Multi-element ultra-high temperature oxide whisker and preparation method and application thereof

Abstract

The invention relates to a multi-element superhigh-temperature oxide whisker suitable for a 2500 DEG C high-temperature oxidation environment as well as a preparation method and application thereof, and belongs to the technical field of ceramics. The preparation method comprises the following steps: firstly, preparing an organic precursor of an Hf-Zr multi-element ultra-high-temperature oxide by taking HfCl4 and ZrCl4 as raw materials by adopting a sol-gel technology, then ball-milling and mixing the organic precursor, NaCl, Na3PO4 and NH4F powder, putting the mixture into a muffle furnace of 950 DEG C for low-temperature heat treatment, and finally cleaning and drying the powder subjected to low-temperature heat treatment to obtain the Hf-Zr multi-element ultra-high-temperature oxide whisker. The process is simple in operation flow and short in process period, can be used for preparing the Hf-Zr multi-element superhigh-temperature oxide whisker with the melting point higher than 2500 DEG C under the heat treatment condition of lower than 1000 DEG C, and is suitable for industrial-grade mass production. The Hf-Zr multi-element superhigh temperature oxide whisker prepared by the method has a high length-diameter ratio, the distribution uniformity of each element in the whisker is high, and the designability of the whisker components is strong.

Description

Technical Field

[0001] The present invention belongs to the technical field of ceramics, and particularly relates to a multi-component ultra-high temperature oxide whisker and a preparation method and application thereof. Background Art

[0002] During the high Mach flight of a high-speed aircraft, the ultra-high temperature environment (>2500 °C) generated poses a severe challenge to the temperature resistance and service life of the thermal protection system. Ultra-high temperature ceramics with high melting points, high mechanical strength, low density, low expansion coefficients, high chemical inertness, and excellent oxidation and ablation resistance have become one of the best choices for the thermal protection systems of a new generation of high-speed aircraft. However, the inherent brittleness of ultra-high temperature ceramics makes them prone to cracking and failure during service in an ultra-high temperature environment, resulting in catastrophic accidents. How to improve the toughness of ultra-high temperature ceramics has become the key to ensuring their long-life and reliable service. Introducing low-dimensional toughening phases into ultra-high temperature ceramics to form ceramic matrix composites has become one of the important ways to improve the toughness of ceramics at present. Among them, ceramic matrix composites formed by using whiskers with a one-dimensional structure to toughen ultra-high temperature ceramics have been widely used in various aerospace thermal protection systems. Utilizing the strong interaction between the whiskers and the ceramic matrix, the externally applied stress is effectively transferred to the whiskers to prevent the rapid propagation of cracks, thereby enhancing the load-bearing capacity and fracture toughness of the entire composite material. Currently reported one-dimensional structure whisker toughening materials include carbide whiskers and oxide whiskers. Carbide whiskers may generate SiO 2 or CO 2 , resulting in the deterioration of the whisker structure or damage to the matrix interface. Compared with carbide whiskers, oxide whiskers are in an oxidized state themselves and are not easily further oxidized in a high-temperature oxygen-containing environment, and have better long-life service stability.

[0003] Currently reported ultra-high temperature oxide whiskers mainly focus on single-component zirconium-based oxide whiskers. In Patent 1 "Jiang Weihui, Wang Tao, Liu Jianmin, etc. A preparation method of zirconia whiskers with a high aspect ratio, CN108456921A [P].2018.", the authors used zirconium oxychloride as the precursor, potassium chloride as the molten salt, and trisodium phosphate dodecahydrate as the whisker growth aid to prepare zirconia whiskers, and the length and average aspect ratio of the whiskers were as high as 5-6 and 30. In Document 3 "J. Liu, T. Wang, Q. Gao, et al. Effect of NaF content on the preparation of zirconia whiskers by molten salt method [J], Advanced Powder Technology, 2021, 32(4): 998-1003", the authors used NaVO 3The ZrO₂ / NaF composite salt was successfully prepared by the molten salt method to obtain zirconia whiskers that grow along the

[001] direction, have a smooth surface, and no obvious defects. When the NaF addition content is 10%, the obtained monoclinic zirconia whiskers have a length of 1-3 μm and a diameter of 100-300 nm. Although the melting point of zirconia is as high as 2600 °C, with the continuous improvement of the service performance of high-speed aircraft, the service temperature faced by the thermal protection system has also increased significantly. The mechanical strength of zirconia whiskers will decline sharply in a high-temperature environment above 2500 °C. In addition, zirconia undergoes two phase transitions at 1170 °C and 2370 °C, and the stress introduced during the phase transition is likely to cause zirconia to crack and fail.

[0004] Therefore, aiming at the problems of insufficient temperature resistance, mechanical properties, and thermal stability of traditional zirconia whiskers, it is urgent to develop ultra-high temperature oxide whiskers with higher melting points and high phase transition temperatures to provide a new material selection scheme for the thermal protection system of the new generation of high-speed aircraft. Summary of the Invention

[0005] To solve the above problems, the present invention proposes a multi-component ultra-high temperature oxide whisker suitable for a 2500 °C high-temperature oxidation environment, a preparation method thereof, and an application, which solve the problems of insufficient temperature resistance, mechanical properties, and poor thermal stability of the ultra-high temperature oxide whiskers prepared by the prior art.

[0006] To achieve the above object, the present invention is realized through the following technical solutions: The first object of the present invention is to propose a multi-component ultra-high temperature oxide whisker with the chemical formula (Hf x Zr 1-x )O 2 , with a micron-scale needle-like morphology and an average aspect ratio of the whiskers of 5.0-13.1.

[0007] Adding other stabilizer components to zirconia can inhibit the high-temperature phase transition of zirconia, improve the thermal stability of zirconia, and reduce the volume change and cracking risk caused by phase transition. However, in zirconia whiskers, the introduction of multiple components will affect the nucleation rate and growth direction of zirconia whiskers. Multicomponent zirconia tends to grow into grains and is difficult to form a low-dimensional whisker structure. The Hf-Zr binary component oxide whisker proposed by the present invention has a needle-like morphology and a stable phase structure.

[0008] The second object of the present invention is to propose a preparation method for the above multi-component ultra-high temperature oxide whisker, which has the ability to withstand a 2500 °C high-temperature environment, and specifically includes the following steps: (1) Prepare an organic precursor of Hf-Zr oxide solid solution by the sol-gel method; (2) Mix and grind the organic precursor with molten salt and catalyst powder to form a mixed powder; (3) Heat up the mixed powder for heat treatment. After the heat treatment is completed, wash, filter, and dry it to obtain the multi-component ultra-high temperature oxide whiskers.

[0009] Preferably, in step (1), polyethylene glycol and citric acid monohydrate are used as chelating agents, and absolute ethanol is used as a solvent; the mass ratio of the absolute ethanol, citric acid monohydrate, and polyethylene glycol is (10~12):1:0.5.

[0010] More preferably, in step (1), first dissolve the chelating agent in absolute ethanol to form a chelating agent solution, and then add HfCl 4 and ZrCl 4 to the chelating agent solution, and heat to 65~75 °C and stir for 5~6 h to form a gel.

[0011] More preferably, the molar ratio of the HfCl 4 and ZrCl 4 is (1 / 3~3):1. HfO 2 and ZrO 2 have the same crystal structure and similar crystallographic constants, so the two can be solid-solved in any proportion to form an infinite solid solution, which makes the composition of the multi-component ultra-high temperature oxide (Hf-Zr)O 2 whiskers have strong designability. In the whiskers prepared in the present invention, HfO 2 and ZrO 2 also have any solid solution ratio. Preferably, the whiskers prepared in the range of (1~3):(1~3) have good morphology and thermal stability.

[0012] Preferably, the molten salt in step (2) is and NaCl, and the catalysts are Na 3 PO 4 and NH 4 F. Using NH 4 F as a catalyst to catalyze the growth of hafnium oxide and zirconium oxide into whiskers is one of the inventive points of the present invention. Common whisker growth catalysts include NaF, etc., which have a good effect on guiding the growth of zirconium oxide whiskers in a specific direction. Generally, it is considered that the thermal stability of NH 4 F is poor, and it is not used as a catalyst for single-component whisker growth. The present invention proposes to use NH 4 F as a catalyst for Hf-Zr binary oxide whiskers. The molten salt-assisted heat treatment can catalyze the whisker growth under the heat treatment conditions below 1000 °C, and obtain Hf-Zr binary ultra-high temperature oxide whiskers with good morphology.

[0013] More preferably, the organic precursor, NaCl, Na 3 PO 4 、NH4 The mass ratio of F is 10: (10 - 12):1:1.84, and the mixed powder needs to be mixed by a planetary ball mill at a rotational speed of 350 - 400 rpm for 30 - 60 min.

[0014] Preferably, the heat treatment temperature described in step (3) is 900 - 950 °C.

[0015] Preferably, the heat treatment process described in step (3) is as follows: heating to the heat treatment temperature at a rate of 3 °C / min, holding for 4.5 - 5.5 h, then cooling to 480 - 520 °C at a rate of 3 °C / min, and then naturally cooling to room temperature.

[0016] The third object of the present invention is to propose the application of the above-mentioned multi-component ultra-high temperature oxide whiskers as matrix reinforcement materials in thermal protection materials, especially as matrix reinforcement materials for ceramic matrix composites.

[0017] Compared with the prior art, the present invention has the following beneficial effects: The multi-component ultra-high temperature oxide whiskers proposed by the present invention aim at the problems of insufficient temperature resistance, limited mechanical strength, and insufficient thermal stability caused by easy phase change during high-temperature service of traditional single-component ZrO 2 By introducing HfO 2 into single-component ZrO 2 as a modification element to improve its service performance. The transition metal oxide HfO 2 formed by the Hf element belonging to the same IVB group has higher melting point, elastic modulus, hardness, and higher phase change temperature compared with ZrO 2 . In addition, since HfO 2 and ZrO 2 have the same crystal structure and similar crystallographic constants, the two can form an infinite solid solution by solid solution in any proportion, and the composition of the Hf-Zr multi-component ultra-high temperature oxide whiskers can be adjusted within any range on the basis of being successfully prepared, making the composition of the multi-component zirconia whiskers have strong designability.

[0018] The present invention uses a composite process of sol-gel and molten salt-assisted heat treatment to prepare multi-component ultra-high temperature oxide whiskers. First, an organic precursor of Hf-Zr multi-component ultra-high temperature oxide is prepared by sol-gel technology, which can achieve uniform mixing of Hf and Zr elements at the atomic scale and further improve the composition uniformity of the subsequent whiskers. Secondly, through NaCl molten salt-assisted heat treatment, Na 3 PO 4 and NH 4F co - guides the whisker growth, enabling the preparation of Hf - Zr multi - component ultra - high - temperature oxide whiskers with a high melting point above 2500 °C under heat treatment conditions below 1000 °C. The composite process has a simple operation flow and a short process cycle. Under the effective guidance of NH 4 F for whisker growth, the prepared whiskers have a high aspect ratio and are suitable for industrial - scale mass production.

[0019] During the whisker preparation process, Na 3 PO 4 and NH 4 F are selected as catalysts to guide the directional growth of whiskers, which can efficiently catalyze the one - dimensional growth of HfO 2 , ZrO 2 and their solid solutions, realizing the introduction of HfO 2 components with a higher melting point and a higher phase - change temperature into single - component ZrO 2 whiskers, significantly improving the defects of insufficient temperature resistance, mechanical properties and thermal stability of single - component ZrO 2 whiskers. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a schematic diagram of the process flow for preparing Hf - Zr multi - component ultra - high - temperature oxide whiskers of the present invention; Figure 2 is the microscopic morphology of the Hf - Zr multi - component ultra - high - temperature oxide whiskers prepared by the present invention, where: (a) the microscopic morphology of (Hf 0.75 Zr 0.25 )O 2 whiskers; (b) the microscopic morphology of (Hf 0.5 Zr 0.5 )O 2 whiskers; (c) the microscopic morphology of (Hf 0.25 Zr 0.75 )O 2 whiskers; Figure 3 is the EDS elemental surface distribution map of the (Hf 0.25 Zr 0.75 )O 2 whiskers prepared by the present invention; Figure 4 is the microscopic morphology of the (Hf 4 F - free condition. 0.5 Zr 0.5 )O 2 whiskers prepared under the DETAILED DESCRIPTION OF THE INVENTION

[0021] To enable those skilled in the art to better understand the solution of the present invention, the following will clearly and completely describe the technical solution in the embodiments of the present invention in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative work shall fall within the protection scope of the present invention.

[0022] It should be noted that the terms "first", "second", etc. in the description and claims of the present invention and the above-mentioned accompanying drawings are used to distinguish similar objects, and do not necessarily need to be used to describe a specific order or sequence. It should be understood that such data can be interchanged under appropriate circumstances so that the embodiments of the present invention can be implemented in an order other than that shown or described. In addition, the terms "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device comprising a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0023] The following further describes the present invention in detail with reference to the accompanying drawings: See Figure 1 , which is a schematic process flow diagram for the preparation of Hf-Zr multi-component ultra-high temperature oxide whiskers in the present invention, specifically including the following steps: Step 1: Weigh anhydrous ethanol, polyethylene glycol, and citric acid monohydrate according to a mass ratio of (10~12):1:0.5 and place them in a three-necked flask. Heat to 50~60 °C and stir magnetically for 10~60 min to form a colorless and clear solution. Subsequently, add HfCl in a molar ratio of (1 / 3~3):1 4 and ZrCl 4 . Further raise the temperature to 65~75 °C, preferably 70 °C, and stir magnetically for 5~6 h to form a milky white sol. Finally, place the sol in an electric heating blast drying oven at 170~180 °C for drying for 18~24 h to form a dry gel, obtaining an organic precursor of multi-component ultra-high temperature oxide (Hf x Zr 1-x )O 2 .

[0024] Step 2: Weigh the organic precursor, three inorganic salt powders of NaCl, Na 3 PO 4 , and NH 4 F according to a mass ratio of 10:(10~12):1:1.84 and place them in a planetary ball mill jar. Use a planetary ball mill to mix at a rotation speed of 350~400 rpm for 30~60 min to obtain a uniformly mixed raw material powder.

[0025] Step 3: Place the mixed powder obtained in Step 2 in an alumina crucible, and then place the crucible in the isothermal zone of a muffle furnace. Heat it from room temperature to 900 - 950 °C at a rate of 3 °C / min and hold for 4.5 - 5.5 h, preferably 5 h. Then cool it to 480 - 520 °C at a rate of 3 °C / min, preferably cool to 500 °C and then cut off the power supply to cool naturally with the furnace. Through heat treatment, the organic precursor is transformed into inorganic multi-metal oxides. At the same time, the generated multi-metal oxides dissolve and precipitate in the molten salt, and finally multi-metal oxide whiskers are formed.

[0026] Step 4: Place the heat-treated mixed powder in Step 3 in a beaker, add deionized water and heat it on a hot plate until boiling. After maintaining the boiling state for a certain time, use a vacuum filtration device to separate the deionized water dissolving the inorganic salts from the multi-metal oxide whiskers. Finally, place the whiskers in an electrothermal blast dryer at 70 - 80 °C and dry for 12 h to complete the preparation of multi-metal ultra-high temperature oxide (Hf x Zr 1-x )O 2 whiskers.

[0027] Example 1 Step 1: Place 160 g of anhydrous ethanol, 16 g of citric acid monohydrate, and 8 g of polyethylene glycol in a three-necked flask. Add a magnetic stir bar to the three-necked flask and place it on a magnetic stirrer. Heat the flask to 50 °C and stir magnetically for 30 min to fully dissolve the citric acid monohydrate to form a colorless and clear solution. Subsequently, slowly add 0.015 mol of HfCl 4 and 0.005 mol of ZrCl 4 to the uniformly mixed solution in Step 1. Further heat the three-necked flask to 70 °C and continue magnetic stirring for 5 h to obtain a milky white sol. Pour the sol into a beaker and place it in an electrothermal blast drying oven at 180 °C and let it stand for 24 h to fully remove the solvent in the sol to form a yellowish-brown xerogel, obtaining the organic precursor of multi-metal ultra-high temperature oxide (Hf 0.75 Zr 0.25 )O 2 .

[0028] Step 2: Weigh the organic precursor prepared in Step 1 and three inorganic salts, namely NaCl, Na 3 PO 4 , and NH 4 F, in a mass ratio of 10:12:1:1.84 and place them in a polytetrafluoroethylene ball milling jar. Use zirconia balls as grinding media for planetary ball milling. The rotation speed and ball milling time of the planetary ball milling are set to 350 rpm and 30 min respectively. Through ball milling, the above four powders are fully mixed and homogenized.

[0029] Step 3: Take out 10 g of the uniformly mixed powder in Step 2 and place it in an alumina crucible. The alumina crucible is covered with an alumina ceramic sheet to prevent damage to the heat treatment furnace caused by the volatilization of halogen elements during subsequent heat treatment. Place the encapsulated alumina crucible in the constant temperature zone of a muffle furnace. The muffle furnace uses silicon carbide rods as heating elements. Program control is used to slowly heat up to 950 °C at a rate of 3 °C / min and hold for 5 h, and then program control is used to slowly cool down to 500 °C at a rate of 3 °C / min. Subsequently, the muffle furnace is powered off and naturally cooled to room temperature to complete the transformation of the organic precursor into inorganic oxide (Hf 0.75 Zr 0.25 )O 2 whiskers.

[0030] Step 4: Place the heat-treated mixed powder in a beaker, add 500 mL of deionized water to the beaker, seal the beaker with plastic wrap, place the sealed beaker in the constant temperature zone of a hot plate, and set the temperature of the hot plate to 300 °C. Heat the deionized water in the beaker to boiling and keep it boiling for 5 min to fully dissolve the three inorganic salts of NaCl, Na 3 PO 4 , NH 4 F. Subsequently, use a vacuum filtration apparatus to separate the undissolved multi-component ultra-high temperature oxide (Hf 0.75 Zr 0.25 )O 2 whiskers from the deionized water dissolving the three inorganic salts of NaCl, Na 3 PO 4 , NH 4 F. Finally, place the separated multi-component ultra-high temperature oxide (Hf 0.75 Zr 0.25 )O 2 whiskers in an electrothermal blast drying oven at 70 °C for drying for 12 h to complete the preparation of the multi-component ultra-high temperature oxide (Hf 0.75 Zr 0.25 )O 2 whiskers.

[0031] Analyze the microstructure and phase composition of the prepared multi-component ultra-high temperature oxide (Hf 0.75 Zr 0.25 )O 2 whiskers ( Figure 2 (a) in 0.75 Zr 0.25 )O 2 The size of the whiskers prepared in this example is relatively uniform, and the average aspect ratio of the whiskers is 9.10 ± 2.38, proving that the multi-component ultra-high temperature oxide (Hf 0.75 Zr 0.25 )O2 Successful preparation of whiskers.

[0032] Example 2 Step 1: Place 170 g of absolute ethanol, 16 g of citric acid monohydrate, and 8 g of polyethylene glycol in a three-necked flask. Add a magnetic stir bar to the three-necked flask and place it on a magnetic stirrer. Heat the flask to 55 °C and stir magnetically for 45 min to fully dissolve the citric acid monohydrate to form a colorless and clear solution. Subsequently, slowly add 0.01 mol of HfCl 4 and 0.01 mol of ZrCl 4 to the solution obtained in Step 1 and mixed evenly. Further heat the three-necked flask to 70 °C and continue magnetic stirring for 5 h to obtain a milky white sol. Pour the sol into a beaker and place it in an electrothermal blast drying oven at 170 °C and let it stand for 18 h to fully remove the solvent in the sol to form a yellowish-brown xerogel, and obtain an organic precursor of multi-component ultra-high temperature oxide (Hf 0.5 Zr 0.5 )O 2 .

[0033] Step 2: Weigh the organic precursor prepared in Step 1, NaCl, Na 3 PO 4 , and NH 4 F, three inorganic salts in a mass ratio of 10:12:1:1.84 and place them in a polytetrafluoroethylene ball milling tank. Use zirconia balls as grinding media for planetary ball milling. The rotational speed and ball milling time of the planetary ball milling are set to 380 rpm and 45 min respectively. Through ball milling, the above four powders are fully mixed evenly.

[0034] Step 3: Take out 10 g of the powders mixed evenly in Step 2 and place them in an alumina crucible. The alumina crucible is covered with an alumina ceramic sheet to avoid damage to the heat treatment furnace caused by the volatilization of halogen elements during the subsequent heat treatment process. Place the encapsulated alumina crucible in the constant temperature zone of a muffle furnace. The muffle furnace uses silicon carbide rods as heating elements. Program control to slowly heat up to 930 °C at a rate of 3 °C / min and hold for 5 h, then program control to slowly cool down to 500 °C at a rate of 3 °C / min. Subsequently, turn off the power of the muffle furnace and let it cool naturally to room temperature to complete the transformation of the organic precursor into inorganic oxide (Hf 0.5 Zr 0.5 )O 2 whiskers.

[0035] Step 4, Place the heat-treated mixed powder in a beaker, add 500 mL of deionized water to the beaker, seal the beaker with plastic wrap, place the sealed beaker in the constant temperature zone of a hot plate, set the temperature of the hot plate to 300 °C, heat the deionized water in the beaker to boiling and maintain the boiling state for 5 min to fully dissolve the three inorganic salts of NaCl, Na 3 PO 4 , NH 4 F. Subsequently, use a vacuum filtration apparatus to separate the undissolved multi-component ultra-high temperature oxide (Hf 0.5 Zr 0.5 )O 2 whiskers from the deionized water dissolving the three inorganic salts of NaCl, Na 3 PO 4 , NH 4 F. Finally, place the separated multi-component ultra-high temperature oxide (Hf 0.5 Zr 0.5 )O 2 whiskers in an electrothermal blast drying oven at 70 °C for drying for 12 h to complete the preparation of the multi-component ultra-high temperature oxide (Hf 0.5 Zr 0.5 )O 2 whiskers.

[0036] Analyze the micro-morphology of the prepared multi-component ultra-high temperature oxide (Hf 0.5 Zr 0.5 )O 2 whiskers ( Figure 2 (b) in), the average aspect ratio of the (Hf 0.5 Zr 0.5 )O 2 whiskers prepared in this example is 7.47 ± 2.45, proving the successful preparation of the multi-component ultra-high temperature oxide (Hf 0.5 Zr 0.5 )O 2 whiskers.

[0037] Example 3 Step 1, Place 170 g of anhydrous ethanol, 16 g of citric acid monohydrate, and 8 g of polyethylene glycol in a three-necked flask, add a magnetic stirrer bar to the three-necked flask and place it in a magnetic stirrer, heat the flask to 60 °C and stir magnetically for 60 min to fully dissolve the citric acid monohydrate to form a colorless and clear solution. Subsequently, add 0.005 mol of HfCl 4 and 0.015 mol of ZrCl 4Slowly add it to the solution evenly mixed in Step 1, and further heat the three-necked flask to 70 °C and continue magnetic stirring for 5 h to obtain a milky white sol. Pour the sol into a beaker and place it in an electrothermal blast drying oven at 175 °C for 22 h to stand still, fully remove the solvent in the sol to form a yellowish-brown xerogel, and obtain an organic precursor of multi-component ultra-high temperature oxide (Hf 0.25 Zr 0.75 )O 2 .

[0038] Step 2, Weigh the organic precursor prepared in Step 1, NaCl, Na 3 PO 4 , NH 4 F three inorganic salts according to the mass ratio of 10:12:1:1.84 and place them in a polytetrafluoroethylene ball milling jar. Use zirconia balls as grinding media for planetary ball milling. The planetary ball milling speed and ball milling time are set to 400 rpm and 60 min respectively. Through ball milling, the above four powders are fully mixed evenly.

[0039] Step 3, Take out 10 g of the evenly mixed powder in Step 2 and place it in an alumina crucible. The alumina crucible is covered with an alumina ceramic sheet to avoid damage to the heat treatment furnace caused by the volatilization of halogen elements during the subsequent heat treatment process. Place the encapsulated alumina crucible in the constant temperature zone of a muffle furnace. The muffle furnace uses silicon carbide rods as heating elements. Program control is used to slowly heat up to 940 °C at a rate of 3 °C / min and hold for 5 h, and then program control is used to slowly cool down to 500 °C at a rate of 3 °C / min. Subsequently, the muffle furnace is powered off and naturally cooled to room temperature to complete the transformation of the organic precursor into inorganic oxide (Hf 0.25 Zr 0.75 )O 2 whiskers.

[0040] Step 4, Place the heat-treated mixed powder in a beaker, add 500 mL of deionized water to the beaker, seal the beaker with plastic wrap, place the sealed beaker in the constant temperature zone of a hot plate, and the temperature of the hot plate is set to 300 °C. Heat the deionized water in the beaker to boiling and keep it boiling for 5 min to fully dissolve NaCl, Na 3 PO 4 , NH 4 F three inorganic salts. Subsequently, use a vacuum filtration device to filter out the undissolved multi-component ultra-high temperature oxide (Hf 0.25 Zr 0.75 )O 2 whiskers and the dissolved NaCl, Na 3 PO 4 , NH 4Separate the deionized water of three kinds of inorganic salts. Finally, place the separated multi-component ultra-high temperature oxide (Hf 0.25 Zr 0.75 )O 2 whiskers in an electrothermal blast drying oven at 70 °C for 12 h to complete the preparation of the multi-component ultra-high temperature oxide (Hf 0.25 Zr 0.75 )O 2 whiskers.

[0041] Perform a microscopic morphology analysis on the prepared multi-component ultra-high temperature oxide (Hf 0.25 Zr 0.75 )O 2 whiskers ( Figure 2 (c)). In this example, the prepared (Hf 0.25 Zr 0.75 )O 2 whiskers have relatively uniform sizes, and their average aspect ratio is 9.86 ± 3.15, proving the successful preparation of the multi-component ultra-high temperature oxide (Hf 0.25 Zr 0.75 )O 2 whiskers.

[0042] Comparative example Step 1: Place 180 g of absolute ethanol, 16 g of citric acid monohydrate, and 8 g of polyethylene glycol in a three-necked flask. Add a magnetic stir bar to the three-necked flask and place it on a magnetic stirrer. Heat the flask to 55 °C and stir magnetically for 45 min to fully dissolve the citric acid monohydrate to form a colorless and clear solution. Subsequently, slowly add 0.01 mol of HfCl 4 and 0.01 mol of ZrCl 4 to the solution mixed evenly in Step 1. Further heat the three-necked flask to 70 °C and continue magnetic stirring for 5 h to obtain a milky white sol. Pour the sol into a beaker and place it in an electrothermal blast drying oven at 170 °C for 18 h to fully remove the solvent in the sol to form a yellowish-brown xerogel, obtaining the organic precursor of the multi-component ultra-high temperature oxide (Hf 0.5 Zr 0.5 )O 2 .

[0043] Step 2: Weigh the organic precursor obtained in Step 1, NaCl, and Na 3 PO 4 two inorganic salts in a mass ratio of 10:12:1 and place them in a polytetrafluoroethylene ball milling jar. Use zirconia balls as grinding media for planetary ball milling. The planetary ball milling speed and ball milling time are set to 380 rpm and 45 min respectively. Through ball milling, the above four powders are fully mixed evenly.

[0044] Step 3: Take out 10 g of the uniformly mixed powder in Step 2 and place it in an alumina crucible. The alumina crucible is covered with an alumina ceramic sheet to prevent damage to the heat treatment furnace caused by the volatilization of halogen elements during subsequent heat treatment. Place the encapsulated alumina crucible in the isothermal zone of a muffle furnace. The muffle furnace uses silicon carbide rods as heating elements. Program control is used to slowly heat up to 930 °C at a rate of 3 °C / min and hold for 5 h, and then program control is used to slowly cool down to 500 °C at a rate of 3 °C / min. Subsequently, the muffle furnace is powered off and naturally cooled to room temperature to complete the transformation of the organic precursor into inorganic oxide (Hf 0.5 Zr 0.5 )O 2 whiskers.

[0045] Step 4: Place the heat-treated mixed powder in a beaker, add 500 mL of deionized water to the beaker, seal the beaker with plastic wrap, place the sealed beaker in the isothermal zone of a hot plate, and set the temperature of the hot plate to 300 °C. Heat the deionized water in the beaker to boiling and keep it boiling for 5 min to fully dissolve the two inorganic salts, NaCl and Na 3 PO 4 . Subsequently, use a vacuum filtration apparatus to separate the undissolved multi-component ultra-high temperature oxide (Hf 0.5 Zr 0.5 )O 2 whiskers from the deionized water in which NaCl and Na 3 PO 4 are dissolved. Finally, place the separated multi-component ultra-high temperature oxide (Hf 0.5 Zr 0.5 )O 2 whiskers in an electrothermal blast drying oven at 70 °C for drying for 12 h to complete the preparation of the multi-component ultra-high temperature oxide (Hf 0.5 Zr 0.5 )O 2 whiskers.

[0046] Analyze the microscopic morphology of the prepared multi-component ultra-high temperature oxide (Hf 0.5 Zr 0.5 )O 2 whiskers ( Figure 4 ). In this example, the prepared (Hf 0.5 Zr 0.5 )O 2 whiskers do not have typical one-dimensional characteristics and present a morphological feature of a large number of irregularly shaped particles stacked, proving that the introduction of the whisker growth catalyst NH 4 F and its synergistic effect with Na 3 PO 4 for (Hf-Zr)O in the present invention2 The preparation of multi - component oxide whiskers is necessary.

[0047] Test example: Figure 1 For the multi - component ultra - high temperature oxide (Hf - Zr)O in the present invention 2 Schematic diagram of the preparation process flow of whiskers; Figure 2 For the multi - component ultra - high temperature oxide (Hf - Zr)O prepared by the present invention 2 Micro - morphology of whiskers. The (Hf 0.75 Zr 0.25 )O 2 whiskers ( Figure 2 in (a)) exhibit a typical needle - like morphology, the whisker size is uniform, and the average aspect ratio of the whiskers is 9.10 ± 2.38. The (Hf 0.5 Zr 0.5 )O 2 whiskers ( Figure 2 in (b)) have a slightly different microstructure from that of Example 1. In addition to the whiskers with needle - like morphology, hexagonal particles can also be observed. The length of the whiskers is relatively short and the size uniformity is slightly worse than that of Example 1. The average aspect ratio of the whiskers is 7.47 ± 2.45. The multi - component ultra - high temperature oxide (Hf 0.25 Zr 0.75 )O 2 whiskers ( Figure 2 in (c)) have a microstructure close to that of Example 1. Compared with Example 2, the number of hexagonal particles decreases. The length of the whiskers is the largest among the three examples, the size uniformity of the whiskers is the worst, and the average aspect ratio of the whiskers is 9.86 ± 3.15. The formation mechanism of the whiskers is attributed to the fact that during the heat treatment process, the nano - oxide particles transformed from the organic precursor can dissolve and precipitate in the molten salt, and directional growth to form whiskers due to the catalytic effect of fluorine element during the precipitation process.

[0048] Figure 3 For the (Hf 0.25 Zr 0.75 )O 2 EDS elemental surface distribution map of whiskers prepared by the present invention. The Hf element and Zr element inside the whiskers show uniform distribution at the micron scale, which benefits from the sol - gel technology that can achieve uniform mixing of Hf element and Zr element in the precursor at the atomic scale.

[0049] Figure 4 For the (Hf 0.5 Zr 0.5 )O 2 micro - structure of whiskers prepared according to the specific implementation manner described in Example 4 of the present invention. The whisker growth catalyst NH is not introduced4 (Hf 0.5 Zr 0.5 )O 2 whiskers do not have a typical one-dimensional structure but present an irregular particle morphology, thus proving that NH 4 F and Na 3 PO 4 synergy is the key to promoting the formation of the one-dimensional structure of whiskers. Therefore, it is necessary to introduce NH 4 F as a catalyst for the directional growth of whiskers.

[0050] The above content is only to illustrate the technical idea of the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution according to the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A multi-component ultra-high temperature oxide whisker, characterized in that: The chemical formula is (Hf x Zr 1-x )O2, the morphology is micron-sized needle-like, and the average aspect ratio of the oxide whiskers is 5.0~13.

1.

2. A method for preparing the multi-component ultrahigh temperature oxide whiskers according to claim 1, characterized in that: The following steps are involved: (1) The organic precursor of Hf-Zr oxide solid solution was prepared by sol-gel method; (2) mixing and grinding the organic precursor, molten salt and catalyst powder to form a mixed powder; (3) The mixed powder is heated to perform heat treatment, and after the heat treatment is completed, the mixed powder is washed, filtered, and dried to obtain the multi-component ultra-high temperature oxide whiskers.

3. The method for preparing multi-component ultrahigh temperature oxide whiskers according to claim 2, characterized in that: In the step (1), polyethylene glycol and citric acid monohydrate are used as chelating agents, and anhydrous ethanol is used as a solvent; the mass ratio of anhydrous ethanol, citric acid monohydrate and polyethylene glycol is (10-12):1:0.

5.

4. The method for preparing multi-component ultrahigh temperature oxide whiskers according to claim 3, characterized in that: In the step (1), the chelating agent is first dissolved in anhydrous ethanol to form a chelating agent solution, and then HfCl4 and ZrCl4 are added to the chelating agent solution, and the solution is heated to 65-75°C and stirred for 5-6 hours to form a gel.

5. The method for preparing multi-component ultrahigh temperature oxide whiskers according to claim 2 or claim 3, characterized in that: The molar ratio of HfCl4 and ZrCl4 is (1 / 3~3):

1.

6. The method for preparing multi-component ultrahigh temperature oxide whiskers according to claim 2, characterized in that: The molten salt in step (2) is NaCl, and the catalysts are Na3PO4 and NH4F.

7. The method for preparing multi-component ultrahigh temperature oxide whiskers according to claim 6, characterized in that: The mass ratio of the organic precursor to NaCl, Na3PO4, and NH4F is 10:(10-12):1:1.84, and the mixture is mixed in a planetary ball mill at a speed of 350-400 rpm for 30-60 min.

8. The method for preparing multi-component ultrahigh temperature oxide whiskers according to claim 2, characterized in that: The heat treatment temperature in step (3) is 900-950°C.

9. The method for preparing multi-component ultrahigh temperature oxide whiskers according to claim 2 or claim 8, characterized in that: The heat treatment process described in step (3) is: heating to the heat treatment temperature at a rate of 3°C / min, keeping the temperature for 4.5-5.5 hours, then cooling to 480-520°C at a rate of 3°C / min, and then naturally cooling to room temperature.

10. Application of the multi-component ultra-high temperature oxide whiskers according to claim 1 or prepared according to claims 2-9 in thermal protection materials, characterized in that: Used as matrix reinforcement material for ceramic matrix composites.

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