Vanadium dioxide ultrafine powder, preparation method thereof and corresponding coating

Abstract

The invention relates to the field of vanadium dioxide preparation and coatings, and discloses vanadium dioxide ultrafine powder, a preparation method thereof and a corresponding coating. The preparation method comprises the following steps: adding a first slow release agent into a solution containing VO < 2 + > to obtain a first solution; wherein the first slow-release agent comprises urea; adding a second slow-release agent into the first solution to obtain a second solution; wherein the second slow-release agent comprises one or more of carboxymethyl cellulose, polyoxyethylene, polyvinylpyrrolidone, polyvinyl alcohol and polyacrylamide; carrying out heat preservation on the second solution at a first preset temperature, and then filtering and drying to obtain precursor powder; and carrying out heat preservation on the precursor powder at a second preset temperature to obtain the vanadium dioxide ultrafine powder. The technological process is simple, large-scale batch preparation of the vanadium dioxide powder at low temperature and normal pressure can be achieved, and the prepared powder is high in purity, small in particle size and good in uniformity and can be widely applied to the fields of intelligent window coatings, optoelectronic switches, thermistors and the like.

Description

Technical Field

[0001] The present invention relates to the technical fields of vanadium dioxide preparation and coating technology, and particularly relates to a vanadium dioxide ultrafine powder, a preparation method thereof, and a corresponding coating. Background Art

[0002] As the temperature rises, vanadium dioxide transforms from the monoclinic structure M phase with insulating properties to the tetragonal rutile structure R phase with metallic properties. During this process, mutations in transmittance, reflectivity, resistivity, magnetic susceptibility, etc. will occur. Based on the mutated properties before and after the phase change, VO2 is widely used in fields such as intelligent temperature control materials, terahertz devices, optoelectronic switches, and thermistors.

[0003] The preparation of vanadium dioxide is roughly divided into two directions. One direction uses pentavalent vanadium compounds as raw materials, and a reducing agent is added during the reaction, and VO2 is obtained through different methods such as hydrothermal method, chemical precipitation method, solid-phase roasting method, etc. Among them, the reducing agent is mostly an organic compound, such as oxalic acid, methanol, citric acid, etc. Another direction uses tetravalent vanadium sources as raw materials, and precursor products such as vanadyl acetylacetonate, vanadyl triisopropoxide, vanadyl dichloride, vanadyl oxalate, vanadyl sulfate, vanadyl oxalate, etc. are obtained through a liquid-phase method. The precursor is subjected to high-temperature heat treatment or directly high-temperature thermal decomposition to obtain VO2.

[0004] When using a pentavalent vanadium source as a raw material to prepare VO2, a reduction step must be added, and the most used method is the hydrothermal method, which has complex preparation conditions, a long process flow, and is not conducive to batch amplification. When directly using a tetravalent vanadium source (such as vanadyl sulfate and vanadyl oxalate, etc.) to prepare vanadium dioxide, if the hydrothermal method or solvothermal method is used, the same problems as those faced by the pentavalent vanadium source exist. If the conventional chemical precipitation or thermal decomposition method is used, although the process is simple and easy to prepare in batches, the current methods all have problems such as difficulty in nanoparticle size reduction, poor particle size uniformity, and difficulty in ensuring phase purity, and the prepared powder is difficult to be applied to the backend glass coating or heat insulation film.

[0005] Based on this, the prior art still needs to be improved. Summary of the Invention

[0006] The main object of the present invention is to provide a vanadium dioxide ultrafine powder, a preparation method thereof, and a corresponding coating, so as to solve the technical problem in the prior art that it is necessary to use complex preparation conditions and a long process flow to prepare a vanadium dioxide powder with nanoparticle size, uniform particle size, and high phase purity.

[0007] According to one aspect of the present invention, a preparation method of a vanadium dioxide ultrafine powder is provided, including: Adding a first slow-release agent to a solution containing VO 2+ to obtain a first solution; wherein the first slow-release agent includes urea; Add a second slow-release agent to the first solution to obtain a second solution; wherein the second slow-release agent includes one or more of carboxymethyl cellulose, polyethylene oxide, polyvinylpyrrolidone, polyvinyl alcohol, and polyacrylamide; Keep the second solution at a first predetermined temperature, then filter and dry it to obtain a precursor powder; Keep the precursor powder at a second predetermined temperature to obtain vanadium dioxide ultrafine powder.

[0008] According to an embodiment of the present invention, the solution containing VO 2+ includes vanadyl sulfate solution.

[0009] According to an embodiment of the present invention, the molar ratio of the first slow-release agent to the V element in the solution containing VO 2+ is (5-10):1.

[0010] According to an embodiment of the present invention, the mass of the second slow-release agent is 1-5‰ of the mass of the first solution.

[0011] According to an embodiment of the present invention, before adding the second slow-release agent to the first solution, the method further includes adding a dopant to the first solution.

[0012] According to an embodiment of the present invention, the dopant includes tungstic acid and / or ammonium tungstate; and / or the dopant is added according to the atomic percentage of the doped element in the vanadium dioxide ultrafine powder being 1-6 at%.

[0013] According to an embodiment of the present invention, heating the second solution to the first predetermined temperature and keeping it warm includes: heating the second solution to 80-100°C under water bath conditions and keeping it warm for 1-2 h.

[0014] According to an embodiment of the present invention, drying includes: vacuum drying at a temperature of 50-80°C for 3-12 h.

[0015] According to an embodiment of the present invention, keeping the precursor powder at the second predetermined temperature includes: placing the precursor powder in a vacuum or inert gas atmosphere and keeping it at a temperature of 500-600°C for 1-2.5 h.

[0016] According to another aspect of the present invention, a vanadium dioxide ultrafine powder is provided. The vanadium dioxide ultrafine powder is prepared by the method described above, and the crystal form of the vanadium dioxide ultrafine powder is the M phase, and the average particle size is less than 50 nm.

[0017] According to another aspect of the present invention, a coating is provided, which contains the vanadium dioxide ultrafine powder as described above.

[0018] In the technical solution of the present invention, the generation rate of hydroxide ions is reduced by the first slow-release agent, and the diffusion rate of hydroxide ions is reduced by the second slow-release agent. A simple atmospheric pressure heating method can be used to prepare vanadium dioxide ultrafine powder with nano-sized dimensions, good particle size uniformity, and high phase purity, so as to realize the batch preparation of vanadium dioxide ultrafine powder. The prepared vanadium dioxide ultrafine powder can be well applied to fields such as smart window coatings, optoelectronic switches, and thermistors. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0020] Figure 1 A flowchart showing a method for preparing vanadium dioxide ultrafine powder according to an embodiment of the present invention; Figure 2 A flowchart showing a method for preparing vanadium dioxide ultrafine powder according to another embodiment of the present invention; Figure 3 A flowchart showing a method for preparing vanadium dioxide ultrafine powder according to another embodiment of the present invention; Figure 4 An X-ray diffraction pattern of a precursor powder according to an embodiment of the present invention; Figure 5a An XRD pattern of the target product of Example 1 of the present invention; Figure 5b An SEM image of the target product of Example 1 of the present invention; Figure 6a An XRD pattern of the target product of Example 2 of the present invention; Figure 6b An SEM image of the target product of Example 2 of the present invention; Figure 7a An XRD pattern of the target product of Example 3 of the present invention; Figure 7b An SEM image of the target product of Example 3 of the present invention; Figure 8a An XRD pattern of the target product of Example 4 of the present invention; Figure 8b An SEM image of the target product of Example 4 of the present invention; Figure 8c A DSC curve of the target product of Example 4 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0021] To make the objectives, technical solutions and advantages of the present invention more clear and understandable, the following further elaborates on the embodiments of the present invention in detail with reference to specific embodiments and the accompanying drawings.

[0022] It should be noted that all the expressions using "first" and "second" in the embodiments of the present invention are for distinguishing two entities or parameters with the same name but different ones. It can be seen that "first" and "second" are only for the convenience of expression and should not be construed as a limitation on the embodiments of the present invention. This will not be elaborated one by one in the subsequent embodiments.

[0023] Figure 1 The flowchart showing the preparation method of vanadium dioxide ultrafine powder according to an embodiment of the present invention is referred to Figure 1 , and the preparation method of vanadium dioxide ultrafine powder includes the following steps: S11, adding a first slow-release agent to a solution containing VO 2+ to obtain a first solution; wherein the first slow-release agent includes urea; S13, adding a second slow-release agent to the first solution to obtain a second solution; wherein the second slow-release agent includes one or more of carboxymethyl cellulose, polyethylene oxide, polyvinylpyrrolidone, polyvinyl alcohol, and polyacrylamide; S15, keeping the second solution at a first predetermined temperature, then filtering and drying to obtain a precursor powder; S17, keeping the precursor powder at a second predetermined temperature to obtain vanadium dioxide ultrafine powder.

[0024] The present invention uses the first slow-release agent and the second slow-release agent to carry out two-stage slow-release effects on hydroxide ions. By the method of slowly releasing hydroxide ions in two stages, the generation rate and diffusion rate of hydroxide ions are reduced. Thus, vanadium dioxide ultrafine powder with nano-sized dimensions, good particle size uniformity, and high phase purity can be prepared by a simple atmospheric pressure heating method, which is conducive to the batch preparation of vanadium dioxide ultrafine powder. The following specifically explains the two-stage slow-release process: The first slow-release agent used in the first-stage slow-release process includes urea. Adding urea to a solution containing VO 2+ at room temperature will not result in precipitation. However, in the range of the first predetermined temperature (such as 80-100 °C), the urea in the solution will slowly decompose to release ammonia and carbon dioxide. The reaction process does not directly produce ammonia and carbon dioxide but involves multiple reaction steps. First, the urea molecule reacts with water molecules to form intermediate products. Secondly, the intermediate products continue to decompose in water and finally generate ammonia and carbon dioxide. The existence and specific decomposition steps of the intermediate products may vary depending on reaction conditions (such as temperature, pressure, pH value, etc.). The main reaction formulas involved in this method are as follows:

[0025] Therefore, the main principle of the first-stage slow release is that during the heating process, each urea molecule will slowly hydrolyze to release hydroxide ions, and each hydroxide ion combines with the vanadyl ions in the solution at any position at the same time. The "one-to-one" combination of the two achieves the purpose of uniform precipitation. This process avoids the local instantaneous release of a large amount of OH - , resulting in an explosive nucleation and agglomeration phenomenon. For example, when ammonia water or ammonium bicarbonate is directly added, local "agglomeration" problems will occur. 2+ Explosive nucleation and agglomeration phenomenon, such as local "agglomeration" problems will occur when using ammonia water or directly adding ammonium bicarbonate.

[0026] In addition, the decomposition of urea is a slow process, and the solution contains OH - , H + , CO3 2- , HCO3 - , NH4 + and other multiple ions coexist. These ions combine with VO 2+ ions to form a precursor substance of macromolecule (NH4)5((VO)6(CO3)4(OH)9)(H2O) 10 . The XRD pattern thereof is shown in Figure 4 . This macromolecular precursor will transform into a small-molecule VO2 intermediate during the thermal decomposition process, thereby realizing the transformation of the powder into nanoparticles, and the average particle size of the nanopowder is less than 50 nm.

[0027] The main principle of the second-stage slow release is to add an organic polymer material that can increase the viscosity of the solution to the solution, restrict the mass transfer behavior of the particles in the solution, and reduce the diffusion rate of OH - in the solution, that is, reduce the diffusion rate of OH - and VO 2+ contact frequency, avoid secondary overgrowth, and thus effectively control the particle size of the reaction product. It is required that this type of organic polymer material can neither react with vanadyl ions nor be miscible with the aqueous solution to form a clear and transparent liquid, and its function is only to increase the solution viscosity and will not act as a surfactant and flocculant. The organic polymer materials that meet the present invention include: carboxymethyl cellulose, polyethylene oxide, polyvinylpyrrolidone, polyvinyl alcohol, polyacrylamide.

[0028] In step S11, the solution containing VO 2+ can include a vanadyl sulfate solution. The concentration of the solution containing VO 2+ can be 0.5~1.5 mol / L. A certain volume of the solution containing VO 2+ can be measured and added to the reaction vessel, and then a first slow release agent is added to the solution, and stirred at room temperature until the first slow release agent is completely dissolved to obtain a first solution.

[0029] In step S11, the molar ratio of the first slow-release agent to the V element in the solution containing VO 2+ is (5 to 10):1, ensuring that the first slow-release agent can fully react with VO 2+ . The urea molecule hydrolyzes to release sufficient hydroxide ions to combine with VO 2+ in the solution.

[0030] In step S13, after adding the second slow-release agent to the first solution, stir until the solution becomes clear and transparent to obtain a second solution. The mass of the second slow-release agent can be 1 to 5‰ of the mass of the first solution, ensuring that the second corrosion inhibitor appropriately increases the solution viscosity to reduce the diffusion rate of hydroxide ions in the solution.

[0031] In step S15, the second solution can be heated to 80 to 100 °C under a water bath condition and kept warm for 1 to 2 h, ensuring that urea slowly hydrolyzes to release hydroxide ions to combine with VO 2+ . After the reaction ends, filter and wash, and vacuum-dry the washed material at a temperature of 50 to 80 °C for 3 to 12 h to obtain the precursor powder.

[0032] In step S17, the precursor powder can be placed in a vacuum or inert gas atmosphere and kept at a temperature of 500 to 600 °C for 1 to 2.5 h. After the reaction ends, maintain the vacuum or inert gas atmosphere. After the temperature drops to room temperature, take it out to obtain VO2 nanometer powder.

[0033] Figure 2 The flowchart showing the preparation method of vanadium dioxide ultrafine powder according to another embodiment of the present invention is shown. Figure 2 The main difference between the shown embodiment and Figure 1 the shown embodiment is that in Figure 2 the shown embodiment, before adding the second slow-release agent to the first solution in step S13, the preparation method further includes step S12: adding doping to the first solution. By adding a dopant, the properties of the vanadium dioxide powder are further improved. For example, by doping tungsten elements, the phase transition temperature of the vanadium dioxide powder is reduced. The dopant can include tungstic acid (H2WO4) and / or ammonium tungstate ((NH4) 10 H2(W2O7)6). The dopant can be added according to the atomic percentage of the doped element in the vanadium dioxide ultrafine powder being 1 to 6 at%. Of course, other elements can be selected for doping according to actual needs.

[0034] Figure 3 The flowchart showing a specific embodiment of the present invention is shown. As Figure 3 shown, first, add the first slow-release agent to the solution containing VO 2+ such as vanadyl sulfate solution) and stir to dissolve to obtain 1 #Solution (corresponding to the first solution); then, add 1 # to the solution a tungsten dopant, and stir evenly to obtain 2 # solution (corresponding to the first solution after adding the dopant); then, add 2 # to the solution a second slow-release agent, and stir until the solution is clear and transparent to obtain 3 # solution (corresponding to the second solution); then, heat 3 # solution to precipitate a solid, and filter, wash, and dry it to obtain a precursor powder; then, calcine the precursor powder to obtain tungsten-doped vanadium dioxide nanometer powder. The main steps of the present invention after adding the corresponding raw materials are one-step precipitation - one-step calcination, and the process method is simple.

[0035] The present invention also provides a vanadium dioxide ultrafine powder, which is prepared by the method as described above. The crystal form of the vanadium dioxide ultrafine powder is the M phase, and the average particle size is less than 50 nm.

[0036] The present invention also provides a coating, which comprises the vanadium dioxide ultrafine powder as described above, and may also comprise a film-forming agent, a diluent, and various possible additives.

[0037] In summary, the technical solution of the present invention has the following beneficial effects: (1) The present invention overcomes the limitation that conventional liquid-phase precipitation is difficult to scale up, and realizes the large-scale batch preparation of VO2 powder under low temperature and normal pressure. (2) The main steps of the present invention are one-step precipitation - one-step calcination, and the process method is simple, low-cost, and easy to popularize and apply. (3) The VO2 powder obtained by the present invention has the advantages of high purity, small particle size, good uniformity, etc., and can be widely used in fields such as smart window coatings, optoelectronic switches, and thermistors.

[0038] The following is an illustration according to specific examples.

[0039] Example 1 Measure 250 mL of a vanadyl sulfate solution with a concentration of 0.5 mol / L and pour it into a three-necked flask. Add 75 g of urea, and stir until the urea is completely dissolved. Then add 0.62 g of tungstic acid, stir evenly, continue to add 0.8 g of polyacrylamide, and finally stir the solution until it is clear and transparent. Place the three-necked flask in a water bath and heat it to 100 °C, and keep it warm for 1 h. After the heat preservation is over, filter and wash the precipitate product, and dry it in a vacuum drying oven at 50 °C for 6 h. Then place the dried precursor powder in a vacuum tube furnace and keep it warm at 500 °C for 1 h. After the temperature drops to room temperature, obtain the target product of W-VO2 nanometer powder. The XRD pattern and SEM image of the target product are respectively as Figure 5a 、 5b shown. It can be seen that the crystal form of the powder is the M phase, and the average particle size is less than 50 nm.

[0040] Example 2 Measure 1000 mL of vanadyl sulfate solution with a concentration of 1.5 mol / L and pour it into a three-necked flask. Add 450 g of urea and stir. After the urea is completely dissolved, add 3.75 g of tungstic acid and stir evenly. Then continue to add 1.2 g of carboxymethyl cellulose, and finally stir the solution until it is clear and transparent. Place the three-necked flask in a water bath and heat it to 90 °C, and keep it warm for 1.5 h. After the insulation is completed, filter and wash the precipitate product, and dry it in a vacuum drying oven at 50 °C for 6 h. Then place the dried precursor powder in a vacuum tube furnace and keep it at 550 °C for 2.5 h. After the temperature drops to room temperature, the target product of W-VO2 nanometer powder is obtained. The XRD pattern and SEM image of the target product are respectively as Figure 6a 、 6b shown. It can be seen that the crystal form of the powder is the M phase, and the average particle size is less than 50 nm.

[0041] Example 3 Measure 10 L of vanadyl sulfate solution with a concentration of 1.0 mol / L and pour it into a glass reaction kettle. Add 4.8 kg of urea and stir. After the urea is completely dissolved, add 102 g of ammonium tungstate and stir evenly. Then continue to add 55 g of polyvinylpyrrolidone, and finally stir the solution until it is clear and transparent. Place the three-necked flask in a water bath and heat it to 80 °C, and keep it warm for 2 h. After the insulation is completed, filter and wash the precipitate product, and dry it in a vacuum drying oven at 50 °C for 6 h. Then place the dried precursor powder in a vacuum tube furnace and keep it at 550 °C for 2.0 h. After the temperature drops to room temperature, the target product of W-VO2 nanometer powder is obtained. The XRD pattern and SEM image of the target product are respectively as Figure 7a 、 7b shown. It can be seen that the crystal form of the powder is the M phase, and the average particle size is less than 50 nm.

[0042] Example 4 Measure 50 L of vanadyl sulfate solution with a concentration of 1.0 mol / L and pour it into a glass reaction kettle. Add 21 kg of urea and stir. After the urea is completely dissolved, add 765 g of ammonium tungstate and stir evenly. Then continue to add 110 g of polyvinyl alcohol, and finally stir the solution until it is clear and transparent. Place the three-necked flask in a water bath and heat it to 100 °C, and keep it warm for 1.5 h. After the insulation is completed, filter and wash the precipitate product, and dry it in a vacuum drying oven at 50 °C for 6 h. Then place the dried precursor powder in a vacuum tube furnace and keep it at 600 °C for 1.5 h. After the temperature drops to room temperature, the target product of W-VO2 nanometer powder is obtained. The XRD pattern, SEM image, and DSC curve of the target product are respectively as Figure 8a 、 8b 、8c shown. It can be seen that the crystal form of the powder is the M phase, the average particle size is less than 50 nm, and the phase transition temperature is 42.3 °C.

[0043] Those of ordinary skill in the art should understand that any discussion of the above embodiments is merely exemplary and is not intended to imply that the scope (including the claims) disclosed by the embodiments of the present invention is limited to these examples; under the concept of the embodiments of the present invention, the technical features in the above embodiments or different embodiments can also be combined, and there are many other variations in different aspects of the embodiments of the present invention as described above, which are not provided in detail for the sake of brevity. Therefore, any omission, modification, equivalent replacement, improvement, etc. made within the spirit and principle of the embodiments of the present invention shall be included within the protection scope of the embodiments of the present invention.

Claims

1. A preparation method of vanadium dioxide ultrafine powder, characterized in that, Comprising: Add a first sustained-release agent to the solution containing VO 2+ to obtain a first solution; Wherein the first sustained-release agent comprises urea; Adding a second sustained-release agent to the first solution to obtain a second solution; wherein the second sustained-release agent comprises one or more of carboxymethyl cellulose, polyethylene oxide, polyvinylpyrrolidone, polyvinyl alcohol, and polyacrylamide; Keeping the second solution at a first predetermined temperature, then filtering and drying to obtain a precursor powder; Keeping the precursor powder at a second predetermined temperature to obtain the vanadium dioxide ultrafine powder.

2. The method according to claim 1, characterized in that, The VO-containing 2+ solution includes a vanadyl sulfate solution.

3. The method according to claim 1, characterized in that The molar ratio of the first sustained-release agent to the V element in the solution containing VO 2+ is (5 to 10):

1.

4. The method according to claim 1, wherein The mass of the second sustained-release agent is 1 to 5‰ of the mass of the first solution.

5. The method according to claim 1, characterized in that, Before adding the second sustained-release agent to the first solution, the method further comprises adding a dopant to the first solution.

6. The method according to claim 5, characterized in that The dopant comprises tungstic acid and / or ammonium tungstate; and / or the dopant is added according to the atomic percentage of the doped element in the vanadium dioxide ultrafine powder being 1 to 6 at%.

7. The method according to claim 1, wherein Heating the second solution to the first predetermined temperature and keeping it warm includes: heating the second solution to 80 to 100°C under water bath conditions and keeping it warm for 1 to 2 h; and / or performing the drying includes: vacuum drying at a temperature of 50 to 80°C for 3 to 12 h.

8. The method according to claim 1, characterized in that Keeping the precursor powder at the second predetermined temperature includes: placing the precursor powder in a vacuum or inert atmosphere environment and keeping it at a temperature of 500 to 600°C for 1 to 2.5 h.

9. A vanadium dioxide ultrafine powder, characterized in that, The vanadium dioxide ultrafine powder is prepared by the method according to any one of claims 1-8, and the crystal form of the vanadium dioxide ultrafine powder is the M phase, and the average particle size is less than 50 nm.

10. A coating, characterized in that, Comprising the vanadium dioxide ultrafine powder according to claim 9.

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