JP6990153B2 - Manufacturing method of vanadium dioxide - Google Patents

Description

The present invention relates to a method for producing vanadium dioxide, which is useful as a thermochromic material or the like.

Thermochromic materials have the property that their optical properties change reversibly depending on the temperature, and films and glasses that utilize these properties are being developed. For example, when a thermochromic material is used for the window glass, it is possible to reflect the sunlight in the summer to block the heat and let the sunlight pass through in the winter to utilize the heat. The energy-saving technology using the above is attracting attention.

Vanadium dioxide is known as a thermochromic material. Vanadium dioxide exhibits a monoclinic crystal structure below the phase transition temperature and has semiconducting properties. On the other hand, above the phase transition temperature, it changes to a rutile-type crystal structure and exhibits metallic properties. With this phase transition, the resistance of vanadium dioxide and the transmittance in the infrared region change significantly. When applying a vanadium dioxide thermochromic material to windows, transparency is required in addition to thermochromic properties, and the particle size is required to be on the nano-order.

Examples of the method for producing this nano-order vanadium dioxide include a method of pulverizing a material obtained by synthesizing vanadium oxide and tungsten oxide by a melting method with a bead mill (see Patent Document 1), and oxidizing a vanadium oxide compound with hydrogen peroxide. Then, a method of precipitating a porous vanadium oxide at a predetermined temperature, pulverizing the surface, and then performing a reduction treatment (see Patent Document 2) has been proposed.
However, the methods described in Patent Documents 1 and 2 are not industrially advantageous because they require complicated steps.

In addition, a method for producing vanadium dioxide by hydrothermal synthesis has also been proposed (see, for example, Patent Documents 3 and 4), but it is hoped that an industrially advantageous method will be developed in consideration of energy saving, cost saving, environmental consideration, and the like. It is rare.

In addition, the present inventor first prepared a raw material mixture containing divanadium pentoxide and an organic acid as a method for producing vanadium dioxide particularly useful as a heat storage agent, and spray-dried the raw material mixture. Then, a method of firing at 600 to 900 ° C. after obtaining a reaction precursor was proposed (see Patent Document 5).

Japanese Unexamined Patent Publication No. 2000-23329 Japanese Unexamined Patent Publication No. 2011-136873 Japanese Unexamined Patent Publication No. 2017-186398 Japanese Unexamined Patent Publication No. 2017-110144 JP-A-2017-132677

However, according to the method of Patent Document 5, there is a problem that the firing temperature is high and it is difficult to produce nano-order vanadium dioxide.

Therefore, it is an object of the present invention to provide a method for producing vanadium dioxide having an average particle size of nano-order of primary particles useful as a thermochromic material by an industrially advantageous method.

As a result of diligent research in view of the above circumstances, the present inventor mixes divanadium pentoxide and a carbon material source to obtain a raw material mixture, and calcins this raw material mixture in an inert gas atmosphere to obtain vanadium oxide. In the method, when the carbon material source as a reducing agent is excessive as compared with the conventional method, a calcined product containing VO ₂ as a main component can be obtained in a low temperature range in a specific temperature range, and vanadium dioxide thus obtained can be obtained. It has been found that the primary particle size is nano-order and nano-order particles can be obtained by crushing or pulverizing, and the present invention has been completed.

That is, the present invention comprises a raw material mixing step of mixing divanadium pentoxide and a carbon material source to obtain a raw material mixture, and firing the raw material mixture at 300 ° C. or higher and lower than 340 ° C. in an inert gas atmosphere to obtain a fired body. In the raw material mixing step including the firing step of obtaining, the molar ratio (C / V) of the carbon atom in the carbon material source to the vanadium atom in divanadium pentoxide is 2.2 or more. This is a method for producing vanadium dioxide.

According to the present invention, vanadium dioxide having an average particle size of nano-order primary particles useful as a thermochromic material can be produced by an industrially advantageous method.

It is an X-ray diffraction pattern of the raw material mixture obtained by the raw material mixing step of Example 1. FIG. 6 is an SEM image of the raw material mixture obtained in Example 1. It is an X-ray-diffraction diagram of the vanadium dioxide sample obtained in Example 1. 6 is an SEM image of the vanadium dioxide sample obtained in Example 1. It is an X-ray-diffraction diagram of the vanadium oxide sample obtained in Comparative Example 1.

Hereinafter, the present invention will be described based on the preferred embodiment thereof.

<Ingredient mixing process>
The raw material mixing step according to the present invention is a step of mixing vanadium pentoxide and a carbon material source to prepare a raw material mixture.

Examples of the carbon material source used in the raw material mixing step include a material consisting only of carbon atoms and a material that is thermally decomposed by firing in a firing step described later to generate carbon. Specific examples of the carbon material source include carbon materials and organic compounds having a hydroxyl group.

Examples of the carbon material include carbon black, carbon fiber, graphite, activated carbon and the like. The carbon black is not limited by any manufacturing method, for example, furnace black obtained by the furnace method, channel black obtained by the channel method, acetylene black obtained by the acetylene method, and thermal. Examples include thermal black obtained by the method. Examples of the carbon fiber include polyacrylonitrile-based carbon fiber and pitch-based carbon fiber.

Examples of the organic compound having a hydroxyl group include saccharides, polyhydric alcohols, organic acids and the like.

Examples of saccharides include monosaccharides such as fructose, disaccharides such as sucrose and lactose, oligosaccharides in which about 3 to 20 molecules of monosaccharides are bound, polysaccharides such as starch and cellulose, and sugar alcohols such as xylitol and sorbitol. Can be mentioned.

Examples of polyhydric alcohols include dihydric alcohols such as ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol and tetraethylene glycol, trihydric alcohols such as glycerin and trimethylolpropane, and 4 or more in the molecule. Examples thereof include alcohols having a valence of 4 or more having a hydroxyl group, and polymers having a large number of hydroxyl groups such as polyvinyl alcohol.

Examples of the organic acid include monocarboxylic acids such as formic acid, acetic acid, glycolic acid, lactic acid and gluconic acid, dicarboxylic acids such as oxalic acid, maleic acid, malonic acid, malonic acid, tartaric acid and succinic acid, and the number of carboxyl groups. Carboxylic acids such as citric acid, which is No. 3, can be mentioned.

Among these organic compounds having hydroxyl groups, the organic acid is suitable from the viewpoint that divanadium pentoxide can be easily reduced and divanadium pentoxide can be dissolved in an aqueous solvent when mixed in a wet manner as described later. preferable.

In the raw material mixing step, it is important that the molar ratio (C / V) of the carbon atom in the carbon material source to the vanadium atom in divanadium pentoxide is 2.2 or more.
The reason for this is that if the amount of carbon material source that reduces divanadium pentoxide is less than the above amount, a raw material mixture with excellent reactivity cannot be obtained, and when firing is performed at the firing temperature described later, the raw material is pentoxide. This is because divanadium remains unreacted.
Further, since the unreacted carbon material source may remain as it is in the target vanadium dioxide, carbon in the carbon material source with respect to the vanadium atom in divanadium pentoxide from the viewpoint of obtaining high-purity vanadium dioxide. The molar ratio (C / V) of the atom is preferably 2.2 to 4.5, more preferably 2.4 to 4.0.

The divanadium pentoxide and the carbon material source can be mixed wet or dry, but when an organic acid is used as the carbon material source, the raw material mixture is prepared by mixing divanadium pentoxide and the organic acid in an aqueous solvent. A process of mixing to obtain a raw material solution in which each raw material is dissolved (hereinafter, may be referred to as "raw material dissolution step") and then spray-drying the raw material solution (hereinafter, may be referred to as "spray drying step") is performed. It is particularly preferable that the product obtained through the process is obtained from the viewpoint of producing a raw material mixture having excellent reactivity.

Hereinafter, a preferable raw material mixing step will be described.
From the viewpoint of completely dissolving each raw material in the raw material dissolution step, the amount of divanadium pentoxide added is preferably 10 to 40 parts by mass, preferably 15 to 30 parts by mass with respect to 100 parts by mass of the water solvent. Is even more preferable. Further, as the organic acid used in the raw material dissolution step, a carboxylic acid is preferable, and oxalic acid is more preferable, because it has a high ability to dissolve divanadium pentoxide. Further, in the raw material dissolution step, from an economical point of view, the molar ratio (C / V) of the carbon atom in the organic acid to the vanadium atom in divanadium pentoxide is preferably 2.2 to 4.5. It is more preferably 2.8 to 4.0.

The melting temperature in the raw material melting step is not particularly limited, but it is preferably 15 to 100 ° C., preferably 20 to 60 ° C. from the viewpoint of industrial advantage.

The spray drying step is a step of spray-drying the raw material solution prepared in the raw material dissolving step to obtain a raw material mixture. The raw material mixture obtained by spray drying is one in which each raw material is uniformly blended at the molecular level and has excellent reactivity.

In the spray drying method, a raw material mixture is obtained by atomizing the raw material solution by a predetermined means and drying the fine droplets generated thereby. There are a method using a rotating disk and a method using a pressure nozzle for atomizing the raw material solution. Any method can be used in the spray drying step.

In the spray drying method, the size of the droplets of the atomized raw material solution affects stable drying and the properties of the obtained dry powder. Specifically, if the size of the raw material particles of the pulverized product is too small with respect to the size of the droplets, the droplets become unstable and it becomes difficult to dry them successfully. From this point of view, the size of the droplets of the atomized raw material solution is preferably 1 to 50 μm, more preferably 3 to 30 μm. It is desirable to determine the supply amount of the raw material solution to the spray drying device in consideration of this viewpoint.

The drying temperature in the spray drying device is adjusted so that the hot air inlet temperature is 180 to 300 ° C, preferably 200 to 250 ° C, and the hot air outlet temperature is 100 to 200 ° C, preferably 105 to 150 ° C. It is preferable to adjust the temperature to the above because it prevents the powder from absorbing moisture and facilitates the recovery of the powder.

In addition, by-component elements can be added to the raw material mixture for the purpose of changing the phase transition temperature of vanadium dioxide.

The subcomponent element is preferably one or more selected from the group of Cr, W, Mo, Nb, Ta, Os, Ir, Ru and Re. The subcomponent element may be the subcomponent element itself or a compound containing the subcomponent element. Examples of the compound containing the subcomponent element include oxides of the subcomponent element, metallic acids such as molybdenum acid and tungonic acid, metal acid salts or ammonium salts thereof, alcoholates of the subcomponent element, and organic acid salts of the subcomponent element. Can be mentioned. By-component elements can be added to the raw material mixture as solutions, suspensions or powders. Further, when the raw material dissolving step is provided, divanadium pentoxide, an organic acid and a subcomponent element may be mixed in an aqueous solvent.

It is preferable that the amount of the subcomponent element added is appropriately adjusted according to the composition of vanadium dioxide represented by the general formula (1) described later.

The raw material mixture obtained in the raw material mixing step may be in an amorphous state or a crystalline state, but the amorphous state has excellent composition uniformity and the reaction. It is preferable from the viewpoint of producing a raw material mixture having excellent properties.

Further, the raw material mixture may be a reaction product of divanadium pentoxide and a carbon material source, or a reaction product of divanadium pentoxide and a carbon material source and an auxiliary component element added as necessary.

<Baking process>
The firing step is a step of firing the raw material mixture obtained in the raw material mixing step at a predetermined temperature in an inert gas atmosphere to obtain a fired body.

In the firing step, by firing at a lower temperature than in Patent Document 5, the grain growth of the obtained fired body can be suppressed, so that vanadium dioxide having an average primary particle size of nano-order can be finally obtained. ..

It is important that the firing temperature in the firing step is 300 ° C. or higher and lower than 340 ° C.
The reason for this is that at calcination temperatures below 300 ° C, monoclinic vanadium dioxide is not produced, while above 340 ° C, V ₅ O ₉ and / or V ₄ O ₇ is produced and monoclinic vanadium dioxide is produced. Because it does not generate. From the viewpoint of obtaining higher purity vanadium dioxide, the firing temperature is preferably 320 ° C. or higher and lower than 340 ° C.
The firing time is not particularly limited, and a satisfactory fired body can be obtained in usually 1 hour or more, preferably 2 to 30 hours.

Examples of the inert gas that can be used include nitrogen gas, argon gas, helium gas and the like.

After firing, the fired body is cooled to room temperature and, if necessary, crushed, crushed, classified, etc. to obtain a product. From the viewpoint of obtaining higher purity vanadium dioxide, it is preferable to cool the fired body in an inert gas atmosphere. As the inert gas, the same as in the firing step can be used. The cooling rate is not particularly limited, and is usually 200 ° C./hour or less, preferably 30 to 100 ° C./hour.

The vanadium dioxide obtained by the above-mentioned production method has the following general formula (1): which has high purity in X-ray diffraction.
V _1-x M _x O ₂ (1)
(In the formula, M represents at least one or two or more subcomponent elements selected from the group of Cr, W, Mo, Nb, Ta, Os, Ir, Ru and Re. X represents 0 ≦ x ≦ 0. It is preferably monoclinic vanadium dioxide represented by.).

In the present specification, vanadium dioxide having high purity in X-ray diffraction means that monoclinic vanadium dioxide in X-ray diffraction is contained as a main component, and _{V3 O 7 other} than the target substance. May contain vanadium oxide.
The content of _{V3O 7} is 2θ with respect to the main peak (a) of vanadium dioxide appearing near 2θ = 27.8 ° when an X-ray diffraction analysis of a vanadium dioxide sample is performed using Cu—Kα beam as a radiation source. The height ratio ((b) / (a)) of the main peak ₍ b) of V3 _O7 appearing at = 24.9 ° is preferably 0.3 or less, and more preferably 0.25 or less. preferable.

Further, regarding the physical characteristics of vanadium dioxide obtained by the above-mentioned production method, the average particle size of the primary particles determined by the scanning electron microscope (SEM) observation method is preferably 100 nm or less, and more preferably 20 to 80 nm. The BET specific surface area is preferably 30 m ² / g or more, and more preferably 35 to 70 m ² / g. In the present specification, the average primary particle size obtained by the SEM observation method is defined as an arbitrary 100 particles extracted from the SEM image of a vanadium dioxide sample, the primary particle size of each particle is measured, and these are used. Arithmetic mean value.

Vanadium dioxide obtained by the above-mentioned production method can be expected to be used not only as a material showing a thermochromic phenomenon in which optical properties such as transmittance and reflectance change reversibly depending on temperature, but also as a heat storage material.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited to these Examples.
<X-ray diffraction analysis>
X-ray diffraction analysis was performed using a D8 Advance S manufactured by Bruker. Cu-Kα was used as the radiation source. The measurement conditions were a tube voltage of 40 kV, a tube current of 40 mA, and a scanning speed of 0.1 ° / sec.

[Example 1]
<Ingredient mixing process>
In a container, 300 g of V ₂ O ₅ , 581.3 g of oxalic acid / dihydrate salt and 1500 g of ion-exchanged water are charged at room temperature (20 ° C.), and then stirred at room temperature (20 ° C.) for 24 hours to dissolve the raw materials in water. The raw material solution was prepared.
Next, the raw material solution was supplied to a spray drying device in which the temperature of the hot air inlet was set to 220 ° C. and the outlet temperature was set to 120 ° C., and the raw material mixture was obtained by spray drying. The result of X-ray diffraction analysis of the obtained raw material mixture is shown in FIG. As can be seen from FIG. _{1, no diffraction peak of V2 O 5 was} observed in the raw material mixture, and it was confirmed that the raw material mixture was amorphous. Moreover, the SEM image of the obtained raw material mixture is shown in FIG.

<Baking process>
The raw material mixture obtained in the raw material mixing step was put into an alumina crucible and fired at 330 ° C. for 4 hours in a furnace in a nitrogen gas atmosphere. After firing, it was cooled to room temperature (20 ° C.) as it was in a nitrogen gas atmosphere. Next, a vanadium dioxide sample was obtained by crushing the fired body with a bead crusher.

The result of X-ray diffraction analysis of the obtained vanadium dioxide sample is shown in FIG. As can be seen from FIG. ₃ , traces of V3 O ₇ could be confirmed, but it was confirmed that it was monoclinic vanadium dioxide. Further, as a result of X _- ray diffraction analysis, the height ratio of the main peak ₍ b) of V3 O7 appearing at 2θ = 24.9 ° to the main peak (a) of vanadium dioxide appearing at 2θ = 27.8 ° ((() b) / (a)) was 0.06, and it was confirmed that monoclinic vanadium dioxide having high purity by X-ray diffraction was obtained. Moreover, the SEM image of the vanadium dioxide sample obtained in Example 1 is shown in FIG.

[Comparative Example 1]
In Example 1, a sample was prepared in the same manner as in Example 1 except that the firing temperature in the firing step was changed to 350 ° C.

The result of X-ray diffraction analysis of the obtained sample is shown in FIG. As can be seen from FIG. ₅ , the diffraction peak of monoclinic vanadium dioxide was not observed, but the diffraction peak of V4 _O7 was observed.

[Comparative Example 2]
<Ingredient mixing process>
20 g of _{V 2} O, 13.86 g of oxalic acid / dihydrate and 100 g of ion-exchanged water are charged in a container at room temperature (25 ° C.), then heated to 80 ° C. for 3 hours and heat-treated to V ₂ O. A slurry of the raw material mixture in which ₅ was partially dissolved was obtained.
Next, a slurry of the raw material mixture was supplied to a spray drying device in which the temperature of the hot air inlet was set to 220 ° C. and the outlet temperature was set to 120 ° C., and spray dried to obtain a reaction precursor. As a result of X _- ray diffraction analysis of the obtained reaction precursor, a diffraction peak of _V2O5 was confirmed.

<Baking process>
The reaction precursor obtained in the raw material mixing step was put into an alumina crucible and calcined at 330 ° C. for 4 hours in a furnace in a nitrogen gas atmosphere. After firing, it was cooled to room temperature (20 ° C.) as it was in a nitrogen gas atmosphere. Next, a sample obtained by crushing the fired body with a bead crusher was used as a sample.

As a result of X-ray diffraction analysis of the obtained sample, no diffraction peak of monoclinic vanadium dioxide was observed, and it was confirmed that the sample contained VO ₂ and V ₂ O ₅ .

[Example 2]
<Ingredient mixing process>
A container is charged with V ₂ O ₅ 300 g, oxalic acid / dihydrate 581.3 g, ion-exchanged water 1500 g and ammonium metatungstate ammonium solution (WO ₃ equivalent 50% by weight) 5 g at room temperature (20 ° C.), and then at room temperature. The raw material was dissolved in water by stirring at (20 ° C.) for 24 hours to prepare a raw material solution. The molar ratio (C / V) of the carbon atom in the oxalic acid / _dihydrate to the vanadium atom in V2 O ₅ was 2.8.
Next, the raw material solution was supplied to a spray drying device in which the temperature of the hot air inlet was set to 220 ° C. and the outlet temperature was set to 120 ° C., and the raw material mixture was obtained by spray drying. As a result of X-ray diffraction analysis of the obtained raw material mixture, no diffraction peak was observed, and it was confirmed that the mixture was amorphous.

<Baking process>
The raw material mixture obtained in the raw material mixing step was put into an alumina crucible and fired at 330 ° C. for 4 hours in a furnace in a nitrogen gas atmosphere. After firing, it was cooled to room temperature (20 ° C.) as it was in a nitrogen gas atmosphere. Next, the fired body was pulverized by a bead crusher to obtain a vanadium dioxide sample doped with 0.7% by mass as W atoms.

As a result of X-ray diffraction analysis of the obtained vanadium dioxide sample, traces of impurities of vanadium oxide compound such as _V3O7 could be confirmed, but it was a monoclinic vanadium dioxide having high purity by X _- ray diffraction. It was confirmed. Further, as a result of X _- ray diffraction analysis, the height ratio of the main peak ₍ b) of V3 O7 appearing at 2θ = 24.9 ° to the main peak (a) of vanadium dioxide appearing at 2θ = 27.8 ° ((() b) / (a)) was 0.24.

〔Evaluation of the physical properties〕
For each sample obtained in Examples and Comparative Examples, the average primary particle size and the BET specific surface area were measured. The results are shown in Table 2. The results of X-ray diffraction analysis of each sample are also shown in Table 2.

Claims (9)

A raw material mixing step of mixing divanadium pentoxide and a carbon material source to obtain a raw material mixture,
A firing step of calcining the raw material mixture at 300 ° C. or higher and lower than 340 ° C. in an inert gas atmosphere to obtain a calcined body is included.
A method for producing vanadium dioxide, which comprises a molar ratio (C / V) of carbon atoms in a carbon material source to vanadium atoms in divanadium pentoxide of 2.2 or more in the raw material mixing step. In the raw material mixing step, the carbon material source is an organic acid, and in the raw material mixing step, divanadium pentoxide and an organic acid are mixed in an aqueous solvent to obtain a raw material solution in which each raw material is dissolved. The method for producing vanadium dioxide according to claim 1, further comprising a step of spray-drying the raw material solution. The second aspect of claim 2, wherein in the raw material mixing step, the molar ratio (C / V) of the carbon atom in the organic acid to the vanadium atom in divanadium pentoxide is 2.2 to 4.5. How to make vanadium dioxide. The method for producing vanadium dioxide according to claim 2 or 3, wherein the organic acid is a carboxylic acid. The method for producing vanadium dioxide according to any one of claims 2 to 4, wherein the organic acid is oxalic acid. The method for producing vanadium dioxide according to any one of claims 1 to 5, wherein the raw material mixing step further includes a step of adding a subcomponent element. The method for producing vanadium dioxide according to claim 6, wherein the subcomponent element is one or more selected from Cr, W, Mo, Nb, Ta, Os, Ir, Ru and Re. .. The method for producing vanadium dioxide according to any one of claims 1 to 7, wherein the produced vanadium dioxide has an average primary particle size of 100 nm or less. The method for producing vanadium dioxide according to any one of claims 1 to 8, further comprising a step of cooling the fired body to room temperature in an atmosphere of an inert gas after the firing step.

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