A chromium tantalate precursor, its preparation method and application

Abstract

This invention discloses a chromium tantalate precursor, its preparation method, and its applications. The preparation method uses tantalum and chromium sources as raw materials, anhydrous alcohol as solvent and reaction reagent, and acetylacetone as a complexing agent. Through substitution reaction, complexation reaction, hydrolysis, and dehydration condensation, a uniformly cross-linked and structurally stable chromium tantalate precursor can be prepared. The chromium tantalate precursor prepared by this invention has the following technical advantages: the pyrolysis process of the chromium tantalate precursor is highly controllable, and it can be converted into high-purity, single-phase chromium tantalate powder without chromium oxide or tantalum oxide residues; the chromium tantalate precursor is in solution state, and a chromium tantalate coating can be directly prepared on the surface of complex-shaped substrates through an impregnation-pyrolysis process. The coating forms a chemical bond with the substrate, exhibiting strong adhesion and high density. Simultaneously, chromium tantalate-based fiber-reinforced composite materials can be prepared, significantly broadening the application scenarios of chromium tantalate in the field of environmental barrier materials.

Description

Technical Field

[0001] This invention belongs to the field of ceramic materials technology, and relates to a chromium tantalate precursor, its preparation method, and its application. Background Technology

[0002] Currently, the synthesis and application of chromium tantalate (CrTaO4) face significant limitations. Existing technologies primarily utilize Cr2O3 and Ta2O5 as raw materials, preparing CrTaO4 powder through a high-temperature solid-state reaction. Regarding coating preparation, current methods only allow for the deposition of CrTaO4 powder as a coating using physical methods such as plasma spraying. This process has inherent drawbacks: the coating is prone to porosity and cracking, exhibits weak adhesion to the substrate, and suffers from difficulty in controlling thickness uniformity, leading to unstable protective performance. Furthermore, high-temperature solid-state reactions cannot be used to prepare complex-shaped components or composite materials, severely limiting the application of CrTaO4 in high-end applications such as irregularly shaped high-temperature components and fiber-reinforced composites.

[0003] For the reasons stated above, this invention is proposed. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a chromium tantalate precursor with uniform crosslinking and stable structure, as well as its preparation method and application.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A method for preparing a chromium tantalate precursor involves using tantalum and chromium sources as raw materials, anhydrous alcohol as solvent and reaction reagent, and acetylacetone as a complexing agent, followed by substitution reaction, complexation reaction, hydrolysis, and dehydration condensation.

[0006] The above preparation method, further improved, includes the following steps: S1. Construct a reaction system in an anhydrous and oxygen-free environment; S2. Add anhydrous alcohol to the reaction system and add tantalum source to carry out substitution reaction; S3. After the substitution reaction is completed, the reaction system is heated to the preset temperature, and acetylacetone is added dropwise to carry out the complexation reaction. S4. After the complexation reaction is completed, chromium source and deionized water are added successively, and hydrolysis reaction is carried out under preset temperature conditions. S5. Dehydration condensation of the products of the hydrolysis reaction; S6. The dehydration condensation product is subjected to vacuum distillation to obtain the chromium tantalate precursor.

[0007] In a further improvement to the above preparation method, in step S2, the molar ratio of the tantalum source to the anhydrous alcohol is 1:6 to 10; the tantalum source is TaCl5 powder; the anhydrous alcohol is at least one of anhydrous ethanol, anhydrous glacial alcohol, and anhydrous n-butanol; the addition rate of the tantalum source is 2 g / min to 3 g / min; the substitution reaction is carried out under stirring conditions; the substitution reaction time is 1 h to 2 h; the substitution reaction process also includes: absorbing the waste gas generated during the reaction using a drying tower containing NaOH.

[0008] In a further improvement to the above preparation method, in step S3, the preset temperature is 60℃~70℃; the molar ratio of acetylacetone to tantalum source is 1~2:1; the dropping rate of acetylacetone is 1 mL / min~2 mL / min; and the complexation reaction time is 1 h~2 h.

[0009] In a further improvement to the above preparation method, in step S4, the molar ratio of the chromium source to the tantalum source is 1:1; the chromium source is CrCl3·6H2O powder; the molar ratio of the deionized water to the tantalum source is 3-4:1; the dropping rate of the deionized water is 1 mL / min-2 mL / min; and the hydrolysis reaction time is 1 h-2 h.

[0010] The above preparation method is further improved in step S1, which involves constructing a reaction system in an anhydrous and oxygen-free environment by the following steps: setting up a Schlenk reaction apparatus and repeating the operation of vacuuming and introducing dry nitrogen gas until the reaction system is in an anhydrous and oxygen-free environment; the operation of vacuuming and introducing dry nitrogen gas is repeated 3 to 5 times; the purity of the dry nitrogen gas is not less than 99.999%.

[0011] In a further improvement to the above preparation method, in step S6, the vacuum distillation is carried out at a temperature of 60℃~70℃; the vacuum degree of the vacuum distillation is 0~0.01 MPa; and the vacuum distillation time is 0.5 h~1 h.

[0012] As a general technical concept, the present invention also provides a chromium tantalate precursor, which is prepared by the above-described preparation method.

[0013] As a general technical concept, the present invention also provides the application of the above-mentioned chromium tantalate precursor as a raw material in the preparation of chromium tantalate.

[0014] The above application is further improved by using chromium tantalate precursor as raw material for multi-stage heating pyrolysis to obtain chromium tantalate.

[0015] The above application, further improved, involves multi-stage pyrolysis using chromium tantalate precursor as raw material, including the following stages: (1) First stage: The chromium tantalate precursor was placed in a pyrolysis device and heated to 80°C at a heating rate of 5°C / min and held for 1 h; (2) Second stage: Heat to 200℃ at a heating rate of 5℃ / min and hold for 1 h; (3) Third stage: Heat to 700℃ at a heating rate of 5℃ / min and hold for 1 h; (4) Fourth stage: Heat to 1120℃ at a heating rate of 5℃ / min and hold for 2 h to obtain chromium tantalate.

[0016] In a further improvement to the above application, the multi-stage heating pyrolysis is carried out in an argon atmosphere or an air atmosphere; the pyrolysis equipment is a tube furnace or a muffle furnace.

[0017] As a general technical concept, the present invention also provides the application of the above-mentioned chromium tantalate precursor as a raw material in the preparation of chromium tantalate coatings or chromium tantalate-based composite materials.

[0018] For example, CrTaO4 coatings or CrTaO4-based composites can be prepared from chromium tantalate precursors in solution via a precursor impregnation pyrolysis process, but this is not the only option.

[0019] Compared with the prior art, the advantages of the present invention are as follows: (1) In view of the shortcomings of solid-phase reaction synthesis of CrTaO4 powder, such as the inability to prepare powder, limited application, and poor adaptability, this invention creatively proposes a method for preparing chromium tantalate precursor. Using tantalum source and chromium source as raw materials, anhydrous alcohol as solvent and reaction reagent, and acetylacetone as complexing agent, a uniformly crosslinked and structurally stable chromium tantalate precursor is prepared through substitution reaction, complexation reaction, hydrolysis, and dehydration condensation. This chromium tantalate precursor has the following technical effects: (1.1) The pyrolysis process of this chromium tantalate precursor is highly controllable. It can be converted into high-purity, single-phase CrTaO4 powder by holding at 1120℃ for 2 h, with no Cr2O3 or Ta2O5 residues. The purity and crystallinity of the product far exceed those of traditional solid-phase reactions.

[0020] (1.2) The chromium tantalate precursor is in solution state, and CrTaO4 coating can be directly prepared on the surface of complex-shaped substrates through impregnation-pyrolysis process. The coating forms a chemical bond with the substrate, with strong bonding force and high density, which solves the inherent defects of spray coating. At the same time, CrTaO4-based fiber-reinforced composite materials can be prepared through multiple impregnation-pyrolysis processes, which solves the problem that traditional technology can only prepare powder or coating and has a single application form, and significantly broadens the application scenarios of CrTaO4 in the field of environmental barrier materials.

[0021] (2) In the preparation method of the chromium tantalate precursor of the present invention, anhydrous alcohol is added first, and then the tantalum source is added to the anhydrous alcohol. This is beneficial to control the rate of the substitution reaction. It can not only avoid the large amount of evaporation of anhydrous alcohol due to the violent exothermic reaction, but also avoid the rapid release of the reaction byproduct hydrogen chloride. In particular, by controlling the addition rate of the tantalum source to 2 g / min to 3 g / min, the controllable preparation of the reaction can be achieved.

[0022] (3) In the preparation method of the chromium tantalate precursor of the present invention, acetylacetone is added dropwise to the reaction system, which is beneficial to control the rate of complexation reaction. At the same time, by controlling the dropwise acceleration rate of acetylacetone to 1 mL / min to 2 mL / min, the complexing agent and the metal alkoxide can be fully contacted and reacted. In addition, if the dropwise acceleration rate is too fast, the reaction will be insufficient, while if the dropwise acceleration rate is too slow, the reaction efficiency will be low.

[0023] (4) In the preparation method of the chromium tantalate precursor of the present invention, a chromium source is first added to dissolve the chromium source into the system, and then deionized water is added dropwise to promote the hydrolysis reaction. At the same time, by controlling the dropping rate of deionized water to 1 mL / min to 2 mL / min, the hydrolysis reaction is fully carried out. In addition, if the dropping rate is too fast, the reaction is not sufficient, and if the dropping rate is too slow, the reaction efficiency is low. Attached Figure Description

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0025] Figure 1 This is a schematic diagram of the Schlenk reaction apparatus in Embodiment 1 of the present invention.

[0026] Figure 2 The infrared spectrum of the chromium tantalate precursor prepared in Example 1 of this invention.

[0027] Figure 3 The 1H NMR spectrum of the chromium tantalate precursor prepared in Example 1 of this invention.

[0028] Figure 4 The thermogravimetric curves of the chromium tantalate precursor cured at 200°C in air and argon are shown in comparison diagrams of Examples 1 and 2 of the present invention.

[0029] Figure 5 The images show the XRD patterns of chromium tantalate prepared in Examples 1-2 and Comparative Examples 1-4 of this invention.

[0030] Figure 6 This is a TEM-EDS image of chromium tantalate prepared in Example 1 of the present invention.

[0031] Figure 7This is a TEM-EDS image of chromium tantalate prepared in Example 2 of the present invention.

[0032] Legend: Detailed Implementation The present invention will be further described below with reference to the accompanying drawings and specific preferred embodiments, but this does not limit the scope of protection of the present invention.

[0033] In the following embodiments of the present invention, unless otherwise specified, the materials and instruments used are commercially available, the equipment used is conventional equipment, and the data obtained are the average values ​​of more than three repeated experiments.

[0034] Example 1 A method for preparing a chromium tantalate precursor, using tantalum and chromium sources as raw materials, anhydrous alcohol as solvent and reagent, and acetylacetone as complexing agent, is carried out through substitution reaction, complexation reaction, hydrolysis, and dehydration condensation, comprising the following steps: S1. Construct a reaction system in an anhydrous and oxygen-free environment, specifically as follows: Building such Figure 1 The Schlenk reaction apparatus shown includes a double-row tube, a three-necked flask, a constant-pressure dropping funnel, a powder feeding funnel, and a condenser. After checking the airtightness, the vacuuming and purging of 99.999% high-purity nitrogen were repeated three times to ensure that the reaction system was in an anhydrous and oxygen-free environment.

[0035] S2. Anhydrous ethanol is added to the reaction system, and a tantalum source is added to carry out a substitution reaction, specifically as follows: At room temperature, 162 mL of anhydrous ethanol was added to a three-necked flask through a constant pressure dropping funnel, and then 100 g of TaCl5 powder was slowly added through a powder feeding funnel at a rate of 2.5 g / min. The molar ratio of TaCl5 to anhydrous ethanol was 1:10. The mixture was magnetically stirred for 1 h to generate tantalum ethoxide through a substitution reaction until the solution gradually changed from colorless to milky white. The HCl waste gas generated during the reaction was absorbed by a NaOH drying tower through a double-row pipe to complete the substitution reaction and generate tantalum ethoxide. The reaction equation is shown in equation (1). (1) S3. After the substitution reaction is complete, the reaction system is heated to the preset temperature, and acetylacetone is added dropwise to carry out the complexation reaction, specifically as follows: The reaction system was heated to 60℃, and 57 mL of acetylacetone was slowly added dropwise through a constant pressure dropping funnel. The dropping rate of acetylacetone was 1.5 mL / min, and the molar ratio of TaCl5 to acetylacetone was 1:2. The reaction was kept at this temperature for 1 h to allow acetylacetone to form a stable complex with tantalum ethoxide. The solution turned yellowish-white. The reaction equation for the stable complex formed by acetylacetone and tantalum ethoxide is shown in equation (2). (2) S4. After the complexation reaction is complete, a chromium source and deionized water are added sequentially, and a hydrolysis reaction is carried out under preset temperature conditions, specifically as follows: 74 g of CrCl3·6H2O powder was added to the system, with a molar ratio of CrCl3·6H2O to TaCl5 of 1:1. Then, 15 mL of deionized water was slowly added dropwise at a rate of 1.5 mL / min, with a molar ratio of deionized water to TaCl5 of 3:1. The reaction was maintained at 60 °C for 2 h to promote controlled hydrolysis of the complex, generating a hydroxyl-containing intermediate, specifically [Cr(H2O)6] after the dissociation of CrCl3·6H2O. 3+ It can also be reversibly hydrolyzed to form [Cr(H2O)5(OH)] 2+ (Equation (3)); acetylacetone ethanol tantalum undergoes controlled hydrolysis, and the ethoxy group is replaced by a hydroxyl group (Equation (4)). Finally, the hydroxyl-containing tantalum complex undergoes dehydration or de-alcoholization condensation with the chromium hydroxy complex, and forms a three-dimensional network precursor through Ta-O-Ta and Ta-O-Cr bond polymerization (Equations (5~8)):

[0036] S5. The product of dehydration condensation is subjected to vacuum distillation to obtain the chromium tantalate precursor, specifically: The reaction product was subjected to vacuum distillation at 70°C and 0.005 MPa for 0.5 h to remove excess ethanol solvent, resulting in a dark green viscous CrTaO4 precursor solution, which is the chromium tantalate precursor of the present invention.

[0037] The infrared spectrum of the CrTaO4 precursor in this embodiment is as follows: Figure 2 As shown. By Figure 2 It can be known that 3325 cm -1 The broad peak nearby originates from the OH stretching vibration of the hydrogen bonds between associated ethanol molecules, at 1423 cm⁻¹. -1 The weak peak at 2975 cm⁻¹ belongs to the OH bending vibration of ethanol, proving the presence of ethanol solvent in the precursor. -1 and 2932 cm -1 The characteristic wavenumber peaks are the antisymmetric stretching vibration peaks of the -CH3 and -CH2- groups, which may originate from the ethoxy group of tantalum ethoxide or the methyl group of the acetylacetone ligand. (1355 cm⁻¹) -1 CH bending vibration peak and 1287 cm -1 The C-S stretching vibration peak also confirms the presence of the aforementioned functional groups. (1523 cm⁻¹) -1 and 1569 cm -1The characteristic peaks at these positions belong to the C=C stretching vibration of the enol acetylacetone ligand and the conjugated ring skeleton vibration of the acetylacetone ligand (acac), respectively, indicating that acetylacetone undergoes complexation with tantalum ethoxide, transforming from the keto form to the enol form. (1027 cm⁻¹) -1 The characteristic peaks of the CO-Ta bond also confirm the formation of the Ta-O coordination bond. (829 cm⁻¹) -1 The nearby characteristic peaks may be attributed to Ta-Cl bonds, indicating that TaCl5 and ethanol may only undergo partial substitution. (664 cm⁻¹) -1 The characteristic peaks may belong to Cr-O bonds, attributed to [Cr(H2O)6]. 3+ The [Cr(H₂O)₅(OH)] formed after hydrolysis 2+ Cr-OH and Ta-OH can undergo further dehydration condensation to eventually generate the CrTaO4 precursor.

[0038] Furthermore, the CrTaO4 precursor in this embodiment is used... 1 H NMR characterization, results as follows Figure 3 As shown. By Figure 3 It can be seen that the resonance peak at 2.5 ppm is the solvent peak of DMSO. The resonance peak at 1.0 ppm belongs to the H in the ethoxy-terminated methyl group and the methyl group on the saturated carbon side of enol acetylacetone. The peaks at 1.9–2.0 ppm belong to the H in the methyl group attached to the unsaturated carbon of enol acetylacetone. The characteristic peak at 3.4 ppm belongs to the H in the methylene group of the ethoxy group. The characteristic peak at 4.2 ppm comes from the hydroxyl H in the precursor that has not undergone dehydration condensation or the hydroxyl H in the solvent ethanol.

[0039] In summary, 1 ¹H NMR confirmed that the complexation of tantalum ethoxide with acetylacetone enabled controlled hydrolysis, which facilitated subsequent dehydration condensation crosslinking reactions.

[0040] One application of the chromium tantalate precursor prepared in this embodiment as a raw material in the preparation of chromium tantalate specifically involves using the chromium tantalate precursor as a raw material for multi-stage pyrolysis to obtain chromium tantalate powder, including the following stages: (1) First stage: The chromium tantalate precursor (CrTaO4 precursor solution) is placed in an Al2O3 boat and placed in a pyrolysis device (muffle furnace). In an air atmosphere, the temperature is raised to 80℃ at a heating rate of 5℃ / min and held for 1 h (solvent evaporation) to evaporate the residual solvent in the precursor.

[0041] (2) Second stage: Heat to 200℃ at a heating rate of 5℃ / min and keep warm for 1 h (crosslinking and curing) to allow the precursor to fully crosslink and cure.

[0042] (3) Third stage: Heat to 700℃ at a heating rate of 5℃ / min and hold for 1 h (inorganic transformation) to cause the precursor to undergo inorganic transformation.

[0043] (4) Fourth stage: Heat to 1120℃ at a heating rate of 5℃ / min and hold for 2 h (solid phase reaction) to allow the inorganic products to undergo a solid phase reaction to generate CrTaO4 powder. After natural cooling, chromium tantalate is obtained.

[0044] Comparative Example 1 An application of the chromium tantalate precursor prepared in Example 1 above as a raw material in the preparation of chromium tantalate specifically involves using the chromium tantalate precursor as a raw material for multi-stage pyrolysis to obtain chromium tantalate powder, including the following stages: (1) First stage: The chromium tantalate precursor (CrTaO4 precursor solution) was placed in an Al2O3 boat and put into a pyrolysis device (muffle furnace). In an air atmosphere, the temperature was raised to 80℃ at a heating rate of 5℃ / min and held for 1 h to evaporate the residual solvent in the precursor.

[0045] (2) Second stage: Heat to 200℃ at a heating rate of 5℃ / min and hold for 1 h (solvent evaporation).

[0046] (3) Third stage: Heat to 700℃ at a heating rate of 5℃ / min and hold for 1 h (inorganic transformation).

[0047] (4) Fourth stage: Heat to 900℃ at a heating rate of 5℃ / min, hold for 2 h (solid phase reaction), and after natural cooling, chromium tantalate is obtained.

[0048] Comparative Example 2 An application of the chromium tantalate precursor prepared in Example 1 above as a raw material in the preparation of chromium tantalate specifically involves using the chromium tantalate precursor as a raw material for multi-stage pyrolysis to obtain chromium tantalate powder, including the following stages: (1) First stage: The chromium tantalate precursor (CrTaO4 precursor solution) is placed in an Al2O3 boat and placed in a pyrolysis device (muffle furnace). In an air atmosphere, the temperature is raised to 80℃ at a heating rate of 5℃ / min and held for 1 h (solvent evaporation) to evaporate the residual solvent in the precursor.

[0049] (2) Second stage: Heat to 200℃ at a heating rate of 5℃ / min (crosslinking and curing), and keep warm for 1 h to allow the precursor to fully crosslink and cure; (3) Third stage: Heat to 700℃ at a heating rate of 5℃ / min (inorganic transformation + solid-phase reaction), keep warm for 2h, and then cool naturally to obtain chromium tantalate.

[0050] Example 2 An application of the chromium tantalate precursor prepared in Example 1 above as a raw material in the preparation of chromium tantalate specifically involves using the chromium tantalate precursor as a raw material for multi-stage pyrolysis to obtain chromium tantalate powder, including the following stages: (1) First stage: The chromium tantalate precursor (CrTaO4 precursor solution) is placed in an Al2O3 boat and placed in a pyrolysis device (muffle furnace). Under an argon atmosphere, the temperature is increased to 80℃ at a heating rate of 5℃ / min and held for 1 h (solvent evaporation) to evaporate the residual solvent in the precursor.

[0051] (2) Second stage: Heat to 200℃ at a heating rate of 5℃ / min and keep warm for 1 h (crosslinking and curing) to allow the precursor to fully crosslink and cure.

[0052] (3) Third stage: Heat to 700℃ at a heating rate of 5℃ / min and hold for 1 h (inorganic transformation) to cause the precursor to undergo inorganic transformation.

[0053] (4) Fourth stage: Heat to 1120℃ at a heating rate of 5℃ / min and hold for 2 h (solid phase reaction) to allow the inorganic products to undergo a solid phase reaction to generate CrTaO4 powder. After natural cooling, chromium tantalate is obtained.

[0054] Comparative Example 3 An application of the chromium tantalate precursor prepared in Example 1 above as a raw material in the preparation of chromium tantalate specifically involves using the chromium tantalate precursor as a raw material for multi-stage pyrolysis to obtain chromium tantalate powder, including the following stages: (1) First stage: The chromium tantalate precursor (CrTaO4 precursor solution) was placed in an Al2O3 boat and placed in a pyrolysis device (muffle furnace). Under an argon atmosphere, the temperature was raised to 80℃ at a heating rate of 5℃ / min and held for 1 h to allow the residual solvent in the precursor to evaporate.

[0055] (2) Second stage: Heat to 200℃ at a heating rate of 5℃ / min and hold for 1 h (solvent evaporation).

[0056] (3) Third stage: Heat to 700℃ at a heating rate of 5℃ / min and hold for 1 h (inorganic transformation).

[0057] (4) Fourth stage: Heat to 900℃ at a heating rate of 5℃ / min, hold for 2 h (solid phase reaction), and after natural cooling, chromium tantalate is obtained.

[0058] Comparative Example 4 An application of the chromium tantalate precursor prepared in Example 1 above as a raw material in the preparation of chromium tantalate specifically involves using the chromium tantalate precursor as a raw material for multi-stage pyrolysis to obtain chromium tantalate powder, including the following stages: (1) First stage: The chromium tantalate precursor (CrTaO4 precursor solution) is placed in an Al2O3 boat and placed in a pyrolysis device (muffle furnace). Under an argon atmosphere, the temperature is increased to 80℃ at a heating rate of 5℃ / min and held for 1 h (solvent evaporation) to evaporate the residual solvent in the precursor.

[0059] (2) Second stage: Heat to 200℃ at a heating rate of 5℃ / min (crosslinking and curing), and keep warm for 1 h to allow the precursor to fully crosslink and cure; (3) Third stage: Heat to 700℃ at a heating rate of 5℃ / min (inorganic transformation + solid-phase reaction), keep warm for 2h, and then cool naturally to obtain chromium tantalate.

[0060] In Examples 1 and 2, the thermogravimetric curves of the CrTaO4 precursor cured at 200℃ in air and argon are as follows: Figure 4 As shown. By Figure 4 It can be seen that when pyrolysis is carried out in an air atmosphere, the pyrolysis process of CrTaO4 precursor can be divided into the following three stages: (1) Room temperature ~ 208℃ is mainly the stage of volatilization of residual solvent and adsorbed water in precursor powder. There is almost no mass change before 102℃, and the weight loss is 2.5% from 102 to 208℃; (2) 208~405℃ is the main weight loss range of precursor. The precursor undergoes inorganic transformation, the three-dimensional network macromolecular structure is destroyed, the organic components decompose, part of which escapes in the form of gaseous small molecules, and the rest remains in the form of pyrolytic carbon. The cracking reaction of precursor reaches the maximum rate at 319℃, and inorganic transformation is basically completed at 405℃, with a weight loss of 31.6% and transformation into amorphous ceramic; (3) 405℃~806℃ is the oxidation stage. The pyrolytic carbon remaining in the inorganic process is oxidized in this stage as the temperature increases, and escapes in the form of CO and CO2 until only oxides remain in the pyrolysis products. The weight loss is 2.5% in this stage. In summary, the CrTaO4 precursor undergoes solvent evaporation, cross-linking and curing, inorganication and oxidation processes during pyrolysis, and its quality tends to stabilize after 806℃, with a ceramic yield of 63.2%.

[0061] In addition, such as Figure 4As shown, when pyrolysis is carried out in an argon atmosphere, it can be divided into the following four stages: (1) Room temperature ~ 211℃ is similar to that in air, mainly the volatilization stage of residual solvent and adsorbed moisture in the precursor powder, with a weight loss of 8.2%. (2) 211~655℃ is the main weight loss range of the precursor. The precursor undergoes inorganic transformation, the three-dimensional network macromolecular structure is destroyed, the organic components decompose, and some escape in the form of gaseous small molecules. Unlike air pyrolysis, under oxygen-deficient conditions, the organic components are more retained as pyrolytic carbon. The cracking reaction of the precursor reaches its maximum rate at 407℃, but it is only -0.127% / min, which is much smaller than the pyrolysis rate of -1.492% / min at 319℃ in air, indicating that the oxidation reaction of organic matter is more intense. The precursor loses 18.9% weight at 508℃. Further weight loss occurred between 508 and 655℃, but the rate slowed down, remaining at around -0.01% / min. Inorganization was basically completed at 655℃, with a weight loss of 1.5% in this range. (3) The crystallization stage occurred between 655℃ and 841℃. The amorphous ceramics generated after inorganication crystallized into oxides such as Cr2O3 and Ta2O5 in this stage, with a weight loss of only 0.4%. (4) The carbothermic reduction stage occurred after 841℃. Due to the increase in temperature, the carbothermic reduction reaction could proceed spontaneously thermodynamically. The pyrolytic carbon remaining during the inorganication process reacted with the oxide ceramics. The pyrolytic carbon was consumed and escaped in the form of CO, with a continuous weight loss rate of around -0.02% / min. Finally, at 1120℃, the yield of the precursor ceramics was 65.3%, slightly higher than that under air conditions.

[0062] XRD tests were performed on the products (chromium tantalate) obtained in Examples 1-2 and Comparative Examples 1-4 to investigate the effect of pyrolysis temperature on the crystal phase composition of the products. The results are as follows: Figure 5 As shown. By Figure 5 It can be seen that when pyrolysis is carried out in an air atmosphere, at 700℃, the pyrolysis products contain Cr2O3 (PDF#38-1429) and Ta2O5 (PDF#89-2843) phases (Comparative Example 2). At 900℃, the CrTaO4 (PDF#39-1428) phase appears, while the diffraction peak intensities of Ta2O5 and Cr2O3 decrease (Comparative Example 1), indicating that the solid-state reaction has begun. At 1120℃, the diffraction peaks of Ta2O5 and Cr2O3 phases completely disappear, leaving only the CrTaO4 phase in the system (Example 1), indicating that the solid-state reaction has been completed. The CrTaO4 grain size was calculated using XRD characteristic peaks, and the result was 49.8 ± 2.2 nm. In summary, the product of Example 1 (chromium tantalate) is a pure CrTaO4 phase, while Comparative Example 1 contains only a small amount of CrTaO4, and Comparative Example 2 contains no CrTaO4, consisting entirely of Cr2O3 and Ta2O5.

[0063] In addition, by Figure 5It can be seen that when pyrolysis is carried out in an argon atmosphere at 700℃, the main phase in the pyrolysis products of Comparative Example 4 is CrTaO4 (PDF#39-1428), with trace amounts of Cr2O3 (PDF#38-1429) phase. The difference from the air pyrolysis products at 700℃ is that the inert environment of argon inhibits the vigorous oxidation reaction, the organic ligands decompose primarily through thermal cracking, the oxygen partial pressure in the system is extremely low, and carbothermic reduction has not yet started. At this time, Cr... 3+ With Ta 5+ Interdiffusion at the solid-phase interface is achieved through local atomic rearrangement, which thermodynamically tends to form composite oxides with lower entropy values. Therefore, CrTaO4 preferentially crystallizes as the main crystalline phase. Simultaneously, influenced by the local enrichment of oxygen-containing groups in the precursor and trace amounts of residual oxygen in the atmosphere, some Cr... 3+ Trace amounts of Cr2O3 are formed locally, and the overall system consists of CrTaO4 and trace amounts of Cr2O3. No low-valent tantalum oxides or carbides were found. At 900℃, the product of Comparative Example 3 is a mixed phase of Cr2O3, Ta4O5 (PDF#37-0118), and CrTaO4. The thermogravimetric curve shows a further decrease at this temperature, which is related to the formation of Ta4O5 and the consumption of free carbon. At this stage, the carbothermic reduction reaction officially begins: the amorphous carbon produced by the pyrolysis of the precursor has sufficient reactivity to begin to capture oxygen from Ta2O5 or the amorphous Ta-O phase in the system, generating the thermodynamically unstable low-valent oxide Ta4O5. The CO gas generated by the reduction reaction is continuously carried away by the argon gas flow, driving the reaction forward, while the free carbon is consumed in the process. The absence of TaC indicates that the current temperature only meets the conditions for partial reduction of Ta2O5, not for deep reduction to form carbides. At 1120℃, the solid-phase diffusion rate increases significantly with increasing temperature, and Cr... 3+ With Ta 5+ Ions were able to migrate sufficiently and achieve homogeneous mixing. The Cr2O3 and Ta4O5 intermediate phases were completely consumed in the solid-state synthesis reaction, ultimately forming a well-crystallized and structurally stable CrTaO4 in Example 2. At this point, the system still contained undepleted carbon, and the thermogravimetric curve showed a slow weight loss. Calculations of the XRD characteristic peaks in Example 2 indicated that the CrTaO4 grain size was 20.5 ± 1.7 nm.

[0064] The product obtained in Example 1 was subjected to TEM-EDS testing, and the results are as follows: Figure 6 As shown. By Figure 6 The TEM results show equiaxed grains with diameters comparable to those calculated by XRD. The energy dispersive spectroscopy (EDS) spectrum shows uniform distribution of Cr, Ta, and O elements, with the C element likely originating from the carbon film on the TEM stage. The molar ratios of Cr, Ta, and O are very close to the theoretical ratio of 1:1:4, confirming that Example 1 produced high-purity CrTaO4.

[0065] In addition, the product obtained in Example 2 was subjected to TEM-EDS testing, and the results are as follows: Figure 7 As shown in the figure. The results indicate that the grain size is also comparable to the XRD calculation results, and is smaller than that of Example 1. The presence of free carbon and the lower oxygen partial pressure inhibited oxide crystallization. In the energy dispersive spectroscopy (EDS) spectrum, Cr, Ta, and O elements are uniformly distributed, and the C element content is much higher than that of Example 1, reaching a mass fraction of 25.74%, which reduces the purity of the product.

[0066] In summary, the scheme in Example 1 is optimal. The CrTaO4 precursor, after pyrolysis in air at 1120℃ for 2 h, can generate high-purity CrTaO4 powder with fine grain size. Therefore, the precursor solution prepared in this invention can also be used as a raw material to prepare CrTaO4 coatings or CrTaO4-based composite materials via a precursor impregnation pyrolysis process.

[0067] The results above show that, compared with conventional solid-phase reaction synthesis of CrTaO4 powder, the preparation method of the chromium tantalate precursor of the present invention, using tantalum and chromium sources as raw materials, anhydrous alcohol as solvent and reaction reagent, and acetylacetone as complexing agent, obtains a uniformly cross-linked and structurally stable chromium tantalate precursor through substitution reaction, complexation reaction, hydrolysis, and dehydration condensation. This chromium tantalate precursor can bring the following unexpected technical effects: (1.1) The pyrolysis process of this chromium tantalate precursor is highly controllable. It can be converted into high-purity, single-phase CrTaO4 powder by holding at 1120℃ for 2 h, with no Cr2O3 or Ta2O5 residues. The purity and crystallinity of the product far exceed those of traditional solid-phase reactions.

[0068] (1.2) The chromium tantalate precursor is in solution state, and CrTaO4 coating can be directly prepared on the surface of complex-shaped substrates through impregnation-pyrolysis process. The coating forms a chemical bond with the substrate, with strong bonding force and high density, which solves the inherent defects of spray coating. At the same time, CrTaO4-based fiber-reinforced composite materials can be prepared through multiple impregnation-pyrolysis processes, which solves the problem that traditional technology can only prepare powder or coating and has a single application form, and significantly broadens the application scenarios of CrTaO4 in the field of environmental barrier materials.

[0069] The above embodiments are merely preferred embodiments of the present invention, and the scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a chromium tantalate precursor, characterized in that, The solution was prepared by using tantalum and chromium sources as raw materials, anhydrous alcohol as solvent and reaction reagent, and acetylacetone as complexing agent, through substitution reaction, complexation reaction, hydrolysis, and dehydration condensation.

2. The preparation method according to claim 1, characterized in that, Includes the following steps: S1. Construct a reaction system in an anhydrous and oxygen-free environment; S2. Add anhydrous alcohol to the reaction system and add tantalum source to carry out substitution reaction; S3. After the substitution reaction is completed, the reaction system is heated to the preset temperature, and acetylacetone is added dropwise to carry out the complexation reaction. S4. After the complexation reaction is complete, add the chromium source to dissolve it into the system, add deionized water dropwise, and carry out the hydrolysis reaction under the preset temperature conditions. S5. Dehydration condensation of the products of the hydrolysis reaction; S6. The dehydration condensation product is subjected to vacuum distillation to obtain the chromium tantalate precursor.

3. The preparation method according to claim 2, characterized in that, In step S2, the molar ratio of the tantalum source to the anhydrous alcohol is 1:6 to 10; the tantalum source is TaCl5 powder; the anhydrous alcohol is at least one of anhydrous ethanol, anhydrous propanol, and anhydrous n-butanol; the addition rate of the tantalum source is 2 g / min to 3 g / min; the substitution reaction is carried out under stirring conditions; the substitution reaction time is 1 h to 2 h; the substitution reaction process also includes: absorbing the waste gas generated during the reaction using a drying tower containing NaOH; In step S3, the preset temperature is 60℃~70℃; the molar ratio of acetylacetone to tantalum source is 1~2:1; the dropping rate of acetylacetone is 1 mL / min~2 mL / min; and the complexation reaction time is 1 h~2 h. In step S4, the molar ratio of the chromium source to the tantalum source is 1:1; the chromium source is CrCl3·6H2O powder; the molar ratio of the deionized water to the tantalum source is 3 to 4:1; the dropping rate of the deionized water is 1 mL / min to 2 mL / min; and the hydrolysis reaction time is 1 h to 2 h.

4. The preparation method according to claim 2 or 3, characterized in that, In step S1, the method for constructing a reaction system in an anhydrous and oxygen-free environment includes the following steps: setting up a Schlenk reaction apparatus, repeatedly performing the vacuuming-introduction of dry nitrogen gas operation until the reaction system is in an anhydrous and oxygen-free environment; the vacuuming-introduction of dry nitrogen gas operation is repeated 3 to 5 times; the purity of the dry nitrogen gas is not less than 99.999%; In step S6, the vacuum distillation is carried out at a temperature of 60℃~70℃; the vacuum degree of the vacuum distillation is 0~0.01MPa; and the vacuum distillation time is 0.5 h~1 h.

5. A chromium tantalate precursor, characterized in that, The chromium tantalate precursor is prepared by the preparation method according to any one of claims 1 to 4.

6. The use of the chromium tantalate precursor as described in claim 5 as a raw material in the preparation of chromium tantalate.

7. The application according to claim 6, characterized in that, Chromium tantalate was obtained by multi-stage pyrolysis using chromium tantalate precursor as raw material.

8. The application according to claim 7, characterized in that, Multi-stage pyrolysis using chromium tantalate precursor as raw material. Includes the following stages: (1) First stage: The chromium tantalate precursor was placed in a pyrolysis device and heated to 80°C at a heating rate of 5°C / min and held for 1 h; (2) Second stage: Heat to 200℃ at a heating rate of 5℃ / min and hold for 1 h; (3) Third stage: Heat to 700℃ at a heating rate of 5℃ / min and hold for 1 h; (4) Fourth stage: Heat to 1120℃ at a heating rate of 5℃ / min and hold for 2 h to obtain chromium tantalate.

9. The application according to claim 8, characterized in that, The multi-stage heating pyrolysis is carried out in an argon atmosphere or an air atmosphere; the pyrolysis equipment is a tube furnace or a muffle furnace.

10. The use of the chromium tantalate precursor as described in claim 5 as a raw material in the preparation of chromium tantalate coatings or chromium tantalate-based composite materials.

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