Hafnium oxide polymer ceramic precursor and preparation method thereof

Abstract

This invention discloses a hafnium oxide polymer ceramic precursor and its preparation method. The method includes the following steps: 1) Adding an organic hafnium source to a solvent and stirring under reflux for 0.5–5 h; adding a complexing agent mixture at a heating temperature of 50–100 °C and continuing stirring and reflux for 0.5–6 h; 2) Adding the mixture to the reaction system obtained in step 1), and refluxing for 0.5–3 h after the addition is complete; subsequently removing the solvent by atmospheric or vacuum distillation, and cooling to room temperature to obtain the hafnium oxide polymer ceramic precursor. This invention uses two complexing agents to coordinate and stabilize the organic hafnium source. By adjusting the amount, type, and ratio of the two complexing agents, the linearity and molecular weight of the precursor are improved, thereby enhancing the spinning performance of the precursor. The softening point of the obtained ceramic precursor is between 120 and 200 °C, the highest ceramic yield is 56%, and the highest molecular weight reaches 3400.

Description

Technical Field

[0001] This invention belongs to the field of composite fiber materials technology, specifically relating to a hafnium oxide polymer ceramic precursor and its preparation method. Background Technology

[0002] The aerospace industry requires aircraft materials to operate in neutral or oxidizing environments at temperatures above 1100°C. Ultra-high temperature ceramics, as a class of ceramic materials with high hardness, high melting point, high temperature resistance, and chemical stability, can be used in aero engines, leading edges of wings for long-duration hypersonic flight, aircraft nose cones, and transatmospheric flight materials. However, due to their fracture brittleness, ultra-high temperature ceramics are prone to cracking or spalling at high temperatures, which can easily lead to serious aircraft malfunctions. Strengthening and toughening ultra-high temperature ceramics with high-melting-point materials, while reducing surface cracks and spalling and maintaining their oxidation resistance in ultra-high temperature environments, has great application potential. Hafnium oxide (HfO2) has a high melting point (approximately 2900°C), a low coefficient of thermal expansion, and excellent chemical stability, thermal stability, and oxidation resistance, making it an ideal high-temperature resistant material.

[0003] Cornell University has developed a method to generate 3-5 nm HfO2-acetate nanoparticles by reacting hafnium isopropoxide with acetic acid. These nanoparticles are then mixed in a high concentration into a polyvinyl alcohol (PVA) solution to create a uniform spinning solution for electrospinning, resulting in PVA / HfO2 hybrid fibers. After calcination, these fibers form pure inorganic hafnium oxide fibers.

[0004] Huazhong University of Science and Technology dissolved a mixture of hafnium acetylacetonate and polyvinylpyrrolidone in a mixed solvent of dimethylformamide and chloroform, and stirred vigorously to prepare a spinning solution. Fibers were then prepared by electrospinning. During the spinning process, the solvent evaporated, and the organic hafnium source compound adhered to the long organic fiber chain. After calcination, hafnium oxide ceramic fibers were obtained.

[0005] Electrospinning cannot produce continuous ceramic fibers, and the fiber ceramics prepared by the above methods have low yields and poor microstructure density. Currently, there are no reports on the preparation of continuous hafnium oxide ceramic fibers.

[0006] Our research group previously (CN110592724A) successfully prepared bulk aluminum-silicon-hafnium polymer precursors suitable for melt spinning by co-co-hydrolysis and polycondensation using single complexing agents on aluminum, silicon, and hafnium sources. These precursors had a softening point of up to 135℃, with a molar ratio of metal element to complexing agent of 1:0.5–0.9. Hafnium primarily exhibits a tetravalent oxidation state in compounds. When hafnium sources are coordinated and hydrolyzed separately, single complexing agents and small amounts of complexing agent cannot produce high molecular weight hafnium oxide polymer ceramic precursors. Summary of the Invention

[0007] The purpose of this invention is to provide a hafnium oxide polymer ceramic precursor and its preparation method. In the preparation of the hafnium oxide polymer ceramic precursor, two complexing agents are used to coordinate and stabilize the organic hafnium source. By adjusting the amount, type, and ratio of the two complexing agents, the linearity and molecular weight of the precursor are improved, thereby enhancing the spinning performance of the precursor. The obtained ceramic precursor has a softening point between 120 and 200°C, a ceramic yield of up to 56%, and a molecular weight as high as 3400.

[0008] The method for preparing hafnium oxide polymer ceramic precursor provided by the present invention includes the following steps:

[0009] 1) Add the organic hafnium source to the solvent and stir and reflux to dissolve for 0.5 to 5 hours; add any one of the complexing agent mixture solutions ab at a certain proportion at a heating temperature of 50 to 100°C, and continue stirring and heating under reflux for 0.5 to 6 hours.

[0010] 2) Add any one of the mixed solutions E1 in a certain proportion to the reaction system obtained in step 1), and reflux the reaction for 0.5 to 3 hours after the addition is complete; then remove the solvent by atmospheric distillation or vacuum distillation, and cool to room temperature to obtain the hafnium oxide polymer ceramic precursor;

[0011] The complexing agent mixture a is a mixture of acetic acid and methyl acetoacetate;

[0012] The complexing agent mixture solution b is a mixture of acetylacetone and ethyl acetoacetate;

[0013] The mixture e is composed of water and n-propanol;

[0014] The mixture f is composed of water and isopropanol;

[0015] The mixture g is composed of water and ethylene glycol methyl ether;

[0016] The mixture h is composed of water and ethylene glycol ethyl ether;

[0017] The mixture i is composed of water and ethylene glycol butyl ether.

[0018] In step 1) of the above method, the organic hafnium source is selected from at least one of ethanol hafnium, n-propanol hafnium, isopropanol hafnium, n-butanol hafnium, and tert-butanol hafnium;

[0019] The solvent is selected from at least one of methanol, ethanol, n-propanol, isopropanol, n-butanol, tert-butanol, ethylene glycol methyl ether, and ethylene glycol ethyl ether;

[0020] The amount of the complexing agent mixture added is 0.3 to 1.5 molar times that of the organic hafnium source;

[0021] In the complexing agent mixed solution a, the molar ratio of acetic acid and methyl acetoacetate is 1:12 to 20; specifically 1:15, 1:12, and 1:20.

[0022] In the complexing agent mixed solution b, the molar ratio of acetylacetone to ethyl acetoacetate is 1:0.5 to 3; specifically 1:1, 1:3, and 1:0.5.

[0023] In step 2), the mass ratio of water to n-propanol in the mixture e is 1:1 to 10; specifically, it is 1:8.

[0024] In the mixture f, the mass ratio of water to isopropanol is 1:1 to 10; specifically, it is 1:1.

[0025] In the mixture g, the mass ratio of water to ethylene glycol methyl ether is 1:1 to 10; specifically 1:4.

[0026] In the mixture h, the mass ratio of water to ethylene glycol ethyl ether is 1:1 to 10; specifically 1:10.

[0027] In the mixture i, the mass ratio of water to ethylene glycol butyl ether is 1:1 to 10; specifically 1:7 and 1:3.

[0028] The molar ratio of the organic hafnium source to any one of the waters in the mixture ei is 1:0.1 to 0.8; specifically, 1:0.4, 1:0.5, 1:0.7, 1:0.2, and 1:0.6.

[0029] The mixture ei is added by dripping; the dripping rate is 0.5 to 6 drops / s; specifically 1 to 2 drops / s.

[0030] In the atmospheric distillation or vacuum distillation step, the temperature is 130–230°C;

[0031] The distillation time is 0.5 to 6 hours; specifically 2 to 5 hours.

[0032] The softening point of the obtained hafnium oxide polymer ceramic precursor is between 120 and 200 °C.

[0033] Furthermore, the hafnium oxide polymer ceramic precursor prepared according to the above method and its application in fiber preparation are also within the scope of protection of this invention. The fiber is a continuous hafnium oxide ceramic fiber; in the application, the fiber is obtained by melt spinning.

[0034] Compared with the prior art, the present invention has the following advantages:

[0035] 1. The hafnium oxide polymer ceramic precursor provided by the present invention is prepared by hydrolysis and polycondensation. Before hydrolysis, two complexing agents are used to coordinate the organic hafnium source. By adjusting the amount, type and ratio of the two complexing agents, the linearity and molecular weight of the precursor are improved, making the polymer ceramic precursor more conducive to spinning, thereby improving the strength of the fiber filament.

[0036] 2. This precursor exhibits high softening point, ceramic yield, and molecular weight. The softening point ranges from 120 to 200°C, the highest ceramic yield is 56%, and the highest molecular weight is 3400. Using this precursor to prepare continuous hafnium oxide polymer ceramic fibers results in less waste gas generation during the spinning and subsequent sintering processes, thus minimizing environmental pollution.

[0037] This invention proposes a novel method for preparing hafnium oxide polymer ceramic precursors suitable for melt spinning. Two complexing agents are used to coordinate an organic hafnium source before hydrolysis. By adjusting the amount, type, and ratio of the two complexing agents, the linearity of the precursor is improved. Compared with a single complexing agent, the molecular weight is nearly doubled, making the polymer precursor more stable during spinning. Furthermore, the hafnium oxide fibers prepared through melt spinning and calcination exhibit excellent tensile strength. Attached Figure Description

[0038] Figure 1 Photograph of the hafnium oxide polymer ceramic precursor prepared in Example 1 of the present invention.

[0039] Figure 2 This is the infrared absorption spectrum of the hafnium oxide polymer ceramic precursor prepared in Example 1 of the present invention.

[0040] Figure 3 This is a scanning electron microscope image of the hafnium oxide polymer ceramic fiber prepared in Example 1 of the present invention.

[0041] Figure 4 This is a viscosity-temperature curve of the hafnium oxide polymer ceramic precursor prepared in Example 4 of the present invention. Detailed Implementation

[0042] The present invention will now be described in further detail with reference to specific embodiments. The given embodiments are merely illustrative of the invention and not intended to limit its scope. The embodiments provided below can serve as a guide for further improvements by those skilled in the art and do not constitute a limitation on the invention in any way.

[0043] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Unless otherwise specified, the materials and reagents used in the following examples are commercially available.

[0044] Example 1

[0045] Hafnium propoxide was dissolved in ethylene glycol ethyl ether and stirred and refluxed for 5 h. Then, it was heated to 70 °C with stirring, and a complexing agent mixture of acetylacetone and ethyl acetoacetate with a molar ratio of 1:1 was added. The mixture was heated and refluxed for 1 h. Then, a mixture of water and ethylene glycol butyl ether with a mass ratio of 1:7 (hafnium propoxide to water) was added dropwise at a rate of 1 drop / s. The mixture was refluxed for 2 h after the addition was complete. The temperature was then raised to 230 °C for vacuum distillation. After holding at this temperature for 3 h, the mixture was cooled to room temperature to obtain the hafnium oxide polymer ceramic precursor.

[0046] The hafnium oxide polymer ceramic precursor obtained in this embodiment has a softening point of 200°C, a molecular weight of 3400, and a ceramic yield of 56%.

[0047] Hafnium oxide polymer ceramic precursor was heated to 35°C above its softening point until it melted into a homogeneous melt and residual bubbles were removed. Then, melt spinning was performed at an extrusion pressure of 10 MPa, a spinneret orifice diameter of 0.2 mm, and a winding rate of 700 m / min to obtain fiber precursors. The obtained fiber precursors were placed in a constant temperature and humidity chamber and held at 400°C and 85% relative humidity for 1 hour, then cooled to room temperature to obtain infusible fibers. The obtained infusible fibers were placed in a debinding furnace and heated to 700°C at a rate of 1°C / min, held for 2 hours, and then allowed to cool naturally to room temperature. The obtained inorganic fibers were placed in a sintering furnace and heated to 1400°C at a rate of 10°C / min, held for 60 minutes to obtain continuous hafnium oxide ceramic fibers with an average diameter of 8 μm and an average tensile strength of 1.6 GPa.

[0048] A photograph of the hafnium oxide polymer precursor obtained in this embodiment is attached. Figure 1 It is a reddish-brown transparent solid.

[0049] The infrared absorption spectrum of the hafnium oxide polymer precursor obtained in this embodiment is shown in the appendix. Figure 2 As shown in the figure, it is located at 3343cm. -1 and 1100cm -1 The peak at 2800–3000 cm⁻¹ is the absorption peak of the stretching vibration of -OH. -1 The peaks at 1462 and 1381 cm⁻¹ are absorption peaks of the stretching vibration of -CH₃. -1 The peak at 475 cm⁻¹ is the absorption peak of the stretching vibration of C=O and C-CH₃. -1 The peak at that point is the absorption peak of Hf-O-Hf.

[0050] The scanning electron microscope (SEM) image of the hafnium oxide continuous ceramic fiber obtained in this embodiment is attached. Figure 3The fiber diameter is uniformly distributed and the surface is free of defects.

[0051] Example 2

[0052] Hafnium isopropoxide was dissolved in n-propanol and heated under reflux for 5 hours with stirring. Then, it was heated to 75°C with stirring, and a complexing agent mixture of acetic acid and methyl acetoacetate with a molar ratio of 0.5 times that of hafnium isopropoxide was added, wherein the molar ratio of acetic acid to methyl acetoacetate was 1:15. The mixture was heated under reflux for 2 hours. Then, a mixture of water and ethylene glycol methyl ether with a mass ratio of 1:4 and a molar ratio of hafnium isopropoxide to water of 1:0.5 was added dropwise at a dropping rate of 4 drops / s. The mixture was refluxed for 1 hour after the addition was completed. The temperature was then raised to 210°C for atmospheric distillation, and the mixture was kept at this temperature for 6 hours before being cooled to room temperature to obtain the hafnium oxide polymer ceramic precursor.

[0053] The hafnium oxide polymer ceramic precursor obtained in this embodiment has a softening point of 190°C, a molecular weight of around 2100, and a ceramic yield of 54%.

[0054] Hafnium oxide continuous ceramic fibers with an average diameter of 8 μm and an average tensile strength of 1.1 GPa were obtained by melt spinning, isothermal and humidity treatment and segmented sintering of the precursor (the same operation as in Example 1).

[0055] Example 3

[0056] Hafnium tert-butoxide was dissolved in tert-butanol and stirred under reflux for 4 hours. Then, it was heated to 70°C with stirring, and a complexing agent mixture of acetylacetone and ethyl acetoacetate with a molar ratio of 1:3 was added at a concentration of 1.5 times that of hafnium tert-butoxide. The mixture was then heated under reflux for 1 hour. Next, a mixture of water and ethylene glycol ethyl ether with a mass ratio of 1:10 (hafnium tert-butoxide to water) was added dropwise at a rate of 0.5 drops / s. The mixture was then refluxed for 2.5 hours after the addition was complete. The temperature was then raised to 180°C for vacuum distillation. After holding at this temperature for 1 hour, the mixture was cooled to room temperature to obtain the hafnium oxide polymer ceramic precursor.

[0057] The hafnium oxide polymer ceramic precursor obtained in this embodiment has a softening point of 165°C, a molecular weight of around 3100, and a ceramic yield of 50%.

[0058] Hafnium oxide continuous ceramic fibers with an average diameter of 8 μm and an average tensile strength of 1.5 GPa were obtained by melt spinning, isothermal and humidity treatment and segmented sintering of the precursor (the same operation as in Example 1).

[0059] Example 4

[0060] Hafnium ethanol was dissolved in methanol and heated under reflux for 2 hours with stirring. Then, it was heated to 50°C with stirring, and a complexing agent mixture of acetic acid and methyl acetoacetate with a molar ratio of 0.6 times that of hafnium ethanol (1:12) was added. The mixture was heated under reflux for 4 hours. A mixture of water and isopropanol with a mass ratio of 1:1 (1:0.2) was then added dropwise at a rate of 6 drops / s. The mixture was refluxed for 1 hour after the addition was complete. The temperature was then raised to 130°C for vacuum distillation. After holding at this temperature for 0.5 hours, the mixture was cooled to room temperature to obtain the hafnium oxide polymer ceramic precursor.

[0061] The hafnium oxide polymer ceramic precursor obtained in this embodiment has a softening point of 120°C, a molecular weight of around 2200, and a ceramic yield of 40%.

[0062] Hafnium oxide continuous ceramic fibers with an average diameter of 8 μm and an average tensile strength of 1.0 GPa were obtained by melt spinning, isothermal and humidity treatment and segmented sintering of the precursor (the same operation as in Example 1).

[0063] Example 5

[0064] Hafnium ethanol was dissolved in ethylene glycol ethyl ether and stirred and refluxed for 1 h. Then, it was heated to 100 °C with stirring, and a complexing agent mixture of acetylacetone and ethyl acetoacetate with a molar ratio of 1:0.5 was added. The mixture was heated and refluxed for 2 h. Then, a mixture of water and ethylene glycol butyl ether with a mass ratio of 1:3 (hafnium ethanol to water) was added dropwise at a rate of 3 drops / s. The mixture was refluxed for 2 h after the addition was complete. The temperature was then raised to 220 °C for vacuum distillation. After holding at this temperature for 3.5 h, the mixture was cooled to room temperature to obtain the hafnium oxide polymer ceramic precursor.

[0065] The hafnium oxide polymer ceramic precursor obtained in this embodiment has a softening point of 195°C, a molecular weight of around 3200, and a ceramic yield of 55%.

[0066] Hafnium oxide continuous ceramic fibers with an average diameter of 8 μm and an average tensile strength of 1.4 GPa were obtained by melt spinning, isothermal and humidity treatment and segmented sintering of the precursor (the same operation as in Example 1).

[0067] Example 6

[0068] Hafnium n-butoxide was dissolved in ethylene glycol methyl ether and stirred under reflux for 3.5 h. Then, it was heated to 95 °C with stirring, and a complexing agent mixture of acetic acid and methyl acetoacetate with a molar ratio of 0.9 times that of hafnium n-butoxide (1:20) was added. The mixture was then heated under reflux for 4 h. Next, a mixture of water and n-propanol with a mass ratio of 1:8 (1:0.6) was added dropwise at a rate of 3.5 drops / s. The mixture was then refluxed for 1 h. Finally, the temperature was raised to 190 °C for atmospheric distillation, and the mixture was kept at this temperature for 2 h before being cooled to room temperature to obtain the hafnium oxide polymer ceramic precursor.

[0069] The hafnium oxide polymer ceramic precursor obtained in this embodiment has a softening point of 175°C, a molecular weight of around 2900, and a ceramic yield of 51%.

[0070] Hafnium oxide continuous ceramic fibers with an average diameter of 8 μm and an average tensile strength of 0.9 GPa were obtained by melt spinning, isothermal and humidity treatment and segmented sintering of the precursor (the same operation as in Example 1).

[0071] Example 7

[0072] Hafnium propoxide was dissolved in ethylene glycol ethyl ether and stirred and refluxed for 5 h. Then, it was heated to 70 °C with stirring, and a complexing agent mixture of acetylacetone and ethyl acetoacetate with a molar ratio of 1:0.5 was added. The mixture was heated and refluxed for 1 h. Then, a mixture of water and ethylene glycol butyl ether with a mass ratio of 1:7 (hafnium propoxide to water molar ratio of 1:0.4) was added dropwise at a dropping rate of 1 drop / s. The mixture was refluxed for 2 h after the addition was complete. The temperature was then raised to 230 °C for vacuum distillation. After holding at this temperature for 3 h, the mixture was cooled to room temperature to obtain the hafnium oxide polymer ceramic precursor.

[0073] The hafnium oxide polymer ceramic precursor obtained in this embodiment has a softening point of 200°C, a molecular weight of 3200, and a ceramic yield of 56%.

[0074] Hafnium oxide continuous ceramic fibers with an average diameter of 8 μm and an average tensile strength of 1.5 GPa were obtained by melt spinning, isothermal and humidity treatment and segmented sintering of the precursor (the same operation as in Example 1).

[0075] Example 8

[0076] Hafnium propoxide was dissolved in ethylene glycol ethyl ether and stirred and refluxed for 5 h. Then, it was heated to 70 °C with stirring, and a complexing agent mixture of acetylacetone and ethyl acetoacetate with a molar ratio of 1:2 was added. The mixture was heated and refluxed for 1 h. Then, a mixture of water and ethylene glycol butyl ether with a mass ratio of 1:7 (hafnium propoxide to water molar ratio of 1:0.4) was added dropwise at a dropping rate of 1 drop / s. The mixture was refluxed for 2 h after the addition was complete. The temperature was then raised to 230 °C for vacuum distillation. After holding at this temperature for 3 h, the mixture was cooled to room temperature to obtain the hafnium oxide polymer ceramic precursor.

[0077] The hafnium oxide polymer ceramic precursor obtained in this embodiment has a softening point of 200°C, a molecular weight of 3100, and a ceramic yield of 56%.

[0078] Hafnium oxide continuous ceramic fibers with an average diameter of 8 μm and an average tensile strength of 1.4 GPa were obtained by melt spinning, isothermal and humidity treatment and segmented sintering of the precursor (the same operation as in Example 1).

[0079] Example 9

[0080] Hafnium propoxide was dissolved in ethylene glycol ethyl ether and stirred and refluxed for 5 h. Then, it was heated to 70 °C with stirring, and a complexing agent mixture of acetylacetone and ethyl acetoacetate with a molar ratio of 1:3 was added. The mixture was heated and refluxed for 1 h. Then, a mixture of water and ethylene glycol butyl ether with a mass ratio of 1:7 (hafnium propoxide to water) was added dropwise at a rate of 1 drop / s. The mixture was refluxed for 2 h after the addition was complete. The temperature was then raised to 230 °C for vacuum distillation. After holding at this temperature for 3 h, the mixture was cooled to room temperature to obtain the hafnium oxide polymer ceramic precursor.

[0081] The hafnium oxide polymer ceramic precursor obtained in this embodiment has a softening point of 200°C, a molecular weight of 3000, and a ceramic yield of 56%.

[0082] Hafnium oxide continuous ceramic fibers with an average diameter of 8 μm and an average tensile strength of 1.3 GPa were obtained by melt spinning, isothermal and humidity treatment and segmented sintering of the precursor (the same operation as in Example 1).

[0083] Example 10

[0084] Hafnium propoxide was dissolved in ethylene glycol ethyl ether and stirred and refluxed for 5 h. Then, it was heated to 70 °C with stirring, and a complexing agent mixture of acetylacetone and ethyl acetoacetate with a molar ratio of 0.5 times that of hafnium propoxide was added, wherein the molar ratio of acetylacetone to ethyl acetoacetate was 1:1. The mixture was heated and refluxed for 1 h. Then, a mixture of water and ethylene glycol butyl ether with a mass ratio of 1:7 and a molar ratio of hafnium propoxide to water of 1:0.4 was added dropwise at a dropping rate of 1 drop / s. The mixture was refluxed for 2 h after the addition was complete. The temperature was then raised to 230 °C for vacuum distillation, and the mixture was kept at this temperature for 3 h before being cooled to room temperature to obtain the hafnium oxide polymer ceramic precursor.

[0085] The hafnium oxide polymer ceramic precursor obtained in this embodiment has a softening point of 200°C, a molecular weight of 2700, and a ceramic yield of 56%.

[0086] Hafnium oxide continuous ceramic fibers with an average diameter of 8 μm and an average tensile strength of 1.0 GPa were obtained by melt spinning, isothermal and humidity treatment and segmented sintering of the precursor (the same operation as in Example 1).

[0087] Example 11

[0088] Hafnium propoxide was dissolved in ethylene glycol ethyl ether and stirred and refluxed for 5 h. Then, it was heated to 70 °C with stirring, and a complexing agent mixture of acetylacetone and ethyl acetoacetate with a molar ratio of 0.8 times that of hafnium propoxide was added, wherein the molar ratio of acetylacetone to ethyl acetoacetate was 1:1. The mixture was heated and refluxed for 1 h. Then, a mixture of water and ethylene glycol butyl ether with a mass ratio of 1:7 and a molar ratio of hafnium propoxide to water of 1:0.4 was added dropwise at a dropping rate of 1 drop / s. The mixture was refluxed for 2 h after the addition was complete. The temperature was then raised to 230 °C for vacuum distillation, and the mixture was kept at this temperature for 3 h before being cooled to room temperature to obtain the hafnium oxide polymer ceramic precursor.

[0089] The hafnium oxide polymer ceramic precursor obtained in this embodiment has a softening point of 200°C, a molecular weight of 2900, and a ceramic yield of 56%.

[0090] Hafnium oxide continuous ceramic fibers with an average diameter of 8 μm and an average tensile strength of 1.2 GPa were obtained by melt spinning, isothermal and humidity treatment and segmented sintering of the precursor (the same operation as in Example 1).

[0091] Example 12

[0092] Hafnium propoxide was dissolved in ethylene glycol ethyl ether and stirred and refluxed for 5 h. Then, it was heated to 70 °C with stirring, and a complexing agent mixture of acetylacetone and ethyl acetoacetate with a molar ratio of 1:1 was added. The mixture was heated and refluxed for 1 h. Then, a mixture of water and ethylene glycol butyl ether with a mass ratio of 1:7 (hafnium propoxide to water) was added dropwise at a rate of 1 drop / s. The mixture was refluxed for 2 h after the addition was complete. The temperature was then raised to 230 °C for vacuum distillation. After holding at this temperature for 3 h, the mixture was cooled to room temperature to obtain the hafnium oxide polymer ceramic precursor.

[0093] The hafnium oxide polymer ceramic precursor obtained in this embodiment has a softening point of 200°C, a molecular weight of 3000, and a ceramic yield of 56%.

[0094] Hafnium oxide continuous ceramic fibers with an average diameter of 8 μm and an average tensile strength of 1.2 GPa were obtained by melt spinning, isothermal and humidity treatment and segmented sintering of the precursor (the same operation as in Example 1).

[0095] Comparative Example 1

[0096] Hafnium propoxide was dissolved in ethylene glycol ethyl ether and heated under reflux for 5 hours with stirring. Then, it was heated to 70°C with stirring, and acetylacetone with a molar fraction equal to that of hafnium propoxide was added. The mixture was then heated under reflux for 1 hour. Next, a mixture of water and ethylene glycol butyl ether with a mass ratio of 1:7 (hafnium propoxide to water molar ratio of 1:0.4) was added dropwise at a rate of 1 drop / s. The mixture was then refluxed for 2 hours after the addition was complete. The temperature was then raised to 230°C for vacuum distillation. After holding at this temperature for 3 hours, the mixture was cooled to room temperature to obtain the hafnium oxide polymer ceramic precursor.

[0097] The hafnium oxide polymer ceramic precursor obtained in this embodiment has a softening point of 200°C, a molecular weight of around 1500, and a ceramic yield of 56%.

[0098] Hafnium oxide continuous ceramic fibers with an average diameter of 8 μm and an average tensile strength of 0.8 GPa were obtained by melt spinning, isothermal and humidity treatment and segmented sintering of the precursor (the same operation as in Example 1).

[0099] Comparative Example 2

[0100] Hafnium propoxide was dissolved in ethylene glycol ethyl ether and stirred and refluxed for 5 h. Then, it was heated to 70 °C with stirring, and ethyl acetoacetate with a molar fraction equal to that of hafnium propoxide was added. The mixture was then refluxed for 1 h. Next, a mixture of water and ethylene glycol butyl ether with a mass ratio of 1:7 (hafnium propoxide to water molar ratio of 1:0.4) was added dropwise at a rate of 1 drop / s. The mixture was then refluxed for 2 h. The temperature was then raised to 230 °C for vacuum distillation. After holding at this temperature for 3 h, the mixture was cooled to room temperature to obtain the hafnium oxide polymer ceramic precursor.

[0101] The hafnium oxide polymer ceramic precursor obtained in this embodiment has a softening point of 200°C, a molecular weight of around 1300, and a ceramic yield of 56%.

[0102] Hafnium oxide continuous ceramic fibers with an average diameter of 8 μm and an average tensile strength of 0.7 GPa were obtained by melt spinning, isothermal and humidity treatment and segmented sintering of the precursor (the same operation as in Example 1).

[0103] Comparing Comparative Examples 1 and 2 with Example 1, it can be seen that when using a single complexing agent, acetylacetone or ethyl acetoacetate, under the same synthesis conditions, hafnium oxide polymer precursors with the same softening point and ceramic yield are prepared, but their molecular weight is about 1 / 2 lower than that of precursors using both complexing agents. Under the same fiber preparation conditions, the tensile strength of fibers using a single complexing agent is lower than that of fibers prepared using both complexing agents.

[0104] Comparative Example 3

[0105] Hafnium ethanol was dissolved in methanol and heated under reflux for 2 hours with stirring. Then, it was heated to 50°C with stirring, and acetic acid with a molar fraction of 0.6 times that of hafnium ethanol was added. The mixture was then heated under reflux for 4 hours. A mixture of water and isopropanol with a mass ratio of 1:1 (hafnium ethanol to water molar ratio of 1:0.2) was added dropwise at a rate of 6 drops / s. The mixture was then refluxed for 1 hour after the addition was complete. The temperature was then raised to 130°C for vacuum distillation. After holding at this temperature for 0.5 hours, the mixture was cooled to room temperature to obtain the hafnium oxide polymer ceramic precursor.

[0106] The hafnium oxide polymer ceramic precursor obtained in this embodiment has a softening point of 120°C, a molecular weight of around 1100, and a ceramic yield of 40%.

[0107] Hafnium oxide continuous ceramic fibers with an average diameter of 8 μm and an average tensile strength of 0.5 GPa were obtained by melt spinning, isothermal and humidity treatment and segmented sintering of the precursor (the same operation as in Example 1).

[0108] Comparative Example 4

[0109] Hafnium ethanol was dissolved in methanol and heated under reflux for 2 hours with stirring. Then, it was heated to 50°C with stirring, and methyl acetoacetate with a molar fraction of 0.6 times that of hafnium ethanol was added. The mixture was then heated under reflux for 4 hours. A mixture of water and isopropanol with a mass ratio of 1:1 (hafnium ethanol to water molar ratio of 1:0.2) was added dropwise at a rate of 6 drops / s. The mixture was then refluxed for 1 hour after the addition was complete. The temperature was then raised to 130°C for vacuum distillation. After holding at this temperature for 0.5 hours, the mixture was cooled to room temperature to obtain the hafnium oxide polymer ceramic precursor.

[0110] The hafnium oxide polymer ceramic precursor obtained in this embodiment has a softening point of 120°C, a molecular weight of around 1200, and a ceramic yield of 40%.

[0111] Hafnium oxide continuous ceramic fibers with an average diameter of 8 μm and an average tensile strength of 0.6 GPa were obtained by melt spinning, isothermal and humidity treatment and segmented sintering of the precursor (the same operation as in Example 1).

[0112] Comparing Comparative Examples 3 and 4 with Example 4, it can be seen that when using a single complexing agent, acetic acid or methyl acetoacetate, under the same synthesis conditions, hafnium oxide polymer precursors with the same softening point and ceramic yield are prepared, but their molecular weight is nearly 1 / 2 lower than that of precursors using both complexing agents. Under the same fiber preparation conditions, the tensile strength of fibers using a single complexing agent is lower than that of fibers prepared using both complexing agents.

[0113] The present invention has been described in detail above. Those skilled in the art will recognize that the invention can be practiced in a wide range of ways with equivalent parameters, concentrations, and conditions without departing from its spirit and scope, and without requiring unnecessary experiments. While specific embodiments have been provided, it should be understood that further modifications can be made to the invention. In summary, according to the principles of the invention, this application is intended to include any changes, uses, or improvements to the invention, including changes made using conventional techniques known in the art that depart from the scope disclosed herein.

Claims

1. A method for preparing a hafnium oxide polymer ceramic precursor, comprising the following steps: 1) Add the organic hafnium source to the solvent and stir and reflux to dissolve for 0.5~5h; add any one of the complexing agent mixture solutions ab at a certain proportion at a heating temperature of 50~100°C, and continue stirring and heating under reflux for 0.5~6h. 2) Add any one of the mixed solutions E1 in a certain proportion to the reaction system obtained in step 1), and reflux the reaction for 0.5 to 3 hours after the addition is complete; then remove the solvent by atmospheric distillation or vacuum distillation, and cool to room temperature to obtain the hafnium oxide polymer ceramic precursor; The complexing agent mixture a is a mixture of acetic acid and methyl acetoacetate; The complexing agent mixture solution b is a mixture of acetylacetone and ethyl acetoacetate; The mixture e is composed of water and n-propanol; The mixture f is composed of water and isopropanol; The mixture g is composed of water and ethylene glycol methyl ether; The mixture h is composed of water and ethylene glycol ethyl ether; The mixture i is composed of water and ethylene glycol butyl ether; In step 1), the amount of the complexing agent mixture added is 0.3 to 1.5 molar times that of the organic hafnium source; In the complexing agent mixture solution a, the molar ratio of acetic acid and methyl acetoacetate is 1:12~20; In the complexing agent mixed solution b, the molar ratio of acetylacetone and ethyl acetoacetate is 1:0.5~3.

2. The method according to claim 1, characterized in that: In step 1), the organic hafnium source is selected from at least one of ethanol hafnium, n-propanol hafnium, isopropanol hafnium, n-butanol hafnium, and tert-butanol hafnium; The solvent is selected from at least one of methanol, ethanol, n-propanol, isopropanol, n-butanol, tert-butanol, ethylene glycol methyl ether, and ethylene glycol ethyl ether.

3. The method according to claim 1, characterized in that: In step 2), the mass ratio of water to n-propanol in the mixture e is 1:1~10; In the mixture f, the mass ratio of water to isopropanol is 1:1~10; In the mixture g, the mass ratio of water to ethylene glycol methyl ether is 1:1~10; In the mixture h, the mass ratio of water to ethylene glycol ethyl ether is 1:1~10; In the mixture i, the mass ratio of water to ethylene glycol butyl ether is 1:1~10.

4. The method according to claim 1, characterized in that: The molar ratio of the organic hafnium source to any one of the waters in the mixture is 1:0.1~0.

8.

5. The method according to claim 1, characterized in that: The mixture ei is added by dropping; the dropping rate is 0.5~6 drops / s. In the atmospheric distillation or vacuum distillation step, the temperature is 130~230°C; The distillation time is 0.5 to 6 hours.

6. A hafnium oxide polymer ceramic precursor prepared by the method of any one of claims 1-5.

7. The hafnium oxide polymer ceramic precursor according to claim 6, characterized in that: The softening point of the hafnium oxide polymer ceramic precursor is between 120 and 200°C, the ceramic yield is 40% to 56%, and the molecular weight is 2100 to 3400.

8. The application of the hafnium oxide polymer ceramic precursor according to claim 6 or 7 in the preparation of fibers, wherein the fibers are continuous hafnium oxide ceramic fibers; and the fibers are obtained by melt spinning.

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