JP6501103B2 - Method of producing vanadium dioxide - Google Patents

Description

  The present invention relates to a method for producing industrially useful vanadium dioxide conveniently and inexpensively.

  It has been reported that vanadium dioxide causes metal-semiconductor dislocation at about 70 ° C., which is relatively near room temperature, and the electric conductivity changes reversibly greatly (Non-patent Document 1). The metal-semiconductor dislocation is said to be accompanied by the structural change between the monoclinic structure on the low temperature side and the tetragonal structure on the high temperature side. The metal-semiconductor dislocation also causes a thermochromic phenomenon in which optical characteristics such as transmittance and reflectance change. In this thermochromic phenomenon, although the change in the visible light range is small, the infrared transmittance particularly at the high temperature side is greatly reduced. For this reason, application research to what is called so-called smart glass or automatic light control glass is actively conducted from the tendency of energy saving in recent years. In addition, vanadium dioxide is also being studied for application to microactuators, resistance change memory elements, and the like that utilize the change in volume with dislocations.

  As an application to smart glass, Patent Document 1 discloses a method of forming vanadium dioxide on a transparent substrate by sputtering. However, the production of smart glass by the sputtering method uses a large amount of electric power, and there is a problem that when the smart glass is adopted for an existing building, the glass needs to be replaced. If vanadium dioxide can be obtained as a powder, it can be converted into smart glass by coating and applying vanadium dioxide to glass or laminating a vanadium dioxide-coated film to glass.

Patent Document 2 discloses a method of producing vanadium dioxide powder. This is a method of producing vanadium dioxide by controlling the temperature and pressure of ammonium metavanadate (NH ₄ VO ₃ ), but toxic ammonia gas is generated as a by-product of the reaction, and the pressure is controlled while heating It requires complicated operations, and it can not be said to be a simple method. Patent Document 3 discloses a method of producing vanadium dioxide by irradiating a solution containing vanadium with a laser under an inert gas atmosphere. However, this also has the problem of using a large power of a laser.

  Patent Document 4 discloses a method of producing a precursor by reacting a solution containing a vanadium alkoxide with a basic aqueous solution to prepare a precursor, and reducing and calcining the precursor in a hydrogen atmosphere to produce vanadium dioxide. In this method, there is a problem that there is a danger of explosion because it uses an expensive chemical called vanadium alkoxide and is reduced in hydrogen. In addition, vanadium dioxide is manufactured industrially by heating vanadium pentoxide in a reducing gas such as hydrogen, but there is a danger of explosion because it is reduced in hydrogen as in the method described in Patent Document 4. . Further, since the melting point of vanadium pentoxide is relatively low at 690 ° C., the reduction at high temperature causes the vanadium pentoxide to be melted, and thus the pulverization and classification steps are required. Conversely, the reduction at low temperature results in the reduction There is a problem that the time is increased and the consumption of energy and reducing gas is increased.

JP 2000-137251 A Japanese Patent Application Publication No. 10-509942 JP, 2014-94881, A JP, 2013-71859, A

F. J. Morin, PHYSICAL REVIEW LETTERS, 1959, vol. 3, p. 34-36

  The present invention has been made in view of such circumstances, and it is an object of the present invention to simply and inexpensively produce industrially useful vanadium dioxide. Another object of the present invention is to simply and inexpensively manufacture vanadium dioxide to which different metals are added. Furthermore, it aims at providing products, such as a thermochromic substrate using vanadium dioxide manufactured by these methods.

  As a result of intensive investigations, the inventor found that vanadium pentoxide is reduced by firing a mixture of vanadium pentoxide powder and carbon powder in an inert gas atmosphere to obtain desired vanadium dioxide powder. The present invention has been completed.

  The method for producing vanadium dioxide of the present invention calcinates a mixture containing an oxide containing vanadium and a carbon source. In the method for producing vanadium dioxide of the present invention, the oxide containing vanadium is preferably vanadium pentoxide. In the method for producing vanadium dioxide of the present invention, the stoichiometric ratio of carbon in the carbon source to vanadium pentoxide is preferably 0.475 to 1, and more preferably 0.475 to 0.55. In the method for producing vanadium dioxide of the present invention, the carbon source is preferably carbon or a carbon compound.

  In the method for producing vanadium dioxide of the present invention, the mixture is preferably fired under one or more gas atmospheres selected from helium, neon, argon and nitrogen, and it is more preferable to bake the mixture under nitrogen gas atmosphere . In the method for producing vanadium dioxide of the present invention, it is preferable to bake the mixture at a temperature of 500 to 1000 ° C., and more preferable to bake the mixture at a temperature of 600 to 800 ° C.

  The process for producing heterometallic vanadium dioxide of the present invention calcinates a mixture containing an oxide containing vanadium, a carbon source, and a compound of a metal other than vanadium. The method of producing heterometallic vanadium dioxide according to another aspect of the present invention calcinates a mixture containing an oxide containing vanadium, a carbon source, an oxide of a metal other than vanadium or an ion solution of this metal.

  The thermochromic product of the present invention comprises vanadium dioxide or heterometallic vanadium dioxide produced by the production method of the present invention.

  According to the present invention, vanadium dioxide can be obtained conveniently and inexpensively. Further, according to another aspect of the present invention, vanadium dioxide to which a foreign metal is added can be obtained conveniently and inexpensively. Furthermore, it is possible to inexpensively manufacture products utilizing optical, physical and magnetic properties by metal-semiconductor dislocation of vanadium dioxide, such as thermochromic substrates, using these vanadium dioxide and dissimilar metal-added vanadium dioxide as raw materials become.

It is a schematic cross section of the baking furnace used in the Example. FIG. 7 is a temperature-resistance characteristic of the vanadium dioxide obtained in Example 1 and the dissimilar metal-added vanadium dioxide obtained in Example 19. FIG.

  Hereinafter, the manufacturing method of the present invention will be described in detail based on embodiments and examples with reference to the drawings. In addition, duplication explanation is omitted suitably. Moreover, when describing "-" between two numerical values and expressing a numerical range, these two numerical values shall also be included in a numerical range.

The method for producing vanadium dioxide of the present invention calcinates a mixture containing an oxide containing vanadium and a carbon source. As a specific example, there is mentioned a method in which powder of an oxide containing vanadium and powder of a carbon source are mixed and molded, and firing is carried out in a furnace. The oxide containing vanadium is preferably vanadium pentoxide (V ₂ O ₅ ). Vanadium pentoxide is generally obtained as a by-product of producing uranium or from smoke dust of a plant fueled with petroleum, but it is not particularly limited in its production method. The carbon source is preferably carbon itself or a carbon compound.

  It is straightforward to use carbon itself such as carbon black, acetylene black, furnace black and graphite as a carbon source, but compounds that decompose and carbonize before volatilizing when heated with vanadium pentoxide and impurities other than carbon remain at firing temperature It is also possible to use a non-organic compound as a carbon source. Such compounds include paraffin, ethylene vinyl acetate, cellulose, polyethylene oxide, stearic acid and the like.

  When these compounds are carbonized in a reducing atmosphere, they are known to volatilize as various low molecular weight components such as hydrocarbons and furan. Therefore, it is necessary to adjust the amount of these compounds to be mixed with vanadium pentoxide to the reaction conditions and the like. Therefore, it is convenient to use carbon itself as a carbon source. Although calcination can be performed in the atmosphere, in order to prevent reoxidation of vanadium dioxide, it is preferable to perform calcination under one or more gas atmospheres selected from helium, neon, a rare gas such as argon, and nitrogen. It is more preferable to bake in nitrogen gas atmosphere from the lowest thing among these.

  The inert gas prevents the oxidation of the carbon source by the oxygen present around the mixture. For this reason, it is possible to use a rare gas such as helium, neon or argon as an atmosphere gas at the time of firing, but it is appropriate to use nitrogen from the viewpoint of cost. Further, in the method for producing vanadium dioxide of the present invention, since the by-product is only carbon dioxide, no special recovery and processing equipment is required. For this reason, the method for producing vanadium dioxide of the present invention is practicable on an industrial scale.

The chemical reaction for producing vanadium dioxide from vanadium pentoxide and a carbon source can be represented by the formula: 2V ₂ O ₅ + C → 4VO ₂ + CO ₂ , which is very simple. Heating is required to advance this chemical reaction. 500-1000 degreeC is preferable and, as for the temperature at the time of baking the mixture containing a vanadium pentoxide and a carbon source, 600-800 degreeC is more preferable. When the calcination temperature is too low, there is a problem that the crystallinity of the obtained vanadium dioxide is low or the reaction takes time. If the firing temperature is too high, energy consumption for heating may be increased, vanadium sublimation loss, formation of vanadium oxide other than vanadium dioxide and the like may occur.

  As in the present invention, when by-products are not generated in the inorganic synthesis by calcination, although the crystals generally grow with the calcination time, the growth tends to be saturated. For this reason, it is known that crystal growth is not sufficiently performed in a short time firing, and energy consumption increases in a long time firing. Therefore, in the production method of the present invention, the firing may be performed only for the time when crystal growth is sufficiently performed.

  The stoichiometric ratio of vanadium pentoxide in the mixture and carbon in the carbon source is ideally 2: 1 in the chemical reaction formula, but the heating and firing under an inert gas atmosphere tends to reduce the heat Is reduced to vanadium dioxide even if is less than the stoichiometric ratio. In addition, when the carbon in the mixture is more than the stoichiometric ratio, formation of vanadium oxide other than vanadium dioxide may occur, or carbon may remain in vanadium dioxide after formation. For this reason, it is preferable that vanadium pentoxide: carbon is 2: 0.95 to 2: 2 as the stoichiometric ratio of vanadium pentoxide and carbon in the carbon source, ie, the substance mass ratio (so-called molar ratio). It is more preferable that it is 2: 0.95-2: 1.1. In other words, the stoichiometric ratio of carbon in the carbon source to vanadium pentoxide is preferably 0.475 to 1, and more preferably 0.475 to 0.55.

  For example, it is desirable that the coating layer of smart glass be composed of a material having a transition temperature closer to room temperature than the transition temperature of vanadium dioxide itself of about 70.degree. When niobium, tungsten, etc. in the stable oxidation state exist in the crystal lattice of vanadium dioxide, that is, vanadium dioxide is doped if vanadium, etc. is present in the crystal lattice of vanadium dioxide, which is higher in valence than tetravalent of vanadium in vanadium dioxide which is the stable oxidation state of vanadium. It is known that the transition temperature falls below 70.degree.

  The method for producing the dissimilar metal-added vanadium dioxide of the present invention is a method of firing a mixture containing an oxide containing vanadium, a carbon source, and a compound of a metal other than vanadium. In addition, another method of producing different-metal-added vanadium dioxide according to the present invention is a method of firing an oxide containing vanadium, a carbon source, an oxide of a metal other than vanadium or a mixture containing ions of this metal. . As a specific example, a powder of an oxide containing vanadium, a powder of a carbon source, an oxide of a metal having a valence higher than 4 in a stable oxidation state, a salt of this metal, or an ion solution of this metal After mixing and shaping, and firing in a furnace. By these methods, foreign metal-doped vanadium dioxide having a transition temperature lower than 70 ° C. is obtained.

  Note that instead of a metal having a valence higher than four in the stable oxidation state, a metal having a valence of four or less in the stable oxidation state, such as gallium having a valence of three in the stable oxidation state, is used. A method of producing these dissimilar metal-added vanadium dioxide may be performed. When a metal having a valence of 3 in a stable oxidation state is added, the transition temperature often becomes high, but the transition temperature may become low in some cases. Further, foreign metal-added vanadium dioxide having a high transition temperature can be used, for example, in a gas sensor.

  A substrate excellent in thermochromic properties can be produced by applying and drying a suspension of vanadium dioxide or dissimilar metal-added vanadium dioxide obtained by the production method of the present invention on a transparent substrate. The inexpensive manufacturing method increases the possibility of further application expansion. The thermochromic product of the present invention represented by an automatic light control glass has the vanadium dioxide or the dissimilar metal-added vanadium dioxide obtained by the production method of the present invention. Specifically, the vanadium dioxide or the dissimilar metal-added vanadium dioxide is coated on the surface of the glass.

  EXAMPLES The embodiments of the present invention will be described in more detail by way of the following examples, but the present invention is not limited by these examples. FIG. 1 schematically shows a furnace used for firing of the manufacturing method of the present invention. Note that the dimensions and dimensional ratio of the furnace in the drawings do not necessarily coincide with the dimensions and dimensional ratio of the actual product.

1. Preparation of vanadium dioxide and dissimilar metal-doped vanadium dioxide (Examples 1 to 16)
First, vanadium pentoxide (made by Wako Pure Chemical Industries, Ltd.) and Carbon Black (made by Alfa Aesar), which is a carbon source, are mixed in a mortar at a stoichiometric ratio shown in Table 1 and mixed. Powder was prepared. Next, this mixed powder was put into a tableting machine and pressure-molded to obtain pellets. Then, this pellet, which is a sample, is placed in a tubular furnace shown in FIG. 1, and the temperature is raised to the firing temperature shown in Table 1 at a temperature rising rate of 500.degree. C./hour while flowing nitrogen. After holding for only the firing time, the temperature was lowered to room temperature by natural cooling, to obtain a fired pellet. Next, the fired pellets were crushed in a mortar to obtain fired powder.

(Example 17)
First, 0.2 g of paraffin (Wako Pure Chemical Industries, Ltd.) as a carbon source was dissolved in 2 mL of toluene to prepare a paraffin solution. Next, 0.40 mL of this paraffin solution is added to 0.50 g of vanadium pentoxide (manufactured by Wako Pure Chemical Industries, Ltd.), and mixed in a mortar while warming until the solvent odor disappears, and the mixed powder which is a mixture is Prepared. Then, this mixed powder was molded, fired, and crushed in the same manner as in Example 1 to obtain a paraffin-based baked powder.
The stoichiometry V ₂ O ₅ : C was calculated by setting the chemical formula of paraffin to C _n H _{2 n + 2} .

(Example 18)
First, 0.066 g of polyethylene glycol (Kanto Chemical, 6,000 degree of polymerization) as a carbon source is added to 0.50 g of vanadium pentoxide (manufactured by Wako Pure Chemical Industries, Ltd.) and mixed in a mortar to obtain a mixed powder Was prepared. Next, this mixed powder was molded, calcined and pulverized in the same manner as in Example 1 to obtain a PEG-based calcined powder. Incidentally, the stoichiometric ratio of PEG formula as _{C 2n H 4n + 2 O n} V 2 O 5: was calculated C.

(Examples 19 and 20)
First, to 2.066 g of the mixed powder prepared in Example 1, 0.444 mL (Example 19) or 1.36 mL of an Nb-based dip coating solution (SYM-NB05 manufactured by High Purity Chemical Laboratory Co., Ltd.) as a Nb source. After adding (Example 20), mixing was performed in a mortar while warming until the solvent odor disappeared, to prepare a mixed powder which is a mixture. Next, this mixed powder was molded, fired and crushed in the same manner as in Example 1 to obtain a 1% Nb-added fired powder (Example 19) or a 3% Nb-added fired powder (Example 20).

(Example 21)
First, 0.0824 g of gallium acetylacetonate (Ga (acac) ₃ manufactured by Alfer Aesar) as a Ga source is added to 1.033 g of the mixed powder prepared in Example 1, and then mixed in a mortar to obtain a mixture. Was prepared mixed powder. Next, this mixed powder was molded and fired in the same manner as in Example 1 (at 700 ° C. for 5 hours), and pulverized to obtain a 2% Ga-added fired powder.

(Comparative example)
0.5 g of vanadium pentoxide (manufactured by Wako Pure Chemical Industries, Ltd.) was molded, fired and pulverized in the same manner as in Example 1 to obtain a calcined powder of vanadium pentoxide.

2. Evaluation and examination (Evaluation-1: crystalline)
The crystal structure of the calcined powder of vanadium dioxide and the dissimilar metal-added vanadium dioxide obtained in Examples and Comparative Examples was identified by X-ray diffraction using XRD (manufactured by Rigaku, Smart Lab). The measurement conditions were a voltage of 40 kV, a current of 30 mA, a scanning speed of 2 ° / min, and a diffraction angle 2θ of 10 to 70 °. When only a clean VO ₂ peak ((011) plane, 2θ = 27.8 °, etc.) is confirmed, "○", in addition to the VO ₂ peak, another oxide peak such as V ₂ O ₅ When confirmed, or when the crystallinity of VO ₂ is obviously bad is denoted by “Δ”, when the peak of VO ₂ is not confirmed, or when the sample can not be recovered, it is denoted by “x”. The results are shown in Table 1.

(Evaluation-2: Metal-semiconductor dislocation temperature)
After press-forming the calcined powder of vanadium dioxide and dissimilar metal-added vanadium dioxide obtained in Examples and Comparative Examples, a Peltier heater (manufactured by Ampere, UTC-100) and a digital source meter (manufactured by Keithley, Model 2400 general-purpose source) The temperature-resistance characteristic was measured using a meter). As the measurement conditions, the temperature range was -10 ° C to 114 ° C, the temperature step was 4 ° C, and the measurement current was 1 mA. The temperature-resistance characteristics of the vanadium dioxide obtained in Example 1 and the dissimilar metal-added vanadium dioxide obtained in Example 19 are shown in FIG. Further, in the temperature-resistance characteristic, the inflection point of the resistance at the time of temperature rise was taken as the metal-semiconductor dislocation temperature. The results are also shown in Table 1.

(Study of stoichiometry of vanadium pentoxide and carbon in mixed powder)
As shown in Table 1, it was found that vanadium dioxide was formed by firing vanadium pentoxide and a carbon source under an inert gas atmosphere. From Example 1 and Examples 3 to 5, at a calcination temperature of 700 ° C., the stoichiometric ratio of vanadium pentoxide to carbon in the carbon source is vanadium pentoxide: carbon = 2: 0.95 to 2: 2 Sometimes, only clear VO ₂ peaks were detected by X-ray diffraction. In Example 6 in which vanadium pentoxide: carbon = 2: 3, the crystallinity of generated VO ₂ was not good. In Example 2 in which vanadium pentoxide: carbon = 2: 0.9, a peak of V ₂ O ₅ of the raw material was observed by X-ray diffraction. Therefore, the preferred range of the stoichiometric ratio of vanadium pentoxide and carbon in the carbon source is vanadium pentoxide: carbon = 2: 0.95-2: 2.

Incidentally, vanadium pentoxide firing temperature is at 700 ° C. Only VO ₂ is generated: Carbon = 2: 1.25 Example 16 The mixed powder of stoichiometric ratio was calcined at 900 ° C., in an X-ray diffraction And a peak appeared to be a vanadium oxide in which vanadium is reduced more than VO ₂ . It is considered that the amount of carbon source is large, the reaction temperature is high and the reducing power is also high. On the other hand, in Example 15 in which the mixed powder of vanadium pentoxide: carbon = 2: 1.1 was fired at 900 ° C., only VO ₂ was produced. Therefore, the more preferable stoichiometric ratio range of vanadium pentoxide and carbon in the carbon source is vanadium pentoxide: carbon = 2: 0.95-2: 1.1. The most preferred stoichiometry of vanadium pentoxide and carbon in the carbon source can be said to be when vanadium pentoxide: carbon is approximately 2: 1.

(Study of firing temperature)
As can be seen from Examples 8 to 13, when the mixed powder of vanadium pentoxide: carbon = 2: 1 stoichiometry was calcined at 600 to 1000 ° C., only VO ₂ was formed. VO ₂ was formed even at a firing temperature of 550 ° C. of Example 7, but the crystallinity was not good. Although the crystallinity may be improved by extending the firing time at a firing temperature of 550 ° C., the firing temperature is preferably 600 ° C. or more in order to produce VO ₂ simply and inexpensively. Although it is thought that even if this mixed powder is fired at a temperature higher than 1000 ° C., only VO ₂ is formed, the firing temperature is preferably 1000 ° C. or less, more preferably 800 ° C. or less, in order to suppress energy consumption.

(Study of firing time)
From Example 1, Example 12, and Example 13 in which mixed powder of vanadium pentoxide: carbon = 2: 1 at a stoichiometric ratio was fired at 700 ° C., a preferable range of the firing time was examined. Although a difference in crystallinity was somewhat observed in the baking time of 10 minutes to 10 hours which seems to be practical, the range of the baking time was not particularly limited because only VO ₂ was generated in each case.

(Examination of the type of carbon source)
In Example 17 and Example 18, it was examined whether or not VO ₂ was formed even when the carbon source was changed to paraffin and polyethylene glycol. VO ₂ was formed at any carbon source. Therefore, the carbon source is not limited to carbon, and it is considered to be a substance which is carbonized at the sintering temperature of the mixed powder to remain as a carbon source, that is, a substance in which carbon remains in a high temperature reducing atmosphere.

(Examination of the addition of dissimilar metals)
In Example 19 and Example 20, niobium was doped so that the molar ratio of vanadium to foreign metal in the fired powder would be 99: 1 and 97: 3, to obtain heterometallic-doped vanadium dioxide. As shown in Table 1, the transition temperature of the vanadium dioxide of Example 1 was 72.degree. C. substantially as described in the literature, while the transition temperature of the dissimilar metal-doped vanadium dioxide of Example 19 was 56.degree. The transition temperatures of the 20 dissimilar metal-doped vanadium dioxides are each lowered to 40.degree. This indicates that niobium is doped in the VO ₂ lattice. Therefore, it was found that, in the method for producing vanadium dioxide of the present invention, mixing different metal solutions and the like with the mixed powder before firing can easily produce vanadium dioxide doped with different metals, that is, different metal-added vanadium dioxide. .

(Summary)
Having described the present invention based on the embodiments and examples, materials shown herein, the composition, structure, and such usage is not intended to limit the present _{invention, 2V 2 O 5 + C →} 4VO 2 + CO _The raw materials that cause the chemical reaction of ₂ , the equipment such as a furnace, and the environment may be sufficient.

  According to the present invention, vanadium dioxide and dissimilar metal-added vanadium dioxide can be provided easily and inexpensively based on inexpensive raw materials without using a special device or a special gas. Applications utilizing changes in properties of vanadium dioxide due to metal-insulator dislocations include, for example, automatic light control glass utilizing thermochromic properties. The vanadium dioxide and the dissimilar metal-added vanadium dioxide produced by the production method of the present invention can be used for thermochromic products typified by automatic light control glass utilizing change of physical property at transition temperature. However, it is not difficult to imagine that the required transition temperature changes depending on the application and use conditions. In the present invention, it is also possible to dope different metals, that is, to change the dislocation point. Therefore, although the application to automatic light control glass has been considered, the possibility of development to new fields is broadened because it is a simple process.

Claims (7)

A method of producing vanadium dioxide, which comprises mixing vanadium pentoxide powder and carbon source powder, forming the mixture, and firing in a furnace ,
The manufacturing method of vanadium dioxide whose stoichiometric ratio of carbon in said carbon source to said vanadium pentoxide is 0.475-1 . In claim 1,
The manufacturing method of the vanadium dioxide whose stoichiometric ratio of carbon in the said carbon source with respect to the said vanadium pentoxide is 0.475-0.55. In claim 1 or 2 ,
The method for producing vanadium dioxide, which is a compound in which the carbon source decomposes and carbonizes before being volatilized when heated together with carbon and vanadium pentoxide, or an organic compound which does not leave impurities other than carbon at a firing temperature. In any one of claims 1 to 3 ,
A method of producing vanadium dioxide, wherein said calcination is performed under one or more gas atmospheres selected from helium, neon, argon and nitrogen. In any one of claims 1 to 3 ,
The manufacturing method of vanadium dioxide which carries out the above-mentioned calcination under nitrogen gas atmosphere. In claim 4 or 5 ,
The manufacturing method of the vanadium dioxide which carries out the said baking at the temperature of 600-1000 degreeC. In claim 4 or 5 ,
The manufacturing method of the vanadium dioxide which carries out the said baking at the temperature of 600-800 degreeC.

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