A1 include: first, dissolving a boron source and a metal source M containing a metal element in a solvent; after complete dissolution, adding a dispersant; then adding a carbon source and dissolving it completely; and finally stirring continuously for a period of time to obtain a clear sol A1. The boron source is boric acid, and the carbon source is sucrose or sorbitol; The elemental ratios between the boron source and the carbon source and the metal M source, respectively, are B / M = 2~4 and C / M = 5~10.

3. The method for preparing ultrafine single-phase boride powder at low temperature according to claim 1, characterized in that, The molecular weight cutoff of the dialysis membrane is 300 Da~100 kDa; The volume ratio of the strong base anion exchange resin to the sol A1 to be exchanged is (0.25~2):1, and the exchange time after the strong base anion exchange resin is added is 2~8 h; Strongly basic anion exchange resins are strongly basic anion exchange resins containing quaternary ammonium groups.

4. The method for preparing ultrafine single-phase boride powder at low temperature according to claim 1, characterized in that, The steps for preparing dry precursor gel C1 include: slowly adding citric acid solution dropwise to sol B1, and after the addition is complete, refluxing in a water bath at 30~90℃, followed by continuous stirring and evaporation at this temperature to obtain a wet gel, and finally drying to obtain dry precursor gel C1.

5. The method for preparing ultrafine single-phase boride powder at low temperature according to claim 1, characterized in that, Dry precursor gel C1 was ground to obtain boride amorphous precursor powder, which was then dry-pressed and placed in a vacuum carbon tube furnace. The powder was heated to a pyrolysis temperature of 1300-1700℃ at a heating rate of 5-10℃ / min and held at that temperature to obtain ultrafine single-phase boride powder.

6. A method for preparing ultrafine high-entropy boride powder at low temperature, characterized in that, Includes the following steps: Sol A2 was prepared by dissolving a metal source, boron source, carbon source, and dispersant in a solvent. Sol A2 was then dialyzed or exchanged using a dialysis membrane or a strongly basic anion exchange resin after activation treatment to remove anions, yielding sol B2. Sol B2 was then gelled and dried to obtain a dry precursor gel C2. The dry precursor gel C2 was then ground, compressed into tablets, and pyrolyzed at high temperature to obtain ultrafine high-entropy boride powder. The metal source was a metal M source containing five metal elements, specifically inorganic nitrates M(NO3) of the five transition metals Zr, Hf, Nb, Ta, and Ti in equimolar or non-equimolar ratios. m Chloride MCl m Or an organic alkoxide, where the value of m is determined by the valence state of the metal ion.

7. The method for preparing ultrafine high-entropy boride powder at low temperature according to claim 6, characterized in that, The steps for preparing sol A2 include: at room temperature, dissolving a chelating agent and a metal M source containing five metal elements in a solvent, stirring to form a clear sol, then dissolving a boron source and a carbon source in deionized water to form a clear solution, adding the solution dropwise into the above sol, and stirring continuously at room temperature to obtain sol A2. The ratios of the boron source and carbon source to the total metal elements in the metal M source, B / M, are 2~4 and C / M, respectively, which are 5~8.

8. The method for preparing ultrafine high-entropy boride powder at low temperature according to claim 6, characterized in that, The steps for preparing dry precursor gel C2 include: placing sol B2 in a three-necked flask, continuously stirring and evaporating under reflux at a gelation temperature of 30~90℃, then pouring it into a beaker and continuing to stir to obtain a wet gel, and finally placing it in a vacuum drying oven to dry and form dry precursor gel C2.

9. The method for preparing ultrafine high-entropy boride powder at low temperature according to claim 6, characterized in that, The molecular weight cutoff of the dialysis membrane is 300 Da~100 kDa; The volume ratio of the strong base anion exchange resin to the sol A2 to be exchanged is (0.25~2):1, and the exchange time after the strong base anion exchange resin is added is 2~8 h; Strongly basic anion exchange resins are strongly basic anion exchange resins containing quaternary ammonium groups.

10. The method for preparing ultrafine high-entropy boride powder at low temperature according to claim 6, characterized in that, High-entropy boride precursor powder was obtained by grinding the dry precursor gel C2, and then dry-pressed and placed in a vacuum carbon tube furnace. The powder was heated to a pyrolysis temperature of 1300-1800℃ at a heating rate of 5-10℃ / min and held at that temperature to obtain ultrafine high-entropy boride powder.

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