JP2016160148A - Production method of vanadium dioxide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide vanadium dioxide excellent in heat storage property by an industrially advantageous method.SOLUTION: There is provided a production method of vanadium dioxide represented by following general formula (1) VMO(1), where M represents one or more kind selected from a group of Cr, W, Mo, Nb, Ta, Os, Ir, Ru and Re and x represents 0≤x≤0.5. The production method comprises a first step of adding alkali to a solution containing a vanadium source and performing a reaction to prepare a slurry containing deposited precipitate, a second step of applying a hydrothermal reaction to the slurry to obtain a reaction precursor, a third step of firing the reaction precursor in an inactive gas atmosphere to obtain a fired product and a fourth step of anneal-treating the fired product and if needed, adding an M source to a solution containing the vanadium source and/or a slurry containing the precipitate.SELECTED DRAWING: Figure 6

Description

  The present invention relates to a method for producing vanadium dioxide particularly useful as a heat storage material.

  The heat storage material is a material that can store heat in a substance and take out the heat as necessary. By heat storage, the temperature of the heat storage material itself or the space where the heat storage material is placed can be kept constant.

  Thermal storage methods include sensible heat storage, latent heat storage, and chemical heat storage, and are classified according to the physicochemical phenomenon used during heat storage.

  Latent heat storage uses the transition heat associated with the phase change and transition of materials, and stores and uses the transition heat as thermal energy.Latent heat storage has a higher heat storage density than phase sensible heat storage, Heat can be supplied at a constant transition temperature, and it has excellent durability because it only repeats phase transitions compared to chemical heat storage.

  Patent Document 1 and Patent Document 2 below propose using a vanadium dioxide-based strongly correlated electron transition metal compound as a new type of latent heat storage material using electronic phase transition heat. This type of heat storage material uses a phase transition of multiple degrees of freedom including the degree of freedom of spin, which is the internal degree of freedom of electrons, and the degree of freedom of orbit, and is a phase transition that occurs in the solid state. Therefore, there is no worry that the heat storage material leaks from the container. In addition, unlike solid-liquid phase transitions such as inorganic salt hydrates, there is no risk of phase separation or decomposition during phase transitions, and volume changes during phase transitions are small compared to solid-liquid phase transitions. There are also advantages such as having conductivity.

  As a method for producing a vanadium dioxide-based strongly correlated electron transition metal compound, Patent Document 1 and Patent Document 2 propose a method in which a mixture obtained by mixing a predetermined amount of each raw material is vacuum sealed and heated. However, this is not an industrially advantageous method.

  In addition, as a method for producing a vanadium dioxide-based strongly correlated electron transition metal compound, Patent Document 3 listed below hydrothermally reacts a precipitate obtained by adding an alkali to a solution containing a soluble vanadium compound. A method has been proposed. Patent Document 4 below discloses a method of firing a reaction product obtained by reacting a solution containing a tetravalent vanadium compound with a solution of a substance complexing with the vanadium compound and a dopant element in an inert gas. Proposed.

JP, 2014-210835, A JP 2010-163510 A Special table 2014-505651 gazette JP 2014-198645 A

However, according to the method of Patent Document 3, vanadium dioxide can be obtained by an industrially advantageous method, but it is difficult to obtain a material having excellent heat storage characteristics.
Accordingly, an object of the present invention is to provide vanadium dioxide having excellent heat storage characteristics in an industrially advantageous manner.

  As a characteristic of the material used for latent heat storage, in addition to the large amount of transition heat, there is a difference in the phase transition temperature between the temperature rising process and the temperature decreasing process so that temperature unevenness of the heat storage characteristics does not occur during temperature rising and cooling. It is required to be as small as possible.

As a result of intensive studies in view of the above circumstances, the present inventors have found that the following general formula (1)
V _1-x M _x O ₂ (1)
(In the formula, M represents one or more elements selected from the group consisting of Cr, W, Mo, Nb, Ta, Os, Ir, Ru, and Re. X represents 0 ≦ x ≦ 0.5. A method for producing vanadium dioxide represented by:
In the reaction precursor obtained by adding an alkali to the solution containing the vanadium source and reacting to precipitate a precipitate, and then subjecting the resulting precipitate to a hydrothermal reaction, a phase transition accompanying endothermic generation is observed. Although there is no, a phase transition associated with endothermic heat generation is observed in the fired product obtained by firing the reaction precursor in an inert gas atmosphere. Further, it was found that the difference between the endothermic start temperature and the exothermic start temperature is reduced by annealing the fired product, and the present invention has been completed.

That is, the method for producing vanadium dioxide to be provided by the present invention comprises the following general formula (1):
V _1-x M _x O ₂ (1)
(In the formula, M represents one or more elements selected from the group consisting of Cr, W, Mo, Nb, Ta, Os, Ir, Ru, and Re. X represents 0 ≦ x ≦ 0.5. A method for producing vanadium dioxide represented by:
A first step of preparing a slurry containing a precipitate formed by adding an alkali to a solution containing a vanadium source and performing a reaction, then a second step of subjecting the slurry to a hydrothermal reaction to obtain a reaction precursor, A third step of firing the reaction precursor in an inert gas atmosphere to obtain a fired product, and then a fourth step of annealing the fired product, and optionally a solution containing the vanadium source and / or the precipitation The M source is added to the slurry containing the product.

  According to the production method of the present invention, vanadium dioxide useful as a heat storage material can be provided by an industrially advantageous method.

2 is an X-ray diffraction diagram of a reaction precursor sample obtained in the second step of Example 1. FIG. The figure which shows the differential scanning calorimetry result of the reaction precursor sample obtained at the 2nd process of Example 1. FIG. 3 is an X-ray diffraction pattern of a fired product sample obtained in the third step of Example 1. FIG. The figure which shows the differential scanning calorimetry result of the baked product sample obtained at the 3rd process of Example 1. FIG. FIG. 4 is an X-ray diffraction pattern of an annealed product sample obtained in the fourth step of Example 1. The figure which shows the differential scanning calorimetry result of the annealed product sample obtained at the 4th process of Example 1. FIG. 4 is an SEM photograph of an annealed product sample obtained in the fourth step of Example 1. FIG.

Hereinafter, the present invention will be described based on preferred embodiments thereof.
Vanadium dioxide obtained by the production method of the present invention is a compound represented by the following general formula (1).
V _1-x M _x O ₂ (1)
(In the formula, M represents one or more elements selected from the group consisting of Cr, W, Mo, Nb, Ta, Os, Ir, Ru, and Re. X represents 0 ≦ x ≦ 0.5. Show.)

  In latent heat storage, heat storage is performed near the phase transition temperature. M in the formula of the general formula (1) is an element added as necessary in the present invention.

  For example, when the vanadium dioxide obtained by the production method of the present invention is used as a heat storage material, the phase transition temperature is adjusted to a desired temperature by adjusting the values of M and x in the formula of the general formula (1). Can be prepared. For example, by substituting a part of vanadium vanadium with an element such as W, Ta, Nb, Ru, Mo, Re or the like, the phase transition temperature can be lowered as compared with unsubstituted vanadium dioxide. Further, it is known that the phase transition temperature decreases as the substitution amount increases (Japanese Patent Laid-Open No. 2010-163510). In addition, by replacing a part of vanadium of vanadium dioxide with Cr, the phase transition temperature can be made higher than that of unsubstituted vanadium dioxide. Further, it is known that the phase transition temperature increases as the substitution amount increases (Japanese Patent Laid-Open No. 2014-210835).

  The first step according to this production method is a step of preparing a slurry containing a precipitate by adding an alkali to a solution containing a vanadium source and performing a reaction to precipitate the precipitate.

  The solution containing the vanadium source according to the first step is a solution in which the vanadium source is dissolved in an aqueous solvent.

As the vanadium source according to the first step, a tetravalent vanadium compound is preferably used. Examples of the tetravalent vanadium compound include vanadyl sulfate (VOSO ₄ ), vanadyl dichloride (VOCl ₂ ), vanadyl oxalate (VOC ₂ O ₄ ), and the like. These vanadium compounds may be hydrated or anhydrous.

  The aqueous solvent for dissolving the vanadium source is not limited to water, and may be a mixed solvent of water and a hydrophilic solvent.

  The concentration of the vanadium source in the solution containing the vanadium source is preferably 0.5 to 5% by mass, more preferably 1 to 3% by mass in terms of anhydride.

  As an alkali which concerns on a 1st process, ammonia water, sodium hydroxide, potassium hydroxide, sodium carbonate, sodium hydrogencarbonate, potassium carbonate, potassium hydrogencarbonate etc. are mentioned, for example. These alkalis are preferably used as an aqueous solution dissolved in water.

  The amount of alkali added is 0.1 to 3, preferably 0.4 to 0.6, in terms of the molar ratio of vanadium ions in the solution containing the vanadium source to the alkali (vanadium ions / alkali). This is preferable from the viewpoint of depositing a precipitate.

  Since the reaction according to the first step is basically a neutralization reaction, the alkali may be added so that the reaction solution has a pH of 5 to 9, preferably 6 to 8.

  The alkali is preferably added at a constant rate so that a stable quality can be obtained.

  The addition temperature of the alkali is preferably 5 to 50 ° C., preferably 10 to 35 ° C., from the viewpoint of depositing the precipitate with high yield.

In the first step, an aging reaction can be performed for the purpose of improving the yield after adding an alkali, if necessary.
The temperature of the aging reaction is 5 to 50 ° C., preferably 10 to 35 ° C., and the time of the aging reaction is 15 minutes or more, preferably 0.5 to 3 hours.

  By performing the above operation, a slurry containing precipitates precipitated by the reaction can be obtained, and the slurry can be subjected to the hydrothermal reaction in the second step as it is. However, in this production method, the slurry concentration is 0 if necessary. The concentration can be adjusted to 1 to 5% by mass, preferably 0.5 to 3% by mass, and the second step can be performed.

  Moreover, in this manufacturing method, M source can be added to the solution containing the said vanadium source and / or the slurry containing the said precipitate as needed, and the 2nd process mentioned later can be performed.

  The M source to be added may be the M element itself or a compound containing the M element. Examples of the compound containing M element include an oxide of M element, a metal acid such as molybdic acid or tungstic acid or a metal acid salt thereof, an alcoholate of M element, or an organic acid salt of M element.

  The addition amount of the M source is preferably adjusted according to the composition of the obtained vanadium dioxide and added.

The second step is a step of obtaining a reaction precursor by subjecting a slurry containing any one of the following deposits (a) to (d) obtained in the first step to a hydrothermal reaction.
(A) Slurry containing a precipitate (not including M element).
(B) A slurry containing an M element and a precipitate obtained by adding an M source to a solution containing the vanadium source.
(C) A slurry containing M element and a precipitate obtained by adding an M source to the slurry containing the precipitate.
(D) An M source is added to the solution containing the vanadium source to prepare a slurry containing M element and a precipitate, and the M element and the precipitate further added with the M source are added to the slurry containing the M element and the precipitate. Containing slurry.

  The reaction precursor itself is vanadium dioxide represented by the general formula (1) in a single layer by X-ray diffraction analysis, but the reaction precursor itself is a temperature increasing process and a temperature decreasing process in differential scanning calorimetry. In both cases, no clear phase transition is observed.

  The reaction conditions for the hydrothermal reaction are preferably a reaction temperature of 150 to 400 ° C., preferably 200 to 300 ° C., from the viewpoint of easily obtaining highly crystalline vanadium dioxide. The reaction time is 1 hour or longer, preferably 3 to 15 hours.

  After completion of the hydrothermal reaction, the slurry after completion of the reaction is subjected to solid-liquid separation by a conventional method, and a reaction precursor can be obtained by washing, drying, pulverization, pulverization and the like as necessary.

  The third step is a step in which the reaction precursor obtained in the second step is fired to obtain a fired product. The calcined product itself is vanadium dioxide represented by the general formula (1) in a single layer by X-ray diffraction analysis, but the calcined product is different from the above-described reaction precursor in the differential scanning calorimetry. A clear phase transition is observed in both the temperature process and the temperature decrease process, and the difference between the endothermic start temperature and the exothermic start temperature is 3 ° C. or more.

  The firing conditions in the third step are preferably a firing temperature of 800 to 1050 ° C., preferably 900 to 1000 ° C., from the viewpoint of easily obtaining highly crystalline vanadium dioxide.

  The firing atmosphere is an inert gas atmosphere to prevent oxidation of vanadium. Examples of the inert gas that can be used include nitrogen gas, argon gas, and helium gas.

  The firing time is 1 hour or longer, preferably 3 to 10 hours.

  Firing may be performed as many times as desired. Alternatively, for the purpose of making the powder characteristics uniform, the fired material may be pulverized and then refired.

  The obtained fired product is pulverized or crushed to a desired particle size as necessary, and is subjected to an annealing treatment in the next fourth step in a powder state.

  The fourth step is a step of obtaining the target vanadium dioxide by annealing the fired product obtained in the third step.

The fired product obtained in the third step is vanadium dioxide represented by the general formula (1) in a single layer by X-ray diffraction analysis as described above, and in the differential scanning calorimetry, the temperature raising process and the temperature lowering process. A clear phase transition is observed in both cases, and there is a difference of 3 ° C. or more between the endothermic onset temperature and the exothermic onset temperature.
In this production method, the burned product is annealed in the fourth step, whereby the difference between the endothermic start temperature and the exothermic start temperature can be converted to vanadium dioxide, preferably 2 ° C. or less. Although the reason for this is not clear, the present inventors speculate that the fired product obtained in the third step has oxygen deficiency, and the annealing process repairs the structure of oxygen deficiency in the structure. doing.

  The annealing treatment condition is that if the treatment temperature is too high, it changes to pentavalent vanadium and it is difficult to obtain the desired vanadium dioxide, so the annealing treatment temperature is 100 to 550 ° C., particularly 200 to 400 ° C. It is preferable from the viewpoint that the oxygen deficiency site can be repaired while preventing vanadium oxidation.

  The annealing time is preferably 1 hour or longer, particularly 3 to 10 hours. The annealing treatment is performed in an oxidizing atmosphere such as oxygen or air. Note that the annealing treatment can be performed as many times as necessary.

  In addition, after annealing, the product is crushed, crushed, classified, etc. as necessary.

The vanadium dioxide of the present invention thus obtained has the following general formula (1) as determined by X-ray diffraction analysis.
V _1-x M _x O ₂ (1)
(In the formula, M represents one or more elements selected from the group consisting of Cr, W, Mo, Nb, Ta, Os, Ir, Ru, and Re. X represents 0 ≦ x ≦ 0.5. In the differential scanning calorimetry, a clear phase transition is observed in both the temperature rising process and the temperature lowering process, and the difference between the endothermic start temperature and the exothermic start temperature is preferably 2 ° C. The following vanadium dioxide.

  Vanadium dioxide obtained by this production method is expected to be used as a heat storage material, in addition to being used as a material exhibiting a thermochromic phenomenon in which optical properties such as transmittance and reflectance change reversibly depending on temperature.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to these Examples.

(Measurement of phase transition temperature and heat quantity)
In each Example, the phase transition temperature and the calorific value were measured as follows.
The sample is enclosed in a closed cell (SUS cell) for differential scanning calorimetry (DSC), and 100 ° C. at a temperature rising rate of 1 ° C./min with a differential scanning calorimeter (model DSC6200, manufactured by SII Eporide Service) The temperature was raised to 20 ° C. and then lowered to 20 ° C. The endothermic peak generated during the temperature rising process and the starting temperature and calorific value of the exothermic peak generated during the temperature falling process were measured.

{Example 1}
First step;
15.63 g of vanadyl sulfate (VOSO ₄ ) hydrate salt was dissolved in 500 ml of ion-exchanged water (solution A). Separately, 125 ml of a 1 mol / L sodium hydroxide aqueous solution was prepared (solution B).
Liquid B was added to liquid A with stirring at a constant rate over 30 minutes at 20 ° C. (vanadium ion / alkali molar ratio 0.49). The pH of the reaction solution after the addition was 7.3. Next, an aging reaction was performed with stirring at 20 ° C. for 30 minutes to obtain a 0.9 mass% slurry containing a precipitate.
Second step;
620 g of the slurry containing the precipitate obtained in the first step was put into a 1 L autoclave and subjected to a hydrothermal reaction at 250 ° C. for 6 hours.
Next, the slurry after the reaction was solid-liquid separated and vacuum dried at 120 ° C. to obtain a reaction precursor sample.
The average particle diameter obtained by the laser diffraction / scattering method of the obtained reaction precursor sample was 36.6 μm. Moreover, the primary particle diameter calculated | required from SEM observation was 10 nm. As a result of XRD analysis, it was confirmed that the pattern of the diffraction peak coincided with VO ₂ and was a single-layer VO ₂ . An X-ray diffraction pattern of the reaction precursor sample is shown in FIG.
In addition, by differential scanning calorimetry using a differential scanning calorimeter, the starting temperature of the phase transition in the temperature rising and cooling processes and the amount of heat accompanying the phase transition were measured. As a result, phase transition could not be confirmed. The result is shown in FIG.
Third step;
Next, the reaction precursor sample obtained in the second step was put into an alumina crucible and fired at 1000 ° C. for 5 hours in a nitrogen atmosphere to obtain a fired product sample.
As a result of XRD analysis of the fired product sample, it was confirmed that the pattern of the diffraction peak coincided with VO ₂ and was a single layer VO ₂ . An X-ray diffraction pattern of the fired product sample is shown in FIG.
In the same manner as the reaction precursor sample, the starting temperature of the phase transition in the temperature rising and cooling process and the amount of heat accompanying the phase transition were measured by differential scanning calorimetry using a differential scanning calorimeter. The results of differential scanning calorimetry are shown in FIG.
The fourth step;
Next, the fired product obtained in the third step was put into an alumina crucible and subjected to an aryl treatment at 300 ° C. for 5 hours in the air to obtain an annealed product sample.
As a result of XRD analysis of the annealed product sample, it was confirmed that the pattern of the diffraction peak coincided with VO ₂ and was a single layer VO ₂ . The X-ray diffraction pattern of the annealed product sample is shown in FIG.
In the same manner as the reaction precursor sample, the starting temperature of the phase transition in the temperature rising and cooling process and the amount of heat accompanying the phase transition were measured by differential scanning calorimetry using a differential scanning calorimeter. The results of differential scanning calorimetry are shown in FIG.

{Example 2}
An annealed product sample was obtained by reacting under the same conditions as in Example 1 except that the firing temperature in the third step was 950 ° C.
As a result of XRD analysis of the fired product sample obtained in the third step, it was confirmed that the pattern of the diffraction peak coincided with VO ₂ and was a single-layer VO ₂ . Further, the firing temperature of the fired product sample was measured for the start temperature of the phase transition in the process of temperature increase and decrease, and the amount of heat accompanying the phase transition.
As a result of XRD analysis on the annealed product sample obtained in the fourth step, it was confirmed that the pattern of the diffraction peak coincided with VO ₂ and was a single-layer VO ₂ . In addition, the annealing treatment product samples were measured for the phase transition start temperature during the temperature rising and cooling process and the amount of heat accompanying the phase transition.

{Example 3}
An annealed product sample was obtained by performing the reaction under the same conditions as in Example 1 except that the firing temperature in the third step was 900 ° C.
As a result of XRD analysis of the fired product obtained in the third step, it was confirmed that the pattern of the diffraction peak coincided with VO ₂ and was a single layer VO ₂ . In addition, the firing temperature was measured for the phase transition start temperature during the temperature rise and fall processes, and the amount of heat accompanying the phase transition.
As a result of XRD analysis on the annealed product sample obtained in the fourth step, it was confirmed that the pattern of the diffraction peak coincided with VO ₂ and was a single-layer VO ₂ . In addition, the annealing treatment product samples were measured for the phase transition start temperature during the temperature rising and cooling process and the amount of heat accompanying the phase transition.

Note) "-" indicates that no phase transition was observed.

 As can be seen from the results in Table 2, the difference between the endothermic start temperature and the exothermic start temperature is reduced by annealing the fired product sample obtained in the third step in the fourth step.

Claims (6)

The following general formula (1)
V _1-x M _x O ₂ (1)
(In the formula, M represents one or more elements selected from the group consisting of Cr, W, Mo, Nb, Ta, Os, Ir, Ru, and Re. X represents 0 ≦ x ≦ 0.5. A method for producing vanadium dioxide represented by:
A first step of preparing a slurry containing a precipitate formed by adding an alkali to a solution containing a vanadium source and performing a reaction, then a second step of subjecting the slurry to a hydrothermal reaction to obtain a reaction precursor, A third step of firing the reaction precursor in an inert gas atmosphere to obtain a fired product, and then a fourth step of annealing the fired product, and optionally a solution containing the vanadium source and / or the precipitation The manufacturing method of vanadium dioxide characterized by adding M source to the slurry containing a thing.   The method for producing vanadium dioxide according to claim 1, wherein the vanadium source is a tetravalent vanadium compound.   The method for producing vanadium dioxide according to claim 1, wherein the vanadium source is vanadyl sulfate.   The method for producing vanadium dioxide according to any one of claims 1 to 3, wherein the firing temperature in the third step is 800 to 1050 ° C.   The method for producing vanadium dioxide according to any one of claims 1 to 4, wherein the annealing process in the fourth step is performed in a temperature range of 100 to 550 ° C.   It is used as a heat storage material, The manufacturing method of vanadium dioxide as described in any one of Claims 1 thru | or 5 characterized by the above-mentioned.