A hafnium oxide continuous ceramic fiber and a method of making the same

Abstract

The application discloses a hafnium oxide continuous ceramic fiber and a preparation method thereof. The method comprises the following steps: melting and spinning a hafnium oxide polymer precursor block to obtain a fiber raw yarn; performing constant-temperature and constant-humidity treatment to obtain a non-fusible fiber; performing slow-speed heating sintering to realize inorganic treatment and obtain an inorganic fiber; and performing high-temperature holding sintering to realize ceramic treatment and obtain the hafnium oxide continuous ceramic fiber. By using two kinds of complexing agents to coordinate hafnium sources, by adjusting the adding amount and the type of the two kinds of complexing agents, the linear degree and the molecular weight of the precursor are improved, the hafnium oxide continuous ceramic fiber is prepared by using a melting and spinning method, and the obtained fiber is thin in diameter and high in strength.

Description

Technical Field

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

[0002] Continuous ceramic fibers are primarily used as high-temperature structural materials in aerospace, aviation, and weaponry. Among these, oxide fibers, due to their excellent high-temperature oxidation resistance, show greater promise in high-temperature long-term thermal structural materials and high-temperature long-term oxygen-exposed thermal insulation materials. Currently, commercially available oxide fibers in developed countries mainly include alumina fibers, zirconium oxide fibers, aluminum zirconium fibers, aluminum silicate mullite fibers, and yttrium aluminum garnet fibers. Oxide fibers exhibit reduced mechanical strength and poor high-temperature creep resistance at high temperatures due to abnormal grain growth within the fiber. Therefore, selecting oxide components that are more stable at high temperatures is crucial for improving the high-temperature resistance of oxide fibers.

[0003] Hafnium oxide (HfO2) possesses a high melting point (approximately 2900℃), a low coefficient of thermal expansion, and excellent chemical, thermal, and antioxidant properties, making it an ideal high-temperature resistant material. Tianjin University prepared continuous SiCO / HfO2 ceramic fibers by magnetically stirring a mixture of dimethyldiethoxysilane, tetraethoxysilane, hafnium oxychloride octahydrate, and ethanol, thickening it with polyvinylpyrrolidone, and then manually drawing the solution into fibers using a glass rod. After drying and pyrolysis, these fibers were obtained. Cornell University and Huazhong University of Science and Technology prepared uniformly dispersed spinning solutions by mixing organic hafnium sources with spinning auxiliaries, then prepared fibers via electrospinning, and finally calcined to remove the organic components, yielding hafnium oxide ceramic fibers. However, manual fiber drawing is limited to laboratory research and cannot be stably mass-produced; electrospinning cannot produce continuous ceramic fibers, and the fiber ceramics prepared by the above methods have low yields and poor microstructure density.

[0004] Currently, there are no reports on the preparation of continuous hafnium oxide ceramic fibers. Summary of the Invention

[0005] The purpose of this invention is to provide a continuous hafnium oxide ceramic fiber and its preparation method. The continuous hafnium oxide ceramic fiber is prepared by polymer precursor melt spinning, which is a simple process with less waste gas generated during production and less environmental pollution; the obtained continuous hafnium oxide ceramic fiber has a diameter of 7-13 μm and a tensile strength of up to 1.6 GPa.

[0006] The method for preparing continuous hafnium oxide ceramic fibers provided by the present invention includes the following steps:

[0007] 1) The hafnium oxide polymer precursor bulk is melt-spun to obtain fiber filaments;

[0008] 2) The fiber filaments obtained in step 1) are subjected to constant temperature and humidity treatment to obtain non-melting fibers;

[0009] 3) The infusible fibers obtained in step 2) are subjected to slow heating and sintering to achieve inorganic treatment, resulting in inorganic fibers;

[0010] 4) The inorganic fibers obtained in step 3) are subjected to high-temperature heat preservation sintering to achieve ceramicization treatment, and hafnium oxide continuous ceramic fibers are obtained.

[0011] In step 1) of the above method, the hafnium oxide polymer precursor bulk is prepared by the following method: hafnium propoxide is dissolved in ethylene glycol ethyl ether, stirred and heated under reflux for 0.5-5 h (specifically 5 h), then heated to 50-100 °C under stirring, and a complexing agent mixture of acetylacetone and ethyl acetoacetate with a molar fraction of 1 molar fraction of hafnium propoxide is added, wherein the molar ratio of acetylacetone to ethyl acetoacetate is 1:0.5-3, and heated under reflux for 0.5-6 h; then a mixture of water and ethylene glycol butyl ether with a mass ratio of 1:7 is added dropwise, wherein the molar ratio of hafnium propoxide to water is 1:0.4, and the reflux reaction is carried out for 2 h after the addition is completed; the temperature is further raised to 230 °C for vacuum distillation, and after holding at this temperature for 3 h, it is cooled to room temperature to obtain the hafnium oxide polymer ceramic precursor bulk.

[0012] The molar ratio of acetylacetone to ethyl acetoacetate can be 1:0.5, 1:1, 1:2, or 1:3, with 1:1 being preferred.

[0013] Step 1) of the above method involves heating the hafnium oxide polymer ceramic precursor to 20–50°C above its softening point, melting it into a homogeneous melt, and removing residual air bubbles before melt spinning.

[0014] Specifically, the heating temperature for melt spinning is 25-50°C, 35°C, 25°C, 50°C, 30°C, 40°C, or 45°C higher than the softening point.

[0015] The extrusion method is nitrogen pressurized extrusion; the extrusion pressure is 2-25 MPa, specifically 10, 20, 2, 25, 5, and 15 MPa.

[0016] The spinneret orifice diameter is 0.1–0.5 mm; specifically 0.2, 0.4, 0.1, 0.5, and 0.3 mm.

[0017] The winding speed of the spool is 300-800 m / min; specifically 700, 800, 500, 300, 600, and 400 m / min.

[0018] In step 2) of the above method, the constant temperature range is 100 to 600℃; specifically, it is 400℃, 550℃, 100℃, 600℃, 200℃, 300℃, and 500℃.

[0019] The constant humidity range is 45%–95%; specifically 85%, 95%, 50%, 70%, 60%, 80%, and 45%.

[0020] The constant temperature and humidity treatment time is 0.5 to 5 hours; specifically 1, 2, 5, 0.5, 3, and 4 hours.

[0021] Step 2) of the above method also includes cooling and dehumidifying to the ambient temperature and humidity after the constant temperature and humidity treatment, which can be natural cooling and dehumidification.

[0022] In step 3) of the above method, the slow heating sintering is to raise the temperature from room temperature to the inorganic temperature and sinter (i.e., inorganicate) at the inorganic temperature.

[0023] The heating rate from room temperature to the inorganic temperature is 0.2–10 °C / min; specifically 1, 5, 10, 2, and 0.2 °C / min.

[0024] The inorganication temperature is 650–900℃; specifically 700, 900, 650, 800, 750, and 850℃.

[0025] The inorganization time is 0.5 to 5 hours; specifically 2, 4, 0.5, 3, 1, and 5 hours.

[0026] Step 3) of the above method further includes a cooling-to-room-temperature operation after slow heating and sintering, wherein the cooling method is natural cooling.

[0027] In step 4) of the above method, the high-temperature holding sintering involves raising the temperature from room temperature to the ceramization temperature and then sintering (i.e., ceramization) at the ceramization temperature.

[0028] The rate of increase from room temperature to ceramization temperature is 5–30 °C / min; specifically 10, 25, 20, 5, 15, and 30 °C / min.

[0029] The ceramization temperature is 1000–1800℃; specifically 1400, 1700, 1500, 1000, 1200, 1800, 1100, and 1600℃.

[0030] The ceramization time ranges from 5 to 120 minutes; specifically 60, 30, 120, 20, 5, 40, and 90 minutes.

[0031] The atmosphere for ceramicization is air.

[0032] The resulting hafnium oxide continuous ceramic fibers have an average diameter of 7–13 μm and an average tensile strength of up to 1.6 GPa.

[0033] The hafnium oxide continuous ceramic fiber prepared by the above method and its application in the preparation of materials with at least one of the properties of structural reinforcement and high-temperature insulation are also within the scope of protection of this invention.

[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. Using this precursor to prepare continuous hafnium oxide ceramic fibers results in less waste gas generated during the spinning process and subsequent sintering process, thus reducing environmental pollution.

[0036] 2. Hafnium oxide continuous ceramic fibers prepared by melt spinning and calcination of hafnium oxide polymer ceramic precursors have a diameter of 7-13 μm and a tensile strength of up to 1.6 GPa.

[0037] This invention uses two complexing agents to coordinate a hafnium source. By adjusting the amount and type of the two complexing agents, the linearity and molecular weight of the precursor are improved. Hafnium oxide continuous ceramic fibers are prepared by melt spinning, resulting in fibers with fine diameter and high strength. Attached Figure Description

[0038] Figure 1 This is a photograph of the hafnium oxide continuous ceramic fiber obtained in Example 1 of the present invention.

[0039] Figure 2 The image shows the XRD pattern of the hafnium oxide continuous ceramic fiber obtained in Example 1 of this invention.

[0040] Figure 3 This is a SEM image of the hafnium oxide continuous ceramic fiber obtained in Example 1 of the present invention. Detailed Implementation

[0041] 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.

[0042] 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.

[0043] Example 1

[0044] 1) 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 was added dropwise at a dropping rate of 1 drop / s. The molar ratio of hafnium propoxide to water was 1:0.4. 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 a hafnium oxide polymer ceramic precursor with a softening point of 200 °C, a molecular weight of 3400, and a ceramic yield of 56%.

[0045] 2) The hafnium oxide polymer ceramic precursor obtained in step 1) is heated to 35°C above the softening point. After it melts into a uniform melt and removes residual bubbles, it is melt-spun. The extrusion pressure is 10 MPa, the spinneret orifice diameter is 0.2 mm, and the winding and take-up rate is 700 m / min to obtain fiber filaments.

[0046] 3) Place the fiber filaments obtained in step 2) in a constant temperature and humidity chamber, keep them at 400℃ and 85% relative humidity for 1 hour, and cool them to room temperature to obtain non-melting fibers.

[0047] 4) Place the non-melting fiber obtained in step 3) in a desizing furnace, heat it to 700℃ at a rate of 1℃ / min, keep it at that temperature for 2 hours, and then let it cool naturally to room temperature.

[0048] 5) Place the inorganic fibers obtained in step 4) in a sintering furnace, heat to 1400℃ at a rate of 10℃ / min, and hold for 60min to obtain continuous hafnium oxide ceramic fibers.

[0049] The hafnium oxide continuous ceramic fiber obtained in this embodiment has an average diameter of 8 μm, a crystal form of monoclinic hafnium dioxide, and an average tensile strength of 1.6 GPa.

[0050] A photograph of the hafnium oxide continuous ceramic fiber obtained in this embodiment is attached. Figure 1 .

[0051] The XRD pattern of the hafnium oxide continuous ceramic fiber obtained in this embodiment is shown in the appendix. Figure 2 It has a monoclinic hafnium dioxide crystal form.

[0052] The SEM image of the hafnium oxide continuous ceramic fiber obtained in this embodiment is attached. Figure 3 The fibers have a uniform diameter and no obvious defects are visible on the surface.

[0053] Example 2

[0054] 1) The operation is the same as in Example 1;

[0055] 2) The hafnium oxide polymer ceramic precursor obtained in step 1) is heated to 25°C above the softening point. After it melts into a uniform melt and removes residual bubbles, it is melt-spun. The extrusion pressure is 20 MPa, the spinneret orifice diameter is 0.4 mm, and the winding and take-up rate is 800 m / min to obtain fiber filaments.

[0056] 3) Place the fiber filaments obtained in step 2) in a constant temperature and humidity chamber, keep them at 400℃ and 85% relative humidity for 1 hour, and cool them to room temperature to obtain non-melting fibers.

[0057] 4) Place the non-melting fiber obtained in step 3) in a desizing furnace, heat it to 700℃ at a rate of 1℃ / min, keep it at that temperature for 2 hours, and then let it cool naturally to room temperature.

[0058] 5) Place the inorganic fibers obtained in step 4) in a sintering furnace, heat to 1400℃ at a rate of 10℃ / min, and hold for 60min to obtain continuous hafnium oxide ceramic fibers.

[0059] The fiber has an average diameter of 11 μm, a monoclinic hafnium dioxide crystal form, and an average tensile strength of 1.3 GPa.

[0060] Example 3

[0061] 1) The operation is the same as in Example 1;

[0062] 2) The hafnium oxide polymer ceramic precursor obtained in step 1) is heated to 35°C above the softening point. After it melts into a uniform melt and removes residual bubbles, it is melt-spun. The extrusion pressure is 10 MPa, the spinneret orifice diameter is 0.2 mm, and the winding and take-up rate is 700 m / min to obtain fiber filaments.

[0063] 3) Place the fiber filaments obtained in step 2) in a constant temperature and humidity chamber, keep them at 550℃ and 95% relative humidity for 2 hours, and cool them to room temperature to obtain non-melting fibers.

[0064] 4) Place the non-melting fiber obtained in step 3) in a desizing furnace, heat it to 700℃ at a rate of 1℃ / min, keep it at that temperature for 2 hours, and then let it cool naturally to room temperature.

[0065] 5) Place the inorganic fibers obtained in step 4) in a sintering furnace, heat to 1400℃ at a rate of 10℃ / min, and hold for 60min to obtain continuous hafnium oxide ceramic fibers.

[0066] The hafnium oxide continuous ceramic fiber obtained in this embodiment has an average diameter of 8 μm, a crystal form of monoclinic hafnium dioxide, and an average tensile strength of 1.5 GPa.

[0067] Example 4

[0068] 1) The operation is the same as in Example 1;

[0069] 2) The hafnium oxide polymer ceramic precursor obtained in step 1) is heated to 35°C above the softening point. After it melts into a uniform melt and removes residual bubbles, it is melt-spun. The extrusion pressure is 10 MPa, the spinneret orifice diameter is 0.2 mm, and the winding and take-up rate is 700 m / min to obtain fiber filaments.

[0070] 3) Place the fiber filaments obtained in step 2) in a constant temperature and humidity chamber, keep them at 400℃ and 85% relative humidity for 1 hour, and cool them to room temperature to obtain non-melting fibers.

[0071] 4) Place the non-melting fiber obtained in step 3) in a desizing furnace, heat it to 900°C at a rate of 5°C / min, keep it at that temperature for 4 hours, and then let it cool naturally to room temperature.

[0072] 5) Place the inorganic fibers obtained in step 4) in a sintering furnace, heat to 1400℃ at a rate of 10℃ / min, and hold for 60min to obtain continuous hafnium oxide ceramic fibers.

[0073] The hafnium oxide continuous ceramic fiber obtained in this embodiment has an average diameter of 8 μm, a crystal form of monoclinic hafnium dioxide, and an average tensile strength of 1.4 GPa.

[0074] Example 5

[0075] 1) The operation is the same as in Example 1;

[0076] 2) The hafnium oxide polymer ceramic precursor obtained in step 1) is heated to 35°C above the softening point. After it melts into a uniform melt and removes residual bubbles, it is melt-spun. The extrusion pressure is 10 MPa, the spinneret orifice diameter is 0.2 mm, and the winding and take-up rate is 700 m / min to obtain fiber filaments.

[0077] 3) Place the fiber filaments obtained in step 2) in a constant temperature and humidity chamber, keep them at 400℃ and 85% relative humidity for 1 hour, and cool them to room temperature to obtain non-melting fibers.

[0078] 4) Place the non-melting fiber obtained in step 3) in a desizing furnace, heat it to 700℃ at a rate of 1℃ / min, keep it at that temperature for 2 hours, and then let it cool naturally to room temperature.

[0079] 5) Place the inorganic fibers obtained in step 4) in a sintering furnace, heat them to 1700℃ at a rate of 25℃ / min, and hold for 30min to obtain continuous hafnium oxide ceramic fibers.

[0080] The hafnium oxide continuous ceramic fiber obtained in this embodiment has an average diameter of 8 μm, a cubic phase hafnium dioxide crystal form, and an average tensile strength of 1.2 GPa.

[0081] Example 6

[0082] 1) The operation is the same as in Example 1;

[0083] 2) The hafnium oxide polymer ceramic precursor obtained in step 1) is heated to 50°C above the softening point. After it melts into a uniform melt and removes residual bubbles, it is melt-spun. The extrusion pressure is 2MPa, the spinneret orifice diameter is 0.1mm, and the winding and take-up rate is 500m / min to obtain fiber filaments.

[0084] 3) Place the fiber filaments obtained in step 2) in a constant temperature and humidity chamber, keep them at 100°C and 50% relative humidity for 5 hours, and cool them to room temperature to obtain non-melting fibers.

[0085] 4) Place the non-melting fiber obtained in step 3) in a desizing furnace, heat it to 700℃ at a rate of 1℃ / min, keep it at that temperature for 2 hours, and then let it cool naturally to room temperature.

[0086] 5) Place the inorganic fibers obtained in step 4) in a sintering furnace, heat to 1500℃ at a rate of 10℃ / min, and hold for 60min to obtain hafnium oxide continuous ceramic fibers.

[0087] The hafnium oxide continuous ceramic fiber obtained in this embodiment has an average diameter of 7 μm, a crystal form of monoclinic hafnium dioxide and cubic hafnium dioxide, and an average tensile strength of 1.1 GPa.

[0088] Example 7

[0089] 1) The operation is the same as in Example 1;

[0090] 2) The hafnium oxide polymer ceramic precursor obtained in step 1) is heated to 30°C above the softening point. After it melts into a uniform melt and removes residual bubbles, it is melt-spun. The extrusion pressure is 25 MPa, the spinneret orifice diameter is 0.5 mm, and the winding and take-up rate is 300 m / min to obtain fiber filaments.

[0091] 3) Place the fiber filaments obtained in step 2) in a constant temperature and humidity chamber, keep them at 400℃ and 85% relative humidity for 1 hour, and cool them to room temperature to obtain non-melting fibers.

[0092] 4) Place the non-melting fiber obtained in step 3) in a desizing furnace, heat it to 700℃ at a rate of 1℃ / min, keep it at that temperature for 2 hours, and then let it cool naturally to room temperature.

[0093] 5) Place the inorganic fibers obtained in step 4) in a sintering furnace, heat them to 1000℃ at a rate of 20℃ / min, and hold for 120min to obtain hafnium oxide continuous ceramic fibers.

[0094] The hafnium oxide continuous ceramic fiber obtained in this embodiment has an average diameter of 13 μm, a crystal form of monoclinic hafnium dioxide, and an average tensile strength of 1.0 GPa.

[0095] Example 8

[0096] 1) The operation is the same as in Example 1;

[0097] 2) The hafnium oxide polymer ceramic precursor obtained in step 1) is heated to 40°C above the softening point. After it melts into a uniform melt and removes residual bubbles, it is melt-spun. The extrusion pressure is 10 MPa, the spinneret orifice diameter is 0.3 mm, and the winding and take-up rate is 600 m / min to obtain fiber filaments.

[0098] 3) Place the fiber filaments obtained in step 2) in a constant temperature and humidity chamber, keep them at 400℃ and 85% relative humidity for 1 hour, and cool them to room temperature to obtain non-melting fibers.

[0099] 4) Place the non-melting fiber obtained in step 3) in a desizing furnace, heat it to 650°C at a rate of 10°C / min, keep it at that temperature for 0.5 hours, and then let it cool naturally to room temperature.

[0100] 5) Place the inorganic fibers obtained in step 4) in a sintering furnace, heat to 1400℃ at a rate of 10℃ / min, and hold for 60min to obtain continuous hafnium oxide ceramic fibers.

[0101] The hafnium oxide continuous ceramic fiber obtained in this embodiment has an average diameter of 9 μm, a crystal form of monoclinic hafnium dioxide, and an average tensile strength of 1.1 GPa.

[0102] Example 9

[0103] 1) The operation is the same as in Example 1;

[0104] 2) The hafnium oxide polymer ceramic precursor obtained in step 1) is heated to 45°C above the softening point. After it melts into a uniform melt and removes residual bubbles, it is melt-spun. The extrusion pressure is 5 MPa, the spinneret orifice diameter is 0.2 mm, and the winding and take-up rate is 400 m / min to obtain fiber filaments.

[0105] 3) Place the fiber filaments obtained in step 2) in a constant temperature and humidity chamber, keep them at 600℃ and 70% relative humidity for 0.5h, and cool them to room temperature to obtain non-melting fibers.

[0106] 4) Place the non-melting fiber obtained in step 3) in a desizing furnace, heat it to 800℃ at a rate of 2℃ / min, keep it at that temperature for 3 hours, and then let it cool naturally to room temperature.

[0107] 5) Place the inorganic fibers obtained in step 4) in a sintering furnace, heat them to 1200℃ at a rate of 5℃ / min, and hold for 20min to obtain continuous hafnium oxide ceramic fibers.

[0108] The hafnium oxide continuous ceramic fiber obtained in this embodiment has an average diameter of 10 μm, a crystal form of monoclinic hafnium dioxide, and an average tensile strength of 1.3 GPa.

[0109] Example 10

[0110] 1) The operation is the same as in Example 1;

[0111] 2) The hafnium oxide polymer ceramic precursor obtained in step 1) is heated to 30°C above the softening point. After it melts into a uniform melt and removes residual bubbles, it is melt-spun. The extrusion pressure is 20 MPa, the spinneret orifice diameter is 0.4 mm, and the winding and take-up rate is 500 m / min to obtain fiber filaments.

[0112] 3) Place the fiber filaments obtained in step 2) in a constant temperature and humidity chamber, keep them at 200℃ and 60% relative humidity for 3 hours, and cool them to room temperature to obtain non-melting fibers.

[0113] 4) Place the non-melting fiber obtained in step 3) in a desizing furnace, heat it to 750°C at a rate of 5°C / min, keep it at that temperature for 0.5 hours, and then let it cool naturally to room temperature.

[0114] 5) Place the inorganic fibers obtained in step 4) in a sintering furnace, heat to 1800℃ at a rate of 15℃ / min, and hold for 5 minutes to obtain continuous hafnium oxide ceramic fibers.

[0115] The hafnium oxide continuous ceramic fiber obtained in this embodiment has an average diameter of 12 μm, a cubic phase hafnium dioxide crystal form, and an average tensile strength of 1.0 GPa.

[0116] Example 11

[0117] 1) The operation is the same as in Example 1;

[0118] 2) The hafnium oxide polymer ceramic precursor obtained in step 1) is heated to 50°C above its softening point. After it melts into a uniform melt and removes residual bubbles, it is melt-spun. The extrusion pressure is 15 MPa, the spinneret orifice diameter is 0.2 mm, and the winding and take-up rate is 800 m / min to obtain fiber filaments.

[0119] 3) Place the fiber filaments obtained in step 2) in a constant temperature and humidity chamber, keep them at 300℃ and 80% relative humidity for 2 hours, and cool them to room temperature to obtain non-melting fibers.

[0120] 4) Place the non-melting fiber obtained in step 3) in a desizing furnace, heat it to 850℃ at a rate of 0.2℃ / min, keep it at that temperature for 1 hour, and then let it cool naturally to room temperature.

[0121] 5) Place the inorganic fibers obtained in step 4) in a sintering furnace, heat them to 1100℃ at a rate of 5℃ / min, and hold for 40min to obtain continuous hafnium oxide ceramic fibers.

[0122] The hafnium oxide continuous ceramic fiber obtained in this embodiment has an average diameter of 7 μm, a crystal form of monoclinic hafnium dioxide, and an average tensile strength of 1.3 GPa.

[0123] Example 12

[0124] 1) The operation is the same as in Example 1;

[0125] 2) The hafnium oxide polymer ceramic precursor obtained in step 1) is heated to 25°C above the softening point. After it melts into a uniform melt and removes residual bubbles, it is melt-spun. The extrusion pressure is 25 MPa, the spinneret orifice diameter is 0.3 mm, and the winding and take-up rate is 800 m / min to obtain fiber filaments.

[0126] 3) Place the fiber filaments obtained in step 2) in a constant temperature and humidity chamber, keep them at 500℃ and 45% relative humidity for 4 hours, and cool them to room temperature to obtain non-melting fibers.

[0127] 4) Place the non-melting fiber obtained in step 3) in a desizing furnace, heat it to 800℃ at a rate of 2℃ / min, keep it at that temperature for 5 hours, and then let it cool naturally to room temperature.

[0128] 5) Place the inorganic fibers obtained in step 4) in a sintering furnace, heat them to 1600℃ at a rate of 30℃ / min, and hold for 90min to obtain continuous hafnium oxide ceramic fibers.

[0129] The hafnium oxide continuous ceramic fibers obtained in this embodiment have an average diameter of 9 μm, crystal forms of monoclinic hafnium dioxide and cubic hafnium dioxide, and an average tensile strength of 1.0 GPa.

[0130] Example 13

[0131] 1) Hafnium propoxide was dissolved in ethylene glycol ethyl ether and refluxed with stirring for 5 hours. Then, the mixture was heated to 70°C with stirring, and a complexing agent solution of acetylacetone and ethyl acetoacetate (1 molar ratio of acetylacetone to ethyl acetoacetate 1:0.5) was added. The mixture was refluxed for 1 hour. Next, a mixture of water and ethylene glycol butyl ether (1:7 mass ratio of hafnium propoxide to water 1:0.4) was added dropwise at a rate of 1 drop / s. The mixture was refluxed for 2 hours after the addition was complete. The temperature was then raised to 230°C for vacuum distillation, held at this temperature for 3 hours, and then cooled to room temperature to obtain a hafnium oxide polymer ceramic precursor. The softening point was 200°C, the molecular weight was 3200, and the ceramic yield was 56%.

[0132] 2) 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).

[0133] Example 14

[0134] 1) Hafnium propoxide was dissolved in ethylene glycol ethyl ether and refluxed with stirring for 5 hours. Then, under stirring, the mixture was heated to 70°C, and a complexing agent solution of acetylacetone and ethyl acetoacetate (1 molar ratio of acetylacetone to ethyl acetoacetate) was added. The mixture was refluxed for 1 hour. Next, a mixture of water and ethylene glycol butyl ether (1:7 mass ratio of hafnium propoxide to water, 1:0.4 molar ratio of hafnium propoxide to water) was added dropwise at a rate of 1 drop / s. The mixture was refluxed for 2 hours after the addition was complete. The temperature was then raised to 230°C for vacuum distillation, held at this temperature for 3 hours, and then cooled to room temperature to obtain a hafnium oxide polymer ceramic precursor. The softening point was 200°C, the molecular weight was 3100, and the ceramic yield was 56%.

[0135] 2) 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).

[0136] Example 15

[0137] 1) Hafnium propoxide was dissolved in ethylene glycol ethyl ether and refluxed with stirring for 5 hours. Then, under stirring, the mixture was heated to 70°C, and a complexing agent solution of acetylacetone and ethyl acetoacetate (1 molar ratio of acetylacetone to ethyl acetoacetate) was added. The mixture was refluxed for 1 hour. Next, a mixture of water and ethylene glycol butyl ether (1:7 mass ratio of hafnium propoxide to water, 1:0.4 molar ratio of hafnium propoxide to water) was added dropwise at a rate of 1 drop / s. The mixture was refluxed for 2 hours after the addition was complete. The temperature was then raised to 230°C for vacuum distillation, held at this temperature for 3 hours, and then cooled to room temperature to obtain a hafnium oxide polymer ceramic precursor. The softening point was 200°C, the molecular weight was around 3000, and the ceramic yield was 56%.

[0138] 2) 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).

[0139] Comparative Example 1

[0140] 1) Hafnium propoxide was dissolved in ethylene glycol ethyl ether and refluxed with stirring for 5 hours. Then, the mixture was heated to 70°C with stirring, and acetylacetone with a molar fraction equal to that of hafnium propoxide was added. The mixture was refluxed for 1 hour. A mixture of water and ethylene glycol butyl ether (mass ratio 1:7, hafnium propoxide to water molar ratio 1:0.4) was then added dropwise at a rate of 1 drop / s. The mixture was refluxed for 2 hours after the addition was complete. The temperature was then raised to 230°C for vacuum distillation, held at this temperature for 3 hours, and then cooled to room temperature to obtain a hafnium oxide polymer ceramic precursor. The softening point was 200°C, the molecular weight was approximately 1500, and the ceramic yield was 56%.

[0141] 2) 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).

[0142] Comparative Example 2

[0143] 1) Hafnium propoxide was dissolved in ethylene glycol ethyl ether and refluxed with stirring for 5 hours. Then, the mixture was heated to 70°C with stirring, and ethyl acetoacetate (1 molar fraction of hafnium propoxide) was added. The mixture was refluxed for 1 hour. A mixture of water and ethylene glycol butyl ether (mass ratio 1:7, hafnium propoxide to water molar ratio 1:0.4) was then added dropwise at a rate of 1 drop / s. The mixture was refluxed for 2 hours after the addition was complete. The temperature was then raised to 230°C for vacuum distillation, held at this temperature for 3 hours, and then cooled to room temperature to obtain a hafnium oxide polymer ceramic precursor. The softening point was 200°C, the molecular weight was approximately 1300, and the ceramic yield was 56%.

[0144] 2) 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).

[0145] 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 continuous hafnium oxide ceramic fibers, comprising the following steps: 1) The hafnium oxide polymer precursor bulk is melt-spun to obtain fiber filaments; 2) The fiber filaments obtained in step 1) are subjected to constant temperature and humidity treatment to obtain non-melting fibers; 3) The infusible fibers obtained in step 2) are subjected to slow heating and sintering to achieve inorganic treatment, thereby obtaining inorganic fibers; 4) The inorganic fibers obtained in step 3) are subjected to high-temperature sintering to achieve ceramicization treatment, resulting in continuous hafnium oxide ceramic fibers; In step 1), the hafnium oxide polymer precursor bulk is prepared by the following method: hafnium propoxide is dissolved in ethylene glycol ethyl ether, stirred and heated under reflux for 0.5-5 h, then heated to 50-100°C under stirring, and a complexing agent mixture of acetylacetone and ethyl acetoacetate with a molar fraction of 1 molar fraction of hafnium propoxide is added, wherein the molar ratio of acetylacetone to ethyl acetoacetate is 1:0.5-3, and heated under reflux for 0.5-6 h; then a mixture of water and ethylene glycol butyl ether with a mass ratio of 1:7 is added dropwise, wherein the molar ratio of hafnium propoxide to water is 1:0.4, and the reflux reaction is carried out for 2 h after the addition is complete; the temperature is further raised to 230°C for vacuum distillation, and after holding at this temperature for 3 h, it is cooled to room temperature to obtain the hafnium oxide polymer precursor bulk. In step 3), the slow heating sintering is to raise the temperature from room temperature to the inorganic temperature and sinter at the inorganic temperature to achieve inorganication; The heating rate from room temperature to inorganic temperature is 0.2~10°C / min; The ceramization temperature is 1000~1800℃.

2. The method according to claim 1, characterized in that: Step 1) involves heating the hafnium oxide polymer precursor bulk to 20-50°C above its softening point, melting it into a homogeneous melt, and removing any residual air bubbles before melt spinning. The extrusion method is nitrogen pressurized extrusion, and the extrusion pressure is 2~25MPa; The spinneret orifice diameter is 0.1~0.5mm; The winding speed of the spool is 300~800m / min.

3. The method according to claim 1, characterized in that: In step 2), the constant temperature range is 100~600°C; The constant humidity range is 45% to 95%. The constant temperature and humidity treatment time is 0.5~5 hours.

4. The method according to claim 1, characterized in that: In step 3), the inorganication temperature is 650~900°C; The inorganization time is 0.5~5h.

5. The method according to claim 1, characterized in that: In step 4), the high-temperature holding sintering involves raising the temperature from room temperature to the ceramization temperature, and then sintering at the ceramization temperature to achieve ceramization. The rate of temperature increase from room temperature to ceramization temperature is 5~30℃ / min; The ceramization time is 5~120 min; The atmosphere for ceramicization is air.

6. Hafnium oxide continuous ceramic fibers prepared by the method of any one of claims 1-5.

7. The hafnium oxide continuous ceramic fiber according to claim 6, characterized in that: The hafnium oxide continuous ceramic fiber has an average diameter of 8 μm, a monoclinic hafnium dioxide crystal form, and an average tensile strength of 1.6 GPa.

8. The use of the hafnium oxide continuous ceramic fiber of claim 6 or 7 in the preparation of a material having at least one of the properties of structural reinforcement and high-temperature insulation.

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