A method for synthesizing monoclinic hafnium dioxide nanorods and their applications

Abstract

This invention discloses a method for synthesizing monoclinic hafnium dioxide nanorods. The method uses hafnium oxide and potassium hydrofluoric acid as raw materials, and synthesizes uniform monoclinic hafnium dioxide nanorods through a two-step process of high-temperature calcination and subsequent hydrolysis. This method utilizes common, simple, and readily available raw materials, has a short reaction time and low reaction temperature, avoids complex procedures, and simplifies the process. The synthesized monoclinic hafnium dioxide nanorods are uniform in size and exhibit minimal agglomeration. This invention also discloses the application of the monoclinic hafnium dioxide nanorods synthesized by the above method in coating plastic or metal surfaces.

Description

Technical Field

[0001] This invention belongs to the field of nano-multifunctional materials technology, specifically relating to a method for synthesizing monoclinic hafnium dioxide (HfO2) nanorods and their applications, particularly a method for synthesizing monoclinic hafnium dioxide nanorods with uniform particle size and the application of hafnium dioxide nanorods in coating plastic or metal surfaces. Background Technology

[0002] Nanomaterials, due to their unique physical and chemical properties that differ from mesoscopic and microscopic materials, have broad application prospects in fields such as chemistry, biology, environment, optics, electronics, information, and new energy. With the rapid development of nanoscience and nanomaterials research in the past decade, various morphological characteristics and corresponding functions of nanomaterials have been discovered one after another, which has further promoted the synthesis, preparation, and development of more new nanomaterials with different morphological characteristics.

[0003] Hafnium dioxide (HfO2) is a crucial structural and functional material with excellent physical and chemical properties, including a high melting point (approximately 2900℃), high hardness, wide bandgap, high dielectric constant, good thermal and chemical stability, excellent resistance to laser damage, good transparency in the ultraviolet to infrared bands, high refractive index, and low extinction coefficient. Therefore, hafnium dioxide is widely used in optical thin films, high-performance devices, high-energy lasers, fast-ion conductor fuel cells, oxygen sensors, refractory materials, oxygen-insulating material coatings, and control rods for nuclear reactors. It also holds promise for applications in broader fields such as automotive exhaust and atmospheric environmental monitoring, fuel cells, and metallurgy. Furthermore, hafnium dioxide dielectric materials possess a simple cubic crystal structure, a wide bandgap, a high k-value, a significant conduction band shift and bandgap advantage over silicon, and good thermodynamic stability and lattice matching with silicon. It is currently one of the most promising new high-k gate dielectric materials to replace silicon dioxide and is attracting increasing attention.

[0004] Compared to other nano-oxide functional materials, there are not many methods for preparing and synthesizing nano-hafnium dioxide, which can be summarized as hydrothermal method, chemical vapor deposition method, sol-gel method and physical vapor deposition method.

[0005] In the above synthesis processes, a variety of reagents are used, including hafnium raw materials, precipitants, stabilizers, and solvents. Currently used hafnium raw materials include hafnium dichloride hexahydrate (HfCl2·6H2O), hafnium sulfate tetrahydrate (Hf(SO4)2·4H2O), hafnium oxychloride octahydrate (HfOCl2·8H2O), hafnium chloride (HfCl4), isobutoxy hafnium, and metallic Hf and / or hafnium dioxide, with some inorganic or organic reagents used as auxiliary reagents (such as hydrochloric acid, borax, polyethylene glycol, ethanol, octadecyltrichlorosilane, acetone, toluene, etc.). Therefore, in the existing process for synthesizing nano hafnium dioxide, the types of hafnium source materials used are relatively limited, and the products are prone to agglomeration. There is a need to further develop new high-quality and inexpensive hafnium source materials to obtain better products. At the same time, the existing process uses a variety of inorganic and organic reagents, some of which are rare and expensive, increasing the synthesis cost and making the synthesis process too complex. There is also an urgent need to simplify the synthesis process to reduce the synthesis cost. Summary of the Invention

[0006] The present invention aims to provide a method for synthesizing monoclinic hafnium dioxide nanorods. The method uses micron-sized hafnium dioxide powder and potassium hydrofluoric acid as raw materials, and synthesizes monoclinic hafnium dioxide nanorods through a two-step process of high-temperature calcination and subsequent hydrolysis. The monoclinic hafnium dioxide nanorods have uniform particles and are basically free of agglomeration.

[0007] Another objective of this invention is to provide the application of monoclinic hafnium dioxide nanorods synthesized by the above method in coating plastic or metal surfaces.

[0008] The first objective of this invention can be achieved through the following technical solution: a method for synthesizing monoclinic hafnium dioxide nanorods, comprising the following steps:

[0009] (1) Using hafnium dioxide and potassium hydrofluoric acid powder as initial raw materials, place the two raw materials in a container and cover it. Heat the container and adjust the heating temperature to 350-400℃ for 0.25-1 hour to allow the solid powder to fully melt and react. After the reaction, cool the container and add dilute hydrofluoric acid solution to the container. Heat the container again to boiling and stir continuously until the solid in the container is completely dissolved. Stop heating.

[0010] (2) Filter the solution in the container while it is still hot and collect the filtrate;

[0011] (3) Dilute the filtrate obtained in step (2) with deionized water to obtain a dilute solution. Place the dilute solution in a hydrothermal reaction vessel, seal it, and heat the hydrothermal reaction vessel. Adjust the temperature inside the hydrothermal reaction vessel to 150-500℃. Adjust the pressure inside the hydrothermal reaction vessel to 10-100MPa by injecting inert gas into the hydrothermal reaction vessel. The reaction time is 10-15 hours. After the reaction, cool it rapidly to room temperature.

[0012] (4) Open the hydrothermal reaction vessel and obtain monoclinic hafnium dioxide nanorods through subsequent processing.

[0013] This invention uses micron-sized hafnium dioxide powder and potassium hydrofluoric acid as raw materials to synthesize uniform monoclinic hafnium dioxide nanorods through a two-step method of high-temperature calcination and subsequent hydrolysis. The entire process uses only four inorganic reagents: hafnium dioxide, potassium hydrofluoric acid, hydrofluoric acid, and ethanol. The raw materials are common, simple, and readily available. The reaction time is extremely short, and the reaction temperature is low, avoiding complex processes and simplifying the technology. The synthesized monoclinic hafnium dioxide nanorods are uniform in size and show virtually no agglomeration.

[0014] In the above method for synthesizing monoclinic hafnium dioxide nanorods:

[0015] Optionally, the mass ratio of hafnium dioxide and potassium hydrofluoric acid in step (1) is 1:2 to 3.

[0016] Optionally, the volume percentage of the dilute hydrofluoric acid solution in step (1) is 3-8%, more preferably 5%, and the amount added is 40-60%, more preferably 50%, of the total volume of the container.

[0017] Optionally, the container in step (1) is a crucible, which is a nickel-based alloy crucible or a precious metal crucible.

[0018] Optionally, a Teflon stirring rod may be used for stirring in step (1).

[0019] More preferably, in step (1), the container is heated to 350°C for 0.5 hours.

[0020] Optionally, in step (2), a silver evaporating dish or an evaporating dish with a Teflon liner is used to collect the filtrate.

[0021] Optionally, the molar concentration of the dilute solution in step (3) is 0.01 to 0.02 mol / L.

[0022] More preferably, the reaction temperature described in step (3) is 250–350 °C.

[0023] Optionally, the inert gas in step (3) is argon or helium.

[0024] Optionally, the reaction time mentioned in step (3) includes the time required for heating.

[0025] Optionally, the rapid cooling described in step (3) is to rapidly cool the hydrothermal reaction vessel using ice water or compressed air.

[0026] In one preferred embodiment of the present invention, in step (3), the dilute solution is directly added to the hydrothermal reaction vessel, and the volume of the dilute solution accounts for 30-80% of the total volume of the hydrothermal reaction vessel; the hydrothermal reaction vessel is a hydrothermal reactor, which is a sealed high-temperature and high-pressure reactor. The high-temperature and high-pressure reactor is connected to a high-precision ultra-high-pressure pressure gauge, a vent pipe, and a shut-off valve. The high-temperature and high-pressure reactor has a metal shell, and the metal shell is provided with a strong acid and strong alkali resistant liner. The strong acid and strong alkali resistant liner is made of polytetrafluoroethylene, polyphenylene ester, or polyimide plastic, or the strong acid and strong alkali resistant liner is made of silver, gold, or platinum inert metal, or the strong acid and strong alkali resistant liner is made of gold-palladium or silver-palladium alloy.

[0027] Optionally, the hydrothermal reactor is a conventional hydrothermal reactor, the sealed high-temperature and high-pressure reactor is a conventional sealed high-temperature and high-pressure reactor, and the metal shell is conventional stainless steel or Hastelloy.

[0028] When using this technical solution, optionally, in step (4), opening the hydrothermal reaction vessel and obtaining monoclinic hafnium dioxide nanorods through subsequent processing includes: opening the hydrothermal reaction vessel, recovering the residual solution in the hydrothermal reaction vessel, washing the inner wall of the hydrothermal reaction vessel with deionized water, collecting the washing fluid to obtain nano hafnium dioxide turbid liquid, centrifuging the obtained turbid liquid, taking the lower layer precipitate, washing and drying the lower layer precipitate to obtain monoclinic hafnium dioxide nanorods with uniform particle size.

[0029] When using this technical solution, optionally, the bottom of the hydrothermal reaction vessel in step (3) is provided with a sample collection plate, which is a sample collection plate made of plastic or inert metal; the step (4) of opening the hydrothermal reaction vessel and obtaining monoclinic hafnium dioxide nanorods through subsequent processing includes: opening the hydrothermal reaction vessel, recovering the residual solution in the hydrothermal reaction vessel, taking out the sample collection plate, washing and drying, and then preparing monoclinic hafnium dioxide nanorods with uniform particle size on the surface of the sample collection plate.

[0030] Optionally, the plastic is polytetrafluoroethylene, polyphenylene oxide, polyimide, etc., and the inert metal is silver, gold, or platinum, etc.

[0031] Optionally, the cleaning or washing process involves washing with deionized water and anhydrous ethanol 2 to 3 times in succession.

[0032] Alternatively, drying can be achieved by air drying or storage in a desiccator.

[0033] Therefore, in order to directly deposit nano hafnium dioxide on plastic or metal, the plastic or inert metal can also be placed at the bottom of the hydrothermal reaction vessel described in step (3) of this invention.

[0034] As another preferred technical solution of the present invention, in step (3), the dilute solution is first added to the precious metal vessel, and then the precious metal vessel is placed in the hydrothermal reaction vessel. The precious metal is silver, gold or platinum; or the precious metal is gold-palladium or silver-palladium alloy. The high-temperature and high-pressure reactor is connected to a high-precision ultra-high pressure gauge, a gas pipeline and a shut-off valve. The high-temperature and high-pressure reactor has a metal shell.

[0035] When using this technical solution, optionally, in step (4), opening the hydrothermal reaction vessel and obtaining monoclinic hafnium dioxide nanorods through subsequent processing includes: opening the hydrothermal reactor, taking out the precious metal vessel, recovering the residual solution in the precious metal vessel, washing the inner wall of the precious metal vessel with deionized water, collecting the washing fluid to obtain nano hafnium dioxide turbid liquid, centrifuging the obtained turbid liquid, taking the lower precipitate, washing and drying the lower precipitate to obtain monoclinic hafnium dioxide nanorods.

[0036] Optionally, the cleaning process involves washing with deionized water and anhydrous ethanol 2 to 3 times.

[0037] Alternatively, drying can be achieved by air drying or storage in a desiccator.

[0038] Optionally, the residual solution is mainly composed of potassium hexafluorohafnium acid, hydrofluoric acid, and potassium fluoride.

[0039] The first objective of the present invention can be achieved by the following technical solution: the application of monoclinic hafnium dioxide nanorods synthesized by the above method in coating on plastic or metal surfaces.

[0040] The plastics include organic plastics such as polytetrafluoroethylene, polyphenylene oxide, and polyimide, and the metals include common stainless steel, nickel-based alloys, molybdenum-based alloys, gold, silver, copper, and platinum.

[0041] The core of the hafnium dioxide nanorod preparation method of the present invention lies in synthesizing potassium hexafluorohafnate from hafnium dioxide and potassium hydrofluoric acid at high temperature, and then generating nano hafnium dioxide crystals by hydrolysis of potassium hexafluorohafnate. By controlling the temperature, pressure and fluorine fugacity, monoclinic hafnium dioxide short rod-shaped nanocrystals with uniform particle size can be produced.

[0042] Using readily available and relatively inexpensive nano-hafnium dioxide powder as the hafnium source, the following melting reaction first occurs between hafnium dioxide and potassium hydrofluoric acid at high temperature:

[0043] HfO2+4KHF2→K2HfF6+2HF↑+2H2O↑

[0044] The final products of the reaction are potassium hexafluorohafnate and excess potassium hydrofluoric acid. The potassium hexafluorohafnate is redissolved by adding dilute hydrofluoric acid solution, and then separated from the potassium hydrofluoric acid by repeated filtration and recrystallization, thus obtaining a high-purity potassium hexafluorohafnate filtrate.

[0045] Then, deionized water was added to the potassium hexafluorohafnate filtrate to prepare a dilute potassium hexafluorohafnate solution. The dilute potassium hexafluorohafnate solution was placed in a hydrothermal reactor, and the reactor was heated and pressurized. Under hydrothermal conditions, potassium hexafluorohafnate reacted with water in the following hydrolysis reaction:

[0046] K₂HfF₆ + 2H₂O → HfO₂↓ + 4HF + 2KF

[0047] After the reaction is complete, the hydrothermal reactor is rapidly cooled to room temperature. The obtained precipitate is then washed and dried to obtain a monoclinic hafnium dioxide nanorod sample.

[0048] In the method for preparing hafnium dioxide nanorods of the present invention, the core reagents used are hafnium dioxide and potassium hydrofluoride, avoiding the complex process of using multiple raw materials such as hafnium source + precipitant ± stabilizer ± solvent in the existing process. Potassium hexafluorohafnate synthesized by melting hafnium dioxide and potassium hydrofluoride undergoes hydrolysis to generate hafnium dioxide nanocrystals and hydrogen fluoride. The fluoride ions generated by the ionization of hydrogen fluoride adsorb onto the (111) and (200) surfaces of the hafnium dioxide nanocrystals, reducing the surface energy of the (111) and (200) surfaces and promoting the growth of the (111) and (200) surfaces; at the same time, hydrogen fluoride dissolves the development of other crystal faces of the hafnium dioxide crystals, thereby finally synthesizing rod-shaped hafnium dioxide crystals with well-developed (111) and (200) surfaces and weaker development of other crystal faces. Since the potassium hexafluorohafnium hydrolysis reaction in step (3) of this invention is an incomplete reaction, the recovery solution in step (4) of this invention mainly contains potassium hexafluorohafnium, potassium fluoride and hydrogen fluoride. A certain amount of hafnium dioxide powder is added to the recovery solution, and the obtained recovery solution can continue to be used as the initial raw material of this invention. On the one hand, it can effectively recover and reduce costs, and on the other hand, it can eliminate hydrofluoric acid pollution and maintain process safety.

[0049] Compared with the prior art, the synthesis method of the present invention has the following beneficial effects:

[0050] (1) The synthesis method of the present invention uses common and inexpensive nano hafnium dioxide powder and potassium hydrofluoric acid reagent. Potassium hexafluorohafnate is synthesized by high-temperature calcination of the two initial reagents. Short rod-shaped hafnium dioxide nanocrystals are generated by the hydrolysis reaction of potassium hexafluorohafnate under hydrothermal conditions. Thus, hafnium dioxide nanocrystals with specific morphology can be prepared by simple common reagents, which expands and enriches the preparation process of hafnium dioxide nanomaterials.

[0051] (2) The synthesis method of the present invention only requires four common and inexpensive reagent raw materials: hafnium dioxide, potassium hydrofluoric acid, hydrofluoric acid and ethanol. It avoids the need for the proportioning and weighing of various expensive precursors, precipitants, stabilizers and solvents and other morphology control agents and the sequential process steps in the traditional process. Therefore, the method is simple, easy to operate and control, and relatively low in cost.

[0052] (3) The recovery solution obtained by the synthesis method of the present invention mainly contains potassium hexafluorohafnium, potassium fluoride and hydrogen fluoride. Hafnium dioxide powder is added to the recovery solution for further treatment, and potassium fluoride and hydrofluoric acid can be further synthesized into potassium hexafluorohafnium. Therefore, the recovered solution can be used as the initial raw material of the present invention. On the one hand, it can effectively recover and reduce costs, and on the other hand, it can eliminate hydrofluoric acid pollution and maintain process safety.

[0053] (4) The synthesis method of the present invention uses common and inexpensive hafnium dioxide and potassium hydrofluoric acid reagents to synthesize pure potassium hexafluorohafnium acid crystals through two initial reagents. Potassium hexafluorohafnium acid can be used as an intermediate product for the preparation of hafnium dioxide nanorods or as an additional chemical product. Attached Figure Description

[0054] Figure 1 This is the XRD powder diffraction pattern of the filtrate condensate in Example 1 of the present invention. The arrows represent the main diffraction peaks of potassium hexafluorohafnium acid.

[0055] Figure 2 The images shown are micrographs (a) to (b) and scanning electron microscope images (c) to (d) at different magnifications of the hafnium dioxide nanorod coating prepared in Example 1 of this invention, wherein (a) is magnified 50 times, (b) is magnified 400 times, (c) is magnified 20,000 times, and (d) is magnified 50,000 times.

[0056] Figure 3 The images are scanning electron microscope (SEM) images (a) to (d) of the hafnium dioxide nanorod sample prepared in Example 2 of the present invention at different magnifications, where (a) is magnified by 15,000 times, (b) by 12,000 times, (c) by 40,000 times, and (d) by 6,000 times.

[0057] Figure 4 The images are scanning electron microscope (SEM) images (a) to (d) of the hafnium dioxide nanorod sample prepared in Example 3 of the present invention at different magnifications, where (a) is magnified 4,000 times, (b) is magnified 10,000 times, (c) is magnified 15,000 times, and (d) is magnified 30,000 times.

[0058] Figure 5The images (a) to (d) are scanning electron microscope images of hafnium dioxide nanorods prepared in Example 4 of this invention at different magnifications, where (a) is magnified 10,000 times, (b) is magnified 10,000 times, (c) is magnified 15,000 times, and (d) is magnified 40,000 times.

[0059] Figure 6 The images shown are micrographs (a) to (b) and scanning electron microscope images (c) to (d) at different magnifications of the hafnium dioxide nanorod coating prepared in Example 5 of this invention, wherein (a) is magnified 50 times, (b) is magnified 400 times, (c) is magnified 4,000 times, and (d) is magnified 15,000 times.

[0060] Figure 7 The images shown are micrographs (a) to (b) and scanning electron microscope images (c) to (d) at different magnifications of the hafnium dioxide nanorod coating prepared in Example 6 of this invention, wherein (a) is magnified 50 times, (b) is magnified 400 times, (c) is magnified 4,000 times, and (d) is magnified 6,000 times.

[0061] Figure 8 The images (a) to (d) are scanning electron microscope images of hafnium dioxide nanorods prepared in Example 7 of the present invention at different magnifications, where (a) is magnified 2,500 times, (b) is magnified 6,000 times, (c) is magnified 10,000 times, and (d) is magnified 20,000 times.

[0062] Figure 9 Comparison of laser Raman spectra of hafnium dioxide nanorod samples and standard hafnium dioxide powder under different conditions for this invention;

[0063] Figure 10 The following are μ-XRD powder diffraction patterns of hafnium dioxide nanorod samples under different conditions according to the present invention: (1) is the result of the monoclinic hafnium dioxide nanorod sample synthesized in Example 1 of the present invention; (2) is the result of the monoclinic hafnium dioxide nanorod sample synthesized in Example 2 of the present invention; (3) is the result of the monoclinic hafnium dioxide nanorod sample synthesized in Example 3 of the present invention; (4) is the result of the monoclinic hafnium dioxide nanorod sample synthesized in Example 4 of the present invention; (5) is the result of the monoclinic hafnium dioxide nanorod sample synthesized in Example 5 of the present invention; and (6) is the result of the monoclinic hafnium dioxide nanorod sample synthesized in Example 6 of the present invention. The vertical axis Intensity (Counts) is calculated, and the horizontal axis Two-Theta (deg) is the diffraction angle. Detailed Implementation

[0064] The present invention will be further described below with reference to specific embodiments. The following embodiments are for illustrative purposes only and should not be construed as limiting the present invention. Unless otherwise specified, the raw materials used in the following embodiments are commercially available or conventionally traded materials, and the methods and equipment used in the following embodiments are conventionally used methods and equipment in the art.

[0065] The present invention will be further described below with reference to the embodiments and accompanying drawings, but the scope of protection of the present invention, such as the reaction apparatus, reaction temperature, reaction time and volume of the reaction liquid, is not limited to the embodiments described.

[0066] Example 1

[0067] The method for synthesizing monoclinic hafnium dioxide nanorods provided in this embodiment includes the following steps:

[0068] (1) Place 0.51g of hafnium dioxide (HfO2, 99.99% purity, micron-sized powder, Aladdin, the same below) and 1.02g of potassium hydrofluoric acid (KHF, 99% purity, Aladdin, the same below) powder into a silver crucible, cover it, place the silver crucible on an electric furnace, set the temperature of the electric furnace to 350℃, heat for half an hour to allow the solid powder to fully melt and react. After cooling slightly, open the crucible lid, add 5% hydrofluoric acid by volume to the crucible until it reaches half the volume of the crucible, continue to turn on the electric furnace to heat to boiling, and use a Teflon rod to stir continuously to make the solid in the crucible completely dissolve, and stop heating;

[0069] (2) While still hot, pour the solution from the crucible onto filter paper for filtration. Use a silver evaporating dish to collect the filtrate. Repeat the filtration process three times to obtain the filtrate. After condensation, the filtrate yields rod-shaped powder crystals. Figure 1 XRD analysis confirmed that it was potassium hexafluorohafnium acid crystals;

[0070] (3) The filtrate obtained in step (2) is diluted with deionized water to obtain a 0.01 mol / L reaction solution. The reaction solution is then loaded into a 200 mL hydrothermal reactor. The hydrothermal reactor is a common sealed high-temperature and high-pressure reactor. The high-temperature and high-pressure reactor is connected to a high-precision ultra-high pressure gauge, a gas pipeline, and gas inlet and outlet shut-off valves. The high-temperature and high-pressure reactor has a stainless steel or Hastelloy metal shell. A flat gold sheet is placed at the bottom of the reactor. After tightening the reactor, the outlet shut-off valve is closed and the inlet shut-off valve is opened. Argon gas is injected into the reactor through the gas pipeline to a pressure of 80 MPa. The gas inlet shut-off valve is closed to stop the gas injection. The reactor is heated by a heating furnace and the reaction temperature is set to 250°C. After the temperature reaches 250°C, the inlet shut-off valve in step (3) is opened and argon gas is injected to a pressure of 100 MPa. The reaction time is maintained for 12 hours. After the reaction is completed, the reactor in step (3) is cooled down to room temperature by pouring ice water over it.

[0071] (4) Open the gas outlet shut-off valve of the reactor in step (3) to release pressure, then open the reactor, recover the residual solution in the reactor, take out the gold sheet in the reactor in step (3), wash it with deionized water 2 to 3 times, and after air drying, a layer of hafnium dioxide coating can be seen on the surface of the gold sheet.

[0072] Figure 2 Image (a) and image (b) are photomicrographs of the coating layer at different magnifications; Figure 2 Figures (c) to (d) show scanning electron microscope images of hafnium dioxide at different magnifications. Morphologically, these hafnium dioxide nanocrystals are short columnar with a particle size of tens to 300 nanometers and are dispersed.

[0073] Figure 9 Laser Raman spectroscopy analysis showed that although there was significant fluorescence interference in the low-wavelength range, the laser Raman peak intensity of the nanocrystals synthesized at 250℃ was relatively obvious, exhibiting 10 Raman scattering peaks similar to those of standard hafnium dioxide powder, namely at 115 cm⁻¹. -1 138cm -1 151cm -1 258cm -1 385cm -1 500cm -1 582cm -1 641cm -1 and 672cm -1 This indicates that the short rod-shaped nanocrystals are hafnium dioxide crystals.

[0074] Figure 10XRD powder diffraction analysis showed that hafnium dioxide crystals are monoclinic and have multiple crystal planes such as (111), (200), (020), (022), and (300).

[0075] Example 2

[0076] The method for synthesizing monoclinic hafnium dioxide nanorods provided in this embodiment includes the following steps:

[0077] (1) The filtrate obtained in step (2) of Example 1 is diluted with deionized water to prepare a 0.01 mol / L reaction solution. 5 mL of the prepared reaction solution is put into a 4.5 mm diameter gold tube and then sealed. The gold tube is then placed into a high-temperature and high-pressure reactor. The high-temperature and high-pressure reactor is connected to a high-precision ultra-high pressure gauge, a gas pipe and a shut-off valve. The high-temperature and high-pressure reactor has a stainless steel or Hastelloy metal shell. After tightening the reactor, argon gas is injected into the reactor through the gas pipe to a pressure of 80 MPa. The shut-off valve is closed to stop the gas injection. The reactor is heated by a heating furnace and the reaction temperature is set to 300 °C. After the temperature rises to 300 °C, the shut-off valve is opened and argon gas is injected to a pressure of 100 MPa. The reaction time is maintained for 10 hours. After the reaction is completed, the reactor is cooled down to room temperature by pouring ice water over it.

[0078] (2) Open the reactor in step (1), take out the gold tube and break it open, recover the residual solution in the precious metal vessel, wash the inner wall of the gold tube with deionized water, collect the washing fluid to obtain nano hafnium dioxide turbid liquid, put the obtained turbid liquid in a centrifuge for centrifugation, after centrifugation, take out the lower precipitate and rinse it with deionized water 2-3 times, and finally air dry the precipitate to obtain monoclinic hafnium dioxide nano rods with uniform particle size.

[0079] Figure 3 Figures (a) to (d) show the morphology and particle size of hafnium dioxide nanorods at different magnifications, with particle sizes ranging from tens of nanometers to 400 nanometers.

[0080] Figure 9 Laser Raman spectroscopy analysis showed that although there was significant fluorescence interference in the low-wavelength range, the laser Raman peak intensity of the nanocrystals synthesized at 300℃ was relatively obvious, exhibiting 10 Raman scattering peaks similar to those of standard hafnium dioxide powder, namely at 115 cm⁻¹. -1 138cm -1 151cm -1 258cm -1 385cm -1 500cm -1 582cm -1 641cm -1 and 672cm -1This indicates that the short rod-shaped nanocrystals are hafnium dioxide crystals.

[0081] Figure 10 XRD powder diffraction analysis showed that hafnium dioxide crystals are monoclinic and have multiple crystal planes such as (111), (200), (020), (022), and (300).

[0082] Example 3

[0083] The method for synthesizing monoclinic hafnium dioxide nanorods provided in this embodiment includes the following steps:

[0084] (1) The filtrate obtained in step (2) of Example 1 is diluted with deionized water to obtain a 0.01 mol / L reaction solution. The obtained reaction solution is loaded into a 200 mL hydrothermal reactor. The hydrothermal reactor is a sealed high-temperature and high-pressure reactor. The high-temperature and high-pressure reactor is connected to a high-precision ultra-high pressure gauge, a gas pipeline, and gas inlet and outlet shut-off valves. The high-temperature and high-pressure reactor has a stainless steel or Hastelloy metal shell with a silver lining in the metal shell. A flat gold sheet is placed at the bottom of the reactor. After tightening the reactor, the outlet shut-off valve is closed and the inlet shut-off valve is opened. Argon gas is injected into the reactor through the gas pipeline to a pressure of 50 MPa. The gas inlet shut-off valve is closed to stop the gas injection. The reactor is heated by a heating furnace and the reaction temperature is set to 400℃. After the temperature rises to 400℃, the inlet shut-off valve is opened and argon gas is injected to a pressure of 80 MPa. The reaction time is maintained for 15 hours. After the reaction is completed, the reactor is cooled down to room temperature by pouring ice water over it.

[0085] (2) Open the gas outlet shut-off valve of the reactor in step (1) to release pressure, then open the reactor, recover the residual solution in the reactor, take out the gold sheet in the reactor, wash it with deionized water 2 to 3 times, and after air drying, a layer of hafnium dioxide coating can be seen on the surface of the gold sheet.

[0086] Figure 4 The scanning electron microscope image in (a) shows a hafnium dioxide nanofilm; Figure 4 Figures (b) to (d) are scanning electron microscope images of hafnium dioxide at different magnifications. Morphologically, these hafnium dioxide particles are relatively euhedral short rods with a particle size of 100 nm to 500 nm.

[0087] Figure 9 Laser Raman spectroscopy analysis showed that although there was significant fluorescence interference in the low-wavelength range, the laser Raman peak intensity of the nanocrystals synthesized at 400℃ was relatively obvious, exhibiting 10 Raman scattering peaks similar to those of standard hafnium dioxide powder, namely at 115 cm⁻¹. -1 138cm -1 151cm -1 258cm-1 385cm -1 500cm -1 582cm -1 641cm -1 and 672cm -1 This indicates that the short rod-shaped nanocrystals are hafnium dioxide crystals.

[0088] Figure 10 XRD powder diffraction analysis showed that hafnium dioxide crystals are monoclinic and have multiple crystal planes such as (111), (200), (020), (022), and (300).

[0089] Example 4

[0090] The method for synthesizing monoclinic hafnium dioxide nanorods provided in this embodiment includes the following steps:

[0091] (1) The filtrate obtained in step (2) of Example 1 is diluted with deionized water to prepare a 0.01 mol / L reaction solution. 5 mL of the prepared reaction solution is put into a 4.5 mm diameter gold tube and then sealed. The gold tube is then placed into a high-temperature and high-pressure reactor. The high-temperature and high-pressure reactor is connected to a high-precision ultra-high pressure gauge, a gas pipe and a shut-off valve. The high-temperature and high-pressure reactor has a stainless steel or Hastelloy metal shell. After tightening the reactor, argon gas is injected into the reactor through the gas pipe to a pressure of 80 MPa. The shut-off valve is closed to stop the gas injection. The reactor is heated by a heating furnace and the reaction temperature is set to 500 °C. After the temperature rises to 500 °C, the shut-off valve is opened and argon gas is injected to a pressure of 100 MPa. The reaction time is maintained for 12 hours. After the reaction is completed, the reactor is cooled down to room temperature by pouring ice water over it.

[0092] (2) Open the reactor in step (1), take out the gold tube and break it open. Wash the inner wall of the gold tube with deionized water and collect the washing fluid to obtain nano hafnium dioxide turbid liquid. Place the obtained turbid liquid in a centrifuge for centrifugation. After centrifugation, take out the lower precipitate and rinse it with deionized water 2-3 times. Finally, let the precipitate air dry naturally to obtain hafnium dioxide nano rods.

[0093] Figure 5 Figures (a) to (d) show the morphology and particle size of hafnium dioxide nanorods at different magnifications, with particle sizes ranging from 100 nm to 500 nm.

[0094] Figure 9 Laser Raman spectroscopy analysis showed that the nanocrystals synthesized at 500℃ exhibited significant laser Raman peak intensity, possessing 10 Raman scattering peaks similar to those of standard hafnium dioxide powder, namely at 115 cm⁻¹. -1 138cm -1 151cm-1 258cm -1 385cm -1 500cm -1 582cm -1 641cm -1 and 672cm -1 This indicates that the short rod-shaped nanocrystals are hafnium dioxide crystals.

[0095] Figure 10 XRD powder diffraction analysis showed that hafnium dioxide crystals are monoclinic and have multiple crystal planes such as (111), (200), (020), (022), and (300).

[0096] Example 5

[0097] The method for synthesizing monoclinic hafnium dioxide nanorods provided in this embodiment includes the following steps:

[0098] (1) The filtrate obtained in step (2) of Example 1 is diluted with deionized water to obtain a 0.02 mol / L reaction solution. The obtained reaction solution is loaded into a 200 mL hydrothermal reactor. The hydrothermal reactor is a sealed high-temperature and high-pressure reactor. The high-temperature and high-pressure reactor is connected to a high-precision ultra-high pressure gauge, a gas pipeline, and gas inlet and outlet shut-off valves. The high-temperature and high-pressure reactor has a stainless steel or Hastelloy metal shell with a silver lining in the metal shell. A flat gold sheet is placed at the bottom of the reactor. After tightening the reactor, the outlet shut-off valve is closed and the inlet shut-off valve is opened. Argon gas is injected into the reactor through the gas pipeline to a pressure of 80 MPa. The inlet shut-off valve is closed to stop the gas injection. The reactor is heated by a heating furnace and the reaction temperature is set to 300°C. After the temperature rises to 300°C, the inlet shut-off valve is opened and argon gas is injected to a pressure of 100 MPa. The reaction time is maintained for 12 hours. After the reaction is completed, the reactor is cooled down to room temperature by pouring ice water over it.

[0099] (2) Open the gas outlet shut-off valve of the reactor in step (1) to release pressure, then open the reactor, recover the residual solution in the reactor, take out the gold sheet in the reactor in step (1), wash it with deionized water 2-3 times, and after air drying, a hafnium dioxide coating can be seen on the surface of the gold sheet. Figure 5 Scanning electron microscope images (a) and (b) show hafnium dioxide nanofilms.

[0100] Figure 6 Figures (a) and (b) are micrographs of the coating layer at different magnifications, and figures (c) to (d) are scanning electron microscope images of hafnium dioxide at different magnifications. Morphologically, these hafnium dioxide particles are relatively euhedral short rods with a particle size of 200 nm to 800 nm.

[0101] Figure 9 Laser Raman spectroscopy analysis showed that the nanocrystals synthesized at 300℃ exhibited significant laser Raman peak intensity, possessing 10 Raman scattering peaks similar to those of standard hafnium dioxide powder, namely at 115 cm⁻¹. -1 138cm -1 151cm -1 258cm -1 385cm -1 500cm -1 582cm -1 641cm -1 and 672cm -1 This indicates that the short rod-shaped nanocrystals are hafnium dioxide crystals.

[0102] Figure 10 XRD powder diffraction analysis showed that hafnium dioxide crystals are monoclinic and have multiple crystal planes such as (111), (200), (020), (022), and (300).

[0103] Example 6

[0104] The method for synthesizing monoclinic hafnium dioxide nanorods provided in this embodiment includes the following steps:

[0105] (1) The filtrate obtained in step (2) of Example 1 is diluted with deionized water to obtain a 0.02 mol / L reaction solution. The obtained reaction solution is loaded into a 200 mL hydrothermal reactor. The hydrothermal reactor is a sealed high-temperature and high-pressure reactor. The high-temperature and high-pressure reactor is connected to a high-precision ultra-high pressure gauge, a gas pipeline, and gas inlet and outlet shut-off valves. The high-temperature and high-pressure reactor has a stainless steel or Hastelloy metal shell with a silver lining in the metal shell. A flat gold sheet is placed at the bottom of the reactor. After tightening the reactor, the outlet shut-off valve is closed and the inlet shut-off valve is opened. Argon gas is injected into the reactor through the gas pipeline to a pressure of 60 MPa. The gas inlet shut-off valve is closed to stop the gas injection. The reactor is heated by a heating furnace and the reaction temperature is set to 400℃. After the temperature rises to 400℃, the inlet shut-off valve is opened and argon gas is injected to a pressure of 80 MPa. The reaction time is maintained for 15 hours. After the reaction is completed, the reactor is cooled down to room temperature by pouring ice water over it.

[0106] (2) Open the gas outlet shut-off valve of the reactor in step (1) to release pressure, then open the reactor, recover the residual solution in the reactor, take out the gold sheet in the reactor in step (1), wash it with deionized water 2 to 3 times, and after air drying, a layer of hafnium dioxide coating can be seen on the surface of the gold sheet.

[0107] Figure 7 The scanning electron microscope images (a) and (b) show hafnium dioxide nanofilms; Figure 7Figures (c) to (d) are scanning electron microscope images of hafnium dioxide at different magnifications. Morphologically, these hafnium dioxide particles are relatively euhedral short rods with a particle size of 200 nm to 1500 nm.

[0108] Figure 9 Laser Raman spectroscopy analysis showed that the nanocrystals synthesized at 400℃ exhibited significant laser Raman peak intensity, possessing 10 Raman scattering peaks similar to those of standard hafnium dioxide powder, namely at 115 cm⁻¹. -1 138cm -1 151cm -1 258cm -1 385cm -1 500cm -1 582cm -1 641cm -1 and 672cm -1 This indicates that the short rod-shaped nanocrystals are hafnium dioxide crystals.

[0109] Figure 10 XRD powder diffraction analysis showed that hafnium dioxide crystals are monoclinic and have multiple crystal planes such as (111), (200), (020), (022), and (300).

[0110] Example 7

[0111] The method for synthesizing monoclinic hafnium dioxide nanorods provided in this embodiment includes the following steps:

[0112] (1) The filtrate obtained in step (2) of Example 1 is diluted with deionized water to prepare a 0.02 mol / L reaction solution. 5 mL of the prepared reaction solution is put into a 4.5 mm diameter gold tube and then sealed. The gold tube is then placed into a high-temperature and high-pressure reactor. The high-temperature and high-pressure reactor is connected to a high-precision ultra-high pressure gauge, a gas pipe and a shut-off valve. The high-temperature and high-pressure reactor has a stainless steel or Hastelloy metal shell. After tightening the reactor, argon gas is injected into the reactor through the gas pipe to a pressure of 80 MPa. The shut-off valve is closed to stop the gas injection. The reactor is heated by a heating furnace and the reaction temperature is set to 500 °C. After the temperature rises to 500 °C, the shut-off valve is opened and argon gas is injected to a pressure of 100 MPa. The reaction time is maintained for 12 hours. After the reaction is completed, the reactor is cooled down to room temperature by pouring ice water over it.

[0113] (2) Open the reactor in step (1), take out the gold tube in step (1) and break it open. Wash the inner wall of the gold tube with deionized water and collect the washing fluid to obtain nano hafnium dioxide turbid liquid. Place the obtained turbid liquid in a centrifuge for centrifugation. After centrifugation, take out the lower precipitate and rinse it with deionized water 2-3 times. Finally, let the precipitate air dry naturally to obtain hafnium dioxide nano rods.

[0114] Figure 8 Figures (a) to (d) show the morphology and particle size of hafnium dioxide nanorods at different magnifications, with particle sizes ranging from 200 nm to 1000 nm.

[0115] Figure 9 Laser Raman spectroscopy analysis showed that the nanocrystals synthesized at 500℃ exhibited significant laser Raman peak intensity, possessing 10 Raman scattering peaks similar to those of standard hafnium dioxide powder, namely at 115 cm⁻¹. -1 138cm -1 151cm -1 258cm -1 385cm -1 500cm -1 582cm -1 641cm -1 and 672cm -1 This indicates that the short rod-shaped nanocrystals are hafnium dioxide crystals.

[0116] The above embodiments are only used to illustrate the present invention, and the scope of protection of the present invention is not limited to the above embodiments. Those skilled in the art can achieve the purpose of the present invention based on the above disclosure. Any improvements and modifications made based on the concept of the present invention fall within the scope of protection of the present invention, and the specific scope of protection is determined by the claims.

Claims

1. A method for synthesizing monoclinic hafnium dioxide nanorods, characterized in that, The method comprises the following steps: (1) taking hafnium dioxide and potassium bifluoride powder as initial raw materials, placing the two raw materials in a container and covering, heating the container, adjusting the heating temperature to 350-400 DEG C, heating for 0.25-1 hour, so that the solid powder is fully molten and reacted, cooling after reaction, adding dilute hydrofluoric acid solution to the container, heating the container to boiling again, and continuously stirring to make the solid in the container completely dissolved, and stopping heating; (2) filtering the solution in the container while hot, and collecting the filtrate; (3) diluting the filtrate prepared in step (2) with deionized water to prepare a dilute solution, placing the dilute solution in a hydrothermal reaction container, sealing the hydrothermal reaction container, adjusting the temperature in the hydrothermal reaction container to 150-500 DEG C, adjusting the pressure in the hydrothermal reaction container to 10-100 MPa by injecting inert gas into the hydrothermal reaction container, and reacting for 10-15 hours, and then rapidly cooling to room temperature; (4) opening the hydrothermal reaction container, and obtaining monoclinic hafnium dioxide nanorods through subsequent processing. The mass ratio of hafnium dioxide and potassium bifluoride in step (1) is 1:2-3; The molar concentration of the dilute solution in step (3) is 0.01-0.02 mol / L.

2. The method for synthesizing monoclinic hafnium dioxide nanorods according to claim 1, characterized in that, In step (1), the volume percentage of the dilute hydrofluoric acid solution is 3-8%, and the amount of addition is 40-60% of the total volume of the container; the container in step (1) is a crucible, and the crucible is a nickel-based alloy crucible or a noble metal crucible; the stirring in step (1) uses a Teflon stirring rod.

3. The method for synthesizing monoclinic hafnium dioxide nanorods according to claim 1, characterized in that, In step (2), the filtrate is collected using a silver evaporating dish or an evaporating dish with a Teflon lining.

4. The method for synthesizing monoclinic hafnium dioxide nanorods according to claim 1, characterized in that, In step (3), the inert gas is argon or helium.

5. The method for synthesizing monoclinic hafnium dioxide nanorods according to claim 1, characterized in that, In step (3), the dilute solution is directly added to the hydrothermal reaction container, and the volume of the dilute solution accounts for 30-80% of the total volume of the hydrothermal reaction container; the hydrothermal reaction container is a hydrothermal reaction kettle, the hydrothermal reaction kettle is a sealed high-temperature and high-pressure reaction kettle, the high-temperature and high-pressure reaction kettle is connected with a high-precision ultrahigh-pressure pressure gauge, a ventilation pipeline and a stop valve, the high-temperature and high-pressure reaction kettle has a metal shell, the metal shell is provided with a strong acid and alkali resistant lining, the strong acid and alkali resistant lining is polytetrafluoroethylene, polyphenyl ester or polyimide plastic, or the strong acid and alkali resistant lining is silver, gold or platinum inert metal, or the strong acid and alkali resistant lining is gold-palladium or silver-palladium alloy.

6. The method of claim 5, wherein the monoclinic Hf02 nanorods are synthesized by the method comprising the steps of: In step (4), opening the hydrothermal reaction container and obtaining monoclinic hafnium dioxide nanorods through subsequent processing comprises: opening the hydrothermal reaction container, recovering the residual solution in the hydrothermal reaction container, washing the inner wall of the hydrothermal reaction container with deionized water, collecting the washing fluid to obtain a nanometer hafnium dioxide slurry, centrifuging the obtained slurry, taking the lower layer precipitate, and washing and drying the lower layer precipitate to obtain monoclinic hafnium dioxide nanorods with uniform particle size.

7. The method for synthesizing monoclinic hafnium dioxide nanorods according to claim 5, characterized in that, The bottom of the hydrothermal reaction container in step (3) is provided with a sample collection sheet, which is a plastic or inert metal sample collection sheet; and opening the hydrothermal reaction container in step (4) to obtain monoclinic hafnium dioxide nanorods through subsequent treatment includes: opening the hydrothermal reaction container, recovering the residual solution in the hydrothermal reaction container, taking out the sample collection sheet, and washing and drying to obtain hafnium dioxide nanorods with uniform particle size on the surface of the sample collection sheet.

8. The method of claim 1, wherein the monoclinic hafnium dioxide nanorods are synthesized by a process comprising: In step (3), the dilute solution is first added to the noble metal container, and then the noble metal container is placed in the hydrothermal reaction container, wherein the noble metal is silver, gold or platinum; or the noble metal is gold-palladium or silver-palladium alloy.

9. The method for synthesizing monoclinic hafnium dioxide nanorods according to claim 8, characterized in that, In step (4), opening the hydrothermal reaction container to obtain monoclinic hafnium dioxide nanorods through subsequent treatment includes: opening the hydrothermal reactor, taking out the noble metal container, recovering the residual solution in the noble metal container, washing the inner wall of the noble metal container with deionized water, collecting the washed fluid to obtain a hafnium dioxide nanorod slurry, centrifuging the obtained slurry, taking the lower layer precipitate, and washing and drying the lower layer precipitate to obtain monoclinic hafnium dioxide nanorods with uniform particle size.

10. Use of monoclinic hafnium dioxide nanorods synthesized by the method of any one of claims 1-9 in plastic or metal surface coating.

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