Soluble ZrC / ZrB2 complex-phase ultrahigh-temperature ceramic precursor and preparation method thereof

Abstract

The invention discloses a preparation method of a soluble ZrC / ZrB2 complex-phase ultrahigh-temperature ceramic precursor. The preparation method comprises the following steps: S1, dissolving zirconium tetrachloride in absolute ethyl alcohol, adding acetylacetone, heating and stirring to obtain a zirconium-containing precursor solution; s2, dissolving a boron source in an absolute ethyl alcohol solution, adding concentrated sulfuric acid, heating, stirring and removing moisture to obtain a boron-containing mixed solution; s3, dropwise adding the boron-containing mixed solution into the zirconium-containing precursor solution, and continuously heating and stirring to obtain a mixed solution; s4, adding a hydroxyl-containing carbon source into the mixed solution, and stirring to obtain viscous reddish brown liquid; and S5, removing redundant solvent in the reddish brown liquid, and performing vacuum drying to obtain the soluble ZrC / ZrB2 complex-phase superhigh-temperature ceramic precursor. The soluble ZrC / ZrB2 complex-phase superhigh-temperature ceramic precursor provided by the invention solves the problems of high raw material cost, high pyrolysis temperature and low solubility of the prepared precursor in a low-toxicity environment-friendly solvent in the existing preparation of the ZrC ceramic precursor.

Description

Technical Field

[0001] This invention belongs to the field of ceramic organic precursor technology, specifically relating to soluble ZrC / ZrB2 multiphase ultra-high temperature ceramic precursors. This invention also relates to a method for preparing the above-mentioned soluble ZrC / ZrB2 multiphase ultra-high temperature ceramic precursors. Background Technology

[0002] Ultra-high temperature ceramics, especially carbides and borides of refractory metals Zr, Hf, and Ta, possess excellent properties such as high melting point, high strength, high modulus, high hardness, good thermodynamic stability, and good thermal conductivity. Therefore, they are widely used in various critical components of aircraft, such as nose cones, wing leading edges, and engine hot sections. ZrC and ZrB2 ceramics, due to their superior properties, are among the most promising ultra-high temperature materials. Currently, the main methods for synthesizing ZrC and ZrB2 include direct synthesis, self-propagating high-temperature synthesis (SHS), carbothermal reduction, and liquid-phase precursor methods.

[0003] The direct synthesis method involves reacting zirconium powder or zirconium hydride powder with graphite or carbon black at high temperatures under inert gas or vacuum to directly synthesize ZrC. However, Zr or ZrH2 powder is expensive and requires a high-temperature environment above 1500 °C, resulting in high energy consumption. The self-propagating high-temperature synthesis method utilizes the high temperature and heat released by the chemical reaction of raw materials under initial ignition conditions to spontaneously carry out the combustion reaction, thereby obtaining products with specific compositions and structures. However, due to its rapid reaction rate, the reaction may not be completely completed, resulting in more impurities, and the reaction process, product structure, and properties are not easy to control. The carbothermic reduction method uses carbon black to reduce zirconium oxide. This method requires a high degree of uniformity in the mixing of raw materials. If the mixing uniformity is not ideal, the purity of the synthesized ZrC ceramic powder is easily reduced. The liquid-phase precursor method uses a liquid-phase chemical process to achieve atomic-scale mixing of a solution containing metal ions and a carbon source, fix it in the form of a precursor, and then obtain high-temperature ceramics through thermal decomposition. Because the preparation process forms an amorphous metastable phase with a large reaction contact area, it overcomes the shortcomings of other methods that require micron-sized powder particles with large particle sizes and low sintering activity. It is a commonly used method for the low-temperature preparation of ultrafine ceramic powders that has developed rapidly in recent years.

[0004] Liu Dan et al. synthesized a zirconium precursor solution using zirconium oxychloride octahydrate and acetylacetone as zirconium and carbon sources, respectively, and hydrochloric acid and nitric acid as solvent and catalyst, respectively, with the aid of other alcohol reagents. The precursor solution has a network or chain structure, and the powder formed after drying the solution has a honeycomb porous structure. After pyrolysis, it generates ZrC powder with high purity. Although the ZrC prepared by this method has small particle size, high purity, and relatively low pyrolysis temperature, the large amount of highly corrosive, high safety risk, and high cost of nitric acid and hydrochloric acid used in the preparation process obviously restricts the further development of this process. (Mei Bing, Su Xunjia, Hou Genliang, et al. Preparation of ZrC powder by liquid-phase precursor conversion method and synthesis mechanism [J]. Solid Rocket Technology, 2008, (03): 275-278+287.)

[0005] Chinese invention patent CN201710913312.5, filed on September 30, 2017, entitled "A Method for Preparing a Zirconium-Containing Ceramic Precursor," uses zirconium propoxide, acetylacetone, and ethylene glycol as raw materials to prepare a zirconium-containing ceramic precursor with Zr-O-Zr as the main chain. This polymer exhibits good solubility in tetrahydrofuran, toluene, and xylene. After heating this zirconium-containing polymer in a tube furnace at 1600 °C for 3 h in a high-purity argon atmosphere, the resulting ZrC and ZrO2 ceramics have a zirconium content of 36.34% (At%) and a ceramic conversion rate of 32.66%. Although this method solves the problem of poor solubility of products from previous precursor synthesis methods, its solvents include toluene, xylene, and other Class III carcinogenic agents, resulting in excessively high pyrolysis temperatures, low ceramic conversion rates, and residual ZrCl4 raw material and unreacted tetragonal and monoclinic ZrO2 phases in the pyrolysis products of the ZrC ceramic precursor. Their team further disclosed a ceramic precursor using phenylboronic acid, zirconium n-propoxide, and acetylacetone as raw materials in Chinese invention patent application number CN201910138807, entitled "A boron-, zirconium n-propoxide-, silicon-containing single-source ceramic precursor and its preparation method". Although the precursor has good solubility in common low-boiling-point organic solvents, its raw materials, phenylboronic acid and zirconium n-propoxide, are expensive, and the target product can only be obtained after holding at 1600 ℃ for 5 h in a high-purity argon atmosphere in a tube furnace. The pyrolysis temperature is high, the time is long, and the energy consumption is large.

[0006] The Chinese invention patent "A Soluble Zirconium Carbide Ceramic Precursor and Its Preparation Method", filed on May 22, 2015, with publication number CN201510269866, uses zirconium tetrachloride, toluene, acetylacetone and various carbon sources to prepare a soluble zirconium carbide ceramic precursor. The invention has a simple process and the raw materials are readily available, but its preparation process has the same problems as the other patents mentioned above: first, the ceramic yield is too low, only 24% at 1200℃, and it requires high-temperature pyrolysis at 1600℃; second, its precursor can only be dissolved in highly toxic solvents such as toluene and xylene.

[0007] In summary, the current preparation of ZrC ceramic precursors mainly faces problems such as high raw material costs, high pyrolysis temperatures and long pyrolysis times. Most precursors are only soluble in highly toxic solvents such as toluene, xylene, and chloroform, and have poor solubility in non-toxic or slightly toxic reagents such as ethanol and ethyl acetate. Summary of the Invention

[0008] The first objective of this invention is to provide a method for preparing soluble ZrC / ZrB2 multiphase ultra-high temperature ceramic precursors, which solves the problems of high raw material cost, high pyrolysis temperature, and low solubility of the prepared precursors in low-toxicity and environmentally friendly solvents such as anhydrous ethanol and ethyl acetate in the prior art.

[0009] The first objective of this invention is to provide a soluble ZrC / ZrB2 multiphase ultra-high temperature ceramic precursor prepared by the above method.

[0010] The first technical solution adopted in this invention is: a method for preparing a soluble ZrC / ZrB2 multiphase ultra-high temperature ceramic precursor, as detailed below: S1. Under an inert atmosphere, zirconium tetrachloride is dissolved in a first anhydrous ethanol solution, followed by the addition of acetylacetone solution, and heated and stirred to obtain a zirconium-containing precursor solution with the molecular formula (C2H5O)2Zr(acac)2. S2. Dissolve the boron source in a second anhydrous ethanol solution, then add concentrated sulfuric acid solution, heat and stir and remove water to obtain a boron-containing mixed solution with the molecular formula B(OC2H5)3. S3. Add the boron-containing mixed solution dropwise to the zirconium-containing precursor solution. After the addition is complete, continue heating and stirring to obtain the mixed solution. S4. Add a hydroxyl-containing carbon source to the mixed solution and stir at a certain temperature to obtain a viscous reddish-brown liquid; S5. Excess solvent in the reddish-brown liquid is removed by rotary evaporation and vacuum drying to obtain a zirconium carbide and zirconium boride multiphase ultra-high temperature ceramic precursor with good solubility.

[0011] The invention is further characterized by: The ratio of the amount of zirconium tetrachloride in S1 to the amount of the first anhydrous ethanol solution is 1:10~20. The molar ratio of the first anhydrous ethanol solution to acetylacetone in S1 is 1:0.15~0.30; The heating temperature in S1 is 40~80 ℃, and the heating time is 1~2h.

[0012] The boron source in S2 is boric acid or boron anhydride. Before use, the boron source needs to be pretreated by low-temperature baking to remove water. The low-temperature baking temperature is 40~60℃ and the time is 60~90min. When the boron source is boric acid, the molar ratio of boric acid to zirconium tetrachloride is 5~2:1; when the boron source is boric anhydride, the molar ratio of boric anhydride to zirconium tetrachloride is 1.5~3:1. When the boron source is boric acid, the mass ratio of concentrated sulfuric acid to boric acid is 0.16:1; when the boron source is boric anhydride, the mass ratio of concentrated sulfuric acid to boric anhydride is 0.05:1. The mass ratio of concentrated sulfuric acid to boric acid added is 0.16:1. If the selected boron source is boric anhydride, the mass ratio is 0.05:1. The ratio of the amount of boron source substance to the amount of the second anhydrous ethanol solution is 1:5~10; The concentration of concentrated sulfuric acid in S2 is 99.99%.

[0013] The specific method for S2 is as follows: Nitrogen or argon gas is introduced before and during the reaction to purge air. Concentrated sulfuric acid is added to the mixed solution of boron source and second anhydrous ethanol as a catalyst. The mixture is heated to 40-80℃ and stirred for 1-1.5 h to obtain the reaction solution. Toluene or cyclohexane is added to the reaction solution. Toluene or cyclohexane forms a low-boiling-point azeotrope with the water generated in the reaction solution. A water separator is installed on the reflux apparatus. Toluene or cyclohexane is mixed with the reaction solution and added to the water separator for heating and reflux. The generated triethyl borate-water-solvent azeotrope vapor condenses and flows into the water separator. The water settles at the bottom and is quickly separated. The organic layers such as solvent, ethanol, and triethyl borate flow back to the reaction flask. Under continuous reflux, the water separator is observed until the volume of the lower water layer no longer increases within 30-45 minutes. Then the separation is stopped, and a relatively pure boron-containing mixed solution is obtained.

[0014] The volume ratio of toluene or cyclohexane to the second anhydrous ethanol is 1:1; When toluene is used as an azeotropic solvent, the heating temperature is 105~110℃; when cyclohexane is used as an azeotropic solvent, the heating temperature is 90~95℃. The concentration of either toluene or cyclohexane is 99.99%.

[0015] The heating temperature in S3 is 60~80℃, and the time is 30~40min.

[0016] In S3, the boron-containing mixed solution is added to the zirconium-containing precursor solution at a rate of 2-3 drops / s.

[0017] The hydroxyl-containing carbon source in S4 is a phenolic hydroxyl-containing carbon source or an alcoholic hydroxyl-containing carbon source, among which phenolic hydroxyl-containing carbon sources include: phenol, hydroquinone, resorcinol, catechol or bisphenol A; Hydroxyl-containing carbon source alcohols include: 1,4-butanediol, ethylene glycol, glycerol, or butanetetraol; The hydroxyl-containing carbon source is one or two of the above substances in any ratio; Phenol, hydroquinone, resorcinol, catechol, or bisphenol A; hydroxyl-containing carbon source alcohols include: 1,4-butanediol, ethylene glycol, glycerol, or butanetetraethanolamine, wherein the hydroxyl-containing carbon source is one or a mixture of two of the above substances in any proportion. The molar ratio of hydroxyl-containing carbon source to zirconium tetrachloride is 20~25:1.

[0018] The stirring temperature in S4 is 60-80 ℃, and the stirring time is 1-2 hours.

[0019] The vacuum drying temperature in S54 is 45~60 ℃, and the drying time is controlled between 24~48 h.

[0020] The second technical solution adopted in this invention is: a soluble ZrC / ZrB2 multiphase ultra-high temperature ceramic precursor prepared by the above preparation method.

[0021] The beneficial effects of this invention are: (1) The method for preparing the soluble ZrC / ZrB2 multiphase ultra-high temperature ceramic precursor of the present invention uses zirconium-containing precursor prepared by coordination chelation of zirconium tetrachloride, anhydrous ethanol and acetylacetone (Hacac) to obtain a multiphase ceramic precursor with a main chain of BO-Zr-OC through transesterification reaction between B-containing and Zr-containing precursors and nucleophilic substitution reaction with hydroxyl-containing carbon source. During the pyrolysis process, ZrC and ZrB2 ultra-high temperature ceramics are generated simultaneously. The two ceramics have a synergistic effect, jointly promoting performance improvement and reducing production costs; the precursor production process is optimized. (2) The method for preparing the soluble ZrC / ZrB2 multiphase ultra-high temperature ceramic precursor of the present invention pretreats the boron source, so that the ester exchange reaction between the borate ester generated by boric acid / boric anhydride and the zirconium-containing precursor and the substitution reaction between the boron ester and the hydroxyl-containing carbon source can jointly construct a more stable precursor molecular chain, reducing the dissipation of B during the pyrolysis process; at the same time, the two liquid precursors containing B and Zr are mixed to achieve atomic or molecular level mixing of the reactants, thereby reducing the pyrolysis temperature of the ceramic precursor and shortening the pyrolysis time. The precursor is then subjected to pyrolysis ceramicization treatment at 1400 °C under vacuum to generate uniform and stable ZrC and ZrB2 ultra-high temperature multiphase ceramics. (3) The soluble ZrC / ZrB2 multiphase ultra-high temperature ceramic precursor prepared by this invention has low raw material costs, is simple to prepare, and is easy to operate; it has a low pyrolysis temperature and short time, resulting in a high ceramic yield and reduced energy consumption (1400 ℃, 2 h, ceramic yield reaches 41%); it also improves the solubility of the organoceramic precursor, exhibiting good solubility in various organic reagents (soluble in ethanol, ethyl acetate, tetrahydrofuran, etc.). Utilizing its low pyrolysis temperature, short time, and good solubility, it can be further used to prepare composite materials using the precursor impregnation pyrolysis (PIP) method, which has practical value. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the synthesis mechanism of the method for preparing soluble ZrC / ZrB2 multiphase ultra-high temperature ceramic precursors according to the present invention; Figure 2 This describes the macroscopic morphology of the zirconium-containing precursor powder prepared in Example 1 of this invention; Figure 3 This is the infrared spectrum of the zirconium-containing precursor prepared in Example 1 of this invention; Figure 4 This is the X-ray diffraction pattern of the product obtained by pyrolysis of the zirconium-containing precursor prepared in Example 1 of the present invention at 1400 °C; Figure 5 This is a microscopic morphology image of the product obtained by pyrolysis of the precursor prepared in Example 1 of the present invention at 1400 °C. Figure 6 This is the X-ray diffraction pattern of the precursor obtained in Example 2 of this invention after pyrolysis at 1400 °C. Detailed Implementation

[0023] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0024] The present invention discloses a method for preparing a soluble ZrC / ZrB2 multiphase ultra-high temperature ceramic precursor, the specific method of which is as follows: S1. Under an inert atmosphere, a certain amount of zirconium tetrachloride is dissolved in a first anhydrous ethanol solution, and the reaction is refluxed to generate zirconium ethoxide solution. Then, acetylacetone solution is added, and the mixture is heated and stirred at a temperature of 40~80 ℃ for 1~2 h. Excess solvent is evaporated by condensation to obtain a reddish-brown solution with a certain viscosity, i.e., a zirconium-containing precursor solution with the molecular formula (C2H5O)2Zr(acac)2. The ratio of the amount of zirconium tetrachloride to the amount of the first anhydrous ethanol solution is 1:10~20. The molar ratio of the first anhydrous ethanol solution to acetylacetone is 1:0.15~0.3.

[0025] S2. Dissolve a certain number of moles of boron source in a second anhydrous ethanol solution, then add 3-5 drops of concentrated sulfuric acid solution as a catalyst. The concentration of concentrated sulfuric acid is 99.99%. Heat to 40-80℃, stir for 1-2 hours, and remove water to obtain a boron-containing mixed solution with the molecular formula B(OC2H5)3. The specific method is as follows: Nitrogen or argon gas is introduced before and during the reaction to purge air. Concentrated sulfuric acid is added to the mixed solution of boron source and second anhydrous ethanol as a catalyst, and the mixture is stirred for 1 to 1.5 h to obtain the reaction solution. Toluene or cyclohexane is added to the reaction solution. Toluene or cyclohexane forms a low-boiling-point azeotrope with the water generated in the reaction solution. A water separator is installed on the reflux apparatus. Toluene or cyclohexane is mixed with the reaction solution and added to the water separator for heating and reflux. The generated triethyl borate-water-solvent azeotrope vapor condenses and flows into the water separator. The water settles at the bottom and is quickly separated. The organic layers such as solvent, ethanol, and triethyl borate flow back to the reaction flask. Under continuous reflux, the water separator is observed until the volume of the lower water layer no longer increases within 30-45 minutes. Then the separation is stopped, and a relatively pure boron-containing mixed solution is obtained.

[0026] The volume ratio of toluene or cyclohexane to the second anhydrous ethanol is 1:1. When toluene is used as an azeotropic solvent, the heating temperature is 105~110℃; when cyclohexane is used as an azeotropic solvent, the heating temperature is 90~95℃. The concentration of toluene or cyclohexane is 99.99%.

[0027] The boron source is boric acid or boron anhydride. Before use, the boron source needs to be pretreated by low-temperature baking to remove water. The low-temperature baking temperature is 40~60℃ and the time is 60~90min.

[0028] If the boron source is boric acid, the molar ratio of boric acid to zirconium tetrachloride is 5~2:1. If the boron source is boric anhydride, the molar ratio of boric anhydride to zirconium tetrachloride is 1.5~3:1.

[0029] When the boron source is boric acid, the mass ratio of concentrated sulfuric acid to boric acid is 0.16:1; when the boron source is boric anhydride, the mass ratio of concentrated sulfuric acid to boric anhydride is 0.05:1. The ratio of the amount of boron source substance to the amount of the second anhydrous ethanol solution is 1:5~10.

[0030] S3. Add the boron-containing mixed solution dropwise to the zirconium-containing precursor solution. After the addition is complete, the dropping rate is 2-3 drops / s. Continue heating and stirring to obtain a mixed solution. An ester exchange reaction occurs between the two solutions, fixing the B atoms in the structure. Specifically, the electrophilic B atoms in the B-containing precursor exchange with the nucleophilic ethoxy groups in the Zr-containing precursor to generate a mixed metal alkoxide, forming a BO-Zr chain. B is fixed in the structure, reducing the risk of pyrolysis and volatilization.

[0031] The heating temperature is 60~80℃ and the time is 30~40min.

[0032] S4. Add a certain amount of hydroxyl-containing carbon source to the mixed solution and stir at 60-80 ℃ for 1-2 hours to obtain a viscous reddish-brown liquid; The hydroxyl-containing carbon source is either a phenolic hydroxyl-containing carbon source or an alcoholic hydroxyl-containing carbon source. The phenolic hydroxyl-containing carbon sources include: phenol, hydroquinone, resorcinol, catechol, or bisphenol A. The hydroxyl-containing carbon source alcohols include: 1,4-butanediol, ethylene glycol, glycerol, or butanetetraol. The hydroxyl-containing carbon source is one or a mixture of two of the above substances in any proportion. The molar ratio of hydroxyl-containing carbon source to zirconium tetrachloride is 20~25:1.

[0033] S5. Excess solvent in the reddish-brown liquid is removed by rotary evaporation and vacuum drying to obtain a zirconium carbide and zirconium boride multiphase ultra-high temperature ceramic precursor with good solubility.

[0034] The vacuum drying temperature is 45~60 ℃, and the drying time is controlled between 24~48 h.

[0035] A soluble ZrC / ZrB2 multiphase ultra-high temperature ceramic precursor was prepared using the preparation method of the present invention.

[0036] This invention primarily utilizes the transesterification reaction between a zirconium-containing precursor prepared by coordination chelation with zirconium tetrachloride, anhydrous ethanol, and acetylacetone, and a boron-containing precursor prepared by esterification with boric acid / boric anhydride, anhydrous ethanol, and a small amount of concentrated sulfuric acid, as well as a substitution reaction with a hydroxyl-containing carbon source, to jointly construct a soluble composite ceramic precursor with BO-Zr-OC as the main chain. This addresses the issues of high pyrolysis temperature and long pyrolysis time. The synthesis mechanism diagram of this invention is shown below. Figure 1 As shown.

[0037] This invention uses cheaper boric acid and boric anhydride as boron sources, reducing production costs. It optimizes the precursor production process by pretreating the boron source, enabling the ester exchange reaction between the boric acid / boric anhydride-generated ester and the zirconium-containing precursor, as well as the substitution reaction with the hydroxyl-containing carbon source, to jointly construct a more stable precursor molecular chain, reducing boron dissipation during pyrolysis. Simultaneously, mixing the two boron- and zirconium-containing liquid precursors achieves atomic or molecular-level mixing of the reactants, thereby lowering the pyrolysis temperature and shortening the pyrolysis time of the ceramic precursor. Pyrolysis at 1400 °C under vacuum produces uniform and stable ZrC and ZrB2 ultra-high temperature multiphase ceramics. Furthermore, it improves the solubility of the organoceramic precursor, making it soluble in alcohols such as methanol and ethanol, as well as reagents such as ethyl acetate, tetrahydrofuran, and N,N-dimethylformamide (DMF). Utilizing its excellent solubility, high-density ceramic matrix composites can be prepared using the PIP process.

[0038] This invention features readily available raw materials, stable process, low pyrolysis temperature and short time, high ceramic yield (41% ceramic yield after holding at 1400℃ for 2 hours), and good solubility of the prepared ZrC / ZrB2 ceramic precursor in organic solvents. This broadens the freedom of material design and processing adaptability, and can be used to prepare ceramic matrix composites using the PIP process.

[0039] Example 1 The preparation method of the soluble ZrC / ZrB2 multiphase ultra-high temperature ceramic precursor in this embodiment is as follows: S1. Under a nitrogen atmosphere, 1 mol of zirconium tetrachloride was dissolved in 10 mol of the first anhydrous ethanol solution to produce zirconium ethoxide solution. Then, 3 mol of acetylacetone solution was added, and the mixture was heated and stirred at 40 °C for 2 h. The excess solvent was then evaporated by condensation to obtain a reddish-brown solution with a certain viscosity, namely the zirconium-containing precursor solution with the molecular formula (C2H5O)2Zr(acac)2. S2. Before and during the reaction, nitrogen gas is introduced to purge air. 2 mol of boric acid is fully dissolved in 20 mol of the second anhydrous ethanol solution. The boric acid needs to be baked at 40°C for 90 min before use. Then, a 99.99% concentrated sulfuric acid solution is added as a catalyst. The mass ratio of the added concentrated sulfuric acid to boric acid is 0.16:1. The mixture is heated to 60°C and stirred for 1 h, and the water is removed. 20 mol of 99.99% toluene was added to the reaction solution. Toluene and water generated in the reaction solution formed a low-boiling-point azeotrope. A water separator was installed on the reflux apparatus. The toluene and the reaction solution were mixed and added together into the water separator and heated under reflux at a temperature of 110°C. The generated triethyl borate-water-solvent azeotrope vapor condensed and flowed into the water separator. The water settled at the bottom and was quickly separated. The organic layers such as solvent, ethanol, and triethyl borate flowed back to the reaction flask. Under continuous reflux, the water separator was observed until the volume of the lower water layer no longer increased within 30-45 minutes. The separation was then stopped, and a relatively pure boron-containing mixed solution with the molecular formula B(OC2H5)3 was obtained. S3. Add the boron-containing mixed solution dropwise to the zirconium-containing precursor solution. After the addition is complete, the addition rate is 3 drops / s. Continue heating to 60℃ and stirring for 30 minutes to obtain the mixed solution. S4. Add 1 mol of 1,4-butanediol and 20 mol of hydroquinone to the mixed solution, stir at 80°C for 1 h to obtain a viscous reddish-brown liquid. S5. Excess solvent in the reddish-brown liquid was removed by rotary evaporation, and the liquid was vacuum dried in a vacuum drying oven at 60°C for 30 hours to obtain a zirconium carbide and zirconium boride multiphase ultra-high temperature ceramic precursor with good solubility.

[0040] like Figure 2 The image shows the macroscopic morphology of the soluble ZrC / ZrB2 multiphase ultra-high temperature ceramic precursor powder prepared in this embodiment.

[0041] like Figure 3 The image shows the infrared spectrum of the soluble ZrC / ZrB2 multiphase ultra-high temperature ceramic precursor obtained in this embodiment. The image shows the spectrum at 543 cm⁻¹. -1 908 cm -1 1462 cm -1 The figure shows Zr-O, BO-Zr, and Zr-OC bonds, respectively. It can be seen from the figure that the precursor may be a linear macromolecule with Zr-OBC as its molecular backbone. like Figure 4 The X-ray diffraction pattern of the pyrolysis products obtained after sintering in a vacuum at 1400 °C for 2 h is shown. The products are pure ZrC and ZrB2, without any other impurities. like Figure 5 The figure shows the microstructure of the precursor pyrolysis products. As can be seen from the figure, the pyrolysis products are uniform in size and relatively dispersed.

[0042] Example 2 The preparation method of the soluble ZrC / ZrB2 multiphase ultra-high temperature ceramic precursor in this embodiment is as follows: S1. Under an argon atmosphere, 1 mol of zirconium tetrachloride was dissolved in 20 mol of the first anhydrous ethanol solution to produce zirconium ethoxide solution. Then, 3 mol of acetylacetone solution was added, and the mixture was heated and stirred at 60°C for 1 h. The excess solvent was then evaporated by condensation to obtain a reddish-brown solution with a certain viscosity, namely the zirconium-containing precursor solution with the molecular formula (C2H5O)2Zr(acac)2. S2. Before and during the reaction, argon gas is introduced to purge air. 3 mol of boron anhydride is fully dissolved in 20 mol of the second anhydrous ethanol solution. The boron anhydride needs to be baked at 50°C for 80 min before use. Then, a 99.99% concentrated sulfuric acid solution is added as a catalyst. The mass ratio of the added concentrated sulfuric acid to the boron anhydride is 0.05:1. The mixture is heated to 40°C and stirred for 1.5 h to remove moisture. 20 mol of 99.99% cyclohexane was added to the reaction solution. The cyclohexane formed a low-boiling-point azeotrope with the water generated in the reaction solution. A water separator was installed on the reflux apparatus. The cyclohexane and the reaction solution were mixed and added together into the water separator and heated to reflux at a temperature of 95°C. The generated triethyl borate-water-solvent azeotrope vapor condensed and flowed into the water separator. The water settled at the bottom and was quickly separated. The organic layers such as solvent, ethanol, and triethyl borate flowed back to the reaction flask. The water separator was observed under continuous reflux until the volume of the lower water layer no longer increased within 30-45 minutes. The separation was then stopped, and a relatively pure boron-containing mixed solution with the molecular formula B(OC2H5)3 was obtained. S3. Add the boron-containing mixed solution dropwise to the zirconium-containing precursor solution. After the addition is complete, the addition rate is 2 drops / s. Continue heating to 80℃ and stirring for 40 minutes to obtain the mixed solution. S4. Add 1 mol of phenol and 20 mol of glycerol to the mixed solution, stir at 60°C for 2 hours to obtain a viscous reddish-brown liquid. S5. Excess solvent in the reddish-brown liquid was removed by rotary evaporation, and the liquid was vacuum dried in a vacuum drying oven at 45°C for 48 hours to obtain a zirconium carbide and zirconium boride multiphase ultra-high temperature ceramic precursor with good solubility.

[0043] The X-ray diffraction pattern of the pyrolysis product obtained after sintering the soluble ZrC / ZrB2 multiphase ultra-high temperature ceramic precursor prepared at 1400 ℃ in an argon atmosphere for 2 h is shown below. Figure 6 As shown in the figure, the products are only ZrC and ZrB2, with no other impurities.

[0044] Example 3 The preparation method of the soluble ZrC / ZrB2 multiphase ultra-high temperature ceramic precursor in this embodiment is as follows: S1. Under an argon atmosphere, 1 mol of zirconium tetrachloride was dissolved in 18 mol of the first anhydrous ethanol solution to produce zirconium ethoxide solution. Then, 3 mol of acetylacetone solution was added, and the mixture was heated and stirred at 80°C for 1 hour. Excess solvent was evaporated by condensation to obtain a reddish-brown solution with a certain viscosity, namely the zirconium-containing precursor solution with the molecular formula (C2H5O)2Zr(acac)2. S2. Before and during the reaction, argon gas is introduced to purge air. 3 mol of boric acid is fully dissolved in 18 mol of the second anhydrous ethanol solution. The boric acid needs to be baked at 60°C for 60 min before use. Then, a 99.99% concentrated sulfuric acid solution is added as a catalyst. The mass ratio of the added concentrated sulfuric acid to boric acid is 0.16:1. The mixture is heated to 50°C and stirred for 1.5 h to remove moisture. 18 mol of 99.99% cyclohexane was added to the reaction solution. The cyclohexane formed a low-boiling-point azeotrope with the water generated in the reaction solution. A water separator was installed on the reflux apparatus. The cyclohexane and the reaction solution were mixed and added to the water separator and heated to reflux at 90°C. The generated triethyl borate-water-solvent azeotrope vapor condensed and flowed into the water separator. The water settled at the bottom and was quickly separated. The organic layers such as solvent, ethanol, and triethyl borate flowed back to the reaction flask. The water separator was observed under continuous reflux until the volume of the lower water layer stopped increasing within 30-45 minutes. The separation was then stopped, and a relatively pure boron-containing mixed solution with the molecular formula B(OC2H5)3 was obtained. S3. Add the boron-containing mixed solution dropwise to the zirconium-containing precursor solution. After the addition is complete, the addition rate is 2 drops / s. Continue heating to 70℃ and stirring for 40 minutes to obtain the mixed solution. S4. Add 25 mol of ethylene glycol to the mixed solution and stir at 70°C for 2 hours to obtain a viscous reddish-brown liquid. S5. Excess solvent in the reddish-brown liquid was removed by rotary evaporation, and the liquid was vacuum dried in a vacuum drying oven at 50°C for 24 hours to obtain a zirconium carbide and zirconium boride multiphase ultra-high temperature ceramic precursor with good solubility.

[0045] Example 4 The preparation method of the soluble ZrC / ZrB2 multiphase ultra-high temperature ceramic precursor in this embodiment is the same as in Example 1, except that: S2. Before and during the reaction, nitrogen gas is introduced to purge air. 1.5 mol of boron anhydride is fully dissolved in 15 mol of the second anhydrous ethanol solution. The boron anhydride needs to be baked at 40°C for 90 min before use. Then, a 99.99% concentrated sulfuric acid solution is added as a catalyst. The mass ratio of the added concentrated sulfuric acid to the boron anhydride is 0.05:1. The mixture is heated to 65°C and stirred for 1 h, and the water is removed. 15 mol of 99.99% toluene was added to the reaction solution. Toluene and water generated in the reaction solution formed a low-boiling-point azeotrope. A water separator was installed on the reflux apparatus. The toluene and the reaction solution were mixed and added together into the water separator and heated under reflux at a temperature of 110°C. The generated triethyl borate-water-solvent azeotrope vapor condensed and flowed into the water separator. The water settled at the bottom and was quickly separated. The organic layers such as solvent, ethanol, and triethyl borate flowed back to the reaction flask. Under continuous reflux, the water separator was observed until the volume of the lower water layer stopped increasing within 30-45 minutes. The separation was then stopped, and a relatively pure boron-containing mixed solution with the molecular formula B(OC2H5)3 was obtained.

[0046] The remaining steps are the same as in Example 1.

[0047] Example 5 The preparation method of the soluble ZrC / ZrB2 multiphase ultra-high temperature ceramic precursor in this embodiment is the same as in Example 1, except that: S4. Add 2 mol of resorcinol and 20 mol of catechol to the mixed solution, stir at 70°C for 1 h to obtain a viscous reddish-brown liquid. The remaining steps are the same as in Example 1.

[0048] Example 6 The preparation method of the soluble ZrC / ZrB2 multiphase ultra-high temperature ceramic precursor in this embodiment is the same as in Example 1, except that: S1. Under a nitrogen atmosphere, 1 mol of zirconium tetrachloride was dissolved in 15 mol of the first anhydrous ethanol solution to produce zirconium ethoxide solution. Then, 2.5 mol of acetylacetone solution was added, and the mixture was heated and stirred at 40 °C for 2 h. The excess solvent was then evaporated by condensation to obtain a reddish-brown solution with a certain viscosity, namely the zirconium-containing precursor solution with the molecular formula (C2H5O)2Zr(acac)2. The remaining steps are the same as in Example 1.

[0049] Comparative Example 1 A soluble zirconium carbide ceramic precursor and its preparation method are disclosed below: Under inert gas protection, 1 part of ZrC14 powder and 6-8 parts of toluene were added to a container and stirred until ZrC14 was dispersed in the toluene. Then, 4-5 parts of alcohol were added to the container and the mixture was stirred and heated for 2-3 hours. Finally, acetylacetone and 1.1 parts of carbon source were added to the container and the mixture was heated and stirred for 5-6 hours to obtain a soluble zirconium carbide ceramic precursor.

[0050] Comparative Example 2 A method for preparing a multiphase ceramic material, the specific method is as follows: Using synthesized silyne resin PTSA as the silicon source, PBS (1,7-carborane) as the boron source, and zirconium-containing polymer ZMP as the zirconium source, a homogeneous boron-zirconium-silicon precursor PBZ was obtained by blending in mass ratios of 1:1:1.2, 1:1:1.5, and 1:1:2. This precursor was then heat-treated at 1600–1800 °C for 3–5 h under a high-purity argon atmosphere to obtain a B / Zr / Si / C multiphase ceramic material.

[0051] Compared to Example 1, Comparative Example 2 uses PBS, a relatively expensive boron source, and the precursor needs to be pyrolyzed at above 1600°C for 3 hours to generate multiphase ceramics, which greatly increases the industrialization cost of the invention. In contrast, Example 1 uses boric acid and boric anhydride, which are inexpensive sources. By mixing the raw materials at the atomic level, the pyrolysis temperature is greatly reduced, allowing pure ZrC and ZrB2 to be generated at 1400°C for 2 hours without any other impurities.

[0052] The solubility of the soluble ZrC / ZrB2 multiphase ultra-high temperature ceramic precursors prepared in Examples 1-6 and the multiphase ceramic materials prepared in Comparative Examples 1-2 in various common solvents is shown in Table 1. Table 1. Solubility of the precursor prepared in this example in various common solvents.

[0053] As can be seen from Table 1, the soluble ZrC / ZrB2 multiphase ultra-high temperature ceramic precursors prepared in Examples 1 to 6 all have good solubility in the above solvents. Among them, compared with existing ceramic precursors, the soluble ZrC / ZrB2 multiphase ultra-high temperature ceramic precursors prepared by the method of the present invention have higher solubility in environmentally friendly, low-toxicity solvents such as anhydrous ethanol and ethyl acetate.

[0054] Compared to Example 1, the precursor material prepared in Comparative Example 1 is only soluble in highly toxic reagents such as xylene and tetrahydrofuran, and has low solubility in environmentally friendly, low-toxicity solvents such as anhydrous ethanol and ethyl acetate. Comparative Example 2, on the other hand, is insoluble in the above reagents. It can be seen that the ZrC / ZrB2 multiphase ultra-high temperature ceramic precursor prepared by the method of this invention exhibits good solubility in a variety of reagents.

[0055] This invention adds element B in the form of more stable triethyl borate, and constructs a soluble composite ceramic precursor with BO-Zr-OC as the main chain through transesterification reaction between boron-containing precursors and substitution reaction with hydroxyl-containing carbon sources. This improves the solubility of the precursor, making it soluble in environmentally friendly and low-toxicity reagents such as anhydrous ethanol and ethyl acetate.

[0056] In Example 1, the prepared precursor had a solubility of 65.7 wt.% in anhydrous ethanol and 59.4 wt.% in ethyl acetate.

[0057] The ceramic yields of the soluble ZrC / ZrB2 multiphase ultra-high temperature ceramic precursors prepared in Examples 1-6 and the multiphase ceramic materials prepared in Comparative Examples 1-2 at different pyrolysis temperatures are shown in Table 2.

[0058] Table 2. Ceramic yield of the precursor prepared in this embodiment at different pyrolysis temperatures.

[0059] As can be seen from Table 2, the soluble ZrC / ZrB2 multiphase ultra-high temperature ceramic precursors prepared in Examples 1-6 can be converted into pure ZrC and ZrB2 during high-temperature pyrolysis at 1400℃, with a ceramic yield of about 42%.

[0060] In summary, the present invention has the advantages of readily available raw materials, low pyrolysis temperature, short pyrolysis time, high ceramic yield, and good solubility of the prepared precursor in environmentally friendly and low-toxicity organic solvents, including anhydrous ethanol and ethyl acetate.

Claims

1. A method for preparing a soluble ZrC / ZrB2 multiphase ultra-high temperature ceramic precursor, characterized in that, Specifically as follows: S1. Under an inert atmosphere, zirconium tetrachloride is dissolved in a first anhydrous ethanol solution, followed by the addition of acetylacetone solution, and heated and stirred to obtain a zirconium-containing precursor solution with the molecular formula (C2H5O)2Zr(acac)2. S2. Dissolve the boron source in a second anhydrous ethanol solution, then add concentrated sulfuric acid solution, heat and stir and remove water to obtain a boron-containing mixed solution with the molecular formula B(OC2H5)3. S3. Add the boron-containing mixed solution dropwise to the zirconium-containing precursor solution. After the addition is complete, continue heating and stirring to obtain the mixed solution. S4. Add a hydroxyl-containing carbon source to the mixed solution and stir at a certain temperature to obtain a viscous reddish-brown liquid; S5. Excess solvent in the reddish-brown liquid is removed by rotary evaporation and vacuum drying to obtain a zirconium carbide and zirconium boride multiphase ultra-high temperature ceramic precursor with good solubility.

2. The method for preparing the soluble ZrC / ZrB2 multiphase ultra-high temperature ceramic precursor according to claim 1, characterized in that, The ratio of the amount of zirconium tetrachloride in S1 to the amount of the first anhydrous ethanol solution is 1:10~20. The molar ratio of the first anhydrous ethanol solution to acetylacetone in S1 is 1:0.15~0.30; The heating temperature in S1 is 40~80 ℃, and the heating time is 1~2h.

3. The method for preparing the soluble ZrC / ZrB2 multiphase ultra-high temperature ceramic precursor according to claim 1, characterized in that, The boron source in S2 is boric acid or boric anhydride. Before use, the boron source needs to undergo a low-temperature baking pretreatment to remove water. The low-temperature baking temperature is 40~60℃ and the time is 60~90min. When the boron source is boric acid, the molar ratio of boric acid to zirconium tetrachloride is 5~2:1; when the boron source is boric anhydride, the molar ratio of boric anhydride to zirconium tetrachloride is 1.5~3:

1. When the boron source is boric acid, the mass ratio of concentrated sulfuric acid to boric acid is 0.16:1; when the boron source is boric anhydride, the mass ratio of concentrated sulfuric acid to boric anhydride is 0.05:

1. The mass ratio of concentrated sulfuric acid to boric acid added is 0.16:

1. If the selected boron source is boric anhydride, the mass ratio is 0.05:

1. The ratio of the amount of boron source substance to the amount of the second anhydrous ethanol solution is 1:5~10. The concentration of concentrated sulfuric acid in S2 is 99.99%.

4. The method for preparing the soluble ZrC / ZrB2 multiphase ultra-high temperature ceramic precursor according to claim 3, characterized in that, The specific method of S2 is as follows: Nitrogen or argon gas is introduced before and during the reaction to purge air. Concentrated sulfuric acid is added to the mixed solution of boron source and second anhydrous ethanol as a catalyst. The mixture is heated to 40-80℃ and stirred for 1-1.5 h to obtain the reaction solution. Toluene or cyclohexane is added to the reaction solution. Toluene or cyclohexane forms a low-boiling-point azeotrope with the water generated in the reaction solution. A water separator is installed on the reflux apparatus. Toluene or cyclohexane is mixed with the reaction solution and added to the water separator for heating and reflux. The generated triethyl borate-water-solvent azeotrope vapor condenses and flows into the water separator. The water settles at the bottom and is quickly separated. The organic layers such as solvent, ethanol, and triethyl borate flow back to the reaction flask. Under continuous reflux, the water separator is observed until the volume of the lower water layer no longer increases within 30-45 minutes. Then the separation is stopped, and a relatively pure boron-containing mixed solution is obtained.

5. The method for preparing the soluble ZrC / ZrB2 multiphase ultra-high temperature ceramic precursor according to claim 4, characterized in that, The volume ratio of toluene or cyclohexane to the second anhydrous ethanol is 1:1; When toluene is used as an azeotropic solvent, the heating temperature is 105~110℃; when cyclohexane is used as an azeotropic solvent, the heating temperature is 90~95℃. The concentration of toluene or cyclohexane is 99.99%.

6. The method for preparing the soluble ZrC / ZrB2 multiphase ultra-high temperature ceramic precursor according to claim 1, characterized in that, The heating temperature in S3 is 60~80℃, and the heating time is 30~40min. In step S3, the boron-containing mixed solution is added to the zirconium-containing precursor solution at a rate of 2-3 drops / s.

7. The method for preparing the soluble ZrC / ZrB2 multiphase ultra-high temperature ceramic precursor according to claim 1, characterized in that, The hydroxyl-containing carbon source in S4 is a phenolic hydroxyl-containing carbon source or an alcoholic hydroxyl-containing carbon source, wherein the phenolic hydroxyl-containing carbon source includes: phenol, hydroquinone, resorcinol, catechol or bisphenol A; The hydroxyl-containing carbon source alcohols include: 1,4-butanediol, ethylene glycol, glycerol, or butanetetraol; The hydroxyl-containing carbon source is one or two of the above substances in any ratio; Phenol, hydroquinone, resorcinol, catechol, or bisphenol A; hydroxyl-containing carbon source alcohols include: 1,4-butanediol, ethylene glycol, glycerol, or butanetetraethanolamine, wherein the hydroxyl-containing carbon source is one or a mixture of two of the above substances in any proportion. The molar ratio of the hydroxyl-containing carbon source to zirconium tetrachloride is 20-25:

1.

8. The method for preparing the soluble ZrC / ZrB2 multiphase ultra-high temperature ceramic precursor according to claim 1, characterized in that, The stirring temperature in S4 is 60-80 ℃, and the stirring time is 1-2 h.

9. The method for preparing the soluble ZrC / ZrB2 multiphase ultra-high temperature ceramic precursor according to claim 1, characterized in that, The vacuum drying temperature in S54 is 45~60 ℃, and the drying time is controlled between 24~48 h.

10. A soluble ZrC / ZrB2 multiphase ultra-high temperature ceramic precursor prepared by any of the preparation methods described in claims 1 to 9.

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