Method for improving oxidation resistance of vanadium dioxide

Abstract

The invention belongs to the technical field of material preparation and anti-oxidation treatment, and particularly relates to a method for improving the oxidation resistance of vanadium dioxide. Vanadium dioxide powder is subjected to hydrogenation annealing treatment, hydrogen atoms are injected into crystal lattices on the surface of the sample on the basis that the original phase and high crystallinity of the vanadium dioxide sample are not damaged, and experiments find that the treatment method improves the stability and oxidation resistance of the surface of the vanadium dioxide sample. According to the method for improving the oxidation resistance of the vanadium dioxide, provided by the invention, the vanadium dioxide does not generate surface oxidation within 30 days on the basis of not changing the phase of the vanadium dioxide and not damaging the crystallinity of the sample, and the storage time is prolonged.

Description

Technical Field

[0001] The present invention belongs to the technical field of material preparation and antioxidant treatment, and more specifically, relates to a method for improving the antioxidant property of vanadium dioxide. Background Art

[0002] Vanadium dioxide is a strongly correlated metal oxide that undergoes a reversible structural phase transition from a low-temperature monoclinic phase to a high-temperature rutile phase at 68 °C. Along with this phase transition, the electrical, optical, and magnetic properties of vanadium dioxide change significantly. Among them, the change in electrical conductivity can reach up to four orders of magnitude, which is called the metal-insulator transition (MIT). This metal-insulator transition property endows vanadium dioxide with broad application prospects, such as thermochromic smart windows, laser protection coatings, uncooled infrared detectors, etc. Patent CN114702850A discloses a temperature-controlled coating of vanadium dioxide composite powder. After the coating is formed into a film, the visible light transmittance is not less than 70%, the sunlight regulation ability is not less than 10.1%, and the phase transition temperature is reduced to near room temperature, showing great application potential in the field of thermochromic smart windows. Patent CN202210306843.9 discloses an infrared light switch based on thermoelectric synergistic regulation of vanadium dioxide thin films. By the huge change in the infrared light transmittance before and after the phase transition of vanadium dioxide, an on-off state of infrared light is formed, which has very high practical value.

[0003] The metal-insulator transition property of vanadium dioxide brings extremely broad application prospects, but at the same time, there is also a problem that cannot be ignored. That is, vanadium dioxide is not stable. The most stable vanadium oxide at room temperature is vanadium pentoxide. Therefore, vanadium dioxide will gradually oxidize to vanadium pentoxide in the air, losing its phase transition property, which greatly restricts the popularization of the practical application of vanadium dioxide. However, most of the current patents on vanadium dioxide are methods for making devices using vanadium dioxide as raw materials, and little attention is paid to how to prevent sample oxidation in practical applications, which is an inevitable problem in the practical application of vanadium dioxide. Improving the antioxidant property of materials can increase the service life of devices and thus improve the practical use value.

[0004] Therefore, it is necessary to develop a new method for preparing vanadium dioxide powder, so that the prepared sample has strong antioxidant property, is easy to store, and has a long service life. Summary of the Invention

[0005] Aiming at the defects of the prior art, the purpose of the present invention is to provide a method for improving the antioxidant property of vanadium dioxide, so as to solve the technical problems that devices made of vanadium dioxide in the prior art are difficult to avoid oxidation during actual use, resulting in reduced service life of the devices, etc.

[0006] To achieve the above object, the present invention provides a method for improving the antioxidant property of vanadium dioxide, comprising the following steps: annealing vanadium dioxide powder in an atmosphere containing hydrogen so that hydrogen atoms enter the interstitial sites of the vanadium dioxide lattice to form O-H bonds, and the phase and crystallinity of the vanadium dioxide powder remain unchanged before and after the annealing treatment, thereby improving the antioxidant property of vanadium dioxide.

[0007] Preferably, the atmosphere containing hydrogen is a mixed atmosphere of hydrogen and an inert gas, wherein the volume percentage of hydrogen is 10% to 60%, and more preferably 10% to 30%.

[0008] Preferably, the inert gas is one or more of argon, helium and neon.

[0009] Preferably, the temperature of the annealing treatment is 100°C to 300°C.

[0010] Preferably, the time of the annealing treatment is 2h to 5h.

[0011] Preferably, the vanadium dioxide powder is prepared by a hydrothermal reduction method, a sol-gel method or an electrospinning method.

[0012] Preferably, the preparation method of the vanadium dioxide powder comprises the following steps:

[0013] (1) Disperse a vanadium source and a reducing agent in deionized water, heat and stir to mix evenly, and react to form a precursor;

[0014] (2) Perform a hydrothermal reaction on the precursor obtained in step (1), separate the solid and liquid of the precipitate obtained by the hydrothermal reaction, and perform high-temperature annealing on the obtained solid phase in a protective atmosphere to obtain vanadium dioxide powder.

[0015] Preferably, in step (1), the vanadium source is vanadium pentoxide or ammonium metavanadate, and the reducing agent is hydrazine hydrate or oxalic acid dihydrate; the temperature during stirring is 45 - 60°C, and the stirring time is 40 - 60 min.

[0016] Preferably, in step (2), the time of the hydrothermal reaction is 24h to 72h, and the temperature is 180°C to 240°C; the temperature of the high-temperature annealing is 550°C to 700°C, and the time is 1h to 4h; the protective atmosphere is nitrogen and / or argon.

[0017] Generally speaking, compared with the prior art by the above technical solution conceived by the present invention, the following

[0018] Advantages are achieved:

[0019] (1) The present invention anneals vanadium dioxide powder in an atmosphere containing hydrogen. Experiments have found that annealing can cause hydrogen atoms to enter the interstitial sites of the vanadium dioxide lattice to form O-H bonds, hydrogenating the surface of the vanadium dioxide powder, and ensuring that the phase and crystallinity of vanadium dioxide do not change before and after annealing. Through comparison, it is found that the antioxidant property of the vanadium dioxide powder after hydrogenation annealing is significantly enhanced compared to before treatment.

[0020] (2) The present invention is equivalent to providing a method for preparing vanadium dioxide powder with long-term antioxidant property. In some embodiments, the vanadium dioxide powder prepared by the hydrothermal method is hydrogenated, injecting hydrogen atoms into the lattice on the surface of the sample, improving the surface stability and antioxidant ability of the sample, and endowing it with a higher service life and practical value. The method for preparing vanadium dioxide powder with long-term antioxidant property provided by the present invention can prevent surface oxidation within 30 days without changing the phase of vanadium dioxide and without destroying the crystallinity of the sample, extending the storage time. The preparation method is simple. Compared with other methods of coating the sample to improve its antioxidant property, the preparation method of the present invention has excellent effects, is simple and repeatable, has low cost, is conducive to the large-scale production of antioxidant vanadium dioxide powder, and is of great significance for promoting the practical application of vanadium dioxide. Description of the Drawings

[0021] Figure 1 Schematic flow chart of the method for preparing vanadium dioxide powder with long-term antioxidant property in Example 1.

[0022] Figure 2 X-ray diffraction instrument characterization results of the vanadium dioxide powder with long-term antioxidant property prepared in Example 1.

[0023] Figure 3 X-ray photoelectron spectroscopy characterization result diagram of the vanadium dioxide powder with long-term antioxidant property prepared in Example 1.

[0024] Figure 4 Comparison of X-ray photoelectron spectroscopy characterization results of the vanadium dioxide powder (original sample) without antioxidant treatment in Example 1 before and after natural placement for 30 days.

[0025] Figure 5 Comparison of X-ray photoelectron spectroscopy characterization results of the vanadium dioxide powder with long-term antioxidant property prepared in Example 1 before and after natural placement for 30 days.

[0026] Figure 6 Raman spectroscopy characterization results of the vanadium dioxide powder (original sample) without antioxidant treatment and the vanadium dioxide powder obtained by antioxidant treatment in Example 1 after natural placement for 30 days.

[0027] Figure 7X-ray diffraction characterization results of the vanadium dioxide powder prepared in Comparative Example 1.

[0028] Figure 8 X-ray photoelectron spectroscopy characterization results of the vanadium dioxide powder prepared in Comparative Example 1 after being placed naturally for 30 days. Detailed implementation manners

[0029] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0030] The present invention provides a method for improving the antioxidant property of vanadium dioxide, which includes the following steps: placing the vanadium dioxide powder in an atmosphere containing hydrogen for annealing treatment, enabling hydrogen atoms to enter the lattice interstitial sites of vanadium dioxide to form O-H bonds, and through detections such as XRD or Raman, the phase and crystallinity of the vanadium dioxide powder do not change before and after the annealing treatment, so as to improve the antioxidant property of vanadium dioxide while maintaining its phase change function.

[0031] In some embodiments, the atmosphere containing hydrogen is a mixed atmosphere of hydrogen and an inert gas, wherein the volume percentage of hydrogen is 10% to 60%, more preferably 10% to 30%. The inert gas is one or more of argon, helium and neon.

[0032] In some embodiments, the temperature of the annealing treatment is 100°C to 300°C, and the time of the annealing treatment is 2h to 5h.

[0033] The raw material of the vanadium dioxide powder in the present invention is not limited by the source or preparation method, and can be vanadium dioxide powder prepared by various methods, including but not limited to vanadium dioxide powder prepared by hydrothermal reduction method, sol-gel method or electrospinning method, and its antioxidant property can be improved by the method of the present invention.

[0034] Taking the hydrothermal method as an example, in some embodiments, the preparation method of the vanadium dioxide powder includes the following steps:

[0035] (1) Disperse the vanadium source and the reducing agent in deionized water, heat and stir to mix evenly, and react to form a blue precursor; the vanadium source is vanadium pentoxide or ammonium metavanadate, and the reducing agent is hydrazine hydrate or oxalic acid dihydrate; the temperature during stirring is 45 - 60°C, and the stirring time is 40 - 60 min; as the stirring time increases, the precursor solution will change from the original orange-yellow suspension to a dark blue transparent solution;

[0036] (2) Hydrothermally react the precursor described in step (1), perform solid-liquid separation on the blue-black precipitate obtained from the hydrothermal reaction, and subject the obtained solid phase to high-temperature annealing under a protective atmosphere to obtain vanadium dioxide powder.

[0037] In some embodiments, the time of the hydrothermal reaction is 24 h to 72 h, the temperature is 180 °C to 240 °C, and after the hydrothermal reaction is completed, wait for the hydrothermal reaction kettle to cool to room temperature before opening the kettle lid; the temperature of the high-temperature annealing is 550 °C to 700 °C, and the time is 1 h to 4 h; the protective atmosphere is nitrogen and / or argon. The particle size of the vanadium dioxide powder prepared by the hydrothermal method is 100 nm to 100 μm.

[0038] In some embodiments of the present invention, the original vanadium dioxide powder is annealed in hydrogen at a certain concentration to obtain a black vanadium dioxide powder with long-term antioxidant ability. The steps include: placing the original vanadium dioxide powder in a quartz carrier and transferring it to a tube furnace. Start the tube furnace and ventilate it. Only pass the protective gas before reaching the established hydrogenation temperature. When the tube furnace rises to the hydrogenation temperature, pass hydrogen, and hydrogen and the protective gas are mixed to form hydrogen at a certain concentration. After the operation of the tube furnace is completed, stop ventilating after cooling to room temperature.

[0039] In some embodiments, the quartz carrier refers to a quartz tile with openings at both ends. All quartz products used, such as quartz tubes and quartz tiles, are cleaned with absolute ethanol in advance to ensure that no other impurities are introduced.

[0040] In some embodiments, the protective gas refers to argon, the volume concentration of hydrogen is 10 - 60%, preferably 15% - 30%, and the hydrogen annealing temperature is 100 °C - 300 °C.

[0041] The present invention places the original vanadium dioxide powder in an atmosphere containing hydrogen and anneals it under appropriate temperature conditions. Experiments have found that a large number of protons enter the surface lattice of vanadium dioxide, and it does not affect its own phase and high crystallinity. After testing, it is found that the vanadium dioxide powder after hydrogen annealing treatment has significantly enhanced antioxidant properties compared to the original powder. When placed at room temperature for 30 days, basically no +5 valence V is detected. Using the vanadium dioxide powder with long-term antioxidant properties prepared by the present invention to make devices such as thermochromic smart windows or uncooled infrared sensors can greatly improve the performance and service life of the devices.

[0042] In some embodiments of the present invention, the vanadium dioxide powder obtained by the hydrothermal method is hydrogenated, so that hydrogen atoms enter the lattice gaps of vanadium dioxide, making the surface of vanadium dioxide have higher stability, thereby preventing the oxidation of vanadium dioxide. The oxidation of vanadium dioxide often starts from the surface of the sample. In the following embodiments of the present invention, the oxidation state of the elements on the surface of the sample is detected to determine whether the sample has been oxidized, so as to test whether the hydrogenation treatment method of the present invention can improve its antioxidant property.

[0043] The following are the embodiments:

[0044] Example 1

[0045] As Figure 1 shown, prepare vanadium dioxide powder with long-term antioxidant property according to the following method:

[0046] Prepare the precursor. Weigh 0.4 g of vanadium pentoxide and 1.11 g of oxalic acid dihydrate, dissolve them in 30 ml of deionized water, and stir at 50 °C for 50 min on a constant-temperature magnetic stirring table to obtain a precursor solution. It can be found that the orange-yellow suspension will turn into a dark blue clear solution.

[0047] Hydrothermal reaction. First, wash the polytetrafluoroethylene inner liner three times alternately with dilute nitric acid, absolute ethanol, and deionized water, and then dry the inner liner with a nitrogen air gun. Transfer the precursor solution to the inner liner of the reaction kettle, then install the inner liner into the stainless steel outer shell, tighten the shell, put it into a constant-temperature forced-air drying oven, set the temperature to 200 °C, and the time to 24 h, and start the drying oven.

[0048] Centrifugal cleaning. After the hydrothermal reaction is completed and the reaction kettle is naturally cooled to room temperature, open the kettle lid. It is found that a blue-black precipitate appears at the bottom of the reaction kettle. Collect the precipitate into a centrifuge tube and wash it three times with absolute ethanol and deionized water respectively.

[0049] Drying. Transfer the centrifugally cleaned sample to a beaker, cover the beaker mouth with plastic wrap, and drill holes in the plastic wrap. Then transfer it to a forced-air drying oven dedicated to drying samples, with a temperature of 60 °C and a time of 8 h.

[0050] High-temperature annealing. Anneal the black powder obtained after drying in a tube furnace, using argon as the protective gas with a gas flow rate of 100 sccm. The annealing temperature is 600 °C, and the annealing time is 2 h. Close the argon gas after the temperature of the tube furnace drops below 100 °C to obtain pure-phase vanadium dioxide powder.

[0051] Antioxidant treatment. The obtained pure-phase vanadium dioxide was placed in a tube furnace. First, argon was introduced with an argon flow rate of 100 sccm. When the temperature rose to 200 °C, hydrogen was introduced with a hydrogen volume concentration of 15%. The argon flow rate was 85 sccm and the hydrogen flow rate was 15 sccm. After maintaining at 200 °C for 3 hours, the tube furnace was naturally cooled to room temperature and then hydrogen and argon were turned off. The sample was taken out to obtain black vanadium dioxide powder with long-term antioxidant properties.

[0052] Example 2

[0053] Other contents are the same as those in Example 1, except that during the annealing process, the hydrogen volume concentration is 25%.

[0054] Example 3

[0055] Other contents are the same as those in Example 1, except that during the annealing process, the hydrogen annealing temperature is 300 °C.

[0056] Data analysis was performed on the above examples:

[0057] As Figure 2 shown, the phase characterization of the sample after antioxidant treatment in Example 1 was carried out by an X-ray diffractometer, and the results are shown in the figure. It was found that the crystal structure of the sample did not change at all after antioxidant treatment and remained pure-phase vanadium dioxide, and maintained good crystallinity. In the figure, VO2(M) PDF#72-0514 represents the peak of the vanadium dioxide PDF standard card in the database. This shows that the antioxidant treatment does not change the original phase of vanadium dioxide and does not affect the performance of the metal-insulator phase transition of vanadium dioxide.

[0058] As Figure 3 shown, the X-ray photoelectron spectroscopy characterization results of the sample after antioxidant treatment in Example 1 were tested. It can be seen that a large number of protons entered the lattice of vanadium dioxide, and the area of the O-H peak increased greatly. This indicates that a large number of hydrogen atoms entered the lattice of vanadium dioxide and combined with the oxygen atoms in the lattice, manifested as O-H.

[0059] To verify the effect of the antioxidant treatment, we respectively placed the sample after antioxidant treatment in Example 1 and the original sample (i.e., the pure-phase vanadium dioxide powder obtained in the high-temperature annealing step of Example 1, that is, the vanadium dioxide sample without the hydrogen annealing step) naturally for 30 days, and performed X-ray photoelectron spectroscopy tests on the samples before and after 30 days to characterize the electronic state on the surface of vanadium dioxide. From Figure 4It can be found that the signal of vanadium ions with a valence of +5 was generated when the original sample was just prepared, although the intensity was not high. After 30 days of storage, a very obvious peak of vanadium ions with a valence of +5 appeared on the surface, and the intensity was even higher than that of vanadium ions with a valence of +4, indicating that the sample had undergone very serious oxidation at this time. For the sample treated with antioxidant, no peak of vanadium ions with a valence of +5 was found on the surface when it was just prepared, only some peaks of vanadium ions with a valence of +3, as Figure 5 shown, indicating that a layer of HVO2 film was formed on the surface of the sample after antioxidant treatment. After 30 days of storage, only a very small peak of vanadium ions with a valence of +5 appeared in the sample, and vanadium ions with a valence of +4 were still the valence state of most electrons on the surface of vanadium dioxide. It shows that the degree of oxidation of vanadium dioxide treated with antioxidant is still very low after 30 days of natural storage. This layer of HVO2 film can greatly delay the oxidation of vanadium dioxide without changing the phase of vanadium dioxide.

[0060] In addition, in order to further characterize the state of the sample surface, Raman spectroscopy was used to characterize the original sample and the antioxidant sample after 30 days of storage, as Figure 6 shown. It was found that the Raman signal on the surface of the original sample had completely changed to the peak shape of vanadium pentoxide after 30 days, indicating that serious oxidation had occurred on its surface. The sample treated with antioxidant still maintained its original state after 30 days of storage, and the peak shape of vanadium dioxide was still on the surface. The conclusion obtained from the above results is consistent with the previous one. Antioxidant treatment can greatly delay the oxidation process of vanadium dioxide without changing the phase of vanadium dioxide.

[0061] Comparative Example 1

[0062] Other contents are the same as those in Example 1, except that during the annealing process, the hydrogen annealing temperature is 500 °C.

[0063] Figure 7 XRD pattern of the vanadium dioxide powder prepared in Comparative Example 1. In the figure, VO2(M) PDF#72-0514 represents the peak of the vanadium dioxide PDF standard card in the database, and V2O3 PDF#71-0280 represents the peak of the vanadium trioxide PDF standard card in the database. From Figure 7 it can be seen that the phase of the vanadium dioxide powder has changed after hydrogen annealing at 500 °C, and a very strong peak of V2O3 appears, which will undoubtedly likely affect the phase change function of vanadium dioxide in device applications.

[0064] Figure 8The XPS spectrum of the vanadium dioxide powder obtained in Comparative Example 1 after being placed for 30 days shows that after the vanadium dioxide powder prepared by hydrogen annealing treatment at 500 °C in Comparative Example 1 was placed for 30 days, a very obvious peak of vanadium ions with a +5 valence appeared on the surface, and the intensity was as high as that of vanadium ions with a +4 valence, indicating that the sample had undergone very serious oxidation at this time. Thus, it shows that the antioxidant effect of the sample obtained by treatment at 500 °C is not good.

[0065] Those skilled in the art can easily understand that the above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for improving the antioxidant property of vanadium dioxide, characterized in that, It includes the following steps: placing vanadium dioxide powder in an atmosphere containing hydrogen for annealing treatment, enabling hydrogen atoms to enter the lattice interstitial sites of vanadium dioxide to form O-H bonds, and the phase and crystallinity of the vanadium dioxide powder remaining unchanged before and after the annealing treatment to improve the antioxidant property of vanadium dioxide.

2. The method according to claim 1, wherein The atmosphere containing hydrogen is a mixed atmosphere of hydrogen and an inert gas, where the volume percentage of hydrogen is 10% to 60%, preferably 10% to 30%.

3. The method according to claim 2, wherein The inert gas is one or more of argon, helium, and neon.

4. The method according to claim 1, wherein The temperature of the annealing treatment is 100°C to 300°C.

5. The method according to claim 1, wherein The time of the annealing treatment is 2h to 5h.

6. The method according to claim 1, wherein The vanadium dioxide powder is prepared by a hydrothermal reduction method, a sol-gel method, or an electrospinning method.

7. The method according to claim 1, characterized in that, The preparation method of the vanadium dioxide powder includes the following steps: (1) Disperse a vanadium source and a reducing agent in deionized water, heat and stir to mix evenly, and react to form a precursor; (2) Perform a hydrothermal reaction on the precursor in step (1), separate the solid and liquid of the precipitate obtained from the hydrothermal reaction, and subject the obtained solid phase to high-temperature annealing under a protective atmosphere to obtain vanadium dioxide powder.

8. The method according to claim 7, wherein In step (1), the vanadium source is vanadium pentoxide or ammonium metavanadate, and the reducing agent is hydrazine hydrate or oxalic acid dihydrate; the temperature during stirring is 45 - 60°C, and the stirring time is 40 - 60 min.

9. The method according to claim 7, wherein In step (2), the time of the hydrothermal reaction is 24h to 72h, and the temperature is 180°C to 240°C; the temperature of the high-temperature annealing is 550°C to 700°C, and the time is 1h to 4h; the protective atmosphere is nitrogen and / or argon.

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