WO2015151355A1 - Vanadium oxide and manufacturing method therefor - Google Patents

Abstract

This invention provides vanadium-oxide particles that have a median diameter of at least 2 µm, consist primarily of the oxide of tetravalent vanadium (V⁴⁺), and can absorb a large amount of heat.

Description

Vanadium oxide and method for producing the same

The present invention relates to vanadium oxide and a method for producing the same.

It is known that various oxides such as V ₂ O ₃ , VO ₂ , and V ₂ O ₅ exist as vanadium oxides. Among these, VO ₂ is known as a substance that undergoes an electronic phase transition, and its use as a heat storage material has been proposed using the latent heat associated with this electronic phase transition (Patent Document 1).

JP 2010-163510 A

The present inventor has found that vanadium oxide used as a heat storage material as described above can be used for cooling electronic devices. For efficient cooling, high-purity VO ₂ with large latent heat is required. However, since vanadium oxide has phases with different oxygen contents and vanadium valences, such high-purity VO ₂ Even if it can be produced on a small scale, it has been difficult to produce a large amount stably. In particular, commercially available VO ₂ is generally produced by heat-treating NH ₄ VO ₃ in an atmosphere in which tetravalent vanadium is stable, but is obtained by simply heating in such an atmosphere. It was found that the obtained VO ₂ had a small endotherm for use in a cooling device.

Further, the present inventor has found that even in the case of VO ₂ having high purity and powder X-ray diffraction measurement, the endothermic amount is greatly different, that is, the same single-phase VO _2. However, it has been found that there is a difference in the endothermic amount.

Therefore, an object of the present invention is to provide a vanadium oxide having a large endothermic amount and a method capable of stably producing a large amount of such vanadium oxide.

The present inventor found that vanadium oxide has different endothermic properties when the particle size is different, even if the crystallinity measured by powder X-ray diffraction is the same, that is, the endothermic property is affected by the particle size. As a result of further investigation, it was found that when the median diameter is 2 μm or more, excellent endothermic properties are exhibited.

It has also been found that vanadium oxide particles having particularly excellent endothermic properties can be obtained by controlling the oxygen partial pressure and temperature during synthesis.

According to the first aspect of the present invention, there is provided vanadium oxide particles whose main component is an oxide of tetravalent vanadium (V ⁴⁺ ) having a median diameter of 2 μm or more.

According to the second aspect of the present invention, there is provided a material containing the above vanadium oxide particles.

According to a third aspect of the present invention, there is provided a method for producing the vanadium oxide particles as described above:
(1) comprising at least one divalent to pentavalent oxide of vanadium and optionally at least one oxide of M (where M is selected from W, Ta, Mo and Nb) A temperature raising step for heating the raw material to a temperature of 850 ° C. or higher and 1200 ° C. or lower; and (2) a high temperature holding step for holding the raw material at a temperature after the temperature rising. There, 1 × is at ¹⁰ -11 MPa or less, at least part time of the high temperature holding step, the oxygen partial pressure, 1 × ^{10 -7} ~ method is 1 × ¹⁰ -10 MPa is provided.

According to the present invention, vanadium oxide particles having a large endothermic amount are provided. Moreover, according to the present invention, it is possible to stably synthesize such vanadium particles in a large amount.

FIG. 1 is a schematic perspective view of a “sheath” used in the examples. FIG. 2 is a schematic cross-sectional view of the sheath of FIG. 1 filled with VO _x for explaining a surface portion, a center portion, and a bottom surface portion in the embodiment. FIG. 3 shows the results of powder X-ray diffraction measurement of VO ₂ of sample numbers 1 and 2. FIG. 4 is a graph showing the relationship between the endothermic amount and the median diameter of sample numbers 1 to 15.

The vanadium oxide particles of the present invention contain a tetravalent vanadium (V ⁴⁺ ) oxide, that is, VO ₂ as a main component.

Here, the main component means a component contained in the vanadium oxide particles by 90% by mass or more, particularly 95% by mass or more, preferably 98% by mass or more, more preferably 98% by mass or more, for example, 98.0 to It means 99.8% by mass or substantially 100% by weight. The main component includes that the vanadium oxide particles are substantially composed of the component. Other components include oxides of vanadium other than tetravalent, specifically, but not limited to VO, V ₂ O ₃ , V ₂ O ₅ , V ₃ O ₇ , V ₄ O ₇ , V ₅ O ₉ , V ₆ O ₁₁ , V ₆ O _{13 and the} like.

In one embodiment, the vanadium oxide particles of the present invention may contain other atoms, for example, one or more atoms selected from the group consisting of W, Ta, Mo and Nb. By including (doping) such atoms, the temperature at which vanadium oxide undergoes phase transition can be adjusted.

Preferably, the vanadium oxide particles of the present invention contain V and M (wherein M is at least one selected from W, Ta, Mo and Nb), and the total of V and M is 100 mol parts. In this case, the oxide contains an oxide in which the molar part of M is 0 to about 5 parts by mole. Note that M is not an essential component, and the content molar part of M may be 0.

In another preferred embodiment, the vanadium oxide particles of the present invention have the formula:
V _1-x M _x O ₂
(In the formula, M is W, Ta, Mo or Nb, and x is 0 or more and 0.05 or less)
Or one or more oxides represented by:

The vanadium oxide particles of the present invention have a median diameter of 2 μm or more, preferably 10 μm or more. The vanadium oxide particles having a median diameter of 2 μm or more have a large endothermic amount, and the endothermic amount increases as the median diameter increases (see FIG. 4).

In the present specification, the “median diameter” of vanadium oxide particles is defined as the particle diameter at which the cumulative value is 50% in a cumulative curve obtained by obtaining the particle size distribution on a volume basis and setting the total volume to 100%. . The average particle size can be measured using a laser diffraction / scattering soot particle size / particle size distribution measuring apparatus.

When the vanadium oxide of the present invention is substantially composed of VO ₂ , it may have an endothermic amount of preferably 40 J / g or more, more preferably 50 J / g or more, and even more preferably 60 J / g or more. When other elements, such as W, are doped, the endotherm can change, for example, preferably has an endotherm of 30 J / g or more, more preferably 40 J / g or more, and even more preferably 45 J / g or more. Can do.

The endothermic amount can be measured by differential scanning calorimetry (DSC).

In one aspect, the present invention provides a material containing the above vanadium oxide particles. Such a material is not particularly limited, but can be used for a cooling device of electronic equipment, a heat storage material, and the like.

In one aspect, the present invention provides a method for producing vanadium oxide particles having excellent endothermic properties.

The method of the present invention includes (1) a temperature raising step and (2) a high temperature holding step.

Hereinafter, the temperature raising process will be described.

First, at least one selected from the group consisting of divalent to pentavalent oxides of vanadium and simple vanadium, and optionally at least one M (where M is W, Ta, Mo and Nb). A raw material containing a selected oxide). This raw material is preferably a powder.

The raw materials may contain various vanadium oxides, such as VO, V ₂ O ₃ , V ₂ O ₅ , V ₃ O ₇ , V ₄ O ₇ , V ₅ O ₉ , V ₆ O ₁₁ , and V ₆ O ₁₃ or the like may be included. Moreover, VO _2, in particular the particle size can be used as VO ₂ also raw material is less than 2 [mu] m.

Furthermore, the raw material may contain one or more elements selected from other elements such as W, Ta, Mo and Nb. These elements can preferably be included as oxides, for example as WO ₃ , Ta ₂ O ₅ , MoO ₃ , Nb ₂ O ₅ .

In a preferred embodiment, the molar ratio of V and O contained in the raw material is about 1: 2. With such a ratio, it is possible to prompt a change in the VO _2.

Next, the above raw material is gradually heated (heated) in a reducing atmosphere.

The temperature rise is performed until the temperature of the raw material reaches a temperature of 850 ° C. or higher and 1200 ° C. or lower, preferably 900 ° C. or higher and 1100 ° C. or lower.

The temperature raising step is not particularly limited, but is performed, for example, for 1 to 10 hours, preferably 3 to 6 hours.

The temperature raising step is performed in a stronger reducing atmosphere, and the oxygen partial pressure is lower in the temperature raising step than in the high temperature holding step. Preferably, the oxygen partial pressure at 800 ° C. in the temperature raising step is 1 × 10 ⁻¹¹ MPa or less, more preferably 1 × 10 ⁻¹² MPa or less. By setting such an oxygen partial pressure, V ₂ O _{5 having} a low melting point (about 800 ° C.) is likely to become a vanadium oxide having a higher melting point and a lower valence, such as VO ₂ or V ₂ O ₃ . The melting of the raw material in the temperature raising step can be prevented. As a result, necking or the like between the raw material particles is prevented, the oxygen concentration in the reaction system is kept more uniform, and vanadium oxide with high purity can be obtained.

Thus, in one embodiment, the raw material includes V ₂ O ₅ .

The oxygen concentration in the temperature raising step may be lower than the oxygen concentration in the high temperature holding step, and may be an oxygen concentration at which vanadium is reduced to less than tetravalent at the temperature at that time, and is not necessarily constant. For example, at a lower temperature, the oxygen concentration may be relatively low, and the oxygen concentration may be gradually increased as the temperature increases, and vice versa.

Hereinafter, the high temperature holding process will be described.

The raw material heated in the temperature raising step is held at the temperature after the temperature elevation, that is, 850 ° C. to 1200 ° C.

The holding time is not particularly limited as long as the raw material reduced in the temperature raising step is sufficiently oxidized to VO ₂ , and is, for example, 1 hour or longer, preferably 2 to 6 hours.

The high temperature holding step is performed in an atmosphere in which vanadium is tetravalent and stable, for example, under an oxygen partial pressure of 1 × 10 ⁻⁷ to 1 × 10 ⁻¹⁰ MPa for at least a part of the holding step.

During the high temperature holding step, the oxygen concentration is preferably controlled so as not to be in an oxidizing atmosphere where vanadium becomes pentavalent. By controlling in this way, vanadium becomes pentavalent and it is possible to prevent the melting point from being lowered.

According to the method of the present invention, it is possible to stably synthesize a large amount of vanadium oxide having a large median diameter, particularly 10 μm or more, and having a high purity and a large endothermic amount. Although not bound by any theory, the reason why vanadium oxide having a large endotherm can be obtained by the method of the present invention is considered as follows. First. By raising the temperature of the vanadium oxide raw material in a reducing atmosphere stronger than the high temperature holding step, vanadium is easily reduced and the amount of pentavalent vanadium is reduced. That is, in the process, V ₂ O ₅ having a low melting point (about 800 ° C.) is reduced, and the melting point of the raw material vanadium oxide becomes high (specifically, higher than 800 ° C.). By increasing the melting point, non-uniform atmosphere due to melting of vanadium oxide is prevented in the high temperature holding step. Furthermore, since vanadium is more likely to proceed with a reaction that acquires oxygen (that is, an oxidation reaction) than a reaction that loses oxygen (that is, a reduction reaction), the vanadium is once reduced rather than the target tetravalent, and then to the tetravalent. It is considered that more uniform VO ₂ can be obtained by oxidation.

In a preferred embodiment, the method of the present invention may include a temperature lowering step in which the oxygen concentration is controlled.

The oxygen partial pressure at 800 ° C. in the temperature lowering step is preferably 1 × 10 ⁻¹⁰ MPa or less, more preferably 1 × 10 ⁻¹¹ MPa or less so that VO ₂ obtained in the temperature lowering holding step is not oxidized. It is. In order not to be reduced again, the oxygen partial pressure at 800 ° C. is preferably 1 × 10 ⁻¹³ MPa or more, preferably 1 × 10 ⁻¹² MPa or more.

The temperature lowering step is not particularly limited, but is performed, for example, for 1 to 10 hours, preferably 3 to 6 hours.

・ Commercially available VO ₂
For commercial VO ₂ (Sample No. 1), differential scanning calorimetry (DSC: Differential scanning calorimetry) was performed to evaluate the heat absorption amount (latent heat). As a result, the endothermic amount was 35 J / g.

- as a production starting material of the VO ₂ from commercial VO _2, commercial VO ₂ of the above 120g weighed, partially stabilized zirconia polyethylene pot container (PSZ: Partial Stabilized Zirconia) balls, pure water, dispersing agent (San Nopco Ltd. : SN5468) and wet milled for 16 hours. Thereafter, the mixed slurry was dried, sized, put into a mullite sheath of 100 × 100 × 50 mm ³ (internal volume 90 × 90 × 40 mm ³ ) shown in FIG. Heat treatment was performed in a nitrogen atmosphere.

As shown in Table 1, the heat treatment was performed by changing the oxygen partial pressure at 800 ° C. in the temperature raising step, the temperature and oxygen partial pressure in the high temperature holding step, and the oxygen partial pressure at 800 ° C. in the temperature lowering step. 2 to 11 (numbers marked with * are comparative examples). The starting temperature in the temperature raising step was room temperature, and the temperature was raised to a predetermined temperature in 3.5 hours. The high temperature holding process was 4 hours. In the temperature lowering step, the mixture was allowed to stand until it reached room temperature and cooled to obtain VO ₂ particles.

During the heat treatment, the oxygen partial pressure was controlled by keeping the water vapor amount and nitrogen amount constant in the section of 150 ° C. or higher, monitoring the oxygen partial pressure, and adjusting the hydrogen amount. The oxygen partial pressure was monitored by sampling the gas in the furnace and measuring with a zirconia oxygen partial pressure meter.

· As _{V 0.995} W _0.005 production starting material of the O ₂ from the commercial VO _2, in addition to commercial VO _2, was prepared tungsten oxide (WO _3). This was weighed so as to have a total weight of 120 g at a mixing ratio (molar ratio) of VO ₂ / WO ₃ = 0.995 / 0.005. In other steps, the sample numbers 12 to 15 were heat-treated in the same manner as in the production of VO ₂ to obtain V _0.995 W _0.005 O ₂ particles. The processing conditions are shown in Table 2 below.

・ Characteristic test (powder X-ray diffraction measurement)
The sample numbers 1 to 15 prepared above were subjected to powder X-ray diffraction (XRD) measurement to evaluate crystallinity. In the XRD measurement of sample numbers 2 to 15, as shown in FIG. 2, the samples were sampled from the surface portion, the central portion, and the bottom portion of the sheath and measured. The results are shown in Table 3 below. Further, a chart of powder X-ray diffraction of Sample No. 1 and Sample No. 2 is shown in FIG.

(Differential scanning calorimetry)
The sample numbers 1 to 15 created above were subjected to differential scanning calorimetry (DSC) to evaluate the endothermic amount (latent heat amount). The results are also shown in Table 3 below.

(Particle size measurement)
With respect to the sample numbers 1 to 15 prepared above, the particle diameter (median diameter) was measured using a laser diffraction / scattering type particle size distribution analyzer LA-920 manufactured by Horiba. Prior to the measurement, an appropriate amount of the sample was added to the aqueous solution of sodium hexametaphosphate and dispersed with an ultrasonic cleaner for about 10 minutes, and then the measurement was performed. This makes it possible to accurately measure the particle size distribution by agglomerating a sample in which the powder is agglomerated and suppressing the precipitation of powder having a large particle size. Also, as a precaution, the particle size and particle shape of the sample are confirmed with a field emission scanning electron microscope (FE-SEM), and the particle size and primary particle size measured with a laser diffraction / scattering particle size distribution analyzer are almost the same. Confirmed the same. The measurement results are also shown in Table 3 below. In order to investigate the relationship between the endothermic amount and the median diameter, the results for each sample were plotted in a graph of endothermic amount (J / g) -median diameter (μm). The results are shown in FIG.

　※表３において異相生成とはＸＲＤの回折強度から主成分であるＶＯ_２に対して、他の酸化バナジウムが２０％以上存在していたことを示す。

* In Table 3, heterogeneous generation means that 20% or more of other vanadium oxide was present with respect to VO _{2 as the} main component from the diffraction intensity of XRD.

As shown in FIG. 3, and VO ₂ commercial sample No. 1, between VO ₂ heat treated sample No. 2, the observable crystallinity by powder X-ray diffraction measurement difference was observed. The crystals of sample numbers 3-7, 9 and 11-15 were also single phase. However, as shown in Table 3, it was confirmed that there was a difference in the endothermic amount even with VO ₂ which was the same single phase.

As shown in FIG. 4, the particle diameter (median diameter) and the endothermic amount showed a strong interphase, and it was confirmed that the endothermic amount improved as the particle size increased. Thus, it was confirmed that the particle size can be used as an index of the endothermic amount.

Further, from these results, VO ₂ of sample numbers 2 to 7, 9 and 11 having a median diameter of 2 μm or more has an endotherm of 40 J / g or more, whereas sample numbers having a median diameter of less than 2 μm No. 1 had a small endotherm of 35 J / g. Further, VO ₂ of Sample Nos. 12 to 15 doped with W having a median diameter of 2 μm or more may have an endotherm of 30 J / g or more even though the endotherm is reduced by doping with W. confirmed. In particular, it was confirmed that Sample Nos. 2 to 7 having a median diameter of 10 μm or more have a very excellent endothermic amount of 60 J / g or more. It was also confirmed that VO ₂ having such an excellent endothermic amount can be produced by the production method of the present invention.

Since the vanadium oxide of the present invention has a high latent heat, it can be suitably used for various applications such as a cooling device for electronic equipment.

Claims (8)

Vanadium oxide particles mainly composed of tetravalent vanadium (V ⁴⁺ ) oxide having a median diameter of 2 μm or more. The vanadium oxide particles according to claim 1, wherein the median diameter is 10 μm or more. Vanadium oxide particles according to claim 1 or 2, wherein the median diameter is 50 µm or less. V and M (wherein M is at least one selected from W, Ta, Mo and Nb), and the content of M is 0 mol when the total of V and M is 100 mol The vanadium oxide particles according to any one of claims 1 to 3, comprising an oxide in an amount of from 5 parts to 5 parts by mole. Formula: V _1-x M _x O ₂
(In the formula, M is W, Ta, Mo or Nb, and x is 0 or more and 0.05 or less)
The vanadium oxide particles according to any one of claims 1 to 4, comprising one or more oxides represented by: A material containing vanadium oxide according to any one of claims 1 to 5. A method for producing vanadium oxide particles according to any one of claims 1 to 5, comprising:
(1) comprising at least one divalent to pentavalent oxide of vanadium and optionally at least one oxide of M (where M is selected from W, Ta, Mo and Nb) A temperature raising step for heating the raw material to a temperature of 850 ° C. or higher and 1200 ° C. or lower; and (2) a high temperature holding step for holding the raw material at a temperature after the temperature rising, and in the temperature rising step, an oxygen partial pressure at 800 ° C. Is 1 × 10 ⁻¹¹ MPa or less, and the oxygen partial pressure is 1 × 10 ⁻⁷ to 1 × 10 ⁻¹⁰ MPa in at least a part of the high temperature holding step. The manufacturing method according to claim 7, wherein the raw material contains V ₂ O _5.

Images