CN1304299C - Process for preparing vanadium dioxide nano powder - Google Patents

Abstract

The invention discloses a method for preparing vanadium dioxide nano-powder material. The process steps are the preparation of a precursor and the thermal decomposition of the precursor in sequence. The preparation of the precursor uses V ₂ O ₅ and oxalic acid as raw materials, and the weight ratio of V ₂ O ₅ and oxalic acid is 1:1-3; put the V ₂ O ₅ and oxalic acid in the ratio into the reaction vessel and add water at 40 Stir at ~70°C until the reduction reaction between V ₂ O ₅ and oxalic acid is completed, then evaporate the obtained solution to dryness to obtain a solid vanadyl oxalate precursor; Heating to 350°C-500°C, holding the heat for 20-40 minutes, then turning off the power supply of the heating furnace, keeping the vacuum in the furnace, allowing the decomposition products to cool down to room temperature to obtain vanadium dioxide nano-powder material. MoO ₃ or N ₅ H ₃₇ W ₆ O ₂₄ is added when preparing the precursor to obtain Mo-doped or W-doped vanadium dioxide nanopowder material.

Description

Preparation method of vanadium dioxide nano powder material

Technical field

The invention belongs to a method for preparing a vanadium dioxide powder material, in particular to a method for preparing a vanadium dioxide nanometer powder material.

Background technique

_VO2 is a typical phase-change compound. As the phase transition occurs, the resistivity, magnetic susceptibility, optical refractive index, transmittance, and reflectance change abruptly, and the phase transition process is reversible. These characteristics can make VO ₂ applied to smart temperature-controlled glass of buildings, photoelectric switch materials, thermistor materials, erasable optical storage materials, laser blinding weapon protection devices, photochromic materials, and modulators of submicron wave radiation and so on. Therefore, the research on VO ₂ and its preparation method has very important value.

The Chinese patent application with the application number 95196132.2 discloses a method for preparing vanadium dioxide particles. The method uses industrial ammonium hexavanadate (AHV) or ammonium hexavanadate (AMV) prepared as a raw material. (AHV) ammonium is used as a precursor, and non-doped vanadium dioxide particles are obtained by pyrolysis of the above precursor, or doped vanadium dioxide particles are obtained by pyrolysis after doping in the above precursor. Its pyrolysis is carried out at a temperature of about 400° C. and 650° C. and a heating rate of at least 100° C./minute, and the gas generated by the pyrolysis is kept within a certain range and in direct contact with the reaction medium for at least 1/2 hour, preferably for 1 hour. The problems of the above method are: 1. The raw material contains ammonium, so the content of ammonium must be controlled to ensure the accurate _VO2 structure, which brings difficulties to the process control; 2. The heating rate of the precursor pyrolysis is at least 100 °C /min, thus the power of the heating furnace is relatively large, which increases the cost of the equipment; 3, the prepared vanadium dioxide particle size is micron (size less than micron).

The Chinese patent application with application number 00117321.9 discloses a preparation method of vanadium dioxide nano-powder material. The steps of the method are: 1) using H ₂ C ₂ O ₄ .2H ₂ O and N ₂ H ₄ . VOCl ₂ was prepared by reducing V ₂ O ₅ in hydrochloric acid medium; 2) reacting the prepared VOCl ₂ solution with (NH ₄ ) ₂ CO ₃ or NH ₄ HCO ₃ to prepare vanadyl(IV) basic ammonium carbonate precursor, in The precursor is ultrasonically crushed in absolute ethanol to a particle size of ≤2 μm; 3) The prepared precursor is thermally decomposed in an inert atmosphere or an atmosphere containing an inert atmosphere to obtain VO ₂ powder at a heating temperature of 350-700°C. By doping Cr, Mo, W in the precursor, the vanadium dioxide nano-powder doped with Cr, Mo, W is obtained. The above method not only has complicated process steps, but also has adverse effects on the environment and the health of operators because hydrochloric acid and ammonia-containing substances are used as raw materials.

Contents of Invention

The purpose of the present invention is to overcome the deficiencies of the prior art and provide a new method for preparing undoped and doped vanadium dioxide nano-powder materials. This method not only simplifies the process, is beneficial to environmental protection, and is easy to control the quality.

Technical scheme of the present invention is as follows;

One, the preparation method of undoped vanadium dioxide nanopowder material

The process steps are the preparation of the precursor and the thermal decomposition of the precursor in sequence.

1. Preparation of precursor

Using V ₂ O _{5 and} oxalic acid (H ₂ C ₂ O ₄ 2H ₂ O) as raw materials, the weight ratio of V ₂ O ₅ to oxalic acid is 1:1 to 1: ₃ ; and oxalic acid into the reaction vessel and add water, the water can submerge V ₂ O ₅ and oxalic acid (the amount of water added is not strictly required), and then stir at normal pressure and 40-70°C until the V ₂ O ₅ and oxalic acid Until the reduction reaction is completed (the reduction reaction is completed to obtain a blue liquid without precipitation, generally 2 to 3 hours), after the reduction reaction is completed, the obtained solution is evaporated to dryness to obtain a solid vanadyl oxalate precursor, and its chemical formula is VO(C ₂ O ₄ ) ₂ ·H ₂ O.

2. Thermal decomposition of precursors

Any one of the following three processes can be used for the thermal decomposition of the precursor.

(1) Pulverize the obtained vanadyl oxalate precursor and put it into a heating furnace, heat it at a speed of 3-10°C/min under normal pressure to 250°C-300°C and start vacuuming, and continue to vacuumize under vacuum conditions. Heating at a rate of 3-10°C/min to 350°C-500°C, keeping the temperature for 20-40 minutes, then turning off the power of the heating furnace, maintaining the vacuum in the furnace, allowing the decomposition products to cool to room temperature to obtain vanadium dioxide nanopowder materials.

(2) After pulverizing the obtained vanadyl oxalate precursor, heat it in a heating furnace to 150°C-250°C (the heating rate is not strictly required, it can be 5-15°C/min) and keep it warm for 20-30 minutes, then vacuumize, Heating to 350-500°C at a speed of 3-10°C/min under vacuum conditions, keeping the temperature for 20-40 minutes, then turning off the power supply of the heating furnace, keeping the vacuum in the furnace, allowing the decomposition products to cool to room temperature to obtain vanadium dioxide Nano powder material.

(3) Pulverize the obtained precursor vanadyl oxalate and put it into a heating furnace, heat it to 350 ° C ~ 500 ° C at a speed of 3 ~ 10 ° C / min under vacuum conditions, and turn off the power supply of the heating furnace after keeping it for 20 ~ 40 minutes. Keeping the vacuum in the furnace, allowing the decomposition product to cool down to room temperature to obtain vanadium dioxide nanopowder material.

Two, the preparation method of Mo-doped vanadium dioxide nano-powder material

The process steps are the preparation of the precursor and the thermal decomposition of the precursor in sequence.

1. Preparation of precursor

Using V ₂ O ₅ , oxalic acid and MoO ₃ as raw materials, the formula of V ₂ O ₅ and MoO ₃ is calculated by weight percentage: V ₂ O ₅ 94-99%, MoO ₃ 1-6%, V ₂ O ₅ and oxalic acid The weight ratio is 1:1～1:3;

First, mix the V ₂ O ₅ and MoO ₃ in the above ratio evenly, put them into a heating container and heat them to a molten state under normal pressure (the temperature is 800°C to 900°C), and then pour the melt into a tank filled with water. in the reaction vessel and stirred (the addition of water is not strictly required, so as to disperse the V ₂ O ₅ and MoO ₃ melt), then add oxalic acid to the above solution and continue to stir until the reduction reaction is completed (reduction After the reaction is completed to obtain a blue liquid without precipitation (generally 2 to 4 hours), after the reduction reaction is completed, the obtained solution is evaporated to dryness to obtain a solid precursor of vanadyl oxalate doped with Mo ions.

2. Thermal decomposition of precursors

Any one of the following three processes can be used for the thermal decomposition of the precursor.

(1) Pulverize the obtained vanadyl oxalate precursor and put it into a heating furnace, heat it at a speed of 3-10°C/min under normal pressure to 250°C-300°C and start vacuuming, and continue to vacuumize under vacuum conditions. Heating at a rate of 3-10°C/min to 350°C-500°C, keeping the temperature for 20-40 minutes, then turning off the power supply of the heating furnace, keeping the vacuum in the furnace, allowing the decomposition products to cool to room temperature to obtain Mo-doped vanadium dioxide nanopowder body material.

(2) After pulverizing the obtained vanadyl oxalate precursor, heat it in a heating furnace to 150°C-250°C (the heating rate is not strictly required, it can be 5-15°C/min) and keep it warm for 20-30 minutes, then vacuumize, Heating to 350-500°C at a rate of 3-10°C/min under vacuum conditions, keeping the temperature for 20-40 minutes, then turning off the power supply of the heating furnace, keeping the vacuum in the furnace, allowing the decomposition products to cool to room temperature to obtain Mo-doped Vanadium dioxide nano powder material.

(3) Pulverize the obtained vanadyl oxalate precursor and put it into a heating furnace, heat it to 350 ° C ~ 500 ° C at a speed of 3 ~ 10 ° C / min under vacuum conditions, and turn off the power supply of the heating furnace after holding the temperature for 20 ~ 40 minutes. Keeping the vacuum in the furnace, allowing the decomposition product to cool down to room temperature to obtain the Mo-doped vanadium dioxide nanopowder material.

Three, the preparation method of W-doped vanadium dioxide nano-powder material

The process steps are the preparation of the precursor and the thermal decomposition of the precursor in sequence.

1. Preparation of precursor

Using V ₂ O ₅ , oxalic acid and N ₅ H ₃₇ W ₆ O ₂₄ as raw materials, the formula of V ₂ O ₅ and N ₅ H ₃₇ W ₆ O ₂₄ is calculated by weight percentage: V ₂ O ₅ 94-99%, N ₅ H ₃₇ W ₆ O ₂₄ 1~6%, the weight ratio of V ₂ O ₅ to oxalic acid is 1:1~1:3;

Put the V ₂ O ₅ , oxalic acid, and N ₅ H ₃₇ W ₆ O ₂₄ in the ratio into the reaction vessel and add water, and the water will cover the V ₂ O ₅ , oxalic acid, and N ₅ H ₃₇ W ₆ O ₂₄ (water There is no strict requirement on the amount of addition), and then under normal pressure, stir at 40-70°C until the reduction reaction is completed (the reduction reaction is completed to obtain a blue liquid without precipitation, generally 2 to 4 hours), the reduction reaction After completion, the obtained solution is evaporated to dryness to obtain a solid vanadyl oxalate precursor doped with W ions;

2. Thermal decomposition of precursors

Any one of the following three processes can be used for the thermal decomposition of the precursor.

(1) Pulverize the obtained vanadyl oxalate precursor and put it into a heating furnace, heat it at a speed of 3-10°C/min under normal pressure to 250°C-300°C and start vacuuming, and continue to vacuumize under vacuum conditions. Heating at a speed of 3-10°C/min to 350°C-500°C, keeping the temperature for 20-40 minutes, then turning off the power supply of the heating furnace, keeping the vacuum in the furnace, allowing the decomposition product to cool to room temperature to obtain W-doped vanadium dioxide nanopowder body material;

(2) After pulverizing the obtained vanadyl oxalate precursor, heat it in a heating furnace to 150°C-250°C (the heating rate is not strictly required, it can be 5-15°C/min) and keep it warm for 20-30 minutes, and then heat it under vacuum Heating to 350°C-500°C at a rate of 3-10°C/min under certain conditions, and keeping the temperature for 20-40 minutes, then turn off the power supply of the heating furnace, keep the vacuum in the furnace, and let the decomposition products cool to room temperature to obtain W-doped carbon dioxide Vanadium nano powder material;

(3) Pulverize the obtained vanadyl oxalate precursor and put it into a heating furnace, heat it to 350 ° C ~ 500 ° C at a speed of 3 ~ 10 ° C / min under vacuum conditions, and turn off the power supply of the heating furnace after holding the temperature for 20 ~ 40 minutes. Keeping the vacuum in the furnace, allowing the decomposition products to cool down to room temperature to obtain W-doped vanadium dioxide nanopowder material.

Above-mentioned three kinds of preparation methods all also adopted following technical measures:

1. The raw material V ₂ O ₅ used is industrial grade or chemical reagent grade.

2. In the step of preparing the precursor, the surfactant polyethylene glycol can be added, and the amount of polyethylene glycol added is 2-5% (percentage by weight) of the total weight of V ₂ O ₅ and oxalic acid.

3. In the thermal decomposition step of the precursor, the vacuum degree in the heating furnace is controlled at 20Pa-60Pa.

4. Anneal the undoped and doped vanadium dioxide nano-powder material obtained by thermal decomposition. The annealing process is to heat up to 400 ° C ~ 600 ° C under vacuum conditions for 1 ~ 4 hours, and then under vacuum conditions ( Vacuum degree is 10～20Pa) Cool to room temperature.

The present invention has the following beneficial effects:

1. Since oxalic acid is used as the V ₂ O ₅ reducing agent, there is no pollution, which is beneficial to environmental protection and the health of operators, and it is easy to control the quality of vanadium dioxide nano-powder materials.

2. The reduction reaction of V ₂ O ₅ and oxalic acid can directly obtain the precursor vanadyl oxalate, thus simplifying the process flow of precursor preparation.

3. The process of doping different metal elements is simple and easy to operate.

4. The thermal decomposition temperature of the precursor is low, and the decomposition time is short, which is beneficial to energy saving.

5. The thermal decomposition and heating speed of the precursor is slow, so the power requirement of the heating furnace is small, and the equipment investment can be reduced.

6. A surfactant is added in the precursor preparation step, which is beneficial to the pulverization of the precursor and improves the dispersibility of the nano-powder.

7. The particle size of the obtained vanadium dioxide nano-powder is less than 50nm, and the powder particles are nearly spherical, with good uniformity and high purity.

8. The obtained vanadium dioxide nano-powder material has obvious phase transition characteristics, and the phase transition temperature of the doped powder can be reduced from 68 °C without doping to about 30-35 °C.

9. The source of raw materials is wide and easy to obtain, which is convenient for industrial production.

Description of drawings

Fig. 1 is the transmission electron microscope (TEM) photograph of undoped vanadium dioxide nanopowder material of the present invention;

Fig. 2 is the X-ray diffraction (XRD) analysis result figure of undoped vanadium dioxide nano-powder material of the present invention;

Fig. 3 is the X-ray diffraction (XRD) analysis result figure of the vanadium dioxide nano-powder body material doped with MoO ₃ 3%;

Fig. 4 is the transmission electron microscope (TEM) photograph of the vanadium dioxide nanopowder material of doping MoO ₃ 3%;

Fig. 5 is a graph of X-ray diffraction (XRD) analysis results of vanadium dioxide nanopowder material doped with N ₅ H ₃₇ W ₆ O ₂₄ 3%.

Detailed ways

Embodiment 1: Preparation of undoped vanadium dioxide nanopowder material

It is 1:2. Pass V ₂ O ₅ and oxalic acid, and stir at normal pressure and 60°C for about 2.5 hours to complete the reduction reaction, and evaporate the obtained solution to dryness at 90°C to obtain a vanadyl oxalate precursor. Keep warm at 200°C for 25 minutes, then vacuumize, heat to 400°C at a speed of 5°C/min under the condition of vacuum degree of 45Pa and keep warm for 30 minutes, then turn off the power supply of the heating furnace, keep the vacuum degree in the furnace, and let the decomposition products cool down to At room temperature, VO ₂ nanopowder was obtained. 4 The weight ratio of chemical reagent grade V ₂ O ₅ to oxalic acid is 1:3. Put V ₂ O ₅ and oxalic acid into the reaction vessel, add water to submerge the V ₂ O ₅ and oxalic acid, stir at normal pressure and 70°C for about 2 hours to complete the reduction reaction, and then add 5% of the total weight of V ₂ O ₅ and oxalic acid. Ethylene glycol, and the obtained solution was evaporated to dryness at 90° C. to obtain a vanadyl oxalate precursor. Put the precursor into a tubular heating furnace after being pulverized, and heat it to 450°C at a speed of 8°C/min under a vacuum of 35Pa and keep it for 25 minutes. Cool to room temperature to obtain _VO2 nanopowder. Raise the temperature to 600°C for 1 hour under the condition of vacuum degree of 10Pa, turn off the power of the heating furnace, keep the vacuum degree in the furnace, and cool to room temperature. ≤50nm

The TEM photo of the undoped vanadium dioxide nanopowder material prepared in this example is shown in FIG. 1 , and the XRD analysis results are shown in FIG. 2 . Figure 1 shows that the particle size of the obtained vanadium dioxide nanopowder is less than 50nm, the powder particles are nearly spherical, and have good uniformity. Figure 2 shows that the product obtained by thermal decomposition is a crystal structure of vanadium dioxide.

Embodiment 2: Preparation of Mo-doped vanadium dioxide nanopowder material

The first group: select industrial grade V ₂ O ₅ , the formula of V ₂ O ₅ and MoO ₃ is calculated by weight percentage: V ₂ O ₅ 99%, MoO ₃ 1%; the weight ratio of V ₂ O ₅ to oxalic acid is 1 : 1.

(1) Preparation of precursor

Mix the V ₂ O ₅ and MoO ₃ in the above ratio evenly and put them into a container, heat to 800°C under normal pressure to be in a molten state, then pour the melt into a reaction container filled with water and stir ( The amount of water added should be enough to disperse the _V2O5 and _MoO3 melts), then add the measured oxalic acid to the above solution and continue to stir until the reduction reaction is completed ( _about 3 hours), after the reduction reaction is completed A blue liquid without precipitation was obtained, and the obtained solution was evaporated to dryness at 90° C. to obtain a solid precursor of vanadyl oxalate doped with Mo ions.

(2) Thermal decomposition of precursors

Put the obtained vanadyl oxalate precursor into a tubular heating furnace after pulverization, and start vacuuming when it is heated to 250 °C at a rate of 3 °C/min under normal pressure, and the vacuum degree is controlled at 55 Pa. Heating at a rate of ℃/min to 350 ℃, keeping the temperature for 40 minutes, turning off the power supply of the heating furnace, keeping the vacuum in the furnace, allowing the decomposition product to cool to room temperature to obtain Mo-doped vanadium dioxide nanopowder material. The particle size of the Mo-doped vanadium dioxide nanometer powder is ≤40nm, and the phase transition temperature is 60°C.

The second group: use chemical reagent grade V ₂ O ₅ , the formula of V ₂ O ₅ and MoO ₃ is calculated by weight percentage: V ₂ O ₅ 97%, MoO ₃ 3%; the weight ratio of V ₂ O ₅ and oxalic acid is 1:1.5.

(1) Preparation of precursor

Mix the V ₂ O ₅ and MoO ₃ in the above ratio evenly, put them into a container, heat to 850°C under normal pressure to form a molten state, then pour the melt into a reaction container filled with water and stir (water The addition amount can disperse V ₂ O ₅ and MoO ₃ melts get final product), then add metered oxalic acid and V ₂ O ₅ and the polyethylene glycol of oxalic acid gross weight 3% in the above-mentioned solution and continue to stir, Until the reduction reaction is completed (about 2.5 hours), a blue liquid without precipitation is obtained after the reduction reaction is completed, and the obtained solution is evaporated to dryness at 80° C. to obtain a solid precursor of vanadyl oxalate doped with Mo ions.

(2) Thermal decomposition of precursors

After pulverizing the obtained vanadyl oxalate precursor, heat it in a tubular heating furnace at 8°C/min to 150°C for 30 minutes, then vacuumize it, and heat it to 400°C at a speed of 5°C/min at a vacuum degree of 45Pa After 30 minutes of heat preservation, turn off the power supply of the heating furnace, keep the vacuum in the furnace, and allow the decomposition product to cool to room temperature to obtain the Mo-doped vanadium dioxide nanopowder material. The particle size of the Mo-doped vanadium dioxide nanometer powder is ≤50nm, and the phase transition temperature is 50°C.

The XRD analysis results of the Mo-doped vanadium dioxide nanopowder material prepared in this example are shown in FIG. 3 , and the TEM photos are shown in FIG. 4 . Figure 3 shows that the product obtained by thermal decomposition is a crystal structure of vanadium dioxide. Figure 4 shows that the particle size of the obtained Mo-doped vanadium dioxide nanopowder is ≤50nm, the powder particles are nearly spherical, and have good uniformity.

The third group: use chemical reagent grade V ₂ O ₅ , the formula of V ₂ O ₅ and MoO ₃ is calculated by weight percentage: V ₂ O ₅ 95%, MoO ₃ 5%; the weight ratio of V ₂ O ₅ and oxalic acid is 1:2.

(1) Preparation of precursor

Mix the V ₂ O ₅ and MoO ₃ in the above ratio evenly, put them into a container, heat to 900°C under normal pressure to be in a molten state, then pour the melt into a reaction container filled with water and stir ( The amount of water added should be able to disperse V ₂ O ₅ and MoO ₃ melts), then add metered oxalic acid and polyethylene glycol with 4% of the total weight of V ₂ O ₅ and oxalic acid in the above solution and continue to stir , until the reduction reaction is completed (about 2.5 hours), a blue liquid without precipitation is obtained after the reduction reaction is completed, and the obtained solution is evaporated to dryness at 100° C. to obtain a solid precursor of vanadyl oxalate doped with Mo ions.

(2) Thermal decomposition of precursors

The obtained vanadyl oxalate precursor was pulverized and put into a tubular heating furnace, heated to 450°C at a speed of 7°C/min under a vacuum of 35Pa, and turned off the power supply of the heating furnace after holding for 25 minutes to maintain the vacuum in the furnace , allowing the decomposition product to cool to room temperature to obtain Mo-doped vanadium dioxide nanopowder material.

(3) Annealing

Raise the temperature to 600°C for 1 hour under the condition of vacuum degree of 20 Pa, turn off the power supply of the heating furnace, keep the vacuum degree in the furnace, and cool to room temperature.

The particle size of the Mo-doped vanadium dioxide nanometer powder is ≤50nm, and the phase transition temperature is 40°C.

The fourth group: choose industrial grade V ₂ O ₅ , the formula of V ₂ O ₅ and MoO ₃ is calculated by weight percentage: V ₂ O ₅ 94%, MoO ₃ 6%; the weight ratio of V ₂ O ₅ and oxalic acid is 1 : 3.

(1) Preparation of precursor

Mix the V ₂ O ₅ and MoO ₃ in the above ratio evenly, put them into a heating container, heat to 900°C under normal pressure to become a molten state, then pour the melt into a reaction container filled with water and stir ( The amount of water added should be able to disperse V ₂ O ₅ and MoO ₃ melt), then add measured oxalic acid to the above solution and continue to stir until the reduction reaction is completed (about 2 hours), after the reduction reaction is completed A blue liquid without precipitation was obtained, and the obtained solution was evaporated to dryness at 100° C. to obtain a solid precursor of vanadyl oxalate doped with Mo ions.

(2) Thermal decomposition of precursors

The obtained vanadyl oxalate precursor was pulverized and put into a tubular heating furnace, and heated to 500°C at a rate of 7°C/min under a vacuum of 25Pa, and turned off the power supply of the heating furnace after holding for 20 minutes to maintain the vacuum in the furnace , allowing the decomposition product to cool to room temperature to obtain Mo-doped vanadium dioxide nanopowder material.

(3) Annealing

Raise the temperature to 500°C for 2 hours under the condition of vacuum degree of 10 Pa, turn off the power supply of the heating furnace, keep the vacuum degree in the furnace, and cool to room temperature.

The particle size of the Mo-doped vanadium dioxide nanometer powder is ≤50nm, and the phase transition temperature is 35°C.

Embodiment 3: Preparation of W-doped vanadium dioxide nanopowder material

The first group: select industrial grade V ₂ O ₅ , the formula of V ₂ O ₅ and N ₅ H ₃₇ W ₆ O ₂₄ is calculated by weight percentage: V ₂ O ₅ 99%, N ₅ H ₃₇ W ₆ O ₂₄ 1% ; The weight ratio of V ₂ O ₅ to oxalic acid is 1:1

(1) Preparation of precursor

Put the ratio of V ₂ O ₅ , oxalic acid, N ₅ H ₃₇ W ₆ O ₂₄ and V ₂ O ₅ and polyethylene glycol with 2% of the total weight of oxalic acid into the reaction vessel and add water at normal pressure and 40°C. Stir for about 3 hours to complete the reduction reaction. It is advisable to add water so that the raw materials in the reaction vessel are submerged. When the reduction reaction is completed, a blue liquid without precipitation is obtained. The obtained solution is evaporated to dryness at 80°C to obtain the mixed Solid vanadyl oxalate precursor for W ions.

(2) Thermal decomposition of precursors

Put the obtained vanadyl oxalate precursor into a tubular heating furnace after pulverization, and start vacuuming when it is heated to 250 °C at a rate of 3 °C/min under normal pressure, and the vacuum degree is controlled at 55 Pa. Heat at a rate of ℃/min to 350 ℃, keep the temperature for 40 minutes, turn off the power of the heating furnace, keep the vacuum in the furnace, and let the decomposition product cool to room temperature to obtain W-doped vanadium dioxide nanopowder material.

The particle size of the W-doped vanadium dioxide nanometer powder is ≤40nm, and the phase transition temperature is 40°C.

The second group: use chemical reagent grade V ₂ O ₅ , the formula of V ₂ O ₅ and N ₅ H ₃₇ W ₆ O ₂₄ is calculated by weight percentage: V ₂ O ₅ 97%, N ₅ H ₃₇ W ₆ O ₂₄ 3 %; The weight ratio of V ₂ O ₅ to oxalic acid is 1:1.5.

(1) Preparation of precursor

Put the ratio of V ₂ O ₅ , oxalic acid, N ₅ H ₃₇ W ₆ O ₂₄ into the reaction vessel, add water and stir at normal pressure and 50°C for about 3 hours to complete the reduction reaction. The amount of water added is equal to the reaction vessel It is advisable to submerge the raw materials in it. When the reduction reaction is completed, a blue liquid without precipitation is obtained. The obtained solution is evaporated to dryness at 90° C. to obtain a solid vanadyl oxalate precursor doped with W ions.

(2) Thermal decomposition of precursors

After pulverizing the obtained vanadyl oxalate precursor, heat it to 150°C at a rate of 5°C/min in a tubular heating furnace for 30 minutes, then evacuate it, and heat it to 400°C at a rate of 5°C/min at a vacuum degree of 45Pa. After 30 minutes of heat preservation, turn off the power supply of the heating furnace, keep the vacuum in the furnace, and let the decomposition product cool to room temperature to obtain W-doped vanadium dioxide nanopowder material.

(3) Annealing

Raise the temperature to 500°C for 2 hours under the condition of vacuum degree of 20 Pa, turn off the power supply of the heating furnace, keep the vacuum degree in the furnace, and cool to room temperature.

The particle size of the W-doped vanadium dioxide nanometer powder is ≤50nm, and the phase transition temperature is 32°C.

The XRD analysis results of the W-doped vanadium dioxide nanopowder material prepared in this example are shown in Figure 5, which shows that the product obtained by thermal decomposition has a vanadium dioxide crystal structure.

The third group: use chemical reagent grade V ₂ O ₅ , the formula of V ₂ O ₅ and N ₅ H ₃₇ W ₆ O ₂₄ is calculated by weight percentage: V ₂ O ₅ 95%, N ₅ H ₃₇ W ₆ O ₂₄ 5 %; The weight ratio of V ₂ O ₅ to oxalic acid is 1:2.

(1) Preparation of precursor

Put V ₂ O ₅ , oxalic acid, N ₅ H ₃₇ W ₆ O ₂₄ and polyethylene glycol with a total weight of 4% of V ₂ O ₅ and oxalic acid in the reaction vessel and add water at normal pressure and 60°C. Stir for about 2.5 hours to complete the reduction reaction. It is advisable to add water so that the raw materials in the reaction vessel are submerged. When the reduction reaction is completed, a blue liquid without precipitation is obtained. The obtained solution is evaporated to dryness at 100°C to obtain the mixed Solid vanadyl oxalate precursor with W ions.

(2) Thermal decomposition of precursors

The obtained vanadyl oxalate precursor was pulverized and put into a tubular heating furnace, heated to 450°C at a speed of 7°C/min under a vacuum of 35Pa, and turned off the power supply of the heating furnace after holding for 25 minutes to maintain the vacuum in the furnace , allowing the decomposition product to cool to room temperature to obtain W-doped vanadium dioxide nanopowder material.

(3) Annealing

Raise the temperature to 600°C for 1 hour under the condition of vacuum degree of 10 Pa, turn off the power supply of the heating furnace, keep the vacuum degree in the furnace, and cool to room temperature.

The particle size of the W-doped vanadium dioxide nanometer powder is ≤50nm, and the phase transition temperature is 30°C.

The fourth group: select industrial grade V ₂ O ₅ , the formula of V ₂ O ₅ and N ₅ H ₃₇ W ₆ O ₂₄ is calculated by weight percentage: V ₂ O ₅ 94%, N ₅ H ₃₇ W ₆ O ₂₄ 6% ; The weight ratio of V ₂ O ₅ to oxalic acid is 1:3.

(1) Preparation of precursor

Put V ₂ O ₅ , oxalic acid, N ₅ H ₃₇ W ₆ O ₂₄ and polyethylene glycol with 5% total weight of V ₂ O ₅ and oxalic acid in the reaction vessel and add water at normal pressure and 70°C. Stir for 2 hours to complete the reduction reaction. It is advisable to add water so that the raw materials in the reaction vessel are submerged. When the reduction reaction is completed, a blue liquid without precipitation is obtained. The obtained solution is evaporated to dryness at 80°C to obtain Solid vanadyl oxalate precursor for W ions.

(2) Thermal decomposition of precursors

The obtained vanadyl oxalate precursor was pulverized and put into a tubular heating furnace, and heated to 500°C at a rate of 7°C/min under a vacuum of 25Pa, and turned off the power supply of the heating furnace after holding for 20 minutes to maintain the vacuum in the furnace , allowing the decomposition product to cool to room temperature to obtain W-doped vanadium dioxide nanopowder material.

The particle size of the W-doped vanadium dioxide nanometer powder is ≤50nm, and the phase transition temperature is 28°C.

Claims (6)

1, a kind of preparation method of vanadium dioxide nano powder, processing step is followed successively by the preparation of presoma and the thermolysis of presoma, it is characterized in that:

(1) preparation of presoma

With V ₂O ₅With oxalic acid be raw material, V ₂O ₅With the weight ratio of oxalic acid be 1: 1～1: 3, with the V of described proportioning ₂O ₅Put into reaction vessel and add water with oxalic acid, V is crossed in water logging ₂O ₅Get final product with oxalic acid, stir normal pressure, 40～70 ℃ then, up to V ₂O ₅Till finishing with the reduction reaction of oxalic acid, after reduction reaction is finished, obtaining solution evaporate to dryness is promptly obtained solid oxalic acid vanadyl presoma;

(2) thermolysis of presoma

To put into process furnace after the pulverizing of obtaining oxalic acid vanadyl presoma, begin to vacuumize when under normal pressure, being heated to 250 ℃～300 ℃ with the speed of 3～10 ℃/min, vacuum degree control in the process furnace is at 20～60Pa, and under vacuum condition, continue to be heated to 350 ℃～500 ℃ with the speed of 3～10 ℃/min, be incubated and close the process furnace power supply after 20～40 minutes, keep the vacuum tightness in the stove, allow degradation production be cooled to room temperature and obtain vanadium dioxide nano powder;

Or obtaining oxalic acid vanadyl presoma is pulverized back speed with 5～15 ℃/min in process furnace be heated to 150 ℃～250 ℃ insulations 20～30 minutes, vacuumize then, vacuum degree control in the process furnace is at 20～60Pa, speed with 3～10 ℃/min under vacuum condition is heated to 350 ℃～500 ℃, be incubated and close the process furnace power supply after 20～40 minutes, keep the vacuum tightness in the stove, allow degradation production be cooled to room temperature and obtain vanadium dioxide nano powder;

Or will put into process furnace after the pulverizing of obtaining presoma oxalic acid vanadyl, speed with 3～10 ℃/min under the condition of vacuum tightness 20～60Pa is heated to 350 ℃～500 ℃, be incubated and close the process furnace power supply after 20～40 minutes, keep the vacuum tightness in the stove, allow degradation production be cooled to room temperature and obtain vanadium dioxide nano powder.

2, a kind of preparation method of vanadium dioxide nano powder, processing step is followed successively by the preparation of presoma and the thermolysis of presoma, it is characterized in that:

(1) preparation of presoma

With V ₂O ₅, oxalic acid and MoO ₃Be raw material, V ₂O ₅With MoO ₃Prescription by weight percentage ratio count: V ₂O ₅94～99%, MoO ₃1～6%, V ₂O ₅With the weight ratio of oxalic acid be 1: 1～1: 3, at first with the V of described proportioning ₂O ₅With MoO ₃Put into heating container after mixing and under normal pressure, be heated to molten state, pour into this melt in the reaction vessel that water is housed then and stir, add oxalic acid and proceed stirring in above-mentioned solution again, till reduction reaction was finished, the add-on of water was can disperse V ₂O ₅With MoO ₃Melt gets final product, and after reduction reaction is finished, obtaining solution evaporate to dryness is promptly obtained being mixed with Mo ionic oxalic acid vanadyl solid precursor;

(2) thermolysis of presoma

To put into process furnace after the pulverizing of obtaining oxalic acid vanadyl presoma, begin to vacuumize when under normal pressure, being heated to 250 ℃～300 ℃ with the speed of 3～10 ℃/min, vacuum degree control in the process furnace is at 20～60Pa, and under vacuum condition, continue to be heated to 350 ℃～500 ℃ with the speed of 3～10 ℃/min, be incubated and close the process furnace power supply after 20～40 minutes, keep the vacuum tightness in the stove, allow degradation production be cooled to room temperature and obtain to mix the vanadium dioxide nano powder of Mo;

Or obtaining oxalic acid vanadyl presoma is pulverized back speed with 5～15 ℃/min in process furnace be heated to 150 ℃～250 ℃ insulations 20～30 minutes, vacuumize then, vacuum degree control in the process furnace is at 20～60Pa, speed with 3～10 ℃/min under vacuum condition is heated to 350 ℃～500 ℃, be incubated and close the process furnace power supply after 20～40 minutes, keep the vacuum tightness in the stove, allow degradation production be cooled to room temperature and obtain to mix the vanadium dioxide nano powder of Mo;

Or will put into process furnace after the pulverizing of obtaining oxalic acid vanadyl presoma, speed with 3～10 ℃/min under the condition of vacuum tightness 20～60Pa is heated to 350 ℃～500 ℃, be incubated and close the process furnace power supply after 15～40 minutes, keep the vacuum tightness in the stove, allow degradation production be cooled to room temperature and obtain to mix the vanadium dioxide nano powder of Mo.

3, a kind of preparation method of vanadium dioxide nano powder, processing step is followed successively by the preparation of presoma and the thermolysis of presoma, it is characterized in that:

(1) preparation of presoma

With V ₂O ₅, oxalic acid and N ₅H ₃₇W ₆O ₂₄Be raw material, V ₂O ₅With N ₅H ₃₇W ₆O ₂₄Prescription by weight percentage ratio count: V ₂O ₅94～99%, N ₅H ₃₇W ₆O ₂₄1～6%, V ₂O ₅With the weight ratio of oxalic acid be 1: 1～1: 3, with the V of described proportioning ₂O ₅, oxalic acid and N ₅H ₃₇W ₆O ₂₄Put into reaction vessel and add water, V is crossed in water logging ₂O ₅, oxalic acid and N ₅H ₃₇W ₆O ₂₄Get final product, stir normal pressure, 40～70 ℃ then, till reduction reaction is finished, after reduction reaction is finished, obtaining solution evaporate to dryness is promptly obtained being mixed with W ionic solid oxalic acid vanadyl presoma;

(2) thermolysis of presoma

To put into process furnace after the pulverizing of obtaining oxalic acid vanadyl presoma, begin to vacuumize when under normal pressure, being heated to 250 ℃～300 ℃ with the speed of 3～10 ℃/min, vacuum degree control in the process furnace is at 20～60Pa, and under vacuum condition, continue to be heated to 350 ℃～500 ℃ with the speed of 3～10 ℃/min, be incubated and close the process furnace power supply after 20～40 minutes, keep the vacuum tightness in the stove, allow degradation production be cooled to room temperature and obtain to mix the vanadium dioxide nano powder of W;

Or obtaining oxalic acid vanadyl presoma is pulverized back speed with 5～15 ℃/min in process furnace be heated to 150 ℃～250 ℃ insulations 20～30 minutes, vacuumize then, vacuum degree control in the process furnace is at 20～60Pa, speed with 3～10 ℃/min under vacuum condition is heated to 350 ℃～500 ℃, be incubated and close the process furnace power supply after 20～40 minutes, keep the vacuum tightness in the stove, allow degradation production be cooled to room temperature and obtain to mix the vanadium dioxide nano powder of W;

Or will put into process furnace after the pulverizing of obtaining oxalic acid vanadyl presoma, speed with 3～10 ℃/min under the condition of vacuum tightness 20～60Pa is heated to 350 ℃～500 ℃, be incubated and close the process furnace power supply after 20～40 minutes, keep the vacuum tightness in the stove, allow degradation production be cooled to room temperature and obtain to mix the vanadium dioxide nano powder of W.

4, according to the preparation method of claim 1 or 2 or 3 described vanadium dioxide nano powders, it is characterized in that with the technology that thermolysis obtains the vanadium dioxide nano powder anneal it being under vacuum condition, to be warmed up to 400 ℃～600 ℃ insulations 1～4 hour, under vacuum condition, be cooled to room temperature then.

5,, it is characterized in that in the presoma preparation process adding that surfactant polyethylene, the add-on of polyoxyethylene glycol are arranged is V according to the preparation method of claim 1 or 2 or 3 described vanadium dioxide nano powders ₂O ₅With 2～5% of oxalic acid gross weight.

6, according to the preparation method of claim 1 or 2 or 3 described vanadium dioxide nano powders, it is characterized in that V ₂O ₅Be technical grade or chemical reagent-grade.

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